IL-4- and IL-5-dependent protective immunity to Onchocerca volvulus infective larvae in BALB/cBYJ mice.

A significant reduction in challenge worm survival occurred when BALB/cBYJ mice were vaccinated against Onchocerca volvulus infective third stage larvae (L3) by using irradiated O. volvulus L3. Challenge infections consisted of L3 implanted in diffusion chambers, which were used as a means to contain, and thus efficiently recover, the larvae from the host. The goal of the present study was to describe the mechanism of immune-mediated killing of O. volvulus L3 in diffusion chambers in mice. Direct contact between host cells and parasites was required for killing of larvae in immunized hosts. To define the mechanism of immune-mediated killing in this system, the time of influx of cells and cytokines into the infection site was compared with the time challenge infections were killed. The only cell type that was found to increase in diffusion chambers in immunized mice was eosinophils; maximal levels of eosinophils were coincident with the time of parasite killing. IL-5 was found in diffusion chambers of immunized mice coincident with the time of parasite killing; IL-5 was not found in diffusion chambers recovered from control mice. Significant levels of IFN-gamma were absent in the diffusion chambers of both groups. Immunized mice were treated with mAb to eliminate IL-5 or IL-4 to assess the role these cytokines or their by-products play in larval killing. Elimination of either IL-5 or IL-4 significantly reduced the protective effects of vaccination against larval O. volvulus.