Blocking 2B4/CD48 interaction using anti-2B4 or anti-CD48 mAbs reduces NK killing against CD48^–RMA/S tumor targets. (A) Phenotype of LAK cells as determined by FACS; LAK cultures, produced by either negative depletion or positive selection, contain greater than 96% CD3^–NK1.1⁺ cells (top). These NK cells are all 2B4⁺, CD48⁺, and CD2⁺ (bottom). (B) RMA/S tumor cells do not express any measurable level of CD48 on their surface. Solid line represents staining from anti-CD48 mAbs, whereas filled line represents its isotype control (hamster IgG). (C-D) RMA/S targets (2000) were mixed with LAK cells at the E/T ratio indicated in each figure and subjected to 4-hour ⁵¹Cr release assay. Where indicated, 5 μg/mL anti-CD48, anti-2B4, or anti-CD2 mAbs was added in the presence or absence of 5 μg/mL anti-CD16/32 mAbs (2.4G2) to the effector cells prior to addition of target cells. Data are shown as mean ± SD and are representative of data from 5 independent experiments.