Inhibition of PARP proteolysis by TPA and IL-4. (A) Inhibition of dexamethasone-induced PARP proteolysis by TPA. B-CLL lymphocytes from three patients were incubated with 100 nmol/L TPA in the presence or absence of 10 μmol/L dexamethasone for 48 hours. (B) Inhibition of spontaneous PARP proteolysis. Cells from patient 6 were incubated for 48 hours either in the absence of any factor (C) or with 100 nmol/L TPA, or IL-4 (10 ng/mL). (C) Inhibition of fludarabine-induced PARP cleavage. Cells from patient 5 were incubated with the indicated factors for 24 hours. The concentrations used were 100 nmol/L TPA and 5 μg/mL fludarabine. Western blot of PARP was performed with protein extracts from these cells as previously described.