TMPRSS2 and infection: We also performed Western blot analysis of cells and supernatants after infection with an MOI of 1 for 24 h in the absence of active TMPRSS2, using an antibody targeting the S2 subunit of SARS-CoV S. The immunoblots revealed that the 100-fold reduction in viral titers was accompanied by a strong reduction in the detection of total S in infected cells and no detection of S in the supernatant (Figure 4F).