Analysis, characterization, and diagnostic utility of filarial antigen fractions isolated from immune complexes in bancroftian filariasis.

Circulating immune complexes isolated from clinical filarial patients' sera by 3% polyethylene glycol precipitation were analyzed by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) on vertical slab gel. Silver staining of the gel after electrophoresis revealed 20 and 30 protein bands without and with reduction of immune complexes, respectively, in the molecular weight range of 148-18K. Filarial antigen in protein eluates from gel slices was detected by sandwich enzyme-linked immunosorbent assay. The eluates from four gel slices, viz., IC-2, IC-4, IC-7, and IC-9, showed filarial antigenic activity. These antigen fractions were characterized and explored for their diagnostic use. IC-7 and IC-9 fractions and microfilariae excretory-secretory (mf ES) antigen share common antigenic determinants as revealed by the fact that saturation of immobilized antibodies with IC-7 or IC-9 inhibited the binding of mf ES antigen coupled to penicillinase. IC-9 fraction appears to be useful in serological differentiation of Wuchereria bancrofti infected persons from those with disease manifestations. Biochemical characterization of the IC-9 fraction revealed the protein nature of the antigen. Comparison of the electrophoretic profiles of immune complexes and W. bancrofti mf ES antigen revealed several common protein bands. The 55 K protein band with antigenic activity was observed in both preparations.