ACE2 and infection: Infection by SARS-CoV-2 involves the action of the virus spike protein (S), which involves angiotensin-converting enzyme 2 (ACE2) as the entry receptor (a metallopeptidase on the membrane of many target host cells) [8], and the engagement of the cellular serine protease TMPRSS2, allowing S2 to facilitate the fusion of the virus envelope with the cell membrane, which facilitates viral RNA entry into the cytoplasm of the target host cells [9].