Role of IL-5 in innate and adaptive immunity to larval Strongyloides stercoralis in mice

Protective immunity to Strongyloides stercoralis infective larvae in mice h as been shown to be dependent on IL-5 based on mAb depletion studies. The g oal of this study was to determine the functional role of IL-5 during the i nnate and adaptive immune response to larval S. stercoralis in mice. In the se studies, three strains of mice were used: wild-type C57BL/6J (WT), IL-5 knockout (KO), and IL-5 transgenic (TG). Innate responses to the larvae ind icated that there was enhanced survival in the KO animals and decreased sur vival in the TG animals compared with WT. Furthermore, killing of larvae in TG mice was associated with eosinophil infiltration and degranulation, In studying the adaptive immune response, it was observed that immunization of KO mice did not lead to the development of protective immunity. Experiment s were then performed to determine whether RO mice reconstituted with Abs o r cells could then develop protective immunity. KO mice displayed protectiv e immunity via a granulocyte-dependent mechanism following injection of pur ified IgM from immune wild-type animals. Immunity in KO mice could also be reconstituted by the injection of eosinophils at the time of immunization. These eosinophils did not participate in actively killing the challenge inf ection, but rather were responsible for the induction of a protective Ab re sponse. We conclude that IL-5 is required in the protective immune response for the production of eosinophils, and that eosinophils were involved in l arval killing during innate immunity and in the induction of protective Abs in the adaptive immune response.