PDE4B levels decrease in CLL cells after culture but are partially maintained by treatment with 10 μmol/L rolipram. RNA was isolated from 20 million CLL cells (derived from patient no. 12) immediately after cell purification (CT), or after 6 hours culture in media alone (6Hr) or with addition of 10 μmol/L rolipram (Roli). Equal loading and transfer of RNA was confirmed by hybridization with an actin probe as shown. These results are representative of Northern analysis performed on leukemic cells from two patients.