T1 B cells have reduced capacity to enter cell cycle following B-cell receptor engagement. T1, mature, and intermediate B-cell populations (Figure 4A) were cultured alone (NIL) or stimulated with various combinations of IL-4 (100 ng/mL), anti-IgM (10 μg/mL), anti-CD40 (1 μg/mL), or BAFF (200 ng/mL) for 48 hours. Afterward, hypotonic propidium iodide staining was carried out to determine apoptotic and cycling cells. Forward/side scatter and FL2 width gating were used to gate out nuclear fragments and doublets. The FL2 area was examined to identify the frequency of sub G₀/G₁ apoptotic cells (left number) and S/G₂ cycling cells (right number). A representative experiment is shown in the top panel, and the means ± SEM of 4 independent experiments is shown in the bottom panel. Unpaired t tests were used to detect significant differences (^*P <.05; ^**P <.01).