Airway neutrophils are primed for neutrophil extracellular trap formation in bronchiectasis: preliminary data from the BRILLIANT cohort study

<bold>Introduction:</bold> Neutrophil extracellular traps (NETs) are implicated in the pathophysiology of bronchiectasis. Prior studies examined sputum NET complexes as indirect measures of NETs, but no prior studies examined airway neutrophils via bronchoscopy to directly measure NET formation and airway neutrophil function. <bold>Methods:</bold> Neutrophils were isolated from peripheral blood and bronchoalveolar lavage. NETs were measured using in-plate fluorometry while neutrophil percentage was counted on cytospin. Lung function was measured by spirometry. <bold>Results:</bold> Bronchiectasis patients (n=37, age= 67.2±13 years, BSI 6.2±3.3 (mean±SD) 57% female, and healthy volunteers (n=8 age 45±16 years, 75% female) were enrolled onto an observational cohort study. Airway neutrophils of bronchiectasis patients spontaneously produced large amounts of NETs without stimulation (mean=59861au vs peripheral neutrophils 12211au)(p<0.0001). Patient airway neutrophils NET release was significantly less responsive to LPS versus controls (fold change 1.23 vs 1.66, p=0.0096). NETs correlated to airway neutrophil numbers (p<0.0001). However, adjusting for the % of neutrophils identified subgroups based on NET formation per neutrophil. Patients releasing high NETs per airway neutrophil had greater disease severity assessed by lung function vs minimal neutrophilia: FEV1% (61.2±12.8 vs 101.4±16.4, p=0.006) and FVC% (73.6±19.7 vs 105.5±25.4, p=0.0294). FEV1% was not associated with airway neutrophil number or percentage. <bold>Conclusions:</bold> Airway neutrophils in bronchiectasis are primed for NETosis producing maximal NETs without stimulation. Production of airway NETs is associated with worse lung function.