SARS-CoV-2 entry factors are highly expressed in nasal epithelial cells together with innate immune genes

Using single-cell RNA seq datasets from healthy individuals, expressions of ACE2 and TMPRSS2, as well as other genes potentially associated with SARS-CoV-2 pathogenesis in multiple tissues were analyzed.  ACE2 expression was relatively lower than that of TMPRSS2, which may indicate that the limiting factor for viral entry is TMPRSS2. More detailed analysis demonstrated that ACE2 expressed higher in the upper than the lower respiratory tracts, which is consistent with the fact that nasal swab have yielded higher viral loads than throat swab. Moreover, various genes related with immune response co-express with ACE2 in the upper respiratory tracts.