Identification of IgG- and IgA-producing cell populations in patients with CVID or IgAD. Representative results are shown in panel A for CVID patients and in panel B for subjects with IgAD. Expression of CD138 and surface IgG or IgA on lymphogated cells was analyzed before and after magnetic separation of CD138⁺ plasma cells from 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) for 5 days. 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. Images of ELISPOT assay were taken after 20 hours of incubation of 5 × 10⁴ PBMCs for IgG production (A) or 1 × 10⁶ PBMCs for IgA production (B).