Bancroftian filariasis in Tanzania: Specific antibody responses in relation to long-term observations on microfilaremia

Following a 16-year clinical and parasitologic follow-up survey for Bancroftian filariasis in three endemic communities in northeastern Tanzania, serum antibody responses were analyzed in selected individuals in relation to the long-term observations on microfilaremia. Comparison of responses in three categories of adults (microfilaria [mf] positive at both surveys, mf positive at first but mf negative at the second survey, and mf negative at both surveys, respectively) indicated no significant differences between the mean levels of filarial-specific IgG1, IgG2, IgG3, IgG4, or IgE (measured by ELISA). However, specific IgG2 to the sheath of Wyuchereria bancrofti mf (measured by an indirect fluorescence antibody test [IFAT]) was detected only in the third category. Comparison of responses in two categories of children born around the time of the first survey (to mf-positive and mf-negative mothers, respectively) showed a significantly higher mean level of filarial-specific IgG4 in the first than in the latter category, whereas the mean levels of filarial-specific IgG1, IgG2, IgG3, and IgE, and the prevalences of IgG2 IFAT positivity were similar. The overall prevalence of IgG2 TT;AT positivity was considerably higher in the child study population (45.5%) than in the adult study population (16.7%). In both populations, however, a clear association between IgG2 IFAT positivity and a negative microfilarial status and negative specific circulating antigen status was seen. The study suggests that specific anti-sheath-antibodies are associated with an immunologic resistance mechanism that in the endemic community is expressed with highest prevalence in young individuals before development of patent microfilaremia.