Recruited monocytes/macrophages drive pulmonary neutrophilic inflammation and irreversible lung tissue remodeling in cystic fibrosis.

Persistent neutrophil-dominated lung inflammation contributes to lung damage in cystic fibrosis (CF). However, the mechanisms that drive persistent lung neutrophilia and tissue deterioration in CF are not well characterized. Starting from the observation that, in patients with CF, c-c motif chemokine receptor 2 (CCR2)+ monocytes/macrophages are abundant in the lungs, we investigate the interplay between monocytes/macrophages and neutrophils in perpetuating lung tissue damage in CF. Here we show that CCR2+ monocytes in murine CF lungs drive pathogenic transforming growth factor ß (TGF-ß) signaling and sustain a pro-inflammatory environment by facilitating neutrophil recruitment. Targeting CCR2 to lower the numbers of monocytes in CF lungs ameliorates neutrophil inflammation and pathogenic TGF-ß signaling and prevents lung tissue damage. This study identifies CCR2+ monocytes as a neglected contributor to the pathogenesis of CF lung disease and as a therapeutic target for patients with CF, for whom lung hyperinflammation and tissue damage remain an issue despite recent advances in CF transmembrane conductance regulator (CFTR)-specific therapeutic agents.