Intrinsic neutrophil dysregulation in programmed cell death promotes neutrophilic inflammation in cystic fibrosis

Neutrophilic inflammation constitutes a major pathology in cystic fibrosis (CF), a life-shortening genetic disorder. However, the underlying mechanisms remain incompletely understood. Here we report our investigation into CF neutrophil recruitment, apoptosis and clearance to determine if any neutrophil intrinsic defect is involved in the pathogenesis. Congenic fluorescent wild-type (WT) and CF mice were generated and used as bone marrow (BM) donors. Non-fluorescent WT and CF recipients were transplanted with a mixture of EGFP-WT and DsRed-CF BM cells and interrogated for neutrophil recruitment and apoptosis in the same lung after zymosan challenge. Additionally, ex vivo neutrophil migration and apoptosis were also examined to confirm the in vivo findings. Moreover, DsRed-WT or DsRed-CF BM cells were transfused into non-fluorescent CF recipients that had been intratracheally challenged with zymosan. Percentages of apoptotic cell-laden macrophages in the lungs were compared. The data indicate that CF and WT neutrophils exhibited a similar migratory capacity and were equally recruited to the same lung, regardless of the recipient phenotype. However, CF neutrophils displayed a significantly delayed apoptosis. Such an anomaly was linked to reduced hypochlorous acid production. Moreover, CF macrophages exhibited a significantly higher expression of efferocytosis marker MerTK, and a greater capacity of efferocytosis, implying that macrophage phagocytosis of apoptotic cells is not impaired in this experimental setting. These findings suggest that intrinsically dysregulated programmed cell death affects CF neutrophil fate decision and fuels neutrophilic inflammation in CF lungs.