Resistance to reinfection with Schistosoma haematobium in Gambian children: analysis of their immune responses.

The relationship between reinfection with Schistosoma haematobium and immunological parameters was studied in a group of Gambian children aged from 8 to 13 years. Each individual's exposure to infection was assessed from observations of water contact, cercarial densities and infected snail densities at water contact sites. Eosinophil counts were made and responses to egg antigen (SEA) and adult worm antigen (WWH) measured by ELISA. Low levels of reinfection were associated with a high eosinophil count, high levels of antibodies against WWH and SEA, increased age and low exposure. In a multiple regression analysis of the association of reinfection with eosinophil count, antibody levels, exposure, age and sex, the effects of eosinophil count and exposure were still very significant after allowing for all the other variables. The effects of the antibody levels were close to significance after allowance for exposure and eosinophil count (for WWH: P = 0.09; for SEA: P = 0.07), although the evidence was less clear after additional allowance was made for age and sex. The ability of sera from the children to recognize different parasite antigens was also examined by immunoprecipitation of labelled schistosomulum surface, WWH, SEA and S. haematobium adult worm mRNA in vitro translation products. Schistosomulum surface antigens were recognized by all the sera and there was little variation in this response. There was more variation in their responses to SEA and WWH and a marked heterogeneity in the response to in vitro translation products. However, the pattern of antigen recognition appeared unrelated to susceptibility to reinfection.