Human schistosomiasis mansoni: intensity of infection differentially affects the production of interleukin-10, interferon-gamma and interleukin-13 by soluble egg antigen or adult worm antigen stimulated cultures

Profile of T and B lymphocytes in individuals resistant to Schistosoma mansoni infection

The mechanisms involved in the development of resistance to infection/reinfection by Schistosoma mansoni still arouse great interest and controversy. Some authors demonstrate that resistance to infection is attributed to a mixed Th1 and Th2 response and resistance to reinfection after repeated treatments through mechanisms associated with the Th2 response. Through flow cytometry, the phenotypic characterization of B and T lymphocytes in individuals residing in endemic areas with low parasite loads over 10 years was evaluated for the first time in humans. In this study, individuals with low parasite loads for Schistosoma mansoni had a higher proportion of Th1 and Th2 cells. In addition, lymphocytes from these individuals showed a higher degree of expression of costimulatory molecules CD28 and CTLA-4 and regulatory molecules FoxP3 and IL-10, when compared to individuals with high parasite loads. Our data indicate that the control of the parasite load of S. mansoni must be associated with a Th1, Th2, and regulatory response, and that further studies are needed to elucidate the possibility of mechanisms associated with the hyporesponsiveness of lymphocytes from individuals with high parasite loads.

The therapeutic implications of activated immune responses via the enigmatic immunoglobulin D

Immunoglobulin D (IgD) is an enigmatic antibody and the least appreciated member of the immunoglobulin (Ig) family. Since its discovery over half a century ago, the essence of its function in the immune system has been somewhat enigmatic and less well-defined than other antibody classes. Membrane-bound IgD (mIgD) is mostly recognized as B-cell receptor (BCR) while secreted IgD (sIgD) has been recently implicated in 'arming' basophils and mast cells in mucosal innate immunity. Activations of immune responses via mIgD-BCR or sIgD by specific antigens or anti-IgD antibody thereby produce a broad and complex mix of cellular, antibody and cytokine responses from both the innate and adaptive immune systems. Such broadly activated immune responses via IgD were initially deemed to potentiate and exacerbate the onset of autoimmune and allergic conditions. Paradoxically, treatments with anti-IgD antibody suppressed and ameliorated autoimmune conditions and allergic inflammations in mouse models without compromising the host's general immune defence, demonstrating a unique and novel therapeutic application for anti-IgD antibody treatment. Herein, this review endeavored to collate and summarize the evidence of the unique characteristics and features of activated immune responses via mIgD-BCR and sIgD that revealed an unappreciated immune-regulatory function of IgD in the immune system via an amplifying loop of anti-inflammatory Th2 and tolerogenic responses, and highlighted a novel therapeutic paradigm in harnessing these immune responses to treat human autoimmune and allergic conditions.

Association of IL-9, IL-10, and IL-17 Cytokines With Hepatic Fibrosis in Human Schistosoma mansoni Infection

This is a case series study to evaluate immunological markers associated with schistosomiasis advanced fibrosis, including 69 patients from an endemic area from the State of Sergipe and from the Hepatology Service of the University Hospital in Sergipe, Brazil. Hepatic fibrosis was classified based on Niamey protocol for ultrasonography (US). Immune response to Schistosoma mansoni antigens was evaluated by stimulating peripheral blood mononuclear cells (PBMCs) from these patients with either adult worm (SWAP-10 μg/ml) or egg (SEA-10 μg/ml) antigens or purified protein derivative of turberculin (PPD-10 μg/ml) or phytohemagglutinin (PHA-1 μg/ml) for 72 h. The levels of IFN-γ, TNF-α, IL-5, IL-10, and IL-17 were measured in these supernatants by ELISA and IL-9 by Luminex. Single nucleotide polymorphisms in IL-17, IL10, and CD209 genes were genotyped using TaqMan probe by qPCR. Higher levels of IL-9, IL-10, and IL-17 were found in PBMC supernatants of patients with advanced hepatic fibrosis. Direct correlations were detected between IL-9 and IL-17 levels with US spleen sizes, portal vein diameters, and periportal thickening. The CD209 rs2287886 AG polymorphism patients produce higher IL-17 levels. Together, these data suggest a role of these cytokines in the immunopathogenesis of advanced fibrosis in human schistosomiasis.

Association of IL-9, IL-10, and IL-17 Cytokines With Hepatic Fibrosis in Human Schistosoma mansoni Infection

This is a case series study to evaluate immunological markers associated with schistosomiasis advanced fibrosis, including 69 patients from an endemic area from the State of Sergipe and from the Hepatology Service of the University Hospital in Sergipe, Brazil. Hepatic fibrosis was classified based on Niamey protocol for ultrasonography (US). Immune response to Schistosoma mansoni antigens was evaluated by stimulating peripheral blood mononuclear cells (PBMCs) from these patients with either adult worm (SWAP-10 μg/ml) or egg (SEA-10 μg/ml) antigens or purified protein derivative of turberculin (PPD-10 μg/ml) or phytohemagglutinin (PHA-1 μg/ml) for 72 h. The levels of IFN-γ, TNF-α, IL-5, IL-10, and IL-17 were measured in these supernatants by ELISA and IL-9 by Luminex. Single nucleotide polymorphisms in IL-17, IL10, and CD209 genes were genotyped using TaqMan probe by qPCR. Higher levels of IL-9, IL-10, and IL-17 were found in PBMC supernatants of patients with advanced hepatic fibrosis. Direct correlations were detected between IL-9 and IL-17 levels with US spleen sizes, portal vein diameters, and periportal thickening. The CD209 rs2287886 AG polymorphism patients produce higher IL-17 levels. Together, these data suggest a role of these cytokines in the immunopathogenesis of advanced fibrosis in human schistosomiasis.

Impact of fascioliasis reinfection on Fasciola hepatica egg shedding: relationship with the immune-regulatory response

Fascioliasis is a disease caused by liver flukes. In human fascioliasis hyperendemic areas, reinfection and chronicity are the norm. Control strategies in humans require the use of egg count techniques to calculate the appropriate treatment dose for colic risk prevention. The present study investigates how fascioliasis reinfection affects liver fluke egg shedding and its relationship with the immune-regulatory response. The experimental design reproduced the usual reinfection/chronicity conditions in human fascioliasis endemic areas and included Fasciola hepatica primo-infected Wistar rats (PI) and rats reinfected at 4 weeks (R4), 8 weeks (R8), 12 weeks (R12), and negative control rats. In a longitudinal study (0-20 weeks post-infection, p.i.), serical IgG1 levels and eggs per gram of faeces (epg) were analyzed. In a cross-sectional study, the expression of the genes associated with Th1 (Ifng, Il12a, Il12b, Nos2), Th2 (Il4, Arg1), Treg (Foxp3, Il10, Tgfb, Ebi3), and Th17 (Il17) in the spleen and thymus was analyzed. In R8 and R12, transiently higher averages of epg and epg/worm in reinfected groups vs PI group were detected at least in the weeks following reinfection. The kinetics of IgG1 levels shows that reinfected groups followed a pattern similar to the one in the PI group, but transiently higher averages of IgG1 levels in reinfected groups vs the PI group were detected in the weeks following reinfection. Epg correlated with IgG1 levels and also with systemic Il10 and thymic Ifng, and Il10 expression levels. These results suggest that epg depends on the Th1 and Treg phenotype and that the determination of the fluke burden by epg is likely to be an overestimation in cases of recent reinfection in low burden situations. A strategy to facilitate the implementation of epg count techniques and the subsequent decision on the appropriate treatment dose for each patient to prevent colic risk is required.

Liver damage in schistosomiasis is reduced by adipose tissue-derived stem cell therapy after praziquantel treatment

Background

In view of the potential immunosuppressive and regenerative properties of mesenchymal stem cells (MSC), we investigated whether transplantation of adipose tissue-derived stem cells (ASC) could be used to control the granulomatous reaction in the liver of mice infected with Schistosoma mansoni after Praziquantel (PZQ) treatment.

Methodology/Prinicpal findings

C57BL/6 mice infected with S. mansoni were treated with PZQ and transplanted intravenously with ASC from uninfected mice. Liver morpho-physiological and immunological analyses were performed. The combined PZQ/ASC therapy significantly reduced the volume of hepatic granulomas, as well as liver damage as measured by ALT levels. We also observed that ASC accelerated the progression of the granulomatous inflammation to the advanced/curative phase. The faster healing interfered with the expression of CD28 and CTLA-4 molecules in CD4⁺ T lymphocytes, and the levels of IL-10 and IL-17 cytokines, mainly in the livers of PZQ/ASC-treated mice.

Conclusions

Our results show that ASC therapy after PZQ treatment results in smaller granulomas with little tissue damage, suggesting the potential of ASC for the development of novel therapeutic approaches to minimize hepatic lesions as well as a granulomatous reaction following S. mansoni infection. Further studies using the chronic model of schistosomiasis are required to corroborate the therapeutic use of ASC for schistosomiasis.

Schistosomiasis is the second most prevalent parasitic disease in the world and is caused by the Schistosoma trematode. This disease is characterized by a granulomatous reaction around parasite eggs trapped in the tissues. The liver is one of the most affected organs and can develop severe fibrosis. Praziquantel (PZQ) is the treatment for schistosomiasis and kills the adult the worm; however, inflammation still persists around the eggs in the tissues. Mesenchymal stem cells (MSC) have been extensively studied as an alternative therapy to repair tissues and to stop inflammation due to their potential to differentiate in several cells types (bone, cartilage, fat, tendon, muscle, and marrow stroma), and to interfere with immune responses. This scenario has motivated the authors to investigate the use of MSC extract from adipose tissue (ASC) associated with PZQ to treat schistosomiasis. Briefly, mice were treated with PZQ followed by ASC injection showing significant reduction of the granulomas and normal levels of the enzyme alanine aminotransferase, an indicator of liver damage. These results suggest that ASC has the potential to be used as a novel therapeutic approach to control inflammation following infection by S. mansoni or liver disorders. Although the findings are promising, further studies using the chronic model of schistosomiasis are required to confirm using ASC for schistosomiasis therapy.

Systemic Cytokine and Chemokine Profiles in Individuals With Schistosoma mansoni Infection and Low Parasite Burden

Intestinal schistosomiasis, caused by the parasitic trematode Schistosoma mansoni, is a chronic disease and the prolonged and continuous exposure to S. mansoni antigens results in a deviation of the host's immune response. For diagnosis, the Kato-Katz (KK) method is recommended, however, this method showed low accuracy in areas of low endemicity. This study aimed to characterize the cytokine and chemokine profile of individuals with an extremely low parasite load (<4 eggs per gram of feces), e.g., individuals who were detected by alternative parasitological methods, such as the saline gradient and/or Helmintex®. In order to search for immunological markers for infection, the immunological profile in serum samples of these individuals was then compared with patients detected with the KK method and with a higher parasite load and with individuals repetitively negative by extensive stool exams. The study was conducted in Northern Minas Gerais in a rural area of the Municipality of Januária. Serum samples of a total of 139 parasitologically well-characterized individuals were assessed for the following immunological markers by commercially available immunoassays: TNF-α, IL-1β, IL-6, IL-17A, IL-5, IL-10, IL-13, IL-33, IL-27, CCL3, CCL5, CXCL10, CCL11, and CCL17. As a result, there were no significant differences in concentrations or frequencies for immunological markers between egg-negative individuals or individuals with ultra-low (<4 epg) or low (4-99 epg) parasite loads. However, we found significant correlations between egg counts and eosinophil counts and between egg counts and IL-1β or TNF-α concentrations. The most striking alterations were found in individuals with the highest parasite load (≥100 epg). They had significantly higher TNF-α concentrations in serum when compared with individuals with a low parasite load (4-99 epg) and CCL17 concentrations were significantly elevated when compared with egg-negative individuals. Radar diagrams of frequencies for cytokine and chemokine responders in each infection group confirmed a distinct profile only in the infection group with highest parasite loads (≥100 epg).

Functional Studies of T Regulatory Lymphocytes in Human Schistosomiasis in Western Kenya

Immunoregulation is considered a common feature of Schistosoma mansoni infections, and elevated levels of T regulatory (Treg) lymphocytes have been reported during chronic human schistosomiasis. We now report that the removal of Treg (CD4+/CD25^hi/CD127^low lymphocytes) from peripheral blood mononuclear cells (PBMCs) of S. mansoni–infected individuals leads to increased levels of phytohemagglutinin (PHA)-stimulated interferon gamma (IFNγ) production and decreased interleukin-10 (IL-10) responses. Exposure to schistosome antigens did not result in measurable IFNγ by either PBMC or Treg-depleted populations. Interleukin-10 responses to soluble egg antigens (SEA) by PBMC were unchanged by Treg depletion, but the depletion of Treg greatly decreased IL-10 production to soluble worm antigenic preparation (SWAP). Proliferative responses to PHA increased upon Treg removal, but responses to SEA or SWAP did not, unless only initially low responders were evaluated. Addition of anti-IL-10 increased PBMC proliferative responses to either SEA or SWAP, but did not alter responses by Treg-depleted cells. Blockade by anti-transforming growth factor-beta (TGF-β) increased SEA but not SWAP proliferative responses by PBMC, whereas anti-TGF-β increased both SEA- and SWAP-stimulated responses by Treg-depleted cultures. Addition of both anti-IL-10 and anti-TGF-β to PBMC or Treg-depleted populations increased proliferation of both populations to either SEA or SWAP. These studies demonstrate that Treg appear to produce much of the antigen-stimulated IL-10, but other cell types or subsets of Treg may produce much of the TGF-β. The elevated levels of Treg seen in chronic schistosomiasis appear functional and involve IL-10 and TGF-β in antigen-specific immunoregulation perhaps leading to regulation of immunopathology and/or possibly decreased immunoprotective responses.

Protection and pathology during parasite infection: IL-10 strikes the balance

The host response to infection requires an immune response to be strong enough to control the pathogen but also restrained, to minimize immune-mediated pathology. The conflicting pressures of immune activation and immune suppression are particularly apparent in parasite infections, where co-evolution of host and pathogen has selected many different compromises between protection and pathology. Cytokine signals are critical determinants of both protective immunity and immunopathology, and, in this review, we focus on the regulatory cytokine IL-10 and its role in protozoan and helminth infections. We discuss the sources and targets of IL-10 during parasite infection, the signals that initiate and reinforce its action, and its impact on the invading parasite, on the host tissue, and on coincident immune responses.

Epidemiology of schistosomiasis in Gezira area Central Sudan and analysis of cytokine profiles

OBJECTIVE

To determine and compare anti-schistosoma IgG, interleukin-10 (IL-10) and interferon-γ(IFN-γ) levels in the serum of patients and endemic controls and to investigate the epidemiological situation of Al-Hebaika village in the northern part of Gezira Agricultural Irrigation Scheme in 2005.

METHODS

During 2005 survey, serum were collected from 118 villagers. Sixty eight were parasitological positive (patients), and 50 were negative (endemic controls). Indirect ELISA was used to measure and compare the levels of immunoglobulin G (IgG) against Schistsoma mansoni (S. mansoni) soluble worm antigen (SWA) in the patients and endemic control groups from the village and compared with 20 healthy non endemic controls. Sandwich ELISA was also used to measure and compare IL-10 and IFN-γ in the serum of the selected groups.

RESULTS

The overall prevalence of S. haematobium was 20.0% and 0.9% in the first and the second surveys respectively, while the intensity of infection was the same in the two surveys 1.38 [geometric mean egg count (GMFC)]. The overall prevalence of S. mansoni infection was 68.5% and 15.4%, while the intensity of infection was 2.75 (GMEC) and 1.70 (GMEC) in the two surveys respectively. IgG reactivity against SWA showed no significant difference between Schistosoma positive patients and endemic controls. However, there were high significant differences between each of these two groups and the non endemic control group (P= 0,000). Schistosoma patients and exposed controls had significantly higher IL-10 concentration compared with non endemic controls. While endemic controls showed significantly higher IFN-γ concentration than patients (P = 0.000). Also there was very significant difference between IFN-γ levels of each of patients endemic controls and that of the non endemic controls (P = 0.003).

CONCLUSIONS

The study concluded that IFN-γ has a role in the natural resistant to schistosoma mansoni infection. The prevalence and intensity of S. mansoni in the Gezira Irrigation Scheme was greatly reduced. S. haematobium has disappeared from the area.

Cytokine profile, proliferation and phosphorylation of ERK1/2 and Akt in circulating mononuclear cells from individuals during the chronic intestinal phase of Schistosomiasis mansoni infection

Background

The immune response to Schistosoma mansoni is characterized by a granulomatous reaction around the parasite eggs that are trapped in the host liver, and this reaction modulates the immune response during the chronic phase of the disease. The typical peripheral blood mononuclear cell (PBMC) response of patients during the chronic intestinal phase of infection is characterized by a decreased response to an S. mansoni soluble egg antigen. To obtain a greater understanding of Schistosoma infections, this study investigated the effects of the soluble egg antigen (SEA) and soluble adult worm antigen (SWAP) of S. mansoni on cellular proliferation, cytokine production, and ERK1/2 and Akt phosphorylation in PBMCs from infected (XTO) and egg-negative (NI) individuals living in the same endemic area.

Methods

The activation status was evaluated by cell immunophenotypic staining (cytometry). The cell proliferation assay was by CFSE method. Cytokine detection assay (Th1 and Th2) was by Cytometric Bead and Array phosphorylation status was by ELISA.

Results

The XTO, NI and BD (blood donor) individuals from an area not endemic for schistosomiasis were compared. The CD4⁺ T lymphocyte proliferation rate was lower in the XTO group, but not the NI group, after SEA stimulation compared to the BD group. The CD8⁺ T cell proliferation rate was lower in the XTO group in the unstimulated cultures and after both SEA and SWAP stimulation compared to the BD group. Cytokine analysis after either SEA or SWAP stimulation showed a balanced cytokine pattern in the XTO and NI groups. ERK1/2 and Akt phosphorylation were only marginally detected in all groups; however, a decrease in ERK 1/2 phosphorylation was observed in the SWAP-stimulated XTO group compared to both the NI and BD groups.

Conclusions

The data indicate that SEA-stimulated CD4⁺ T cells from infected patients have a lower proliferation rate than the same cells from the NI group. Furthermore, we observed that SWAP stimulation influences ERK1/2 phosphorylation in the XTO group.

Integrated analysis of innate, Th1, Th2, Th17, and regulatory cytokines identifies changes in immune polarisation following treatment of human schistosomiasis

Background. Schistosomiasis elicits cross-regulatory immune responses, but it is unclear how antihelminthic treatment affects this balance. This study integrates data on 13 cytokines elicited by 3 schistosome to examine how praziquantel treatment alters immune polarization and whether post-treatment cytokine profiles influence reinfection status.

Methods. Venous blood from 72 Schistosoma haematobium–exposed participants was cultured with schistosome egg, adult worm, and cercaria antigens pre– and 6 weeks post–praziquantel treatment. Innate inflammatory (tumor necrosis factor α [TNF-α], interleukin(IL-)-6, IL-8), Th1 (interferon γ [IFN-γ], IL-2, IL-12p70), Th2 (IL-4, IL-5, IL-13), Th17 (IL-17A, IL-21, IL-23p19), and regulatory (IL-10) cytokines were quantified via enzyme-linked immunosorbent assay. Cytokine data was integrated using nonmetric multidimensional scaling and factor analysis.

Results. Egg-specific cytokine phenotypes became more proinflammatory post-treatment due to increased TNF-α, IL-6, IL-8, IFN-γ, IL-12p70, and IL-23 levels. Post-treatment cercariae-specific responses were also more proinflammatory reflecting elevated IL-8. In contrast, post-treatment adult worm-specific responses were less inflammatory, reflecting lower post-treatment IL-6. A combination of egg-induced IL-6, IL-12p70, IL-21, and IL-23 and adult worm-induced IL-5 and IL-21 post-treatment was associated with reduced reinfection risk 18 months later.

Conclusions. Praziquantel treatment markedly alters polarization of schistosome-specific cytokine responses, and these changes, particularly in response to egg-stage parasites, may promote resistance to reinfection.

Age-related patterns in human myeloid dendritic cell populations in people exposed to Schistosoma haematobium infection

BACKGROUND

Urogenital schistosomiasis is caused by the helminth parasite Schistosoma haematobium. In high transmission areas, children acquire schistosome infection early in life with infection levels peaking in early childhood and subsequently declining in late childhood. This age-related infection profile is thought to result from the gradual development of protective acquired immunity. Age-related differences in schistosome-specific humoral and cellular responses have been reported from several field studies. However there has not yet been a systematic study of the age-related changes in human dendritic cells, the drivers of T cell polarisation.

METHODS

Peripheral blood mononuclear cells were obtained from a cohort of 61 Zimbabwean aged 5-45 years with a S. haematobium prevalence of 47.5%. Two subsets of dendritic cells, myeloid and plasmacytoid dendritic cells (mDCs and pDCs), were analyzed by flow cytometry.

FINDINGS

In this population, schistosome infection levels peaked in the youngest age group (5-9 years), and declined in late childhood and adulthood (10+ years). The proportions of both mDCs and pDCs varied with age. However, for mDCs the age profile depended on host infection status. In the youngest age group infected people had enhanced proportions of mDCs as well as lower levels of HLA-DR on mDCs than un-infected people. In the older age groups (10-13 and 14-45 years) infected people had lower proportions of mDCs compared to un-infected individuals, but no infection status-related differences were observed in their levels of HLA-DR. Moreover mDC proportions correlated with levels of schistosome-specific IgG, which can be associated with protective immunity. In contrast proportions of pDCs varied with host age, but not with infection status.

CONCLUSIONS

Our results show that dendritic cell proportions and activation in a human population living in schistosome-endemic areas vary with host age reflecting differences in cumulative history of exposure to schistosome infection.

Acquired immune heterogeneity and its sources in human helminth infection

Similarities in the immunobiology of different parasitic worm infections indicate that co-evolution of humans and helminths has shaped a common anti-helminth immune response. However, recent in vitro and immuno-epidemiological studies highlight fundamental differences and plasticity within host-helminth interactions. The 'trade-off' between immunity and immunopathology inherent in host immune responses occurs on a background of genetic polymorphism, variable exposure patterns and infection history. For the parasite, variation in life-cycle and antigen expression can influence the effector responses directed against them. This is particularly apparent when comparing gastrointestinal and tissue-dwelling helminths. Furthermore, insights into the impact of anti-helminthic treatment and co-infection on acquired immunity suggest that immune heterogeneity arises not from hosts and parasites in isolation, but also from the environment in which immune responses develop. Large-scale differences observed in the epidemiology of human helminthiases are a product of complex host-parasite-environment interactions which, given potential for exposure to parasite antigens in utero, can arise even before a parasite interacts with its human host. This review summarizes key differences identified in human acquired immune responses to nematode and trematode infections of public health importance and explores the factors contributing to these variations.

Hepatic stellate cells and parasite-induced liver fibrosis

Fibrogenesis is a common feature of many diseases where there is severe insult to the liver. The hepatic stellate cell trans-differentiation into a myofibroblast has been identified as an important event in liver fibrogenesis and has been well investigated over the last few years in a number of liver diseases. The trans-differentiation process can be monitored in vitro by evaluation of biomarkers that are characteristic of normal quiescent hepatic stellate cells or activated myofibroblasts. Two major parasitic diseases associated with liver injury and fibrosis are schistosomiasis and echinococcosis. Recent studies have highlighted a role for activated hepatic stellate cells in both murine and human schistosomiasis as well as demonstrating that schistosome antigens are able to regulate this trans-differentiation process. Study of the hepatic stellate cell and its interaction with parasite-derived antigens may be pivotal in our understanding of the pathology associated with schistosomiasis and other parasitic diseases, including echinococcosis, as well as revealing new information on the trans-differentiation process in this cell type.

At homeostasis filarial infections have expanded adaptive T regulatory but not classical Th2 cells

Despite the well-documented immune suppression associated with human helminth infections, studies characterizing the immune response at the single-cell level are scanty. We used multiparameter flow cytometry to characterize the type of effector (Th1, Th2, and Th17) and regulatory (natural T regulatory cells [nTregs] and adaptive Treg cells [aTreg/type 1 regulatory cells (Tr1s)]) CD4(+) and CD8(+) T cells in filaria-infected (Fil(+)) and -uninfected (Fil(-)) individuals at homeostasis (in the absence of stimulation). Frequencies of CD4(+) lymphocytes spontaneously producing IL-4, IL-10, and IL-17A were significantly higher in Fil(+), as were those of IL-10(+)/IL-4(+) double-producing CD4(+) cells. Interestingly, frequencies of Th17 and aTreg/Tr1s but not classical Th1 or Th2 cells were significantly increased in Fil(+) compared to Fil(-) individuals. Although the frequency of nTreg was increased in Fil(+), IL-10 was overwhelmingly produced by CD4(+)CD25(-) cells. Moreover, the concentration of IL-10 produced spontaneously in vitro strongly correlated with the integrated geometric mean fluorescence intensity of IL-10-producing aTreg/Tr1s in Fil(+). Together, these data show that at steady state, IL-10-producing aTreg/Tr1 as well as nTreg and effector Th17 CD4(+) cells are expanded in vivo in human filarial infections. Moreover, we have established baseline ex vivo frequencies of effector and Tregs at homeostasis at a population level.

[Schistosoma-associated chronic septicemic salmonellosis: evolution of knowledge and immunopathogenic mechanisms]

Chronic septicemic salmonellosis is an individualized clinical entity characterized by prolonged fever with enlargement of the liver and spleen that occurs in Schistosoma-infected individuals who are coinfected with Salmonella. Several immunopathogenic mechanisms are involved, and they depend on the peculiarities of the interactions between Salmonella and various species of the genus Schistosoma. The modifications to the immune system that are caused by parasite infection are responsible for the evolution of the disease. In this review, we analyze the evolution of the knowledge on this entity and discuss the possible immuno-physiopathogenic mechanisms that contribute towards its development.

Review series on helminths, immune modulation and the hygiene hypothesis: immunity against helminths and immunological phenomena in modern human populations: coevolutionary legacies?

Although the molecules and cells involved in triggering immune responses against parasitic worms (helminths) remain enigmatic, research has continued to implicate expansions of T-helper type 2 (Th2) cells and regulatory T-helper (T(reg)) cells as a characteristic response to these organisms. An intimate association has also emerged between Th2 responses and wound-healing functions. As helminth infections in humans are associated with a strong Th2/T(reg) immunoregulatory footprint (often termed a 'modified Th2' response), plausible links have been made to increased susceptibility to microbial pathogens in helminth-infected populations in the tropics and to the breakdowns in immunological control (allergy and autoimmunity) that are increasing in frequency in helminth-free developed countries. Removal of helminths and their anti-inflammatory influence may also have hazards for populations exposed to infectious agents, such as malaria and influenza, whose worst effects are mediated by excessive inflammatory reactions. The patterns seen in the control of helminth immunity are discussed from an evolutionary perspective. Whilst an inability to correctly regulate the immune system in the absence of helminth infection might seem highly counter-adaptive, the very ancient and pervasive relationship between vertebrates and helminths supports a view that immunological control networks have been selected to function within the context of a modified Th2 environment. The absence of immunoregulatory stimuli from helminths may therefore uncover maladaptations that were not previously exposed to selection.

Immuno-epidemiology of Schistosoma mansoni infections in endemic populations co-infected with soil-transmitted helminths: present knowledge, challenges, and the need for further studies

This article reviews studies on epidemiological and immunological interactions between Schistosoma mansoni and soil-transmitted helminths (STH) in co-infected patients from endemic areas. In Brazil, co-infections with schistosomes and intestinal nematodes, such as Ascaris lumbricoides, Trichuris trichiura and the hookworms, are still common, especially in poor rural areas. Important factors in the co-occurrence of different helminth species are favorable environmental conditions supporting intermediate hosts and the survival of larval stages outside the human host, widespread poverty, and low levels of hygiene and sanitation. The few existing epidemiological surveys on helminth co-infections in humans indicate positive associations between schistosomes and STH, which means high prevalences of mixed infections, as well as higher intensities of infection in co-infected patients. However, these positive interactions appear to depend on the number of different helminth species present and on the intensity of infection in each individual. For the humoral immune response in co-infected patients, much cross-reactivity in antibody responses against antigenic preparations from schistosomes and STH is observed. Data on cellular immune responses in multiply infected patients are still scarce and additive effects on the cellular reactivity and the down-modulation of cytokines are proposed.

Potential immunomodulatory effects of plant lectins in Schistosoma mansoni infection

Lectins are sugar-binding glycoproteins that can stimulate, in a non-antigen-specific fashion, lymphocytes, leading to proliferation and cytokine production. Some lectins are utilized as in vitro mitogenic lymphocyte stimulators and their use as immunomodulators against infectious diseases has been evaluated experimentally. In the experimental murine model, the immune response to schistosomiasis is Th1-like during the initial stage of infection, with a shift towards a Th2-like response after oviposition. We report the response of schistosomiasis patients' (n=37) peripheral blood mononuclear cells (PBMC) to stimulation by lectins, including newly isolated lectins from Brazilian flora, and by Schistosomamansoni soluble egg antigens (SEA). Cytokine production upon lectin stimulation ex vivo was assessed in PBMC supernatants, collected at 24 and 72 h, by sandwich ELISA to IL-5, IL-10, TNF-alpha and IFN-gamma. In PBMC from infected patients all but one of the lectins induced a Th2-like cytokine response, characterized by elevated IL-5 production that was higher than that induced by SEA stimulation alone. Our results show that the Th2 environment present during schistosomiasis is not affected and that it may be further stimulated by the presence of lectins.

Eosinophil activation status, cytokines and liver fibrosis in Schistosoma mansoni infected patients

We have been investigating whether human eosinophils play an important role in schistosomiasis mansoni morbidity. Our main focus has been on the activation-related cell surface markers (CD23/CD69/CD25/HLA-DR/CD28/CD80) and the detection of TNF-alpha, IL-4 and IL-5 in peripheral blood eosinophils from chronic Schistosoma mansoni-infected patients. Our studies compare both, intestinal (INT) and individuals with periportal fibrosis (FIB). Our major findings, point to distinct profile of activation-related surface markers on eosinophils as the hallmark of disease morbidity during chronic S. mansoni infection. Up-regulation of several activation-related markers was observed on eosinophils from FIB group, but not INT, which include early activation markers, such as CD69 and CD23. INT displayed a distinct profile, with up-regulation of molecules related to the late activation (CD25, HLA-DR, CD28 and CD80). These results suggest that some immunoregulatory events may take place controlling the early eosinophil activation in the INT group. Higher levels of eosinophil-derived cytokines were observed in FIB, regardless the antigen stimulation in vitro. A mixed cytokine pattern, characterized by positive correlation between TNF-alpha, IL-4 and IL-5 was observed in both INT and FIB. However, lack of correlation between the cytokine expression and the eosinophil activation status points out that even those FIB patients presenting minor increment on eosinophil activation displayed higher levels of cytokine-positive eosinophils. Indeed, the positive association between lymphocyte-derived IL-10 and the eosinophils cytokine profile was observed exclusively in INT further emphasize our hypothesis that immunoregulatory events take place controlling disease morbidity in human schistosomiasis. The impaired IL-10-driven immunoregulatory function may play an important role on the establishment of pathology in patients bearing periportal fibrosis.

Human schistosomiasis mansoni: immune responses during acute and chronic phases of the infection

Schistosoma mansoni infection may occur either as an acute infection in individuals who have recently visited an endemic area, with no previous contact with the parasite, or as a lasting chronic disease, if not interrupted by specific chemotherapy. The acute phase is characterized by symptoms such as fever, cough, diarrhea, anorexia, and arthralgias in combination with leukocytosis and eosinophilia, and a high cellular immune response to schistosome antigens especially those from the parasite's eggs. In the chronic phase, most patients living in endemic areas are asymptomatic, and their immune responses to egg antigens are modulated. A few develop periportal fibrosis of the liver, which may result in the hepatosplenic form of the disease. The humoral response (IgG, IgM and IgE) in acute patients to egg and worm antigens does not differ from the chronic phase. However, a high level of IgG and IgM antibodies to KLH were detected in acute patients. Acute patients express a considerably higher in vitro cellular responsiveness than do chronic patients, especially to egg antigens. They present a mixed profile of Th1 and Th2 cytokines. Ultrasound examinations of endemic population reveal a high heterogeneity between the patients as regards the presence and intensity of periportal fibrosis. Most patients are asymptomatic and their immune responses to schistosoma egg antigens (SEA) are modulated. In contrast, a high percentage of patients with incipient fibrosis (early stage of hepatosplenic) responded strongly to SEA. Patients with advanced hepatosplenic disease were likely to be non-responders to SEA. Most of the chronic patients presented a Th2 profile with low production of interferon-gamma (IFN-gamma). The intensity of infection favors the production of interleukin (IL)-10. After adjusting for age, sex, and intensity of infection, a strong correlation was observed between the production of IL-13 and the degree of fibrosis. Chronic asymptomatic patients and those with incipient fibrosis expressed very high levels of heterogeneity of their antibody responses. IgG response to soluble worm antigen preparation (SWAP) was distinct and significantly higher in hepatosplenic patients than in those asymptomatic or with incipient fibrosis. Levels of IgG4 to SEA were significantly higher in sera from patients with incipient fibrosis as compared to uninfected and hepatosplenic groups. Polyclonal idiotypic antibodies and their fragments F(ab')2, directly stimulate in culture T cells of schistosomiasis patients in presence of IL-1. Polyclonal idiotypic antibodies are able to modulate in vitro granuloma formation around SEA-polyacrylamide. The importance of idiotypes for protection or pathology in schistosomiasis is still not clear.

Coinfection with the intestinal nematode Heligmosomoides polygyrus markedly reduces hepatic egg-induced immunopathology and proinflammatory cytokines in mouse models of severe schistosomiasis

Infection with the trematode helminth Schistosoma mansoni results in a parasite egg-induced, CD4 T-cell-mediated, hepatointestinal granulomatous and fibrosing inflammation that varies greatly in severity, with a higher frequency of milder forms typically occurring in regions where the disease is endemic. One possible explanation for this is that in these regions the degree of inflammation is lessened by widespread concurrent infection with gastrointestinal nematodes. We tested this hypothesis by establishing a murine coinfection model in which mice were infected with the intestinal nematode parasite Heligmosomoides polygyrus prior to infection with S. mansoni. In CBA mice that naturally display a severe form of schistosomiasis, preinfection with H. polygyrus resulted in a marked reduction in schistosome egg-induced hepatic immunopathology, which was associated with significant decreases in the levels of interleukin-17 (IL-17), gamma interferon, tumor necrosis factor alpha, IL-23, IL-6, and IL-1beta and with increases in the levels of IL-4, IL-5, IL-10, and transforming growth factor beta in mesenteric lymph node cells, purified CD4 T cells, and isolated liver granuloma cells. There also were increases in liver Ym1 and forkhead box P3 transcription factor expression. In another model of high-pathology schistosomiasis induced in C57BL/6 mice by immunization with schistosome egg antigens in complete Freund's adjuvant, coinfection with the nematodes also resulted in a marked inhibition of hepatic immunopathology accompanied by similar shifts in cytokine production. These findings demonstrate that intestinal nematodes prevent Th1- and Th17-cell-mediated inflammation by promoting a strong Th2-polarized environment associated with increases in the levels of alternatively activated macrophages and T regulatory cells, which result in significant amelioration of schistosome-induced immunopathology.

Effect of chemotherapy with praziquantel on the production of cytokines and morbidity associated with schistosomiasis mansoni

The objective of the present study was to test the hypothesis that treatment of schistosomiasis mansoni with praziquantel can alter significantly the immune response of patients and generate a reversal of the level of fibrosis. Peripheral blood mononuclear cell (PBMC) samples were collected from, and abdominal ultrasound examinations conducted on, volunteers infected with Schistosoma mansoni and living in an area where the disease is endemic, both prior to and one year after treatment with praziquantel. Subjects were classified into groups according to the level of pathology (i.e., absent, incipient, moderate, or severe fibrosis). PBMCs were stimulated with schistosome soluble egg antigens (SEA), and the levels of production of the cytokines gamma interferon (IFN-gamma), tumor necrosis factor alpha, transforming growth factor beta, and interleukin-4 (IL-4), IL-10, and IL-13 were determined. The chemotherapy was effective in reducing morbidity, particularly for individuals presenting with severe fibrosis. When levels of cytokine production in posttreatment PBMC cultures stimulated by SEA were categorized as low or high, significant differences in the distribution of IL-13 levels between groups presenting with or not presenting with fibrosis were established. Comparison of pre- and posttreatment SEA-induced cytokine levels in individuals who had experienced no change in the grade of fibrosis following chemotherapy revealed that the level of IFN-gamma decreased in subjects with fibrosis whereas that of IL-10 decreased in individuals with and without fibrosis. The data suggest that chemotherapy is effective in reducing the morbidity of the disease and that the level of IL-13 may be a useful indicator of the persistence of fibrosis following treatment.

Schistosome vaccines: a critical appraisal

An effective schistosome vaccine is a desirable control tool but progress towards that goal has been slow. Protective immunity has been difficult to demonstrate in humans, particularly children, so no routes to a vaccine have emerged from that source. The concept of concomitant immunity appeared to offer a paradigm for a vaccine operating against incoming larvae in the skin but did not yield the expected dividends. The mining of crude parasite extracts, the use of monoclonal antibodies and protein selection based on immunogenicity produced a panel of vaccine candidates, mostly of cytoplasmic origin. However, none of these performed well in independent rodent trials, but glutathione-S-transferase from Schistosoma haematobium is currently undergoing clinical trials as an anti-fecundity vaccine. The sequencing of the S. mansoni transcriptome and genome and the development of proteomic and microarray technologies has dramatically improved the possibilities for identifying novel vaccine candidates, particularly proteins secreted from or exposed at the surface of schistosomula and adult worms. These discoveries are leading to a new round of protein expression and protection experiments that will enable us to evaluate systematically all the major targets available for immune intervention. Only then will we know if schistosomes have an Achilles' heel.

Cytokine responses to Schistosoma haematobium in a Zimbabwean population: contrasting profiles for IFN-gamma, IL-4, IL-5 and IL-10 with age

BACKGROUND

The rate of development of parasite-specific immune responses can be studied by following their age profiles in exposed and infected hosts. This study determined the cytokine-age profiles of Zimbabweans resident in a Schistosoma haematobium endemic area and further investigated the relationship between the cytokine responses and infection intensity.

METHODS

Schistosome adult worm antigen-specific IFN-gamma, IL-4, IL-5 and IL-10 cytokine responses elicited from whole blood cultures were studied in 190 Zimbabweans exposed to S. haematobium infection (aged 6 to 40 years old). The cytokines were measured using capture ELISAs and the data thus obtained together with S. haematobium egg count data from urine assays were analysed using a combination of parametric and nonparametric statistical approaches.

RESULTS

Age profiles of schistosome infection in the study population showed that infection rose to peak in childhood (11-12 years) followed by a sharp decline in infection intensity while prevalence fell more gradually. Mean infection intensity was 37 eggs/10 ml urine (SE 6.19 eggs/10 ml urine) while infection prevalence was 54.7%. Measurements of parasite-specific cytokine responses showed that IL-4, IL-5 and IL-10 but not IFN-gamma followed distinct age-profiles. Parasite-specific IL-10 production developed early, peaking in the youngest age group and declining thereafter; while IL-4 and IL-5 responses were slower to develop with a later peak. High IL-10 producers were likely to be egg positive with IL-10 production increasing with increasing infection intensity. Furthermore people producing high levels of IL-10 produced little or no IL-5, suggesting that IL-10 may be involved in the regulation of IL-5 levels. IL-4 and IFN-gamma did not show a significant relationship with infection status or intensity and were positively associated with each other.

CONCLUSION

Taken together, these results show that the IL-10 responses develop early compared to the IL-5 response and may be down-modulating immunopathological responses that occur during the early phase of infection. The results further support current suggestions that the Th1/Th2 dichotomy does not sufficiently explain susceptibility or resistance to schistosome infection.

Cytokine expression in hamsters experimentally infected with Opisthorchis viverrini

The cytokine mRNA expression of IL-12, IFN-gamma, TGF-beta, IL-4, and IL-10 were investigated in spleen, liver and mesenteric lymph nodes (MLN) in hamsters experimentally infected with Opisthorchis viverrini. Animals were infected with 5, 25 or 100 metacercariae (Mc) and examined by RT-PCR and real-time PCR at 2 weeks, 2 and 6 months after infection. The cytokine expression was compared using HPRT. The IL-12 was significantly expressed at 2 weeks in the liver of the 5- and 25-Mc-infected groups. It is correlated with the inflammation intensity found in the liver at the same time. The production of IFN-gamma was not increased. The significant increase in expression of IL-10 was observed in the 6-month group in the spleen, which may suppress the Th1 and lead to a Th2 response. The IL-4 and TGF-beta expressions in MLN were significantly increased, and correlated with the dose of infection, especially in the 6-month groups. The TGF-beta level in MLN was 15-fold higher than in the uninfected control, compared to a twofold increase in spleen and liver. Because this parasite resides in the bile duct, the regulatory cytokine levels of mucosal immunity were enhanced more than those in systemic immunity. These results indicate the predominance of Th2 responses in chronic O. viverrini infection, and the high level of TGF-beta may inhibit the immune functions, which allows the parasites to evade host immune response.

Cytokine production associated with periportal fibrosis during chronic schistosomiasis mansoni in humans

Volunteers living in an area where schistosomiasis mansoni is endemic were subjected to ultrasound examination and classified into groups according to the levels of fibrosis diagnosed, namely, absence of indications of fibrosis (group 0), incipient fibrosis (group 1), and moderate/severe fibrosis (group 2). Peripheral blood mononuclear cells (PBMC) collected from the volunteers were stimulated with soluble antigens from adult schistosomes or from schistosome eggs, and the production of the cytokines gamma interferon, tumor necrosis factor alpha, transforming growth factor beta (TGF-beta), interleukin-4 (IL-4), IL-10, and IL-13 was determined. Potential associations of the level of fibrosis with age, sex, intensity of infection, and cytokine production were investigated between the three groups. Univariate analysis identified associations of age (>50), gender (male), and absence of eggs/g of feces with moderate/severe fibrosis and an association of intensity of infection (>100 eggs) with incipient fibrosis. When cytokine production in PBMC cultures stimulated by soluble egg antigens was categorized as low or high, significant differences in the distribution of IL-13 levels were established between groups 0 and 2. No significant differences were detected between the groups in the cytokines produced by PBMC cultures stimulated with soluble antigens from adult schistosomes. When all variables were tested in multivariate analyses, only IL-13 was strongly associated with fibrosis (odds ratio = 5.8; 95% confidence interval [CI] = 1.1 to 30.5). While high levels of TGF-beta appeared to be associated with protection against fibrosis, the strength of the association was low.

Immunopathogenic mechanisms in schistosomiasis: what can be learnt from human studies?

Studies in mice indicate that schistosome egg-induced granuloma formation and hepatic fibrosis depend markedly on cytokine regulation, with interleukin 10 having a central role. There is no clear consensus about the pattern of cytokine production and regulation that causes a minority of chronically exposed patients to develop severe hepatosplenic (HS) disease, which is characterized by periportal fibrosis and portal hypertension. HS disease and the progression of hepatic fibrosis are associated with the production of profibrotic type 2 cytokines in the early stages of infection with Schistosoma mansoni. However, other studies indicate that HS disease is characterized by a predominant T helper 1 profile. Until new tools and approaches are developed to study human disease in endemic areas, investigators must either speculate about indirect evidence from human studies or rely more heavily on findings generated from experimental models of the disease.

Familial aggregation of human infection with Schistosoma japonicum in the Poyang Lake region, China

Despite the success of extensive control measures that have been implemented in China for over 50 years, the number of individuals infected with Schistosoma japonicum remains high in the existing endemic areas. A variance components analysis was undertaken to estimate the heritable and environmental components that contribute to S. japonicum infection in the Poyang Lake region of Jiangxi Province, PR China. The total target population was 3148 from four separate administrative villages. Two thousand seven hundred and five of these comprised 400 families ranging in size from 3 to 188. After adjustments were made for gender, water contact and past history of having had schistosomiasis, the heritable component was estimated to account for as much as 58% of the phenotype variation under the polygenic model. Household was not shown to be an important environmental factor. Incorporating village effects indicated that the results were valid for the total population. We conclude that genetic heritability in this region is high and plays an important role in determining risk of infection with S. japonicum.

Vaccine-linked chemotherapy: can schistosomiasis control benefit from an integrated approach?

The present strong emphasis on gross organ pathology (liver, kidneys, bladder) in schistosomiasis needs to be replaced with a more balanced view of the disease that also takes into account systemic symptoms that are less easy to assess, such as retarded growth, cognitive development and the effect of continuing low-level blood loss. Access to better estimates of disease burdens, morbidity and mortality is delivering results that bring into question the wisdom of downgrading the impact of the disease. In this scenario, the simplistic approach of exclusive drug treatment might not be sufficient and, in the worst-case scenario, might even exacerbate pathology. To meet this challenge, the repositioning of vaccines within the totality of disease control through the combined use of chemotherapy and vaccination is recommended as the basis for a novel, more-versatile approach to control. Studies on human correlate responses in endemic areas have opened the way to assess the protective value of specific antigens through the cytokine responses and antibodies they elicit. Moreover, vaccine formulations based on novel adjuvants could improve the final outcome through selective manipulation of the immune response. Thus, the tools of vaccine-linked chemotherapy are in principle already available and could shortly be put to the test in clinical trials.