Signaling for lytic granule convergence requires Src kinase activity. Time-lapse frames of lytic granule movement in YTS GFP-tubulin cells pretreated with (A) DMSO or PP2 on an (B) anti-CD28– or (C) an anti-CD11a–coated surface. In each image, confocal immunofluorescence in the plane of the MTOC is shown. Green, GFP-tubulin; red, LysoTracker-loaded acidified organelles. Zero minutes represents the time at which the NK cell appeared to contact the glass surface. Quantitative analyses of lytic granule distance from the MTOC of PP2- or DMSO-treated YTS GFP-tubulin cells on (D) anti-CD28– or (E) anti-CD11a–coated surfaces as a function of time as measured by mean MTOC to granule distance in 9 cells per condition; error bars show ±SD. Mean distance of lytic granules from the MTOC was significantly greater in PP2-treated NK cells than in DMSO-treated NK cells (***P < .001).