Isolation of a novel B-cell subpopulation from tonsillar B lymphocytes. (A) IgD⁺CD38⁻ B cells (lymphocyte gate not shown) are further separated into Bm1 (small CD23⁻) and Bm2 (small CD23⁺) naive B-cell subpopulations along with a novel subpopulation (large CD23⁻) using CD23 expression and forward scatter (FSC). (B) CD69, CD71, and AID expression is shown for each IgD⁺CD38⁻ subpopulation as well as germinal center and memory B cells. Bars are set to indicate the mean fluorescence intensity range at which populations were considered positive. (C) Immunoprecipitation and Western blot were performed on 100 000 cells each from naive (Bm1 and Bm2), pro-GC, pre-GC (IgD⁺CD38⁺), and GC (Bm3 and Bm4) subpopulations with polyclonal (IP) and monoclonal (blot) antibodies to AID, which migrates at 27 kDa.