cAMP inhibits IR-induced cell death in different lymphoid cell types. (A) TK6 and WTK1 cells were cultured in the absence or presence of forskolin or 8-CPT-cAMP for 30 minutes before exposure to 10 Gy IR. After 18 hours, cells were analyzed for PI uptake (n = 4). *P < .05 (relative to cells treated with IR only). (B) EU-3 cells were treated with or without IBMX or forskolin for 90 minutes or 30 minutes, respectively, before 10 Gy IR. Cells were analyzed for PI uptake 12 hours after IR (n = 4). *P < .05 (relative to cells treated with IR only). (C) PHA-stimulated human CD4⁺ T cells or SAC-stimulated PBMCs were treated with or without forskolin or 8-CPT-cAMP for 30 minutes before exposure to 10 Gy IR. After 24 hours, cells were analyzed for PI uptake. The B-cell fraction of PBMCs was identified by staining the cells with FITC-conjugated antibodies against CD19, and PI uptake was assessed in this subpopulation (T cells, n = 5; B cells, n = 6). *P < .05 relative to cells treated with IR only.