Trypsin-dependency and kinetics of PEDV entry into cells. A Vero cells were seeded in 6-well plates until confluence. Cells were washed with PBS and infected with PEDV strains (MOI = 0.5) without trypsin or in the presence of trypsin (10 μg/mL) or trypsin and 25 μg/mL SBTI. Cells were collected for qRT-PCR at 12 hpi. B, C Vero cells (B) and IPEC-J2 cells (C) were incubated with PEDV GDS01 and GDS09 strains, respectively, at 4 °C for 1 h and shifted to 37 °C immediately to initiate internalization. At 0, 15, 30, 45, 60, 75, 90, 105, and 120 min after incubation, the cells were treated with proteinase K (1 mg/mL) at 4 °C for 30 min to inactivate the non-internalized virions. The control cells were washed with PBS. The invasion rates were calculated by qRT-PCR analysis. ****P < 0.001.