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

Schistosoma mansoni egg-derived extracellular vesicles: A promising vaccine candidate against murine schistosomiasis

Extracellular vesicles (EVs) are protein-loaded nano-scaled particles that are extracellularly released by eukaryotes and prokaryotes. Parasite's EVs manipulate the immune system, making them probable next-generation vaccines. Schistosomal EVs carry different proteins of promising immunizing potentials. For evaluating the immune-protective role of Schistosoma mansoni (S. mansoni) egg-derived EVs against murine schistosomiasis, EVs were isolated from cultured S. mansoni eggs by progressive sequential cooling ultra-centrifugation technique. Isolated EVs were structurally identified using transmission electron microscope and their protein was quantified by Lowry's technique. Experimental mice were subcutaneously immunized with three doses of 20 μg EVs (with or without alum adjuvant); every two weeks, then were challenged with S. mansoni cercariae two weeks after the last immunizing dose. Six weeks post infection, mice were sacrificed for vaccine candidate assessment. EVs protective efficacy was evaluated through parasitological, histopathological, and immunological parameters. Results showed significant reduction of tegumentally deranged adult worms, hepatic and intestinal egg counts reduction by 46.58%, 93.14% and 93.17% respectively, accompanied by remarkable amelioration of sizes, numbers and histopathology of hepatic granulomata mediated by high interferon gamma (IFN γ) and antibody level. Using sera from vaccinated mice, the molecular weight of EVs' protein components targeted by the antibody produced was recognized by western immunoblot. Results revealed two bands of ~ 14 KDa and ~ 21 KDa, proving that EVs are able to stimulate specific antibodies response. In conclusion, the present study highlighted the role of S. mansoni-egg derived EVs as a potential vaccine candidate against murine schistosomiasis mansoni.

Effect of maternal praziquantel treatment for Schistosoma japonicum infection on the offspring susceptibility and immunologic response to infection at age six, a cohort study

In areas endemic to schistosomiasis, fetal exposure to schistosome antigens prime the offspring before potential natural infection. Praziquantel (PZQ) treatment for Schistosoma japonicum infection in pregnant women has been demonstrated to be safe and effective. Our objectives were to evaluate whether maternal PZQ treatment modifies the process of in utero sensitization to schistosome antigens potentially impacting later risk of infection, as well as immune response to S. japonicum. We enrolled 295 children at age six, born to mothers with S. japonicum infection who participated in a randomized control trial of PZQ versus placebo given at 12-16 weeks gestation in Leyte, The Philippines. At enrollment, we assessed and treated current S. japonicum infection and measured serum cytokines. During a follow-up visit four weeks later, we assessed peripheral blood mononuclear cell (PBMC) cytokine production in response to soluble worm antigen preparation (SWAP) or soluble egg antigen (SEA). Associations between maternal treatment group and the child's S. japonicum infection status and immunologic responses were determined using multivariate linear regression analysis. PZQ treatment during pregnancy did not impact the prevalence (P = 0.12) or intensity (P = 0.59) of natural S. japonicum infection among children at age six. Among children with infection at enrollment (12.5%) there were no significant serum cytokine concentration differences between maternal treatment groups. Among children with infection at enrollment, IL-1 production by PBMCs stimulated with SEA was higher (P = 0.03) in the maternal PZQ group compared to placebo. Among children without infection, PBMCs stimulated with SEA produced greater IL-12 (P = 0.03) and with SWAP produced less IL-4 (P = 0.01) in the maternal PZQ group compared to placebo. Several cytokines produced by PBMCs in response to SWAP and SEA were significantly higher in children with S. japonicum infection irrespective of maternal treatment: IL-4, IL-5, IL-10, and IL-13. We report that maternal PZQ treatment for S. japonicum shifted the PBMC immune response to a more inflammatory signature but had no impact on their offspring's likelihood of infection or serum cytokines at age six, further supporting the safe use of PZQ in pregnant women. Trial Registration: ClinicalTrials.gov NCT00486863.

Changing our view of the Schistosoma granuloma to an ecological standpoint

Schistosomiasis, a neglected parasitic tropical disease that has plagued humans for centuries, remains a major public health burden. A primary challenge to understanding schistosomiasis is deciphering the most remarkable pathological feature of this disease, the granuloma - a highly dynamic and self-organized structure formed by both host and parasite components. Granulomas are considered a remarkable example of how parasites evolved with their hosts to establish complex and intimate associations. However, much remains unclear regarding life within the granuloma, and strategies to restrain its development are still lacking. Here we explore current information on the hepatic Schistosoma mansoni granuloma in the light of Ecology and propose that this intricate structure acts as a real ecosystem. The schistosomal granuloma is formed by cells (biotic component), protein scaffolds, fibres, and chemical compounds (abiotic components) with inputs/outputs of energy and matter, as complex as in classical ecosystems. We review the distinct cell populations ('species') within the granuloma and examine how they integrate with each other and interact with their microenvironment to form a multifaceted cell community in different space-time frames. The colonization of the hepatic tissue to form granulomas is explained from the point of view of an ecological succession whereby a community is able to modify its physical environment, creating conditions and resources for ecosystem construction. Remarkably, the granuloma represents a dynamic evolutionary system that undergoes progressive changes in the 'species' that compose its community over time. In line with ecological concepts, we examine the granuloma not only as a place where a community of cells is settled (spatial niche or habitat) but also as a site in which the functional activities of these combined populations occur in an orchestrated way in response to microenvironmental gradients such as cytokines and egg antigens. Finally, we assert how the levels of organization of cellular components in a granuloma as conventionally defined by Cell Biology can fit perfectly into a hierarchical structure of biological systems as defined by Ecology. By rethinking the granuloma as an integrating and evolving ecosystem, we draw attention to the inner workings of this structure that are central to the understanding of schistosomiasis and could guide its future treatment.

Interleukin-4 Receptor Alpha Expressing B Cells Are Essential to Down-Modulate Host Granulomatous Inflammation During Schistosomasis

Schistosomiasis (bilharzia) is a parasitic helminth disease that can cause severe inflammatory pathology leading to organ damage in humans. Failure of the host to regulate egg-driven granulomatous inflammation causes host morbidity during chronic infection with Schistosoma mansoni. Although the importance of B cells in regulating pathology during chronic infection has been well defined, the specific contribution of IL-4Rα-expressing B cells is still unknown. To address this, we examined B cell-specific IL-4Rα-deficient (mb1^creIL-4Rα^−/lox) mice in three experimental models of schistosomiasis: high-dose (100 cercariae), low dose (30 cercariae), and a synchronous egg challenge. In the high dose model, we found that mice deficient in IL-4Rα-expressing B cells were more susceptible to acute schistosomiasis than B cell-deficient (μMT) mice, succumbing to infection at the acute stage whereas μMT mice survived until the chronic stage. An S. mansoni egg challenge model demonstrated that deleting IL-4Rα expression specifically on B cells resulted in increased lung granulomatous pathology, suggesting a role for this B cell subset in controlling granulomatous pathology. In agreement with this, a low dose model of schistosomiasis—which mimics the course of clinical chronic disease—demonstrated that depleting IL-4Rα-expressing B cells in mb1^creIL-4Rα^−/lox mice considerably impaired the host ability to down-modulate granulomatous inflammation in the liver and gut during chronic schistosomiasis. Taken together, our findings indicate that within the B cell compartment, IL-4Rα-expressing B cells in particular down-modulate the deleterious egg-driven tissue granulomatous inflammation to enable host survival during schistosomiasis in mice.

IL-4Rα-expressing CD11c+ cells contribute to driving optimal cellular responses during Schistosoma mansoni infection in mice

Development of IL‐4 receptor alpha (IL‐4Rα)‐dependent cellular immunity regulates host protection against acute schistosomiasis. In this study, we investigated the importance of IL‐4Rα‐expressing CD11c⁺ cells in driving the development of optimal cellular responses to Schistosoma mansoni infection by using CD11c^creIL‐4Rα^−/lox BALB/c mice, which lacked IL‐4Rα expression on dendritic cells and alveolar macrophages. Abrogation of IL‐4Rα expression on CD11c⁺ cells affected activation of CD4⁺ T cells, resulting in reduced numbers of effector CD4⁺ T cells and impaired production of Th1 and Th2 cytokines by CD4⁺ T cells ex vivo. However, secretion of both type 1 and type 2 Ab isotypes was unchanged in infected CD11c‐specific IL‐4Rα‐deficient mice compared to littermate controls. Together, these data demonstrate that IL‐4Rα‐expressing CD11c⁺ cells play an important role in maintaining cellular immunity during schistosomiasis in mice.

Possible antifibrotic effect of GDC-0449 (Vismodegib), a hedgehog-pathway inhibitor, in mice model of Schistosoma-induced liver fibrosis

Liver fibrosis is a pathological process complicating schistosomiasis. It is an active process of continuous extracellular matrix accumulation. In Egypt, schistosomiasis re-infection is a continuing problem especially in rural areas. In this study we examined the antifibrotic effect of GDC-0449 (Vismodegib), a hedgehog-pathway inhibitor as a new molecular target for Schistosoma-induced liver fibrosis, in addition to exploring its effect as antischistosomal drug. The effect of GDC-0449 alone or combined with Praziquantel was tried experimentally in infected mice with Schistosoma mansoni. Fifty CD-1 Swiss female albino mice were used, forty mice were infected with Schistosoma mansoni cercariae. Animals were grouped into five groups; uninfected control, infected untreated, infected treated with Praziquantel (500mg/kg/day) for two days, infected treated with GDC-0449 (40mg/kg/day) for seven days, and infected treated with combined Praziquantel and GDC-0449. Parasitological and chemical parameters, hydroxyproline level and liver granuloma were assessed. Liver fibrosis was reduced significantly evidenced by reduced hydroxyproline levels [P<0.01 for combined (Praziquantel/GDC-0449) treatment groups, P<0.001 for GDC-0449-treated group]. Also, histopathological examination of liver tissues revealed that the mean diameter of granulomas was statistically reduced (P=0.001) with a reduction rate of 24.4% on treatment with GDC-0449. In GDC-0449/Praziquantel combined treatment group, number and mean diameter of the granulomas were reduced significantly P<0.001, and P=0.001 respectively. No antischistosomal effect was recorded for GDC-0449 in this study.

Protective role of IL-22 against Schistosoma mansoni soluble egg antigen-induced granuloma in Vitro

The role of T helper-17 (Th17) lymphocytes in the regulation of Schistosoma mansoni soluble egg antigen (SEA)-induced granuloma is unknown. This study examined the effect of Th17 cytokines (IL-17 and IL-22) on granulocyte recruitment and functions during SEA-induced granuloma formation in vitro in Schistosoma-infected and noninfected individuals. Granulocytes were isolated from 27 Schistosoma-infected patients and 13 controls and were used for granuloma induction using SEA-conjugated polyacrylamide beads in the presence of Th17 cytokines. Granuloma index was assessed, and granulocyte mediators such as tumour necrosis factor (TNF-α), hydrogen peroxide (H2 O2 ) and nitric oxide (NO) were measured in the culture supernatant at the 7th day using enzyme-linked immunosorbent assay (ELISA). Schistosoma-infected patients had significant larger SEA-induced granuloma than controls. IL-17 (125 pg/mL) induced the optimum size for granuloma within 3-7 days. However, IL-22 at different concentrations up to 300 pg/mL had no effect on granuloma formation. Using both cytokines simultaneously, IL-22 suppressed the effect of IL-17 and prevented granuloma formation. IL-17 significantly decreased TNF-α, H2 O2 and NO levels in Schistosoma-infected individuals. In contrast, IL-22 increased TNF-α and H2 O2 levels. In conclusion, IL-17 accelerates SEA-induced granuloma formation and inhibits granulocytes functions in Schistosoma-infected patients, while IL-22 inhibited the granuloma formation, but enhanced granulocyte functions.

Biochemical and histological changes in liver of Nectomys squamipes naturally infected by Schistosoma mansoni

The South American water rat Nectomys squamipes is a wild mammal reservoir of Schistosoma mansoni in Brazil. In the present study, wild rodents were collected in the field and categorized into two groups: infected and uninfected by S. mansoni. Blood was collected to analyze changes in the serum glucose level (mg/dL) and liver fragments were used to determine the hepatic glycogen content (mg of glucose/g tissue). The histological examination showed inflammatory granulomatous lesions in different phases of development in the liver of rodents naturally infected with S. mansoni, in some cases with total or partial occlusion of the vascular lumen. Early lesions were characterized by the presence of inflammatory infiltrate around morphologically intact recently deposited eggs. Despite the significance of these histological lesions, the biochemical changes differed in extent. N. squamipes naturally infected by S. mansoni showed no variation in hepatic glycogen reserves. These findings were accompanied by a significant increase in plasma glucose contents, probably as a consequence of amino acids deamination, which are degraded, resulting in the formation of intermediates used as precursors for the glucose formation, without compromising the reserves of liver glycogen. In the wild, naturally infected N. squamipes can maintain S. mansoni infections without undergoing alterations in its carbohydrate metabolism, which minimizes the deleterious effects of S. mansoni.

Schistosomiasis does not affect the outcome of HCV infection in genotype 4-infected patients

Although reports suggest that Schistosoma mansoni increases hepatitis C virus (HCV) morbidity and chronicity, its impact on HCV spontaneous resolution is not clear. HCV genotype, viral load, abdominal ultrasonographic findings, and HCV-specific cell-mediated immunity (CMI) were examined among 141 healthcare workers infected with HCV (68 workers with and 73 workers without S. mansoni). HCV genotype 4 was dominate, and viral loads were 2.62 ± 0.69 × 10(6) and 4.24 ± 1.4 × 10(6) IU/mL among patients with and without coinfection, respectively (P = 0.309); 23.5% with and 32.9% without coinfection had spontaneously resolved HCV infection (P = 0.297). Interferon-γ spot-forming cells/10(6) peripheral blood mononuclear cells among responding viremic patients with and without coinfection were 716 ± 194 and 587 ± 162, whereas among aviremic patients, it was 794 ± 272 and 365 ± 36 (P > 0.05), respectively. In conclusion, there was no statistical difference in HCV spontaneous resolution, viral load, liver pathology, or CMI in patients with or without S. mansoni coinfection, suggesting that it did not impact the outcome of HCV infection.

Association of Schistosoma mansoni-specific IgG and IgE antibody production and clinical schistosomiasis status in a rural area of Minas Gerais, Brazil

Background

Studies in murine models and human populations have indicated that the collagen-rich granulomatous response against parasite eggs trapped in the liver is associated with the development of severe hepatosplenic schistosomiasis, characterized by periportal fibrosis and portal hypertension. The role of the humoral response in parasite susceptibility has been well established, but its participation in disease severity remains poorly understood. In this work, we evaluated the relationship between parasite-reactive IgE and IgG levels and schistosomiasis morbidity in infected patients with similar parasite burdens.

Methodology/Principal Findings

Ninety-seven Schistosoma mansoni-infected individuals were subjected to clinical examination and abdominal ultrasound analysis. IgG reactivity and IgE concentration against Schistosoma mansoni soluble egg antigens (SEA) and adult worm antigen preparation (SWAP) were evaluated by ELISA assay. Multivariable linear regression models were used to evaluate the relationship between parasite-reactive antibodies and the co-variables investigated. The study population showed low parasite burden (median 30 eggs/g feces), constant re-infection, and signs of fibrosis was detected in more than 30% of individuals. Most infected individuals showed IgG reactivity, and the median concentrations of IgE anti-SEA and anti-SWAP antibodies were 1,870 and 1,375 ng/mL, respectively. There was no association between parasite burden and antibody response or any parameter of disease severity. However, IgG anti-SWAP level was positively associated with morbidity parameters, such as spleen size and thickness of portal vein at the entrance and secondary branch. In contrast, the data also revealed independent inverse correlations between concentration of parasite-reactive IgE and gallbladder wall thickness, a marker of fibrosis in schistosomiasis.

Conclusions/Significance

The data indicate that IgG anti-SWAP is positively associated with severe schistosomiasis, independently of parasite burden, while high production of parasite-specific IgE is associated with mild disease in the human population. Antibody profiles are good correlates for schistosomiasis severity and could be tested as biomarkers of disease severity.

IL-10R blockade during chronic schistosomiasis mansoni results in the loss of B cells from the liver and the development of severe pulmonary disease

In schistosomiasis patients, parasite eggs trapped in hepatic sinusoids become foci for CD4+ T cell-orchestrated granulomatous cellular infiltrates. Since the immune response is unable to clear the infection, the liver is subjected to ongoing cycles of focal inflammation and healing that lead to vascular obstruction and tissue fibrosis. This is mitigated by regulatory mechanisms that develop over time and which minimize the inflammatory response to newly deposited eggs. Exploring changes in the hepatic inflammatory infiltrate over time in infected mice, we found an accumulation of schistosome egg antigen-specific IgG1-secreting plasma cells during chronic infection. This population was significantly diminished by blockade of the receptor for IL-10, a cytokine implicated in plasma cell development. Strikingly, IL-10R blockade precipitated the development of portal hypertension and the accumulation of parasite eggs in the lungs and heart. This did not reflect more aggressive Th2 cell responsiveness, increased hepatic fibrosis, or the emergence of Th1 or Th17 responses. Rather, a role for antibody in the prevention of severe disease was suggested by the finding that pulmonary involvement was also apparent in mice unable to secrete class switched antibody. A major effect of anti-IL-10R treatment was the loss of a myeloid population that stained positively for surface IgG1, and which exhibited characteristics of regulatory/anti-inflammatory macrophages. This finding suggests that antibody may promote protective effects within the liver through local interactions with macrophages. In summary, our data describe a role for IL-10-dependent B cell responses in the regulation of tissue damage during a chronic helminth infection.

Anti-inflammatory/anti-fibrotic effects of the hepatoprotective silymarin and the schistosomicide praziquantel against Schistosoma mansoni-induced liver fibrosis

BACKGROUND

Praziquantel (PZQ) is an isoquinoline derivative (2-cyclohexylcarbonyl-1, 2, 3, 6, 7, 11b-hexahydro-4H-pyrazino{2,1-a}-isoquinoline-4-one), and is currently the drug of choice for all forms of schistosomiasis. Silymarin, a standardized milk thistle extract, of which silibinin is the main component, is known for its hepatoprotective, anti-inflammatory, antioxidant activities, and hepatocyte regeneration. This study investigates the anti-inflammatory/anti-fibrotic effects of silymarin and/or PZQ on schistosomal hepatic fibrosis.

METHODS

Schistosoma mansoni-infected mice were divided into two large groups (I & II), each with four subgroups and were run in parallel. (i) Infected untreated; (ii) treated with silymarin, starting from the 4th (3 weeks before PZQ therapy) or 12th (5 weeks after PZQ therapy) weeks post infection (PI); (iii) treated with PZQ in the 7th week PI; and (iv) treated with silymarin, as group (ii) plus PZQ as group (iii). Comparable groups of uninfected mice run in parallel with the infected groups. Mice of groups I and II were killed 10 and 18 weeks PI, respectively. Hepatic content of hydroxyproline (HYP), serum levels and tissue expression of matrix metalloproteinase-2 (MMP-2), transforming growth factor-β1 (TGF-β1) and number of mast cells were determined. In addition, parasitological, biochemical and histological parameters that reflect disease severity and morbidity were examined.

RESULTS

Silymarin caused a partial decrease in worm burden; hepatic tissue egg load, with an increase in percentage of dead eggs; modulation of granuloma size, with significant reduction of hepatic HYP content; tissue expression of MMP-2, TGF-β1; number of mast cells, with conservation of hepatic reduced glutathione (GSH). PZQ produced complete eradication of worms, eggs and alleviated liver inflammation and fibrosis. The best results were obtained, in most parameters studied, in groups of mice treated with silymarin in addition to PZQ.

CONCLUSIONS

Our results point to silymarin as a promising anti-inflammatory and anti-fibrotic agent; it could be introduced as a therapeutic tool with PZQ in the treatment of schistosomal liver fibrosis, but further studies on mechanisms of silymarin and PZQ in chronic liver diseases may shed light on developing therapeutic methods in clinical practice.

In vivo imaging of tissue eosinophilia and eosinopoietic responses to schistosome worms and eggs

Using a sensitive transgenic reporter mouse system and in vivo biophotonic imaging techniques, we present a dynamic analysis of eosinophil responses to schistosome infection. Use of this methodology provided previously unattainable detail on the spatial and temporal distribution of tissue eosinophilia and eosinopoietic responses to schistosome worms and eggs. Dramatic hepatic and intestinal eosinophilia in response to the deposition of schistosome eggs, with accompanying eosinopoiesis in the bone marrow, was observed between weeks 8 and 10 p.i., with subsequent downregulation evident by week 11. Contrary to expectations, we also demonstrate that schistosome parasites themselves induce significant intestinal eosinophilia and eosinopoiesis in the bone marrow at very early stages during prepatent infection.

Schistosoma infection inhibits cellular immune responses to core HCV peptides

Patients coinfected with hepatitis C virus (HCV) and the trematode, Schistosoma mansoni, have an increased incidence of viral persistence and accelerated fibrosis. To investigate immunological mechanisms responsible for this more aggressive natural history of HCV, the core HCV-specific T-cell responses were analysed in 44 donated blood units rejected because they had antibodies to HCV (anti-HCV). Half also had anti-S. mansoni antibodies, evidence of past or active infection. HCV-specific ELISPOT responses were examined using pools of 180 overlapping 9-mer peptides with offsets of one covering the core of HCV genotype 4a. Comparison of T-cell responses in blood units positive for both anti-HCV and anti-Schistosoma antibodies with blood units positive only for anti-HCV antibodies showed a significant decrease in core-specific T-cell IFN-gamma (505+/- 46 vs. 803 +/- 66 ISC/10(6) cells, P < 0.001), IL-4 (2 +/- 108 vs. 641 +/- 131 ISC/10(6) cells, P < 0.001), and IL-10 (159 +/- 105 vs. 466 +/- 407 ISC/10(6) cells, P < 0.002) responses. In contrast, there was no significant difference in cell-mediated immune response (CMI) to PHA mitogen between these two groups. Therefore, we concluded T cells from persons with anti-Schistosoma have reduced IFN-gamma, IL-4, and IL-10 secreting HCV-specific T-cell responses. This may explain why Schistosoma coinfection increases persistence and severity of HCV infection.

Comparison of immune responses of Schistosoma mansoni-infected mice with distinct chronic forms of the disease

BACKGROUND

Schistosoma mansoni-infected mice tend to present with either one of two different hepatic pathological patterns during chronic infection: periportal fibrosis (PF) with portal concentration of periovular granulomas and fibrosis or isolated granulomas (IG), with scattered periovular granulomas within the liver. These are models for the two clinical presentations of schistosomiasis, the severe hepatosplenic and the mild intestinal forms. In the present work, we examined the relationship between the development of these histopathological aspects and immunological markers in S. mansoni-infected mice. Although BALB/c mice with PF and IG had similar egg numbers in the liver, PF mice had higher liver collagen contents than mice with IG. Cultured spleen cells from mice with PF and IG had similar proliferation 20 and 40 weeks after S. mansoni infection upon stimulation with parasite egg antigen (SEA) or mitogen (Con A). Production of IL-4 upon SEA stimulation was higher in cell cultures from mice with PF, whereas IL-5 and IFN-gamma levels were not statistically different between PF and IG groups. Mice with IG had similar serum concentrations of total IgE and anti-SEA IgG1, IgG2a, IgG2b and IgG3 compared to sera from PF mice. Levels of IgG1 and IgG2a antibodies were the highest and the lowest detected, respectively. In conclusion, isogenic BALB/c mice infected with S. mansoni that develop periportal fibrosis or isolated granulomas have similar immunological patterns despite the two pathologic forms of schistosomal liver fibrosis.

Dexamethasone treatment improves morphological and hematological parameters in chronic experimental schistosomiasis

Schistosomiasis, a chronic disease with considerable social impact, is an important health problem in many countries. To investigate the possible use of immunomodulators as coadjuvants in the treatment of chronic Schistosoma mansoni infection, we evaluated the effect of dexamethasone on histological, hematological, and biochemical parameters that reflect disease severity and morbidity. Animals treated from the first day or after 35 days of infection, were analyzed. In both groups, dexamethasone: (1) induced a decrease in the number of granulomas in hepatic tissue without affecting the alanine aminotransferase profile, (2) reduced splenomegaly and hepatomegaly associated with disease, and (3) improved hemoglobin concentration, hematocrit values and reduced the percentage of reticulocytes, preventing the development of anemia that occurs in the chronic phase of infection. These data suggest that treatment with dexamethasone results in a mild course of murine schistosomiasis and point to this drug as a promising agent to complement S. mansoni specific treatment.

Natural Schistosoma mansoni infection in Nectomys squamipes: histopathological and morphometric analysis in comparison to experimentally infected N. squamipes and C3H/He mice

Histopathologic and morphometric (area, perimeter, major and minor diameters) analysis of hepatic granulomas isolated from twelve naturally infected Nectomys squamipes were compared to four experimentally infected ones and six C3H/He mice. Liver paraffin sections were stained for cells and extracellular matrix. Both groups of N. squamipes presented peculiar granulomas consisting predominantly of large macrophages, full of schistosome pigment, characterizing an exudative-macrophage granuloma type, smaller than the equivalent granuloma type in mouse. Naturally infected animals exhibited granulomas in different stages of development, including large number of involutional types. Morphometric analysis showed that all measurements were smaller in naturally infected animals than in other groups. The results demonstrated that both N. squamipes groups reproduced, with small variations, the hepatic granuloma aspects already described in cricetidium (Calomys callosus), showing a genetic tendency to set up strong macrophage responses and small granulomas. Unexpectedly, natural infection did not engender distinguished histopathological characteristics distinct from those derived from experimental single infection, showing changes predominantly secondary to the duration of infection. It appears that the variability of the inocula (and the number of infections?) interfere more with the quantity than with the quality of the pathological changes, denoting some morpho-functional determinism in the response to schistosomal infection dependent on the animal species.

CD154 plays a central role in regulating dendritic cell activation during infections that induce Th1 or Th2 responses

We compared splenic DC activation during infection with either the Th2 response-inducing parasite Schistosoma mansoni or with the Th1 response-inducing parasite Toxoplasma gondii. CD8alpha(+) DC from schistosome-infected mice exhibited a 2- to 3-fold increase in the expression of MHC class II, CD80, and CD40 (but not CD86) compared with DC from uninfected control animals, while CD8alpha(-) DC exhibited a 2- to 3-fold increase in the expression of MHC class II and CD80 and no alteration, compared with DC from uninfected mice, in the expression of CD86 or CD40. Intracellular staining revealed that DC did not produce IL-12 during infection with S. mansoni. In contrast, infection with T. gondii resulted in a more pronounced increase in the expression of activation-associated molecules (MHC class II, CD80, CD86, and CD40) on both CD8alpha(-) and CD8alpha(+) splenic DC and promoted elevated IL-12 production by DC. Analysis of MHC class I and of additional costimulatory molecules (ICOSL, ICAM-1, OX40L, 4-1BBL, and B7-DC) revealed a generally similar pattern, with greater indication of activation in T. gondii-infected mice compared with S. mansoni-infected animals. Strikingly, the activation of DC observed during infection with either parasite was not apparent in DC from infected CD154(-/-) mice, indicating that CD40/CD154 interactions are essential for maintaining DC activation during infection regardless of whether the outcome is a Th1 or a Th2 response. However, the ability of this activation pathway to induce IL-12 production by DC is restrained in S. mansoni-infected, but not T. gondii-infected, mice by Ag-responsive CD11c(-) cells.

Dexamethasone, a drug for attenuation of Schistosoma mansoni infection morbidity

To investigate the possible use of immunomodulators as coadjuvants in the treatment of chronic schistosomiasis, the study described in the present report evaluated the effects of dexamethasone on several parameters which reflect disease severity and morbidity. Parasitological, immunological, and histological parameters were analyzed in animals treated from the first day of infection or after 35 days of infection. In both situations, dexamethasone had no effect on the parasite burden but altered the egg distribution in tissue, indicating that under the schedule used it did not interfere with the development of adult worms or oviposition. Treated mice showed a decrease in the number of eggs in hepatic tissue, reduced granuloma sizes, reduced levels of granuloma maturation, and reduced collagen contents. Dexamethasone-treated mice also had decreased gamma interferon, interleukin-12 (IL-12), and IL-4 levels in serum and increased IL-10 levels in serum. Taken together, these data suggested a decrease in the severity of murine schistosomiasis and point to dexamethasone as a convenient and promising coadjuvant agent in the therapy of this infection.

Experimental models of Schistosoma mansoni infection

Experimental models of Schistosoma mansoni infections in mammals have contributed greatly to our understanding of the pathology and pathogenesis of infection. We consider here hepatic and extrahepatic disease in models of acute and chronic infection. Experimental schistosome infections have also contributed more broadly to our understanding of granulomatous inflammation and our understanding of Th1 versus Th2 related inflammation and particularly to Th2-mediated fibrosis of the liver.

Patterns of chemokine expression in models of Schistosoma mansoni inflammation and infection reveal relationships between type 1 and type 2 responses and chemokines in vivo

To explore the roles of chemokines in type 1 and type 2 responses in vivo, we examined mRNA expression for a panel of up to 17 chemokines in experimental mouse models using Schistosoma mansoni. These studies revealed that Mig (monokine induced by gamma interferon), cytokine-responsive gene 2/10-kDa interferon-inducible protein, RANTES, lymphotactin, macrophage inflammatory protein 1beta (MIP-1beta), JE/monocyte chemoattractant protein 1, and MIP-2 are associated with type 1 egg-induced responses and that thymus-derived chemotactic agent 3 (TCA3), eotaxin, MIP-1alpha, and MIP-1gamma are associated with type 2 egg-induced responses. After cercarial infection, both type 1-associated and type 2-associated chemokines were elevated in the livers of infected mice presensitized with eggs and recombinant interleukin-12 (rIL-12), a regimen that diminishes pathology. Neutralization of IL-12 or gamma interferon during egg deposition reversed the effects of prior treatment with rIL-12, leading to a return to larger granulomas; persistently elevated expression of TCA3, eotaxin, and MIP-1alpha; and a marked reduction in the expression of type 1-associated chemokines despite the maintenance of a dominant type 1 cytokine response in the draining lymph nodes. Our findings suggest that there are patterns of coordinate chemokine expression characteristic of type 1 and type 2 responses in vivo; that the cells recruited by a given pattern of chemokines may differ, depending on the composition of peripheral populations; and that patterns of tissue expression of chemokines may determine the character of an inflammatory response independently of the dominant pattern of differentiation of antigen-specific T cells. Our data reveal new relationships between chemokines and polarized immune responses and suggest that end organ inflammation might be altered by chemokine blockade without necessitating reversal of the phenotype of the majority of differentiated T cells.

Elevated serum levels of TNF-alpha, sTNF-RI and sTNF-RII in murine schistosomiasis correlate with schistosome oviposition and circumoval granuloma formation

Levels of circulating tumour necrosis factor (TNF-alpha) and its soluble receptors are elevated in chronic human schistosomiasis. However, the kinetics of TNF-alpha production and release of its soluble receptors have not been studied in humans or animals. Here we report on increased levels of TNF-alpha and its soluble receptors in murine schistosomiasis, beginning with schistosome oviposition and circumoval granuloma formation. TNF-alpha, sTNF-RI and sTNF-RII were measured in sera of mice infected with Schistosoma mansoni each week for 10 weeks postinfection. TNF-alpha levels increased gradually in all mice during the first 3 weeks. From 6th week postinfection, TNF-alpha levels in infected mice increased steadily, whereas those of uninfected mice remained essentially unchanged. sTNF-RI levels fluctuated in all mice during the first 3 weeks, and increased in infected mice during the following 5 weeks. sTNF-RII levels were similar in all mice for the first 4 weeks but increased in infected mice throughout the remainder of the experimental period. These data may be helpful in understanding pathogenesis in schistosomiasis as TNF-alpha plays a crucial role in circumoval granuloma formation and adversely affects schistosome fecundity.

Interleukin-12 promotes pathologic liver changes and death in mice coinfected with Schistosoma mansoni and Toxoplasma gondii

We previously demonstrated that mice concurrently infected with Schistosoma mansoni and Toxoplasma gondii undergo accelerated mortality which is preceded by severe liver damage. Abnormally high levels of serum tumor necrosis factor alpha (TNF-alpha) in the dually infected mice suggested a role for this and related proinflammatory mediators in the pathologic alterations. In order to evaluate the factors involved in increased inflammatory-mediator production and mortality, interleukin-12(-/-) (IL-12(-/-)) mice were coinfected with S. mansoni and T. gondii, and survival and immune responses were monitored. These IL-12(-/-) mice displayed decreased liver damage and prolonged time to death relative to wild-type animals also coinfected with these parasites. Relative to the response of cells from the coinfected wild-type animals, levels of TNF-alpha, gamma interferon, and NO produced by splenocytes from coinfected IL-12(-/-) mice were reduced, and levels of IL-5 and IL-10 were increased, with the net result that the immune response of the dually infected IL-12(-/-) mice was similar to that of the wild-type mice infected with S. mansoni alone. While dually infected wild-type animals succumb in the absence of overt parasitemia, the delayed death in the absence of IL-12 is associated with relatively uncontrolled T. gondii replication. These data support the view that S. mansoni-infected mice are acutely sensitive to infection with T. gondii as a result of their increased hepatic sensitivity to high levels of proinflammatory cytokines; IL-12 and TNF-alpha are implicated in this process.

IL-10 and the dangers of immune polarization: excessive type 1 and type 2 cytokine responses induce distinct forms of lethal immunopathology in murine schistosomiasis

To dissect the controversial roles of type 1 and type 2 cytokines to the pathogenesis of schistosomiasis, we generated IL-10/IL-4- and IL-10/IL-12-deficient mice that develop highly polarized type 1 and type 2 cytokine responses, respectively. Interestingly, the Th1-polarized IL-10/IL-4-deficient mice rapidly lost weight at the onset of egg-laying and displayed 100% mortality by wk 9 postinfection. This acute mortality was linked to overexpression of the proinflammatory mediators IFN-gamma, TNF-alpha, and inducible NO and the formation of nonfibrotic granulomas. Elevated serum aspartate transaminase levels confirmed that mortality was in part attributable to acute hepatotoxicity. In contrast, the Th2-polarized IL-10/IL-12-deficient mice developed a progressive wasting disease that correlated with increased hepatic fibrosis, formation of large eosinophil-rich granulomas, a 10-fold increase in IL-4 and IL-13, and significant mortality during the chronic stages of infection. Surprisingly, IL-10-deficient mice displayed pathological features that were characteristic of both extremes, while wild-type mice developed relatively successful long term chronic infections. These data demonstrate that IL-10 significantly suppresses type 1 and type 2 cytokine development in IL-4- and IL-12-deficient mice, respectively, thereby impeding the development of severe egg-induced pathology in the single cytokine-deficient animals. Together, these findings reveal the central regulatory role of IL-10 in the pathogenesis of schistosomiasis and illustrate that excessive type 1 and type 2 cytokine responses trigger distinct, but equally detrimental, forms of pathology following infection.

Significance of schistosomal granuloma modulation

Hepatic Schistosoma mansoni periovular granulomas undergo changes in size, cellular composition and appearance with time. This phenomenon, known as "immunological modulation", has been thought to reflect host immunological status. However, as modulation has not been observed outside the liver, participation of local factors, hitherto little considered, seems crucial. Components of the extracellular matrix of periovular granulomas of the mouse were particularly studied in three different organs (liver, lung and intestine) and during three periods of infection time (acute, intermediate and chronic) by means of histological, biochemical and immunofluorescence techniques, while quantitative data were evaluated by computerized morphometry, in order to investigate participation of local factors in granuloma modulation. Results confirmed modulation as a exclusively hepatic phenomenon, since pulmonary and intestinal granulomas, formed around mature eggs, did not change size and appearance with time. The matricial components which were investigated (Type I, III and IV collagens, fibronectin, laminin, proteoglycans and elastin) were found in all granulomas and in all organs examined. However, their presence was much more prominent in the liver. Elastin was only found in hepatic granulomas of chronic infection. The large amount of extracellular matrix components found in hepatic granulomas was the main change responsible for the morphological aspects of modulation. Therefore, the peculiar environment of the liver ultimately determines the changes identified in schistosomal granuloma as "modulation".

Collagen arrangement in hepatic granuloma in mice infected with Schistosoma mansoni: dependence on fiber radiation centers

The collagen structure of isolated and in situ liver granuloma from Swiss Webster mice infected with Schistosoma mansoni was sequentially and three-dimensionally analyzed during different times of infection (early acute, acute, transitional acute-chronic, and chronic phases) by laser scanning confocal microscopy and electron scanning variable vacuum microscopy. The initial granuloma structure is characterized by vascular collagen residues and by anchorage points (or fiber radiation centers), from where collagenous fibers are angularly shed and self-assembled. During the exudative-productive stage, the self-assembly of these fibers minimizes energy and mass through continuous tension and focal compression. The curvature or angles between collagen fibers probably depends on the fibroblastic or myofibroblastic organization of stress fibers. Gradually, the loose unstable lattice of the exudative-productive stage transforms into a highly packed and stable architecture as a result of progressive compactness. The three-dimensional architecture of granulomas provides increased tissue integrity, efficient distribution of soluble compounds and a haptotactic background to the cells.