The bacterial serine protease inhibitor ecotin inhibits neutrophil elastase enzymatic activity in cystic fibrosis sputa

Cystic Fibrosis (CF) airway disease is characterized by impaired mucociliary clearance, chronic, polymicrobial infections and robust, neutrophil-dominated inflammation. Pulmonary disease is the leading cause of morbidity and mortality in people with CF and is due to progressive airflow obstruction and ultimately respiratory failure. One of the earliest abnormalities in CF airway disease is the recruitment of neutrophils to the lungs. Neutrophil activation leads to the release of their intracellular content, including neutrophil elastase (NE), that damages lung tissues in CF. Our goal is to characterize a known bacterial NE inhibitor, ecotin, in the CF airway environment. Our results indicate that ecotins cloned from four Gram-negative bacterial species (<i>Campylobacter rectus</i>, <i>Campylobacter showae</i>, <i>Escherichia coli</i> and <i>Pseudomonas aeruginosa)</i> inhibit NE activity in CF sputum samples in a dose-dependent manner. Although we observed differences in the NE-inhibitory activity of the tested ecotins with the <i>Campylobacter</i> homologs being the most effective in NE inhibition in CF sputa, none of the ecotins impaired the ability of human neutrophils to kill major CF respiratory pathogens, <i>P. aeruginosa</i> or <i>S. aureus</i>, <i>in vitro</i>. Overall, we demonstrate that bacterial ecotins inhibit NE activity in CF sputa without compromising bacterial killing by neutrophils.