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 Ba ncroftian filariasis in three endemic communities in northeastern Tanz ania, serum antibody responses were analyzed in selected individuals i n relation to the long-term observations on microfilaremia. Comparison of responses in three categories of adults (microfilaria [mf] positiv e at both surveys, mf positive at first but mf negative at the second survey, and mf negative at both surveys, respectively) indicated no si gnificant differences between the mean levels of filarial-specific IgG 1, IgG2, IgG3, IgG4, or IgE (measured by ELISA). However, specific IgG 2 to the sheath of Wyuchereria bancrofti mf (measured by an indirect f luorescence antibody test [IFAT]) was detected only in the third categ ory. 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-sp ecific IgG4 in the first than in the latter category, whereas the mean levels of filarial-specific IgG1, IgG2, IgG3, and IgE, and the preval ences of IgG2 IFAT positivity were similar. The overall prevalence of IgG2 TT;AT positivity was considerably higher in the child study popul ation (45.5%) than in the adult study population (16.7%). In both popu lations, however, a clear association between IgG2 IFAT positivity and a negative microfilarial status and negative specific circulating ant igen status was seen. The study suggests that specific anti-sheath-ant ibodies are associated with an immunologic resistance mechanism that i n the endemic community is expressed with highest prevalence in young individuals before development of patent microfilaremia.