AUTHOR=Mahida Rahul Y. , Scott Aaron , Parekh Dhruv , Lugg Sebastian T. , Belchamber Kylie B. R. , Hardy Rowan S. , Matthay Michael A. , Naidu Babu , Thickett David R. TITLE=Assessment of Alveolar Macrophage Dysfunction Using an in vitro Model of Acute Respiratory Distress Syndrome JOURNAL=Frontiers in Medicine VOLUME=Volume 8 - 2021 YEAR=2021 URL=https://www.frontiersin.org/journals/medicine/articles/10.3389/fmed.2021.737859 DOI=10.3389/fmed.2021.737859 ISSN=2296-858X ABSTRACT=Background: Impaired alveolar macrophage (AM) efferocytosis may contribute to Acute Respiratory Distress Syndrome (ARDS) pathogenesis, however studies are limited by the difficulty in obtaining primary AMs from ARDS patients. Our objective was to determine whether an in vitro model of ARDS can recapitulate the same AM functional defect observed in vivo, and be used to further investigate pathophysiological mechanisms. Methods: AMs were isolated from the lung tissue of patients undergoing lobectomy, then treated with pooled broncho-alveolar lavage (BAL) fluid previously collected from ARDS patients. AM phenotype and effector functions (efferocytosis and phagocytosis) were assessed by flow cytometry. Rac1 gene expression was assessed using RT-qPCR. Results: ARDS BAL treatment of AMs decreased efferocytosis (p=0.0006) and Rac1 gene expression (p=0.016), however bacterial phagocytosis was preserved. Expression of AM efferocytosis receptors MerTK (p=0.015) and CD206 (p=0.006) increased, whereas expression of the anti-efferocytosis receptor SIRPĪ± decreased following ARDS BAL treatment (p=0.036). Rho-associated kinase inhibition partially restored AM efferocytosis in an in vitro model of ARDS (p=0.009). Conclusions: Treatment of lung resection tissue AMs with ARDS BAL fluid induces an impairment in efferocytosis similar to that observed in ARDS patients. However, AM phagocytosis is preserved following ARDS BAL treatment. This specific impairment in AM efferocytosis can be partially restored by inhibition of Rho-associated kinase. This in vitro model of ARDS is a useful tool to investigate the mechanisms by which the inflammatory alveolar microenvironment of ARDS induces AM dysfunction.