CD56^dim NK cells produce cytokines and chemokines upon target cell recognition. Resting NK cells were mixed with S2 cells expressing ligands for NK-cell receptors (A) or K562 cells (B), as indicated, and incubated for 6 hours at 37°C. After stimulation, the cells were surface stained with fluorochrome-conjugated anti-CD56 mAb, fixed, permeabilized, and stained intracellularly with fluorochrome-conjugated mAbs to cytokines and chemokines. The percentage of CD56^dim or CD56^bright NK cells producing IFN-γ, TNF-α, MIP-1α, and MIP-1β, as indicated, was determined by flow cytometry. Values represent mean ± SD of at least 6 different donors. (C) Sorted CD56^dim or CD56^bright NK cells were incubated alone or with K562 cells for 6 hours at 37°C. Supernatants were harvested, and the concentrations of cytokines and chemokines were determined by a multiplex immunoassay. Values represent mean ± SD of 5 different donors. (D) Resting NK cells were incubated alone or stimulated with 10 ng/mL IL-12, 100 ng/mL IL-15, or 100 ng/mL IL-18, or combinations thereof, for 24 hours at 37°C. After stimulation, the cells were surface stained with fluorochrome-conjugated anti-CD56 mAb, fixed, permeabilized, and stained intracellularly with fluorochrome-conjugated mAbs to cytokines and chemokines. The percentage of CD56^dim or CD56^bright NK cells producing IFN-γ, TNF-α, MIP-1α, and MIP-1β, as indicated, was determined by flow cytometry. Values represent mean ± SD of 5 different donors. For clarity, selected statistical analyses are indicated. *P < .05, **P < .01, ***P < .001.