The indicated NK cell clones were stained with anti-CD158a (EB6) or anti-CD158b (GL183) or anti-CD94 (HP-3B1) or anti-CD8 (astra 102) mAbs or with mAb NKVFS1, which recognizes a common epitope of CD158a, CD158b, and p50.3 molecules followed by PE-conjugated GAM antiserum. Samples were analyzed on a FACSort (Becton Dickinson), and results are expressed as follows: −, not reactive; +, reactive; CD8 antigen was expressed at different levels on NK cell clones, which homogeneously expressed the other surface antigens indicated in Table1; +/−, CD8 was present on 5% to 10% of NK cells (mean fluorescence intensity [MFI], 10-1000; ++, CD8⁺ NK cells > 90%, MFI 10-1000; +++, all NK cells were CD8⁺, MFI > 500). Also indicated for each clone is the functional behavior of CD158a or CD158b or p50.3 or CD94 molecules in a killing assay using as target cells the murine mastocytoma P815. Activating means that P815 lysis is strongly increased in the presence of mAb directed to the indicated molecules at the effector-target ratio (E/T) of 2:1. Inhibiting means that P815 lysis is strongly inhibited (> 75%) in the presence of mAb directed to the indicated surface molecules at the E/T ratio of 20:1. Notably, when CD158a and CD158b function as inhibiting or activating receptors they are represented by p58.1 and p58.2 (KIR2DL) or p50.1 and p50.2 (KIR2DS) molecules, respectively.3