DIRECT BINDING AND FUNCTIONAL TRANSFER OF NK CELL INHIBITORY RECEPTORS REVEAL NOVEL PATTERNS OF HLA-C ALLOTYPE RECOGNITION

Cytotoxicity of human NK cells is under negative control of killer cel l Ig-like receptors (KIR) specific for HLA class I. To determine the s pecificity of five KIR containing two Ig domains (KIR2D), direct bindi ng of soluble recombinant KIR2D to a panel of HLA class I transfectant s was assayed. One soluble KIR2D, derived from an inhibitory receptor with a long cytoplasmic tail (KIR2DL1), bound to HLA-C allotypes conta ining asparagine 77 and lysine 80 in the heavy chain, as expected, sin ce these allotypes inhibit lysis by NK cells expressing KTR2DL1. Surpr isingly, another KIR2D (KIR2DL2), which inhibits NK lysis of cells exp ressing HLA-C molecules with serine 77 and asparagine 80, bound to HLA -C allotypes carrying either amino acid motif, Expression of the KIR2D L receptors in NK cells using recombinant vaccinia viruses confirmed t hese patterns of recognition, and identified KIR2DL3 as another KIR re acting with both groups of HLA-C allotypes, Mutagenesis of amino acid 44 in KIR2DL1 and KIR2DL2 suggested this residue controls the affinity of KIR for the 77/80 motif of HLA-C molecules. Two other soluble KIR2 D, derived from noninhibitory receptors with short cytoplasmic tails ( KIR2DS), did not bind to any of the HLA class I allotypes tested. One of these receptors (KIR2DS2) is closely related in sequence to KIR2DL2 , Substitution of tyrosine 45 with the phenylalanine conserved in othe r KIR was sufficient to permit specific binding of KIR2DS2 to HLA-C. T hese results show that KIR2DL receptors are specific for HLA-C, but th at recognition of HLA-C allotypes appears more permissive than indicat ed by previous functional experiments.