Variation of the short c-FLIP isoform expression in chimpanzee cells as well as primary B and T cells. (A) Expression of c-FLIP isoforms in EB176, LTR2008, primary B cells (left panel) and primary T cells (right panel) was analyzed by reverse transcription PCR. Human peripheral T cells (donors 1 and 2) were either left untreated or stimulated with PHA-L (5 μg/mL) for 16 hours. Activated T cells (d1) were washed with PBS and stimulated with IL-2 (25 U/mL) for another 5 days (d6). The indicated cell lines expressing c-FLIP_L and c-FLIP_R were used as control. (B) Freshly prepared human peripheral B cells (left panel) or T cells of 4 different blood donors (right panel) were either left untreated or stimulated with LPS (10 μg/mL) or PHA-L (5 μg/mL) for 16 hours. Lysates from Raji and PMA/ionomycin-treated HuT78 cells were loaded as positive controls for c-FLIP_R and c-FLIP_S, respectively. c-FLIP expression was determined by Western blot analysis. Tubulin served as a loading control.