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 immunofluorescence (IFA) and immunoblot with endemic Egyptian sera (n = 115) with the aim of identifying targets of protective immunity. Human sera variably recognized 14 major bands in L3 by immunoblot. The statistical significance of group differences in antibody prevalence was assessed by the chi-squared test. Children and young adults (aged 10-20 years) tended to have antibodies to more L3 somatic antigens than older adults, with significant differences for bands at 66, 60 and 5 kDa. Infected subjects had more consistent antibody responses to antigens at 55, 50 and 6 kDa than endemic normal subjects with negative serum filarial antigen tests, who are presumed to be uninfected. A 5 kDa antigen was preferentially recognized by the latter group. Antibodies to L3 surface antigens were equally prevalent in uninfected children (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 recognition of antigens at 66, 40 and 14 kDa in immunoblots relative to IFA-negative sera. Additional studies are needed to further characterize antigens identified in this study and to establish whether they are indeed targets of protective immunity in humans.