Fig. 3.

PRRSV infection activates caspases. Both adherent and floating cells were labeled with FITC-conjugated z-VAD-FMK at 24 h (A), 48 h (B), and 60 h (C) p.i. as described in Materials and methods. The percentage of positive cells is indicated in each panel. These results are representative of three independent experiments. Caspase-8 (D), caspase-9 (E), and caspase-3 (F) activities of mock or PRRSV-infected cells were determined at the indicated times p.i. Cytoplasmic extracts from both adherent and floating cells were prepared and analyzed for each caspase activity using a colorimetric assay with specific substrate for each caspase. Results are expressed as O.D. values from 100 μg of protein. ELISAs were performed in triplicate, and values are shown as mean ± SD. These results are representative of at least three independent experiments. *; P < 0.05 compared to mock-infected cells at the same point.