DL1 signaling enhances B-cell proliferation after CD40 or BCR stimulation. (A) CFSE-labeled FO B cells were stimulated with anti-CD40 antibodies for 72 hours on OP9-DL1 (solid lines) or OP9-Ctrl (dashed lines) cultures without or with GSI. (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 no treatment (NT), n = 9; IgM and IgM+GSI, n = 5 (12.5 μg/mL anti-IgM); CD40 and CD40+GSI, n = 6.