TMPRSS2 and COVID-19: The present narrative review aims to elucidate and summarize data on organ-specific distribution of ACE2 and TMPRSS2 with emphasis on the link between abundance, localization, and susceptibility to COVID-19; the changes that occur with age and with special focus on differences between sexes in relation to susceptibility and pathophysiology including circulating peptides in patients with SARS-CoV-2 infection.