ACE2 and viral infectious disease: On the other hand, the introduction of the ACE2 and transmembrane protease serine 2 (TMPRSS2) genes [17] resulted in cells becoming susceptible to viral infection and replication as well as IL-6 production [29,30], suggesting that ACE2 is essential for viral entry to the cytoplasm, the site of viral replication, by way of phagocytic vesicles or endosomes.