Modulation of CD40L expression in CLL B cells by stimulation in vitro. Freshly isolated CLL B cells were exposed to media alone (A); to the combination of IL-2 (40 U/mL) and SAC (1:60,000 dilution) (B); to IL-4 (10 ng/mL) (C); to a murine MoAb to CD40 (1 μg/mL) (D); or to an F(ab′)2 preparation of antihuman IgM (0.5 μg/mL) (E). After 60 hours in culture, the cells were washed and then analyzed by two-color immunofluorescence cytometry using CD19-FITC and CD3-FITC, together with CD40L-PE (clone 89-76) or with a negative, control PE-conjugated antibody. The linear histograms reflect PE fluorescence intensity after exposure to CD40L-PE and the shaded, background histograms reflect PE fluorescence intensity after exposure to a control antibody, in each case analyzed among the gated, CD19-FITC–positive cells.
