Surface phenotype of B cells from healthy control donors and XLP patients. (A) PBMCs from a healthy control donor and a representative XLP patient, XLP5, were stained with anti-CD20 mAb, and the frequency of B cells in the lymphocyte population determined (leftmost panels; frequency shown as percentage). In the remaining panels, purified CD20⁺ B cells were dual-stained with mAbs specific for CD27 and either CD10, IgD, IgM, IgG, or IgA to obtain the FACS profiles shown. (B) Summary of B-cell surface phenotype data obtained from 6 healthy control donors and 4 XLP patients (XLP5-8). Results are expressed (left to right) as the percentage of PBMCs that were CD20⁺ B cells, and the percentage of CD20⁺ B cells that had the transitional, naïve, or memory cell phenotypes shown. The mean value for each group is denoted by the horizontal bar.