TMPRSS2 and infection: TMPRSS2 eases the infection of SARS-CoV by two independent mechanisms; a) by ACE2 cleavage that enhances the viral entry and stimulates viral uptake by cathepsin L-dependent entry, not activating SARS-S for entry (Figure 2A), b) by SARS-S cleavage at the host cell surface that activates the spike protein for membrane fusion (Figure 2B) (Heurich et al., 2014).