CLL cells, WMC cultured with IL-2, and resting and activated CD19⁺ B cells vary in their sensitivity to rolipram-induced apoptosis. (Top) One million WMC were cultured with the indicated concentration of rolipram with (▪) or without (▧) the addition of 40 μmol/L forskolin for 72 hours in the presence of 2 U/mL IL-2. Apoptosis was determined by Hoechst 33342 flow cytometry. (Middle) CD19⁺ peripheral B cells were purified by adherence to anti-CD19 magnetic beads. These cells were then cultured with the indicated concentration of rolipram with (▪) or without (□) 40 μmol/L forskolin. In addition, an identical set of cells were stimulated through their surface Ig by the addition of 10 μg/mL of Fab′₂ goat anti-human IgG/M 30 minutes before addition of rolipram with (▧) or without (▧) forskolin. (Bottom) CLL cells from two patients were cultured using an experimental design similar to that described for the middle panel. Rolipram was used at 10 μmol/L and forskolin at 40 μmol/L. (□), Media patient no. 1; (▪), anti-Ig patient no. 1; (▧), media patient no. 2; (▧), anti-Ig patient no. 2. The SEMs of triplicate cultures are indicated.