As mentioned above, the SARS-CoV-2 S protein is necessary for infection, and this is related to its binding on the angiotensin-converting enzyme (ACE)-2 receptor expressed by host cells, and the receptor-mediated virus entry depends on a serine protease, transmembrane serine protease 2 (TMPRSS2) (Figure 1B) [9,33,34,35]. Here, TMPRSS2 is linked to infection.