Induction of caspase activity by dCF and dAd. Cell lysates from U937 and THP-1 cells treated with various concentrations of dCF and 10 μmol/L dAd for 2 days were assayed for protease activity toward Ac-YVAD-MCA (▪) or Ac-DEVD-MCA (•). Values are the mean SD for three separate experiments.