KIR2DL1 is expressed on all NK cells derived from the patient. (A) Bulk NK cultures derived from the patient were incubated with 721.221 targets (221; □), or with 721.221 transfected with HLA-Cw4 (Cw4; ▪), at the indicated effector-target (E/T) ratios. (B) Fluorescence-activated cell sorter (FACS) analysis for KIR2DL1 expression of bulk NK cultures derived from the patient (left) and a representative healthy donor (right) using the EB6 mAb. Staining (open histograms) is shown overlaid on background (shaded histograms). The NK cells were incubated for one hour with or without anti-KIR2DL1 mAb HP3E4 or the anti-CD99 mAb 12E7 and then tested against the various targets as in panel A. Shown is a representative NK clone (C) and NK bulk cultures (D), both derived from the patient.