ATF4 and infection: According to immunoblotting analysis, we found that the level of phosphorylated eIF2α was up-regulated at later stage of infection, and the ATF4 and CHOP were both up-regulated at the time coinciding with eIF2α activation (Figure 1D), suggesting that the p-eIF2α-ATF4-CHOP signaling was activated by CSFV infection; however, we could not find a suitable antibody against p-PERK in PK-15 cells.