Immunological responses associated with morbidity in human schistosoma mansoni infection

Abstract

A study was carried out to investigate the cellular and humoural immune responses to S.mansoni antigens and mitogen concanavalin A in relation to the presence or absence of hepatosplenic disease in human schistosomiasis mansoni. This study was also aimed at determining whether anti-idiotypic responses with specificity for egg stage antigens was associated with morbidity in S.mansoni infected patients in Kenya. Study patients were recruited from two schistosomiasis foci, Kambu and Miu in Machakos district, Kenya. A total of fifty six patients were recruited into the study. For cellular and humoural studies, patients were divided into three categories based on their area of residence, age, egg count and morbidity status as assessed by the presence or absence of hepatosplenic disease. The categories were:, group 1 - patients without morbidity from Miu, a low morbidity schistosomiasis mansoni foci, group 2 - patients without morbidity from Kambu, a high morbidity foci" group 3 - patients with hepatosplenic disease from Kambu. Patients 'in, the three groups were closely matched for age and egg load. Blood was collected from the patient-s and processed to recover peripheral blood mononuclear cell? (PBMC) and plasma for in vitro stimulation and humoural assays respectively. The S.mansoni antigens used for stimulation were soluble worm antigen (SWA), soluble -7..gg .antigen (SEA), glutathione-Stransferase (P28), and concanavalin A-binding and non-binding fractions of SEA. Concanavalin A was used as a mitogen. Suqernatants from antigen and mitogen stimulated cultures were collected after 2 and 4 days and assayed for cytokines, Tumour necrosis factor (TNF), InterleukinS (lLS) and Interferon gamma (IFNy). No supernatants were collected from cultures stimulated with concanavalin A-binding and non-binding fraction of SEA. Results of proliferative responses showed that patients with morbidity produced higher values in responses to S.mansoni antigens(SWA, SEA) and concanavalin A and lower values in response to P28. Patients without morbidity produced significantly higher proliferative values(p<O.OS, Oneway anova) compared to values for patients with morbidity in response to stimulation of PBMCswith non-conA binding fraction of SEA. On comparing the cytokine production between the two time points at which the supernatants were collected, higher levels of TNFwere produced in 2 compared to 4 day supernatants in antigen stimulated cultures. In contrast, peak levels of TNF were produced in 4 day supernatants in cultures stimulated with concanavalin A. For IFNy, and ·ILS higher levels were found in 4 compared to 2 day supernatants. The highest level of TNF was produced in response to SEA followed by SWA, P28 and concanavalin A: When proliferative and cytokine responses were correlated, significant positive correlation coefficients were obtained between proliferation to concanavalin' A with IFNy and TNF cytokine levels. While proliferation and~LSproduction to P28 were significantly correlated (p<O.OS), proiiferation to SWA and SEA did not show any significant correlation with peak levels of either TNF, ILS or IFNy. Analysis of cytokine production in the three categories showed that patients with hepatosplenic disease (group 3),