Therapeutic potential of carbon monoxide in multiple sclerosis

Carbon monoxide (CO) is produced during the catabolism of free haem, catalyzed by haem oxygenase (HO) enzymes, and its physiological roles include vasodilation, neurotransmission, inhibition of platelet aggregation and anti-proliferative effects on smooth muscle. In vivo preclinical studies have shown that exogenously administered quantities of CO may represent an effective treatment for conditions characterized by a dysregulated immune response. The carbon monoxide-releasing molecules (CORMs) represent a group of compounds capable of carrying and liberating controlled quantities of CO in the cellular systems. This review covers the physiological and anti-inflammatory properties of the HO/CO pathway in the central nervous system. It also discusses the effects of CORMs in preclinical models of inflammation. The accumulating data discussed herein support the possibility that CORMs may represent a novel class of drugs with disease-modifying properties in multiple sclerosis.

HCG hastens both the development of mammary carcinoma and the metastatization of HCG/LH and ERBB-2 receptor-positive cells in mice

Breast cancer is more frequent in human nulliparae, whereas its incidence is reduced by early fullterm pregnancy. Rodent studies suggest that chorionic gonadotropin secretion during pregnancy affords protection by inducing breast structure differentiation. Opposite effects, however, have been observed in cancer prone transgenic mice overexpressing the β subunit of chorionic gonadotropin or pituitary luteinic hormone (LH). Here we assessed the effect of administration of human chorionic gonadotropin (hCG) for 21 days (corresponding to the duration of a mouse pregnancy) in virgin female mice transgenic for the activated rat (r-) ERBB-2 oncogene (BALB-neuT). In these mice, the onset of atypical mammary duct hyperplasia and its progression towards multiple mammary carcinomas is accelerated by hCG. hCG enhances the in vitro proliferation and in vivo metastatization of tumor cells from a BALB-neuT mammary tumor expressing the hCG/LH as well as the ERBB-2 receptors. These findings suggest that hCG favours the growth and progression of hCG/LH and ERBB-2 receptor-positive breast tumors.

Analysis of eosinophils and myeloid progenitor responses to modified forms of MPIF-2

Myeloid progenitor inhibitory factor (MPIF)-2 is a beta-chemokine with select and potent activities on eosinophils and myeloid progenitors. In the beta-chemokine family, biological activity is modulated by differential processing of the amino-terminus. Here, for MPIF-2, we describe the biological activities of NH(2)-terminal deletion mutants and compare regions necessary for eosinophil and myeloid progenitor activities. Five MPIF-2 proteins with deletions at the amino-terminus were produced in Escherichia coli and assayed for calcium mobilization, chemotaxis and receptor binding activities on eosinophils, and for their ability to inhibit colony formation of human myeloid bone marrow progenitors. For eosinophils, deletion of the first two amino acids did not markedly alter activity, while subsequent truncations result in a complete loss of activity. One of the MPIF-2 mutants, MPIF-2 (P30-R99) was converted from an agonist to an antagonist of eotaxin, MPIF-2 and MCP-4 functional responses in eosinophil calcium flux and chemotaxis assays. Surprisingly, while displaying a complete loss of agonist activity toward eosinophils, MPIF-2 (P30-R99) retains ability to inhibit human bone marrow myeloid progenitor cell colony formation. In addition, processing at the amino terminus of MPIF-2 in vivo, may result in a chemokine with altered biological activities.

Observation of an unexpected third receptor molecule in the crystal structure of human interferon-gamma receptor complex

BACKGROUND

Molecular interactions among cytokines and cytokine receptors form the basis of many cell-signaling pathways relevant to immune function. Interferon-gamma (IFN-gamma) signals through a multimeric receptor complex consisting of two different but structurally related transmembrane chains: the high-affinity receptor-binding subunit (IFN-gammaRalpha) and a species-specific accessory factor (AF-1 or IFN-gammaRbeta). In the signaling complex, the two receptors probably interact with one another through their extracellular domains. Understanding the atomic interactions of signaling complexes enhances the ability to control and alter cell signaling and also provides a greater understanding of basic biochemical processes.

RESULTS

The crystal structure of the complex of human IFN-gamma with the soluble, glycosylated extracellular part of IFN-gammaRalpha has been determined at 2.9 A resolution using multiwavelength anomalous diffraction methods. In addition to the expected 2:1 complex, the crystal structure reveals the presence of a third receptor molecule not directly associated with the IFN-gamma dimer. Two distinct intermolecular contacts, involving the edge strands of the C-terminal domains, are observed between this extra receptor and the 2:1 receptor-ligand complex thereby forming a 3:1 complex.

CONCLUSIONS

The observed interactions in the 2:1 complex of the high-affinity cell-surface receptor with the IFN-gamma cytokine are similar to those seen in a previously reported structure where the receptor chains were not glycosylated. The formation of beta-sheet packing interactions between pairs of IFN-gammaRalpha receptors in these crystals suggests a possible model for receptor oligomerization of Ralpha and the structurally homologous Rbeta receptors in the fully active IFN-gamma signaling complex.

Essential pathogenetic role for interferon (IFN-)gamma in concanavalin A-induced T cell-dependent hepatitis: exacerbation by exogenous IFN-gamma and prevention by IFN-gamma receptor-immunoglobulin fusion protein

We have studied the effects of either exogenously-administered interferon (IFN-)gamma or of a nonimmunogenic mouse IFN-gamma receptor-Immunoglobulin (IFN-gamma R-Ig) fusion protein on the development of Concanavalin (Con)A-induced hepatitis in NMRI mice. PBS-treated control mice injected with 20 mg/kg ConA developed classical serological and histological signs of hepatitis with elevation of transaminases in the blood and infiltration of the liver by mononuclear cells and neutrophils. Treating the mice with rat IFN-gamma 24 h prior to and 1 h after ConA-challenge markedly exacerbated these signs of hepatitis in a dose-dependent fashion. Moreover, mice injected with lower, non hepatitogenic, doses of ConA (10, 5 mg/kg) became fully susceptible to develop hepatitis upon similar treatment with IFN-gamma. Concordantly, ConA-induced hepatitis was abrogated by either IFN-gamma R-Ig fusion protein or anti-IFN-gamma mAb. These data provide further evidence for the central pathogenetic role of endogenous IFN-gamma in ConA-induced hepatitis and demonstrate the feasibility to prevent disease development by means of a non immunogenic IFN-gamma R-Ig fusion protein.

Tumor rejection and immune memory elicited by locally released LEC chemokine are associated with an impressive recruitment of APCs, lymphocytes, and granulocytes

The human beta chemokine known as LEC (also called NCC-4, HCC-4, or LMC) displays chemotactic activity for monocytes and dendritic cells. The possibility that its local presence increases tumor immunogenicity is addressed in this paper. TSA parental cells (TSA-pc) are poorly immunogenic adenocarcinoma cells that grow progressively, kill both nu/nu and syngeneic BALB/c mice, and give rise to lung metastases. TSA cells engineered to release LEC (TSA-LEC) are still able to grow in nu/nu mice, but are promptly rejected and display a marginal metastatic phenotype in BALB/c mice. Rejection is associated with a marked T lymphocyte and granulocyte infiltration, along with extensive macrophage and dendritic cell recruitment. NK cells and CD4+ T lymphocytes are uninfluential in TSA-LEC cell rejection, whereas both CD8+ lymphocytes and polymorphonuclear leukocytes play a major role. An antitumor immune memory is established very quickly after rejection, since 6 days later 75% of BALB/c mice were already resistant to a TSA-pc challenge. Spleen cells from rejecting mice display specific cytotoxic activity against TSA-pc and secrete IFN-gamma and IL-2 when restimulated by TSA-pc. The ability of LEC to markedly improve recognition of poorly immunogenic cells by promoting APC-T cell cross-talk suggests that it could be an effective component of antitumor vaccines.

Dichotomic effects of IFN-gamma on the development of systemic lupus erythematosus-like syndrome in MRL-lpr / lpr mice

Systemic lupus erythematosus (SLE)-prone female MRL-lpr / lpr (MRL-lpr) mice were treated with mouse or rat IFN-gamma under different experimental conditions, both prophylactically in 6- to 8 week-old animals and therapeutically in 12- to 18-week-old SLE-affected mice. It was found that IFN-gamma heterogeneously modulated the course of the disease in MRL-lpr mice. When administered prophylactically, IFN-gamma favorably modulated the histological, serological and clinical signs of the disease. Relative to untreated or PBS-treated control animals, the MRL-lpr mice which received IFN gamma were virtually free of inflammatory infiltration of the kidneys and the lungs, had lower levels of azotemia with reduction of both circulating IgG1, IgG2a and IgG3 and anti-double strand (ds) and single strand (ss) DNA antibodies, milder skin vasculitis, significantly reduced enlargement of their lymph nodes and lower weight of the spleens. IFN-gamma also lowered the rate of mortality of MRL-lpr mice. In contrast to these findings, therapeutically administered IFN-gamma worsened the course of the disease in MRL-lpr mice, which exhibited increased proteinuria, higher levels of IgG2a and IgG3 and anti-ds and -ss DNA antibodies, more aggressive nephritis and died at an earlier age than PBS-treated control mice. The dichotomic effect of IFN-gamma on disease manifestation in MRL-lpr mice offers new insights into the complex role of this cytokine in the regulation of systemic autoimmunity such as SLE.

Baculovirus stimulates antiviral effects in mammalian cells

Herein, we report that Autographa californica nucleopolyhedrovirus, a member of the Baculoviridae family, is capable of stimulating antiviral activity in mammalian cells. Baculoviruses are not pathogenic to mammalian cells. Nevertheless, live baculovirus is shown here to induce interferons (IFN) from murine and human cell lines and induces in vivo protection of mice from encephalomyocarditis virus infection. Monoclonal antibodies specific for the baculovirus envelope gp67 neutralize baculovirus-dependent IFN production. Moreover, UV treatment of baculovirus eliminates both infectivity and IFN-inducing activity. In contrast, the IFN-inducing activity of the baculovirus was unaffected by DNase or RNase treatment. These data demonstrate that IFN production can be induced in mammalian cells by baculovirus even though the cells fail to serve as a natural host for an active viral infection. Baculoviruses, therefore, provide a novel model in which to study at least one alternative mechanism for IFN induction in mammalian cells.

A "stealth effect": adenocarcinoma cells engineered to express TRAIL elude tumor-specific and allogeneic T cell reactions

BALB/c mammary adenocarcinoma cells engineered to express TNF-related apoptosis-inducing ligand (TRAIL)/APO-2 ligand (APO-2L) on their membrane (TSA-TRAIL) grow with kinetics similar to that of parental cells (TSA-pc) in vitro and in nu/nu mice. In contrast, TSA-TRAIL cells grow faster than TSA-pc in normal BALB/c mice. In DBA/2 mice, which differ from BALB/c mice at minor histocompatibility Ags, they also grow faster and display a higher percentage of tumor takes than TSA-pc. In fully histoincompatible C57BL/6 (B6) mice, TSA-TRAIL cells form evident tumors that are slowly rejected by most mice, but outgrow in a few. In contrast, TSA-pc cells are rejected at once by B6 mice. Since TRAIL/APO-2L induces apoptosis by interacting with a variety of specific receptors, this rapid growth in both syngeneic and allogeneic mice may be the result of an immunosuppressive mechanism. The following evidence supports this hypothesis: 1) TSA-TRAIL cells overcome the strong immunity against TSA-pc cells elicited in BALB/c mice by preimmunization with TSA cells engineered to release IL-4; 2) their rejection by B6 mice does not prime a CTL-mediated memory; 3) thymidine uptake by T lymphocytes unstimulated or stimulated by allogeneic cells is inhibited when TSA-TRAIL cells are added as third party cells; 4) CTL kill TSA-pc but not TSA-TRAIL cells in 48-h assays; and 5) activated lymphocytes interacting with TSA-TRAIL cells in vivo and in vitro undergo apoptosis.

Failure of exogenously administered interferon-gamma or blockage of endogenous interleukin-4 with specific inhibitors to augment the incidence of autoimmune diabetes in male NOD mice

Interferon (IFN)-gamma and interleukin (IL)-4 are prototypic type 1 and type 2 cytokines which are known to play pathogenetic and protective roles, respectively, in NOD mouse IDDM. The capacity of male NOD mice to produce more IL-4 and less IFN-gamma within the insulitic lesions than females has been suggested to contribute to their lower incidence of diabetes. In this study we have tested the effects of prolonged prophylactic treatment of male NOD mice with rat IFN-gamma, mouse IFN-gamma, anti-IL-4 monoclonal antibody (mAb) and recombinant murine soluble IL-4 receptor (smIL-4R) on the diabetogenic events leading to insulitis and diabetes. None of these treatments influenced spontaneous and/or cyclophosphamide-induced autoimmune diabetogenesis in male NOD mice. Control mice exhibited comparable histological signs of insulitis and incidence of diabetes to those treated with either mouse/rat IFN-gamma or specific IL-4 inhibitors. On the contrary, both clinical and histological signs of diabetes were suppressed by prophylactic treatment with anti-IFN-gamma mAb. These findings indicate that the autoimmune diathesis of male NOD mice towards IDDM cannot be augmented by manipulation of endogenous IFN-gamma or IL-4.

Dendritic cells and MPIF-1: chemotactic activity and inhibition of endogenous chemokine production by IFN-gamma and CD40 ligation

We have examined the biological activity of the CC chemokine myeloid progenitor inhibitory factor 1 (MPIF-1) on human dendritic cells. MPIF-1 has chemotactic activity on dendritic cells derived from either peripheral blood monocytes or cord blood CD34+ progenitors. However, chemokine treatment did not induce further cell activation or maturation. In addition, MPIF-1 is constitutively released by monocyte-derived dendritic cells but not macrophages or monocytes (resting or stimulated). The proinflammatory stimuli lipopolysaccharide and tumor necrosis factor alpha, which induced the release of monocyte chemotactic protein-1, macrophage inflammatory protein-1alpha (MIP-1alpha), MIP-1beta, and interleukin-8, did not affect MPIF-1 release. In contrast, CD40 ligation and interferon-gamma treatment, while stimulating the production of the other chemokines, caused a pronounced reduction of MPIF-1 transcript and protein release. Thus, in dendritic cells the regulation of the production and release of MPIF-1 is distinct in comparison to other CC and CXC chemokines.

Paradoxical antidiabetogenic effect of gamma-interferon in DP-BB rats

Previous studies have shown that anti-gamma-interferon (IFN-gamma) antibody reduces the frequency of autoimmune IDDM in the DP-BB rat. We tested the effects of systemically administered recombinant rat IFN-gamma in both DP-BB and DR-BB rats. Unexpectedly, IFN-gamma markedly reduced the incidence of IDDM as compared with control rats when administered six times per week at a dosage of 280,000 U between ages 30-35 to 105 days or ages 60-64 to 105 days. A lower dosage (28,000 U on alternate days) was also protective when administered to DP-BB rats between birth and age 60 days. However, long-lasting protection against IDDM development over the 1-year study period was achieved only by the highest dosage of IFN-gamma administered from age 30 to 105 days. Ex vivo production of tumor necrosis factor-alpha from splenic lymphoid cells (SLCs) and peritoneal macrophages of the rats treated with IFN-gamma was comparable with that of controls; however, SLCs from the IFN-gamma-treated animals secreted lower amounts of IFN-gamma after stimulation with concanavalin A. IFN-gamma treatment also markedly reduced the frequency of phenotypically activated SLC-expressing class II antigens and interleukin-2 receptor. Finally, in agreement with the observed antidiabetogenic effects, exogenously administered IFN-gamma induced neither insulitis nor IDDM development in DR-BB rats, a subline of DP-BB rats in which autoimmune diabetes rarely occurs spontaneously but can be induced by administration of polyinosinic-polycytidilic acid.

The interferon gamma (IFN-gamma) receptor: a paradigm for the multichain cytokine receptor

With the purification and cloning of the interferon gamma (IFN-gamma) receptor chains the mechanism of IFN-gamma action and the resultant signal transduction events were delineated in remarkable detail. The interferon gamma (IFN-gamma) receptor complex consists of two chains: IFN-gammaR1, the ligand-binding chain, and IFN-gammaR2, the accessory chain. Binding of IFN-gamma causes oligomerization of the two IFN-gamma receptor subunits, IFN-gammaR1 and IFN-gammaR2, which initiates the signal transduction events: activation of Jak1 and Jak2 receptor associated protein tyrosine kinases, phosphorylation of the IFN-gammaR1 intracellular domain on Tyr440 followed by phosphorylation and activation of Stat1alpha, the latent transcriptional factor. With all these steps established, the IFN-gamma receptor complex has provided the basic model for understanding the receptors for other members of the family of class II cytokine receptors.

Interferon immunogenicity: preclinical evaluation of interferon-alpha 2a

A preclinical evaluation of the immunogenicity of various preparations of interferon-alpha (IFN-alpha) was performed with in vitro and in vivo animal models. The distribution of genes for IFN-alpha 2a, IFN-alpha 2b, and IFN-alpha 2c in various cell populations and the response of human T cell clones to IFN-alpha peptides were investigated. The immunogenicity of IFN-alpha in IFN-alpha 2b transgenic mice and factors that influence the immunogenicity of IFN-alpha in normal mice were also studied. The genes for IFN-alpha 2a and IFN-alpha 2b were found in KG-1 cells, whereas IFN-alpha 2b and IFN-alpha 2c genes were present in Namalwa cells. No difference in proliferation of human T cells, T cell lines, or T cell clones could be obtained with IFN-alpha peptides. In transgenic mice bearing the human IFN-alpha 2b gene, no antibody response was obtained following immunization with either IFN-alpha 2a or IFN-alpha 2b. Normal mice immunized with either IFN-alpha 2a or IFN-alpha 2b produced equivalent titers of antibodies, which cross-reacted with both IFNs. Studies evaluating the relative immunogenicity of IFN-alpha in normal mice demonstrated that a number of treatment and host variables can modulate immunogenicity of IFN-alpha preparations.

Genetic differences in immune reactivity to mercuric chloride (HgCl2): immunosuppression of H-2d mice is mediated by interferon-gamma (IFN-gamma)

Upon treatment with HgCl2, H-2s mice, such as B10.S, develop an activation of B lymphocytes that depends, at least partially, on activation of T helper type 2 (Th2) cells and results in increased serum levels of IgG1 and IgE, appearance of IgG autoantibodies, and development of immune glomerulonephritis and vasculitis. Results of previous studies and of experiments presented here indicate that the B cell activation and systemic autoimmune disease fail to develop in MHC-congenic B10.D2 (H-2d) and B10.BR (H-2k) mice treated with HgCl2, although B10.D2 T cells showed signs of activation by and specificity for HgCl2 comparable to those seen in strain B10.S. Here, we report that following HgCl2 injections the antibody response to sheep erythrocytes is normal in B10.S, but suppressed in B10.D2 mice. This suppression was prevented by MoAb to mouse IFN-gamma. Conversely, treatment of B10.D2 mice with murine recombinant IFN-gamma (rIFN-gamma) was able to reproduce the immunosuppression seen after HgCl2 treatment. In B10.S mice, it took administration of both rIFN-gamma and HgCl2 to suppress the anti-sheep erythrocyte response. Although rIFN-gamma diminished the increase in IgE serum levels of HgCl2-treated B10.S mice, it failed to prevent their autoantibody production and immune glomerulonephritis. These findings further strengthen the concept that B10.S mice react to HgCl2 by preferential activation of their Th2 cells producing IL-4, whereas B10.D2 mice react to HgCl2 by preferential activation of their Th1 cells, which produce IFN-gamma and thus suppress antibody responses.

Differential cytokine production in stimulated blood cultures from intensive care patients with bacterial infections

Mice infected with bacteria develop an interferon-gamma (IFN-gamma) dependent hypersensitivity to lipopolysaccharide (LPS) and other bacterial components. The broader aim of this study is to find out whether such hypersensitivity also occurs in patients suffering from bacterial infections. The capacity of stimulated peripheral blood cells from infected, intensive-care patients to produce cytokines (IFN-gamma, tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6)) was compared to that of healthy donors. Culturing of the cells was carried out preferentially in whole blood diluted 1:3. Whole blood cultures (WBC) were stimulated with lipopolysaccharide (LPS), whole killed Salmonella typhimurium and Staphylococcus aureus and concanavalin A (ConA), and the cytokine production was determined. Two main findings emerged from this study: The IFN-gamma production by WBC of patients was, compared to healthy donors, markedly suppressed, regardless of stimulus used. Further, patients' WBC exhibited a suppressed TNF-alpha production after stimulation with LPS. Surprisingly, following stimulation with bacteria (S. typhimurium and S. aureus) an elevated TNF-alpha and IL-6 response was obtained. Thus, in severely infected patients the cytokine responses of peripheral blood cells to LPS may be suppressed, while the response to other bacterial components is enhanced.

CKbeta8, a novel CC chemokine that predominantly acts on monocytes

We have studied the biological properties of a new human CC chemokine, CKbeta8, consisting of 99 amino acids including six cysteines. CKbeta8 mRNA transcripts were induced in monocytes by IL-1beta and, to a lesser extent, by IFNgamma, and were detected in RNA extracted from normal human liver and gastrointestinal tract. CKbeta8 is chemotactic for monocytes, but is inactive on IL-2 conditioned T lymphocytes, eosinophils and neutrophils. Desensitization experiments indicate that CKbeta8 and MIP-1beta completely share receptors on monocytes and that the CKbeta8 receptor, which appears to differ from the known ones, is also recognized by MCP-1, MCP-2, MCP-3, MCP-4, MIP-1alpha and RANTES.

Molecular and functional characterization of two novel human C-C chemokines as inhibitors of two distinct classes of myeloid progenitors

Two novel human beta-chemokines, Ck beta-8 or myeloid progenitor inhibitory factor 1 (MPIF-1), and Ck beta-6 or MPIF-2, were discovered as part of a large scale cDNA sequencing effort. The MPIF-1 and MPIF-2 cDNAs were isolated from aortic endothelium and activated monocyte libraries, respectively. Both of the cDNAs were cloned into a baculovirus vector and expressed in insect cells. The mature recombinant MPIF-1 protein consists of 99 amino acids and is most homologous to macrophage inflammatory protein (MIP)-1alpha, showing 51% identity. It displays chemotactic activity on resting T lymphocytes and monocytes, a minimal but significant activity on neutrophils, and is negative on activated T lymphocytes. MPIF-1 is also a potent suppressor of bone marrow low proliferative potential colony-forming cells, a committed progenitor that gives rise to granulocyte and monocyte lineages. The mature recombinant MPIF-2 has 93 amino acid residues and shows 39 and 42% identity with monocyte chemoattractant protein (MCP)-3 and MIP-1alpha, respectively. It displays chemotactic activity on resting T lymphocytes, a minimal activity on neutrophils, and is negative on monocytes and activated T lymphocytes. On eosinophils, MPIF-2 produces a transient rise of cytosolic Ca2+ and uses the receptor for eotaxin and MCP-4. In hematopoietic assays, MPIF-2 strongly suppressed the colony formation by the high proliferative potential colony-forming cell (HPP-CFC), which represents a multipotential hematopoietic progenitor.

Prevention of spontaneous autoimmune diabetes in diabetes-prone BB rats by prophylactic treatment with antirat interferon-gamma antibody

The role of endogenous interferon-gamma (IFN gamma) in the development of insulin-dependent diabetes mellitus (IDDM) in diabetes-prone BB rats was evaluated. Several groups of these animals were treated under different, experimental conditions with a purified polyclonal antibody (Ab), antirat IFN gamma. The results show that when administered at doses of 100 or 200 micrograms/week from the 30/33th until the 105th day of age, the anti-IFN gamma Ab reversibly reduced the incidence of IDDM compared to that in control rats treated with either irrelevant rabbit IgG or PBS. Moreover, when given up to the 105th day of age, these doses of anti-IFN gamma Abs exerted comparable preventive effects regardless of whether application started as early as within 24 h after birth or at the end of the prediabetic period (e.g. 70/75 days). In contrast, under none of the above experimental conditions did larger doses of anti-IFN gamma Ab (500 micrograms or 1 mg/week) exert antidiabetogenic effects in the BB rats. Apparently, this was due to the exuberant production of neutralizing Abs elicited by the large amount of the xenogeneic Ab injected. At histoimmunological analyses, the BB rats treated with 200 micrograms/ week anti-IFN gamma Abs from 30-80 days of age exhibited a milder insulitic process along with diminished spleen frequency of activated lymphoid cells (MHC class II and interleukin-2 receptor positive). Taken together, these results provide further in vivo evidence for the central pathogenic role of IFN gamma in BB rat IDDM and anticipate the usefulness of specific IFN gamma inhibitors in the prevention of the disease in the clinical setting. Defining novel and less immunogenic forms of specific IFN gamma inhibitors than xenogeneic Abs is important for improving the efficiency of anti-IFN gamma-oriented approaches.

Mouse macrophages carrying both subunits of the human interferon-gamma (IFN-gamma) receptor respond to human IFN-gamma but do not acquire full protection against viral cytopathic effect

Studies of hamster-human and mouse-human somatic fibroblast hybrids and transfected mouse fibroblasts have demonstrated that signaling through the human interferon-gamma receptor (hu-IFN-gammaR) requires the formation of a complex consisting of ligand (IFN-gamma), a ligand binding receptor chain (IFN-gammaR1), and a signal transducing receptor chain (IFN-gammaR2). To date, the ability of this receptor complex to transduce the full repertoire of biological signals has been difficult to assess due to the limited number of activities that IFN-gamma can exert on fibroblasts. The current report assesses the ability of hu-IFN-gammaR chains to transduce signals in the absence of background human gene products by expressing hu-IFN-gammaR2 in a transformed macrophage cell line (F10/96) derived from a hu-IFN-gammaR1 transgenic mouse. Our results indicate that F10/96 clones expressing both human receptor proteins bind hu-IFN-gamma with an affinity comparable to that of human cells. Binding of either human or mouse IFN-gamma to its respective receptor elicits classic IFN-gamma responses such as up-regulation of major histocompatibility complex antigens, enhanced expression of IRF-1, and increased production of NO2- radicals, interleukin-6, tumor necrosis factor-alpha, and granulocyte macrophage-colony stimulating factor. However, hu-IFN-gamma could not fully protect the clones from cytopathic effects of encephalomyocarditis virus and vesicular stomatitis virus while mo-IFN-gamma could. These results demonstrate that while co-expression of hu-IFN-gammaR1 and hu-IFN-gammaR2 is necessary and sufficient for most IFN-gamma-induced responses, it is not sufficient to confer a generalized antiviral state. These findings further suggest that additional species-specific accessory factor(s) are necessary for full signaling potential through the IFN-gamma receptor complex. The nature and potential role of such factors in IFN-gammaR signaling is discussed.

The intracellular domain of the second chain of the interferon-gamma receptor is interchangeable between species

In this report we show that the mouse interferon (IFN)-gamma R1 and IFN-gamma R2 subunits expressed in hamster cells are capable of rendering the cells sensitive to mouse IFN-gamma as measured by induction of class I MHC antigens and the activation of the transcription factor Stat1 alpha. However, these cells showed no antiviral protection in response to IFN-gamma when challenged with vesicular stomatitis virus (VSV) but limited protection when challenged with encephalomyocarditis virus (EMCV). Furthermore, the cytoplasmic domains of the IFN-gamma R2 subunits, like the cytoplasmic domains of the IFN-gamma R1 chains, can be interchanged between species with no loss of biologic activity, demonstrating that the species-specific interaction of the IFN-gamma R1 and IFN-gamma R2 chains involves only the extracellular domains of the two proteins.

The effects of a nonimmunogenic form of murine soluble interferon-gamma receptor on the development of autoimmune diabetes in the NOD mouse

Previous studies have shown that in vivo treatment with antiinterferon-gamma (anti-IFNgamma) monoclonal antibodies (mAbs) prevents the development of autoimmune diabetes in NOD mice. Although these findings anticipate that specific anti-IFNgamma therapies may be useful for the prevention/treatment of human insulin-dependent diabetes mellitus, there are several reasons why the use of anti-IFNgamma mAb may be difficult in the clinical setting. With the aim to develop alternative forms of specific anti-IFNgamma therapies, we recently produced a nonimmunogenic form of the soluble IFNgamma receptor (sIFNgammaR) that binds and neutralizes murine IFNgamma with an affinity higher than that of anti-IFNgamma mAb. In this study we compared the efficacy of sIFNgammaR to that of two anti-IFNgamma mAbs (XMG 1.2 and AN-18) in the prevention of spontaneous and accelerated (cyclophosphamide-induced) forms of autoimmune diabetes in NOD mice. The results show that in the spontaneous model, sIFNgammaR could prevent histological and clinical signs of autoimmune diabetes as efficiently as the two mAbs. Under ex vivo conditions, sIFNgammaR exhibited a more powerful modulatory effect than XMG 1.2 mAb on cytokine secretion from splenic lymphoid cells, which resulted in a significant reduction of Concanavalin A-induced IL-2 secretion and an augmented release of both unstimulated and lipopolysaccharide-induced IL-6. Moreover, although both mAbs were immunogenic and elicited formation of high titers of anti-rat IgG, sIFNgammaR did not induce antibody formation. Unexpectedly, in the cyclophosphamide-induced model, sIFNgammaR turned out to be less effective than either of the two anti-IFNgamma mAbs. Taken together, these data support the role of IFNgamma in the pathogenesis of NOD mice, but, more importantly, suggest that a nonimmunogenic approach is possible to the diminution of the effects of IFNgamma in this model.

Switching on of the proliferation or apoptosis of activated human T lymphocytes by IFN-gamma is correlated with the differential expression of the alpha- and beta-chains of its receptor

To find out how physiologically secreted IFN-gamma controls either the proliferation or the apoptosis of human T lymphocytes, the kinetics of expression of the alpha- and beta-chains of its receptor (IFN-gamma R) were sequentially followed on T lymphocytes first activated with PHA and then cultured in the presence of IL-2, and related to the kinetics of expression of Fas, Bcl-2, and IL-2R p55 chain. Both IFN-gamma R chains were poorly expressed on the membrane of resting T lymphocytes. Following their stimulation with PHA, IFN-gamma R alpha but not IFN gamma R beta-chain up-modulated before T lymphocyte entry into the S phase, and then IFN-gamma R alpha down-modulated when they passed through the S and G2/M. The ensuing proliferative response was inhibited by an anti-IFN-gamma R alpha mAb that impeded the binding of IFN-gamma. When PHA-activated T lymphoblasts were cultured for 16 days with IL-2, IFN-gamma R alpha expression increased, whereas that of the beta-chain remained barely detectable. Fas and Bcl-2 were both highly expressed. When these T lymphoblasts were restimulated by PHA, OKT3, or Staphylococcus enterotoxin beta-pokeweed mitogen, both chains up-modulated and most cells underwent apoptosis in a way apparently independent of Bcl-2, but not of Fas. This apoptosis, too, was prevented by the anti-IFN-gamma R alpha mAb. Physiologically secreted IFN-gamma is thus involved in the activation of resting T lymphocytes and in the apoptosis of reactivated lymphoblasts. However, high expression of IFN-gamma R beta took place when IFN-gamma induced apoptosis, but not when it induced proliferation. In conclusion, a correlation exists between differential expression of the IFN-gamma R beta-chain and the delivery by IFN-gamma of proliferative or apoptotic signals.

Switching on of the proliferation or apoptosis of activated human T lymphocytes by IFN-gamma is correlated with the differential expression of the alpha- and beta-chains of its receptor

To find out how physiologically secreted IFN-gamma controls either the proliferation or the apoptosis of human T lymphocytes, the kinetics of expression of the alpha- and beta-chains of its receptor (IFN-gamma R) were sequentially followed on T lymphocytes first activated with PHA and then cultured in the presence of IL-2, and related to the kinetics of expression of Fas, Bcl-2, and IL-2R p55 chain. Both IFN-gamma R chains were poorly expressed on the membrane of resting T lymphocytes. Following their stimulation with PHA, IFN-gamma R alpha but not IFN gamma R beta-chain up-modulated before T lymphocyte entry into the S phase, and then IFN-gamma R alpha down-modulated when they passed through the S and G2/M. The ensuing proliferative response was inhibited by an anti-IFN-gamma R alpha mAb that impeded the binding of IFN-gamma. When PHA-activated T lymphoblasts were cultured for 16 days with IL-2, IFN-gamma R alpha expression increased, whereas that of the beta-chain remained barely detectable. Fas and Bcl-2 were both highly expressed. When these T lymphoblasts were restimulated by PHA, OKT3, or Staphylococcus enterotoxin beta-pokeweed mitogen, both chains up-modulated and most cells underwent apoptosis in a way apparently independent of Bcl-2, but not of Fas. This apoptosis, too, was prevented by the anti-IFN-gamma R alpha mAb. Physiologically secreted IFN-gamma is thus involved in the activation of resting T lymphocytes and in the apoptosis of reactivated lymphoblasts. However, high expression of IFN-gamma R beta took place when IFN-gamma induced apoptosis, but not when it induced proliferation. In conclusion, a correlation exists between differential expression of the IFN-gamma R beta-chain and the delivery by IFN-gamma of proliferative or apoptotic signals.

Monocyte chemotactic protein 4 (MCP-4), a novel structural and functional analogue of MCP-3 and eotaxin

A novel human CC chemokine complementary DNA was identified in a library constructed from human fetal RNA, cloned into a baculovirus vector, and expressed in Sf9 insect cells. The mature recombinant protein that was released had the NH2-terminal sequence pyro-QPDALNVPSTC...and consisted of 75 amino acids. Minor amounts of two variants of 77 and 82 residues (NH2 termini: LAQPDA...and FNPQGLAQPDA...) were released as well. The novel chemokine was designated monocyte chemotactic protein 4 (MCP-4) and the variants were designated (LA)MCP-4 and (FNPQGLA)MCP-4. MCP-4 shares the pyroglutamic acidproline NH2-terminal motif and 56-61% sequence identity with the three known monocyte chemotactic proteins and is 60% identical to eotaxin. It has marked functional similarities to MCP-3 and eotaxin. Like MCP-3, MCP-4 is a chemoattractant of high efficacy for monocytes and T lymphocytes. On these cells, it binds to receptors that recognize MCP-1, MCP-3, and RANTES. On eosinophils, MCP-4 has similar efficacy and potency as MCP-3, RANTES, and cotaxin. It shares receptors with eotaxin and shows full cross-desensitization with this cosinophil-selective chemokine. Of the two variants, only (LA)MCP-4 could be purified in sufficient quantities for testing and was found to be at least 30-fold less potent than MCP-4 itself. This suggests that the 75-residue form with the characteristic NH2 terminus of an MCP is the biologically relevant species.

IFN-gamma restores HIV- and non-HIV-specific cell mediated immune response in vitro and its activity is neutralized by antibodies from patients with AIDS

The addition of IFN-gamma to cultures of peripheral blood mononuclear cells (PBMCs) obtained from asymptomatic HIV-infected patients increased cell proliferation in response to HIV envelope synthetic peptides (Env), influenza A virus (VIRUS), and allogeneic lymphocytes (ALLO) but not to phytohaemagglutinin (PHA) stimulation. F(Ab)2 fragments of IgG purified from the sera of HIV-seropositive patients specifically interfered with IFN-gamma-induced cell proliferation in response to recall antigens. Neutralization of the lymphokine activity was found to be sustained by specific IFN-gamma antibodies. Data obtained demonstrate that IFN-gamma can restore the cell-mediated immunity of a number of asymptomatic HIV+ individuals in vitro, while IFN-gamma antibodies present in sera of patients with AIDS interfere with the activity of the lymphokine.

Aspects of molecular interaction between HIV p17 and human gamma interferon

We describe the specific interaction between high-purity recombinant human immunodeficiency virus (HIV) type 1 p17 and human gamma interferon (hIFN-gamma) proteins. This interaction was found to be dose dependent and to involve conformational epitopes on both sides. Specificity was confirmed by competition ELISA, using monoclonal antibodies (MAbs) to hIFN-gamma as specific reagents. By competition experiments we also identified the epitope(s) on the hIFN-gamma molecule involved in p17 binding, very close to the receptor binding site. The kinetic constants were determined by surface plasmon resonance (SPR) analysis. The affinity constant (KA) of the complex was 2.78 x 10(8) M-1, that is, the ratio between a low dissociation rate constant (Koff)(1 x 10(-5)sec-1) and a high association rate constant (Kon) (3 x 10(3) M-1sec-1). However, p17 did not displace the binding of hIFN-gamma to its cellular receptor, nor did it interfere with the capability of the lymphokine to induce de novo expression of HLA-DR antigens on human monocytic cells or to inhibit the proliferation of tumor cells.

CD4+ and CD8+ lymphocytes of patients with AIDS synthesize increased amounts of interferon-gamma

Individual cells capable of interferon-gamma (IFN-gamma) synthesis are easily detected by immunofluorescence and flow cytometric analysis using an anti-IFN-gamma monoclonal antibody as specific reagent. By IFN-gamma flow cytometry assay, we demonstrated that HIV-seropositive patients, starting at the early stage of viral infection, generally have an increased percentage of lymphocytes potentially able to produce IFN-gamma, compared with healthy blood donors. IFN-gamma expression in patient lymphocytes was observed to increase with the progressive stages of HIV infection, with the highest figures occurring in stage C patients. Such increased IFN-gamma expression involved both CD4+ and CD8+ T cell subsets. Most interestingly, we found patients at the same stage of HIV infection who had similar numbers of total and CD4+ lymphocytes but highly different percentages of lymphocytes potentially capable of producing IFN-gamma.

Variable region cDNA sequences and characterization of murine anti-human interferon gamma receptor monoclonal antibodies that inhibit receptor binding by interferon gamma

Murine monoclonal antibodies (mAbs) are described that recognize the extracellular human interferon gamma receptor alpha-chain (IFN gamma R) and inhibit the binding to it of interferon gamma. The inhibitory activities (IC50s) of these mAbs, quantified by radioimmunoassay using native receptor on human Raji cells, lie in the range 0.5-24 nM, whereas their relative affinities for the immobilised recombinant extracellular receptor, determined using surface plasmon resonance technology, are in the range 0.6-40.9 nM. Nine mAbs derived from one immunization, were shown by variable region cDNA sequencing to be clonally related, with mAb A6 from this group showing the highest affinity for the receptor. Another two mAbs, gamma R38 and gamma R99, derived from a separate immunization, are clonally unrelated to each other and to those in the A6 family. From the V-region sequences, the L-chains of mAbs A6, gamma R38 and gamma R99 were shown to belong to the V kappa 34C, V kappa 34C and V kappa 1 families, whereas the H-chains belong to the 3069, J606 and J558 families, respectively. The mAbs A6 and gamma R38 recognize overlapping epitopes on the N-terminal Ig-like domain of the IFN gamma R, whereas the gamma R99 epitope is located largely in the membrane proximal Ig-like domain. Sequence comparisons with Ig structures solved by X-ray diffraction allowed deductions concerning likely CDR canonical conformations. These studies provide essential information for crystallographic and mutagenesis experiments aimed at understanding the molecular basis of the interactions of these mAbs with the extracellular IFN gamma R.

The in vivo antiviral activity of interleukin-12 is mediated by gamma interferon

The injection of 20 ng of mouse interleukin-12 (IL-12) protects mice from a lethal infection with encephalomyocarditis virus. In vitro, an anti-gamma interferon (anti-IFN-gamma) monoclonal antibody but not an anti-IL-12 monoclonal antibody neutralizes the antiviral activity present in the supernatants of splenocytes stimulated with IL-12. Finally, IL-12 fails to protect 129 Sv/Ev IFN-gamma R0/0 mice against encephalomyocarditis virus infection. These results demonstrate that IL-12 exerts its antiviral activity through the induction of endogenous IFN-gamma.

Interaction between the components of the interferon gamma receptor complex

Interferon gamma (IFN-gamma) signals through a multimeric receptor complex consisting of two different chains: the IFN-gamma receptor binding subunit (IFN-gamma R, IFN-gamma R1), and a transmembrane accessory factor (AF-1, IFN-gamma R2) necessary for signal transduction. Using cell lines expressing different cloned components of the IFN-gamma receptor complex, we examined the function of the receptor components in signal transduction upon IFN-gamma treatment. A specific IFN-gamma R2:IFN-gamma cross-linked complex was observed in cells expressing both IFN-gamma R1 and IFN-gamma R2 indicating that IFN-gamma R2 (AF-1) interacts with IFN-gamma and is closely associated with IFN-gamma R1. We show that the intracellular domain of IFN-gamma R2 is necessary for signaling. Cells coexpressing IFN-gamma R1 and truncated IFN-gamma R2, lacking the COOH-terminal 51 amino acids (residues 286-337), or cells expressing IFN-gamma R1 alone were unresponsive to IFN-gamma treatment as measured by MHC class I antigen induction. Jak1, Jak2, and Stat1 alpha were activated, and IFN-gamma R1 was phosphorylated only in cells expressing both IFN-gamma R1 and IFN-gamma R2. Jak2 kinase was shown to associate with the intracellular domain of the IFN-gamma R2.

The Jak kinases differentially associate with the alpha and beta (accessory factor) chains of the interferon gamma receptor to form a functional receptor unit capable of activating STAT transcription factors

Interferon gamma (IFN gamma) induces the expression of early response genes by tyrosine phosphorylation of Jak kinases and transcription factors referred to as STAT proteins. The topology of the IFN gamma receptor is partially understood and the relationship between the alpha chain that binds the ligand and the beta chain that is required for signal transduction is undefined. In a cell line which expresses only the human alpha chain, we show that these cells did not activate Jak kinases or STAT proteins with human IFN gamma, even though Jak1 co-immunoprecipitated with the alpha chain. In cells unexposed to IFN gamma, Jak1 preferentially associated with the alpha chain, while Jak2 associated with the beta chain. There was evidence for Jak1 kinase activity in untreated cells. For Jak2, kinase activity was IFN gamma-dependent. Although the alpha chain was tyrosine-phosphorylated in response to ligand, we found no evidence for tyrosine phosphorylation of the beta chain. These data are consistent with a model of the IFN gamma receptor in which Jak1 associates with the alpha chain, whereas Jak2 associates with the beta chain. IFN gamma clusters at least two receptor units which results in the tyrosine phosphorylation of Jak1 and Jak2, the activation of Jak2 kinase activity, and the recruitment of STAT1 alpha resulting in its activation by tyrosine phosphorylation.

Biphasic effect of interferon-gamma in murine collagen-induced arthritis

Interferon-gamma (IFN-gamma) exerts both enhancing and suppressing influences on collagen-induced arthritis (CIA), depending on the route and protocol of administration. To study the role of IFN-gamma on the autoimmune process of CIA, we treated DBA/1 mice with two different rat monoclonal antibodies (mAb) to murine IFN-gamma. Treatments, given twice weekly for 4 weeks, consisted of intraperitoneal injections of either mAb. In early treatments, starting from the day of immunization with type II collagen (CII), the severity of arthritis was reduced in both groups of anti-IFN-gamma-treated mice compared with control groups. Moreover, anti-CII antibody levels decreased in the sera of these mice. CIA was also down-regulated in mice treated from days 14 or 28 post immunization. In contrast, late treatments with anti-IFN-gamma mAb either induced aggravating effects, or did not affect the course of the disease. On the other hand, administration of high doses (8 x 10(4) U three times/week) of rat recombinant IFN-gamma exerted a transient increase of CIA severity. These findings suggest that IFN-gamma may play a critical role during both the induction and the course of CIA, first enhancing the immune response, and then regulating the arthritis process.

Interferon-gamma receptor extracellular domain-IgG fusion protein produced in Chinese hamster ovary cells as mixture of glycoforms

Glycosylation of proteins fulfills important functions and because of its diversity contributes to apparent protein heterogeneity. We investigated the heterogeneity of a fusion protein comprising the extracellular domain of the human interferon-gamma (IFN-gamma) receptor and parts of the human IgG3 constant region, a potential IFN-gamma antagonist. The protein was produced in Chinese hamster ovary (CHO) cells and was secreted into the culture medium as an 175 kD glycoprotein. Glycosylation represented approximately one-third of the apparent molecular mass of the fusion protein, consisted of N- and O-linked carbohydrate moieties, and included sialic acid residues as part of both N- and O-linked oligosaccharides. Fusion protein forms with different apparent molecular masses and charges were separated by ion-exchange chromatography. Preparative electrofocusing revealed a wide spectrum of glycoforms. Glycosylation of the fusion protein and of soluble IFN-gamma receptors, comprising the extracellular domain of the native sequence, expressed in insect and CHO cells did not interfere with affinity of ligand binding.

Interleukin-12 is required for interferon-gamma production and lethality in lipopolysaccharide-induced shock in mice

Several cytokines, in particular tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma), have been shown to be responsible for pathological reactions which may lead to shock and death observed in infection with Gram-negative bacteria and in response to endotoxins (lipopolysaccharides, LPS). Priming of mice with the avirulent Bacille Calmette Guérin (BCG) vaccine strain of Mycobacterium bovis increases the sensitivity of mice to the lethal effect of LPS and results in an efficient priming for cytokine production. In response to low doses (1 microgram/mouse) of LPS, BCG-primed mice produce interleukin-12 (IL-12) which controls IFN-gamma production, as demonstrated by the ability of neutralizing anti-IL-12 antibodies to suppress IFN-gamma production. However, the concentration of the biologically active IL-12 p70 heterodimer is similar in the serum of both BCG-primed or unprimed mice, reaching levels of 1-3 ng/ml at 3-6 h after LPS injection, whereas IFN-gamma production was observed only in BCG-primed mice. The priming effect of BCG on IFN-gamma production appears to be mostly due to its ability to increase TNF-alpha production, which acts as cofactor with LPS-induced IL-12 in inducing IFN-gamma production, as shown by the ability of injection of TNF-alpha and LPS (1 microgram/mouse), but not LPS alone, to induce IFN-gamma production. However, in addition to TNF-alpha, other LPS-induced cofactor(s) are required in cooperation with IL-12 to induce optimal IFN-gamma production, because co-injection of TNF-alpha and IL-12, sufficient to induce serum concentrations of both cytokines higher and more persistent than those obtained by injection of LPS, was not sufficient to induce IFN-gamma production in vivo. Neutralizing anti-IL-12 antibodies, in addition to inhibiting the in vivo LPS-induced IFN-gamma production, also completely protect BCG-primed mice injected with up to 10 micrograms of LPS from shock-induced death. Thus, IL-12 is required for IFN-gamma production and lethality in an endotoxic shock model in mice.

Interferon gamma receptor extracellular domain expressed as IgG fusion protein in Chinese hamster ovary cells. Purification, biochemical characterization, and stoichiometry of binding

Agents that antagonize the functions of interferon gamma (IFN gamma) are potential pharmaceuticals against several immunological and inflammatory disorders. IFN gamma receptor-immunoglobulin G fusion proteins (IFN gamma R-IgG) function as antagonists of endogenous IFN gamma and have longer half-lives in vivo in comparison with soluble IFN gamma receptors (sIFN gamma R), consisting of the extracellular region of the native sequence. A fusion protein comprising the extracellular domain of the human IFN gamma receptor and the hinge, CH2 and CH3 domains of the human IgG3 constant region, was expressed in Chinese hamster ovary cells. The IFN gamma R-IgG3 fusion protein was secreted into the culture medium as a 175-kDa glycoprotein and was purified over Protein G-Sepharose, DEAE-Sepharose, and size exclusion chromatography. IFN gamma R-IgG3 bound IFN gamma in solid phase assays and ligand blots, competed for the binding of radiolabeled IFN gamma to the cell surface receptor of Raji cells, and inhibited the IFN gamma-mediated antiviral activity with an efficiency at least one order of magnitude higher than that of the soluble receptor produced in the same expression system. Two IFN gamma R-IgG3 fusion proteins bound two IFN gamma dimers forming a complex of approximately 380 kDa. In immunodiffusion assays, the IFN gamma R-IgG3 fusion protein did not precipitate IFN gamma. Dissociation of bound IFN gamma from IFN gamma R-IgG3 was 2-fold slower than from the sIFN gamma R produced in insect cells.

Dissection of the extracellular human interferon gamma receptor alpha-chain into two immunoglobulin-like domains. Production in an Escherichia coli thioredoxin gene fusion expression system and recognition by neutralizing antibodies

The extracellular interferon gamma receptor alpha-chain (IFN gamma R) is believed to comprise two discrete approximately 110 amino acid immunoglobulin-like domains, perhaps similar to those seen in the crystal structure of the extracellular human growth hormone receptor [De Vos, A. M., Ultsch, M., & Kossiakoff, A. (1992) Science 255, 306-312], a distant relative in the cytokine receptor superfamily. In accord with this idea, we show that these IFN gamma R immunoglobulin-like domains can be produced separately in a soluble form with a native-like fold. The N-terminal domain (residues 1-108), with a Cys105 to Ser105 mutation, was produced at a high level, in a soluble form, as a thioredoxin-interferon gamma receptor fragment fusion protein in the cytoplasm of Escherichia coli. Upon extraction, the receptor Cys60-Cys68 disulfide bond formed spontaneously, to generate a native-like structure directly without the need for refolding. Cleavage of the fusion protein by enterokinase released the receptor fragment (approximately 12 kDa), which was recognized by several neutralizing antibodies with affinities, measured using surface plasmon resonance technology, that were essentially indistinguishable from those seen with the full length extracellular IFN gamma R produced in eukaryotic cells. Circular dichroism and 1D 1H nuclear magnetic resonance spectra indicated that the receptor fragment adopts a folded state, with mainly beta-sheet and reverse turn secondary structure. The second membrane-proximal Ig-like domain of the IFN gamma R (residues 90-229) was produced, albeit less efficiently, and characterized in a similar way. The production of these two independently folded proteins provides experimental support for the two domain organization of the IFN gamma R and opens new avenues for structural studies on these Ig-like molecules by NMR and crystallographic methods.

Role of interferon-gamma in mediating the antitumor efficacy of interleukin-12

Although interleukin-12 (IL-12) has marked antitumor activity against the murine Renca renal cell carcinoma in vivo, no antiproliferative activity with IL-12 was observed against these tumor cells in vitro; in contrast, interferon-gamma (IFN-gamma) had growth inhibitory activity. Since one of the properties of IL-12 is its ability to stimulate production of IFN-gamma, the role of IFN-gamma in mediating the antitumor activity of IL-12 was evaluated. Substantially diminished antitumor activity was observed in mice injected with IL-12 and neutralizing antibody to murine IFN-gamma compared with mice receiving IL-12 alone, indicating that IFN-gamma was required for the optimal antitumor efficacy of IL-12. However, several lines of investigation suggest that the antitumor effect of IL-12 is not mediated solely through the induction of IFN-gamma. Exogenous administration of IFN-gamma to Renca tumor-bearing euthymic mice resulted in less antitumor efficacy than that which could be obtained with IL-12. In addition, the antitumor effect of IL-12 was reduced in nude mice compared with euthymic mice, but an approximately 10-fold higher level of serum IFN-gamma was induced in nude than in euthymic mice. Thus, these results indicate that induction of high serum levels of IFN-gamma is not sufficient to mediate the antitumor efficacy of IL-12.

Experimental therapy of systemic lupus erythematosus: the treatment of NZB/W mice with mouse soluble interferon-gamma receptor inhibits the onset of glomerulonephritis

Female NZB/W F1 mice develop an autoimmune disease similar to human systemic lupus erythematosus (SLE), and ultimately die of glomerulonephritis. Starting at the age of 16 weeks NZB/W F1 mice were treated for a period of 19 weeks with soluble interferon-gamma receptor (sIFN-gamma R), anti-IFN-gamma monoclonal antibody (mAb) or IFN-gamma. All mice treated with sIFN-gamma R or anti-IFN-gamma mAb were alive 4 weeks after the treatment was discontinued, whereas 50% of mice died in the placebo groups and 78% of the mice died in the IFN-gamma-treated group. Histologically, there was severe membrano-proliferative glomerulonephritis in IFN-gamma- and placebo-treated mice, and minimal or no mesangioproliferative disease in mice receiving sIFN-gamma R or anti-IFN-gamma mAb. The renal mononuclear infiltrate (T lymphocytes and monocytes), expression of major histocompatibility complex class II antigen and glomerular immunoglobulin and complement deposition were reduced in those mice. These data suggest that an IFN-gamma inhibitor, such as the soluble IFN-gamma R, can be used for SLE therapy in the early stages of the disease.

Human PBMC proliferative response to Leishmania infantum promastigotes is inhibited by anti-IFN-gamma mAb gamma 123

PBMC from individuals both exposed and non-exposed to leishmaniae proliferative and produce interferon-gamma (IFN-gamma) following stimulation with Leishmania antigens. We studied the kinetics of the proliferative response of PBMC from non-exposed individuals and from patients recovering from visceral leishmaniasis due to Leishmania infantum, using heat-killed stationary-phase promastigotes of L. infantum as stimulating agent. The kinetics of both groups followed a similar temporal pattern, with higher values in the patient's group. Moreover, we observed that in both groups the activation was dose-dependently inhibited following the addition of gamma 123 anti-IFN-gamma monoclonal antibody. These results indicate the need for IFN-gamma in the activation process of PBMC induced by Leishmania antigens and stress the role of IFN-gamma in the immune response to leishmaniasis. The relevance of the elucidation of the immune response mechanism in human leishmaniasis for therapy and vaccination is briefly discussed.

Interleukin 12, interferon gamma, and tumor necrosis factor alpha are the key cytokines of the generalized Shwartzman reaction

The Shwartzman reaction is elicited by two injections of lipopolysaccharide (LPS) in mice. The priming LPS injection is given in the footpad, whereas the lethal LPS challenge is given intravenously 24 h later. The injection of interferon gamma (IFN-gamma) or interleukin 12 (IL-12) instead of the LPS priming injection induced the lethal reaction in mice further challenged with LPS. Antibodies against IFN-gamma when given together with the priming agent, prevented the lethal reaction in mice primed with either LPS, IL-12, or IFN-gamma. Antibodies against IL-12, when given together with the priming agent, prevented the lethal reaction in mice primed with either LPS or IL-12 but not with IFN-gamma. These results strongly suggest that LPS induces the release of IL-12, that IL-12 induces the production of IFN-gamma, and that IFN-gamma is the cytokine that primes macrophages and other cell types. Upon LPS challenge, the lethal Shwartzman reaction is induced by a massive production of inflammatory cytokines that act on the target sites already sensitized by IFN-gamma. If mixtures of TNF and IL-1 or mixtures of TNF and IFN-gamma are used to challenge mice previously primed with IFN-gamma or IL-12, mortality is induced. In the same conditions, the individual cytokines or a mixture of IL-1 and IFN-gamma do not replace the LPS challenge. When the mice are primed with LPS, the combination of TNF, IL-1, and IFN-gamma induced only a partial mortality incidence suggesting that the involvement of other LPS-induced factors.

First trimester human trophoblast expresses both interferon-gamma and interferon-gamma-receptor

Interferon-gamma (IFN-gamma) is a lymphokine, produced by activated T lymphocytes, which plays a key regulatory role in the host immunological responses. In addition, IFN-gamma is expressed by human and porcine trophoblast. As IFN-gamma exerts its biological functions through specific cell surface receptors and a great number of IFN-gamma receptors (IFN-gamma R) have been purified from human placenta, we have examined the relative distribution of IFN-gamma and IFN-gamma R in human placental tissues at different stages of pregnancy. By using immunohistochemical analysis and monoclonal antibodies, it was found that IFN-gamma expression is intense in the first trimester but almost imperceptible at term, whereas the expression of IFN-gamma R is present at both stages of pregnancy. For both lymphokine and receptor, the most intense expression was observed in villous syncytiotrophoblast and in extravillous interstitial trophoblast. From these results it appears that the expression of IFN-gamma R in trophoblast is related to the presence of the lymphokine in the early phase of gestation but not later. On this basis, it can be argued that IFN-gamma exerts its functional role via an autocrine and/or a paracrine loop mainly during the first trimester.

Serum amyloid protein (SAP) as a marker of autoimmune disease in mice

Acute phase proteins are good markers of inflammatory processes. To clarify whether Serum Amyloid Protein (SAP) can be a marker for the onset of SLE disease in mice, we measured constitutive and inducible SAP levels in normal mice of different strains, in C57Bl/6 lpr/lpr (B6lpr) and [NZB x NZW]F1 (NZB/W) SLE-prone mice, in mice that develop Lupus-like syndrome during chronic Graft versus Host (GvH) reaction and in mice suffering acute GvH reaction. In comparison to B6lpr, NZB/W mice showed higher blood levels of SAP but those levels did not correlate with autoimmune parameters. In B6lpr, the SAP levels steadily increased with age and correlated with some of the parameters used for monitoring the SLE disease. High levels of SAP were also found in mice suffering acute GvH reaction whereas the lupus-like chronic GvH disease was associated with limited increase of SAP levels.

Radiation inactivation of human gamma-interferon: cellular activation requires two dimers

gamma-Interferon (IFN-gamma) is a 17-kDa broad-spectrum cytokine which exerts its effects on a variety of target cells through its interaction with the IFN-gamma receptor. Although physicochemical studies of Escherichia coli-derived IFN-gamma, as well as its crystal structure, demonstrate that it is a homodimer in solution (M(r) 34,000), previous radiation inactivation studies yielded a functional size for IFN-gamma of 63-73 kDa in an antiviral assay. To understand the relationship between the solution form of IFN-gamma and the moiety that actually binds to the cellular receptor and activates cells, we examined irradiated nonradioactive and 32P-labeled IFN-gamma for its migration in SDS/polyacrylamide gels (to determine its physical integrity), its binding to cells, its reactivity in an ELISA, and its antiviral activity. The functional size of IFN-gamma differed in the assays, being 22 +/- 2 kDa for the physical destruction of IFN-gamma, 56 +/- 2 kDa for the cellular binding assay, 45-50 kDa for reactivity in the ELISA, and 72 +/- 6 kDa for antiviral activity. The results from the binding assays constitute direct evidence that IFN-gamma binds to its cellular receptor as a dimer. However, for antiviral activity, the functional mass is equivalent to a tetramer. This is consistent with models involving ligand-induced receptor dimerization, whereby two dimers acting in concert (equivalent to the target size of a tetramer) are required to activate cells in the antiviral assay.

Interferon-gamma induces tyrosine phosphorylation of interferon-gamma receptor and regulated association of protein tyrosine kinases, Jak1 and Jak2, with its receptor

Interferon-gamma (IFN-gamma) induces the expression of a set of early response genes by tyrosine phosphorylation of latent transcription factors such as p91. Although the tyrosine kinases, Jak1 and Jak2, have recently been shown to be critical for signal transduction by IFN-gamma, evidence is lacking for both tyrosine phosphorylation of the IFN-gamma receptor (IFN-gamma R) and the interaction between Jak1, Jak2, and the IFN-gamma R. In this report, we show that binding of IFN-gamma to HeLa cells initiated a series of events that resulted in the extremely rapid (15 s) tyrosine phosphorylation of not only Jak1, Jak2, and p91 but also the IFN-gamma R. Coimmunoprecipitation experiments revealed that Jak1 was associated with the IFN-gamma R prior to ligand binding, whereas Jak2 became part of the IFN-gamma R-Jak1 complex immediately after ligand binding. H2O2/vanadate treatment of cells for 15 min resulted in only the tyrosine phosphorylation of Jak1 and IFN-gamma R. Only after 60 min of this treatment did we observe tyrosine phosphorylation of Jak2 and p91 and assembly of the transcription factor complex FcRF gamma that binds to the promoter of the fcgr1 gene. These data suggest that JAK1 associates with the IFN-gamma R prior to ligand binding. IFN-gamma treatment of cells results in recruitment of JAK2 into the IFN-gamma R-Jak1 complex followed by assembly of the transcription factor FcRF gamma complex.

Environmental signals influencing expression of the IFN-gamma receptor on human T cells control whether IFN-gamma promotes proliferation or apoptosis

IFN-gamma R expression is subject to contrasting modulation on human T cells. IFN-gamma R constitutive expression is low on three human malignant T cells (ST4, PF382, and Jurkat) growing in medium supplemented with serum. The addition of IFN-gamma down-modulates IFN-gamma R expression and increases both proliferation and MHC class I Ag expression. By contrast, when malignant T cells are cultured in medium without serum, IFN-gamma R expression dramatically increases and the cells undergo a slow apoptotic death. The addition of IFN-gamma enhances apoptosis and inhibits cell rescue in serum-supplemented medium. This opposite ability of IFN-gamma to stimulate malignant T cell proliferation or death correlates with the intensity of IFN-gamma R cell expression, high expression being a marker for cell apoptosis. IFN-gamma R up-modulation also occurs on malignant T cells undergoing apoptosis after treatment with dexamethasone, on irradiated normal CD3+ PBL, and on cultured normal CD3+ thymocytes. Moreover, the ability of IFN-gamma to augment apoptosis of highly IFN-gamma R-positive thymocytes suggests that its role in promoting T cell apoptosis is also important in physiologic conditions.