Bleomycin and IL-1β-mediated pulmonary fibrosis is IL-17A dependent

Idiopathic pulmonary fibrosis (IPF) is a destructive inflammatory disease with limited therapeutic options. To better understand the inflammatory responses that precede and concur with collagen deposition, we used three models of pulmonary fibrosis and identify a critical mechanistic role for IL-17A. After exposure to bleomycin (BLM), but not Schistosoma mansoni eggs, IL-17A produced by CD4(+) and gamma delta(+) T cells induced significant neutrophilia and pulmonary fibrosis. Studies conducted with C57BL/6 il17a(-/-) mice confirmed an essential role for IL-17A. Mechanistically, using ifn gamma(-/-), il10(-/-), il10(-/-) il12p40(-/-), and il10(-/-) il17a(-/-) mice and TGF-beta blockade, we demonstrate that IL-17A-driven fibrosis is suppressed by IL-10 and facilitated by IFN-gamma and IL-12/23p40. BLM-induced IL-17A production was also TGF-beta dependent, and recombinant IL-17A-mediated fibrosis required TGF-beta, suggesting cooperative roles for IL-17A and TGF-beta in the development of fibrosis. Finally, we show that fibrosis induced by IL-1 beta, which mimics BLM-induced fibrosis, is also highly dependent on IL-17A. IL-17A and IL-1 beta were also increased in the bronchoalveolar lavage fluid of patients with IPF. Together, these studies identify a critical role for IL-17A in fibrosis, illustrating the potential utility of targeting IL-17A in the treatment of drug and inflammation-induced fibrosis.