Soluble interferon-gamma receptors and methods for their production

Abstract: The present invention relates to soluble IFN-γ receptors, to DNA sequences coding for these soluble IFN-γ receptors and methods for making these.

Description: The present invention relates to soluble interferon-gamma receptors comprising the extracellular domain of the natural interferon-gamma receptor capable of specifically binding interferon-gamma (IFN-γ) and missing the cytoplasmic and transmembrane domains of the natural IFN-γ receptor, to DNA sequences coding for these soluble IFN-γ receptors, to expression vectors and transformants expressing these soluble IFN-γ receptors and methods for making these using recombinant DNA technology. In addition, the present invention relates to the use of these soluble IFN-γ receptors as therapeutically active agents for the treatment of diseases, especially for the treatment of autoimmune diseases, chronic inflammations, delayed hypersensitivities and allotransplant rejections and multiple sclerosis. As has been shown with other polypeptide hormones and lymphokines, interferons (IFNs) act on various cells via specific cell surface receptors. IFN-α and IFN-β share a common receptor which is distinct from the IFN-γ receptor (Branca and Baglioni, Nature 294, 768-770 [1981]). The existence of a specific receptor for IFN-γ on various cells was demonstrated by cross-linking experiments, by binding of radiolabeled IFN-γ and by specific competition with unlabeled IFN-γ. Cross-linked complexes between IFN-γ and its receptor with a M r ranging from 70,000 to 165,000 have been described (Rubinstein et al., Immunol. Rev. 97, 29-50 [1987]). Despite this apparent heterogeneity, most binding studies revealed only one class of IFN-γ binding sites with a dissociation constant of about 10⁻¹¹ to 10⁻¹⁰M (Sarkar and Gupta, Proc. Natl. Acad. Sci. USA 81, 5160-5164 [1984], Uecer et al., Cancer Res. 46, 5339-5343 [1986], Novick et al., J. Biol. Chem. 262, 8483-8487 [1987]). Human IFN-γ receptors have been purified from Raji cells by affinity chromatography on immobilized recombinant human IFN-γ (Aguet and Merlin, J. Exp. Med. 165, 988-999 [1987], Calderon et al., Proc. Natl. Acad. Sci. USA 85, 4837-4841 [1988]). A major protein species of apparent M r of 90 Kd (p90) was highly enriched and shown to bind human IFN-γ specifically. However, an additional 50 Kd (p50) component of human IFN-γ receptor might be detected. Some evidence suggested that the intact IFN-γ receptor is indeed the p90 protein and that p50 may be a proteolytic degradation product of p90 (Aguet and Merlin, supra, Sheehan et al., J. Immunol. 140, 4231-4237 [1988]). In general, IFN-γ receptors seem to be expressed to a lesser extend on normal cells (up to 10³ sites per cell) than on tumor cells. Thus, some human carcinoma and B-cell lines were reported to express on the order of 10⁴ binding sites per cell (Uecer et al., supra, Aguet and Merlin, supra). In conclusion the human IFN-γ receptor is an ubiquitous membrane anchored protein of about 90 Kd molecular mass. EP-A-240 975 discloses the isolation of natural human interferon gamma receptor protein from various cell types by ligand affinity chromatography. The receptors were identified as proteins of 90-140 Kd molecular mass, i.e. comprising the extracellular, cytoplasmic and transmembrane domains (full length receptor proteins). Molecular cloning and expression of the human IFN-γ receptor has been described (Aguet et al., Cell 55, 273-280 [1988]). However, because the natural IFN-γ receptor as well as the recombinant IFN-γ receptor are membrane anchored proteins, they have the disadvantage that they are insoluble in physiological solution. Consequently, search or design of IFN-γ agonists and antagonists, and administration of purified IFN-γ receptor to mammals to inhibit IFN-γ binding to its specific receptor thereby preventing, suppressing and/or modulating the course of autoimmune disorders, chronic inflammations, delayed hypersensitivities and allotransplant rejections was difficult to accomplish. To solve the foregoing problem, the soluble IFN-γ receptors of the present invention have been produced by culturing transformants carrying an expression vector containing a DNA sequence coding for a soluble IFN-γ receptor and isolating said soluble IFN-γ receptor. More precisely, the present invention provides soluble IFN-γ receptors capable of specifically binding IFN-γ comprising the N-terminal portion of the natural IFN-γ receptor containing at least amino acids 26-246 of the natural IFN-γ receptor sequence shown in Figure 1 or 2 and missing the cytoplasmic and transmembrane domains of the natural IFN-γ receptor. The term "Soluble IFN-γ receptors" as used herein refers to IFN-γ receptors which are soluble in physiological solutions without addition of detergents. The term "cytoplasmic and transmembrane domains of the natural IFN-γ receptor" as used in describing the soluble IFN-γ receptors of the present invention refers to amino acids 247-489 of the natural IFN-γ receptor sequence shown in Fig. 1 or 2. The soluble IFN-γ receptors of the present invention may contain amino acid substitutions if such substitutions do not generally alter the IFN-γ binding activity and solubility. Amino acid substitutions in proteins and polypeptides which do not essentially alter biological activity are known in the art and described, e.g. by H. Neurath and R.L. Hill in "The Proteins", Academic Press, New York (1979), in particular in Fig. 6 of page 14. The most frequently observed amino acid substitutions are Ala/Ser, Val/Ile, Asp/Glu, Thr/Ser, Ala/Gly, Ala/Thr, Ser/Asn, Ala/Val, Ser/Gly, Tyr/Phe, Ala/Pro, Lys/Arg, Asp/Asn, Leu/Ile, Leu/Val, Ala/Glu, Asp/Gly and vice versa. The soluble IFN-γ receptors of the present invention can additionally contain sequences of several amino acids which are coded for by "linker" sequences. These sequences arise as a result from the expression vectors used for expression of the soluble IFN-γ receptors as defined above. The soluble IFN-γ receptors of the present invention can also contain specific sequences that preferably bind to an affinity carrier material. Examples of such sequences are sequences containing at least two adjacent histidine residues (see in this respect European Patent Application Publication No. 282 042). Such sequences bind selectively to nitrilotriacetic acid nickel chelate resins (Hochuli and Döbeli, Biol. Chem. Hoppe-Seyler 368, 748 (1987); European Patent Application Publication No. 253 303). Soluble IFN-γ receptors which contain such a specific sequence can, therefore, be separated selectively from the remaining polypeptides. The specific sequence can be linked either to the C-terminus or the N-terminus of the soluble IFN-γ receptor amino acid sequences. Preferred soluble IFN-γ receptors of the present invention are those with the designations P25H6C, P28H6A, P41H6, P25C and P57 (see e.g. Figs. 44 and 87 and Table 1). The present invention also provides DNA sequences which code for the soluble IFN-γ receptors of the present invention, expression vectors which contain these DNA sequences, host cells containing such vectors for the production of the soluble IFN-γ receptors and processes for the production of such DNA sequences, recombinant vectors and host cells. Methods for the expression, isolation and purification of the soluble IFN-γ receptors are also described. Because the complete DNA sequence of the gene coding for the natural IFN-γ receptor is known (Aguet et al., supra), amino acid sequences coding for the soluble IFN-γ receptors of the present invention can be chemically synthesized using standard methods known in the art, preferably solid state methods, such as the methods of Merrifield (J. Am. Chem. Soc. 85, 2149-2154 [1963]). Alternatively, the soluble IFN-γ receptors of the present invention can be produced using methods of DNA recombinant technology (Maniatis et al. in "Molecular Cloning - A Laboratory Manual", Cold Spring Harbor Laboratory [1982]). Preferably, a DNA sequence coding for a soluble IFN-γ receptor comprising the extracellular domain of the natural IFN-γ receptor and missing the cytoplasmic and transmembrane domains of the natural IFN-γ receptor is prepared from DNA coding for the natural IFN-γ receptor and subsequently incorporated into a suitable expression vector which produces the requisite expression signals. Expression vectors suitable for use in prokaryotic host cells are mentioned, for example, in the aforementioned textbook of Maniatis et al. Especially suitable vectors are plasmids of the pDS family [Bujard et al., Methods in Enzymology, eds. Wu and Grossmann, Academic Press, Inc., Vol. 155, 416-433 (1987)]. Such prokaryotic expression vectors which contain the DNA sequences coding for the soluble IFN-γ receptors of the present invention operatively linked with an expression control sequence can be incorporated using conventional methods into any suitable prokaryotic host cell. The selection of a suitable prokaryotic host cell is determined by different factors which are well-known in the art. Thus, for example, compatibility with the chosen vector, toxicity of the expression product, expression characteristics, necessary biological safety precautions and costs play a role and a compromise between all of these factors must be found. Suitable prokaryotic host organisms include gram-negative and gram-positive bacteria, for example E.coli and B.subtilis strains. Especially preferred prokaryotic host organisms of the present invention are E.coli strain M15 (described as strain OZ 291 by Villarejo et al. in J. Bacteriol. 120, 466-474 [1974] and E.coli W3110 [ATCC No. 27325]). In addition to the aforementioned E.coli strain, however, other generally accessible E.coli strains such as E.coli 294 (ATCC No. 31446) and E.coli RR1 (ATCC No. 31343) can also be used. Expression vectors suitable for use in mammalian host cells include but are not limited to pBC12MI, pBC12BI, pSV2dhFr, p91023(B), pcDV1, pRSVcat, pGA291, pGA293, pGA296, pBC12/HIV/IL-2 and pGA300. Vectors pBC12BI and pBC12/HIV/IL-2 are preferred. Such vectors are preferably introduced into suitable mammalian host cells by transfection. Mammalian host cells that could be used include e.g. human Hela, H9 and Jurkat cells, mouse NIH3T3 and C127 cells, CV1 African green monkey kidney cells, quail QC1-3 cells, Chinese hamster ovary (CHO) cells, mouse L cells and the COS cell lines. The COS-1 cell line is preferred. The manner in which the expression of the soluble IFN-γ receptors of the present invention is carried out depends on the chosen expression vector/host cell system. Usually, the prokaryotic host organisms which contain a desired expression vector are grown under conditions which are optimal for the growth of the prokaryotic host organisms. At the end of the exponential growth, when the increase in cell number per unit time decreases, the expression of the desired soluble IFN-γ receptor is induced, i.e. the DNA coding for the desired soluble IFN-γ receptor is transcribed and the transcribed mRNA is translated. The induction can be carried out by adding an inducer or a derepressor to the growth medium or by altering a physical paramter, e.g. a change in temperature. In the expression vectors used in the preferred embodiments of the present invention, the expression is controlled by the lac repressor. By adding isopropyl-β-D-thiogalactopyranoside (IPTG), the expression control sequence is derepressed and the synthesis of the desired soluble IFN-γ receptor is thereby induced. The mammalian host cells which contain a desired expression vector are grown under conditions which are optimal for the growth of the mammalian host cells. A typical expression vector contains the promoter element, which mediates the transcription of mRNA, the protein coding sequence, and the signals required for efficient termination and polyadenylation of the transcript. Additional elements may include enhancers and intervening sequences bounded by spliced donor and acceptor sites. Most of the vectors used for the transient expression of a given coding sequence carry the SV40 origin of replication, which allows them to replicate to high copy numbers in cells (e.g. COS cells) that constitutively express the T antigen required to initiate viral DNA synthesis. Transient expression is not limited to COS cells. Any mammalian cell line that can be transfected can be utilized for this purpose. Elements that control a high efficient transcription include the early or the late promoters from SV40 and the long terminal repeats (LTRs) from retroviruses, e.g. RSV, HIV, HTLVI. However, also cellular signals can be used (e.g. human-β-actin-promoter). Alternatively stable cell lines carrying a gene of interest integrated into the chromosome can be selected upon co-transfection with a selectable marker such as gpt, dhfr, neomycin or hygromycin. Now, the transfected gene can be amplified to express large quantities of a foreign protein. The dihydrofolate reductase (DHFR) is a useful marker to develop lines of cells carrying more than 1000 copies of the gene of interest. The mammalian cells are grown in increasing amounts of methotrexate. Subsequently, when the methotrexate is withdrawn, cell lines contain the amplified gene integrated into the chromosome. In the expression vectors used in the preferred embodiments of the present invention, the expression is controlled by the Rous sarcoma virus LTR. The baculovirus-insect cell vector system can also be used for the production of the soluble IFN-γ receptors of the present invention (for review see Luclow and Summers, Bio/Technology 6, 47-55 [1988]). The soluble IFN-γ receptors produced in insect cells infected with recombinant baculovirus can undergo post-translational processing including N-glycosylation (Smith et al., Proc. Nat. Acad. Sci. USA 82, 8404-8408) and O-glycosylation (Thomsen et al., 12. International Herpesvirus Workshop, University of Philadelphia, Pennsylvania). For the isolation of small amounts of soluble IFN-γ receptors expressed in prokaryotic host cells for analytical purposes, e.g. for polyacrylamide gel electrophoresis, the host cells can be disrupted by treatment with a detergent, e.g. sodium dodecyl sulphate (SDS). Larger quantities of these soluble IFN-γ receptors can be obtained by mechanical [Charm et al., Meth. Enzymol. 22, 476-556 (1971)], enzymatic (lysozyme treatment) or chemical (detergent treatment, urea or guanidinium hydrochloride treatment, etc.) treatments followed by use of known methods, e.g. by centrifugation at different gravities, precipitation with ammonium sulphate, dialysis (at normal pressure or at reduced pressure), preparative isoelectric focusing, preparative gel electrophoresis or by various chromatographic methods such as gel filtration, high performance liquid chromatography (HPLC), ion exchange chromatography, reverse phase chromatography and affinity chromatography (e.g. on Sepharose R Blue C1-6B or on carrier-bound monoconal antibodies which are directed against the native IFN-γ receptor and the soluble IFN-γ receptors of the present invention). Preferably, the IFN-γ receptors expressed in prokaryotic host cells are obtained after the following steps: (I) Disruption of the cells and extraction of the proteins with guanidine-hydrochhloride; (II) Ni-chelate affinity chromatography using a nitrolotriacetic acid (NTA) resin as described in European Patent Applications Publication Nos. 282 042 and 253 303; (III) Chromatography on a sizing column in the presence of urea; (IV) Dialysis (refolding); and (V) Chromatography on an anion exchanger column. The soluble IFN-γ receptors expressed in mammalian host cells or in the baculovirus-insect cell vector system can be isolated from the host cell medium using standard protein purification methods. The soluble IFN-γ receptors can be used for the preparations of pharmaceutical compositions and for the treatment of autoimmune diseases, e.g. type 1 diabetes or lupus erythematosus or rheumatoid arthritis, chronic inflammations, e.g. Schwartzman Reaction, delayed hypersensitivity allotransplant rejections and multiple sclerosis. They may be administered in pharmaceutically acceptable oral, injectable or topical compositions and modes. Dosage and dose rate may parallel that currently being used in clinical applications of the known IFNs, lymphokines like IFN-α typically about 8-53 µg/m² (1.8-10x10⁶ U/m²) daily or 3 days per week. The pharmaceutical compositions of the present invention contain soluble IFN-γ receptors in association with a compatible pharmaceutically acceptable carrier material. Any conventional carrier material can be utilized. The carrier material can be an organic or inorganic one suitable for enteral, percutaneous or parenteral administration. Suitable carriers include water, gelatin, gum arabic, lactose, starch, magnesium stearate, talc, vegetable oils, polyalkylene-glycols, petroleum jelly and the like. Furthermore, the pharmaceutical preparations may contain other pharmaceutically active agents. Additional additives such as flavouring agents, preservatives, stabilizers, emulsifying agents, buffers and the like may be added in accordance with accepted practices of pharmaceutical compounding. The pharmaceutical preparations can be made up in any conventional form including: a) a solid form for oral administration such as tablets, capsules, pills, powders, granules and the like; b) a liquid form for oral administration such as solutions, syrups, suspensions, elixirs and the like; c) preparations for parenteral administration such as sterile solutions, suspensions or emulsions; and d) preparations for topical administrations such as solutions, suspensions, ointments, creams, gels, micronized powders, aerosols and the like. The pharmaceutical preparations may be sterilized and/or may contain adjuvants such as preservatives, stabilizers, wetting agents, emulsifiers, salts for varying the osmotic pressure and/or buffers. Parenteral dosage forms may be infusions or injectable solutions which can be injected intravenously or intramuscularly. These preparations can also contain other medicinally active substances. Additional additives such as preservatives, stabilizers, emulsifying agents, buffers and the like may be added in accordance with accepted practices of pharmaceutical compounding. Furthermore, antibodies can be raised against the soluble IFN-γ receptors of the present invention. These antibodies can be used in a well-known manner for diagnostic or therapeutic purposes as well as for purification purposes. Such antibodies can be produced by injecting a mammalian or avian animal with a sufficient amount of a vaccine formulation comprising a soluble IFN-γ receptor of the present invention and a compatible pharmaceutical carrier to elicit the production of antibodies against said receptor. The appropriate amount of the soluble IFN-γ receptor which would be required would be known to one of skill in the art or could be determined by routine experimentation. As used in connection with this invention, the term "pharmaceutical carrier" can mean either the standard compositions which are suitable for human administration or the typical adjuvants employed in animal vaccinations. Suitable adjuvants for the vaccination of animals include but are not limited to Freund's complete or incomplete adjuvant (not suitable for human or livestock use). Adjuvant 65 (containing peanut oil, mannide monooleate and aluminum phosphate and alum; surfactants such as hexadecylamine, octadecylamine, lysolecithin, dimethyldioctadecylammonium bromide, N₁-N-dioctadecyl-N'-N-bis(2-hydroxyethylpropanediamine), methoxyhexadecylglycerol, and pluronic polyols; polyanions such as pyran, dextran sulfate, poly IC, polyacrylic acid, carbopol; peptides such as muramyl dipeptide, dimentylglycine, tuftsin; and oil emulsions. The soluble IFN-γ receptors could also be administered following incorporation into liposomes or other microcarriers, or after conjugation to polysaccharides, other proteins or other polymers or in combination with Quil-A to form "Iscoms" (immunostimulating complexes) (Morein et al., Nature 308, 457 [1984]). Typically, the initial vaccination is followed some weeks later by one or more "booster" vaccinations, the net effect of which is the production of high titers of antibodies against the soluble IFN-γ receptors which can be harvested in the usual way. Another method consists in using the well-known Koehler and Milstein technique for producing monoclonal antibodies. In order to find out different monoclonal antibodies which are directed against the same antigen but against different epitopes, the method of Stähli et al. [J. of Immunological Methods 32, 297-304 (1980)] can be used. Finally, the soluble IFN-γ receptors of the present invention are useful in screening methods for identifying IFN-γ agonists or antagonists. Having now generally described this invention, the same will become better understood by reference to the specific examples, which are included herein for purpose of illustration only and are not intended to be limiting unless otherwise specified, in connection with the following figures: The following abbreviations and symbols used are: B, Bg, Bs, E, H, N, Nh, P, Pv, S, Sa, Sm, Sp, X and Xb which indicate cleavage sites for restriction enzymes BamHI, BglII, BstEII, EcoRI, HindIII, NcoI, NheI, PstI, PvuI, SalI, SacI, SmaI, SphI, XhoI and XbaI, respectively. represents the regulatable promoter/operator element N25OPSN25OP29; represents ribosomal binding sites RBSII, RBSII,NcoI and RBSII,SphI; → represents coding regions under control of these ribosomal binding sites and open reading frames in plasmids replicating in COS-cells; represents a region encoding six histidine residues; represents terminators t o and T1; ⇆ represents the region required for DNA replication in E.coli (repl.); represents coding regions for dihydrofolate reductase (dhfr), chloramphenicol acetyltransferase (cat), β-lactamase (bla), lac repressor (lac1), neomycin phosphotransferase (neo); the tetracyclin resistance protein (tet', interrupted) and rat preproinsulin; represents the long terminal repeat (LTR) of Rous sarcoma virus; represents a region of the SV40 virus required for replication in COS-cells (ori); and ▭ represents signal peptides S.P.1 and S.P.2, the 5'-intron (5') and 3'-intron (3') of the rat preproinsulin gene, the polyadenylation signal of the same gene (polyA) and a region encoding three translational stop codons (stop). Figure 1 displays the nucleotide sequence of the SacI/Asp718I fragment of plasmid pBABLUE with the coding region for the human IFN-γ receptor and the amino acid sequence of the human IFN-γ receptor predicted therefrom. In the nucleotide sequence, the recognition sites for several restriction enzymes are indicated. In the amino acid sequence, the numbers refer to the position of the amino acid with respect to the methionine at position 1. Figure 2 displays the amino acid sequence of the human IFN-γ receptor as predicted from the nucleotide sequence displayed in Fig. 1. In this sequence the putative signal peptide is indicated by a series of circles, whereas the transmembrane region is indicated by a series of stars. Potential N-linked glycosylation sites are overlined and cysteine residues are marked by a cross. Figure 3 is a schematic drawing of the plasmid pDS56/RBSII,NcoI. Figure 4 displays the complete nucleotide sequence of plasmid pDS56/RBSII,NcoI. In this sequence, the recognition sequences of the restriction enzymes depicted in Fig. 3 are indicated. The amino acid sequence shown represents the open reading frame under control of ribosomal binding site RBSII,NcoI. Figure 5 is a schematic drawing of the plasmid pDS56/RBSII,SphI. Figure 6 displays the complete nucleotide sequence of plasmid pDS56/RBSII,SphI. In this sequence, the recognition sequences of the restriction enzymes depicted in Fig. 5 are indicated. The amino acid sequence shown represents the open reading frame under control of ribosomal binding site RBSII,SphI. Figure 7 is a schematic drawing of the plasmid pDS56/RBSII,6xHis. Figure 8 displays the complete nucleotide sequence of plasmid pDS56/RBSII,6xHis. In this sequence, the recognition sequences of the restriction enzymes depicted in Fig. 7 are indicated. The amino acid sequence shown represents the open reading frame under control of ribosomal binding site RBSII. Figure 9 is a schematic drawing of the plasmid pDS56/RBSII-6xHis. Figure 10 displays the complete nucleotide sequence of plasmid pDS56/RBSII-6xHis. In this sequence, the recognition sequences of the restriction enzymes depicted in Fig. 9 are indicated. The amino acid sequence shown represents the open reading frame under control of ribosomal binding site RBSII. Figure 11 is a schematic drawing of the plasmid pDS781/RBSII,6xHis. Figure 12 displays the complete nucleotide sequence of plasmid pDS781/RBSII,6xHis. In this sequence, the recognition sequences of the restriction enzymes depicted in Fig. 11 are indicated. The amino acid sequence shown represents the open reading frame under control of ribosomal binding site RBSII. Figure 13 is a schematic drawing of the plasmid pDHFR-(0/-1)-6xHis. Figure 14 displays the complete nucleotide sequence of plasmid pDHFR-(0/-1)-6xHis. In this sequence, the recognition sequences of the restriction enzymes depicted in Fig. 13 are indicated. The amino acid sequence shown represents the open reading frame under control of ribosomal binding site RBSII. Figure 15 is a schematic drawing of the plasmid pDMI,1. Figure 16 displays the complete nucleotide sequence of plasmid pDMI,1. In this sequence, the recognition sequences of the restriction enzymes depicted in Fig. 15 are indicated. The amino acids shown enclose the open reading frames encoding the neomycin phosphotransferase (Met,Phe) and the lac repressor (Met,Gln; in brackets to indicate the reverse orientation of the gene). Figure 17 displays the nucleotide sequences of the linkers, primers and adaptors used in the construction of plasmids. Recognition sequences for BamHI and BglII are indicated, cohesive ends produced upon cleavage with certain restriction enzymes are labeled. Figure 18 displays the nucleotide sequence of DNA fragment F7 and the amino acid sequence predicted therefrom. In the nucleotide sequence, the recognition sites for several restriction enzymes are indicated. The amino acid sequence comprises as indicated amino acids 1 to 212 of the human IFN-γ receptor. Figure 19 displays the nucleotide sequence of DNA fragment F26 and the amino acid sequence predicted therefrom. In the nucleotide sequence, the recognition sites for several restriction enzymes are indicated. The amino acid sequence comprises as indicated amino acids 15 to 212 of the human IFN-γ receptor. Figure 20 displays the amino acid sequence of protein P26H6 comprising as indicated amino acids 15 to 212 of the 17man IFN-γ receptor. Figure 21 displays the nucleotide sequence of DNA fragment F12 and the amino acid sequence predicted therefrom. In the nucleotide sequence, the recognition sites for several restriction enzymes are indicated. The amino acid sequence comprises as indicated amino acids 26 to 416 of the human IFN-γ receptor. Figure 22 displays the nucleotide sequence of DNA fragment F27 and the amino acid sequence predicted therefrom. In the nucleotide sequence, the recognition sites for several restriction enzymes are indicated. The amino acid sequence comprises as indicated amino acids 26 to 416 of the human IFN-γ receptor. Figure 23 displays the nucleotide sequence of DNA fragment F25 and the amino acid sequence predicted therefrom. In the nucleotide sequence, the recognition sites for several restriction enzymes are indicated. The amino acid sequence comprises as indicated amino acids 26 to 246 of the human IFN-γ receptor. Figure 24 displays the amino acid sequence of protein P25H6A comprising as indicated amino acids 26 to 246 of the human IFN-γ receptor. Figure 25 displays the amino acid sequence of protein P25H6B comprising as indicated amino acids 26 to 246 of the human IFN-γ receptor. Figure 26 displays the amino acid sequence of protein P25H6C comprising as indicated amino acids 26 to 246 of the human IFN-γ receptor. Figure 27 displays the amino acid sequence of protein P6H25 comprising as indicated amino acids 26 to 246 of the human IFN-γ receptor. Figure 28 displays the amino acid sequence of protein P28H6A comprising as indicated amino acids 15 to 246 of the human IFN-γ receptor. Figure 29 displays the nucleotide sequence of DNA fragment F28 and the amino acid sequence predicted therefrom. In the nucleotide sequence, the recognition sites for several restriction enzymes are indicated. The amino acid sequence comprises as indicated amino acids 15 to 246 of the human IFN-γ receptor. Figure 30 displays the amino acid sequence of protein P28H6B comprising as indicated amino acids 15 to 246 of the human IFN-γ receptor. Figure 31 displays the amino acid sequence of protein P6H28 comprising as indicated amino acids 15 to 246 of the human IFN-γ receptor. Figure 32 displays the nucleotide sequence of DNA fragment F41 and the amino acid sequence predicted therefrom. In the nucleotide sequence, the recognition sites for several restriction enzymes are indicated and the nucleotides are given in which fragment F28 differs from fragment F41. The amino acid sequence comprises as indicated amino acids 15 to 246 of the human IFN-γ receptor. Figure 33 displays the amino acid sequence of protein P41H6 comprising as indicated amino acids 15 to 246 of the human IFN-γ receptor. Figure 34 displays the nucleotide sequence of DNA fragment F43 and the amino acid sequence predicted therefrom. In the nucleotide sequence, the recognition sites for several restriction enzymes are indicated. The amino acid sequence comprises as indicated amino acids 13 to 246 of the human IFN-γ receptor. Figure 35 displays the amino acid sequence of protein P43H6 comprising as indicated amino acids 13 to 246 of the human IFN-γ receptor. Figure 36 displays the nucleotide sequence of DNA fragment F44 and the amino acid sequence predicted therefrom. In the nucleotide sequence, the recognition sites for several restriction enzymes are indicated. The amino acid sequence comprises as indicated amino acids 16 to 246 of the human IFN-γ receptor. Figure 37 displays the amino acid sequence of protein P44H6 comprising as indicated amino acids 16 to 246 of the human IFN-γ receptor. Figure 38 displays the nucleotide sequence of DNA fragment F45 and the amino acid sequence predicted therefrom. In the nucleotide sequence, the recognition sites for several restriction enzymes are indicated. The amino acid sequence comprises as indicated amino acids 18 to 246 of the human IFN-γ receptor. Figure 39 displays the amino acid sequence of protein P45H6 comprising as indicated amino acids 18 to 246 of the human IFN-γ receptor. Figure 40 displays the nucleotide sequence of DNA fragment F46 and the amino acid sequence predicted therefrom. In the nucleotide sequence, the recognition sites for several restriction enzymes are indicated. The amino acid sequence comprises as indicated amino acids 19 to 246 of the human IFN-γ receptor. Figure 41 displays the amino acid sequence of protein P46H6 comprising as indicated amino acids 18 to 246 of the human IFN-γ receptor. Figure 42 is a summary of the plasmids used for production of receptor derivatives in E.coli, of the proteins encoded by these plasmids and of the regions of the human IFN-γ receptor contained in these proteins. Figure 43 is a schematic summary of the amino acid sequences of the protease expressed in E.coli. Stretches of amino acids of the human IFN-γ receptor (Receptor) present in these proteins are represented by stars. Figure 44 is a summary of activities of the receptor derivatives expressed in E.coli. Monoclonal antibody and human IFN-γ receptor are abbreviated by mAb and ligand, respectively, whereas n.t. indicates, that this activity of the very protein has not been tested for. Figure 45 is a summary of the purification of protein P41H6. Figure 46 is a schematic drawing of the plasmid p79BGL. Figure 47 displays the complete nucleotide sequence of plasmid p79BGL. In the sequence, the recognition sequences of the restriction enzymes depicted in Fig. 46 are indicated. The star at position 279 marks the first nucleotide of the transcripts initiated within the LTR, a polyadenylation signal is overlined. A short open reading frame starting at position 505 of the sequence is represented by the encoded amino acids. Three translational stop codons to the right of the unique cleavage site for restriction enzyme BamHI are overlined. Figure 48 is a schematic drawing of the plasmid p79DBAM. Figure 49 displays the complete nucleotide sequence of plasmid p79DBAM. In this sequence, the recognition sequences of the restriction enzymes depicted in Fig. 48 are indicated. The star at position 279 marks the first nucleotide of the transcripts initiated within the LTR. Three translation stop codons to the right of the unique cleavage site for restriction enzyme BamHI and a polyadenylation signal are overlined. Figure 50 is a schematic drawing of the plasmid p238BGL. Figure 51 displays the complete nucleotide sequence of plasmid p238BGL. In this sequence, the recognition sequences of the restriction enzymes depicted in Fig. 50 are indicated. The star at position 279 marks the first nucleotide of the transcripts initiated within the LTR. Three translational stop codons to the right of the cleavage site for restriction enzyme BglII and a polyadenylation signal are over lined. In the amino acid sequence shown, signal peptide S.P.1 is indicated by circles. Figure 52 is a schematic drawing of the plasmid p238BAM. Figure 53 displays the complete nucleotide sequence of plasmid p238BAM. In this sequence, the recognition sequences of the restriction enzymes depicted in Fig. 52 are indicated. The star at position 279 marks the first nucleotide of the transcripts initiated within the LTR. Three translational stop codons to the right of the unique cleavage site for restriction enzyme BamHI and a polyadenylation signal are overlined. In the amino acid sequence shown, signal peptide S.P.1 is indicated by circles. Figure 54 is a schematic drawing of the plasmid p264BGL. Figure 55 displays the complete nucleotide sequence of plasmid p264BGL. In this sequence, the recognition sequences of the restriction enzymes depicted in Fig. 54 are indicated. The star at position 279 marks the first nucleotide of the transcripts initiated within the LTR. Three translational stop codons to the right of the unique cleavage site for restriction enzyme BglII and a polyadenylation signal are overlined. In the amino acid sequence shown, signal peptide S.P.1 is indicated by circles. Figure 56 is a schematic drawing of the plasmid p264BAM. Figure 57 displays the complete nucleotide sequence of plasmid p264BAM. In this sequence, the recognition sequences of the restriction enzymes depicted in Fig. 56 are indicated. The star at position 279 marks the first nucleotide of the transcripts initiated within the LTR. Three translational stop codons to the right of the unique cleavage site for restriction enzyme BamHI and a polyadenylation signal are overlined. In the amino acid sequence shown, signal peptide S.P.1 is indicated by circles. Figure 58 is a schematic drawing of the plasmid p267BGL. Figure 59 displays the complete nucleotide sequence of plasmid p267BGL. In this sequence, the recognition sequences of the restriction enzymes depicted in Fig. 58 are indicated. The star at position 279 marks the first nucleotide of the transcripts initiated within the LTR. Three translational stop codons to the right of the unique cleavage site for restriction enzyme BglII and a polyadenylation signal are overlined. In the amino acid sequence shown, signal peptide S.P.2 is indicated by circles. Figure 60 is a schematic drawing of the plasmid p267BAM. Figure 61 displays the complete nucleotide sequence of plasmid p267BAM. In the sequence, the recognition sequences of the restriction enzymes depicted in Fig. 60 are indicated. The star at position 279 marks the first nucleotide of the transcripts initiated within the LTR. Three tranlational stop codons to the right of the unique cleavage site for restriction enzyme BamHI and a polyadenylation signal are overlined. In the amino acid sequence shown, signal peptide S.P.2 is indicated by circles. Figure 62 displays the nucleotide sequence of DNA fragment F1 and the amino acid sequence predicted therefrom. In the nucleotide sequence, the recognition sites for several restriction enzymes are indicated. The amino acid sequence comprises as indicated amino acids 1 to 489 of the human IFN-γ receptor. Figure 63 displays the nucleotide sequence of DNA fragment F3 and the amino acid sequence predicted therefrom. In the nucleotide sequence, the recognition sites for several restriction enzymes are indicated. The amino acid sequence comprises as indicated amino acids 1 to 367 of the human IFN-γ receptor. Figure 64 displays the nucleotide sequence of DNA fragment F30 and the amino acid sequence predicted therefrom. In the nucleotide sequence, the recognition sites for several restriction enzymes are indicated. The amino acid sequence comprises as indicated amino acids 1 to 281 of the human IFN-γ receptor. Figure 65 displays the nucleotide sequence of DNA fragment F31 and the amino acid sequence predicted therefrom. In the nuecleotide sequence, the recognition sites for several restriction enzymes are indicated. The amino acid sequence comprises as indicated amino acids 1 to 489 of the human IFN-γ receptor. Figure 66 displays the amino acid sequence of protein PF1 comprising the entire human IFN-γ receptor. Figure 67 displays the amino acid sequence of protein PF3 comprising amino acids 1 to 367 of the human IFN-γ receptor. Figure 68 displays the amino acid sequence of protein PBGLF12 comprising as indicated amino acids 26 to 416 of the human IFN-γ receptor and signal peptide S.P.2, which is indicated by circles. Figure 69 displays the amino acid sequence of protein PF30 comprising as indicated amino acids 1 to 281 of the human IFN-γ receptor. Figure 70 displays the amino acid sequence of protein PF12F1 comprising as indicated amino acids 26 to 489 of the human IFN-γ receptor and signal peptide S.P.2, which is indicated by circles. Figure 71 displays the amino acid sequence of protein PF12F12 comprising as indicated amino acids 26 to 416 of the human IFN-γ receptor and signal peptide S.P.2, which is indicated by circles. Figure 72 displays the amino acid sequence of protein PF12F3 comprising as indicated amino acids 26 to 367 of the human IFN-γ receptor and signal peptide S.P.2, which is indicated by circles. Figure 73 displays the amino acid sequence of protein PF12F30 comprising as indicated amino acids 26 to 281 of the human IFN-γ receptor and signal peptide S.P.2 which is indicated by circles. Figure 74 displays the amino acid sequence of protein P28A comprising as indicated amino acids 15 to 246 of the human IFN-γ receptor and signal peptide S.P.1, which is indicated by circles. Figure 75 displays the amino acid sequence of protein P28B comprising as indicated amino acids 15 to 246 of the human IFN-γ receptor and signal peptide S.P.1, which is indicated by circles. Figure 76 displays the amino acid sequence of protein P28C comprising as indicated amino acids 15 to 246 of the human IFN-γ receptor and signal peptide S.P.2, which is indicated by circles. Figure 77 displays the amino acid sequence of protein P28D comprising as indicated amino acids 15 to 246 of the human IFN-γ receptor and signal peptide S.P.2, which is indicated by circles. Figure 78 displays the amino acid sequence of protein P25A comprising as indicated amino acids 26 to 246 of the human IFN-γ receptor and signal peptide S.P.1, which is indicated by circles. Figure 79 displays the amino acid sequence of protein P25B comprising as indicated amino acids 26 to 246 of the human IFN-γ receptor and signal peptide S.P.1, which is indicated by circles. Figure 80 displays the amino acid sequence of protein P25C comprising as indicated amino acids 26 to 246 of the human IFN-γ receptor and signal peptide S.P.2, which is indicated by circles. Figure 81 displays the amino acid sequence of protein P25D comprising as indicated amino acids 26 to 246 of the human IFN-γ receptor and signal peptide S.P.2, which is indicated by circles. Figure 82 is a summary of the plasmids used for production of cell-bound receptor derivatives in COS-1 cells, of the proteins encoded by these plasmids, of the regions of the human IFN-γ receptor contained in these proteins and of the signal peptides directing these proteins to the surface of the cells. Human IFN-γ receptor is abbreviated by receptor. Figure 83 is a schematic summary of the amino acid sequences of the cell-bound proteins expressed in COS-1 cells. Stretches of amino acids of the human IFN-γ receptor (Receptor) present in these proteins are represented by stars, signal peptides S.P.2 is indicated by circles. Figure 84 is a summary of the capacity to bind IFN-γ (ligand) shown by the cell-bound Receptors produced in COS-1 cells. The symbol + + indicates that transfected cells bind 3-5 fold more IFN-γ than mock transfected cells. Figure 85 is a summary of the plasmids used for the production in COS-1 cells of secreted proteins, of the proteins encoded by these plasmids, of the regions of the human IFN-γ receptor contained in these proteins and of the nature of the signal peptides directing the secretion of these proteins. Figure 86 is a schematic summary of the amino acid sequences of the proteins secreted upon production in COS-1 cells. Strechtes of amino acids of the human IFN-γ receptor present in these proteins are represented by stars, signal peptide S.P.1 is indicated by crosses and signal peptide S.P.2 is indicated by circles. Figure 87 is a summary of activities of the proteins secreted upon production in COS-1 cells. Radioimmune assay and human IFN-γ are abbreviated by RIA and ligand, respectively, whereas n.t. indicates, that this activity of the very protein has not been tested for. The symbol + + indicates that about 50 fold more of the proteins secreted were bound by both cold and radiolabelled mAb. Unless otherwise specified, percentages given below for solids in solid mixtures, liquids in liquids and solids in liquids are on a wt/wt, vol/vol and wt/vol basis, respectively. Example 1 Description of the source of the DNA used for the expression of the soluble human IFN-γ receptors Several cDNAs encoding the human IFN-γ receptor have been described (Aguet et al., supra). One of these cDNAs was cloned into the EcoRI restriction endonuclease cleavage site of the λZAP vector (Strategene). Following the circularization procedure provided by Stratagene, plasmid pBABLUE was obtained, in which the gene for the human IFN-γ receptor is flanked by several restriction endonuclease cleavage sites. Plasmid pBABLUE was the source of the DNA for the expression of the soluble human IFN-γ receptors. The nucleotide sequence of the relevant part of this plasmid is shown together with the deduced amino acid sequence of the human IFN-γ receptor in Fig. 1. For convenience, the amino acid sequence of the human IFN-γ receptor with its relevant characteristics is also shown in Fig. 2. Example 2 Description of plasmids used for the cloning of human IFN-γ receptor encoding DNA fragments and expression in E.coli of the soluble human IFN-γ receptors A. Principles Plasmids pDS56/RBSII,NcoI (Figs. 3 and 4), pDS56/RBSII,SphI (Figs. 5 and 6), pDS56/RBSII,6xHis (Figs. 7 and 8), pDS56/RBSII-6xHis (Figs. 9 and 10), pDS781/RBSII,6xHis (Figs. 11 and 12) and pDHFR-(0/-1)-6xHis (Figs. 13 and 14) were used for the cloning of relevant DNA fragments and the expression in E.coli of the soluble human IFN-γ receptor of the present invention. The following E.coli cells transformed with these plasmids were deposited at the Deutsche Sammlung von Microorganismen in Braunschweig on April 6, 1989, in accordance with the Budapest Treaty: E.coli M15 (pDS56/RBSII,NcoI ; pDMI,1), DSM No.: 5302, E.coli M15 (pDS56/RBSII,SphI ; pDMI,1), DSM No.: 5300, E.coli M15 (pDS56/RBSII,6xHis ; pDMI,1), DSM No.: 5298, E.coli M15 (pDS56/RBSII-6xHis ; pDMI,1), DSM No.: 5299, E.coli M15 (pDS781/RBSII,6xHis ; pDMI,1), DSM No.: 5301 and E.coli M15 (pDHFR-(0/-1)-6xHis ; pDMI,1), DSM No.: 5297. The above-mentioned vectors contain the regulatable promoter/operator element N250PSN250P29 and the ribosomal binding sites RBSII,SphI, RBSII,NcoI or RBSII. These ribosomal binding sites were derived from the ribosomal binding site of the promoter P G25 of the E.coli phage T5 (R. Gentz, Dissertation, Universität Heidelberg, BRD [1984]) and were obtained via DNA synthesis. Due to the high efficiency of expression, the above-mentioned plasmids can be maintained in E.coli cells only if the promoter/operator element is repressed by the binding of a lac repressor to the operator. The lac repressor is coded in the lacI gene. N250PSN250P29 can be repressed efficiently only when a sufficient number of repressor molecules is present in the cells. Therefore, the lacI q allel, which contains a promoter mutant which leads to an increased expression of the repressor gene, was used. This lacI q allel is present in the plasmid pDMI,1 (Figs. 15 and 16). This plasmid carries, in addition to the lac-I gene, the neo gene, which confers kanamycin resistance to the bacteria and which is used as the selection marker. pDMI,1 is compatible with the aforementioned plasmids. E.coli cells which are transformed with such expression vectors must contain pDMI,1 to guarantee that the expression vector is held stable in the cells. An induction of this system is achieved by adding IPTG to the medium at the desired cell density. B. Plasmid pDS56/RBSII,NcoI The part of pDS56/RBSII,NcoI (Figs. 3 and 4) which lies between the restriction cleavage sites for XbaI and XhoI and which contains the replication region and the gene for β-lactamase (which confers ampicillin resistance to the cells) was derived originally from the plasmid pBR322 (Bolivar et al., Gene 2, 95-113 [1977]; Sutcliffe, Cold Spring Harbor Symp. Quant. Biol. 43, 77-90 [1979]). However, the gene for β-lactamase is modified by elimination of the cleavage sites for the restriction enzymes HincII and PstI. These alterations in the DNA sequence have no effect on the amino acid sequence of the β-lactamase. The remaining part of the plasmid carries the regulatable promoter/operator element N250PSOP29 followed by the ribosomal binding site RBSII,NcoI, which is part of an EcoRI/BamHI fragment, cleavage sites for the restriction enzymes SaII,PstI and HindIII, the terminator t o of E.coli phage lambda (Schwarz et al., Nature 272, 410-414 [1978]), the promoter-free gene of chloramphenicol acetyltransferase (Marcoli et al., FEBS Letters, 110, 11-14 [1980]) and the terminator T1 of the E.coli rrnB operon (Brosius et al., J. Mol. Biol. 148, 107-127 [1981]). C. Plasmid pDS56/RBSII,SpHI Plasmid pDS56/RBSII,SphI (Figs. 5 and 6) is similar to plasmid pDS56/RBSII,NcoI but contains the ribosomal binding site RBSII,SphI. D. Plasmid pDS56/RBSII,6xHis Plasmid pDS56/RBSII,6xHis (Figs. 7 and 8) is similar to plasmid pDS56/RBSII,NcoI but contains the ribosomal binding site RBSII followed by a region encoding six histidine residues. E. Plasmid pDS56/RBSII-6xHis Plasmid pDS56/RBSII-6xHis (Figs. 9 and 10) is similar to plasmid pDS56/RBSII,NcoI but contains the ribosomal binding site RBSII followed by cleavage sites for the restriction enzymes BamHI and BglII, a region encoding six histidine residues, and a translational stop codon preceeding the cleavage site for restriction enzyme HindIII. F. Plasmid pDS781/RBSII,6xHis The part of plasmid pDS781/RBSII,6xHis (Figs. 11 and 12) which lies between the restriction cleavage sites for XbaI and XhoI and which contains the replication region and the gene for β-lactamase (which confers ampicillin resistance to the cells) was derived originally from the plasmid pBR322 (Bolivar et al., supra; Sutcliffe, supra). However, the gene for β-lactamase is modified in the manner described for the plasmid pDS5/RBSII,NcoI. The remaining part of the plasmid carries the regulatable promoter/operator element N250PSN250P29 followed by the ribosomal binding site RBSII; a region encoding six histidine residues; a BamHI restriction endonuclease cleavage site, the dihydrofolate reductase (DHFR) gene of mouse cell line AT-3000 (Chang et al., Nature 275, 617-624 [1978]; Masters et al., Gene 21, 59-63 [1983]), which has been altered by introducing a cleavage site for the restriction enzyme BglII immediately prior to the end of the structural gene; a translational stop codon; a cleavage site for the restriction enzyme HindIII; the terminator t o (Schwarz et al., supra); the promoter-free gene for chloramphenicol acetyltransferase (Marcoli et al., supra) and the terminator T1 (Brosius et al., supra). G. Plasmid pDHFR-(0/-1)-6xHis Plasmid pDHFR-(0/-1)-6xHis (Figs. 13 and 14) is similar to plasmid pDS781/RBSII,6xHis but contains the region encoding six histidine residues between the cleavage site for the restriction enzyme BglII and the translational stop codon preceeding the cleavage site for the restriction enzyme HindIII. H. Plasmid pDMI,1 Plasmid pDMI,1 (Figs. 15 and 16) carries the gene for neomycin phosphotransferase from the transposon Tn5 (Beck et al., Gene 19, 327-336 [1982]), which confers kanamycin resistance to E.coli cells, and the lacI gene (Farabough, Nature 274, 765-769 [1978]) with the promoter mutation I q (Calos, Nature 274, 762-765 [1978]), which codes for the lac repressor. Moreover, plasmid pDMI,1 contains a region of the plasmid pACYC184 (Chang and Cohen, J. Bacteriol. 134, 1141-1156 [1978]), which contains all information required for the replication and stable transmission to the daughter cells. Example 3 Construction of plasmids used for the expression of the soluble human IFN-γ receptors in E.coli A. Principles The methods used for the construction of plasmids are well known for those that are skilled in the art, e.g. from the laboratory manual "Molecular Cloning" by Maniatis et al. Cold Spring Harbor Laboratory, 1982. These methods include the use of restriction enzymes to selectively cut DNA, the use of Klenow enzyme to fill-in protruding ends generated by action of restriction enzymes, the analysis of intact plasmids and of DNA fragments by electrophoresis in agarose or polyacrylamide gels, the isolation of DNA out of those gels, the ligation of DNA fragments, the transformation of DNA into competent E.coli cells and the preparation of such cells, and the growth of transformed E.coli cells. Plasmid DNA was extracted from those cells according to the method of Birnboim and Doly (Nucleic Acids Res. 7, 1513-1523 [1979]. Plasmid DNA used for the transfection of COS-1 cells was prepared by CsCl/Ethidium bromide centrifugation as described (Vinograd et al., Proc. Natl. Acad. Sci. USA 71, 1790-1794 [1967]). Oligonucleotides (linkers, adaptors, primers) were either purchased or synthesized using controlled pore glass (CPG) as support material (Kiefer et al., Immunol. Methods 3, 69-83 [1985]; Adams et al., J. Amer. Chem. Soc. 105, 661-663 [1983]). Oligonucleotide-directed in vitro mutagenesis was performed using the 'Oligonucleotide-directed in vitro mutagenesis system' of Amersham. DNA sequences were verified by sequencing single-stranded or double-stranded DNA using the Sequenase R system of United States Biochemical Corporation. B. Construction of plasmid pDS56/RBSII-F26-6xHis encoding protein P26H6 Plasmid pDS56/RBSII-F26-6xHis was constructed in two steps; 1) a DNA fragment, termed F7, was prepared from plasmid pBABLUE and integrated into plasmid pDHFR-(0/-1)-6xHis resulting in plasmid pDHFR-F7-6xHis and 2) a DNA fragment, termed F26, was prepared from this plasmid and integrated into plasmid pDS56/RBSII-6xHis resulting in plasmid pDS56/RBSII-F26-6xHis. 1. Construction of plasmid pDHFR-F7-6xHis Plasmid pBABLUE was digested with restriction endonucleases XbaI and ScaI (see Fig. 1). The protruding ends of the resulting DNA fragments were filled-in using Klenow enzyme before phosphorylated BglII-linkers (linker 1, Fig. 17) were added. After cleavage with restriction enzyme BglII, fragment F7 was isolated from the resulting mixture of DNA fragments. The nucleotide sequence and the deduced amino acid sequence of F7 are shown in Fig. 18. Fragment F7 encodes amino acids 1 to 212 of the human IFN-γ receptor and some additional amino acids. Finally, fragment F7 was integrated into the unique cleavage site for restriction enzyme BglII of plasmid pDHFR-(0/-1)-6xHis (see Figs. 13 and 14) resulting in plasmid pDHFR-F7-6xHis. 2. Construction of plasmid pDS56/RBSII-F26-6xHis Plasmid pDHFR-F7-6xHis was digested with restriction enzyme HaeIII. To the ends of the resulting DNA fragments a phosphorylated DNA adaptor (adaptor 1, Fig. 17) was ligated before the DNA was digested with restriction enzymes BamHI and BglII. Subsequently, fragment F26 was isolated from the mixture of DNA fragments. The nucleotide sequence and the deduced amino acid sequence of F26 are shown in Fig. 19. Fragment F26 encodes amino acids 15 to 212 of the human IFN-γ receptor and some additional amino acids. Finally, fragment F26 was integrated in the proper orientation into the unique cleavage sites for restriction enzymes BamHI and BglII of plasmid PDHFR-(0/-1)-6xHis (see Figs. 13 and 14), thereby replacing the gene for DHFR. In the resulting plasmid pDS56/RBSII-F26-6xHis the coding region for the receptor is in frame with the region encoding six histidines. Plasmid pDS56/RBSII-F26-6xHis encodes protein P26H6 (see Fig. 20) and was used for the production of this protein. C. Construction of plasmids pDS56/RBSII-F25-6xHis(A), pDS56/RBSII-F25-6xHis(B) and pDS56/RBSII-F25-6xHis(C) encoding proteins P25H6A, P25H6B and P25H6C, respectively Plasmids pDS56/RBSII-F25-6xHis(A), pDS56/RBSII-F25-6xHis(B) and pDS56/RBSII-F25-6xHis(C) were constructed in three steps: 1) a DNA fragment, termed F12, was prepared from plasmid pBABLUE and integrated into plasmid pDHFR-(0/-1)-6xHis resulting in plasmid pDHFR-F12-6xHis; 2) a DNA fragment of this plasmid was integrated into plasmid M13mp19 and a cleavage site for the restriction enzyme BamHI was introduced into the gene for the human IFN-γ receptor by in-vitro mutagenesis resulting in fragment F27; and 3) a DNA fragment, termed F25, was prepared from the mutagenized DNA and integrated in three different ways into plasmid pDS56/RBSII-6xHis resulting in plasmids pDS56/RBSII-F25-6xHis(A), pDS56/RBSII-F25-6xHis(B) and pDS56/RBSII-F25-6xHis(C). 1. Construction of plasmid pDHFR-F12-6xHis Plasmid pBABLUE was digested with restriction enzymes HaeIII and PvuII (see Fig. 1). To the ends of the resultung DNA fragments BglII-linkers (linker 2, Fig. 17) were added. After cleavage with restriction enzyme BglII, fragment F12 was isolated from the mixture of DNA fragments. The nucleotide sequence and the deduced amino acid sequence of F12 are shown in Fig. 21. Fragment F12 encodes amino acids 26 to 416 of the human IFN-γ receptor and some additional amino acids. Finally, fragment F12 was integrated into the unique cleavage site for restriction enzyme BglII of plasmid pDHFR-(0/-1)-6xHis (see Figs. 13 and 14) resulting in plasmid pDHFR-F12-6xHis. 2. Preparation of fragment F27 The EcoRI/HindIII fragment of plasmid pDHFR-F12-6xHis comprising the ribosomal binding site RBSII, the gene for DHFR, fragment F12 and the region encoding six histidines was integrated into the unique cleavage sites for EcoRI and HindIII of plasmid M13mp19 (Pharmacia). In the resulting plasmid, the gene for the receptor was mutagenized using primer 1 (Fig. 17) to introduce a cleavage site for the restriction enzyme BamHI just in front of the DNA encoding the transmembrane region of the receptor (see Figs. 1,2 and 22). The resulting plasmid carries fragment F27, whose nucleotide sequence and deduced amino acid sequence are shown in Fig. 22. Since the DNA sequence was mutagenized without affecting the encoded amino acid sequence of the receptor, fragment F27 differs from fragment F12 only by the presence of the cleavage site for restriction enzyme BamHI (see Figs. 21 and 22). 3. Construction of plasmids pDS56/RBSII-F25-6xHis(A), pDS56/RBSII-F25-6xHis(B) and pDS56/RBSII-F25-6xHis(C) The mutagenized DNA was digested with restriction enzymes BglII and BamHI and fragment F25 was isolated from the resulting mixture of DNA fragments. The nucleotide sequence and deduced amino acid sequence of F25 are shown in Fig. 23. Fragment F25 encodes amino acids 26 to 246 of the human IFN-γ receptor (amino acid 246 preceedes the transmembrane region of the receptor) and some additional amino acids. Finally, fragment F25 was integrated in the proper orientation in three different ways into the unique cleavage sites for BamHI and BglII of plasmid pDS56/RBSII-6xHis (see Figs. 9 and 10): 1) into the BamHI site of the plasmid resulting in plasmid pDS56/RBSII-F25-6xHis(A), 2) between the BamHI and BglII sites of the plasmid, thereby replacing some nucleotides of the plasmid, resulting in plasmid pDS56/RBSII-F25-6xHis(B), and 3) into the BglII site of the plasmid resulting in plasmid pDS56/RBSII-F25-6xHis(C). Plasmids pDS56/RBSII-F25-6xHis(A), pDS56/RBSII-F25-6xHis(B) and pDS56/RBSII-F25-6xHis(C) encode proteins P25H6A (Fig. 24), P25H6B (Fig. 25) and P25H6C (Fig. 26), respectively, and were used for the production of these proteins. D. Construction of plasmid pDS56/RBSII,6xHis-F25 encoding protein P6H25 Plasmid pDS56/RBSII,6xHis-F25 was constructed by integrating fragment F25 (Fig. 23) into the unique cleavage site for restriction enzyme BamHI of plasmid pDS56/RBSII,6xHis (Figs. 7 and 8). Plasmid pDS56/RBSII,6xHis-F25 encodes protein P6H25 (Fig. 27) and was used for the production of this protein. E. Construction of plasmid pDS56/RBSII-F28-6xHis(A) encoding protein P28H6A For construction of plasmid pDS56/RBSII-F28-6xHis(A) first fragments BamHI-F26'-PpuMI and PpuMI-F25'-BamHI were isolated from plasmids pDS56/RBSII-F26-6xHis and pDS56/RBSII-F25-6xHis(A), respectively. Subsequently, these DNA fragments were together integrated into plasmid pDS56/RBSII-6xHis resulting in plasmid pDS56/RBSII-F28-6xHis(A). 1. Preparation of fragment BamHI-F26'-PpuMI Plasmid pDS56/RBSII-F26-6xHis (see Example 3.B) was digested with restriction enzymes BamHI and PpuMI. From the resulting mixture of DNA fragments, fragment BamHI-F26'-PpuMI (see Fig. 19) was isolated. 2. Preparation of fragment PpuMI-F25'-BamHI Plasmid pDS56/RBSII-F25-6xHis(A) (see Example 3.C) was digested with restriction enzymes PpuMI and BamHI. From the resulting mixture of DNA fragment, fragment PpuMI-F25'-BamHI (see Fig. 23) was isolated. 3. Assembly of plasmid pDS56/RBSII-F28-6xHis(A) Together, fragments BamHI-F26'-PpuMI and PpuMI-F25'-BamHI were integrated into the unique cleavage site for restriction enzyme BamHI of plasmid pDS56/RBSII-6xHis (see Figs. 9 and 10). The resulting plasmid pDS56/RBSII-F28-6xHis(A) encodes protein P28H6A (Fig. 28) and was used for the production of this protein, which comprises amino acids 15 to 246 of the human IFN-γ receptor. F. Construction of plasmid pDS56/RBSII-F28-6xHis(B) encoding protein P28H6B For construction of plasmid pDS56/RBSII-F28-6xHis(B) first fragment F28 was isolated from plasmid pDS56/RBSII-F28-6xHis(A). Subsequently, this DNA fragment was integrated into plasmid pDS56/RBSII-6xHis resulting in plasmid pDS56/RBSII-F28-6xHis(B). 1. Preparation of fragment F28 Plasmid pDS56/RBSII-F28-6xHis(A) was digested with restriction enzyme BamHI. From the resulting mixture of DNA fragments, fragment F28 (Fig. 29) encoding amino acids 15 to 246 of the human IFN-γ receptor and one additional amino acid was isolated. 2. Assembly of plasmid pDS56/RBSII-F28-6xHis(B) Fragment F28 was integrated between the unique cleavage sites for restriction enzymes BamHI and BglII of plasmid pDS56/RBSII-6xHis. The resulting plasmid pDS56/RBSII-F28-6xHis(B) encodes protein P28H6B (Fig. 30) and was used for the production of this protein, which comprises amino acids 15 to 246 of the human IFN-γ receptor. G. Construction of plasmid pDS56/RBSII,6xHis-F28 encoding protein P6H28 Plasmid pDS56/RBSII,6xHis-F28 was constructed by integrating fragment F28 (see Example 3.F, Fig. 29) into the unique cleavage site for restriction enzyme BamHI of plasmid pDS56/RBSII,6xHis (see Figs. 7 and 8). The resulting plasmid pDS56/RBSII,6xHis-F28 encodes protein P6H28 (Fig. 31), which comprises amino acids 15 to 246 of the human IFN-γ receptor, and was used for the production of this protein. H. Construction of plasmid pDS56/RBSII-F41-6xHis Plasmid pDS56/RBSII-F41-6xHis was constructed in two steps: 1) a DNA fragment of plasmid pDS56/RBSII-F28-6xHis(A) comprising fragment F28 was mutagenized on the DNA level without affecting the amino acid sequence of the encoded human IFN-γ receptor and 2) from the mutagenized DNA, fragment F41 was isolated and integrated into plasmid pDS56/RBSII-6xHis resulting in plasmid pDS56/RBSII-F41-6xHis. 1. Mutagenesis of fragment F28 The EcoRI/HindIII fragment of plasmid pDS56/RBSII-F28-6xHis(A) (see Example 3.E) comprising the ribosomal binding site RBSII, fragment F28 encoding amino acids 15 to 246 of the human IFN-γ receptor (see Fig. 29), and the region encoding six histidine residues was integrated into the unique cleavage sites for restriction enzymes EcoRI and HindIII of plasmid M13mp19 (Pharmacia). In the resulting plasmid, the gene for the receptor was simultaneously mutagenized using primers 2 and 3 (Fig. 17). Due to this mutagenesis, some nucleotides in the DNA preceeding the regions encoding amino acids 53 and 142 of the human IFN-γ receptor were exchanged without affecting the amino acid sequence of the receptor (compare Figs. 29 and 32). The resulting plasmid carries fragment F41, which nucleotide sequence and deduced amino acid sequence are shown in Fig. 32. 2. Assembly of plasmid pDS56/RBSII-F41-6xHis The mutagenized DNA was digested with restriction enzyme BamHI and fragment F41 (Fig. 32) was isolated from the resulting mixture of DNA fragments. Fragment F41 encodes amino acids 15 to 246 of the human IFN-γ receptor and one additional amino acid. Finally, fragment F41 was integrated into the unique cleavage site for BamHI of plasmid pDS56/RBSII-6xHis (see Figs. 9 and 10) resulting in plasmid pDS56/RBSII-F41-6xHis. This plasmid encodes protein P41H6 (Fig. 33), which comprises amino acids 15 to 246 of the human IFN-γ receptor, and was used for the production of this protein. Proteins P28H6A (see Fig. 28) and P41H6A are identical. I. Construction of plasmid pDS56/RBSII,NcoI-F43-6xHis encoding protein P43H6 Plasmid pDS56/RBSII,NcoI-F43-6xHis was constructed in three steps: 1) fragment F43 was prepared by modifying the 5'-end of fragment F41, 2) fragments XhoI/NcoI and BamHI/XhoI were isolated from plasmids pDS56/RBSII,NcoI and pDS56/RBSII-6xHis, respectively, and 3) all three fragments were assembled resulting in plasmid pDS56/RBSII,NcoI-F43-6xHis. 1. Preparation of fragment F43 Plasmid pDS56/RBSII-F14-6xHis (see Example 3.H. and Fig. 32) was cut at its unique cleavage site for restriction enzyme Asp718I. To the ends of the resulting DNA fragment a phosphorylated DNA adaptor (adaptor 2, Fig. 17) was ligated, before the DNA was digested with restriction enzymes NcoI and BamHI. Subsequently, fragment F43 was isolated from the mixture of DNA fragments. The nucleotide sequence and the deduced amino acid sequence of F43 are shown in Fig. 34. Fragment F43 encodes amino acids 13 to 246 of the human IFN-γ receptor and one additional methionine residue. 2. Preparation of fragments XhoI/NcoI and BamHI/XhoI Plasmid pDS56/RBSII,NcoI (see Figs. 3 and 4) was digested with restriction enzymes XhoI and NcoI. From the resulting mixture of DNA fragments, fragment XhoI/NcoI comprising N250PSN250P29 and RBSII,NcoI was isolated. Plasmid pDS56/RBSII-6xHis (see Figs. 9 and 10) was digested with restriction enzymes BamHI and XhoI. From the resulting mixture of DNA fragments, fragment BamHI/XhoI containing the replication region was isolated. 3. Assembly of plasmid pDS56/RBSII,NcoI-F43-6xHis DNA fragments XhoI/NcoI, F43 and BamHI/XhoI were assembled resulting in plasmid pDS56/RBSII,NcoI-F43-6xHis. This plasmid encodes protein P43H6 (Fig. 35), which comprises amino acids 13 to 246 of the human IFN-γ receptor, and was used for the production of this protein. J. Construction of plasmid pDS56/RBSII,SpHI-F44-6xHis encoding protein P44H6 Plasmid pDS56/RBSII,SphI-F44-6xHis was constructed in three steps: 1) fragment F44 was prepared by modifying the 5'-end of fragment F41, 2) fragment XhoI/SphI was isolated from plasmid pDS56/RBSII,SphI, and 3) fragments F44, XhoI/SphI and BamHI/XhoI were assembled resulting in plasmid pDS56/RBSII,SphI-F44-6xHis. 1. Preparation of fragment F44 Plasmid pDS56/RBSII-F41-6xHis (see Example 3.H and Fig. 32) was cut at its unique cleavage site for restriction enzyme Asp718I. To the ends of the resulting DNA fragment a phosphorylated adaptor (adaptor 3, Fig. 17) was ligated, before the DNA was digested with restriction enzymes SphI and BamHI. Subsequently, fragment F44 was isolated from the mixture of DNA fragments. The nucleotide sequence and the deduced amino acid sequence of F44 are shown in Fig. 36. Fragment F44 encodes amino acids 16 to 246 of the human IFN-γ receptor and one additional methionine residue. 2. Preparation of fragment XhoI/SphI Plasmid pDS56/RBSII,SphI (see Figs. 5 and 6) was digested with restriction enzymes XhoI and SphI. From the resulting mixture of DNA fragments, fragment XhoI/SphI comprising N250PSN250P29 and RBSII,SphI was isolated. 3. Assembly of plasmid pDS56/RBSII,SphI-F44-6xHis DNA fragments XhoI/SphI, F44 and BamHI/XhoI (see above) were assembled resulting in plasmid pDS56/RBSII,SphI-F44-6xHis. This plasmid encodes protein P44H6 (Fig. 37), which comprises amino acids 16 to 246 of the human IFN-γ receptor, and was used for the production of this protein. K. Construction of plasmid pDS56/RBSII,NcoI-F45-6xHis encoding protein P45H6 Plasmid pDS56/RBSII,NcoI-F45-6xHis was constructed in two steps: 1) fragment F45 was prepared by modifying the 5'-end of fragment F41 and 2) fragments XhoI/NcoI, F45 and BamHI/XhoI were assembled resulting in plasmid pDS56/RBSII,NcoI-F45-6xHis. 1. Preparation of fragment F45 Plasmid pDS56/RBSII-F41-6xHis (see Example 3.H and Fig. 32) was cut at its unique cleavage site for restriction enzyme Asp718I. To the ends of the resulting DNA fragment a phosphorylated adaptor (adaptor 4, Fig. 17) was ligated, before the DNA was digested with restriction enzymes NcoI and BamHI. Subsequently, fragment F45 was isolated from the mixture of DNA fragments. The nucleotide sequence and the deduced amino acid sequence of F45 are shown in Fig. 38. Fragment F45 encodes amino acids 18 to 246 of the human IFN-γ receptor and one additional methionine residue. 2. Assembly of plasmid pDS56/RBSII,NcoI-F45-6xHis DNA fragments XhoI/NcoI (see above), F45 and BamHI/XhoI (see above) were assembled resulting in plasmid pDS56/RBSII,NcoI-F45-6xHis. This plasmid encodes protein P45H6 (Fig. 39), which comprises amino acids 18 to 246 of the human IFN-γ receptor, and was used for the production of this protein. L. Construction of plasmid pDS56/RBSII,NcoI-F46-6xHis encoding protein P46H6 Plasmid pDS56/RBSII,NcoI-F46-6xHis was constructed in two steps: 1) fragment F46 was prepared by modifying the 5'-end of fragment F41 and 2) fragments XhoI/NcoI, F46 and BamHI/XhoI were assembled resulting in plasmid pDS56/RBSII,NcoI-F46-6xHis. 1. Preparation of fragment F46 Plasmid pDS56/RBSII-F41-6xHis (see Example 3.H and Fig. 32) was digested with restriction enzyme HaeIII. To the ends of the resulting DNA fragments a phosphorylated adaptor (adaptor 5, Fig. 17) was ligated, before the DNA was digested with restriction enzymes NcoI and BamHI. Subsequently, fragment F46 was isolated from the mixture of DNA fragments. The nucleotide sequence and the deduced amino acid sequence of F46 are shown in Fig. 40. Fragment F46 encodes amino acids 19 to 246 of the human IFN-γ receptor. 2. Assembly of plasmid pDS56/RBSII,NcoI-F46-6xHis DNA fragments XhoI/NcoI (see Example 3.I), F46 and BamHI/XhoI (see Example 3.I) were assembled resulting in plasmid pDS56/RBSII,NcoI-F46-6xHis. This plasmid encodes protein P46H6 (Fig. 41), which comprises amino acids 19 to 246 of the human IFN-γ receptor, and was used for the production of this protein. Example 4 Expression of human IFN-γ receptor derivatives in E.coli including the soluble human IFN-γ receptors of the present invention (for short human IFN-γ receptor derivatives) E.coli M15 cells containing plasmid pDMI,1 were transformed independently with the plasmids shown in Fig. 42 and subsequently grown at 37°C in LB medium (10 g bacto tryptone, 5 g yeast extract, 5 g NaCl per litre) containing 100 mg/l ampicillin and 25 mg/l kanamycin. At an optical density at 600 nm of about 0.7 to 1.0 IPTG was added to a final concentration of 2mM. After additional 2.5 to 5 h at 37°C the cells were harvested by centrifugation and analyzed for the presence of the expected derivatives of the human IFN-γ receptor (Fig. 42) by SDS-PAGE (polyacrylamide electrophoresis in presence of sodium dodecylsulfate) under reducing conditions (3% β-mercaptoethanol in the sample buffer) as described in the literature (Laemmli, Nature 227, 680-685 [1970]). The expected amino acid sequences of the various human IFN-γ receptor derivatives expressed in E.coli are shown in Fig. 43. Also included in this figure are the amino acid sequences of proteins P53 and P142. These proteins are produced in addition to the expected proteins in E.coli cells containing e.g. plasmid pDS56/RBSII-F28-6xHis(A) but are produced to an about 5 fold lower yield in E.coli cells containing plasmid pDS56/RBSII-F41-6xHis. Plasmid pDS56/RBSII-F41-6xHis carries fragment F41, which differs from fragment F28 contained in plasmid pDS56/RBSII-F28-6xHis(A) not by the encoded amino acid sequence but only by some nucleotides preceeding the regions encoding the methionine residues at positions 53 and 142 of the human IFN-γ receptor (see Fig. 32). Therefore, proteins P53 and P142 are the products of internal start of translation within the mRNA and contain the methionine residues at position 53 and 142, respectively, of the receptor as their N-terminal amino acids. Almost all proteins listed in Fig. 42 were produced in E.coli to a level of more than 5 mg/l of culture. The exceptions were proteins P43H6, P44H6, P45H6 and P46H6, which were producted to a level of about 0.1-0.5 mg/l of culture. Example 5 Characterization of human IFN-γ derivatives expressed in E.coli The human IFN-γ derivatives expressed in E.coli were extracted from the cells and enriched by Ni-chelate affinity chromatography, before they were analyzed for their recognition by monoclonal antibodies directed against the receptor purified from Raji cells and their ability to bind IFN-γ specifically. A. Enrichment of the receptor derivatives by Ni-chelate affinity chromatography 10 g E.coli cells containing one of the various receptor derivatives were thawed, before 100 ml of buffer A (6 M guanidine-hydrochloride, 0.1 M sodium phosphate, pH 8.0) were added. After stirring (100 rpm) for 2 h, the suspension was centrifuged for 10 minutes at 10000 xg. The supernatant was loaded at 42 ml/h onto a column (1.6 x 4 cm) containing 8 ml of the NTA-resin described in European Patent Applications Nos. 253 303 and 282 042. Then, the column was washed with 50 ml of buffer A. Subsequently, the column was washed with 30 ml of buffer B (8 M urea, 0.1 M sodium phosphate, 0.01 M Tris, pH 8.0), and then with 50 ml of buffer B, pH 6.5. Finally, the receptor derivative was eluted with buffer B, pH 4.5. B. Recognition of the receptor derivatives by monoclonal antibodies First, the isolated receptor derivatives were separated by SDS-PAGE (Laemmli, supra, sample buffer without β-mercaptoethanol) in a 12% polyacrylamide gel. Then, the proteins were electrotransfered from the gel to nitrocellulose paper in a TRANS-BLOT™CELL (Biorad). This transfer was performed according to the instructions of the manufacturer under cooling with water for 2.5 h in a buffer containing 192 mM glycine, 25 mM Tris, 20% methanol, pH 8.3. Subsequently, the nitrocellulose paper was first incubated for 1.5 h in buffer C (8.1 mM NaH₂PO₄, 1.5 mM KH₂PO₄, 2.7 mM KCl, 137 mM NaCl, 1% defatted milk-powder, pH 7.2) and then incubated for 4 h in buffer C containing a radiolabelled monoclonal antibody against native human IFN-γ receptor as described in Example 10.C. After removal of this solution, the nitrocellulose paper was washed three times for 10 minutes each in buffer C and then three times in buffer C lacking the milk-powder but containing 0.02% Tween 20. After drying of the nitrocellulose paper, proteins recognized by the monoclonal antibody were visualized by autoradiography. As summarized in Fig. 44, all the proteins, with exception of protein P142, were recognized by the monoclonal antibody. C. Ability of the receptor derivatives to bind IFN-γ The ability of the receptor derivatives to bind IFN-γ was analyzed by following the same procedure as described under B., except that iodinated IFN-γ (see Example 9) replaced the monoclonal antibody. As summarized in Fig. 44, all receptor derivatives comprising at least amino acids 26 to 246 of the human IFN-γ receptor were able to bind IFN-γ, whereas proteins lacking amino acids 1 to 52 or 213 to 489 of the receptor did not bind the ligand. The receptor derivatives comprising amino acids 26 to 246 of the human IFN-γ receptor did not bind IFN-γ in experiments, in which the proteins were loaded in sample buffer containing 3% β-mercaptoethanol onto the polyacrylamide gels. Example 6 Extraction and purification of soluble human IFN-γ receptors from E.coli cells Protein P41H6 (see Figs. 33, 42 and 43) expressed in E.coli was purified and obtained as a soluble protein. The recovery procedure included the following steps: (I) Disruption of the cells and extraction of the proteins with guanidine-hydrochloride; (II) Ni-chelate affinity chromatography (most of the bacterial proteins were removed); (III) Chromatography on a sizing column in the presence of urea (polymeric forms of protein P41H6 were removed); (IV) Refolding of the protein under removal of urea; and (V) Chromatography on an anion exchanger column (smaller fragments and wrong conformational forms of P41H6 were removed). Step I: Disruption of the cells and extraction of the proteins 100 g of frozen (-70°C) cells containing protein P41H6 were kept at 4°C for 16 h. Then, the thawed cells were suspended in 1 liter of buffer E (7 M guanidine-hydrochloride, 0.1 M sodium phosphate, pH 8.0) using a Polytron homogenizer. This suspension was sonicated for 5 minutes with a Branson sonifier (position 8) and then stirred at 22°C for 1 h. The resulting suspension was kept on ice for 1 h and then centrifuged at 12000 xg for 1 h. Finally, the supernatant containing protein P41H6 was collected. Step II: Ni-chelate affinity chromatography A column (5 x 5 cm), containing 100 ml NTA-resin, which was prepared as described in European Patent Applications Publication Nos. 253 303 and 282 042, was loaded with Ni⁺⁺, washed with 0.2 M acetic acid and equilibrated in buffer E at 4°C (all further operations were carried out at 4°C). The supernatant of step I was loaded at 50 ml/h onto this column, before the column was washed first with 1 l of buffer E and then with 1 l of buffer F (7 M urea, 0.1 M Tris/HCl, pH 8.0). Proteins still bound to the NTA-resin were eluted with 1 l of buffer G (7 M urea, 0.1 M Tris-maleate, pH 6.3) and, finally, with 1 l of buffer H (7 M urea, 0.1 M Tris-maleate, pH 5.9). The collected fractions were analyzed by SDS-PAGE under reducing and non reducing conditions for presence of protein P41H6. Those fractions containing protein p41H6 mainly in its monomeric form were combined resulting in a volume of about 1 liter. Step III: Sizing column The solution of step II with protein P41H6 in buffer H was concentrated under nitrogen pressure to a volume of 20 ml using an ultrafiltration system (Amicon; membrane cut-off 10000 M r ). This solution was loaded at a flow-rate of 30 ml/h onto a column (5 x 90 cm) containing 1,8 l of Sephadex G-100 (Pharmacia) equilibrated in buffer I (7 M urea, 0.05 M Tris/HCl, pH 7.5). Then, the column was further developed at the same flow-rate with 700 ml of buffer I. The appearance of protein in the collected fractions was monitored by UV-absorption. Two protein peaks were obtained and analyzed by SDS-PAGE. The first peak appeared after 450 - 500 ml of solution had passed the column and contained mainly polymeric forms of protein P41H6. The second peak appeared after 550 - 600 ml of solution had been collected and contained protein P41H6 in monomeric form together with some additional proteins, e.g. proteins P53 and P142 (see Example 4). Fractions containing protein P41H6 in its monomeric form were combined resulting in a volume of about 100 ml. Step IV: Refolding The solution of step III containing protein P41H6 in its monomeric form was adjusted to 10 mM benzamidine-HCl, 1 mM phenylmethane-sulfonyl fluoride (PMSF) and 5 µg/ml aprotinin by adding solid benzamidine-HCl, a solution of 0,2 M PMSF in DMSO and aprotinin. The resulting solution was then dialyzed (dialysis tubing cut-off 10000 M r ) against 3 liters of 100 mM Tris/HCl, 10% glycerol, 10 mM benzamidine, 1 mM PMSF and 5 µg/ml aprotinin at 4°C with three changes of the dialysis buffer. Subsequently, the solution was centrifuged for 30 minutes at 10000 xg, before the supernatant containing protein P41H6 in its monomeric form was either frozen or directly worked up. Step V: Chromatography on an ion-exchanger column The solution of step IV containing protein P41H6 was dialyzed against 50 mM sodium phosphate, 0.2 M NaCl, 1 mM PMSF and 1 mM benzamidine-HCl, pH 7.0. After centrifugation for 30 minutes at 10000 xg, the supernatant was applied at 50 ml/h onto a column (1.5 x 25 cm) containing 45 ml Polybuffer exchanger 94 (Pharmacia) equilibrated in 50 mM sodium phosphate, 200 mM NaCl, 1 mM PMSF and 1 mM benzamidine-HCl, pH 6.0. The column was washed with 200 ml of the same buffer, before the protein was eluted with a gradient from 0.2 M to 0.6 M NaCl in 50 mM sodium-phosphate, pH 6.0. 10 ml fractions were collected and analysed by SDS-PAGE. Fragments containing mainly protein P41H6 in its monomeric form were combined and the resulting fractions were stored at -20°C. The purification of protein P41H6 described above is summarized in Fig. 45. 17 mg of soluble and monomeric P41H6 with a purity of about 85% were obtained from 100 g of cells. Proteins P26H6, P25H6C and P28H6A (see Fig. 43) were purified according to the protocol described above, except that step V was omitted. Since only 10 g of cells were processed, the sizes of the columns and the volumes of the solutions were reduced proportionally. All three proteins were obtained with a purity of about 50% as soluble and monomeric molecules. In contrast to protein P26H6, proteins P25H6C, P28H6A and P41H6 were able to bind IFN-γ (see Example 5 and Fig. 44) and inhibited the binding of IFN-γ to the human IFN-γ receptor present on Raji cells (see Example 10). Furthermore, proteins P25H6C and P28H6A were able to inhibit the antiviral activity caused by IFN-γ (see Example 10, protein P41H6 was not included in this test). Therefore, proteins P25H6C, P28H6A and P41H6 contain that region of the human IFN-γ receptor, which is essential for the binding of its ligand, in an active form. Example 7 Description of plasmids used for the expression of receptor derivatives in COS-cells A. Principles Plasmids p79BGL (Figs. 46 and 47), p79DBAM (Figs. 48 and 49) p238BGL (Figs. 50 and 51), p238BAM (Figs. 52 and 53), p264BGL (Figs. 54 and 55), p264BAM (Figs. 56 and 57), p267BGL (Figs. 58 and 59) and p267BAM (Figs. 60 and 61) were used for the expression of derivatives of the human IFN-γ receptor in COS-cells. The following E.coli cells transformed with these plasmids were deposited at the Deutsche Sammlung von Microorganismen in Braunschweig on April 6, 1989, in accordance with the Budapest Treaty: E.coli M15 (p79BGL), DSM No.: 5296, E.coli M15 (p79DBAM), DSM No.: 5295, E.coli M15 (p238BGL), DSM No.: 5294, E.coli M15 (p238BAM), DSM No.: 5293, E.coli M15 (p264BGL), DSM No.: 5292, E.coli M15 (p264BAM), DSM No.: 5291, E.coli M15 (p267BGL), DSM No.: 5290 and E.coli M15 (p267BAM), DSM No.: 5289. The above mentioned vectors all contain a region originally derived from plasmid pBR322 (Bolivar et al., supra; Sutcliffe, supra), which comprises the replication region, the gene for β-lactamase and parts of the tetracycline resistance gene of this plasmid. Therefore the above mentioned vectors can be stably maintained in E.coli cells grown in the presence of ampicillin. Futhermore, these plasmids contain the replication region originally derived from the simian virus SV40, allowing at least the transient maintenance of these plasmids in monkey COS-1 cells. The additional characteristics of the plasmids used for expression in COS-1 cells are described in the following chapters. B. Plasmid p79BGL Plasmid p79BGL (Figs. 46 and 47) carries in addition to the region necessary for its maintenance in E.coli and in COS-1 cells the long terminal repeat (LTR) of rous sarcoma virus. This promoter is followed by the gene for rat preproinsulin, in which parts of the coding region have been replaced by a region encoding several translational stop codons. Therefore, plasmid p79BGL contains downstream of its promoter a 5 - untranslated region, a region encoding a translational initiation codon, a unique cleavage site for restriction enzyme BamHI, several translational stop codons and a polyadenylation signal. C. Plasmid p79DBAM Plasmid p79DBAM (Figs. 48 and 49) is similar to plasmid p79BGL but lacks the region between the BglII and BamHI restriction sites of plasmid p79BGL. Therefore, plasmid p79DBAM does not encode a translational initiation codon between its promoter and its unique cleavage site for restriction enzyme BamHI. D. Plasmid p238BGL Plasmid p238BGL (Figs. 50 and 51) carries the same replication regions and promoter as plasmid p79BGL. However, in plasmid p238BGL the LTR is followed by: 1) a region encoding the signal peptide of the interleukin-2 receptor (S.P.1), 2) unique cleavage sites for restriction enzymes SacI and BglII, 3) a region encoding several translational stop codons and 4) a polyadenylation signal. E. Plasmid p238BAM Plasmid p238BAM (Figs. 52 and 53) is similar to plasmid p238BGL but contains instead of a BglII site a unique cleavage site for restriction enzyme BamHI. F. Plasmid p264BGL Plasmid p264BGL (Figs. 54 and 55) carries the same replication regions and promoter as plasmid p79BGL. However, in plasmid p264BGL the LTR is followed by: 1) a region encoding the signal peptide of interleukin-2 receptor (S.P.1), 2) unique cleavage sites for restriction enzymes SacI and BglII, 3) a region encoding several translational stop codons, 4) the 3'intron of the rat preproinsulin gene and 5) a polyadenylation signal. G. Plasmid p264BAM Plasmid p264BAM (Figs. 56 and 57) is similar to plasmid p264BGL but contains instead of a BglII site a unique cleavage site for restriction enzyme BamHI. H. Plasmid p267BGL Plasmid p267BGL (Figs. 58 and 59) carries the same replication regions and promoter as plasmid p79BGL. However, in plasmid p267BGL the LTR is followed by: 1) the 5'-untranslated region and the 5'-intron of the rat preproinsulin gene, 2) a region encoding the slightly modified signal peptide of the interleukin-2 receptor (S.P.2), 3) unique cleavage sites for restriction enzymes SacI and BglII, 4) a region encoding several translational stop codons and 5) a polyadenylation signal. I. Plasmid p267BAM Plasmid p267BAM (Figs. 60 and 61) is similar to plasmid p267BGL but contains instead of a BglII site a unique cleavage site for restriction enzyme BamHI. Example 8 Construction of plasmids used for expression of receptor derivatives in COS-cells A. Principles DNA fragments encoding various parts of the human IFN-γ receptor were prepared and integrated first in such a way into some of the plasmids described in Example 2, that they easily could be recovered after amplification of the resulting plasmids. Then, these fragments were integrated into the plasmids suitable for expression in COS-cells. B. Preparation of DNA fragments F1, F3, F12, F25, F26, F28, F30 and F31 1. Preparation of DNA fragment F1 Plasmid pBABLUE was digested with restriction endonucleases XbaI and HindIII (See Fig. 1). The protruding ends of the resulting DNA fragments were filled-in using Klenow enzyme before phosphorylated BglII-linkers (linker 1, Fig. 17) were added. After cleavage with restriction enzyme BglII, fragment F1 was isolated from the resulting mixture of DNA fragments and was integrated into the unique cleavage site for restriction enzyme BglII of plasmid pDHFR-(0/-1)-6xHis (see Figs. 13 and 14) resulting in plasmid pDHFR-F1-6xHis. After amplification, this plasmid was cleaved with restriction enzyme BglII and fragment F1 was isolated. The nucleotide sequence and deduced amino acid sequence of F1 are shown in Fig. 62. Fragment F1 encodes the entire human IFN-γ receptor and some additional amino acids. Furthermore, this fragment contains parts of the 3'-untranslated region of the receptor gene. 2. Preparation of DNA fragment F3 Plasmid pBABLUE was digested with restriction enzyme SmaI (see Fig. 1). To the ends of the resulting DNA fragments BglII-linkers (linker 2, Fig. 17) were added. After cleavage with restriction enzyme BglII, fragment F3 was isolated from the mixture of DNA fragments and integrated into the unique cleavage site for restriction enzyme BglII of plasmid pDHFR-(0/-1)-6xHis (see Figs. 13 and 14) resulting in plasmid pDHFR-F3-6xHis. After amplification, this plasmid was cleaved with restriction enzyme BglII and fragment F3 was isolated. The nucleotide sequence and the deduced amino acid sequence of F3 are shown in Fig. 63. Fragment F3 encodes amino acids 1 to 367 of the human IFN-γ receptor and some additional amino acids. 3. Preparation of DNA fragment F12 The preparation of fragment F12 (Fig. 21) is described in Example 3.C.1. Fragment F12 encodes amino acids 26 to 416 of the human IFN-γ receptor and some additional amino acids. 4. Preparation of DNA fragment F25 The preparation of fragment F25 (Fig. 23) is described in Example 3.C.3. Fragment F25 encodes amino acids 26 to 246 of the human IFN-γ receptor and some additional amino acids. 5. Preparation of DNA fragment F26 The preparation of fragment F26 (Fig. 19) is described in Example 3.B.2. Fragment F26 encodes amino acids 15 to 212 of the human IFN-γ receptor and some additional amino acids. 6. Preparation of DNA fragment F28 The preparation of fragment F28 (Fig. 29) is described in Example 3.F.1. Fragment F28 encodes amino acids 15 to 246 of the human IFN-γ receptor and one additional amino acid. 7. Preparation of DNA fragment F30 For preparation of fragment F30, plasmid pDHFR-F3-6xHis (see Example 8.B.2) was cleaved with restriction Enzyme SspI (see Figs. 1 and 63). To the ends of the resulting DNA fragments phosphorylated BglII-linkers (linker 3, Fig. 17) were ligated. After cleavage with restriction enzyme BglII, fragment F30 was isolated from the mixture of DNA fragments. The nucleotide sequence and the deduced amino acid sequence of F30 are shown in Fig. 64. Fragment F30 encodes amino acids 1 to 281 of the human IFN-γ receptor and some additional amino acids. 8. Preparation of DNA fragment F31 For preparation of fragment F31, plasmid pDHFR-F1-6xHis (see Example 8.B.1) was incubated with restriction enzymes BglII and MboI (see Figs. 1 and 62) and fragment F31 was isolated from the mixture of DNA fragments. The nucleotide sequence and deduced amino acid sequence of F31 are shown in Fig. 65. Fragment F31 encodes the entire human IFN-γ receptor and some additional amino acids. In contrast to fragment F1 (Fig. 62), which also encodes the entire receptor, fragment F31 does not contain the 3'-untranslated region of the receptor gene. C. Construction of plasmids expressing repressor derivatives, which contain the transmembrane region of the receptor 1. Construction of plasmid p79DBAM-F1 Plasmid p79DBAM-F1 was constructed by integrating fragment F1 (see Example 8.B.1) into the unique cleavage site for restriction enzyme BamHI of plasmid p79DBAM (Figs. 48 and 49). The resulting plasmid p79DBAM-F1 encodes protein PF1 (Fig. 66) comprising the entire human IFN-γ receptor. 2. Construction of plasmid p79DBAM-F3 Plasmid p79DBAM-F3 was constructed by integrating fragment F3 (see Example 8.B.2) into the unique cleavage site for restriction enzymes BamHI of plasmid p79DBAM (Figs. 48 and 49). The resulting plasmid p79DBAM-F3 encodes protein PF3 (Fig. 67) and was used for the production of this protein, which comprises amino acids 1 to 367 of the human IFN-γ receptor. 3. Construction of plasmid p79DBGLBAM-F3 Plasmid p79DBGLBAM-F3 was constructed by inserting fragment F3 (see Example 8.B.2) between the unique cleavage sites for restriction enzymes BglII and BamHI of plasmid p79BGL (Figs. 46 and 47), thereby replacing parts of plasmid p79BGL. The resulting plasmid p79DBGLBAM-F3 encodes like plasmid p79DBAM-F3 protein PF3 (Fig. 67) and was used for the expression of this protein, which comprises amino acids 1 to 367 of the human IFN-γ receptor. 4. Construction of plasmid p79DBAM-F12 Plasmid p79DBAM-F12 was constructed by integrating fragment F12 (see Example 8.B.3) into the unique cleavage site for restriction enzyme BamHI of plasmid p79DBAM (Figs. 48 and 49). The resulting plasmid p79DBAM-F12 encodes amino acids 26 to 416 of the human IFN-γ receptor. 5. Construction of plasmid p267BGL-F12 Plasmid p267BGL-F12 was constructed by integrating fragment F12 (see Example 8.B.3) into the unique cleavage site for restriction enzyme BglII of plasmid p267BGL (Figs. 58 and 59). The resulting plasmid p267BGL-F12 encodes protein PBGLF12 (Fig. 68) and was used for the production of this protein, which comprises signal peptide S.P.2 and amino acids 26 to 416 of the human IFN-γ receptor. 6. Construction of plasmid p79DBAM-F30 Plasmid p79DBAM-F30 was constructed by integrating fragment F30 (see Example 8.B.7) into the unique cleavage site for restriction enzyme BamHI of plasmid p79DBAM (Figs. 48 and 49). The resulting plasmid p79DBAM-F30 encodes protein PF30 (Fig. 69) and was used for the production of this protein, which comprises amino acids 1 to 281 of the human IFN-γ receptor. 7. Construction of plasmid p79DBGLBAM-F30 Plasmid p79DBGLBAM-F30 was constructed by inserting fragment F30 (see Example 8.B.7) between the unique cleavage sites for restriction enzymes BglII and BamHI of plasmid p79BGL (Figs. 46 and 47), thereby replacing parts of plasmid p79BGL. The resulting plasmid p79DBGLBAM-F30 encodes like plasmid p79DBAM-F30 protein PF30 (Fig. 69) and was used for the production of this protein, which comprises amino acids 1 to 281 of the human IFN-γ receptor. 8. Construction of plasmid p79DBAM-F31 Plasmid p79DBAM-F31 was constructed by integrating fragment F31 (see Example 8.B.8) into the unique cleavage site for restriction enzyme BamHI of plasmid p79DBAM (Figs. 48 and 49). The resulting plasmid p79DBAM-F31 encodes like plasmid p79DBAM-F1 protein PF1 (Fig. 66), which comprises the entire human IFN-γ receptor. 9. Construction of plasmid p79DBAM-F1/F3 Plasmid p79DBAM-F1/F3 was constructed by combining fragment PvuI-F1'-EcoRV of plasmid p79DBAM-F1 (see Example 8.C.1) which contains parts of the gene for β-lactamase, the replication region, the RSV promoter and the 5'-end of fragment F1 (Fig. 62), with fragment EcoRV-F3'-PvuI of plasmid p79DBAM-F3 (see Example 8.C.2), which contains the 3-end of fragment F3 (Fig. 63), the polyadenylation signal and parts of the gene for β-lactamase. The resulting plasmid p79DBAM-F1/F3 encodes like plasmids p79DBAM-F3 and p79DBGLBAM-F3 protein PF3 (Fig. 67) and was used for the production of this protein, which comprises amino acids 1 to 367 of the human IFN-γ receptor. 10. Construction of plasmid p79DBAM-F1/F30 Plasmid p79DBAM-F1/F30 was constructed by combining fragment PvuI-F1'-EcoRV of plasmid p79DBAM-F1 (see Example 8.C.1) with fragment EcoRV-F30'-PvuI of plasmid p79DBAM-F30 (see Example 8.C.6), which comprises the 3'-end of fragment F30 (Fig. 64), the polyadenylation signal and parts of the gene for β-lactamase. The resulting plasmid p79DBAM-F1/F30 encodes like plasmids p79DBAM-F30 and p79DBGLBAM-F30 protein PF30 (Fig. 69) and was used for the production of this protein, which comprises amino acids 1 to 281 of the human IFN-γ receptor. 11. Construction of plasmid p267BGL/79DBAM-F12/F1 Plasmid p267BGL/79DBAM-F12/F1 was constructed by combining fragment PvuI-F12'-EcoRV of plasmid p267BGL-F12 (see Example 8.C.5), which comprises parts of the gene for β-lactamase, the replication region, the RSV promoter, the region encoding signal peptide S.P.2 and the 5'-end of fragment F12 (Fig. 21), with fragment EcoRV-F1'-PvuI of plasmid p79DBAM-F1 (see Example 8.C.1), which contains the 3'-end of fragment F1 (Fig. 62), the polyadenylation signal and parts of the gene for β-lactamase. The resulting plasmid p267BGL/79DBAM-F12/F1 encodes protein PF12F1 (Fig. 70) and was used for production of this protein, which comprises signal peptide S.P.2 and amino acids 26 to 489 of the human IFN-γ receptor. 12. Construction of plasmid p267BGL/79DBAM-F12/F31 Plasmid p267BGL/79DBAM-F12/F31 was constructed by combining fragment PvuI-F12'-EcoRV (see Example 8.C.11), with fragment EcoRV-F31'-PvuI of plasmid p79DBAB-F31 (see Example 8.C.8), which comprises the 3'-end of fragment F31 (Fig. 65), the polyadenylation signal and parts of the gene for β-lactamase. The resulting plasmid p267BGL/79DBAM-F12/F31 encodes like plasmid p267BGL/79DBAM-F12/F1 protein PF12F1 (Fig. 70) and was used for production of this protein, which comprises signal peptide S.P.2 and amino acids 26 to 489 of the human IFN-γ receptor. 13. Construction of plasmid p267BGL/79DBAM-F12/F12 Plasmid p267BGL/79DBAM-F12/F12 was constructed by combining fragment PvuI-F12'-EcoRV (see Example 8.C.11), with fragment EcoRV-F12'-PvuI of plasmid p79DBAM-F12 (see Example 8.C.4), which comprises the 3'-end of fragment F12 (Fig. 21), the polyadenylation signal and parts of the gene for β-lactamase. The resulting plasmid p267BGL/79DBAM-F12/F12 encodes protein PF12F12 (Fig. 71) and was used for the production of this protein, which comprises signal peptide S.P.2 and amino acids 26 to 416 of the human IFN-γ receptor. 14. Construction of plasmid p267BGL/79DBAM-F12/F3 Plasmid p267BGL/79DBAM-F12/F3 was constructed by combining fragment PvuI-F12'-EcoRV (see Example 8.C.11) with fragment EcoRV-F3'-PvuI (see Example 8.C.9). The resulting plasmid p267BGL/79DBAM-F12/F3 encodes protein PF12F3 (Fig. 72) and was used for the production of this protein, which comprises signal peptide S.P.2 and amino acids 26 to 367 of the human IFN-γ receptor. 15. Construction of plasmid p267BGL/79DBAM-F12/F30 Plasmid p267BGL/79DBAM-F12/F30 was constructed by combining fragment PvuI-F12'-EcoRV (see Example 8.C.11) with fragment EcoRV-F30'-PvuI (see Example 8.C.10). The resulting plasmid p267BGL/79DBAM-F12/F30 encodes protein PF12F30 (Fig. 73) and was used for the production of this protein, which comprises signal peptide S.P.2 and amino acids 26 to 281 of the human IFN-γ receptor. D. Construction of plasmids used for the production of secreted receptor derivatives in COS-1 cells 1. Principles Plasmids encoding receptor derivatives expected to be secreted into the medium by COS-1 cells containing these plasmids were constructed by integrating DNA fragments F25 (see Example 3.C.1 and Fig. 23) or F28 (see Example 3.F.2 and Fig. 29) into plasmids described in Example 7. In the resulting plasmids a signal peptide is linked to the information encoded by fragments F25 and F28. Since these fragments encode only amino acids 26 to 246 and 15 to 246 of the human IFN-γ receptor, respectively, but not its transmembrane region, the expressed proteins are expected to be secreted into the medium by COS-cells transfected with these plasmids. 2. Construction of plasmid p238BAM-F28 Plasmid p238BAM-F28 was constructed by intergrating fragment F28 into the unique cleavage site for restriction enzyme BamHI of plasmid p238BAM (see Figs. 52 and 53). The resulting plasmid encodes protein P28A (Fig. 74) and was used for the production of this protein, which comprises signal peptide S.P.1 and amino acids 15 to 246 of the human IFN-γ receptor. 3. Construction of plasmid p238BGL-F28 Plasmid p238BGL-F28 was constructed by integrating fragment F28 into the unique cleavage site for restriction enzyme BglII of plasmid p238BGL (see Figs. 50 and 51). The resulting plasmid encodes protein P28B (Fig. 75) and was used for the production of this protein, which comprises signal peptide S.P.1 and amino acids 15 to 246 of the human IFN-γ receptor. 4. Construction of plasmid p264BAM-F28 Plasmid p264BAM-F28 was constructed by integrating fragment F28 into the unique cleavage site for restriction enzyme BamHI of plasmid p264BAM (see Figs. 56 and 57). The resulting plasmid encodes like plasmid p238BAM-F28 protein P28A (Fig. 74) and was used for the production of this protein, which comprises amino acids 15 to 246 of the human IFN-γ receptor. 5. Construction of plasmid p264BGL-F28 Plasmid p264BGL-F28 was constructed by integrating fragment F28 into the unique cleavage site for restriction enzyme BglII of plasmid p264BGL (see Figs. 54 and 55). The resulting plasmid encodes like plasmid p238BGL-F28 protein P28B (Fig. 75) and was used for the production of this protein, which comprises signal peptide S.P.1 and amino acids 15 to 246 of the human IFN-γ receptor. 6. Construction of p267BAM-F28 Plasmid p267BAM-F28 was constructed by integrating fragment F28 into the unique cleavage site for restriction enzyme BamHI of plasmid p267BAM (see Figs. 60 and 61). The resulting plasmid encodes protein P28C (Fig. 76) and was used for the production of this protein, which comprises signal peptide S.P.2 and amino acids 15 to 246 of the human IFN-γ receptor. 7. Construction of plasmid p267BGL-F28 Plasmid p267BGL-F28 was constructed by integrating fragment F28 into the unique cleavage site for restriction enzyme BglII of plasmid p267BGL (see Figs. 58 and 59). The resulting plasmid encodes protein P28D (Fig. 77) and was used for the production of this protein, which comprises signal peptide S.P.2 and amino acids 15 to 246 of the human IFN-γ receptor. 8. Construction of plasmid p238BAM-F25 Plasmid p238BAM-F25 was constructed by integrating fragment F25 into the unique cleavage site for restriction enzyme BamHI of plasmid p238BAM (see Figs. 52 and 53). The resulting plasmid encodes protein P25A (Fig. 78) and was used for the production of this protein, which comprises signal peptide S.P.1 and amino acids 26 to 246 of the human IFN-γ receptor. 9. Construction of plasmid p238BGL-F25 Plasmid p238BGL-F25 was constructed by integrating fragment F25 into the unique cleavage site for restriction enzyme BglII of plasmid p238BGL (see Figs. 50 and 51). The resulting plasmid encodes protein P25B (Fig. 79) and was used for the production of this protein, which comprises signal peptide S.P.1 and amino acids 26 to 246 of the human IFN-γ receptor. 10. Construction of plasmid p264BAM-F25 Plasmid p264BAM-F25 was constructed by integrating fragment F25 into the unique cleavage site for restriction enzyme BamHI of plasmid p264BAM (see Figs. 56 and 57). The resulting plasmid encodes like plasmid p238BAM-F25 protein P25A (Fig. 78) and was used for the production of this protein, which comprises signal peptide S.P.1 and amino acids 26 to 246 of the human IFN-γ receptor. 11. Construction of plasmid p267BAM-F25 Plasmid p267BAM-F25 was constructed by integrating fragment F25 into the unique cleavage site for restriction enzyme BamHI of plasmid p267BAM (see Figs. 60 and 61). The resulting plasmid encodes protein P25C (Fig. 80) and was used for the production of this protein, which comprises signal peptide S.P.2 and amino acids 26 to 246 of the human IFN-γ receptor. 12. Construction of plasmid p267BGL-F25 Plasmid p267BGL-F25 was constructed by integrating fragment F25 into the unique cleavage site for restriction enzyme BglII of plasmid p267BGL (see Figs. 58 and 59). The resulting plasmid encodes protein P25D (Fig. 81) and was used for the production of this protein, which comprises signal peptide S.P.2 and amino acids 26 to 246 of the human IFN-γ receptor. Example 9 Expression of membrane bound derivatives of the human IFN-γ receptor in COS-cells A. Principles Plasmids encoding derivatives of the human IFN-γ receptor, which contain a signal peptide and the transmembrane region of the receptor, were transfected into COS-1 cells. Due to the presence of the transmembrane region, upon expression these receptor derivatives are expected to be present on the surface of the transfected cells. Therefore, the ability of the receptor derivatives to bind IFN-γ could be analyzed by measuring the amount of IFN-γ binding specifically to the surface of intact cells. The plasmids used in this experiment and the proteins encoded by these plasmids are listed in Fig. 82, whereas the amino acid sequences of these proteins are summarized in Fig. 83. B. Transfection of COS-1 cells and expression of the receptor derivatives COS-1 cells (ATCC CRL 1650) were harvested by trypsinization (PBS, 0.25% trypsin), washed by phosphate buffered saline (PBS: 8.1 mM NaH₂PO₄, 1.5 mM KH₂PO₄, 2.7 mM KCl, 137 mM NaCl, pH 7.2), counted and resuspended in Dulbecco's Modified Eagle Medium (DMEM) from Gibco containing 5% Fetal Bovine Serum (FBS), before 2x10⁶ cells were distributed in 60 mm tissue culture disks (Falcon). After 24 h at 37°C in a carbon dioxide incubator (5% CO₂), the 70% confluent cell monolayer was washed with PBS and covered with 1 ml of PBS containing 3 mg/ml DEAE Dextran (Pharmacia) and 5 µg plasmid DNA. After 30 minutes at 37°C, the transfection cocktail was removed and 4 ml Iscove's Modified Dulbecco's Medium (IMDM) from Gibco containing 10% FBS and 100 µg chloroquine (Sigma) were distributed in each plate. The plates were incubated for 2.5 h at 37°C in a carbon dioxide incubator, before the medium was aspirated and the cell monolayers were covered with IMDM medium containing 10% FBS and 10% DMSO. After 2.5 minutes at room temperature, the DMSO containing medium was substituted with IMDM medium containing 10% FBS. After incubation for 72 h at 37°C in a carbon dioxide incubator, the transfected cells were tested for their cell surface expression of human IFN-γ receptor. C. Binding of IFN-γ to receptor derivatives expressed on the surface of transfected COS-1 cells COS-1 transfected with DNA encoding membrane anchored receptor derivatives were harvested, washed with PBS, counted and resuspended in HHB buffer (HHB: Hank's balanced salt solution, 15 mM Hepes and 1% Bovine serum albumine) to have 10⁷ cells per ml. A volume of 100 µl of each cell suspension was distributed in U-bottomed polystyrene microtiter plates (Costar), before 2 ng (200 U) of iodinated human IFN-γ (2x10⁴ dpm/ng) labeled according to Aguet and Merlin (supra) were added. After 90 minutes on ice, the plates were centrifuged for 5 minutes at 100xg, before the supernatant with unbound radioactive IFN-γ was discarded and the cells were washed twice with HHBT buffer (HHBT: HHB with 0.01% Triton X-100). The cells were resuspended in 200 µl HHBT, transferred to flexible U-bottomed PVC microtiter plates (Dynatech) and once more centrifuged. The flexible plates were cut and the radioactivity present in each well was determined. After subtraction of the radioactivity obtained in experiments, in which COS-1 cells transfected with plasmids not encoding the receptor were analyzed, the resulting values are a measure for the ability of the receptor derivatives to bind IFN-γ. As summarized in Fig. 84, all receptor derivatives were expressed on the surface of the COS-1 cells and were able to bind IFN-γ. These results demonstrate that 1) the cDNA present in plasmid pBABLUE (see Fig. 1) encodes a signal peptide active at least in COS-1 cells, 2) amino acids 282 to 489 of the human IFN-γ receptor are not essential for its expression and its ability to bind IFN-γ, and 3) amino acids 1 to 26 of the receptor are not essential for the binding of IFN-γ. Example 10 Expression of soluble human IFN-γ receptors in COS-1 cells A. Principle Plasmids encoding derivatives of the human IFN-γ receptor, which contain a signal peptide but lack the transmembrane region of the receptor, were transfected into COS-1 cells. Due to the absence of the transmembrane region, upon expression the receptor derivatives were expected to be secreted into the culture medium. Therefore, the culture medium of the transfected cells was analyzed in a radioimmuno assay (RIA) for the presence of soluble human IFN-γ receptors. Furthermore, the capacity of such molecules to bind IFN-γ was analyzed by testing: 1) their ability to inhibit the binding of IFN-γ to the human IFN-γ receptor present on Raji cells, and 2) their ability to inhibit the antiviral activity caused by IFN-γ. The plasmids used in this experiment and the proteins encoded by these plasmids are listed in Fig. 85, whereas the amino acid sequences of these proteins are summarized in Fig. 86. B. Transfection of COS-1 cells and expression of soluble human IFN-γ receptors COS-1 cells were harvested by trypsinization, washed with PBS, counted and resuspended in DMEM 5% FBS medium, before 2x10⁶ cells were distributed in 60 mm tissue culture disks (Falcon). After 24 h at 37°C in a carbon dioxide incubator, the 70% confluent cell monolayer was washed with PBS, before 1 ml of PBS containing 3 mg/ml DEAE Dextran (Pharmacia) and 5 µg plasmid DNA were added. After 30 minutes at 37°C, the transfection cocktail was removed and 4 ml IMDM medium containing 10% FBS and 100 µg chloroquine (Sigma) were added to each plate. The plates were incubated for 2.5 h at 37°C in a carbon dioxide incubator, before the medium was aspirated and the cell monolayers were covered with IMDM medium containing 10% FBS and 10% DMSO. After 2.5 minutes at room temperature, the DMSO containing medium was substituted with IMDM medium containing 10% FBS. After incubation for 72 h at 37°C in a carbon dioxide incubator the supernatants of the transfected cells were harvested and tested for the presence of soluble human IFN-γ receptors. C. Detection of soluble human IFN-γ receptors Monoclonal antibodies were made according to Fazekas de St.Groth and Scheidegger (J. Immunol. Methods 35, 1-21 [1980]). Among the monoclonal antibodies obtained against native human IFN-γ receptor protein extracted and then affinity purified according to Aguet and Merlin (supra), the antibody γR38/D12 inhibited IFN-γ binding to cell-bound human IFN-γ receptor but did not precipitate the complexes formed by IFN-γ with its receptor. This antibody reacted with an epitope located in the extracellular region of human IFN-γ receptor, between aa 26-133. Another monoclonal antibody, γR99/1H4 inhibited IFN-γ binding to the cell-bound receptor and precipitated the complexes between IFN-γ and its receptor. This antibody reacted with an epitope located in the extracellular region of human IFN-γ receptor, between as 70-210. The described antibodies were believed to recognize structural epitopes because they bound only the non-reduced form of the human IFN-γ receptor. Both monoclonal antibodies against human IFN-γ receptor were IgG1 and were affinity purified on protein G column (Pharmacia) according to Pharmacia instructions. The antibody γR99/1H4 was radiolabelled by ¹²⁵I in presence of chloramine T according to Hunter (Handbook of Experimental Immunology, D.M. Weir ed., Blackwell Scientific Publications Oxford [1973]). The stock solution of antibody γR38/D12 was diluted with PBS to have 5 µg/ml of pure antibody. A volume of 100 µl of this solution containing 0.5 µg of pure antibody was distributed in each well of PVC flat-bottomed microtiter plates (Dynatech) to coat the plastic. The coating reaction was performed overnight at 4°C. The residual binding capacity of plastic was then blocked by adding to each well 250 µl of PBS containing 3% Bovine serum albumine (BSA) and by incubating the microtiter plates at room temperature for at least 2 h. After blocking, the plates were washed 3 times with PBS and the RIA performed as follow. The supernatants containing soluble human IFN-γ receptor derivatives released by transfected COS-1 cells, were diluted 1:5, 1:50, 1:500, 1:5000 with medium (Optimem Gibco, 2% FBS). The stock solutions of soluble human IFN-γ receptor derivatives (see Example 6) were diluted with medium to have 30 ng/ml, 10 ng/ml, 3 ng/ml, 1 ng/ml, 0.3 ng/ml and 0.1 ng/ml of the soluble receptor. A volume of 100 µl from each dilution was distributed in 3 wells of coated plates and 20 µl of a solution containing 3 ng (180'000 dpm) of iodinated antibody γR99/1H4 were immediately added. After 3 h of incubation at room temperature, with occasional shakings, the plates were washed 6 times with PBS. After the last washing, the plates were air-dried, cut and the radioactivity of each well was determined. The concentration of soluble human IFN-γ receptor released by transfected COS-1 cells was determined on the basis of a standard curve produced with soluble IFN-γ receptor purified from E.coli. Fig. 87 summarizes the proteins which could be detected in the supernatants of the transfected COS-1 cells. D. Inhibition of IFN-γ binding to Raji cells by soluble human IFN-γ receptors The binding capacity of soluble human IFN-γ receptors expressed in E.coli or in COS-1 cells was determined by inhibition of IFN-γ binding to Raji cell surface receptor. The solutions containing the soluble human IFN-γ receptors were serially diluted with PBS and 50 µl of each solution were distributed in triplicate in the wells of polystyrene U-bottomed microtiter plates (Costar). A volume of 50 µl with 2 ng (200 U) iodinated IFN-γ of a preparation with 2x10⁴ dpm/ng was added to each well after dilution in HHB medium. Then 100 µl of HHB medium containing 10⁶ Raji cells (ATCC CCL 86) were added. After incubation for 90 minutes at 0°C, the plates were centrifuged for 5 minute at 100xg, before the supernatant with unbound radioactive IFN-γ was discarded and the cells were washed twice with HHBT buffer. Then the cells were resuspended in 200 µl HHBT, transferred to flexible U-bottomed PVC microtiter plates (Dynatech) and once more centrifuged. The flexible plates were cut and the radioactivity in each well was determined. In Figs 44 and 87 the proteins inhibiting the binding of IFN-γ to Raji cells are summarized. E. Inhibition of the antiviral activity of IFN-γ by soluble human IFN-γ receptors The binding capacity of soluble human IFN-γ receptors expressed in E.coli or in COS-1 cells was determined by the inhibition of antiviral activity exerted by IFN-γ. The solutions containing the soluble receptors were serially diluted with Minimal Essential Medium (MEM) from GIBCO additionated with 5% FBS. A volume of 50 µl of each dilution was distributed in triplicate to the wells of tissue culture grade flat-bottomed microtiter plates (Costar). Then 25 µl containing 0.25 pg of IFN-γ (1 U/ml of a preparation of IFN-γ with a specific activity of 10⁸ U/mg) were added to each well. After 1 h at room temperature the IFN-γ activity therein was determined by the cytopathic effect (CPE) reading method according to Armstrong (Methods in Enzymology, S. Pestka ed., vol. 78 page 38, Academic Press New York [1981]). Thus, 50 µl of a WISH cell (ATCC CCL 25) suspension (4x10⁵ cells/ml) in 5% FBS-containing MEM were placed in each well of the 96-well microplates and incubation was conducted in a carbon dioxide gas incubator (5% CO₂) at 37°C. After 24 h the culture supernatants were discarded and 100 µl of MEM medium with 2% FBS and 1000 plaque forming units of Encephalomyocarditis (EMC) Virus (ATCC VR-129B) were added to each well. The plates were incubated for 90 minutes at 37°C, the medium discarded and substituted with 100 µl 2% FBS-containing MEM. About 24 h later, when the cells in wells not containing IFN-γ show 100% CPE, the medium was discarded and the remaining adherent cells were washed with PBS. Then 100 µl of a crystal violet solution (1% crystal violet, 10% ethanol in water) were added to each well. After 5 minutes, the unbound dye was removed by washing with water before the stained monolayers were dried. Finally, the dye associated with the cells was extracted in 100 µl methylcellosolve and quantitated by reading the absorbance at 550 nm in a Titertek Multiskan R MC (Flow Laboratories). Since the amount of dye is proportional to the number of cells present per well, the obtained absorbance readings are a measure for the protection of IFN-γ against the viral cytopatic effect. The capacity of the soluble human IFN-γ receptors to inhibit this protection is summarized in Figs. 44 and 87. Example 11 Expression of soluble human IFN-γ receptors using the baculovirus expression system A. Construction of transfer vector pN57 The baculovirus transfer vector pVL941 (Luckow and Summers 1989 Virology 170, 31-39 [1989]) was digested with BamHI and then treated with calf intestinal alkaline phosphatase. The dephosphorylated vector was then isolated from an agarose gel as described above. The vector was ligated with a fragment encoding the extracellular domain of the IFN-γ receptor (amino acids 1-246 of Fig. 2). E.coli strain HB 101 was transformed and transformants which had the gene in the correct orientation for expression from the polyhedrin promoter were identified by restriction analysis and sequencing. The resulting transfer vector pN57 was isolated from E.coli using standard procedures. E.coli HB 101 cells transformed with transfervector pN57 were deposited at the Deutsche Sammlung von Mikroorganismen in Braunschweig on January 19, 1990 in accordance with the Budapest Treaty, the accession no. being DSM 5751. B. Transfection of insect cells and isolation of recombinant baculoviruses The transfer vector pN57 was transfected into Sf9 cells (ATCC CRL1711) together with the DNA of the baculovirus AcMNPV (described in European patent appliction, Publ. No. 127839) Polyhedrin minus viruses were identified and plaques purified using standard techniques (Summers and Smith 1986, "Manual of Methods for Baculovirus and Insect Culture Procedures, Texas Agricultural Experimental Station). One of the isolated recombinant virus was deriguated V57. C. Detection of soluble human IFN-γ receptor (designated protein N57) in the medium of Sf9-cells infected with the recombinant virus V57 Sf9 cells were infected with the recombinant virus V57 at a multiplicity of 10. 72 hours post transfection the cells were removed by centrifugation (2 x 15 minutes, 15000 rpm, 4°C) and the supernatant was analysed for released soluble human IFN-γ receptor using the RIA as described in Example 10 above. Furthermore, the capacity of such molecules to bind IFN-γ was analysed by testing their ability to inhibit the binding of IFN-γ to the human IFN-γ receptor present on Raji cells as described in Example 10. The result of these tests are summarized in Table 1 below. In summary, proteins P25H6C, P28H6A and P41H6 expressed in E.coli, protein P25C expressed in COS-1 cells and protein N57 expressed in the baculovirus-insect cell vector system were able to bind IFN-γ. Therefore, these soluble IFN-γ receptor molecules contain the region of the human IFN-γ receptor, which is essential for the binding of IFN-γ, in an active form and inhibited the biological activity of IFN-γ.

Claims: A soluble IFN-γ receptor capable of specifically binding IFN-γ comprising the N-terminal portion of the natural IFN-γ receptor containing at least amino acids 26-246 of the natural IFN-γ receptor sequence and missing the cytoplasmic and transmembrane domains of the natural IFN-γ receptor. A soluble IFN-γ receptor of claim 1 selected from the group consisting of P25H6C, P28H6A, P41H6 and P25C characterized by the amino acid sequences given in Figures 43 and 86. A soluble IFN-γ receptor of claim 1 which is protein N57 encoded by transfer vector pN57 (DSM 5751). A DNA sequence coding for a soluble IFN-γ receptor as claimed in claims 1 and 2. A DNA sequence coding for a soluble IFN-γ receptor as claimed in claim 3. An expression vector comprising a DNA sequence as claimed in claim 4 and being capable of directing expression of the DNA sequence in a compatible prokaryotic or mammalian host cell. A prokaryotic or mammalian host cell transformed with an expression vector of claim 6. A recombinant baculovirus comprising a DNA sequence as claimed in claim 5. An insect host cell infected with a recombinant baculovirus of claim 8. A method for the production of a soluble IFN-γ receptor as claimed in claims 1 and 2 comprising culturing a transformed prokaryotic or mammalian host cell in a suitable medium so that said receptor is expressed and purifying and refolding said receptor. A method for the production of a soluble IFN-γ receptor as claimed in claims 1 and 3 comprising culturing an infected insect host cell in a suitable medium so that said receptor is expressed and purifying said receptor from the insect cell medium. A soluble IFN-γ receptor as claimed in claim 1-3 for use as a therapeutically active agent. A soluble IFN-γ receptor as claimed in claims 1-3 for use as a therapeutically active agent for the treatment of autoimmune diseases, chronic inflammations, delayed hypersensitivities, allotransplant rejections and multiple sclerosis. A pharmaceutical composition comprising a soluble IFN-γ receptor as claimed in claims 1-3 and a compatible pharmaceutically acceptable carrier material. The use of a soluble IFN-γ receptor as claimed in claim s 1-3 for the preparation of pharmaceutical compositions. The use of a soluble IFN-γ receptor as claimed in claims 1-3 for the preparation of pharmaceutical compositions for the treatment of autoimmune diseases, chronic inflammations, delayed hypersensitivities, allotransplant rejections and multiple sclerosis. The use of a soluble IFN-γ receptor as claimed in claims 1-3 for identifying IFN-γ agonists or antagonists.

Inventors: FOUNTOULAKIS MICHAEL, GAROTTA GIANNI, STUEBER DIETRICH, FOUNTOULAKIS, MICHAEL, GAROTTA, GIANNI, STUEBER, DIETRICH, Stüber, Dietrich
Applicants: HOFFMANN LA ROCHE, F. HOFFMANN-LA ROCHE AG
Application year: 1990
Main classification: C12N15
IPC codes: C07K14, C12N15, C12N5, A61K38, C07H21, C12N7, C12P21, A61P37, A61P25, C07K16, C12N1, G01N33, A61K39, A61P29, C12R1