Age- and sex-related differences in antibody responses against Schistosoma mansoni soluble egg antigen in a cohort of school children in Ethiopia.

Acquired immunity is believed to be the main factor in the age-related differences in prevalence and intensity of Schistosoma infections. We studied antibody responses against S. mansoni soluble egg antigen (SEA) by ELISA in children before treatment, 5 weeks and one year after treatment. After screening for S. mansoni infection, positive children were treated with praziquantel (40 mg per kg body weight). Infection rate was significantly higher in boys younger than 12 years than in girls in the same age group. Levels of all antibody isotypes, except IgG1 (before treatment) or IgA (one year after treatment), were higher in children older or equal to 12 years than in those younger. The difference between age groups was significant for IgE, IgM, IgG3 and IgG4 (before treatment) and IgE (one year after treatment). Similarly, all antibody isotypes, except IgE, before treatment were higher in boys than in girls. At 5 weeks after treatment, IgG, IgE and IgG1 showed an increasing tendency, whereas IgM and IgG3 tended to decrease. One year after treatment, significant decreases were observed in IgG, IgG1 and IgG4 and a significant increase in IgG2 levels. The study presents further evidence for the difference in acquired immunity between younger and older children, and between boys and girls. The study also suggests that praziquantel differentially affects antibody responses against S. mansoni SEA.