IL‐17A contributes to HSV1 infection‐induced acute lung injury in a mouse model of pulmonary fibrosis

BACKGROUND: Patients with idiopathic pulmonary fibrosis (IPF) often experience acute exacerbation (AE) after an episode of common cold. AIMS: To establish a mouse model of virus infection‐induced AE‐IPF and investigate the mechanism underlying the AE‐IPF. METHODS: Herpes simplex virus 1 (HSV1) was inoculated intranasally to wild‐type (WT) and IL‐17A gene knockout (IL‐17A(‐/‐)) mice 21 days after intratracheal administration of bleomycin (BLM). RESULTS: HSV1 infection caused acute exacerbation in mice with BLM‐induced fibrosis. Compared with the BLM+Saline mice, the mice with BLM+HSV1 showed significantly higher acute lung injury (ALI) score (P < 0.0001), lower survival rate (100% vs 21.4%, P < 0.0001), poorer lung function and higher inflammatory response representing by increased total inflammatory cells in bronchoalveolar lavage fluid (BALF) (P = 0.0323), increased proportion of Th17 cells in peripheral blood (P = 0.0004) and higher inflammatory factors in BALF. In addition, HSV1 infection increased the expression of endoplasmic reticulum stress (ERS)‐related proteins in mice with BLM‐induced fibrosis. The inhibition of ERS by tauroursodeoxycholic acid (TUDCA, an ERS inhibitor) significantly reduced the IL‐17A levels in BALF (P = 0.0140) and TH17 cells in the peripheral blood (P = 0.0084) of mice with BLM+HSV1, suggesting that suppression of ERS may reduce TH17 response in mice with AE‐IPF. Compared with WT mice with BLM+HSV1, IL‐17A(‐/‐) mice with BLM+HSV1 had lower ALI score (P = 0.0119), higher survival rate (78.6% vs 21.4%, P = 0.004), improved lung function, and milder inflammatory response. CONCLUSIONS: HSV1 infection in addition to BLM‐induced IPF can successfully establish AE‐IPF in mice. IL‐17A and ERS promote lung inflammation in AE‐IPF development.