The Behçet's disease-associated variant of the aminopeptidase ERAP1 shapes a low-affinity HLA-B*51 peptidome by differential subpeptidome processing.

A low-activity variant of endoplasmic reticulum aminopeptidase 1 (ERAP1), Hap10, is associated with the autoinflammatory disorder Behçet's disease (BD) in epistasis with HLA-B*51, which is the main risk factor for this disorder. The role of Hap10 in BD pathogenesis is unknown. We sought to define the effects of Hap10 on the HLA-B*51 peptidome and to distinguish these effects from those due to HLA-B*51 polymorphisms unrelated to disease. The peptidome of the BD-associated HLA-B*51:08 subtype expressed in a Hap10-positive cell line was isolated, characterized by mass spectrometry, and compared with the HLA-B*51:01 peptidome from cells expressing more active ERAP1 allotypes. We additionally performed synthetic peptide digestions with recombinant ERAP1 variants and estimated peptide-binding affinity with standard algorithms. In the BD-associated ERAP1 context of B*51:08, longer peptides were generated; of the two major HLA-B*51 subpeptidomes with Pro-2 and Ala-2, the former one was significantly reduced, and the latter was increased and showed more ERAP1-susceptible N-terminal residues. These effects were readily explained by the low activity of Hap10 and the differential susceptibility of X-Pro and X-Ala bonds to ERAP1 trimming and together resulted in a significantly altered peptidome with lower affinity. The differences due to ERAP1 were clearly distinguished from those due to HLA-B*51 subtype polymorphism, which affected residue frequencies at internal positions of the peptide ligands. The alterations in the nature and affinity of HLA-B*51·peptide complexes probably affect T-cell and natural killer cell recognition, providing a sound basis for the joint association of ERAP1 and HLA-B*51 with BD.

A combined large-scale meta-analysis identifies COG6 as a novel shared risk locus for rheumatoid arthritis and systemic lupus erythematosus.

OBJECTIVES: During the last years, genome-wide association studies (GWASs) have identified a number of common genetic risk factors for rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). However, the genetic overlap between these two immune-mediated diseases has not been thoroughly examined so far. The aim of the present study was to identify additional risk loci shared between RA and SLE. METHODS: We performed a large-scale meta-analysis of GWAS data from RA (3911 cases and 4083 controls) and SLE (2237 cases and 6315 controls). The top-associated polymorphisms in the discovery phase were selected for replication in additional datasets comprising 13 641 RA cases and 31 921 controls and 1957 patients with SLE and 4588 controls. RESULTS: The rs9603612 genetic variant, located nearby the COG6 gene, an established susceptibility locus for RA, reached genome-wide significance in the combined analysis including both discovery and replication sets (p value=2.95E-13). In silico expression quantitative trait locus analysis revealed that the associated polymorphism acts as a regulatory variant influencing COG6 expression. Moreover, protein-protein interaction and gene ontology enrichment analyses suggested the existence of overlap with specific biological processes, specially the type I interferon signalling pathway. Finally, genetic correlation and polygenic risk score analyses showed cross-phenotype associations between RA and SLE. CONCLUSIONS: In conclusion, we have identified a new risk locus shared between RA and SLE through a meta-analysis including GWAS datasets of both diseases. This study represents the first comprehensive large-scale analysis on the genetic overlap between these two complex disorders.

A large-scale genetic analysis reveals a strong contribution of the HLA class II region to giant cell arteritis susceptibility.

We conducted a large-scale genetic analysis on giant cell arteritis (GCA), a polygenic immune-mediated vasculitis. A case-control cohort, comprising 1,651 case subjects with GCA and 15,306 unrelated control subjects from six different countries of European ancestry, was genotyped by the Immunochip array. We also imputed HLA data with a previously validated imputation method to perform a more comprehensive analysis of this genomic region. The strongest association signals were observed in the HLA region, with rs477515 representing the highest peak (p = 4.05 × 10(-40), OR = 1.73). A multivariate model including class II amino acids of HLA-DRß1 and HLA-DQα1 and one class I amino acid of HLA-B explained most of the HLA association with GCA, consistent with previously reported associations of classical HLA alleles like HLA-DRB1(∗)04. An omnibus test on polymorphic amino acid positions highlighted DRß1 13 (p = 4.08 × 10(-43)) and HLA-DQα1 47 (p = 4.02 × 10(-46)), 56, and 76 (both p = 1.84 × 10(-45)) as relevant positions for disease susceptibility. Outside the HLA region, the most significant loci included PTPN22 (rs2476601, p = 1.73 × 10(-6), OR = 1.38), LRRC32 (rs10160518, p = 4.39 × 10(-6), OR = 1.20), and REL (rs115674477, p = 1.10 × 10(-5), OR = 1.63). Our study provides evidence of a strong contribution of HLA class I and II molecules to susceptibility to GCA. In the non-HLA region, we confirmed a key role for the functional PTPN22 rs2476601 variant and proposed other putative risk loci for GCA involved in Th1, Th17, and Treg cell function.

Novel association of acid phosphatase locus 1*C allele with systemic lupus erythematosus.

The red cell acid phosphatase (ACP1) gene, which encodes a low-molecular-weight phosphotyrosine phosphatase, has been suggested as a common genetic factor of autoimmunity. In the present study, we aim to investigate the possible association of ACP1 with the susceptibility of systemic lupus erythematosus (SLE). A total of 1,546 SLE patients and 1,947 healthy individuals from 4 Caucasians populations were included in the present study. Four single-nucleotide polymorphisms (SNPs) were genotyped in this study: rs10167992, rs11553742, rs7576247, and rs3828329. ACP1*A, ACP1*B, and ACP1*C codominant ACP1 alleles were determined using 2 of the SNPs and analyzed. After the meta-analysis test was performed, a significant association of rs11553742*T was observed (p(pooled) = 0.005, odds ratios = 1.37 [1.10-1.70]), retaining significance after multiple testing was applied (p(FDR) = 0.019). Our data indicate for first time the association of rs11553742*T with increased susceptibility in SLE patients.

Identification of a new putative functional IL18 gene variant through an association study in systemic lupus erythematosus.

Interleukin-18 (IL-18) is a proinflammatory cytokine that plays an important role in chronic inflammation and autoimmune disorders. In this study, we aimed to determine the potential role of the IL18 gene in SLE. To define the genetic association of the IL18 and SLE, we have genotyped nine SNPs in an independent set of Spanish cases and controls. The IL18 polymorphisms were genotyped by PCR, using a predeveloped TaqMan allele discrimination assay. Two SNPs were still significant after fine mapping of the IL18 gene. The SNP (rs360719) surviving correction for multiple tests was genotyped in two replication cohorts from Italy and Argentina. After the analysis, a significance with rs360719 C-allele remained across the sets and after the meta-analysis (Pooled OR = 1.37, 95% CI 1.21-1.54, combined P = 3.8E-07, Pc = 1.16E-06). Quantitative real-time PCR was performed to assess IL18 mRNA expression in PBMC from subjects with different IL18 rs360719 genotypes. We tested the effect of the IL18 rs360719 polymorphism on the transcription of IL18 by electrophoretic mobility shift assay and western blot. We found a significant increase in the relative expression of IL18 mRNA in individuals carrying the rs360719 C-risk allele; in addition we show that the polymorphism creates a binding site for the transcriptional factor OCT-1. These findings suggest that the novel IL18 rs360719 variant may play an important role in determining the susceptibility to SLE and it could be a key factor in the expression of the IL18 gene.

Analysis of vascular endothelial growth factor (VEGF) functional variants in rheumatoid arthritis.

The vascular endothelial growth factor (VEGF) is one of the most important pro-angiogenic mediators related to inflammation-associated synovial angiogenesis. The aim of this study was to asses the role of -1154 G-->A (rs1570360) and -634 G-->C (rs2010963) VEGF gene functional variants with rheumatoid arthritis (RA). The population under study was composed of a total of 753 unrelated RA patients and 801 healthy controls. The VEGF -1154 G-->A and -634 G-->C polymorphism genotyping was performed by real-time polymerase chain reaction technology, using TaqMan 5' allelic discrimination assay. No evidence of association was observed between the -1154 G-->A and the -634 G-->C VEGF polymorphisms, or inferred VEGF haplotypes with RA susceptibility or clinical manifestations. Our results suggest that the analyzed VEGF promoter polymorphisms may not play a relevant role in RA pathogenesis in our population.

Hla-DPB1 mismatch in HLA-A-B-DRB1 identical sibling donor stem cell transplantation and acute graft-versus-host disease.

BACKGROUND: The role of human leukocyte antigen (HLA)-DPB1 as a transplantation antigen is controversial. A higher incidence of acute graft-versus-host disease (aGVHD) has been described after unrelated donor bone marrow transplant when both HLA-DPB1 alleles were mismatched. METHODS: We investigated the impact of a single HLA-DPB1 mismatch after HLA-A-B-DRB1 identical sibling donor transplantation on aGVHD. We analyzed 627 adult patient-donor pairs and identified 30 pairs without HLA-DPB1 identity (4.78%). In 17 cases, the patient had an allele that was not shared by the donor. RESULTS: The cumulative incidence of grades II-IV aGVHD was higher in the HLA-DPB1 mismatched group (66.7% vs. 35.7%, p=0.012). The HLA-DPB1 mismatch was identified by multivariate analysis as an independent risk factor for aGVHD (p=0.020, RR=2.68, 95% CI: 1.73-3.62). CONCLUSIONS: HLA-DPB1 can mediate alloreactive responses. A single HLA-DPB1 mismatch increases the risk of aGVHD after sibling donor stem cell transplantation.