Development of antibody isotype responses to Schistosoma mansoni in an immunologically naive immigrant population: Influence of infection duration, infection intensity, and host age

We have identified the influence of host and parasite factors that give ris e to characteristic antibody isotype profiles,vith age seen in human popula tions living in different areas of schistosomiasis endemicity. This is impo rtant in the immunobiology of this disease. It is also of interest in the c ontest of human responses to chronic antigen stimulation, vaccines, allerge ns, and other pathogens. In populations exposed to endemic schistosomiasis, factors such as intensity and duration of infection are age dependent. The y therefore confound the influence of host age on antiparasite responses. H ere, we resolved these confounding factors by comparing the developing anti body responses of an immunologically naive immigrant population as they acq uired the infection for the first time with those of chronically infected r esident inhabitants of the same region of Schistosoma mansoni endemicity in Kenya. Recent arrival in the area strongly favored immunoglobulin G3 (IgG3 ) responses against the parasite. The antibody isotype responses associated with human susceptibility to reinfection after chemotherapy were elevated in those suffering high intensities of infection (IgG4 responses against wo rm and egg antigens) or were characteristic responses of young children irr espective of the intensity or duration of infection (IgG2 responses against egg antigen). IgE responses against the adult worm, a response associated with resistance to reinfection after chemotherapy, increased with the ages of infected individuals and were also favored in those currently suffering higher intensities of infection.