ACE2 and infection: Based on the in-depth study on the infection mechanism of COVID-19 virus, three major action sites may be key targets for treatment, including COVID-19 virus spike protein receptor binding domain angiotensin-converting enzyme 2 (ACE2) [18,19], COVID-19 virus main protease (COVID-19 virus Mpro) [20], and COVID-19 virus RNA-dependent RNA polymerase (COVID-19 virus RdRp) [21].