LAK cells generated from 2B4- or CD48-KO mice showed reduced cytotoxicity, but their spontaneous NK cytotoxicity is intact when analyzed ex vivo. (A) Ex vivo analysis of NK cytotoxicity from WT, 2B4-KO, or CD48-KO mice; enriched NK cells using negative depletion (left, WT and 2B4-KO) or positive selection of DX5⁺CD3^– (right, WT and CD48-KO) were used for 4-hour ⁵¹Cr release assay using Yac-1 targets. Yac-1 targets were used for ex vivo analysis because resting NK cells did not lyse RMA/S cells. (B) NK cells were enriched from WT, 2B4-KO, or CD48-KO mice using negative depletion and cultured in 5000 U/mL h-rIL-2 for 6 days prior to the 4-hour ⁵¹Cr release assay using RMA/S targets. Data are shown as mean ± SD and are representative of data from 4 independent experiments.