ACE2 and infection: The receptor-binding domain (RBD) of the SARS-CoV-2 S protein binds to ACE2 receptors, and it manifests a higher ACE2 binding affinity than that of SARS-CoV, and it could block the binding and attachment of SARS-CoV-2 RBD to ACE2-expressing cells inhibiting their infection to the host cells [30].