ACE2 and viral infectious disease: NL63 viral infection causes transmembrane ACE2 and TMPRSS2 downregulation together with intracellular nucleocapsid production: Transmembrane TMPRSS2 plays an important role in NL63, SARS-CoV, and SARS-CoV-2 Spike protein priming and viral entry by cleaving Spike protein at the S1/S2 and the S2′ sites [17,27,56,57,58,59,60].