F-actin recruitment was increased in HCs memory B cells. (A-D) TIRFM and IRM analysis of phalloidin staining in the contact zone of HCs and WAS (P1-12) naive and memory B cells incubated with membrane-tethered Fab′–anti-Ig. TIRFM analysis of the spatial relationship of BCR with F-actin (A-D) in the contact zone of splenic B cells incubated with membrane-tethered Fab′–anti-Ig. The colocalization coefficients between BCR and F-actin staining were determined using NIS-Elements AR 3.2 software (F). The quantification of MFI of the basal level of F-actin in naive or memory B cells from HCs or WAS (P1-12) patients by flow cytometry (G). Shown are representative images (A-D), and the average MFI (E) or colocalization coefficients (F) (±SD) from ∼50 individual cells of 3 independent experiments. Bars, 2.5 µm. *P < .01, compared with WAS naive or memory B cells.