The ILT2(LIR1) and CD94/NKG2A NK cell receptors respectively recognize HLA-G1 and HLA-E molecules co-expressed on target cells

Previous studies on NK recognition of HLA-G1 employed as targets 721.221 tr ansfectants (.221-G1) that unknowingly co-expressed the HLA-E molecule, sub sequently found to be a major ligand for the CD94/NKG2 receptors. In the pr esent study we re-evaluated the relative role played by CD94/NKG2 and ILT2( LIR1) molecules in recognition of HLA-G1 by NK clones. We employed as targe ts .221-G1 cells and a surface HLA-E-negative transfectant,.221- G1(E-neg), generated by site-directed mutagenesis of the HLA-G1 leader sequence. The antagonistic effects of receptor- (i.e. CD94/NKG2A, ILT2) and ligand-specif ic mAb (i.e. HLA-G, HLA-E) were assessed. In addition, binding of an ILT2-I g fusion protein to the .221-AEH, expressing only HLA-E, and the .221-G1(E- neg) transfectants was analyzed. Our data demonstrate that NK recognition o f cells expressing HLA-G1 involves at least two non-overlapping receptor-li gand systems: the CD94/NKG2 interaction with HLA-E, and the engagement of t he ILT2(LIR1) receptor by HLA-G1 molecules.