HUMAN Fc gamma RECEPTOR III

Abstract: Soluble and membrane-bound forms of human Fc gamma RIII are provided, together with nucleic acids capable of encoding the same. Soluble Fc gamma RIIIs are useful in ameliorating the serum platelet deficiency associated with immune thrombocytopenic purpura. Cells expressing membrane-bound Fc gamma RIIIs are useful components in assays for serum immune complexes.

Description: HUMAN FC7 RECEPTOR III Field of the Invention The invention relates generally to therapeutic compounds, and more particularly to soluble and membrane- bound forms of a low-affinity receptor for human immunoglobulin G, nucleic acids encoding the same, and diagnostic and therapeutic uses of such receptors. BACKGROUND Receptors for the Fc portion of immunoglobulin G (IgG) play a central role in cellular immune defenses. Three types of such receptors have been identified: A 72 ilodalton ( D) receptor with high affinity for monomeric IgG is found on monocytes and some macrophages, a 40 D receptor with low affinity for monomeric IgG is found on monocytes, neutrophils, eosinophils, platelets and certain human tumor-cell lines, and a 50-70 kD receptor with low affinity for monomeric IgG is found on neutrophils, eosinophils, natural killer cells, and macrophages. These three types of FC receptor are referred to as FC7RI, FC7RII, and FC 7 RIII, respectively: Unkeless et al., Ann. Rev. Immunol. , Vol. 6, pgs. 251-281 (1988). It is believed that Fc 7 RIII-mediated removal IgG-coated platelets plays an important part in the pathogenesis of immune thrombocytopenic purpura (ITP) , a platelet-deficiency condition characterized by excessive bleeding: von de Borne, pgs. 222-256, in Immunohaematology, Engelfriet et al. , eds. (Elsevier, Amsterdam, 1984). Clarkson et al.., New England J. Med. , Vol. 314, pgs. 1236-1239 (1986), report that the infusion of ligand-blocking anti-FcγRIII antibody into a patient with refractory ITP resulted in a transient increase in platelet count. This observation suggests that the most deleterious manifestation of ITP could be temporarily ameliorated by the administration of agents that block or compete with FcγRIII for binding sites on IgG-coated platelets. In a separate area of clinical immunology, elevated serum levels of aggregates consisting of immunoglobulin and antigen (so-called "immune complexes") have been correlated with a wide variety of disorders, particularly autoimmune diseases, such as systemic lupus erythematosus (SLE) , and rheumatoid arthritis. The level of such complexes has become an important diagnostic for presence of autoimmune disorders; e.g. Theofilopoulos et al. , Am. J. Pathol. , Col..100, pgs. 531-591 (1980). Present assays for the serum level of immune complexes include solid-phase assays which take advantage of the affinity of the complexes for certain complement or rheumatoid factor proteins, and cellular assays which take advantage of the property of Raji cells to preferentially bind immune complexes; Theofilopoulos et al., chapter 28, and Toth et al., chapter 29, in Rose et al., eds. Manual of Clinical Immunology, 3rd Ed. (American Society for Microbiology, Washington, D.C., 1986) . Unfortunately, like many mammalian-cell based assays, the Raji-cell assay is difficult to perform, and requires elaborate controls and standards because of the inherent variability of Raji-cell binding to immune complexes. In light of the foregoing, it would be advantageous for the medical community to have alternative assay methods for immune complexes utilizing well characterized, widely available, and conveniently cultured cell lines. It would also be advantageous if soluble FC 7 RS could be produced in sufficient quantity to permit practical emergency therapy for refactory cases of ITP. SUMMARY OF THE INVENTION The present invention is directed to soluble and membrane-bound human FC7RIII polypeptides, their muteinε, nucleic acids capable of encoding the same, and diagnostic and therapeutic uses of such polypeptides and muteins. The invention is based on the discovery of a cDNA encoding a human FC 7 RIII. A cDNA clone, pcD(SR ) containing the Fc 7 RIII-encoding insert (illustrated in Figure 1) is deposited in E„ coli K12 strain MC1061 with the American Type Culture Collection (ATCC) , Rockville, Maryland, USA, under accession number 67707. Preferred embodiments of the invention include proteins having a ino acid sequences selected from the group of 2-fold substituted and 1-fold deleted sequences defined by the formulas: X(Arg) - X(Thr) - X(Glu) - X(Asp) - X(Leu) - X(Pro) - X(Lys) - X(Ala) - X(Val) - X(Val) - X(Phe) - X(Leu) - X(Glu) - X(Pro) - X(Gln) - X(Trp) - X(Tyr) - X(Arg) - X(Val) - X(Leu) - X(Glu) - X(Lys) - X(Asp) - X(Ser) - X(Val) - X(Thr) - X(Leu) - X(Lys) - X(Cys) - X(Gln) - X(Gly) - X(Ala) - X(Tyr) - X(Ser) - X(Pro) - X(Glu) - X(Aεp) - X(Asn) - X(Ser) - X(Thr) - X(Gln) - X(Trp) - X(Phe) - X(His) - X(Aεn) - X(Glu) - X(Asn) - X(Leu) - X(Ile) - X(Ser) - X(Ser) - X(Gln) - X(Ala) - X(Ser) - X(Ser) - X(Tyr) - X(Phe) - X(Ile) - X(Aεp) - X(Ala) X(Ala) - X(Thr) - X(Val) - X(Asp) - X(Asp) - X(Ser) X(Gly) - X(Glu) - X(Tyr) - X(Arg) - X(Cys) - X(Gln) X(Thr) - X(Asn) - X( eu) - X(Ser) - X(Thr) - X(Leu) X(Ser) - X(Asp) - X(Pro) - X(Val) - X(Gln) - X(Leu) X(Glu) - X(Val) - X(His) - X(Val) - X(Gly) - X(Trp) X(Leu) - X(Leu) - X(Leu) - X(Gln) - X(Ala) - X(Pro) X(Arg) - X(Trp) - X(Val) - X(Phe) - X(Lys) - X(Glu) X(Glu) - X(Asp) - X(Pro) - X(Ile) - X(His) - X(Leu) X(Arg) - X(Cys) - X(His) - X(Ser) - X(Trp) - X(Lys) X(Asn) - X(Thr) - X(Ala) - X(Leu) - X(His) - X(Lyε) X(Val) - X(Thr) - X(Tyr) - X(Leu) - X(Gln) - X(Asn) X(Gly) - X( yε) - X(Asp) - X(Arg) - X(Lys) - X(Tyr) X(Phe) - X(His) - X(His) - X(Asn) - X(Ser) - X(Asp) X(Phe) - X(Hiε) - X(Ile) - X(Pro) - X(Lys) - X(Ala) X(Thr) - X(Leu) - X(Lys) - X(Asp) - X(Ser) - X(Gly) X(Ser) - X(Tyr) - X(Phe) - X(Cys) - X(Arg) - X(Gly) X(Leu) - X(Val) - X(Gly) - X(Ser) - X( ys) - X(Asn) X(Val) - X(Ser) - X(Ser) - X(Glu) - X(Thr) - X(Val) X(Asn) - X(Ile) - X(Thr) - X(Ile) - X(Thr) - X(Gln) X(Gly) - X(Leu) - X(Ala) - X(Val) - X(Ser) - X(Thr) X(Ile) - X(Ser) - X(Ser) - X(Phe) - X(Ser) - X(Pro) X(Pro) - X(Gly) Formula 1 and X(Arg) - X(Thr) - X(Glu) - X(Asp) - X(Leu) - X(Pro) X(Lys) - X(Ala) - X(Val) - X(Val) - X(Phe) - X(Leu) X(Glu) - X(Pro) - X(Gln) - X(Trp) - X(Tyr) - X(Arg) X(Val) - X(Leu) - X(Glu) - X(Lys) - X(Asp) - X(Ser) X(Val) - X(Thr) - X(Leu) - X(Lys) - X(Cys) - X(Gln) X(Gly) - X(Ala) - X(Tyr) - X(Ser) - X(Pro) - X(Glu) X(Asp) - X(Asn) - X(Ser) - X(Thr) - X(Gln) - X(Trp) 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 3 c φ ft tn r-\ φ c φ Φ 3 3 c 0 ft Ul 3 φ r-\ φ r-H r-\ r- Ul u Φ id r-H rH A r-i φ φ φ Ul Ul φ rH rH <d A 13 o H < CO > H ft H CO • ft < o co CD H > ft 1 1 1 1 1 1 1 1 1 1 ' 1 1 1 1 1 1 1 1 1 1 1 1 1 U) 3 c ft r-H 3 ft ft Ul V. Ul Ul 3 φ JH Φ 3 u •H φ A rH Ul Ul Φ Ul A A ι •rH φ 1 A φ rH Φ φ r-i co EH < < > in < EH EH X EH ft CO H CO ~- X X X X X X X X X X X X X X X X X X X X X X X X X 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 φ φ id >1 3 3 3 & • < c r-H φ φ u 3 rH c >1 φ 0 A r-i φ i-l r-H φ r-l Φ rH Ul rd A A A φ φ rd Ul rH rH u ft H CO < o H CO < < > ft ft EH co > < H ft o x x x x x x x x x x x x x x x x x x x x x x x x x O 00 O Sequence and Structure 1972, Vol. 5, pgs. 89-99. It is clear that deletions of amino acids may also be made in the above-identified sequence without altering biological function, particularly if only a few amino acids are deleted and amino acids that are critical to a functional conformation are not removed or displaced, e.g. some cysteine residues: Anfisen, "Principles That Govern The Folding of Protein Chains", Science, Vol. 181, pgs. 223- 230 (1973) . Proteins and uteins produced by deletions are within the purview of the present invention. Whenever an amino acid residue of a protein of Formula I or II is referred to herein by number, such a number is in reference to the N-terminus of the protein. Preferred, and more preferred, groups of synonymous amino acids for each amino are listed in Table I. The respective groups for each amino acid are indicated by slashes (_ ) . Amino acids to the left of the slash make up the most preferred group. All the amino acids on the same line make up the more preferred group. As used herein, "N-fold substituted" in reference to Formula I or II describes a group of amino acid sequences differing from the -native amino acid sequences of Formula III or IV, respectively, by zero-N substitutions, such that the replacing amino acid is selected from the appropriate group of amino acids synonymous to the amino acid at the location of the substitution. That is, if the X(Ala) is at. the location for substitution, then the Ala at that location can be replaced with Ser, Thr, or Gly. Likewise, as used herein, the term "N-fold deleted" in reference to Formula I or II describes a group of amino acid sequences differing from the native amino acid sequences of Formula III or IV, respectively, by zero-N deletions of amino acids. Throughout, standard abbreviations are used to designate amino acids, nucleotideε, restriction endonucleaseε, and the like; e.g. Cohn, "Nomenclature and Symbolism of a-Amino Acids," Methods in Enzymology, Vol. 106, pgs. 3-17 (1984) ; Wood et al. Biochemistry: A Problems Approach, 2nd ed. (Benjamin, Menlo Park, 1981) ; and Roberts, "Directory of Restriction Endonucleaseε", Methods in Enzymology, Vol. 68, pgs. 27-40 (1979). Table I Preferred and More Preferred Groups of Synonymous Amino Acids Amino Acid Synonymous Groups Ala Ala Ser / Thr Gly Arg Arg / Lys Asn Aεn Aεp / Ser Aεp Asp Glu / Asn Cys Cys Gin Gin / Glu Glu Glu Aεp / Gin Gly Gly Ala / Ser His His / Asn lie He Val / Leu Leu Leu Val / lie Lys Lys Arg / Asn Met Met / Leu Phe Phe Pro Pro / Ala Ser Ser Ala Thr / Gly Asn Thr Thr Ser Ala / Lys Trp Trp Tyr Tyr Val Val He / Ala Leu Brief Deεcription of The Drawingε Figure 1, parts A and B (on two sheets to be read side-by-side) illustrates the nucleotide sequence of the cDNA insert of pcD(SRα)-GP5; Figure 2 illustrates the relative location of the stop codon inserted to produce a soluble human FC 7 RIII, secreted as an FC 7 RIII mutant; Figure 3 illustrates the result of gel electrophoretic analysis of the soluble FC 7 RIII produced in Example III below; and Figure 4 parts A and B (on two sheets to be read side-by-side) illustrates the necleotide sequence of the cDNA insert of pcD(SR )-NL10. DETAILED DESCRIPTION OF THE INVENTION The present invention includes nucleic acids encoding polypeptides capable of binding to the Fc portion of human IgG. These polypeptides are derived from human FC 7 RIII. The invention includes soluble and membrane-bound polypeptides for human FC 7 RIII. These and other modified versions of the polypeptides are readily produced using standard protein engineering techniques. Once nucleic acid sequence and/or amino acid sequence information is available for a native protein, a variety of techniques become available for producing virtually any mutation in the native sequence. Shortle, in Science, Vol. 229, pgs. 1193-1201 (1985), reviews techniques for mutating nucleic acids which are applicable to the present invention. Preferably, mutants of the protein of the present invention are produced by site-specific oligonucleotide-directed mutagenesis, e.g. Zoller and Smith, Methods in Enzymology, Vol. 100, pgs. 468-500 (1983), and Mark et al., U.S. Patent 4,518,584 entitled "Human Recombinant Interleukin-2 Muteins", which are incorporated by reference; or by so-called "cassette" mutagenesis described by Wells et al. in Gene, Vol. 34, pgs. 315-323 (1985), by Estell et al. in Science, Vol. 233, pgs. 659-663 (1986), and also essentially by Mullenbach et al. in J. Biol. Che . , Vol. 261, pgs. 719- 722 (1986), and by Feretti et al. in Proc. Natl. Acad. Sci. , Vol. 83, pgs. 597-603 (1986). Polypeptides with amino acid modifications (i.e. muteins) may be desirable in a variety of circumstances. For example, undesirable side effects might be reduced by certain muteins, particularly if the side effect is associated with a different part of the polypeptide from that of the desired activity. In some expreεεion systems, the native polypeptide may be suεceptible to degradation by proteaεes. In such cases, selected substitutionε and/or deletions of amino acids which change the susceptible sequences can significantly enhance yields, e.g. British patent application 2173-804- A where Arg at position 275 of human tissue plas inogen activator is replaced by Gly or Glu. Muteins may also increase yields in purification procedures and/or increase shelf lives of proteins by eliminating amino acids suεceptible to oxidation, acylation, alkylation, or other chemical modifications. For example, methionine readily undergoes oxidation to form a sulfoxide, which in many proteins is associated with loss of biological activity: e.g. Brot and Weissbach, Arch. Biochem. Biophys. , Vol. 223, pg. 271 (1983). Methionineε can often be replaced by more inert amino acids with little or no loss of biological activity, e.g. Australian patent application AU-A-52451/86. In bacterial expresεion systems, yields can sometimeε be increaεed by eliminating or replacing conformationally ineεεential cysteine residues, e.g. Mark et al., U.S. Patent 4,518,584. Preferably, soluble forms of the FC 7 RIII of the invention are produced by introducing a stop codon prior to (i.e. in the 5'- or "upstream* direction of) the coding region for the transme brane and intracellular portions of the Fc-γRIII cDNA. This is conveniently done by site-specific mutagenesis. Transmembrane regions are readily identified by the presence of an amino acid segment containing from about 20-25 residues having high average hydrophobicity, e.g. Wickner, Science, Vol. 210, pgs. 861-868 (1980) , and Greene et al. , Ann. Rev. Immunol. , Vol. 4, pgε. 69-95 (1986). Plas id pcD(SRα)-GP5 is similar to the pcD shuttle vector described by Okayama and Berg, Mol. Cell. Biol. , Vol. 2, pgs. 161-170 (1983), and Vol. 3, pgs. 280- 289 (1983) , except that the SV40 promoter has been modified to improve expression by the downstream insertion of a portion of the long terminal repeat (LTR) from a HTLV(I) retrovirus, described by Takebe et al., Mol. Cell. Biol., Vol. 8, pgε. 466-472 (1988). The plasmid is conveniently propagated in E^ coli K12 strain MC1061, or like host. The immunoglobulin G binding property of the FcγRIIIs of the invention is measured by standard techniques, e.g. (1) in the case of membrane-bound FC 7 RIII: the ability of cells transfected with the FC 7 RIII cDNA to form roεettes in the presence of IgG- coated red blood cellε (RBCε) or to preferentially bind human IgG aggregated by heat treatment; or (2) in the case of soluble FC 7 RIII: the ability to preferentially remove FC T RIII from solution by an immunoadsorbent column comprising human IgG, or to inhibit rosette formation between IgG-coated RBCs and cells known to have FC 7 RIIIS. The former easurementε can be made with fluoreεcently labeled human IgG moleculeε, e.g. Haugland, Handbook of Fluorescent Probes (Molecular Probes, Inc., Junction City, OR, 1985) . The latter measurements can b made by constructing an IgG column from isolated human IgG and a commercially available activated sepharose column, e.g. from Bio-Rad Laboratories (Richmond, CA) . Rosette assays are standard in the art, e.g. Winchester et al., chapter 31, in Rose et al., eds., Manual of Clinical Laboratory Immunology, 3rd Ed. (American Society for Microbiology, Washington, D.C., 1986) . Once the cDNA of the invention has been cloned, a wide range of expression systems (i.e. combinations of host and expresεion vector) can be used to produce the proteinε of the invention. Possible types of host cells include, but are not limited to, bacterial, yeaεt, inεect, mammalian, and the like. Selecting an expreεsion system, and optimizing protein production thereby, involves the consideration and balancing of many factorε, including (1) the nature of the protein to be expreεsed, e.g. the protein may be poisonous to some host organisms, it may be susceptible to degradation by host proteases, or it may be expressed in inactive conformations or in insoluble form in some hosts, (2) the nature of the messenger RNA (mRNA) corresponding to the protein of interest, e.g. the mRNA may have sequences particularly susceptible to host endonucleaεeε, which draεtically reduce the functional lifetime of the mRNA, or the mRNA may form εecondary structures that mask the εtart codon or ribosome binding site, thereby inhibiting initiatioii of translation in some hosts, (3) the selection, availability, and arrangement of host-compatible expreεsion-control sequences in the 3'- and 5'-regions flanking the coding region — these include promoters, 5'- and 3'-protector sequences, ribosome binding sites, transcription terminators, enhancers, polyadenylate addition sites, cap sites, intron-splice εites, and the like, (4) whether the protein has a secretion-signal sequence which can be processed by the host, or whether an expression-control sequence encoding a signal sequence endogenous to the host must be spliced onto the region encoding the mature protein, (5) the available modes and efficiencies of transfection or transformation of the host, and whether transient or stable expression is desired, (6) the scale and cost of the host culture system deεired for expresεing the protein, (7) whether, and what type of, poεttranεlational modificationε are deεired, e.g. the extent and kind of glycoεylation desired may affect the choice of host, (8) the eaεe with which the expressed protein can be separated from proteins and other materials of the hoεt cells and/or culture medium e.g. in some cases it may be desirable to express a fusion protein with a specialized signal sequence to aid in later purification steps, e.g. Sassenfeld et al., Biotechnology, January 1984, (9) the stability and copy number of a particular vector in a selected host, e.g. HofSchneider et al. , eds. Gene Cloning in Organisms Other than E. coli (Springer Verlag, Berlin, 1982) , and (10) like factors known to those skilled in the art. Many reviews are available which provide guidance for making choices and/or modificationε of specific expression systems in light of the recited factors, e.g., de Boer and Shepard, "Strategies for Optimizing Foreign Gene Expression in Escherichia coli" pgε. 205-247, in Kroon, ed. Genes: Structure and Expression (John Wiley S- Sons, New York, 1983), review several E. coli expreεsion systems; Kucherlapati et al., Critical Reviews in Biochemistry, Vol. 16, Issue 4, pgs. 349-379 (1984), and Banerji et al., Genetic Engineering, Vol. 5, pgs. 19-31 (1983) review methods for transfecting and transforming mammalian cells; Reznikoff and Gold, edε., Maximizing Gene Expression (Butterworths, Boston, 1986) review selected topics in gene expression in E. coli, yeast, and mammalian cells; and Thilly, Mammalian Cell Technology (Butterworths, Boston, 1986) reviews mammalian expresεion εystems. Likewise, many reviews are available which describe techniques and conditions for linking and/or manipulating specific cDNAs and expression control sequenceε to create and/or modify expresεion vectors suitable for use with the present invention: e.g. Maniatis et al.. Molecular Cloning: A Laboratory Manual (Cold Spring Harbor Laboratory, N.Y., 1982); Glover, DNA Cloning: A Practical Approach, Vol. I and II (IRL Press, Oxford, 1985) , and Perbal, A Practical Guide to Molecular Cloning (John Wiley & Sons, N.Y., 1984). Suitable expresεion εyεtemε for the invention include those disclosed by Itakura and Riggs, U.S. patent 4,704,362 (bacterial expresεion), by Clark et al., U.S. patent 4,675,285 and by Hamer U.S. patent 4,599,308 (mammalian expreεεion) , and by Kurjan et al., U.S. patent 4,546,082 (yeast expresεion). Accordingly, the above patentε are incorporated by reference. Whenever SV40-baεed vectors are used, e.g. pcD vectors, a preferred host is the COS7 cell line, described by Gluzman, Cell, Vol. 23, pgs. 175-182 (1981) and available from the ATCC under accession number CRL1651. Soluble FC 7 RIIIS of the invention are administered as a pharmaceutical composition for treating ITP. Such compositions contain an effective amount of the FC 7 RIII in a pharmaceutical carrier. A pharmaceutical carrier can be any compatible, non-toxic substance suitable for delivering the compositions of the invention to a patient. Generally, compositions useful for parenteral administration of such drugs are well known, e.g. Remington's Pharmaceutical Science, 15th Ed. (Mack Publishing Company, Easton, PA 1980) . Alternatively, compositions of the invention may be introduced into a patient's body by an implantable drug delivery system, e.g. Urquhart et al., Ann. Rev. Pharmacol. Toxicol., Vol. 24, pgs. 199-236 (1984). When administered parenterally, the soluble FcγRIIIs will be formulated in a unit dosage injectable form (solution, suspension, emulsion) in association with a pharmaceutical carrier. Such carriers are inherently non-toxic and non-therapeutic. Examples of such carriers are normal saline, Ringer's solution, dextrose solution, and Hank's solution. Nonaqueous carrierε εuch as fixed oils and ethyl oleate may also be used. A preferred carrier is 5% dextrose/saline. The carrier may contain minor amounts of additives such as substanceε that enhance isotonicity and chemical stability, e.g., buffers and preservatives. The soluble FC7RIII is preferably formulated in purified form substantially free of aggregates and other proteins at a concentration in the range of about 5 to 30 mg/ml, and preferably at a concentration in the range of about 10 to 20 mg/ml. Selecting an administration regimen to deliver to a patient an amount of soluble FC 7 RIII which is effective inameliorating the thrombopenia associated with ITP depends on several factors, including the serum turnover rate of the soluble FC7RIII, the serum level of competing endogenous FcγRIII associated with the immune disorder, the posεible im unogenicity of the soluble FcγRIII, and the like. Preferably, an administration regimen maximizes the amount of soluble FC7RIII delivered to the patient consistent with an acceptable level of side effects. Accordingly, the amount of soluble FC 7 RIII delivered depends in part on the particular soluble FcγRIII employed and the severity of the disease being treated. Guidance in selecting appropriate doses is found in the literature on therapeutic uses of antibodies and antibody fragments, which are polypeptides of roughly the same size as the soluble FC 7 RIIIS, e.g. Bach et al., chapter 22, in Ferrone et al., eds., Handbook of Monoclonal Antibodies (Nogeε Publications, Park Ridge, NJ, 1985); and Russell, pgs. 303-357, and Smith et al., pgs. 365-389, in Haber et al. , eds. Antibodies in Human Diagnosis and Therapy (Raven Press, New York, 1977) . Preferably, the dose is in the range of about 1-20 mg/kg per day, more preferably about 1-10 mg/kg per day. EXAMPLES The following exampleε serve to illustrate the present invention. Selection of vectors and hosts as well as the concentration of reagents, temperatures, and the values of other variables are only to exemplify application of the present invention and are not to be considered limitations thereof. Example I. Construction of stable mammalian cell transformants which express human FC 7 RIII Preferably, mammalian cell lines capable of εtable expresεion of the FC 7 RIII are produced by cotransfecting a host mammalian cell with a vector carrying a selectable marker and a vector carrying a host-compatible promoter and the FC7RIII cDNA insert. For pcD(SRα)-GP5, suitable hosts include Chinese hamster ovary cells, COS monkey cells, and ouεe L cellε, εuch as a thy idine kinaεe deficient mutant (tk~) L cell available from the American Type Culture Collection under accession number CCL 1.3. The selectable marker allows one to select host cells which have a high probability of containing the FC 7 RIII gene fully integrated into the host genome. Typically, the ratio of pcD(SRα)-GP5 to the marker-containing vector in the transfection solution is about 10:1. Thus, if the marker gene is integrated into the host genome, it is very likely that pcD(SR )-GP5 will also be integrated by virtue of its higher concentration. The selectable marker also provideε a means of preventing the cultures of desired transformantε from being overgrown by revertant cellε. tk~ mouεe L cellε are cotransfected with pcD(SRα)-GP5 and pSV2tk, a pSV2 plasmid carrying a thy idine kinase gene under control of the SV40 early promoter. The pSV2 plasmid is described by Mulligan et al., Science, Vol. 203, pgε. 1422-1427 (1980), and by Subramani et al. , Mol. Cell. Biol., Vol. 1, pgs. 854-864 (1981) , and is available from the American Type Culture Collection under accession number 37146. Both plasmids are amplified in E. coli, e.g. strain HB101 available from the ATCC under accesεion number 33694, and purified by cesium chloride equilibrium centrifugation. A suεpension of abut 1 x 10 5 of tk~ " L cells in 10 ml of Dulbecco's Modified Eagle Medium (DME) with 10% fetal bovine serum is placed in a Falcon 3003 dish and cultured at 37°C for 20 hours in a 5% carbon dioxide gas incubator, after which the medium is replaced by 10 ml of fresh DME with 10% fetal bovine serum. The culture is incubated for an additional 4 hours. After incubation, 0.5 ml of solution A (50 mM Hepes, 280 M NaCl, 1.5 mM sodium phosphate buffer, pH 7.22) and 0.5 ml of solution B (2M CaCl 2 , 10 μ q pcD(SRα)-GP5, 1 μ q pSV2tk) are added to the culture medium, and the culture is incubated at 37°C for 24 hours in a 5% C0 2 atmosphere, after which the cells are placed in a selective medium with HAT (e.g. Sigma Chemical Co., St. Louis, MO). After two weeks the surviving colonies are subcloned by limiting dilution, and cloneε are aεsayed for expresεion of FC7RIII. Example II. Use of stable L cell transformant expressing membrane-bound FC 7 RIII to measure serum levels of immune complex A stably transformed mammalian cell expressing the FC 7 RIII of the invention can replace the Raji cell line in asεays for immune complexes, e.g. Theofilopoulos et al., chapter 28, Manual of Clinical Laboratory Immunology, 3rd Ed. (American Society for Microbiology, Washington, D.C. 1986). Antiserum to human IgG is prepared in rabbits, and the IgG fraction is isolated by ammonium sulfate precipitation followed by fractionation on an anion- exchange chromatography column (DEAE-cellulose 52; Whatman Chemical Separation Ltd. , Maidstone, England) . Antiεerum from commercial εources may also be used. The IgG fraction of the antiεerum iε brought to 5 mg/ml, and 1 ml iε labeled with 125 I. After iodination and dialysis, the antiserum is diluted to 1 mg/ml with phosphate-buffered saline (PBS) to give a specific activity of about 3 x 10 5 cpm/μg. Cells transformed with the FC 7 RIII cDNA are harvested after 72 hours of culture, and portions of 2 x 10 6 cells in 200 i of medium are placed in 1.5-ml plastic Eppendorf conical tubes (Brinkmann Instru entε, Inc., Weεtbury, N.Y.; catalog no. 22-36-411-1). One ml. of Spinner medium (Eagle minimal medium without Ca 2+ and Mg 2+ ) is added to each tube, and the cells are centrifuged at 800 x g for 8 min. Supernatant fluids are aspirated, and the cell pellets are resuspended in 50 μ l of Spinner medium. Serum to be teεted iε diluted fourfold in 0.15 M NaCl (phyεiological εaline) , and 25 μl iε added to the tranεformed cellε. After a 45-min incubation period at 37°C with gentle εhaking by hand every 5 to 10 min, the cellε are waεhed three times with Spinner medium. After the final wash, the cells, gently shaken every 5 to 10 minutes, are allowed to react for 30 min at 4°C with 125 I-labeled rabbit anti-human IgG diluted with Spinner medium containing 10 g of human serum albumin (HSA) per liter. After incubation, the cells are washed three times, supernatant fluids are completely aspirated, and radioactivity of the cell pellet is determined in a gamma counter. All assayε ' are done in duplicate. The amount of uptake, expreεεed as absolute counts, percentage of the input, or micrograms of antibody, is referred to a standard curve of radioactive antibody uptake by cells incubated wath normal human serum (complement source) containing various amounts of aggregated human IgG (AHG) . The quantity of immune complex in serum is equated to an amount of AHG after correction for the dilution factor and is expressed as micrograms of AHG equivalent per milliliter of serum. The soluble AHG iε formed from a solution of 6.5 mg of Cohn fraction II or isolated human IgG per ml of phyεiological saline, heated at 63°C for 30 min, and centrifuged (1,500 x g, 15 min) to remove insoluble large aggregates. The εupernatant iε then diluted with buffer to yield a final concentration of approximately 1.6 mg/ml. Portions (0.5 ml) of this preparation are stored at -70°C and can be used for as long aε 1 month. The εtandard curve of radioactive antibody uptake iε constructed as followε. Fifty-microliter portionε of AHG (80 μq of protein) are εerially diluted (11 twofold dilutions) in saline. Subsequently, 50 μ l of a twofold dilution of normal human serum (source of complement) , freshly obtained or stored at -70°C, is added to each dilution of AHG, mixed carefully, and incubated at 37°C for 30 min. Thereafter, 25 μl of each mixture is added to 2 x 10 6 cells in duplicate (fourfold final dilutions of serum containing from 20 μq to about 20 ng of AHG) ; the mixture is incubated, washed, and reacted with radiolabeled antibody. Radioactivity is then counted as with the test sera. A base line of radioactive antibody uptake (background) by cells incubated with 25 μl of a fourfold dilution of normal human serum, used as a source of complement in the reference curve, is also established. Standard preparatins of IgG aggregates and of tetanus toxoid-human anti-tetanus toxoid immune complexes have recently been developed under the auspices of the International Union of Im unologistε and are available through the Swisε Red Cross Blood Transfuεion Service, e.g. Nydegger et al., Clin. Exp. Immunol., Vol. 58, pgs. 502-509 (1984) . Example III. Conεtruction of a soluble human FC7RIII Soluble FC 7 RIII was constructed using site- specific oligonucleotide-directed mutagenesis of the FC 7 RIII cDNA inεert of pcD(SRα)-GP5. The entire cDNA insert of pcD(SRα)-GP5 was εubcloned as a 2.4 kilobase Bam HI fragment into the Bluescript KS plasmid (Stratagene, San Diego, CA) and single-stranded DNA was then prepared. A synthetic oligonucleotide (minimum size about 18 nucleotides) encoding a TAA stop codon and a Bam HI site (with mutations shown in boldface in Figure 2) was used as a primer for complementary strand synthesiε uεing DNA poly eraεe I large fragment (Amerεham, Arlington Heights, IL) . Figure 2 indicateε the position of the stop codon and Bam HI site relative to the major domains encoded by the FC 7 RIII cDNA: S represents the region encoding the signal peptide, EC represents the region encoding the extracellular domain of FC7RIII, H repreεents the region encoding the hydrophobic, or transmembrane, domain of FC7RIII, and C represents the region encoding the cytoplasmic domain. Introducing the stop codon as indicated by Figure 2 produces a mutant FC 7 RIII lacking both the cytoplasmic and transmembrane domains; it is soluble as shown by the designation "sFc-γRIII" beside the modified DNA sequence. After the identity of the mutant was confirmed by DNA sequence analysis, it was subcloned back into the Bam HI site of the pcD(SRα) vector, amplified in E. coli, and transfected into COS 7 cells by electroporation. One day prior to transfection, approximately (1.5-2.0) x 10 6 COS 7 monkey cells were seeded onto individual 100 mm plates in Dulbecco's modified Eagle's medium (DME) containing 6% fetal calf serum and 2 mM glutamine. To perform the transfection, cells were harveεted by trypsinization and counted, washed twice in serum-free DME, and suεpended to (1-7) x 10 6 cellε per ml in serum-free DME. DNA was added to 25 μg/ml and the mixture was allowed to stand at room temperature for 10 minuteε, after which 0.8 ml waε pulsed in a 0.4 cm sterile cuvette with a Bio Rad (Richmond, CA) Gene Puls.er at 250 volts and 960 microfaradε. After pulεing, cellε were allowed to εtand for 10 minuteε and then were plated at (1.5-2.0) x 10 6 per 100 mm pf te in DME pluε 6% fetal calf serum. Supernatants were harvested and assayed for soluble FcγRIII after 72 hours. The soluble FC7RIII in the COS7 culture supernatants was analyzed further by gel electrophoresis, and immunopreci itated. The results of this are illustrated in Figure 3. Lanes 1, 3 and 6 each contain proteins from culture supernatants of C0S7 cells transfected with the pcD carrying the soluble FcγRIII cDNA. Lane 1 proteins were immunoprecipitated with a non-specific mouse IgG 2 antibody; Lane 3 proteins were immunoprecipitated with human IgG, presumably by the binding of the Fc portion of the antibody with the soluble FC 7 RIII; and Lane 6 proteins were immunoprecipitated with the monoclonal antibody 3G8 which is specific for the extracellular domain of FC 7 RIII. Size markers adjacent to the Control lane (lane 1) are in kilodaltons. The soluble FC7RIII corresponds to the broad band at about 40 kilodaltons. Lanes 4 and 7 contain proteins from culture supernatants of COS7 cellε transfected with the pcD carrying the soluble FC 7 RIII cDNA and cultured in the presence of tunicamycin. Tunicamycin inhibits the posttranεlational attachment of N-linked carbohydrates to proteins. It was applied in an attempt to determine the nature of the apparent heterogeneity of the 40 kilodalton band. As shown in Figure 2, the tunicamycin causeε the appearance of two bands of lower molecular weight, which is consistent with the deglycosylation of the soluble FC 7 RIII. Tunicamycin was added to the cultures as disclosed by Martens et al., PNAS _8 : 809-813 (1987) . Lanes 2 and 5 contain proteins from culture supernatants of COS7 cells which had undergone the same manipulations as the COS cellε of laneε 3 and 4 and lanes 6 and 7, reεpectively, with the exception that no plasmid DNA waε included in the transfection protocol. Example IV Isolation of a Variant human FC7RIII from Natural Killer Cells. A cDNA library was constructed from mRNA extracted from a human natural killer (NK) cell line using the pcD(SRα) expression vector. The library was screened with a probe constructed from the cDNA insert of pcD(SRα)-GP5, which was radiolabeled with 31 P by random- primed DNA labeling (Boehringer Mannheim, Indianapolis, IN) . A clone pcD(SRα)-NL10 was obtained that exhibited human IgG binding activity. The sequence of the cDNA insert of pcD(SRα)-NL10 is illustrated in Figure 4. It can be seen that the amino acid sequence of this FcγRIII and that encoded by pcD(SRα)-GP5 are very similar, differing in the extracellular domain by only six amino acids. The descriptions of the foregoing embodiments of the invention have been presented for purpose of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise formε disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments are chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with such modifications as are εuited to the particular use contemplated. It iε intended that the scope of the invention be defined by the claims appended hereto. Applicants have deposited pcD(SRα)-GP5 with the American Type Culture Collection Rockville, MD, USA (ATCC) , under accession number 67707. This depoεit iε made under the Budapeεt Treaty for the Deposit of Microorganisms; and also under conditions as provided under ATCC's agreement for Culture Deposit for Patent Purposeε, which aεsures that the deposit will be made available to the US Commisεioner of Patentε and Trademarkε pursuant to 35 U.S.C. 122 and 37 C.F.R. 1.14, and will be made available to the public upon iεsue of a U.S. patent, which requires that the deposit be maintained. Availability of the deposited strain is not to be contrued as a license to practice the invention in contravention of the rights granted under the authority of any government in accordance with its patent laws.

Claims: CLAIMS: 1. A protein consiεting of soluble or membrane- bound human FcγRIII. 2. The protein of claim 1 consisting of the extracellular domain of a human FC 7 RIII. 3. The protein of claim 1 having an amino acid sequence selected from the group consiεting of 2-fold εubεtituted and 1-fold deleted sequences defined by the formula: X(Arg) - X(Thr) - X(Glu) - X(Asp) - X(Leu) - X(Pro) - X(Lys) - X(Ala) - X(Val) - X(Val) - X(Phe) - X(Leu) - X(Glu) - X(Pro) - X(Gln) - X(Trp) - X(Tyr) - X(Arg) - X(Val) - X(Leu) - X(Glu) - X(Lyε) - X(Aεp) - X(Ser) - X(Val) - X(Thr) - X(Leu) - X(Lyε) - X(Cyε) - X(Gln) - X(Gly) - X(Ala) - X(Tyr) - X(Ser) - X(Pro) - X(Glu) - X(Aεp) - X(Aεn) - X(Ser) - X(Thr) - X(Gln) - X(Trp) - X(Phe) - X(Hiε) - X(Aεn) - X(Glu) - X(Aεn) - X(Leu) - X(Ile) - X(Ser) - X(Ser) - X(Gln) - X(Ala) - X(Ser) - X(Ser) - X(Tyr) - X(Phe) - X(Ile) - X(Asp) - X(Ala) - X(Ala) - X(Thr) - X(Val) - X(Aεp) - X(Asp) - X(Ser) - X(Gly) - X(Glu) - X(Tyr) - X(Arg) - X(Cys) - X(Gln) - X(Thr) - X(Asn) - X(Leu) - X(Ser) - X(Thr) - X(Leu) - X(Ser) - X(Aεp) - X(Pro) - X(Val) - X(Gln) - X(Leu) - X(Glu) - X(Val) - X(His) - X(Val) - X(Gly) - X(Trp) -4. X(Leu) - X(Leu) - X(Leu) - X(Gln) - X(Ala) - X(Pro) - X(Arg) - X(Trp) - X(Val) - X(Phe) - X(Lys) - X(Glu) - X(Glu) - X(Aεp) - X(Pro) - X(Ile) - X(His) - X(Leu) - X(Arg) - X(Cyε) - X(His) - X(Ser) - X(Trp) - X(Lys) - X(Asn) - X(Thr) - X(Ala) - X(Leu) - X(His) - X(Lys) - X(Val) - X(Thr) - X(Tyr) - X(Leu) - X(Gln) - X(Asn) - X(Gly) - X(Lys) - X(Asp) - X(Arg) - X(Lys) - X(Tyr) - X(Phe) - X(Hiε) - X(His) - X(Asn) - X(Ser) - X(Asp) X(Phe) - X(His) - X(Ile) - X(Pro) - X(Lys) - X(Ala) X(Thr) - X(Leu) - X( ys) - X(Asp) - X(Ser) - X(Gly) X(Ser) - X(Tyr) - X(Phe) - X(Cys) - X(Arg) - X(Gly) X(Leu) - X(Val) - X(Gly) - X(Ser) - X( yε) - X(Aεn) X(Val) - X(Ser) - X(Ser) - X(Glu) - X(Thr) - X(Val) X(Aεn) - X(He) - X(Thr) - X(Ile) - X(Thr) - X(Gln) X(Gly) - X(Leu) - X(Ala) - X(Val) - X(Ser) - X(Thr) X(Ile) - X(Ser) - X(Ser) - X(Phe) - X(Ser) - X(Pro) X(Pro) - X(Gly) or X(Arg) - X(Thr) - X(Glu) - X(Aεp) - X(Leu) - X(Pro) X(Lys) - X(Ala) - X(Val) - X(Val) - X(Phe) - X(Leu) X(Glu) - X(Pro) - X(Gln) - X(Trp) - X(Tyr) - X(Arg) X(Val) - X(Leu) - X(Glu) - X(Lyε) - X(Aεp) - X(Ser) X(Val) - X(Thr) - X(Leu) - X(Lyε) - X(Cys) - X(Gln) X(Gly) - X(Ala) - X(Tyr) - X(Ser) - X(Pro) - X(Glu) X(Aεp) - X(Asn) - X(Ser) - X(Thr) - X(Gln) - X(Trp) X(Phe) - X(Hiε) - X(Asn) - X(Glu) - X(Ser) - X(Leu) X(Ile) - X(Ser) - X(Ser) - X(GIn) - X(Ala) - X(Ser) X(Ser) - X(Tyr) - X(Phe) - X(Ile) - X(Aεp) - X(Ala) X(Ala) - X(Thr) - X(Val) - X(Aεp) - X(Aεp) - X(Ser) X(Gly) - X(Glu) - X(Tyr) - X(Arg) - X(Cyε) - X(Gln) X(Thr) - X(Aεn) - X(Leu) - X(Ser) - X(Thr) - X(Leu) X(Ser) - X(Asp) - X(Pro) - X(Val) - X(Gln) - X(Leu) X(Glu) - X(Val) - X(Hiε) - X(Ile) - X(Gly) - X(Trp) X(Leu) - X(Leu) - X(Leu) - X(Gln) - X(Ala) - X(Pro) X(Arg) - X(Trp) - X(Val) - X(Phe) - X(Lys) - X(Glu) X(Glu) - X(Asp) - X(Pro) - X(Ile) - X(His) - X(Leu) X(Arg) - X(Cyε) - X(Hiε) - X(Ser) - X(Trp) - X(Lyε) X(Asn) - X(Thr) - X(Ala) - X(Leu) - X(His) - X(Lyε) X(Val) - X(Thr) - X(Tyr) - X(Leu) - X(Gln) - X(Asn) X(Gly) - X(Lyε) - X(Gly) - X(Arg) - X(Lys) - X(Tyr) X(Phe) X(Hiε) X(His) - X(Asn) X(Ser) X(Aεp) X(Phe) X(Tyr) X(Ile) - X(Pro) X(Lyε) X(Ala) X(Thr) X(Leu) X( ys) - X(Asp) X(Ser) X(Gly) X(Ser) X(Tyr) X(Phe) - X(Cys) X(Arg) X(Gly) X(Leu) X(Phe) X(Gly) - X(Ser) X(Lys) X(Asn) X(Val) X(Ser) X(Ser) - X(Glu) X(Thr) X(Val) X(Asn) X(Ile) X(Thr) - X(Ile) X(Thr) X(Gln) X(Gly) X(Leu) X(Ala) - X(Val) X(Ser) X(Thr) X(Ile) X(Ser) X(Ser) - X(Phe) X(Phe) X(Pro) X(Pro) X(Gly) wherein: X(Ala represents Ala, Ser, Thr or Gly; X(Arg represents Arg or Lys; X(Aεn representε Aεn, Aεp or Ser; X(Aεp repreεents Asp, Glu, or Asn; X(Cys is Cys; X(Gln represents Gin or Glu; X(Glu representε Glu, Aεp or Gin; X(Gly represents Gly, Ala or Ser; X(His represents His or Asn; X(Ile representε He, Val, or Leu; X(Leu repreεentε Leu, Val, or lie; X(Lyε repreεentε Lyε, Arg, or Asn; X(Met repreεentε Met or Leu; X(Phe is Phe; X(Pro represents Pro or Ala; X(Ser represents Ser, Ala, Thr, Gly, or Asn; X(Thr represents Thr, Ser, Ala, or Lys; X(Trp is Trp; X(Tyr is Tyr; and X(Val repreεents Val, He, Ala, or Leu. 4. The protein of claim 3 wherein said group consiεts of 1-fold εubεtituted sequences of said formulas. 5. The protein of claim 3 wherein: X (Ala represents Ala or Ser; X (Arg is Arg; X(Asn represents Asn or Asp; X(Aεp representε Aεp or Glu; X(Cys is Cys; X (Gln is Gin; X(Glu represents Glu or Asp; X (Gly represents Gly or Ala; X (His is His; X(He represents He or Val; X(Leu represents Leu or Val; X(Lys represents Lys or Arg; X(Met is Met; X (Phe iε Phe; X(Pro iε Pro; X (Ser represents Ser, Ala or Thr; X (Thr represents Thr, Ser or Ala; X(Trp is Trp; X(Tyr is Tyr; and X (Val representε Val or He. 6. The protein of claim 5 wherein εaid group conεists of 1-fold substituted sequences of said formulas. 7. The protein of claim 6 having the amino acid sequence: Arg - Thr - Glu - Asp - Leu - Pro Lyε Ala Val Val - Phe - Leu - Glu - Pro - Gin - Trp - Tyr - Arg Val - Leu - Glu - Lys - Asp - Ser - Val - Thr - Leu Lys - Cys - Gin - Gly - Ala - Tyr - Ser - Pro - Glu Asp - Asn - Ser - Thr - Gin - Trp - Phe - Hiε - Asn Glu - Asn - Leu - He - Ser - Ser - Gin - Ala - Ser Ser - Tyr - Phe - He - Asp - Ala - Ala - Thr - Val Asp - Asp - Ser - Gly - Glu - Tyr - Arg - Cyε - Gin Thr - Aεn - Leu - Ser - Thr - Leu - Ser - Aεp - Pro Val - Gin - Leu - Glu - Val - Hiε - Val - Gly - Trp Leu - Leu - Leu - Gin - Ala - Pro - Arg - Trp - Val Phe - Lyε - Glu - Glu - Asp - Pro - He - His - Leu Arg - Cyε - Hiε - Ser - Trp - Lyε - Aεn - Thr - Ala Leu - His - Lyε - Val - Thr - Tyr_ - Leu - Gin - Asn Gly - Lys - Asp - Arg - Lys - Tyr - Phe - His - His Asn - Ser - Asp - Phe - His - He - Pro - Lys - Ala Thr - Leu - Lys - Asp - Ser - Gly - Ser - Tyr - Phe Cys - Arg - Gly - Leu - Val - Gly - Ser - Lyε - Asn Val - Ser - Ser - Glu - Thr - Val - Aεn - He - Thr He - Thr - Gin - Gly - Leu - Ala - Val - Ser - Thr He - Ser - Ser - Phe - Ser - Pro - Pro - Gly or Arg - Thr - Glu - Asp - Leu - Pro - Lys - Ala - Val Val - Phe - Leu - Glu - Pro - Gin - Trp - Tyr - Arg Val - Leu - Glu - Lys - Asp - Ser - Val - Thr - Leu Lys - Cys - Gin - Gly - Ala - Tyr - Ser - Pro - Glu Asp - Asn - Ser - Thr - Gin - Trp - Phe - His - Asn Glu - Ser - Leu - He - Ser - Ser - Gin - Ala - Ser Ser - Tyr - Phe - He - Asp - Ala - Ala - Thr - Val Asp - Asp - Ser - Gly - Glu - Tyr - Arg - Cys - Gin Thr - Asn - Leu - Ser — Thr — Leu - Ser - Asp - Pro Val - Gin - Leu - Glu - Val - His - He - Gly - Trp Leu - Leu - Leu - Gin - Ala - Pro - Arg - Trp - Val Phe - Lys - Glu - Glu - Asp - Pro - He - His - Leu Arg - Cys - His - Ser - Trp - Lys - Asn - Thr - Ala Leu - His - Lys - Val - Thr - Tyr - Leu - Gin - Asn Gly - Lys - Gly - Arg - Lys - Tyr - Phe - His - His Aεn - Ser - Asp - Phe - Tyr - He - Pro - Lys - Ala Thr - Leu - Lys - Asp - Ser - Gly - Ser - Tyr - Phe Cys - Arg - Gly - Leu - Phe - Gly - Ser - Lys - Asn Val - Ser - Ser - Glu - Thr - Val - Asn - He - Thr He - Thr - Gin - Gly - Leu - Ala - Val - Ser - Thr He - Ser - Ser - Phe - Phe - Pro - Pro - Gly. 8. A nucleic acid capable of encoding soluble or membrane-bound human FC 7 RIII. 9. The nucleic acid of claim 8 capable of encoding a polypeptide having an amino acid sequence selected from the 2-fold subεtituted and 1-fold deleted sequences defined by the formula: X(Arg) - X(Thr) - X(Glu) - X(Asp) - X(Leu) - X(Pro) X(Lyε) - X(Ala) - X(Val) - X(Val) - X(Phe) - X(Leu) X(Glu) - X(Pro) - X(Gln) - X(Trp) - X(Tyr) - X(Arg) X(Val) - X(Leu) - X(Glu) - X( yε) - X(Asp) - X(Ser) X(Val) - X(Thr) - X(Leu) - X(Lys) - X(Cys) - X(Gln) X(Gly) - X(Ala) - X(Tyr) - X(Ser) - X(Pro) - X(Glu) X(Aεp) - X(Asn) - X(Ser) - X(Thr) - X(Gln) - X(Trp) X(Phe) - X(His) - X(Asn) - X(Glu) - X(Asn) - X(Leu) X(Ile) - X(Ser) - X(Ser) - X(Gln) - X(Ala) - X(Ser) X(Ser) - X(Tyr) - X(Phe) - X(He) - X(Asp) - X(Ala) X(Ala) - X(Thr) - X(Val) - X(Aεp) - X(Asp) - X(Ser) X(Gly) - X(Glu) - X(Tyr) - X(Arg) - X(Cyε) - X(Gln) X(Thr) - X(Aεn) - X(Leu) - X(Ser) - X(Thr) - X(Leu) X(Ser) - X(Asp) - X(Pro) - X(Val) - X(Gln) - X(Leu) X(Glu) - X(Val) - X(Hiε) - X(Val) - X(Gly) - X(Trp) X(Leu) - X(Leu) - X(Leu) - X(Gln) - X(Ala) - X(Pro) X(Arg) - X(Trp) - X(Val) - X(Phe) - X( ys) - X(Glu) X(Glu) - X(Asp) - X(Pro) - X(He) - X(His) - X(Leu) X(Arg) - X(Cys) - X(Hiε) - X(Ser) - X(Trp) - X(Lys) X(Asn) - X(Thr) - X(Ala) - X(Leu) - X(His) - X(Lys) ) - X(Tyr) - X(Leu) - X(Gl X(Asn) X(Val) - X(Thr n) - X(Gly) - X(Lys) - X(Aεp) - X(Arg) - X(Lyε) - X(Tyr) X(Phe) - X(His) - X(His) - X(Aεn) - X(Ser) - X(Aεp) X(Phe) - X(His) - X(He) - X(Pro) - X(Lyε) - X(Ala) X(Thr) - X(Leu) - X(Lyε) - X(Asp) - X(Ser) - X(Gly) X(Ser) - X(Tyr) - X(Phe) - X(Cys) - X(Arg) - X(Gly) - X(Asn) X(Leu) - X(Val) - X(Gly) - X(Ser) - X(Lys) X(Val) - X(Ser) - X(Ser) - X(Glu) - X(Thr) - X(Val) X(Aεn) - X(Ile) - X(Thr) - X(He) - X(Thr) - X(Gln) X(GlyJ - X(Leu) - X(Ala) - X(Val) - X(Ser) - X(Thr) X(Ile) - X(Ser) - X(Ser) - X(Phe) - X(Ser) - X(Pro) X(Pro) - X(Gly) or X(Arg) - X(Thr) - X(Glu) - X(Aεp) - X(Leu) - X(Pro) X(Lyε) - X(Ala) - X(Val) - X(Val) - X(Phe) - X(Leu) X(Glu) - X(Pro) - X(Gln) - X(Trp) - X(Tyr) - X(Arg) X(Val) - X(Leu) - X(Glu) - X( ys) - X(Asp) - X(Ser) X(Val) - X(Thr) - X(Leu) - X(Lys) - X(Cyε) - X(Gln) X(Gly) - X(Ala) - X(Tyr) - X(Ser) - X(Pro) - X(Glu) X(Asp) - X(Asn) - X(Ser) - X(Thr) - X(Gln) - X(Trp) X(Phe) - x(His) - X(Aεn) - X(Glu) - X(Ser) - X(Leu) X(He) - X(Ser) - X(Ser) - X(Gln) - X(Ala) - X(Ser) X(Ser) - X(Tyr) - X(Phe) - X(Ile) - X(Aεp) - X(Ala) X(Ala) - X(Thr) - X(Val) - X(Asp) - X(Aέp) - X(Ser) x(Gly) - X(Glu) - X(Tyr) - X(Arg) - X(Cys) - X(Gln) X(Thr) - X(Aεn) - X(Leu) - X(Ser) - X(Thr) - X(Leu) Val — Gin - Leu - Glu - Val - His - Val - Gly - Trp Leu - Leu - Leu - Gin - Ala - Pro - Arg - Trp - Val Phe - Lys - Glu - Glu - Asp - Pro - He - His - Leu Arg - Cyε - His - Ser - Trp - Lys - Asn - Thr - Ala Leu - His - Lys - Val - Thr - Tyr - Leu - Gin - Asn Gly - Lys - Aεp - Arg - Lys - Tyr - Phe - His - His Aεn - Ser - Asp - Phe - His - He - Pro - Lys - Ala Thr - Leu - Lys - Asp - Ser - Gly - Ser - Tyr - Phe Cys - Arg - Gly - Leu - Val - Gly - Ser - Lys - Asn Val - Ser - Ser - Glu - Thr - Val - Asn - He - Thr He - Thr - Gin - Gly - Leu - Ala - Val - Ser - Thr He - Ser - Ser - Phe - Ser - Pro - Pro - Gly and Arg - Thr - Glu — Asp — Leu - Pro - Lyε Ala - Val Val - Phe - Leu - Glu - Pro - Gin - Trp - Tyr - Arg Val - Leu - Glu - Lys - Asp - Ser - Val - Thr - Leu Lyε - Cyε - Gin - Gly - Ala - Tyr - Ser - Pro - Glu Asp - Asn - Ser - Thr - Gin - Trp - Phe - His - Asn Glu - Ser - Leu - He - Ser - Ser - Gin - Ala - Ser Ser - Tyr - Phe - He - Aεp - Ala - Ala - Thr - Val Aεp - Asp - Ser - Gly - Glu - Tyr - Arg - Cys - Gin Thr - Asn - Leu - Ser - Thr - Leu - Ser - Asp - Pro Val - Gin - Leu - Glu - Val - Hiε - He - Gly - Trp Leu - Leu - Leu - Gin - Ala - Pro - Arg - Trp - Val Phe - Lys - Glu - Glu - Aεp - Pro - He - His - Leu Arg - Cyε - His - Ser - Trp - Lyε - Aεn - Thr - Ala Leu - Hiε - Lyε - Val - Thr - Tyr - Leu - Gin - Asn Gly - Lys - Gly - Arg - Lyε - Tyr - Phe - His - His Asn - Ser - Aεp - Phe - Tyr - He - Pro - Lys - Ala Thr - Leu - Lyε - Asp - Ser - Gly - Ser - Tyr - Phe Cys - Arg - Gly - Leu - Phe - Gly - Ser - Lys - Asn Val - Ser - Ser - Glu - Thr - Val - Asn - He - Thr He - Thr - Gin - Gly - Leu - Ala - Val - Ser - Thr He - Ser - Ser - Phe - Phe - Pro - Pro - Gly. 11. A method of treating immune thrombocytopenic purpura in a person, the method comprising administering an effective amount of soluble human FC 7 RIII. 12. The method of claim 11 wherein said step of administering includes intravenous delivery of an amount of said soluble human FC 7 RIII in the range of about 1-20 mg/kg body weight of said person per day. 13. A method of detecting immune complexes in a sample, the method comprising the steps of: providing cells transformed by a vector carrying a cDNA insert encoding an FcγRIII, the FC7RIII being expresεed on the surface of the cells; exposing the cells to the sample containing immune complex so that the immune complex can adhere to the surface of the cells by way of the FC 7 RIIIS; labeling the immune complex adhering to the εurfaceε of the cellε; and meaεuring the amount of labeled immune complex adhering to the cellε. - 14. The method of claim 13 wherein said cellε are mouεe L cellε or COS monkey cells and said vector is selected from pcD(SRα)-GP5 and pcD(SRα)-NL10.

Inventors: MOORE KEVIN W, PELTZ GARY A, MOORE, KEVIN, W., PELTZ, GARY, A.
Applicants: SCHERING BIOTECH CORP, SCHERING BIOTECH CORPORATION
Application year: 1989
Main classification: C07K13
IPC codes: A61K38, A61P7, A61P37, C07K14, C12N5, C12N13, C12N15, C12P21, C12R1, G01N33