It is well known that ACE2, and putatively also sialic acids, represent the “doors” by which COVID-19 enters endothelial cells and pericytes; ACE2 receptors are ubiquitous, and are not only present in the endothelial cells of the alveolar membrane [71,72,73,74,75,76,77,78]. Here, ACE2 is linked to COVID-19.