Keywords:
Air trapping; degranulation; mucus plugging; proteolysis; scavenging
Abstract:
Rationale: Neutrophils are recruited to the airways of individuals with cystic fibrosis (CF).In adolescents and adults with CF, airway neutrophils actively exocytose the primary granule protease elastase (NE), whose extracellular activity correlates with lung damage. During childhood, free extracellular NE activity is measurable only in a subset of patients, and the exocytic function of airway neutrophils is unknown. Objective: We sought to measure NE exocytosis by airway neutrophils in relation to free extracellular NE activity and lung damage in CF children. Methods: We measured lung damage using chest computed tomography (CT) coupled with the PRAGMA-CF scoring system. Concomitantly, we phenotyped blood and bronchoalveolar lavage fluid (BALF) leukocytes by flow and image cytometry, and measured free extracellular NE activity using spectrophotometric and Forster resonance energy transfer (FRET) assays. Children with airway inflammation linked to aerodigestive disorder were enrolled as controls. Measurements and main results: CF but not disease control children harbored BALF neutrophils with high exocytosis of primary granules, prior to the detection of bronchiectasis. This measure of NE exocytosis correlated with lung damage (Rho=0.55, p=0.0008), while the molecular measure of free extracellular NE activity did not. This discrepancy may be due to the inhibition of extracellular NE by BALF antiproteases and its binding to leukocytes. Conclusions: NE exocytosis by airway neutrophils occurs in all CF children, and its cellular measure correlates with early lung damage. These findings implicate live airway neutrophils in early CF pathogenesis, which should instruct biomarker development and anti-inflammatory therapy in CF children.