ACE2 and infection: ACE2 expression is a significant predictor of infection at the cell type level as ACE2 expression was increased in the 4 susceptible cell populations: ciliated (Fig 4B), basal (Fig 4C), club (Fig 4D), and BC/club (Fig 4E) relative to the non-susceptible cell types: neuroendocrine (Fig 4F), ionocytes (Fig 4G), tuft cells (Fig 4H), and goblet cells (Fig 4I).