Ex vivo and in vivo analysis of NK cytotoxicity from WT or 2B4-KO mice. (A-B) Each mouse was injected with 500 μg polyI:C in the presence or absence of 200 μg anti-2B4 or anti-CD48 mAbs as indicated in the figures. At 48 hours after injection, spleens were removed, and NK cells were partially enriched using negative depletion. The resulting splenocytes were subjected to 4-hour ⁵¹Cr release assay using RMA/S cells as a target. In panel A, injection of anti-2B4 mAb partially depleted (∼50%) NK cells from the spleen of WT (wild type) mice (right); thus, the number of NK cells from anti-2B4 mAb-treated mice was adjusted to that of untreated controls. Data are shown as mean ± SD and are representative of data from 6 independent experiments. (C) WT and 2B4-KO mice were injected intraperitoneally with 10 × 10⁶ CFSE-labeled tumor cells. The number of tumor cells recovered from the peritoneum after 3 days was calculated on the basis of absolute number of peritoneal exudate cells multiplied by the percentage of CFSE-labeled tumor cells as determined by flow cytometry. Data are shown as mean ± SE pooled from 3 independent experiments (n = 15 for both WT and 2B4-KO). *P < .05 as compared with WT versus 2B4KO.