IL-4 exacerbates anaphylaxis.

We evaluated whether IL-4, a cytokine critical for inducing allergic responses, also contributes to the effector phase of allergy. Pretreatment of mice with IL-4 or the related cytokine, IL-13, rapidly and dramatically increased the severity of anaphylaxis induced by cross-linking Fc(epsilon)RI or FcgammaRIII. This effect was inhibited by endogenously produced IFN-gamma, was T cell-, B cell-, and common gamma-chain-independent, and required IL-4Ralpha and Stat6. IL-4Ralpha signaling also enhanced anaphylaxis in mice infected with a nematode parasite that stimulates IL-4/IL-13 production. IL-4 exacerbated anaphylaxis by acting synergistically with vasoactive mediators to increase vascular permeability. Synergy between IL-4 and vasoactive mediators during the effector phase of allergic inflammation may both contribute to allergic immunopathology and enhance protective immunity against gastrointestinal worms.