Engagement of 2B4 inhibits the dNK-mediated cytolytic activity. CD56, CD16, NCRs, and 2B4 surface expression by (A) rIL-2–activated dNK or (B) pNK cells. The percentages of positive cells are indicated in the upper quadrants. Gray profiles represent negative controls. (C) Polyclonally activated dNK or (D) pNK cells were analyzed for cytolytic activity in a redirected killing assay against the FcγR⁺ P815 target cell line in the presence of mAbs specific for the indicated NCRs either in the absence (▪) or in the presence (▦) of an anti-2B4 mAb. The E/T ratio used was 5:1. All the mAbs used in these experiments were of the IgG1 isotype. Similar results were obtained in 5 independent experiments.