TMPRSS4 and infection: Yet, SARS-CoV replication was no more reduced after treatment of the cells with the broad-range serine-protease inhibitor aprotinin than it was with the TMPRSS2-specific PPMO T-ex5 (Figure 4E,H), suggesting that TMPRSS4 and other endogenous serine proteases are not involved in SARS-CoV S activation during infection in these cells.