Isolation and phenotypic characterization of peripheral blood memory B-cell subsets. (A) Gating strategy to identify 2 naive and 6 memory B-cell subsets based on expression of CD24, CD38, CD27, and IgH isotypes. (B) H&E staining of sorted subsets revealed a typical lymphocytic morphology with large nucleus (purple) and little cytoplasm (pink; ×63, original magnification; bars represent 5 μm). (C) All 6 memory B cell subsets showed up-regulation of CD80, CD180 and TACI as compared with naive B cells. Expression levels are shown in black and isotype controls as filled, gray histograms. Red lines indicate mode expression levels for each molecule on naive mature B cells.