Representative expression of CD27, CD138, and surface IgD, IgG, and IgA on lymphogated cells in patients with CVID or IgAD. Cell surface expression of these markers is presented in panels A and C for CVID patients and in panels B and D for subjects with IgAD 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-B) Quadrant markers were positioned to include naive mature B cells (UL), natural effector B cells (UR), and IgD⁻ memory B cells (LR). The circle tags a population of CD27^high IgD⁻ B cells. (C) Quadrant markers were positioned to separate CD138⁺ plasma cells (UL) from sIgG⁺ B cells (LR). (D) Regions were positioned to separate CD138⁺ plasma cells (UL) from sIgA⁺ B cells (LR).