AID^−/− GC B cells outnumber WT GC B cells in mixed BM chimeric mice. (A) Mixed BM chimeric mice were immunized with NP-CGG, and splenocytes were analyzed by flow cytometry 7, 11, 14, and 21 days later. B220⁺ B cells were divided into follicular B cells (GL7⁻ Fas⁻) or GC B cells (GL7⁺ Fas⁺). The level of chimerism among splenic follicular and GC B cells was determined by taking the ratio of the percentage of AID^−/− B cells (CD45.1⁻ CD45.2⁺) to WT B cells (CD45.1⁺ CD45.2⁻). The chimerism among GC B cells was then divided by the chimerism among follicular B cells to produce a normalized ratio whereby values < 1 indicate a skew toward AID^−/− B cells. (B) Normalized ratios of splenic GC B cells from mixed BM chimeric mice from various time points after immunization were compared with those of control BM chimeric mice harvested at day 14 after immunization. Each dot represents an individual mouse, solid lines represent median values, and the dotted line represents a normalized ratio of 1. Statistics represent comparisons between experimental mice and the control chimeras. Data are pooled from 6 independent experiments. *P ≤ .05; **P ≤ .01; and ***P ≤ .001. (C) Normalized ratios of splenic GC B cells from mixed BM chimeric mice reconstituted with different ratios of AID^−/−: WT BM cells and harvested at day 14 after immunization are compared with one another.