Resistance in murine schistosomiasis is contingent on activated IL-2 receptor-bearing L3T4+ lymphocytes, negatively regulated by Lyt-2+ cells, and uninfluenced by the presence of IL-4.

These studies assess the roles of subpopulations of T lymphocytes in inducing and modulating resistance to Schistosoma mansoni. C57BL/6 mice were depleted in vivo of L3T4+, Lyt-1+, Lyt-2+, IL-2R+ cells, or IL-4 by administration of appropriate mAb. Resistance and various correlative parameters of the immune response were studied in normal, depleted, and congenitally athymic mice. Depletion of T lymphocytes by anti-L3T4 or anti-IL-2R mAb reduced the development and expression of resistance, IgG2a and IgE antibody formation, and delayed type hypersensitivity reactivity against schistosome Ag. Depletion with anti-IL-4 antibody led to profound suppression of IgE-eosinophil-mediated antibody-dependent cell-mediated cytotoxicity and passive cutaneous anaphylaxis responses against the parasite and no effect on IgG2a antibody, Ag-mediated blast transformation, or resistance. Depletion of Lyt-2+ cells produced augmented development and expression of resistance and an increase in the immunological parameters of anti-schistosome reactivity. These studies suggest that protective immunity to S. mansoni in mice, induced by irradiated cercariae, is dependent on L3T4+, IL-2R+ lymphocytes and negatively regulated by Lyt-2+ cells. IL-4 does not appear to be essential for the development of resistance but is essential for the IgE response to the parasite.