Interestingly, infection with low SARS-CoV-2 titers induces a downregulation of NRP1 and ACE2 but an upregulation of TMPRSS2 expression in alveolar epithelial cells illustrating how multiple factors affect SARS-CoV-2 susceptibility and contribute to SARS-CoV-2 spread in the distal lung (99). This evidence concerns the gene TMPRSS2 and infection.