2.2  Virus Inoculation
IPEC-J2 cells approaching ∼80% confluence were washed twice with sterile phosphate buffered saline (PBS; 0.01 M, pH 7.4), and then mock infected or infected with PDCoV CHN-HN-1601 strain at a multiplicity of infection (MOI) of 0.1 TCID50 per cell. After adsorption for 1.5 h at 37 °C, the cells were rinsed once with sterile PBS and serum-free DMEM/F12 medium containing 5 μg/mL of trypsin (Sigma-Aldrich) was added. The cells were further cultured at 37 °C for the specified time points until different assays had been performed. Viral propagation in IPEC-J2 cells was evaluated by observing cytopathic effect (CPE), determination of one-step growth curve and immunofluorescence assay (IFA) using the mAb 1A3 against PDCoV.