(226) Mechanism of Pepsin-Induced Neutrophil Recruitment and Activation via Epithelial Cells in Mucosal Injury.

Introduction: Pepsin is a pivotal injurious factor in laryngopharyngeal reflux (LPR), yet its role in shaping the local inflammatory microenvironment remains unclear. This study aims to investigate whether pepsin can influence the recruitment and activation of neutrophils by modulating the immune functions of epithelial cells.

Methods: Mucosal biopsies were collected from patients diagnosed with LPR (n=33) based on 24-hour multichannel intraluminal impedance-pH monitoring, and from asymptomatic controls (n=16). Immunohistochemistry was performed to detect pepsin and the neutrophil marker myeloperoxidase (MPO). In vitro, human laryngeal epithelial cells were stimulated with pepsin. IL-8 secretion was measured by ELISA, and the chemotactic capacity of conditioned media was assessed using a Transwell assay. Neutrophil activation (via CD11b) and their impact on epithelial barrier integrity were evaluated.

Results: Histological analysis revealed significantly higher neutrophil infiltration in pepsin-positive mucosal areas of LPR patients, showing spatial co-localization. In vitro, pepsin stimulation dose-dependently increased IL-8 secretion from epithelial cells. Conditioned media from these cells exhibited significant chemotactic activity towards neutrophils. Recruited neutrophils displayed an activated phenotype and impaired epithelial barrier function.

Conclusions: Pepsin can induce epithelial cells to release IL-8, which in turn programmatically recruits and activates neutrophils. These activated neutrophils release effector substances, leading to inflammatory injury of the mucosal barrier.