Differential expression of the c-FLIP isoforms in selected cell lines. (A) Reverse transcription polymerase chain reaction was used to determine the abundance of specific different c-FLIP RNA isoforms within the different human cell lines tested. β-Actin served as a loading control. (B) Analysis of c-FLIP protein expression of the selected cell lines by Western blotting. As the short c-FLIP isoforms are only inducibly expressed in most cell types, cell lines were stimulated in an appropriate manner. The human T-cell lines Jurkat, HuT78, and CEM were stimulated for 16 hours with 20 ng/mL PMA and 1 μM ionomycin. Daudi cells were cocultered with L cells, a mouse fibroblast cell line, stably expressing the CD40L for 72 hours. For a better visualization of short c-FLIP isoform levels, a long exposure is additionally shown. As loading control, tubulin expression levels are presented.