Figure 1.

In some cells, ACE2 expression is higher (left cell), whereas in other cells, ACE2 expression is lower (right cell). In the case of the airways, this renders the more highly expressing upper airway cells inherently more permissive to infection by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Nevertheless, in other cells (central cell), ACE2 expression is high, and yet the population remains resistant to SARS-CoV-2 infection. This phenotype is potentially dictated by the expression levels of additional proviral factors, or restrictive host factors such as IFN-stimulated genes (ISGs).