PROS1 and infection: The infection of both SARS-CoV and SARS-CoV-2 is initiated by the attachment of the S protein to the host receptor angiotensin-converting enzyme 2 (ACE2) (Li et al., 2003; Hoffmann et al., 2020; Shang et al., 2020), followed by the S protein priming by cellular proteases such as TMPRSS2 (Glowacka et al., 2011; Shulla et al., 2011; Reinke et al., 2017; Hoffmann et al., 2020).