Terminally differentiated CD16⁺ NK cells acquire functional capacity after IL-15–mediated preactivation. Distribution of KIR⁺ (A) and CD16⁺ (B) NK cells in splenic CD56^bright, CD56^dim, and CD56⁻ NK-cell subsets of hu-NSG mice, as gated in the top panels of (A) in comparison to isotype control staining or (B) staining on marker negative CD3⁺ cells (gray shaded histograms). Degranulation (C) and IFN-γ production (D) of unstimulated and preactivated CD16⁺ and CD16⁻ NK cells after coculture with K562 cells were analyzed. A representative experiment of 2 is shown in panels A and B, while panels C and D represent composite data of 2 independent experiments. Numbers in plots represent frequencies within gates or marker regions.