Jurgen van Heemst

A molecular basis for the association of the HLA-DRB1 locus, citrullination, and rheumatoid arthritis

A comprehensive structural portrait of the association between citrullination, the HLA-DRB1 locus, and T cell autoreactivity in rheumatoid arthritis.

Genetics of rheumatoid arthritis: what have we learned?

Genes of the major histocompatibility complex (MHC) have received much attention in immunology, genetics, and ecology because they are highly polymorphic and play important roles in parasite resistance and mate choice. Until recently, the MHC of passerine birds was not well-described. However, the genome sequencing of the zebra finch (Taeniopygia guttata) has partially redressed this gap in our knowledge of avian MHC genes. Here, we contribute further to the understanding of the zebra finch MHC organization by mapping SNPs within or close to known MHC genes in the zebra finch genome. MHC class I and IIB genes were both mapped to zebra finch chromosome 16, and there was no evidence that MHC class I genes are located on chromosome 22 (as suggested by the genome assembly). We confirm the location in the MHC region on chromosome 16 for several other genes (BRD2, FLOT1, TRIM7.2, GNB2L1, and CSNK2B). Two of these (CSNK2B and FLOT1) have not previously been mapped in any other bird species. In line with previous results, we also find that orthologs to the immune-related genes B-NK and CLEC2D, which are part of the MHC region in chicken, are situated on zebra finch chromosome Z and not among other MHC genes in the zebra finch.

Communication between human mast cells and CD4(+) T cells through antigen-dependent interactions.

Mast cells (MCs) are immune cells residing in tissues where pathogens are first encountered. It has been indicated that MCs might also be involved in setting the outcome of T‐cell responses. However, little is known about the capacity of human MCs to express MHC class II and/or to capture and present antigens to CD4+ T cells. To study the T‐cell stimulatory potential of human MCs, CD34+ stem cell derived MCs were generated. These cells expressed HLA‐DR when stimulated with IFN‐γ, and, importantly, presented peptide and protein for activation of antigen‐specific CD4+ T cells. The interplay between MC and T cell led to increased HLA‐DR expression on MCs. MCs were present in close proximity to T cells in tonsil and expressed HLA‐DR and CD80, indicating their ability to present antigens to CD4+ T cells in T‐cell areas of human LNs. Our data show that MCs can present native antigens to human CD4+ T cells and that HLA‐DR expressing MCs are present in tonsil tissue, indicating that human MCs can directly activate T cells and provide a rationale to study the potential of MCs to prime and/or skew human T‐cell responses.

Crossreactivity to vinculin and microbes provides a molecular basis for HLA-based protection against rheumatoid arthritis

The HLA locus is the strongest risk factor for anti-citrullinated protein antibody (ACPA)(+) rheumatoid arthritis (RA). Despite considerable efforts in the last 35 years, this association is poorly understood. Here we identify (citrullinated) vinculin, present in the joints of ACPA(+) RA patients, as an autoantigen targeted by ACPA and CD4(+) T cells. These T cells recognize an epitope with the core sequence DERAA, which is also found in many microbes and in protective HLA-DRB1*13 molecules, presented by predisposing HLA-DQ molecules. Moreover, these T cells crossreact with vinculin-derived and microbial-derived DERAA epitopes. Intriguingly, DERAA-directed T cells are not detected in HLA-DRB1*13(+) donors, indicating that the DERAA epitope from HLA-DRB1*13 mediates (thymic) tolerance in these donors and explaining the protective effects associated with HLA-DRB1*13. Together our data indicate the involvement of pathogen-induced DERAA-directed T cells in the HLA-RA association and provide a molecular basis for the contribution of protective/predisposing HLA alleles.

HLA and rheumatoid arthritis: How do they connect?

Abstract Rheumatoid arthritis (RA) is a destructive autoimmune disease that mainly affects synovial joints. RA patients can be subdivided in two distinct disease subsets based on the presence of anti-citrullinated protein antibodies (ACPA). These two disease phenotypes are associated with different environmental and genetic risk factors and clinical parameters. The HLA class II locus is the most important risk factor for ACPA-positive RA (ACPA+ RA). ACPA can be found up to 10 years before diagnosis and can be used as a predictive biomarker. During progression from breaking tolerance to a citrullinated protein to ACPA+ RA, the ACPA response matures. Recent work implicates the HLA class II locus as a risk factor in the progression from ACPA positivity to ACPA+ RA. We now propose that this locus directly influences the maturation of the ACPA response, most likely via antigen-specific T-cells providing help to ACPA-producing B-cells allowing for maturation of the citrullinated protein-specific autoantibody response. We present and discuss several models and underlying data, including antibody cross-reactivity, molecular mimicry, and neo-antigen formation, that could explain the HLA–RA connection.

Fine-mapping the human leukocyte antigen locus in rheumatoid arthritis and other rheumatic diseases: identifying causal amino acid variants?

Purpose of reviewTo provide an update on and the context of the recent findings obtained with novel statistical methods on the association of the human leukocyte antigen (HLA) locus with rheumatic diseases. Recent findingsNovel single nucleotide polymorphism fine-mapping data obtained for the HLA locus have indicated the strongest association with amino acid positions 11 and 13 of HLA-DRB1 molecule for several rheumatic diseases. On the basis of these data, a dominant role for position 11/13 in driving the association with these diseases is proposed and the identification of causal variants in the HLA region in relation to disease susceptibility implicated. SummaryThe HLA class II locus is the most important risk factor for several rheumatic diseases. Recently, new statistical approaches have identified previously unrecognized amino acid positions in the HLA-DR molecule that associate with anticitrullinated protein antibody-negative and anticitrullinated protein antibody-positive rheumatoid arthritis. Likewise, similar findings have been made for other rheumatic conditions such as giant-cell arteritis and systemic lupus erythematosus. Interestingly, all these studies point toward an association with the same amino acid positions: amino acid positions 11 and 13 of the HLA-DR &bgr; chain. As both these positions influence peptide binding by HLA-DR and have been implicated in antigen presentation, the novel fine-mapping approach is proposed to map causal variants in the HLA region relevant to rheumatoid arthritis and several rheumatic diseases. If these interpretations are correct, they would direct the biological research aiming to address the explanation for the HLA-disease association. Here, we provide an overview of the recent findings and evidence from literature that, although relevant new insights have been obtained on HLA-disease associations, the interpretation of the biological role of these amino acids as causal variants explaining that such associations should be taken with caution.

Protective effect of HLA-DRB1*13 alleles during specific phases in the development of ACPA-positive RA

Objective Human leucocyte antigen (HLA)-DRB1*13 alleles are associated with protection from anticitrullinated protein antibody (ACPA)-positive rheumatoid arthritis (RA). It is, however, unknown at which phase of disease development (seroconversion, ACPA maturation, disease onset or outcome) these alleles are most important. We therefore examined the effect of HLA-DRB1*13 on: ACPA presence (systemic autoimmunity associated with RA) in individuals with and without RA, on ACPA characteristics and on clinical outcome measures. Methods The effect of HLA-DRB1*13 on ACPA presence in subjects with or without RA (non-RA) was assessed in the Swedish twin registry (n=10 748). ACPA characteristics were studied in patients with ACPA-positive RA from the Swedish Epidemiological Investigation of RA (EIRA, n=1224) and the Dutch Leiden Early Arthritis Clinic (EAC, n=441). Disease activity at inclusion and disease outcome (disease-modifying antirheumatic drugs (DMARD)-free sustained remission and radiographic progression) was assessed in patients with RA from the EAC. Results HLA-DRB1*13 is associated with protection from ACPA-positive RA (prevalence 16% vs 28% in ACPA-negative non-RA), but not with significant protection from ACPA in individuals without RA (prevalence: 22%, p value 0.09). HLA-DRB1*13 is associated with lower ACPA-levels (EIRA: 447 U/ml versus 691 U/ml, p value= 0.0002) and decreased citrullinated epitope recognition (EIRA: p<0.0001). No association between HLA-DRB1*13 and disease activity or outcome was found. Conclusions These data indicate that HLA-DRB1*13 mainly affects the onset of ACPA-positive RA in ACPA-positive non-RA individuals. In RA, HLA-DRB1*13 influences ACPA characteristics but not the disease course. This implies that therapeutic strategies aimed at emulating the HLA-DBR1*13 protective effect may be most effective in ACPA-positive healthy individuals at risk for RA.

The increased ability to present citrullinated peptides is not unique to HLA-SE molecules: arginine-to-citrulline conversion also enhances peptide affinity for HLA-DQ molecules

BackgroundPresentation of citrullinated neo-epitopes by HLA-DRB1 molecules that carry the shared epitope (SE) sequence was proposed to explain the association between HLA and seropositive RA. Although it is shown that several HLA-DRB1-SE molecules display enhanced binding affinities for citrullinated ligands, the ability of other HLA molecules to present citrullinated epitopes has not been investigated in a systematic manner. To better understand the HLA-RA connection, we aimed to investigate if the enhanced capacity to present arginine-to-citrulline-converted peptides is unique for HLA-SE alleles.MethodsWe selected four HLA molecules (one HLA-DR and three HLA-DQ molecules) that could potentially prefer citrulline over arginine residues in specific pockets and in addition two HLA-SE alleles as a method validation control. The affinity of peptides containing arginine/citrulline residues at positions interacting with the various peptide-binding pockets was compared by HLA class II peptide affinity assays.ResultsPocket 4 of HLA-DRB1*04:04 and -DRB1*04:05 displayed a preference for citrulline over arginine, a property found in other pockets as well. HLA-DRB1*03:01 did not display an enhanced affinity for peptides containing a citrulline. In contrast, several peptide-binding pockets of the analyzed HLA-DQ molecules showed enhanced affinities for citrulline compared to arginine residues: i.e., pockets 4, 6, 7, and 9 of HLA-DQ2 and pockets 1, 6, and 9 of HLA-DQ7 and HLA-DQ8.ConclusionsArginine-to-citrulline conversion of peptides can also enhance the binding affinity for non-HLA-SE molecules. Hence the capacity to present citrullinated neo-epitopes is not confined to HLA-SE molecules, opening the possibility that also other HLA molecules could potentiate a possible breach of T cell tolerance toward citrullinated antigens.

Molecular basis for increased susceptibility of Indigenous North Americans to seropositive rheumatoid arthritis

Objective The pathogenetic mechanisms by which HLA-DRB1 alleles are associated with anticitrullinated peptide antibody (ACPA)-positive rheumatoid arthritis (RA) are incompletely understood. RA high-risk HLA-DRB1 alleles are known to share a common motif, the ‘shared susceptibility epitope (SE)’. Here, the electropositive P4 pocket of HLA-DRB1 accommodates self-peptide residues containing citrulline but not arginine. HLA-DRB1 His/Phe13β stratifies with ACPA-positive RA, while His13βSer polymorphisms stratify with ACPA-negative RA and RA protection. Indigenous North American (INA) populations have high risk of early-onset ACPA-positive RA, whereby HLA-DRB1*04:04 and HLA-DRB1*14:02 are implicated as risk factors for RA in INA. However, HLA-DRB1*14:02 has a His13βSer polymorphism. Therefore, we aimed to verify this association and determine its molecular mechanism. Methods HLA genotype was compared in 344 INA patients with RA and 352 controls. Structures of HLA-DRB1*1402-class II loaded with vimentin-64Arg59-71, vimentin-64Cit59-71 and fibrinogen β−74Cit69-81 were solved using X-ray crystallography. Vimentin-64Cit59-71-specific and vimentin59-71-specific CD4+ T cells were characterised by flow cytometry using peptide-histocompatibility leukocyte antigen (pHLA) tetramers. After sorting of antigen-specific T cells, TCRα and β-chains were analysed using multiplex, nested PCR and sequencing. Results ACPA+ RA in INA was independently associated with HLA-DRB1*14:02. Consequent to the His13βSer polymorphism and altered P4 pocket of HLA-DRB1*14:02, both citrulline and arginine were accommodated in opposite orientations. Oligoclonal autoreactive CD4+ effector T cells reactive with both citrulline and arginine forms of vimentin59-71 were observed in patients with HLA-DRB1*14:02+ RA and at-risk ACPA- first-degree relatives. HLA-DRB1*14:02-vimentin59-71-specific and HLA-DRB1*14:02-vimentin-64Cit59-71-specific CD4+ memory T cells were phenotypically distinct populations. Conclusion HLA-DRB1*14:02 broadens the capacity for citrullinated and native self-peptide presentation and T cell expansion, increasing risk of ACPA+ RA.