CD45RB expression during the germinal center reaction and peripheral B-cell development. Within lymph nodes (tonsils), small resting naive B cells transition into activated pro-GC B cells after encountering antigen and accessory help. This transition coincides with elevated surface RB expression by a fraction of cells. However, RB expression can decrease as early as the pre-GC B-cell stage and remains low among centroblasts during phases of GC-associated somatic hypermutation and proliferation. Elevated surface RB is again observed among a fraction of centrocytes, presumably during B-cell receptor–mediated selection, and remains high in approximately 1 of every 2 plasmablast and memory B cells within lymph nodes. Compared with their tonsillar counterparts, a significantly lower percentage of circulating peripheral blood memory B cells are RB^bright.