CADHERIN-LIKE ASYMMETRY PROTEIN-1, AND METHODS FOR ITS USE

Abstract: The present invention relates to molecules involved in cell-cell interactions in the immune system. In particular, the invention relates to a cell surface protein which contains certain classical cadherin characteristics, but it exhibits an apical distribution pattern on the surface of lymphocytes. The membrane location of this molecule correlates with the contact interface between T and B cells, and antibodies against an extracellular domain of this protein disrupt T cell/B cell interactions.

Description: CADHERIN-LIKE ASYMMETRY PROTEIN-1, AND METHODS FOR ITS USE The present invention relates to molecules involved in cell-cell interactions in the immune system. In particular, the invention relates to a cell surface protein that contains certain classical cadherin characteristics, but it exhibits an apical distribution pattern on the surface of lymphocytes. The membrane location of this molecule correlates with the contact interface between T and B cells, and antibodies against an extracellular domain of this protein disrupt T cell/B cell interactions. BACKGROUND OF THE INVENTION The generation of an immune response against an antigen is carried out by a number of distinct immune cell types which work in concert in the context of the particular antigen. An antigen introduced into the immune system first encounters an antigen presenting cell. An antigen presenting cell processes the antigen and presents antigenic fragments to helper T cells (TH), which, in turn, stimulate two types of immune responses; i.e., cellular and humoral immune responses. TH respond to antigen stimulation by producing lymphokines which "help" or activate other effector cell types in the immune system. TH activate B cells to secrete antibodies which function as the major effector molecule in humoral immune responses. Antibodies neutralize foreign antigens and cooperate with other effector cells in mediating antibody-dependent cellular cytotoxicity. Additionally, TH regulate cellular immune responses by stimulating another T cell subset to develop into antigen-specific cytotoxic effector cells, which directly kill antigen-expressing target cells. TH are distinguished from cytotoxic T lymphocytes (CTL) and B cells by their expression of a cell surface glycoprotein marker termed CD4. In the mouse, type 1 helper T cells (THI) produce interleukin-2 (IL-2) and γ-interferon (γ-IFN) upon activation by an antigen presenting cell, while type 2 helper T cells (TH2) produce IL-4 and IL-5. Based on the profile of lymphokine production, THI appear to be involved in promoting the activation and proliferation of other T cell subsets such as CTL, whereas TH2 specifically regulate B cell proliferation and differentiation, antibody synthesis, and antibody class switching. -ι- CTL express the CD8 surface marker. Unlike most TH, these cells display cytolytic activity by direct contact with target cells, although they are also capable of producing certain lymphokines. In vivo, these cells are particularly important in situations where an antibody response alone is inadequate. There is a preponderance of experimental evidence that cellular immune responses play a principal role in the defense against viral infections and cancer. In the immune system, immune cells communicate with each other by direct contact via surface proteins and by secretory cytokines which bind surface receptors. In most cases, cell surface molecules are distributed evenly throughout the cell membrane. However, certain cell surface proteins have been shown to cluster after lymphocyte activation. For example, an antigenic fragment presented by an antigen presenting cell brings together the T cell receptor (TCR) and other co-receptors into a complex. Cellular polarity reflects specialization of the cell surface membrane into domains that allow cells to assess and respond quickly to their environment (Drubin and Nelson, 1996, Cell 84: 335-44). In the immune system, migrating T lymphocytes exhibit functional polarity (Negulescu et al., 1996, Immunity 4: 421-30). Cells that encounter antigen at their leading edge readily activate, whereas those that encounter antigen at the uropod do so much more poorly. Since TCR density does not seem to be greater at the cell's leading edge prior to antigen activation, other molecule(s) may be responsible for this intrinsic polarity. Several cytoplasmic molecules display polar distribution in lymphocytes before antigen activation. For instance, spectrin, ankyrin, and the microtubule-organizing center ("MTOC") demarcate a structural pole in T cells that has been suggested to be important in the directional delivery of signaling molecules after cell-cell coupling (Geiger etal., 1982, J. Cell Biol. 95: 137-43; Gregorio etal., 1994, J. Cell Biol. 125: 345- 58; Kupfer et al., 1986, J. Exp. Med. 163: 489-98; Kupfer ef a/., 1994, J. Exp. Med. 179: 1507-15; Lee et al., 1988, Cell 55: 807-16). However, prior to the present invention, a cell surface molecule had not been identified to have a polar distribution on lymphocytes before antigen activation. SUMMARY OF THE INVENTION A novel mammalian cell surface molecule is provided, designated cadherin-like asymmetry protein-1 (Clasp-1). In particular, polynucleotides comprising coding sequences for Clasp-1, polynucleotides that selectively hybridize to Clasp-1 coding sequences, expression vectors containing such polynucleotides, genetically-engineered host cells containing such polynucleotides, Clasp-1 polypeptides, Clasp-1 fusion proteins, therapeutic compositions, Clasp-1 domain mutants, antibodies specific for Clasp-1 , methods for detecting the expression of Clasp-1, and methods of inhibiting an immune response by interfering with Clasp-1 function. A wide variety of uses are encompassed by the invention, including but not limited to, treatment of autoimmune diseases and hypersensitivities, prevention of transplantation rejection responses, and augmentation of immune responsiveness in immunodeficiency states. The invention is based, in part, on Applicants' discovery of Clasp-1 as a type I transmembrane protein containing certain cadherin domains and other protein domains known to be involved in signal transduction. Clasp-1 is expressed in lymphoid tissues and the brain, but is undetectable in most major adult organs. In particular, Clasp-1 is expressed in both T and B cells, as well as macrophages. The cell surface distribution pattern of Clasp-1 in lymphocytes is apical, and it is localized at the pole associated with the leading edge of the cell. More importantly, Clasp-1 is concentrated at the interface between T cell/B cell clusters, and antibodies directed to its extracellular domain inhibit T cell/B cell interactions. BRIEF DESCRIPTION OF THE DRAWINGS Figure la: Clasp-1 amino acid sequence (SEQ ID NO:1). The 3.9 kb open reading frame (ORF) is flanked by multiple stop codons in all three reading frames and a polyadenylation signal (AATAAA) located 620 bp downstream of the translation termination codon. The sequences corresponding to the original degenerate PCR primers are marked by arrows. The propeptide extends from amino acid residues 1-120 ending in the putative cadherin processing signal RAQR (Pigott and Power, 1993, The Adhesion Molecule Facts Book, Academic Press Limited) (triangle). The extracellular domain contains four potential N-glycosylation sites (hexagons) and a cluster of cysteines (double underlines) before the 20 amino acid residue transmembrane domain (shade and double-underline) typical of classical cadherins (Hofman and Stoffel, 1993, Biol. Chem. Hoppe-Seyler 374: 166). The cytoplasmic domain contains a CRK-SH3 binding domain (Knudsen et al., 1994, J. Biol. Chem. 269: 32781-87) (shade and underline, residues 850-856), four cadherin sequence motifs (underlines), tyrosine phosphorylation sites (circles), and coiled/coils domains (boxes) (Lupas et al., 1991 , Science 252: 1162-64). The combination of SH2/SH3 binding sites may permit interaction and regulation through adaptor proteins, and the coiled coil domains may permit direct association with the cytoskeleton. Figure 1b: Schematic domain structure of Clasp-1. Clasp-I contains a signal peptide (S) terminating in the cadherin proteolytic processing signal at amino acid residue #120. The extracellular domain (EC) has four glycosylation sites (hexagons) and a cluster of cysteines ("Cs") typical of cadherins. The transmembrane domain (TM) is followed by a cadherin-like domain (CAD) which contains the CRK-SH3 binding domain (pentagon) and tyrosine phosphorylation sites (star), and a coiled/coil domain ("C/C"). Figure 2: Cadherin sequence motifs. The cadherin sequence motifs are composed of four stretches of conserved cadherin amino acid sequences (A-D) which are separated by nearly identical numbers of amino acids (in parentheses). Motif A is also the CRK-SH3 binding domain and is similar to the E-cadherin sequence. Figure 3a: Clasp-1 is predominantly expressed in lymphoid tissues and in the brain. Ten μg of total RNA were loaded and probed with the Clasp-1 cDNA sequence to reveal a 13 kb band, suggesting that the 5' untranslated region was very long, or that it was a polycistronic message. The initiation methionine is predicted from the Kozak consensus sequence. Lane: 1) thymus, 2) spleen, 3) small intestine, 4) skin, 5) muscle, 6) lymph node, 7) lung, 8) liver, 9) kidney, 10) heart, 11) colon, 12) bone marrow, 13) brain. Clasp-1 is found in the thymus, spleen, lymph node and the brain. Figure 3b: Clasp-1 is expressed in both T and B lymphocytes. Ten μg of total RNA were loaded in each lane. Lane: 1) S194 (IgA plasmacytoma), 2) NFS 40 (pre-B cell), 3) J558L (IgA plasmacytoma), 4) HSIC 5 (pre-B cell), 5) HAFTLJ (pro- granulocytemacrophage cell), 6) Bal 17 (mature B cell), 7) BAC 14 (pre-B cell), 8) 5CC7 (CD4 T cell). Clasp-1 is expressed in most cell lines tested; it is absent in J558 and in low levels in S194, both plasmacytomas. Figure 3c: Clasp-1 protein is about 130 kd molecular weight in both T and B cells. Western blots of 2B4 cytoplasm/membrane (lane 1) or nuclei (lane 2) and CH27 cytoplasm/membrane (lane 3) or nuclei (lane 4) were probed with a goat antiserum to the cytoplasmic domain of Clasp-1. A 130K Clasp-1 band was seen in both T and B cells in the cytosol/membrane fraction. The same 130 kd band was detected with antisera to the putative extracellular domain of Clasp-1. A minor band of 55 kd may represent a degradation product of Clasp-1 or a cross-reactive protein. Figure 4a-4f: Clasp-1 localizes to the MOMA-1 marginal zone and appears to be focally distributed in T and B lymphocytes. Mice were perfusion-fixed. Their spleens were removed, cryoprotected, cryosectioned (7 micron) and probed with rabbit antiserum to Clasp-1-cyto followed by rhodamine-conjugated goat anti-rabbit (red). A second FITC stain (green) was applied to CD3 ( Figures 4a, 4d), B220 (Figures 4b, 4e), or MOMA-1 (Figures 4c, 4f). Figures 4a-4c are low power views (16X objective) and Figures 4d-4f are high power views (63X objective). Low power views showed that anti- Clasp-1 antiserum stained cells in the peri-arteriolar lymphocyte sheath (PALS). The T cell zone, B cell zone, marginal zone, and central arterioles are labeled by T, B, M, and c respectively. In the T cell zone, staining was mostly punctate except for a few scattered cells with dendritic morphology. In the B cell zone, the dominant staining was dendritic and heavily concentrated in the marginal zone (Figure 4e, arrow). Co-staining with macrophage markers showed localization to the MOMA-1 metallo-macrophage zone. High power views showed that Clasp-1 in T (Figure 4d) and B (Figure 4e) cells was organized as a "cap" associated with the plasma membrane (Figure 4d, arrow head), or as a "ball" in the cytoplasm (Figure 4e, arrow head). Furthermore, in T cells, the asymmetrically located Clasp-1 was concentrated at the periphery of T cell clusters as they intruded into the B cell zone (Figure 4d, arrow head). In the MOMA-1 region, anti-Clasp-1 antiserum stained macrophage-like cells that were distinct from MOMA-1 , but appeared to contact MOMA-1 macrophages (Figures 4e and 4f, arrow). Figure 4g: Clasp-1 forms an apical cap on the surface of B220 positive spleen B cells. Spleen cell suspensions were cytospun onto poly-L-lysine coated glass slides, fixed in periodate-lysine-paraformaldehyde (McLean and Nakane, 1974, J. Histochem. Cytochem. 22: 1077-83), stained with goat anti-Clasp-EC 12A (plus biotin conjugated mouse monoclonal anti-goat, followed by PE-conjugated strepavidin) and anti-B220- FITC. While most B cells were Clasp-1 negative, when Clasp-1 was present, it was organized into a membrane surface apical domain. Figure 4h: Clasp-1 forms an apical cap or ring in CD3-positive splenic T cells. Spleen cell suspensions were cytospun onto poly-L-lysine coated glass slides, fixed in periodate-lysine-paraformaldehyde, permeabilized in CSK (Greenberg and Edelman, 1983 Cell 33: 767-79), blocked, and stained with rabbit anti-Clasp-cyto (plus rhodamine conjugated anti-rabbit Fab'2) and anti-CD3-FITC. Clasp-1 was organized into a cap or a ring. Figure 4i: Clasp-1 forms an apical cap on the surface of D10 T cells. D10 T cells were prepared as described under Figure 3g above, and stained with goat anti-Clasp- EC 12A (plus biotin conjugated mouse monoclonal anti-goat, followed by PE-conjugated strepavidin) and anti-CD3-FITC. Clasp-1 formed a membrane apical domain. Figure 4j: Clasp-1 is located on the same side of the cell as the MTOC. D10 and 2B4 T cells were prepared as described under Figure 4h above, and stained with rabbit anti-Clasp-cyto (plus rhodamine conjugated anti-rabbit Fab'2), monoclonal rat anti-α- tubulin (YOL 1/34, plus FITC-conjugated mouse anti-rat Fab'2), and counterstained with DAPI. The MTOC (green) was always located between the Clasp-1 surface and the nucleus. Figure 5a: Clasp-1 in productive and non-productive T-B cell interactions. 3A9 and 5b HEL TCR transgenic splenocytes were cultured in the presence of HEL peptide for 10 hours. Cells were cytospun, fixed, permeabilized and stained for Clasp-1 (red) and CD3 (green). The corresponding phase-contrast (PC) picture is adjacent to each set. Figure 5a: Productive T-B cell couples were followed by T cell blast transformation (note the loss of condensed chromatin and nuclear border in the phase contrast picture of the T cells). All pairs show accumulation of Clasp-1 at the cell-cell interface. Figure 5b: In non-productive T-B interaction (T cell was not undergoing blast transformation), Clasp-1 was not facing the cell-cell interface. Figure 6a: Goat anti-Clasp-EC 12 blocks T-B cell coupling. 2B4 T cell hybridoma with specificity for moth cytochrome c (MCC) in the context of l-E k was mixed with CH27 B cell loaded with MCC peptide. Gamma-bind (Pharmacia, NJ) purified goat anti-Clasp- EC12 or preimmune serum was added at 0, 50, 150 and 300 μg/ml. At 150 μg/ml, goat anti-Clasp-ECI2 inhibited cell conjugate formation maximally, while pre-immune serum had minimal effect even up to 450 μg/ml. More than 100 cell couples were counted per sample. Figure 6b: Goat anti-Clasp-EC 12 blocks T cell activation. 2B4 T cell hybridoma with specificity for moth cytochrome c (MCC) in the context of l-E k was mixed with CH27 B cell loaded with MCC peptide. Gamma-bind (Pharmacia, NJ) purified goat anti-Clasp- EC12 or pre-immune serum was added at 0, 125, 500 and 1 ,000 μg/ml. IL-2 levels were measured after 48 hours of co-incubation and found to diminish in a dose dependent fashion. Pre-immune serum did not inhibit T cell activation as measured by IL-2 stimulation. Samples were performed in triplicate. BRIEF DESCRIPTION OF THE SEQUENCE LISTING The amino acid sequence of mouse CLASP-1 is provided as SEQ ID NO:1. The nucleotide sequence of the mouse CLASP-1 cDNA is provided in SEQ ID NO:2, which also shows the position of the start and stop of translation, and the encoded polypeptide. The nucleotide sequence of human CLASP-1 is provided as SEQ ID NO:3, with the encoded polypeptide, which is also shown in SEQ ID NO:4. DETAILED DESCRIPTION OF THE INVENTION Nucleic acid molecules that comprise mammalian Clasp-1 coding sequences and polypeptide encoded by the sequences are provided. In a specific embodiment by way of example, mouse and human Clasp-1 cDNA molecules were isolated, and their nucleotide and deduced amino acid sequences characterized. While Clasp-1 shares sequence homology with cadherin-encoding genes from different species, both the nucleotide coding sequences and the deduced amino acid sequences of Clasp-1 are unique. In accordance with the invention, any nucleotide sequence that encodes an amino acid sequence of a Clasp-1 gene product can be used to generate recombinant molecules that direct the expression of Clasp-1 polypeptides. The invention also provides isolated or purified nucleic acids consisting of at least 8 nucleotides {i.e., a hybridizable portion) of a Clasp-1 sequence or its complement; in other embodiments, the nucleic acids consist of at least 25 (continuous) nucleotides, 50 nucleotides, 100 nucleotides, 150 nucleotides, or 200 nucleotides of a Clasp-1 sequence, or a full-length Clasp-1 coding sequence. In another embodiment, the nucleic acids are smaller than 35, 200 or 500 nucleotides in length. Nucleic acids can be single or double stranded. The invention also relates to nucleic acids that selectively hybridize to or complementary to the foregoing sequences. In specific aspects, nucleic acids are provided that comprise a sequence complementary to at least 10, 25, 50, 100, or 200 nucleotides or the entire coding region of a Clasp-1 coding sequence. In a specific embodiment, a nucleic acid is provided that hybridizes to a Clasp-1 nucleic acid {e.g., having SEQ ID NO:2, SEQ ID NO:3) or its complement, or to a nucleic acid encoding a Clasp-1 derivative. Depending on the desired result, hybridization may be performed under condition of low, moderate or high stringency. Where it is desirable to hybridize to novel sequences, the hybridization may utilize the 5' region of the provided sequences. For example, a nucleic acid may be determined to hybridize under stringent conditions to a probe selected from nucleotides 1 to approximately 3990 of SEQ ID NO:3. By way of example and not limitation, procedures using such conditions of low stringency are as follows (see also Shilo and Weinberg, 1981 , Proc. Natl. Acad. Sci. USA 78:6789-6792): Filters containing DNA are pretreated for 6 h at 40°C in a solution containing 35% formamide, 5X SSC, 50 mM Tris-HCI (pH 7.5), 5 mM EDTA, 0.1% PVP, 0.1% Ficoll, 1% BSA, and 500 μg/ml denatured salmon sperm DNA. Hybridizations are carried out in the same solution with the following modifications: 0.02% PVP, 0.02% Ficoll, 0.2% BSA, 100 μg/ml salmon sperm DNA, 10% (wt/vol) dextran sulfate, and 5-20 X 10 6 cpm 32 P-labeled probe is used. Filters are incubated in hybridization mixture for 18-20 h at 40°C, and then washed for 1.5 h at 55°C in a solution containing 2X SSC, 25 mM Tris-HCI (pH 7.4), 5 mM EDTA, and 0.1% SDS. The wash solution is replaced with fresh solution and incubated an additional 1.5 h at 60°C. Filters are blotted dry and exposed for autoradiography. If necessary, filters are washed for a third time at 65-68 °C and reexposed to film. Other conditions of low stringency which may be used are well known in the art (e.g., as employed for cross-species hybridizations). By way of example and not limitation, procedures using such conditions of high stringency are as follows: Prehybridization of filters containing DNA is carried out for 8 h to overnight at 65°C in buffer composed of 6X SSC, 50 mM Tris-HCI (pH 7.5), 1 mM EDTA, 0.02% PVP, 0.02% Ficoll, 0.02% BSA, and 500 μg/ml denatured salmon sperm DNA. Filters are hybridized for 48 h at 65°C in prehybridization mixture containing 100 μg/ml denatured salmon sperm DNA and 5-20 X 10 6 cpm of 32 P-labeled probe. Washing of filters is done at 37°C for 1 h in a solution containing 2X SSC, 0.01% PVP, 0.01 % Ficoll, and 0.01% BSA. This is followed by a wash in 0.1X SSC at 50°C for 45 min before autoradiography. Other conditions of high stringency which may be used are well known in the art. Examples of procedures using such conditions of moderate stringency are as follows: Filters containing DNA are pretreated for 6 h at 55°C in a solution containing 6X SSC, 5X Denhart's solution, 0.5% SDS and 100 μg/ml denatured salmon sperm DNA. Hybridizations are carried out in the same solution and 5-20 X 10 6 cpm 32 P-labeled probe is used. Filters are incubated in hybridization mixture for 18-20 h at 55°C, and then washed twice for 30 minutes at 60°C in a solution containing 1X SSC and 0.1% SDS. Filters are blotted dry and exposed for autoradiography. Other conditions of moderate stringency which may be used are well-known in the art. Washing of filters is done at 37°C for 1 h in a solution containing 2X SSC, 0.1% SDS. In order to clone the full length cDNA sequence from any species encoding the entire Clasp-1 cDNA, or to clone variant forms of the molecule, labeled DNA probes made from nucleic acid fragments corresponding to any partial cDNA disclosed herein may be used to screen a cDNA library derived from lymphoid cells or brain cells. More specifically, oligonucleotides corresponding to either the 5' or 3' terminus of the cDNA sequence may be used to obtain longer nucleotide sequences. Briefly, the library may be plated out to yield a maximum of 30,000 pfu for each 150 mm plate. Approximately 40 plates may be screened. The plates are incubated at 37°C until the plaques reach a diameter of 0.25 mm or are just beginning to make contact with one another (3-8 hours). Nylon filters are placed onto the soft top agarose and after 60 seconds, the filters are peeled off and floated on a DNA denaturing solution consisting of 0.4N sodium hydroxide. The filters are then immersed in neutralizing solution consisting of 1M Tris-HCI, pH 7.5, before being allowed to air dry. The filters are prehybridized in hybridization buffer such as casein buffer containing 10% dextran sulfate, 0.5M NaCl, 50mM Tris-HCI, pH 7.5, 0.1% sodium pyrophosphate, 1% casein, 1% SDS, and denatured salmon sperm DNA at 0.5 mg/ml for 6 hours at 60°C. The radiolabelled probe is then denatured by heating to 95°C for 2 minutes and then added to the prehybridization solution containing the filters. The filters are hybridized at 60 °C for 16 hours. The filters are then washed in 1X wash mix (10X wash mix contains 3M NaCl, 0.6M Tris base, and 0.02M EDTA) twice for 5 minutes each at room temperature, then in 1X wash mix containing 1% SDS at 60°C for 30 minutes, and finally in 0.3X wash mix containing 0.1 % SDS at 60 °C for 30 minutes. The filters are then air dried and exposed to x-ray film for autoradiography. After developing, the film is aligned with the filters to select a positive plaque. If a single, isolated positive plaque cannot be obtained, the agar plug containing the plaques will be removed and placed in lambda dilution buffer containing 0.1M NaCl, 0.01 M magnesium sulfate, 0.035M Tris HCI, pH 7.5, 0.01% gelatin. The phage may then be replated and rescreened to obtain single, well isolated positive plaques. Positive plaques may be isolated and the cDNA clones sequenced using primers based on the known cDNA sequence. This step may be repeated until a full length cDNA is obtained. It may be necessary to screen multiple cDNA libraries from different tissues to obtain a full length cDNA. In the event that it is difficult to identify cDNA clones encoding the complete 5' terminal coding region, an often encountered situation in cDNA cloning, the RACE (Rapid Amplification of cDNA Ends) technique may be used. RACE is a proven PCR-based strategy for amplifying the 5' end of incomplete cDNAs. 5'-RACE-Ready RNA synthesized from human tissues containing a unique anchor sequence is commercially available (Clontech). To obtain the 5' end of the cDNA, PCR is carried out on δ'-RACE-Ready cDNA using the provided anchor primer and the 3' primer. A secondary PCR reaction is then carried out using the anchored primer and a nested 3' primer according to the manufacturer's instructions. Once obtained, the full length cDNA sequence may be translated into amino acid sequence and examined for certain landmarks such as a continuous open reading frame flanked by translation initiation and termination sites, a cadherin-like domain, an SH3 binding domain, and finally overall structural similarity to the Clasp-1 gene disclosed herein. POLYPEPTIDES ENCODED BY THE Clasp-1 CODING SEQUENCE In accordance with the invention, Clasp-1 polynucleotides encoding Clasp-1 polypeptides, mutant polypeptides, peptide fragments of Clasp-1 , Clasp-1 fusion proteins or functional equivalents thereof, may be used to generate recombinant DNA molecules that direct the expression of Clasp-1 protein, Clasp-1 peptide fragments, fusion proteins or a functional equivalent thereof, in appropriate host cells. Such Clasp- 1 polynucleotide sequences, as well as other polynucleotides that selectively hybridize to at least a part of such Clasp-1 polynucleotides or their complements, may also be used in nucleic acid hybridization assays, Southern and Northern blot analyses, etc. Due to the inherent degeneracy of the genetic code, other DNA sequences which encode substantially the same or a functionally equivalent amino acid sequence, may be used in the practice of the invention for the expression of the Clasp-1 protein. Such DNA sequences include those which are capable of hybridizing to the mouse Clasp-1 sequence or its complementary sequence under low, moderate or high stringent conditions as described above. Altered DNA sequences which may be used in accordance with the invention include deletions, additions or substitutions of different nucleotide residues resulting in a sequence that encodes the same or a functionally equivalent gene product. The gene product itself may contain deletions, additions or substitutions of amino acid residues within a Clasp-1 sequence, which result in a silent change thus producing a functionally equivalent Clasp-1 protein. Such conservative amino acid substitutions may be made on the basis of similarity in polarity, charge, solubility, hydrophobicity, hydrophilicity, and/or the amphipathic nature of the residues involved. For example, negatively charged amino acids include aspartic acid and glutamic acid; positively charged amino acids include lysine, histidine and arginine; amino acids with uncharged polar head groups having similar hydrophilicity values include the following: glycine, asparagine, glutamine, serine, threonine, tyrosine; and amino acids with nonpolar head groups include alanine, valine, isoleucine, leucine, phenylalanine, proline, methionine, tryptophan. The DNA sequences of the invention may be engineered in order to alter a Clasp-1 coding sequence for a variety of ends, including but not limited to, alterations which modify processing and expression of the gene product. For example, mutations may be introduced using techniques which are well known in the art, e.g., site-directed mutagenesis, to insert new restriction sites, to alter glycosylation patterns, phosphorylation, etc. Based on the domain organization of the Clasp-1 protein, a large number of Clasp-1 mutant polypeptides can be constructed by rearranging the nucleotide sequences that encode the Clasp-1 extracellular, transmembrane and cytoplasmic domains. In another embodiment of the invention, a Clasp-1 or a modified Clasp-1 sequence may be ligated to a heterologous sequence to encode a fusion protein. For example, for screening of peptide libraries for molecules that bind Clasp-1 , it may be useful to produce a chimeric Clasp-1 protein expressing a heterologous epitope that is recognized by a commercially available antibody. A fusion protein may also be engineered to contain a cleavage site located between a Clasp-1 sequence and the heterologous protein sequence, so that the Clasp-1 may be cleaved away from the heterologous moiety. Alternatively, the expression characteristics of an endogenous Clasp-1 gene within a cell population may be modified by inserting a heterologous DNA regulatory element into the genome of the cell line such that the inserted regulatory element is operatively linked with the endogenous Clasp-1 gene. For example, an endogenous Clasp-1 gene which is normally "transcriptionally silent", i.e., an Clasp-1 gene which is normally not expressed, or is expressed only at very low levels in a cell population, may be activated by inserting a regulatory element which is capable of promoting the expression of a normally expressed gene product in the cells. Alternatively, a transcriptionally silent, endogenous Clasp-1 gene may be activated by insertion of a promiscuous regulatory element that works across cell types. A heterologous regulatory element may be inserted into a cell line population, such that it is operatively linked with an endogenous Clasp-1 gene, using techniques, such as targeted homologous recombination, which are well known to those of skill in the art, (see e.g., in Chappel, U.S. Patent No. 5,272,071; PCT publication No. WO 91/06667, published May 16, 1991). In an alternate embodiment of the invention, the coding sequence of Clasp-1 could be synthesized in whole or in part, using chemical methods well known in the art. (See, e.g., Caruthers et al., 1980, Nuc. Acids Res. Symp. Ser. 7:215-233; Crea and Horn, 180, Nuc. Acids Res. 9(7θ):2331 ; Matteucci and Caruthers, 1980, Tetrahedron Letter 21:1 '19; and Chow and Kempe, 1981 , Nuc. Acids Res. 9(12):2807-28W.) Alternatively, the protein itself could be produced using chemical methods to synthesize a Clasp-1 amino acid sequence in whole or in part. For example, peptides can be synthesized by solid phase techniques, cleaved from the resin, and purified by preparative high performance liquid chromatography. (See Creighton, 1983, Proteins Structures And Molecular Principles, W.H. Freeman and Co., N.Y. pp. 50-60). The composition of the synthetic polypeptides may be confirmed by amino acid analysis or sequencing (e.g., the Edman degradation procedure; see Creighton, 1983, Proteins, Structures and Molecular Principles, W.H. Freeman and Co., N.Y., pp. 34-49). EXPRESSION SYSTEMS In order to express a biologically active Clasp-1, the nucleotide sequence coding for Clasp-1, or a functional equivalent, is inserted into an appropriate expression vector, i.e. , a vector which contains the necessary elements for the transcription and translation of the inserted coding sequence. Clasp-1 gene products as well as host cells or cell lines transfected or transformed with recombinant Clasp-1 expression vectors can be used for a variety of purposes. These include, but are not limited to, generating antibodies {i.e., monoclonal or polyclonal) that competitively inhibit activity of Clasp-1 proteins and neutralize its activity; antibodies that activate Clasp-1 function and antibodies that detect its presence on the cell surface or in solution. Anti-Clasp-1 antibodies may be used in detecting and quantifying expression of Clasp-1 levels in cells and tissues such as lymphocytes and macrophages, as well as isolating Clasp-1- positive cells from a cell mixture. Methods which are well known to those skilled in the art can be used to construct expression vectors containing the Clasp-1 coding sequence and appropriate transcriptional/translational control signals. These methods include in vitro recombinant DNA techniques, synthetic techniques and in vivo recombination/genetic recombination. (See, e.g., the techniques described in Sambrook et al., 1989, Molecular Cloning A Laboratory Manual, Cold Spring Harbor Laboratory, N.Y. and Ausubel et al., 1989, Current Protocols in Molecular Biology, Greene Publishing Associates and Wiley Interscience, N.Y.) A variety of host-expression vector systems may be utilized to express the Clasp- 1 coding sequence. These include, but are not limited to, microorganisms such as bacteria transformed with recombinant bacteriophage DNA, plasmid DNA, or cosmid DNA expression vectors containing the Clasp-1 coding sequence; yeast transformed with recombinant yeast expression vectors containing the Clasp-1 coding sequence; insect cell systems infected with recombinant virus expression vectors (e.g., baculovirus) containing the Clasp-1 coding sequence; plant cell systems infected with recombinant virus expression vectors (e.g.. cauliflower mosaic virus, CaMV; tobacco mosaic virus, TMV) or transformed with recombinant plasmid expression vectors (e.g., Ti plasmid) containing the Clasp-1 coding sequence; or animal cell systems. The expression elements of these systems vary in their strength and specificities. Depending on the host/vector system utilized, any of a number of suitable transcription and translation elements, including constitutive and inducible promoters, may be used in the expression vector. For example, when cloning in bacterial systems, inducible promoters such as pL of bacteriophage λ, plac, ptrp, ptac (ptrp-lac hybrid promoter; cytomegalovirus promoter) and the like may be used; when cloning in insect cell systems, promoters such as the baculovirus polyhedron promoter may be used; when cloning in plant cell systems, promoters derived from the genome of plant cells (e.g., heat shock promoters; the promoter for the small subunit of RUBISCO; the promoter for the chlorophyll α/β binding protein) or from plant viruses (e.g., the 35S RNA promoter of CaMV; the coat protein promoter of TMV) may be used; when cloning in mammalian cell systems, promoters derived from the genome of mammalian cells (e.g., metallothionein promoter) or from mammalian viruses (e.g., the adenovirus late promoter; the vaccinia virus 7.5K promoter) may be used; when generating cell lines that contain multiple copies of the Clasp-1 DNA, SV40-, BPV- and EBV-based vectors may be used with an appropriate selectable marker. In bacterial systems a number of expression vectors may be advantageously selected depending upon the use intended for the expressed Clasp-1 product. For example, when large quantities of Clasp-1 protein are to be produced for the generation of antibodies or to screen peptide libraries, vectors which direct the expression of high levels of fusion protein products that are readily purified may be desirable. Such vectors include, but are not limited to, the E. co/ expression vector pUR278 (Ruther et al., 1983, EMBO J. 2:1791), in which the Clasp-1 coding sequence may be ligated into the vector in frame with the lacZ coding region so that a hybrid protein is produced; plN vectors (Inouye & Inouye, 1985, Nucleic acids Res. 13:3101-3109; Van Heeke & Schuster, 1989, J. Biol. Chem. 264:5503-5509); and the like. pGEX vectors may also be used to express foreign polypeptides as fusion proteins with glutathione S- transferase (GST). In general, such fusion proteins are soluble and can be purified easily from lysed cells by adsorption to glutathione-agarose beads followed by elution in the presence of free glutathione. The pGEX vectors are designed to include thrombin or factor Xa protease cleavage sites so that the cloned polypeptide of interest can be released from the GST moiety. In yeast, a number of vectors containing constitutive or inducible promoters may be used. (Current Protocols in Molecular Biology, Vol. 2, 1988, Ed. Ausubel et al., Greene Publish. Assoc. & Wiley Interscience, Ch. 13; Grant et al., 1987, Expression and Secretion Vectors for Yeast, jn Methods in Enzymology, Eds. Wu & Grossman, 1987, Acad. Press, N.Y., Vol. 153, pp. 516-544; Glover, 1986, DNA Cloning, Vol. II, IRL Press, Wash., D.C., Ch. 3; and Bitter, 1987, Heterologous Gene Expression in Yeast, Methods in Enzymology, Eds. Berger & Kimmel, Acad. Press, N.Y., Vol. 152, pp. 673- 684; and The Molecular Biology of the Yeast Saccharomyces, 1982, Eds. Strathern et al., Cold Spring Harbor Press, Vols. I and II.) In cases where plant expression vectors are used, the expression of the Clasp-1 coding sequence may be driven by any of a number of promoters. For example, viral promoters such as the 35S RNA and 19S RNA promoters of CaMV (Brisson et al., 1984, Nature 310:511-514), or the coat protein promoter of TMV (Takamatsu et al., 1987, EMBO J. 6:307-311) may be used; alternatively, plant promoters such as the small subunit of RUBISCO (Coruzzi et al., 1984, EMBO J. 3:1671-1680; Broglie et al., 1984, Science 224:838-843); or heat shock promoters, e.g., soybean hsp17.5-E or hsp17.3-B (Gurley et al., 1986, Mol. Cell. Biol. 6:559-565) may be used. These constructs can be introduced into plant cells using Ti plasmids, Ri plasmids, plant virus vectors, direct DNA transformation, microinjection, electroporation, etc. (Weissbach & Weissbach, 1988, Methods for Plant Molecular Biology, Academic Press, NY, Section VIII, pp. 421-463; and Grierson & Corey, 1988, Plant Molecular Biology, 2d Ed., Blackie, London, Ch. 7-9.) An alternative expression system which could be used to express Clasp-1 is an insect system. In one such system, Autographa califomica nuclear polyhedrosis virus (AcNPV) is used as a vector to express foreign genes. The virus grows in Spodoptera frugiperda cells. The Clasp-1 coding sequence may be cloned into non-essential regions (e.g., the polyhedron gene) of the virus and placed under control of an AcNPV promoter (e.g., the polyhedron promoter). Successful insertion of the Clasp-1 coding sequence will result in inactivation of the polyhedron gene and production of non- occluded recombinant virus (Le., virus lacking the proteinaceous coat coded for by the polyhedron gene). These recombinant viruses are then used to infect Spodoptera frugiperda cells in which the inserted gene is expressed, (e.g., see Smith et al., 1983, J. Viol. 46:584; Smith, U.S. Patent No. 4,215,051). In mammalian host cells, a number of viral based expression systems may be utilized. In cases where an adenovirus is used as an expression vector, the Clasp-1 coding sequence may be ligated to an adenovirus transcription/translation control complex, e.g., the late promoter and tripartite leader sequence. This chimeric gene may then be inserted in the adenovirus genome by in vitro or in vivo recombination. Insertion in a non-essential region of the viral genome (e.g., region E1 or E3) will result in a recombinant virus that is viable and capable of expressing Clasp-1 in infected hosts, (e.g., See Logan & Shenk, 1984, Proc. Natl. Acad. Sci. USA 81 :3655-3659). Alternatively, the vaccinia 7.5K promoter may be used. (See, e ^ g., Mackett et al., 1982, Proc. Natl. Acad. Sci. USA 79:7415-7419; Mackett et al., 1984, J. Virol. 49:857-864; Panicali et al., 1982, Proc. Natl. Acad. Sci. USA 79:4927-4931). Regulatable expression vectors such as the tetracycline repressible vectors may also be used to express a coding sequence in a controlled fashion. Specific initiation signals may also be required for efficient translation of inserted Clasp-1 coding sequences. These signals include the ATG initiation codon and adjacent sequences. In cases where an entire Clasp-1 gene, including its own initiation codon and adjacent sequences, is inserted into the appropriate expression vector, no additional translational control signals may be needed. However, in cases where only a portion of the Clasp-1 coding sequence is inserted, exogenous translational control signals, including the ATG initiation codon, must be provided. Furthermore, the initiation codon must be in phase with the reading frame of the Clasp-1 coding sequence to ensure translation of the entire insert. These exogenous translational control signals and initiation codons can be of a variety of origins, both natural and synthetic. The efficiency of expression may be enhanced by the inclusion of appropriate transcription enhancer elements, transcription terminators, etc. (see Bittner et al., 1987, Methods in Enzymol. 153:516-544). In addition, a host cell strain may be chosen which modulates the expression of the inserted sequences, or modifies and processes the gene product in a specific fashion desired. Such modifications (e.g., glycosylation) and processing (e.g., cleavage) of protein products may be important for the function of the protein. The presence of several consensus N-glycosylation sites in the Clasp-1 extracellular domain support the possibility that proper modification may be important for Clasp-1 function. Different host cells have characteristic and specific mechanisms for the post- translational processing and modification of proteins. Appropriate cell lines or host systems can be chosen to ensure the correct modification and processing of the foreign protein expressed. To this end, eukaryotic host cells which possess the cellular machinery for proper processing of the primary transcript, glycosylation, and phosphorylation ofthe gene product may be used. Such mammalian host cells include, but are not limited to, CHO, VERO, BHK, HeLa, COS, MDCK, 293, WI38, etc. For long-term, high-yield production of recombinant proteins, stable expression is preferred. For example, cell lines which stably express Clasp-1 may be engineered. Rather than using expression vectors which contain viral origins of replication, host cells can be transformed with the Clasp-1 DNA controlled by appropriate expression control elements (e.g., promoter, enhancer, sequences, transcription terminators, polyadenylation sites, etc.), and a selectable marker. Following the introduction of foreign DNA, engineered cells may be allowed to grow for 1-2 days in an enriched medium, and then switched to a selective medium. The selectable marker in the recombinant plasmid confers resistance to the selection and allows cells to stably integrate the plasmid into their chromosomes and grow to form foci which in turn can be cloned and expanded into cell lines. This method may advantageously be used to engineer cell lines which express the Clasp-1 protein on the cell surface. Such engineered cell lines are particularly useful in screening for molecules or drugs that affect Clasp-1 function. A number of selection systems may be used, including but not limited to, the herpes simplex virus thymidine kinase (Wigler, et al., 1977, Cell 11:223), hypoxanthine- guanine phosphoribosyltransferase (Szybalska & Szybalski, 1962, Proc. Natl. Acad. Sci. USA 48:2026), and adenine phosphoribosyltransferase (Lowy, et al., 1980, Cell 22:817) genes which can be employed in tk " , hgprt " or aprt " cells, respectively. Also, antimetabolite resistance can be used as the basis of selection for dhfr, which confers resistance to methotrexate (Wigler, et al., 1980, Natl. Acad. Sci. USA 77:3567; O'Hare, et al., 1981 , Proc. Natl. Acad. Sci. USA 78:1527); gpt, which confers resistance to mycophenolic acid (Mulligan & Berg, 1981), Proc. Natl. Acad. Sci. USA 78:2072); neo, which confers resistance to the aminoglycoside G-418 (Colberre-Garapin, et al., 1981 , J. Mol. Biol. 150:1); and hygro, which confers resistance to hygromycin (Santerre, et al., 1984, Gene 30:147). Additional selectable genes have been described, namely trpB, which allows cells to utilize indole in place of tryptophan; hisD, which allows cells to utilize histinol in place of histidine (Hartman & Mulligan, 1988, Proc. Natl. Acad. Sci. USA 85:8047); ODC (ornithine decarboxylase) which confers resistance to the omithine decarboxylase inhibitor, 2-(difluoromethyl)-DL-omithine, DFMO (McConlogue L., 1987, In: Current Communications in Molecular Biology, Cold Spring Harbor Laboratory ed.) and glutamine synthetase (Bebbington et al., 1992, Biotech 10:169). IDENTIFICATION OF CELLS THAT EXPRESS Clasp-1 The host cells which contain the coding sequence and which express a biologically active Clasp-1 gene product or fragments thereof may be identified by at least four general approaches; (a) DNA-DNA or DNA-RNA hybridization; (b) the presence or absence of "marker" gene functions; (c) assessing the level of transcription as measured by the expression of Clasp-1 mRNA transcripts in the host cell; and (d) detection ofthe gene product as measured by immunoassay or by its biological activity. Prior to the identification of gene expression, the host cells may be first mutagenized in an effort to increase the level of expression of Clasp-1, especially in cell lines that produce low amounts of Clasp-1. In the first approach, the presence of the Clasp-1 coding sequence inserted in the expression vector can be detected by DNA-DNA or DNA-RNA hybridization using probes comprising nucleotide sequences that are homologous to the Clasp-1 coding sequence, respectively, or portions or derivatives thereof. In the second approach, the recombinant expression vector/host system can be identified and selected based upon the presence or absence of certain "marker" gene functions (e.g., thymidine kinase activity, resistance to antibiotics, resistance to methotrexate, transformation phenotype, occlusion body formation in baculovirus, etc.). For example, if the Clasp-1 coding sequence is inserted within a marker gene sequence of the vector, recombinants containing the Clasp-1 coding sequence can be identified by the absence of the marker gene function. Alternatively, a marker gene can be placed in tandem with the Clasp-1 sequence under the control of the same or different promoter used to control the expression of the Clasp-1 coding sequence. Expression of the marker in response to induction or selection indicates expression of the Clasp-1 coding sequence. In the third approach, transcriptional activity for the Clasp-1 coding region can be assessed by hybridization assays. For example, RNA can be isolated and analyzed by Northern blot using a probe homologous to the Clasp-1 coding sequence or particular portions thereof. Alternatively, total nucleic acids of the host cell may be extracted and assayed for hybridization to such probes. Additionally, reverse transcription-polymerase chain reactions may be used to detect low levels of gene expression. In the fourth approach, the expression of the Clasp-1 protein product can be assessed immunologically, for example by Western blots, immunoassays such as radioimmuno-precipitation, enzyme-linked immunoassays and the like. This can be achieved by using an anti-Clasp-1 antibody. Alternatively, Clasp-1 protein may be expressed as a fusion protein with green-fluorescent protein to facilitate its detection in cells (United States Patent Nos. 5,491 ,084; 5,804,387; 5,777,079). USES OF Clasp-1 ENGINEERED HOST CELLS In one embodiment of the invention, the Clasp-1 protein and/or cell lines that express Clasp-1 may be used to screen for antibodies, peptides, small molecules, natural and synthetic compounds or other cell bound or soluble molecules that bind to the Clasp-1 protein resulting in stimulation or inhibition of Clasp-1 function. For example, anti-Clasp-1 antibodies may be used to inhibit or stimulate Clasp-1 function and to detect its presence. Alternatively, screening of peptide libraries with recombinantly expressed soluble Clasp-1 protein or cell lines expressing Clasp-1 protein may be useful for identification of therapeutic molecules that function by inhibiting or stimulating the biological activity of Clasp-1. The uses of the Clasp-1 protein and engineered cell lines, described in the subsections below, may be employed equally well for homologous Clasp-1 genes in various species. In a specific embodiment of the invention, cell lines have been engineered to express the extracellular domain of Clasp-1 fused to another molecule such as GST. In addition, Clasp-1 or its extracellular domain may be fused to an immunoglobulin constant region (Hollenbaugh and Aruffo, 1992, Current Protocols in Immunology, Unit 10.19; Aruffo et al., 1990, Cell 61 :1303) to produce a soluble molecule with increased half life. The soluble protein or fusion protein may be used in binding assays, affinity chromatography, immunoprecipitation, Western blot, and the like. Synthetic compounds, natural products, and other sources of potentially biologically active materials can be screened in assays that are well known in the art. Random peptide libraries consisting of all possible combinations of amino acids attached to a solid phase support may be used to identify peptides that are able to bind to a specific domain of Clasp-1 (Lam, K.S. et al., 1991 , Nature 354: 82-84). The screening of peptide libraries may have therapeutic value in the discovery of pharmaceutical agents that stimulate or inhibit the biological activity of Clasp-1. Identification of molecules that are able to bind to the Clasp-1 protein may be accomplished by screening a peptide library with recombinant soluble Clasp-1 protein. Methods for expression and purification of Clasp-1 may be used to express recombinant full length Clasp-1 or fragments of Clasp-1 depending on the functional domains of interest. Such domains include Clasp-1 extracellular domain, transmembrane domain, cytoplasmic domain, SH2 domain, SH3 domain and coiled/coil domain. In a specific embodiment, a portion of the Clasp-1 extracellular domain corresponding to amino acid residues #131-327 is shown to contain a binding site that interacts with itself or other proteins. To identify and isolate the peptide/solid phase support that interacts and forms a complex with Clasp-1 , it is necessary to label or "tag" the Clasp-1 molecule. The Clasp-1 protein may be conjugated to enzymes such as alkaline phosphatase or horseradish peroxidase or to other reagents such as fluorescent labels which may include fluorescein isothiocyanate (FITC), phycoerythrin (PE) or rhodamine. Conjugation of any given label to Clasp-1 may be performed using techniques that are well known in the art. Alternatively, Clasp-1 expression vectors may be engineered to express a chimeric Clasp-1 protein containing an epitope for which a commercially available antibody exist. The epitope-specific antibody may be tagged with a detectable label using methods well known in the art including an enzyme, a fluorescent dye or colored or magnetic beads. The "tagged" Clasp-1 conjugate is incubated with the random peptide library for 30 minutes to one hour at 22°C to allow complex formation between Clasp-1 and peptide species within the library. The library is then washed to remove any unbound protein. If Clasp-1 has been conjugated to alkaline phosphatase or horseradish peroxidase the whole library is poured into a petri dish containing substrates for either alkaline phosphatase or peroxidase, for example, 5-bromo-4-chloro-3-indoyl phosphate (BCIP) or 3,3',4,4"-diaminobenzidine (DAB), respectively. After incubating for several minutes, the peptide/solid phase-Clasp-1 complex changes color, and can be easily identified and isolated physically under a dissecting microscope with a micromanipulator. If a fluorescent tagged Clasp-1 molecule has been used, complexes may be isolated by fluorescence activated sorting. If a chimeric Clasp-1 protein expressing a heterologous epitope has been used, detection of the peptide/Clasp-1 complex may be accomplished by using a labeled epitope-specific antibody. Once isolated, the identity of the peptide attached to the solid phase support may be determined by peptide sequencing. In addition to using soluble Clasp-1 molecules, in another embodiment, it is possible to detect peptides that bind to cell-associated Clasp-1 using intact cells. The use of intact cells is preferred for use with cell surface molecules. Methods for generating cell lines expressing Clasp-1 are described above. The cells used in this technique may be either live or fixed cells. The cells may be incubated with the random peptide library and bind to certain peptides in the library to form a "rosette" between the target cells and the relevant solid phase support/peptide. The rosette can thereafter be isolated by differential centrifugation or removed physically under a dissecting microscope. Techniques for screening combinatorial libraries are known in the art (Gallop et al., 1994, J. Med. Chem., 37:1233; Gordon, 1994, J. Med. Chem., 37:1385). As an alternative to whole cell assays for membrane bound receptors or receptors that require the lipid domain of the cell membrane to be functional, Clasp-1 molecules can be reconstituted into liposomes where label or "tag" can be attached. ANTI-Clasp-1 ANTIBODIES Various procedures known in the art may be used for the production of antibodies to epitopes of the natural and recombinantly produced Clasp-1 protein. Such antibodies include, but are not limited to, polyclonal, monoclonal, chimeric, single chain, humanized, a complementarity determining region, Fab fragments, F(ab') 2 and fragments produced by an Fab expression library as well as anti-idiotypic antibodies. Antibodies which compete for Clasp-1 binding are especially preferred for diagnostics and therapeutics. Monoclonal antibodies that bind Clasp-1 may be radioactively labeled allowing one to follow their location and distribution in the body after injection. Radioisotope tagged antibodies may be used as a non-invasive diagnostic tool for imaging de novo lymphoid tumors and metastases that express Clasp-1. Immunotoxins may also be designed which target cytotoxic agents to specific sites in the body. For example, high affinity Clasp-1 specific monoclonal antibodies may be covalently complexed to bacterial or plant toxins, such as diphtheria toxin or ricin. A general method of preparation of antibody/hybrid molecules may involve use of thiol-crosslinking reagents such as SPDP, which attack the primary amino groups on the antibody and by disulfide exchange, attach the toxin to the antibody. The hybrid antibodies may be used to specifically eliminate Clasp-1 expressing lymphocytes. For the production of antibodies, various host animals may be immunized by injection with the recombinant or naturally purified Clasp-1 protein, fusion protein or peptides, including but not limited to goats, rabbits, mice, rats, hamsters, etc. Various adjuvants may be used to increase the immunological response, depending on the host species, including but not limited to Freund's (complete and incomplete), mineral gels such as aluminum hydroxide, surface active substances such as lysolecithin, pluronic polyols, polyanions, peptides, oil emulsions, keyhole limpet hemocyanin, dinitrophenol, and potentially useful human adjuvants such as BCG (bacilli Calmette-Guerin) and Corynebacterium parvum. Monoclonal antibodies to Clasp-1 may be prepared by using any technique which provides for the production of antibody molecules by continuous cell lines in culture. These include, but are not limited to, the hybridoma technique originally described by Kohler and Milstein, (Nature, 1975, 256:495-497), the human B-cell hybridoma technique (Kosbor et al., 1983, Immunology Today, 4:72; Cote et al., 1983, Proc. Natl. Acad. Sci. USA, 80:2026-2030) and the EBV-hybridoma technique (Cole et al., 1985, Monoclonal Antibodies and Cancer Therapy, Alan R. Liss, Inc., pp. 77-96). In addition, techniques developed for the production of "chimeric antibodies" (Morrison et al., 1984, Proc. Natl. Acad. Sci. USA, 81:6851-6855; Neuberger et al., 1984, Nature, 312:604-608; Takeda et al., 1985, Nature, 314:452-454) by splicing the genes from a mouse antibody molecule of appropriate antigen specificity together with genes from a human antibody molecule of appropriate biological activity can be used. Alternatively, techniques described for the production of single chain antibodies (U.S. Patent 4,946,778) can be adapted to produce Clasp-1 -specific single chain antibodies. Hybridomas may be screened using enzyme-linked immunosorbent assays (ELISA) in order to detect cultures secreting antibodies specific for refolded recombinant Clasp-1. Cultures may also be screened by ELISA to identify those cultures secreting antibodies specific for mammalian-produced Clasp-1. Confirmation of antibody specificity may be obtained by western blot using the same antigens. Subsequent ELISA testing may use recombinant Clasp-1 fragments to identify the specific portion of the Clasp-1 molecule with which a monoclonal antibody binds. Additional testing may be used to identify monoclonal antibodies with desired functional characteristics such as staining of histological sections, immunoprecipitation of Clasp-1 , inhibition of Clasp-1 binding or stimulation of Clasp-1 to transmit an intracellular signal. Determination of the monoclonal antibody isotype may be accomplished by ELISA, thus providing additional information concerning purification or function. Antibody fragments which contain specific binding sites of Clasp-1 may be generated by known techniques. For example, such fragments include, but are not limited to, the F(ab') 2 fragments which can be produced by pepsin digestion of the antibody molecule and the Fab fragments which can be generated by reducing the disulfide bridges of the F(ab') 2 fragments. Alternatively, Fab expression libraries may be constructed (Huse et al., 1989, Science, 246:1275-1281) to allow rapid and easy identification of monoclonal Fab fragments with the desired specificity to Clasp-1. Anti- Clasp-1 antibodies may be used to identify, isolate, inhibit or eliminate Clasp-1- expressing cells. USES OF C/asp-7 POLYNUCLEOTIDE A Clasp-1 polynucleotide or fragments thereof may be used for diagnostic and/or therapeutic purposes. In particular, since Clasp-1 is expressed in lymphocytes, a Clasp-1 polynucleotide may be used to detect the expression of Clasp-1 as a lymphocyte marker. For diagnostic purposes, a Clasp-1 polynucleotide may be used to detect Clasp-1 gene expression or aberrant Clasp-1 gene expression in disease states. Included in the scope of the invention are oligonucleotide sequences, such as antisense RNA and DNA molecules and ribozymes, that function to inhibit expression of Clasp-1. Clasp-1 polynucleotide may be used to construct transgenic and knockout animals for screening of Clasp-1 agonists and antagonists. TRANSGENIC AND KNOCKOUT ANIMALS The Clasp-1 gene products can also be expressed in transgenic animals. Animals of any species, including, but not limited to, mice, rats, rabbits, guinea pigs, pigs, micro-pigs, goats, sheep, and non-human primates, e.g., baboons, monkeys, and chimpanzees may be used to generate Clasp-1 transgenic animals. The term "transgenic," as used herein, refers to animals expressing Clasp-1 gene sequences from a different species (e.g., mice expressing human Clasp-1 gene sequences), as well as animals that have been genetically engineered to overexpress endogenous {i.e., same species) Clasp-1 sequences or animals that have been genetically engineered to no longer express endogenous Clasp-1 gene sequences {i.e., "knock-out" animals), and their progeny. Any technique known in the art may be used to introduce a Clasp-1 transgene into animals to produce the founder lines of transgenic animals. Such techniques include, but are not limited to pronuclear microinjection (Hoppe and Wagner, 1989, U.S. Pat. No. 4,873,191); retrovirus mediated gene transfer into germ lines (Van der Putten, et al., 1985, Proc. Natl. Acad. Sci., USA 82:6148-6152); gene targeting in embryonic stem cells (Thompson, et al., 1989, Cell 56:313-321); electroporation of embryos (Lo, 1983, Mol. Cell. Biol. 3:1803-1814); and sperm-mediated gene transfer (Lavitrano et al., 1989, Cell 57:717-723) (For a review of such techniques, see Gordon, 1989, Transgenic Animals, Intl. Rev. Cytol. 115, 171-229) Any technique known in the art may be used to produce transgenic animal clones containing a Clasp-1 transgene, for example, nuclear transfer into enucleated oocytes of nuclei from cultured embryonic, fetal or adult cells induced to quiescence (Campbell, et al., 1996, Nature 380:64-66; Wilmut, et al., Nature 385:810-813). The present invention provides for transgenic animals that carry a Clasp-1 transgene in all their cells, as well as animals that carry the transgene in some, but not all their cells, i.e., mosaic animals. The transgene may be integrated as a single transgene or in concatamers, e.g., head-to-head tandems or head-to-tail tandems. The transgene may also be selectively introduced into and activated in a particular cell type by following, for example, the teaching of Lasko et al. (Lasko, et al., 1992, Proc. Natl. Acad. Sci. USA 89:6232-6236). The regulatory sequences required for such a cell-type specific activation will depend upon the particular cell type of interest, and will be apparent to those of skill in the art. When it is desired that the Clasp-1 transgene be integrated into the chromosomal site of the endogenous Clasp-1 gene, gene targeting is preferred. Briefly, when such a technique is to be utilized, vectors containing some nucleotide sequences homologous to the endogenous Clasp-1 gene are designed for the purpose of integrating, via homologous recombination with chromosomal sequences, into and disrupting the function of the nucleotide sequence of the endogenous Clasp-1 gene. The transgene may also be selectively introduced into a particular cell type, thus inactivating the endogenous Clasp-1 gene in only that cell type, by following, for example, the teaching of Gu, et al. (1994, Science 265: 103-106). The regulatory sequences required for such a cell-type specific inactivation will depend upon the particular cell type of interest, and will be apparent to those of skill in the art. Once transgenic animals have been generated, the expression of the recombinant Clasp-1 gene may be assayed utilizing standard techniques. Initial screening may be accomplished by Southern blot analysis or PCR techniques to analyze animal tissues to assay whether integration of the transgene has taken place. The level of mRNA expression of the transgene in the tissues of the transgenic animals may also be assessed using techniques that include, but are not limited to, Northern blot analysis of tissue samples obtained from the animal, in situ hybridization analysis, and RT-PCR (reverse transcriptase PCR). Samples of Clasp-1 gene-expressing tissue, may also be evaluated immunocytochemically using antibodies specific for the Clasp-1 transgene product. DIAGNOSTIC USES OF Clasp-1 POLYNUCLEOTIDE A Clasp-1 polynucleotide may have a number of uses in the diagnosis of diseases or disorders resulting from aberrant expression of Clasp-1 such as immunodeficient states. For example, the Clasp-1 DNA sequence may be used in hybridization assays of biopsies or autopsies to detect abnormalities of Clasp-1 expression; e.g., Southern or Northern analysis, including in situ hybridization assays and PCR. In that connection, PCR primers of 15-30 nucleotides may be used. A preferred length of a PCR primer is about 18-22 nucleotides. However, the length of primers may be adjusted by one skilled in the art. With respect to a Clasp-1 probe, a polynucleotide of 300-500 nucleotides is preferred. Various hybridization techniques are well known in the art, and are in fact the basis of many commercially available diagnostic kits. THERAPEUTIC USES OF Clasp-1 POLYNUCLEOTIDE A Clasp-1 polynucleotide may be useful in the treatment of various abnormal conditions. By introducing gene sequences into cells, gene therapy can be used to treat conditions in which the cells do not express normal Clasp-1 or express abnormal/inactive Clasp-1. In some instances, the polynucleotide encoding a Clasp-1 is intended to replace or act in the place of a functionally deficient endogenous gene. Alternatively, abnormal conditions characterized by overexpression can be treated using the gene therapy techniques described below. In a specific embodiment, nucleic acids comprising a sequence encoding a Clasp-1 protein or functional derivative thereof, are administered to promote Clasp-1 function, by way of gene therapy. Gene therapy refers to therapy performed by the administration of a nucleic acid to a subject. In this embodiment of the invention, the nucleic acid produces its encoded protein that mediates a therapeutic effect by promoting Clasp-1 function. Any of the methods for gene therapy available in the art can be used according to the present invention. Exemplary methods are described below. For general reviews of the methods of gene therapy, see Goldspiel et al., 1993, Clinical Pharmacy 12:488-505; Wu and Wu, 1991 , Biotherapy 3:87-95; Tolstoshev, 1993, Ann. Rev. Pharmacol. Toxicol. 32:573-596; Mulligan, 1993, Science 260:926-932; and Morgan and Anderson, 1993, Ann. Rev. Biochem. 62:191-217; May, 1993, TIBTECH 11 (5): 155-215). Methods commonly known in the art of recombinant DNA technology which can be used are described in Ausubel et al. (eds.), 1993, Current Protocols in Molecular Biology, John Wiley & Sons, NY; and Kriegler, 1990, Gene Transfer and Expression, A Laboratory Manual, Stockton Press, NY. In a preferred aspect, the therapeutic composition comprises a Clasp-1 nucleic acid that is part of an expression vector that encodes a Clasp-1 protein or fragment or chimeric protein thereof in a suitable host. In particular, such a nucleic acid has a promoter operably linked to the Clasp-1 coding region, said promoter being inducible or constitutive, and, optionally, tissue-specific. In another particular embodiment, a nucleic acid molecule is used in which the Clasp-1 coding sequences and any other desired sequences are flanked by regions that promote homologous recombination at a desired site in the genome, thus providing for intrachromosomal expression of the Clasp-1 nucleic acid (Koller and Smithies, 1989, Proc. Natl. Acad. Sci. USA 86:8932- 8935; Zijlstra et al., 1989, Nature 342:435-438). Delivery of the nucleic acid into a patient may be either direct, in which case the patient is directly exposed to the nucleic acid or nucleic acid-carrying vector, or indirect, in which case, cells are first transformed with the nucleic acid in vitro, then transplanted into the patient. These two approaches are known, respectively, as in vivo or ex vivo gene therapy. In a specific embodiment, the nucleic acid is directly administered in vivo, where it is expressed to produce the encoded product. This can be accomplished by any of numerous methods known in the art, e.g., by constructing it as part of an appropriate nucleic acid expression vector and administering it so that it becomes intracellular, e.g., by infection using a defective or attenuated retroviral or other viral vector (see U.S. Patent No. 4,980,286), or by direct injection of naked DNA, or by use of microparticle bombardment (e.g., a gene gun; Biolistic, Dupont), or coating with lipids or cell-surface receptors or transfecting agents, encapsulation in liposomes, microparticles, or microcapsules, or by administering it in linkage to a peptide which is known to enter the nucleus, by administering it in linkage to a ligand subject to receptor-mediated endocytosis (see e.g., Wu and Wu, 1987, J. Biol. Chem. 262:4429-4432) (which can be used to target cell types specifically expressing the receptors), etc. In another embodiment, a nucleic acid-ligand complex can be formed in which the ligand comprises a fusogenic viral peptide to disrupt endosomes, allowing the nucleic acid to avoid lysosomal degradation. In yet another embodiment, the nucleic acid can be targeted in vivo for cell specific uptake and expression, by targeting a specific receptor (see, e.g., PCT Publications WO 92/06180 dated April 16, 1992; WO 92/22635 dated December 23, 1992; WO92/20316 dated November 26, 1992; WO93/14188 dated July 22, 1993; WO 93/20221 dated October 14, 1993). Alternatively, the nucleic acid can be introduced intracellularly and incorporated within host cell DNA for expression, by homologous recombination (Koller and Smithies, 1989, Proc. Natl. Acad. Sci. USA 86:8932-8935; Zijlstra et al., 1989, Nature 342:435-438). In a specific embodiment, a viral vector that contains the Clasp-1 nucleic acid is used. For example, a retroviral vector can be used (see Miller et al., 1993, Meth. Enzymol. 217:581-599). These retroviral vectors have been modified to delete retroviral sequences that are not necessary for packaging of the viral genome and integration into host cell DNA. The Clasp-1 nucleic acid to be used in gene therapy is cloned into the vector, which facilitates delivery of the gene into a patient. More detail about retroviral vectors can be found in Boesen et al., 1994, Biotherapy 6:291-302, which describes the use of a retroviral vector to deliver the mdrl gene to hematopoietic stem cells in order to make the stem cells more resistant to chemotherapy. Other references illustrating the use of retroviral vectors in gene therapy are: Clowes et al., 1994, J. Clin. Invest. 93:644-651 ; Kiem et al., 1994, Blood 83:1467-1473; Salmons and Gunzberg, 1993, Human Gene Therapy 4:129-141 ; and Grossman and Wilson, 1993, Curr. Opin. in Genetics and Devel. 3:110-114. Adenoviruses are other viral vectors that can be used in gene therapy. Adenoviruses are especially attractive vehicles for delivering genes to respiratory epithelia. Adenoviruses naturally infect respiratory epithelia where they cause a mild disease. Other targets for adenovirus-based delivery systems are liver, the central nervous system, endothelial cells, and muscle. Adenoviruses have the advantage of being capable of infecting non-dividing cells. Kozarsky and Wilson (1993, Current Opinion in Genetics and Development 3:499-503) present a review of adenovirus-based gene therapy. Bout et al., (1994, Human Gene Therapy 5:3-10) demonstrated the use of adenovirus vectors to transfer genes to the respiratory epithelia of rhesus monkeys. Other instances of the use of adenoviruses in gene therapy can be found in Rosenfeld et al., 1991 , Science 252:431-434; Rosenfeld et al., 1992, Cell 68:143-155; and Mastrangeli et al., 1993, J. Clin. Invest. 91 :225-234. Adeno-associated virus (AAV) has also been proposed for use in gene therapy (Walsh et al., 1993, Proc. Soc. Exp. Biol. Med. 204:289-300. Another approach to gene therapy involves transferring a gene to cells in tissue culture by such methods as electroporation, lipofection, calcium phosphate mediated transfection, or viral infection. Usually, the method of transfer includes the transfer of a selectable marker to the cells. The cells are then placed under selection to isolate those cells that have taken up and are expressing the transferred gene. Those cells are then delivered to a patient. In this embodiment, the nucleic acid is introduced into a cell prior to administration in vivo of the resulting recombinant cell. Such introduction can be carried out by any method known in the art, including but not limited to transfection, electroporation, microinjection, infection with a viral or bacteriophage vector containing the nucleic acid sequences, cell fusion, chromosome-mediated gene transfer, microcell- mediated gene transfer, spheroplast fusion, etc. Numerous techniques are known in the art for the introduction of foreign genes into cells (see e.g., Loeffler and Behr, 1993, Meth. Enzymol. 217:599-618; Cohen et al., 1993, Meth. Enzymol. 217:618-644; Cline, 1985, Pharmac. Ther. 29:69-92) and may be used in accordance with the present invention, provided that the necessary developmental and physiological functions of the recipient cells are not disrupted. The technique should provide for the stable transfer of the nucleic acid to the cell, so that the nucleic acid is expressible by the cell and preferably heritable and expressible by its cell progeny. The resulting recombinant cells can be delivered to a patient by various methods known in the art. In a preferred embodiment, epithelial cells are injected, e.g., subcutaneously. In another embodiment, recombinant skin cells may be applied as a skin graft onto the patient. Recombinant blood cells (e.g., hematopoietic stem or progenitor cells) are preferably administered intravenously. The amount of cells envisioned for use depends on the desired effect, patient state, etc., and can be determined by one skilled in the art. Cells into which a nucleic acid can be introduced for purposes of gene therapy encompass any desired, available cell type, and include but are not limited to epithelial cells, endothelial cells, keratinocytes, fibroblasts, muscle cells, hepatocytes; blood cells such as T lymphocytes, B lymphocytes, monocytes, macrophages, neutrophils, eosinophils, megakaryocytes, granulocytes; various stem or progenitor cells, in particular hematopoietic stem or progenitor cells, e.g., as obtained from bone marrow, umbilical cord blood, peripheral blood, fetal liver, etc. In a preferred embodiment, the cell used for gene therapy is autologous to the patient. In a specific embodiment, the nucleic acid to be introduced for purposes of gene therapy comprises an inducible promoter operably linked to the coding region, such that expression of the nucleic acid is controllable by controlling the presence or absence of the appropriate inducer of transcription. Oligonucleotide sequences, that include anti-sense RNA and DNA molecules and ribozymes that function to inhibit the translation of a Clasp-1 mRNA are within the scope of the invention. Such molecules are useful in cases where downregulation of Clasp-1 expression is desired. Anti-sense RNA and DNA molecules act to directly block the translation of mRNA by binding to targeted mRNA and preventing protein translation. In regard to antisense DNA, oligodeoxyribonucleotides derived from the translation initiation site, e.g., between -10 and +10 regions of a Clasp-1 nucleotide sequence, are preferred. The antisense oligonucleotide may comprise at least one modified base moiety which is selected from the group including, but not limited to, 5-fluorouracil, 5-bromouracil, 5-chlorouracil, 5-iodouracil, hypoxanthine, xanthine, 4-acetylcytosine, 5-(carboxyhydroxylmethyl) uracil, 5-carboxymethylaminomethyl-2-thiouridine, 5-carboxymethylaminomethyluracil, dihydrouracil, beta-D-galactosylqueosine, inosine, N6-isopentenyladenine, 1-methylguanine, 1-methylinosine, 2,2-dimethylguanine, 2-methyladenine, 2-methylguanine, 3-methylcytosine, 5-methylcytosine, N6-adenine, 7-methylguanine, 5-methylaminomethyluracil, 5-methoxyaminomethyl-2-thiouracil, beta- D-mannosylqueosine, 5'-methoxycarboxymethyluracil, 5-methoxyuracil, 2-methylthio-N6-isopentenyladenine, uracil-5-oxyacetic acid (v), wybutoxosine, pseudouracil, queosine, 2-thiocytosine, 5-methyl-2-thiouracil, 2-thiouracil, 4-thiouracil, 5-methyluracil, uracil-5-oxyacetic acid methylester, uracil-5-oxyacetic acid (v), 5-methyl- 2-thiouracil, 3-(3-amino-3-N-2-carboxypropyl) uracil, (acp3)w, and 2,6-diaminopurine. Ribozymes are enzymatic RNA molecules capable of catalyzing the specific cleavage of RNA. The mechanism of ribozyme action involves sequence specific hybridization of the ribozyme molecule to complementary target RNA, followed by endonucleolytic cleavage. Within the scope of the invention are engineered hammerhead motif ribozyme molecules that specifically and efficiently catalyze endonucleolytic cleavage of Clasp-1 RNA sequences. Specific ribozyme cleavage sites within any potential RNA target are initially identified by scanning the target molecule for ribozyme cleavage sites which include the following sequences, GUA, GUU and GUC. Once identified, short RNA sequences of between 15 and 20 ribonucleotides corresponding to the region of the target gene containing the cleavage site may be evaluated for predicted structural features such as secondary structure that may render the oligonucleotide sequence unsuitable. The suitability of candidate targets may also be evaluated by testing their accessibility to hybridization with complementary oligonucleotides, using ribonuclease protection assays. Endogenous target gene expression can also be reduced by inactivating or "knocking out" the target gene or its promoter using targeted homologous recombination (e.g., see Smithies, et al., 1985, Nature 317:230-234; Thomas and Capecchi, 1987, Cell 51 :503-512; Thompson, et al., 1989, Cell 5:313-321 ; each of which is incorporated by reference herein in its entirety). For example, a mutant, nonfunctional target gene (or a completely unrelated DNA sequence) flanked by DNA homologous to the endogenous target gene (either the coding regions or regulatory regions of the target gene) can be used, with or without a selectable marker and/or a negative selectable marker, to transfect cells that express the target gene in vivo. Insertion of the DNA construct, via targeted homologous recombination, results in inactivation of the target gene. Such approaches are particularly suited in the agricultural field where modifications to ES (embryonic stem) cells can be used to generate animal offspring with an inactive target gene (e.g., see Thomas and Capecchi, 1987 and Thompson, 1989, supra). However, this approach can be adapted for use in humans provided the recombinant DNA constructs are directly administered or targeted to the required site in vivo using appropriate viral vectors. Alternatively, endogenous target gene expression can be reduced by targeting deoxyribonucleotide sequences complementary to the regulatory region of the target gene {i.e., the target gene promoter and/or enhancers) to form triple helical structures that prevent transcription of the target gene in target cells in the body. (See generally, Helene, 1991 , Anticancer Drug Des., 6(6):569-584; Helene, et al., 1992, Ann. N.Y. Acad. Sci., 660:27-36; and Maher, 1992, Bioassays 14(12):807-815). Nucleic acid molecules to be used in triplex helix formation for the inhibition of transcription should be single stranded and composed of deoxynucleotides. The base composition of these oligonucleotides must be designed to promote triple helix formation via Hoogsteen base pairing rules, which generally require sizeable stretches of either purines or pyrimidines to be present on one strand of a duplex. Nucleotide sequences may be pyrimidine-based, which will result in TAT and CGC triplets across the three associated strands of the resulting triple helix. The pyrimidine-rich molecules provide base complementarily to a purine-rich region of a single strand of the duplex in a parallel orientation to that strand. In addition, nucleic acid molecules may be chosen that are purine-rich, for example, contain a stretch of G residues. These molecules will form a triple helix with a DNA duplex that is rich in GC pairs, in which the majority of the purine residues are located on a single strand of the targeted duplex, resulting in GGC triplets across the three strands in the triplex. Alternatively, the potential sequences that can be targeted for triple helix formation may be increased by creating a so called "switchback" nucleic acid molecule. Switchback molecules are synthesized in an alternating 5'-3', 3'-5' manner, such that they base pair with first one strand of a duplex and then the other, eliminating the necessity for a sizeable stretch of either purines or pyrimidines to be present on one strand of a duplex. The anti-sense RNA and DNA molecules, ribozymes and triple helix molecules of the invention may be prepared by any method known in the art for the synthesis of RNA molecules. These include techniques for chemically synthesizing oligodeoxyri- bonucleotides well known in the art such as for example solid phase phosphoramidite chemical synthesis. Alternatively, RNA molecules may be generated by in vitro and in vivo transcription of DNA sequences encoding the antisense RNA molecule. Such DNA sequences may be incorporated into a wide variety of vectors which contain suitable RNA polymerase promoters such as the T7 or SP6 polymerase promoters. Alternatively, antisense cDNA constructs that synthesize antisense RNA constitutively or inducibly, depending on the promoter used, can be introduced stably into cell lines. Various modifications to the DNA molecules may be introduced as a means of increasing intracellular stability and half-life. Possible modifications include, but are not limited to, the addition of flanking sequences of ribo- or deoxy- nucleotides to the 5' and/or 3' ends of the molecule or the use of phosphorothioate or 2' O-methyl rather than phosphodiesterase linkages within the oligodeoxyribonucleotide backbone. Methods for introducing polynucleotides into such cells or tissue include methods for in vitro introduction of polynucleotides such as the insertion of naked polynucleotide, i.e., by injection into tissue, the introduction of a Clasp-1 polynucleotide in a cell ex vivo, the use of a vector such as a virus, (retrovirus, adenovirus, adeno-associated virus, etc.), phage or plasmid, etc. or techniques such as electroporation or calcium phosphate precipitation. USES OF Clasp-1 PROTEIN The subject gene may be employed for producing all or portions of Clasp-1 polypeptides. Fragments of interest include glycosylation sites, which may affect the stability and/or activity of the polypeptide, the protein interaction sites, etc. Such domains will usually include at least about 20 amino acids of the provided sequence, more usually at least about 50 amino acids, and may include 100 amino acids or more, up to the complete domain. Binding contacts may be comprised of non-contiguous sequences, which are brought into proximity by the tertiary structure of the protein. The sequence of such fragments may be modified through manipulation of the coding sequence, as described above. Truncations may be performed at the carboxy or amino terminus of the fragment, e.g. to determine the minimum sequence required for biological activity. A polypeptide of particular interest comprises the mature portion of the Clasp-1 protein, i.e. the fragment that remain after cleavage of the signal peptide, or the propeptide sequence. Determination of this cleavage site may be determined experimentally, by producing the polypeptide in an expression system capable such cleavage, and then determining the terminus of the mature protein. Alternatively, the cleavage site may be determined by deduction, after comparison with known cleavage sites. For example, the cleavage site of the mouse Clasp-1 polypeptide is between residue 120 and 121. In the human homolog, a putative cleavage site (arg pro gin arg) is between residues 104 and 105. Assays for the biological activity of the protein or fragments thereof may be determined as described in the art. Numerous in vitro assays for determining lymphocyte activation are known in the art, or as provided in the Examples. Inhibition of cellular adhesion and cell-cell contacts, is determined through in vivo or in vitro models (for reviews, see Fukuda (1995) Bioorg Med Chem 3(3):207-215; Zanetta et al. (1994) Histol Histopathol 9(2): 385-412). With the availability of the protein or fragments thereof in large amounts, by employing an expression host, the protein may be isolated and purified in accordance with conventional ways. A lysate may be prepared of the expression host and the lysate purified using HPLC, exclusion chromatography, gel electrophoresis, affinity chromatography, or other purification technique. The purified protein will generally be at least about 80% pure, preferably at least about 90% pure, and may be up to and including 100% pure. Pure is intended to mean free of other proteins, as well as cellular debris. The Clasp-1 protein is expressed in lymphocytes, and is specifically localized at the interface of T cell-B cell interactions. Therefore, a soluble Clasp-1 , a Clasp-1 fragment containing an extracellular domain or an anti-Clasp-1 antibody may be used to inhibit T cell-B cell interactions, thereby inhibiting an immune response. It is believed that the involvement of Clasp-1 in T cell-B cell contact occurs prior to B cell activation by the TH, thus inhibition of Clasp-1 binding can interfere with an early stage of the immune response. Autoimmune disorders that may be treated by disrupting Clasp-1 function, include, but are not limited to, multiple sclerosis, juvenile diabetes, rheumatoid arthritis, pemphigus, pemphigoid, epidermolysis bullosa acquista, lupus, Rh incompatibility, etc. Additionally, since Clasp-1 contains domains capable of transducing an intracellular signal, cell surface Clasp-1 may be triggered by an anti-Clasp-1 antibody or soluble Clasp-1 or a fragment thereof in order to enhance the activation state of a lymphocyte. FORMULATION AND ROUTE OF ADMINISTRATION A Clasp-1 polypeptide, a fragment thereof or an anti-Clasp-1 antibody may be administered to a subject per se or in the form of a pharmaceutical or therapeutic composition. Pharmaceutical compositions comprising the proteins of the invention may be manufactured by means of conventional mixing, dissolving, granulating, dragee-making, levigating, emulsifying, encapsulating, entrapping or lyophilizing processes. Pharmaceutical compositions may be formulated in conventional manner using one or more physiologically acceptable carriers, diluents, excipients or auxiliaries which facilitate processing of the protein or active peptides into preparations which can be used pharmaceutically. Proper formulation is dependent upon the route of administration chosen. For topical administration the proteins of the invention may be formulated as solutions, gels, ointments, creams, suspensions, etc. as are well-known in the art. Systemic formulations include those designed for administration by injection, e.g. subcutaneous, intravenous, intramuscular, intrathecal or intraperitoneal injection, as well as those designed for transdermal, transmucosal, oral or pulmonary administration. For injection, the proteins of the invention may be formulated in aqueous solutions, preferably in physiologically compatible buffers such as Hanks's solution, Ringer's solution, or physiological saline buffer. The solution may contain formulatory agents such as suspending, stabilizing and/or dispersing agents. Alternatively, the proteins may be in powder form for constitution with a suitable vehicle, e.g., sterile pyrogen-free water, before use. For transmucosal administration, penetrants appropriate to the barrier to be permeated are used in the formulation. Such penetrants are generally known in the art. For oral administration, a composition can be readily formulated by combining the proteins with pharmaceutically acceptable carriers well known in the art. Such carriers enable the proteins to be formulated as tablets, pills, dragees, capsules, liquids, gels, syrups, slurries, suspensions and the like, for oral ingestion by a patient to be treated. For oral solid formulations such as, for example, powders, capsules and tablets, suitable excipients include fillers such as sugars, such as lactose, sucrose, mannitol and sorbitol; cellulose preparations such as maize starch, wheat starch, rice starch, potato starch, gelatin, gum tragacanth, methyl cellulose, hydroxypropylmethyl-cellulose, sodium carboxymethylcellulose, and/or polyvinylpyrrolidone (PVP); granulating agents; and binding agents. If desired, disintegrating agents may be added, such as the cross-linked polyvinylpyrrolidone, agar, or alginic acid or a salt thereof such as sodium alginate. If desired, solid dosage forms may be sugar-coated or enteric-coated using standard techniques. For oral liquid preparations such as, for example, suspensions, elixirs and solutions, suitable carriers, excipients or diluents include water, glycols, oils, alcohols, etc. Additionally, flavoring agents, preservatives, coloring agents and the like may be added. For buccal administration, the proteins may take the form of tablets, lozenges, etc. formulated in conventional manner. For administration by inhalation, the proteins for use according to the present invention are conveniently delivered in the form of an aerosol spray from pressurized packs or a nebulizer, with the use of a suitable propellant, e.g., dichlorodifluoromethane, trichlorofluoromethane, dichlorotetrafluoroethane, carbon dioxide or other suitable gas. In the case of a pressurized aerosol the dosage unit may be determined by providing a valve to deliver a metered amount. Capsules and cartridges of e.g. gelatin for use in an inhaler or insufflator may be formulated containing a powder mix of the compound and a suitable powder base such as lactose or starch. The proteins may also be formulated in rectal or vaginal compositions such as suppositories or retention enemas, e.g, containing conventional suppository bases such as cocoa butter or other glycerides. In addition to the formulations described previously, the proteins may also be formulated as a depot preparation. Such long acting formulations may be administered by implantation (for example subcutaneously or intramuscularly) or by intramuscular injection. Thus, for example, the proteins may be formulated with suitable polymeric or hydrophobic materials (for example as an emulsion in an acceptable oil) or ion exchange resins, or as sparingly soluble derivatives, for example, as a sparingly soluble salt. Alternatively, other pharmaceutical delivery systems may be employed. Liposomes and emulsions are well known examples of delivery vehicles that may be used to deliver the proteins or peptides of the invention. Certain organic solvents such as dimethylsulfoxide also may be employed, although usually at the cost of greater toxicity. Additionally, the proteins may be delivered using a sustained-release system, such as semipermeable matrices of solid polymers containing the therapeutic agent. Various sustained-release materials have been established and are well known by those skilled in the art. Sustained-release capsules may, depending on their chemical nature, release the proteins for a few weeks up to over 100 days. Depending on the chemical nature and the biological stability of the therapeutic reagent, additional strategies for protein stabilization may be employed. As the proteins and peptides of the invention may contain charged side chains or termini, they may be included in any of the above-described formulations as the free acids or bases or as pharmaceutically acceptable salts. Pharmaceutically acceptable salts are those salts which substantially retain the biologic activity of the free bases and which are prepared by reaction with inorganic acids. Pharmaceutical salts tend to be more soluble in aqueous and other protic solvents than are the corresponding free base forms. EFFECTIVE DOSAGES Clasp-1 polypeptides, Clasp-1 fragments and anti-Clasp-1 antibodies will generally be used in an amount effective to achieve the intended purpose. For use to inhibit an immune response, the proteins of the invention, or pharmaceutical compositions thereof, are administered or applied in a therapeutically effective amount. By therapeutically effective amount is meant an amount effective ameliorate or prevent the symptoms, or prolong the survival of, the patient being treated. Determination of a therapeutically effective amount is well within the capabilities of those skilled in the art, especially in light of the detailed disclosure provided herein. For systemic administration, a therapeutically effective dose can be estimated initially from in vitro assays. For example, a dose can be formulated in animal models to achieve a circulating concentration range that includes the IC 50 as determined in cell culture {i.e., the concentration of test compound that inhibits 50% of Clasp-1 binding interactions). Such information can be used to more accurately determine useful doses in humans. Initial dosages can also be estimated from in vivo data, e.g., animal models, using techniques that are well known in the art. One having ordinary skill in the art could readily optimize administration to humans based on animal data. Dosage amount and interval may be adjusted individually to provide plasma levels of the proteins which are sufficient to maintain therapeutic effect. Usual patient dosages for administration by injection range from about 0.1 to 5 mg/kg/day, preferably from about 0.5 to 1 mg/kg/day. Therapeutically effective serum levels may be achieved by administering multiple doses each day. In cases of local administration or selective uptake, the effective local concentration of the proteins may not be related to plasma concentration. One having skill in the art will be able to optimize therapeutically effective local dosages without undue experimentation. The amount of Clasp-1 administered will, of course, be dependent on the subject being treated, on the subject's weight, the severity of the affliction, the manner of administration and the judgment of the prescribing physician. The therapy may be repeated intermittently while symptoms detectable or even when they are not detectable. The therapy may be provided alone or in combination with other drugs. In the case of autoimmune disorders, the drugs that may be used in combination with Clasp-1 or fragments thereof include, but are not limited to, steroid and non-steroid immunosuppressive agents. TOXICITY Preferably, a therapeutically effective dose of the proteins described herein will provide therapeutic benefit without causing substantial toxicity. Toxicity of the proteins described herein can be determined by standard pharmaceutical procedures in cell cultures or experimental animals, e.g., by determining the LD 50 (the dose lethal to 50% of the population) or the LD 100 (the dose lethal to 100% of the population). The dose ratio between toxic and therapeutic effect is the therapeutic index. The data obtained from these cell culture assays and animal studies can be used in formulating a dosage range that is not toxic for use in human. The dosage of the proteins described herein lies preferably within a range of circulating concentrations that include the effective dose with little or no toxicity. The dosage may vary within this range depending upon the dosage form employed and the route of administration utilized. The exact formulation, route of administration and dosage can be chosen by the individual physician in view of the patient's condition. {See, e.g., FingI et al., 1975, In: The Pharmacological Basis of Therapeutics. Ch.1 , p.1). SCREENING ASSAYS In vitro studies may use purified Clasp-1 macromolecules to screen large compound libraries for inhibitory drugs; or the purified target molecule may be used for a rational drug design program, which requires first determining the structure of the target or, the structure of the macromolecular target in association with its customary substrate or ligand. This information is then used to design inhibitory compounds which must be synthesized and tested further. Test results are used to refine the molecular models and drug design process in an iterative fashion until a lead compound emerges. Drug screening may be performed using an in vitro model, a genetically altered cell, or purified protein. One can identify ligands or substrates that bind to, modulate or mimic the action of the target genetic sequence or its product. A wide variety of assays may be used for this purpose, including labeled in vitro protein-protein binding assays, electrophoretic mobility shift assays, immunoassays for protein binding, and the like. The purified protein may also be used for determination of three-dimensional crystal structure, which can be used for modeling intermolecular interactions. The term "agent" as used herein describes any molecule, e.g. protein or pharmaceutical, with the capability of altering or mimicking the physiological function of RAB. Generally a plurality of assay mixtures are run in parallel with different agent concentrations to obtain a differential response to the various concentrations. Typically, one of these concentrations serves as a negative control, i.e. at zero concentration or below the level of detection. Candidate agents encompass numerous chemical classes, though typically they are organic molecules, preferably small organic compounds having a molecular weight of more than 50 and less than about 2,500 daltons. Candidate agents comprise functional groups necessary for structural interaction with proteins, particularly hydrogen bonding, and typically include at least an amine, carbonyl, hydroxyl or carboxyl group, preferably at least two of the functional chemical groups. The candidate agents often comprise cyclical carbon or heterocyclic structures and/or aromatic or polyaromatic structures substituted with one or more of the above functional groups. Candidate agents are also found among biomolecules including peptides, saccharides, fatty acids, steroids, purines, pyrimidines, derivatives, structural analogs or combinations thereof. Candidate agents are obtained from a wide variety of sources including libraries of synthetic or natural compounds. For example, numerous means are available for random and directed synthesis of a wide variety of organic compounds and biomolecules, including expression of randomized oligonucleotides and oligopeptides. Alternatively, libraries of natural compounds in the form of bacterial, fungal, plant and animal extracts are available or readily produced. Additionally, natural or synthetically produced libraries and compounds are readily modified through conventional chemical, physical and biochemical means, and may be used to produce combinatorial libraries. Known pharmacological agents may be subjected to directed or random chemical modifications, such as acylation, alkylation, esterification, amidification, etc. to produce structural analogs. Where the screening assay is a binding assay, one or more of the molecules may be joined to a label, where the label can directly or indirectly provide a detectable signal. Various labels include radioisotopes, fluorescers, chemiluminescers, enzymes, specific binding molecules, particles, e.g. magnetic particles, and the like. Specific binding molecules include pairs, such as biotin and streptavidin, digoxin and antidigoxin efc. For the specific binding members, the complementary member would normally be labeled with a molecule that provides for detection, in accordance with known procedures. A variety of other reagents may be included in the screening assay. These include reagents like salts, neutral proteins, e.g. albumin, detergents, etc that are used to facilitate optimal protein-protein binding and/or reduce non-specific or background interactions. Reagents that improve the efficiency of the assay, such as protease inhibitors, nuclease inhibitors, anti-microbial agents, efc. may be used. The mixture of components are added in any order that provides for the requisite binding. Incubations are performed at any suitable temperature, typically between 4 and 40° C. Incubation periods are selected for optimum activity, but may also be optimized to facilitate rapid high-throughput screening. Typically between 0.1 and 1 hours will be sufficient. The compounds having the desired biological activity may be administered in a an acceptable carrier to a host for treatment of fungal infection, or prevention of infection, efc. The inhibitory agents may be administered in a variety of ways. Depending upon the manner of introduction, the compounds may be formulated in a variety of ways. The concentration of therapeutically active compound in the formulation may vary from about 0.01-100 wt.%. The invention having been described, the following examples are offered by way of illustration and not limitation. EXPERIMENTAL Example 1 cDNA Cloning of CLASP-1 Degenerate oligonucleotide primers were designed on the basis of a highly conserved cytoplasmic domain of classical cadherins corresponding to sequences TAPPYD and FKKLAD. The 5' sense primer had the sequence of GGAATTCCACNGCNCCNCCNTA(CT)GA (SEQ ID NO:5) and the 3' anti-sense primer had the sequence of GCTCTAGATCNGCNA(AG)(CT)TT(CT)TT(AG)AA (SEQ ID NO:6). Total RNA was prepared from mouse thymocytes according to the method of Chomczynski and Sacchi (1987, Anal. Biochem. 162: 156-59), and the RNA was primed with oligo dT and reverse transcribed with MMTV reverse transcriptase (BRL, NY) according to the method of Suzuki etal., (1988, Cell Regul. 2: 807-16). The cDNA was then used for hot start (Ampli-wax, Perkin Elmer, CA) Polymerase Chain Reaction (PCR) in Promega PCR buffer (Promega, Wl) containing Mg (1.5-3.0 mM), 1 μg primer each, 2.5 units of AmpliTaq (Perkin Elmer, CA). The Perkin Elmer Thermocycler (Perkin Elmer, CA) was set to 94°C for a 30 second denaturation, 37°C for a 2 minute annealing, and ramped over 2 minutes to 65°C, which was maintained for a 3 minute extension reaction, for 35 cycles. The PCR products were resolved in 3% NuSieve agarose (FMC, ME): 1% agarose (BRL, NY). The band of predicted size was excised, purified using Sephaglas (Pharmacia, NJ), and reamplified for 20 rounds using the same program. The final product was gel purified, digested with EcoR1 and Xba1 (New England Biolabs, MA), and cloned into pBluescript KS (Stratagene, La Jolla, CA) at the corresponding sites, and its nucleotide sequence determined. Half of the PCR clones sequenced were identical. A representative clone was used to screen a mouse neonatal thymus library to obtain a complete cDNA sequence designated Clasp-1. RESULTS Degenerate oligonucleotides corresponding to consensus sequences of cadherins and other adhesion molecule families were made for use in PCR of cDNA prepared from mouse thymocytes. In addition to several classical cadherin molecules, a sequence that accounted for half of the clones and displayed several features of classical cadherins was isolated (Figure 1a-1b). The full length cDNA clone (SEQ ID NO:2) contains an open reading frame that encodes a 1 ,289 amino acid type I transmembrane protein which shares a number of cadherin features, including the cadherin proteolytic processing signal (Pigott and Power, 1993, The Adhesion Molecule Facts Book, Academic Press Limited), glycosylation sites, a cluster of cysteines proximal to the transmembrane domain (Hofman and Stoffel, 1993, Biol. Chem. Hoppe- Seyler 374: 166), and a cytoplasmic domain that exhibits several cadherin sequence motifs (Figure 2). The processed polypeptide begins at amino acid residue #121 after the amino acid sequence RAQR (Figure 1a). This gene was named Clasp-1 for cadherin-like asymmetry protein. Classical cadherins are transmembrane glycoproteins that mediate homotypic calcium-dependent adhesion through their extracellular domains and connect with the cytoskeleton via catenins through their cytoplasmic domains (Kemler, 1993, Trends Genet. 9: 317-21 ; Geiger and Ayalon, 1992, Annu. Rev. Cell Biol. 8: 307-32; Takeichi, 1991 , Science 251: 1451-55). Unique features of Clasp-1 which are not shared with cadherins include an SH3 binding domain (Knudsen et al., 1994, J. Biol. Chem. 269: 32781-87), several potential tyrosine phosphorylation sites, and coiled/coil domains (Lupas et al., 1991 , Science 252: 1162-64) (Figure la and 1b). Based on its structural characteristics, Clasp-1 may provide a direct interaction between signal transduction pathways and the cytoskeleton. FASTA searches of Clasp-1 (Pearson and Lipman, 1988, Proc. Natl. Acad. Sci. USA 85: 2444-48; Ladunga et al., 1996, J. Mol. Biol. 259: 840-54) revealed similarities with two cDNAs of unknown function, the rat RNTRG (GenBank X68101) and a putative C. elegans gene, CELF46fH5.4 (GenBank U41543). RNTRG is about 75% identical to Clasp-1. Therefore, Clasp-1 is a cell surface cadherin-like protein that contains domains known to be involved in signal transduction pathways. Example 2 Expression Pattern of Clasp-1 And Cellular Localization of its Encoded Product Th1 cells (5CC7), pro-GMB cells (HAFTLJ), pre-B cells (NFS40, HSIC5, BAC14), mature B ceils (BAL17), and plasmacytomas (S194, J598L) were maintained as cultured cell lines. RNA were extracted from these cells for Northern blot analysis. Northern blot analysis: Ten micrograms (μg) total RNA from each cell sample were loaded onto a 1% agarose formaldehyde gel, transferred onto BioBlot nitrocellulose paper (Costar, MA) and crosslinked with Stratalink (Stratagene, La Jolla, CA). Prehybridization and hybridization were performed in 50% formamide, 25mM sodium phosphate (pH 6.5), 1X Denhardt's solution, 200 μg/ml herring sperm DNA, and 5X SSC, at 65°C. Probes corresponding to the coding sequence of Clasp-1 were prepared using Ready-To-Go Labeling Kit (Pharmacia, NJ) according to the manufacturer's instructions, and desalted using pasteur pipet G-50 Sephadex column in TEN (10 mM Tris-HCI, pH 8, 1 mM EDTA, and 100 mM NaCl). The final wash of the blots was in 0.1 X SCC at 60°C. Autoradiography was performed on Kodak XOMAT film at -80°C with an enhancing screen. Cytospin and immunofluorescence: Cells were cytospun (Cytospin 1 , Shandon]) onto poly-L-lysine (Sigma #P2636, MA) slides, fixed in periodate-lysine- paraformaldehyde (McLean and Nakane, 1974, J. Histochem. Cytochem. 22: 1077-83). Primary antibodies were added at 20-30 μg/ml in 10% normal donkey serum, TBS-C (50 mM Tris-HCI, pH 7.4, 150 mM NaCl, 1 mM CaCI 2 ), and 0.4% saponin, and incubated overnight at 4°C. After washing, secondary antibodies (Jackson Immunoresearch, PA) were added and incubated at 37°C for 30 minutes. For extracellular staining, a three-step sandwich assay was used. The first step was Gamma-bind purified goat antisera in 10% normal mouse serum, 10% normal rat serum, TBS-C for overnight at 4°C in a humidifying chamber; the second step was biotin-conjugated monoclonal anti-goat antibody (Sigma, MO) at 1/50 dilution for 2 hours at room temperature; and the last step was strepavidin-PE (Molecular Probes, OR) at 1/50 for 1 hour at room temperature. A FITC-conjugated anti-B200 or anti-CD3 antibody was also added at the last step. Immunohistochemistry: Four-week-old mice were anesthetized and perfusion fixed with 4% paraformaldehyde in 0.1 M cacodylate (pH 7.4). Spleen cryosections (5-7 μm) were permeabilized with CSK (50 mM NaCl, 300 mM sucrose, 10 mM Pipes at pH 6.8, 3 mM MgCI 2 , 0.5% Triton X-100, and 1 mM PMSF) for 10 minutes, and blocked with PBS + 20% normal goat serum, 0.2% BSA, 50 mM NH 4 CI, 25 mM glycine, and 25 mM lysine for 2 hours at room temperature (Greenberg and Edelman, 1983, Cell 33: 767-79). Sections were incubated in 100 μl of the primary antibody in TBS-C + 25% normal goat serum overnight at 4°C and washed three times in TBS-C. One hundred μl of a secondary antibody (Jackson Immunoresearch, PA) was added for two hours at room temperature. Stained sections were examined under Nikon Biophot or Zeiss Axiophot fluorescent microscope and photographs were taken using Kodak Elite ASA 100. RESULTS When lymphoid tissues (thymus, spleen, lymph nodes and bone marrow) were tested for Clasp-1 expression by RNA blot analysis, a 13 kb Clasp-1 transcript was detected. The same transcript was also observed in the brain, but was missing from the liver, lung, muscle, kidney, and skin (Figure 3a). Further analysis in lymphoid cell lines indicated that the Clasp-1 transcript was present in lymphocytes of both T and B cell lineage (Figure 3b). However, the transcript was either absent or minimally expressed in several plasmacytoma lines (S194 and J558L), suggesting that the gene may be turned off in terminally differentiated B cells. Immunostaining of spleen cryosections with an anti-Clasp-1 antiserum revealed that protein expression was most prominent in the marginal zone of the spleen (Figure 4c, M), and in the T (Figure 4a, T) and B (Figure 4b, B) cell zones of the periarterial lymphatic sheaths (PALS). Anti-Clasp-1 antibody also stained macrophages in the MOMA-1 subregion of the marginal zone, an important site for T cell-dependent humoral response (Claassen etal., 1986, Eur. J. Immunol. 16: 492-97), but did not stain the MOMA-I macrophages themselves (van Vliet et al., 1985, J. Histochem. Cytochem. 33: 40-44; Kraal et al., 1988, Immunol. Lett. 17: 139-44) (Figure 4c, 4f). In the PALS, most of the T cells expressed Clasp-I, whereas most of the B cells did not (Figure 4d, 4e). It is noteworthy that the staining pattern in T lymphocytes was apical, and where cells were arranged in clusters their apices were pointed into the B cell zone (Figure 4d, arrow head). Isolated lymphocytes from spleens also displayed the same apical distribution as lymphocytes in vivo (Figure 4g, 4h). T cells (D10) grown in the absence of antigen also exhibited the same surface polar distribution (Figure 4i), as well as B cells (CH27, Figure 4j), indicating that the apical grouping was not the result of antigen-induced crosslinking, but was an inherent property of Clasp-1 itself. To orient the structure to a subcellular landmark {i.e., the microtubule-organizing center), T cells (D10 and 2B4) were stained for both α-tubulin (green) and Clasp-I (red). The apical Clasp-I structure was always observed on the same side of the nucleus (blue) as the microtubule- organizing center (Figure 4k). For most cell types examined, the centrisome was always on the same side of the nucleus as the leading edge, indicating that Clasp-1 pole was associated with the leading edge. To examine the role of Clasp-1 in cell conjugate formation during antigen- presentation by B cells, splenic lymphocytes from 3A9 mice, transgenic for TCR to hen egg lysozyme (HEL 46-61 peptide:l-A k ) (Ho et al., J. Exp. Med. 179: 1539-49), were cultured in the presence of the HEL peptide and allowed to form conjugate T-B cell pairs (Sagerstrom et al., 1993, Proc. Natl. Acad. Sci. USA 90: 8987-91). Cultured cells were removed at 4, 10 and 36 hours. T-B cell pairs were observed by 4 hours, and by 10 hours more than 95% of the tight T-B cell pairs demonstrated early blast transformation (loss of nuclear membrane definition and heterochromatin). In productive interacting cell pairs, Clasp-1 was always found at the cell-cell interface (Figure 5a EXAMPLE 3 INHIBITION OF T CELL-B CELL COUPLING BY ANTI-Clasp-1 ANTIBODY Fusion Protein and Antibodies: A coding sequence for amino acid residues 121- 327 of Clasp-1 (SEQ ID NOS:1 and 2) was cloned into pGEX-4T-1 (Pharmacia, NJ) at the BamH1/Not 1 site and it was referred to as GST-Clasp-EC12A. GST-Clasp-cyto was a construct that contained DNA encoding amino acid residues 969-1289 of Clasp-1 cloned into pGEX-4T-3 (Pharmacia, NJ) at the Notl/EcoRI sites. Fusion proteins were expressed and purified according to instructions from Pharmacia using glutathione- Sepharose columns (Pharmacia, NJ) and used as immunogens for the generation of rabbit and goat antisera. Antibodies MOMA-1 (Kraal and Janse, 1986, Immunology 58: 665-669) and ER-TR-9 (van Vliet et al., 1985, J. Histochem. Cytochem. 33: 40-44) were used as described. Anti-CD4-FITC, CD8-FITC, CD3-FITC, CD45R (B220)-FITC antibodies were purchased from Caltag, CA. YOL 1/34 was purchased from Sera-Tec, (NC). Western Blot analysis: Cells were lysed in 50 mM Hepes (pH 7.4), 150 mM NaCl, 10% glycerol, 1% Triton X-100, Aprotinin (I U /ml), leupeptin (2 μg/ml), pepstatin (I μg/ml), antipain (2 μg/ml), PMSF (1 mM), and 100 μl/ml Sepharose 6L to preclear the lysate. Cell lysate was electrophoresed on 10% SDS-PAGE, blotted onto a PVDF membrane (Millipore, MA) (Harlow and Lane, 1988, Antibodies: A Laboratory Manual, Cold Spring Harbor Laboratory), and blocked overnight in 5% non-fat milk and 2% BSA in TBS-C. Protein-A or Gamma-bind (Pharmacia, NJ) purified anti-Clasp antibodies were added at 10 μg/ml in 0.5% non-fat milk, 0.2% BSA, 50 mM PO 4 (pH 7.4), 0.3 M NaCl, 0.1% Tween-20 and incubated for 2 hours at room temperature. After washing, goat anti-rabbit HRP-conjugated antibodies (Biomeda) were added at 1/5,000 dilution for 1 hour at room temperature, and visualized with ECL (Amersham, IL). Cell conjugation and inhibition assay: 2B4 or D10 T cells and CH27 B cells (loaded overnight with 10 μM moth cytochrome c peptide 88-103 or with conalbumin) were resuspended at 3.4 x 10 5 cells/ml in RPMI + 10% FCS. 120 μl of each cell type were mixed in a 8 well coverslip slide chamber (Nunc, NY) and Gammabind (Pharmacia, NY) purified goat anti-Clasp-EC12A or anti-Clasp-cyto antibodies were added to a final concentration of 0, 50, and 150 μg/ml (pre-immune serum up to 450 μg/ml). Cells were allowed to couple for 5-7 hours at 37°C, then counted in a hemacytometer. For each sample, 100-150 couples were counted and normalized against the total number of cells (typical frequencies were between 7-10%). Percent inhibition was calculated against the frequency of couples in the positive control after subtraction of the frequency of non-specific couples in samples where CH27 B cells were not loaded with moth cytochrome c peptide. RESULTS Antibodies were generated against Clasp-1 fusion proteins. When Western blot analysis was performed using extracts from CH 27 (a mature B cell line) and 2B4 (a T cell hybridoma), antibodies raised against GST-fusion proteins containing either the extracellular domain (Clasp-EC12A) or the cytoplasmic domain (Clasp-cyto) identified a band of about 130 kD molecular weight, which was consistent with the deduced molecular weight of 134 kD (Figure 3c) of Clasp-1. In order to explore the role of Clasp-1 in the establishment of physical linkage between T and B cells, the ability of the antibodies directed against the extracellular domain of Clasp-1 to prevent T-B cell coupling was assessed (Stowers et al., 1995, Proc. Natl. Acad. Sci. USA 92:5027-5031). T cell hybridoma, 2B4, specific for moth cytochrome c:l-E k as mixed with a B cell, CH27, loaded with moth cytochrome c peptide, in the presence of anti-Clasp-EC 12A IgG antiserum. As shown in Figure 6a, T-B cell pairing was blocked in a dose-dependent fashion by the anti-Clasp-EC 12A antiserum, whereas the pre-immune serum had minimal effect on cell coupling even at high antibody concentrations. Similar findings were obtained in another antigen-specific system (D10 T cell line, specific for conalbumin:l-A k ). Furthermore, results of IL-2 assays of T cell activation also mirrored the coupling results (Figure 6b). Thus, the Clasp-1 apical surface domain participates in marking the functional polarity in T cells prior to antigen encounter and in mediating cell-cell interactions between T and B cells following T cell engagement. The present invention is not to be limited in scope by the exemplified embodiments which are intended as illustrations of single aspects of the invention, and any clones, DNA or amino acid sequences which are functionally equivalent are within the scope of the invention. Indeed, various modifications of the invention in addition to those described herein will become apparent to those skilled in the art from the foregoing description and accompanying drawings. Such modifications are intended to fall within the scope of the appended claims. It is also to be understood that all base pair sizes given for nucleotides are approximate and are used for purposes of description. All publications cited herein are incorporated by reference in their entirety.

Claims: WHAT IS CLAIMED IS: 1. An isolated polynucleotide encoding a mammalian CLASP-1 protein. 2. The isolated polynucleotide of Claim 1 , wherein said polynucleotide hybridizes under stringent conditions to the nucleotide sequence of SEQ ID NO:2 or SEQ ID NO:3. 3. The isolated polynucleotide of Claim 2, wherein said polynucleotide comprises the coding sequence as set forth in SEQ ID NO:2 or SEQ ID NO:3. 4. The isolated polynucleotide of Claim 1 , wherein said polynucleotide encodes a mature form of a mammalian Clasp-1 protein. 5. An isolated polynucleotide that hybridizes under stringent conditions to the nucleotide sequence as shown in SEQ ID NO:2, SEQ ID NO:3, or the complements thereof. 6. The isolated polynucleotide of Claim 5, wherein said polynucleotide hybridizes to the 5' region of the nucleotide sequence of SEQ ID NO:3. A recombinant vector comprising the polynucleotide of Claim 1. 8. The recombinant vector of Claim 7, wherein said polynucleotide is operatively associated with a regulatory sequence that controls expression of th epolynucleotide in a host cell. 9. A genetically-engineered host cell containing the polynucleotide of Claim 1 , or progeny thereof. 10. The genetically-engineered host cell of Claim 9, in which the nucleotide sequence of the polynucleotide is operatively associated with a regulatory sequence that controls expression of the polynucleotide in a host cell, or progeny thereof. 11. A method for producing a polypeptide comprising: (a) culturing the genetically-engineered host cell of Claim 10; and (b) recovering the polypeptide from the cultured host cell or its cultured medium. 12. An isolated mammalian Clasp-1 polypeptide. 13. The isolated polypeptide of Claim 12, wherein said polypeptide is a mature form of a mammalian Clasp-1 protein. 14. The isolated polypeptide of Claim 12, wherein said polypeptide comprises the amino acid sequence set forth in SEQ ID NO:1 , or a fragment thereof. 15. The isolated polypeptide of Claim 12, wherein said polypeptide comprises the amino acid sequence set forth in SEQ ID NO:4, or a fragment thereof. 16. The polypeptide of Claim 12, which is cell membrane-associated. 17. The polypeptide of Claim 12 which is soluble. 18. The polypeptide of Claim 12 which is produced by a recombinant DNA method. 19. The polypeptide of Claim 12 which is produced by a chemical synthetic method. 20. The polypeptide of Claim 12 which is fused with a heterologous polypeptide. 21. A pharmaceutical composition comprising the polypeptide of claim 18 and a pharmaceutically acceptable carrier. 22. An antibody which specifically binds to a mammalian Clasp-1 polypeptide or a fragment of the antibody that binds said polypeptide. 23. The fragment of the antibody of Claim 22 which is a Fab, a (Fab') 2 , a Fv, a CDR or a single chain Fv. 24. The antibody of Claim 22 which is a polyclonal antibody. 25. The antibody of Claim 22 which is a monoclonal antibody. 26. A method of inhibiting an immune response comprising contacting a hematopoietic cell with an effective amount of a mammalian Clasp-1 protein or a fragment thereof; and inhibiting activation of said cell. 27. The method of Claim 26 in which the hematopoietic cell is a lymphocyte. 28. The method of Claim 26 in which the lymphocyte is a T lymphocyte. 29. The method of Claim 26 in which the lymphocyte is a B lymphocyte. 30. A method of inhibiting an immune response in a subject, comprising administering to the subject a therapeutically effective amount of a mammalian Clasp-1 protein or a fragment thereof to inhibit the immune response. 31. The method of Claim 30 in which the immune response is directed to an antigen expressed by a cell in the subject. 32. A method of inhibiting an immune response in a subject, comprising administering to the subject a therapeutically effective amount of an antibody which specifically binds a mammalian Clasp-1 protein, to inhibit the immune response. 33. A method of treating an autoimmune disease in a subject, comprising administering to the subject a therapeutically effective amount of mammalian Clasp-1 protein.

Inventors: DAVIS MARK M, LU PETER S, DAVIS, MARK, M., LU, PETER, S.
Applicants: UNIV LELAND STANFORD JUNIOR, THE BOARD OF TRUSTEES OF THE LELAND STANFORD JUNIOR UNIVERSITY
Application year: 1999
Main classification: C07H21
IPC codes: A61K31, A61K35, A61K38, A61K39, A61K48, A61P3, A61P17, A61P19, A61P25, A61P29, A61P37, C07K14, C07K16, C07K19, C12N1, C12N5, C12N15, C12P21, C12Q1