Neutrophil extracellular trap formation in peripheral blood and airway neutrophils in bronchiectasis and CF

Introduction: Neutrophil extracellular traps (NETs) are composed of DNA, histones and antimicrobial peptides. NETs are designed to trap and kill pathogens but have been linked to disease severity in bronchiectasis (BE) and cystic fibrosis (CF). We studied the effect of airway mediators on NET formation in BE and CF. Methods: Peripheral blood neutrophils were stimulated with PMA and C5a to generate NETs. We simulated the airway environment by treating neutrophils with autologous sputum supernatant. Phagocytosis was assessed with FITC-labelled Pseudomonas aeruginosa . Results: We recruited 5 patients with CF and 5 with BE. We observed similar levels of spontaneous NET formation in BE, CF and healthy controls (HC). Sputum pre-treatment of neutrophils enhanced NET formation in response to PMA (mean increase 82.5% 95% CI 55-109%, p <img width="316" height="212" id="fig1" alt="Figure1" src="/Cms_Data/Contents/Forms/Folders/Submission/~contents/RDZ2MBTZ8K5V9QKP/ERS.jpg " /> An increase in the NET component neutrophil elastase resulted in a decrease in phagocytosis of P. aeruginosa by sputum neutrophils (figure), r-0.74, p=0.01. Phagocytosis failure could be replicated by treating peripheral neutrophils with sputum. Conclusion: Sputum from patients with BE and CF contains mediators that promote NET formation and inhibit phagocytosis of bacteria.