PLCγ2-mediated B cell spreading and antigen aggregation in the absence of IP₃R or PKCβ. (A–C) WT, IP₃R-KO, or PKCβ-KO DT40 B cells were settled onto bilayers containing anti-IgM as antigen (Ag). (A) Brightfield (left) and TIRFM (right) visualizing antigen. Bar, 5 μm. (B) Quantification of PLCγ2-GFP–containing microsignalosomes present after 3 min. Data are representative of two experiments, and the number of microsignalosomes was measured in 6–14 cells, representing a total of 892 microsignalosomes. Mean numbers are as follows: WT, 33 ± 4; IP₃R-KO, 22 ± 3; and PKCβ-KO, 21 ± 8. ns, not significantly different. (C) Quantification of (left) contact area by confocal microscopy and (right) antigen accumulation.