Inhibition of DL1-mediated BCR- and CD40-mediated proliferation. (A) FO B cells were labeled with CFSE and stimulated with either anti-IgM (12.5 μg/mL) or anti-CD40 in the presence of DMSO, U0126, LY294002, or SB203580 for 72 hours on OP9-DL1 (solid lines) or OP9-Ctrl (dashed lines) cultures. Results are representative of at least 3 independent experiments. (B) Histogram presents the fold increase in the number of B cells recovered from OP9-DL1 versus OP9-Ctrl cultures after 72 hours of the indicated treatment. Error bars represent SEM. For IgM+DMSO, n = 5; IgM+U0126, n = 4; IgM+LY294002, n = 3; IgM+SB203580, n = 5; CD40+DMSO, n = 4; CD40+U0126, n = 4; CD40+LY294002, n = 4; CD40+SB203580, n = 4.