Effect of IRF4 on pre-BCR down-regulation and cell-cycle withdrawal is attenuated in the presence of IkarosDN. IRF4,8^−/− pre-B cells were coinfected with IRF4 (YFP) and IkarosDN (GFP). The infected cells consist of 3 distinct populations: YFP⁺GFP⁻, YFP⁺GFP⁺, and YFP⁻GFP⁺. At 3 days after infection, the cells were stained with anti-λ5 antibody and Hoechst dye and analyzed by FACS. The λ5 expression and cell-cycle status in the 3 distinct populations of cells were analyzed separately. The result is a representative of 3 independent experiments, and the numbers represent percentages of the cycling cells.