ABSTRACT
A low molecular weight antigenic fraction has been isolated from saline-soluble extracts of cattle filarial parasite Setaria digitata. This glycoprotein fraction (Fr III) which appears to have low phosphorylcholine content cross-reacted with infective larval (L3) antigens of Wuchereria bancrofti. Binding of human chronic filarial serum with L3 antigens could be inhibited partially by Fr III. The fraction elicited immediate cutaneous hypersensitivity reaction in people living in Wuchereria bancrofti endemic regions. The proportion of skin test positive cases was found to be highest in endemic normals in contrast to infected cases. IgE levels were however not different in chronic filariasis and in endemic normals (or in asymptomatic microfilaraemic carriers). On the other hand, specific IgG level was considerably enhanced only in chronic filariasis.