EVIDENCE FOR PROTECTIVE IMMUNITY TO BANCROFTIAN FILARIASIS IN THE COOK-ISLANDS

To challenge the concept of protective immunity in lymphatic filariasi s, 19 adult residents of a Wuchereria bancrofti-endemic island who had been diagnosed 17 years earlier as putatively immune endemic normals (PI/EN) were reexamined, Even with continued exposure to infection, al l 19 had maintained their apparent infection-free status. Studies to d efine the mechanisms underlying this putative immunity revealed that c ellular immune responses (including proliferation; generation of inter leukin [IL]-2, IL-5, IL-10, interferon-gamma, and granulocyte-macropha ge colony-stimulating factor) to adult- and microfilarial-stage antige ns, hut not antibody responses, were markedly greater than those of 20 age-matched, infected patients. Furthermore, the PI/EN group was comp rised of high- and low-responding persons who were clinically indistin guishable. These findings provide evidence that protective immunity to lymphatic filariasis does occur and that it is probably T cell-mediat ed.