Background: Cystic Fibrosis (CF) is a multi-system disease caused by mutations in the CF transmembrane conductance regulator (CFTR) gene. CF lung disease is associated with airway obstruction and tissue damage due to mucus dehydration, opportunistic bacterial infections, and systemic inflammation. Respiratory inflammation and infection can induce neutrophil extracellular trap (NET) formation (NETosis) in CF lungs. NETosis is a process of programmed cell death that can utilize either NADPH-oxidase (NOX)-dependent or -independent pathways to release a cocktail of neutrophilic DNA and antimicrobial proteins into the extracellular environment. While NETs have been reported to play an important role in the pathogenesis of CF lung disease, the role of NOX-dependent or -independent mechanisms of NETosis in CF neutrophils is not known. This study therefore assessed the NOX-dependent and -independent NETotic capacity of CF neutrophils.

Hypothesis: CF neutrophils will release more DNA than non-CF neutrophils.

Methods: Neutrophil were isolated from peripheral blood samples from CF and non-CF study participants. The neutrophils were exposed to NOX-dependent and -independent agonists and the release of NETs and reactive oxygen species (ROS) was measured. The samples were also subjected to confocal imaging for NETotic biomarkers DNA, myeloperoxidase, and citrullinated histone 3.

Results: CF neutrophils released more baseline DNA and less ROS than their non-CF counterparts. CF neutrophils produced less NOX-dependent NETs and ROS than the non-CF neutrophils. Interestingly, CF neutrophils produced more NOX-independent NETs.  

Conclusion: The CF neutrophils display a dimorphic behaviour for the NOX-dependent and independent NETotic pathways. This study provides new insights on neutrophilic behaviour in CF and new factors to consider when searching for potential therapeutic targets.