Rationale: Neutrophil counts in bronchoalveolar lavage fluid in idiopathic pulmonary fibrosis are associated with worse outcomes; however, the underlying mechanisms are unknown. Neutrophil extracellular trap formation is associated with worse outcomes in several chronic lung diseases however, there is an unknown role in idiopathic pulmonary fibrosis.
Objectives: To determine the relationship between neutrophil extracellular trap formation in the lungs of idiopathic pulmonary fibrosis patients and clinical outcomes.
Methods: In a discovery cohort of 156 patients with idiopathic pulmonary fibrosis, we measured neutrophil extracellular trap markers in bronchoalveolar lavage fluid, including extracellular DNA, DNA-myeloperoxidase complexes, calprotectin, and neutrophil elastase. We assessed the correlation of these markers with baseline pulmonary function and survival. In a subset of 50 patients, label-free quantitative proteomics was performed to identify the source of extracellular DNA. A validation cohort of 52 patients was similarly assessed.
Measurements and main results: Neutrophil extracellular trap markers in the discovery cohort were significantly correlated with worse pulmonary function (p<0.03). Higher levels of these markers predicted worse survival after adjusting for gender, age, and baseline physiologic severity (hazard ratio range: 1.79 - 2.19). Proteomics revealed a significant correlation between extracellular DNA levels and proteins related to neutrophil extracellular trap formation. The validation cohort showed that extracellular DNA levels were associated with reduced pulmonary function (p=0.04) and trend towards worse survival (hazard ratio=2.16).
Conclusions: Neutrophil extracellular trap formation markers were associated with disease severity and worse survival in idiopathic pulmonary fibrosis. These findings suggest neutrophil extracellular trap formation contributes to lung injury and decreased survival and may represent a potential therapeutic target.