HUMAN CYTOKINE RECEPTOR

Abstract: Cytokines and their receptors have proven usefulness in both basic research and as therapeutics. The present invention provides a new human cytokine receptor designated as "Zcytor16".

Description: HUMAN CYTOKINE RECEPTOR TECHNICAL FIELD The present invention relates generally to a new protein expressed by human cells. In particular, the present invention relates to a novel gene that encodes a receptor, designated as "Zcytorlβ," and to nucleic acid molecules encoding Zcytorlό polypeptides, and antibodies to the polypeptide. BACKGROUND OF THE INVENTION Cytokines are soluble, small proteins that mediate a variety of biological effects, including the regulation of the growth and differentiation of many cell types (see, for example, Arai et al., Anna. Rev. Biochem. 59:783 (1990); Mosmann, Curr. Opin. Immunol. 3:311 (1991); Paul and Seder, Cell 76:241 (1994)). Proteins that constitute the cytokine group include interleukins, interferons, colony stimulating factors, tumor necrosis factors, and other regulatory molecules. For example, human interleukin- 17 is a cytokine which stimulates the expression of interleukin-6, intracellular adhesion molecule 1, interleukin-8, granulocyte macrophage colony- stimulating factor, and prostaglandin E2 expression, and plays a role in the preferential maturation of CD34+ hematopoietic precursors into neutrophils (Yao et ai, J. Immunol. 755:5483 (1995); Fossiez et al., J. Exp. Med. 183:2593 (1996)). Receptors that bind cytokines are typically composed of one or more integral membrane proteins that bind the cytokine with high affinity and transduce this binding event to the cell through the cytoplasmic portions of the certain receptor subunits. Cytokine receptors have been grouped into several classes on the basis of similarities in their extracellular ligand binding domains. For example, the receptor chains responsible for binding and/or transducing the effect of interferons are members of the class π cytokine receptor family, based upon a characteristic 200 residue extracellular domain. The demonstrated in vivo activities of cytokines and their receptors illustrate the clinical potential of, and need for, other cytokines, cytokine receptors, cytokine agonists, and cytokine antagonists. BRIEF SUMMARY OF THE INVENTION The present invention provides a novel receptor, designated "Zcytorlo." The present invention also provides Zcytorlo polypeptides and Zcytorlo fusion proteins, as well as nucleic acid molecules encoding such polypeptides and proteins, and methods for using these nucleic acid molecules and amino acid sequences. DETAILED DESCRIPTION OF THE INVENTION I. Overview An illustrative nucleotide sequence that encodes Zcytorlo is provided by SEQ ID NO:l. The encoded polypeptide has the following amino acid sequence: MMPKHCFLGF LISFFLTGVA GTQSTHESLK PQRVQFQSRN FHNILQWQPG RALTGNSSVY FVQYKTYGQR QWKNKEDCWG TQELSCDLTS ETSDIQEPYY GRVRAASAGS YSEWSMTPRF TPWWETKIDP PVMNITQVNG SLLVILHAPN LPYRYQKEKN VSIEDYYELL YRVFENNSL EKEQKVYEGA HRAVEIEALT PHSSYCVVAE IYQPMLDRRS QRSEERCVEI P (SEQ ID NO:2). The 231 amino acid polypeptide represents the extracellular domain, also called a cytokine-binding domain, of a new class II cytokine receptor. Features of the Zcytorlβ polypeptide include putative signal sequences at amino acid residues 1 to 21, or 1 to 22, of SEQ ID NO: 2, immunoglobulin superfamily (lg) domains at amino acid residues 22 to 108, and 112 to 210, of SEQ ID NO:2, and a linker that resides between the lg domains (i.e., at amino acid residues 109 to 111 of SEQ ID NO:2). The Zcytorlo gene is expressed in lymphoid, placenta, spleen, tonsil and other tissue, and resides in human chromosome 6q24.1-25.2. As described below, the present invention provides isolated polypeptides comprising an amino acid sequence that is at least 70%, at least 80%, or at least 90% identical to a reference amino acid sequence of SEQ ID NO:2 selected from the group consisting of: (a) amino acid residues amino acid residues 21 to 231, (b) amino acid residues 21 to 210, (c) amino acid residues 22 to 231, (d) amino acid residues 22 to 210, (e) amino acid residues 22 to 108, (f) amino acid residues 112 to 210, and (g) amino acid residues 21 to 110, wherein the isolated polypeptide specifically binds with an antibody that specifically binds with a polypeptide consisting of the amino acid sequence of SEQ ID NO:2. Illustrative polypeptides include polypeptides comprising either amino acid residues 22 to 231 of SEQ ID NO:2 or amino acid residues 22 to 210 of SEQ ID NO:2. Moreover, the present invention also provides isolated polypeptides as disclosed above that bind IL-TIF (e.g., human IL-TIF polypeptide sequence as shown in SEQ ID NO: 15). The human IL-TIF polynucleotide sequence is shown in SEQ ID NO: 14. The present invention also provides isolated polypeptides comprising at least 15 contiguous amino acid residues of an amino acid sequence of SEQ ID NO: 2 selected from the group consisting of: (a) amino acid residues amino acid residues 21 to 231, (b) amino acid residues 21 to 210, (c) amino acid residues 22 to 231, (d) amino acid residues 22 to 210, (e) amino acid residues 22 to 108, (f) amino acid residues 112 to 210, and (g) amino acid residues 21 to 110. Ηlustrative polypeptides include polypeptides that either comprise, or consist of, amino acid residues (a) to (g). Moreover, the present invention also provides isolated polypeptides as disclosed above that bind IL-TIF. The present invention also includes variant Zcytorlo polypeptides, wherein the amino acid sequence of the variant polypeptide shares an identity with amino acid residues 22 to 210 of SEQ ID NO:2 selected from the group consisting of at least 70% identity, at least 80% identity, at least 90% identity, at least 95% identity, or greater than 95% identity, and wherein any difference between the amino acid sequence of the variant polypeptide and the corresponding amino acid sequence of SEQ ID NO:2 is due to one or more conservative amino acid substitutions. Moreover, the present invention also provides isolated polypeptides as disclosed above that bind IL-TIF. The present invention further provides antibodies and antibody fragments that specifically bind with such polypeptides. Exemplary antibodies include polyclonal antibodies, murine monoclonal antibodies, humanized antibodies derived from murine monoclonal antibodies, and human monoclonal antibodies. Illustrative antibody fragments include F(ab') 2 , F(ab) 2 , Fab', Fab, Fv, scFv, and minimal recognition units. The present invention further includes compositions comprising a carrier and a peptide, polypeptide, or antibody described herein. The present invention also provides isolated nucleic acid molecules that encode a Zcytorlo polypeptide, wherein the nucleic acid molecule is selected from the group consisting of: (a) a nucleic acid molecule comprising the nucleotide sequence of SEQ ID NO:3, (b) a nucleic acid molecule encoding an amino acid sequence that comprises either amino acid residues 22 to 231 of SEQ ID NO:2 or amino acid residues 22 to 210 of SEQ ID NO:2, and (c) a nucleic acid molecule that remains hybridized following stringent wash conditions to a nucleic acid molecule comprising the nucleotide sequence of nucleotides 64 to 630 of SEQ ID NO:l, or the complement of the nucleotide sequence of nucleotides 64 to 630 of SEQ ID NO:l. Illustrative nucleic acid molecules include those in which any difference between the amino acid sequence encoded by nucleic acid molecule (c) and the corresponding amino acid sequence of SEQ ID NO:2 is due to a conservative amino acid substitution. The present invention further contemplates isolated nucleic acid molecules that comprise nucleotides 64 to 630 of SEQ ID NO:l. Moreover, the present invention also provides isolated polynucleotides that encode polypeptides as disclosed above that bind IL-TIF. The present invention also includes vectors and expression vectors comprising such nucleic acid molecules. Such expression vectors may comprise a transcription promoter, and a transcription terminator, wherein the promoter is operably linked with the nucleic acid molecule, and wherein the nucleic acid molecule is operably linked with the transcription terminator. The present invention further includes recombinant host cells and recombinant viruses comprising these vectors and expression vectors. Illustrative host cells include bacterial, yeast, fungal, insect, mammalian, and plant cells. Recombinant host cells comprising such expression vectors can be used to produce Zcytorlo polypeptides by culturing such recombinant host cells that comprise the expression vector and that produce the Zcytorlo protein, and, optionally, isolating the Zcytorlo protein from the cultured recombinant host cells. In addition, the present invention provides pharmaceutical compositions comprising a pharmaceutically acceptable carrier and at least one of such an expression vector or recombinant virus comprising such expression vectors. The present invention further includes pharmaceutical compositions, comprising a pharmaceutically acceptable carrier and a polypeptide described herein. The present invention also contemplates methods for detecting the presence of Zcytorlo RNA in a biological sample, comprising the steps of (a) contacting a Zcytorlo nucleic acid probe under hybridizing conditions with either (i) test RNA molecules isolated from the biological sample, or (ii) nucleic acid molecules synthesized from the isolated RNA molecules, wherein the probe has a nucleotide sequence comprising a portion of the nucleotide sequence of SEQ ID NO:l, or its complement, and (b) detecting the formation of hybrids of the nucleic acid probe and either the test RNA molecules or the synthesized nucleic acid molecules, wherein the presence of the hybrids indicates the presence of Zcytorlo RNA in the biological sample. For example, suitable probes consist of the following nucleotide sequences of SEQ ID NO:l: nucleotides 64 to 324, nucleotides 64 to 630, nucleotides 334 to 630, and nucleotides 64 to 693. Other suitable probes consist of the complement of these nucleotide sequences, or a portion of the nucleotide sequences or their complements. The present invention further provides methods for detecting the presence of Zcytorlo polypeptide in a biological sample, comprising the steps of: (a) contacting the biological sample with an antibody or an antibody fragment that specifically binds with a polypeptide consisting of the amino acid sequence of SEQ ID NO:2, wherein the contacting is performed under conditions that allow the binding of the antibody or antibody fragment to the biological sample, and (b) detecting any of the bound antibody or bound antibody fragment. Such an antibody or antibody fragment may further comprise a detectable label selected from the group consisting of radioisotope, fluorescent label, chemiluminescent label, enzyme label, bioluminescent label, and colloidal gold. The present invention also provides kits for performing these detection methods. For example, a kit for detection of Zcytorlo gene expression may comprise a container that comprises a nucleic acid molecule, wherein the nucleic acid molecule is selected from the group consisting of (a) a nucleic acid molecule comprising the nucleotide sequence of nucleotides 64 to 630 of SEQ ID NO:l, (b) a nucleic acid molecule comprising the complement of nucleotides 64 to 630 of the nucleotide sequence of SEQ ID NO:l, (c) a nucleic acid molecule that is a fragment of (a) consisting of at least eight nucleotides, and (d) a nucleic acid molecule that is a fragment of (b) consisting of at least eight nucleotides. Such a kit may also comprise a second container that comprises one or more reagents capable of indicating the presence of the nucleic acid molecule. On the other hand, a kit for detection of Zcytorlo protein may comprise a container that comprises an antibody, or an antibody fragment, that specifically binds with a polypeptide consisting of the amino acid sequence of SEQ ID NO:2. The present invention also contemplates anti-idiotype antibodies, or anti- idiotype antibody fragments, that specifically bind an antibody or antibody fragment that specifically binds a polypeptide consisting of the amino acid sequence of SEQ ID NO:2. An exemplary anti-idiotype antibody binds with an antibody that specifically binds a polypeptide consisting of amino acid residues 22 to 210 of SEQ ID NO:2. The present invention also provides isolated nucleic acid molecules comprising a nucleotide sequence that encodes a Zcytorlo secretion signal sequence and a nucleotide sequence that encodes a biologically active polypeptide, wherein the Zcytorlo secretion signal sequence comprises an amino acid sequence of residues 1 to 21, of SEQ ID NO:2. Illustrative biologically active polypeptides include Factor Vila, proinsulin, insulin, follicle stimulating hormone, tissue type plasminogen activator, tumor necrosis factor, interleukin, colony stimulating factor, interferon, erythropoietin, and thrombopoietin. Moreover, the present invention provides fusion proteins comprising a Zcytorlo secretion signal sequence and a polypeptide, wherein the Zcytorlo secretion signal sequence comprises an amino acid sequence of residues 1 to 21, of SEQ ID NO:2. The present invention also provides fusion proteins, comprising a Zcytorlo polypeptide and an immunoglobulin moiety. In such fusion proteins, the immunoglobulin moiety may be an immunoglobulin heavy chain constant region, such as a human F c fragment. The present invention further includes isolated nucleic acid molecules that encode such fusion proteins. The present invention also provides monomeric, homodimeric, heterodimeric and multimeric receptors comprising a zcytorlo extracellular domain. Such receptors are soluble or membrane bound, and act as antagonists of the zcytorlo ligand, IL-TIF (e.g., the human IL-TIF as shown in SEQ ID NO: 15). In a preferred embodiment, such receptors are soluble receptors comprising at least one zcytorlo extracellular domain polypeptide comprising amino acids 22-231, or 22-210 of SEQ ID NO:2. The present invention further includes isolated nucleic acid molecules that encode such receptor polypeptides. The present invention also provides polyclonal and monoclonal antibodies to monomeric, homodimeric, heterodimeric and multimeric receptors comprising a zcytorlo extracellular domain such as those described above. Moreover, such antibodies can be used antagonize the binding to the zcytorlo ligand, IL-TIF (SEQ ID NO: 15), to the zcytorlo receptor. The present invention also provides a method for detecting a genetic abnormality in a patient, comprising: obtaining a genetic sample from a patient; producing a first reaction product by incubating the genetic sample with a polynucleotide comprising at least 14 contiguous nucleotides of SEQ ID NO: l or the complement of SEQ ID NO:l, under conditions wherein said polynucleotide will hybridize to complementary polynucleotide sequence; visualizing the first reaction product; and comparing said first reaction product to a control reaction product from a wild type patient, wherein a difference between said first reaction product and said control reaction product is indicative of a genetic abnormality in the patient. The present invention also provides a method for detecting a cancer in a patient, comprising: obtaining a tissue or biological sample from a patient; incubating the tissue or biological sample with an antibody as described above under conditions wherein the antibody binds to its complementary polypeptide in the tissue or biological sample; visualizing the antibody bound in the tissue or biological sample; and comparing levels of antibody bound in the tissue or biological sample from the patient to a normal control tissue or biological sample, wherein an increase in the level of antibody bound to the patient tissue or biological sample relative to the normal control tissue or biological sample is indicative of a cancer in the patient. The present invention also provides a method for detecting a cancer in a patient, comprising: obtaining a tissue or biological sample from a patient; labeling a polynucleotide comprising at least 14 contiguous nucleotides of SEQ ID NO: 1 or the complement of SEQ ID NO:l; incubating the tissue or biological sample with under conditions wherein the polynucleotide will hybridize to complementary polynucleotide sequence; visualizing the labeled polynucleotide in the tissue or biological sample; and comparing the level of labeled polynucleotide hybridization in the tissue or biological sample from the patient to a normal control tissue or biological sample, wherein an increase in the labeled polynucleotide hybridization to the patient tissue or biological sample relative to the normal control tissue or biological sample is indicative of a cancer in the patient. These and other aspects of the invention will become evident upon reference to the following detailed description. In addition, various references are identified below and are incorporated by reference in their entirety. 2. Definitions In the description that follows, a number of terms are used extensively. The following definitions are provided to facilitate understanding of the invention. As used herein, "nucleic acid" or "nucleic acid molecule" refers to polynucleotides, such as deoxyribonucleic acid (DNA) or ribonucleic acid (RNA), oligonucleotides, fragments generated by the polymerase chain reaction (PCR), and fragments generated by any of ligation, scission, endonuclease action, and exonuclease action. Nucleic acid molecules can be composed of monomers that are naturally- occurring nucleotides (such as DNA and RNA), or analogs of naturally-occurring nucleotides (e.g., α-enantiomeric forms of naturally-occurring nucleotides), or a combination of both. Modified nucleotides can have alterations in sugar moieties and/or in pyrimidine or purine base moieties. Sugar modifications include, for example, replacement of one or more hydroxyl groups with halogens, alkyl groups, amines, and azido groups, or sugars can be functionalized as ethers or esters. Moreover, the entire sugar moiety can be replaced with sterically and electronically similar structures, such as aza-sugars and carbocyclic sugar analogs. Examples of modifications in a base moiety include alkylated purines and pyrimidines, acylated purines or pyrimidines, or other well-known heterocyclic substitutes. Nucleic acid monomers can be linked by phosphodiester bonds or analogs of such linkages. Analogs of phosphodiester linkages include phosphorothioate, phosphorodithioate, phosphoroselenoate, phosphorodiselenoate, phosphoroanilothioate, phosphoranilidate, phosphoramidate, and the like. The term "nucleic acid molecule" also includes so- called "peptide nucleic acids," which comprise naturally-occurring or modified nucleic acid bases attached to a polyamide backbone. Nucleic acids can be either single stranded or double stranded. The term "complement of a nucleic acid molecule" refers to a nucleic acid molecule having a complementary nucleotide sequence and reverse orientation as compared to a reference nucleotide sequence. For example, the sequence 5' ATGCACGGG 3' is complementary to 5' CCCGTGCAT 3'. The term "contig" denotes a nucleic acid molecule that has a contiguous stretch of identical or complementary sequence to another nucleic acid molecule. Contiguous sequences are said to "overlap" a given stretch of a nucleic acid molecule either in their entirety or along a partial stretch of the nucleic acid molecule. The term "degenerate nucleotide sequence" denotes a sequence of nucleotides that includes one or more degenerate codons as compared to a reference nucleic acid molecule that encodes a polypeptide. Degenerate codons contain different triplets of nucleotides, but encode the same amino acid residue (i.e., GAU and GAC triplets each encode Asp). The term "structural gene" refers to a nucleic acid molecule that is transcribed into messenger RNA (mRNA), which is then translated into a sequence of amino acids characteristic of a specific polypeptide. An "isolated nucleic acid molecule" is a nucleic acid molecule that is not integrated in the genomic DNA of an organism. For example, a DNA molecule that encodes a growth factor that has been separated from the genomic DNA of a cell is an isolated DNA molecule. Another example of an isolated nucleic acid molecule is a chemically-synthesized nucleic acid molecule that is not integrated in the genome of an organism. A nucleic acid molecule that has been isolated from a particular species is smaller than the complete DNA molecule of a chromosome from that species. A "nucleic acid molecule construct" is a nucleic acid molecule, either single- or double-stranded, that has been modified through human intervention to contain segments of nucleic acid combined and juxtaposed in an arrangement not existing in nature. "Linear DNA" denotes non-circular DNA molecules having free 5' and 3' ends. Linear DNA can be prepared from closed circular DNA molecules, such as plasmids, by enzymatic digestion or physical disruption. "Complementary DNA (cDNA)" is a single-stranded DNA molecule that is formed from an mRNA template by the enzyme reverse transcriptase. Typically, a primer complementary to portions of mRNA is employed for the initiation of reverse transcription. Those skilled in the art also use the term "cDNA" to refer to a double- stranded DNA molecule consisting of such a single-stranded DNA molecule and its complementary DNA strand. The term "cDNA" also refers to a clone of a cDNA molecule synthesized from an RNA template. A "promoter" is a nucleotide sequence that directs the transcription of a structural gene. Typically, a promoter is located in the 5' non-coding region of a gene, proximal to the transcriptional start site of a structural gene. Sequence elements within promoters that function in the initiation of transcription are often characterized by consensus nucleotide sequences. These promoter elements include RNA polymerase binding sites, TATA sequences, CAAT sequences, differentiation-specific elements (DSEs; McGehee et ai, Mol. Endocrinol. 7:551 (1993)), cyclic AMP response elements (CREs), serum response elements (SREs; Treisman, Seminars in Cancer Biol. 1:41 (1990)), glucocorticoid response elements (GREs), and binding sites for other transcription factors, such as CRE/ATF (O'Reilly et al, J. Biol. Chem. 2(57:19938 (1992)), AP2 (Ye et al., J. Biol. Chem. 269:25728 (1994)), SP1, cAMP response element binding protein (CREB; Loeken, Gene Expr. 3:253 (1993)) and octamer factors (see, in general, Watson et al., eds., Molecular Biology of the Gene, 4th ed. (The Benjamin/Cummings Publishing Company, Inc. 1987), and Lemaigre and Rousseau, Biochem. I. 303:1 (1994)). If a promoter is an inducible promoter, then the rate of transcription increases in response to an inducing agent. In contrast, the rate of transcription is not regulated by an inducing agent if the promoter is a constitutive promoter. Repressible promoters are also known. A "core promoter" contains essential nucleotide sequences for promoter function, including the TATA box and start of transcription. By this definition, a core promoter may or may not have detectable activity in the absence of specific sequences that may enhance the activity or confer tissue specific activity. A "regulatory element" is a nucleotide sequence that modulates the activity of a core promoter. For example, a regulatory element may contain a nucleotide sequence that binds with cellular factors enabling transcription exclusively or preferentially in particular cells, tissues, or organelles. These types of regulatory elements are normally associated with genes that are expressed in a "cell-specific," "tissue-specific," or "organelle-specific" manner. An "enhancer" is a type of regulatory element that can increase the efficiency of transcription, regardless of the distance or orientation of the enhancer relative to the start site of transcription. "Heterologous DNA" refers to a DNA molecule, or a population of DNA molecules, that does not exist naturally within a given host cell. DNA molecules heterologous to a particular host cell may contain DNA derived from the host cell species (i.e., endogenous DNA) so long as that host DNA is combined with non-host DNA (i.e., exogenous DNA). For example, a DNA molecule containing a non-host DNA segment encoding a polypeptide operably linked to a host DNA segment comprising a transcription promoter is considered to be a heterologous DNA molecule. Conversely, a heterologous DNA molecule can comprise an endogenous gene operably linked with an exogenous promoter. As another illustration, a DNA molecule comprising a gene derived from a wild-type cell is considered to be heterologous DNA if that DNA molecule is introduced into a mutant cell that lacks the wild-type gene. A "polypeptide" is a polymer of amino acid residues joined by peptide bonds, whether produced naturally or synthetically. Polypeptides of less than about 10 amino acid residues are commonly referred to as "peptides." A "protein" is a macromolecule comprising one or more polypeptide chains. A protein may also comprise non-peptidic components, such as carbohydrate groups. Carbohydrates and other non-peptidic substituents may be added to a protein by the cell in which the protein is produced, and will vary with the type of cell. Proteins are defined herein in terms of their amino acid backbone structures; substituents such as carbohydrate groups are generally not specified, but may be present nonetheless. A peptide or polypeptide encoded by a non-host DNA molecule is a "heterologous" peptide or polypeptide. An "integrated genetic element" is a segment of DNA that has been incorporated into a chromosome of a host cell after that element is introduced into the cell through human manipulation. Within the present invention, integrated genetic elements are most commonly derived from linearized plasmids that are introduced into the cells by electroporation or other techniques. Integrated genetic elements are passed from the original host cell to its progeny. A "cloning vector" is a nucleic acid molecule, such as a plasmid, cosmid, or bacteriophage, that has the capability of replicating autonomously in a host cell. Cloning vectors typically contain one or a small number of restriction endonuclease recognition sites that allow insertion of a nucleic acid molecule in a determinable fashion without loss of an essential biological function of the vector, as well as nucleotide sequences encoding a marker gene that is suitable for use in the identification and selection of cells transformed with the cloning vector. Marker genes typically include genes that provide tetracycline resistance or ampicillin resistance. An "expression vector" is a nucleic acid molecule encoding a gene that is expressed in a host cell. Typically, an expression vector comprises a transcription promoter, a gene, and a transcription terminator. Gene expression is usually placed under the control of a promoter, and such a gene is said to be "operably linked to" the promoter. Similarly, a regulatory element and a core promoter are operably linked if the regulatory element modulates the activity of the core promoter. A "recombinant host" is a cell that contains a heterologous nucleic acid molecule, such as a cloning vector or expression vector. In the present context, an example of a recombinant host is a cell that produces Zcytorlo from an expression vector. In contrast, Zcytorlo can be produced by a cell that is a "natural source" of Zcytorlo, and that lacks an expression vector. "Integrative transformants" are recombinant host cells, in which heterologous DNA has become integrated into the genomic DNA of the cells. A "fusion protein" is a hybrid protein expressed by a nucleic acid molecule comprising nucleotide sequences of at least two genes. For example, a fusion protein can comprise at least part of a Zcytorlo polypeptide fused with a polypeptide that binds an affinity matrix. Such a fusion protein provides a means to isolate large quantities of Zcytorlo using affinity chromatography. The term "receptor" denotes a cell-associated protein that binds to a bioactive molecule termed a "ligand." This interaction mediates the effect of the ligand on the cell. Receptors can be membrane bound, cytosolic or nuclear; monomeric (e.g., thyroid stimulating hormone receptor, beta-adrenergic receptor) or multimeric (e.g., PDGF receptor, growth hormone receptor, IL-3 receptor, GM-CSF receptor, G-CSF receptor, erythropoietin receptor and IL-6 receptor). Membrane-bound receptors are characterized by a multi-domain structure comprising an extracellular ligand-binding domain and an intracellular effector domain that is typically involved in signal transduction. In certain membrane-bound receptors, the extracellular ligand-binding domain and the intracellular effector domain are located in separate polypeptides that comprise the complete functional receptor. In general, the binding of ligand to receptor results in a conformational change in the receptor that causes an interaction between the effector domain and other molecule(s) in the cell, which in turn leads to an alteration in the metabolism of the cell. Metabolic events that are often linked to receptor-ligand interactions include gene transcription, phosphorylation, dephosphorylation, increases in cyclic AMP production, mobilization of cellular calcium, mobilization of membrane lipids, cell adhesion, hydrolysis of inositol lipids and hydrolysis of phospholipids. A "soluble receptor" is a receptor polypeptide that is not bound to a cell membrane. Soluble receptors are most commonly ligand-binding receptor polypeptides that lack transmembrane and cytoplasmic domains, and other linkage to the cell membrane such as via glycophosphoinositol (gpi). Soluble receptors can comprise additional amino acid residues, such as affinity tags that provide for purification of the polypeptide or provide sites for attachment of the polypeptide to a substrate, or immunoglobulin constant region sequences. Many cell-surface receptors have naturally occurring, soluble counterparts that are produced by proteolysis or translated from alternatively spliced mRNAs. Soluble receptors can be monomeric, homodimeric, heterodimeric, or multimeric, with multimeric receptors generally not comprising more than 9 subunits, preferably not comprising more than 6 subunits, and most preferably not comprising more than 3 subunits. Receptor polypeptides are said to be substantially free of transmembrane and intracellular polypeptide segments when they lack sufficient portions of these segments to provide membrane anchoring or signal transduction, respectively. Soluble receptors of class I and class π cytokine receptors generally comprise the extracellular cytokine binding domain free of a transmsmbrane domain and intracellular domain. For example, representative soluble receptors include a soluble receptor for CRF2-4 (Genbank Accession No. Z17227) as shown in SEQ ID NO:35; a soluble receptor for IL-10R (Genbank Accession No.s U00672 and NM_001558) as shown in SEQ ID NO:36; and a soluble receptor for zcytorl l (US Patent No. 5,965,704) as shown in SEQ ID NO:34. It is well within the level of one of skill in the art to delineate what sequences of a known class I or class π cytokine sequence comprise the extracellular cytokine binding domain free of a transmsmbrane domain and intracellular domain. Moreover, one of skill in the art using the genetic code can readily determine polynucleotides that encode such soluble receptor polyptides. The term "secretory signal sequence" denotes a DNA sequence that encodes a peptide (a "secretory peptide") that, as a component of a larger polypeptide, directs the larger polypeptide through a secretory pathway of a cell in which it is synthesized. The larger polypeptide is commonly cleaved to remove the secretory peptide during transit through the secretory pathway. An "isolated polypeptide" is a polypeptide that is essentially free from contaminating cellular components, such as carbohydrate, lipid, or other proteinaceous impurities associated with the polypeptide in nature. Typically, a preparation of isolated polypeptide contains the polypeptide in a highly purified form, i.e., at least about 80% pure, at least about 90% pure, at least about 95% pure, greater than 95% pure, or greater than 99% pure. One way to show that a particular protein preparation contains an isolated polypeptide is by the appearance of a single band following sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis of the protein preparation and Coomassie Brilliant Blue staining of the gel. However, the term "isolated" does not exclude the presence of the same polypeptide in alternative physical forms, such as dimers or alternatively glycosylated or derivatized forms. The terms "amino-terminal" and "carboxyl-terminal" are used herein to denote positions within polypeptides. Where the context allows, these terms are used with reference to a particular sequence or portion of a polypeptide to denote proximity or relative position. For example, a certain sequence positioned carboxyl-terminal to a reference sequence within a polypeptide is located proximal to the carboxyl terminus of the reference sequence, but is not necessarily at the carboxyl terminus of the complete polypeptide. The term "expression" refers to the biosynthesis of a gene product. For example, in the case of a structural gene, expression involves transcription of the structural gene into mRNA and the translation of mRNA into one or more polypeptides. The term "splice variant" is used herein to denote alternative forms of RNA transcribed from a gene. Splice variation arises naturally through use of alternative splicing sites within a transcribed RNA molecule, or less commonly between separately transcribed RNA molecules, and may result in several mRNAs transcribed from the same gene. Splice variants may encode polypeptides having altered amino acid sequence. The term splice variant is also used herein to denote a polypeptide encoded by a splice variant of an mRNA transcribed from a gene. As used herein, the term "immunomodulator" includes cytokines, stem cell growth factors, lymphotoxins, co-stimulatory molecules, hematopoietic factors, and synthetic analogs of these molecules. The term "complement/anti-complement pair" denotes non-identical moieties that form a non-covalently associated, stable pair under appropriate conditions. For instance, biotin and avidin (or streptavidin) are prototypical members of a complement/anti-complement pair. Other exemplary complement/anti-complement pairs include receptor/ligand pairs, antibody/antigen (or hapten or epitope) pairs, sense/antisense polynucleotide pairs, and the like. Where subsequent dissociation of the complement/anti-complement pair is desirable, the complement/anti-complement pair preferably has a binding affinity of less than 10 9 M "1 . An "anti-idiotype antibody" is an antibody that binds with the variable region domain of an immunoglobulin. In the present context, an anti-idiotype antibody binds with the variable region of an anti-Zcytorl6 antibody, and thus, an anti-idiotype antibody mimics an epitope of Zcytorlo. An "antibody fragment" is a portion of an antibody such as F(ab') 2 , F(ab) 2 , Fab', Fab, and the like. Regardless of structure, an antibody fragment binds with the same antigen that is recognized by the intact antibody. For example, an anti-Zcytorl6 monoclonal antibody fragment binds with an epitope of Zcytorlo. The term "antibody fragment" also includes a synthetic or a genetically engineered polypeptide that binds to a specific antigen, such as polypeptides consisting of the light chain variable region, "Fv" fragments consisting of the variable regions of the heavy and light chains, recombinant single chain polypeptide molecules in which light and heavy variable regions are connected by a peptide linker ("scFv proteins"), and minimal recognition units consisting of the amino acid residues that mimic the hypervariable region. A "chimeric antibody" is a recombinant protein that contains the variable domains and complementary determining regions derived from a rodent antibody, while the remainder of the antibody molecule is derived from a human antibody. "Humanized antibodies" are recombinant proteins in which murine complementarity determining regions of a monoclonal antibody have been transfeπed from heavy and light variable chains of the murine immunoglobulin into a human variable domain. As used herein, a "therapeutic agent" is a molecule or atom which is conjugated to an antibody moiety to produce a conjugate which is useful for therapy. Examples of therapeutic agents include drugs, toxins, immunomodulators, chelators, boron compounds, photoactive agents or dyes, and radioisotopes. A "detectable label" is a molecule or atom which can be conjugated to an antibody moiety to produce a molecule useful for diagnosis. Examples of detectable labels include chelators, photoactive agents, radioisotopes, fluorescent agents, paramagnetic ions, or other marker moieties. The term "affinity tag" is used herein to denote a polypeptide segment that can be attached to a second polypeptide to provide for purification or detection of the second polypeptide or provide sites for attachment of the second polypeptide to a substrate. In principal, any peptide or protein for which an antibody or other specific binding agent is available can be used as an affinity tag. Affinity tags include a poly- histidine tract, protein A (Nilsson et al., EMBO J. 4:1015 (1985); Nilsson et ai, Methods Enzymol. 198:3 (1991)), glutathione S transferase (Smith and Johnson, Gene 67:31 (1988)), Glu-Glu affinity tag (Grussenmeyer et ai, Proc. Natl. Acad. Sci. USA 82:1952 (1985)), substance P, FLAG peptide (Hopp et ai, Biotechnology 5:1204 (1988)), streptavidin binding peptide, or other antigenic epitope or binding domain. See, in general, Ford et ai, Protein Expression and Purification 2:95 (1991). DNA molecules encoding affinity tags are available from commercial suppliers (e.g., Pharmacia Biotech, Piscataway, NJ). A "naked antibody" is an entire antibody, as opposed to an antibody fragment, which is not conjugated with a therapeutic agent. Naked antibodies include both polyclonal and monoclonal antibodies, as well as certain recombinant antibodies, such as chimeric and humanized antibodies. As used herein, the term "antibody component" includes both an entire antibody and an antibody fragment. An "immunoconjugate" is a conjugate of an antibody component with a therapeutic agent or a detectable label. As used herein, the term "antibody fusion protein" refers to a recombinant molecule that comprises an antibody component and a Zcytorlo polypeptide component. Examples of an antibody fusion protein include a protein that comprises a Zcytorlo extracellular domain, and either an Fc domain or an antigen- biding region. A "target polypeptide" or a "target peptide" is an amino acid sequence that comprises at least one epitope, and that is expressed on a target cell, such as a tumor cell, or a cell that carries an infectious agent antigen. T cells recognize peptide epitopes presented by a major histocompatibility complex molecule to a target polypeptide or target peptide and typically lyse the target cell or recruit other immune cells to the site of the target cell, thereby killing the target cell. An "antigenic peptide" is a peptide which will bind a major histocompatibility complex molecule to form an MHC-peptide complex which is recognized by a T cell, thereby inducing a cytotoxic lymphocyte response upon presentation to the T cell. Thus, antigenic peptides are capable of binding to an appropriate major histocompatibility complex molecule and inducing a cytotoxic T cells response, such as cell lysis or specific cytokine release against the target cell which binds or expresses the antigen. The antigenic peptide can be bound in the context of a class I or class π major histocompatibility complex molecule, on an antigen presenting cell or on a target cell. In eukaryotes, RNA polymerase II catalyzes the transcription of a structural gene to produce mRNA. A nucleic acid molecule can be designed to contain an RNA polymerase π template in which the RNA transcript has a sequence that is complementary to that of a specific mRNA. The RNA transcript is termed an "anti- sense RNA" and a nucleic acid molecule that encodes the anti-sense RNA is termed an "anti-sense gene." Anti-sense RNA molecules are capable of binding to mRNA molecules, resulting in an inhibition of mRNA translation. An "anti-sense oligonucleotide specific for Zcytorlo" or a "Zcytorlo anti-sense oligonucleotide" is an oligonucleotide having a sequence (a) capable of forming a stable triplex with a portion of the Zcytorlo gene, or (b) capable of forming a stable duplex with a portion of an mRNA transcript of the Zcytorlo gene. A "ribozyme" is a nucleic acid molecule that contains a catalytic center. The term includes RNA enzymes, self-splicing RNAs, self-cleaving RNAs, and nucleic acid molecules that perform these catalytic functions. A nucleic acid molecule that encodes a ribozyme is termed a "ribozyme gene." An "external guide sequence" is a nucleic acid molecule that directs the endogenous ribozyme, RNase P, to a particular species of intracellular mRNA, resulting in the cleavage of the mRNA by RNase P. A nucleic acid molecule that encodes an external guide sequence is termed an "external guide sequence gene." The term "variant Zcytorlo gene" refers to nucleic acid molecules that encode a polypeptide having an amino acid sequence that is a modification of SEQ ID NO:2. Such variants include naturally-occurring polymorphisms of Zcytorlo genes, as well as synthetic genes that contain conservative amino acid substitutions of the amino acid sequence of SEQ ID NO:2. Additional variant forms of Zcytorl6 genes are nucleic acid molecules that contain insertions or deletions of the nucleotide sequences described herein. A variant Zcytorlo gene can be identified, for example, by determining whether the gene hybridizes with a nucleic acid molecule having the nucleotide sequence of SEQ ID NO:l, or its complement, under stringent conditions. Alternatively, variant Zcytorl6 genes can be identified by sequence comparison. Two amino acid sequences have "100% amino acid sequence identity" if the amino acid residues of the two amino acid sequences are the same when aligned for maximal correspondence. Similarly, two nucleotide sequences have "100% nucleotide sequence identity" if the nucleotide residues of the two nucleotide sequences are the same when aligned for maximal correspondence. Sequence comparisons can be performed using standard software programs such as those included in the LASERGENE bioinformatics computing suite, which is produced by DNASTAR (Madison, Wisconsin). Other methods for comparing two nucleotide or amino acid sequences by determining optimal alignment are well-known to those of skill in the art (see, for example, Peruski and Peruski, The Internet and the New Biology: Tools for Genomic and Molecular Research (ASM Press, Inc. 1997), Wu et al. (eds.), "Information Superhighway and Computer Databases of Nucleic Acids and Proteins," in Methods in Gene Biotechnology, pages 123-151 (CRC Press, Inc. 1997), and Bishop (ed.), Guide to Human Genome Computing, 2nd Edition (Academic Press, Inc. 1998)). Particular methods for determining sequence identity are described below. Regardless of the particular method used to identify a variant Zcytorlo gene or variant Zcytorlo polypeptide, a variant gene or polypeptide encoded by a variant gene may be functionally characterized the ability to bind specifically to an anti- Zcytorlό antibody. A variant Zcytorlo gene or variant Zcytorlo polypeptide may also be functionally characterized the ability to bind to its ligand, EL-TIF, using a biological or biochemical assay described herein. The term "allelic variant" is used herein to denote any of two or more alternative forms of a gene occupying the same chromosomal locus. Allelic variation arises naturally through mutation, and may result in phenotypic polymorphism within populations. Gene mutations can be silent (no change in the encoded polypeptide) or may encode polypeptides having altered amino acid sequence. The term allelic variant is also used herein to denote a protein encoded by an allelic variant of a gene. The term "ortholog" denotes a polypeptide or protein obtained from one species that is the functional counterpart of a polypeptide or protein from a different species. Sequence differences among orthologs are the result of speciation. "Paralogs" are distinct but structurally related proteins made by an organism. Paralogs are believed to arise through gene duplication. For example, α- globin, β-globin, and myoglobin are paralogs of each other. The present invention includes functional fragments of Zcytorlo genes. Within the context of this invention, a "functional fragment" of a Zcytorlo gene refers to a nucleic acid molecule that encodes a portion of a Zcytorlo polypeptide which is a domain described herein or at least specifically binds with an anti-Zcytorl6 antibody. Due to the imprecision of standard analytical methods, molecular weights and lengths of polymers are understood to be approximate values. When such a value is expressed as "about" X or "approximately" X, the stated value of X will be understood to be accurate to ±10%. 3. Production of Zcytorlo Polynucleotides or Genes Nucleic acid molecules encoding a human Zcytorlo gene can be obtained by screening a human cDNA or genomic library using polynucleotide probes based upon SEQ ID NO:l. These techniques are standard and well-established. As an illustration, a nucleic acid molecule that encodes a human Zcytorlo gene can be isolated from a cDNA library. In this case, the first step would be to prepare the cDNA library by isolating RNA from a tissue, such as tonsil tissue, using methods well-known to those of skill in the art. In general, RNA isolation techniques must provide a method for breaking cells, a means of inhibiting RNase-directed degradation of RNA, and a method of separating RNA from DNA, protein, and polysaccharide contaminants. For example, total RNA can be isolated by freezing tissue in liquid nitrogen, grinding the frozen tissue with a mortar and pestle to lyse the cells, extracting the ground tissue with a solution of phenol/chloroform to remove proteins, and separating RNA from the remaining impurities by selective precipitation with lithium chloride (see, for example, Ausubel et al. (eds.), Short Protocols in Molecular Biology, 3 rd Edition, pages 4-1 to 4-6 (John Wiley & Sons 1995) ["Ausubel (1995)"]; Wu et al, Methods in Gene Biotechnology, pages 33-41 (CRC Press, Inc. 1997) ["Wu (1997)"]). Alternatively, total RNA can be isolated by extracting ground tissue with guanidinium isothiocyanate, extracting with organic solvents, and separating RNA from contaminants using differential centrifugation (see, for example, Chirgwin et al, Biochemistry 18:52 (1979); Ausubel (1995) at pages 4-1 to 4-6; Wu (1997) at pages 33- 41). In order to construct a cDNA library, poly(A) + RNA must be isolated from a total RNA preparation. Poly(A) + RNA can be isolated from total RNA using the standard technique of oligo(dT)-cellulose chromatography (see, for example, Aviv and Leder, Proc. Nat'l Acad. Sci. USA 69:1408 (1972); Ausubel (1995) at pages 4-11 to 4- 12). Double-stranded cDNA molecules are synthesized from poly(A) + RNA using techniques well-known to those in the art. (see, for example, Wu (1997) at pages 41-46). Moreover, commercially available kits can be used to synthesize double- stranded cDNA molecules. For example, such kits are available from Life Technologies, Inc. (Gaithersburg, MD), CLONTECH Laboratories, Inc. (Palo Alto, CA), Promega Corporation (Madison, WI) and STRATAGENE (La Jolla, CA). Various cloning vectors are appropriate for the construction of a cDNA library. For example, a cDNA library can be prepared in a vector derived from bacteriophage, such as a λgtlO vector. See, for example, Huynh et al, "Constructing and Screening cDNA Libraries in λgtlO and λgtl l," in DNA Cloning: A Practical Approach Vol. I, Glover (ed.), page 49 (IRL Press, 1985); Wu (1997) at pages 47-52. Alternatively, double-stranded cDNA molecules can be inserted into a plasmid vector, such as a PBLUESCRIPT vector (STRATAGENE; La Jolla, CA), a LAMDAGEM-4 (Promega Corp.) or other commercially available vectors. Suitable cloning vectors also can be obtained from the American Type Culture Collection (Manassas, VA). To amplify the cloned cDNA molecules, the cDNA library is inserted into a prokaryotic host, using standard techniques. For example, a cDNA library can be introduced into competent E. coli DH5 or DH10B cells, which can be obtained, for example, from Life Technologies, Inc. or GIBCO BRL (Gaithersburg, MD). A human genomic library can be prepared by means well known in the art (see, for example, Ausubel (1995) at pages 5-1 to 5-6; Wu (1997) at pages 307-327). Genomic DNA can be isolated by lysing tissue with the detergent Sarkosyl, digesting the lysate with proteinase K, clearing insoluble debris from the lysate by centrifugation, precipitating nucleic acid from the lysate using isopropanol, and purifying resuspended DNA on a cesium chloride density gradient. DNA fragments that are suitable for the production of a genomic library can be obtained by the random shearing of genomic DNA or by the partial digestion of genomic DNA with restriction endonucleases. Genomic DNA fragments can be inserted into a vector, such as a bacteriophage or cosmid vector, in accordance with conventional techniques, such as the use of restriction enzyme digestion to provide appropriate termini, the use of alkaline phosphatase treatment to avoid undesirable joining of DNA molecules, and ligation with appropriate ligases. Techniques for such manipulation are well known in the art (see, for example, Ausubel (1995) at pages 5-1 to 5-6; Wu (1997) at pages 307- 327). Alternatively, human genomic libraries can be obtained from commercial sources such as Research Genetics (Huntsville, AL) and the American Type Culture Collection (Manassas, VA). A library containing cDNA or genomic clones can be screened with one or more polynucleotide probes based upon SEQ ID NO:l, using standard methods (see, for example, Ausubel (1995) at pages 6-1 to 6-11). Nucleic acid molecules that encode a human Zcytorlo gene can also be obtained using the polymerase chain reaction (PCR) with oligonucleotide primers having nucleotide sequences that are based upon the nucleotide sequences of the Zcytorlo gene, as described herein. General methods for screening libraries with PCR are provided by, for example, Yu et al, "Use of the Polymerase Chain Reaction to Screen Phage Libraries," in Methods in Molecular Biology, Vol. 15: PCR Protocols: Current Methods and Applications, White (ed.), pages 211-215 (Humana Press, Inc. 1993). Moreover, techniques for using PCR to isolate related genes are described by, for example, Preston, "Use of Degenerate Oligonucleotide Primers and the Polymerase Chain Reaction to Clone Gene Family Members," in Methods in Molecular Biology, Vol. 15: PCR Protocols: Current Methods and Applications, White (ed.), pages 317- 337 (Humana Press, Inc. 1993). Anti -Zcytorlo antibodies, produced as described below, can also be used to isolate DNA sequences that encode human Zcytorl6 genes from cDNA libraries. For example, the antibodies can be used to screen λgtl l expression libraries, or the antibodies can be used for immunoscreening following hybrid selection and translation (see, for example, Ausubel (1995) at pages 6-12 to 6-16; Margolis et al, "Screening λ expression libraries with antibody and protein probes," in DNA Cloning 2: Expression Systems, 2nd Edition, Glover et al. (eds.), pages 1-14 (Oxford University Press 1995)). As an alternative, a Zcytorlo gene can be obtained by synthesizing nucleic acid molecules using mutually priming long oligonucleotides and the nucleotide sequences described herein (see, for example, Ausubel (1995) at pages 8-8 to 8-9). Established techniques using the polymerase chain reaction provide the ability to synthesize DNA molecules at least two kilobases in length (Adang et al, Plant Molec. Biol. 27:1131 (1993), Bambot et al, PCR Methods and Applications 2:266 (1993), Dillon et al., "Use of the Polymerase Chain Reaction for the Rapid Construction of Synthetic Genes," in Methods in Molecular Biology, Vol. 15: PCR Protocols: Current Methods and Applications, White (ed.), pages 263-268, (Humana Press, Inc. 1993), and Holowachuk et al, PCR Methods Appl. 4:299 (1995)). The nucleic acid molecules of the present invention can also be synthesized with "gene machines" using protocols such as the phosphoramidite method. If chemically-synthesized double stranded DNA is required for an application such as the synthesis of a gene or a gene fragment, then each complementary strand is made separately. The production of short genes (60 to 80 base pairs) is technically straightforward and can be accomplished by synthesizing the complementary strands and then annealing them. For the production of longer genes (>300 base pairs), however, special strategies may be required, because the coupling efficiency of each cycle during chemical DNA synthesis is seldom 100%. To overcome this problem, synthetic genes (double-stranded) are assembled in modular form from single-stranded fragments that are from 20 to 100 nucleotides in length. For reviews on polynucleotide synthesis, see, for example, Glick and Pasternak, Molecular Biotechnology, Principles and Applications of Recombinant DNA (ASM Press 1994), Itakura et al, Annu. Rev. Biochem. 53:323 (1984), and Climie et al, Proc. Nat'lAcad. Sci. USA 87:633 (1990). The sequence of a Zcytorlo cDNA or Zcytorl6 genomic fragment can be determined using standard methods. Zcytorlo polynucleotide sequences disclosed herein can also be used as probes or primers to clone 5' non-coding regions of a Zcytorlo gene. Promoter elements from a Zcytorl6 gene can be used to direct the expression of heterologous genes in, for example, tonsil tissue of transgenic animals or patients treated with gene therapy. The identification of genomic fragments containing a Zcytorlo promoter or regulatory element can be achieved using well-established techniques, such as deletion analysis (see, generally, Ausubel (1995)). Cloning of 5' flanking sequences also facilitates production of Zcytorlo proteins by "gene activation," as disclosed in U.S. Patent No. 5,641,670. Briefly, expression of an endogenous Zcytorlo gene in a cell is altered by introducing into the Zcytorlo locus a DNA construct comprising at least a targeting sequence, a regulatory sequence, an exon, and an unpaired splice donor site. The targeting sequence is a Zcytorlo 5' non-coding sequence that permits homologous recombination of the construct with the endogenous Zcytorlo locus, whereby the sequences within the construct become operably linked with the endogenous Zcytorlo coding sequence. In this way, an endogenous Zcytorl6 promoter can be replaced or supplemented with other regulatory sequences to provide enhanced, tissue-specific, or otherwise regulated expression. 4. Production of Zcytorlo Gene Variants The present invention provides a variety of nucleic acid molecules, including DNA and RNA molecules, that encode the Zcytorlo polypeptides disclosed herein. Those skilled in the art will readily recognize that, in view of the degeneracy of the genetic code, considerable sequence variation is possible among these polynucleotide molecules. SEQ ID NO:3 is a degenerate nucleotide sequence that encompasses all nucleic acid molecules that encode the Zcytorlo polypeptide of SEQ ED NO:2. Those skilled in the art will recognize that the degenerate sequence of SEQ D NO:3 also provides all RNA sequences encoding SEQ ID NO:2, by substituting U for T. Moreover, the present invention also provides isolated soluble monomeric, homodimeric, heterodimeric and multimeric receptor polypeptides that comprise at least one zcytorlo receptor subunit that is substantially homologous to the receptor polypeptide of SEQ ID NO:3. Thus, the present invention contemplates Zcytorlo polypeptide-encoding nucleic acid molecules comprising nucleotide 1 to nucleotide 693 of SEQ ID NO:l, and their RNA equivalents. Table 1 sets forth the one-letter codes used within SEQ ID NO:3 to denote degenerate nucleotide positions. "Resolutions" are the nucleotides denoted by a code letter. "Complement" indicates the code for the complementary nucleotide(s). For example, the code Y denotes either C or T, and its complement R denotes A or G, A being complementary to T, and G being complementary to C. Table 1 The degenerate codons used in SEQ ED NO: 3, encompassing all possible codons for a given amino acid, are set forth in Table 2. Table 2 One of ordinary skill in the art will appreciate that some ambiguity is introduced in determining a degenerate codon, representative of all possible codons encoding an amino acid. For example, the degenerate codon for serine (WSN) can, in some circumstances, encode arginine (AGR), and the degenerate codon for arginine (MGN) can, in some circumstances, encode serine (AGY). A similar relationship exists between codons encoding phenylalanine and leucine. Thus, some polynucleotides encompassed by the degenerate sequence may encode variant amino acid sequences, but one of ordinary skill in the art can easily identify such variant sequences by reference to the amino acid sequences of SEQ ID NO:2. Variant sequences can be readily tested for functionality as described herein. Different species can exhibit "preferential codon usage." In general, see, Grantham et al, Nucl. Acids Res. 5:1893 (1980), Haas et al. Curr. Biol 6:315 (1996), Wain-Hobson et al, Gene 13:355 (1981), Grosjean and Fiers, Gene 18:199 (1982), Holm, Nuc. Acids Res. 14:3015 (1986), Ikemura, J. Mol. Biol. 158:513 (1982), Sharp and Matassi, Curr. Opin. Genet. Dev. 4:851 (1994), Kane, Curr. Opin. Biotechnol. 6:494 (1995), and Makrides, Microbiol Rev. 60:512 (1996). As used herein, the term "preferential codon usage" or "preferential codons" is a term of art referring to protein translation codons that are most frequently used in cells of a certain species, thus favoring one or a few representatives of the possible codons encoding each amino acid (See Table 2). For example, the amino acid threonine (Thr) may be encoded by ACA, ACC, ACG, or ACT, but in mammalian cells ACC is the most commonly used codon; in other species, for example, insect cells, yeast, viruses or bacteria, different Thr codons may be preferential. Preferential codons for a particular species can be introduced into the polynucleotides of the present invention by a variety of methods known in the art. Introduction of preferential codon sequences into recombinant DNA can, for example, enhance production of the protein by making protein translation more efficient within a particular cell type or species. Therefore, the degenerate codon sequences disclosed herein serve as a template for optimizing expression of polynucleotides in various cell types and species commonly used in the art and disclosed herein. Sequences containing preferential codons can be tested and optimized for expression in various species, and tested for functionality as disclosed herein. The present invention further provides variant polypeptides and nucleic acid molecules that represent counterparts from other species (orthologs). These species include, but are not limited to mammalian, avian, amphibian, reptile, fish, insect and other vertebrate and invertebrate species. Of particular interest are Zcytorlo polypeptides from other mammalian species, including mouse, porcine, ovine, bovine, canine, feline, equine, and other primate polypeptides. Orthologs of human Zcytorlo can be cloned using information and compositions provided by the present invention in combination with conventional cloning techniques. For example, a Zcytorlo cDNA can be cloned using mRNA obtained from a tissue or cell type that expresses Zcytorl6 as disclosed herein. Suitable sources of mRNA can be identified by probing northern blots with probes designed from the sequences disclosed herein. A library is then prepared from mRNA of a positive tissue or cell line. A Zcytør76-encoding cDNA can be isolated by a variety of methods, such as by probing with a complete or partial human cDNA or with one or more sets of degenerate probes based on the disclosed sequences. A cDNA can also be cloned using the polymerase chain reaction with primers designed from the representative human Zcytorlo sequences disclosed herein. In addition, a cDNA library can be used to transform or transfect host cells, and expression of the cDNA of interest can be detected with an antibody to Zcytorlo polypeptide. Those skilled in the art will recognize that the sequence disclosed in SEQ ID NO:l represents a single allele of human Zcytorlo, and that allelic variation and alternative splicing are expected to occur. Allelic variants of this sequence can be cloned by probing cDNA or genomic libraries from different individuals according to standard procedures. Allelic variants of the nucleotide sequences disclosed herein, including those containing silent mutations and those in which mutations result in amino acid sequence changes, are within the scope of the present invention, as are proteins which are allelic variants of the amino acid sequences disclosed herein. cDNA molecules generated from alternatively spliced mRNAs, which retain the properties of the Zcytorlo polypeptide are included within the scope of the present invention, as are polypeptides encoded by such cDNAs and mRNAs. Allelic variants and splice variants of these sequences can be cloned by probing cDNA or genomic libraries from different individuals or tissues according to standard procedures known in the art. Using the methods discussed above, one of ordinary skill in the art can prepare a variety of polypeptides that comprise a soluble receptor subunit that is substantially homologous to SEQ ED NO:l or SEQ ED NO:2, SEQ ED NO: 13, amino acids 22-210 of SEQ ID NO:2, or allelic variants thereof and retain the ligand-binding properties of the wild-type zcytorlo receptor. Such polypeptides may also include additional polypeptide segments as generally disclosed herein. Within certain embodiments of the invention, the isolated nucleic acid molecules can hybridize under stringent conditions to nucleic acid molecules comprising nucleotide sequences disclosed herein. For example, such nucleic acid molecules can hybridize under stringent conditions to nucleic acid molecules comprising the nucleotide sequence of SEQ ID NO:l, to nucleic acid molecules consisting of the nucleotide sequence of nucleotides 64 to 693 of SEQ ID NO:l, or to nucleic acid molecules comprising a nucleotide sequence complementary to SEQ ID NO:l or to nucleotides 64 to 693 of SEQ ID NO:l. In general, stringent conditions are selected to be about 5°C lower than the thermal melting point (T m ) for the specific sequence at a defined ionic strength and pH. The T m is the temperature (under defined ionic strength and pH) at which 50% of the target sequence hybridizes to a perfectly matched probe. A pair of nucleic acid molecules, such as DNA-DNA, RNA-RNA and DNA-RNA, can hybridize if the nucleotide sequences have some degree of complementarity. Hybrids can tolerate mismatched base pairs in the double helix, but the stability of the hybrid is influenced by the degree of mismatch. The T m of the mismatched hybrid decreases by 1°C for every 1-1.5% base pair mismatch. Varying the stringency of the hybridization conditions allows control over the degree of mismatch that will be present in the hybrid. The degree of stringency increases as the hybridization temperature increases and the ionic strength of the hybridization buffer decreases. Stringent hybridization conditions encompass temperatures of about 5-25°C below the T m of the hybrid and a hybridization buffer having up to 1 M Na + . Higher degrees of stringency at lower temperatures can be achieved with the addition of formamide which reduces the T m of the hybrid about 1°C for each 1% formamide in the buffer solution. Generally, such stringent conditions include temperatures of 20- 70°C and a hybridization buffer containing up to 6x SSC and 0-50% formamide. A higher degree of stringency can be achieved at temperatures of from 40-70°C with a hybridization buffer having up to 4x SSC and from 0-50% formamide. Highly stringent conditions typically encompass temperatures of 42-70°C with a hybridization buffer having up to lx SSC and 0-50% formamide. Different degrees of stringency can be used during hybridization and washing to achieve maximum specific binding to the target sequence. Typically, the washes following hybridization are performed at increasing degrees of stringency to remove non-hybridized polynucleotide probes from hybridized complexes. The above conditions are meant to serve as a guide and it is well within the abilities of one skilled in the art to adapt these conditions for use with a particular polynucleotide hybrid. The T m for a specific target sequence is the temperature (under defined conditions) at which 50% of the target sequence will hybridize to a perfectly matched probe sequence. Those conditions which influence the T m include, the size and base pair content of the polynucleotide probe, the ionic strength of the hybridization solution, and the presence of destabilizing agents in the hybridization solution. Numerous equations for calculating T m are known in the art, and are specific for DNA, RNA and DNA-RNA hybrids and polynucleotide probe sequences of varying length (see, for example, Sambrook et al, Molecular Cloning: A Laboratory Manual, Second Edition (Cold Spring Harbor Press 1989); Ausubel et al, (eds.), Current Protocols in Molecular Biology (John Wiley and Sons, Inc. 1987); Berger and Kimmel (eds.), Guide to Molecular Cloning Techniques, (Academic Press, Enc. 1987); and Wetmur, Crit. Rev. Biochem. Mol. Biol. 26:221 (1990)). Sequence analysis software such as OLIGO 6.0 (LSR; Long Lake, MN) and Primer Premier 4.0 (Premier Biosoft International; Palo Alto, CA), as well as sites on the Internet, are available tools for analyzing a given sequence and calculating T m based on user defined criteria. Such programs can also analyze a given sequence under defined conditions and identify suitable probe sequences. Typically, hybridization of longer polynucleotide sequences, >50 base pairs, is performed at temperatures of about 20-25°C below the calculated T m . For smaller probes, <50 base pairs, hybridization is typically carried out at the T m or 5-10°C below. This allows for the maximum rate of hybridization for DNA-DNA and DNA-RNA hybrids. The length of the polynucleotide sequence influences the rate and stability of hybrid formation. Smaller probe sequences, <50 base pairs, reach equilibrium with complementary sequences rapidly, but may form less stable hybrids. Incubation times of anywhere from minutes to hours can be used to achieve hybrid formation. Longer probe sequences come to equilibrium more slowly, but form more stable complexes even at lower temperatures. Incubations are allowed to proceed overnight or longer. Generally, incubations are carried out for a period equal to three times the calculated Cot time. Cot time, the time it takes for the polynucleotide sequences to reassociate, can be calculated for a particular sequence by methods known in the art. The base pair composition of polynucleotide sequence will effect the thermal stability of the hybrid complex, thereby influencing the choice of hybridization temperature and the ionic strength of the hybridization buffer. A-T pairs are less stable than G-C pairs in aqueous solutions containing sodium chloride. Therefore, the higher the G-C content, the more stable the hybrid. Even distribution of G and C residues within the sequence also contribute positively to hybrid stability. In addition, the base pair composition can be manipulated to alter the T m of a given sequence. For example, 5-methyldeoxycytidine can be substituted for deoxycytidine and 5-bromodeoxuridine can be substituted for thymidine to increase the T m> whereas 7-deazz-2'- deoxyguanosine can be substituted for guanosine to reduce dependence on T m . The ionic concentration of the hybridization buffer also affects the stability of the hybrid. Hybridization buffers generally contain blocking agents such as Denhardt's solution (Sigma Chemical Co., St. Louis, Mo.), denatured salmon sperm DNA, tRNA, milk powders (BLOTTO), heparin or SDS, and a Na + source, such as SSC (lx SSC: 0.15 M sodium chloride, 15 mM sodium citrate) or SSPE (lx SSPE: 1.8 M NaCl, 10 mM NaH 2 PO 4 , 1 mM EDTA, pH 7.7). Typically, hybridization buffers contain from between 10 mM - 1 M Na + . The addition of destabilizing or denaturing agents such as formamide, tetralkylammonium salts, guanidinium cations or thiocyanate cations to the hybridization solution will alter the T m of a hybrid. Typically, formamide is used at a concentration of up to 50% to allow incubations to be carried out at more convenient and lower temperatures. Formamide also acts to reduce non-specific background when using RNA probes. As an illustration, a nucleic acid molecule encoding a variant Zcytorlo polypeptide can be hybridized with a nucleic acid molecule having the nucleotide sequence of SEQ ID NO:l (or its complement) at 42°C overnight in a solution comprising 50% formamide, 5x SSC, 50 mM sodium phosphate (pH 7.6), 5x Denhardt's solution (lOOx Denhardt's solution: 2% (w/v) Ficoll 400, 2% (w/v) polyvinylpyrrolidone, and 2% (w/v) bovine serum albumin), 10% dextran sulfate, and 20 μg/ml denatured, sheared salmon sperm DNA. One of skill in the art can devise variations of these hybridization conditions. For example, the hybridization mixture can be incubated at a higher temperature, such as about 65°C, in a solution that does not contain formamide. Moreover, premixed hybridization solutions are available (e.g., EXPRESSHYB Hybridization Solution from CLONTECH Laboratories, Inc.), and hybridization can be performed according to the manufacturer's instructions. Following hybridization, the nucleic acid molecules can be washed to remove non-hybridized nucleic acid molecules under stringent conditions, or under highly stringent conditions. Typical stringent washing conditions include washing in a solution of 0.5x - 2x SSC with 0.1% sodium dodecyl sulfate (SDS) at 55 - 65°C. As an illustration, nucleic acid molecules encoding a variant Zcytorlo polypeptide remain hybridized with a nucleic acid molecule having the nucleotide sequence of SEQ ID NO:l (or its complement) under stringent washing conditions, in which the wash stringency is equivalent to 0.5x - 2x SSC with 0.1% SDS at 55 - 65°C, including 0.5x SSC with 0.1% SDS at 55°C, or 2xSSC with 0.1% SDS at 65°C. One of skill in the art can readily devise equivalent conditions, for example, by substituting SSPE for SSC in the wash solution. Typical highly stringent washing conditions include washing in a solution of O.lx - 0.2x SSC with 0.1% sodium dodecyl sulfate (SDS) at 50 - 65°C. For example, nucleic acid molecules encoding a variant Zcytorlo polypeptide remain hybridized with a nucleic acid molecule having the nucleotide sequence of SEQ ID NO: 1 (or its complement) under highly stringent washing conditions, in which the wash stringency is equivalent to O.lx - 0.2x SSC with 0.1% SDS at 50 - 65°C, including O.lx SSC with 0.1% SDS at 50°C, or 0.2xSSC with 0.1% SDS at 65°C. The present invention also provides isolated Zcytorlo polypeptides that have a substantially similar sequence identity to the polypeptides of SEQ ED NO:2, or their orthologs. The term "substantially similar sequence identity" is used herein to denote polypeptides having at least 70%, at least 80%, at least 90%, at least 95% or greater than 95% sequence identity to the sequences shown in SEQ ID NO:2, or their orthologs. The present invention also contemplates Zcytorlo variant nucleic acid molecules that can be identified using two criteria: a determination of the similarity between the encoded polypeptide with the amino acid sequence of SEQ ED NO:2, and a hybridization assay, as described above. Such Zcytorlo variants include nucleic acid molecules (1) that remain hybridized with a nucleic acid molecule having the nucleotide sequence of SEQ ED NO:l (or its complement) under stringent washing conditions, in which the wash stringency is equivalent to 0.5x - 2x SSC with 0.1% SDS at 55 - 65°C, and (2) that encode a polypeptide having at least 70%, at least 80%, at least 90%, at least 95% or greater than 95% sequence identity to the amino acid sequence of SEQ ID NO:2. Alternatively, Zcytorlo variants can be characterized as nucleic acid molecules (1) that remain hybridized with a nucleic acid molecule having the nucleotide sequence of SEQ ID NO: 1 (or its complement) under highly stringent washing conditions, in which the wash stringency is equivalent to O.lx - 0.2x SSC with 0.1% SDS at 50 - 65°C, and (2) that encode a polypeptide having at least 70%, at least 80%, at least 90%, at least 95% or greater than 95% sequence identity to the amino acid sequence of SEQ ID NO:2. Percent sequence identity is determined by conventional methods. See, for example, Altschul et al, Bull. Math. Bio. 48:603 (1986), and Henikoff and Henikoff, Proc. Natl Acad. Sci. USA S9:10915 (1992). Briefly, two amino acid sequences are aligned to optimize the alignment scores using a gap opening penalty of 10, a gap extension penalty of 1, and the "BLOSUM62" scoring matrix of Henikoff and Henikoff (ibid.) as shown in Table 3 (amino acids are indicated by the standard one- letter codes). The percent identity is then calculated as: ([Total number of identical matches]/ [length of the longer sequence plus the number of gaps introduced into the longer sequence in order to align the two sequences])(100). > _s rH CN ro rH 1 CO <ψ oo CN CN 1 1 O. F- rH rH ^f CN I I 1 1 P-. yD CN CN rH 00 H 1 1 1 1 LT) O CN rH rH rH rH 1 1 1 1 1 LΠ 00 O 00 CN CN 1 1 1 1 1 1 1 <Φ N CN O 00 CN rH CN H H 1 1 1 1 1 <tf CN ro H o 00 CN H 00 rH 00 1 1 1 1 1 1 ffi co ro ro rH CN H CN rH CN CN CN 00 1 1 1 1 1 1 1 1 1 VD CN CN 00 00 CN o CN CN 00 00 1 1 1 1 I 1 1 1 1 w LO CN o ro ro H CN 00 H o H 00 CN CN 1 1 1 1 1 1 1 1 1 σ Lfl CN CN o ro CN r-t O 00 O rH CN rH CN 1 1 1 1 1 1 1 1 1 u σi ro ro ro H rH 00 rH CN 00 rH rH CN CN 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Q VD n o CN rH rH ro rH 00 00 H o rH 00 00 1 1 1 1 1 1 1 1 1 1 1 1 1 £ D H ro O O O rH ro 00 o CN 00 CN H O CN 00 1 1 1 1 1 1 1 1 1 Hi in O CN ro H O CN O ro CN CN 00 CN rH H 00 CN 00 1 1 1 1 1 1 1 1 1 1 1 1 : <* H CN CN o rH O CN rH rH H CN H O 00 CN o 1 1 1 1 1 1 1 1 1 1 1 • 1 1 <; ς.; s Q u α ω m h ^ 2 fc ft θ- E-ι 5 H > o Those skilled in the art appreciate that there are many established algorithms available to align two amino acid sequences. The "FASTA" similarity search algorithm of Pearson and Lipman is a suitable protein alignment method for examining the level of identity shared by an amino acid sequence disclosed herein and the amino acid sequence of a putative Zcytorlo variant. The FASTA algorithm is described by Pearson and Lipman, Proc. Nat'l Acad. Sci. USA 85:2444 (1988), and by Pearson, Meth. Enzymol 183:63 (1990). Briefly, FASTA first characterizes sequence similarity by identifying regions shared by the query sequence (e.g., SEQ ID NO:2) and a test sequence that have either the highest density of identities (if the ktup variable is 1) or pairs of identities (if ktup=2), without considering conservative amino acid substitutions, insertions, or deletions. The ten regions with the highest density of identities are then rescored by comparing the similarity of all paired amino acids using an amino acid substitution matrix, and the ends of the regions are "trimmed" to include only those residues that contribute to the highest score. If there are several regions with scores greater than the "cutoff value (calculated by a predetermined formula based upon the length of the sequence and the ktup value), then the trimmed initial regions are examined to determine whether the regions can be joined to form an approximate alignment with gaps. Finally, the highest scoring regions of the two amino acid sequences are aligned using a modification of the Needleman-Wunsch-Sellers algorithm (Needleman and Wunsch, J. Mol. Biol. 48:444 (1970); Sellers, SIAM J. Appl. Math. 26:lcll (1974)), which allows for amino acid insertions and deletions. Illustrative parameters for FASTA analysis are: ktup=l, gap opening penalty=10, gap extension penalty=l, and substitution matrix=BLOSUM62. These parameters can be introduced into a FASTA program by modifying the scoring matrix file ("SMATREX"), as explained in Appendix 2 of Pearson, Meth. Enzymol. 183:63 (1990). FASTA can also be used to determine the sequence identity of nucleic acid molecules using a ratio as disclosed above. For nucleotide sequence comparisons, the ktup value can range between one to six, preferably from three to six, most preferably three, with other parameters set as described above. The present invention includes nucleic acid molecules that encode a polypeptide having a conservative amino acid change, compared with an amino acid sequence disclosed herein. For example, variants can be obtained that contain one- or more amino acid substitutions of SEQ ED NO:2, in which an alkyl amino acid is substituted for an alkyl amino acid in a Zcytorlo amino acid sequence, an aromatic amino acid is substituted for an aromatic amino acid in a Zcytorlo amino acid sequence, a sulfur-containing amino acid is substituted for a sulfur-containing amino acid in a Zcytorlo amino acid sequence, a hydroxy-containing amino acid is substituted for a hydroxy-containing amino acid in a Zcytorl6 amino acid sequence, an acidic amino acid is substituted for an acidic amino acid in a Zcytorlo amino acid sequence, a basic amino acid is substituted for a basic amino acid in a Zcytorlo amino acid sequence, or a dibasic monocarboxylic amino acid is substituted for a dibasic monocarboxylic amino acid in a Zcytorlo amino acid sequence. Among the common amino acids, for example, a "conservative amino acid substitution" is illustrated by a substitution among amino acids within each of the following groups: (1) glycine, alanine, valine, leucine, and isoleucine, (2) phenylalanine, tyrosine, and tryptophan, (3) serine and threonine, (4) aspartate and glutamate, (5) glutamine and asparagine, and (6) lysine, arginine and histidine. The BLOSUM62 table is an amino acid substitution matrix derived from about 2,000 local multiple alignments of protein sequence segments, representing highly conserved regions of more than 500 groups of related proteins (Henikoff and Henikoff, Proc. Nat'l Acad. Sci. USA 59:10915 (1992)). Accordingly, the BLOSUM62 substitution frequencies can be used to define conservative amino acid substitutions that may be introduced into the amino acid sequences of the present invention. Although it is possible to design amino acid substitutions based solely upon chemical properties (as discussed above), the language "conservative amino acid substitution" preferably refers to a substitution represented by a BLOSUM62 value of greater than -1. For example, an amino acid substitution is conservative if the substitution is characterized by a BLOSUM62 value of 0, 1, 2, or 3. According to this system, preferred conservative amino acid substitutions are characterized by a BLOSUM62 value of at least 1 (e.g., 1, 2 or 3), while more prefeπed conservative amino acid substitutions are characterized by a BLOSUM62 value of at least 2 (e.g., 2 or 3). Particular variants of Zcytorl6 are characterized by having at least 70%, at least 80%, at least 90%, at least 95% or greater than 95% sequence identity to the corresponding amino acid sequence (e.g., SEQ ID NO:2), wherein the variation in amino acid sequence is due to one or more conservative amino acid substitutions. Conservative amino acid changes in a Zcytorl6 gene can be introduced, for example, by substituting nucleotides for the nucleotides recited in SEQ ID NO:l. Such "conservative amino acid" variants can be obtained by oligonucleotide-directed mutagenesis, linker-scanning mutagenesis, mutagenesis using the polymerase chain reaction, and the like (see Ausubel (1995) at pages 8-10 to 8-22; and McPherson (ed.), Directed Mutagenesis: A Practical Approach (IRL Press 1991)). A variant Zcytorlo polypeptide can be identified by the ability to specifically bind anti-Zcytorl6 antibodies. The proteins of the present invention can also comprise non-naturally occurring amino acid residues. Non-naturally occurring amino acids include, without limitation, tran_s-3-methylproline, 2,4-methanoproline, c/s-4-hydroxyproline, trans-4- hydroxyproline, N-methylglycine, //ø-threonine, methylthreonine, hydroxyethylcysteine, hydroxyethylhomocysteine, nitroglutamine, homoglutamine, pipecolic acid, thiazolidine carboxylic acid, dehydroproline, 3- and 4-methylproline, 3,3-dimethylproline, tert-leucine, norvaline, 2-azaphenylalanine, 3-azaphenylalanine, 4- azaphenylalanine, and 4-fluorophenylalanine. Several methods are known in the art for incorporating non-naturally occuπing amino acid residues into proteins. For example, an in vitro system can be employed wherein nonsense mutations are suppressed using chemically aminoacylated suppressor tRΝAs. Methods for synthesizing amino acids and aminoacylating tRΝA are known in the art. Transcription and translation of plasmids containing nonsense mutations is typically earned out in a cell-free system comprising an E. coli S30 extract and commercially available enzymes and other reagents. Proteins are purified by chromatography. See, for example, Robertson et al, J. Am. Chem. Soc. 113:2122 (1991), Ellman et al, Methods Enzymol 202:301 (1991), Chung et al, Science 259:806 (1993), and Chung et al, Proc. Nat'l Acad. Sci. USA 90:10145 (1993). In a second method, translation is caπied out in Xenopus oocytes by microinjection of mutated mRNA and chemically aminoacylated suppressor tRNAs (Turcatti et al, J. Biol. Chem. 271:19991 (1996)). Within a third method, E. coli cells are cultured in the absence of a natural amino acid that is to be replaced (e.g., phenylalanine) and in the presence of the desired non-naturally occurring amino acid(s) (e.g., 2-azaphenylalanine, 3-azaphenylalanine, 4-azaphenylalanine, or 4- fluorophenylalanine). The non-naturally occuπing amino acid is incorporated into the protein in place of its natural counterpart. See, Koide et al, Biochem. 33:1410 (1994). Naturally occuπing amino acid residues can be converted to non-naturally occuπing species by in vitro chemical modification. Chemical modification can be combined with site-directed mutagenesis to further expand the range of substitutions (Wynn and Richards, Protein Sci. 2:395 (1993)). A limited number of non-conservative amino acids, amino acids that are not encoded by the genetic code, non-naturally occuπing amino acids, and unnatural amino acids may be substituted for Zcytorlo amino acid residues. Essential amino acids in the polypeptides of the present invention can be identified according to procedures known in the art, such as site-directed mutagenesis or alanine-scanning mutagenesis (Cunningham and Wells, Science 244:1081 (1989), Bass et al, Proc. Nat'l Acad. Sci. USA &5:4498 (1991), Coombs and Corey, "Site- Directed Mutagenesis and Protein Engineering," in Proteins: Analysis and Design, Angeletti (ed.), pages 259-311 (Academic Press, Inc. 1998)). In the latter technique, single alanine mutations are introduced at every residue in the molecule, and the resultant mutant molecules are tested for biological activity to identify amino acid residues that are critical to the activity of the molecule. See also, Hilton et al, J. Biol. Chem. 271:4699 (1996). Although sequence analysis can be used to further define the Zcytorlo ligand binding region, amino acids that play a role in Zcytorlo binding activity (such as binding of zcytorlo to ligand IL-TIF, or to an anti-zcytorl6 antibody) can also be determined by physical analysis of structure, as determined by such techniques as nuclear magnetic resonance, crystallography, electron diffraction or photoaffinity labeling, in conjunction with mutation of putative contact site amino acids. See, for example, de Vos et al, Science 255:306 (1992), Smith et al, J. Mol. Biol. 224:899 (1992), and Wlodaver et al, FEBS Lett. 309:59 (1992). Multiple amino acid substitutions can be made and tested using known methods of mutagenesis and screening, such as those disclosed by Reidhaar-Olson and Sauer (Science 241:53 (1988)) or Bowie and Sauer (Proc. Nat'l Acad. Sci. USA 86:2152 (1989)). Briefly, these authors disclose methods for simultaneously randomizing two or more positions in a polypeptide, selecting for functional polypeptide, and then sequencing the mutagenized polypeptides to determine the spectrum of allowable substitutions at each position. Other methods that can be used include phage display (e.g., Lowman et al, Biochem. 30:10832 (1991), Ladner et al, U.S. Patent No. 5,223,409, Huse, international publication No. WO 92/06204, and region-directed mutagenesis (Derbyshire et al, Gene 46:145 (1986), and Ner et al, DNA 7:127, (1988)). Moreover, Zcytorlo labeled with biotin or FITC can be used for expression cloning of Zcytorlo ligands. Variants of the disclosed Zcytorlo nucleotide and polypeptide sequences can also be generated through DNA shuffling as disclosed by Stemmer, Nature 370:389 (1994), Stemmer, Proc. Nat'l Acad. Sci. USA 97:10747 (1994), and international publication No. WO 97/20078. Briefly, variant DNA molecules are generated by in vitro homologous recombination by random fragmentation of a parent DNA followed by reassembly using PCR, resulting in randomly introduced point mutations. This technique can be modified by using a family of parent DNA molecules, such as allelic variants or DNA molecules from different species, to introduce additional variability into the process. Selection or screening for the desired activity, followed by additional iterations of mutagenesis and assay provides for rapid "evolution" of sequences by selecting for desirable mutations while simultaneously selecting against detrimental changes. Mutagenesis methods as disclosed herein can be combined with high- throughput, automated screening methods to detect activity of cloned, mutagenized polypeptides in host cells. Mutagenized DNA molecules that encode biologically active polypeptides, or polypeptides that bind with anti -Zcytorlo antibodies, can be recovered from the host cells and rapidly sequenced using modern equipment. These methods allow the rapid determination of the importance of individual amino acid residues in a polypeptide of interest, and can be applied to polypeptides of unknown structure. The present invention also includes "functional fragments" of Zcytorlo polypeptides and nucleic acid molecules encoding such functional fragments. Routine deletion analyses of nucleic acid molecules can be performed to obtain functional fragments of a nucleic acid molecule that encodes a Zcytorlo polypeptide. As an illustration, DNA molecules having the nucleotide sequence of SEQ ID NO: 1 can be digested with Bal31 nuclease to obtain a series of nested deletions. The fragments are then inserted into expression vectors in proper reading frame, and the expressed polypeptides are isolated and tested for the ability to bind anti-Zcytorl6 antibodies. One alternative to exonuclease digestion is to use oligonucleotide-directed mutagenesis to introduce deletions or stop codons to specify production of a desired fragment. Alternatively, particular fragments of a Zcytorlo gene can be synthesized using the polymerase chain reaction. This general approach is exemplified by studies on the truncation at either or both termini of interferons have been summarized by Horisberger and Di Marco, Pharmac. Ther. 66:507 (1995). Moreover, standard techniques for functional analysis of proteins are described by, for example, Treuter et al, Molec. Gen. Genet. 240:113 (1993), Content et al., "Expression and preliminary deletion analysis of the 42 kDa 2-5A synthetase induced by human interferon," in Biological Interferon Systems, Proceedings of ISIR-TNO Meeting on Interferon Systems, Cantell (ed.), pages 65-72 (Nijhoff 1987), Herschman, "The EGF Receptor," in Control of Animal Cell Proliferation, Vol. 1, Boynton et al, (eds.) pages 169-199 (Academic Press 1985), Coumailleau et al, J. Biol. Chem. 270:29270 (1995); Fukunaga et al, J. Biol. Chem. 270:25291 (1995); Yamaguchi et al, Biochem. Pharmacol. 50:1295 (1995), and Meisel et al, Plant Molec. Biol. 30:1 (1996). Analysis of the particular sequences disclosed herein provide a set of illustrative functional fragments presented in Table 4. Table 4 The present invention also contemplates functional fragments of a Zcytorlo gene that have amino acid changes, compared with an amino acid sequence disclosed herein. A variant Zcytorlo gene can be identified on the basis of structure by determining the level of identity with disclosed nucleotide and amino acid sequences, as discussed above. An alternative approach to identifying a variant gene on the basis of structure is to determine whether a nucleic acid molecule encoding a potential variant Zcytorlo gene can hybridize to a nucleic acid molecule comprising a nucleotide sequence, such as SEQ ID NO: 1. The present invention also provides polypeptide fragments or peptides comprising an epitope-bearing portion of a Zcytorlo polypeptide described herein. Such fragments or peptides may comprise an "immunogenic epitope," which is a part of a protein that elicits an antibody response when the entire protein is used as an immunogen. Immunogenic epitope-bearing peptides can be identified using standard methods (see, for example, Geysen et al, Proc. Nat'l Acad. Sci. USA 87:3998 (1983)). In contrast, polypeptide fragments or peptides may comprise an "antigenic epitope," which is a region of a protein molecule to which an antibody can specifically bind. Certain epitopes consist of a linear or contiguous stretch of amino acids, and the antigenicity of such an epitope is not disrupted by denaturing agents. It is known in the art that relatively short synthetic peptides that can mimic epitopes of a protein can be used to stimulate the production of antibodies against the protein (see, for example, Sutcliffe et al, Science 279:660 (1983)). Accordingly, antigenic epitope- bearing peptides and polypeptides of the present invention are useful to raise antibodies that bind with the polypeptides described herein. Antigenic epitope-bearing peptides and polypeptides can contain at least four to ten amino acids, at least ten to fifteen amino acids, or about 15 to about 30 amino acids of an amino acid sequence disclosed herein. Such epitope-bearing peptides and polypeptides can be produced by fragmenting a Zcytorlo polypeptide, or by chemical peptide synthesis, as described herein. Moreover, epitopes can be selected by phage display of random peptide libraries (see, for example, Lane and Stephen, Curr. Opin. Immunol. 5:268 (1993), and Cortese et al, Curr. Opin. Biotechnol. 7:616 (1996)). Standard methods for identifying epitopes and producing antibodies from small peptides that comprise an epitope are described, for example, by Mole, "Epitope Mapping," in Methods in Molecular Biology, Vol. 10, Manson (ed.), pages 105-116 (The Humana Press, Inc. 1992), Price, "Production and Characterization of Synthetic Peptide-Derived Antibodies," in Monoclonal Antibodies: Production, Engineering, and Clinical Application, Ritter and Ladyman (eds.), pages 60-84 (Cambridge University Press 1995), and Coligan et al. (eds.), Current Protocols in Immunology, pages 9.3.1 - 9.3.5 and pages 9.4.1 - 9.4.11 (John Wiley & Sons 1997). For any Zcytorlo polypeptide, including variants and fusion proteins, one of ordinary skill in the art can readily generate a fully degenerate polynucleotide sequence encoding that variant using the information set forth in Tables 1 and 2 above. Moreover, those of skill in the art can use standard software to devise Zcytorlo variants based upon the nucleotide and amino acid sequences described herein. Accordingly, the present invention includes a computer-readable medium encoded with a data structure that provides at least one of the following sequences: SEQ ED NO:l, SEQ ED NO:2, and SEQ ED NO:3. Suitable forms of computer-readable media include magnetic media and optically-readable media. Examples of magnetic media include a hard or fixed drive, a random access memory (RAM) chip, a floppy disk, digital linear tape (DLT), a disk cache, and a ZIP disk. Optically readable media are exemplified by compact discs (e.g., CD-read only memory (ROM), CD-rewritable (RW), and CD- recordable), and digital versatile/video discs (DVD) (e.g., DVD-ROM, DVD-RAM, and DVD+RW). 6. Production of Zcytorlo Polypeptides The polypeptides of the present invention, including full-length polypeptides; soluble monomeric, homodimeric, heterodimeric and multimeric receptors; full-length receptors; receptor fragments (e.g. ligand-binding fragments), functional fragments, and fusion proteins, can be produced in recombinant host cells following conventional techniques. To express a Zcytorlo gene, a nucleic acid molecule encoding the polypeptide must be operably linked to regulatory sequences that control transcriptional expression in an expression vector and then, introduced into a host cell. In addition to transcriptional regulatory sequences, such as promoters and enhancers, expression vectors can include translational regulatory sequences and a marker gene which is suitable for selection of cells that carry the expression vector. Expression vectors that are suitable for production of a foreign protein in eukaryotic cells typically contain (1) prokaryotic DNA elements coding for a bacterial replication origin and an antibiotic resistance marker to provide for the growth and selection of the expression vector in a bacterial host; (2) eukaryotic DNA elements that control initiation of transcription, such as a promoter; and (3) DNA elements that control the processing of transcripts, such as a transcription termination/polyadenylation sequence. As discussed above, expression vectors can also include nucleotide sequences encoding a secretory sequence that directs the heterologous polypeptide into the secretory pathway of a host cell. For example, a Zcytorlo expression vector may comprise a Zcytorlo gene and a secretory sequence derived from any secreted gene. Zcytorlo proteins of the present invention may be expressed in mammalian cells. Examples of suitable mammalian host cells include African green monkey kidney cells (Vero; ATCC CRL 1587), human embryonic kidney cells (293- HEK; ATCC CRL 1573), baby hamster kidney cells (BHK-21, BHK-570; ATCC CRL 8544, ATCC CRL 10314), canine kidney cells (MDCK; ATCC CCL 34), Chinese hamster ovary cells (CHO-K1; ATCC CCL61; CHO DG44 (Chasin et al, Som. Cell. Molec. Genet. 12:555, 1986)), rat pituitary cells (GH1; ATCC CCL82), HeLa S3 cells (ATCC CCL2.2), rat hepatoma cells (H-4-H-E; ATCC CRL 1548) SV40-transformed monkey kidney cells (COS-1; ATCC CRL 1650) and murine embryonic cells (NEH- 3T3; ATCC CRL 1658). For a mammalian host, the transcriptional and translational regulatory signals may be derived from viral sources, such as adenovirus, bovine papilloma virus, simian virus, or the like, in which the regulatory signals are associated with a particular gene which has a high level of expression. Suitable transcriptional and translational regulatory sequences also can be obtained from mammalian genes, such as actin, collagen, myosin, and metallothionein genes. Transcriptional regulatory sequences include a promoter region sufficient to direct the initiation of RNA synthesis. Suitable eukaryotic promoters include the promoter of the mouse metallothionein I gene (Hamer et al, J. Molec. Appl. Genet. 7:273 (1982)), the TK promoter of Herpes virus (McKnight, Cell 37:355 (1982)), the SV40 early promoter (Benoist et al, Nature 290:304 (1981)), the Rous sarcoma virus promoter (Gorman et al, Proc. Nat'l Acad. Sci. USA 79:6111 (1982)), the cytomegalovirus promoter (Foecking et al, Gene 45: 101 (1980)), and the mouse mammary tumor virus promoter (see, generally, Etcheverry, "Expression of Engineered Proteins in Mammalian Cell Culture," in Protein Engineering: Principles and Practice, Cleland et al (eds.), pages 163-181 (John Wiley & Sons, Inc. 1996)). Alternatively, a prokaryotic promoter, such as the bacteriophage T3 RNA polymerase promoter, can be used to control Zcytorlo gene expression in mammalian cells if the prokaryotic promoter is regulated by a eukaryotic promoter (Zhou et al, Mol. Cell. Biol. 70:4529 (1990), and Kaufman et al, Nucl. Acids Res. 79:4485 (1991)). In certain embodiments, a DNA sequence encoding a Zcytorlo monomeric or homodimeric soluble receptor polypeptide, or a DNA sequence encoding an additional subunit of a heterodimeric or multimeric Zcytorlo soluble receptor, e.g., CRF2-4 or IL10R, polypeptide is operably linked to other genetic elements required for its expression, generally including a transcription promoter and terminator, within an expression vector. The vector will also commonly contain one or more selectable markers and one or more origins of replication, although those skilled in the art will recognize that within certain systems selectable markers may be provided on separate vectors, and replication of the exogenous DNA may be provided by integration into the host cell genome. Selection of promoters, terminators, selectable markers, vectors and other elements is a matter of routine design within the level of ordinary skill in the art. Many such elements are described in the literature and are available through commercial suppliers. Multiple components of a soluble receptor complex can be co- transfected on individual expression vectors or be contained in a single expression vector. Such techniques of expressing multiple components of protein complexes are well known in the art. An expression vector can be introduced into host cells using a variety of standard techniques including calcium phosphate transfection, liposome-mediated transfection, microprojectile-mediated delivery, electroporation, and the like. The transfected cells can be selected and propagated to provide recombinant host cells that comprise the expression vector stably integrated in the host cell genome. Techniques for introducing vectors into eukaryotic cells and techniques for selecting such stable transformants using a dominant selectable marker are described, for example, by Ausubel (1995) and by Muπay (ed.), Gene Transfer and Expression Protocols (Humana Press 1991). For example, one suitable selectable marker is a gene that provides resistance to the antibiotic neomycin. In this case, selection is caπied out in the presence of a neomycin-type drug, such as G-418 or the like. Selection systems can also be used to increase the expression level of the gene of interest, a process refeπed to as "amplification." Amplification is caπied out by culturing transfectants in the presence of a low level of the selective agent and then increasing the amount of selective agent to select for cells that produce high levels of the products of the introduced genes. A suitable amplifiable selectable marker is dihydrofolate reductase, which confers resistance to methotrexate. Other drug resistance genes (e.g., hygromycin resistance, multi-drug resistance, puromycin acetyltransferase) can also be used. Alternatively, markers that introduce an altered phenotype, such as green fluorescent protein, or cell surface proteins such as CD4, CD8, Class I MHC, placental alkaline phosphatase may be used to sort transfected cells from untransfected cells by such means as FACS sorting or magnetic bead separation technology. Zcytorlo polypeptides can also be produced by cultured mammalian cells using a viral delivery system. Exemplary viruses for this purpose include adenovirus, retroviruses, herpesvirus, vaccinia virus and adeno-associated virus (AAV). Adenovirus, a double-stranded DNA virus, is cuπently the best studied gene transfer vector for delivery of heterologous nucleic acid (for a review, see Becker et al., Meth. Cell Biol. 43:161 (1994), and Douglas and Curiel, Science & Medicine 4:44 (1997)). Advantages of the adenovirus system include the accommodation of relatively large DNA inserts, the ability to grow to high-titer, the ability to infect a broad range of mammalian cell types, and flexibility that allows use with a large number of available vectors containing different promoters. By deleting portions of the adenovirus genome, larger inserts (up to 7 kb) of heterologous DNA can be accommodated. These inserts can be incorporated into the viral DNA by direct ligation or by homologous recombination with a co- transfected plasmid. An option is to delete the essential E7 gene from the viral vector, which results in the inability to replicate unless the E7 gene is provided by the host cell. Adenovirus vector-infected human 293 cells (ATCC Nos. CRL-1573, 45504, 45505), for example, can be grown as adherent cells or in suspension culture at relatively high cell density to produce significant amounts of protein (see Garnier et al, Cytotechnol 75: 145 (1994)). Zcytorlo can also be expressed in other higher eukaryotic cells, such as avian, fungal, insect, yeast, or plant cells. The baculovirus system provides an efficient means to introduce cloned Zcytorlo genes into insect cells. Suitable expression vectors are based upon the Autographa californica multiple nuclear polyhedrosis virus (AcMNPV), and contain well-known promoters such as Drosophila heat shock protein (hsp) 70 promoter, Autographa californica nuclear polyhedrosis virus immediate-early gene promoter ( e-7) and the delayed early 39K promoter, baculovirus plO promoter, and the Drosophila metallothionein promoter. A second method of making recombinant baculovirus utilizes a transposon-based system described by Luckow (Luckow, et al, J. Virol. 67:4566 (1993)). This system, which utilizes transfer vectors, is sold in the BAC-to-BAC kit (Life Technologies, Rockville, MD). This system utilizes a transfer vector, PFASTBAC (Life Technologies) containing a Tn7 transposon to move the DNA encoding the Zcytorlo polypeptide into a baculovirus genome maintained in E. coli as a large plasmid called a "bacmid." See, Hill-Perkins and Possee, J. Gen. Virol. 71:911 (1990), Bonning, et al, J. Gen. Virol. 75:1551 (1994), and Chazenbalk, and Rapoport, J. Biol. Chem. 270:1543 (1995). In addition, transfer vectors can include an in-frame fusion with DNA encoding an epitope tag at the C- or N-terminus of the expressed Zcytorlo polypeptide, for example, a Glu-Glu epitope tag (Grussenmeyer et al, Proc. Nat'l Acad. Sci. 82:1952 (1985)). Using a technique known in the art, a transfer vector containing a Zcytorl6 gene is transformed into E. coli, and screened for bacmids which contain an interrupted lacZ gene indicative of recombinant baculovirus. The bacmid DNA containing the recombinant baculovirus genome is then isolated using common techniques. The illustrative PFASTBAC vector can be modified to a considerable degree. For example, the polyhedrin promoter can be removed and substituted with the baculovirus basic protein promoter (also known as Pcor, p6.9 or MP promoter) which is expressed earlier in the baculovirus infection, and has been shown to be advantageous for expressing secreted proteins (see, for example, Hill-Perkins and Possee, J. Gen. Virol 71:911 (1990), Bonning, et al, I. Gen. Virol. 75:1551 (1994), and Chazenbalk and Rapoport, J. Biol. Chem. 270:1543 (1995). Εn such transfer vector constructs, a short or long version of the basic protein promoter can be used. Moreover, transfer vectors can be constructed which replace the native Zcytorlo secretory signal sequences with secretory signal sequences derived from insect proteins. For example, a secretory signal sequence from Εcdysteroid Glucosyltransferase (ΕGT), honey bee Melittin (Invitrogen Corporation; Carlsbad, CA), or baculovirus gp67 (PharMingen: San Diego, CA) can be used in constructs to replace the native Zcytorlo secretory signal sequence. The recombinant virus or bacmid is used to transfect host cells. Suitable insect host cells include cell lines derived from JP B-Sf-21, a Spodoptera frugiperda pupal ovarian cell line, such as Sβ (ATCC CRL 1711), S/21AΕ, and S/21 (Invitrogen Corporation; San Diego, CA), as well as Drosophila Schneider-2 cells, and the HIGH FIVEO cell line (Invitrogen) derived from Trichoplusia ni (U.S. Patent No. 5,300,435). Commercially available serum-free media can be used to grow and to maintain the cells. Suitable media are Sf900 fl™ (Life Technologies) or ESF 921™ (Expression Systems) for the Sf9 cells; and Ex-cellO405™ (JRH Biosciences, Lenexa, KS) or Express FiveO™ (Life Technologies) for the T. ni cells. When recombinant virus is used, the cells are typically grown up from an inoculation density of approximately 2-5 x 10 5 cells to a density of 1-2 x 10 cells at which time a recombinant viral stock is added at a multiplicity of infection (MOI) of 0.1 to 10, more typically near 3. Established techniques for producing recombinant proteins in baculovirus systems are provided by Bailey et al, "Manipulation of Baculovirus Vectors," in Methods in Molecular Biology, Volume 7: Gene Transfer and Expression Protocols, Muπay (ed.), pages 147-168 (The Humana Press, Enc. 1991), by Patel et al, "The baculovirus expression system," in DNA Cloning 2: Expression Systems, 2nd Edition, Glover et al. (eds.), pages 205-244 (Oxford University Press 1995), by Ausubel (1995) at pages 16-37 to 16-57, by Richardson (ed.), Baculovirus Expression Protocols (The Humana Press, Inc. 1995), and by Lucknow, "Insect Cell Expression Technology," in Protein Engineering: Principles and Practice, Cleland et al. (eds.), pages 183-218 (John Wiley & Sons, Inc. 1996). Fungal cells, including yeast cells, can also be used to express the genes described herein. Yeast species of particular interest in this regard include Saccharomyces cerevisiae, Pichia pastoris, and Pichia methanolica. Suitable promoters for expression in yeast include promoters from GAL7 (galactose), PGK (phosphoglycerate kinase), ADH (alcohol dehydrogenase), AOX1 (alcohol oxidase), HIS4 (histidinol dehydrogenase), and the like. Many yeast cloning vectors have been designed and are readily available. These vectors include Yip-based vectors, such as YIp5, YRp vectors, such as YRpl7, YEp vectors such as YEpl3 and YCp vectors, such as YCpl9. Methods for transforming S. cerevisiae cells with exogenous DNA and producing recombinant polypeptides therefrom are disclosed by, for example, Kawasaki, U.S. Patent No. 4,599,311, Kawasaki et al, U.S. Patent No. 4,931,373, Brake, U.S. Patent No. 4,870,008, Welch et al, U.S. Patent No. 5,037,743, and Muπay et al, U.S. Patent No. 4,845,075. Transformed cells are selected by phenotype determined by the selectable marker, commonly drug resistance or the ability to grow in the absence of a particular nutrient (e.g., leucine). A suitable vector system for use in Saccharomyces cerevisiae is the POT1 vector system disclosed by Kawasaki et al. (U.S. Patent No. 4,931,373), which allows transformed cells to be selected by growth in glucose-containing media. Additional suitable promoters and terminators for use in yeast include those from glycolytic enzyme genes (see, e.g., Kawasaki, U.S. Patent No. 4,599,311, Kingsman et al, U.S. Patent No. 4,615,974, and Bitter, U.S. Patent No. 4,977,092) and alcohol dehydrogenase genes. See also U.S. Patents Nos. 4,990,446, 5,063,154, 5,139,936, and 4,661,454. Transformation systems for other yeasts, including Hansenula polymorpha, Schizosaccharomyces pombe, Kluyveromyces lactis, Kluyveromyces fragilis, Ustilago maydis, Pichia pastoris, Pichia methanolica, Pichia guillermondii and Candida maltosa are known in the art. See, for example, Gleeson et al, J. Gen. Microbiol 132:3459 (1986), and Cregg, U.S. Patent No. 4,882,279. Aspergillus cells may be utilized according to the methods of Mc Knight et al, U.S. Patent No. 4,935,349. Methods for transforming Acremonium chrysogenum are disclosed by Su ino et al, U.S. Patent No. 5,162,228. Methods for transforming Neurospora are disclosed by Lambowitz, U.S. Patent No. 4,486,533. For example, the use of Pichia methanolica as host for the production of recombinant proteins is disclosed by Raymond, U.S. Patent No. 5,716,808, Raymond, U.S. Patent No. 5,736,383, Raymond et al, Yeast 74:11-23 (1998), and in international publication Nos. WO 97/17450, WO 97/17451, WO 98/02536, and WO 98/02565. DNA molecules for use in transforming P. methanolica will commonly be prepared as double-stranded, circular plasmids, which are preferably linearized prior to transformation. For polypeptide production in P. methanolica, the promoter and terminator in the plasmid can be that of a P. methanolica gene, such as a P. methanolica alcohol utilization gene (AUG1 or AUG2). Other useful promoters include those of the dihydroxyacetone synthase (DHAS), formate dehydrogenase (FMD), and catalase (CAT) genes. To facilitate integration of the DNA into the host chromosome, it is prefeπed to have the entire expression segment of the plasmid flanked at both ends by host DNA sequences. A suitable selectable marker for use in Pichia methanolica is a P. methanolica ADE2 gene, which encodes phosphoribosyl-5-aminoimidazole carboxylase (AIRC; EC 4.1.1.21), and which allows ade2 host cells to grow in the absence of adenine. For large-scale, industrial processes where it is desirable to minimize the use of methanol, host cells can be used in which both methanol utilization genes (AUG1 and AUG2) are deleted. For production of secreted proteins, host cells can be deficient in vacuolar protease genes (PEP4 and PRB1). Electroporation is used to facilitate the introduction of a plasmid containing DNA encoding a polypeptide of interest into P. methanolica cells. P. methanolica cells can be transformed by electroporation using an exponentially decaying, pulsed electric field having a field strength of from 2.5 to 4.5 kV/cm, preferably about 3.75 kV/cm, and a time constant (t) of from 1 to 40 milliseconds, most preferably about 20 milliseconds. Expression vectors can also be introduced into plant protoplasts, intact plant tissues, or isolated plant cells. Methods for introducing expression vectors into plant tissue include the direct infection or co-cultivation of plant tissue with Agrobacterium tumefaciens, microprojectile-mediated delivery, DNA injection, electroporation, and the like. See, for example, Horsch et al, Science 227:1229 (1985), Klein et al, Biotechnology 70:268 (1992), and Miki et al, "Procedures for Introducing Foreign DNA into Plants," in Methods in Plant Molecular Biology and Biotechnology, Glick et al. (eds.), pages 67-88 (CRC Press, 1993). Alternatively, Zcytorlo genes can be expressed in prokaryotic host cells. Suitable promoters that can be used to express Zcytorlo polypeptides in a prokaryotic host are well-known to those of skill in the art and include promoters capable of recognizing the T4, T3, Sp6 and T7 polymerases, the P R and P L promoters of bacteriophage lambda, the trp, recA, heat shock, lacUV5, tac, Ipp-lacSpr, phoA, and lacZ promoters of E. coli, promoters of B. subtilis, the promoters of the bacteriophages of Bacillus, Streptomyces promoters, the int promoter of bacteriophage lambda, the bla promoter of pBR322, and the CAT promoter of the chloramphenicol acetyl transferase gene. Prokaryotic promoters have been reviewed by Glick, J. Ind. Microbiol. 7:277 (1987), Watson et al, Molecular Biology of the Gene, 4th Ed. (Benjamin Cummins 1987), and by Ausubel et al. ( 1995 ). Suitable prokaryotic hosts include E. coli and Bacillus subtilus. Suitable strains of E. coli include BL21(DE3), BL21(DE3)pLysS, BL21(DE3)pLysE, DH1, DH4I, DH5, DH5I, DH5IF, DH5EVICR, DH10B, DH10B/p3, DH11S, C600, HB101, JM101, JM105, JM109, JM110, K38, RR1, Y1088, Y1089, CSH18, ER1451, and ER1647 (see, for example, Brown (ed.), Molecular Biology Labfax (Academic Press 1991)). Suitable strains of Bacillus subtilus include BR151, YB886, Mil 19, MI120, and B170 (see, for example, Hardy, "Bacillus Cloning Methods," in DNA Cloning: A Practical Approach, Glover (ed.) (ERL Press 1985)). When expressing a Zcytorlo polypeptide in bacteria such as E. coli, the polypeptide may be retained in the cytoplasm, typically as insoluble granules, or may be directed to the periplasmic space by a bacterial secretion sequence. In the former case, the cells are lysed, and the granules are recovered and denatured using, for example, guanidine isothiocyanate or urea. The denatured polypeptide can then be refolded and dimerized by diluting the denaturant, such as by dialysis against a solution of urea and a combination of reduced and oxidized glutathione, followed by dialysis against a buffered saline solution. In the latter case, the polypeptide can be recovered from the periplasmic space in a soluble and functional form by disrupting the cells (by, for example, sonication or osmotic shock) to release the contents of the periplasmic space and recovering the protein, thereby obviating the need for denaturation and refolding. Methods for expressing proteins in prokaryotic hosts are well-known to those of skill in the art (see, for example, Williams et al, "Expression of foreign proteins in E. coli using plasmid vectors and purification of specific polyclonal antibodies," in DNA Cloning 2: Expression Systems, 2nd Edition, Glover et al. (eds.), page 15 (Oxford University Press 1995), Ward et al, "Genetic Manipulation and Expression of Antibodies," in Monoclonal Antibodies: Principles and Applications, page 137 (Wiley-Liss, Inc. 1995), and Georgiou, "Expression of Proteins in Bacteria," in Protein Engineering: Principles and Practice, Cleland et al. (eds.), page 101 (John Wiley & Sons, Enc. 1996)). Standard methods for introducing expression vectors into bacterial, yeast, insect, and plant cells are provided, for example, by Ausubel (1995). General methods for expressing and recovering foreign protein produced by a mammalian cell system are provided by, for example, Etcheverry, "Expression of Engineered Proteins in Mammalian Cell Culture," in Protein Engineering: Principles and Practice, Cleland et al. (eds.), pages 163 (Wiley-Liss, Inc. 1996). Standard techniques for recovering protein produced by a bacterial system is provided by, for example, Grisshammer et al, "Purification of over-produced proteins from E. coli cells," in DNA Cloning 2: Expression Systems, 2nd Edition, Glover et al. (eds.), pages 59-92 (Oxford University Press 1995). Established methods for isolating recombinant proteins from a baculovirus system are described by Richardson (ed.), Baculovirus Expression Protocols (The Humana Press, Inc. 1995). As an alternative, polypeptides of the present invention can be synthesized by exclusive solid phase synthesis, partial solid phase methods, fragment condensation or classical solution synthesis. These synthesis methods are well-known to those of skill in the art (see, for example, Meπifield, J. Am. Chem. Soc. 85:2149 (1963), Stewart et al, "Solid Phase Peptide Synthesis" (2nd Edition), (Pierce Chemical Co. 1984), Bayer and Rapp, Chem. Pept. Prot. 3:3 (1986), Atherton et al, Solid Phase Peptide Synthesis: A Practical Approach (ERL Press 1989), Fields and Colowick, "Solid-Phase Peptide Synthesis," Methods in Enzymology Volume 289 (Academic Press 1997), and Lloyd- Williams et al, Chemical Approaches to the Synthesis of Peptides and Proteins (CRC Press, Inc. 1997)). Variations in total chemical synthesis strategies, such as "native chemical ligation" and "expressed protein ligation" are also standard (see, for example, Dawson et al, Science 266:116 (1994), Hackeng et al, Proc. Nat'l Acad. Sci. USA 94:7845 (1997), Dawson, Methods Enzymol. 287: 34 (1997), Muir et al, Proc. Nat'l Acad. Sci. USA 95:6705 (1998), and Severinov and Muir, J. Biol. Chem. 273:16205 (1998)). Peptides and polypeptides of the present invention comprise at least six, at least nine, or at least 15 contiguous amino acid residues of SEQ ID NO:2. As an illustration, polypeptides can comprise at least six, at least nine, or at least 15 contiguous amino acid residues of any of the following amino acid sequences of SEQ ID NO: 2: amino acid residues amino acid residues 21 to 231, amino acid residues 21 to 210, amino acid residues 22 to 231, amino acid residues 22 to 210, amino acid residues 22 to 108, amino acid residues 112 to 210, and amino acid residues 21 to 110. Within certain embodiments of the invention, the polypeptides comprise 20, 30, 40, 50, 100, or more contiguous residues of these amino acid sequences. Nucleic acid molecules encoding such peptides and polypeptides are useful as polymerase chain reaction primers and probes. Moreover, zcytorlo polypeptides can be expressed as monomers, homodimers, heterodimers, or multimers within higher eukaryotic cells. Such cells can be used to produce zcytorlo monomeric, homodimeric, heterodimeric and multimeric receptor polypeptides that comprise at least one zcytorlo polypeptide ("zcytorlό- comprising receptors" or "zcytorlό-comprising receptor polypeptides"), or can be used as assay cells in screening systems. Within one aspect of the present invention, a polypeptide of the present invention comprising the zcytorlo extracellular domain is produced by a cultured cell, and the cell is used to screen for ligands for the receptor, including the natural ligand, IL-TIF, as well as agonists and antagonists of the natural ligand. To summarize this approach, a cDNA or gene encoding the receptor is combined with other genetic elements required for its expression (e.g., a transcription promoter), and the resulting expression vector is inserted into a host cell. Cells that express the DNA and produce functional receptor are selected and used within a variety of screening systems. Each component of the monomeric, homodimeric, heterodimeric and multimeric receptor complex can be expressed in the same cell. Moreover, the components of the monomeric, homodimeric, heterodimeric and multimeric receptor complex can also be fused to a transmembrane domain or other membrane fusion moiety to allow complex assembly and screening of transfectants as described above. Mammalian cells suitable for use in expressing Zcytorlo receptors and transducing a receptor-mediated signal include cells that express other receptor subunits that may form a functional complex with Zcytorlo. These subunits may include those of the interferon receptor family or of other class II or class I cytokine receptors, e.g., CRF2-4 (Genbank Accession No. Z17227), EL-10R (Genbank Accession No.s U00672 and NM_001558), zcytorl l (US Patent No. 5,965,704), zcytor7 (US Patent No. 5,945,511), and EL-9R. It is also prefeπed to use a cell from the same species as the receptor to be expressed. Within a prefeπed embodiment, the cell is dependent upon an exogenously supplied hematopoietic growth factor for its proliferation. Prefeπed cell lines of this type are the human TF-1 cell line (ATCC number CRL- 2003) and the AML-193 cell line (ATCC number CRL-9589), which are GM-CSF-dependent human leukemic cell lines and BaF3 (Palacios and Steinmetz, Cell 41: 727-734, (1985)) which is an IL-3 dependent murine pre-B cell line. Other cell lines include BHK, COS-1 and CHO cells. Suitable host cells can be engineered to produce the necessary receptor subunits or other cellular component needed for the desired cellular response. This approach is advantageous because cell lines can be engineered to express receptor subunits from any species, thereby overcoming potential limitations arising from species specificity. Species orthologs of the human receptor cDNA can be cloned and used within cell lines from the same species, such as a mouse cDNA in the BaF3 cell line. Cell lines that are dependent upon one hematopoietic growth factor, such as GM- CSF or IL-3, can thus be engineered to become dependent upon another cytokine that acts through the zcytorlo receptor, such as IL-TEF. Cells expressing functional receptor are used within screening assays. A variety of suitable assays are known in the art. These assays are based on the detection of a biological response in a target cell. One such assay is a cell proliferation assay. Cells are cultured in the presence or absence of a test compound, and cell proliferation is detected by, for example, measuring incorporation of tritiated thymidine or by colorimetric assay based on the metabolic breakdown of 3-(4,5-dimethylthiazol-2-yl)- 2,5-diphenyl tetrazolium bromide (MTT) (Mosman, J. Immunol. Meth.. 65: 55-63, (1983)). An alternative assay format uses cells that are further engineered to express a reporter gene. The reporter gene is linked to a promoter element that is responsive to the receptor-linked pathway, and the assay detects activation of transcription of the reporter gene. A prefeπed promoter element in this regard is a serum response element, or SRE. See, e.g., Shaw et al, Cell 56:563-512, (1989). A prefeπed such reporter gene is a luciferase gene (de Wet et al, Mol. Cell. Biol. 7:725, (1987)). Expression of the luciferase gene is detected by luminescence using methods known in the art (e.g., Baumgartner et al, J. Biol. Chem. 269:29094-29101, (1994); Schenborn and Goiffin, Promega Notes 47:11, 1993). Luciferase activity assay kits are commercially available from, for example, Promega Corp., Madison, WI. Target cell lines of this type can be used to screen libraries of chemicals, cell-conditioned culture media, fungal broths, soil samples, water samples, and the like. For example, a bank of cell-conditioned media samples can be assayed on a target cell to identify cells that produce ligand. Positive cells are then used to produce a cDNA library in a mammalian expression vector, which is divided into pools, transfected into host cells, and expressed. Media samples from the transfected cells are then assayed, with subsequent division of pools, re-transfection, subculturing, and re-assay of positive cells to isolate a cloned cDNA encoding the ligand. A natural ligand for the Zcytorlδ receptor can also be identified by mutagenizing a cell line expressing the full-length receptor or receptor fusion (e.g., comprising the zcytorlδ extracellular domain fused to the transmembrane and signaling domain of another cytokine receptor) and culturing it under conditions that select for autocrine growth. See WIPO publication WO 95/21930. Within a typical procedure, EL-3 dependent BaF3 cells expressing Zcytorlo and the necessary additional subunits are mutagenized, such as with 2-ethylmethanesulfonate (EMS). The cells are then allowed to recover in the presence of EL-3, then transfeπed to a culture medium lacking EL-3 and EL-4. Surviving cells are screened for the production of a zcytorlo ligand (e.g., EL-TEF), such as by adding soluble receptor to the culture medium or by assaying conditioned media on wild-type BaF3 cells and BaF3 cells expressing the receptor. Using this method, cells and tissues expressing IL-TIF can be identified. Moreover several IL-TEF responsive cell lines are known (Dumontier et al., J. Immunol. 164:1814-1819, 2000; Dumoutier, L. et al., Proc. NatT. Acad. Sci. 97: 10144-10149, 2000; Xie MH et al., J. Biol. Chem. 275: 31335-31339, 2000; Kotenko SV et al., JBC in press), as well as those that express the IL-TIF receptor subunit zcytorl l. For example, the following cells are responsive to IL-TIF: TK-10 (Xie MH et al., supra.) (human renal carcinoma); SW480 (ATCC No. CCL-228) (human colon adenocarcinoma); HepG2 (ATCC No. HB-8065) (human hepatoma); PC 12 (ATCC No. CRL- 1721) (murine neuronal cell model; rat pheochromocytoma); and MES13 (ATCC No. CRL- 1927) (murine kidney mesangial cell line). In addition, some cell lines express zcytorl 1 (IL-TIF receptor) are also candidates for responsive cell lines to IL-TEF: A549 (ATCC No. CCL-185) (human lung carcinoma); G-361 (ATCC No. CRL-1424) (human melanoma); and Caki-1 (ATCC No. HTB-46) (human renal carcinoma). These cells can be used in assays to assess the functionality of zcytorlo as an IL-TEF antagonist or anti -inflammatory factor. An additional screening approach provided by the present invention includes the use of hybrid receptor polypeptides. These hybrid polypeptides fall into two general classes. Within the first class, the intracellular domain of Zcytorlo, is joined to the ligand-binding domain of a second receptor. It is prefeπed that the second receptor be a hematopoietic cytokine receptor, such as mpl receptor (Souyri et al, Cell 63: 1137-1147, (1990). The hybrid receptor will further comprise a transmembrane domain, which may be derived from either receptor. A DNA construct encoding the hybrid receptor is then inserted into a host cell. Cells expressing the hybrid receptor are cultured in the presence of a ligand for the binding domain (e.g., TPO in the case the mpl receptor extracellular domain is used) and assayed for a response. This system provides a means for analyzing signal transduction mediated by Zcytorlo while using readily available ligands. This system can also be used to determine if particular cell lines are capable of responding to signals transduced by Zcytorlδ monomeric, homodimeric, heterodimeric and multimeric receptors of the present invention. A second class of hybrid receptor polypeptides comprise the extracellular (ligand-binding) domain of Zcytorlo (approximately residues 22 to 231 of SEQ ED NO:2; SEQ ED NO: 13) with an intracellular domain of a second receptor, preferably a hematopoietic cytokine receptor, and a transmembrane domain. Hybrid zacytorl l monomers, homodimers, heterodimers and multimers of the present invention receptors of this second class are expressed in cells known to be capable of responding to signals transduced by the second receptor. Together, these two classes of hybrid receptors enable the identification of a responsive cell type for the development of an assay for detecting EL-TEF. Moreover, such cells can be used in the presence of EL-TEF to assay the soluble receptor antagonists of the present invention in a competition-type assay. In such assay, a decrease in the proliferation or signal transduction activity of IL-TIF in the presence of a soluble receptor of the present invention demonstrates antagonistic activity. Moreover IL-TIF-soluble receptor binding assays can also be used to assess whether a soluble receptor antagonizes IL-TEF activity. 7. Production of Zcytorlo Fusion Proteins and Conjugates One general class of Zcytorlo analogs are variants having an amino acid sequence that is a mutation of the amino acid sequence disclosed herein. Another general class of Zcytorlo analogs is provided by anti-idiotype antibodies, and fragments thereof, as described below. Moreover, recombinant antibodies comprising anti- idiotype variable domains can be used as analogs (see, for example, Monfardini et al, Proc. Assoc. Am. Physicians 708:420 (1996)). Since the variable domains of anti- idiotype Zcytorlo antibodies mimic Zcytorlo, these domains can provide Zcytorlo binding activity. Methods of producing anti-idiotypic catalytic antibodies are known to those of skill in the art (see, for example, Joron et al, Ann. N Y Acad. Sci. 672:216 (1992), Friboulet et al, Appl Biochem. Biotechnol. 47:229 (1994), and Avalle et al, Ann. N Y Acad. Sci. 864:118 (1998)). Another approach to identifying Zcytorlo analogs is provided by the use of combinatorial libraries. Methods for constructing and screening phage display and other combinatorial libraries are provided, for example, by Kay et al, Phage Display of Peptides and Proteins (Academic Press 1996), Verdine, U.S. Patent No. 5,783,384, Kay, et. al, U.S. Patent No. 5,747,334, and Kauffman et al, U.S. Patent No. 5,723,323. Zcytorlo polypeptides have both in vivo and in vitro uses. As an illustration, a soluble form of Zcytorlo can be added to cell culture medium to inhibit the effects of the Zcytorlo ligand produced by the cultured cells. Fusion proteins of Zcytorlo can be used to express Zcytorlo in a recombinant host, and to isolate the produced Zcytorlo. As described below, particular Zcytorlo fusion proteins also have uses in diagnosis and therapy. One type of fusion protein comprises a peptide that guides a Zcytorlo polypeptide from a recombinant host cell. To direct a Zcytorlo polypeptide into the secretory pathway of a eukaryotic host cell, a secretory signal sequence (also known as a signal peptide, a leader sequence, prepro sequence or pre sequence) is provided in the Zcytorlo expression vector. While the secretory signal sequence may be derived from Zcytorlo, a suitable signal sequence may also be derived from another secreted protein or synthesized de novo. The secretory signal sequence is operably linked to a Zcytor76-encoding sequence such that the two sequences are joined in the coπect reading frame and positioned to direct the newly synthesized polypeptide into the secretory pathway of the host cell. Secretory signal sequences are commonly positioned 5' to the nucleotide sequence encoding the polypeptide of interest, although certain secretory signal sequences may be positioned elsewhere in the nucleotide sequence of interest (see, e.g., Welch et al, U.S. Patent No. 5,037,743; Holland et al, U.S. Patent No. 5,143,830). Although the secretory signal sequence of Zcytorlo or another protein produced by mammalian cells (e.g., tissue-type plasminogen activator signal sequence, as described, for example, in U.S. Patent No. 5,641,655) is useful for expression of Zcytorlo in recombinant mammalian hosts, a yeast signal sequence is prefeπed for expression in yeast cells. Examples of suitable yeast signal sequences are those derived from yeast mating phermone α-factor (encoded by the MFal gene), invertase (encoded by the SUC2 gene), or acid phosphatase (encoded by the PH05 gene). See, for example, Romanos et al, "Expression of Cloned Genes in Yeast," in DNA Cloning 2: A Practical Approach, 2 nd Edition, Glover and Hames (eds.), pages 123-167 (Oxford University Press 1995). Zcytorlo monomeric, homodimeric, heterodimeric and multimeric receptor polypeptides can be prepared by expressing a truncated DNA encoding the extracellular domain, for example, a polypeptide which contains SEQ ID NO: 13, amino acids 22-210 of SEQ ID NO:2, or the coπesponding region of a non-human receptor. It is prefeπed that the extracellular domain polypeptides be prepared in a form substantially free of transmembrane and intracellular polypeptide segments. To direct the export of the receptor domain from the host cell, the receptor DNA is linked to a second DNA segment encoding a secretory peptide, such as a t-PA secretory peptide. To facilitate purification of the secreted receptor domain, a C-terminal extension, such as a poly-histidine tag, substance P, Flag™ peptide (Hopp et al, Biotechnology 6:1204- 1210, (1988); available from Eastman Kodak Co., New Haven, CT) or another polypeptide or protein for which an antibody or other specific binding agent is available, can be fused to the receptor polypeptide. Moreover, heterodimeric and multimeric non-zcytorl6 subunit extracellular cytokine binding domains are a also prepared as above. In an alternative approach, a receptor extracellular domain of zcytorlo or other class I or II cytokine receptor component can be expressed as a fusion with immunoglobulin heavy chain constant regions, typically an F c fragment, which contains two constant region domains and a hinge region but lacks the variable region (See, Sledziewski, AZ et al., US Patent No. 6,018,026 and 5,750,375). The soluble zcytorlo, soluble zcytorl 6/CRF2-4 heterodimers, and monomeric, homodimeric, heterodimeric and multimeric polypeptides of the present invention include such fusions. Such fusions are typically secreted as multimeric molecules wherein the Fc portions are disulfide bonded to each other and two receptor polypeptides are aπayed in closed proximity to each other. Fusions of this type can be used to affinity purify the cognate ligand from solution, as an in vitro assay tool, to block signals in vitro by specifically titrating out ligand, and as antagonists in vivo by administering them parenterally to bind circulating ligand and clear it from the circulation. To purify ligand, a Zcytorl 6-Ig chimera is added to a sample containing the ligand (e.g., cell-conditioned culture media or tissue extracts) under conditions that facilitate receptor-ligand binding (typically near-physiological temperature, pH, and ionic strength). The chimera-ligand complex is then separated by the mixture using protein A, which is immobilized on a solid support (e.g., insoluble resin beads). The ligand is then eluted using conventional chemical techniques, such as with a salt or pH gradient. In the alternative, the chimera itself can be bound to a solid support, with binding and elution carried out as above. The chimeras may be used in vivo to regulate inflammatory responses including acute phase responses such as serum amyloid A (SAA), C-reactive protein (CRP), and the like. Chimeras with high binding affinity are administered parenterally (e.g., by intramuscular, subcutaneous or intravenous injection). Circulating molecules bind ligand and are cleared from circulation by normal physiological processes. For use in assays, the chimeras are bound to a support via the F c region and used in an ELISA format. The present invention further provides a variety of other polypeptide fusions and related multimeric proteins comprising one or more polypeptide fusions. For example, a soluble zcytorlo receptor or soluble zcytorlo heterodimeric polypeptide, such as soluble zcytorl 6/CRF2-4, can be prepared as a fusion to a dimerizing protein as disclosed in U.S. Patents Nos. 5,155,027 and 5,567,584. Prefeπed dimerizing proteins in this regard include immunoglobulin constant region domains, e.g., IgGγl, and the human K light chain. Immunoglobulin-soluble zcytorlo receptor or immunoglobulin-soluble zcytorlo heterodimeric or multimeric polypeptide, such as immunoglobulin-soluble zcytorl 6/CRF2-4 fusions can be expressed in genetically engineered cells to produce a variety of multimeric zcytorlo receptor analogs. Auxiliary domains can be fused to soluble zcytorlo receptor or soluble zcytorlo heterodimeric or multimeric polypeptides, such as soluble zcytorl 6/CRF2-4 to target them to specific cells, tissues, or macromolecules (e.g., collagen, or cells expressing the zcytorlo ligand, EL-TEF). A zcytorlo polypeptide can be fused to two or more moieties, such as an affinity tag for purification and a targeting domain. Polypeptide fusions can also comprise one or more cleavage sites, particularly between domains. See, Tuan et al., Connective Tissue Research 34: 1-9, 1996. In bacterial cells, it is often desirable to express a heterologous protein as a fusion protein to decrease toxicity, increase stability, and to enhance recovery of the expressed protein. For example, Zcytorlo can be expressed as a fusion protein comprising a glutathione S-transferase polypeptide. Glutathione S-transferease fusion proteins are typically soluble, and easily purifiable from E. coli lysates on immobilized glutathione columns. In similar approaches, a Zcytorlo fusion protein comprising a maltose binding protein polypeptide can be isolated with an amylose resin column, while a fusion protein comprising the C-terminal end of a truncated Protein A gene can be purified using IgG-Sepharose. Established techniques for expressing a heterologous polypeptide as a fusion protein in a bacterial cell are described, for example, by Williams et al, "Expression of Foreign Proteins in E. coli Using Plasmid Vectors and Purification of Specific Polyclonal Antibodies," in DNA Cloning 2: A Practical Approach, 2 nd Edition, Glover and Hames (Eds.), pages 15-58 (Oxford University Press 1995). En addition, commercially available expression systems are available. For example, the PENPOINT Xa protein purification system (Promega Corporation; Madison, WE) provides a method for isolating a fusion protein comprising a polypeptide that becomes biotinylated during expression with a resin that comprises avidin. Peptide tags that are useful for isolating heterologous polypeptides expressed by either prokaryotic or eukaryotic cells include polyHistidine tags (which have an affinity for nickel-chelating resin), c-myc tags, calmodulin binding protein (isolated with calmodulin affinity chromatography), substance P, the RYIRS tag (which binds with anti-RYIRS antibodies), the Glu-Glu tag, and the FLAG tag (which binds with anti-FLAG antibodies). See, for example, Luo et al, Arch. Biochem. Biophys. 329:215 (1996), Morganti et al, Biotechnol. Appl. Biochem. 23:61 (1996), and Zheng et al, Gene 186:55 (1997). Nucleic acid molecules encoding such peptide tags are available, for example, from Sigma-Aldrich Corporation (St. Louis, MO). The present invention also contemplates that the use of the secretory signal sequence contained in the Zcytorlo polypeptides of the present invention to direct other polypeptides into the secretory pathway. A signal fusion polypeptide can be made wherein a secretory signal sequence derived from amino acid residues 1 to 21, or 1 to 22, of SEQ ED NO:2 is operably linked to another polypeptide using methods known in the art and disclosed herein. The secretory signal sequence contained in the fusion polypeptides of the present invention is preferably fused amino-terminally to an additional peptide to direct the additional peptide into the secretory pathway. Such constructs have numerous applications known in the art. For example, these novel secretory signal sequence fusion constructs can direct the secretion of an active component of a normally non-secreted protein, such as a receptor. Such fusions may be used in a transgenic animal or in a cultured recombinant host to direct peptides through the secretory pathway. With regard to the latter, exemplary polypeptides include pharmaceutically active molecules such as Factor Vila, proinsulin, insulin, follicle stimulating hormone, tissue type plasminogen activator, tumor necrosis factor, interleukins (e.g., interleukin-1 (EL-1), EL-2, IL-3, EL-4, EL-5, EL-6, EL-7, EL-8, EL-9, EL- 10, EL-11, IL-12, EL-13, EL-14, and IL-15), colony stimulating factors (e.g., granulocyte- colony stimulating factor (G-CSF) and granulocyte macrophage-colony stimulating factor (GM-CSF)), interferons (e.g., interferons-α, -β, -γ, -ω, -δ, and -τ), the stem cell growth factor designated "SI factor," erythropoietin, and thrombopoietin. The Zcytorlo secretory signal sequence contained in the fusion polypeptides of the present invention is preferably fused amino-terminally to an additional peptide to direct the additional peptide into the secretory pathway. Fusion proteins comprising a Zcytorlo secretory signal sequence can be constructed using standard techniques. Another form of fusion protein comprises a Zcytorlo polypeptide and an immunoglobulin heavy chain constant region, typically an F c fragment, which contains two or three constant region domains and a hinge region but lacks the variable region. As an illustration, Chang et al, U.S. Patent No. 5,723,125, describe a fusion protein comprising a human interferon and a human immunoglobulin Fc fragment. The C- terminal of the interferon is linked to the N-terminal of the Fc fragment by a peptide linker moiety. An example of a peptide linker is a peptide comprising primarily a T cell inert sequence, which is immunologically inert. An exemplary peptide linker has the amino acid sequence: GGSGG SGGGG SGGGG S (SEQ ID NO:4). In this fusion protein, an illustrative Fc moiety is a human γ4 chain, which is stable in solution and has little or no complement activating activity. Accordingly, the present invention contemplates a Zcytorlo fusion protein that comprises a Zcytorlo moiety and a human Fc fragment, wherein the C-terminus of the Zcytorlo moiety is attached to the N- terminus of the Fc fragment via a peptide linker, such as a peptide consisting of the amino acid sequence of SEQ ED NO:4. The Zcytorlo moiety can be a Zcytorlo molecule or a fragment thereof. For example, a fusion protein can comprise amino acid residues 22 to 210 of SEQ ED NO:2 and an Fc fragment (e.g., a human Fc fragment). In another variation, a Zcytorlo fusion protein comprises an IgG sequence, a Zcytorlo moiety covalently joined to the aminoterminal end of the IgG sequence, and a signal peptide that is covalently joined to the aminoterminal of the Zcytorlo moiety, wherein the IgG sequence consists of the following elements in the following order: a hinge region, a CH 2 domain, and a CH 3 domain. Accordingly, the IgG sequence lacks a CRi domain. The Zcytorlo moiety displays a Zcytorlo activity, as described herein, such as the ability to bind with a Zcytorlo ligand. This general approach to producing fusion proteins that comprise both antibody and nonantibody portions has been described by LaRochelle et al, EP 742830 (WO 95/21258). Fusion proteins comprising a Zcytorlo moiety and an Fc moiety can be used, for example, as an in vitro assay tool. For example, the presence of a Zcytorlo ligand in a biological sample can be detected using a Zcytorl 6-immunoglobulin fusion protein, in which the Zcytorlo moiety is used to bind the ligand, and a macromolecule, such as Protein A or anti-Fc antibody, is used to bind the fusion protein to a solid support. Such systems can be used to identify agonists and antagonists that interfere with the binding of a Zcytorlo ligand to its receptor. Other examples of antibody fusion proteins include polypeptides that comprise an antigen-binding domain and a Zcytorlo fragment that contains a Zcytorlo extracellular domain. Such molecules can be used to target particular tissues for the benefit of Zcytorlo binding activity. The present invention further provides a variety of other polypeptide fusions. For example, part or all of a domain(s) confeπing a biological function can be swapped between Zcytorlo of the present invention with the functionally equivalent domain(s) from another member of the cytokine receptor family. Polypeptide fusions can be expressed in recombinant host cells to produce a variety of Zcytorlo fusion analogs. A Zcytorlo polypeptide can be fused to two or more moieties or domains, such as an affinity tag for purification and a targeting domain. Polypeptide fusions can also comprise one or more cleavage sites, particularly between domains. See, for example, Tuan et al, Connective Tissue Research 34: 1 (1996). Fusion proteins can be prepared by methods known to those skilled in the art by preparing each component of the fusion protein and chemically conjugating them. Alternatively, a polynucleotide encoding both components of the fusion protein in the proper reading frame can be generated using known techniques and expressed by the methods described herein. General methods for enzymatic and chemical cleavage of fusion proteins are described, for example, by Ausubel (1995) at pages 16-19 to 16- 25. Zcytorlo polypeptides can be used to identify and to isolate Zcytorlo ligands. For example, proteins and peptides of the present invention can be immobilized on a column and used to bind ligands from a biological sample that is run over the column (Hermanson et al. (eds.), Immobilized Affinity Ligand Techniques, pages 195-202 (Academic Press 1992)). As such, zcytorlo polypeptides of the present invention can be used to identify and isolate EL-TEF for either diagnostic, or production purposes. The activity of a Zcytorlo polypeptide can also be observed by a silicon- based biosensor microphysiometer, which measures the extracellular acidification rate or proton excretion associated with receptor binding and subsequent physiologic cellular responses. An exemplary device is the CYTOSENSOR Microphysiometer manufactured by Molecular Devices, Sunnyvale, CA. A variety of cellular responses, such as cell proliferation, ion transport, energy production, inflammatory response, regulatory and receptor activation, and the like, can be measured by this method (see, for example, McConnell et al, Science 257:1906 (1992), Pitchford et al, Meth. Enzymol. 228:84 (1997), Arimilli et al, I. Immunol. Meth. 212:49 (1998), Van Liefde et al, Eur. J. Pharmacol. 346:S1 (1998)). The microphysiometer can be used for assaying eukaryotic, prokaryotic, adherent, or non-adherent cells. By measuring extracellular acidification changes in cell media over time, the microphysiometer directly measures cellular responses to various stimuli, including agonists, ligands, or antagonists of Zcytorlo. For example, the microphysiometer is used to measure responses of an Zcytorl 6-expressing eukaryotic cell, compared to a control eukaryotic cell that does not express Zcytorlo polypeptide. Suitable cells responsive to Zcytorl 6-modulating stimuli include recombinant host cells comprising a Zcytorlo expression vector, and cells that naturally express Zcytorlo. Extracellular acidification provides one measure for a Zcytorl 6-modulated cellular response. In addition, this approach can be used to identify ligands, agonists, and antagonists of Zcytorlo ligand, IL-TIF. For example, a molecule can be identified as an agonist of Zcytorlo ligand by providing cells that express a Zcytorlo polypeptide, culturing a first portion of the cells in the absence of the test compound, culturing a second portion of the cells in the presence of the test compound, and determining whether the second portion exhibits a cellular response, in comparison with the first portion. Alternatively, a solid phase system can be used to identify a Zcytorlo ligand, or an agonist or antagonist of a Zcytorlo ligand. For example, a Zcytorlo polypeptide or Zcytorlo fusion protein, or zcytorlo monomeric, homodimeric, heterodimeric or multimeric soluble receptor can be immobilized onto the surface of a receptor chip of a commercially available biosensor instrument (BIACORE, Biacore AB; Uppsala, Sweden). The use of this instrument is disclosed, for example, by Karlsson, Immunol. Methods 145:229 (1991), and Cunningham and Wells, J. Mol Biol 234:554 (1993). In brief, a Zcytorlo polypeptide or fusion protein is covalently attached, using amine or sulfhydryl chemistry, to dextran fibers that are attached to gold film within a flow cell. A test sample is then passed through the cell. If a ligand is present in the sample, it will bind to the immobilized polypeptide or fusion protein, causing a change in the refractive index of the medium, which is detected as a change in surface plasmon resonance of the gold film. This system allows the determination of on- and off-rates, from which binding affinity can be calculated, and assessment of stoichiometry of binding. This system can also be used to examine antibody-antigen interactions, and the interactions of other complement/anti-complement pairs. Zcytorlo binding domains can be further characterized by physical analysis of structure, as determined by such techniques as nuclear magnetic resonance, crystallography, electron diffraction or photoaffinity labeling, in conjunction with mutation of putative contact site amino acids of Zcytorlo ligand agonists. See, for example, de Vos et al, Science 255:306 (1992), Smith et al, J. Mol. Biol. 224:899 (1992), and Wlodaver et al, FEBS Lett. 309:59 (1992). The present invention also contemplates chemically modified Zcytorlo compositions, in which a Zcytorlo polypeptide is linked with a polymer. Illustrative Zcytorlo polypeptides are soluble polypeptides that lack a functional transmembrane domain, such as a polypeptide consisting of amino acid residues 22 to 210 of SEQ ED NO:2. Typically, the polymer is water soluble so that the Zcytorlo conjugate does not precipitate in an aqueous environment, such as a physiological environment. An example of a suitable polymer is one that has been modified to have a single reactive group, such as an active ester for acylation, or an aldehyde for alkylation, In this way, the degree of polymerization can be controlled. An example of a reactive aldehyde is polyethylene glycol propionaldehyde, or mono-(Cl-ClO) alkoxy, or aryloxy derivatives thereof (see, for example, Harris, et al, U.S. Patent No. 5,252,714). The polymer may be branched or unbranched. Moreover, a mixture of polymers can be used to produce Zcytorlo conjugates. Zcytorlo conjugates used for therapy can comprise pharmaceutically acceptable water-soluble polymer moieties. Suitable water-soluble polymers include polyethylene glycol (PEG), monomethoxy-PEG, mono-(Cl-C10)alkoxy-PEG, aryloxy- PEG, poly-(N-vinyl pyπolidone)PEG, tresyl monomethoxy PEG, PEG propionaldehyde, bw-succinimidyl carbonate PEG, propylene glycol homopolymers, a polypropylene oxide/ethylene oxide co-polymer, polyoxyethylated polyols (e.g., glycerol), polyvinyl alcohol, dextran, cellulose, or other carbohydrate-based polymers. Suitable PEG may have a molecular weight from about 600 to about 60,000, including, for example, 5,000, 12,000, 20,000 and 25,000. A Zcytorlo conjugate can also comprise a mixture of such water-soluble polymers. One example of a Zcytorlo conjugate comprises a Zcytorlo moiety and a polyalkyl oxide moiety attached to the N-terminus of the Zcytorlo moiety. PEG is one suitable polyalkyl oxide. As an illustration, Zcytorlo can be modified with PEG, a process known as "PEGylation." PEGylation of Zcytorlo can be caπied out by any of the PEGylation reactions known in the art (see, for example, EP 0 154 316, Delgado et al, Critical Reviews in Therapeutic Drug Carrier Systems 9:249 (1992), Duncan and Spreafico, Clin. Pharmacokinet. 27:290 (1994), and Francis et al, Int I Hematol 68: 1 (1998)). For example, PEGylation can be performed by an acylation reaction or by an alkylation reaction with a reactive polyethylene glycol molecule. En an alternative approach, Zcytorlo conjugates are formed by condensing activated PEG, in which a terminal hydroxy or amino group of PEG has been replaced by an activated linker (see, for example, Karasiewicz et al, U.S. Patent No. 5,382,657). PEGylation by acylation typically requires reacting an active ester derivative of PEG with a Zcytorlo polypeptide. An example of an activated PEG ester is PEG esterified to N-hydroxysuccinimide. As used herein, the term "acylation" includes the following types of linkages between Zcytorlo and a water soluble polymer: amide, carbamate, urethane, and the like. Methods for preparing PEGylated Zcytorlo by acylation will typically comprise the steps of (a) reacting a Zcytorlo polypeptide with PEG (such as a reactive ester of an aldehyde derivative of PEG) under conditions whereby one or more PEG groups attach to Zcytorlo, and (b) obtaining the reaction product(s). Generally, the optimal reaction conditions for acylation reactions will be determined based upon known parameters and desired results. For example, the larger the ratio of PEG:Zcytorl6, the greater the percentage of polyPEGylated Zcytorlo product. The product of PEGylation by acylation is typically a polyPEGylated Zcytorlo product, wherein the lysine ε-amino groups are PEGylated via an acyl linking group. An example of a connecting linkage is an amide. Typically, the resulting Zcytorlo will be at least 95% mono-, di-, or tri-pegylated, although some species with higher degrees of PEGylation may be formed depending upon the reaction conditions. PEGylated species can be separated from unconjugated Zcytorlo polypeptides using standard purification methods, such as dialysis, ultrafiltration, ion exchange chromatography, affinity chromatography, and the like. PEGylation by alkylation generally involves reacting a terminal aldehyde derivative of PEG with Zcytorlo in the presence of a reducing agent. PEG groups can be attached to the polypeptide via a -CH -NH group. Derivatization via reductive alkylation to produce a monoPEGylated product takes advantage of the differential reactivity of different types of primary amino groups available for derivatization. Typically, the reaction is performed at a pH that allows one to take advantage of the pKa differences between the ε-amino groups of the lysine residues and the α-amino group of the N-terminal residue of the protein. By such selective derivatization, attachment of a water-soluble polymer that contains a reactive group such as an aldehyde, to a protein is controlled. The conjugation with the polymer occurs predominantly at the N-terminus of the protein without significant modification of other reactive groups such as the lysine side chain amino groups. The present invention provides a substantially homogenous preparation of Zcytorlo monopolymer conjugates. Reductive alkylation to produce a substantially homogenous population of monopolymer Zcytorlo conjugate molecule can comprise the steps of: (a) reacting a Zcytorlo polypeptide with a reactive PEG under reductive alkylation conditions at a pH suitable to permit selective modification of the α-amino group at the amino terminus of the Zcytorlo, and (b) obtaining the reaction product(s). The reducing agent used for reductive alkylation should be stable in aqueous solution and able to reduce only the Schiff base formed in the initial process of reductive alkylation. Illustrative reducing agents include sodium borohydride, sodium cyanoborohydride, dimethylamine borane, trimethylamine borane, and pyridine borane. For a substantially homogenous population of monopolymer Zcytorlo conjugates, the reductive alkylation reaction conditions are those that permit the selective attachment of the water-soluble polymer moiety to the N-terminus of Zcytorlo. Such reaction conditions generally provide for pKa differences between the lysine amino groups and the α-amino group at the N-terminus. The pH also affects the ratio of polymer to protein to be used. In general, if the pH is lower, a larger excess of polymer to protein will be desired because the less reactive the N-terminal α-group, the more polymer is needed to achieve optimal conditions. If the pH is higher, the polymer: Zcytorl 6 need not be as large because more reactive groups are available. Typically, the pH will fall within the range of 3 to 9, or 3 to 6. This method can be employed for making zcytorl 6-comprising homodimeric, heterodimeric or multimeric soluble receptor conjugates. Another factor to consider is the molecular weight of the water-soluble polymer. Generally, the higher the molecular weight of the polymer, the fewer number of polymer molecules which may be attached to the protein. For PEGylation reactions, the typical molecular weight is about 2 kDa to about 100 kDa, about 5 kDa to about 50 kDa, or about 12 kDa to about 25 kDa. The molar ratio of water-soluble polymer to Zcytorlo will generally be in the range of 1:1 to 100:1. Typically, the molar ratio of water-soluble polymer to Zcytorlo will be 1:1 to 20:1 for polyPEGylation, and 1:1 to 5:1 for monoPEGylation. General methods for producing conjugates comprising a polypeptide and water-soluble polymer moieties are known in the art. See, for example, Karasiewicz et al, U.S. Patent No. 5,382,657, Greenwald et al, U.S. Patent No. 5,738, 846, Nieforth et al, Clin. Pharmacol. Ther. 59:636 (1996), Monkarsh et al, Anal. Biochem. 247:434 (1997)). This method can be employed for making zcytorl 6-comprising homodimeric, heterodimeric or multimeric soluble receptor conjugates. The present invention contemplates compositions comprising a peptide or polypeptide described herein. Such compositions can further comprise a carrier. The carrier can be a conventional organic or inorganic caπier. Examples of carriers include water, buffer solution, alcohol, propylene glycol, macrogol, sesame oil, corn oil, and the like. 8. Isolation of Zcytorlo Polypeptides The polypeptides of the present invention can be purified to at least about 80% purity, to at least about 90% purity, to at least about 95% purity, or greater than 95% purity with respect to contaminating macromolecules, particularly other proteins and nucleic acids, and free of infectious and pyrogenic agents. The polypeptides of the present invention may also be purified to a pharmaceutically pure state, which is greater than 99.9% pure. In certain preparations, purified polypeptide is substantially free of other polypeptides, particularly other polypeptides of animal origin. Fractionation and/or conventional purification methods can be used to obtain preparations of Zcytorlo purified from natural sources (e.g., tonsil tissue), synthetic Zcytorlo polypeptides, and recombinant Zcytorlo polypeptides and fusion Zcytorlo polypeptides purified from recombinant host cells. En general, ammonium sulfate precipitation and acid or chaotrope extraction may be used for fractionation of samples. Exemplary purification steps may include hydroxyapatite, size exclusion, FPLC and reverse-phase high performance liquid chromatography. Suitable chromatographic media include derivatized dextrans, agarose, cellulose, polyacrylamide, specialty silicas, and the like. PEI, DEAE, QAE and Q derivatives are suitable. Exemplary chromatographic media include those media derivatized with phenyl, butyl, or octyl groups, such as Phenyl-Sepharose FF (Pharmacia), Toyopearl butyl 650 (Toso Haas, Montgomeryville, PA), Octyl-Sepharose (Pharmacia) and the like; or polyacrylic resins, such as Amberchrom CG 71 (Toso Haas) and the like. Suitable solid supports include glass beads, silica-based resins, cellulosic resins, agarose beads, cross-linked agarose beads, polystyrene beads, cross-linked polyacrylamide resins and the like that are insoluble under the conditions in which they are to be used. These supports may be modified with reactive groups that allow attachment of proteins by amino groups, carboxyl groups, sulfhydryl groups, hydroxyl groups and/or carbohydrate moieties. Examples of coupling chemistries include cyanogen bromide activation, N-hydroxysuccinimide activation, epoxide activation, sulfhydryl activation, hydrazide activation, and carboxyl and amino derivatives for carbodiimide coupling chemistries. These and other solid media are well known and widely used in the art, and are available from commercial suppliers. Selection of a particular method for polypeptide isolation and purification is a matter of routine design and is determined in part by the properties of the chosen support. See, for example, Affinity Chromatography: Principles & Methods (Pharmacia LKB Biotechnology 1988), and Doonan, Protein Purification Protocols (The Humana Press 1996). Additional variations in Zcytorlo isolation and purification can be devised by those of skill in the art. For example, anti-Zcytorl6 antibodies, obtained as described below, can be used to isolate large quantities of protein by immunoaffinity purification. The polypeptides of the present invention can also be isolated by exploitation of particular properties. For example, immobilized metal ion adsorption (IMAC) chromatography can be used to purify histidine-rich proteins, including those comprising polyhistidine tags. Briefly, a gel is first charged with divalent metal ions to form a chelate (Sulkowski, Trends in Biochem. 3:1 (1985)). Histidine-rich proteins will be adsorbed to this matrix with differing affinities, depending upon the metal ion used, and will be eluted by competitive elution, lowering the pH, or use of strong chelating agents. Other methods of purification include purification of glycosylated proteins by lectin affinity chromatography and ion exchange chromatography (M. Deutscher, (ed.), Meth. Enzymol. 782:529 (1990)). Within additional embodiments of the invention, a fusion of the polypeptide of interest and an affinity tag (e.g., maltose-binding protein, an immunoglobulin domain) may be constructed to facilitate purification. Moreover, the ligand-binding properties of zcytorlo extracellular domain can be exploited for purification, for example, of zcytorl 6-comprising soluble receptors; for example, by using affinity chromatography wherein IL-TIF ligand is bound to a column and the zcytorl 6-comprising receptor is bound and subsequently eluted using standard chromatography methods. Zcytorlo polypeptides or fragments thereof may also be prepared through chemical synthesis, as described above. Zcytorlo polypeptides may be monomers or multimers; glycosylated or non-glycosylated; PEGylated or non- PEGylated; and may or may not include an initial methionine amino acid residue. 9. Production of Antibodies to Zcytorl6 Proteins Antibodies to Zcytorlo can be obtained, for example, using the product of a Zcytorlo expression vector or Zcytorlo isolated from a natural source as an antigen. Particularly useful anti-Zcytorl6 antibodies "bind specifically" with Zcytorlo. Antibodies are considered to be specifically binding if the antibodies exhibit at least one of the following two properties: (1) antibodies bind to Zcytorlo with a threshold level of binding activity, and (2) antibodies do not significantly cross-react with polypeptides related to Zcytorlo. With regard to the first characteristic, antibodies specifically bind if they bind to a Zcytorlo polypeptide, peptide or epitope with a binding affinity (K a ) of 10 6 M " 1 or greater, preferably 10 7 M "1 or greater, more preferably 10 8 M "1 or greater, and most preferably 10 9 M "1 or greater. The binding affinity of an antibody can be readily determined by one of ordinary skill in the art, for example, by Scatchard analysis (Scatchard, Ann. NY Acad. Sci. 51:660 (1949)). With regard to the second characteristic, antibodies do not significantly cross-react with related polypeptide molecules, for example, if they detect Zcytorlo, but not presently known polypeptides using a standard Western blot analysis. Examples of known related polypeptides include known cytokine receptors. Anti-Zcytorl6 antibodies can be produced using antigenic Zcytorlo epitope-bearing peptides and polypeptides. Antigenic epitope-bearing peptides and polypeptides of the present invention contain a sequence of at least nine, or between 15 to about 30 amino acids contained within SEQ ID NO:2 or another amino acid sequence disclosed herein. However, peptides or polypeptides comprising a larger portion of an amino acid sequence of the invention, containing from 30 to 50 amino acids, or any length up to and including the entire amino acid sequence of a polypeptide of the invention, also are useful for inducing antibodies that bind with Zcytorlo. It is desirable that the amino acid sequence of the epitope-bearing peptide is selected to provide substantial solubility in aqueous solvents (i.e., the sequence includes relatively hydrophilic residues, while hydrophobic residues are typically avoided). Moreover, amino acid sequences containing proline residues may be also be desirable for antibody production. As an illustration, potential antigenic sites in Zcytorlo were identified using the Jameson- Wolf method, Jameson and Wolf, CABIOS 4:181, (1988), as implemented by the PROTEAN program (version 3.14) of LASERGENE (DNASTAR; Madison, WE). Default parameters were used in this analysis. The Jameson-Wolf method predicts potential antigenic determinants by combining six major subroutines for protein structural prediction. Briefly, the Hopp- Woods method, Hopp et al, Proc. Nat'l Acad. Sci. USA 78:3824 (1981), was first used to identify amino acid sequences representing areas of greatest local hydrophilicity (parameter: seven residues averaged). En the second step, Emini's method, Emini et al, J. Virology 55:836 (1985), was used to calculate surface probabilities (parameter: surface decision threshold (0.6) = 1). Third, the Karplus-Schultz method, Karplus and Schultz, Naturwissenschaften 72:212 (1985), was used to predict backbone chain flexibility (parameter: flexibility threshold (0.2) = 1). In the fourth and fifth steps of the analysis, secondary structure predictions were applied to the data using the methods of Chou-Fasman, Chou, "Prediction of Protein Structural Classes from Amino Acid Composition," in Prediction of Protein Structure and the Principles of Protein Conformation, Fasman (ed.), pages 549-586 (Plenum Press 1990), and Garnier-Robson, Garnier et al, J. Mol. Biol. 120:91 (1978) (Chou-Fasman parameters: conformation table = 64 proteins; α region threshold = 103; β region threshold = 105; Garnier- Robson parameters: α and β decision constants = 0). In the sixth subroutine, flexibility parameters and hydropathy/solvent accessibility factors were combined to determine a surface contour value, designated as the "antigenic index." Finally, a peak broadening function was applied to the antigenic index, which broadens major surface peaks by adding 20, 40, 60, or 80% of the respective peak value to account for additional free energy derived from the mobility of surface regions relative to interior regions. This calculation was not applied, however, to any major peak that resides in a helical region, since helical regions tend to be less flexible. The results of this analysis indicated that the following amino acid sequences of SEQ ID NO:2 would provide suitable antigenic peptides: amino acids 24 to 42 ("antigenic peptide 1"), amino acids 24 to 33 ("antigenic peptide 2"), 37 to 42 ("antigenic peptide 3"), amino acids 48 to 55 ("antigenic peptide 4"), amino acids 68 to 81 ("antigenic peptide 5"), amino acids 88 to 97 ("antigenic peptide 6"), amino acids 126 to 132 ("antigenic peptide 7"), amino acids 156 to 165 ("antigenic peptide 8"), amino acids 178 to 185 ("antigenic peptide 9"), and amino acids 216 to 227 ("antigenic peptide 10"). The present invention contemplates the use of any one of antigenic peptides 1 to 10 to generate antibodies to Zcytorlo. The present invention also contemplates polypeptides comprising at least one of antigenic peptides 1 to 10. Moreover, suitable antigens also include the zcytorlo polypeptides comprising a zcytorlo cytokine binding, or extracellular domain disclosed above in combination with another class I or II cytokine extracellular domain, such as those that form soluble zcytorlo heterodimeric or multimeric polypeptides, such as soluble zcytorl 6/CRF2-4, zcytorlό/zcytorl l, zcytorl 6/zcytor7, and the like. Polyclonal antibodies to recombinant Zcytorlo protein or to Zcytorlo isolated from natural sources can be prepared using methods well-known to those of skill in the art. See, for example, Green et al, "Production of Polyclonal Antisera," in Immunochemical Protocols (Manson, ed.), pages 1-5 (Humana Press 1992), and Williams et al., "Expression of foreign proteins in E. coli using plasmid vectors and purification of specific polyclonal antibodies," in DNA Cloning 2: Expression Systems, 2nd Edition, Glover et al. (eds.), page 15 (Oxford University Press 1995). The immunogenicity of a Zcytorlo polypeptide can be increased through the use of an adjuvant, such as alum (aluminum hydroxide) or Freund's complete or incomplete adjuvant. Polypeptides useful for immunization also include fusion polypeptides, such as fusions of Zcytorlo or a portion thereof with an immunoglobulin polypeptide or with maltose binding protein. The polypeptide immunogen may be a full-length molecule or a portion thereof. If the polypeptide portion is "hapten-like," such portion may be advantageously joined or linked to a macromolecular caπier (such as keyhole limpet hemocyanin (KLH), bovine serum albumin (BSA) or tetanus toxoid) for immunization. Although polyclonal antibodies are typically raised in animals such as horses, cows, dogs, chicken, rats, mice, rabbits, guinea pigs, goats, or sheep, an anti- Zcytorlo antibody of the present invention may also be derived from a subhuman primate antibody. General techniques for raising diagnostically and therapeutically useful antibodies in baboons may be found, for example, in Goldenberg et al, international patent publication No. WO 91/11465, and in Losman et al, Int. J. Cancer 46:310 (1990). Alternatively, monoclonal anti-Zcytorl6 antibodies can be generated. Rodent monoclonal antibodies to specific antigens may be obtained by methods known to those skilled in the art (see, for example, Kohler et al, Nature 256:495 (1975), Coligan et al. (eds.), Current Protocols in Immunology, Vol. 1, pages 2.5.1-2.6.7 (John Wiley & Sons 1991) ["Coligan"], Picksley et al, "Production of monoclonal antibodies against proteins expressed in E. coli," in DNA Cloning 2: Expression Systems, 2nd Edition, Glover et al. (eds.), page 93 (Oxford University Press 1995)). Briefly, monoclonal antibodies can be obtained by injecting mice with a composition comprising a Zcytorlo gene product, verifying the presence of antibody production by removing a serum sample, removing the spleen to obtain B-lymphocytes, fusing the B-lymphocytes with myeloma cells to produce hybridomas, cloning the hybridomas, selecting positive clones which produce antibodies to the antigen, culturing the clones that produce antibodies to the antigen, and isolating the antibodies from the hybridoma cultures. In addition, an anti-Zcytorl6 antibody of the present invention may be derived from a human monoclonal antibody. Human monoclonal antibodies are obtained from transgenic mice that have been engineered to produce specific human antibodies in response to antigenic challenge. In this technique, elements of the human heavy and light chain locus are introduced into strains of mice derived from embryonic stem cell lines that contain targeted disruptions of the endogenous heavy chain and light chain loci. The transgenic mice can synthesize human antibodies specific for human antigens, and the mice can be used to produce human antibody-secreting hybridomas. Methods for obtaining human antibodies from transgenic mice are described, for example, by Green et al, Nature Genet. 7:13 (1994), Lonberg et al, Nature 368:856 (1994), and Taylor et al, Int. Immun. 6:579 (1994). Monoclonal antibodies can be isolated and purified from hybridoma cultures by a variety of well-established techniques. Such isolation techniques include affinity chromatography with Protein-A Sepharose, size-exclusion chromatography, and ion-exchange chromatography (see, for example, Coligan at pages 2.7.1-2.7.12 and pages 2.9.1-2.9.3; Baines et al, "Purification of Immunoglobulin G (IgG)," in Methods in Molecular Biology, Vol. 10, pages 79-104 (The Humana Press, Enc. 1992)). For particular uses, it may be desirable to prepare fragments of anti- Zcytorlό antibodies. Such antibody fragments can be obtained, for example, by proteolytic hydrolysis of the antibody. Antibody fragments can be obtained by pepsin or papain digestion of whole antibodies by conventional methods. As an illustration, antibody fragments can be produced by enzymatic cleavage of antibodies with pepsin to provide a 5S fragment denoted F(ab') 2 . This fragment can be further cleaved using a thiol reducing agent to produce 3.5S Fab' monovalent fragments. Optionally, the cleavage reaction can be performed using a blocking group for the sulfhydryl groups that result from cleavage of disulfide linkages. As an alternative, an enzymatic cleavage using pepsin produces two monovalent Fab fragments and an Fc fragment directly. These methods are described, for example, by Goldenberg, U.S. patent No. 4,331,647, Nisonoff et al, Arch Biochem. Biophys. 89:230 (1960), Porter, Biochem. J. 73:119 (1959), Edelman et al, in Methods in Enzymology Vol. 1, page 422 (Academic Press 1967), and by Coligan at pages 2.8.1-2.8.10 and 2.10.-2.10.4. Other methods of cleaving antibodies, such as separation of heavy chains to form monovalent light-heavy chain fragments, further cleavage of fragments, or other enzymatic, chemical or genetic techniques may also be used, so long as the fragments bind to the antigen that is recognized by the intact antibody. For example, Fv fragments comprise an association of V H and V L chains. This association can be noncovalent, as described by Enbar et al, Proc. Nat'l Acad. Sci. USA 69:2659 (1972). Alternatively, the variable chains can be linked by an intermolecular disulfide bond or cross-linked by chemicals such as glutaraldehyde (see, for example, Sandhu, Crit. Rev. Biotech. 12:431 (1992)). The Fv fragments may comprise V H and V L chains which are connected by a peptide linker. These single-chain antigen binding proteins (scFv) are prepared by constructing a structural gene comprising DNA sequences encoding the V H and V domains which are connected by an oligonucleotide. The structural gene is inserted into an expression vector which is subsequently introduced into a host cell, such as E. coli. The recombinant host cells synthesize a single polypeptide chain with a linker peptide bridging the two V domains. Methods for producing scFvs are described, for example, by Whitlow et al, Methods: A Companion to Methods in Enzymology 2:91 (1991) (also see, Bird et al, Science 242:423 (1988), Ladner et al, U.S. Patent No. 4,946,778, Pack et al, Bio/Technology 77:1271 (1993), and Sandhu, supra). As an illustration, a scFV can be obtained by exposing lymphocytes to Zcytorlo polypeptide in vitro, and selecting antibody display libraries in phage or similar vectors (for instance, through use of immobilized or labeled Zcytorlo protein or peptide). Genes encoding polypeptides having potential Zcytorlo polypeptide binding domains can be obtained by screening random peptide libraries displayed on phage (phage display) or on bacteria, such as E. coli. Nucleotide sequences encoding the polypeptides can be obtained in a number of ways, such as through random mutagenesis and random polynucleotide synthesis. These random peptide display libraries can be used to screen for peptides which interact with a known target which can be a protein or polypeptide, such as a ligand or receptor, a biological or synthetic macromolecule, or organic or inorganic substances. Techniques for creating and screening such random peptide display libraries are known in the art (Ladner et al, U.S. Patent No. 5,223,409, Ladner et al, U.S. Patent No. 4,946,778, Ladner et al, U.S. Patent No. 5,403,484, Ladner et al, U.S. Patent No. 5,571,698, and Kay et al, Phage Display of Peptides and Proteins (Academic Press, Inc. 1996)) and random peptide display libraries and kits for screening such libraries are available commercially, for instance from CLONTΕCH Laboratories, Inc. (Palo Alto, CA), Εnvitrogen Inc. (San Diego, CA), New England Biolabs, Inc. (Beverly, MA), and Pharmacia LKB Biotechnology Inc. (Piscataway, NJ). Random peptide display libraries can be screened using the Zcytorlo sequences disclosed herein to identify proteins which bind to Zcytorlo. Another form of an antibody fragment is a peptide coding for a single complementarity-determining region (CDR). CDR peptides ("minimal recognition units") can be obtained by constructing genes encoding the CDR of an antibody of interest. Such genes are prepared, for example, by using the polymerase chain reaction to synthesize the variable region from RNA of antibody-producing cells (see, for example, Laπick et al, Methods: A Companion to Methods in Enzymology 2:106 (1991), Courtenay-Luck, "Genetic Manipulation of Monoclonal Antibodies," in Monoclonal Antibodies: Production, Engineering and Clinical Application, Ritter et al. (eds.), page 166 (Cambridge University Press 1995), and Ward et al, "Genetic Manipulation and Expression of Antibodies," in Monoclonal Antibodies: Principles and Applications, Birch et al, (eds.), page 137 (Wiley-Liss, Inc. 1995)). Alternatively, an anti-Zcytorl6 antibody may be derived from a "humanized" monoclonal antibody. Humanized monoclonal antibodies are produced by transfeπing mouse complementary determining regions from heavy and light variable chains of the mouse immunoglobulin into a human variable domain. Typical residues of human antibodies are then substituted in the framework regions of the murine counterparts. The use of antibody components derived from humanized monoclonal antibodies obviates potential problems associated with the immunogenicity of murine constant regions. General techniques for cloning murine immunoglobulin variable domains are described, for example, by Orlandi et al, Proc. Nat'l Acad. Sci. USA 86:3833 (1989). Techniques for producing humanized monoclonal antibodies are described, for example, by Jones et al, Nature 321:522 (1986), Carter et al, Proc. Nat'l Acad. Sci. USA 89:4285 (1992), Sandhu, Crit. Rev. Biotech. 12:431 (1992), Singer et al, J. Immun. 750:2844 (1993), Sudhir (ed.), Antibody Engineering Protocols (Humana Press, Inc. 1995), Kelley, "Engineering Therapeutic Antibodies," in Protein Engineering: Principles and Practice, Cleland et al. (eds.), pages 399-434 (John Wiley & Sons, Inc. 1996), and by Queen et al, U.S. Patent No. 5,693,762 (1997). Polyclonal anti-idiotype antibodies can be prepared by immunizing animals with anti-Zcytorl6 antibodies or antibody fragments, using standard techniques. See, for example, Green et al, "Production of Polyclonal Antisera," in Methods In Molecular Biology: Immunochemical Protocols, Manson (ed.), pages 1-12 (Humana Press 1992). Also, see Coligan at pages 2.4.1-2.4.7. Alternatively, monoclonal anti- idiotype antibodies can be prepared using anti-Zcytorl6 antibodies or antibody fragments as immunogens with the techniques, described above. As another alternative, humanized anti-idiotype antibodies or subhuman primate anti-idiotype antibodies can be prepared using the above-described techniques. Methods for producing anti-idiotype antibodies are described, for example, by Irie, U.S. Patent No. 5,208,146, Greene, et. al, U.S. Patent No. 5,637,677, and Varthakavi and Minocha, J. Gen. Virol. 77: 1875 ( 1996). 70. Use of Zcytorlo Nucleotide Sequences to Detect Gene Expression and Gene Structure Nucleic acid molecules can be used to detect the expression of a Zcytorlo gene in a biological sample. Suitable probe molecules include double- stranded nucleic acid molecules comprising the nucleotide sequence of SEQ ID NO:l, or a portion thereof, as well as single-stranded nucleic acid molecules having the complement of the nucleotide sequence of SEQ ID NO:l, or a portion thereof. Probe molecules may be DNA, RNA, oligonucleotides, and the like. As used herein, the term "portion" refers to at least eight nucleotides to at least 20 or more nucleotides. Illustrative probes bind with regions of the Zcytorlo gene that have a low sequence similarity to comparable regions in other cytokine receptor genes. In a basic assay, a single-stranded probe molecule is incubated with RNA, isolated from a biological sample, under conditions of temperature and ionic strength that promote base pairing between the probe and target Zcytorlo RNA species. After separating unbound probe from hybridized molecules, the amount of hybrids is detected. In addition, as zcytorlo is spleen-specific, polynucleotide probes, anti- zcytorlό antibodies, and detection the presence of zcytorlo polypeptides in tissue can be used to assess whether spleen tissue is present, for example, after surgery involving the excision of a diseased or cancerous spleen. As such, the polynucleotides, polypeptides, and antibodies of the present invention can be used as an aid to determine whether all spleen tissue is excised after surgery, for example, after surgery for spleen cancer. In such instances, it is especially important to remove all potentially diseased tissue to maximize recovery from the cancer, and to minimize recuπence. Prefeπed embodiments include fluorescent, radiolabeled, or calorimetrically labeled antibodies, that can be used in situ. Moreover, anti-zcytorl6 antibodies and binding frangments can be used for tagging and sorting cells that specifically-express Zcytorlo, such as mononuclear cells, lymphoid cells, e.g, activated CD4+ T-cells and CD 19+ B-cells, and other described herein. Such methods of cell tagging and sorting are well known in the art (see, e.g., "Molecular Biology of the Cell", 3 rd Ed., Albert, B. et al. (Garland Publishing, London & New York, 1994). One of skill in the art would recognize the importance of separating cell tissue types to study cells, and the use of antibodies to separate specific cell tissue types. Basically, antibodies that bind to the surface of a cell type are coupled to various matrices such as collagen, polysaccharide beads, or plastic to form an affinity surface to which only cells recognized by the antibodies will adhere. The bound cells are then recovered by conventional techniques. Other methods involve separating cells by a fluorescence-activated cell sorter (FACS). En this technique one labels cells with antibodies that are coupled to a fluorescent dye. The labeled cells are then separated from unlabeled cells in a FACS machine. In FACS sorting individual cells traveling in single file pass through a laser beam and the fluorescence of each cell is measured. Slightly further down-stream, tiny droplets, most containing either one or no cells, are formed by a vibrating nozzle. The droplets containing a single cell are automatically give a positive or negative charge at the moment of formation, depending on whether the cell they contain is fluorescent, and then deflected by a strong electric field into an appropriate container. Such machines can select 1 cell in 1000 and sort about 5000 cells each second. This produces a uniform population of cells for cell culture. One of skill in the art would recognize that the antibodies to the Zcytorlo polypeptides of the present invention are useful, because not all tissue types express the Zcytorlo receptor and because it is important that biologists be able to separate specific cell types for further study and/or therapeutic re-implantation into the body. This is particularly relevant in cells such as immune cells, wherein zcytorlo is expressed. Moreover, use of Zcytorlo polynucleotide probes, anti-zcytorlό antibodies, and detection the presence of zcytorlo polypeptides in tissue can be used in the diagnosis and/or prevention of spontaneous abortions, or to monitor placental health and function. Since Zcytorlo is expressed in the placenta, it could play a role in the critical functions of placenta, such as proliferation or survival of trophoblast cells, and the like. Thus, zcytorlo could be essential for the function of the placenta, thus maturation of embryos. Therefore, a supplement of Zcytorlo polypeptide, or anti- zcytorlό antibodies may be beneficial in the prevention and treatment of certain types of spontaneous abortions, or premature birth of babies caused by abnormal expression of Zcytorlo in the placenta, or as a diagnostic to assess the function of the placenta. For example, as zcytorlo is normally expressed in placenta, the absence of zcytorlo expression may be indicative of abnormal placenta function. Well-established hybridization methods of RNA detection include northern analysis and dot/slot blot hybridization (see, for example, Ausubel (1995) at pages 4-1 to 4-27, and Wu et al. (eds.), "Analysis of Gene Expression at the RNA Level," in Methods in Gene Biotechnology, pages 225-239 (CRC Press, Enc. 1997)). Nucleic acid probes can be detectably labeled with radioisotopes such as 32 P or 35 S. Alternatively, Zcytorlo RNA can be detected with a nonradioactive hybridization method (see, for example, Isaac (ed.), Protocols for Nucleic Acid Analysis by Nonradioactive Probes (Humana Press, Inc. 1993)). Typically, nonradioactive detection is achieved by enzymatic conversion of chromogenic or chemiluminescent substrates. Illustrative nonradioactive moieties include biotin, fluorescein, and digoxigenin. Zcytorlo oligonucleotide probes are also useful for in vivo diagnosis. As an illustration, 18 F-labeled oligonucleotides can be administered to a subject and visualized by positron emission tomography (Tavitian et al, Nature Medicine 4:467 (1998)). Numerous diagnostic procedures take advantage of the polymerase chain reaction (PCR) to increase sensitivity of detection methods. Standard techniques for performing PCR are well-known (see, generally, Mathew (ed.), Protocols in Human Molecular Genetics (Humana Press, Inc. 1991), White (ed.), PCR Protocols: Current Methods and Applications (Humana Press, Enc. 1993), Cotter (ed.), Molecular Diagnosis of Cancer (Humana Press, Inc. 1996), Hanausek and Walaszek (eds.), Tumor Marker Protocols (Humana Press, Inc. 1998), Lo (ed.), Clinical Applications of PCR (Humana Press, Inc. 1998), and Meltzer (ed.), PCR in Bioanalysis (Humana Press, Inc. 1998)). PCR primers can be designed to amplify a portion of the Zcytorlo gene that has a low sequence similarity to a comparable region in other proteins, such as other cytokine receptor proteins. One variation of PCR for diagnostic assays is reverse transcriptase-PCR (RT-PCR). In the RT-PCR technique, RNA is isolated from a biological sample, reverse transcribed to cDNA, and the cDNA is incubated with Zcytorl 6 primers (see, for example, Wu et al. (eds.), "Rapid Isolation of Specific cDNAs or Genes by PCR," in Methods in Gene Biotechnology, pages 15-28 (CRC Press, Inc. 1997)). PCR is then performed and the products are analyzed using standard techniques. As an illustration, RNA is isolated from biological sample using, for example, the gunadinium-thiocyanate cell lysis procedure described above. Alternatively, a solid-phase technique can be used to isolate mRNA from a cell lysate. A reverse transcription reaction can be primed with the isolated RNA using random oligonucleotides, short homopolymers of dT, or Zcytorlo anti-sense oligomers. Oligo- dT primers offer the advantage that various mRNA nucleotide sequences are amplified that can provide control target sequences. Zcytorlo sequences are amplified by the polymerase chain reaction using two flanking oligonucleotide primers that are typically 20 bases in length. PCR amplification products can be detected using a variety of approaches. For example, PCR products can be fractionated by gel electrophoresis, and visualized by ethidium bromide staining. Alternatively, fractionated PCR products can be transfeπed to a membrane, hybridized with a detectably-labeled Zcytorlo probe, and examined by autoradiography. Additional alternative approaches include the use of digoxigenin-labeled deoxyribonucleic acid triphosphates to provide chemiluminescence detection, and the C-TRAK colorimetric assay. Another approach for detection of Zcytorlo expression is cycling probe technology (CPT), in which a single-stranded DNA target binds with an excess of DNA-RNA-DNA chimeric probe to form a complex, the RNA portion is cleaved with RNAase H, and the presence of cleaved chimeric probe is detected (see, for example, Beggs et al, J. Clin. Microbiol. 34:2985 (1996), Bekkaoui et al, Biotechniques 20:240 (1996)). Alternative methods for detection of Zcytorlo sequences can utilize approaches such as nucleic acid sequence-based amplification (NASBA), cooperative amplification of templates by cross-hybridization (CATCH), and the ligase chain reaction (LCR) (see, for example, Marshall et al, U.S. Patent No. 5,686,272 (1997), Dyer et al, J. Virol. Methods 60:161 (1996), Ehricht et al, Eur. J. Biochem. 243:358 (1997), and Chadwick et al, J. Virol. Methods 70:59 (1998)). Other standard methods are known to those of skill in the art. Zcytorlo probes and primers can also be used to detect and to localize Zcytorlo gene expression in tissue samples. Methods for such in situ hybridization are well-known to those of skill in the art (see, for example, Choo (ed.), In Situ Hybridization Protocols (Humana Press, Inc. 1994), Wu et al. (eds.), "Analysis of Cellular DNA or Abundance of mRNA by Radioactive In Situ Hybridization (RISH)," in Methods in Gene Biotechnology, pages 259-278 (CRC Press, Inc. 1997), and Wu et al. (eds.), "Localization of DNA or Abundance of mRNA by Fluorescence In Situ Hybridization (RISH)," in Methods in Gene Biotechnology, pages 279-289 (CRC Press, Inc. 1997)). Various additional diagnostic approaches are well-known to those of skill in the art (see, for example, Mathew (ed.), Protocols in Human Molecular Genetics (Humana Press, Enc. 1991), Coleman and Tsongalis, Molecular Diagnostics (Humana Press, Inc. 1996), and Elles, Molecular Diagnosis of Genetic Diseases (Humana Press, Inc., 1996)). Suitable test samples include blood, urine, saliva, tissue biopsy, and autopsy material. The Zcytorlo gene resides in human chromosome 6q24.1-25.2. This region is associated with various disorders, including insulin dependent diabetes mellitus, retinal cone dystrophy, breast cancer, and Parkinson disease. Moreover, defects in the zcytorlo locus itself may result in a heritable human disease states as discussed herein. One of skill in the art would appreciate that defects in cytokine receptors are known to cause particular diseases in humans. For example, polymorphisms of cytokine receptors are associated with pulmonary alveolar proteinosis, familial periodic fever, and erythroleukemia. Moreover, growth hormone receptor mutation results in dwarfism (Amselem, S et al., New Eng. J. Med. 321: 989- 995, 1989), EL-2 receptor gamma mutation results in severe combined immunodeficiency (SCED) (Noguchi, M et al., Cell 73: 147-157, 1993), c-Mpl mutation results in thrombocytopenia (Ehara, K et al., Proc. Nat. Acad. Sci. 96: 3132-3136, 1999), and severe mycobacterial and Salmonella infections result in interleukin- 12 receptor-deficient patients (de Jong, R et al., Science 280: 1435-1438, 1998), amongst others. Thus, similarly, defects in zcytorlo can cause a disease state or susceptibility to disease or infection. As the Zcytorlo gene is located at 6q24.1-25.2, zcytorlo polynucleotide probes can be used to detect chromosome 6q24.1-25.2 loss, trisomy, duplication or translocation associated with human diseases, such as inflammatory diseases, chronic inflammation, dysfunction of inflammatory response, immune cell cancers, bone maπow cancers, spleen cancers, prostate cancer, thyroid, parathyroid or other cancers, or immune diseases. Moreover, molecules of the present invention, such as the polypeptides, antagonists, agonists, polynucleotides and antibodies of the present invention would aid in the detection, diagnosis prevention, and treatment associated with a zcytorlo genetic defect. Thus, Zcytorlo nucleotide sequences can be used in linkage-based testing for various diseases, and to determine whether a subject's chromosomes contain a mutation in the Zcytorl 6 gene. Detectable chromosomal abeπations at the Zcytorlo gene locus include, but are not limited to, aneuploidy, gene copy number changes, loss of heterogeneity of 6q24.1-25.2, translocation in 6q24.1- 25.2, insertions, deletions, restriction site changes and rearrangements. Of particular interest are genetic alterations that inactivate a Zcytorlo gene, or gross chromosomal alterations in and around the zcytorlo locus. Similarly, defects in the Zcytorlo gene itself may result in a heritable human disease state. Moreover, one of skill in the art would appreciate that defects in cytokine receptors are known to cause disease states in humans. For example, growth hormone receptor mutation results in dwarfism (Amselem, S et al., New Eng. J. Med. 321: 989-995, 1989), EL-2 receptor gamma mutation results in severe combined immunodeficiency (SCED) (Noguchi, M et al., Cell 73: 147-157, 1993), c-Mpl mutation results in thrombocytopenia (Ihara, K et al., Proc. Nat. Acad. Sci. 96: 3132-3136, 1999), and severe mycobacterial and Salmonella infections result in interleukin- 12 receptor-deficient patients (de Jong, R et al., Science 280: 1435-1438, 1998), amongst others. Thus, similarly, defects in zcytorlo can cause a disease state or susceptibility to disease or infection. As, zcytorlo is a cytokine receptor within a chromosomal region where abeπations may be involved in cancer, and is shown to be expressed in ovarian cancer, the molecules of the present invention could also be directly involved in cancer formation or metastasis. As the Zcytorlo gene is located at the 6q24.1-25.2 region zcytorlo, polynucleotide probes can be used to detect chromosome 6q24.1-25.2 loss, loss of heterogeneity (LOH), trisomy, duplication or translocation associated with human diseases, such as immune cell cancers, neuroblastoma, bone marrow cancers, thyroid, parathyroid, prostate, melanoma, or other cancers, or immune diseases. Moreover, molecules of the present invention, such as the polypeptides, antagonists, agonists, polynucleotides and antibodies of the present invention would aid in the detection, diagnosis prevention, and treatment associated with a Zcytorl6 genetic defect. A diagnostic could assist physicians in determining the type of disease and appropriate associated therapy, or assistance in genetic counseling. As such, the inventive anti-zcytorl6 antibodies, polynucleotides, and polypeptides can be used for the detection of zcytorlo polypeptide, mRNA or anti-zcytorl6 antibodies, thus serving as markers and be directly used for detecting or genetic diseases or cancers, as described herein, using methods known in the art and described herein. Further, zcytorlo polynucleotide probes can be used to detect abnormalities or genotypes associated with chromosome 6q24.1-25.2 deletions and translocations associated with human diseases, other translocations involved with malignant progression of tumors or other 6q24.1-25.2 mutations, which are expected to be involved in chromosome rearrangements in malignancy; or in other cancers, or in spontaneous abortion. Similarly, zcytorlo polynucleotide probes can be used to detect abnormalities or genotypes associated with chromosome 6q24.1-25.2 trisomy and chromosome loss associated with human diseases. Thus, zcytorlo polynucleotide probes can be used to detect abnormalities or genotypes associated with these defects. As discussed above, defects in the Zcytorlo gene itself may result in a heritable human disease state. For example, zcytorlo expression is elevated in several tissue-specific human cancers, as described herein. Molecules of the present invention, such as the polypeptides, antagonists, agonists, polynucleotides and antibodies of the present invention would aid in the detection, diagnosis prevention, and treatment associated with a zcytorlo genetic defect. In addition, zcytorlo polynucleotide probes can be used to detect allelic differences between diseased or non-diseased individuals at the zcytorlo chromosomal locus. As such, the zcytorlo sequences can be used as diagnostics in forensic DNA profiling. In general, the diagnostic methods used in genetic linkage analysis, to detect a genetic abnormality or abeπation in a patient, are known in the art. Analytical probes will be generally at least 20 nt in length, although somewhat shorter probes can be used (e.g., 14-17 nt). PCR primers are at least 5 nt in length, preferably 15 or more, more preferably 20-30 nt. For gross analysis of genes, or chromosomal DNA, a zcytorlo polynucleotide probe may comprise an entire exon or more. Exons are readily determined by one of skill in the art by comparing zcytorlo sequences (SEQ ED NO:l) with the human genomic DNA for zcytorlo. In general, the diagnostic methods used in genetic linkage analysis, to detect a genetic abnormality or aberration in a patient, are known in the art. Most diagnostic methods comprise the steps of (a) obtaining a genetic sample from a potentially diseased patient, diseased patient or potential non-diseased caπier of a recessive disease allele; (b) producing a first reaction product by incubating the genetic sample with a zcytorlo polynucleotide probe wherein the polynucleotide will hybridize to complementary polynucleotide sequence, such as in RFLP analysis or by incubating the genetic sample with sense and antisense primers in a PCR reaction under appropriate PCR reaction conditions; (iii) Visualizing the first reaction product by gel electrophoresis and/or other known method such as visualizing the first reaction product with a zcytorlo polynucleotide probe wherein the polynucleotide will hybridize to the complementary polynucleotide sequence of the first reaction; and (iv) comparing the visualized first reaction product to a second control reaction product of a genetic sample from wild type patient. A difference between the first reaction product and the control reaction product is indicative of a genetic abnormality in the diseased or potentially diseased patient, or the presence of a heterozygous recessive carrier phenotype for a non-diseased patient, or the presence of a genetic defect in a tumor from a diseased patient, or the presence of a genetic abnormality in a fetus or pre- implantation embryo. For example, a difference in restriction fragment pattern, length of PCR products, length of repetitive sequences at the zcytorlo genetic locus, and the like, are indicative of a genetic abnormality, genetic aberration, or allelic difference in comparison to the normal wild type control. Controls can be from unaffected family members, or unrelated individuals, depending on the test and availability of samples. Genetic samples for use within the present invention include genomic DNA, mRNA, and cDNA isolated form any tissue or other biological sample from a patient, such as but not limited to, blood, saliva, semen, embryonic cells, amniotic fluid, and the like. The polynucleotide probe or primer can be RNA or DNA, and will comprise a portion of SEQ ID NO: l, the complement of SEQ ID NO: l, or an RNA equivalent thereof. Such methods of showing genetic linkage analysis to human disease phenotypes are well known in the art. For reference to PCR based methods in diagnostics see see, generally, Mathew (ed.), Protocols in Human Molecular Genetics (Humana Press, Inc. 1991), White (ed.), PCR Protocols: Current Methods and Applications (Humana Press, Inc. 1993), Cotter (ed.), Molecular Diagnosis of Cancer (Humana Press, Inc. 1996), Hanausek and Walaszek (eds.), Tumor Marker Protocols (Humana Press, Inc. 1998), Lo (ed.), Clinical Applications of PCR (Humana Press, Inc. 1998), and Meltzer (ed.), PCR in Bioanalysis (Humana Press, Inc. 1998)). Abeπations associated with the Zcytorlo locus can be detected using nucleic acid molecules of the present invention by employing molecular genetic techniques, such as restriction fragment length polymorphism (RFLP) analysis, short tandem repeat (STR) analysis employing PCR techniques, amplification-refractory mutation system analysis (ARMS), single-strand conformation polymorphism (SSCP) detection, RNase cleavage methods, denaturing gradient gel electrophoresis, fluorescence-assisted mismatch analysis (FAMA), and other genetic analysis techniques known in the art (see, for example, Mathew (ed.), Protocols in Human Molecular Genetics (Humana Press, Inc. 1991), Marian, Chest 108:255 (1995), Coleman and Tsongalis, Molecular Diagnostics (Human Press, Enc. 1996), Elles (ed.) Molecular Diagnosis of Genetic Diseases (Humana Press, Inc. 1996), Landegren (ed.), Laboratory Protocols for Mutation Detection (Oxford University Press 1996), Birren et al. (eds.), Genome Analysis, Vol. 2: Detecting Genes (Cold Spring Harbor Laboratory Press 1998), Dracopoli et al. (eds.), Current Protocols in Human Genetics (John Wiley & Sons 1998), and Richards and Ward, "Molecular Diagnostic Testing," in Principles of Molecular Medicine, pages 83-88 (Humana Press, Enc. 1998)). The protein truncation test is also useful for detecting the inactivation of a gene in which translation-terminating mutations produce only portions of the encoded protein (see, for example, Stoppa-Lyonnet et al, Blood 97:3920 (1998)). According to this approach, RNA is isolated from a biological sample, and used to synthesize cDNA. PCR is then used to amplify the Zcytorl6 target sequence and to introduce an RNA polymerase promoter, a translation initiation sequence, and an in-frame ATG triplet. PCR products are transcribed using an RNA polymerase, and the transcripts are translated in vitro with a T7-coupled reticulocyte lysate system. The translation products are then fractionated by SDS-PAGE to determine the lengths of the translation products. The protein truncation test is described, for example, by Dracopoli et al. (eds.), Current Protocols in Human Genetics, pages 9.11.1 - 9.11.18 (John Wiley & Sons 1998). The present invention also contemplates kits for performing a diagnostic assay for Zcytorl6 gene expression or to detect mutations in the Zcytorl6 gene. Such kits comprise nucleic acid probes, such as double-stranded nucleic acid molecules comprising the nucleotide sequence of SEQ ID NO:l, or a portion thereof, as well as single-stranded nucleic acid molecules having the complement of the nucleotide sequence of SEQ ID NO:l, or a portion thereof. Probe molecules may be DNA, RNA, oligonucleotides, and the like. Kits may comprise nucleic acid primers for performing PCR. Such kits can contain all the necessary elements to perform a nucleic acid diagnostic assay described above. A kit will comprise at least one container comprising a Zcytorlo probe or primer. The kit may also comprise a second container comprising one or more reagents capable of indicating the presence of Zcytorl 6 sequences. Examples of such indicator reagents include detectable labels such as radioactive labels, fluorochromes, chemiluminescent agents, and the like. A kit may also comprise a means for conveying to the user that the Zcytorlo probes and primers are used to detect Zcytorlo gene expression. For example, written instructions may state that the enclosed nucleic acid molecules can be used to detect either a nucleic acid molecule that encodes Zcytorlo, or a nucleic acid molecule having a nucleotide sequence that is complementary to a Zcytør76-encoding nucleotide sequence. The written material can be applied directly to a container, or the written material can be provided in the form of a packaging insert. 77. Use of Anti-Zcy tor 16 Antibodies to Detect Zcytorlo or Antagonize Zcytorlo Binding to IL-TIF The present invention contemplates the use of anti-Zcytorl6 antibodies to screen biological samples in vitro for the presence of Zcytorlo. In one type of in vitro assay, anti-Zcytorl6 antibodies are used in liquid phase. For example, the presence of Zcytorlo in a biological sample can be tested by mixing the biological sample with a trace amount of labeled Zcytorlo and an anti-Zcytorl6 antibody under conditions that promote binding between Zcytorlo and its antibody. Complexes of Zcytorlo and anti- Zcytorlό in the sample can be separated from the reaction mixture by contacting the complex with an immobilized protein which binds with the antibody, such as an Fc antibody or Staphylococcus protein A. The concentration of Zcytorlo in the biological sample will be inversely proportional to the amount of labeled Zcytorlo bound to the antibody and directly related to the amount of free labeled Zcytorlo. Ηlustrative biological samples include blood, urine, saliva, tissue biopsy, and autopsy material. Alternatively, in vitro assays can be performed in which anti-Zcytorl6 antibody is bound to a solid-phase carrier. For example, antibody can be attached to a polymer, such as aminodextran, in order to link the antibody to an insoluble support such as a polymer-coated bead, a plate or a tube. Other suitable in vitro assays will be readily apparent to those of skill in the art. In another approach, anti-Zcytorl6 antibodies can be used to detect Zcytorlo in tissue sections prepared from a biopsy specimen. Such immunochemical detection can be used to determine the relative abundance of Zcytorlo and to determine the distribution of Zcytorlo in the examined tissue. General immunochemistry techniques are well established (see, for example, Ponder, "Cell Marking Techniques and Their Application," in Mammalian Development: A Practical Approach, Monk (ed.), pages 115-38 (ERL Press 1987), Coligan at pages 5.8.1-5.8.8, Ausubel (1995) at pages 14.6.1 to 14.6.13 (Wiley Interscience 1990), and Manson (ed.), Methods In Molecular Biology, Vol. 10: Immunochemical Protocols (The Humana Press, Enc. 1992)). Immunochemical detection can be performed by contacting a biological sample with an anti-Zcytorl6 antibody, and then contacting the biological sample with a detectably labeled molecule which binds to the antibody. For example, the detectably labeled molecule can comprise an antibody moiety that binds to anti-Zcytorl6 antibody. Alternatively, the anti-Zcytorl6 antibody can be conjugated with avidin/streptavidin (or biotin) and the detectably labeled molecule can comprise biotin (or avidin/streptavidin). Numerous variations of this basic technique are well-known to those of skill in the art. Alternatively, an anti-Zcytorl6 antibody can be conjugated with a detectable label to form an anti-Zcytorl6 immunoconjugate. Suitable detectable labels include, for example, a radioisotope, a fluorescent label, a chemiluminescent label, an enzyme label, a bioluminescent label or colloidal gold. Methods of making and detecting such detectably-labeled immunoconjugates are well-known to those of ordinary skill in the art, and are described in more detail below. The detectable label can be a radioisotope that is detected by autoradiography. Isotopes that are particularly useful for the purpose of the present invention are 3 H, 125 1, 131 1, 35 S and 14 C. Anti-Zcytorl6 immunoconjugates can also be labeled with a fluorescent compound. The presence of a fluorescently-labeled antibody is determined by exposing the immunoconjugate to light of the proper wavelength and detecting the resultant fluorescence. Fluorescent labeling compounds include fluorescein isothiocyanate, rhoda- mine, phycoerytherin, phycocyanin, allophycocyanin, o-phthaldehyde and fluorescamine. Alternatively, anti-Zcytorl6 immunoconjugates can be detectably labeled by coupling an antibody component to a chemiluminescent compound. The presence of the chemiluminescent-tagged immunoconjugate is determined by detecting the presence of luminescence that arises during the course of a chemical reaction. Examples of chemi- luminescent labeling compounds include luminol, isoluminol, an aromatic acridinium ester, an imidazole, an acridinium salt and an oxalate ester. Similarly, a bioluminescent compound can be used to label anti-Zcytorl6 immunoconjugates of the present invention. Bioluminescence is a type of chemiluminescence found in biological systems in which a catalytic protein increases the efficiency of the chemiluminescent reaction. The presence of a bioluminescent protein is determined by detecting the presence of luminescence. Bioluminescent compounds that are useful for labeling include luciferin, luciferase and aequorin. Alternatively, anti-Zcytorl6 immunoconjugates can be detectably labeled by linking an anti-Zcytorlό antibody component to an enzyme. When the anti-Zcytorl6- enzyme conjugate is incubated in the presence of the appropriate substrate, the enzyme moiety reacts with the substrate to produce a chemical moiety which can be detected, for example, by spectrophotometric, fluorometric or visual means. Examples of enzymes that can be used to detectably label polyspecific immunoconjugates include β-galactosidase, glucose oxidase, peroxidase and alkaline phosphatase. Those of skill in the art will know of other suitable labels which can be employed in accordance with the present invention. The binding of marker moieties to anti-Zcytorl6 antibodies can be accomplished using standard techniques known to the art. Typical methodology in this regard is described by Kennedy et al, Clin. Chim. Acta 70:1 (1976), Schurs et al, Clin. Chim. Acta 81:1 (1977), Shih et al, Int'l J. Cancer 46:1101 ( 1990), Stein et al, Cancer Res. 50: 1330 (1990), and Coligan, supra. Moreover, the convenience and versatility of immunochemical detection can be enhanced by using anti-Zcytorlό antibodies that have been conjugated with avidin, streptavidin, and biotin (see, for example, Wilchek et al. (eds.), "Avidin-Biotin Technology," Methods In Enzymology, Vol. 184 (Academic Press 1990), and Bayer et al, "Immunochemical Applications of Avidin-Biotin Technology," in Methods In Molecular Biology, Vol. 10, Manson (ed.), pages 149-162 (The Humana Press, Enc. 1992). Methods for performing immunoassays are well-established. See, for example, Cook and Self, "Monoclonal Antibodies in Diagnostic Immunoassays," in Monoclonal Antibodies: Production, Engineering, and Clinical Application, Ritter and Ladyman (eds.), pages 180-208, (Cambridge University Press, 1995), Perry, "The Role of Monoclonal Antibodies in the Advancement of Immunoassay Technology," in Monoclonal Antibodies: Principles and Applications, Birch and Lennox (eds.), pages 107-120 (Wiley-Liss, Inc. 1995), and Diamandis, Immunoassay (Academic Press, Inc. 1996). The present invention also contemplates kits for performing an immunological diagnostic assay for Zcytorlo gene expression. Such kits comprise at least one container comprising an anti-Zcytorlό antibody, or antibody fragment. A kit may also comprise a second container comprising one or more reagents capable of indicating the presence of Zcytorlo antibody or antibody fragments. Examples of such indicator reagents include detectable labels such as a radioactive label, a fluorescent label, a chemiluminescent label, an enzyme label, a bioluminescent label, colloidal gold, and the like. A kit may also comprise a means for conveying to the user that Zcytorlo antibodies or antibody fragments are used to detect Zcytorlo protein. For example, written instructions may state that the enclosed antibody or antibody fragment can be used to detect Zcytorlo. The written material can be applied directly to a container, or the written material can be provided in the form of a packaging insert. Alternative techniques for generating or selecting antibodies useful herein include in vitro exposure of lymphocytes to soluble zcytorlo monomeric receptor or soluble zcytorlo homodimeric, heterodimeric or multimeric polypeptides, and selection of antibody display libraries in phage or similar vectors (for instance, through use of immobilized or labeled soluble zcytorlo monomeric receptor or soluble zcytorlo homodimeric, heterodimeric or multimeric polypeptides). Genes encoding polypeptides having potential binding domains such as soluble zcytorlo monomeric receptor or soluble zcytorlo homodimeric, heterodimeric or multimeric polypeptide can be obtained by screening random peptide libraries displayed on phage (phage display) or on bacteria, such as E. coli. Nucleotide sequences encoding the polypeptides can be obtained in a number of ways, such as through random mutagenesis and random polynucleotide synthesis. These random peptide display libraries can be used to screen for peptides which interact with a known target which can be a protein or polypeptide, such as a ligand or receptor, a biological or synthetic macromolecule, or organic or inorganic substances. Techniques for creating and screening such random peptide display libraries are known in the art (Ladner et al., US Patent NO. 5,223,409; Ladner et al., US Patent NO. 4,946,778; Ladner et al., US Patent NO. 5,403,484 and Ladner et al., US Patent NO. 5,571,698) and random peptide display libraries and kits for screening such libraries are available commercially, for instance from Clontech (Palo Alto, CA), Invitrogen Inc. (San Diego, CA), New England Biolabs, Enc. (Beverly, MA) and Pharmacia LKB Biotechnology Inc. (Piscataway, NJ). Random peptide display libraries can be screened using the soluble zcytorlo monomeric receptor or soluble zcytorlo homodimeric, heterodimeric or multimeric polypeptide sequences disclosed herein to identify proteins which bind to zcytorl 6-comprising receptor polypeptides. These "binding polypeptides," which interact with soluble zcytorl 6-comprising receptor polypeptides, can be used for tagging cells; for isolating homolog polypeptides by affinity purification; they can be directly or indirectly conjugated to drugs, toxins, radionuclides and the like. These binding polypeptides can also be used in analytical methods such as for screening expression libraries and neutralizing activity, e.g., for blocking interaction between EL-TEF ligand and receptor, or viral binding to a receptor. The binding polypeptides can also be used for diagnostic assays for determining circulating levels of soluble zcytorl 6-comprising receptor polypeptides; for detecting or quantitating soluble or non-soluble zcytorl 6-comprising receptors as marker of underlying pathology or disease. These binding polypeptides can also act as "antagonists" to block soluble or membrane-bound zcytorlo monomeric receptor or zcytorlo homodimeric, heterodimeric or multimeric polypeptide binding (e.g. to ligand) and signal transduction in vitro and in vivo. Again, these binding polypeptides serve as anti-zcytorl6 monomeric receptor or anti-zcytorl6 homodimeric, heterodimeric or multimeric polypeptides and are useful for inhibiting IL-TEF activity, as well as receptor activity or protein-binding. Antibodies raised to the natural receptor complexes of the present invention may be prefeπed embodiments, as they may act more specifically against the IL-TIF, or more potently than antibodies raised to only one subunit. Moreover, the antagonistic and binding activity of the antibodies of the present invention can be assayed in the IL-TIF proliferation, signal trap, luciferase or binding assays in the presence of IL-TIF and zcytorl 6-comprising soluble receptors, and other biological or biochemical assays described herein. Antibodies to monomeric zcytorlo receptor or zcytorlo homodimeric, heterodimeric or multimeric zcytorl 6-containing receptors may be used for tagging cells that express zcytorl 6 receptors; for isolating soluble zcytorl 6-comprising receptor polypeptides by affinity purification; for diagnostic assays for determining circulating levels of soluble zcytorl 6-comprising receptor polypeptides; for detecting or quantitating soluble zcytorl 6-comprising receptors as marker of underlying pathology or disease; in analytical methods employing FACS; for screening expression libraries; for generating anti-idiotypic antibodies that can act as IL-TIF agonists; and as neutralizing antibodies or as antagonists to block zcytorlo receptor function, or to block IL-TEF activity in vitro and in vivo. Suitable direct tags or labels include radionuclides, enzymes, substrates, cofactors, biotin, inhibitors, fluorescent markers, chemiluminescent markers, magnetic particles and the like; indirect tags or labels may feature use of biotin-avidin or other complement/anti-complement pairs as intermediates. Antibodies herein may also be directly or indirectly conjugated to drugs, toxins, radionuclides and the like, and these conjugates used for in vivo diagnostic or therapeutic applications. Moreover, antibodies to soluble zcytorl 6-comprising receptor polypeptides, or fragments thereof may be used in vitro to detect denatured or non- denatured zcytorl 6-comprising receptor polypeptides or fragments thereof in assays, for example, Western Blots or other assays known in the art. Antibodies to soluble zcytorlo receptor or soluble zcytorlo homodimeric, heterodimeric or multimeric receptor polypeptides are useful for tagging cells that express the coπesponding receptors and assaying their expression levels, for affinity purification, within diagnostic assays for determining circulating levels of receptor polypeptides, analytical methods employing fluorescence-activated cell sorting. Moreover, divalent antibodies, and anti-idiotypic antibodies may be used as agonists to mimic the effect of the zcytorlo ligand, IL-TIF. Antibodies herein can also be directly or indirectly conjugated to drugs, toxins, radionuclides and the like, and these conjugates used for in vivo diagnostic or therapeutic applications. For instance, antibodies or binding polypeptides which recognize soluble zcytorlo receptor or soluble zcytorlo homodimeric, heterodimeric or multimeric receptor polypeptides of the present invention can be used to identify or treat tissues or organs that express a coπesponding anti-complementary molecule (i.e., a zcytorl 6-comprising soluble or membrane-bound receptor). More specifically, antibodies to soluble zcytorl 6-comprising receptor polypeptides, or bioactive fragments or portions thereof, can be coupled to detectable or cytotoxic molecules and delivered to a mammal having cells, tissues or organs that express the zcytorl 6-comprising receptor such as zcytorl 6-expressing cancers, or certain disease states. Suitable detectable molecules may be directly or indirectly attached to polypeptides that bind zcytorl 6-comprising receptor polypeptides, such as "binding polypeptides," (including binding peptides disclosed above), antibodies, or bioactive fragments or portions thereof. Suitable detectable molecules include radionuclides, enzymes, substrates, cofactors, inhibitors, fluorescent markers, chemiluminescent markers, magnetic particles and the like. Suitable cytotoxic molecules may be directly or indirectly attached to the polypeptide or antibody, and include bacterial or plant toxins (for instance, diphtheria toxin, Pseudomonas exotoxin, ricin, abrin and the like), as well as therapeutic radionuclides, such as iodine-131, rhenium- 188 or yttrium-90 (either directly attached to the polypeptide or antibody, or indirectly attached through means of a chelating moiety, for instance). Binding polypeptides or antibodies may also be conjugated to cytotoxic drugs, such as adriamycin. For indirect attachment of a detectable or cytotoxic molecule, the detectable or cytotoxic molecule can be conjugated with a member of a complementary/ anticomplementary pair, where the other member is bound to the binding polypeptide or antibody portion. For these purposes, biotin streptavidin is an exemplary complementary/ anticomplementary pair. In another embodiment, binding polypeptide-toxin fusion proteins or antibody-toxin fusion proteins can be used for targeted cell or tissue inhibition or ablation (for instance, to treat cancer cells or tissues). Alternatively, if the binding polypeptide has multiple functional domains (i.e., an activation domain or a ligand binding domain, plus a targeting domain), a fusion protein including only the targeting domain may be suitable for directing a detectable molecule, a cytotoxic molecule or a complementary molecule to a cell or tissue type of interest. In instances where the fusion protein including only a single domain includes a complementary molecule, the anti-complementary molecule can be conjugated to a detectable or cytotoxic molecule. Such domain-complementary molecule fusion proteins thus represent a generic targeting vehicle for cell/tissue-specific delivery of generic anti-complementary- detectable/ cytotoxic molecule conjugates. In another embodiment, zcytorlo binding polypeptide-cytokine or antibody-cytokine fusion proteins can be used for enhancing in vivo killing of target tissues (for example, spleen, pancreatic, blood, lymphoid, colon, and bone marrow cancers), if the binding polypeptide-cytokine or anti- zcytorlo receptor antibody targets the hyperproliferative cell (See, generally, Hornick et al., Blood 89:4437-47, 1997). The described fusion proteins enable targeting of a cytokine to a desired site of action, thereby providing an elevated local concentration of cytokine. Suitable anti-zcytorl6 monomer, homodimer, heterodimer or multimer antibodies target an undesirable cell or tissue (i.e., a tumor or a leukemia), and the fused cytokine mediates improved target cell lysis by effector cells. Suitable cytokines for this purpose include interleukin 2 and granulocyte-macrophage colony-stimulating factor (GM-CSF), for instance. Alternatively, zcytorlo receptor binding polypeptides or antibody fusion proteins described herein can be used for enhancing in vivo killing of target tissues by directly stimulating a zcytorlo receptor-modulated apoptotic pathway, resulting in cell death of hyperproliferative cells expressing zcytorl 6-comprising receptors. 72. Therapeutic Uses of Polypeptides Having Zcytorlo Activity Amino acid sequences having Zcytorlo activity can be used to modulate the immune system by binding Zcytorlo ligand, and thus, preventing the binding of Zcytorlo ligand with endogenous Zcytorlo receptor. Zcytorlo antagonists, such as anti-Zcytorlό antibodies, can also be used to modulate the immune system by inhibiting the binding of Zcytorlo ligand with the endogenous Zcytorlo receptor. Accordingly, the present invention includes the use of proteins, polypeptides, and peptides having Zcytorlo activity (such as Zcytorlo polypeptides, Zcytorlo analogs (e.g., anti-Zcytorlό anti-idiotype antibodies), and Zcytorlo fusion proteins) to a subject which lacks an adequate amount of this polypeptide, or which produces an excess of Zcytorlo ligand. Zcytorlo antagonists (e.g., anti-Zcytorlό antibodies) can be also used to treat a subject which produces an excess of either Zcytorlo ligand or Zcytorlo. Suitable subjects include mammals, such as humans. Moreover, we have shown that the zcytorlo receptor binds a ligand called T-cell inducible Factor (IL-TIF) (SEQ ED NO: 15; Dumoutier, L. et al., Proc. Nat'l. Acad. Sci. 97:10144-10149, 2000; mouse IL-TIF sequence is shown in Dumontier et al., J. Immunol. 164:1814-1819, 2000). Moreover, commonly owned zcytorl 1 (US Patent No. 5,965,704) and CRF2-4 receptor also bind IL-TEF (See, WEPO publication WO 00/24758; Dumontier et al., J. Immunol. 164: 1814-1819, 2000; Spencer, SD et al., J. Exp. Med. 187:571-578, 1998; Gibbs, VC and Pennica Gene 186:97-101, 1997 (CRF2-4 cDNA); Xie, MH et al., J. Biol. Chem. 275: 31335-31339, 2000; and Kotenko, SV et al., J. Biol. Chem. manuscript in press M007837200). Moreover, IL-lOβ receptor may be involved as a receptor for IL-TIF, and it is believed to be synonymous with CRF2-4 (Dumoutier, L. et al., Proc. Nat'l. Acad. Sci. 97:10144- 10149, 2000; Liu Y et al, J Immunol. 152; 1821-1829, 1994 (IL-10R cDNA). Within prefeπed embodiments, the soluble receptor form of zcytorlo, residues 22-231 of SEQ ED NO:2, (SEQ ID NO: 13) is a monomer, homodimer, heterodimer, or multimer that antagonizes the effects of IL-TIF in vivo. Antibodies and binding polypeptides to such zcytorlo monomer, homodimer, heterodimer, or multimers also serve as antagonists of zcytorlo activity. IL-TIF has been shown to be induced in the presence of EL-9, and is suspected to be involved in promoting Thl-type immune responses, and inflammation. IL-9 stimulates proliferation, activation, differentiation and/or induction of immune function in a variety of ways and is implicated in asthma, lung mastocytosis, and other diseases, as well as activates STAT pathways. Antagonists of IL-TIF or EL-9 function can have beneficial use against such human diseases. The present invention provides such novel antagonists of IL-TEF. IL-TIF has been show to be involved in up-regulate the production of acute phase reactants, such as serum amyloid A (SAA), αl-antichymotrypsin, and haptoglobin, and that IL-TIF expression is increased upon injection of lipopolysaccharide (LPS) in vivo suggesting that IL-TIF is involved in inflammatory response (Dumoutier, L. et al., Proc. Nat'l. Acad. Sci. 97:10144-10149, 2000). Production of acute phase proteins, such as SAA, is considered s short-term survival mechanism where inflammation is beneficial; however, maintenance of acute phase proteins for longer periods contributes to chronic inflammation and can be harmful to human health. For review, see Uhlar, CM and Whitehead, AS, Eur. J. Biochem. 265:501-523, 1999, and Baumann H. and Gauldie, J. Immunology Today 15:74-80, 1994. Moreover, the acute phase protein SAA is implicated in the pathogenesis of several chronic inflammatory diseases, is implicated in atherosclerosis and rheumatoid arthritis, and is the precursor to the amyloid A protein deposited in amyloidosis (Uhlar, CM and Whitehead, supra.). Thus, as IL-TIF acts as a pro-inflammatory molecule and induces production of SAA, antagonists would be useful in treating inflammatory disease and other diseases associated with acute phase response proteins induced by IL- TIF. Such antagonists are provided by the present invention. For example, method of reducing L-TIF-induced or IL-9 induced inflammation comprises administering to a mammal with inflammation an amount of a composition of soluble zcytorl 6- comprising receptor sufficient to reduce inflammation. Moreover, a method of suppressing an inflammatory response in a mammal with inflammation can comprise: (1) determining a level of serum amyloid A protein; (2) administering a composition comprising a soluble zcytorlo cytokine receptor polypeptide as described herein in an acceptable pharmaceutical vehicle; (3) determining a post administration level of serum amyloid A protein; (4) comparing the level of serum amyloid A protein in step (1) to the level of serum amyloid A protein in step (3), wherein a lack of increase or a decrease in serum amyloid A protein level is indicative of suppressing an inflammatory response. The receptors of the present invention include at least one zcytorlo receptor subunit. A second receptor polypeptide included in the heterodimeric soluble receptor belongs to the receptor subfamily that includes Enterleukin-10 receptor, the interferons (e.g., interferon-gamma alpha and beta chains and the interferon-alpha/beta receptor alpha and beta chains), zcytor7, zcytorl 1, and CRF2-4. A second soluble receptor polypeptide included in a heterodimeric soluble receptor can also include a zcytorl 1 soluble receptor subunit, disclosed in the commonly owned US Patent No. 5,965,704; an IL-10R subunit, such as IL-lORα; or a zcytor7 soluble receptor subunit, disclosed in the commonly owned US Patent No. 5,945,511. The zcytorl 1 receptor in conjunction with CRF2-4 and IL-10 Receptor was shown to signal JAK-STAT pathway in response to IL-TIF (Xie et al., supra.; Kotenko et al„ supra.). According to the present invention, in addition to a monomeric or homodimeric zcytorlo receptor polypeptide, a heterodimeric soluble zcytorlo receptor, as exemplified by an embodiment comprising a soluble zcytorlo receptor + soluble CRF2-4 receptor heterodimer (zcytorlo/ CRF2-4), can act as an antagonist of the IL-TIF. Other embodiments include soluble heterodimers comprising zcytorlo/ IL-10R, zcytorl6/EL- 9R, zcytorlό/zcytorl l, zcytorl 6/zcytor7, and other class IE receptor subunits, as well as multimeric receptors including but not limited to zcytorl6/CRF2-4/zcytorl l or zcytorl6/CRF2-4/IL-10R. Analysis of the tissue distribution of the mRNA corresponding zcytorlo cDNA showed that mRNA level was highest in placenta and spleen, and the ligand to which zcytorlo binds (EL-TEF) is implicated in inducing inflammatory response including induction of the acute-phase response (Dumoutier, L. et al., Proc. Nat'l. Acad. Sci. 97: 10144-10149, 2000). Thus, particular embodiments of the present invention are directed toward use of soluble zcytorlo heterodimers as antagonists in inflammatory and immune diseases or conditions such as pancreatitis, type I diabetes (EDDM), pancreatic cancer, pancreatitis, Graves Disease, inflammatory bowel disease (EBD), Crohn's Disease, colon and intestinal cancer, diverticulosis, autoimmune disease, sepsis, organ or bone maπow transplant; inflammation due to trauma, sugery or infection; amyloidosis; splenomegaly; graft versus host disease; and where inhibition of inflammation, immune suppression, reduction of proliferation of hematopoietic, immune, inflammatory or lymphoid cells, macrophages, T-cells (including Thl and Th2 cells), suppression of immune response to a pathogen or antigen, or other instances where inhibition of IL-TIF or IL-9 cytokine production is desired. Moreover, antibodies or binding polypeptides that bind zcytorlo polypeptides, monomers, homodimers, heterodimers and multimers described herein and/or zcytorlo polypeptides, monomers, homodimers, heterodimers and multimers themselves are useful to: 1) Antagonize or block signaling via the IL-TEF receptors in the treatment of acute inflammation, inflammation as a result of trauma, tissue injury, surgery, sepsis or infection, and chronic inflammatory diseases such as asthma, inflammatory bowel disease (EBD), chronic colitis, splenomegaly, rheumatoid arthritis, recuπent acute inflammatory episodes (e.g., tuberculosis), and treatment of amyloidosis, and atherosclerosis, Castleman's Disease, asthma, and other diseases associated with the induction of acute-phase response. 2) Antagonize or block signaling via the IL-TIF receptors in the treatment of autoimmune diseases such as IDDM, multiple sclerosis (MS), systemic Lupus erythematosus (SLE), myasthenia gravis, rheumatoid arthritis, and D3D to prevent or inhibit signaling in immune cells (e.g. lymphocytes, monocytes, leukocytes) via zcytorlo (Hughes C et al., J. Immunol 153: 3319-3325, 1994). Alternatively antibodies, such as monoclonal antibodies (MAb) to zcytorl 6-comprising receptors, can also be used as an antagonist to deplete unwanted immune cells to treat autoimmune disease. Asthma, allergy and other atopic disease may be treated with an MAb against, for example, soluble zcytorlo soluble receptors or zcytorl 6/CRF2-4 heterodimers, to inhibit the immune response or to deplete offending cells. Blocking or inhibiting signaling via zcytorlo, using the polypeptides and antibodies of the present invention, may also benefit diseases of the pancreas, kidney, pituitary and neuronal cells. IDDM, NEDDM, pancreatitis, and pancreatic carcinoma may benefit. Zcytorlo may serve as a target for MAb therapy of cancer where an antagonizing MAb inhibits cancer growth and targets immune-mediated killing. (Holliger P, and Hoogenboom, H: Nature Biotech. 16: 1015-1016, 1998). Mabs to soluble zcytorlo monomers, homodimers, heterodimers and multimers may also be useful to treat nephropathies such as glomerulosclerosis, membranous neuropathy, amyloidosis (which also affects the kidney among other tissues), renal arteriosclerosis, glomerulonephritis of various origins, fibroproliferative diseases of the kidney, as well as kidney dysfunction associated with SLE, IDDM, type II diabetes (NEDDM), renal tumors and other diseases. 3) Agonize or initiate signaling via the EL-TEF receptors in the treatment of autoimmune diseases such as EDDM, MS, SLE, myasthenia gravis, rheumatoid arthritis, and IBD. Anti-soluble zcytorlo, anti-soluble zcytorl 6/CRF2-4 heterodimers and multimer monoclonal antibodies may signal lymphocytes or other immune cells to differentiate, alter proliferation, or change production of cytokines or cell surface proteins that ameliorate autoimmunity. Specifically, modulation of a T-helper cell response to an alternate pattern of cytokine secretion may deviate an autoimmune response to ameliorate disease (Smith JA et al., J. Immunol. 160:4841-4849, 1998). Similarly, agonistic Anti-soluble zcytorlo, anti-solublezcytorl6/CRF2-4 heterodimers and multimer monoclonal antibodies may be used to signal, deplete and deviate immune cells involved in asthma, allergy and atopoic disease. Signaling via zcytorlo may also benefit diseases of the pancreas, kidney, pituitary and neuronal cells. EDDM, NEDDM, pancreatitis, and pancreatic carcinoma may benefit. Zcytorlo may serve as a target for MAb therapy of pancreatic cancer where a signaling MAb inhibits cancer growth and targets immune-mediated killing (Tutt, AL et al., J Immunol. 161: 3175- 3185, 1998). Similarly renal cell carcinoma may be treated with monoclonal antibodies to zcytorl 6-comprising soluble receptors of the present invention. Soluble zcytorlo monomeric, homodimeric, heterodimeric and multimeric polypeptides described herein can be used to neutralize/block IL-TEF activity in the treatment of autoimmune disease, atopic disease, NEDDM, pancreatitis and kidney dysfunction as described above. A soluble form of zcytorlo may be used to promote an antibody response mediated by Th cells and/or to promote the production of EL-4 or other cytokines by lymphocytes or other immune cells. The soluble zcytorl 6-comprising receptors of the present invention are useful as antagonists of the EL-TEF cytokine. Such antagonistic effects can be achieved by direct neutralization or binding of the EL-TEF. In addition to antagonistic uses, the soluble receptors of the present invention can bind EL-TEF and act as carrier proteins for the EL-TEF cytokine, in order to transport the Ligand to different tissues, organs, and cells within the body. As such, the soluble receptors of the present invention can be fused or coupled to molecules, polypeptides or chemical moieties that direct the soluble-receptor-Ligand complex to a specific site, such as a tissue, specific immune cell, or tumor. For example, in acute infection or some cancers, benefit may result from induction of inflammation and local acute phase response proteins by the action of IL- TIF. Thus, the soluble receptors of the present invention can be used to specifically direct the action of the L-TIF. See, Cosman, D. Cytokine 5: 95-106, 1993; and Fernandez-Botran, R. Exp. Opin. Invest. Drugs 9:497-513. 2000. Moreover, the soluble receptors of the present invention can be used to stabilize the IL-TEF, to increase the bioavailability, therapeutic longevity, and/or efficacy of the Ligand by stabilizing the Ligand from degradation or clearance, or by targeting the ligand to a site of action within the body. For example the naturally occuπing IL-6/soluble EL-6R complex stabilizes IL-6 and can signal through the gpl30 receptor. See, Cosman, D. supra., and Fernandez-Botran, R. supra.. Moreover, Zcytorlo may be combined with a cognate ligand such as IL-TIF to comprise a ligand/soluble receptor complex. Such complexes may be used to stimulate responses from cells presenting a companion receptor subunit such as, for example, zcytorl 1 or CRF2-4. The cell specificity of zcytorl 6/ligand complexes may differ from that seen for the ligand administered alone. Furthermore the complexes may have distinct pharmacokinetic properties such as affecting half-life, dose/response and organ or tissue specificity. ZcytoR16/EL-TEF complexes thus may have agonist activity to enhance an immune response or stimulate mesangial cells or to stimulate hepatic cells. Alternatively only tissues expressing a signaling subunit the heterodimerizes with the complex may be affected analogous to the response to EL6/EL6R complexes (Hirota H. et al., Proc. Nat'l. Acad. Sci. 92:4862-4866, 1995; Hirano, T. in Thomason, A. (Ed.) "The Cytokine Handbook", 3 rd Ed., p. 208-209). Soluble receptor/cytokine complexes for EL12 and CNTF display similar activities. Zcytorlo homodimeric, heterodimeric and multimeric receptor polypeptides may also be used within diagnostic systems for the detection of circulating levels of EL-TEF ligand, and in the detection of EL-TEF associated with acute phase inflammatory response. Within a related embodiment, antibodies or other agents that specifically bind to Zcytorlo soluble receptors of the present invention can be used to detect circulating receptor polypeptides; conversely, Zcytorlo soluble receptors themselves can be used to detect circulating or locally-acting IL-TIF polypeptides. Elevated or depressed levels of ligand or receptor polypeptides may be indicative of pathological conditions, including inflammation or cancer. IL-TIF is known to induce associated acute phase inflammatory response. Moreover, detection of acute phase proteins or molecules such as IL-TIF can be indicative of a chronic inflammatory condition in certain disease states (e.g., rheumatoid arthritis). Detection of such conditions serves to aid in disease diagnosis as well as help a physician in choosing proper therapy. Moreover, soluble zcytorlo receptor polypeptides of the present invention can be used as a "ligand sink," i.e., antagonist, to bind ligand in vivo or in vitro in therapeutic or other applications where the presence of the ligand is not desired. For example, in chronic inflammatory conditions or cancers that are expressing large amounts of bioactive EL-TEF, soluble zcytorlo receptor or soluble zcytorlo heterodimeric and multimeric receptor polypeptides, such as soluble zcytorl 6/CRF2-4 can be used as a direct antagonist of the ligand in vivo, and may aid in reducing progression and symptoms associated with the disease, and can be used in conjunction with other therapies (e.g., steroid or chemotherapy) to enhance the effect of the therapy in reducing progression and symptoms, and preventing relapse. Moreover, soluble zcytorlo receptor polypeptides can be used to slow the progression of cancers that over- express zcytorlo receptors, by binding ligand in vivo that could otherwise enhance proliferation of those cancers. Moreover, soluble zcytorlo receptor polypeptides of the present invention can be used in vivo or in diagnostic applications to detect EL-TEF-expressing inflammation or cancers in vivo or in tissue samples. For example, the soluble zcytorlo receptors of the present invention can be conjugated to a radio-label or fluorescent label as described herein, and used to detect the presence of the IL-TEF in a tissue sample using an in vitro ligand-receptor type binding assay, or fluorescent imaging assay. Moreover, radiolabeled soluble zcytorlo receptors of the present invention could be administered in vivo to detect Ligand-expressing solid tumors through a radio-imaging method known in the art. Generally, the dosage of administered Zcytorlo (or Zcytorlo analog or fusion protein) will vary depending upon such factors as the patient's age, weight, height, sex, general medical condition and previous medical history. Typically, it is desirable to provide the recipient with a dosage of Zcytorlo polypeptide which is in the range of from about 1 pg/kg to 10 mg/kg (amount of agent/body weight of patient), although a lower or higher dosage also may be administered as circumstances dictate. Administration of a Zcytorlo polypeptide to a subject can be intravenous, intraarterial, intraperitoneal, intramuscular, subcutaneous, intrapleural, intrathecal, by perfusion through a regional catheter, or by direct intralesional injection. When administering therapeutic proteins by injection, the administration may be by continuous infusion or by single or multiple boluses. Additional routes of administration include oral, mucosal-membrane, pulmonary, and transcutaneous. Oral delivery is suitable for polyester microspheres, zein microspheres, proteinoid microspheres, polycyanoacrylate microspheres, and lipid- based systems (see, for example, DiBase and Moπel, "Oral Delivery of Microencapsulated Proteins," in Protein Delivery: Physical Systems, Sanders and Hendren (eds.), pages 255-288 (Plenum Press 1997)). The feasibility of an intranasal delivery is exemplified by such a mode of insulin administration (see, for example, Hinchcliffe and Ilium, Adv. Drug Deliv. Rev. 35:199 (1999)). Dry or liquid particles comprising Zcytorlo can be prepared and inhaled with the aid of dry-powder dispersers, liquid aerosol generators, or nebulizers (e.g., Pettit and Gombotz, TIBTECH 76:343 (1998); Patton et al, Adv. Drug Deliv. Rev. 35:235 (1999)). This approach is illustrated by the AERX diabetes management system, which is a hand-held electronic inhaler that delivers aerosolized insulin into the lungs. Studies have shown that proteins as large as 48,000 kDa have been delivered across skin at therapeutic concentrations with the aid of low-frequency ultrasound, which illustrates the feasibility of trascutaneous administration (Mitragotri et al, Science 269:850 (1995)). Transdermal delivery using electroporation provides another means to administer a molecule having Zcytorlo binding activity (Potts et al, Pharm. Biotechnol. 70:213 (1997)). A pharmaceutical composition comprising a protein, polypeptide, or peptide having Zcytorlo binding activity can be formulated according to known methods to prepare pharmaceutically useful compositions, whereby the therapeutic proteins are combined in a mixture with a pharmaceutically acceptable caπier. A composition is said to be a "pharmaceutically acceptable carrier" if its administration can be tolerated by a recipient patient. Sterile phosphate-buffered saline is one example of a pharmaceutically acceptable caπier. Other suitable carriers are well-known to those in the art. See, for example, Gennaro (ed.), Remington's Pharmaceutical Sciences, 19th Edition (Mack Publishing Company 1995). For purposes of therapy, molecules having Zcytorlo binding activity and a pharmaceutically acceptable caπier are administered to a patient in a therapeutically effective amount. A combination of a protein, polypeptide, or peptide having Zcytorl 6 binding activity and a pharmaceutically acceptable caπier is said to be administered in a "therapeutically effective amount" if the amount administered is physiologically significant. An agent is physiologically significant if its presence results in a detectable change in the physiology of a recipient patient. For example, an agent used to treat inflammation is physiologically significant if its presence alleviates the inflammatory response. A pharmaceutical composition comprising Zcytorlo (or Zcytorlo analog or fusion protein) can be furnished in liquid form, in an aerosol, or in solid form. Liquid forms, are illustrated by injectable solutions and oral suspensions. Exemplary solid forms include capsules, tablets, and controlled-release forms. The latter form is illustrated by miniosmotic pumps and implants (Bremer et al, Pharm. Biotechnol. 10:239 (1997); Ranade, "Implants in Drug Delivery," in Drug Delivery Systems, Ranade and Hollinger (eds.), pages 95-123 (CRC Press 1995); Bremer et al, "Protein Delivery with Infusion Pumps," in Protein Delivery: Physical Systems, Sanders and Hendren (eds.), pages 239-254 (Plenum Press 1997); Yewey et al, "Delivery of Proteins from a Controlled Release Injectable Implant," in Protein Delivery: Physical Systems, Sanders and Hendren (eds.), pages 93-117 (Plenum Press 1997)). Liposomes provide one means to deliver therapeutic polypeptides to a subject intravenously, intraperitoneally, intrathecally, intramuscularly, subcutaneously, or via oral administration, inhalation, or intranasal administration. Liposomes are microscopic vesicles that consist of one or more lipid bilayers suπounding aqueous compartments (see, generally, Bakker-Woudenberg et al, Eur. J. Clin. Microbiol. Infect. Dis. 12 (Suppl 1):S61 (1993), Kim, Drugs 46:618 (1993), and Ranade, "Site- Specific Drug Delivery Using Liposomes as Carriers," in Drug Delivery Systems, Ranade and Hollinger (eds.), pages 3-24 (CRC Press 1995)). Liposomes are similar in composition to cellular membranes and as a result, liposomes can be administered safely and are biodegradable. Depending on the method of preparation, liposomes may be unilamellar or multilamellar, and liposomes can vary in size with diameters ranging from 0.02 μm to greater than 10 μm. A variety of agents can be encapsulated in liposomes: hydrophobic agents partition in the bilayers and hydrophilic agents partition within the inner aqueous space(s) (see, for example, Machy et al, Liposomes In Cell Biology And Pharmacology (John Libbey 1987), and Ostro et al, American J. Hosp. Pharm. 46:1576 (1989)). Moreover, it is possible to control the therapeutic availability of the encapsulated agent by varying liposome size, the number of bilayers, lipid composition, as well as the charge and surface characteristics of the liposomes. Liposomes can adsorb to virtually any type of cell and then slowly release the encapsulated agent. Alternatively, an absorbed liposome may be endocytosed by cells that are phagocytic. Endocytosis is followed by intralysosomal degradation of liposomal lipids and release of the encapsulated agents (Scherphof et al, Ann. NY. Acad. Sci. 446:368 (1985)). After intravenous administration, small liposomes (0.1 to 1.0 μm) are typically taken up by cells of the reticuloendothelial system, located principally in the liver and spleen, whereas liposomes larger than 3.0 μm are deposited in the lung. This preferential uptake of smaller liposomes by the cells of the reticuloendothelial system has been used to deliver chemotherapeutic agents to macrophages and to tumors of the liver. The reticuloendothelial system can be circumvented by several methods including saturation with large doses of liposome particles, or selective macrophage inactivation by pharmacological means (Claassen et al, Biochim. Biophys. Acta 802:428 (1984)). In addition, incorporation of glycolipid- or polyethelene glycol - derivatized phospholipids into liposome membranes has been shown to result in a significantly reduced uptake by the reticuloendothelial system (Allen et al, Biochim. Biophys. Acta 7068: 133 (1991); Allen et al, Biochim. Biophys. Acta 1150:9 (1993)). Liposomes can also be prepared to target particular cells or organs by varying phospholipid composition or by inserting receptors or ligands into the liposomes. For example, liposomes, prepared with a high content of a nonionic surfactant, have been used to target the liver (Hayakawa et al, Japanese Patent 04- 244,018; Kato et al, Biol. Pharm. Bull. 76:960 (1993)). These formulations were prepared by mixing soybean phospatidylcholine, α-tocopherol, and ethoxylated hydrogenated castor oil (HCO-60) in methanol, concentrating the mixture under vacuum, and then reconstituting the mixture with water. A liposomal formulation of dipalmitoylphosphatidylcholine (DPPC) with a soybean-derived sterylglucoside mixture (SG) and cholesterol (Ch) has also been shown to target the liver (Shimizu et al, Biol. Pharm. Bull. 20:881 (1997)). Alternatively, various targeting ligands can be bound to the surface of the liposome, such as antibodies, antibody fragments, carbohydrates, vitamins, and transport proteins. For example, liposomes can be modified with branched type galactosyllipid derivatives to target asialoglycoprotein (galactose) receptors, which are exclusively expressed on the surface of liver cells (Kato and Sugiyama, Crit. Rev. Ther. Drug Carrier Syst. 74:287 (1997); Murahashi et al, Biol. Pharm. Bull.20:259 (1997)). Similarly, Wu et al, Hepatology 27:112 (1998), have shown that labeling liposomes with asialofetuin led to a shortened liposome plasma half-life and greatly enhanced uptake of asialofetuin-labeled liposome by hepatocytes. On the other hand, hepatic accumulation of liposomes comprising branched type galactosyllipid derivatives can be inhibited by preinjection of asialofetuin (Murahashi et al, Biol. Pharm. Bull.20:259 (1997)). Polyaconitylated human serum albumin liposomes provide another approach for targeting liposomes to liver cells (Kamps et al, Proc. Nat'l Acad. Sci. USA 94:11681 (1997)). Moreover, Geho, et al. U.S. Patent No. 4,603,044, describe a hepatocyte-directed liposome vesicle delivery system, which has specificity for hepatobiliary receptors associated with the specialized metabolic cells of the liver. En a more general approach to tissue targeting, target cells are prelabeled with biotinylated antibodies specific for a ligand expressed by the target cell (Harasym et al, Adv. Drug Deliv. Rev. 32:99 (1998)). After plasma elimination of free antibody, streptavidin-conjugated liposomes are administered. En another approach, targeting antibodies are directly attached to liposomes (Harasym et al, Adv. Drug Deliv. Rev. 32:99 (1998)). Polypeptides having Zcytorlo binding activity can be encapsulated within liposomes using standard techniques of protein microencapsulation (see, for example, Anderson et al, Infect. Immun. 37:1099 (1981), Anderson et al, Cancer Res. 50:1853 (1990), and Cohen et al, Biochim. Biophys. Acta 1063:95 (1991), Alving et al. "Preparation and Use of Liposomes in Immunological Studies," in Liposome Technology, 2nd Edition, Vol. Efl, Gregoriadis (ed.), page 317 (CRC Press 1993), Wassef et al, Meth. Enzymol. 749:124 (1987)). As noted above, therapeutically useful liposomes may contain a variety of components. For example, liposomes may comprise lipid derivatives of poly(ethylene glycol) (Allen et al, Biochim. Biophys. Acta 1150:9 (1993)). Degradable polymer microspheres have been designed to maintain high systemic levels of therapeutic proteins. Microspheres are prepared from degradable polymers such as poly(lactide-co-glycolide) (PLG), polyanhydrides, poly (ortho esters), nonbiodegradable ethylvinyl acetate polymers, in which proteins are entrapped in the polymer (Gombotz and Pettit, Bioconjugate Chem. 6:332 (1995); Ranade, "Role of Polymers in Drug Delivery," in Drug Delivery Systems, Ranade and Hollinger (eds.), pages 51-93 (CRC Press 1995); Roskos and Maskiewicz, "Degradable Controlled Release Systems Useful for Protein Delivery," in Protein Delivery: Physical Systems, Sanders and Hendren (eds.), pages 45-92 (Plenum Press 1997); Bartus et al, Science 287:1161 (1998); Putney and Burke, Nature Biotechnology 16:153 (1998); Putney, Curr. Opin. Chem. Biol. 2:548 (1998)). Polyethylene glycol (PEG)-coated nanospheres can also provide caπiers for intravenous administration of therapeutic proteins (see, for example, Gref et al, Pharm. Biotechnol. 70:167 (1997)). The present invention also contemplates chemically modified polypeptides having binding Zcytorlo activity such as zcytorlo monomeric, homodimeric, heterodimeric or multimeric soluble receptors, and Zcytorlo antagonists, for example anti -zcytorl 6 antibodies or binding polypeptides, which a polypeptide is linked with a polymer, as discussed above. Other dosage forms can be devised by those skilled in the art, as shown, for example, by Ansel and Popovich, Pharmaceutical Dosage Forms and Drug Delivery Systems, 5 th Edition (Lea & Febiger 1990), Gennaro (ed.), Remington's Pharmaceutical Sciences, 19 th Edition (Mack Publishing Company 1995), and by Ranade and Hollinger, Drug Delivery Systems (CRC Press 1996). As an illustration, pharmaceutical compositions may be supplied as a kit comprising a container that comprises a polypeptide with a Zcytorlo extracellular domain, e.g., zcytorlo monomeric, homodimeric, heterodimeric or multimeric soluble receptors, or a Zcytorlo antagonist (e.g., an antibody or antibody fragment that binds a Zcytorlo polypeptide). Therapeutic polypeptides can be provided in the form of an injectable solution for single or multiple doses, or as a sterile powder that will be reconstituted before injection. Alternatively, such a kit can include a dry-powder disperser, liquid aerosol generator, or nebulizer for administration of a therapeutic polypeptide. Such a kit may further comprise written information on indications and usage of the pharmaceutical composition. Moreover, such information may include a statement that the Zcytorlo composition is contraindicated in patients with known hypersensitivity to Zcytorlo. 73. Therapeutic Uses of Zcytorlo Nucleotide Sequences The present invention includes the use of Zcytorlo nucleotide sequences to provide Zcytorlo to a subject in need of such treatment. In addition, a therapeutic expression vector can be provided that inhibits Zcytorl 6 gene expression, such as an anti-sense molecule, a ribozyme, or an external guide sequence molecule. There are numerous approaches to introduce a Zcytorlo gene to a subject, including the use of recombinant host cells that express Zcytorlo, delivery of naked nucleic acid encoding Zcytorlo, use of a cationic lipid caπier with a nucleic acid molecule that encodes Zcytorlo, and the use of viruses that express Zcytorl6, such as recombinant retroviruses, recombinant adeno-associated viruses, recombinant adenoviruses, and recombinant Herpes simplex viruses (see, for example, Mulligan, Science 260:926 (1993), Rosenberg et al, Science 242: 1515 (1988), LaSalle et al, Science 259:988 (1993), Wolff et al, Science 247: 1465 (1990), Breakfield and Deluca, The New Biologist 3:203 (1991)). In an ex vivo approach, for example, cells are isolated from a subject, transfected with a vector that expresses a Zcytorlo gene, and then transplanted into the subject. In order to effect expression of a Zcytorlo gene, an expression vector is constructed in which a nucleotide sequence encoding a Zcytorl 6 gene is operably linked to a core promoter, and optionally a regulatory element, to control gene transcription. The general requirements of an expression vector are described above. Alternatively, a Zcytorlo gene can be delivered using recombinant viral vectors, including for example, adenoviral vectors (e.g., Kass-Eisler et al, Proc. Nat'l Acad. Sci. USA 90:11498 (1993), Kolls et al, Proc. Nat'l Acad. Sci. USA 97:215 (1994), Li et al, Hum. Gene Ther. 4:403 (1993), Vincent et al, Nat. Genet. 5:130 (1993), and Zabner et al, Cell 75:207 (1993)), adenovirus-associated viral vectors (Flotte et al, Proc. Nat'l Acad. Sci. USA 90:10613 (1993)), alphaviruses such as Semliki Forest Virus and Sindbis Virus (Hertz and Huang, J. Vir. 66:857 (1992), Raju and Huang, J. Vir. 65:2501 (1991), and Xiong et al, Science 243: 1188 (1989)), herpes viral vectors (e.g., U.S. Patent Nos. 4,769,331, 4,859,587, 5,288,641 and 5,328,688), parvovirus vectors (Koering et al, Hum. Gene Therap. 5:457 (1994)), pox virus vectors (Ozaki et al, Biochem. Biophys. Res. Comm. 793:653 (1993), Panicali and Paoletti, Proc. Nat'l Acad. Sci. USA 79:4927 (1982)), pox viruses, such as canary pox virus or vaccinia virus (Fisher-Hoch et al, Proc. Nat'l Acad. Sci. USA 86:317 (1989), and Flexner et al, Ann. NY. Acad. Sci. 569:86 (1989)), and retroviruses (e.g., Baba et al, J. Neurosurg 79:729 (1993), Ram et al, Cancer Res. 53:83 (1993), Takamiya et al, J. Neurosci. Res 33:493 (1992), Vile and Hart, Cancer Res. 53:962 (1993), Vile and Hart, Cancer Res. 53:3860 (1993), and Anderson et al, U.S. Patent No. 5,399,346). Within various embodiments, either the viral vector itself, or a viral particle which contains the viral vector may be utilized in the methods and compositions described below. As an illustration of one system, adenovirus, a double-stranded DNA virus, is a well-characterized gene transfer vector for delivery of a heterologous nucleic acid molecule (for a review, see Becker et al, Meth. Cell Biol. 43: 161 (1994); Douglas and Curiel, Science & Medicine 4:44 (1997)). The adenovirus system offers several advantages including: (i) the ability to accommodate relatively large DNA inserts, (ii) the ability to be grown to high-titer, (iii) the ability to infect a broad range of mammalian cell types, and (iv) the ability to be used with many different promoters including ubiquitous, tissue specific, and regulatable promoters. In addition, adenoviruses can be administered by intravenous injection, because the viruses are stable in the bloodstream. Using adenovirus vectors where portions of the adenovirus genome are deleted, inserts are incorporated into the viral DNA by direct ligation or by homologous recombination with a co-transfected plasmid. In an exemplary system, the essential El gene is deleted from the viral vector, and the virus will not replicate unless the El gene is provided by the host cell. When intravenously administered to intact animals, adenovirus primarily targets the liver. Although an adenoviral delivery system with an El gene deletion cannot replicate in the host cells, the host's tissue will express and process an encoded heterologous protein. Host cells will also secrete the heterologous protein if the coπesponding gene includes a secretory signal sequence. Secreted proteins will enter the circulation from tissue that expresses the heterologous gene (e.g., the highly vascularized liver). Moreover, adenoviral vectors containing various deletions of viral genes can be used to reduce or eliminate immune responses to the vector. Such adenoviruses are El-deleted, and in addition, contain deletions of E2A or E4 (Lusky et al, J. Virol. 72:2022 (1998); Raper et al, Human Gene Therapy 9:671 (1998)). The deletion of E2b has also been reported to reduce immune responses (Amalfitano et al, J. Virol. 72:926 (1998)). By deleting the entire adenovirus genome, very large inserts of heterologous DNA can be accommodated. Generation of so called "gutless" adenoviruses, where all viral genes are deleted, are particularly advantageous for insertion of large inserts of heterologous DNA (for a review, see Yeh. and Peπicaudet, FASEB J. 77:615 (1997)). High titer stocks of recombinant viruses capable of expressing a therapeutic gene can be obtained from infected mammalian cells using standard methods. For example, recombinant heφes simplex virus can be prepared in Vero cells, as described by Brandt et al, J. Gen. Virol 72:2043 (1991), Herold et al, J. Gen. Virol 75: 1211 (1994), Visalli and Brandt, Virology 785:419 (1991), Grau et al, Invest. Ophthalmol. Vis. Sci. 30:2474 (1989), Brandt et al, I. Virol. Meth. 36:209 (1992), and by Brown and Macl ^ ean (eds.), HSV Virus Protocols (Humana Press 1997). Alternatively, an expression vector comprising a Zcytorlo gene can be introduced into a subject's cells by lipofection in vivo using liposomes. Synthetic cationic lipids can be used to prepare liposomes for in vivo transfection of a gene encoding a marker (Feigner et al, Proc. Nat'l Acad. Sci. USA 84:7413 (1987); Mackey et al, Proc. Nat'l Acad. Sci. USA 85:8027 (1988)). The use of lipofection to introduce exogenous genes into specific organs in vivo has certain practical advantages. Liposomes can be used to direct transfection to particular cell types, which is particularly advantageous in a tissue with cellular heterogeneity, such as the pancreas, liver, kidney, and brain. Lipids may be chemically coupled to other molecules for the puφose of targeting. Targeted peptides (e.g., hormones or neurotransmitters), proteins such as antibodies, or non-peptide molecules can be coupled to liposomes chemically. Electroporation is another alternative mode of administration. For example, Aihara and Miyazaki, Nature Biotechnology 76:867 (1998), have demonstrated the use of in vivo electroporation for gene transfer into muscle. In an alternative approach to gene therapy, a therapeutic gene may encode a Zcytorlo anti-sense RNA that inhibits the expression of Zcytorlo. Suitable sequences for anti-sense molecules can be derived from the nucleotide sequences of Zcytorlo disclosed herein. Alternatively, an expression vector can be constructed in which a regulatory element is operably linked to a nucleotide sequence that encodes a ribozyme. Ribozymes can be designed to express endonuclease activity that is directed to a certain target sequence in a mRNA molecule (see, for example, Draper and Macejak, U.S. Patent No. 5,496,698, McSwiggen, U.S. Patent No. 5,525,468, Chowrira and McSwiggen, U.S. Patent No. 5,631,359, and Robertson and Goldberg, U.S. Patent No. 5,225,337). In the context of the present invention, ribozymes include nucleotide sequences that bind with Zcytorlo mRNA. In another approach, expression vectors can be constructed in which a regulatory element directs the production of RNA transcripts capable of promoting RNase P-mediated cleavage of mRNA molecules that encode a Zcytorl6 gene. According to this approach, an external guide sequence can be constructed for directing the endogenous ribozyme, RNase P, to a particular species of intracellular mRNA, which is subsequently cleaved by the cellular ribozyme (see, for example, Altman et al, U.S. Patent No. 5,168,053, Yuan et al, Science 263:1269 (1994), Pace et al, international publication No. WO 96/18733, George et al, international publication No. WO 96/21731, and Werner et al, international publication No. WO 97/33991). For example, the external guide sequence can comprise a ten to fifteen nucleotide sequence complementary to Zcytorlo mRNA, and a 3'-NCCA nucleotide sequence, wherein N is preferably a purine. The external guide sequence transcripts bind to the targeted mRNA species by the formation of base pairs between the mRNA and the complementary external guide sequences, thus promoting cleavage of mRNA by RNase P at the nucleotide located at the 5'-side of the base-paired region. In general, the dosage of a composition comprising a therapeutic vector having a Zcytorl 6 nucleotide sequence, such as a recombinant virus, will vary depending upon such factors as the subject's age, weight, height, sex, general medical condition and previous medical history. Suitable routes of administration of therapeutic vectors include intravenous injection, intraarterial injection, intraperitoneal injection, intramuscular injection, intratumoral injection, and injection into a cavity that contains a tumor. As an illustration, Horton et al, Proc. Nat'l Acad. Sci. USA 96:1553 (1999), demonstrated that intramuscular injection of plasmid DNA encoding interferon-α produces potent antitumor effects on primary and metastatic tumors in a murine model. A composition comprising viral vectors, non-viral vectors, or a combination of viral and non-viral vectors of the present invention can be formulated according to known methods to prepare pharmaceutically useful compositions, whereby vectors or viruses are combined in a mixture with a pharmaceutically acceptable carrier. As noted above, a composition, such as phosphate-buffered saline is said to be a "pharmaceutically acceptable carrier" if its administration can be tolerated by a recipient subject. Other suitable caπiers are well-known to those in the art (see, for example, Remington's Pharmaceutical Sciences, 19th Ed. (Mack Publishing Co. 1995), and Gilman's the Pharmacological Basis of Therapeutics, 7th Ed. (MacMillan Publishing Co. 1985)). For puφoses of therapy, a therapeutic gene expression vector, or a administered in a "therapeutically effective amount" if the amount administered is physiologically significant. An agent is physiologically significant if its presence results in a detectable change in the physiology of a recipient subject. For example, an agent used to treat inflammation is physiologically significant if its presence alleviates the inflammatory response. When the subject treated with a therapeutic gene expression vector or a recombinant virus is a human, then the therapy is preferably somatic cell gene therapy. That is, the prefeπed treatment of a human with a therapeutic gene expression vector or a recombinant virus does not entail introducing into cells a nucleic acid molecule that can form part of a human germ line and be passed onto successive generations (i.e., human germ line gene therapy). 74. Production of Transgenic Mice Transgenic mice can be engineered to over-express the Zcytorlo gene in all tissues or under the control of a tissue-specific or tissue-prefeπed regulatory element. These over-producers of Zcytorlo can be used to characterize the phenotype that results from over-expression, and the transgenic animals can serve as models for human disease caused by excess Zcytorlo. Transgenic mice that over-express Zcytorlo also provide model bioreactors for production of Zcytorlo, such as soluble Zcytorlo, in the milk or blood of larger animals. Methods for producing transgenic mice are well- known to those of skill in the art (see, for example, Jacob, "Expression and Knockout of Interferons in Transgenic Mice," in Overexpression and Knockout of Cytokines in Transgenic Mice, Jacob (ed.), pages 111-124 (Academic Press, Ltd. 1994), Monastersky and Robl (eds.), Strategies in Transgenic Animal Science (ASM Press 1995), and Abbud and Nilson, "Recombinant Protein Expression in Transgenic Mice," in Gene Expression Systems: Using Nature for the Art of Expression, Fernandez and Hoeffler (eds.), pages 367-397 (Academic Press, Inc. 1999)). For example, a method for producing a transgenic mouse that expresses a Zcytorlo gene can begin with adult, fertile males (studs) (B6C3fl, 2-8 months of age (Taconic Farms, Germantown, NY)), vasectomized males (duds) (B6D2fl, 2-8 months, (Taconic Farms)), prepubescent fertile females (donors) (B6C3fl, 4-5 weeks, (Taconic Farms)) and adult fertile females (recipients) (B6D2fl, 2-4 months, (Taconic Farms)). The donors are acclimated for one week and then injected with approximately 8 IU/mouse of Pregnant Mare's Serum gonadotrophin (Sigma Chemical Company; St. Louis, MO) I.P., and 46-47 hours later, 8 IU/mouse of human Chorionic Gonadotropin (hCG (Sigma)) E.P. to induce superovulation. Donors are mated with studs subsequent to hormone injections. Ovulation generally occurs within 13 hours of hCG injection. Copulation is confirmed by the presence of a vaginal plug the morning following mating. Fertilized eggs are collected under a surgical scope. The oviducts are collected and eggs are released into urinanalysis slides containing hyaluronidase (Sigma). Eggs are washed once in hyaluronidase, and twice in Whitten's W640 medium (described, for example, by Menino and O'Claray, Biol. Reprod. 77:159 (1986), and Dienhart and Downs, Zygote 4:129 (1996)) that has been incubated with 5% CO 2 , 5% O 2 , and 90% N 2 at 37°C. The eggs are then stored in a 37°C/5% CO 2 incubator until microinjection. Ten to twenty micrograms of plasmid DNA containing a Zcytorl 6 encoding sequence is linearized, gel-purified, and resuspended in 10 mM Tris-HCl (pH 7.4), 0.25 mM EDTA (pH 8.0), at a final concentration of 5-10 nanograms per microliter for microinjection. For example, the Zcytorlo encoding sequences can encode a polypeptide comprising the amino acid sequence of SEQ ID NO:2. Plasmid DNA is microinjected into harvested eggs contained in a drop of W640 medium overlaid by warm, CO 2 -equilibrated mineral oil. The DNA is drawn into an injection needle (pulled from a 0.75mm ID, 1mm OD borosilicate glass capillary), and injected into individual eggs. Each egg is penetrated with the injection needle, into one or both of the haploid pronuclei. Picoliters of DNA are injected into the pronuclei, and the injection needle withdrawn without coming into contact with the nucleoli. The procedure is repeated until all the eggs are injected. Successfully microinjected eggs are transfeπed into an organ tissue-culture dish with pre-gassed W640 medium for storage overnight in a 37°C/5% CO 2 incubator. The following day, two-cell embryos are transfeπed into pseudopregnant recipients. The recipients are identified by the presence of copulation plugs, after copulating with vasectomized duds. Recipients are anesthetized and shaved on the dorsal left side and transferred to a surgical microscope. A small incision is made in the skin and through the muscle wall in the middle of the abdominal area outlined by the ribcage, the saddle, and the hind leg, midway between knee and spleen. The reproductive organs are exteriorized onto a small surgical drape. The fat pad is stretched out over the surgical drape, and a baby seπefine (Roboz, Rockville, MD) is attached to the fat pad and left hanging over the back of the mouse, preventing the organs from sliding back in. With a fine transfer pipette containing mineral oil followed by alternating W640 and air bubbles, 12-17 healthy two-cell embryos from the previous day's injection are transfeπed into the recipient. The swollen ampulla is located and holding the oviduct between the ampulla and the bursa, a nick in the oviduct is made with a 28 g needle close to the bursa, making sure not to tear the ampulla or the bursa. The pipette is transfeπed into the nick in the oviduct, and the embryos are blown in, allowing the first air bubble to escape the pipette. The fat pad is gently pushed into the peritoneum, and the reproductive organs allowed to slide in. The peritoneal wall is closed with one suture and the skin closed with a wound clip. The mice recuperate on a 37°C slide warmer for a minimum of four hours. The recipients are returned to cages in pairs, and allowed 19-21 days gestation. After birth, 19-21 days postpartum is allowed before weaning. The weanlings are sexed and placed into separate sex cages, and a 0.5 cm biopsy (used for genotyping) is snipped off the tail with clean scissors. Genomic DNA is prepared from the tail snips using, for example, a QIAGEN DNEASY kit following the manufacturer's instructions. Genomic DNA is analyzed by PCR using primers designed to amplify a Zcytorlo gene or a selectable marker gene that was introduced in the same plasmid. After animals are confirmed to be transgenic, they are back-crossed into an inbred strain by placing a transgenic female with a wild-type male, or a transgenic male with one or two wild-type female(s). As pups are born and weaned, the sexes are separated, and their tails snipped for genotyping. To check for expression of a transgene in a live animal, a partial hepatectomy is performed. A surgical prep is made of the upper abdomen directly below the zyphoid process. Using sterile technique, a small 1.5-2 cm incision is made below the sternum and the left lateral lobe of the liver exteriorized. Using 4-0 silk, a tie is made around the lower lobe securing it outside the body cavity. An atraumatic clamp is used to hold the tie while a second loop of absorbable Dexon (American Cyanamid; Wayne, N .) is placed proximal to the first tie. A distal cut is made from the Dexon tie and approximately 100 mg of the excised liver tissue is placed in a sterile petri dish. The excised liver section is transfeπed to a 14 ml polypropylene round bottom tube and snap frozen in liquid nitrogen and then stored on dry ice. The surgical site is closed with suture and wound clips, and the animal's cage placed on a 37°C heating pad for 24 hours post operatively. The animal is checked daily post operatively and the wound clips removed 7-10 days after surgery. The expression level of Zcytorlo mRNA is examined for each transgenic mouse using an RNA solution hybridization assay or polymerase chain reaction. In addition to producing transgenic mice that over-express Zcytorlo, it is useful to engineer transgenic mice with either abnormally low or no expression of the gene. Such transgenic mice provide useful models for diseases associated with a lack of Zcytorlo. As discussed above, Zcytorlo gene expression can be inhibited using anti- sense genes, ribozyme genes, or external guide sequence genes. To produce transgenic mice that under-express the Zcytorl 6 gene, such inhibitory sequences are targeted to Zcytorl 6 mRNA. Methods for producing transgenic mice that have abnormally low expression of a particular gene are known to those in the art (see, for example, Wu et al, "Gene Underexpression in Cultured Cells and Animals by Antisense DNA and RNA Strategies," in Methods in Gene Biotechnology, pages 205-224 (CRC Press 1997)). An alternative approach to producing transgenic mice that have little or no Zcytorlo gene expression is to generate mice having at least one normal Zcytorlo allele replaced by a nonfunctional Zcytorlo gene. One method of designing a nonfunctional Zcytorl 6 gene is to insert another gene, such as a selectable marker gene, within a nucleic acid molecule that encodes Zcytorlo. Standard methods for producing these so-called "knockout mice" are known to those skilled in the art (see, for example, Jacob, "Expression and Knockout of Interferons in Transgenic Mice," in Overexpression and Knockout of Cytokines in Transgenic Mice, Jacob (ed.), pages 111- 124 (Academic Press, Ltd. 1994), and Wu et al, "New Strategies for Gene Knockout," in Methods in Gene Biotechnology, pages 339-365 (CRC Press 1997)). Polynucleotides and polypeptides of the present invention will additionally find use as educational tools as a laboratory practicum kits for courses related to genetics and molecular biology, protein chemistry and antibody production and analysis. Due to its unique polynucleotide and polypeptide sequence molecules of zcytorlo can be used as standards or as "unknowns" for testing puφoses. For example, zcytorlo polynucleotides can be used as an aid, such as, for example, to teach a student how to prepare expression constructs for bacterial, viral, and/or mammalian expression, including fusion constructs, wherein zcytorlo is the gene to be expressed; for determining the restriction endonuclease cleavage sites of the polynucleotides; determining mRNA and DNA localization of zcytorlo polynucleotides in tissues (i.e., by Northern and Southern blotting as well as polymerase chain reaction); and for identifying related polynucleotides and polypeptides by nucleic acid hybridization. Zcytorlo polypeptides can be used educationally as an aid to teach preparation of antibodies; identifying proteins by Western blotting; protein purification; determining the weight of expressed zcytorlo polypeptides as a ratio to total protein expressed; identifying peptide cleavage sites; coupling amino and carboxyl terminal tags; amino acid sequence analysis, as well as, but not limited to monitoring biological activities of both the native and tagged protein (i.e., receptor binding, signal transduction, proliferation, and differentiation) in vitro and in vivo. Zcytorlo polypeptides can also be used to teach analytical skills such as mass spectrometry, circular dichroism to determine conformation, especially of the four alpha helices, x-ray crystallography to determine the three-dimensional structure in atomic detail, nuclear magnetic resonance spectroscopy to reveal the structure of proteins in solution. For example, a kit containing the zcytorlo can be given to the student to analyze. Since the amino acid sequence would be known by the professor, the specific protein can be given to the student as a test to determine the skills or develop the skills of the student, the teacher would then know whether or not the student has correctly analyzed the polypeptide. Since every polypeptide is unique, the educational utility of zcytorlo would be unique unto itself. Moreover, since zcytorlo has a tissue-specific expression and is a polypeptide with a class II cytokine receptor structure and a distinct chromosomal localization, and expressin pattern, activity can be measured using proliferation assays; luciferase and binding assays described herein. Moreover, expression of zcytorlo polynucleotides and polypeptides in lymphoid and other tissues can be analyzed in order to train students in the use of diagnostic and tissue-specific identification and methods. Moreover zcytorlo polynucleotides can be used to train students on the use of chromosomal detection and diagnostic methods, since it's locus is known. Moreover, students can be specifically trained and educated about human chromosome 1, and more specifically the locus 6q24.1-25.2 wherein the zcytorlo gene is localized. Such assays are well known in the art, and can be used in an educational setting to teach students about cytokine receptor proteins and examine different properties, such as cellular effects on cells, enzyme kinetics, varying antibody binding affinities, tissue specificity, and the like, between zcytorlo and other cytokine receptor polypeptides in the art. The antibodies which bind specifically to zcytorlo can be used as a teaching aid to instruct students how to prepare affinity chromatography columns to purify zcytorlo, cloning and sequencing the polynucleotide that encodes an antibody and thus as a practicum for teaching a student how to design humanized antibodies. Moreover, antibodies which bind specifically to zcytorlo can be used as a teaching aid for use in detection e.g., of activated CD91+ cells, cell sorting, or ovarian cancer tissue using histological, and in situ methods amongst others known in the art. The zcytorlo gene, polypeptide or antibody would then be packaged by reagent companies and sold to universities and other educational entities so that the students gain skill in art of molecular biology. Because each gene and protein is unique, each gene and protein creates unique challenges and learning experiences for students in a lab practicum. Such educational kits containing the zcytorlo gene, polypeptide or antibody are considered within the scope of the present invention. Within one aspect the present invention provides an isolated polypeptide, comprising at least 15 contiguous amino acid residues of an amino acid sequence of SEQ ID NO:2 selected from the group consisting of: (a) amino acid residues amino acid residues 21 to 231, (b) amino acid residues 21 to 210, (c) amino acid residues 22 to 231, (d) amino acid residues 22 to 210, (e) amino acid residues 22 to 108, (f) amino acid residues 112 to 210, and (g) amino acid residues 21 to 110. In one embodiment, the isolated polypeptide disclosed above comprises an amino acid sequence selected from the group consisting of: (a) amino acid residues amino acid residues 21 to 231, (b) amino acid residues 21 to 210, (c) amino acid residues 22 to 231, (d) amino acid residues 22 to 210, (e) amino acid residues 22 to 108, (f) amino acid residues 112 to 210, and (g) amino acid residues 21 to 110. In another embodiment, the isolated polypeptide disclosed above consists of an amino acid sequence selected from the group consisting of: (a) amino acid residues amino acid residues 21 to 231, (b) amino acid residues 21 to 210, (c) amino acid residues 22 to 231, (d) amino acid residues 22 to 210, (e) amino acid residues 22 to 108, (f) amino acid residues 112 to 210, and (g) amino acid residues 21 to 110. Within a second aspect the present invention provides an isolated polypeptide, comprising an amino acid sequence that is at least 70% identical to a reference amino acid sequence of SEQ ED NO:2 selected from the group consisting of: (a) amino acid residues amino acid residues 21 to 231, (b) amino acid residues 21 to 210, (c) amino acid residues 22 to 231, (d) amino acid residues 22 to 210, (e) amino acid residues 22 to 108, (f) amino acid residues 112 to 210, and (g) amino acid residues 21 to 110. In one embodiment, the isolated polypeptide disclosed above has an amino acid sequence that is at least 80% identical to the reference amino acid sequence. In another embodiment, the isolated polypeptide disclosed above has an amino acid sequence that is at least 90% identical to the reference amino acid sequence. In another embodiment, the isolated polypeptide disclosed above comprises either amino acid residues 22 to 231 of SEQ ID NO:2 or amino acid residues 22 to 210 of SEQ ID NO:2. Within a third aspect the present invention provides an isolated nucleic acid molecule, wherein the nucleic acid molecule is either (a) a nucleic acid molecule comprising the nucleotide sequence of SEQ ID NO: 3, or (b) a nucleic acid molecule that remains hybridized following stringent wash conditions to a nucleic acid molecule consisting of the nucleotide sequence of nucleotides 64 to 630 of SEQ ID NO:l, or the complement of the nucleotide sequence of nucleotides 64 to 630 of SEQ ID NO:l. En one embodiment, the isolated nucleic acid molecule is as disclosed above wherein any difference between the amino acid sequence encoded by the nucleic acid molecule and the coπesponding amino acid sequence of SEQ ID NO:2 is due to a conservative amino acid substitution. In another embodiment, the isolated nucleic acid molecule disclosed above comprises the nucleotide sequence of nucleotides 64 to 630 of SEQ ID NO: 1. Within another aspect the present invention provides a vector, comprising the isolated nucleic acid molecule as disclosed above. Within another aspect the present invention provides an expression vector, comprising the isolated nucleic acid molecule as disclosed above, a transcription promoter, and a transcription terminator, wherein the promoter is operably linked with the nucleic acid molecule, and wherein the nucleic acid molecule is operably linked with the transcription terminator. Within another aspect the present invention provides a recombinant host cell comprising the expression vector as disclosed above, wherein the host cell is selected from the group consisting of bacterium, yeast cell, fungal cell, insect cell, mammalian cell, and plant cell. Within another aspect the present invention provides a method of producing Zcytorlo protein, the method comprising culturing recombinant host cells that comprise the expression vector as disclosed above, and that produce the Zcytorlo protein. In one embodiment, the method disclosed above, further comprises isolating the Zcytorlo protein from the cultured recombinant host cells. Within another aspect the present invention provides an antibody or antibody fragment that specifically binds with the polypeptide as disclosed above. In one embodiment, the antibody disclosed above is selected from the group consisting of: (a) polyclonal antibody, (b) murine monoclonal antibody, (c) humanized antibody derived from (b), and (d) human monoclonal antibody. Within another aspect the present invention provides an anti-idiotype antibody that specifically binds with the antibody as disclosed above. Within another aspect the present invention provides a fusion protein, comprising the polypeptide as disclosed above. In one embodiment, the fusion protein disclosed above further comprises an immunoglobulin moiety. Within another aspect the present invention provides an isolated polynucleotide that encodes a soluble cytokine receptor polypeptide comprising a sequence of amino acid residues that is at least 90% identical to the amino acid sequence as shown in SEQ ID NO:2 from amino acid 22-231 or 22-210, and wherein the soluble cytokine receptor polypeptide encoded by the polynucleotide sequence binds IL-TEF or antagonizes IL-TIF activity. Within another aspect the present invention provides an isolated polynucleotide as disclosed above, wherein the soluble cytokine receptor polypeptide encoded by the polynucleotide forms a homodimeric, heterodimeric or multimeric receptor complex. In one embodiment, the isolated polynucleotide is as disclosed above, wherein the soluble cytokine receptor polypeptide encoded by the polynucleotide forms a heterodimeric or multimeric receptor complex further comprising a soluble Class I or Class II cytokine receptor. En another embodiment, the isolated polynucleotide is as disclosed above, wherein the soluble cytokine receptor polypeptide encoded by the polynucleotide forms a heterodimeric or multimeric receptor complex further comprising a soluble CRF2-4 receptor polypeptide (SEQ ED NO:35), a soluble EL-10 receptor polypeptide (SEQ ED NO:36), or soluble zcytorl 1 receptor polypeptide (SEQ ED NO:34). Within another aspect the present invention provides an isolated polynucleotide that encodes a soluble cytokine receptor polypeptide comprising a sequence of amino acid residues as shown in SEQ ID NO:2 from amino acid 22-231 or 22-210, wherein the soluble cytokine receptor polypeptide encoded by the polynucleotide forms a homodimeric, heterodimeric or multimeric receptor complex. In one embodiment, the isolated polynucleotide is as disclosed above, wherein the soluble cytokine receptor polypeptide encoded by the polynucleotide further comprises a soluble Class I or Class II cytokine receptor. En another embodiment, the isolated polynucleotide is as disclosed above, wherein the soluble cytokine receptor polypeptide encoded by the polynucleotide forms a heterodimeric or multimeric receptor complex further comprising a soluble CRF2-4 receptor polypeptide (SEQ ED NO:35), a soluble EL-10 receptor polypeptide (SEQ ED NO:36), or soluble zcytorl 1 receptor polypeptide (SEQ ED NO: 34). In another embodiment, the isolated polynucleotide is as disclosed above, wherein the soluble cytokine receptor polypeptide further encodes an intracellular domain. In another embodiment, the isolated polynucleotide is as disclosed above, wherein the soluble cytokine receptor polypeptide further comprises an affinity tag. Within another aspect the present invention provides an expression vector comprising the following operably linked elements: (a) a transcription promoter; a first DNA segment encoding a soluble cytokine receptor polypeptide having an amino acid sequence as shown in SEQ ED NO:2 from amino acid 22-231 or 22-210; and a transcription terminator; and (b) a second transcription promoter; a second DNA segment encoding a soluble Class I or Class El cytokine receptor polypeptide; and a transcription terminator; and wherein the first and second DNA segments are contained within a single expression vector or are contained within independent expression vectors. En one embodiment, the expression vector disclosed above further comprising a secretory signal sequence operably linked to the first and second DNA segments. In another embodiment, the expression vector is as disclosed above, wherein the second DNA segment encodes a polypeptide comprising a soluble CRF2-4 receptor polypeptide (SEQ ID NO:35), a soluble IL-10 receptor polypeptide (SEQ ID NO:36), or soluble zcytorl 1 receptor polypeptide (SEQ ID NO:34). Within another aspect the present invention provides a cultured cell comprising an expression vector as disclosed above, wherein the cell expresses the polypeptides encoded by the DNA segments. Within another aspect the present invention provides a cultured cell comprising an expression vector as disclosed above, wherein the first and second DNA segments are located on independent expression vectors and are co-transfected into the cell, and cell expresses the polypeptides encoded by the DNA segments. Within another aspect the present invention provides a cultured cell into which has been introduced an expression vector as disclosed above, wherein the cell expresses a heterodimeric or multimeric soluble receptor polypeptide encoded by the DNA segments. In one embodiment is provided a cell as disclosed above, wherein the cell secretes a soluble cytokine receptor polypeptide heterodimer or multimeric complex. In another embodiment is provided a cell as disclosed above, wherein the cell secretes a soluble cytokine receptor polypeptide heterodimer or multimeric complex that binds EL-TEF or antagonizes EL-TEF activity. Within another aspect the present invention provides a DNA construct encoding a fusion protein comprising: a first DNA segment encoding a polypeptide having a sequence of amino acid residues as shown in SEQ ED NO: 2 from amino acid 22-231 or 22-210; and at least one other DNA segment encoding a soluble Class 1 or Class El cytokine receptor polypeptide, wherein the first and other DNA segments are connected in-frame; and wherein the first and other DNA segments encode the fusion protein. In one embodiment the DNA construct encoding a fusion protein is as disclosed above, wherein at least one other DNA segment encodes a polypeptide comprising a soluble CRF2-4 receptor polypeptide (SEQ ED NO:35), a soluble IL-10 receptor polypeptide (SEQ ID NO:36), or soluble zcytorl 1 receptor polypeptide (SEQ ID NO:34). Within another aspect the present invention provides an expression vector comprising the following operably linked elements: a transcription promoter; a DNA construct encoding a fusion protein as disclosed above; and a transcription terminator, wherein the promoter is operably linked to the DNA construct, and the DNA construct is operably linked to the transcription terminator. Within another aspect the present invention provides a cultured cell comprising an expression vector as disclosed above, wherein the cell expresses a polypeptide encoded by the DNA construct. Within another aspect the present invention provides a method of producing a fusion protein comprising: culturing a cell as disclosed above; and isolating the polypeptide produced by the cell. Within another aspect the present invention provides an isolated soluble cytokine receptor polypeptide comprising a sequence of amino acid residues that is at least 90% identical to an amino acid sequence as shown in SEQ ED NO:2 from amino acid 22-231 or 22-210, and wherein the soluble cytokine receptor polypeptide binds EL- TEF or antagonizes EL-TEF activity. Within another aspect the present invention provides an isolated polypeptide as disclosed above, wherein the soluble cytokine receptor polypeptide forms a homodimeric, heterodimeric or multimeric receptor complex. In one embodiment, the isolated polypeptide is as disclosed above, wherein the soluble cytokine receptor polypeptide forms a heterodimeric or multimeric receptor complex further comprising a soluble Class I or Class II cytokine receptor. In another embodiment, the isolated polypeptide is as disclosed above, wherein the soluble cytokine receptor polypeptide forms a heterodimeric or multimeric receptor complex further comprising a soluble CRF2-4 receptor polypeptide (SEQ ID NO:35), a soluble EL-10 receptor polypeptide (SEQ ED NO:36), or soluble zcytorl 1 receptor polypeptide (SEQ ED NO:34). Within another aspect the present invention provides an isolated soluble cytokine receptor polypeptide comprising a sequence of amino acid residues as shown in SEQ ED NO:2 from amino acid 22-231 or 22-210, wherein the soluble cytokine receptor polypeptide forms a homodimeric, heterodimeric or multimeric receptor complex. In one embodiment, the isolated soluble cytokine receptor polypeptide is as disclosed above, wherein the soluble cytokine receptor polypeptide forms a heterodimeric or multimeric receptor complex further comprising a soluble Class I or Class II cytokine receptor. In another embodiment, the isolated soluble cytokine receptor polypeptide is as disclosed above, wherein the soluble cytokine receptor polypeptide forms a heterodimeric or multimeric receptor complex comprising a soluble CRF2-4 receptor polypeptide (SEQ ID NO:35), a soluble IL-10 receptor polypeptide (SEQ ID NO:36), or soluble zcytorl 1 receptor polypeptide (SEQ ID NO:34). In another embodiment, the isolated soluble cytokine receptor polypeptide is as disclosed above, wherein the soluble cytokine receptor polypeptide further comprises an affinity tag, chemical moiety, toxin, or label. Within another aspect the present invention provides an isolated heterodimeric or multimeric soluble receptor complex comprising soluble receptor subunits, wherein at least one of the soluble receptor subunits comprises a soluble cytokine receptor polypeptide comprising a sequence of amino acid residues as shown in SEQ ID NO:2 from amino acid 22-231 or 22-210. In one embodiment, the isolated heterodimeric or multimeric soluble receptor complex disclosed above, further comprises a soluble Class I or Class EE cytokine receptor polypeptide. In another embodiment, the isolated heterodimeric or multimeric soluble receptor complex disclosed above, further comprises a soluble CRF2-4 receptor polypeptide (SEQ ID NO:35), a soluble IL-10 receptor polypeptide (SEQ ID NO:36), or soluble zcytorl 1 receptor polypeptide (SEQ ID NO:34). Within another aspect the present invention provides a method of producing a soluble cytokine receptor polypeptide that form a heterodimeric or multimeric complex comprising: culturing a cell as disclosed above, and isolating the soluble receptor polypeptides produced by the cell. Within another aspect the present invention provides a method of producing an antibody to soluble cytokine receptor polypeptide comprising: inoculating an animal with a soluble cytokine receptor polypeptide selected from the group consisting of: (a) a polypeptide comprising a monomeric or homodimeric soluble cytokine receptor comprising a polypeptide as shown in SEQ ID NO:2 from amino acid 22-231 or 22-210; (b) a polypeptide of (a) further comprising a soluble cytokine receptor heterodimeric or multimeric receptor complex comprising a soluble Class I or Class II cytokine receptor polypeptide; (c) a polypeptide of (a) further comprising a soluble cytokine receptor heterodimeric or multimeric receptor complex comprising a soluble CRF2-4 receptor polypeptide (SEQ ID NO:35); (d) a polypeptide of (a) further comprising a soluble cytokine receptor heterodimeric or multimeric receptor complex comprising a soluble EL-10 receptor polypeptide (SEQ ED NO:36); and wherein the polypeptide elicits an immune response in the animal to produce the antibody; and isolating the antibody from the animal. Within another aspect the present invention provides an antibody produced by the method as disclosed above, which specifically binds to a homodimeric, heterodimeric or multimeric receptor complex comprising a polypeptide as shown in SEQ ID NO:2 from amino acid 22-231 or 22-210. En one embodiment, the antibody disclosed above is a monoclonal antibody. Within another aspect the present invention provides an antibody which specifically binds to a homodimeric, heterodimeric or multimeric receptor complex as disclosed above. Within another aspect the present invention provides a method for inhibiting EL-TEF-induced proliferation or differentiation of hematopoietic cells and hematopoietic cell progenitors comprising culturing bone marrow or peripheral blood cells with a composition comprising an amount of soluble cytokine receptor polypeptide as shown in SEQ ED NO:2 from amino acid 22-231 or 22-210, sufficient to reduce proliferation or differentiation of the hematopoietic cells in the bone maπow or peripheral blood cells as compared to bone maπow or peripheral blood cells cultured in the absence of soluble cytokine receptor. In one embodiment, the method is as disclosed above, wherein the hematopoietic cells and hematopoietic progenitor cells are lymphoid cells. In another embodiment, the method is as disclosed above, wherein the lymphoid cells are macrophages or T cells. Within another aspect the present invention provides a method of reducing EL-TEF-induced or EL-9 induced inflammation comprising administering to a mammal with inflammation an amount of a composition of a polypeptide as shown in SEQ ED NO:2 from amino acid 22-231 or 22-210 sufficient to reduce inflammation. Within another aspect the present invention provides a method of suppressing an inflammatory response in a mammal with inflammation comprising: (1) determining a level of serum amyloid A protein; (2) administering a composition comprising a soluble zcytorlo cytokine receptor polypeptide as disclosed above in an acceptable pharmaceutical vehicle; (3) determining a post administration level of serum amyloid A protein; (4) comparing the level of serum amyloid A protein in step (1) to the level of serum amyloid A protein in step (3), wherein a lack of increase or a decrease in serum amyloid A protein level is indicative of suppressing an inflammatory response. Within another aspect the present invention provides a method for detecting a genetic abnormality in a patient, comprising: obtaining a genetic sample from a patient; producing a first reaction product by incubating the genetic sample with a polynucleotide comprising at least 14 contiguous nucleotides of SEQ ID NO: 1 or the complement of SEQ ID NO:l, under conditions wherein said polynucleotide will hybridize to complementary polynucleotide sequence; visualizing the first reaction product; and comparing said first reaction product to a control reaction product from a wild type patient, wherein a difference between said first reaction product and said control reaction product is indicative of a genetic abnormality in the patient. Within another aspect the present invention provides a method for detecting a cancer in a patient, comprising: obtaining a tissue or biological sample from a patient; incubating the tissue or biological sample with an antibody as disclosed above under conditions wherein the antibody binds to its complementary polypeptide in the tissue or biological sample; visualizing the antibody bound in the tissue or biological sample; and comparing levels of antibody bound in the tissue or biological sample from the patient to a normal control tissue or biological sample, wherein an increase in the level of antibody bound to the patient tissue or biological sample relative to the normal control tissue or biological sample is indicative of a cancer in the patient. Within another aspect the present invention provides a method for detecting a cancer in a patient, comprising: obtaining a tissue or biological sample from a patient; labeling a polynucleotide comprising at least 14 contiguous nucleotides of SEQ ID NO: 1 or the complement of SEQ ID NO: 1 ; incubating the tissue or biological sample with under conditions wherein the polynucleotide will hybridize to complementary polynucleotide sequence; visualizing the labeled polynucleotide in the tissue or biological sample; and comparing the level of labeled polynucleotide hybridization in the tissue or biological sample from the patient to a normal control tissue or biological sample, wherein an increase in the labeled polynucleotide hybridization to the patient tissue or biological sample relative to the normal control tissue or biological sample is indicative of a cancer in the patient. The invention is further illustrated by the following non-limiting examples. EXAMPLES Example 1 Cloning of zcytorlo and Construction of Mammalian Expression Vectors That Express zcytorlo Soluble Receptors: zcytorlόCEE, zcvtorlόCFLG, zcytorlόCHIS and zcytorl 6-Fc4 A. Cloning of Zcytorlo Extracellular domain Scanning of a translated human genomic database resulted in identification of a class El cytokine receptor named zcytorlo. The sequence for zcytorlo was subsequently identified a clone from an in-house derived shallow tonsil library. The insert in the tonsil library clone was sequenced, and shown to encode the zcytorlo extracellular domain. The polynucleotide sequence of the zcytorlo clone is shown in SEQ ED NO:l and polypeptide sequence shown in SEQ ED NO:2. B. Mammalian Expression Construction of Soluble zcytorlo receptor zcvtorl6-Fc4 Construction of mammalian expression vectors that express zcytorlo soluble receptor zcytorl 6sR/Fc4 An expression vector was prepared to express the soluble zcytorlo polypeptide (zcytorlόsR, i.e., from residue 22 (Thr) to residue 231 (Pro) of SEQ ED NO:2; SEQ ED NO: 13) fused to a C-terminal Fc4 tag (SEQ ED NO:5). A PCR generated zcytorlo DNA fragment of about 630 bp was created using oligo ZC29,181 (SEQ ID NO:6) and oligo ZC29,182 (SEQ ID NO:7) as PCR primers to add BamHI and Bgl2 restriction sites at 5' and 3' ends respectively, of the zcytorlo DNA encoding the soluble receptor. A plasmid containing the zcytorlo cDNA (SEQ ID NO: 1) (Example 1 A) was used as a template. PCR amplification of the zcytorlo fragment was performed as follows: One cycle at 94°C for 1 minute; 25 cycles at 94°C for 30 seconds, 68°C for 90 seconds, followed by an additional 68°C incubation for 4 minutes, and hold at 10°C. The reaction was purified by chloroform/phenol extraction and isopropanol precipitation, and digested with BamHI and Bgl2 (Boehringer Mannheim, Indianapolis, EN). A band of approximately 630 bp, as visualized by 1% agarose gel electrophoresis, was excised and the DNA was purified using a QiaexEI™ purification kit (Qiagen, Valencia, CA) according to the manufacturer's instruction. The Fc4/pzmp20 plasmid is a mammalian expression vector containing an expression cassette having the CMV promoter, human tPA leader peptide, multiple restriction sites for insertion of coding sequences, a Fc4 tag, and a human growth hormone terminator. The plasmid also has an E. coli origin of replication, a mammalian selectable marker expression unit having an SV40 promoter, an enhancer and an origin of replication, as well as a DHFR gene, and SV40 terminator. The zcytorl 6sR/Fc4/pzmp20 expression vector uses the human tPA leader peptide (SEQ ID NO:8 and SEQ ID NO:9) and attaches the Fc4 tag (SEQ ED NO:5) to the C-terminus of the extracellular portion of the zcytorlo polypeptide sequence. Fc4 is the Fc region derived from human IgG, which contains a mutation so that it no longer binds the Fc receptor About 30 ng of the restriction digested zcytorlόsR insert and about 10 ng of the digested vector (which had been cut with Bgl2) were ligated at 11°C overnight. One microliter of ligation reaction was electroporated into DH10B competent cells (Gibco BRL, Rockville, MD) according to manufacturer's direction and plated onto LB plates containing 50 mg/ml ampicillin, and incubated overnight. Colonies were screened by restriction analysis of DNA, which was prepared from 2 ml liquid cultures of individual colonies. The insert sequence of positive clones was verified by sequence analysis. A large-scale plasmid preparation was done using a Qiagen® Mega prep kit (Qiagen) according to manufacturer's instruction. Similar methods are used to prepare non-zcytorl6 subunits of heterodimeric and multimeric receptors, such as CRF2-4 and IL-10R tagged with Fc4. C. Construction of zcytorlo Mammalian Expression Vector containing zcytorlόCEE, zcytorl 6CFLG and zcvtorlόCHIS An expression vector is prepared for the expression of the soluble, extracellular domain of the zcytorlo polypeptide (e.g., amino acids 22-231 of SEQ ID NO:2; SEQ ED NO: 13), pC4zcytorl6CEE, wherein the construct is designed to express a zcytorlo polypeptide comprised of the predicted initiating methionine and truncated adjacent to the predicted transmembrane domain, and with a C-terminal Glu-Glu tag (SEQ ID NO: 10). A zcytorlo DNA fragment comprising the zcytorlo extracellular cytokine binding domain (e.g., SEQ ID NO: 13) is created using PCR, and purified. The excised DNA is subcloned into a plasmid expression vector that has a signal peptide, e.g., the native zcytorlo signal peptide, tPA leader, and attaches a Glu-Glu tag (SEQ ID NO: 10) to the C-terminus of the zcytorlo polypeptide-encoding polynucleotide sequence. Such an expression vector mammalian expression vector contains an expression cassette having a mammalian promoter, multiple restriction sites for insertion of coding sequences, a stop codon and a mammalian terminator. The plasmid can also have an E. coli origin of replication, a mammalian selectable marker expression unit having an SV40 promoter, enhancer and origin of replication, a DHFR gene and the SV40 terminator. Restriction digested zcytorlo insert and previously digested vector are ligated using standard molecular biological techniques, and electroporated into competent cells such as DH10B competent cells (GIBCO BRL, Gaithersburg, MD) according to manufacturer's direction and plated onto LB plates containing 50 mg/ml ampicillin, and incubated overnight. Colonies are screened by restriction analysis of DNA prepared from individual colonies. The insert sequence of positive clones is verified by sequence analysis. A large-scale plasmid preparation is done using a QIAGEN® Maxi prep kit (Qiagen) according to manufacturer's instructions. The same process is used to prepare the zcytorlo soluble homodimeric, heterodimeric or multimeric receptors (including non-zcytorl6 soluble receptor subunits, such as, soluble CRF2-4 or IL-10R) with a C-terminal HIS tag, composed of 6 His residues in a row (SEQ ID NO: 12); and a C-terminal FLAG (SEQ ID NO: 11) tag, zcytorl 6CFLAG. To construct these constructs, the aforementioned vector has either the HIS or the FLAG® tag in place of the glu-glu tag (SEQ ID NO: 10). Example 2 Transfection And Expression of Soluble Receptor Polypeptides The day before the transfection, BHK 570 cells (ATCC No. CRL-10314; ATCC, Manasas, VA) were plated in a 10-cm plate with 50% confluence in normal BHK DMEM (Gibco/BRL High Glucose) media. The day of the transfection, the cells were washed once with Serum Free (SF) DMEM, followed by transfection with the zcytorl 6sR/Fc4/pzmp20 expression plasmids. Sixteen micrograms of zcytorl 6sR-Fc4 DNA construct (Example IB) were diluted into a total final volume of 640μl SF DMEM. A diluted LipofectAMINE™ (Gibco BRL, Gaithersburg, MD) mixture (35μl LipofectAMINE™ in 605 μl SF media) was added to the DNA mix, and incubated for 30 minutes at room temperature. Five milliliters of SF media was added to the DNA/LipofectAMINE™ mixture, which was then added to BHK cells. The cells were incubated at 37°C/5% CO 2 for 5 hours, after which 6.4ml of BHK media with 10% FBS was added. The cells were incubated overnight at 37°C/5% CO . Approximately 24 hours post-transfection, the BHK cells were split into selection media with lμM methotrexate (MTX). The cells were repeatedly split in this manner until stable zcytorl 6sR-Fc4/BHK cell lines were identified. To detect the expression level of the zcytorlo soluble receptor fusion proteins, the transfected BHK cells were washed with PBS and incubated in SF media for 72 hours. The SF condition media was collected and 20 μl of the sample was run on 10% SDS-PAGE gel under reduced conditions. The protein bands were transfeπed to nitrocellulose filter by Western blot, and the fusion proteins were detected using goat-anti-human IgG HRP conjugate (Jackson ImmunoResearch Laboratories, Inc, West Grove, PA). An expression vector containing a different soluble receptor fused to the Fc4 was used as a control. The expression level of the stable zcytorl 6sR-Fc4/BHK cells was approximately 2 mg/L. For protein purification, the transfected BHK cells were transfeπed into T-162 flasks. Once the cells reached about 80% confluence, they were washed with PBS and incubated in 100ml SF media for 72 hours, and then the condition media was collected for protein purification (Example 11). Example 3 Expression of zcytorlo Soluble Receptor in E. coli A. Construction of expression vector pCZR225 that expresses huzcvtorl6/MBP-6H fusion polypeptide An expression plasmid containing a polynucleotide encoding a zcytorlo soluble receptor fused C-terminally to maltose binding protein (MBP) is constructed via homologous recombination. The fusion polypeptide contains an N-terminal approximately 388 amino acid MBP portion fused to the zcytorlo soluble receptor (e.g., SEQ ID NO: 13). A fragment of zcytorlo cDNA (SEQ ID NO:l) is isolated using PCR as described herein. Two primers are used in the production of the zcytorlo fragment in a standard PCR reaction: (1) one containing about 40 bp of the vector flanking sequence and about 25 bp coπesponding to the amino terminus of the zcytorlo, and (2) another containing about 40 bp of the 3' end coπesponding to the flanking vector sequence and about 25 bp coπesponding to the carboxyl terminus of the zcytorlo. Two μl of the 100 μl PCR reaction is run on a 1.0% agarose gel with 1 x TBE buffer for analysis, and the expected approximately fragment is seen. The remaining PCR reaction is combined with the second PCR tube and precipitated with 400 μl of absolute ethanol. The precipitated DNA used for recombining into an appropriately restriction digested recipient vector pTAP98 to produce the construct encoding the MBP-zcytorl6 fusion, as described below. Plasmid pTAP98 is derived from the plasmids pRS316 and pMAL-c2. The plasmid pRS316 is a Saccharomyces cerevisiae shuttle vector (Hieter P. and Sikorski, R., Genetics 122:19-27, 1989). pMAL-C2 (NEB) is an E. coli expression plasmid. It caπies the tac promoter driving MalE (gene encoding MBP) followed by a His tag, a thrombin cleavage site, a cloning site, and the rrnB terminator. The vector pTAP98 is constructed using yeast homologous recombination. lOOng of EcoRl cut pMAL-c2 is recombined with lμg Pvul cut pRS316, lμg linker, and lμg Scal/EcoRl cut pRS316 are combined in a PCR reaction. PCR products are concentrated via 100% ethanol precipitation. Competent yeast cells (S. cerevisiae) are combined with about 10 μl of a mixture containing approximately 1 μg of the zcytorlo receptor PCR product above, and 100 ng of digested pTAP98 vector, and electroporated using standard methods and plated onto URA-D plates and incubated at 30°C. After about 48 hours, the Ura+ yeast transformants from a single plate are picked, DNA isolated, and transformed into electrocompetent E. coli cells (e.g., MC1061, Casadaban et. al. J. Mol. Biol. 138, 179-207), and plated on MM/CA +AMP 100 mg/L plates (Pryor and Leiting, Protein Expression and Pruification 10:309-319, 1997).using standard procedures. Cells are grown in MM/CA with 100 μg/ml Ampicillin for two hours, shaking, at 37°C. lml of the culture is induced with lmM IPTG. 2-4 hours later the 250 μl of each culture is mixed with 250 μl acid washed glass beads and 250 μl Thorner buffer with 5% βME and dye (8M urea, 100 mM Tris pH7.0, 10% glycerol, 2mM EDTA, 5% SDS). Samples are vortexed for one minute and heated to 65°C for 10 minutes. 20 μl are loaded per lane on a 4%-12% PAGE gel (NOVEX). Gels are run in 1XMES buffer. The positive clones are designated pCZR225 and subjected to sequence analysis. One microliter of sequencing DNA is used to transform strain BL21. The cells are electropulsed at 2.0 kV, 25 μF and 400 ohms. Following electroporation, 0.6 ml MM/CA with 100 mg/L Ampicillin. Cells are grown in MM/CA and induced with ETPG as described above. The positive clones are used to grow up for protein purification of the huzcytorl6/MBP-6H fusion protein using standard techniques. Example 4 Zcvtorlό Soluble Receptor Polyclonal Antibodies Polyclonal antibodies are prepared by immunizing female New Zealand white rabbits with the purified huzcytorl6/MBP-6H polypeptide (Example 3), or the purified recombinant zcytorl 6CEE soluble receptor (Example 1; Example 11). The rabbits are each given an initial intraperitoneal (IP) injection of about 200 mg of purified protein in Complete Freund's Adjuvant (Pierce, Rockford, EL) followed by booster EP injections of 100 mg purified protein in Encomplete Freund's Adjuvant every three weeks. Seven to ten days after the administration of the third booster injection, the animals are bled and the serum is collected. The rabbits are then boosted and bled every three weeks. The zcytorl 6-specific polyclonal antibodies are affinity purified from the rabbit serum using an CNBr-SEPHAROSE 4B protein column (Pharmacia LKB) that is prepared using about 10 mg of the appropriate purified zcytorlo polypeptide per gram CNBr-SEPHAROSE, followed by 20X dialysis in PBS overnight. Zcytorl 6-specific antibodies are characterized by an ELISA titer check using 1 mg/ml of the appropriate protein antigen as an antibody target. The lower limit of detection (LLD) of the rabbit anti-zcytorlό affinity purified antibodies is determined using standard methods. Example 5 Zcytorlo Receptor Monoclonal Antibodies Zcytorlo receptor Monoclonal antibodies are prepared by immunizing male BalbC mice (Harlan Sprague Dawley, Indianapolis, IN) with the purified recombinant zcytorlo proteins described herein. The mice are each given an initial intraperitoneal (IP) injection of 20 mg of purified protein in Complete Freund's Adjuvant (Pierce, Rockford, EL) followed by booster EP injections of 10 mg purified protein in Incomplete Freund's Adjuvant every two weeks. Seven to ten days after the administration of the third booster injection, the animals are bled and the serum is collected, and antibody titer assessed. Splenocytes are harvested from high-titer mice and fused to murine SP2/0 myeloma cells using PEG 1500 (Boerhinger Mannheim, UK) in two separate fusion procedures using a 4: 1 fusion ratio of splenocytes to myeloma cells (Antibodies: A Laboratory Manual, E. Harlow and D. Lane, Cold Spring Harbor Press). Following 10 days growth post-fusion, specific antibody-producing hybridomas are identified by ELISA using purified recombinant zcytorlo soluble receptor protein (Example 6C) as an antibody target and by FACS using Baf3 cells expressing the zcytorlo sequence (Example 8) as an antibody target. The resulting hybridomas positive by both methods are cloned three times by limiting dilution. Example 6 Assessing Zcytorlo Receptor Heterodimerization Using ORIGEN Assay Soluble zcytorlo receptor (Example 11), or gpl30 (Hibi, M. et al., Cell 63: 1149-1157, 1990) are biotinylated by reaction with a five-fold molar excess of sulfo- NHS-LC-Biotin (Pierce, Inc., Rockford, IL) according to the manufacturer's protocol. Soluble zcytorlo receptor and another soluble receptor subunit, for example, soluble IL-10R (sIL-lOR) or CRF2-4 receptor (CRF2-4), soluble zcytorl 1 receptor (US Pat. No. 5,965,704) or soluble zcytor7 receptor (US patent No. 5,945,511) are labeled with a five fold molar excess of Ru-BPY-NHS (Igen, Inc., Gaithersburg, MD) according to manufacturer's protocol. The biotinylated and Ru-BPY-NHS-labeled forms of the soluble zcytorlo receptor can be respectively designated Bio-zcytorl6 receptor and Ru- zcytorlo; the biotinylated and Ru-BPY-NHS-labeled forms of the other soluble receptor subunit can be similarly designated. Assays can be carried out using conditioned media from cells expressing a ligand, such as IL-TIF, that binds zcytorlo heterodimeric receptors, or using purified IL-TIF. For initial receptor binding characterization a panel of cytokines or conditioned medium are tested to determine whether they can mediate homodimerization of zcytorlo receptor and if they can mediate the heterodimerization of zcytorlo receptor with the soluble receptor subunits described above. To do this, 50 μl of conditioned media or TBS-B containing purified cytokine, is combined with 50 μl of TBS-B (20 mM Tris, 150 mM NaCl, 1 mg/ml BSA, pH 7.2) containing e.g., 400 ng/ml of Ru-zcytorl6 receptor and Bio-zcytorl6, or 400 ng/ml of Ru-zcytorl6 receptor and e.g., Bio-gpl30, or 400 ng/ml of e.g., Ru-CRF2-4 and Bio-zcytorl6. Following incubation for one hour at room temperature, 30 μg of streptavidin coated, 2.8 mm magnetic beads (Dynal, Inc., Oslo, Norway) are added and the reaction incubated an additional hour at room temperature. 200 μl ORIGEN assay buffer (Igen, Inc., Gaithersburg, MD) is then added and the extent of receptor association measured using an M8 ORIGEN analyzer (Igen, Inc.). Example 7 Construct for Generating a zcytorlo Receptor Heterodimer A vector expressing a secreted human zcytorlo heterodimer is constructed. In this construct, the extracellular cytokine-binding domain of zcytorlo (e.g., SEQ ED NO: 13) is fused to the heavy chain of EgG gamma 1 (IgGγl) while the extracellular portion of the heteromeric cytokine receptor subunit (e.g., an CRF2-4, IL- 9, EL-10, zcytor7, zcytorl 1, IL-4 receptor component) is fused to a human kappa light chain (human K light chain). A. Construction of IgG gamma 1 and human K light chain fusion vectors The heavy chain of IgGγl can be cloned into the Zem229R mammalian expression vector (ATCC deposit No. 69447) such that any desired cytokine receptor extracellular domain having a 5' EcoRI and 3' Nhel site can be cloned in resulting in an N-terminal extracellular domain-C-terminal IgGγl fusion. The IgGγl fragment used in this construct is made by using PCR to isolate the IgGγl sequence from a Clontech hFetal Liver cDNA library as a template. PCR products are purified using methods described herein and digested with Mlul and EcoRI (Boerhinger-Mannheim), ethanol precipitated and ligated with oligos which comprise an desired restriction site linker, into Zem229R previously digested with and EcoRI using standard molecular biology techniques disclosed herein. The human K light chain can be cloned in the Zem228R mammalian expression vector (ATCC deposit No. 69446) such that any desired cytokine receptor extracellular domain having a 5' EcoRI site and a 3' Kpnl site can be cloned in resulting in a N-terminal cytokine extracellular domain-C-terminal human K light chain fusion. As a Kpnl site is located within the human K light chain sequence, a special primer is designed to clone the 3' end of the desired extracellular domain of a cytokine receptor into this Kpnl site: The primer is designed so that the resulting PCR product contains the desired cytokine receptor extracellular domain with a segment of the human K light chain up to the Kpnl site. This primer preferably comprises a portion of at least 10 nucleotides of the 3' end of the desired cytokine receptor extracellular domain fused in frame 5' to fragment cleaved at the Kpnl site. The human K light chain fragment used in this construct is made by using PCR to isolate the human K light chain sequence from the same Clontech human Fetal Liver cDNA library used above. PCR products are purified using methods described herein and digested with Mlul and EcoRI (Boerhinger-Mannheim), ethanol precipitated and ligated with the MluI/EcoRI linker described above, into Zem228R previously digested with and EcoRI using standard molecular biology techniques disclosed herein. B. Insertion of zcytorlo receptor or heterodimeric subunit extracellular domains into fusion vector constructs Using the construction vectors above, a construct having zcytorlo fused to IgGγl is made. This construction is done by PCRing the extracellular cytokine- binding domain of zcytorlo receptor (SEQ ED NO: 13) from a tonsil cDNA library (Clontech) or plasmid (Example IA) using standard methods and oligos that provide EcoRI and Nhel restriction sites. The resulting PCR product is digested with EcoRI and Nhel, gel purified, as described herein, and ligated into a previously EcoRI and Nhel digested and band-purified Zem229R/IgGγl described above. The resulting vector is sequenced to confirm that the zcytorl 6/IgG gamma 1 fusion is coπect. A separate construct having a heterodimeric cytokine receptor subunit extracellular domain fused to K light is also constructed as above. The CRF2-4/human K light chain construction is performed as above by PCRing from, e.g., a lymphocyte cDNA library (Clontech) using standard methods, and oligos that provide EcoRI and Kpnl restriction sites. The resulting PCR product is digested with EcoRI and Kpnl and then ligating this product into a previously EcoRI and Kpnl digested and band-purified Zem228R/human K light chain vector described above. The resulting vector is sequenced to confirm that the cytokine receptor subunit human K light chain fusion is coπect. D. Co-expression of the zcytorlo and heterodimeric cytokine receptor subunit extracellular domain Approximately 15 μg of each of vectors above, are co-transfected into mammalian cells, e.g., BHK-570 cells (ATCC No. CRL-10314) using LipofectaminePlus™ reagent (Gibco/BRL), as per manufacturer's instructions. The transfected cells are selected for 10 days in DMEM + 5%FBS (Gibco/BRL) containing 1 μM of methotrexate (MTX) (Sigma, St. Louis, MO) and 0.5 mg/ml G418 (Gibco/BRL) for 10 days. The resulting pool of transfectants is selected again in 10 μm of MTX and 0.5 mg/ml G418 for about 10 days. The resulting pool of doubly selected cells is used to generate protein. Three Factories (Nunc, Denmark) of this pool are used to generate 10 L of serum free conditioned medium. This conditioned media is passed over a 1 ml protein-A column and eluted in about 10, 750 microliter fractions. The fractions having the highest protein concentration are pooled and dialyzed (10 kD MW cutoff) against PBS. Finally the dialyzed material is submitted for amino acid analysis (AAA) using routine methods. Example 8 Determination of Receptor Subunits That Heterodimerize or Multimerize With zcytorlo Receptor Using a Proliferation Assay Using standard methods described herein, cells expressing a BaF3/zcytorl6-MPL chimera (wherein the extracellular domain of the zcytorlo (e.g., SEQ ED NO: 13) is fused in frame to the intracellular signaling domain of the mpl receptor) are tested for proliferative response in the presence of EL-TEF. Such cells serve as a bioassay cell line to measure ligand binding of monomeric or homodimeric zcytorlo receptors. In addition, BaF3/zcytorl6-MPL chimera cells transfected with an additional heterodimeric cytokine receptor subunit can be assessed for proliferative response in the presence of IL-TIF. In the presence of IL-TIF, if the BaF3/zcytorl6- MPL cells signal, this would suggest that zcytorlo receptor can homodimerize to signal. Transfection of the BaF3/MPL-zcytorl6 cell line with and additional MPL-class II cytokine receptor fusion that signals in the presence of the IL-TEF ligand, such as CRF2-4, determines which heterodimeric cytokine receptor subunits are required for zcytorlo receptor signaling. Use of MPL-receptor fusions for this puφose alleviates the requirement for the presence of an intracellular signaling domain for the zcytorlo receptor. Each independent receptor complex cell line is then assayed in the presence of IL-TIF and proliferation measured using routine methods (e.g., Alamar Blue assay). The BaF3/MPL-zcytorl6 bioassay cell line serves as a control for the monomeric or homodimeric receptor activity, and is thus used as a baseline to compare signaling by the various receptor complex combinations. The untransfected bioassay cell line serves as a control for the background activity, and is thus used as a baseline to compare signaling by the various receptor complex combinations. A BaF3/MPL- zcytorlό without ligand (IL-TIF) is also used as a control. The IL-TIF in the presence of the correct receptor complex, is expected to increase proliferation of the BaF3/zcytorl6-MPL receptor cell line approximately 5 fold over background or greater in the presence of IL-TIF. Cells expressing the components of zcytorlo heterodimeric and multimeric receptors should proliferate in the presence of IL-TIF. Example 9 Reconstitution of zcytorlo Receptor in vitro To identify components involved in the zcytorl 6-signaling complex, receptor reconstitution studies are performed as follows. BHK 570 cells (ATCC No. CRL-10314) transfected, using standard methods described herein, with a luciferase reporter mammalian expression vector plasmid serve as a bioassay cell line to measure signal transduction response from a transfected zcytorlo receptor complex to the luciferase reporter in the presence of EL-TEF. BHK cells do not endogenously express the zcytorlo receptor. An exemplary luciferase reporter mammalian expression vector is the KZ134 plasmid which was constructed with complementary oligonucleotides that contain STAT transcription factor binding elements from 4 genes. A modified c-fos Sis inducible element (m67SIE, or hSIE) (Sadowski, H. et al., Science 261:1739-1744. 1993), the p21 SIE1 from the p21 WAF1 gene (Chin, Y. et al., Science 272:719-722. 1996), the mammary gland response element of the β-casein gene (Schmitt-Ney, M. et al., Mol. Cell. Biol. H:3745-3755, 1991), and a STAT inducible element of the Fcg RI gene, (Seidel, H. et al., Proc. Natl. Acad. Sci. 92:3041-3045, 1995). These oligonucleotides contain Asp718-XhoI compatible ends and were ligated, using standard methods, into a recipient firefly luciferase reporter vector with a c-fos promoter (Poulsen, L.K. et al., J. Biol. Chem. 273:6229-6232, 1998) digested with the same enzymes and containing a neomycin selectable marker. The KZ134 plasmid is used to stably transfect BHK, or BaF3 cells, using standard transfection and selection methods, to make a BHK/KZ134 or BaF3/KZ134 cell line respectively. The bioassay cell line is transfected with zcytorl6-mpl fusion receptor alone, or co-transfected along with one of a variety of other known receptor subunits. Receptor complexes include but are not limited to zcytorl 6-mpl receptor only, various combinations of zcytorl6-mpl receptor with one or more of the CRF2-4, IL-9, IL-10, zcytorl 1, zcytor7 class II cytokine receptor subunits, or IL-4 receptor components, or the EL-2 receptor components (IL-2Rα, EL-2Rβ, EL-2Rγ); zcytorl6-mpl receptor with one or more of the EL-4/EL-13 receptor family receptor components (IL-4Rα, EL-13Rα, EL-13Rα'), as well as other Enterleukin receptors (e.g., IL-15 Rα, EL-7Rα, EL-9Rα, EL- 21R (zalphal l; WIPO publucation WO OO/17235; Parrish-Novak, J et al., Nature 408:57-63, 2000)). Each independent receptor complex cell line is then assayed in the presence of cytokine-conditioned media or purified cytokines and luciferase activity measured using routine methods. The untransfected bioassay cell line serves as a control for the background luciferase activity, and is thus used as a baseline to compare signaling by the various receptor complex combinations. The conditioned medium or cytokine that binds the zyctorlδ receptor in the presence of the coπect receptor complex, is expected to give a luciferase readout of approximately 5 fold over background or greater. As an alternative, a similar assay can be performed wherein Baf3/zcytorl 6-mpl cell lines are co-transfected as described above and proliferation measured (Example 8). Example 10 COS Cell Transfection and Secretion Trap COS cell transfections were performed as follows: A mixture of 0.5 μg DNA and 5 μl lipofectamine (Gibco BRL) in 92ul serum free DMEM media (55 mg sodium pyruvate, 146 mg L-glutamine, 5 mg transferrin, 2.5mg insulin, lμg selenium and 5 mg fetuin in 500ml DMEM) was incubated at room temperature for 30 minutes and then 400 μl serum free DMEM media added. A 500 μl mixture was added onto COS cells plated on 12-well tissue culture plate at 1.5xl0 5 COS cells/well and previously incubated for 5 hours at 37°C. An additional 500 μl 20% FBS DMEM media (100 ml FBS, 55 mg sodium pyruvate and 146 mg L-glutamine in 500 ml DMEM) was added and the plates were incubated overnight. The secretion trap was performed as follows: Media was rinsed off cells with PBS and fixed for 15 minutes with 1.8% Formaldehyde in PBS. Cells were then washed with TNT (0.1M Tris-HCl, 0.15M NaCl, and 0.05% Tween-20 in H 2 O). Cells were permeated with 0.1% Triton-X in PBS for 15 minutes and washed again with TNT. C ells were blocked for 1 hour with TNB (0.1M Tris-HCl, 0.15M NaCl and 0.5% Blocking Reagent (NEN Renaissance TSA-Direct Kit; NEN) in H O. Cells were again washed with TNT. Cells were then incubated for 1 hour with 1-3 μg/ml zcytorlo soluble receptor Fc4 fusion protein (zcytorl 6sR-Fc4) (Example 11) in TNB. Cells were washed with TNT, and then incubated for another hour with 1:200 diluted goat-anti- human Ig-HRP (Fc specific; Jackson ImmunoResearch Laboratories, Inc.) in TNB. Cells were again washed with TNT. Antibodies positively binding to the zcytorl 6sR- Fc4 were detected with fluorescein tyramide reagent diluted 1:50 in dilution buffer (NEN kit) and incubated for 4-6 minutes. Cells were again washed with TNT. Cells were preserved with Vectashield Mounting Media (Vector Labs) diluted 1:5 in TNT. Cells were visualized using FFTC filter on fluorescent microscope. Since zcytorlo is a Class 11 cytokine receptor, the binding of zcytorl 6sR/Fc4 fusion protein with known or oφhan Class II cytokines was tested. The pZP7 expression vectors containing cDNAs of cytokines (including human IL-TIF, interferon alpha, interferon beta, interferon gamma, IL-10, amongst others) were transfected into COS cells, and the binding of zcytorl 6sR/Fc4 to transfected COS cells were caπied out using the secretion trap assay described above. Human IL-TIF showed positive binding. Based on these data, human IL-TIF and zcytorlo is a potential ligand- receptor pair. Example 11 Purification of zcytorl 6-Fc4 Polypeptide From Transfected BHK 570 Cells Unless otherwise noted, all operations were carried out at 4°C. The following procedure was used for purifying zcytorlo polypeptide containing C-terminal fusion to human Fc4 (zcytorl 6-Fc4; Example 1). About 16,500 ml of conditioned media from BHK 570 cells transfected with zcytorl6-Fc4 (Example 2) was filtered through a 0.2 um sterilizing filter and then supplemented with a solution of protease inhibitors, to final concentrations of, 0.001 mM leupeptin (Boerhinger-Mannheim, Indianapolis, EN), 0.001 mM pepstatin (Boerhinger-Mannheim) and 0.4 mM Pefabloc (Boerhinger-Mannheim). A Poros protein A50 column (20 ml bed volume, Applied Biosystems) was packed and washed with 400 ml PBS (Gibco/BRL) The supplemented conditioned media was passed over the column with a flow rate of 15 ml/minute, followed by washing with 800 ml PBS (BRL/Gibco). Zcytorl 6-Fc4 was eluted from the column with 0.1 M Glycine pH 3.0 and 5 ml fractions were collected directly into 0.5 ml 2M Tris pH 7.8, to adjust the final pH to 7.4 in the fractions. Column performance was characterized through western blotting of reducing SDS-PAGE gels of the starting media and column pass through. Western blotting used anti-human IgG HRP (Amersham) antibody, which showed an immunoreactive protein at 60,000 Da in the starting media, with nothing in the pass through, suggesting complete capture. The protein A50 eluted fractions were characterized by reducing SDS PAGE gel. This gel showed an intensely Coomassie stained band at 60,000 Da in fractions 3 to 11. Fractions 3 to 11 were pooled. Protein A 50 elution pool was concentrated from 44 ml to 4 ml using a 30,000 Da Ultrafree Biomax centrifugal concentrator (15 ml volume, Millipore). A Sephacryl S-300 gel filtration column (175 ml bed volume; Pharmacia) was washed with 350 ml PBS (BRL/Gibco). The concentrated pool was injected over the column with a flow rate of 1.5 ml/min, followed by washing with 225 ml PBS (BRL/Gibco). Eluted peaks were collected into 2 ml fractions. Eluted fractions were characterized by reducing and non-reducing silver stained (Geno Technology) SDS PAGE gels. Reducing silver stained SDS PAGE gels showed an intensely stained band at 60,000 Da in fractions 14 - 31, while non-reducing silver stained SDS PAGE gels showed an intensely stained band at 160,000 Da in fractions 14 - 31. Fractions 1 - 13 showed many bands of various sizes. Fractions 14 - 31 were pooled, concentrated to 22 ml using 30,000 Da Ultrafree Biomax centrifugal concentrator (15 ml volume, Millipore). This concentrate was filtered through a 0.2 μm Acrodisc sterilizing filter (Pall Coφoration). The protein concentration of the concentrated pooled fractions was performed by BCA analysis (Pierce, Rockford, IL) and the material was aliquoted, and stored at -80°C according to our standard procedures. The concentration of the pooled fractions was 1.50 mg/ml. Example 12 Human zcytorlo Tissue Distribution in Tissue Panels Using Northern Blot and PCR A. Human zcytorlo Tissue Distribution using Northern Blot and Dot Blot Northern blot analysis was performed using Human Multiple Tissue Northern Blots I, II, EH (Clontech) and an in house generated U-937 northern blot. U- 937 is a human monoblastic promonocytic cell line. The cDNA probe was generated using oligos ZC25,963 (SEQ ID NO: 16) and ZC28,354 (SEQ ID NO: 17). The PCR conditions were as follows: 94° for 1 minute; 30 cycles of 94° , 15 seconds; 60°, 30 seconds; 72° , 30 seconds and a final extension for 5 minutes at 72°. The 364 bp product was gel purified by gel electrophoresis on a 1% TBE gel and the band was excised with a razor blade. The cDNA was extracted from the agarose using the QLAquick Gel Extraction Kit (Qiagen). 94 ng of this fragment was radioactively labeled with 32 P-dCTP using Rediprime II (Amersham), a random prime labeling system, according to the manufacturer's specifications. Unincoφorated radioactivity was removed using a Nuc-Trap column (Stratagene) according to manufacturer's instructions. Blots were prehybridized at 65° for 3 hours in ExpressHyb (Clontech) solution. Blots were hybridized overnight at 65° in Expresshyb solution containing 1.0 x 10 6 cpm/ml of labeled probe, 0.1 mg/ml of salmon sperm DNA and 0.5 μg/ml of human cot-1 DNA. Blots were washed in 2 x SSC, 0.1% SDS at room temperature with several solution changes then washed in 0.1 x SSC. 0.1% SDS at 55° for 30 minutes twice. Transcripts of approximately 1.6 kb and 3.0 kb size were detected in spleen and placenta, but not other tissues examined. The same sized transcripts plus an additional approximate 1.2 kb transcript was detected in U-937 cell line. B. Tissue Distribution in tissue cDNA panels using PCR A panel of cDNAs from human tissues was screened for zcytorlo expression using PCR. The panel was made in-house and contained 94 marathon cDNA and cDNA samples from various normal and cancerous human tissues and cell lines are shown in Table 5, below. The cDNAs came from in-house libraries or marathon cDNAs from in-house RNA preps, Clontech RNA, or Invitrogen RNA. The marathon cDNAs were made using the marathon-Ready™ kit (Clontech, Palo Alto, CA) and QC tested with clathrin primers ZC21195 (SEQ ID NO: 18) and ZC21196 (SEQ ID NO: 19) and then diluted based on the intensity of the clathrin band. To assure quality of the panel samples, three tests for quality control (QC) were run: (1) To assess the RNA quality used for the libraries, the in-house cDNAs were tested for average insert size by PCR with vector oligos that were specific for the vector sequences for an individual cDNA library; (2) Standardization of the concentration of the cDNA in panel samples was achieved using standard PCR methods to amplify full length alpha tubulin or G3PDH cDNA using a 5' vector oligo ZC14,063 (SEQ ID NO:20) and 3' alpha tubulin specific oligo primer ZC17,574 (SEQ ID NO:21) or 3' G3PDH specific oligo primer ZC17,600 (SEQ ID NO:22); and (3) a sample was sent to sequencing to check for possible ribosomal or mitochondrial DNA contamination. The panel was set up in a 96-well format that included a human genomic DNA (Clontech, Palo Alto, CA) positive control sample. Each well contained approximately 0.2-100 pg/μl of cDNA. The PCR reactions were set up using oligos ZC25,963 (SEQ ID NO: 16) and ZC27,659 (SEQ ID NO:23), Advantage 2 DNA Polymerase Mix (Clontech) and Rediload dye (Research Genetics, Inc., Huntsville, AL). The amplification was caπied out as follow: 1 cycle at 94°C for 2 minutes, 30 cycles of 94°C for 20 seconds, 58°C for 30 seconds and 72°C forl minute, followed by 1 cycle at 72°C for 5 minutes. About 10 μl of the PCR reaction product was subjected to standard Agarose gel electrophoresis using a 2% agarose gel. The coπect predicted DNA fragment size was not observed in any tissue or cell line. Subsequent experiments showing expression of zcytorlo indicated that the negative results from this panel were likely due to the primers used. Table 5 An additional panel of cDNAs from human tissues was screened for zcytorlo expression using. PCR. This panel was made in-house and contained 77 marathon cDNA and cDNA samples from various normal and cancerous human tissues and cell lines are shown in Table 6, below. Aside from the PCR reaction, the assay was caπied out as per above. The PCR reactions were set up using oligos ZC25,963 (SEQ ID NO:30) and ZC25,964 (SEQ ED NO:31), Advantage 2 DNA Polymerase Mix (Clontech) and Rediload dye (Research Genetics, Inc., Huntsville, AL). The amplification was carried out as follow: 1 cycle at 94°C for 1 minute, 38 cycles of 94°C for 10 seconds, 60°C for 30 seconds and 72°C for 30 seconds, followed by 1 cycle at 72°C for 5 minutes. The coπect predicted DNA fragment size was observed in bone maπow, fetal heart, fetal kidney, fetal muscle, fetal skin, heart, mammary gland, placenta, salivary gland, skeletal muscle, small intestine, spinal cord, spleen, kidney, fetal brain, esophageal tumor, uterine tumor, stomach tumor, ovarian tumor, rectal tumor, lung tumor and RPMI- 1788 (a B-lymphocyte cell line). Zcytorlo expression was not observed in the other tissues and cell lines tested in this panel. The expression pattern of zcytorlo shows expression in certain tissue-specific tumors especially, e.g., ovarian cancer, stomach cancer, uterine cancer, rectal cancer, lung cancer and esophageal cancer, where zcytor 16 is not expressed in normal tissue, but is expressed in the tumor tissue. One of skill in the art would recognize that the polynucleotides, polypeptides, antibodies, and binding partners of the present invention can be used as a diagnostic to detect cancer, or cancer tissue in a biopsy, tissue, or histologic sample, particularly e.g., ovarian cancer, stomach cancer, uterine cancer, rectal cancer, lung cancer and esophageal cancer tissue. Such diagnostic uses for the molecules of the present invention are known in the art and described herein. In addition, because the expression pattern of zcytorlo, one of IL-TIF' s receptors, shows expression in certain specific tissues as well as tissue-specific tumors, binding partners including the natural liganed, IL-TIF, can also be used as a diagnostic to detect specific tissues (normal or abnormal), cancer, or cancer tissue in a biopsy, tissue, or histologic sample, where IL-TIF receptors are expressed, and particularly e.g., ovarian cancer, stomach cancer, uterine cancer, rectal cancer, lung cancer and esophageal cancer tissue. IL-TIF can also be used to target other tissues wherein its receptors, e.g., zcytorlo and zcytorl 1 are expressed. Moreover, such binding partners could be conjugated to chemotherapeutic agents, toxic moieties and the like to target therapy to the site of a tumor or diseased tissue. Such diagnostic and targeted therapy uses are known in the art and described herein. A commercial 1st strand cDNA panel (Human Blood Fractions MTC Panel, Clontech, Palo Alto, CA) was also assayed as above. The panel contained the following samples: mononuclear cells, activated mononuclear cells, resting CD4+ cells, activated CD4+ cells, resting CD8+ cells, activated CD8+ cells, resting CD 14+ cells, resting CD 19+ cells and activated CD 19+ cells. Activated CD4+ cells and activated CD 19+ cells showed zcytorlo expression, whereas the other cells tested, including resting CD4+ cells and resting CD19+ cells, did not. Table 6 C. Tissue Distribution in Human Tissue and Cell Line RNA Panels Using RT-PCR A panel of RNAs from human cell lines was screened for zcytorlo expression using RT-PCR. The panels were made in house and contained 84 RNAs from various normal and cancerous human tissues and cell lines as shown in Tables 7-10 below. The RNAs were made from in house or purchased tissues and cell lines using the RNAeasy Midi or Mini Kit (Qiagen, Valencia, CA). The panel was set up in a 96-well format with 100 ngs of RNA per sample. The RT-PCR reactions were set up using oligos ZC25,963 (SEQ ID NO:30) and ZC25,964 (SEQ ID NO:31), Rediload dye and SUPERSCRIPT One Step RT-PCR System (Life Technologies, Gaithersburg, MD). The amplification was caπied out as follows: one cycle at 55° for 30 minutes followed by 40 cycles of 94°, 15 seconds; 59°, 30 seconds; 72°, 30 seconds; then ended with a final extension at 72° for 5 minutes. 8 to 10 μls of the PCR reaction product was subjected to standard Agarose gel electrophoresis using a 4% agarose gel. The coπect predicted cDNA fragment size of 184 bps was observed in cell lines U-937, HL-60, ARPE-19, HaCat#l, HaCat#2, HaCat#3, and HaCat#4; bladder, cancerous breast, normal breast adjacent to a cancer, bronchus, colon, ulcerative colitis colon, duodenum, endometrium, esophagus, gastro-esophageal, heart left ventricle, heart ventricle, ileum, kidney, lung, lymph node, lymphoma, mammary adenoma, mammary gland, cancerous ovary, pancreas, parotid and skin, spleen lymphoma and small bowel. Zcytorlo expression was not observed in the other tissues and cell lines tested in this panel. Zcytorlo is detectably expressed by PCR in normal tissues: such as, the digestive system, e.g., esophagus, gastro-esophageal, pancreas, duodenum, lleum, colon, small bowel; the female reproductive system, e.g., mammary gland, endometrium, breast (adjacent to cancerous tissues); and others systems, e.g., lymph nodes, skin, parotid, bladder, bronchus, heart ventricles, and kidney. Moreover, Zcytorlo is detectably expressed by PCR in several human tumors: such as tumors associated with female reproductive tissues e.g., mammary adenoma, ovary cancer, uterine cancer, other breast cancers; and other tissues such as lymphoma, stomach tumor, and lung tumor. The expression of zcytorlo is found in normal tissues of female reproductive organs, and in some tumors associated with these organs. As such, zcytorlo can serve as a marker for these tumors wherein the zcytorlo may be over-expressed. Several cancers positive for zcytorlo are associated with ectodermal/epithelial origin (mammary adenoma, and other breast cancers). Hence, zcytorlo can serve as a marker for epithelial tissue, such as epithelial tissues in the digestive system and female reproductive organs (e.g., endometrial tissue, columnar epithelium), as well as cancers involving epithelial tissues. Moreover, in a prefeπed embodiment, zcytorlo can serve as a marker for certain tissue- specific tumors especially, e.g., ovarian cancer, stomach cancer, uterine cancer, rectal cancer, lung cancer and esophageal cancer, where zcytor 16 is not expressed in normal tissue, but is expressed in the tumor tissue. Use of polynucleotides, polypeptides, and antibodies of the present invention for diagnostic puφoses are known in the art, and disclosed herein. Table 7 Table 8 Table 9 Table 10 Example 13 Construction of Expression Vector Expressing Full-length zcytorl 1 The entire zcytorl 1 receptor (commonly owned US Patent No. 5,965,704) was isolated by digestion with EcoRI and Xhol from plasmid pZP7P, containing full- length zcytorl 1 receptor cDNA (SEQ ID NO:24) and a puromycin resistance gene. The digest was run on a 1% low melting point agarose (Boerhinger Mannheim) gel and the approximately 1.5 kb zcytorl 1 cDNA was isolated using Qiaquick™ gel extraction kit (Qiagen) as per manufacturer's instructions. The purified zcytorl 1 cDNA was inserted into an expression vector as described below. Recipient expression vector pZP7Z was digested with EcoRI (BRL) and Xhol (Boehringer Mannheim) as per manufacturer's instructions, and gel purified as described above. This vector fragment was combined with the EcoRI and Xhol cleaved zcytorl 1 fragment isolated above in a ligation reaction. The ligation was run using T4 Ligase (BRL) at 12°C overnight. A sample of the ligation was electroporated in to DH10B electroMAX™ electrocompetent E. coli cells (25μF, 200Ω, 1.8V). Transformants were plated on LB+Ampicillin plates, and single colonies were picked into 2 ml LB+Ampicillin and grown overnight. Plasmid DNA was isolated using Wizard Minipreps (Promega), and each was digested with ΕcoRI and Xhol to confirm the presence of insert. The insert was approximately 1.5 kb, and was full-length. Digestion with Spel and Pstl was used to confirm the identity of the vector. Example 14 Construction of BaF3 Cells Expressing the CRF2-4 receptor (BaF3/CRF2-4 cells) and BaF3 Cells Expressing the CRF2-4 receptor with the zcytorl 1 receptor (BaF3/CRF2- 4/zcvtorl 1 cells) BaF3 cells expressing the full-length CFR2-4 receptor were constructed, using 30μg of a CFR2-4 expression vector, described below. The BaF3 cells expressing the CFR2-4 receptor were designated as BaF3/CFR2-4. These cells were used as a control, and were further transfected with full-length zcytorl 1 receptor (US Patent No. 5,965,704) and used to construct a screen for EL-TIF activity as described below. A. Construction of BaF3 Cells Expressing the CRF2-4 receptor The full-length cDNA sequence of CRF2-4 (Genbank Accession No. Z17227) was isolated from a Daudi cell line cDNA library, and then cloned into an expression vector pZP7P, as described in Example 6. BaF3, an interleukin-3 (EL-3) dependent pre-lymphoid cell line derived from murine bone maπow (Palacios and Steinmetz, Cell 41: 727-734, 1985; Mathey- Prevot et al., Mol. Cell. Biol. 6: 4133-4135, 1986), was maintained in complete media (RPMI medium (JRH Bioscience Inc., Lenexa, KS) supplemented with 10% heat- inactivated fetal calf serum, 2 ng/ml murine IL-3 (mIL-3) (R & D, Minneapolis, MN), 2 mM L-glutaMax-1™ (Gibco BRL), 1 mM Sodium Pyruvate (Gibco BRL), and PSN antibiotics (GIBCO BRL)). Prior to electroporation, CRF2-4/pZP7P was prepared and purified using a Qiagen Maxi Prep kit (Qiagen) as per manufacturer's instructions. For electroporation, BaF3 cells were washed once in serum-free RPMI media and then resuspended in serum-free RPMI media at a cell density of 10^ cells/ml. One ml of resuspended BaF3 cells was mixed with 30 μg of the CRF2-4/pZP7P plasmid DNA and transfeπed to separate disposable electroporation chambers (GIBCO BRL). Following a 15-minute incubation at room temperature the cells were given two serial shocks (800 lFad/300 V.; 1180 lFad/300 V.) delivered by an electroporation apparatus (CELL- PORATOR™; GIBCO BRL). After a 5-minute recovery time, the electroporated cells were transfeπed to 50 ml of complete media and placed in an incubator for 15-24 hours (37°C, 5% CO2). The cells were then spun down and resuspended in 50 ml of complete media containing 2 μg/ml puromycin in a T-162 flask to isolate the puromycin-resistant pool. Pools of the transfected BaF3 cells, hereinafter called BaF3/CRF2-4 cells, were assayed for signaling capability as described below. Moreover these cells were further transfected with zcytorl 1 receptor as described below. B. Construction of BaF3 Cells Expressing CRF2-4 and zcytorl 1 receptors BaF3/CRF2-4 cells expressing the full-length zcytorl 1 receptor were constructed as per Example 5A above, using 30μg of the zcytorl 1 expression vector, described in Example 6 above. Following recovery, transfectants were selected using 200μg/ml zeocin and 2μg/ml puromycin. The BaF3/CRF2-4 cells expressing the zcytorl 1 receptor were designated as BaF3/CRF2-4/zcytorl 1 cells. These cells were used to screen for IL-TIF activity as well as zcytorlo antagonist activity described EN Example 15. Example 15 Screening for EL-TEF antagonist activity using BaF3/CRF2-4/zcvtorl 1 cells using an Alamar Blue Proliferation Assay A. Screening for EL-TIF activity using BaF3/CRF2-4/zcvtorl 1 cells using an Alamar Blue Proliferation Assay Purified EL-TIF-CEE (Example 19) was used to test for the presence of proliferation activity as described below. Purified zcytorl 6-Fc4 (Example 11) was used to antagonize the proliferative response of the IL-TIF in this assay as described below. BaF3/CRF2-4/zcytorl l cells were spun down and washed in the complete media, described in Example 7A above, but without mIL-3 (hereinafter refeπed to as "mIL-3 free media"). The cells were spun and washed 3 times to ensure the removal of the mIL-3. Cells were then counted in a hemacytometer. Cells were plated in a 96-well format at 5000 cells per well in a volume of 100 μl per well using the mIL-3 free media. Proliferation of the BaF3/CRF2-4/zcytorl 1 cells was assessed using IL- TIF-CEE protein diluted with mIL-3 free media to 50, 10, 2, 1, 0.5, 0.25, 0.13, 0.06 ng/ml concentrations. 100 μl of the diluted protein was added to the BaF3/CRF2- 4/zcytorl 1 cells. The total assay volume is 200 μl. The assay plates were incubated at 37°C, 5% CO for 3 days at which time Alamar Blue (Accumed, Chicago, EL) was added at 20μl/well. Plates were again incubated at 37°C, 5% CO 2 for 24 hours. Alamar Blue gives a fluourometric readout based on number of live cells, and is thus a direct measurement of cell proliferation in comparison to a negative control. Plates were again incubated at 37°C, 5% CO for 24 hours. Plates were read on the Fmax™ plate reader (Molecular Devices Sunnyvale, CA) using the SoftMax™ Pro program, at wavelengths 544 (Excitation) and 590 (Emmission). Results confirmed the dose-dependent proliferative response of the BaF3/CRF2-4/zcytorl 1 cells to EL-TEF-CEE . The response, as measured, was approximately 15-fold over background at the high end of 50ng ml down to a 2-fold induction at the low end of 0.06ng/ml. The BaF3 wild type cells, and BaF3/CRF2-4 cells did not proliferate in response to EL-TEF-CEE , showing that EL-TEF is specific for the CRF2-4/zcytor 11 heterodimeric receptor. In order to determine if zcytorlo is capable of antagonizing IL-TIF activity, the assay described above was repeated using purified soluble zcytorl 6/Fc4. When IL-TIF was combined with zcytorlo at lOμg/ml, the response to IL-TEF at all concentrations was brought down to background. That the presence of soluble zcytorlo ablated the proliferative effects of EL-TEF demonstrates that it is a potent antagonist of the EL-TEF ligand. Example 16 EL-TIF activation of a reporter mini-gene in MES 13 cells and inhibition of activity by zcytorl 6-Fc4 MES 13 cells (ATCC No. CRL-1927) were plated at 10,000 cells/well in 96-well tissue culture clusters (Costar) in DMEM growth medium (Life Technologies) supplemented with pyruvate and 10% serum (HyClone). Next day, the medium was switched to serum free DMEM medium by substituting 0.1% BSA (Fraction V; Sigma) for serum. This medium also contained the adenoviral construct KZ136 (below) that encodes a luciferase reporter mini-gene driven by SRE and STAT elements, at a 1000:1 multiplicity of infection (m.o.i.), i.e. 1000 adenoviral particles per cell. After allowing 24h for the incoφoration of the adenoviral construct in the cells, the media were changed and replaced with serum-free media. Human recombinant IL-TIF with or without a recombinant zcytorl 6-Fc4 fusion was added at the indicated final concentration in the well (as described in Table 11, below). Dilutions of both the IL-TIF and zcytorl 6-Fc4 were performed in serum-free medium. 0.1% BSA was added for a basal assay control. 4h later, cells were lysed and luciferase activity, denoting activation of the reporter gene, was determined in the lysate using an Luciferase Assay System assay kit (Promega) and a Labsystems Luminoskan luminometer (Labsystems, Helsinki, Finland). Activity was expressed as luciferase units (LU) in the lysate. Results are shown in Table 11, below. Table 11 These results demonstrate two things: First, that MES 13 cells respond to human recombinant EL-TEF and therefore possess endogenous functional receptors for the cytokine. Second, that the zcytoR16-Fc4 receptor fusion acts as an antagonist that effectively blocks the response to IL-TIF, even at the highest dose that this cytokine was used. Therefore, zcytolό is an effective antagonist of IL-TEF on cells (MES 13) that are intrinsically capable of responding to IL-TIF, i.e. cells that do not require exogenous expression of additional receptor components to respond to the cytokine. The construction of the adenoviral KZ136 vector was as follows. The original KZ136 vector is disclosed in Poulsen, LK et al. J. Biol. Chem. 273:6228-6232, 1998. The CMV promoter/enhancer and SV40 pA sequences were removed from pACCMV.pLpA (T.C. Becker et al., Meth. Immunology 43:161-189, 1994.) and replaced with a linker containing Asp718/Kpnl and Hindm sites (oligos ZC 13252 (SEQ D NO:26) and ZC 13453 (SEQ ED NO:27)). The STAT/SRE driven luciferase reporter cassette was exised from vector KZ136 (Poulsen, LK et al., supra.).) as a Asp718/Kpnl- HindEEI fragment and inserted into the adapted pAC vector. Recombinant KZ136 Adenovirus was produced by transfection with JM17 Adenovirus into 293 cells as described in T.C. Becker et al. supra.). Plaque purified virus was amplified and used to infect cultured cells at 5-50 pfu/cell 12-48 hours before assay. Luciferase reporter assays were performed as described in 96 well microplates as per Poulsen, LK et al., supra.). Example 17 Construct for Generating CEE-tagged IL-TIF Oligonucleotides were designed to generate a PCR fragment containing the Kozak sequence and the coding region for IL-TIF, without its stop codon. These oligonucleotides were designed with a Kpnl site at the 5' end and a BamHI site at the 3' end to facilitate cloning into pHZ200-CEE, our standard vector for mammalian expression of C-terminal Glu-Glu tagged (SEQ ID NO: 10) proteins. The pHZ200 vector contains an MT-1 promoter. PCR reactions were caπied out using Turbo Pfu polymerase (Stratagene) to amplify a IL-TIF cDNA fragment. About 20 ng human IL-TIF polynucleotide template (SEQ ID NO: 14), and oligonucleotides ZC28590 (SEQ ID NO:28) and ZC28580 (SEQ ID NO:29) were used in the PCR reaction. PCR reaction conditions were as follows: 95°C for 5 minutes,; 30 cycles of 95°C for 60 seconds, 55°C for 60 seconds, and 72°C for 60 seconds; and 72°C for 10 minutes; followed by a 4°C hold. PCR products were separated by agarose gel electrophoresis and purified using a QiaQuick™ (Qiagen) gel extraction kit. The isolated, approximately 600 bp, DNA fragment was digested with Kpnl and BamHI (Boerhinger-Mannheim), gel purified as above and ligated into pHZ200-CEE that was previously digested with Kpnl and BamHI. About one microliter of the ligation reaction was electroporated into DH10B ElectroMax™ competent cells (GIBCO BRL, Gaithersburg, MD) according to manufacturer's direction and plated onto LB plates containing 100 μg/ml ampicillin, and incubated overnight. Colonies were picked and screened by PCR using oligonucleotides ZC28,590 (SEQ ID NO:28) and ZC28,580 (SEQ ID NO:29), with PCR conditions as described above. Clones containing inserts were then sequenced to confirm eπor-free IL-TIF inserts. Maxipreps of the coπect pHZ200-IL-TEF-CEE construct, as verified by sequence analysis, were performed. Example 18 Transfection And Expression Of IL-TIF Soluble Receptor Polypeptides BHK 570 cells (ATCC No. CRL-10314), were plated at about 1.2X10 6 cells/well (6-well plate) in 800 μl of serum free (SF) DMEM media (DMEM, Gibco/BRL High Glucose) (Gibco BRL, Gaithersburg, MD). The cells were transfected with an expression plasmid containing IL-TIF-CEE described above (Example 17), using Lipofectin™ (Gibco BRL), in serum free (SF) DMEM according to manufacturer's instructions. The cells were incubated at 37°C for approximately five hours, then transfeπed to separate 150 mm MAXI plates in a final volume of 30 ml DMEM/5% fetal bovine serum (FBS) (Hyclone, Logan, UT). The plates were incubated at 37°C, 5% CO 2 , overnight and the DNA: Lipofectin™ mixture was replaced with selection media (5% FBS/DMEM with 1 μM methotrexate (MTX)) the next day. Approximately 10-12 days post-transfection, colonies were mechanically picked to 12-well plates in one ml of 5%FCS/DMEM with 5 μM MTX, then grown to confluence. Positive expressing clonal colonies Conditioned media samples were then tested for expression levels via SDS-PAGE and Western analysis. A high-expressing clone was picked and expanded for ample generation of conditioned media for purification of the IL-TIF-CEE expressed by the cells (Example 19). Example 19 Purification of IL-TIF soluble receptors from BHK 570 cells Unless otherwise noted, all operations were carried out at 4°C. The following procedure was used for purifying IL-TIF polypeptide containing C-terminal GluGlu (EE) tags (SEQ ED NO: 10). Conditioned media from BHK cells expressing EL- TEF-CEE (Example 18) was concentrated with an Amicon S10Y3 spiral cartridge on a ProFlux A30. A Protease inhibitor solution was added to the concentrated conditioned media to final concentrations of 2.5 mM ethylenediaminetetraacetic acid (EDTA, Sigma Chemical Co. St. Louis, MO), 0.003 mM leupeptin (Boehringer-Mannheim, Endianapolis, EN), 0.001 mM pepstatin (Boehringer-Mannheim) and 0.4 mM Pefabloc (Boehringer-Mannheim). Samples were removed for analysis and the bulk volume was frozen at -80°C until the purification was started. Total target protein concentrations of the concentrated conditioned media were determined via SDS-PAGE and Western blot analysis with the anti-EE HRP conjugated antibody. About 100 ml column of anti-EE G-Sepharose (prepared as described below) was poured in a Waters AP-5, 5 cm x 10 cm glass column. The column was flow packed and equilibrated on a BioCad Sprint (PerSeptive BioSystems, Framingham, MA) with phosphate buffered saline (PBS) pH 7.4. The concentrated conditioned media was thawed, 0.2 micron sterile filtered, pH adjusted to 7.4, then loaded on the column overnight with about 1 ml/minute flow rate. The column was washed with 10 column volumes (CVs) of phosphate buffered saline (PBS, pH 7.4), then plug eluted with 200 ml of PBS (pH 6.0) containing 0.5 mg/ml EE peptide (Anaspec, San Jose, CA) at 5 ml/minute. The EE peptide used has the sequence EYMPME (SEQ ID NO: 10). The column was washed for 10 CVs with PBS, then eluted with 5 CVs of 0.2M glycine, pH 3.0. The pH of the glycine-eluted column was adjusted to 7.0 with 2 CVs of 5X PBS, then equilibrated in PBS (pH 7.4). Five ml fractions were collected over the entire elution chromatography and absorbance at 280 and 215 nM were monitored; the pass through and wash pools were also saved and analyzed. The EE-polypeptide elution peak fractions were analyzed for the target protein via SDS-PAGE Silver staining and Western Blotting with the anti-EE HRP conjugated antibody. The polypeptide elution fractions of interest were pooled and concentrated from 60 ml to 5.0 ml using a 10,000 Dalton molecular weight cutoff membrane spin concentrator (Millipore, Bedford, MA) according to the manufacturer's instructions. To separate IL-TIF-CEE from other co-purifying proteins, the concentrated polypeptide elution pooled fractions were subjected to a POROS HQ-50 (strong anion exchange resin from PerSeptive BioSystems, Framingham, MA) at pH 8.0. A 1.0 x 6.0 cm column was poured and flow packed on a BioCad Sprint. The column was counter ion charged then equibrated in 20mM TRIS pH 8.0 (Tris (Hydroxymethyl Aminomethane)). The sample was diluted 1:13 (to reduce the ionic strength of PBS) then loaded on the Poros HQ column at 5 ml/minute. The column was washed for 10 CVs with 20mM Tris pH 8.0 then eluted with a 40 CV gradient of 20 mM Tris/ 1 M sodium chloride (NaCl) at 10 ml/minute. 1.5 ml fractions were collected over the entire chromatography and absorbance at 280 and 215 nM were monitored. The elution peak fractions were analyzed via SDS-PAGE Silver staining. Fractions of interest were pooled and concentrated to 1.5-2 ml using a 10,000 Dalton molecular weight cutoff membrane spin concentrator (Millipore, Bedford, MA) according to the manufacturer's instructions. To separate EL-TEF-CEE polypeptide from free EE peptide and any contaminating co-purifying proteins, the pooled concentrated fractions were subjected to size exclusion chromatography on a 1.5 x 90 cm Sephadex S200 (Pharmacia, Piscataway, NJ) column equilibrated and loaded in PBS at a flow rate of 1.0 ml/min using a BioCad Sprint. 1.5 ml fractions were collected across the entire chromatography and the absorbance at 280 and 215 nM were monitored. The peak fractions were characterized via SDS-PAGE Silver staining, and only the most pure fractions were pooled. This material represented purified IL-TIF-CEE polypeptide. This purified material was finally subjected to a 4 ml ActiClean Etox (Sterogene) column to remove any remaining endotoxins. The sample was passed over the PBS equilibrated gravity column four times then the column was washed with a single 3 ml volume of PBS, which was pooled with the "cleaned" sample. The material was then 0.2 micron sterile filtered and stored at -80°C until it was aliquoted. On Western blotted, Coomassie Blue and Silver stained SDS-PAGE gels, the IL-TIF-CEE polypeptide was one major band. The protein concentration of the purified material was performed by BCA analysis (Pierce, Rockford, IL) and the protein was aliquoted, and stored at -80°C according to standard procedures. To prepare anti-EE Sepharose, a 100 ml bed volume of protein G- Sepharose (Pharmacia, Piscataway, NJ) was washed 3 times with 100 ml of PBS containing 0.02% sodium azide using a 500 ml Nalgene 0.45 micron filter unit. The gel was washed with 6.0 volumes of 200 mM triethanolamine, pH 8.2 (TEA, Sigma, St. Louis, MO), and an equal volume of EE antibody solution containing 900 mg of antibody was added. After an overnight incubation at 4°C, unbound antibody was removed by washing the resin with 5 volumes of 200 mM TEA as described above. The resin was resuspended in 2 volumes of TEA, transfeπed to a suitable container, and dimethylpimilimidate-2HCl (Pierce, Rockford, IL) dissolved in TEA, was added to a final concentration of 36 mg/ml of protein G-Sepharose gel. The gel was rocked at room temperature for 45 min and the liquid was removed using the filter unit as described above. Nonspecific sites on the gel were then blocked by incubating for 10 min. at room temperature with 5 volumes of 20 mM ethanolamine in 200 mM TEA. The gel was then washed with 5 volumes of PBS containing 0.02% sodium azide and stored in this solution at 4°C. Example 20 Human zcytorl 1 Tissue Distribution in Tissue Panels Using Northern Blot and PCR A. Human zcytorl 1 Tissue Distribution in tissue panels using PCR A panel of cDNAs from human tissues was screened for zcytorl 1 expression using PCR. The panel was made in-house and contained 94 marathon cDNA and cDNA samples from various normal and cancerous human tissues and cell lines are shown in Table 6 above. Aside from the PCR reaction , the method used was as shown in Example 12. The PCR reactions were set up using oligos ZC 14,666 (SEQ ED NO: 32) and ZC14,742 (SEQ ED NO:33), Advantage 2 cDNA polymerase mix (Clontech, Palo Alto, CA), and Rediload dye (Research Genetics, Inc., Huntsville, AL). The amplification was caπied out as follows: 1 cycle at 94°C for 2 minutes, 40 cycles of 94°C for 15 seconds, 51°C for 30 seconds and 72°C for 30 seconds, followed by 1 cycle at 72°C for 7 minutes. The coπect predicted DNA fragment size was observed in bladder, brain, cervix, colon, fetal brain, fetal heart, fetal kidney, fetal liver, fetal lung, fetal skin, heart, kidney, liver, lung, melanoma, ovary, pancreas, placenta, prostate, rectum, salivary gland, small intestine, testis, thymus, trachea, spinal cord, thyroid, lung tumor, ovarian tumor, rectal tumor, and stomach tumor. Zcytorl 1 expression was not observed in the other tissues and cell lines tested in this panel. A commercial 1st strand cDNA panel (Human Blood Fractions MTC Panel, Clontech, Palo Alto, CA) was also assayed as above. The panel contained the following samples: mononuclear cells, activated mononuclear cells, resting CD4+ cells, activated CD4+ cells, resting CD8+ cells, activated CD8+ cells, resting CD14+ cells, resting CD 19+ cells and activated CD 19+ cells. All samples except activated CD8+ and Activated CD19+ showed expression of zcytorl 1. B. Tissue Distribution of Zcytorl 1 in Human Cell Line and Tissue Panels Using RT-PCR A panel of RNAs from human cell lines was screened for zcytorl 1 expression using RT-PCR. The panels were made in house and contained 84 RNAs from various normal and cancerous human tissues and cell lines as shown in Tables 7-10 above. The RNAs were made from in house or purchased tissues and cell lines using the RNAeasy Midi or Mini Kit (Qiagen, Valencia, CA). The panel was set up in a 96-well format with 100 ngs of RNA per sample. The RT-PCR reactions were set up using oligos ZC14,666 (SEQ ID NO:32) and ZC14.742 (SEQ ID NO:33), Rediload dye and SUPERSCRIPT One Step RT-PCR System(Life Technologies, Gaithersburg, MD). The amplification was carried out as follows: one cycle at 50° for 30 minutes followed by 45 cycles of 94°, 15 seconds; 52°, 30 seconds; 72°, 30 seconds; then ended with a final extension at 72° for 7 minutes. 8 to 10 uls of the PCR reaction product was subjected to standard Agarose gel electrophoresis using a 4% agarose gel. The coπect predicted cDNA fragment size was observed in adrenal gland, bladder, breast, bronchus, normal colon, colon cancer, duodenum, endometrium, esophagus, gastic cancer, gastro- esophageal cancer, heart ventricle, ileum, normal kidney, kidney cancer, liver, lung, lymph node, pancreas, parotid, skin, small bowel, stomach, thyroid, and uterus. Cell lines showing expression of zcytorl 1 were A-431, differentiated CaCO2, DLD-1, HBL-100, HCT-15, HepG2, HepG2+IL6, HuH7, and NHEK #1-4. Zcytorl 1 expression was not observed in the other tissues and cell lines tested in this panel. In addition, because the expression pattern of zcytorl 1, one of EL-TEF's receptors, shows expression in certain specific tissues, binding partners including the natural ligand, EL-TEF, can also be used as a diagnostic to detect specific tissues (normal or abnormal), cancer, or cancer tissue in a biopsy, tissue, or histologic sample, particularly in tissues where IL-TIF receptors are expressed. IL-TIF can also be used to target other tissues wherein its receptors, e.g., zcytorlo and zcytorl 1 are expressed. Moreover, such binding partners could be conjugated to chemotherapeutic agents, toxic moieties and the like to target therapy to the site of a tumor or diseased tissue. Such diagnostic and targeted therapy uses are known in the art and described herein. The expression patterns of zcytorl 1 (above) and zcytorlo (Example 12, and Example 21) indicated target tissues and cell types for the action of IL-TIF, and hence EL-TEF antagonsists, such as zcytorlo. The zcytorl 1 expression generally overlapped with zcytorlo expression in three physiologic systems: digestive system, female reproductive system, and immune system. Moreover, the expression pattern of the receptor (zcytorl 1) indicated that an IL-TIF antagonist such as zcytorlo would have therapeutic application for human disease in two areas: inflammation (e.g., IBD, Chron's disease, pancreatitis) and cancer (e.g., ovary, colon). That is, the polynucleotides, polypeptides and antibodies of the present invention can be used to antagonize the inflammatory, and other cytokine-induced effects of IL-TIF interaction with the cells expressing the zcytorl 1 receptor. Moreover, the expression of zcytorl 1 appeared to be downregulated or absent in an ulcerative colitis tissue, HepG2 liver cell line induced by IL-6, activated CD8+ T-cells and CD 19+ B-cells. However, zcytorlo appeared to be upregulated in activated CD19+ B-cells (Example 12), while zcytorl 1 is downregulated in activated CD 19+ cells, as compared to the resting CD 19+ cells (above). The expression of zcytorl 1 and zcytorlo has a reciprocal correlation in this case. These RT-PCR experiments demonstrate that CD 19+ peripheral blood cells, B lymphocytes, express receptors for IL-TIF, namely zcytoRl l and zcytoRlό. Furthermore B cells display regulated expression of zcytoRl l and zcytoRlό. B-lymphocytes activated with mitogens decrease expression of zcytoRl 1 and increase expression of zcytoRlό. This represents a classical feedback inhibition that would serve to dampen the activity of IL-TEF on B cells and other cells as well. Soluble zcytoRlό would act as an antagonist to neutralize the effects of IL-TIF on B cells. This would be beneficial in diseases where B cells are the key players: Autoimmune diseases including systemic lupus erythmatosus (SLE), myasthenia gravis, immune complex disease, and B-cell cancers that are exacerbated by IL-TIF. Also autoimmune diseases where B cells contribute to the disease pathology would be targets for zcytoRlό therapy: Multiple sclerosis, inflammatory bowel disease (IBD) and rheumatoid arthritis are examples. ZcytoRlό therapy would be beneficial to dampen or inhibit B cells producing IgE in atopic diseases including asthma, allergy and atopic dermatitis where the production of IgE contributes to the pathogenesis of disease. B cell malignancies may exhibit a loss of the "feedback inhibition" described above. Administration of zcytoRlό would restore control of IL-TEF signaling and inhibit B cell tumor growth. The administration of zcytoRlό following surgical resection or chemotherapy may be useful to treat minimal residual disease in patients with B cell malignancies. The loss of regulation may lead to sustain or increased expression of zcytoRl l. Thus creating a target for therapeutic monoclonal antibodies targeting zcytoRl 1. Example 21 Identification of cells expressing zcytorlo using in situ hybridization Specific human tissues were isolated and screened for zcytorlo expression by in situ hybridization. Various human tissues prepared, sectioned and subjected to in situ hybridization included cartilage, colon, appendix, intestine, fetal liver, lung, lymph node, lymphoma, ovary, pancreas, placenta, prostate, skin, spleen, and thymus. The tissues were fixed in 10% buffered formalin and blocked in paraffin using standard techniques. Tissues were sectioned at 4 to 8 microns. Tissues were prepared using a standard protocol ("Development of non-isotopic in situ hybridization" at The Laboratory of Experimental Pathology (LEP), NIEHS, Research Triangle Park, NC; web address http://dir.niehs.nih.gov/dirlep/ish.html). Briefly, tissue sections were deparaffinized with HistoClear (National Diagnostics, Atlanta, GA) and then dehydrated with ethanol. Next they were digested with Proteinase K (50 μg/ml) (Boehringer Diagnostics, Indianapolis, EN) at 37°C for 2 to 7 minutes. This step was followed by acetylation and re-hydration of the tissues. One in situ probe was designed against the human zcytorlo sequence (nucleotide 1-693 of SEQ ID NO:l), and isolated from a plasmid containing SEQ ED NO:l using standard methods. T3 RNA polymerase was used to generate an antisense probe. The probe was labeled with digoxigenin (Boehringer) using an In Vitro transcription System (Promega, Madison, WE) as per manufacturer's instruction. In situ hybridization was performed with a digoxigenin-labeled zcytorlo probe (above). The probe was added to the slides at a concentration of 1 to 5 pmol/ml for 12 to 16 hours at 62.5°C. Slides were subsequently washed in 2XSSC and 0.1XSSC at 55°C. The signals were amplified using tyramide signal amplification (TSA) (TSA, in situ indirect kit; NEN) and visualized with Vector Red substrate kit (Vector Lab) as per manufacturer's instructions. The slides were then counter-stained with hematoxylin (Vector Laboratories, Burlingame, CA). Signals were observed in several tissues tested: The lymph node, plasma cells and other mononuclear cells in peripheral tissues were strongly positive. Most cells in the lymphatic nodule were negative. In lymphoma samples, positive signals were seen in the mitotic and multinuclear cells. In spleen, positive signals were seen in scattered mononuclear cells at the periphery of follicles were positive. In thymus, positive signals were seen in scattered mononuclear cells in both cortex and medulla were positive. In fetal liver, a strong signal was observed in a mixed population of mononuclear cells in sinusoid spaces. A subset of hepatocytes might also have been positive. In the inflamed appendix, mononuclear cells in peyer's patch and infiltration sites were positive. In intestine, some plasma cells and ganglia nerve cells were positive. In normal lung, zcytorlo was expressed in alveolar epithelium and mononuclear cells in interstitial tissue and circulation. In the lung carcinoma tissue, a strong signal was observed in mostly plasma cells and some other mononuclear cells in peripheral of lymphatic aggregates. In ovary carcinoma, epithelium cells were strongly positive. Some interstitial cells, most likely the mononuclear cells, were also positive. There was no signal observed in the normal ovary. En both normal and pancreatitis pancreas samples, acinar cells and some mononuclear cells in the mesentery were positive. En the early term (8 weeks) placenta, signal was observed in trophoblasts. In skin, some mononuclear cells in the inflamed infiltrates in the superficial dermis were positive. Keratinocytes were also weakly positive. In prostate carcinoma, scatted mononuclear cells in interstitial tissues were positive. In articular cartilage, chondrocytes were positive. Other tissues tested including normal ovary and a colon adenocarcinoma were negative. In summary, the in situ data was consistent with expression data described above for the zcytorlo. Zcytorlo expression was observed predominately in mononuclear cells, and a subset of epithelium was also positive. These results confirmed the presence of zcytorlo expression in immune cells and point toward a role in inflammation, autoimmune disease, or other immune function, for example, in binding pro-inflammatory cytokines, including but not limited to IL-TIF. Moreover, detection of zcytorlo expression can be used for example as an marker for mononuclear cells in histologic samples. Zcytorlo is expressed in mononuclear cells, including normal tissues (lymph nodes, spleen, thymus, pancreas and fetal liver, lung), and abnormal tissues (inflamed appendix, lung carcinoma, ovary carcinoma, pancreatitis, inflamed skin, and prostate carcinoma). It is notable that plasma cells in the lymph node, intestine, and lung carcinoma are positive for zcytorlo. Plasma cells are immunologically activated lymphocytes responsible for antibody synthesis. In addition, IL-TIF, is expressed in activated T cells. In addition, the expression of zcytorlo is detected only in activated (but not in resting) CD4+ and CD 19+ cells (Example 12). Thus, zcytorlo can be used as a marker for or as a target in isolating certain lymphocytes, such as mononuclear leucocytes and limited type of activated leucocytes, such as activated CD4+ and CD 19+. Furthermore, the presence of zcytorlo expression in activated immune cells such as activated CD4+ and CD19+ cells showed that zcytorlo may be involved in the body's immune defensive reactions against foreign invaders: such as microorganisms and cell debris, and could play a role in immune responses during inflammation and cancer formation. Moreover, as discussed herein, epithelium form several tissues was positive for zcytorlo expression, such as hepatocytes (endoderm-derived epithelia), lung alveolar epithelium (endoderm-derived epithelia), and ovary carcinoma epithelium (mesoderm-derived epithelium). The epithelium expression of zcytorlo could be altered in inflammatory responses and/or cancerous states in liver and lung. Thus, Zcytolό could be used as marker to monitor changes in these tissues as a result of inflammation or cancer. Moreover, analysis of zcytorlo in situ expression showed that normal ovary epithelium is negative for zcytorlo expression, while it is strongly positive in ovary carcinoma epithelium providing further evidence that zcytorlo polynucleotides, polypeptides and antibodies can be used as a diagnostic marker and/or therapeutic target for the diagnosis and treatment of ovarian cancers, and ovary carcinoma, as described herein. Zcytorlo was also detected in other tissues, such as acinar cells in pancreas (normal and pancreatitis tissues), trophoblasts in placenta (ectoderm-derived), chondrocytes in cartilage (mesoderm-derived), and ganglia cells in intestine (ectoderm- derived). As such, zcytorlo may be involved in differentiation and/or normal functions of coπesponding cells in these organs. As such, potential utilities of zcytorlo include maintenance of normal metabolism and pregnancy, bone formation/homeostasis, and physiological function of intestine, and the like. Example 22 In vivo affects of IL-TIF polypeptide Mice (female, C57B1, 8 weeks old; Charles River Labs, Kingston, NY) were divided into three groups. An adenovirus expressing an IL-TIF polypeptide (# SEQ ID NO: 15) was previously made using standard methods. On day 0, parental or IL-TIF adenovirus was administered to the first (n=8) and second (n=8) groups, respectively, via the tail vein, with each mouse receiving a dose of ~1 x 10 particles in -0.1 ml volume. The third group (n=8) received no treatment. On days 12, mice were weighed and blood was drawn from the mice. Samples were analyzed for complete blood count (CBC) and serum chemistry. Statistically significant elevations in neutrophil and platelet counts were detected in the blood samples from the IL-TIF adenovirus administered group relative to the parental adenovirus treated group. Also, lymphocyte and red blood cell counts were significantly reduced from the EL-TEF adenovirus administered group relative to the parental adenovirus treated group. In addition, the EL-TEF adenovirus treated mice decreased in body weight, while parental adenovirus treated mice gained weight. The results suggested that IL-TIF affects hematopoiesis, i.e., blood cell formation in vivo. As such, EL-TEF could have biological activities effecting different blood stem cells, thus resulting increase or decrease of certain differentiated blood cells in a specific lineage. For instance, EL-TEF appears to reduce lymphocytes, which is likely due to inhibition of the committed progenitor cells that give rise to lymphoid cells. EL- TEF also decreases red blood cells. This finding agrees with the inhibitory effects of EL- TEF on the proliferation and/or growth of myeloid stem cells (Example 23), supporting the notion that EL-TEF could play a role in anemia, infection, inflammation, and/or immune diseases by influencing blood cells involved in these process. Antagnists against EL-TEF, such as antibodies or its soluble receptor zcytorlo, could be used as therapeutic reagents in these diseases. Moreover, these experiments using EL-TEF adenovirus in mice suggest that IL-TIF over-expression increases the level of neutrophils and platelets in vivo. Although this may appear contradictory to the finding seen in K562 cells (Example 23), it is not uncommon to observe diverse activities of a particular protein in vitro versus in vivo. It is conceivable that there are other factors (such as cytokines and modifier genes) involved in the responses to IL-TEF in the whole animal system. Nevertheless, these data strongly support the involvement of IL-TIF in hematopoiesis. Thus, EL-TEF and its receptors are suitable reagents/targets for the diagnosis and treatment in variety of disorders, such as inflammation, immune disorders, infection, anemia, hematopoietic and other cancers, and the like. Example 23 The EL-TEF polypeptide lyses K-562 cells in cytotoxicity assay The K-562 cell line (CRL-243, ATCC) has attained widespread use as a highly sensitive in vitro target for cytotoxicity assays. K-562 blasts are multipotential, hematopoietic malignant cells that spontaneously differentiate into recognizable progenitors of the erythrocytic, granulocytic and monocytic series (Lozzio, BB et al., Proc. Soc. Exp. Biol. Med. 166: 546-550, 1981). K562 cells were plated at 5,000 cells/well in 96-well tissue culture clusters (Costar) in DMEM phenol-free growth medium (Life Technologies) supplemented with pyruvate and 10% serum (HyClone). Next day, human recombinant IL-TIF (Example 19), BSA control or retinoic acid (known to be cytotoxic to K562 cells) were added. Seventy-two hours later, the vital stain MTT (Sigma, St Louis, MO), a widely used indicator of mitochondrial activity and cell growth, was added to the cells at a final concentration of 0.5 mg/ml. MMP is converted to a puφle formazan derivative by mitochondrial dehydrogenases. Four hours later, converted MMP was solubilized by adding an equal volume of acidic isopropanol (0.04N HCl in absolute isopropanol) to the wells. Absorbance was measured at 570nm, with background subtraction at 650nm. In this experimental setting, absorbance reflects cell viability. Results shown in Table 12 are expressed as % cytotoxicity. Table 12 The results indicate that EL-TIF may affect myeloid stem cells. Myeloid stem cells are daughter cells of the universal blood stem cells. They are progenitors of erythrocytes, platelets megakaryocytes, monocytes (or migrated macrophages), neutrophil and basophil, etc. Since K-562 blasts spontaneously differentiate into progenitors of the erythrocytic, granulocytic and monocytic series, it can be considered as myeloid stem cells. Thus, the results demonstrate that IL-TIF has an inhibitory activity on the proliferation and/or growth of myeloid stem cells. Thus IL-TIF could play a role in anemia, infection, inflammation, and/or immune diseases. In addition, an antaganist against IL-TIF, such as antibodies or its soluble receptor zcytorlo, could be used to block EL-TEF's activity on myeloid stem cells, or as therapeutic reagents in diseases such as anemia, infection, inflammation, and/or immune diseases. From the foregoing, it will be appreciated that, although specific embodiments of the invention have been described herein for puφoses of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.

Claims: CLAIMS I claim: 1. An isolated polypeptide, comprising at least 15 contiguous amino acid residues of an amino acid sequence of SEQ ID NO:2 selected from the group of: (a) amino acid residues amino acid residues 21 to 231, (b) amino acid residues 21 to 210, (c) amino acid residues 22 to 231, (d) amino acid residues 22 to 210, (e) amino acid residues 22 to 108, (f) amino acid residues 112 to 210, and (g) amino acid residues 21 to 110. 2. The isolated polypeptide of claim 1, wherein the polypeptide comprises an amino acid sequence selected from the group of: (a) amino acid residues amino acid residues 21 to 231, (b) amino acid residues 21 to 210, (c) amino acid residues 22 to 231, (d) amino acid residues 22 to 210, (e) amino acid residues 22 to 108, (f) amino acid residues 112 to 210, and (g) amino acid residues 21 to 110. 3. The isolated polypeptide of claim 1, wherein the polypeptide consists of an amino acid sequence selected from the group of: (a) amino acid residues amino acid residues 21 to 231, (b) amino acid residues 21 to 210, (c) amino acid residues 22 to 231, (d) amino acid residues 22 to 210, (e) amino acid residues 22 to 108, (f) amino acid residues 112 to 210, and (g) amino acid residues 21 to 110. 4. An isolated polypeptide, comprising an amino acid sequence that is at least 70% identical to a reference amino acid sequence of SEQ ID NO:2 selected from the group of: (a) amino acid residues amino acid residues 21 to 231, (b) amino acid residues 21 to 210, (c) amino acid residues 22 to 231, (d) amino acid residues 22 to 210, (e) amino acid residues 22 to 108, (0 amino acid residues 112 to 210, and (g) amino acid residues 21 to 110. 5. The isolated polypeptide of claim 4, wherein the isolated polypeptide has an amino acid sequence that is at least 80% identical to the reference amino acid sequence. 6. The isolated polypeptide of claim 4, wherein the isolated polypeptide has an amino acid sequence that is at least 90% identical to the reference amino acid sequence. 7. The isolated polypeptide of claim 4, wherein the isolated polypeptide comprises either amino acid residues 22 to 231 of SEQ ID NO:2 or amino acid residues 22 to 210 of SEQ ED NO:2. 8. An isolated nucleic acid molecule, wherein the nucleic acid molecule is either (a) a nucleic acid molecule comprising the nucleotide sequence of SEQ ED NO: 3, or (b) a nucleic acid molecule that remains hybridized following stringent wash conditions to a nucleic acid molecule consisting of the nucleotide sequence of nucleotides 64 to 630 of SEQ ED NO:l, or the complement of the nucleotide sequence of nucleotides 64 to 630 of SEQ ED NO:l. 9. The isolated nucleic acid molecule of claim 8, wherein any difference between the amino acid sequence encoded by the nucleic acid molecule and the corresponding amino acid sequence of SEQ ID NO:2 is due to a conservative amino acid substitution. 10. The isolated nucleic acid molecule of claim 8, comprising the nucleotide sequence of nucleotides 64 to 630 of SEQ ID NO: 1. 11. A vector, comprising the isolated nucleic acid molecule of claim 10. 12. An expression vector, comprising the isolated nucleic acid molecule of claim 10, a transcription promoter, and a transcription terminator, wherein the promoter is operably linked with the nucleic acid molecule, and wherein the nucleic acid molecule is operably linked with the transcription terminator. 13. A recombinant host cell comprising the expression vector of claim 12, wherein the host cell is selected from the group of bacterium, yeast cell, fungal cell, insect cell, mammalian cell, and plant cell. 14. A method of producing a protein, the method comprising culturing recombinant host cells that comprise the expression vector of claim 12, and that produce the protein. 15. The method of claim 14, further comprising isolating the protein from the cultured recombinant host cells. 16. An antibody or antibody fragment that specifically binds with the polypeptide of claim 3. 17. The antibody of claim 16, wherein the antibody is selected from the group of: (a) polyclonal antibody, (b) murine monoclonal antibody, (c) humanized antibody derived from (b), and (d) human monoclonal antibody. 18. An anti-idiotype antibody that specifically binds with the antibody of claim 16. 19. A fusion protein, comprising the polypeptide of claim 3. 20. The fusion protein of claim 19, wherein the fusion protein further comprises an immunoglobulin moiety. 21. An isolated polynucleotide that encodes a soluble cytokine receptor polypeptide comprising a sequence of amino acid residues that is at least 90% identical to the amino acid sequence as shown in SEQ ID NO:2 from amino acid 22-231 or 22-210, and wherein the soluble cytokine receptor polypeptide encoded by the polynucleotide sequence binds IL-TEF or antagonizes IL-TEF activity. 22. An isolated polynucleotide according to claim 21, wherein the soluble cytokine receptor polypeptide encoded by the polynucleotide forms a homodimeric, heterodimeric or multimeric receptor complex. 23. An Isolated polynucleotide according to 22, wherein the soluble cytokine receptor polypeptide encoded by the polynucleotide forms a heterodimeric or multimeric receptor complex further comprising a soluble Class I or Class II cytokine receptor. 24. An isolated polynucleotide according to claim 22, wherein the soluble cytokine receptor polypeptide encoded by the polynucleotide forms a heterodimeric or multimeric receptor complex further comprising a soluble CRF2-4 receptor polypeptide (SEQ ED NO:35), a soluble EL-10 receptor polypeptide (SEQ ED NO:36), or soluble zcytorl 1 receptor polypeptide (SEQ D NO:34). 25. An isolated polynucleotide that encodes a soluble cytokine receptor polypeptide comprising a sequence of amino acid residues as shown in SEQ ID NO: 2 from amino acid 22-231 or 22-210, wherein the soluble cytokine receptor polypeptide encoded by the polynucleotide forms a homodimeric, heterodimeric or multimeric receptor complex. 26. An Isolated polynucleotide according to claim 25, wherein the soluble cytokine receptor polypeptide encoded by the polynucleotide further comprises a soluble Class I or Class II cytokine receptor. 27. An isolated polynucleotide according to claim 25, wherein the soluble cytokine receptor polypeptide encoded by the polynucleotide forms a heterodimeric or multimeric receptor complex further comprising a soluble CRF2-4 receptor polypeptide (SEQ ED NO:35), a soluble EL-10 receptor polypeptide (SEQ ID NO:36), or soluble zcytorl 1 receptor polypeptide (SEQ ID NO: 34). 28. An isolated polynucleotide according to claim 25, wherein the soluble cytokine receptor polypeptide further encodes an intracellular domain. 29. An isolated polynucleotide according to claim 25, wherein the soluble cytokine receptor polypeptide further comprises an affinity tag. 30. An expression vector comprising the following operably linked elements: (a) a transcription promoter; a first DNA segment encoding a soluble cytokine receptor polypeptide having an amino acid sequence as shown in SEQ ED NO:2 from amino acid 22-231 or 22-210; and a transcription terminator; and (b) a second transcription promoter; a second DNA segment encoding a soluble Class I or Class II cytokine receptor polypeptide; and a transcription terminator; and wherein the first and second DNA segments are contained within a single expression vector or are contained within independent expression vectors. 31. An expression vector according to claim 30, further comprising a secretory signal sequence operably linked to the first and second DNA segments. 32. An expression vector according to claim 30, wherein the second DNA segment encodes a polypeptide comprising a soluble CRF2-4 receptor polypeptide (SEQ DD NO:35), a soluble IL-10 receptor polypeptide (SEQ ID NO:36), or soluble zcytorl 1 receptor polypeptide (SEQ ID NO:34). 33. A cultured cell comprising an expression vector according to claim 30, wherein the cell expresses the polypeptides encoded by the DNA segments. 34. A cultured cell comprising an expression vector according to claim 30, wherein the first and second DNA segments are located on independent expression vectors and are co-transfected into the cell, and cell expresses the polypeptides encoded by the DNA segments. 35. A cultured cell into which has been introduced an expression vector according to claim 30, wherein the cell expresses a heterodimeric or multimeric soluble receptor polypeptide encoded by the DNA segments. 36. A cell according to claim 33, wherein the cell secretes a soluble cytokine receptor polypeptide heterodimer or multimeric complex. 37. A cell according to claim 33, wherein the cell secretes a soluble cytokine receptor polypeptide heterodimer or multimeric complex that binds IL-TIF or antagonizes IL- TIF activity. 38. A DNA construct encoding a fusion protein comprising: a first DNA segment encoding a polypeptide having a sequence of amino acid residues as shown in SEQ ID NO:2 from amino acid 22-231 or 22-210; and at least one other DNA segment encoding a soluble Class I or Class II cytokine receptor polypeptide, wherein the first and other DNA segments are connected in-frame; and wherein the first and other DNA segments encode the fusion protein. 39. A DNA construct encoding a fusion protein according to claim 38, wherein at least one other DNA segment encodes a polypeptide comprising a soluble CRF2-4 receptor polypeptide (SEQ ID NO:35), a soluble EL-10 receptor polypeptide (SEQ ID NO:36), or soluble zcytorl 1 receptor polypeptide (SEQ DD NO:34). 40. An expression vector comprising the following operably linked elements: a transcription promoter; a DNA construct encoding a fusion protein according to claim 38; and a transcription terminator, wherein the promoter is operably linked to the DNA construct, and the DNA construct is operably linked to the transcription terminator. 41. A cultured cell comprising an expression vector according to claim 40, wherein the cell expresses a polypeptide encoded by the DNA construct. 42. A method of producing a fusion protein comprising: culturing a cell according to claim 23; and isolating the polypeptide produced by the cell. 43. An isolated soluble cytokine receptor polypeptide comprising a sequence of amino acid residues that is at least 90% identical to an amino acid sequence as shown in SEQ ID NO:2 from amino acid 22-231 or 22-210, and wherein the soluble cytokine receptor polypeptide binds IL-TIF or antagonizes IL-TIF activity. 44. An isolated polypeptide according to claim 43, wherein the soluble cytokine receptor polypeptide forms a homodimeric, heterodimeric or multimeric receptor complex. 45. An isolated polypeptide according to claim 44, wherein the soluble cytokine receptor polypeptide forms a heterodimeric or multimeric receptor complex further comprising a soluble Class I or Class II cytokine receptor. 46. An isolated polypeptide according to claim 44, wherein the soluble cytokine receptor polypeptide forms a heterodimeric or multimeric receptor complex further comprising a soluble CRF2-4 receptor polypeptide (SEQ ID NO:35), a soluble IL-10 receptor polypeptide (SEQ ID NO:36), or soluble zcytorl 1 receptor polypeptide (SEQ ID NO:34). 47. An isolated soluble cytokine receptor polypeptide comprising a sequence of amino acid residues as shown in SEQ ED NO:2 from amino acid 22-231 or 22- 210, wherein the soluble cytokine receptor polypeptide forms a homodimeric, heterodimeric or multimeric receptor complex. 48. An isolated polypeptide according to claim 47, wherein the soluble cytokine receptor polypeptide forms a heterodimeric or multimeric receptor complex further comprising a soluble Class I or Class H cytokine receptor. 49. An isolated polypeptide according to claim 47, wherein the soluble cytokine receptor polypeptide forms a heterodimeric or multimeric receptor complex comprising a soluble CRF2-4 receptor polypeptide (SEQ ED NO:35), a soluble EL-10 receptor polypeptide (SEQ ID NO:36), or soluble zcytorl 1 receptor polypeptide (SEQ ID NO:34). 50. An isolated polypeptide according to claim 47, wherein the soluble cytokine receptor polypeptide further comprises an affinity tag, chemical moiety, toxin, or label. 51. An isolated heterodimeric or multimeric soluble receptor complex comprising soluble receptor subunits, wherein at least one of the soluble receptor subunits comprises a soluble cytokine receptor polypeptide comprising a sequence of amino acid residues as shown in SEQ ID NO:2 from amino acid 22-231 or 22-210. 52. An isolated heterodimeric or multimeric soluble receptor complex according to claim 51, further comprising a soluble Class I or Class H cytokine receptor polypeptide. 53. An isolated heterodimeric or multimeric soluble receptor complex according to claim 51, further comprising a soluble CRF2-4 receptor polypeptide (SEQ ED NO:35), a soluble EL-10 receptor polypeptide (SEQ ED NO:36), or soluble zcytorl 1 receptor polypeptide (SEQ DD NO:34). 54. A method of producing a soluble cytokine receptor polypeptide that form a heterodimeric or multimeric complex comprising: culturing a cell according to claim 33; and isolating the soluble receptor polypeptides produced by the cell. 55. A method of producing an antibody to soluble cytokine receptor polypeptide comprising: inoculating an animal with a soluble cytokine receptor polypeptide selected from the group of: (a) a polypeptide comprising a monomeric or homodimeric soluble cytokine receptor comprising a polypeptide as shown in SEQ ID NO: 2 from amino acid 22- 231 or 22-210; (b) a polypeptide of (a) further comprising a soluble cytokine receptor heterodimeric or multimeric receptor complex comprising a soluble Class I or Class II cytokine receptor polypeptide; (c) a polypeptide of (a) further comprising a soluble cytokine receptor heterodimeric or multimeric receptor complex comprising a soluble CRF2-4 receptor polypeptide (SEQ ED NO:35); (d) a polypeptide of (a) further comprising a soluble cytokine receptor heterodimeric or multimeric receptor complex comprising a soluble IL-10 receptor polypeptide (SEQ ED NO: 36); and wherein the polypeptide elicits an immune response in the animal to produce the antibody; and isolating the antibody from the animal. 56. An antibody produced by the method of claim 55, which specifically binds to a homodimeric, heterodimeric or multimeric receptor complex comprising a polypeptide as shown in SEQ DD NO:2 from amino acid 22-231 or 22-210. 57. The antibody of claim 56, wherein the antibody is a monoclonal antibody. 58. An antibody which specifically binds to a homodimeric, heterodimeric or multimeric receptor complex according to claim 51. 59. A method for inhibiting IL-TIF-induced proliferation or differentiation of hematopoietic cells and hematopoietic cell progenitors comprising culturing bone maπow or peripheral blood cells with a composition comprising an amount of soluble cytokine receptor polypeptide as shown in SEQ DD NO:2 from amino acid 22-231 or 22-210, sufficient to reduce proliferation or differentiation of the hematopoietic cells in the bone maπow or peripheral blood cells as compared to bone marrow or peripheral blood cells cultured in the absence of soluble cytokine receptor. 60. The method of claim 59, wherein the hematopoietic cells and hematopoietic progenitor cells are lymphoid cells. 61. The method of claim 60, wherein the lymphoid cells are macrophages or T cells. 62. A method of reducing IL-TIF-induced or IL-9 induced inflammation comprising administering to a mammal with inflammation an amount of a composition of a polypeptide as shown in SEQ DD NO:2 from amino acid 22-231 or 22-210 sufficient to reduce inflammation. 63. A method of suppressing an inflammatory response in a mammal with inflammation comprising: (1) determining a level of serum amyloid A protein; (2) administering a composition comprising a soluble cytokine receptor polypeptide according to claim 43 in an acceptable pharmaceutical vehicle; (3) determining a post administration level of serum amyloid A protein; (4) comparing the level of serum amyloid A protein in step (1) to the level of serum amyloid A protein in step (3), wherein a lack of increase or a decrease in serum amyloid A protein level is indicative of suppressing an inflammatory response. 64. A method for detecting a genetic abnormality in a patient, comprising: obtaining a genetic sample from a patient; producing a first reaction product by incubating the genetic sample with a polynucleotide comprising at least 14 contiguous nucleotides of SEQ DD NO:l or the complement of SEQ ED NO:l, under conditions wherein said polynucleotide will hybridize to complementary polynucleotide sequence; visualizing the first reaction product; and comparing said first reaction product to a control reaction product from a wild type patient, wherein a difference between said first reaction product and said control reaction product is indicative of a genetic abnormality in the patient. 65. A method for detecting a cancer in a patient, comprising: obtaining a tissue or biological sample from a patient; incubating the tissue or biological sample with an antibody of claim 16 under conditions wherein the antibody binds to its complementary polypeptide in the tissue or biological sample; visualizing the antibody bound in the tissue or biological sample; and comparing levels of antibody bound in the tissue or biological sample from the patient to a normal control tissue or biological sample, wherein an increase in the level of antibody bound to the patient tissue or biological sample relative to the normal control tissue or biological sample is indicative of a cancer in the patient. 66. A method for detecting a cancer in a patient, comprising: obtaining a tissue or biological sample from a patient; labeling a polynucleotide comprising at least 14 contiguous nucleotides of SEQ DD NO: 1 or the complement of SEQ DD NO: 1 ; incubating the tissue or biological sample with under conditions wherein the polynucleotide will hybridize to complementary polynucleotide sequence; visualizing the labeled polynucleotide in the tissue or biological sample; and comparing the level of labeled polynucleotide hybridization in the tissue or biological sample from the patient to a normal control tissue or biological sample, wherein an increase in the labeled polynucleotide hybridization to the patient tissue or biological sample relative to the normal control tissue or biological sample is indicative of a cancer in the patient.

Inventors: CHEN ZHI, KINDSVOGEL WAYNE, PRESNELL SCOTT R, XU WENFENG, CHEN, ZHI, KINDSVOGEL, WAYNE, PRESNELL, SCOTT, R., XU, WENFENG
Applicants: ZYMOGENETICS INC, ZYMOGENETICS, INC.
Application year: 2000
Main classification: C12N15
IPC codes: A61K38, A61P29, C07K14, C07K16, C07K19, C12N1, C12N5, C12N15, C12P21, C12Q1