Failure of P strain mice to respond to vaccination against schistosomiasis correlates with impaired production of IL‐12 and up‐regulation of Th2 cytokines that inhibit macrophage activation

cul-tures of splenocytes from vaccinated P mice demonstrate less macrophage stimulatoryactivity than do supernatants from cells of vaccine-responsive strains such as C57BL/6. Thisis not due either to diminished production of the macrophage-activating cytokine IFN- by Pmice, or to a lesser responsiveness of macrophages from P mice to activation by IFN- .Rather, P splenocytes produce two-to threefold higher amounts of IL-4 and IL-10, cytokineswhich down-regulate the cytotoxic potential of IFN- -treated macrophages. Thus, themacrophage-activating potential of cytokine preparations from vaccinated P mice can becompletely recovered by