PROS1 and infection: Using immunofluorescence of S protein to detect infected cells at 24 hours post infection, we observed that virions produced in 293T-hACE2-ΔFURIN cells were markedly less infectious in Caco2 cells (Fig 4F and 4H), while this difference was less evident in 293T-hACE2 cells (Fig 4G and 4I).