PECAM1 and influenza: To explore the dynamics of endothelial subpopulations during regeneration after viral lung injury, mouse lung ECs were isolated (CD45-EpCAM-CD31+) by FACS on day 0 (D0, uninjured), day 20 (D20), and day 30 (D30) post influenza infection, and subsets/clusters were then identified by single-cell transcriptomic profiling (Fig. 1A).