(A) Surface expression of the CD95 antigen in cells selected for resistance to CD95-mediated apoptosis. Cells were stained with the non–apoptosis-inducing antibody UB2 and analyzed by flow cytometry. In the 8226/F4 cell line, the UB2-specific staining completely overlaps the isotype control. (B) RT-PCR of CD95 antigen mRNA expression. Total RNA was extracted from 8226/S and 8226/F4 cells, and the CD95 antigen expression determined by RT-PCR as previously described. Histone 3.3 was amplified as a control for RNA integrity and equal gel loading.