Nitric Oxide and the Th2 Response Combine to Prevent Severe Hepatic Damage During Schistosoma mansoni Infection

During infection with Schistosoma mansoni, NO production increases following the deposition of parasite eggs in the liver. In wild-type C57BL/6 mice, NO levels peak during the sixth week of infection and are subsequently down-regulated. Inducible NO synthase (iNOS) mRNA was found in diseased liver tissue along with TNF-α and IFN-γ, which are known promoters of iNOS expression. Mice treated with aminoguanidine, a selective inhibitor of iNOS, exhibited cachexia and exacerbated liver pathology, suggesting that NO limits hepatocyte damage when the liver is first exposed to eggs. Hepatic iNOS is up-regulated in SCID mice, indicating that NO production is part of an innate response. Studies with infected highly susceptible IL-4−/− mice revealed that prolonged NO production is in itself deleterious and that a major function of the Th2 response, which is severely compromised in the absence of IL-4, is to regulate NO production. In these animals, plasma NO levels are high compared with those in infected wild-type mice and remain elevated until death. Nevertheless, the underlying importance of NO is illustrated by the finding that aminoguanidine treatment leads to more severe liver disease and reduced time to death in infected IL-4−/− 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-γ, 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-γ 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.

T1/ST2 Expression Is Enhanced on CD4+ T Cells from Schistosome Egg-Induced Granulomas: Analysis of Th Cell Cytokine Coexpression Ex Vivo

Th cells are categorized into subsets based on the cytokine production of in vitro-differentiated Th populations. For in vivo-differentiated Th subsets, little is known about the heterogeneity of cytokine production in single cells. We recently described a molecule, T1/ST2, that is preferentially expressed on the surface of Th2 cells. Here we combined high-gradient magnetic cell separation with four-color single-cell cytometry to analyze simultaneously three intracellular cytokines and T1/ST2 surface expression on CD4+ cells from lungs containing granulomas induced by Schistosoma mansoni eggs. T1/ST2 was highly up-regulated on CD4+ T cells from hepatic granulomas and granulomatous lungs. T1/ST2+ cells from granulomatous lungs preferentially produced type 2 cytokines ex vivo. In the total CD4+ population, coexpression of type 1 and type 2 cytokines occurred frequently. However, such coproduction was drastically reduced in T1/ST2+ cells compared with T1/ST2− cells. Coexpression of type 1 and type 2 cytokines was also rare in cells simultaneously producing two cytokines of one type. These findings indicate that individual CD4+ T cells in vivo have different levels of commitment to a certain Th phenotype. Coexpression of two type 2 cytokines or production of one type 2 cytokine together with surface expression of T1/ST2 indicate advanced commitment to the Th2 phenotype.

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-γ 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-γ, 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.

Biased TCR Repertoire in Infiltrating Lesional T Cells in Human Bancroftian Filariasis

To investigate the hypothesis that T cells recognizing specific Ags localize to the site of disease activity in human bancroftian filariasis, we have compared the repertoire of TCR Vβ gene segments in lesions vs blood in individual patients by RT-PCR ELISA. Vβ14 and Vβ24 were overrepresented (5% greater in tissue compared with PBMCs and/or tissue/PBMC ratios in the highest 5% of all tissue/PBMC ratios for all Vβs for all subjects) in 50% and 40% of study subjects, respectively. Overrepresentation of these two Vβs did not occur in any control subject. In comparing three patient groups, the proportion of individuals meeting at least one criterion for Vβ14 overrepresentation was shown to increase in tandem with our current concepts of disease progression (asymptomatic filariasis = 25%; clinical filariasis with active infection = 60%; clinical filariasis without active infection = 71%). In 6 of the 10 individuals with Vβ14 overrepresentation, Vβ14 represented >20% of the entire lesional Vβ repertoire. All but one of the 20 study subjects had at least one Vβ gene segment that was overrepresented in tissue compared with PBMCs. Only a small number of Vβs, usually three or less, were overrepresented in any single filariasis patient. However, in the same tissue, no differences between patient groups were found when IFN-γ, TNF-α, IL-4, IL-5, and IL-12 mRNA expression were examined. Taken together, these findings suggest that, in principle, in essentially all patients, whether with subclinical or with clinical filariasis, distinct and limited T cell populations are concentrated in affected tissue.

Activated Eosinophils Are the Major Source of Th2-Associated Cytokines in the Schistosome Granuloma

Eosinophils are a numerically dominant cell population within the schistosome granuloma. These granuloma eosinophils can produce a variety of cytokines, including IL-2, IL-4, IL-5, and IFN-γ. Therefore, eosinophils may play a key role in the determination of the unique cytokine microenvironment within the granuloma milieu. These studies investigated the potential role of eosinophils in the regulation of granuloma immunopathology. We have characterized spleen- and granuloma-derived eosinophils based on cellular activation and cytokine production during the development of murine schistosomiasis. Based on the criteria of hypodensity and CD69 expression, granuloma eosinophils were highly activated and very homogeneous at 7 and 11 wk postinfection. Splenic eosinophils were also activated at 7 wk postinfection, but were much more heterogeneous than their granuloma counterparts. By 11 wk postinfection, few hypodense splenic eosinophils were observed. Eosinophils represented the majority of cytokine-producing cells in the granuloma and were a dominant source of IL-4. Eosinophils also produced IL-2, IL-5, and IFN-γ, using the criteria of mRNA in situ hybridization and intracellular cytokine staining by FACS. Granuloma eosinophil activation and cytokine production were greatest at the time of maximum granuloma formation, i.e., 10–12 wk after initial cercarial exposure. Therefore, locally activated eosinophils, not Th2 lymphocytes, produce the majority of Th2 cytokines in the granuloma milieu and may be important determinators of immunopathology in schistosomiasis.

IL-13 Is a Key Regulatory Cytokine for Th2 Cell-Mediated Pulmonary Granuloma Formation and IgE Responses Induced by Schistosoma mansoni Eggs

Schistosoma mansoni egg-induced pulmonary granuloma formation is a cell-mediated inflammatory response associated with dominant Th2-type cytokine expression, tissue eosinophilia, and high levels of serum IgE. In the present study, we show that in vivo blockade of the Th2 cytokine IL-13, using soluble IL-13R α2-Fc fusion protein, significantly reduced the size of pulmonary granulomas in unsensitized as well as egg-sensitized mice. Blocking IL-13 also significantly reduced total serum IgE levels. Interestingly, however, IL-13 blockade did not affect the evolving egg-induced Th2-type cytokine response. IL-4, IL-5, as well as IL-13 responses were indistinguishable in control-Fc- and soluble IL-13R α2-Fc fusion protein-treated animals. The smaller granulomas were also phenotypically like the control Fc-treated mice, displaying a similar eosinophil content. Additional studies in IL-4-deficient mice demonstrated that IL-13 was produced, but at much lower levels than in wild-type mice, while IL-4 expression was completely independent of IL-13. Moreover, while granuloma formation was partially reduced in IL-4-deficient mice, blocking IL-13 in these animals almost completely abrogated granuloma development and the pulmonary eosinophilia, while it simultaneously increased IFN-γ production. Together, these data demonstrate that IL-13 serves as an important mediator of Th2-mediated inflammation and plays a role in eliciting IgE responses triggered by schistosome eggs.

The Schistosome Granuloma: Characterization of Lymphocyte Migration, Activation, and Cytokine Production

Granuloma formation and its regulation are dependent on lymphocytes. Therefore, we compared the characteristics of lymphocytes derived from the spleens and granulomas of Schistosoma mansoni-infected mice during the course of their disease. We examined lymphocyte cell cycle kinetics, migration, expression of activation Ags (CD69 and IL-2R), cytokine production (IL-2, IL-4, IFN-γ), and apoptosis. Lymphocytes in the G2/M phase of the cell cycle and high levels of lymphocyte intracellular IL-2 were found in the spleen but not in the granuloma. Cell trafficking experiments showed Ag-specific recruitment of schistosomal egg Ag (SEA)-reactive lymphoblasts into granulomas in vivo, as well as recruitment to, residence within, and egress from granulomas in vitro. Granuloma-derived lymphocytes were more highly activated than splenic lymphocytes based on higher levels of CD69 and IL-2R expression. While the granuloma microenvironment was rich in Th2 cytokines, during peak granuloma formation, the lymphocytes per se from the spleen and granuloma did not exhibit a dominant Th1 or Th2 cytokine profile, producing low but similar levels of IL-4 and IFN-γ. The discrepancy between high IL-2R expression and low levels of IL-2 protein production by granuloma lymphocytes was associated with increased apoptosis in the granuloma compared with the spleen. These findings support the hypothesis that granulomas may play a role in the regulation of systemic pathology in schistosomiasis by adversely affecting the survival of SEA-reactive, immunopathogenic T lymphocytes.

IFN-γ, IL-12, and TNF-α Are Required to Maintain Reduced Liver Pathology in Mice Vaccinated with Schistosoma mansoni Eggs and IL-12

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.

Identification of the Immunodominant T Cell Epitope of p38, a Major Egg Antigen, and Characterization of the Epitope-Specific Th Responsiveness During Murine Schistosomiasis Mansoni

A recently cloned major Schistosoma mansoni egg Ag p38 induced and elicited strong Th1-type responsiveness in mice of H-2k haplotype. Now, we have identified the immunodominant T cell epitope of p38 and analyzed the dynamics of epitope-specific Th responsiveness during murine schistosomiasis mansoni. Overlapping recombinant and synthetic peptides that encompassed the full-length 354 amino acid of p38 were tested for proliferation and cytokine production in peptide- or p38-sensitized mice. The immunodominant T cell epitope of p38 that elicited pulmonary granuloma formation was localized within peptide P4 (amino acids 235–249). The P4-specific cytokine response of splenocytes that had been sensitized s.c. with p38, P4 or soluble egg Ags in IFA, or i.p. with 3000 eggs was predominantly as the Th1 type, with strong IL-2 and IFN-γ, but trace amounts of IL-4 and IL-5 secretion. At 6.5 wk of infection, splenocytes and mesenteric lymph node cells responded to p38/P4 peptides with predominantly Th1-type responsiveness. This response did not switch to a Th2-type pattern from 8 wk onwards; rather, it underwent down-modulation. Moreover, the hepatic granuloma lymphocytes at 6.5 wk responded to p38/P4 predominantly with Th1-type cytokine production, indicating that they participate in early granuloma formation. From 8 wk onwards an immune deviation to the p38-specific response was observed that was manifested by rising IgG1, IgE, and IgG2a Ab production as opposed to declining Th1- and Th2-type cytokine secretion.

A Pathogenic Role of IL-12 in Blood-Stage Murine Malaria Lethal Strain Plasmodium berghei NK65 Infection

We studied whether the infection with a blood-stage murine malaria lethal Plasmodium berghei NK65 induces IL-12 production, and if so, how the IL-12 production is involved in the protection or pathogenesis. The infection of C57BL/6 mice enhanced mRNA expression of IL-12 p40 and also IFN-γ, IL-4, and IL-10 in both spleen and liver during the early course of the infection. It also enhanced the mRNA expression of TNF-α, Fas ligand, and cytokine-inducible nitric oxide synthase. Increased IL-12 p40 production was also observed in the culture supernatant of spleen cells and in sera of infected mice. In addition, the infection caused massive liver injury with elevated serum glutamic-oxaloacetic transaminase and serum glutamic-pyruvic transaminase activities and body weight loss. Treatment of these infected mice with neutralizing mAb against IL-12 prolonged the survival and diminished the liver injury with reduced elevation of serum serum glutamic-oxaloacetic transaminase and serum glutamic-pyruvic transaminase activities and decreased body weight loss. However, the anti-IL-12 treatment did not affect parasitemia, and all these mice eventually died. Similar results were obtained when infected mice were treated with neutralizing mAb against IFN-γ. Moreover, anti-IL-12 treatment greatly reduced the secretion and mRNA expression of IFN-γ in both spleen and liver. These results suggest that the lethal P. berghei NK65 infection induces IL-12 production and that the IL-12 is involved in the pathogenesis of liver injury via IFN-γ production rather than the protection.

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

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-γ, IL-2, IL-1β, and TNF-α 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.

Induction of Granulomatous Experimental Autoimmune Thyroiditis in IL-4 Gene-Disrupted Mice

To study the role of IL-4 in development of granulomatous experimental autoimmune thyroiditis (EAT), IL-4 gene-disrupted mice expressing the EAT-susceptible H-2k haplotype were generated and used for EAT induction. Spleen cells from mouse thyroglobulin (MTg) and LPS-primed IL-4+/+ and IL-4−/− donors could induce severe granulomatous EAT when spleen cells were activated with MTg and anti-IL-2R mAb in the presence of IL-12. Thyroid lesions had extensive follicular cell proliferation, large numbers of histiocytes, polymorphonuclear leukocytes, and multinucleated giant cells, in addition to lymphocytes and other mononuclear cells. Expression of IFN-γ gene mRNA and production of IFN-γ by effector spleen cells stimulated with MTg and IL-12 were similar for both IL-4+/+ and IL-4−/− mice. Although IL-4 was undetectable in IL-4−/− mice, expression of mRNA for IL-5, IL-10, and IL-13 and production of IL-5 by both MTg-activated spleen cells and anti-CD3-activated CD4+ T cells were comparable for cells from IL-4+/+ and IL-4−/− mice, indicating that the absence of IL-4 did not prevent production of other Th2 cytokines. Production of MTg-specific IgG1 was very low or undetectable in IL-4−/− mice. IL-4 gene mRNA and MTg-specific IgG1 could be detected in IL-4+/+ or IL-4−/− recipients only when they received effector cells from IL-4+/+ donor mice, indicating that IL-4- and IgG1-secreting cells are of donor origin. These results demonstrate that IL-4 is not essential for development of granulomatous EAT.