Release of interleukin 2 and gamma interferon by peripheral mononuclear cells in human Schistosoma mansoni infection normalizes after chemotherapy

Cytokine Response Profiles of School-Aged Children Infected with Schistosomiasis before and after Praziquantel Treatment

Schistosomiasis is a parasitic disease that affects millions of people in 78 countries globally. Children under the age of 14, who have the chronic disease may suffer from anemia and malnutrition that contribute to lost days at school and pervasive learning disabilities. The infection is prevalent in Kenya, especially in endemic areas, contributing to significant morbidity. The cellular response pattern is associated with both the acute and chronic phases of the disease, in which cytokines play a critical role. The objective of this study was to evaluate the cytokine profiles of IL-4, IL-2, IL-10, IL-5, IFN-γ, and TNF in serum samples of infected school-aged children by using flow cytometry before and after treatment. The analysis indicated a shift in the expression of the cytokines after treatment with all the cytokines being downregulated, except TNF. There was a general trend of decrease in the expression of the cytokines at six and twelve weeks after treatment as compared to the pretreatment levels. There were statistically significant differences in the expression in IL-2 (P=0.001^∗∗), IL-4 (P=0.033^∗), IL-10 (P=0.001^∗∗∗), IFN-γ (P=0.023^∗), and IL-5 (P=0.0001^∗∗∗), except in TNF (P=0.095). The reduction in the cytokine levels can be directly related to the influence of the drug praziquantel, modulating the cytokine response by elimination of adult worms, decline in parasitic load, and reduction of morbidity. Therefore, cytokine response is directly related with the influence of treatment in the variation of the immune response.

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.

Use of praziquantel against schistosomiasis: a review of current status

Praziquantel therapy has become an important component of any programme directed towards schistosomiasis control. This disease being prevalent in many disadvantaged countries, where the means and resources are limited, the strategies for its control on a large scale are also beset with various other constraints. In this review, the potentials of praziquantel therapy in containing the intensities, prevalences and schistosomiasis-associated morbidities in endemic areas of different geographical and epidemiological settings are examined. By and large, regular community-based treatment produces a longer term favourable impact on infection levels and morbidity, but the impact on the disease transmission appears limited. Children constitute a high risk group in schistosomiasis. They are usually subjected to more rapid and intense reinfection, but they also appear more responsive to praziquantel therapy in preventing or reversing the effects of the disease. Modern techniques used in the assessment of impact of praziquantel treatment in schistosomiasis control are outlined.

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.

Cytokines, chemokine receptors, CD4+CD25HIGH+ T-cells and clinical forms of human schistosomiasis

Previous studies have demonstrated that distinct immune response profiles can be correlated with the development/maintenance of different clinical forms of human schistosomiasis. We have previously shown that individuals with the more severe clinical forms of the disease such as those presenting different levels of fibrosis or with the hepatosplenic (HS) clinical form of the disease show significantly different immune response when compared with those with the intestinal clinical form (INT). To better understand the immune mechanisms associated with the clinical form of the schistosomiasis, in this study, we present the results of the evaluation, at a single cell level, of the cytokine patterns as well as the chemokine receptors expression by T-cell subsets after in vitro short-term stimulation with soluble egg antigens as well as the ex vivo frequency analysis of putative regulatory CD4+CD25HIGH+ T-cell subset in the peripheral blood mononuclear cells. We observed an increase on IL-4+, IL-5+ and IL-10+ cells both in the CD4+ and CD8+ lymphocytes in INT and a significant decrease on the number of IL-4+, IL-5+ and IL-10+ T-lymphocytes for HS. However, patients with detectable fibrosis presented decrease on IL-10+ (both CD4+ and CD8+ lymphocytes) and basal levels of IL-4 and IL-5. These data suggested that although INT group is under the influence of an effective immunoregulated immune response, mainly due to the high percentage of IL-10+ cells, it presents a mixed type (Type1/Type-2) immune profile. Moreover, the chemokine receptors expression demonstrated that CXCR3 and CXCR4 by CD4+ T-cells in INT may dictate the selective profile of IL-10 associated with the immunomodulatory events in human schistosomiasis. Additionally, the ex vivo analysis also suggests that higher levels of CD4+CD25HIGH+ T-cells may play a role in controlling morbidity in chronic human schistosomiasis. Taken together, these data suggest a major role of IL-10-producing CXCR4+ CD4+ T-cell subset for the asymptomatic outcome of the disease.

Cytokine secretion profile associated with periportal fibrosis in S. mansoni-infected Egyptian patients

Periportal fibrosis (PPF) is a major pathological consequence of S. mansoni infection. Ultrasonography is a well-established tool for diagnosis and grading of schistosomiasis-related pathology. This work is performed to study the effect of schistosomiasis mansoni infection on the cytokine secretion profile in S. mansoni-infected patients at various grades of fibrosis, as determined by ultrasonography using Cairo Working Group classification. The levels of IL-2, IL-4, IL5, IL-10, IFN-gamma, and TNF-alpha were measured in the absence of in vitro antigen stimulation and after stimulation with worm and egg antigens. Simple intestinal (INT) patients are characterized by strong proliferation to worm antigen and high levels of IL-10 and TNF-alpha compared to patients at various grades of infection. GradeII (GdII)-infected patients are characterized by higher IL-5 production than are patients with other clinical forms of the disease. Sharp reduction of almost all cytokines in response to both worm and egg antigens was detected in GdIII-infected patients. These results stressed the role of both IL-10 and TNF-alpha in the early stages of hepatic fibrosis, while IL-5 could be employed as a potential predictive marker for advanced stages. In conclusion, PPF is associated with cytokine production profiles that vary with the magnitude of the fibrosis.

Treatment of human acute schistosomiasis with oxamniquine induces an increase in interferon-gamma response to Schistosoma mansoni antigens

Patients with acute schistosomiasis were studied before and after oxamniquine treatment. They had been exposed to cercariae 5 to 9 weeks before, and presented compatible clinical manifestations, eosinophilia, and high levels of total IgE. Interferon-gamma (IFN-gamma) and interleukin-4 were measured by ELISA in whole blood samples under soluble egg antigen or soluble adult worm preparation stimulation. After treatment, the reduction of leukocytosis and eosinophilia were not significant, but total IgE levels decreased significantly, in contrast to IFN-gamma levels that were significantly increased. The oxamniquine treatment of acute schistosomiasis patients is followed by an improvement of a Th1 response in vitro. If this response has a protective aspect is unknown, and some investigations need to be realized.

Serum IgE levels of tuberculosis patients in a tropical setup with high prevalence of HIV and intestinal parasitoses

Tuberculosis remains a major health problem worldwide in the era of HIV/AIDS. Co-infection with intestinal parasites has been suggested to worsen the outcome of infection by polarizing the immune response towards Th2. This study investigated serum IgE levels of 241 tuberculosis patients and compared the IgE profiles in the tuberculosis patients either with or without intestinal helminthic infection and/or HIV infection. The serum levels of IgE in tuberculosis patients before initiation of antimycobacterial chemotherapy were found to be 1722 +/- 1290 IU/ml (Mean +/- SD) in HIV seronegatives and 2366 +/- 1849 IU/ml in HIV seropositives. Further, the IgE level was significantly higher in patients coinfected with intestinal helminthes and HIV compared to those infected with helminthes or without coinfection (P < 0.05). Anti-tuberculosis chemotherapy significantly reduced serum IgE levels in HIV seronegative tuberculosis patients (P < 0.05). These findings might indicate an active role of therapy in shifting the immune response towards Th1 which is crucial for prognosis in tuberculosis patients.

Expression of matrix metalloproteinases and their inhibitors during the resorption of schistosome egg-induced fibrosis in praziquantel-treated mice

Schistosomiasis mansoni is a tropical helminthic disease characterized by parasite egg-induced granulomatous inflammation and cumulative fibrosis. Because fibrosis is influenced by the imbalance between degradative matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs), we analysed the resorption of fibrous tissue and MMP/TIMP expression in the livers of S. mansoni-infected and praziquantel-cured mice. Worm elimination significantly enhanced survival rate, ameliorated the granulomatous pathology and reduced collagen I, III and IV gene expression at 6 and 12 months post-treatment. Compared to 6 months infected, untreated controls, liver fibrous tissue was resorbed by 71.4% at 12 months after treatment. At 3 months post-treatment, expression of the MMP-2, -3, -8, -10, -13, -14 and -16 genes decreased compared with untreated controls. By 6 months, a highly significant increase in MMP-10 gene expression was manifest. At 12 months, messages for all MMP genes decreased in relation to untreated controls. TIMP-1, -2 and -3 gene expression drastically decreased between 3 and 6 months. At 1 year, only TIMP-1 expression was significantly diminished. Overall, profibrogenic tumour necrosis factor (TNF)-alpha, transforming growth factor (TGF)-beta and inducible nitric oxide synthase (iNOS) gene expression decreased. Antigen-stimulated splenocytes secreted significantly higher levels of interleukin (IL)-4, IL-5, IL-10 and IL-13 cytokines between 3 and 12 months after treatment. Production of interferon (IFN)-gamma was higher than in untreated controls 3 and 6 months after treatment. In conclusion, praziquantel-treated mice showed a slow resorption of liver fibrous tissue. Resorption is attributed to the precipitous drop in TIMP-1 gene expression level, which shifted the balance in favour of MMP message expression and presumed enhanced collagenase activity.

Periportal fibrosis in human Schistosoma mansoni infection is associated with low IL-10, low IFN-gamma, high TNF-alpha, or low RANTES, depending on age and gender

Schistosoma mansoni infection is highly endemic in parts of Uganda, and periportal fibrosis is common in communities along the shore of Lake Albert. In this study, we have identified cellular immune responses associated with fibrosis. A cohort of 199 individuals aged 6-50, resident in the village for at least 10 years or since birth, were examined for evidence of periportal fibrosis by ultrasound using the Niamey protocol. Whole-blood samples were assayed for levels of nine cellular immune molecules (IL-3, IL-4, IL-5, IL-10, IL-13, TNF-alpha, IFN-gamma, IL-1beta, and RANTES) in the absence of in vitro Ag stimulation, and after stimulation with egg and worm Ags. A lack of Ag specificity allowed the number of variables in the analysis to be reduced by factor analysis. The resulting factor scores were then entered into a risk analysis using a classification tree algorithm. Children, adult males, and adult females had different factors associated with fibrosis. Most cases of fibrosis in children (eight of nine) were associated with low (<47th percentile) IL-10 factor scores. Adult females at lowest risk had relatively high IFN-gamma factor scores (>83rd percentile), whereas those at highest risk had a combination of intermediate (32nd to 83rd percentile) IFN-gamma and relatively high (>60th percentile) TNF-alpha factor scores. Adult males at lowest risk of fibrosis had moderate TNF-alpha factor scores (55th to 82nd percentile), and a high risk was associated with either high TNF-alpha factor scores (>82nd percentile), or intermediate TNF-alpha combined with low RANTES factor scores (<58th percentile). These results demonstrate that periportal fibrosis is associated with cytokine production profiles that vary with both age and gender.

Role of incidental and/or cured intestinal parasitic infections on profile of CD4+ and CD8+ T cell subsets and activation status in HIV-1 infected and uninfected adult Ethiopians

Intestinal parasitic infections have been suggested to cause persistent immune activation leading to an unbalanced immune state. Such a state has been proposed to be a major factor in the pathogenesis of AIDS in an African context. The present study investigated the effect of incidental parasitic infection and treatment on the profile of T cell differentiation and activation markers on CD4+ and CD8+ T cells from HIV-1 infected and uninfected adult Ethiopians. Cryopreserved PBMCs from 64 subjects (41 HIV-negative and 23 HIV-positive) with follow-up visits at 6-monthly intervals were used to compare the effect of incidental intestinal parasites and their treatment upon T cell subset profiles and activation status. The samples were stained with antibodies to various T cell differentiation and activation markers allowing naive, memory, effector, memory/effector, activated and resting CD4+ and CD8+ T cell subsets to be quantified by triple-colour FACScan. Incidental intestinal parasitic infections resulted in a significant increase in memory CD4+ T cell numbers both in HIV-negative and HIV-positive subjects (P < 0.05). There was also a significant increase in the percentage of CD8+ HLA-DR+ T cells (P < 0.05) in HIV-positive subjects co-infected with parasites. In HIV-negative subjects, a significant decline in activated cells and a significant increase in resting CD8+ T cells (P < 0.05) was observed after treatment for parasites. These data suggest that intestinal parasitic infections could result in the alteration of T cell subset counts and also in the up-regulation of T cell activation markers in peripheral blood. Treatment of parasitic infections showed a tendency to reduce the activation suggesting that, together with other community based intervention strategies, such treatment could be used to down-regulate immune activation and hence protect the host from being easily attacked by HIV.

HIV infection and tropical parasitic diseases - deleterious interactions in both directions?

HIV and parasitic infections interact and affect each other mutually. Whereas HIV infection may alter the natural history of parasitic diseases, impede rapid diagnosis or reduce the efficacy of antiparasitic treatment, parasitoses may facilitate the infection with HIV as well as the progression from asymptomatic infection to AIDS. We review data on known interactions for malaria, leishmaniasis, Human African Trypanosomiasis, Chagas' disease, onchocerciasis, lymphatic filariasis, schistosomiasis and intestinal helminthiases. The common immunopathogenetic basis for the deleterious effects parasitic diseases may have on the natural history of HIV infection seems to be a particular type of chronic immune activation and a preferential activation of the T helper (Th)2 type of help. Control of parasitic diseases should complement the tools currently used in combating the HIV pandemic.

Identification of a novel T-cell epitope in soluble egg antigen of Schistosoma japonicum

Identification of T-cell epitopes harbored in soluble egg antigen (SEA) of Schistosoma japonicum and study of the immunological properties are essential for understanding the immunopathology and the control of schistosomiasis. As a follow-up to our previous work, the 66- to 80-kDa fragment from SEA was partially digested with protease, fractionated by reverse-phase high-pressure liquid chromatography, and found to be carrying a peptide which stimulated proliferation and gamma interferon (IFN-gamma) production of Th1 clones specific to SEA. Sequence analysis showed that the peptide was composed of 12 amino acids lined up as DLAVELAYLGNL. A synthetic homologue induced proliferation and IFN-gamma and interleukin-2 (IL-2) production, but not IL-4 or IL-6 production, by the Th1 clones as well as by the spleen cells from SEA-immunized mice, thus indicating that the peptide carries a Th1 epitope of SEA.

Interferon- or interleukin-10 production is induced by related Trypanosoma cruzi antigens

The purpose of this study was to evaluate the effects of a crude Trypanosoma cruzi antigen (TCA) and its partially purified subfractions TCF1, TCF2 on peripheral blood mononuclear cells (PBMC) of normal donors and chagasic patients. TCFI and TCF2 stimulated cells from normal donors and chagasic patients in association with a significant production of interleukin (IL)-10. Only PBMC from chagasic patients multiplied after incubation with TCA and released mainly interferon-y but also IL-10. Neither the production of IL-2 and IL-4 nor CD4/CD8 ratios were changed after culture with antigens. These data suggest that some antigens active during the acute phase of T. cruzi infection would stimulate the production of cytokines that promote progression of infection, and the immune system can produce a desired cytokine(s) once the appropriate antigenic stimulus is used.

Cytokine control of the granulomatous response in Schistosoma mansoni-infected baboons: role of exposure and treatment

Variations in exposure and treatment may contribute to heterogeneity in immunity and granuloma-induced pathology in human schistosomiasis. To examine this hypothesis, olive baboons were either repeatedly infected with Schistosoma mansoni cercariae or received an equivalent dose in a single infection. They were then cured with praziquantel and reinfected with a single exposure. Serial liver biopsies were obtained throughout the course of the experiment, and cytokine responses by peripheral blood mononuclear cells were measured every 2 to 3 weeks. Reinfection after treatment resulted in a twofold-smaller granuloma size at 6 and 9 weeks after infection compared to the size for the same period after primary infection (P < 0.001) but had no effect at 16 or 19 weeks postinfection. The pattern of exposure did not influence granuloma size. During primary infection schistosome-soluble egg antigen (SEA)-induced cytokine production correlated with granulomatous inflammation. Cytokine levels peaked during the acute infection, declined with chronic infection, and became undetectable after treatment. Reinfection after treatment stimulated a two- to three-fold increase in SEA-specific interleukin-4 (IL-4), IL-5, IL-10, IL-2, and transforming growth factor beta (TGF-beta) production and a marked rise in SEA-specific immunoglobulin E (IgE) and IgG regardless of the type of exposure. Cytokine production was significantly greater in repeatedly exposed animals (P < 0.001). SEA-induced gamma interferon production, however, did not increase with reinfection after treatment. SEA-induced TGF-beta was the only cytokine that remained elevated as the infection become chronic and correlated with diminished hepatic granuloma size, implying its participation in down-modulation. These studies demonstrate that baboons partially retain their ability to down-modulate the granulomatous response after treatment.

High Levels of TNF, Soluble TNF Receptors, Soluble ICAM-1, and IFN-γ, but Low Levels of IL-5, Are Associated with Hepatosplenic Disease in Human Schistosomiasis Mansoni

In a case-control study based in two areas of Kenya, hepatosplenic schistosomiasis mansoni was shown to be linked with low levels of IL-5 and with correspondingly high IFN-γ, TNF, and circulating soluble TNF receptor I (sTNFR-I), sTNFR-II, and sICAM-1. PBMC from the hepatosplenic cases responded to in vitro Ag stimulation with significantly higher levels of IFN-γ and TNF, but lower levels of IL-5, compared with nonhepatosplenic controls matched for age and infection intensity. Most of these correlations were confounded by differences between geographical areas. However, principle component analysis identified a high IFN-γ and TNF, and low IL-5 axis in the data as the first principle component; this was significantly associated with hepatosplenomegaly (p &lt; 0.0005) even after controlling for area. High plasma levels of sTNFR-I (p &lt; 0.001), sTNFR-II, (p &lt; 0.0001), and sICAM-1 (p &lt; 0.009) were also significantly associated with hepatosplenomegaly, independently of area, in the case of the soluble forms of both TNF receptors. These parameters were negatively related to IL-5. These results suggest that proinflammatory cytokines are involved in the hepatosplenic disease process in infected individuals who have low anti-inflammatory Th2 responses and that sTNFR may be a useful circulating marker for this disease process, perhaps reflecting the level of TNF activity in hepatic tissues.

Evidence of a T helper type 2 activation in human schistosomiasis

The lymphocyte proliferative response and cytokine production to S. mansoni antigen in vitro were evaluated in 22 schistosomiasis patients living in an area endemic for this disease. The majority of patients (86%) showed no lymphocyte proliferative response and none of them showed interferon-gamma (IFN-gamma) production, following in vitro stimulation with soluble adult worm antigen preparation (SWAP). In contrast, interleukin (IL)-5 (2038 +/- 1757 pg/ml) and IL-10 (867 +/- 762 pg/ml) were detected in peripheral blood mononuclear cell (PBMC) cultures stimulated with SWAP. Moreover, mRNA for IL-4 was detected in SWAP-stimulated PBMC from 4 of 6 patients evaluated. Restoration of lymphoproliferative response was achieved in 4 of 6 patients by adding anti-IL-10 monoclonal antibody (mAb) to PBMC cultures [mean stimulation index (SI) in the presence of antigen = 2.7 +/- 2.9; SI in the presence of antigen plus anti-IL-10, 21 +/- 16]. Restoration of IFN-gamma production by addition of anti-IL-10 mAb was achieved in 4 of 12 patients evaluated (248, 350, 687 and 710 pg/ml). Moreover, the addition of IL-10 to PBMC cultures of 3 schistosomiasis patients and 2 cured subjects who had high lymphoproliferative responses to SWAP resulted in the suppression of these responses by 90%, and completely suppressed IFN-gamma production in one of the subjects, whose PBMC produced IFN-gamma after stimulation with SWAP. The presence of IL-4 mRNA, high levels of IL-5, and the absence of IFN-gamma in PBMC culture supernatants from infected patients, supports the conclusion that patients living in an endemic area of schistosomiasis express a predominant T helper type 2 response. The high levels of IL-10 and the ability of neutralizing anti-IL-10 mAb to restore T cell responses indicate that this cytokine plays an important role in the modulation of T cell responses in schistosomiasis.

Interferon-gamma production by peripheral blood mononuclear cells from residents of an area endemic for Schistosoma mansoni

During human schistosomiasis host responses to antigens of various parasite life-cycle stages may contribute to whether the severe, hepatosplenic state develops or the patient remains relatively asymptomatic throughout infection, and may play a role in resistance. This study evaluated production of interferon gamma (IFN-gamma) in vitro by schistosome antigen-stimulated peripheral blood mononuclear cells (PBMCs) from asymptomatic patients, and by PBMCs from apparently uninfected, untreated persons living in areas endemic for Schistosoma mansoni ('endemic normals'). IFN-gamma production parallels PBMC proliferation in that schistosomal egg antigens stimulate patent patients' cells poorly, but strongly stimulate PBMCs from 'endemic normals'. This is proportionally true for antigens from adult worms and cercariae. Although asymptomatic patent patients' cells produced little or no IFN-gamma in response to the 3 schistosomal antigenic extracts, their PBMCs, and PBMCs from 'endemic normals', produced expected amounts of IFN-gamma when exposed to phytohaemagglutinin. This implies that persons with patent infections have schistosome antigen-specific defects in their ability to respond to IFN-gamma production that are not exhibited by putatively resistant 'endemic normals'.

Cytokine control of parasite-specific anergy in human lymphatic filariasis. Preferential induction of a regulatory T helper type 2 lymphocyte subset

The immunological mechanisms involved in maintenance of an asymptomatic microfilaremic state (MF) in patients with lymphatic filariasis remain undefined. MF patients have impaired filarial antigen (Ag)-specific lymphocyte proliferation and decreased frequencies (Fo) of Ag-specific T cells, and yet elevated serum IgE and antifilarial IgG4. To investigate the mechanism of Ag-specific anergy in MF patients in contrast to amicrofilaremic individuals with chronic lymphatic obstruction (CP), the Fo of Ag-specific lymphocytes from peripheral blood mononuclear cells secreting either IL-4 or IFN-gamma were assessed by filter spot enzyme-linked immunosorbent assay, and IL-10 and transforming growth factor-beta (TGF-beta) mRNA transcript levels were assessed by a semiquantitative reverse transcriptase polymerase chain reaction technique. The Fo of filaria-specific IL-4-secreting lymphocytes were equivalent in both MF (geometric mean [GM] = 1:11,700) and CP (GM = 1:29,300 P = 0.08), whereas the Fo of IFN-gamma-secreting lymphocytes were lower in MF (GM = 1:39,300) than in CP (GM = 1:4,200, P < 0.01). When the ratio of IL-4/IFN-gamma (T helper type 2 [Th2]/Th1)-secreting cells was examined, MF subjects showed a predominant Th2 response (8:1) compared with a Th1 response in CP individuals (1:4). mRNA transcript levels of IL-10 were also significantly elevated in MF compared with CP individuals (P < 0.01). Further, IL-10 and TGF-beta were shown to have a role in modulating the Ag-specific anergy among MF subjects, in that neutralizing anti-IL-10 or anti-TGF-beta significantly enhanced lymphocyte proliferation response (by 220-1,300%) to filarial Ags in MF individuals. These findings demonstrate that MF subjects respond to parasite antigen by producing a set of suppressive cytokines that may facilitate persistence of the parasite within humans while producing little clinical disease.

Type 2 cytokines and negative immune regulation in human infections

Recent studies indicate that the human immune response to infection is regulated by the balance between the T helper type 1 cytokines, interleukin-2 and interferon-gamma, and the T helper type 2 cytokines, interleukin-4, interleukin-5 and interleukin-10. Interleukin-4 and interleukin-10 can facilitate antibody production but can also suppress cell-mediated immune responses. The net effect of these negative immunoregulatory cytokines is to favor progression of infection.

Correlation between cell-mediated immunity and degree of infection in subjects living in an endemic area of schistosomiasis

Cell-mediated immunity to Schistosoma mansoni antigens, unrelated antigens and mitogens was evaluated in 50 subjects with the same degree of exposure to infection living in an endemic area of schistosomiasis. The degree of infection, assessed by the number of eggs/g of stool, was variable in this population (0-5604), suggesting differences in susceptibility to infection. Absence of lymphoproliferative response was observed in 56% of this group, despite having a response to purified protein derivative of tuberculin (PPD) and tetanus toxoid (TT) antigens and to pokeweed mitogen. The 50 subjects were divided into two groups, according to their degree of infection. The lymphoproliferative responses to schistosomula and adult worm antigens in the group with a low degree of infection (< 400 eggs/g of stool) were higher than the ones documented in patients with a high degree of infection (> 400 eggs/g of stool), and these differences were statistically significant (p < 0.001). An inverse correlation between the lymphocyte proliferation in response to S. mansoni antigens and the degree of infection was also observed (p = 0.02), indicating that subjects with a lower degree of infection have a higher lymphoproliferative response to schistosomula and adult worm antigens. No differences in the lymphocyte reactivity to other antigens (PPD and TT) were detected in these groups. An impairment of interferon-gamma in vitro production was observed when the lymphocytes from these subjects were stimulated with S. mansoni adult worm antigen, although they produced gamma interferon in response to phytohemagglutinin.

Environmental, genetic and immunological factors in human resistance to Schistosoma mansoni

The design of programs for the control of endemies requires the knowledge of the principal factors that determine parasite transmission and infection levels in exposed populations. In the studies summarized in this article, the role of environmental and host specific factors in the infection by S. mansoni have been evaluated. It is shown that a limited number of factors actually influences infection intensity: water contacts, age, and sex were shown to account for 20 to 25% of infection variance, while 35 to 40% of it was accounted for by the effect of a major codominant gene. A remarkable fact is the important weighting (around 55% of the variance) of factors (the major gene and age) that influence human capacities of resistance. This observation strongly supports control measures aimed at increasing human resistance, such as vaccination. The effect of age on the development of resistance has now been observed in several studies on S. mansoni or S. haematobium. It is, therefore, a constant finding in schistosomiasis infections that resistance develops extremely slowly requiring a long period of exposure to the parasite and repeated infections. These studies provide strong incentives to increase efforts in the evaluation of the immune response of subjects living in endemic areas. Such evaluations are necessary to define vaccine and vaccination programs, and they are also urgently needed to evaluate the effects of chemotherapy on the development of immunity in children and adolescents, as well as on the persistence of protective immunity in adults. Immunological studies begin to provide a clearer picture of the role of acquired immunity in human protection against S. mansoni. It is increasingly clear that the slow development of resistance in children, as well as its alteration in certain age groups, are related to the maturation of parasite specific immunity and its alteration by specific immune factors. Thus, the development of resistance is associated with the maturation of IgE-dependent immunity, whereas blocking Ab may interfere in children and adolescents with the expression of full resistance. This finding raises the question as to whether a vaccine could include major allergens without triggering the well-known deleterious side effects associated with hypersensitivity reactions. The absence of such reactions in subjects with high parasite-specific IgE levels who are exposed to daily infections suggests that this may be feasible.

Human immune responses during schistosomiasis mansoni

Studies of immune responses as they occur in patients with schistosomiasis appear to progress relative to cUrrent technological advances, and to advance despite the understandable inability to pursue in vivo manipulations in this host/parasite system. Emphasis is most often placed on making immunological comparisons between such patient groups as reinfected/non-reinfected, intestinal/hepatosplenic, high/low intensities of infection, infected/uninfected within endemic areas, and those born of infected/uninfected mothers. Based on these types of comparisons, reasonable conjectures can be made regarding the immunological occurrences during this chronic exposure condition. Some consideration is now being given to the immune mechanisms of some of the observations made, and while some of these must then be carried back to experimental models for further manipulation-based analysis, new technological developments continue to assist in the field/bench ability to ask questions that might assist our understanding to a point where this knowledge can be applied to shaping developmental approaches to vaccine development and the goal of alleviating morbidity.

Differential cellular reactivity to adult worm antigens of patients with different clinical forms of schistosomiasis mansoni

Analysis of the proliferation in vitro of peripheral blood mononuclear cells and the production of interferon-gamma (IFN-gamma) in individuals infected with Schistosoma mansoni and showing different clinical forms of the disease, as well as normal putatively immune individuals from an endemic area, was undertaken using total and fractionated soluble adult worm antigens (SWAP). A higher frequency of detectable response to fractionated antigens in T cell Western blot assays was observed in individuals with the more severe forms of the disease. Analysis of variance showed that, in the Western blot assays, there was a statistically significant difference in the level of cellular proliferation to antigens with low molecular weight (less than 21 kDa) between hepatosplenic patients and those with intestinal and hepatointestinal forms of the disease. No correlation between cellular proliferation and IFN-gamma production was observed. Most of the normal individuals from an endemic area failed to show significant proliferative responses to SWAP T cell Western blot assays or to antigen immobilized on nitrocellulose; they did show significant proliferative responses to whole soluble SWAP with positive IFN-gamma production. The results are consistent with the hypothesis that variations in the cellular immune responses to SWAP influence both the development of pathology and resistance to infection in schistosomiasis mansoni.

Changes in the level of IL-2, T cell subsets and the function of T suppressor cells in patients with schistosomiasis japonica

The level of interleukin-2 (IL-2) produced by peripheral blood mononuclear cells in vitro, T cell subsets and the function of T suppressor cells (Ts) in patients with schistosomiasis japonica were investigated. It was found that the level of IL-2 induced by schistosomal antigens was significantly high and positively related to the percentage of CD4+ cells. In the groups of chronic and advanced schistosomiasis japonica, the level of IL-2 induced by schistosomal antigens was markedly lower than that in the group of acute schistosomiasis japonica, but significantly higher than that in the group of normal controls. The IL-2 level was negatively related to the percentage of CD8+ T cells and the ratio of CD4+/CD8+. The level of IL-2 induced by PHA was greatly reduced in the group of advanced schistosomiasis japonica. The changes in the level of IL-2 and its relationship with T cell subsets and the function of Ts are also discussed.

Impaired balance of interleukin-4 and interferon-gamma production in infections with Schistosoma mansoni and intestinal nematodes

In chronic infection with Schistosoma mansoni, IL-4 and IFN-gamma are co-modulated in opposite directions. This was shown when testing sera and cell culture supernatants from 31 Brazilian patients with schistosomiasis before, and three months after treatment with praziquantel. Thorough examinations were undertaken to account for polyparasitism with intestinal nematode infections involving tissue migrating larval stages that may induce analogous changes. Controls free of S. mansoni included a group (n = 17) matching the schistosomiasis patients' parasitation by intestinal nematodes and a group (n = 16) free of helminths other than T. trichiura. Serum IL-4 was greater than 20 pg/ml in 81% of schistosomiasis patients but in only 35 and 25%, respectively, of controls with and without intestinal nematodes. IL-4 data correlated inversely with the mitogen-induced IFN-gamma synthesis. Generation of IL-4 in response to phorbol esters was related to the intensity of infection by schistosomes and intestinal nematodes. The parasitological status three months after therapy with either praziquantel or mebendazole revealed a dichotomy: whereas the ratio of IFN-gamma to IL-4 generated in vitro was identical in uninfected controls and in patients who cleared the parasites, failure to eliminate the parasites was associated with lower IFN-gamma/IL-4 ratios generated in vitro.

Altered generation of interleukin 1 in chronic human schistosomiasis mansoni

Chronic schistosomiasis mansoni is associated with impaired cell-mediated immune responsiveness (CMI). To assess co-stimulatory factors essential in the induction phase of CMI, interleukin 1 (IL-1) concentration was determined in the sera and cell culture supernatants of Schistosoma mansoni-infected patients, and circulating monocytes were phenotyped, labelling membrane IL-1 and HLA-DP. In addition, adherent cell oxidative-burst capacity was investigated. Since involvement of IL-1 beta in the pathogenesis of severe granulomatous lesions could not be ruled out, 17 patients with intestinal schistosomiasis and 17 patients with hepatosplenic schistosomiasis were matched for intensity of infection and monitored 3-6 months after praziquantel therapy. Seventeen age- and sex-matched uninfected residents of the study area in Alagoas, Brazil, acted as controls. Whereas schistosomiasis patients and controls did not differ in the expression of monocyte surface antigens and the capacity of adherent cells to generate H2O2, IL-1 beta release by monocytes in vitro was significantly reduced in both intestinal and hepatosplenic patients. Low concentrations of circulating IL-1 beta were detected in comparable frequencies in untreated patients and controls. Three months after therapy, IL-1 beta was detectable in serum in an increased proportion of intestinal schistosomiasis patients. IL-1 release in vitro gradually increased in all patients and reached control values 6 months after therapy.