Kinetics of p35 and p19 expression in CD40L-activated BCP-ALL. BCP-ALL cells were cultured as indicated in Figure 1 and were stimulated with the CD40 ligand–transfected J558 cell line for different times (4, 8, and 18 hours). The RNA level was determined using RQ-PCR. The amount of each target cRNA synthesized from CD40L-stimulated cells was expressed as an n-fold difference relative to the amount of target cRNA synthesized from nonstimulated cells.