MKI67 and infection: Further, we found 8.2% of actively proliferating hAT2 cells (MKi67+ h3ACs) in uninfected h3ACs (cluster 1), which was more or less maintained across infection progression in infected h3ACs (cluster 2, 10.6%; cluster 3, 12.8%; cluster 4, 3.6%; cluster 5, 30.3%; and cluster 6, 5.1%) (Figure S6F).