CD40 ligation and CD40 ligation plus IL-4 upregulate CD95 expression on nontumoral B cells and induce CD95-based apoptosis. CD95 expression and apoptosis induction were measured on 3-day cultured B cells (Donor NT-1) in mediun alone (A), or with IL-4 (B), CD40Lig-L cells (C) and IL-4 plus CD40Lig-L cells. CD95 expression was analyzed by flow cytometry after staining with anti-CD95 MoAb CH-11 (dashed line) or with IgM control MoAb (solid line) followed by PE-conjugated antimouse IgM. Numbers within histogram plots represent MFI values. For CD95-mediated apoptosis experiments, cultured cells were incubated with 1 μg/mL anti-CD95 MoAb CH-11 or with IgM control MoAb for 18 hours and then double-stained with annexin V-FITC/PI and analyzed by flow cytometry. Numbers within dot plots represent the percentages of cells in early apoptosis (lower right, annexin V⁺/PI-) and in late apoptosis or in necrosis (upper right, annexin V±/PI⁺). Percentages next to the dot plots indicate the specific apoptosis.