Fig. 4

The N-terminal region of PL1pro confers resistance to treatment of IBV with type I IFN and regulates the production of IFN-β. (a) Indirect immunofluorescence assay. H1299 cells were prestimulated with the indicated concentrations of IFN-α (50, 100, 150 ng/ml) for 2 h and subsequently infected with rIBV and rIBV-ΔPL1pro-N at an MOI of 0.5. At 18 h post-infection, cells were fixed and stained for IBV-N(green). Scale bars: 50 μm. (b) Western blot analysis IBV N protein expression. H1299 cells were prestimulated with IFN-α for 2 h and subsequently infected with rIBV and rIBV-ΔPL1pro-N at an MOI of 0.5. At 18 h post-infection, the expression of IBV N protein was assessed by Western blot. The full-length blots are in Additional file 1: Supplemental Fig. 4a. (c) Absence of the N-terminal region of PL1pro upregulates the expression of IFN-β. H1299 cells were infected with rIBV and rIBV-ΔPL1pro-N at MOI of 0.5 and 1, respectively, Western blot was used to detect the expression of IFN-β at the indicated times post-infection, respectively. The full-length blots are in Additional file 1: Supplemental Fig. 4b