FIG. 4.

Determination of apoptosis in monocytes exposed to different concentrations of leukotoxin. (A) Caspase 3 activity in lysate from monocytes exposed for 6 h. The intracellular caspase 3 activity was measured by a fluorometric immunosorbent enzyme assay and expressed as the percentage of control values for cultures incubated without leukotoxin. Values are means ± standard deviations of four experiments. (B) DNA fragmentation in monocytes exposed to leukotoxin for 20 h. The DNA was separated by agarose electrophoresis and stained with ethidium bromide. The experiment was performed in triplicate. Representative results are shown.