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

Controlled recruitment of C-C Motif Chemokine Receptor 2 (CCR2)-positive monocytes into lung tissues is a crucial component of the host immune response to infections. Pathogenesis of cystic fibrosis (CF) lung remodeling, which ultimately leads to respiratory failure, is caused by chronic infections and neutrophilic inflammation, but the immune mechanisms are not fully understood. Here, we show that lung explants from CF patients with severe disease contain abundant CCR2-positive classical monocytes in the submucosal tissues of small airways and areas of tissue remodeling. Recapitulating human CF lung remodeling by repeatedly exposing CF mice to lipopolysaccharide (LPS), and by using genetic ablation or pharmacological inhibition of CCR2, we demonstrate that CCR2-dependent accumulation of classical monocytes and monocyte-derived macrophages drive lung neutrophilia, pathogenic Transforming Growth Factor Beta signaling and irreversible lung tissue scarring. Importantly, six weeks after cessation of LPS exposure, the lungs of CF mice still have elevated numbers of pro-inflammatory monocytes with higher expression of neutrophil chemoattractants, thus perpetuating recruitment of neutrophils and lung tissue damage. Lastly, we demonstrate that the increased accumulation of immune cells to inflamed lungs is driven by dysfunctional CF transmembrane conductance regulator (CFTR) expression in CCR2-positive cells. These studies identify uncontrolled recruitment of CCR2-positive cells as a key driver of lung remodeling, and as a novel therapeutic target for patients with CF for which lung hyper-inflammation and tissue damage remain an issue despite recent advances in CFTR-specific therapeutics. Keywords: monocytes; macrophages; neutrophils; chronic lung inflammation; lipopolysaccharide; recruitment; CC-motif chemokine receptor 2; transforming growth factor beta; lung remodeling; cystic fibrosis In this study, we performed high-throughput sequencing of RNA isolated from lung monocyte and macrophage populations (classical monocytes (cMon), interstitial macrophages (IM), monocyte-derived alveolar macrophages (moAM) and tissue resident alveolar macrophages (trAM)) of WT and B6.129P2-Cftrtm1Unc/J (CF) mice that were exposed to LPS over 5 weeks (time point 1, T1) and after 6 weeks of recovery from LPS (time point 2, T2). Sequencing was performed performed in 2 biological replicates per genotype, cell type and timepoint. For Recovery time points (T2), lung cells were pooled from two mice for each sample.