Apoptosis induced by BHV-1 in MDBK cells. (A) Cell viability changes of BHV-1-infected MDBK cells. Cells were seeded into 96-well culture palates and infected with BHV-1 at different MOI for indicated hours. Cell viability was detected by MTT assay. (B) Morphological changes of BHV-1-infected cells at 2 MOI for indicated hours. (C) Morphological changes of BHV-1-infected cells at different MOI for 48 h. Photomicrographs at inverted microscope of BHV-1-induced CPE (upper panel); Morphological changes under fluorescence microscopy followed by AO and EB staining (lower panel). Arrows indicate condensed chromatin and nuclear fragmentation. (D) DNA fragmentation of BHV-1-infected MDBK cells. Cells were mock-infected or infected with BHV-1 at 2 MOI for indicated hours, and then analyzed by DNA fragmentation assay. (E) Percentage of apoptotic cells. Cells were infected with 2 MOI BHV-1 at different time, and then detected by flow cytometry. Data are mean ± SD from three independent experiments. * p < 0.05, ** p < 0.01 versus mock infection.