ACE2 and COVID-19: Bukowska et al. (2017) confirmed from experimental data that estrogen is able to regulate expression of the ACE/ACE2 axis, which is highly distorted in COVID-19. Also, estrogen inhibits propagation of cytokine storm and can activate B cells for antibody production. Besides, estrogen reduces expression of TMPRSS2, thereby reducing the entry of SARS-CoV-2 to the susceptible cells (Bennink et al., 2021). So, estrogen treatment is suggested to be an effective treatment against COVID-19 (Bennink et al., 2021).