Mutations in STAT3 severely compromise the generation of memory B cells. (A–C) The frequencies of total B cells (A) or transitional (CD20⁺CD10⁺CD27⁻), naive (CD20⁺CD10⁻CD27⁻), and memory (CD20⁺CD10⁻CD27⁺) B cells (B and C) in healthy donors (HD; n = 26–32), STAT3_MUT patients (n = 10), patients with AD-HIES but WT STAT3 alleles (HIES; n = 4–5), STAT1_MUT patients (n = 5–6), or CVID patients (n = 36) were determined by flow cytometry. The values in B correspond to the frequencies (means ± SEM) of transitional (T), naive (N), and memory (M) B cells in the indicated donor populations. (D) memory (CD20⁺CD10⁻CD27⁺) B cells from healthy donors (HD; n = 32), STAT3_MUT patients (n = 10), WT STAT3 AD-HIES patients (n = 5), and CVID patients (n = 31) were labeled with mAbs specific for IgM, IgG, or IgA. The frequency of memory B cells that were IgM⁺, IgG⁺, or IgA⁺ was then determined. The plots in A and B are from representative healthy donors and patients; the graphs in A, C, and D show data points for all donors and patients examined, and the horizontal bars represent means. *, P < 0.05; **, P < 0.01; ***, P < 0.001.