Sorting human B-cell subsets. (A) Human peripheral B cells (CD19⁺) were stained and sorted into 4 populations, according to their expression of CD27 and IgD: IgD⁺CD27^– (naive and transitional), IgD⁺CD27⁺ (IgM memory), IgD^–CD27⁺, and IgD^–CD27^– B cells. Numbers indicate the percentage of subsets in boxes. (B) From the IgD⁺CD27^– gate, naive and transitional cells were further divided into: CD10⁺ transitional and CD10^– naive cells. Numbers indicate the percentage within the IgD⁺CD27^– gate. Data are representative of 3 separate experiments.