PROS1 and viral infectious disease: The human serine protease serine 2 (TMPRSS2) is a transmembrane protease of host cells; it cleaves and activates the S protein of SARS-CoV-2 to bind with ACE2 on the initiated stage of the viral infection (Singh et al., 2020) and reveals that TMPRSS2 is a suitable target for COVID-19 therapy.