Increased proliferation of B cells and lymphoma development in IgH-hEBI2 mice. (A-B). BrdU incorporation after 24 hours (A) and accumulation after 8 days (B) in CD19⁺/B220^hi, CD19⁺/B220^low, and CD19⁺/B220⁻ IgH-hEBI2 and WT spleen cells as detected by FACS. The proliferation is shown as percentage of BrdU incorporation in the total spleen cell population. The results are mean ± SEM of data from 5 to 9 young (12-15 weeks) mice. *P < .05 and ***P < .001 by Student t test. (C). Picture of spleens from age-matched IgH-hEBI2 (top spleen) and WT (bottom spleen) animals. The spleens shown are representative of cases from 16-month-old animals. (D) Spleen weight in IgH-hEBI2 and WT mice over time. The results are data from 14 to 40 mice. *P < .05 and ***P < .001 by Student t test. (E) Kaplan-Meier survival plot of IgH-hEBI2 and WT mice. P < .001. (F) Representative histologic sections from an IgH-hEBI2 lymphoma mouse and an age-matched WT mouse (16 months old). All samples are stained with H&E (original magnification ×100) or PAX5 (B-cell marker) (original magnification ×200 and ×400 for WT and IgH-hEBI2 sections, respectively). (G) PCR analysis of clonality in IgH-hEBI2 mice. The analysis was done with JH4-1 reverse primer for all lanes and forward primers specific for V or D segments as noted above the individual lanes.