Evolution of Immunologic Responsiveness of Persons Living in an Area of Endemic Bancroftian Filariasis: A 17‐Year Follow‐up

On an island in which bancroftian filariasis is endemic, 29 microfilaremic and 16 "endemic normal" (EN) subjects initially studied in 1974-1975 were reevaluated 17 years later. Eleven persons remained microfilaremic, whereas 18 had cleared both microfilaremia and antigenemia. Despite decreased infection on the island, antibody levels remained relatively constant for the subjects with persistent microfilaremia (Mf(+/+)), in contrast to sharp decreases for both EN subjects and subjects with cleared microfilaremia (Mf(+/-)). Although clinically indistinguishable from the EN subjects, the Mf(+/-) group had antibody levels (IgG, IgG4, and IgE) significantly lower than those of the EN subjects. Lymphocyte responses to parasite antigens were marginally greater in Mf(+/-) than in Mf(+/+) subjects, but both groups remained less cell responsive (as measured by proliferation, interleukin-5, interleukin-10, interferon-gamma, and granulocyte-macrophage colony-stimulating factor) than did the EN subjects. These findings suggest that, for microfilaremic persons, complete clearance of infection is not sufficient to restore "normal" immune responsiveness; filarial infection may induce very long-term deficits in the ability to respond to parasite antigens.