Pretumor B cells from LMP2A/λ-MYC mice demonstrate highly proliferative phenotypes. (A) Histograms of Ki-67⁺ purified B cells from 3-week-old representative mice. The number in each histogram indicates the percentage of Ki-67⁺ cells in purified B cells. (B) Combined Ki-67 data from 3 experiments shown as mean ± SD. The differences in the percentage of Ki-67⁺ cells were analyzed by 1-way ANOVA. ***P < .001; ns, not significant. (C) Representative histograms of propidium iodine staining for DNA content in purified pretumor B cells. (D) Pie charts show mean ± SD of cells in different phases of the cell cycle as analyzed in (C). WT: n = 3, LMP2A: n = 3, LMP2A/λ-MYC: n = 4, λ-MYC: n = 4. (E) Immunohistochemistry of B220⁺ cells in representative 3-week-old mouse spleens (original magnification ×20). No 1° Ab, negative control with secondary antibody only.