Apoptosis assay. Time point 24 h post-infection with an MOI of approximately 5 is shown. Black columns correspond to uninfected cells, dark grey columns correspond to strain JF4278 (co-culture), while light grey columns correspond to strain L22/93 (co-culture). The data shown are the mean values of duplicates of three independent experiments. The x-axis represents the conditions tested (Bomac: Bomac cells free of BVDV; Bomac + BVDV: Bomac infected with BVDV), while y-axis represents the values of the measured test relative to untreated and uninfected cells. The values obtained for both Bomac cell lines infected with M. bovis were normalized to values of the corresponding uninfected and untreated cells of each cell line. Standard deviations of individual measurements are indicated as bars. *P < 0.05, **P < 0.01, ***P < 0.001. In order to show the statistical differences observed for untreated cells, two graphs using different scales in the y-axis were merged.