Selective expression of ULBP on the membrane of GPI⁺ K562 cells. (A) GPI^- K562 cells (•) were less susceptible to NK cells than GPI⁺ K562 cells (○). Each value represents the mean (± SD) of triplicate assays. (B) Flow cytometry showed the membrane expression of ULBPs 1-3 in GPI⁺ cells alone (shaded histograms). Dotted lines show nonspecific background staining with isotype-matched control Ig. (C) RT-PCR products showed similar expression of ULBPs 1-3 in GPI⁺ and GPI^- cells. RT-PCR products of ULBP1 and ULBP2 were digested with BamHI and BglII restriction enzymes, respectively. RT-PCR products of ULBP3-transcript were resistant to both enzymes. G3PDH indicates glyceraldehyde 3-phosphate dehydrogenase. ^*Digested fragments of RT-PCR products of each ULBP.