Lymphocytes secrete IL-17A and IL-17F, which enhance innate immune responses. IL-17 expression has not been studied in COPD small airways. The aim of this study was to quantify IL-17A and IL-17F expression in the peripheral lung tissue of patients with COPD compared with control subjects and to identify inflammatory cells that express IL-17.
IL-17 expression was assessed using immunohistochemistry in peripheral lung tissue (18 patients with COPD and 10 smokers and 10 nonsmokers with normal lung function) and induced sputum (12 patients with COPD and six nonsmokers). Alveolar macrophages from eight patients with COPD, eight smokers, and seven nonsmokers were used for reverse transcriptase-polymerase chain reaction (RT-PCR) analysis.
The number of inflammatory cells expressing IL-17A in the small airway subepithelium was higher in patients with COPD than in smokers (P = .01) and nonsmokers (P = .02). IL-17A expression was higher than IL-17F in this region. IL-17A was expressed by lymphocytes, neutrophils, and macrophages (confirmed by RT-PCR). The expression of IL-17F was greater than IL-17A in epithelial cells and lymphoid follicles, although there were no differences among subject groups.
Our findings indicate different roles for IL-17A and IL-17F in the pathogenesis of COPD. IL-17A plays a role in small airway subepithelial inflammation, whereas IL-17F appears to play a more prominent role within lymphoid follicles.