Expression of CD95 and XIAP before and after CD40 ligation on CLL B cells. (A) Surface expression of death receptors on CD19⁺ CLL cells was assessed by flow cytometry 24 hours after coculture with HeLa cells (control, left panel) or HeLa-CD154 cells (CD40 activated, right panel). The dot plots depict the fluorescence of CLL cells stained with a fluorescein isothiocyanate (FITC) fluorochrome-conjugated anti-CD95 mAb and a phycoerythrin (PE)-labeled fluorochrome-conjugated anti-CD19 mAb. The numbers in the upper quadrants represent the percentage of CD19⁺/CD95^- cells (left) and the percentage of CD19⁺/CD95⁺ cells (right). (B) Immunoblot analyses were performed on the CLL cell samples of 3 different patients (CLL 1, CLL 2, and CLL 3) as indicated at the top of the figure. Prior to the preparation of the cell lysates, the CLL cells were cultured for 24 hours with HeLa cells (-) or HeLa-CD154 cells (+), as indicated by the symbols at the bottom of the figure. Cell lysate (15 μg) prepared from each sample was applied to each lane of a polyacrylamide gel for immunoblot analyses with anti-XIAP (top row) or anti-β-actin (bottom row), as indicated on the left.