IL-10 and TGF-beta redundantly protect against severe liver injury and mortality during acute schistosomiasis

The cytokines IL-10 and TGF-beta regulate immunity and inflammation. IL-10 is known to suppress the extent of hepatic damage caused by parasite ova during natural infection with Schistosoma mansoni, but the role of TGF-beta is less clear. Cytokine blockade studies in mice revealed that anti-IL-10R mAb treatment during acute infection modestly increased cytokine production and liver damage, whereas selective anti-TGF-beta mAb treatment had marginal effects. In contrast, mice administered both mAbs developed severe hepatic inflammation, with enlarged, necrotic liver granulomas, cachexia, and >80% mortality by 8 wk postinfection, despite increased numbers of CD4(+)CD25(+)Foxp3(+) T regulatory cells. Blocking both IL-10 and TGF-beta at the onset of egg production also significantly increased IL-4, IL-6, TNF, IFN-gamma, and IL-17 production and markedly increased hepatic, peritoneal, and splenic neutrophilia. In contrast, coadministration of anti-IL-10R and TGF-beta mAbs had little effect upon parasite ova-induced intestinal pathology or development of alternatively activated macrophages, which are required to suppress intestinal pathology. This suggests that inflammation is controlled during acute S. mansoni infection by two distinct, organ-specific mechanisms: TGF-beta and IL-10 redundantly suppress hepatic inflammation while intestinal inflammation is regulated by alternatively activated macrophages.     

Egg deposition is the major stimulus for the production of Th2 cytokines in murine schistosomiasis mansoni.

To characterize Th cell populations induced by helminth infection, spleen cells from mice infected with Schistosoma mansoni were stimulated with parasite (worm or egg Ag) or mitogen (Con A) and the supernatants assayed for the Th1-specific cytokines IFN-gamma and IL-2 and the Th2-specific cytokines IL-4 and IL-5. Th2 cytokine production was not detected in substantial quantity until the 6 to 8th wk of infection and after reaching peak levels at 8 to 12 wk declined slowly thereafter. The time courses of IL-4 and IL-5 production, whereas differing from each other, closely resembled corresponding published data on IgE and peripheral blood eosinophil levels during murine schistosome infection. In contrast, Th1 cytokine responses occurred only during the first 6 wk of infection and were virtually absent during the peak period of Th2 production. To assess the role of egg deposition in the observed pattern of Th response, cytokine production was assayed in mice carrying unisexual schistosome infections in which parasite eggs are absent. Splenocytes from these animals displayed only marginal Th2 cytokine synthesis but greater Th1 cytokine responses than the corresponding cells from mice with bisexual infections. Moreover, cultures of liver tissue or isolated granulomas from infected mice constitutively produced high levels of IL-4 and IL-5 but failed to synthesize significant amounts of IL-2 and IFN-gamma even when stimulated with egg Ag or mitogen. Taken together the data indicate that egg deposition is the major stimulus of Th2 cytokine response in S. mansoni-infected mice and suggest that T cells belonging to this subset must play a major role in egg granuloma formation.     

The pathogenic Th17 cell response to major schistosome egg antigen is sequentially dependent on IL-23 and IL-1β

CBA/J mice infected with the helminth Schistosoma mansoni develop severe CD4 T cell-mediated hepatic granulomatous inflammation against parasite eggs associated with a robust Th17 cell response. We investigated the requisites for Th17 cell development using novel CD4 T cells expressing a transgenic TCR specific for the major Sm-p40 egg Ag, which produce IL-17 when stimulated with live schistosome eggs. Neutralization of IL-23 or blockade of the IL-1 receptor, but not IL-6 neutralization, abrogated egg-induced IL-17 secretion by transgenic T cells, whereas exogenous IL-23 or IL-1β reconstituted their ability to produce IL-17 when stimulated by syngeneic IL-12p40-deficient dendritic cells. Kinetic analysis demonstrated that IL-17 production was initiated by IL-23 and amplified by IL-1β. Significantly, schistosome-infected IL-12p40-deficient or IL-1R antagonist-treated CBA/J mice developed markedly reduced hepatic immunopathology with a dampened egg Ag-specific IL-17 response. These results demonstrate that the IL-23-IL-1-IL-17 axis has a central role in the development of severe schistosome egg-induced immunopathology.     

Experimental murine schistosomiasis in the absence of B7 costimulatory molecules: reversal of elicited T cell cytokine profile and partial inhibition of egg granuloma formation

The granulomatous inflammation in infection with the helminth Schistosoma mansoni represents a cellular hypersensitivity reaction mediated by, and dependent upon, MHC class II-restricted CD4+ Th cells sensitized to parasite egg Ags. The current work examines the role and significance of the B7:CD28/CTLA-4 pathway in providing the costimulation necessary for the activation of these pathogenic T cells. In vitro T cell responses in B7-1-/- mice, 7-8 wk postinfection, were no different from wild-type controls, but the absence of B7-2 molecules resulted in a decrease in egg Ag-induced proliferation with increased IFN-gamma production. Both B7-1-/- and B7-2-/- mice exhibited intact granuloma formation. In contrast, CD4+ Th cells from B7-1/2 double-deficient mice displayed a dramatic loss of proliferative capacity upon stimulation with egg Ag. Most strikingly, these T cells secreted only IFN-gamma, but not IL-4 and IL-10, a pattern entirely opposite to that displayed by wild-type controls. Despite these major differences in T cell reactivity, B7-1/2-/- mice had only a limited reduction of granuloma size and fibrosis, without appreciable difference in cellular composition. These results show that substantial granuloma formation can occur under conditions of limited T cell expansion and restricted Th1-type cytokine production. They also support the notion that the combined effect of B7 signaling is not as critical for Th1 cell activation as it is for the development of the Th2 dominant environment characteristic of the evolving schistosome infection in H-2b mice.     

Neonatal exposure to idiotype induces Schistosoma mansoni egg antigen-specific cellular and humoral immune responses.

Exposure of neonatal mice to appropriate, cross-reactive Id (CRI) preparations alters immune responsiveness, ameliorates pathology, and prolongs survival of animals upon subsequent Schistosoma mansoni infection. However, because schistosome infections profoundly affect host immunobiology, which responses are effected by neonatal Id exposure alone and which responses are influenced by infection is unclear. To directly examine the schistosome soluble egg Ag (SEA)-specific immune responses altered by CRI exposure, neonatal mice were injected with CRI-expressing (CRI+) SEA-specific Ab preparations, SEA-specific Abs that did not express CRI (CRI-), or normal mouse Ig. At 9 wk of age, only mice that were neonatally exposed to CRI+ anti-SEA Abs displayed significant SEA-specific IgG serum levels and spleen cell proliferative responses. SEA-stimulated spleen cells from these CRI+-exposed mice also produced IFN-gamma, although not at significantly higher levels than mice receiving CRI- Id or normal mouse Ig. If CRI+-exposed mice were also injected with SEA at 8 wk of age, the 9-wk IFN-gamma responses were significantly higher than those of the other neonatal injection groups. The presence of both CRI and anti-CRI in the sera of animals neonatally injected with CRI, but receiving no exposure to S. mansoni Ags or infection, suggested a functional idiotypic network led to these responses. These data demonstrate that appropriate idiotypic exposure induces B and T cell responsiveness to the Ag recognized by the Id and support the hypothesis that neonatal idiotypic exposure can be an important immunoregulatory factor in schistosomiasis.     

IL-4 influences IL-2 production and granulomatous inflammation in murine schistosomiasis mansoni.

In previous studies the dynamics of IL-2 production by splenic cells of Schistosoma mansoni infected mice was correlated with the intensity of hepatic granulomatous inflammation. To extend those observations, the present studies examined the role of IL-4 on the immune responsiveness of infected mice. The dynamics of IL-4 production by soluble egg Ag-stimulated splenic cells was similar to that of IL-2: minimal levels at the pre-oviposition or early worm egg deposition stages (4 to 6 wk) peak production coincident with maximal granulomatous response (8 wk) followed by a concurrent decline at the chronic stage (18 to 20 wk) in both parameters. Addition of murine rIL-4 to splenocyte cultures of acutely or chronically infected mice did not significantly enhance the soluble egg Ag-elicited proliferative response. Daily injections of rIL-4 (10 to 1000 U) given for 14 days to groups of mice with acute infection, at the high dose-enhanced IL-2, but not IL-4, production. Similar treatment given to chronically infected mice did not augment diminished lymphokine production. Chronically infected mice treated with 10 to 1000 U of rIL-4 showed significantly enhanced liver granulomatous responses compared with untreated animals and the augmented granulomas contained more enlarged macrophages and connective tissue matrix. Repeated injections of anti-IL-4 mAb (11B11) given to acutely infected mice significantly suppressed splenic cell proliferation, IL-2 and IL-4 production, and hepatic granulomatous inflammation. Similar treatment given to chronically infected mice also diminished the down-modulated granulomatous response. These data demonstrate that IL-4 plays an important role in the egg-directed granulomatous response and participates in the regulation of Ag-specific lymphoproliferation, and IL-2 and IL-4 production during the course of the infection.     

Cutting edge: IPSE/alpha-1, a glycoprotein from Schistosoma mansoni eggs, induces IgE-dependent, antigen-independent IL-4 production by murine basophils in vivo

During infection with the helminth parasite Schistosoma mansoni, the deposition of eggs coincides with the onset of IL-4 production and Th2 development. Although IL-4 is known as a potent inducer of Th2 differentiation, the mechanism by which schistosome eggs induce IL-4 production is not clear. In this study, we demonstrate that the S. mansoni egg Ag (SmEA) induces IgE-dependent IL-4 production by basophils derived from Heligmosomoides polygyrus-infected or OVA/alum-immunized mice in the absence of pathogen-specific IgE. The effect is mediated by the secretory glycoprotein IPSE/alpha-1, because IPSE/alpha-1-depleted SmEA no longer induces cytokine production. Conversely, recombinant IPSE/alpha-1 is sufficient to induce IL-4 production. Importantly, the injection of SmEA or recombinant IPSE/alpha-1 into H. polygyrus-infected 4get/KN2 IL-4 reporter mice rapidly induces the dose-dependent IL-4 production by basophils in the liver, a major site of egg deposition. Thus, IPSE/alpha-1 induces basophils to produce IL-4 even in the absence of Ag-specific IgE.     

Dynamics of the cytokine messenger RNA expression pattern in the liver of baboons infected with Schistosoma mansoni

Periovular granulomas are the major lesions in baboons infected with Schistosoma mansoni. Temporal Northern blot analysis of cytokine messenger RNA (mRNA) expression in granulomatous baboon livers demonstrated tissue-specific expression. Interleukin 1 beta (IL-1beta, IL-6, tumor necrosis factor alpha, and migration inhibitory factor (MIF) mRNAs were expressed strongly at week 6 of infection and decayed thereafter, whereas interferon gamma (IFN-gamma), IL-2, IL-10, and IL-12 mRNAs were first expressed at week 12, with IFN-gamma and IL-12 mRNA expression persisting until week 17. IL-4 and IL-5 mRNAs first appeared at week 12, with IL-4 persisting unchanged and IL-5 increasing by week 17. Thus, egg deposition induced strong hepatic expression of proinflammatory and downregulatory cytokines. The cooccurrence of IL-2, IFN-gamma, IL-4, and IL-5 mRNAs at week 12 confirms that baboons, like humans, show a mixed type 1-type 2 cytokine response. When granulomas had become smaller at 17 wk, IFN-gamma, IL-4, and IL-5 were the only cytokine mRNAs that were expressed strongly, implicating them in granuloma modulation. The early expression of MIF mRNA and MIF's role as the main counterregulator of glucocorticoid immunosuppression ties in with our earlier demonstrations of circulating adrenal steroids changing with the progression of schistosomiasis in baboons and of proinflammatory cytokine mRNA expression in the hypothalamic-pituitary-adrenal axis tissues of infected baboons. Together, these data imply neuroendocrinological influences on disease progression in schistosomiasis.     

Production of IL-10 by CD4+ T lymphocytes correlates with down-regulation of Th1 cytokine synthesis in helminth infection.

After the onset of parasite egg deposition, mice infected with the helminth Schistosoma mansoni mount strong Th2 cytokine responses in the absence of significant Th1 cytokine synthesis. To examine the basis of this immunoregulatory state, spleen or lymph node cells from schistosome-infected mice were stimulated with parasite-specific Ag and the supernatants tested for their capacity to suppress IFN-gamma synthesis by a Th1 cell line. Strong inhibition was observed that was neutralized by a mAb against IL-10, a cytokine previously shown to down-regulate Th1 cytokine synthesis. By means of ELISA measurements the production of IL-10 in schistosome infection was confirmed and shown to depend on CD4+ T cells. IL-10 synthesis stimulated by either mitogen or Ag was observed only at those stages of infection when Th2 response induction and Th1 cytokine down-regulation also occurred and was not detected in mice vaccinated with attenuated parasites. Moreover, the addition of the neutralizing anti-IL-10 mAb to Ag-stimulated spleen cell cultures from infected mice caused a dramatic augmentation in IFN-gamma synthesis. These findings suggest that IL-10 is responsible for the down-regulation of Th1 responses observed in schistosome infections, a phenomenon that may enable the parasite to escape potentially harmful cell-mediated responses.     

Differential regulation of nitric oxide synthase-2 and arginase-1 by type 1/type 2 cytokines in vivo: granulomatous pathology is shaped by the pattern of L-arginine metabolism.

Type 2 cytokines regulate fibrotic liver pathology in mice infected with Schistosoma mansoni. Switching the immune response to a type 1-dominant reaction has proven highly effective at reducing the pathologic response. Activation of NOS-2 is critical, because type 1-deviated/NO synthase 2 (NOS-2)-deficient mice completely fail to control their response. Here, we demonstrate the differential regulation of NOS-2 and arginase type 1 (Arg-1) by type 1/type 2 cytokines in vivo and for the first time show a critical role for arginase in the pathogenesis of schistosomiasis. Using cytokine-deficient mice and two granuloma models, we show that induction of Arg-1 is type 2 cytokine dependent. Schistosome eggs induce Arg-1, while Mycobacterium avium-infected mice develop a dominant NOS-2 response. IFN-gamma suppresses Arg-1 activity, because type 1 polarized IL-4/IL-10-deficient, IL-4/IL-13-deficient, and egg/IL-12-sensitized animals fail to up-regulate Arg-1 following egg exposure. Notably, granuloma size decreases in these type-1-deviated/Arg-1-unresponsive mice, suggesting an important regulatory role for Arg-1 in schistosome egg-induced pathology. To test this hypothesis, we administered difluoromethylornithine to block ornithine-aminodecarboxylase, which uses the product of arginine metabolism, L-ornithine, to generate polyamines. Strikingly, granuloma size and hepatic fibrosis increased in the ornithine-aminodecarboxylase-inhibited mice. Furthermore, we show that type 2 cytokine-stimulated macrophages produce proline under strict arginase control. Together, these data reveal an important regulatory role for the arginase biosynthetic pathway in the regulation of inflammation and demonstrate that differential activation of Arg-1/NOS-2 is a critical determinant in the pathogenesis of granuloma formation.     

IL-10 synergizes with IL-4 and transforming growth factor-beta to inhibit macrophage cytotoxic activity.

After activation with IFN-gamma, thioglycollate-elicited murine peritoneal macrophages kill schistosomula of Schistosoma mansoni in vitro by an L-arginine-dependent mechanism which involves the production of reactive nitrogen oxides (NO). In the present study we demonstrate that the regulatory cytokines IL-10, IL-4, and transforming growth factor-beta (TGF-beta) are potent inhibitors of this extracellular killing function of activated macrophages. Each cytokine was found to suppress killing of schistosomula in a dose-dependent fashion. The activity of IL-10 was not permanent, because subsequent treatment with additional IFN-gamma 2 to 6 h later reversed the inhibition of macrophage larval killing. More importantly, the combination of suboptimal levels of any two of these three cytokines was found to give a potent synergistic suppression of schistosomulum killing by IFN-gamma-treated macrophages. Similarly, IL-10, IL-4, or TGF-beta alone blocked the production of NO, and when used in combination these cytokines exhibited an enhanced inhibitory effect on nitrite production. Macrophage-mediated killing of schistosomula through the generation of NO has been shown previously to be a major effector mechanism of schistosome immunity. The results presented here suggest that the suppression of this mechanism by induction of the regulatory cytokines IL-10, IL-4, and TGF-beta, which are known to be produced during schistosome infection, may be an important strategy used by the parasite to evade macrophage-mediated immune destruction.     

Helminth-modified pulmonary immune response protects mice from allergen-induced airway hyperresponsiveness

It has been shown that the presence of certain helminth infections in humans, including schistosomes, may reduce the propensity to develop allergies in infected populations. Using a mouse model of schistosome worm vs worm + egg infection, our objective was to dissect the mechanisms underlying the inverse relationship between helminth infections and allergies. We have demonstrated that conventional Schistosoma mansoni egg-laying male and female worm infection of mice exacerbates airway hyperresponsiveness. In contrast, mice infected with only schistosome male worms, precluding egg production, were protected from OVA-induced airway hyperresponsiveness. Worm-infected mice developed a novel modified type 2 cytokine response in the lungs, with elevated allergen-specific IL-4 and IL-13 but reduced IL-5, and increased IL-10. Although schistosome worm-only infection is a laboratory model, these data illustrate the complexity of schistosome modulation of host immunity by the worm vs egg stages of this helminth, with the potential of infections to aggravate or suppress allergic pulmonary inflammation. Thus, infection of mice with a human parasitic worm can result in reduced airway inflammation in response to a model allergen.     

Treatment with anti-IL-2 antibodies reduces hepatic pathology and eosinophilia in Schistosoma mansoni-infected mice while selectively inhibiting T cell IL-5 production.

Granulomas around Schistosoma mansoni eggs are a principal cause of morbidity in mice infected with this helminth. In vivo treatment of infected mice with anti-IL-2 antibodies, with or without anti-IL-2 receptor antibodies, significantly diminished the size of circumoval granulomas in the liver and decreased hepatic fibrosis to half that in untreated mice. Antibody-treated animals also displayed a marked reduction in both peripheral blood and tissue eosinophilia while IgE levels were unchanged or increased. Spleen cell cytokine production in response to Ag or mitogen stimulation was selectively altered by in vivo anti-IL-2 administration. IL-5 responses were dramatically reduced, whereas IL-4, IL-2, and IFN-gamma responses were not consistently changed. These findings confirm previous observations, suggesting a role for IL-2 in egg-induced pathology but indicate that the primary function of this cytokine in schistosome-infected mice may be in the generation of Th2- rather than Th1-associated responses.     

Schistosoma mansoni eggs induce antigen-responsive CD44-hi T helper 2 cells and IL-4-secreting CD44-lo cells. Potential for T helper 2 subset differentiation is evident at the precursor level.

Schistosoma mansoni eggs are potent inducers of biased Th2-like immune responses. Using a model system where mice are immunized with isolated schistosome eggs, we demonstrate that CD44 expression, up-regulation of which has been linked to Th cell development, is increased on Th2 cells. We also investigate the functional properties of CD44-lo Th cells recovered from the overtly Th2 environment constituted by lymph nodes draining sites of egg deposition. Production of high levels of IL-4, IL-5, and IL-10 by Th cells responding to egg Ag is shown to be the property of a subpopulation expressing CD44-hi. This population of Th cells cosegregates with a blasting subpopulation expressing more IL-4R (but similar amounts of IL-2R) than Th cells from normal mice. These results indicate that mature Th2 cells responding to schistosome eggs are CD44-hi and suggest that they use IL-4 as a growth factor. In contrast, CD44-lo cells sorted from lymph node populations responding to eggs are able to produce small amounts of IL-4 and IL-2, but no IL-5 or IL-10. This is surprising, because low expression of CD44 is considered a characteristic of Th cell naivite and concomitant ability to produce only IL-2. Thus, in lymph nodes responding to schistosome eggs, potential for Th2 subset differentiation is evident within the CD44-lo precursor Th subpopulation.     

Induction of IL-13 triggers TGF-beta1-dependent tissue fibrosis in chronic 2,4,6-trinitrobenzene sulfonic acid colitis

To investigate the immunopathogenesis of inflammation-associated fibrosis, we analyzed the chronic colitis and late-developing fibrosis occurring in BALB/c mice administered weekly doses of intrarectal 2,4,6-trinitrobenzene sulfonic acid. We showed first in this model that an initial Th1 response involving IL-12p70 and IFN-gamma subsides after 3 wk to be supplanted by an IL-23/IL-25 response beginning after 4-5 wk. This evolution is followed by gradually increasing production of IL-17 and cytokines ordinarily seen in a Th2 response, particularly IL-13, which reaches a plateau at 8-9 wk. In vitro stimulation studies suggest that this IL-13 production is dependent on IL-23 and IL-25, but not on IL-12p70. We then show that IL-13 production results in the induction of an IL-13R formerly thought to function only as a decoy receptor, IL-13Ralpha(2), and this receptor is critical to the production of TGF-beta(1) and the onset of fibrosis. Thus, if IL-13 signaling through this receptor is blocked by administration of soluble IL-13Ralpha(2)-Fc, or by administration of IL-13Ralpha(2)-specific small interfering RNA, TGF-beta(1) is not produced and fibrosis does not occur. These studies show that in chronic 2,4,6-trinitrobenzene sulfonic acid colitis, fibrosis is dependent on the development of an IL-13 response that acts through a novel cell surface-expressed IL-13R to induce TGF-beta(1). A similar mechanism may obtain in certain forms of human inflammatory bowel disease.     

Monokine production by hypersensitivity (Schistosoma mansoni egg) and foreign body (Sephadex bead)-type granuloma macrophages. Evidence for sequential production of IL-1 and tumor necrosis factor

The present study examined the potential role of IL-1 and TNF in granuloma formation. Mice were given i.v. injections of Schistosoma mansoni eggs or Sephadex beads to induce synchronous immune T cell-mediated (hypersensitivity type) or nonimmune (foreign-body type) granulomas, respectively. Granuloma macrophages isolated at 2, 4, 8, 16, and 32 days of granuloma formation were evaluated for their capacity to produce IL-1 and TNF in response to 1 microgram/ml LPS. This was related to circulating levels of the acute phase protein, serum amyloid P (SAP) and expression of Ia Ag by monocytes and macrophages. Macrophages from nonimmune bead lesions were generally weak producers of IL-1 and TNF. In contrast, those from T cell-mediated egg lesions produced significant levels of both monokines. Moreover, there was a clear pattern of sequential monokine production such that IL-1 was produced in greatest amounts early (2 to 4 days), whereas TNF was produced later (8 to 16 days). Levels of SAP showed an initial sharp rise following particle embolization, then decreased rapidly in bead injected animals. However, mice with immune granulomas showed a prolonged elevation in SAP levels that corresponded to the period of maximal IL-1 production (2 to 4 days). Macrophage/monocyte Ia Ag expression was greatest at 8 to 16 days, corresponding to the period of TNF production. Bead injected animals showed low levels of Ia expression over the study period. These findings suggest that IL-1 may be important in the early recruitment stages of granuloma formation while TNF may take part in later maintenance or effector functions. The extent of production of both is likely influenced by the local or systemic milieu of lymphokines.     

CD4 T cells producing pro-inflammatory interleukin-17 mediate high pathology in schistosomiasis

In murine schistosomiasis mansoni, pronounced CD4 T cell-mediated, egg-induced, hepato-intestinal immunopathology and death, whether genetically determined or elicited experimentally, are associated with failure to down-regulate a net pro-inflammatory immune response. Important evidence contributing to this notion comes from the observation that immunization with schistosome egg antigens in CFA (SEA/CFA) causes low pathology C57BL/6 mice to develop an exacerbated form of disease and death in a cytokine milieu characterized by elevated interferon (IFN)-gamma levels. Since such a pro-inflammatory environment presumes a signaling pathway involving interleukin (IL)-12, the SEA/CFA immunization model was used to examine the extent of hepatic immunopathology in the absence of this cytokine. Surprisingly, the IL-12p40 subunit was an absolute requirement for the development of exacerbated disease, whereas the IL-12p35 subunit was not. Moreover, significantly elevated in vitro production of IL-17, but not of IFN-gamma, correlated with the high pathology, and neutralization of IL-17 in vivo resulted in a significant reduction of hepatic inflammation. Our findings clearly demonstrate the pathogenic potential of the novel IL-17-producing T cell subpopulation (ThIL-17), previously shown to mediate chronic inflammation in autoimmune disease. They also imply that IL-23, but not IL-12, is the critical signal necessary to support the pro-inflammatory ThIL-17 subset involved in high pathology schistosomiasis.     

CD4+ Th2 response induced by Schistosoma mansoni eggs develops rapidly, through an early, transient, Th0-like stage.

Data from recent studies of murine schistosomiasis mansoni have indicated that certain characteristics of this infection, such as eosinophilia and elevated IgE, are due largely to the induction of Th2-like immune responses by parasite ova. The present study was designed to examine more closely the genesis and development of these skewed Th responses to schistosome eggs. Accordingly, eggs isolated from infected mice were injected s.c. into normal mice. After inoculation, draining lymph node (LN) cells were recovered, phenotyped, and tested for their ability to proliferate and secrete IL-2 and IFN-gamma (as markers of Th1 function) and IL-4, IL-5, and IL-10 (Th2 cytokines). The results show a maximal LN enlargement of 40- to 100-fold by day 3 after egg inoculation. The CD4/CD8/B cell ratio at this time is similar to that in LN from normal mice, but increases in numbers of cells expressing very low levels of MEL-14 and high levels of Pgp-1 are evident by days 3 and 10, respectively. Surprisingly, the initial detectable Ag-specific response to schistosome eggs, observed at day 1, is the production of IFN-gamma. By day 3, LN cells are capable of proliferating and making IFN-gamma plus IL-2, IL-4, IL-5, and IL-10 when stimulated with soluble egg Ag and, therefore, appear Th0-like. After 7 to 10 days, IFN-gamma production is severely depressed but the response continues to be characterized by IL-4, IL-5, IL-10, and IL-2. Depletion studies indicate that CD4 cells are the major population responsible for Ag-mediated proliferation and cytokine production. Results show that schistosome eggs are autonomous inducers of vigorous Th2-like effector responses. Further, our data, from a system that utilizes an in vivo priming step, support the contentions that skewed Th responses develop via an intermediate Th0 stage is accompanied by a loss of the MEL-14 surface marker and an increase in Pgp-1 expression.     

Reciprocal immunomodulation in a schistosome and hepatotropic virus coinfection model

Human coinfection with the helminth parasite Schistosoma mansoni and hepatitis B and hepatitis C viruses is associated with increased hepatic viral burdens and severe liver pathology. In this study we developed a murine S. mansoni/lymphocytic choriomeningitis virus (LCMV) coinfection model that reproduces the enhanced viral replication and liver pathology observed in human coinfections, and used this model to explore the mechanisms involved. Viral coinfection during the Th2-dominated granulomatous phase of the schistosome infection resulted in induction of a strong LCMV-specific T cell response, with infiltration of high numbers of LCMV-specific IFN-gamma-producing CD8+ cells into the liver. This was associated with suppression of production of the Th2 cytokines dominant during S. mansoni infection and a rapid increase in morbidity, linked to hepatotoxicity. Interestingly, the liver of coinfected mice was extremely susceptible to viral replication. This correlated with a reduced intrahepatic type I IFN response following virus infection. Schistosome egg Ags were found to suppress the type I IFN response induced in murine bone marrow-derived dendritic cells by polyinosinic-polycytidylic acid. These results suggest that suppression of the antiviral type I IFN response by schistosome egg Ags in vivo predisposes the liver to enhanced viral replication with ensuing immunopathological consequences, findings that may be paralleled in human schistosome/hepatotropic virus coinfections.     

Increased human IgE induced by killing Schistosoma mansoni in vivo is associated with pretreatment Th2 cytokine responsiveness to worm antigens

In schistosomiasis endemic areas, children are very susceptible to postchemotherapy reinfection, whereas adults are relatively resistant. Different studies have reported that schistosome-specific IL-4 and IL-5 responses, or posttreatment worm-IgE levels, correlate with subsequent low reinfection. Chemotherapy kills i.v. worms providing an in vivo Ag challenge. We measured anti-worm (soluble worm Ag (SWA) and recombinant tegumental Ag (rSm22.6)) and anti-egg (soluble egg Ag) Ab levels in 177 Ugandans (aged 7-50) in a high Schistosoma mansoni transmission area, both before and 7 wk posttreatment, and analyzed these data in relation to whole blood in vitro cytokine responses at the same time points. Soluble egg Ag-Ig levels were unaffected by treatment but worm-IgG1 and -IgG4 increased, whereas worm-IgE increased in many but not all individuals. An increase in worm-IgE was mainly seen in >15-year-olds and, unlike in children, was inversely correlated to pretreatment infection intensities, suggesting this response was associated both with resistance to pretreatment infection, as well as posttreatment reinfection. The increases in SWA-IgE and rSm22.6-IgE positively correlated with pretreatment Th2 cytokines, but not IFN-gamma, induced by SWA. These relationships remained significant after allowing for the confounding effects of pretreatment infection intensity, age, and pretreatment IgE levels, indicating a link between SWA-specific Th2 cytokine responsiveness and subsequent increases in worm-IgE. An exceptionally strong relationship between IL-5 and posttreatment worm-IgE levels in < 15-year-olds suggested that the failure of younger children to respond to in vivo Ag stimulation with increased levels of IgE, is related to their lack of pretreatment SWA Th2 cytokine responsiveness.