AID expression is reduced among RB⁺ GC and pre-GC B cells. (A) AID transcripts from RB^−/lo and RB⁺ fractions of GC, pre-GC, and Pblast B-cell subsets were semiquantitatively amplified via RT-PCR. RNA concentrations were normalized using beta actin. The 500–base pair molecular weight marker (MW) is indicated to the right. In each case, AID and RB expression were inversely related. (B) The AID expression ratio between RB^−/lo versus RB⁺ fractions (RB^−/lo_{AID EXPRESSION}/RB⁺_{AID EXPRESSION}) was determined by comparing digitally quantified band intensities. Each AID band was first normalized to its respective beta actin band (AID intensity/beta actin intensity = AID^NORM). RB^−/lo versus RB⁺ AID expression ratios were next calculated as (RB^−/lo AID^NORM/RB⁺ AID^NORM). In the case of GC B cells, AID expression is 2.4-fold greater among the RB^−/lo fraction (relative to the RB⁺ counterpart).