ACE2 and COVID-19: It is well established that RBCs, platelets and endothelial cells, which play key roles in COVID-19, are densely coated with sialylated glycans [64,65,70] but have no ACE2 (or, for endothelial cells, minimal ACE2 [69]) and that the various coronavirus strains use several different host-cell receptors for replication [30], yet ACE2 has been the exclusive host-cell target of interest in much of the research on SARS-CoV-2.