Fig. 6.

Caspase-9 activity is dependent on caspase-8 activation and tBID expression is increased in PRRSV-infected cells. (A) Cells were infected with PRRSV and treated with the caspase-8 inhibitor, z-IETD-FMK at 20 μM. Adherent cells were harvested by trypsin treatment and combined with floating cells. Caspase-9 activity was measured using a colorimetric assay with a specific substrate. Values are shown as the means ± SD from triplicate wells and represent two independent experiments. (B) Cell lysates from both adherent and floating cells at different time points after PRRSV infection were immunoblotted and truncated BID was detected. This experiment was repeated two times with similar results. *; P < 0.001 compared to untreated PRRSV-infected cells.