2.7 Indirect immunofluorescence assay (IFA)
Vero cells grown in 6-well plates were mock infected or infected with PEDV CH/ZMDZY/11 and CV777 strain at multiplicity of infection (MOI) of 0.1 in infection medium (DMEM supplemented with 0.3% tryptose phosphate broth, 0.02% Yeast extract, and 10 μg/ml TPCK-treated trypsin). The infected cells were washed three times with phosphate buffered saline (PBS) and fixed with fixed with 4% paraformaldehyde for 10 min at room temperature (RT) and permeabilized with 0.2% Triton X-100 in PBS at RT for 10 min. The cells were blocked with 1% bovine serum albumin (BSA) in PBS for 30 min at RT and then respectively incubated with anti-G1-NTD and –G2-NTD sera at 37 ºC for 2 h. After being washed three times in PBS, the cells were incubated for 1 h at 37 ºC with a goat anti-mouse IgG conjugated to Fluorescein- isothiocyanate (Life Technologies, NY, USA). After washing five times with PBS, the cells staining was visualized using an inverted fluorescence microscope (NikonTS-100, Japan).