Antibody to the Filarial Antigen Wb123 Reflects Reduced Transmission and Decreased Exposure in Children Born following Single Mass Drug Administration (MDA)
To challenge the concept of protective immunity in lymphatic filariasis, 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, all 19 had maintained their apparent infection-free status. Studies to define the mechanisms underlying this putative immunity revealed that cellular immune responses (including proliferation; generation of interleukin [IL]-2, IL-5, IL-10, interferon-gamma, and granulocyte-macrophage colony-stimulating factor) to adult- and microfilarial-stage antigens, but not antibody responses, were markedly greater than those of 20 age-matched, infected patients. Furthermore, the PI/EN group was comprised of high- and low-responding persons who were clinically indistinguishable. These findings provide evidence that protective immunity to lymphatic filariasis does occur and that it is probably T cell-mediated.