Engagement of CD16, but not NK-cell receptors NKp46, NKG2D, 2B4, DNAM-1, or CD2, induces cytotoxicity by resting NK cells. Redirected lysis assay of P815 target cells with IL-2-activated NK cells (A) or resting NK cells (B) at indicated E/T cell ratios. P815 cells were preincubated with IgG1 mAbs to specific NK-cell receptors, as indicated. ⋄ indicates isotype control antibody; ♦, anti-CD16; □, anti-NKp46; ▪, anti-NKG2D;▵, anti-2B4; ▴, anti-CD2; ○, anti-DNAM-1; and ▪, anti-CD56. (C) Lysis of K562 cells by resting (○) and IL-2-activated (▪) NK cells. Experiments are representative of at least 5 independent experiments.