Here, we describe a novel pathogenic entity, the activated PMN (polymorphonuclear leukocyte, i.e., neutrophil)-derived exosome. These CD63 + /CD66b + nanovesicles acquire surface-bound neutrophil elastase (NE) during PMN degranulation, NE being oriented in a configuration resistant to a1-antitrypsin (a1AT). These exosomes bind and degrade extracellular matrix (ECM) via the integrin Mac-1 and NE, respectively, causing the hallmarks of chronic obstructive pulmonary disease (COPD). Due to both ECM targeting and a1AT resistance, exosomal NE is far more potent than free NE. Importantly, such PMN-derived exosomes exist in clinical specimens from subjects with COPD but not healthy controls and are capable of transferring a COPD-like phenotype from humans to mice in an NE-driven manner. Similar findings were observed for another neutrophil-driven disease of ECM remodeling (bronchopulmonary dysplasia [BPD]). These findings reveal an unappreciated role for exosomes in the pathogenesis of disorders of ECM homeostasis such as COPD and BPD, providing a critical mechanism for proteolytic damage.

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Neutrophils are recruited to the airways of patients with acute respiratory distress syndrome (ARDS) where they acquire an activated pro-survival phenotype with an enhanced respiratory burst thought to contribute to ARDS pathophysiology. Our in vitro model enables blood neutrophil transepithelial migration into cell-free tracheal aspirate fluid from patients to recapitulate the primary airway neutrophil phenotype observed in vivo . Neutrophils transmigrated through our model toward airway fluid from children with lower respiratory viral infections coinfected with bacteria had elevated levels of neutrophil activation markers but paradoxically exhibited an inability to kill bacteria and a defective respiratory burst compared with children without bacterial coinfection. The airway fluid from children with bacterial coinfections had higher levels of neutrophil elastase activity, as well as myeloperoxidase levels compared to children without bacterial coinfection. Neutrophils transmigrated into the aspirate fluid from children with bacterial coinfection showed decreased respiratory burst and killing activity against H . influenzae and S . aureus compared to those transmigrated into the aspirate fluid from children without bacterial coinfection. Use of a novel transmigration model recapitulates this pathological phenotype in vitro that would otherwise be impossible in a patient, opening avenues for future mechanistic and therapeutic research.

Highlights d Neutrophils recruited to cystic fibrosis airways undergo de novo RNA transcription d Neutrophil adaptation to CF airways leads to downregulation of their antimicrobial genes d Transcriptional blockade restores CF airway neutrophil bactericidal capacity