IL-2 promotes lytic granule convergence in NK cells. (A) Confocal immunofluorescent microscopy of fixed cells showing anti–α-tubulin (green) and anti-perforin (red) in (left) resting YTS cells or (right) YTS cells treated with IL-2 for 15 minutes or (B) resting eNK cells (leftmost) or eNK cells treated with IL-2 for 5, 10, or 25 minutes before fixation on poly-L-lysine–coated glass slides (PolyPrep; Sigma-Aldrich) for 5 minutes at 37°C. The biotinylated anti-tubulin mAb was detected with Pacific Blue-streptavidin; the anti-perforin antibody was directly fluorescein isothiocyanate conjugated. The measured mean MTOC to lytic granules in each image is provided as white text at the top. Quantitative analyses of lytic granule distance from the MTOC as a feature of IL-2 treatment in (C) YTS cells and (D) eNK cells. Data are representative of 2 separate experiments in each of which ≥30 cells were evaluated per condition. Error bars show ±SD. Mean distance of lytic granules from the MTOC was significantly less in YTS cells after IL-2 treatment (*P < .05) and in eNK cells after ≥10 minutes of IL-2 treatment (*P < .05 at 10 and 25 minutes).