Opening of the cortical actin mesh is not augmented by increasing NKG2D or NKp46 ligation. (A) Top panels: Representative SI images of F-actin in pNK cells stimulated on surfaces coated with 1.0 or 12.0 μg/mL of αNKp46 mAb. The center of the synapse is enlarged in the panels directly below. Bar represents 1 μm. Bottom center panel images: Holes within the actin mesh as heat maps related to hole area with the smallest holes shown in blue (0.01 μm²) and largest (> 3.0 μm²) shown in red. Bottom panels: The domains within the cortical F-actin mesh through which lytic granules of diameters 200 nm (blue) to 800 nm (red) could penetrate. (B) Top panels: Representative SI images of F-actin in pNK cells stimulated on surfaces coated with the NKG2D ligand MICA (1.0 μg/mL, 12.0 μg/mL). As in panel A, the center of the synapse is enlarged in the panels below. Bar represents 1 μm. Bottom middle panels: Heat maps of actin mesh hole areas. Bottom panels: The domains through which lytic granules with diameters ranging from 200 nm to 800 nm may penetrate. Bars represent 5 μm. (C) The mean area of holes within the central region of the pNK cell synapse for cells stimulated as indicated. (D) The proportion of the NK cell synapse predicted to be penetrable by a granule with a diameter of 250 nm for cells stimulated as indicated. Graphs represent mean ± SEM; n = 30 per condition using cells from 3 independent donors. ***P < .0001, compared with poly-L-lysine controls (−) by 1-way ANOVA.