IL-17A-mediated expression of epithelial IL-17C promotes inflammation during acute Pseudomonas aeruginosa pneumonia

Lung epithelial cells are suggested to promote pathogen-induced pulmonary inflammation by the release of chemokines, resulting in enhanced recruitment of circulating leukocytes. Recent studies have shown that the interleukin-17C (IL-17C) regulates innate immune functions of epithelial cells in an autocrine manner. The aim of this study was to investigate the contribution of IL-17C to pulmonary inflammation in a mouse model of acute Pseudomonas aeruginosa pneumonia. Infection with P. aeruginosa resulted in an increased expression of IL-17C in lung tissue of wild-type mice. Numbers of neutrophils and the expression of the neutrophil-recruiting chemokines keratinocyte-derived chemokine and macrophage inflammatory protein 2 were significantly decreased in lungs of IL-17C-deficient (IL-17C^-/-) mice infected with P. aeruginosa at 24 h. Systemic concentrations of interleukin-6 (IL-6) were significantly decreased in infected IL-17C^-/- mice at 24 h and the survival of IL-17C^-/- mice was significantly increased at 48 h. The expression of IL-17C was reduced in infected mice deficient for interleukin-17A (IL-17A), whereas pulmonary concentrations of IL-17A were not affected by the deficiency for IL-17C. Stimulation of primary alveolar epithelial cells with IL-17A resulted in a significantly increased expression of IL-17C in vitro. Our data suggest that IL-17A-mediated expression of epithelial IL-17C amplifies the release of chemokines by epithelial cells and thereby contributes to the recruitment of neutrophils and systemic inflammation during acute P. aeruginosa pneumonia.