GCB-cell formation following immunization. Mice from each strain were immunized with 1-2 × 10⁸ sheep red blood cells into the peritoneum, and the spleens analyzed for germinal center formation 10 days later. (A) Example contour plots show GCB-cell frequencies across the 6 strains that were analyzed. Plots are gated on viable (PI-negative) single B cells (B220⁺), and GCB cells are defined as peanut agglutinin (PNA)-positive and Fas-positive cells. (B) Box plots show the trends of GCB-cell development across 8 Cbp^WT/F, 8 EµBcl2, 5 Cbp^WT/Δ, 7 Cbp^Δ/Δ, 6 Cbp^WT/Δ × EµBcl2, and 6 Cbp^Δ/Δ × EµBcl2 mice. One-way ANOVA showed a significant variability across the strains (P < .001), but post hoc analysis (Tukey) showed that this was driven by significantly higher frequencies of GCB cells in mice carrying the EµBcl2 transgene compared with mice without the EµBcl2 transgene (P < .001 to .040). There was no significant difference between Cbp^WT/F and either Cbp^WT/Δ or Cbp^Δ/Δ mice, nor between EµBcl2 and either Cbp^WT/Δ × EµBcl2 or Cbp^Δ/Δ × EµBcl2 mice (P > .05).