Showing papers by "Thomas A. Wynn published in 1998"

CD4+ T Cell–mediated Granulomatous Pathology in Schistosomiasis Is Downregulated by a B Cell–dependent Mechanism Requiring Fc Receptor Signaling

Abstract: The effector functions of CD4+ T lymphocytes are generally thought to be controlled by distinct populations of regulatory T cells and their soluble products. The role of B cells in the regulation of CD4-dependent host responses is less well understood. Hepatic egg granuloma formation and fibrosis in murine schistosomiasis are dependent on CD4+ lymphocytes, and previous studies have implicated CD8+ T cells or cross-regulatory cytokines produced by T helper (Th) lymphocytes as controlling elements of this pathologic process. In this report, we demonstrate that B cell–deficient (μMT) mice exposed to Schistosoma mansoni develop augmented tissue pathology and, more importantly, fail to undergo the spontaneous downmodulation in disease normally observed during late stages of infection. Unexpectedly, B cell deficiency did not significantly alter T cell proliferative response or cause a shift in the Th1/Th2 balance. Since schistosome-infected Fc receptor–deficient (FcR γ chain knockout) mice display the same exacerbated egg pathology as that observed in infected μMT mice, the B cell– dependent regulatory mechanism revealed by these experiments appears to require receptor-mediated cell triggering. Together, the data demonstrate that humoral immune response/FcR interactions can play a major role in negatively controlling inflammatory disease induced by CD4+ T cells.

IL-10 Regulates Liver Pathology in Acute Murine Schistosomiasis mansoni But Is Not Required for Immune Down-Modulation of Chronic Disease

Abstract: We have used IL-10 gene knockout mice (IL-10T) to examine the role of endogenous IL-10 in the down-modulation of hepatic granuloma formation and lymphocyte responses that occurs in chronic infection with the helminth parasite Schistosoma mansoni. Although IL-10-deficient animals showed 20 to 30% mortality between 8 and 14 wk postinfection, they displayed no alterations in their susceptibility to infection and produced similar numbers of eggs as their wild-type littermates. The IL-10T mice displayed a significant increase in hepatic granuloma size at the acute stage of infection, which was associated with increased IFN-gamma, IL-2, IL-1beta, and TNF-alpha mRNA expression in liver and elevated Th1-type cytokine production by lymphoid cells. Despite developing an enhanced Th1-type cytokine response, the IL-10T mice showed no consistent decrease in their Th2-type cytokine profile. Surprisingly, although granulomatous inflammation was enhanced at the acute stage of infection, the livers of IL-10T mice displayed no significant increase in fibrosis and underwent normal immune down-modulation at the chronic stage of infection. Moreover, the down-modulated state could be induced in IL-10T mice by sensitizing the animals to schistosome eggs before infection, further demonstrating that the major down-regulatory mechanism is not dependent upon IL-10. We conclude that while IL-10 plays an important role in controlling acute granulomatous inflammation, it plays no essential role in the process of immune down-modulation in chronic schistosome infection.

IFN-gamma, IL-12, and TNF-alpha are required to maintain reduced liver pathology in mice vaccinated with Schistosoma mansoni eggs and IL-12.

Abstract: The development of hepatic fibrosis and portal hypertension is the principal cause of morbidity and mortality in schistosomiasis mansoni. Nevertheless, relatively little is known about the mechanisms that lead to excessive collagen deposition during infection with Schistosoma mansoni . In the murine model, infection leads to significant egg-induced granuloma formation, tissue eosinophilia, and hepatic fibrosis. The pathology has been linked to dominant type 2 cytokine expression, and our recent studies showed that sensitizing animals to egg Ags in combination with IL-12, before infection, led to a highly significant reduction in egg-induced immunopathology. In this study, we demonstrate that in contrast with egg/IL-12-sensitized animals that showed marked decreases in pathology, mice similarly sensitized but depleted of IFN-γ, IL-12, or TNF-α at the time of egg laying developed granulomas that were similar to the non-IL-12-treated control group. Although all three anti-cytokine-treated groups exhibited a dominant type 1 response in lymph node cells restimulated ex vivo, the expression of type 2 cytokine mRNA was markedly restored at the site of granuloma formation, which suggests that all three cytokines are required to maintain the suppressed type 2 pattern. Moreover, egg/IL-12-sensitized mice depleted of IFN-γ or IL-12 displayed a partial reduction in IFN-γ production, suggesting that multiple type 1 cytokines were required to maintain polarized type 1 responses to chronic type 2-inducing stimuli. Together, these data reveal key roles for IFN-γ, IL-12, and TNF-α in the protective effects mediated by this IL-12-based vaccine to prevent pathology.

Inducible nitric oxide synthase-deficient mice develop enhanced type 1 cytokine-associated cellular and humoral immune responses after vaccination with attenuated Schistosoma mansoni cercariae but display partially reduced resistance.

Abstract: High levels of nitric oxide (NO) are produced by inducible nitric oxide synthase (iNOS) in response to activating signals from Th1-associated cytokines and play an important role in cytotoxicity and cytostasis against many pathogenic microorganisms. In addition to its direct effector function, NO serves as a potent immunoregulatory factor. NO produced by gamma interferon-activated macrophages immobilizes and kills Schistosoma mansoni larvae, and several studies have indicated a role for this pathway in protective immunity against this parasite. The potential regulatory influence of NO in immunity to S. mansoni is less well understood. In this study, we have used iNOS-deficient mice to determine the role of NO in mice vaccinated with irradiated cercariae of S. mansoni. We show by enzyme-linked immunosorbent assay and reverse transcriptase PCR analysis that vaccinated iNOS-deficient mice develop exacerbated type 1 cytokine responses in the lungs, the site where resistance to infection is primarily manifested. In addition, parasite-specific immunoglobulin G2a (IgG2a) and IgG2b antibody responses were significantly increased in vaccinated iNOS-deficient animals and total IgE antibody levels in serum were decreased relative to those in wild-type controls. Surprisingly, since resistance in this vaccine model is largely Th1 dependent and since Th1-related cellular and humoral immune responses were found to be exacerbated in vaccinated iNOS-deficient mice, vaccine-elicited protective immunity against challenge infection was found to be reduced. These findings demonstrate that iNOS plays a paradoxical role in immunity to S. mansoni, both in the effector mechanism of resistance and in the down regulation of the type 1 cytokine response, which is ultimately required for NO production.

Role of cytokines in the formation and downregulation of hepatic circumoval granulomas and hepatic fibrosis in Schistosoma mansoni-infected mice

Abstract: Schistosoma mansoni infections are associated with a strong Th2 cytokine response. Treatment of mice with IL-12 or anti-IL-2 or anti-IL-4 before i.v. injection of eggs increased IFN-g production and downregulated Th2 responses and pulmonary granuloma size. Conversely, anti-IFN-g antibody treatment increased Th2 responses and granuloma size. Similar manipulation produced less dramatic results in infected mice. However, sensitization of mice with eggs + IL-12 before infection augmented the Th1 response and decreased Th2 cytokines, granuloma size and fibrosis. Antisera to IFN-g, TNF-a or IL-12 during IL-12-egg immunization partly restored granuloma size and fibrosis following infection. Variations in the size of granulomas in acute (8 week) infections may be influenced primarily by the number and state of activation of T cells. In chronic (12-16 week) infections immunologic downmodulation proceeded normally in mice without functional CD8+ cells and in IFN-g KO mice but not in B cell KO (mMT) mice or in mice deficient in FcR expression in spite of the fact that these mice downregulated their T cell and cytokine responses. It is evident that the participation of cytokines in granuloma formation and regulation is complicated and that the mechanisms controlling both these phenomena are likely to involve both T cells and antibody/FcR interactions.

Cytokines as determinants of disease and disease interactions.

Abstract: The immune response to pathogens results in both host resistance and immunopathology. Cytokines and in particular those lymphokines produced by Th1 and Th2 cells play a key role in determining the balance between these two immunologic outcomes. Recent data suggest that interleukin-10, a product of both Th2 cells and macrophages, protects the host against excessive immunopathology. The cytokine environment generated by different pathogens may also influence the course and outcome of infections with unrelated organisms. This relationship may be particularly important in the case of HIV-1 where prior Th1 or Th2 biases established by helminth or intracellular infections may influence either initial viral susceptibility or drive progression to AIDS through immune activation.

Failure of P strain mice to respond to vaccination against schistosomiasis correlates with impaired production of IL-12 and up-regulation of Th2 cytokines that inhibit macrophage activation.

Abstract: In contrast to most inbred strains, P mice fail to develop significant resistance to Schistosoma mansoni infection as a result of vaccination with either radiation-attenuated cercariae or schistosome antigens plus Bacillus Calmette Guerin, and this failure correlates with defects in macrophage larvicidal activity Supernatant fluids from antigen-treated in vitro cultures of splenocytes from vaccinated P mice demonstrate less macrophage stimulatory activity than do supernatants from cells of vaccine-responsive strains such as C57BL/6 This is not due either to diminished production of the macrophage-activating cytokine IFN-gamma by P mice, or to a lesser responsiveness of macrophages from P mice to activation by IFN-gamma Rather, P splenocytes produce two-to threefold higher amounts of IL-4 and IL-10, cytokines which down-regulate the cytotoxic potential of IFN-gamma-treated macrophages Thus, the macrophage-activating potential of cytokine preparations from vaccinated P mice can be completely recovered by in vitro treatment with antibodies to IL-4 or IL-10 Moreover, lower levels of IL-12, a cytokine involved in promoting development of Th1 responses, are produced by splenocytes from P mice as compared to C57BL/6 counterparts These studies indicate that a genetic predisposition toward an impaired production of IL-12 and an increased production of down-regulatory Th2 cytokines correlate with low response to vaccination against S mansoni

Preliminary results on the regulatory role of IFN-gamma and IL-10 human schistosomiasis mansoni.

Abstract: cells from Schistosomamansoni infected mice produced large amounts ofIL-10 and that this response was temporally andmechanistically linked to the downregulation of theTh1 cytokine response (A Sher et al. 1991 JImmunol 147: 2713-2716). The addition of neu-tralizing anti IL-10 mAb to the cultures resulted inan increase in IFN- g production to levels approach-ing those seen before the egg laying phase (EJPearce & A Sher 1991 Exper Parasitol 73: 110-116). Thus, it is clear from in vitro studies on theregulation of cytokine production and the obser-vation of the Th1 and Th2 profiles during S.mansoni infection in mice that Th1 and Th2 re-sponses are counter-regulatory. However, the roleof IL-10 in controlling the cytokine response maybe dependent on the immunological backgroundof the host. T Wynn et al. (1997 J Immunol 159:5014-5023) studied S. mansoni egg induced granu-loma formation and cytokine production in knock-out mice which suggested that IL-10 may play akey role in controlling the development of bothtype 1 and type 2 responses.The present study aimed to compare thecytokine pattern in acute and chronic schistoso-miasis patients and to study the contribution of IL-10 and IFN-g to the regulation of Th1 and Th2 re-sponses.The patients selected for the study presentedacute (n=7), intestinal (n=6), hepatointestinal (n=1)or hepatosplenic (n=9) schistosomiasis mansoni asdefined previously (AD Coutinho & ALCDomingues 1987 Mem Inst Oswaldo Cruz 82 : 335-337). The control group was composed of healthyBrazilian individuals.The cytokine pattern elicited in response tosoluble egg antigens (SEA) and soluble wormadult preparation (SWAP) were compared in acuteand chronic patients. In the absence of IL-10 neu-tralization, the acute patients responded to SEAand SWAP by producing significant quantities ofIFN-g when compared with the chronic patients.There was also a significant IL-10 response incells obtained from acute and chronic patients.Neutralization of IL-10 had no significant effecton the already high levels of IFN-g produced inresponse to SEA in acute patients, while IFN-gproduction was significantly high in chronic pa-tient cells, suggesting that the cytokine regula-tory mechanisms may be different in acute andchronic infection. Neutralization of IFN- g resultedin similarly increased levels of IL-10 in acute andchronic patients, while IL-4 and IL-5 were notaffected, suggesting a counter-regulatory rolebetween IFN-g and IL-10. When spleen ofhepatosplenic patients were used in the experi-ments, the results were similar to those found inperipheral blood mononuclear cells, suggestingthat there is no anatomic differences in the ex-pression of cytokines in antigen stimulated cul-tures where IL-10 was neutralized. These studiesdemonstrate that early infection with S. mansoniis associated with a significant IFN- g response andIL-10 plays an important down-regulatory role inthat response during late infection.