Antibody response to a filarial antigen fraction in individuals exposed to Wuchereria bancrofti infection in India

An antigen fraction (DssdI) was isolated from the aqueous-insoluble components of adult Setaria digitata. Rabbit antiserum to DssdI labeled the sheaths of Wuchereria and Setaria microfilariae suggesting DssdI to be surface associated. Antibody responses to DssdI were determined in Wuchereria bancrofti exposed individuals. IgM titre was highest in endemic normals (EN; asymptomatic amicrofilaraemic) followed by chronic filarial patients (CP) and asymptomatic microfilaraemics (AS). IgG titer was high in both chronic filariasis and endemic normals. The microfilaraemic group had the lowest titer. The seropositivity rate in AS was 28% for IgG and 10% for IgM, in CP 100% for IgG and 33% for IgM, and in EN 86% for both antibodies. An age-dependency of IgM but not of IgG antibodies was observed in endemic normals, with IgM prevalence reaching a plateau by 12 years of age. The subclass composition of the antibody response to DssdI appeared to be primarily IgG3 in endemic normals, IgG1 in chronic filariasis and IgG4 in asymptomatic microfilaraemics. Diethylcarbamazine (DEC) treatment led to a significant increase in IgG and IgM levels in microfilaraemic individuals. Of interest, the expression of IgG subclasses altered. There was an increased IgG3 and IgG1 response associated with a reciprocal decrease in IgG4 following DEC therapy.