Non-neural expression of SARS-CoV-2 entry genes in the olfactory epithelium suggests mechanisms underlying anosmia in COVID-19 patients

David Brann; Tatsuya Tsukahara; Caleb Weinreb; Darren W. Logan; Sandeep Robert Datta

We note several caveats that temper our conclusions. Here, we assume that ACE2 protein levels follow the pattern revealed by analysis of mRNA; while our staining in human OE is consistent with this idea, it remains to be rigorously assessed in all cell types in the OE and bulb. Although current data suggest that ACE2 is the most likely receptor for CoV-2 in vivo, it is possible (although it has not yet been demonstrated) that other molecules such as BSG may enable CoV-2 entry independently of ACE2 ( Figures 3E, 3G , S1, S2) (57, 58) . We also propose that damage to the olfactory system is either due to primary infection or secondary inflammation; it is possible (although has not yet been demonstrated) that cells infected with CoV-2 can form syncytia with cells that do not express ACE2. Such a mechanism could damage neurons adjacent to infected cells. Definitive identification of the pathophysiological mechanisms underlying COVID-19-mediated anosmia will require additional research. Nonetheless, our identification of cells in the OE and OB expressing molecules known to be involved in CoV-2 entry illuminates a path forward for future studies.