Interleukin-17-mediated Immunopathogenesis in Experimental Hypersensitivity Pneumonitis

Rationale: T cells play a critical role in the development of Saccharopolyspora rectivirgula-induced hypersensitivity pneumonitis (HP) but little is known about the role of IL-17A in this disease. Objectives: We examined the role of IL-17A in a murine model of S. rectivirgula antigen (SR-Ag)-induced HP. Methods: Experimental HIP was induced by oropharyngeal instillation of SR-Ag in wild-type and IL-17 gene-deficient mice. Measurements and Main Results: SR-Ag-induced murine HIP was characterized by increased transcript levels of IFN-gamma and IL-12p35 compared with saline-treated control mice. Furthermore, mice with HIP showed increased IL-17 in lung homogenates, bronchoalveolar lavage fluid, and ex-vivo lung cultures compared with control mice. Flow cytometric analysis of SR-Ag-challenged lungs revealed increased Th17 and CD11c(+) cells. The role of IL-17 in SR-induced HP was examined in IL-17deficient (IL17(-/-)) and in wild-type (IL-17(+/+)) mice immunodepleted of IL-17. Histological examination of IL17(-/-) mice challenged with SR-Ag revealed reduced inflammatory cell infiltration, decreased CD11c(+) cells, and reduced levels of inflammatory mediators such as IL-12p70, CCL3, and CXCL9 compared with similarly treated IL17(+/+) mice. Anti-IL-17 antibody treatment of IL-17(+/+) mice with HIP resulted in reduced inflammation and a lower percentage of CD11c(+) cells compared with IgG-treated IL17(+/+) mice with HP. Conclusions: SR-Ag-induced IL-17 plays a pivotal role in the immunopathology of HIP and targeting IL-17 is an attractive therapeutic option for this disease.