Lenalidomide treatment augments opening of cortical actin mesh after NKG2D and LFA-1 ligation. (A) Superresolution images obtained by STED microscopy of membrane proximal F-actin in pNK cells incubated for 120 minutes on coverslips coated with recombinant human ICAM-1 (2.5 µg/mL), anti-NKG2D mAb (3 µg/mL), or both in the presence of DMSO or 1.0 µM lenalidomide (+150 U/mL IL-2). Scale bars, 5 µm. Second column: Holes between actin filaments in the central region of the synapse shown as heat maps, with the smallest holes shown in blue (0.01 µm²) and largest holes shown in red (>3 µm²). Third column: Regions are shown within the actin mesh through which a particle (such as an IFN-γ vesicle) of diameter 200 nm (blue) to 800 nm (red) could fit. (B) Average size of holes in the actin mesh at the pNK synapse for cells stimulated as in panel A. Each data point represents a single cell; red lines shows the mean from 3 donors, n = 18 to 59 per condition. (C) The proportion of the synapse area predicted to be penetrable by a vesicle of 200- to 500-nm diameter for same cells as in panel B. Graph shows mean ± SD. **P < .01, ***P < .001, 1-way ANOVA with Tukey posttest.