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.

Elastase-Positive Neutrophils Are Associated With Refractoriness of Chronic Rhinosinusitis With Nasal Polyps in an Asian Population

“…Specifically, the HR of refractoriness on CRSwNP in Asians was the highest for tissue neutrophilia (HR, 4.38; 95% CI, 1.76–10.85). Although some studies supported that patients with the neutrophilic CRSwNP have less response to treatment with corticosteroids,1633 unlike eosinophils, tissue neutrophilia has not yet been established as a cellular biomarker in NP tissues. Meanwhile, several studies have chosen diverse markers for neutrophils, such as MPO, elastase, and morphologic findings 13141517.…”

The Network of Colonic Host Defense Peptides as an Innate Immune Defense Against Enteropathogenic Bacteria

“…Cathelicidins can promote additional antimicrobial functions in neutrophils, such as induction of neutrophil extracellular trap (NET) formation. Stimulation of human neutrophils with both LL-37 and CRAMP resulted in an increase in NET formation (17,18). Further research is needed to define the importance of these chemoattractant and prophagoctytic effects of cathelicidins in gut physiology and defenses in infectious colitis.…”

Significance of LL-37 on Immunomodulation and Disease Outcome

“…LL-37 induces secondary necrosis of apoptotic neutrophils through the increased expression of antiapoptotic protein Bcl-XL and by blocking the 3 BioMed Research International activation of caspase-3 [49,50] via the activation of FPR and purinergic receptor P2X ligand-gated ion channel 7 (P2X7 receptor) on these cells [46]. NETs which are involved in a variety of chronic inflammatory pathologies can release LL-37 in vivo and ex vivo, and LL-37 also promoted peripheral neutrophils to form NETs in a dose-dependent manner ex vivo [51]. And NETs via C1q/LL-37 specifically inhibited interleukin IL-6 secretion by LPS-activated macrophages [52].…”