LL‐37 promotes neutrophil extracellular trap formation in chronic rhinosinusitis with nasal polyps

Background Neutrophil accumulation has been observed in chronic rhinosinusitis with nasal polyps (CRSwNP). However, the functions of neutrophils are poorly understood. Neutrophils produce neutrophil extracellular traps (NETs), which are involved in a variety of chronic inflammatory pathologies. LL‐37 is the only member of the cathelicidin family in human. Objective Our aims were to examine the presence of NETs in CRSwNP and to investigate the regulatory effect of LL‐37 on NET formation. Methods Nasal polyp tissues were investigated for the presence of NETs by using immunofluorescent (IF) staining. The expression and distribution of LL‐37 were examined by using quantitative RT‐PCR, ELISA, IF, and immunohistochemistry. Purified peripheral neutrophils were stimulated with LL‐37 and stained with IF to identify NETs. NETs% was defined as percentage of NET‐generating neutrophils to the total number of neutrophils. Results Neutrophil extracellular traps were located in the subepithelial layer of nasal polyps and control tissues. Nasal polyps had higher NETs% compared with that of controls (23.01% ± 3.43% vs 4.52% ± 1.33%, P