ACE2 and COVID-19: The gender-associated difference in COVID-19 outcome is thought to be linked to two key mediators of viral attachment to cell membranes, namely, the angiotensin-converting enzyme (ACE) 2 receptor (ACE2) for the spike protein of coronaviruses, and the type 2 transmembrane serine protease (TMPRSS2), which cleaves the spike protein and thereby facilitates the attachment and fusion of the virus to cell membranes (39, 40).