2.6 Immunofluorescence assay
CRFK were grown in 6-well microtitre plates and infected with FPV. After 48 h, the cells were fixed with 4% paraformaldehyde for 15 min and then washed three times with phosphate-buffered saline with Tween-20(PBST). Cells were incubated with anti-FPV monoclonal antibody (Shenzhen Anti Biotechnology Co., Ltd.) at 37 °C for 1 h and then FITC-conjugated rat anti-mouse secondary antibody (BIOMAN (Beijing) Technology Co., Ltd) for 1 h Finally, the labelled cells were observed viafluorescence microscopy (Leal et al., 2007).