PLCγ2 is critical for the propagation of cell spreading in response to membrane-bound antigen. (A–E) B cells were settled onto bilayers containing anti-IgM (A–C) and anti-κ (D and E) as antigen (Ag). (A–C) PLCγ2-KO DT40 B cells. (A, top) DIC (left) and confocal microscopy (right) visualizing antigen. (middle) Confocal microscopy visualizing B cell membrane (PKH26). (bottom) IRM. Bar, 5 μm. (B) Quantification of (left) contact area by IRM and (right) antigen accumulation. (C) SEM images. Bar, 5 μm. (D and E) Naive WT (PLCγ2^+/+CD19Cre^+/−) and PLCγ2-KO (PLCγ2^flox/floxCD19Cre^+/−) cells. (D, top) Confocal microscopy visualizing antigen distribution. (bottom) IRM. Bars, 2.5 μm. (E) Quantification of (left) contact area by IRM and (right) antigen accumulation. Video 4 is available.