Representative expression of CD27, CD138 and surface IgD, IgG, and IgA on lymphogated cells in a healthy donor. Cell surface expression of these markers is presented on a 4-decade log scale as dot plots of correlated x-axis and y-axis fluorescence. FCM analysis was performed at days 0, 3, 5, and 7 with PBMCs cultured in the presence of IL-21 (10 ng/mL), IL-4 (0.5 ng/mL), and anti–human CD40 mAb (2 μg/mL). (A) Quadrant markers were positioned to include naive mature B cells (upper left [UL]), natural effector B cells (upper right [UR]), and IgD⁻ memory B cells (lower right [LR]). The circle tags a population of CD27^high IgD⁻ B cells. (B) Regions were positioned to separate CD138⁺ plasma cells (UL) from sIgA⁺ B cells (LR). (C) Quadrant markers were positioned to separate CD138⁺ plasma cells (UL) from sIgG⁺ B cells (LR).