Cytokine production of CD8+ immune T cells but not of CD4+ T cells from Toxoplasma gondii-infected mice is polarized to a type 1 response following stimulation with tachyzoite-infected macrophages.

To examine whether cytokine production of CD4(+)immune T cells and CD8(+)immune T cells in Toxoplasma gondii-infected mice differ in their responses to infected cells and to soluble antigens of the parasite, we compared the production of interferon-gamma (IFN-gamma), interleukin-2 (IL-2), IL-4, and IL-10 by the immune T cell populations following in vitro stimulation with tachyzoite-infected macrophages and tachyzoite lysate antigens (TLA). Both CD4(+)and CD8(+)immune T cells produced large amounts of IFN-gamma in response to either infected macrophages or TLA, but the CD4(+)T cells produced greater amounts of the cytokine than did the CD8(+)T cells with both stimulations. Both T cell populations also produced IL-2 after stimulation with infected macrophages, whereas only CD4(+)T cells did when stimulated with TLA. CD4(+)immune T cells also produced large amounts of IL-4 and IL-10 after stimulation with infected macrophages, but CD8(+)T cells did not. These results indicate that CD4(+)immune T cells produce IFN-gamma, IL-2, IL-4, and IL-10 in response to infected macrophages, whereas CD8(+)immune T cells produce predominantly IFN-gamma and IL-2. Since IL-4 and IL-10 could suppress IFN-gamma-mediated protective mechanisms against the parasite, the production of these cytokines by CD4(+)immune T cells in response to infected cells could negatively affect their protective activity in vivo.     

The immunosuppressive effects of measles virus on T cell function--failure to affect IL-2 release or cytotoxic T cell activity in vitro.

Measles virus (MV) is known to depress T cell function. In order to determine whether this results from alteration in the production of, or response to, interleukin-2 (IL-2) we studied the effect of in vitro infection with MV on human IL-2 dependent T cell lines. MV produced a cytopathic productive infection in these cells. Class I allospecific cytotoxic T cells retained their cytotoxic activity 48 h after infection. Both cytotoxic and Leu 3a/4a positive T cell lines continued to respond to IL-2 by proliferation up to 26 h after infection. The ability of human tonsillar lymphocytes to generate IL-2 in response to phytohaemagglutinin following MV infection was then studied. In early measles infection (up to 48 h) there was no suppression of IL-2 production: in fact measles infected cells spontaneously released low levels of IL-2 in the absence of lectin. Similarly, IL-2 release was not affected by Herpes simplex virus infection of such cultures, although lymphocytes infected with Sendai or respiratory syncytial viruses produced considerably less IL-2. These observations suggest that MV-induced immunosuppression is not a result of inhibition of differentiated T cell function, IL-2 generation or responsiveness, but may be more directly related to virus-induced cytopathic effects in activated T cells.     

Production of gamma interferon by natural killer cells from Toxoplasma gondii-infected SCID mice: regulation by interleukin-10, interleukin-12, and tumor necrosis factor alpha.

Previous studies of mice have implicated natural killer (NK) cells as mediators of protective activity against Toxoplasma gondii through their production of gamma interferon (IFN-gamma). In the present study, we have compared NK-cell activity in infected and uninfected SCID mice. Our data reveal that infection results in increased levels of IFN-gamma in serum and elevated NK-cell activity but that these NK cells were not cytotoxic for T. gondii-infected P815 cells. Treatment with anti-IFN-gamma antibody abrogated the increase in NK-cell activity and resulted in earlier mortality of infected mice. In vivo treatment with anti-asialo GM1 antiserum reduced NK cell activity and levels of IFN-gamma in serum but did not alter time to death. Spleen cells from infected mice produced higher levels of IFN-gamma than those from uninfected mice when stimulated in vitro with live T. gondii or parasite antigen preparations. Further analysis revealed that interleukin 10 (IL-10) inhibited, whereas tumor necrosis factor alpha (TNF-alpha) and IL-12 enhanced, IFN-gamma production by spleen cells from infected or uninfected mice. The combination of IL-12 and TNF-alpha induced higher levels of IFN-gamma from whole spleen cells of infected mice than from those of uninfected mice. Depletion of the adherent cell population from the spleen cells of infected mice led to a significant reduction in the levels of IFN-gamma produced after stimulation with IL-12 plus TNF-alpha. Similar results did not occur with cells from uninfected mice. These data indicate that other cytokines produced by the adherent cell population from infected mice may be involved in maximal production of IFN-gamma by NK cells stimulated with IL-12 and TNF-alpha. To assess the importance of endogenous IL-12, a polyclonal anti-IL-12 was administered to infected SCID mice. This treatment led to earlier mortality, indicating that endogenous IL-12 mediates resistance to T. gondii.     

犬蛔虫（Toxocaracanis）对感染鼠的细胞免疫和IL－1、IL－2免疫调节作用的影响

应用犬蛔虫（Ｔ．ｃａｒｎｉｓ）的感染性虫卵口饲感染Ｃ３Ｈ／ＨｅＮ鼠，体外培养后观察脾细胞的免疫学变化。感染第１－４周的脾细胞用ＣｏｎＡ刺激，Ｔ细胞的增殖反应，ＩＬ－２的诱生均明显地受到抑制，而且感染鼠脾细胞抑制了正常鼠脾细胞对ＣｏｎＡ的反应。感染鼠的脾细胞经ＳｅｐｈａｄｅｘＧ－１０过柱后，Ｔ细胞则不显示被抑制作用。表明影响Ｔ细胞被抑制作用的是感染鼠的巨噬细胞。相反，感染第１－４周的鼠所产生的ＩｇＧ和ＩｇＭ等抗体的Ｂ细胞活性增强；用ＬＰＳ刺激巨噬细胞诱生的白介素（ＩＬ）ＩＬ－１也增多。     

Enhancing effect of natural killer cell stimulatory factor (NKSF/interleukin-12) on cell-mediated cytotoxicity against tumor-derived and virus-infected cells

Natural killer cell stimulatory factor (NKSF) or interleukin-12 (IL-12) is a heterodimeric cytokine with pleiomorphic effects on T and NK cells, including induction of lymphokine production, mitogenesis, and enhancement of spontaneous cytotoxic activity. Similarly to IL-2, NKSF/IL-12 enhances NK cell-mediated cytotoxicity within a few hours and independently from induced proliferation. This effect is independent from other induced cytokines, because it is not prevented by antibodies neutralizing interferon (IFN)-α, IFN-β IFN-γ, IL-2 or tumor necrosis factor (TNF)-α and, unlike the induction of IFN-γ production by peripheral blood lymphocytes, it does not require HLA class II-positive accessory cells. Enhanced cytotoxicity is accompanied by morphologic changes in NK cells, including a significant increase in the number of cytoplasmic granules. In addition to the previously described ability to enhance the cytotoxic activity of NK cells against tumor-derived target cells, NKSF/IL-12 is also a potent stimulator of cytotoxicity against virus-infected cells, either fibroblasts acutely infected with herpes viruses or T cell lines chronically infected with human immunodeficiency virus-1. NK cell-mediated antibody-dependent cytotoxicity or anti-CD16 antibody-redirected lysis is not significantly enhanced by NKSF/IL-12. However, the ability of resting peripheral blood T cells to mediate anti-CD3 antibody-redirected lysis is enhanced by 18-h incubation with NKSF/IL-12, indicating that this lymphokine can modulate the cytotoxic capability of both NK and T cells.     

Profound effect of the absence of IL-4 on T cell responses during infection with Schistosoma mansoni.

T cell responses of interleukin (IL)-4(-/-) and wild-type (WT) mice infected with the helper T cell 2 (Th2) response-inducing pathogen Schistosoma mansoni were compared. As expected, given the important role of IL-4 in Th2 response induction, the absence of IL-4 resulted in diminished Th2 responses, apparent as reduced production of IL-4, -5, and -10 by CD4(+) cells isolated from the spleens of infected IL-4(-/-) mice. Surprisingly, these cells produced significantly less interferon (IFN)-gamma and proliferated less than did those from infected WT mice after T cell receptor ligation. CD8(+) cells isolated from infected IL-4(-/-) mice also produced less IFN-gamma than WT CD8 cells, although there was no difference in the proliferative responses of these cell populations. After infection, spleens of infected IL-4(-/-) mice did not enlarge to the same extent as those of WT mice, and attrition of the CD8(+) cell population within this lymphoid organ was noted. Taken together, the data indicate that in addition to inhibiting Th2 response development, the lack of IL-4 during schistosomiasis significantly affects additional aspects of T cell responses.     

Generation of IL-2 dependent bovine cytotoxic T lymphocyte clones reactive against BHV-1 infected target cells: loss of genetic restriction and virus specificity

To gain insight into the mechanisms of immunity to bovine herpesvirus type-1 (BHV-1) in particular the importance of the T-cell response, we attempted to clone bovine cytotoxic T lymphocytes that were specific for BHV-1 infected autologous target cells. A number of bovine T cell clones were generated by limiting dilution in the presence of bovine recombinant IL-2 and BHV-1 infected target cells as feeder layers. These clones were maintained in culture on crude IL-2 containing supernatants. In functional studies, 4 of the 16 T cell clones were shown to have high levels of cytotoxic activity specific for autolgous BHV-1 infected target cells with significantly lower cytotoxic activity against uninfected target cells and heterologous BHV-1 infected target cells. Continuous culturing of these 4 T cell clones, using either the crude IL-2 or high concentrations of recombinant bovine IL-2, resulted in the loss of both MHC restricted and BHV-1 specific cytotoxic activity. These clones now exhibit promiscuous type cytotoxic activity with the ability to lyse a variety of target cells. Using flow cytometric analysis, the phenotype of the T cell clones were shown to have bovine T lymphocyte characteristics including expression of the BoT8 marker. This is the first report of cloned bovine cytotoxic T lymphocytes reactive against BHV-1 and the generation from these clones of promiscuous cytotoxic activity against both virus-infected and non-infected bovine target cells.     

Defective NK cell activity following thermal injury.

Peripheral blood mononuclear lymphocytes (PBL) from thermal injury patients were examined for their ability to mediate natural killer (NK) cell activity against K562 tumour cells and against herpes simplex virus type 1 (HSV-1) infected Raji tumour cells. Using fluorescein isothiocyanate-conjugated monoclonal antibodies, the number of T3, T4, T8, Leu11, and Leu7 positive cells in PBL obtained from patients and normal controls was determined. Thermal injury patients had decreased levels of T3+ cells and a T4:T8 ratio which was significantly lower than that found in normal control individuals. Although patients had normal percentages of Leu7+ and Leu11+ cells, they had depressed NK cell activity against both K562 tumour cells and HSV-1 infected Raji cells. NK cell activity against K562 tumour cells was severely depressed during the first 20 days after injury. This defective NK cell activity did not appear to be due to a defect in PBL binding to the K562 tumour cells. In patients, the level of NK cell activity against HSV-1 infected cells did not correlate with the level of NK cell activity against K562 tumour cells. This finding further supports previous reports showing that NK cells which kill K562 tumour cells are different from the NK cell population which kills HSV-1 infected cells. Pretreatment of PBL obtained from patients with IL-2 or IFN-alpha, in some cases greatly enhanced NK cell killing of K562 tumour cells. However, IL-2 or IFN-alpha did not enhance NK cell activity in patients who had severely depressed levels of NK cell activity. Interestingly, in some patients, differential responsiveness to IL-2 and IFN-alpha was observed. In some patients, NK cell activity was enhanced by IL-2 but not by IFN-alpha. These results, while only suggestive, may indicate that different populations of NK cells respond preferentially to IL-2 and that IFN-alpha and/or IL-2 enhance NK cell activity in PBL obtained from some, but not all, thermal injury patients. Finally, this study clearly shows that thermal injury patients have defective NK cell activity not only against K562 tumour cells but also against virus-infected cells.     

Studies on the role of interleukin-12 in acute murine toxoplasmosis.

Interleukin-12 (IL-12) is important in the regulation of resistance to Toxoplasma gondii in mice with severe combined immunodeficiency (SCID). The protective ability of IL-12 in SCID mice appears to be through its activity on natural killer (NK) cells to induce production of interferon-gamma (IFN-gamma). In this study we assessed the role of IL-12 in the acute stage of toxoplasmosis in immunocompetent mice. Administration of IL-12 to BALB/c mice infected with the virulent C56 strain of T. gondii remarkably delayed time to death. The protective activity of IL-12 was abrogated by administration of monoclonal antibodies to IFN-gamma or tumour necrosis factor-alpha (TNF-alpha), and by depletion of NK cells using an antisera against asialoGM1. Whereas BALB/c mice infected with the ME49 strain of T. gondii survived infection, administration of anti-IL-12 to infected mice resulted in 100% mortality accompanied by decreased serum levels of IFN-gamma. Furthermore, this treatment significantly reversed the suppression of spleen cell proliferation to concanavalin A (Con A), which is associated with the acute stage of infection, and resulted in decreased ex vivo production of IFN-gamma, IL-2, IL-4 and IL-10 in response to Con A. Our results indicate an important role for IL-12 in mediating resistance to T. gondii during acute infection in immunocompetent mice, that NK cells are required for this protective activity, and that IL-12 is involved in the immunosuppression which accompanies this infection.     

Stimulation of murine macrophage cathepsin B by serum from patients with rheumatoid arthritis: an indicator of disease activity.

PHA-induced colony formation and interleukin 2 (IL-2) production were studied in four patients with T cell leukaemia (three cases OKT4+/T helper and one case OKT8+/T cytotoxic suppressor). Cases of T helper cell leukaemia showed colony formation that was comparable to normal purified blood T cells and was not dependent on the addition of conditioned medium, containing IL-2 activity, to cultures. In contrast the T suppressor cell leukaemia formed colonies only when cultures were supplemented with IL-2 containing medium. When IL-2 production by PHA stimulated cells was measured culture supernatants from the three T helper cell leukaemias all showed normal or high levels of activity, when compared to normal blood mononuclear cells, whereas the T suppressor cell leukaemia showed no activity.     

Natural killer cells do not play a dominant role in CD4+ subset differentiation in Candida albicans-infected mice.

The effects of in vivo administration of monoclonal antibodies against NK-1.1-bearing cells on the early production of gamma interferon (IFN-gamma) in vitro and development of Th1-associated immunity were studied in mice infected with a live vaccine strain of Candida albicans. At 1 and 4 days postinfection, natural killer (NK) cell-enriched fractions from the spleens of antibody-treated mice displayed a dramatic reduction in 5E6+ lymphocytes and negligible anti-YAC-1 cytotoxic activity in vitro. Nevertheless, the frequency of IFN-gamma-producing cells in those fractions was reduced by less than half, on average, by anti-NK-1.1 treatment in vivo. In addition, the antibody-treated and infected mice demonstrated unchanged T helper cell responses, as measured by yeast-specific footpad reactions, resistance to reinfection, occurrence of antibodies of different isotypes, and production in vitro of interleukin-2 (IL-2), IFN-gamma, IL-4, and IL-10 by CD4+ cells. Therefore, although NK cells may contribute to early IFN-gamma production in Candida-vaccinated mice, these cells apparently do not play a dominant role in the qualitative development of yeast-specific T helper responses.     

IL-33 amplifies both Th1- and Th2-type responses through its activity on human basophils, allergen-reactive Th2 cells, iNKT and NK cells

IL-33 is an IL-1 family member recently identified as the ligand for T1/ST2 (ST2), a member of the IL-1 receptor family. ST2 is stably expressed on mast cells and T(h)2 effector T cells and its function has been studied in the context of T(h)2-associated inflammation. Indeed, IL-33 induces T(h)2 cytokines from mast cells and polarized mouse T cells and leads to pulmonary and mucosal T(h)2 inflammation when administered in vivo. To better understand how this pathway modulates inflammatory responses, we examined the activity of IL-33 on a variety of human immune cells. Human blood-derived basophils expressed high levels of ST2 receptor and responded to IL-33 by producing several pro-inflammatory cytokines including IL-1 beta, IL-4, IL-5, IL-6, IL-8, IL-13 and granulocyte macrophage colony-stimulating factor. Next, utilizing a human T(h)2-polarized T cell culture system derived from allergic donor blood cells, we found that IL-33 was able to enhance antigen-dependent and -independent T cell responses, including IL-5, IL-13 and IFN-gamma production. IL-33 activity was also tested on V alpha 24-positive human invariant NKT (iNKT) cells. In the presence of alpha-galactosylceramide antigen presentation, IL-33 dose dependently enhanced iNKT production of several cytokines, including both IL-4 and IFN-gamma. IL-33 also directly induced IFN-gamma production from both iNKT and human NK cells via cooperation with IL-12. Taken together, these results indicate that in addition to its activity on human mast cells, IL-33 is capable of activating human basophils, polarized T cells, iNKT and NK cells. Moreover, the nature of the responses elicited by IL-33 suggests that this axis may amplify both T(h)1- and T(h)2-oriented immune responses.     

Naive human T cells can be a source of IL-4 during primary immune responses

IL-4 plays a key role in driving the differentiation of CD4+ Th precursors into Th2 cells, both in mice and in humans. The source of IL-4 during primary immune responses is, however, still debated. When IL-4 consumption in in vitro T cell cultures was blocked with a MoAb to the IL-4 receptor alpha-chain (IL-4Ralpha), it became evident that freshly isolated naive (CD45RO-) CD4+ T cells from adults or cord blood produce IL-4 upon activation with anti-CD3 and CD80. IL-4 production by naive T cells is strictly IL-2-dependent. Endogenous IL-4 activity in naive CD4+ T cell cultures modulates the production of interferon-gamma (IFN-gamma) on the one hand and IL-5 and IL-13 on the other hand in opposite directions, and it is partly responsible for the low IFN-gamma production by cord blood T cells. Comparison of the ratio of IL-4/IFN-gamma in supernatants of T cell cultures reveals a skewing towards IL-4 production by cord blood T cells, while naive T cells from (non-atopic) adults predominantly produce IFN-gamma. We conclude that CD4+ naive T cells can produce IL-4 without the need for Th2 differentiation, and therefore that they can be the initial source of IL-4 required at the time of priming for T cell differentiation into Th2 cells.     

Deficiency of interleukin-2 activity upon addition of soluble egg antigen to cultures of spleen cells from mice infected with Schistosoma japonicum.

Schistosoma japonicum-infected C57BL/6 mice show similar dynamics of hepatic granulomatous inflammation (HGI) and delayed hypersensitivity (DH) elicited by soluble egg antigens (SEA) which reach peak levels at 9 weeks of infection and then spontaneously regress. The in vitro SEA-induced proliferation of spleen cells (SC) from infected animals attained its high point and then declined when SC from 5-week-infected mice were used. The present study determined the dynamics of interleukin-2 (IL-2) production by SEA-challenged SC from infected mice in an attempt to link the level of IL-2 production to the spontaneous regression of the aforementioned T-cell-mediated immune responses. The production of IL-2 by SEA-stimulated SC reached its peak when cells from 7-week-infected mice were challenged at least 2 weeks after the peak of the proliferative response, but declined at about the same time as the HGI and DH responses. Therefore, the decline in IL-2 activity cannot alone explain the diminished proliferative response but could account for the reduction in HGI and DH in vivo. Some possible mechanisms that might explain the IL-2 deficiency were examined. This deficiency is not due to the in vitro binding of IL-2 by the SC of infected mice and is, therefore, likely to be due to underproduction of IL-2. Nor is the deficiency explained by reduced numbers of antigen-presenting cells (macrophages and B cells) or of L3T4+ T lymphocytes or by suppression of IL-2 production by macrophages or macrophage products such as prostaglandins. However, suppression of IL-2 production was observed consistently upon coculture of SC from acutely infected mice with SC from mice infected for 10 weeks. The cells which suppress appear to be Lyt2+ T cells. The data are consistent with the hypothesis that suppressor T cells inhibit the production of IL-2 and perhaps of other cytokines or lymphokines and that this suppression explains the spontaneous down-regulation of HGI which occurs during schistosomiasis japonica.     

Interleukin-18 (IL-18) enhances innate IL-12-mediated resistance to Toxoplasma gondii

Innate resistance to Toxoplasma gondii is dependent on the ability of interleukin-12 (IL-12) to stimulate natural killer (NK) cell production of gamma interferon (IFN-gamma). Since IL-18 is a potent enhancer of IL-12-induced production of IFN-gamma by NK cells, SCID mice (which lack an adaptive immune response) were used to assess the role of IL-18 in innate resistance to T. gondii. Administration of anti-IL-18 to SCID mice infected with T. gondii resulted in an early reduction in serum levels of IFN-gamma but did not significantly decrease resistance to this infection. In contrast, administration of exogenous IL-18 to infected SCID mice resulted in increased production of IFN-gamma, reduced parasite burden, and a delay in time to death. The protective effects of IL-18 treatment correlated with increased NK cell numbers and cytotoxic activity at the local site of administration and with elevated levels of inducible nitrous oxide synthose in the spleens of treated mice. In addition, in vivo depletion studies demonstrated that the ability of exogenous IL-18 to enhance resistance to T. gondii was dependent on IL-12, IFN-gamma, and NK cells. Together, these studies demonstrate that although endogenous IL-18 appears to have a limited role in innate resistance to T. gondii, treatment with IL-18 can augment NK cell-mediated immunity to this pathogen.     

Retrovirally induced switch from production of IL-12 to IL-4 in dendritic cells.

Dendritic cells (DC) in HIV-1 infection show a reduced capacity to stimulate primary T cell proliferation. Exposure of bone marrow-derived DC to Rauscher leukemia virus (RLV) provides a mouse model for studying retrovirally induced reduction in stimulatory capacity for T cells. Treatment with IL-12, a cytokine that promotes the development of Th1 cells, has been postulated as a treatment for AIDS and is effective at restoring cell-mediated immunity in mice infected with mouse AIDS virus or with RLV (see Knight, S. C. and Patterson, S., Annu. Rev. Immunol. 1994. 15: 593-615 for references). Here we studied the direct effect of RLV and of IL-12 on bone marrow-derived DC. Normal DC produced IL-12 and IL-10 and stimulated primary allogeneic T cell proliferation. Exposure of DC to RLV caused reduced production of IL-12, production of IL-4 was seen in DC for the first time and T cell stimulation was inhibited. Addition of IL-12 reinstated and enhanced IL-12 synthesis in RLV-treated DC, abrogated production of IL-10 and IL-4 and restored stimulatory activity. Manipulation of cytokine production in DC could be a stratagem that has evolved in the retrovirus to avoid stimulation of cellular responses.     

IL-18, but not IL-12, is required for optimal cytokine production by influenza virus-specific CD8+ T cells

The potent innate cytokines IL-12 and IL-18 are considered to be important antigen-independent mediators of IFN-gamma production by NK cells and T lymphocytes. The present analysis addresses the physiological role of IL-12 and IL-18 in the generation of virus-specific CD8+ T cells. Both wt C57BL/6J (B6) mice and mice with disrupted IL-12p40 (IL-12p40(-/-)) or IL-18 (IL-18(-/-)) genes were infected with an influenza A virus and the characteristics of the resultant epitope-specific CD8+ T cell responses were compared. While IL-12 appeared to have no notable effect on either virus growth or on CD8+ T cell response profiles, the absence of IL-18 was associated with delayed virus clearance from the lung and, despite normal numbers, a significantly reduced production of IFN-gamma, TNF-alpha, and IL-2 by epitope-specific CD8+ T cells. While this cytokine phenotype was broadly maintained in IL-12p40/IL-18 double-knockout mice, no evidence was seen for any additive effect. Together, our results suggest that IL-18, but not IL-12, induces optimal, antigen-specific production of key cytokines by CD8+ T cells for the efficient clearance of influenza virus from the lungs of infected mice.     

Cutaneous leishmaniasis: co-ordinate expression of granzyme A and lymphokines by CD4+ T cells from susceptible mice.

We have recently demonstrated that the frequency of T cells expressing granzyme A is significantly higher in skin lesions and spleens of susceptible BALB/c mice compared with resistant C57BL/6 mice infected with Leishmania major, a cause of human cutaneous leishmaniasis. In the present study, we have performed in vitro studies to characterize the subpopulation, the antigen responsiveness and the lymphokine production pattern of granzyme A-expressing T cells in L. major-infected mice. Using a limiting dilution system for functional analysis of selected T cells at the clonal level, we could show that granzyme A activity in infected BALB/c mice can be assigned to L. major-reactive CD4+ T cells secreting interleukin-2 (IL-2) and IL-4. Granzyme A production was most pronounced in the early phase of infection. On the other hand, granzyme A expression could not be detected in C57BL/6-derived T cells responding to L. major. The data support the suggestion that granzyme A is produced by L. major-responsive CD4+ T cells facilitating lesion formation and the dissemination of infection.     

Immunosuppression during acute Trypanosoma cruzi infection: involvement of Ly6G (Gr1(+))CD11b(+ )immature myeloid suppressor cells

Trypanosoma cruzi infection is associated with a severe unresponsiveness of spleen cells (SC) to antigens and mitogens. A high production of NO by concanavalin A (Con A)-stimulated SC from infected but not from control mice was observed. Neutralization of endogenous IFN-gamma production or treatment with NO synthase (NOS) inhibitor, L-N-monomethyl-arginine, blocked Con A-induced NO production and greatly restored proliferation by SC from infected mice. This was confirmed by using IFN-gammaR(-/-) and inducible NOS (iNOS)(-/- )knockout mice, since unresponsiveness to mitogens of SC from those infected mice was much less pronounced than in control littermates. Interestingly, SC unresponsiveness was associated with a huge increase in CD11b(+) cells that express Ly-6G (Gr1)(+) and other immature myeloid markers These cells were absent in infected IFN-gammaR(-/-) spleens. Purified immature Gr1(+)CD11b(+) cells produced NO and expressed iNOS upon IFN-gamma treatment, and were able to inhibit T cell proliferation. In addition, depletion of myeloid CD11b(+ )cells abrogated NO production and restored mitogen-induced proliferation, but not IL-2 synthesis, in SC from infected mice. IL-2 production and CD25 cell surface expression by mitogen-activated T cells were greatly depressed in SC from IFN-gammaR(-/-) and iNOS(-/- )mice, confirming that Gr1(+)CD11b(+) cells were not involved in their down-regulation. In contrast, IL-5, tumor necrosis factor and IFN-gamma production, and CD69 expression by T cells were not depressed in infected SC. The results indicate the existence of an immunosuppressive mechanism during T. cruzi infection, mediated through IFN-gamma-dependent NO secretion by immature Ly-6G (Gr1)(+)CD11b(+ )myeloid cells.     

Interferon-gamma inhibits the efficacy of interleukin 1 to generate a Th2-cell biased immune response induced by Leishmania major.

Splenic adherent cells from L. major-infected resistant and susceptible mice were restimulated in vitro and analyzed for the expression of IL-1 activity. Three weeks or later after infection, cells from parasite infected susceptible BALB/c mice produced substantially more IL-1 activity than those from non-infected controls or from L. major-infected resistant C57BL/6 animals. More than 95% of the IL-1 bioactivity was mediated by IL-1 alpha, as determined by blocking experiments with an anti-IL-1 alpha antiserum. The strain-specific differences in IL-1 production correlated with different accumulation of IL-1 producing adherent cells in the spleens of infected animals, but also with different IL-1 producing capacity on a per cell basis. When adherent cells were mixed with syngeneic IFN-gamma producing CD4+ T lymphocytes from L. major-infected C57BL mice or from animals that had been pretreated with anti-CD4 monoclonal antibody prior to infection, the level of detectable IL-1 decreased depending on the number of T cells added. This inhibition could be blocked completely with an anti-IFN-gamma antibody. No such effect was seen, when CD4+ cells were used that were derived from parasite-infected BALB/c mice and did not produce IFN-gamma. In contrast to L. major, L. donovani antigen not only failed to induce IL-1 production, but also dose-dependently suppressed the IL-1 activity elaborated by L. major antigen. We conclude from these data that IFN-gamma effectively inhibits the efficacy to IL-1 to generate to Th2-cell biased immune response induced by L. major. A T cell independent and as yet unknown mechanism to inhibit the IL-1 response is used by L. donovani.