A comparison of humoral responses to Schistosoma haematobium in areas with low and high levels of infection.

Antibody responses to Schistosoma haematobium of 280 Zimbabweans were studied in two areas of differing infection levels. 133 of the subjects came from a low infection area with a prevalence of 33.8% and geometric mean infection intensity of 0.8 eggs per 10ml of urine, while 147 of the subjects came from a high infection area with a prevalence of 62.7% and geometric mean intensity of 3.2 eggs per 10 ml of urine. Both the age-prevalence and age-intensity curves exhibited a peak shift. IgA, IgE, IgG, IgG1, IgG2, IgG3, IgG4, and IgM antibody levels against soluble egg antigen (SEA) and whole worm homogenate (WWH) were assayed by ELISA. Females produced significantly more anti-SEA IgG1, IgG4, IgM, anti-WWH IgE and IgG1. People from the high infection area produced significantly more anti-SEA IgE, IgG3 and anti-WWH IgG3 and significantly lower levels of anti-SEA IgA, IgM and anti-WWH IgM when the effects of infection intensity, sex and age had been allowed for. The age profiles of anti-SEA IgA, IgG and anti-WWH IgA and IgM reflected current levels of infection while anti-WWH IgG1, IgG2 and anti-SEA IgG1 evolved more slowly with age, and anti-WWH IgE rose with age in both areas. Some antibody responses, anti-SEA/WWH IgM, anti-SEA IgG1 and possibly anti-SEA/ WWH IgA showed different age profiles in the two areas, with changes in antibody levels occurring at a younger age in the high infection area suggesting that immune responses are evolving more rapidly in residents of this area. This result clearly demonstrates that antibody levels are not a function of age alone.