WASp is required for integrin activation and pSMAC formation at the B-cell immunologic synapse. WT and WASp^−/− B cells were settled onto lipid bilayers containing anti-kappa antibody (green) or antikappa and Alexa532-conjugated ICAM-1 (red) and imaged by confocal microscopy after 20 minutes of interaction. (A) Differential interference contrast (DIC), fluorescence and interference reflection microscopy (IRM) images of representative cells are shown. Quantification of the percentage of B cells forming (B) a cSMAC or (C) an IS (cSMAC + pSMAC) and (D,E) the area of B-cell contact with the bilayer. For each condition, a total of 20 to 50 B cells were analyzed. Bars represent mean values plus or minus SEM. Data are representative of 2 independent experiments. Scale bar represents 2.5 μm. ***P < .001.