Function and regulation of a murine macrophage-specific IgG Fc receptor, Fc gamma R-alpha

Ligand binding specificities of two cloned murine Fc gamma Rs (Fc gamma R-alpha, Fc gamma R-beta [9]) were determined by gene transfer into Fc gamma R negative cell lines. Both receptors were expressed as full-length molecules capable of IgG immune complex binding that was inhibitable by the mAb 2.4G2. The ligand binding profiles of these receptors were indistinguishable whereby both bound immune-complexed mouse IgG1, IgG2a, and IgG2b, but not IgG3. Neither receptor could bind monomeric IgG2a, indicating these receptors to be low-affinity IgG Fc receptors. Accumulation of the Fc gamma R-alpha mRNA can be induced with murine IFN-gamma at a concentration of 200 U/ml in the macrophage-like cell lines RAW 264.7 and J774a. The time course for induction indicates that the mRNA accumulation is transient but does not return to the uninduced level even after 50 h of treatment. Fc gamma R-beta mRNA was not induced by IFN-gamma, rather its expression was down modulated in mouse peritoneal macrophages. Both RAW and J774a cells lines exhibited increased receptor levels after IFN-gamma stimulation as measured by 125I-2.4G2 and ligand binding. In the absence of IFN-gamma, the RAW and J774a cell lines were minimally phagocytic, while P388D1 cells were actively phagocytic. In the presence of IFN-gamma, however, RAW 264.7 and J774a cells were induced to become actively phagocytic. Induction of Fc gamma R-alpha mRNA and protein by IFN-gamma may be part of the process by which macrophages become activated to engulf antibody-coated particles.     

Induction of interferon gamma production by natural killer cell stimulatory factor: characterization of the responder cells and synergy with other inducers

We previously reported that natural killer cell stimulatory factor (NKSF), a heterodimeric lymphokine purified from the conditioned medium of human B lymphoblastoid cell lines, induces interferon gamma (IFN-gamma) production from resting peripheral blood lymphocytes (PBL) and synergizes with interleukin 2 in this activity. In this study, we show that human NKSF induces IFN-gamma production from both resting and activated human PBL and from freshly isolated murine splenocytes. Human T and NK cells produce IFN-gamma in response to NKSF, but resting PBL require the presence of nonadherent human histocompatibility leukocyte antigens DR+ (HLA-DR+) accessory cells to respond to NKSF. The mechanism(s) by which NKSF induces IFN-gamma production results in accumulation of IFN-gamma mRNA, is insensitive to cyclosporin A, and synergizes with those mediated by phytohemagglutinin, phorbol diesters, anti-CD3 antibodies, and allogeneic antigens, but not by Ca2+ ionophores. The ability of NKSF to directly induce IFN-gamma production and to synergize with other physiological IFN-gamma inducers, joined with the previously described ability to enhance lymphocyte cytotoxicity and proliferation, indicates that this lymphokine is a powerful immunopotentiating agent.     

Interferon gamma inhibits apoptotic cell death in B cell chronic lymphocytic leukemia

The malignant, CD5+ B lymphocytes of B cell chronic lymphocytic leukemia (B-CLL) die by apoptosis in vitro. This is in contrast to the prolonged life span of the leukemic cells in vivo and likely reflects the lack of essential growth factors in the tissue culture medium. We found that interferon gamma (IFN-gamma) inhibits programmed cell death and promotes survival of B-CLL cells in culture. This effect may also be important in vivo: increased serum levels of IFN-gamma, ranging from 60 to > 2,200 pg/ml, were found in 7 of 10 B-CLL samples tested, whereas the sera of 10 healthy individuals did not contain detectable levels of this cytokine (< 20 pg/ml). High levels of IFN-gamma message were detected in RNA from T cell-depleted B-CLL peripheral blood samples by Northern blot analysis. Synthesis of IFN-gamma by B-CLL lymphocytes was confirmed by in situ hybridization and flow cytometry. The majority of B-CLL cells (74-82%) expressed detectable levels of IFN- gamma mRNA, and CD19+ B-CLL cells were labeled with anti-IFN-gamma monoclonal antibodies. These results show that IFN-gamma inhibits programmed cell death in B-CLL cells and suggest that the malignant cells are able to synthesize this cytokine. By delaying apoptosis, IFN- gamma may extend the life span of the malignant cells and thereby contribute to their clonal accumulation.     

Response of resting human peripheral blood natural killer cells to interleukin 2

The present study shows that recombinant interleukin 2 (IL-2) purified to homogeneity induces a rapid and potent enhancement of spontaneous cytotoxicity of human peripheral blood lymphocytes. The cells mediating cytotoxicity after 18-h treatment with IL-2 have surface markers of natural killer (NK) cells and are generated from the peripheral blood subset containing spontaneous cytotoxic cells. A parallel production of gamma interferon (IFN-gamma) is induced by recombinant IL-2 (rIL-2), and NK cells appear to be the major producer cells, whereas T cells are unable to produce IFN-gamma under these experimental conditions. However, the kinetics of the enhancement of cytotoxicity are faster than those of IFN-gamma production, and monoclonal anti-IFN-gamma antibodies do not suppress this effect, making it unlikely that the IFN- gamma produced is responsible for the enhancement. The enhancement of NK cell activity induced by rIL-2 precedes any proliferative response of the lymphocytes, which is instead observed in longer-term cultures of both NK and T cells.     

Cytokine-induced proliferation and immunoglobulin production of human B lymphocytes triggered through their CD40 antigen

Human resting B lymphocytes enter a state of sustained proliferation when incubated with both mouse fibroblastic L cells stably expressing Fc gamma RII/CDw32 and anti-CD40 antibodies. We have explored the effects of 11 recombinant human cytokines (CKs) on induced cell proliferation and immunoglobulin (Ig) production. Interleukin 4 (IL-4) was the only CK able to enhance anti-CD40-induced B cell multiplication as measured by enumeration of viable cells, and interferon gamma (IFN-gamma) further stimulated this induced proliferation. IL-4 enhanced the production of IgM and IgG by B cells and induced them to produce IgE. Combinations of IL-4 and IL-2 resulted in the production of large amounts of IgM and IgA. Interestingly, IFN-gamma did not inhibit the production of IgE by cells stimulated with anti-CD40 and IL-4. None of the tested CK combinations resulted in the production of large quantities of IgG. Therefore, this new culture system represents a unique model to study isotype regulation in highly purified human B lymphocytes, in addition to allowing the generation of long-term factor-dependent human B cell lines.     

Advanced glycosylation endproduct-specific receptors on human and rat T- lymphocytes mediate synthesis of interferon gamma: role in tissue remodeling

During normal aging and in chronic diabetes the excessive accumulation of reactive glucose-protein or glucose-lipid adducts known as advanced glycosylation endproducts (AGEs) has been shown to induce tissue dysfunction, in part through interaction with AGE-specific receptors on monocyte/macrophages and other cells. Recognizing that circulating lymphocytes trafficking through tissues interact with tissue AGEs, we searched for the expression of AGE-binding sites on peripheral blood T lymphocytes. Resting rat and human T cells bound 125I-AGE-albumin with an affinity of 7.8 x 10(7) M-1, whereas, after stimulation with phytohemagglutinin (PHA) for 48 h, binding affinity increased to 5.8 x 10(8) M-1. Flow cytometric analysis of resting rat T cells using polyclonal antibodies raised against rat liver AGE-binding proteins (p60 and p90) revealed the constitutive expression of both immunoreactivities. The number of resting CD4+ and CD8+ T cells positive for anti-p60 antibody binding (34.2 and 58.5%, respectively) increased to 92 and 90% of cells after 48-h stimulation with PHA. Exposure of PHA-activated T lymphocytes to AGE-albumin enhanced expression of interferon gamma (IFN-gamma) mRNA 10-fold and induced greater elaboration of the mature protein than did exposure to unmodified protein or PHA treatment alone. These data indicate that T cells contain an inducible system of surface receptors for AGE-modified proteins, and that receptor occupancy is linked to lymphokine production. This T cell AGE-receptor system might serve to target lymphocytes to AGE-rich tissues and involve them in the regulation of tissue homeostasis either by assisting in macrophage-dependent clearance of AGE-proteins, or by exerting direct antiproliferative action on mesenchymal cells. Under conditions of excessive AGE-protein and AGE lipid accumulation (e.g., aging and diabetes), enhanced production of AGE-induced IFN-gamma may accelerate immune responses that contribute to tissue injury.     

Production of natural killer cell stimulatory factor (interleukin 12) by peripheral blood mononuclear cells

Natural killer cell stimulatory factor (NKSF), or interleukin 12 (IL-12), is a 70-kD heterodimeric cytokine composed of two covalently linked chains, p40 and p35. NKSF/IL-12 has multiple effects on T and NK cells and was originally identified and purified from the supernatant fluid of Epstein-Barr virus (EBV)-transformed human B lymphoblastoid cell lines. We have produced a panel of monoclonal antibodies against both chains of NKSF/IL-12. Some of these antibodies have neutralizing activity, and several combinations of them have been used to establish sensitive radioimmunoassays detecting the free p40 chain, the free p35 chain, or the p70 heterodimer. Using these reagents, we have determined that most EBV-transformed human B lymphoblastoid cell lines constitutively produce low levels of the p70 heterodimer and an excess of the free p40 chain, whereas Burkitt lymphoma-derived, T, myeloid, and many solid tumor-derived cell lines produce neither. Production of both p40 and p70 is increased several-fold upon stimulation of the EBV-transformed cell lines with phorbol diesters. The ability of supernatant fluids from unstimulated and phorbol diester-stimulated cell lines to induce interferon gamma (IFN-gamma) production from T and NK cells, one of the effects of NKSF/IL-12, parallels the levels of production of the p70 heterodimer, known to be the biologically active form of NKSF/IL-12. Staphylococcus aureus Cowan I strain (SAC) and other stimuli induce accumulation of p40 mRNA and production of both p40 and p70 by peripheral blood mononuclear cells (PBMC). The producer cells appear to include both adherent cells and nonadherent lymphocytes, possibly B cells. The supernatant fluids from SAC-stimulated PBMC mediate the typical functions of NKSF/IL-12 (i.e., IFN-gamma induction, mitogenic effects on T/NK blasts, enhancement of NK cell cytotoxicity) at concentrations of p70 similar to those at which recombinant NKSF/IL-12 mediates the same functions. Moreover, these activities are significantly inhibited by anti-NKSF/IL-12 antibodies. The neutralizing anti-NKSF/IL-12 antibodies also inhibit 85% of the IFN-gamma production in response to SAC, an NKSF/IL-12 inducer, and approximately 50% of the IFN-gamma production in response to non-NKSF/IL-12-inducers such as IL-2, phytohemagglutinin, and anti-CD3 antibodies. These results indicate that induced or constitutively produced NKSF/IL-12 has a major role in facilitating IFN-gamma production by peripheral blood lymphocytes.(ABSTRACT TRUNCATED AT 400 WORDS)     

Regression of an established tumor genetically modified to release granulocyte colony-stimulating factor requires granulocyte-T cell cooperation and T cell-produced interferon gamma

Using the murine colon adenocarcinoma C-26 cell line, engineered to release granulocyte colony-stimulating factor (G-CSF) (C-26/G-CSF), were studied the mechanisms responsible for inhibition of tumor take in syngeneic animals and of regression of an established tumor in sublethally irradiated mice injected with these cells. Immunocytochemistry and in situ hybridization, performed to characterize tumor-infiltrating leukocytes and their cytokine expression, respectively, indicated that polymorphonuclear leukocytes (PMN) were the major cells responsible for inhibition of tumor take and that they expressed mRNA for interleukin 1 alpha (IL-1 alpha), IL-1 beta, and tumor necrosis factor alpha (TNF-alpha). Expression of interferon gamma (IFN-gamma) and of IL-4 was undetectable, consistent with the absence of T lymphocytes at the site of tumor injection. In mice injected with C-26/G-CSF cells after 600-rad irradiation, the tumors grew to approximately 1.5 cm in 30 d, regressing completely thereafter in 70-80% of mice. During the growing phase, tumors were infiltrated first by PMN (between days 15 and 20), then by macrophages, and last by T lymphocytes. Both CD4+ and CD8+ T cells were present but only CD8 depletion significantly abrogated tumor regression. Depletion of PMN by the RB6-8C5 antigranulocytes monoclonal antibody reduced the number of T cells infiltrating the tumor and prevented tumor regression. In situ hybridization performed at the beginning of tumor regression revealed the presence of mRNA for IL-1 alpha, IL-1 beta, and TNF-alpha, but also the presence of cells, with lymphoid morphology, expressing IFN-gamma. Tumors from mice treated with recombinant IFN- gamma (between days 20 and 35) were rejected faster, whereas mice treated with antibodies to IFN-gamma (from day 20) died of progressive tumor. Cyclosporin A treatment (started at day 20) also abrogated tumor regression. These results indicate that inhibition of tumor take and regression in this model occurs through different mechanisms that involve PMN and PMN-T cell interactions, respectively, as well as a combination of cytokines that, for tumor regression, require IFN-gamma. Thus, gene transfer of a single cytokine gene such as G-CSF into tumor cells appears to be sufficient to trigger the cascade of cell interactions and cytokine production necessary to destroy a cancer nodule.     

Interleukin 10 (IL-10) inhibits human lymphocyte interferon gamma- production by suppressing natural killer cell stimulatory factor/IL-12 synthesis in accessory cells

Natural killer cell stimulatory factor or interleukin 12 (NKSF/IL-12) is a heterodimeric cytokine produced by monocytes/macrophages, B cells, and possibly other accessory cell types primarily in response to bacteria or bacterial products. NKSF/IL-12 mediates pleiomorphic biological activity on T and NK cells and, alone or in synergy with other inducers, is a powerful stimulator of interferon gamma (IFN- gamma) production. IL-10 is a potent inhibitor of monocyte-macrophage activation, that inhibits production of tumor necrosis factor alpha (TNF-alpha), IL-1 and also IFN-gamma from lymphocytes acting at the level of accessory cells. Because TNF-alpha and IL-1 are not efficient inducers of IFN-gamma, the mechanism by which IL-10 inhibits IFN-gamma production is not clear. In this paper, we show that IL-10 is a potent inhibitor of NKSF/IL-12 production from human peripheral blood mononuclear cells activated with Staphylococcus aureus or lipopolysaccharide (LPS). Both the production of the free NKSF/IL-12 p40 chain and the biologically active p70 heterodimer are blocked by IL- 10. NKSF/IL-12 p40 chain mRNA accumulation is strongly induced by S. aureus or LPS and downregulated by IL-10, whereas the p35 mRNA is constitutively expressed and only minimally regulated by S. aureus, LPS, or IL-10. Although IL-10 is able to block the production of NKSF/IL-12, a powerful inducer of IFN-gamma both in vitro and in vivo, the mechanism of inhibition of IFN-gamma by IL-10 cannot be explained only on the basis of inhibition of NKSF/IL-12 because IL-10 can partially inhibit IFN-gamma production induced by NKSF/IL-12, and also, the IFN-gamma production in response to various stimuli in the presence of neutralizing antibodies to NKSF/IL-12. Our findings that antibodies against NKSF/IL-12, TNF-alpha, or IL-1 beta can significantly inhibit IFN-gamma production in response to various stimuli and that NKSF/IL-12 and IL-1 beta can overcome the IL-10-mediated inhibition of IFN-gamma, suggest that IL-10 inhibition of IFN-gamma production is primarily due to its blocking production from accessory cells of the IFN-gamma- inducer NKSF/IL-12, as well as the costimulating molecule IL-1 beta.     

Interferon-gamma inhibits scavenger receptor expression and foam cell formation in human monocyte-derived macrophages.

The scavenger receptor (ScR) mediates uptake of chemically modified low density lipoprotein (LDL) by human monocyte-derived macrophages. It is not down-regulated by high intracellular cholesterol levels, and exposure of macrophages to acetylated or oxidized LDL therefore leads to foam cell development. The hypothesis that this represents an important mechanism for intracellular cholesterol accumulation in atherosclerosis is supported by the finding of ScR expression in foam cells of atherosclerotic plaques. T lymphocytes are also present in such plaques and it is known that T cell products regulate macrophage activation. We have therefore studied the effect of interferon-gamma (IFN gamma), a lymphokine secreted by activated T lymphocytes, on the expression of ScR in human monocyte-derived macrophages. Binding and uptake of acetylated LDL were significantly reduced in macrophages exposed to recombinant IFN gamma or IFN gamma-containing lymphocyte-conditioned media. Competition experiments showed that the IFN gamma-regulated binding and uptake of acetylated LDL was mediated via ScR. IFN gamma exerted its effect on the saturable binding of acetylated LDL by reducing the number of cell surface binding sites without significantly affecting the affinity between acetylated LDL and its receptor. Northern analysis revealed that the type I ScR mRNA was significantly reduced in IFN gamma-treated cells. Finally, IFN gamma treatment reduced intracellular cholesteryl ester accumulation and inhibited the development of foam cells in the cultures. In conclusion, our data show that IFN gamma blocks the development of macrophage-derived foam cells by inhibiting expression of ScR. This suggests that macrophage-T lymphocyte interactions may reduce intracellular cholesterol accumulation in the atherosclerotic plaque.     

Conventional T-bet(+)Foxp3(-) Th1 cells are the major source of host-protective regulatory IL-10 during intracellular protozoan infection

Although interferon gamma (IFN-gamma) secretion is essential for control of most intracellular pathogens, host survival often also depends on the expression of interleukin 10 (IL-10), a cytokine known to counteract IFN-gamma effector functions. We analyzed the source of regulatory IL-10 in mice infected with the protozoan parasite Toxoplasma gondii. Unexpectedly, IFN-gamma-secreting T-bet(+)Foxp3(-) T helper type 1 (Th1) cells were found to be the major producers of IL-10 in these animals. Further analysis revealed that the same IL-10(+)IFN-gamma(gamma) population displayed potent effector function against the parasite while, paradoxically, also inducing profound suppression of IL-12 production by antigen-presenting cells. Although at any given time point only a fraction of the cells appeared to simultaneously produce IL-10 and IFN-gamma, IL-10 production could be stimulated in IL-10(-)IFN-gamma(+) cells by further activation in vitro. In addition, experiments with T. gondii-specific IL-10(+)IFN-gamma(+) CD4 clones revealed that although IFN-gamma expression is imprinted and triggered with similar kinetics regardless of the state of Th1 cell activation, IL-10 secretion is induced more rapidly from recently activated than from resting cells. These findings indicate that IL-10 production by CD4(+) T lymphocytes need not involve a distinct regulatory Th cell subset but can be generated in Th1 cells as part of the effector response to intracellular pathogens.     

Immune interferon inhibits proliferation and induces 2'-5'-oligoadenylate synthetase gene expression in human vascular smooth muscle cells

Proliferation of vascular smooth muscle cells (SMC) contributes to formation of the complicated human atherosclerotic plaque. These lesions also contain macrophages, known to secrete SMC mitogens, and T lymphocytes. Many of the SMC in the lesions express class II major histocompatibility antigens, an indication that activated T cells secrete immune IFN-gamma locally in the plaque. We therefore studied the effect of IFN-gamma on the proliferation of cultured SMC derived from adult human blood vessels. IFN-gamma (1,000 U/ml) reduced [3H]thymidine (TdR) incorporation into DNA by SMC stimulated with the well-defined mitogens IL 1 (from 15.3 +/- 0.7 to 6.2 +/- 0.7 dpm X 10(-3)/24 h) or platelet-derived growth factor (PDGF) (from 18.5 +/- 1.0 to 7.3 +/- 0.7 dpm X 10(-3)/24 h). Kinetic and nuclear labeling studies indicated that this effect of IFN-gamma was not due to altered thymidine transport or specific radioactivity of TdR in the cell. In longer term experiments (4-16 d) IFN-gamma prevented net DNA accumulation by SMC cultures stimulated by PDGF. IFN-gamma also delayed (from 30 to 60 min) the time to peak level of c-fos RNA in IL 1-treated SMC. It is unlikely that cytotoxicity caused these effects of IFN-gamma, as the inhibition of growth was reversible and we detected no cell death in SMC cultures exposed to this cytokine. Activation of 2'-5' oligoadenylate synthetase gene expression may mediate certain antiproliferative and antiviral effects of interferons. Both IFN-gamma and type I IFNs (IFN-alpha or IFN-beta) induced 2'-5' oligoadenylate synthetase mRNA and enzyme activity in SMC cultures, but with concentration dependence and time course that may not account for all of IFN-gamma's cytostatic effect on SMC. The accumulation of SMC in human atherosclerotic lesions is a long-term process that must involve altered balance between growth stimulatory and inhibitory factors. The cytostatic effect of IFN-gamma on human SMC demonstrated here may influence this balance during human atherogenesis, because T cells present in the complicated atherosclerotic plaque likely produce this cytokine.     

Interleukin 12 induces stable priming for interferon gamma (IFN-gamma) production during differentiation of human T helper (Th) cells and transient IFN-gamma production in established Th2 cell clones

Interleukin 12 (IL-12) facilitates the generation of a T helper type 1 (Th1) response, with high interferon gamma (IFN-gamma) production, while inhibiting the generation of IL-4-producing Th2 cells in polyclonal cultures of both human and murine T cells and in vivo in the mouse. In this study, we analyzed the effect of IL-12, present during cloning of human T cells, on the cytokine profile of the clones. The culture system used allows growth of clones from virtually every T cell, and thus excludes the possibility that selection of precommitted Th cell precursors plays a role in determining characteristics of the clones. IL-12 present during the cloning procedures endowed both CD4+ and CD8+ clones with the ability to produce IFN-gamma at levels severalfold higher than those observed in clones generated in the absence of IL-12. This priming was stable because the high levels of IFN-gamma production were maintained when the clones were cultured in the absence of IL-12 for 11 d. The CD4+ and some of the CD8+ clones produced variable amounts of IL-4. Unlike IFN-gamma, IL-4 production was not significantly different in clones generated in the presence or absence of IL-12. These data suggest that IL-12 primes the clone progenitors, inducing their differentiation to high IFN-gamma-producing clones. The suppression of IL-4-producing cells observed in polyclonally generated T cells in vivo and in vitro in the presence of IL-12 is not observed in this clonal model, suggesting that the suppression depends more on positive selection of non-IL-4-producing cells than on differentiation of individual clones. However, antigen- specific established Th2 clones that were unable to produce IFN-gamma with any other inducer did produce IFN-gamma at low but significant levels when stimulated with IL-12 in combination with specific antigen or insoluble anti-CD3 antibodies. This induction of IFN-gamma gene expression was transient, because culture of the established clones with IL-12 for up to 1 wk did not convert them into IFN-gamma producers when stimulated in the absence of IL-12. These results suggest that Th clones respond to IL-12 treatment either with a stable priming for IFN- gamma production or with only a transient low level expression of the IFN-gamma gene, depending on their stage of differentiation.     

Inducibility of class II major histocompatibility complex antigens by interferon gamma is associated with reduced tumorigenicity in C3H mouse fibroblasts transformed by v-Ki-ras

Paired lines of C3H mouse fibroblasts transformed with murine sarcoma virus (Kirsten strain) were prepared that express high or low levels of class II major histocompatibility complex antigen after treatment with interferon gamma (IFN-gamma). Here, we described a comparison of the tumorigenicity of these lines in euthymic syngeneic and thymus-deficient nu/nu mice and in mice depleted of IFN-gamma. The class II-inducible cells are clearly less tumorigenic than the noninducible cells in syngeneic mice, but of similar tumorigenicity in nu/nu mice and in mice treated with antibodies to deplete IFN-gamma. We propose that in this system, IFN-gamma induction of class II antigens on the tumor cell surface operates to limit tumor growth; ras expression, which inhibits induction of class II antigens, prevents this and so allows tumor growth.     

Prevention of injury-induced suppression of T-cell immunity by the CD1d/NKT cell-specific ligand alpha-galactosylceramide

Infection, sepsis, and multiple organ failure continue to be significant factors leading to morbidity and mortality after severe injury. Studies by our laboratory and others have identified injury-induced defects in both innate and adaptive components of host defense. We previously reported that CD1d-restricted natural killer T (NKT) cells actively suppress effector T-cell immunity after burn injury via production of excess IL-4 and failure to produce IFN-gamma. alpha-Galactosylceramide (alpha-GalCer) is a synthetic NKT cell-specific ligand presented exclusively to invariant NKT cells and is known to improve immunity against tumors and infection by promoting IFN-gamma production. Here, we confirmed the role of Valpha14-Jalpha281 invariant NKT cells in mouse model of burn injury-induced suppression of T-cell immunity and further asked whether alpha-GalCer can improve immunity after injury via similar mechanisms. We observed that systemic treatment with alpha-GalCer prevented the injury-induced suppression of Ag-specific T-cell responsiveness both in vitro and in vivo and restored the ability of splenic lymphocytes to produce both IL-2 and IFN-gamma. Moreover, burn injury was associated with diminished expression of major histocompatibility complex II and CD40 on antigen presenting cells that were both restored by alpha-GalCer treatment to levels seen in sham-treated mice. Collectively, these data suggest that, via manipulation of the NKT cell population, we may be able to maintain T-cell function and improve host defense after burn injury.     

Interleukin 10 and interferon gamma regulation of experimental Trypanosoma cruzi infection

Studies were undertaken to determine whether interleukin 10, (IL-10) a cytokine shown to inhibit interferon gamma (IFN-gamma) production, was involved in Trypanosoma cruzi infections in mice. Exogenous IFN-gamma protects mice from fatal infection with T. cruzi. Furthermore, resistant B6D2 mice developed fatal T. cruzi infections when treated with neutralizing anti-IFN-gamma monoclonal antibody (mAb). Thus, endogenous as well as exogenous IFN-gamma is important in mediating resistance to this parasite. Because both T. cruzi-susceptible (B6) and -resistant (B6D2) mouse strains produced IFN-gamma during acute infection, we looked for the concomitant production of mediators that could interfere with IFN-gamma-mediated resistance to T. cruzi. We found that IL-10-specific mRNA was produced in the spleens of mice with acute T. cruzi infections. In addition, spleen cell culture supernatants from infected B6 mice, and to a lesser extent B6D2 mice, elaborated an inhibitor(s) of IFN-gamma production. This inhibitor(s) was neutralized by anti-IL-10 mAb. These experiments demonstrated the production of biologically active IL-10 during T. cruzi infection. In further studies in vitro, it was shown that IL-10 blocked the ability of IFN-gamma to inhibit the intracellular replication of T. cruzi in mouse peritoneal macrophages. Thus, in addition to its known ability to inhibit the production of IFN-gamma, IL-10 (cytokine synthesis inhibitory factor), may also inhibit the effects of IFN-gamma. These experiments demonstrate that IL-10 is produced during infection with a protozoan parasite and suggest a regulatory role for this cytokine in the mediation of susceptibility to acute disease.