B-cell spreading and BCR clustering were reduced in WAS memory B cells. (A-D) TIRFM and interference reflection microscopy (IRM) analysis of PBMCs (P1-12) that were incubated with membrane-tethered Fab′–anti-Ig, HCs naive B cells (A), WAS naive B cells (B), HCs memory B cell (C), and WAS memory B cells (D). Shown are representative images from 1, 3, 5, and 7 minutes. Bar, 2.5 µm. The average values (±standard deviation [SD]) of the MFI of Fab′–anti-Ig in the B-cell contact zone (E) and of the B-cell contact area (F) were determined using TIRFM and IRM images from >300 individual cells of 3 individual experiments. (G) Flow cytometry analysis of the MFI of CD79α in naive or memory B cells of HCs and WAS patients (P1-12). *P < .01, compared with HCs naive B cells.