C4BPA and susceptibility to pneumonia measurement: Among genes upregulated in ACE2-expressing AT2 cells, we identified genes that are highly pertinent to lung epithelial biology and disease such as HHIP (lung branching and COPD [24,25]), FGG (fibrosis, pneumonia, and inflammation [26,27]), and C4BPA (complement system, pneumonia, and infection [28,29]) (Figure 3A,B).