TMPRSS2 and infection: ACE2 and TMPRSS2 expression is observed in ciliated and secretory cells across the airway epithelium, allowing infection to spread further.58,69 In extensively infected AEC2 cell models, gene expression profiling indicated an apoptotic hallmark and a significant downregulation of AEC2-specific genes as well as the surfactant proteins,70 that may induce alveolar collapse, significant tissue damage, and scaring.71