TCL1 protects CD40-stimulated B cells from FASL-induced apoptosis. (A) Isolated B220⁺ spleen B cells from WT (□) or TCL1-tg (▪) mice were treated with 1.5 μg/mL anti-CD40 followed by incubation with FASL (1:50) with or without 10 μg/mL anti-IgM. The percentage of death induced with each condition was determined as described in “Materials and methods.” (B) Surface FAS expression was evaluated in purified B cells isolated from WT and TCL1-tg mice. Cells were either unstimulated (gray hatched line, both WT and TCL1-tg) or treated with anti-CD40 (1.5 μg/mL) with or without 10 μg/mL anti-IgM (WT, hatched line; TCL1-tg, solid black line). The data are representative of 3 separate experiments, and error bars represent standard deviation between experiments.