Anti-LILRB1 monoclonal antibody, clone 4F9 [FITC]

Human cytomegalovirus (HCMV) encodes UL18, a major histocompatibility complex (MHC) class I homologue that binds to the leukocyte immunoglobulin-like receptor (LIR)-1 (also called ILT2/CD85j/LILRB1), an inhibitory receptor expressed on myeloid and lymphoid immune cells. The molecular basis underlying the high affinity binding of UL18 to LIR-1, compared to MHC class I molecules (MHC-I), is unclear. Based on a comparative structural analysis of a molecular model of UL18 with the crystal structure of the HLA-A2/LIR-1 complex, we identified three regions in UL18 influencing interaction with LIR-1. Comparison of the relative binding affinities of mutated UL18 proteins to LIR-1 demonstrated the importance of specific residues in each region. Substitution of residues K42/A43 and Q202, localized in the alpha 1 and alpha 3 domains, respectively, reduced binding affinity to LIR-1 nearly by half. The model also suggested the formation of an additional disulfide bridge in the 0 domain of UL18 between residues C240 and C255, not present in MHC-I. Substitution of either cysteine residue prevented association of UL18 to beta(2)m, abolishing binding to LIR-1. All observed differences in binding affinities translated directly into functional consequences in terms of inhibition of IFN-gamma production by T cells, mediated through the UL18-LIR-1 interaction. The larger amount of interacting regions, combined with an increased stability of the alpha 3 and beta(2)m domains allow a higher recognition affinity of UL18 by LIR-1. (c) 2007 Elsevier Ltd. All rights reserved.

HLA-B27 can form beta-2 microglobulin (beta 2m)-associated heterotrimers (HLA-B27) and beta 2m-free homodimers (13272). Here, we study the role of complexed peptide in the interaction of these forms of B27 with the killer cell immunoglobulin (Ig) -like receptors KlR3DL1 and KIR3DL2 and with Ig-like transcripts LILRB1 and LILRB2. HLA-B27 tetramers complexed with three of five different naturally processed self peptides and three of seven pathogen-derived epitopes bound to KIR3DL1-expressing transfectants and NK cells. Heterotrimeric complexes containing peptides with charged amino acids at position 8 did not bind to KIR3DL1; however, studies with analogue peptides demonstrated that these are not the only peptide residues involved in binding. KIR3DL1 ligation by HLA-B27 inhibited NK cell IFN-gamma production in a peptide-dependent fashion. B27 but not HLA-A2, B7 or B57 heavy chains formed homodimers in the presence of peptide epitopes. B27(2) bound to KIR3DL1, KIR3DL2 and LILRB2 but not LILRB1. KIR3DL2 ligation by B272 inhibited NK and T cell IFN-gamma production. By contrast with HLA heterotrimers, B272 binding to KIR did not depend on the sequence of the bound peptide. Differences in KIR binding to classical HLA and B272 could be involved in the pathogenesis of spondyloarthritis.