Aspergillus fumigatus, an opportunistic fungal pathogen, causes multiple allergic and non-allergic airway diseases. Invasive pulmonary aspergillosis (IPA) is a nonallergic, life-threatening disease of immunocompromised patients. In a murine model of IPA, interleukin (IL)—4-deficient (IL-4−/−) BALB/c mice were used to examine the role of IL-4 in lung pathology and immune responses. IL-4−/− mice were more resistant than wild-type mice to infection caused by multiple intranasal injections of viable A. fumigatus conidia. Resistance was associated with decreased lung inflammatory pathology, impaired T helper (Th)—2 responses (including lung eosinophilia), and an IL-12—dependent Th1 response. In contrast, development of host-detrimental antifungal Th2 cells occurred in IL-12−/− and interferon-γ−/− mice and in IL-4−/− mice when subjected to IL-12 neutralization. These results demonstrate that IL-4 renders mice susceptible to infection with A. fumigatus by inhibition of protective Th1 responses. IL-4 appears to have a distinct role in the pathogenesis of allergic and nonallergic lung diseases caused by the fungu
