Protective immunity against Onchocerca volvulus and O. lienalis infective larvae in mice.

Acquired resistance to both Onchocerca volvulus and O. lienalis infective larvae, implanted within micropore chambers, could be induced in mice following immunization with irradiated L3 larvae. In experiments with O. volvulus in BALB/c and BALB/c. By mice, consistent levels of protection (61-75% reductions compared to challenge controls) were achieved with challenge infections of 2 week duration. In DBA/2 mice, levels of protection against O. lienalis were lower and more variable (42-63%): Moreover a 3 week period between challenge and recovery was required before significant reductions in larval recovery became detectable in vaccinated animals. Immunization of CBA or BALB/c mice with O. lienalis microfilariae, or CBA mice with normal or irradiated O. lienalis L3 larvae, failed to induce killing or growth retardation of developing larvae. Preliminary characterization of the effector mechanisms and cytokines associated with protective immunity against O. volvulus infective larvae revealed elevated levels of eosinophils in peripheral blood and within micropore chambers during challenge infections in vaccinated mice. Spleen cells from the same animals stimulated with parasite antigen induced significant levels of IL-5, IL-4 and IFN gamma. These cytokines were barely detectable in antigen stimulated cells from challenge control mice.