ACE2 and COVID-19: Although COVID-19 pathogenesis has still not been completely elucidated, early reports showed that SARS-CoV-2 binds to the host cell receptor angiotensin-converting enzyme-2 (ACE2) through the RBD domain in the spike (S) protein to infect human epithelial cells in alveoli, which can cause a cytokine storm resulting in respiratory failure and ultimately death.