High-affinity receptor for interferon-gamma (IFN-gamma), a ubiquitous protein occurring in different molecular forms on human cells: blood monocytes and eleven different cell lines have the same IFN-gamma receptor protein

High-affinity receptors for human IFN-gamma were analyzed using 13 different cells, including blood monocytes. Scatchard analysis showed one high-affinity binding site for each cell. One cross-linked complex between IFN-gamma and the receptor was detected, although their apparent molecular masses were variable in different cells, as also confirmed in immunoblots of membrane extracts. Variations in molecular masses were abolished if N-linked glycosylation was absent. Stable tryptic fragments contained the intact binding site for IFN-gamma and antibody epitopes characteristic of the extracellular domain of the IFN-gamma receptor of Raji cells and were of different sizes only if glycosylated. In addition, Northern analysis showed the same mRNA encoding the high-affinity IFN-gamma receptor in each cell analyzed. Thus, all cells including blood monocytes express the same high-affinity IFN-gamma receptor protein. N-linked sugars may give structural stability to the IFN-gamma receptor and are unlikely to be directly involved in IFN-gamma binding.

GM-1, a clone of the monoblastic phagocyte U937 that expresses a large respiratory burst capacity upon activation with interferon-gamma

The human cell line U937 was cloned and screened for the responsiveness to interferon-gamma (INF-gamma). The selected subclone, named GM-1, expressed a high density of IFN-gamma receptors and showed HLA typing similar to that of the parental line but was devoid of the Y chromosome. GM-1 cells display a promyeloid phenotype as revealed by flow cytometry using a panel of murine antibodies. Following treatment with IFN-gamma GM-1 cells differentiated to a more mature monocyte stage and acquired the capacity to mount a respiratory burst. After treatment with differentiation promotors, such as phorbol 12-myristate 13-acetate (PMA), dimethyl sulfoxide (DMSO), and retinoic acid, GM-1 showed a more limited respiratory burst capacity. Superoxide release in IFN-gamma-activated cells was stimulated with f-Met-Leu-Phe, C5a, or PMA. The development of the respiratory burst capacity was accompanied with the expression of cytochrome b558, a component of the phagocyte NADPH-oxidase. GM-1 cells are useful for the study of the effects of IFN-gamma on the respiratory burst. They are more sensitive and yield a more homogenous response to IFN-gamma than U937 cells. The phenotype of GM-1 cells was stable for more than 5 years.

One interferon gamma receptor binds one interferon gamma dimer

We investigated the stoichiometry of the interferon gamma and interferon gamma receptor interaction, using recombinant interferon gamma and recombinant soluble interferon gamma receptor, applying chemical cross-linking and chromatographic techniques, and analyzing the resulting products in denaturing polyacrylamide gels. Interferon gamma cross-linked to itself produced a major band of an apparent molecular mass of 34 kDa, which suggests that it exists as a dimer in physiological buffer and which agrees with published data. Soluble interferon gamma receptor cross-linked to itself produced mainly a 28-kDa band, suggesting that the interferon gamma receptor exists as a monomer. Interferon gamma cross-linked to the soluble interferon gamma receptor resulted in the formation of two main products of apparent molecular masses of 60 and 44 kDa. The predominant 60-kDa band resulted from the cross-linking of one interferon gamma dimer (34 kDa) to one interferon gamma receptor molecule (27 kDa). The 44-kDa band was formed by the cross-linking of one interferon gamma molecule to one interferon gamma receptor. Kinetic studies showed that the cross-linking of interferon gamma dimer to the soluble receptor proceeds through the intermediate formed by cross-linking one molecule of the interferon gamma dimer to the receptor. Reducing and dissociating agents inhibited complex formation. When chromatographed on Sephadex G-100, interferon gamma was eluted as a protein of 34-kDa molecular mass, the soluble interferon gamma receptor as a protein of 40 kDa, and their mixture was eluted in one peak corresponding to an apparent molecular mass of 73 kDa. Sodium dodecyl sulfate-polyacrylamide gel analysis of the eluted mixture showed the presence of both interferon gamma and interferon gamma receptor at a ratio of 2:1. The found results suggest that the interferon gamma receptor binds interferon gamma as a dimer.

Purification and biochemical characterization of a soluble human interferon gamma receptor expressed in Escherichia coli

We purified and characterized a soluble human interferon gamma receptor expressed in Escherichia coli. The soluble receptor comprises the amino acids 15-246 of the encoded protein (Aguet, M., Dembic, Z., and Merlin, G. (1988) Cell 55, 273-280) and was purified from large scale fermentations through four chromatographic steps with an overall recovery of 28%. The refolded soluble receptor shows some heterogeneity on nonreducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis, where it appears as the major band of 27 kDa molecular mass, accompanied by a few minor bands with molecular masses between 26 and 30 kDa. On reducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis it appears as a homogeneous protein of 32 kDa molecular mass. The soluble interferon gamma receptor is an active and stable protein and is recognized by specific antibodies raised against the native receptor. When nonreduced it has the capacity to specifically bind interferon gamma and to compete for the binding of interferon gamma to the cell surface receptor. The observed heterogeneity of the soluble interferon gamma receptor under nonreducing electrophoretic conditions is probably due to different conformational forms resulting from the formation of non-native intramolecular disulfide bonds among the 8 cysteine residues present in the soluble interferon gamma receptor molecule.

Human interferon-gamma receptor. Mapping of epitopes recognized by neutralizing antibodies using native and recombinant receptor proteins

Monoclonal antibodies produced against native interferon-gamma receptor (IFN gamma-R) have been characterized for their capacity to react with purified receptor and receptor-positive cells, to inhibit the binding of IFN gamma to cellular receptor, to precipitate the receptor protein when cross-linked to IFN-gamma, and to recognize the recombinant interferon-gamma receptor and 19 overlapping fragments of this protein expressed in Escherichia coli. The results of this analysis showed that: (i) the extracellular portion of human IFN gamma-R is located between the N terminus and the transmembrane region (amino acids 18-246). (ii) The intracellular domain is between the transmembrane region and the C terminus (amino acids 269-489). (iii) The monoclonal antibodies that react with the IFN gamma-R intracellular domain recognize small linear epitopes. (iv) The human IFN gamma-R binding site is located between the N terminus and the transmembrane region. (v) The monoclonal antibodies that react with IFN gamma-R extracellular domain and inhibit the binding of IFN gamma recognize two different epitopes. One of these epitopes (included between amino acids 26 and 133) is very close to the binding site for IFN gamma. The second (included between amino acids 70 and 210) is related to the binding site for IFN gamma without including it. (vi) These two functional epitopes are conformational and need S-S bridges to maintain their architecture. (vii) These conformational epitopes are formed in receptor fragments expressed in E. coli.

Monoclonal antibodies recognizing both soluble and membrane bound catechol-O-methyltransferase

Both cytosolic, soluble and membrane-bound catechol-O-methyl-transferase (COMT) from pig and rat liver or kidney were recognized by mouse monoclonal antibodies (MAbs) raised against soluble COMT isolated from pig liver. In ELISA, the MAbs Co 16 and Co 54 reacted better with the pig than with the rat enzyme. The MAb Co 60 showed good reactivity with both pig and rat COMT. In addition, all three MAbs recognize the soluble (23 kDa) as well as the membrane-bound (26 kDa) forms of the COMT enzyme.

Structure and membrane topology of the high-affinity receptor for human IFN-gamma: requirements for binding IFN-gamma. One single 90-kilodalton IFN-gamma receptor can lead to multiple cross-linked products and isolated proteins

We analyzed the high affinity receptor for IFN-gamma of Raji cells and human placenta by combining Scatchard analysis, cross-linking experiments, and receptor purification. Only one high affinity binding site was found, Kd 2.1 X 10(-10). The receptor is a 90-kDa glycoprotein. However, multiple cross-linked products of 110 kDa to about 250 kDa could be generated and proteins of 90, 70, and 50 kDa could be obtained upon purification. These proteins all contained the same 90-kDa receptor, or part of it. We suggest that extensive cross-linking and/or proteolysis may explain many of the conflicting results published thus far. The extracellular domain of the 90-kDa receptor protein was highly resistant to digestion with trypsin or proteinase K. Trypsin digestion neither affected the number of binding sites per cell, nor the Kd for IFN-gamma. A cluster of sites for different proteases was found in the intracellular domain. The 50-kDa fragment created by trypsin digestion had the same characteristics as the isolated 50-kDa receptor fragment. It contained the IFN-gamma binding site and the receptor's extracellular and amino-terminal domain. N-linked glycosylation contributed about 15 kDa to its molecular mass, of which 4 kDa were attributable to sialic acid residues. O-Linked glycosylation was not detected. The number of binding sites per cell and the Kd for IFN-gamma were not affected by the presence or absence of N-linked glycosylation. The receptor contained at least one critical disulfide bridge and the reduced receptor could be reactivated in vitro.

Structure and membrane topology of the high-affinity receptor for human IFN-gamma: requirements for binding IFN-gamma. One single 90-kilodalton IFN-gamma receptor can lead to multiple cross-linked products and isolated proteins

We analyzed the high affinity receptor for IFN-gamma of Raji cells and human placenta by combining Scatchard analysis, cross-linking experiments, and receptor purification. Only one high affinity binding site was found, Kd 2.1 X 10(-10). The receptor is a 90-kDa glycoprotein. However, multiple cross-linked products of 110 kDa to about 250 kDa could be generated and proteins of 90, 70, and 50 kDa could be obtained upon purification. These proteins all contained the same 90-kDa receptor, or part of it. We suggest that extensive cross-linking and/or proteolysis may explain many of the conflicting results published thus far. The extracellular domain of the 90-kDa receptor protein was highly resistant to digestion with trypsin or proteinase K. Trypsin digestion neither affected the number of binding sites per cell, nor the Kd for IFN-gamma. A cluster of sites for different proteases was found in the intracellular domain. The 50-kDa fragment created by trypsin digestion had the same characteristics as the isolated 50-kDa receptor fragment. It contained the IFN-gamma binding site and the receptor's extracellular and amino-terminal domain. N-linked glycosylation contributed about 15 kDa to its molecular mass, of which 4 kDa were attributable to sialic acid residues. O-Linked glycosylation was not detected. The number of binding sites per cell and the Kd for IFN-gamma were not affected by the presence or absence of N-linked glycosylation. The receptor contained at least one critical disulfide bridge and the reduced receptor could be reactivated in vitro.

Development of interferon-gamma antagonists as an example of biotechnology application to approach new immunomodulators

Recent applications of recombinant DNA technology have made possible the isolation and structural characterization of previously poorly-described proteins (e.g. Interferon-gamma (IFN gamma) and its specific receptors). These "recombinant proteins" can be developed as new therapeutics, or used in high specific screening. Structural information obtained from the studies on the recombinant proteins and their receptors, can then be used in computer assisted molecular modeling to design non-proteinaceous immunomodulatory, antiinflammatory and antineoplastic molecules. These novel compounds, able to modulate the functions of the endogenous IFN gamma, will show several advantages in respect to the recombinant proteins used as drugs. We would like to illustrate how the application of the modern biotechnology leads to the development of new drugs and, as an example, to describe the procedure which is followed in the case of the IFN gamma.

A simple, rapid and large capacity ELISA for biologically active native and recombinant human IFN gamma

A rapid and sensitive enzyme-immunoassay for native and recombinant human interferon gamma is described. The test is performed in one step at room temperature and is based on the sandwich principle. The IFN gamma preparation is distributed with horse radish peroxidase-labeled monoclonal antibody to IFN gamma in microtiter plates previously coated with a second mab against IFN gamma. The amount of the IFN gamma mab sandwich fixed in the microtiter plate wells is proportional to the color developed after the addition of peroxidase-specific substrate. The two mab's used in the test neutralize IFN gamma and are directed against the same epitope. For this reason they can only detect the biologically active dimeric form of IFN gamma. The IFN gamma-ELISA works in phosphate buffer as well as in tissue culture medium or human serum. As the assay is routinely performed in 2 hours, the limit of detection is 3 U/ml of IFN gamma (0.3 ng/ml). If the assay is performed in 16 hours, the limit of detection decreases to 0.5 U/ml IFN gamma (0.06 ng/ml). The conditions to preserve the activity of IFN gamma preparation as standard are discussed.

In vitro studies in nickel allergy: diagnostic value of a dual parameter analysis

A comparison was made between the diagnostic value of assaying nickel-induced lymphocyte proliferation (lymphocyte transformation test, LTT) and migration inhibition factor (MIF) production in nickel contact sensitivity. Although lymphocyte proliferation was significantly increased in the group of patients with skin test reactivity to nickel, positive LTT were also frequently found in skin test-negative subjects: in 63% of subjects with and in 30% of subjects without a history of metal allergy. This would limit the value of the LTT as an in vitro correlate of skin test reactivity. However, in certain patients positive lymphocyte transformation may reveal nickel sensitization at a time of undetectable skin reactivity. Data obtained with the macrophage migration inhibition test (MMIT) showed a good correlation with nickel patch test reactions. Accurate determination of MIF became feasible by using cells from the human monocytoid cell line U937 as target cells in a microdroplet agarose assay. Using this MMIT, positive reactions occurred in 13% of the healthy controls and false-negative reactions were found in 26% of patients with positive skin test reactivity to nickel. As LTT and MMIT data appeared to be only weakly correlated in the individuals tested, a dual parameter analysis was performed. An excellent correlation [p = 1.8 (10(-8]] was found between skin test and in vitro reactivity for individuals with matching in vitro results (60% of all individuals tested). In those individuals with discordant in vitro data, skin testing will remain indispensable for diagnosing nickel allergy.

Identity between human interferon-gamma and "macrophage-activating factor" produced by human T lymphocytes

Human peripheral blood monocytes purified by counterflow elutriation were activated in vitro by human natural or recombinant interferon-gamma (IFN-gamma) as shown by enhanced killing of Listeria monocytogenes and increased production of H2O2 in response to phorbol myristate acetate. Half-maximal stimulation for macrophage activation (MAF) was observed with 10-20 antiviral U/ml of purified recombinant IFN-gamma. These MAF activities were found to correlate with the antiviral activity dependent on IFN-gamma under several experimental conditions. Both activities were recovered together from supernatants of concanavalin A-stimulated peripheral blood mononuclear cells and in the media of a large number of T cell clones of different specificities. The parallelism between the two activities was also observed upon fractionation of culture media from producing cells and upon treatment of such preparations with low pH and high temperature. Finally, three antibodies with different specificities were found to abrogate the MAF and antiviral activities from lymphocyte culture supernatant. These results indicate that MAF released by stimulated lymphocytes is identical to IFN-gamma.

Functional antagonism between type I and type II interferons on human macrophages

A three-day treatment with IFN-gamma enhanced up to 300% the capacity of human monocytes and macrophages to produce H2O2 during the respiratory burst. IFN-alpha or -beta (type I IFNs), which did not by themselves influence the burst, were found to antagonize the enhancing effect of IFN-gamma (type II IFN). The antagonism was concentration-dependent and required the presence of type I IFNs during the whole period of IFN-gamma pretreatment. These results suggest that the host defense function of mononuclear phagocytes may be controlled by the relative local concentrations of type I and type II IFNs.

Isolation and characterization of Ni-specific T cell clones from patients with Ni-contact dermatitis

Ni-specific T lymphocyte clones (TLC) were isolated from two patients with Ni-contact dermatitis. All of the isolated TLC required both histocompatible antigen-presenting cells (APC) and Ni for induction of proliferation. By using a panel of HLA-typed Epstein Barr virus-transformed B cells (EBV-B cells) as APC and monoclonal anti-DR antibody, the clones were shown to recognize Ni in the context of HLA class II determinants. All of the clones that were isolated are OKT3+, OKT4+, OKT8-. In the presence of Ni, they polyclonally activate autologous B cells, and in the presence of Ni and autologous EBV-B cells, they produce IL 2 and very high levels of IFN-gamma. The Ni-specific clones should be helpful in the identification of the Ni-induced antigen which is recognized by T cells.

Isolation and characterization of Ni-specific T cell clones from patients with Ni-contact dermatitis

Ni-specific T lymphocyte clones (TLC) were isolated from two patients with Ni-contact dermatitis. All of the isolated TLC required both histocompatible antigen-presenting cells (APC) and Ni for induction of proliferation. By using a panel of HLA-typed Epstein Barr virus-transformed B cells (EBV-B cells) as APC and monoclonal anti-DR antibody, the clones were shown to recognize Ni in the context of HLA class II determinants. All of the clones that were isolated are OKT3+, OKT4+, OKT8-. In the presence of Ni, they polyclonally activate autologous B cells, and in the presence of Ni and autologous EBV-B cells, they produce IL 2 and very high levels of IFN-gamma. The Ni-specific clones should be helpful in the identification of the Ni-induced antigen which is recognized by T cells.

A sensitive and quantitative microassay for the detection of mycoplasma contamination: inhibition of IL-2 dependent cell line proliferation

A simple, rapid and sensitive microassay for mycoplasma detection in cell culture is reported. The assay is based on the fact that culture supernatants from contaminated cells inhibit [3H]thymidine incorporation by an IL-2 dependent mouse cytotoxic T cell line (CTLL). The mechanism of inhibition is related to the production by several mycoplasma strains of a pyrimidine-specific nucleoside phosphorylase which can degrade the radiolabelled thymidine used for the measurement of DNA synthesis. These strains were the commonest contaminants in cultures of 24 cell lines from 5 different sources. To establish the sensitivity of the test to detect mycoplasmas we have also used the inhibition assay to monitor the clearance of mycoplasma from 2 contaminated cell lines.

Modulation of expression of HLA components at the cell surface induced by anti-beta 2m reagents

Antibodies against lymphocytes surface components are able to rearrange profoundly the topography of the cell membrane with a differential modulation of surface antigens. Of particular interest is the effect of anti-beta 2m reagents, which are able to suppress completely the reactivity of epitopes carried by the two chains of the ABC dimers, while th expressivity of other antigens, such as DR, is significantly increased. These results have been obtained with immunoradiobinding under a variety of conditions, thus confirming the validity of the "bb" (beta 2m blanketing) test.

Quantitative analysis of cell surface HLA structures by means of monoclonal antibodies

Quantitative data on the binding of murine monoclonal antibodies ot whole human lymphoblastoid lines and peripheral blood lymphocytes (PBL) are reported. Antibodies reacting with beta 2m or a common part of the HLA heavy chains and nonpolymorphic determinants of the DR dimer were used. The equilibrium constant (K) of the reaction and the total number of antigenic determinants was graphically estimated. For the above-mentioned antibodies, K ranged between 5 X 10(8) and 4 C 10(9) l/mole at 0 degrees C and progressively decreased with the increasing temperature. T cells expressed less HLA and beta 2M determinants than the B cells. The number of determinants per surface unit is higher on the B cell from PBL than on E.B. virus-transformed cell lines and is generally very low, suggesting that the complement-dependent cytotoxic activity is a phenomenon depending on membrane fluidity. A portion of beta 2m seems not to be bound to the HLA heavy chains on B cells as well as on T line surface, as already shown for Molt 4 line.

Separation of human cells bearing HLA-DR antigens using a monoclonal antibody rosetting method

A technique is described for enriching, from human blood, cells bearing HLA-DR antigens. The method depends on the use of monoclonal mouse antibody which reacts with HLA-DR structures. Cells to which this antibody has bound can be separated after rosetting with bovine erythrocytes coated with anti-mouse immunoglobulin. The cells thus enriched may be used for HLA-DR typing by standard cytotoxicity methods with allogeneic sera.

Different colony stimulating activity by tumoral ascitic fluid and conditioned media

The effects of intraperitoneal Ehrlich ascites tumor (ET) growth on the kinetics of hemopoietic stem cells in the host bone marrow were studied using the spleen colony and the soft agar culture techniques. There is a decrease in spleen colony forming capacity of bone marrow of ET bearing mice, whereas in vitro assays of the committed macrophage granulocyte precursors, by the soft agar method, show that in the same circumstances a high yield of granulopoietic colonies can still be obtained. A shift of the CFU-c/CFU-s ratio from 15 to 36 thus occurs. Moreover, ascitic fluid from tumoral mice displays strong activity as CSF on normal mouse marrow, twice as strong as the standard mouse embryo CSF. When conditioned medium from cultures of ET cells (ET-CM) is tested, the pattern of agar colonies obtained is different from the previously obtained pattern of growth kinetics; furthermore many colonies are composed of undifferentiated cells. The hypothesis is suggested that among the variety of known CSF's, the ET-CM represents a unique factor, capable of inducing proliferation of marrow CFU-c, but only limited differentiation.

T-cell precursors in mice bearing the Ehrlich ascites tumors

Mice bearing Ehrlich ascites tumors and challenged with sheep erythrocytes produced fewer plaque-forming cells than did normal mice. At the same time the immunosuppression developed, the number of T lymphocytes in the thymus and spleen were reduced significantly. In the spleen, the number of B lymphocytes remained constant during carcinogenesis, whereas that of the macrophages increased significantly, as compared to the controls. In this paper, we demonstrated that the mechanism responsible for thymus and spleen depletion of theta antigen-bearing cells had to be ascribed to fewer T-lymphocyte precursors in the bone marrow of mice with cancer. The reduction of T-lymphocyte precursors was probably caused by the same "soluble factor(s)" produced by Ehrlich ascites tumor cells, which also interfered with the proliferation of myelopoietic stem cells in the bone marrow of mice with this neoplasm, as we previously reported. By performing several reconstitution experiments of lethally X-irradiated hosts, we determined that the immunodepression by Ehrlich ascites tumor cells was readily reversible, and the alteration of the T:B lymphocyte ratio in the spleen had a minor function, if any, in the pathogenesis of the immunosuppression.

Reversibility of the Immunodepression Due to Ehrlich Ascites Carcinoma

Earlier studies from our laboratory indicated that mice bearing Ehrlich ascites carcinoma cells (EAC)2 produce far fewer plaque-forming cells (PFC) after immunization with sheep erythrocytes (SRBC) than do normal animals. The immunodepression develops shortly after a low dose of EAC, before wasting, and does not result from lymphocyte depletion of peripheral organs, as ascertained by cytometric and histologic studies (1, 2).

The failure to produce PFC may be due to lymphocyte malfunction or to some other mechanism such as antigen processing in tumorbearing animals.

In the present study we demonstrate that thymus- and bone marrow-derived lymphocytes, and spleen cells from tumor-bearing and normal donors, transferred to x-irradiated syngeneic mice, produce the same numbers of PFC to SRBC.

Materials and Methods. Animals. C57BL inbred mice, 8 to 12 weeks old, were used.

Tumor. Inocula of 107 cells of a half-diploid and half-tetraploid strain of EAC were injected intraperitoneally (i.p.) into prospective donors of thymus, bone marrow and spleen cells (3).