Endothelial-cell killing by IL-12–activated NK cells. NK-cell–enriched splenocytes from C57BL/6 nude mice were first incubated for 24 hours in medium alone, medium supplemented with IL-12 (10 ng/mL), IFN-γ (100 ng/mL) or a combination of IL-12 (10 ng/mL) and an anti–IFN-γ antibody (5 μg/mL), and then tested for cytotoxicity against ⁵¹Cr-labeled aortic endothelial cells from littermate C57BL/6 nude mice at an E:T ratio of 120:1. Results are expressed as percent specific cytotoxicity, and reflect the mean (±SD) of four replicate cultures.