Firefly luciferase activity, GFP expression and viral titre of recombinant virus. A PK-15 cells were infected with rPRV HN1201-EGFP-Luc (MOI = 0.001, 0.01, 0.1 or 1) for 18 h and then lysed for immunoblotting analysis with antibodies against viral protein gB. β-Actin was used as the loading control. Fluorescence microscopy (B), fluorescence-activated cell sorting (FACS) analysis (C), luciferase assays (D) and TCID50 assays (E) of rPRV HN1201-GFP-Luc (MOI = 0.001, 0.01, 0.1 or 1) proliferation in PK-15 cells for 18 h. Data are shown as the mean ± SD from three independent experiments. Scale bar, 100 μm. F Correlation between luminescence intensity and GFP expression (R2 = 0.9974, p < 0.0001; GraphPad Prism 5, La Jolla, CA, USA). G Correlation between luminescence intensity and infectious viral titres (TCID50) (R2 = 0.9744, p < 0.0001; GraphPad Prism 5, La Jolla, CA, USA).