HLA-B27 Homodimers and Free H Chains Are Stronger Ligands for Leukocyte Ig-like Receptor B2 than Classical HLA Class I

Abstract

Possession of HLA-B27 (B27), strongly predisposes to the development of spondyloarthritis. B27 forms classical heterotrimeric complexes with beta-2-microglobulin (β2m) and peptide, and (β2m–free) free H chain (FHC) forms including B27 dimers (termed B272) at the cell surface. In this study we characterise the interaction of HLA-B27 with LILR, leukocyte Ig-like receptor (LILR)B1 and LILRB2 biophysically, biochemically and by FACS staining. LILRB1 bound to B27 heterotrimers with a KD of 5.3 ±1.5 μM but did not bind B27 FHC. LILRB2 bound to B272 and B27 FHC and B27 heterotrimers with KDs of 2.5, 2.6 and 22 ±6μM respectively. Domain exchange experiments showed that B272 bound to the two membrane distal Ig-like domains of LILRB2. In FACS staining experiments, B27 dimer protein and tetramers stained LILRB2 transfectants five times more strongly than B27 heterotrimers. Moreover, LILRB2Fc bound to dimeric and other B27 FHC forms on B27-expressing cell lines more strongly than other HLA-class I FHCs. B27 transfected cells expressing B27 dimers and FHC inhibited IL-2 production by LILRB2-expressing reporter cells to a greater extent than control HLA-class I transfectants. B27 heterotrimers complexed with the L6M variant of the GAG KK10 epitope bound with a similar affinity to complexes with the wild-type KK10 epitope (with KDs of 15.0±0.8 μM and 16.0±2.0 μM respectively). Disulfide-dependent B27 H chain dimers and multimers are stronger ligands for LILRB2 than HLA-class I heterotrimers and H chains. The stronger interaction of B27 dimers and FHC forms with LILRB2 compared with other HLA class I could play a role in spondyloarthritis pathogenesis.

Critical Role of Endoplasmic Reticulum Aminopeptidase 1 in Determining the Length and Sequence of Peptides Bound and Presented by HLA–B27

“…The HLA-B*27:05 plasmid was constructed using a previously described PHR-SIN lentiviral vector (22). This plasmid was used to transduce HeLa and mFib cells.…”

Interaction of the LILRB1 inhibitory receptor with HLA class Ia dimers

“…In this context, HLA-G displays a unique Cys42 residue, allowing the formation of disulphide-linked dimers, which were shown to establish a high-affinity interaction with LILRB1 [15][16][17]. HLA-B27 β2m-free heavy chains (FHC) dimerizing through Cys67, efficiently interacted with LILRB2 [18].…”

“…In this context, HLA-G displays a unique Cys42 residue, allowing the formation of disulphide-linked dimers, which were shown to establish a high-affinity interaction with LILRB1 [15][16][17]. HLA-B27 β2m-free heavy chains (FHC) dimerizing through Cys67, efficiently interacted with LILRB2 [18].HLA-B7 cytoplasmic Cys residues were shown to play a crucial role in LILRB1 recognition [19]; moreover, Cys325 and Cys339 were reported to be respectively involved in the formation of β2m-associated HLA-B27 and -A2 dimers in exosomes [20,21].Altogether, these observations suggest that these noncanonical HLA class Ia conformers might enhance the interaction with LILRB1. In the present study experimental evidence supporting this hypothesis is provided.…”

The relation between ER stress and HLA-B27 misfolding

“…Rudwaleit et al (2001) found that T cells producing TNF-α and IFN-γ are decreased in healthy controls both HLA-B27+ and HLA-B27-compared to HLA-B27+ AS patients [59]. Another interesting property of HLA-B27 is that β2-microglobulin free heavy chains of HLA-B27 were shown to interact with killer cell immunoglobulin-like receptor 3DL2 (KIR3DL2) and leucocyte immunoglobulin-like receptor B2 (LILRB2) with a higher affinity than heteromeric HLA-B27-β2-microglobulins in patients with spondyloarthropathies [60,61].…”