Epithelium-derived IL17A Promotes Cigarette Smoke-induced Inflammation and Mucus Hyperproduction

The airway epithelium is a central modulator of innate and adaptive immunity in the lung. IL17A expression was found to be increased in the airway epithelium; however, the role of epithelium-derived IL17A in chronic obstructive pulmonary disease (COPD) remains unclear. In this study, we aimed to determine whether epithelium-derived IL17A regulates inflammation and mucus hyperproduction in COPD by using a cultured human bronchial epithelial (HBE) cell line in vitro and an airway epithelium IL17A-specific knockout mouse in vivo. Increased IL17A expression was observed in the mouse airway epithelium upon cigarette smoke (CS) exposure or in a mouse model of COPD that was induced by using CS and Eln (elastin). CS extract (CSE) also triggered IL17A expression in HBE cells. Blocking IL17A or IL17RA (IL17 receptor A) effectively attenuated CSE-induced MUC5AC and the inflammatory cytokines IL6, TNF-α, and IL1β in HBE cells, suggesting that IL17A mediates CSE-induced inflammation and mucin production in an autocrine manner. CSE activated p-JUN (phospho-JUN) and p-JNK (phospho-c-Jun N-terminal kinase), which were also reduced by IL17RA siRNA, and JUN siRNA attenuated CSE-induced IL6 and MUC5AC. In vivo, selective knockout of IL17A in the airway epithelium markedly reduced the neutrophilic infiltration in BAL fluid, peribronchial inflammation, proinflammatory mediators (CXCL1 [CXC ligand 1] and CXCL2), and mucus production in a COPD mouse model. We showed a novel function of airway epithelium-derived IL17A, which can act locally in an autocrine manner to amplify inflammation and increase mucus production in COPD pathogenesis.