ACE2 and infection: The entrance of coronavirus into target cells is facilitated via the viral spike protein; in SARS-CoV-2, the spike glycoprotein, which contains a defined receptor-binding domain (RBD) required for interaction with the host cell receptor angiotensin-converting enzyme 2 (ACE2), regulates both cross-species and human–human infections of SARS-CoV-2 [9].