Endogenous Interleukin 4 Is Required for Development of Protective CD4⁺ T Helper Type 1 Cell Responses to Candida albicans

Interleukin (IL)-4–deficient mice were used to assess susceptibility to systemic or gastrointestinal Candida albicans infections, as well as parameters of innate and elicited T helper immunity. In the early stage of systemic infection with virulent C. albicans, an unopposed interferon (IFN)-γ response renders IL-4–deficient mice more resistant than wild-type mice to infection. Yet, IL-4–deficient mice failed to efficiently control infection in the late stage and succumbed to it. Defective IFN-γ and IL-12 production, but not IL-12 responsiveness, was observed in IL-4–deficient mice that failed to mount protective T helper type 1 cell (Th1)-mediated acquired immunity in response to a live vaccine strain of the yeast or upon mucosal immunization in vivo. In vitro, IL-4 primed neutrophils for cytokine release, including IL-12. However, late treatment with exogenous IL-4, while improving the outcome of infection, potentiated CD4⁺ Th1 responses even in the absence of neutrophils. These findings indicate that endogenous IL-4 is required for the induction of CD4⁺ Th1 protective antifungal responses, possibly through the combined activity on cells of the innate and adaptive immune systems.