Differences in prevalence, intensity of infection and parasite-specific antibody levels do not predict different age-infection profiles.

ABSTRACT

Acquired immunity is believed to influence the age-infection profile of Schistosoma infections. We compared antibody responses against Schistosoma mansoni adult worm antigen (AWA) and soluble egg antigen (SEA) in 164 residents of two communities with different levels of infection. IgG, IgA, IgM, IgE, and IgG subclass 1 to 4 antibodies were determined by ELISA. Seventy-five of the subjects were from Harbu, an area with a prevalence of 39% and an intensity of infection of 116 eggs per gram of stool (EPG), whereas 89 subjects were from Bati, with a prevalence of 66% and intensity of infection of 256 EPG. In both communities the prevalence and the intensity of infection were highest in the age group 10-14 years, although both were significantly higher in Bati than in Harbu. Mean levels of AWA-specific IgA, IgM, IgG, IgG1 and IgG2, and of SEA-specific IgG, IgM, IgG2 and IgG3 were significantly higher in Bati than in Harbu. However, mean levels of IgE against worm and egg antigens were significantly higher in Harbu than in Bati. Significant differences were detected in the levels of IgA, IgE, IgG, IgM, IgG1 and IgG2 against AWA, and in IgE, IgM, IgG2 and IgG3 against SEA according to the place of residence. The levels of anti-AWA IgG, IgG1 and IgG2 and anti-SEA IgG, IgG1 and IgG4 were significantly associated with the intensity of infection. Anti-AWA IgM levels were associated with age, whereas sex and age had interacting effects on the levels of AWA-specific IgG1 and SEA-specific IgG and IgM. Antibody responses exhibited different age-related patterns in the two communities. This may indicate that differences in history of exposure influence the evolution of immune responses. However, the study did not support the view that differences in antibody levels between communities subject to different levels of infection result in a systematic deviation in age-infection profile (the "peak shift").