Inhibition of NK cell-mediated killing with pAb to MICA/B on K562 cells. (A) MICA/B, peptide-anchored membrane proteins, were expressed in both GPI⁺ and GPI^- K562 cells (shaded histograms). Dotted lines show nonspecific background staining with isotype-matched control Ig. (B) Polyclonal antibodies to MICA/B (100 μg/mL) inhibited the killing of both GPI⁺ (□) and GPI^- (▪) cells but did not abolish the difference in their killing. Each value represents the mean (± SD) of triplicate assays (E/T ratio, 16:1). Control indicates isotype-matched control Ig. ^*P < .01.