(455) Impaired recruitment of CCR2⁺ monocytes does not compromise host-defense against pulmonary Pseudomonas aeruginosa infections

Background: Pseudomonas aeruginosa (PA) infections and hyperinflammation drive bronchiectasis in patients with Cystic Fibrosis, which ultimately causes respiratory failure. We have previously shown that C-C Motif Chemokine Receptor 2 (CCR2) positive macrophages are abundant in lung explants of people with CF and that these monocytes and monocyte-derived lung macrophages drive pathological lung neutrophil inflammation and cause non-resolving lung structural damage in Cftr^tm1Unc (CF) mice. Importantly, genetic or pharmacological ablation of CCR2, the major chemokine receptor for recruiting circulating monocytes into inflamed tissues, lowered lung neutrophilia and tissue damage (manuscript in revision). Our data thus support the use of a CCR2 inhibitor as a potential therapeutic approach to preserve lung function in patients with CF. However, the role of recruited CCR2⁺ monocytes during PA infections remains unclear.



Aim: to assess whether inhibition of CCR2⁺ monocyte recruitment compromises the host defense against pulmonary PA infections in WT and CF mice.

Methods: WT and CCR2^-/- mice were infected with 5x10⁶ colony-forming units (CFU) of the PA laboratory strain PAO1 and sacrificed at 3h, 6h, 24h and 48h post infection. To assess the role of CCR2⁺ immune cell recruitment in the CF background, we used CF, and CCR2^-/- x CF double knockout (dKO) mice which were infected and at 24h post infection (n=6-10 mice per group/genotype). We assessed lung and blood immune cell populations, bacterial load in lungs and spleen, and measured cytokines in bronchoalveolar lavage fluids (BALF).

Results: CCR2 deficiency showed a clear lack of recruited monocyte and monocyte-derived macrophage populations in lung tissues following PAO1 infection, while other immune cell populations in lung tissues and blood were not affected throughout the time course when compared to WT mice. Lung and BALF CFUs of PAO1 were not altered between WT and CCR2^-/- mice. Mice with a CF background (CF and dKO) had increased CFUs in lung and BALF at 24h post infection, but CCR2 deficiency did not affect CFU numbers. This indicates that lack of CCR2+ cells in lung tissues does not alter bacterial clearance during acute PAO1-pneumonia. Cytokine levels in BALF (IL17, IFN-γ, IP10, IL6) were elevated in CF and dKO mice compared to WT and CCR2^-/- mice, while the lack of CCR2 did not affect cytokine levels.

Conclusions: We show that inhibition of CCR2 might be a valuable target to prevent lung tissue remodeling in CF, without affecting the host-defense mechanisms against PA. For future direction we plan to assess the host defense in CCR2^-/- and dKO mice during infections with clinical PA strains, as well as the impact of CCR2 inhibitors during PA infections.

Acknowledgements:

References: