Human antibody responses to Wuchereria bancrofti infective larvae

Human IgG antibody responses to Wuchereria bancrofti third stage infective larvae (L3) surface and somatic antigens were studied by indirect immunoflu orescence (IFA) and immunoblot with endemic Egyptian sera (n = 115) with th e aim of identifying targets of protective immunity. Human sera variably re cognized 14 major bands in L3 by immunoblot. The statistical significance o f group differences in antibody prevalence was assessed by the chi-squared test. Children and young adults (aged 10-20 years) tended to have antibodie s to more L3 somatic antigens than older adults, with significant differenc es for bands at 66, 60 and 5 kDa. Infected subjects had more consistent ant ibody responses to antigens at 55, 50 and 6 kDa than endemic normal subject s with negative serum filarial antigen tests, who are presumed to be uninfe cted. A 5 kDa antigen was preferentially recognized by the latter group. An tibodies to L3 surface antigens were equally prevalent in uninfected childr en (75%) and adults (90%) but less prevalent in people with microfilaremia (38%) than in amicrofilaremic subjects with or without filarial antigenemia (81%) (P < 0.001). IFA-positive sera showed significantly enhanced recogni tion of antigens at 66, 40 and 14 kDa in immunoblots relative to IFA-negati ve sera. Additional studies are needed to further characterize antigens ide ntified in this study and to establish whether they are indeed targets of p rotective immunity in humans.