Distinctive interactions at multiple site 2 subsites by allele-specific rat and mouse ly49 determine functional binding and class I MHC specificity

Inhibitory KIR2DL2 Gene: Risk for Deep Endometriosis in Euro-descendants

Endometriosis (EDT) is an inflammatory disease characterized by implantation/growth of endometrial tissue, glands, and/or stroma, outside the uterus. Reduced NK cell cytotoxic activity has been implicated in its pathogenesis, together with other immunologic alterations. We investigated the influence of KIR gene polymorphisms and their HLA ligand combinations in deep endometriosis (DE) susceptibility. One hundred sixty women with a histological diagnosis of DE and 202 control women without the disease, who underwent laparoscopy, were enrolled. The DE group was subdivided into initial (I/II; n = 60) and advanced stages (III/IV, n = 100). KIR and HLA class I gene polymorphisms were typed by PCR-SSP and sequence-based-typing (SBT), respectively. We observed a significant association of KIR2DL2, an inhibitory gene of B haplotype, conferring risk for DE in Euro-descendants. Positive associations of Bx haplotype and centromeric AB segments were also found. However, no association with KIR-HLA ligand combination was observed. Our data suggest KIR2DL2 gene to be a relevant factor favoring NK inhibition in DE in Euro-descendants, contributing to the defective NK cytotoxic activity and impaired clearance of ectopic endometrial cells in the disease.

Mutagenesis of Ly49B reveals key structural elements required for promiscuous binding to MHC class I molecules and new insights into the molecular evolution of Ly49s

Ly49B is a potentially important immunoregulator expressed on mouse myeloid cells, and it is thus an unusual member of the wider Ly49 family whose members are ordinarily found on NK cells. Ly49B displays substantial sequence divergence from other Ly49s and in particular shares virtually no amino acid sequence identity with the residues that have been reported to bind to MHC class I (cI) ligands in other Ly49s. Despite this, we show in this study that the BALB/c, but not the C57, isoform of Ly49B displays promiscuous cI binding. Binding was not significantly affected by inactivation of any of the four predicted N-linked glycosylation sites of Ly49B, nor was it affected by removal of the unique 20-aa C-terminal extension found in Ly49B. However, transfer of these C-terminal 20 aa to Ly49A inhibited cI binding, as did the addition of a hemagglutinin tag to the C terminus of Ly49B, demonstrating unexpectedly that the C-terminal region of Ly49s can play a significant role in ligand binding. Systematic exchange of BALB/c and C57 residues revealed that Trp(166), Asn(167), and Cys(251) are of major importance for cI binding in Ly49B. These residues are highly conserved in the Ly49 family. Remarkably, however, Ly49B(BALB) variants that have C57 residues at positions 166 or 167, and are unable to bind cI multimers, regain substantial cI binding when amino acid changes are made at distal positions, providing an explanation of how highly divergent Ly49s that retain the ability to bind cI molecules might have evolved.

Allelic variation in KIR2DL3 generates a KIR2DL2-like receptor with increased binding to its HLA-C ligand

Although extensive homology exists between their extracellular domains, NK cell inhibitory receptors killer Ig-like receptor (KIR) 2DL2*001 and KIR2DL3*001 have previously been shown to differ substantially in their HLA-C binding avidity. To explore the largely uncharacterized impact of allelic diversity, the most common KIR2DL2/3 allelic products in European American and African American populations were evaluated for surface expression and binding affinity to their HLA-C group 1 and 2 ligands. Although no significant differences in the degree of cell membrane localization were detected in a transfected human NKL cell line by flow cytometry, surface plasmon resonance and KIR binding to a panel of HLA allotypes demonstrated that KIR2DL3*005 differed significantly from other KIR2DL3 allelic products in its ability to bind HLA-C. The increased affinity and avidity of KIR2DL3*005 for its ligand was also demonstrated to have a larger impact on the inhibition of IFN-γ production by the human KHYG-1 NK cell line compared with KIR2DL3*001, a low-affinity allelic product. Site-directed mutagenesis established that the combination of arginine at residue 11 and glutamic acid at residue 35 in KIR2DL3*005 were critical to the observed phenotype. Although these residues are distal to the KIR/HLA-C interface, molecular modeling suggests that alteration in the interdomain hinge angle of KIR2DL3*005 toward that found in KIR2DL2*001, another strong receptor of the KIR2DL2/3 family, may be the cause of this increased affinity. The regain of inhibitory capacity by KIR2DL3*005 suggests that the rapidly evolving KIR locus may be responding to relatively recent selective pressures placed upon certain human populations.

Recognition of class I MHC by a rat Ly49 NK cell receptor is dependent on the identity of the P2 anchor amino acid of bound peptide

Members of the rodent Ly49 receptor family control NK cell responsiveness and demonstrate allele specificity for MHC class I (MHC-I) ligands. For example, the rat Ly49i2 inhibitory NK cell receptor binds RT1-A1(c) but not other rat MHC class Ia or Ib molecules. RT1-A1(c) preferentially binds peptides with proline at the second, or P2, position, which defines it as an HLA-B7 supertype MHC-I molecule. Previously, our laboratory showed that mutations within the MHC-I supertype-defining B-pocket of RT1-A1(c) could lead to alterations in P2 anchor residues of the peptide repertoire bound by RT1-A1(c) and loss of recognition by Ly49i2. Although suggestive of peptide involvement, it was unclear whether the peptide P2 anchor residue or alteration of the RT1-A1(c) primary sequence influenced Ly49i2 recognition. Therefore, we directly investigated the role of the P2 anchor residue of RT1-A1(c)-bound peptides in Ly49i2 recognition. First, fluorescent multimers generated by refolding soluble recombinant RT1-A1(c) with individual synthetic peptides differing only at the P2 anchor residue were examined for binding to Ly49i2 NK cell transfectants. Second, cytotoxicity by Ly49i2-expressing NK cells toward RMA-S target cells expressing RT1-A1(c) bound with peptides that only differ at the P2 anchor residue was evaluated. Our results demonstrate that Ly49i2 recognizes RT1-A1(c) bound with peptides that have Pro or Val at P2, whereas little or no recognition is observed when RT1-A1(c) is complexed with peptide bearing Gln at P2. Thus, the identity of the P2 peptide anchor residue is an integral component of MHC-I recognition by Ly49i2.