SHIP activation is required for attenuation of BLyS receptor expression. (A) CD23⁺ B cells from SHIP KO or littermate control mice were cultured with the indicated stimuli (concentrations of stimuli are indicated in “B-cell subset isolation, culture, and stimulation”). Cells were analyzed by FACS for BLyS receptor expression on live cells at 24 hours after stimulation. Histograms are shown at the top. Gray histograms indicate isotype control; unfilled histograms, unstimulated cell levels; filled black histograms, stimulated cell levels. Median fluorescence intensities (MFI) of populations are shown in bar graphs at bottom. Plots are representative of 2 independent experiments; in all cases, n equals 3 or more. Significance levels are indicated by P values. (B) Proliferation and death profiles of CD23⁺ B cells from SHIP KO or littermate control mice 72 hours after stimulation. B cells were loaded with CFSE and cultured with indicated stimuli. One minute before FACS analysis, TO-PRO-3 was added as a vital dye. Plots are representative of 2 independent experiments.