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

ABSTRACT

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 < 0.0001). NET count was also increased in nasal polyps. NET count correlated with neutrophil count (r = 0.908, P < 0.001). LL-37 protein and mRNA levels were upregulated in nasal polyps. LL-37 was distributed in the epithelial and subepithelial layer and mainly expressed by neutrophils. Moreover, LL-37 promoted peripheral neutrophils to form NETs in a dose-dependent manner ex vivo. Interestingly, dexamethasone did not inhibit the effect of LL-37 on inducing NET formation. Furthermore, peripheral neutrophils from CRSwNP patients were more susceptible to LL-37-mediated NET formation, compared with neutrophils derived from control subjects. In addition, NETs released LL-37 in vivo and ex vivo. CONCLUSION: Neutrophil extracellular traps are significantly increased in nasal polyps and LL-37 induces NET formation in CRSwNP patients. These findings indicate that NETs may contribute to the pathogenesis of neutrophilic inflammation in CRSwNP.