Effect of anti-MHC I mAb OX18 on hepatic NK cell-mediated CC531s cell cytolysis (A, 51Cr release) and apoptosis (B, DNA fragmentation). (A), 51Cr-labeled CC531s cells were incubated at an E:T ratio of 10:1 with freshly isolated hepatic NK cells for 18 hours. Cytolysis was measured in a 51Cr-release assay. (B), [3H]-TdR labeled CC531s cells were incubated at an E:T ratio of 10:1 with hepatic NK cells for 3 hours. Apoptosis was measured in a quantitative DNA fragmentation assay. ConAb, control antibody. *p < 0.05, **p < 0.01 vs. the treatment with medium only (LSD test).