Immune responses to third stage larvae of Onchocerca volvulus in interferon‐gamma and interleukin‐4 knockout mice

To shed clarity on the dichotomy of reported results relative to the significance of T helper‐1 vs T helper‐2 immune responses in onchocerciasis, we compared the survivability of Onchocerca volvulus third‐stage larvae (L3) in immunized mice that had either a targeted disruption of the Interleukin‐4 or Interferon‐gamma gene. Treatment groups consisted of control mice and mice immunized with irradiated O. volvulus L3. All mice were challenged with diffusion chambers containing viable L3. Vaccinated IL‐4−/− were unable to kill this larval target. In contrast, vaccinated IFN‐γ−/− and C57BL/6 mice, exhibited high levels of killing, had elevated levels of IL‐4 and significantly greater numbers of eosinophils in their diffusion chambers than the IL‐4−/−. Whereas, levels of IFN‐γ in all three groups of immunized mice were equivalent to those of control mice, levels of IL‐5 were elevated, even in the IL‐4−/−, indicating that cytokines other than IL‐4 were involved in its production. The protective immune response to third‐stage larvae of O. volvulus in mice vaccinated with irradiated larvae has an absolute IL‐4 requirement.