C5AR1 and COVID-19: This observation validates the drive to understand the immune microenvironment at a whole-lung level and is particularly interesting considering the identification of proinflammatory monocyte-derived macrophages in BALF (15) and the recent report of C5aR1+ macrophages associated with obliterating arteritis in a COVID-19 autopsy sample, implicating mononuclear phagocyte activation and expansion as important pathologic processes in COVID-19 (34).