HDAC9 and infection: As shown in Figure 2C,E, HAT activity significantly increased at 8, 12, 24 or 36 h in PCV2-infected cells, and HDAC activity was extremely reduced at 8, 12 or 24 h post-infection when compared with the control group, but cellular HDAC activity significantly increased at 36 h post-infection (p < 0.05 or p < 0.01).