Pretumor transgenic mouse phenotypes. (A) Total splenocytes were harvested from 3-week-old littermates, stained with B220-APC (y-axis) and IgM-PE or CD43-PE (x-axis), and analyzed by flow cytometry. The percentage B220⁺, IgM⁻, or CD43⁻ (Q1), B220⁺, IgM⁺, or CD43⁺ (Q2), B220⁻, IgM⁻, or CD43⁻ (Q3), and B220⁻, IgM⁺, or CD43⁺ (Q4) is indicated for each genotype. Data are presented for individual mice but are representative of 7 to 14 mice analyzed per genotype (see also summarized data in Tables 1 and 2). (B) Spleens of the indicated genotype were fixed in 10% buffered formalin phosphate followed by paraffin embedding. Spleens were then sectioned and stained with H&E. The beginning of normal splenic structures can be observed (see arrows), with the LMP2A/λ-MYC spleen less organized. The rectangles in the left-hand column represent the area that is magnified in the right-hand column. (C) Spleens were isolated from 3-week-old littermates, and B cells were purified using a MACS protocol with magnetic beads specific for the B-cell marker CD19. Purified B cells were fixed with paraformaldehyde and ethanol and then stained with propidium iodide (x-axis) to measure the percentage of cycling cells. Cells were analyzed by flow cytometry to measure the percentage of cells that fall into the sub G₀, G₀/G₁, or S/G₂/M gates.