The downregulation of CD48 results in reduced NK cell cytotoxicity. (A) ³⁵S-labeled target cells expressing either the AML oncogenic proteins or an empty vector were incubated with an anti-CD48 antibody or an anti-CD99 antibody (used as a control) and then incubated with primary NK cells at the indicated effector to target (E:T) ratios. (B) Flow cytometry analysis of activating NK cell receptors expressed by the human NK cell line YTS eco (black empty histograms). Gray shaded histogram, background staining with the secondary-conjugated antibody only. (C) The ³⁵S-labeled P815 cells, coated with different antibodies (indicated as:anti-CD16, NKp30, NKp46, 2B4, DNAM-1, and anti-hemagglutinin antibody, as a control antibody), were incubated with YTS eco cells at the indicated E:T ratios. (D) The ³⁵S-labeled U937 cells expressing PML-RARA, AML1-ETO, or an empty vector were incubated with YTS eco cells at the indicated E:T ratios. (E) The ³⁵S-labeled target cells expressing either the AML oncogenes or an empty vector were incubated with an anti-CD48 antibody or with an anti-hemagglutinin antibody (used as a control) and then incubated with YTS eco cells (E:T 50:1). One of 2 killing experiments performed is shown.(A-E) *P < .05: **P < .01, ***P < .001, Student t test.