Validation of the reshaped shared epitope HLA-DRB1 classification in rheumatoid arthritis

High-resolution HLA genotyping identifies risk alleles in both class I and II for primary autoimmune neutropenia in early childhood in a Danish cohort

HLA studies in patients with autoimmune neutropenia (AIN) have shown very consistent results for the association with HLA class II alleles at low resolution. This study aimed to examine the association of both HLA class I and class II at high resolution to clarify the contribution of risk alleles to the disease. A total of 107 AIN patients were genotyped for six loci of HLA class I (HLA-A, -B and -C) and class II (HLA-DRB1, -DQB1, and -DPB1) genes by a high-resolution (3-field, 6-digit) analysis and compared with HLA typing of 1000 healthy controls. Compared with the controls, the allele frequencies were significantly higher in AIN patients for A*02:17:01G, C*01:02:01G, DRB1*10:01:01G, DRB1*14:01:01G, DRB1*16:01:01G, DQB1*05:02:01G, and DQB1*05:03:01G but lower significant for C*03:04:01G, DRB1*04:01:01G, DRB1*13:02:01G, DQB1*03:02:01G, and DQB1*06:04:01G. Frequently associated two-locus haplotypes were found to be DRB1*10:01:01G-DQB1*05:01:01G and DRB1*16:01:01G-DQB1*05:02:01G, while the S2 (Q- or D-KRAA) shared epitope (SE) was associated with lower risk. A unique association with HLA alleles was observed between patients with specific anti-HNA-1a antibodies and broad-reacting anti-FcγRIIIb. Anti-HNA-1a antibody-positive patients were associated with C*01:02:01G, DRB1*01:01:01G, DRB1*16:01:01G, DQB1*05:01:01G, DQB1*05:02:01G, DQB1*06:04:01G, and DPB1*10:01:01G; the two-locus haplotypes DRB1*01:01:01G-DQB1*05:01:01G and DRB1*16:01:01G-DQB1*05:02:01G; and the S3P (Q- or R-RRAA) SE. Anti-FcγRIIIb antibody-positive patients were associated with the alleles A*02:17:01G, DRB1*10:01:01G, and DQB1*05:02:01G; the haplotypes DRB1*10:01:01G-DQB1*05:01:01G and DRB1*11:01:02G-DQB1*05:02:01G; and the S3D (DRRAA) SE. The different associations regarding FcγRIIIb antibody specificities could indicate disease heterogeneity.

Human abdominal aortic aneurysm (AAA): Evidence for an autoimmune antigen-driven disease

Abdominal aortic aneurism (AAA) is a complex immunological disease with a strong genetic component, and one of the ten leading causes of death of individuals 55-74 years old worldwide. Strong evidence has been accumulated suggesting that AAA is an autoimmune specific antigen-driven disease. Mononuclear cells infiltrating AAA lesions comprised of T and B lymphocytes and other cells expressing early-, intermediate- and late-activation antigens, and the presence of antigen-presenting cells have been documented, demonstrating an ongoing immune response. The three components of the trimolecular complex, T-cell receptor (TCR)/peptide (antigen)/HLA have been identified in AAA, and specifically: (i) clonal expansions of T-cell clones in AAA lesions; (ii) the association of AAA with particular HLA Class I and Class II; and (iii) self or nonself putative AAA-associated antigens. IgG autoantibodies recognizing proteins present in normal aortic tissue have been reported in patients with AAA. Molecular mimicry, defined as the sharing of antigenic epitopes between microorganisms (bacteria, viruses) and self antigens, maybe is responsible for T-cell responses and antibody production in AAA. Also, the frequency and the suppressor activity of CD4 + CD25 + FOXP3+ Tregs and the expression of FOXP3 transcripts and protein have been reported to be significantly impaired in AAA patients vs normal donors.

Vaccine Can Induce CD4-Mediated Responses to Homocitrullinated Peptides via Multiple HLA-Types and Confer Anti-Tumor Immunity

Homocitrullination is the post translation modification (PTM) of the amino acid lysine to homocitrulline also referred to as carbamylation. This PTM has mainly been studied in relation to autoimmune diseases including rheumatoid arthritis. Homocitrullination of lysines alters their charge which can lead to generation of neoepitopes that are differentially presented by MHC-II and induce modification-specific immune responses. Homocitrullination is often considered a process which triggers autoimmune disease by bypassing self-tolerance however, we suggest that homocitrullination may also have an alternative role in immune responses including protection against cancer. Here we demonstrate that immune responses to homocitrullinated peptides from three different proteins can be induced via multiple HLA-types. Immunization of Balb/c or HLA-transgenic DR4 and DR1 mice can induce modification-specific CD4 mediated IFNγ responses. Healthy human donors show a clear repertoire for the homocitrullinated Vimentin peptide (Vim116-135^Hcit), with modification-specific and oligoclonal responses. Importantly, in vivo homocitrulline specific Vim116-135^Hcit,Cyk8 371-388^Hcit and Aldo 140-157^Hcit responses are able to confer an anti-tumor effect in the murine B16 melanoma model. The Vim116-135^Hcit anti-tumor response was dependent upon tumor expression of MHC-II suggesting the direct recognition of PTMs on tumor is an important anti-tumor mechanism. Cancer patients also have a CD4 repertoire for Vim116-135^Hcit. Together these results suggest that homocitrulline-specific immune responses can be generated in healthy mice and detected in human donors through a variety of HLA-restrictions. Immunization can induce responses to Vim116-135^Hcit,Aldolase 140-157^Hcit and Cyk8 371-388^Hcit which provide anti-tumor therapy across several HLA-types. Our results advance our understanding of homocitrulline-specific immune responses, with implications for a number of fields beyond autoimmunity, including tumor immune surveillance.

Toll-like receptor-7 activation in CD8+ T cells modulates inflammatory mediators in patients with rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune disorder of unknown etiology with aberrant immunological responses leading to inflammation, swelling and pain of the joints. CD8⁺ T cells have been known to be one of the major immune modulators in the progression of RA and the presence of toll-like receptors (TLRs) on these cells further accentuate their role in RA. Herein, we report an increased expression of TLR7 in the endosomes of CD8⁺ T cells of RA patients correlating with disease severity. The stimulation of TLR7 with Imiquimod (IMQ) in these CD8⁺ T cells drives the signalling cascade via NFkB and pERK activation and hence an increase in the mRNA transcripts of signature cytokines and cytolytic enzymes. However, a parallel synthesis of Tristetraprolin (TTP), an mRNA destabilizing protein prevents the translation of the mRNA transcripts, leading to a rapid degeneration of the target mRNA. We thus report that a direct TLR7 ligation by its agonist increases cytokine transcript signature but not an equivalent protein surge.

Recent Developments in Clinical Applications of Mesenchymal Stem Cells in the Treatment of Rheumatoid Arthritis and Osteoarthritis

Mesenchymal stem cell (MSC) therapies have been used as cell-based treatments for decades, owing to their anti-inflammatory, immunomodulatory, and regenerative properties. With high expectations, many ongoing clinical trials are investigating the safety and efficacy of MSC therapies to treat arthritic diseases. Studies on osteoarthritis (OA) have shown positive clinical outcomes, with improved joint function, pain level, and quality of life. In addition, few clinical MSC trials conducted on rheumatoid arthritis (RA) patients have also displayed some optimistic outlook. The largely positive outcomes in clinical trials without severe side effects establish MSCs as promising tools for arthritis treatment. However, further research is required to investigate its applicability in clinical settings. This review discusses the most recent advances in clinical studies on MSC therapies for OA and RA.

The role of posttranslational modifications in generating neo-epitopes that bind to rheumatoid arthritis-associated HLA-DR alleles and promote autoimmune T cell responses

While antibodies to citrullinated proteins have become a diagnostic hallmark in rheumatoid arthritis (RA), we still do not understand how the autoimmune T cell response is influenced by these citrullinated proteins. To investigate the role of citrullinated antigens in HLA-DR1- and DR4-restricted T cell responses, we utilized mouse models that express these MHC-II alleles to determine the relationship between citrullinated peptide affinity for these DR molecules and the ability of these peptides to induce a T cell response. Using a set of peptides from proteins thought to be targeted by the autoimmune T cell responses in RA, aggrecan, vimentin, fibrinogen, and type II collagen, we found that while citrullination can enhance the binding affinity for these DR alleles, it does not always do so, even when in the critical P4 position. Moreover, if peptide citrullination does enhance HLA-DR binding affinity, it does not necessarily predict the generation of a T cell response. Conversely, citrullinated peptides can stimulate T cells without changing the peptide binding affinity for HLA-DR1 or DR4. Furthermore, citrullination of an autoantigen, type II collagen, which enhances binding affinity to HLA-DR1 did not enhance the severity of autoimmune arthritis in HLA-DR1 transgenic mice. Additional analysis of clonal T cell populations stimulated by these peptides indicated cross recognition of citrullinated and wild type peptides can occur in some instances, while in others cases the citrullination generates a novel T cell epitope. Finally, cytokine profiles of the wild type and citrullinated peptide stimulated T cells unveiled a significant disconnect between proliferation and cytokine production. Altogether, these data demonstrate the lack of support for a simplified model with universal correlation between affinity for HLA-DR alleles, immunogenicity and arthritogenicity of citrullinated peptides. Additionally they highlight the complexity of both T cell receptor recognition of citrulline as well as its potential conformational effects on the peptide:HLA-DR complex as recognized by a self-reactive cell receptor.

Diagnostic utility of, and influence of tobacco usage and genetic predisposition on, immunoglobulin A, rheumatoid factor and anti-citrullinated peptide auto-antibodies in South African rheumatoid arthritis patients

Background

The immunoglobulin A isotypes of anti-cyclic citrullinated peptide antibodies (ACPA) and rheumatoid factor (RF) are associated with disease severity and progression in Caucasian rheumatoid arthritis (RA) patients, as well as with genetic predisposition and tobacco use.

Objectives

To compare levels of ACPA-IgA and RF-IgA with those of ACPA-IgG and cRF in a cohort of black South African RA patients and healthy controls.To investigate the relationship between IGA autoantibodies and disease severity, genetic predisposition and tobacco use

Methods

RF-IgA and ACPA-IgA were determined in a cohort of predominantly black South African RA patients (n=75) in relation to serodiagnostic and prognostic potential, as well as tobacco use and genetic predisposition. Healthy control subjects were included to determine sensitivity, specificity and predictive values.

ACPA-IgG/IgA and RF-IgA were determined by enzyme immunoassay and hs-CRP and cRF by nephelometry. Cotinine levels were determined by ELISA.

Results

The frequencies of ACPA-IgA and RF-IgA were 31% and 88% respectively compared to 88% for both types of traditional autoantibody procedures. ACPA-IgA was significantly higher (p=0.007) in patients with short disease duration, while linear regression analysis revealed a positive relationship with baseline disease activity scores. Levels of ACPA-IgG and ACPA-IgA were significantly higher in tobacco users who carried the HLA shared epitope.

Conclusion

Although lacking in serodiagnostic superiority over cRF and ACPA-IgG, inclusion of RF-IgA and ACPA-IgA in autoantibody panels may provide insights into disease pathogenesis, interactions between tobacco usage and HLA genotype in the production of potentially disease-triggering ACPA-IgA antibodies.

Human MHC-II with Shared Epitope Motifs Are Optimal Epstein-Barr Virus Glycoprotein 42 Ligands-Relation to Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic systemic autoimmune disorder of unknown etiology, which is characterized by inflammation in the synovium and joint damage. Although the pathogenesis of RA remains to be determined, a combination of environmental (e.g., viral infections) and genetic factors influence disease onset. Especially genetic factors play a vital role in the onset of disease, as the heritability of RA is 50–60%, with the human leukocyte antigen (HLA) alleles accounting for at least 30% of the overall genetic risk. Some HLA-DR alleles encode a conserved sequence of amino acids, referred to as the shared epitope (SE) structure. By analyzing the structure of a HLA-DR molecule in complex with Epstein-Barr virus (EBV), the SE motif is suggested to play a vital role in the interaction of MHC II with the viral glycoprotein (gp) 42, an essential entry factor for EBV. EBV has been repeatedly linked to RA by several lines of evidence and, based on several findings, we suggest that EBV is able to induce the onset of RA in predisposed SE-positive individuals, by promoting entry of B-cells through direct contact between SE and gp42 in the entry complex.

Genetic and environmental risk factors for rheumatoid arthritis

Multiple genetic and environmental factors have been associated with an increased risk for rheumatoid arthritis (RA). Of these, the strongest associations have been seen with female sex, a family history of RA, the genetic factor the "shared epitope," and exposure to tobacco smoke. There is also renewed interest in mucosal inflammation and microbial factors as contributors to the development of RA. However, the identification of a "preclinical" period of RA that can be defined as local or systemic autoimmunity as measured by autoantibodies and other biomarkers prior to the development of clinically apparent synovitis suggests that the risk factors for RA are acting long prior to first clinical evidence of IA. As such, a major challenge to the field will be to investigate the full spectrum of the development of RA, from initiation and propagation of autoimmunity during preclinical RA and transition to clinically apparent synovitis and classifiable RA, to determine which genetic and environmental factors are important at each stage of disease development. Understanding the exact role and timing of action of risk factors for RA is especially important given the advent of prevention trials in RA, and the hope that a full understanding of genetic and environmental factors in RA could lead to effective preventive interventions.

Autoantibodies to human citrullinated fibrinogen and their subfamilies to the α36-50Cit and β60-74Cit fibrin peptides similarly predict radiographic damages: a prospective study in the French ESPOIR cohort of very early arthritides

OBJECTIVE

To investigate whether subfamilies of the RA-specific autoantibodies to human citrullinated fibrinogen (AhFibA) differentially associate with the RA risk factors, HLA-DRB1 shared epitope containing alleles (SE alleles) and cigarette smoking, and thus help to predict the disease outcome.

METHODS

AhFibA and their anti-α36-50Cit and anti-β60-74Cit subfamilies were assayed by ELISA, at baseline, in the French ESPOIR (Etude et Suivi des Polyarthrites Indifférenciées Récentes) cohort composed of undifferentiated arthritides and RA patients of < 6 months' duration. Cigarette smoking, SE alleles' presence, DAS28, HAQ and modified Sharp-van der Heijde Score data were obtained at baseline, and after follow-up.

RESULTS

After 3 years, 701 patients were classified as having RA according to the ACR/EULAR 2010 criteria. Among them, 349 (50%), 203 (29%) and 257 (37%) were AhFibA-, anti-α36-50Cit- and anti-β60-74Cit-positive, respectively. The presence and titres of AhFibA and their subfamilies similarly associated with SE alleles, irrespective of their fine specificity, without significant effect of smoking. Neither their presence nor their titre was associated with DAS28 or HAQ. The presence of at least one subfamily was associated with a faster Sharp/van der Heijde score progression, albeit without correlation with the titre.

CONCLUSION

AhFibA and their main subfamilies are similarly associated with SE alleles without additional effect of smoking. Whatever their fine specificity was, their presence (but not their titre) similarly constituted a marker of faster joint destruction.

The Protective Role of HLA-DRB1(∗)13 in Autoimmune Diseases

Autoimmune diseases (AIDs) are characterized by a multifactorial aetiology and a complex genetic background, with the MHC region playing a major role. We genotyped for HLA-DRB1 locus 1228 patients with AIDs-213 with Systemic Lupus Erythematosus (SLE), 166 with Psoriasis or Psoriatic Arthritis (Ps + PsA), 153 with Rheumatoid Arthritis (RA), 67 with Systemic Sclerosis (SSc), 536 with Multiple Sclerosis (MS), and 93 with Myasthenia Gravis (MG) and 282 unrelated controls. We confirmed previously established associations of HLA-DRB1^∗15 (OR = 2.17) and HLA-DRB1^∗03 (OR = 1.81) alleles with MS, HLA-DRB1^∗03 with SLE (OR = 2.49), HLA-DRB1^∗01 (OR = 1.79) and HLA-DRB1^∗04 (OR = 2.81) with RA, HLA-DRB1^∗07 with Ps + PsA (OR = 1.79), HLA-DRB1^∗01 (OR = 2.28) and HLA-DRB1^∗08 (OR = 3.01) with SSc, and HLA-DRB1^∗03 with MG (OR = 2.98). We further observed a consistent negative association of HLA-DRB1^∗13 allele with SLE, Ps + PsA, RA, and SSc (18.3%, 19.3%, 16.3%, and 11.9%, resp., versus 29.8% in controls). HLA-DRB1^∗13 frequency in the AIDs group was 20.0% (OR = 0.58). Although different alleles were associated with particular AIDs, the same allele, HLA-DRB1^∗13, was underrepresented in all of the six diseases analysed. This observation suggests that this allele may confer protection for AIDs, particularly for systemic and rheumatic disease. The protective effect of HLA-DRB1^∗13 could be explained by a more proficient antigen presentation by these molecules, favouring efficient clonal deletion during thymic selection.

Circulating anti-citrullinated peptide antibodies, cytokines and genotype as biomarkers of response to disease-modifying antirheumatic drug therapy in early rheumatoid arthritis

Background

To measure circulating anti-citrullinated peptide antibodies (ACPA) and cytokines pre- and 6 months post-therapy as a strategy to predict and optimize responses to traditional disease-modifying antirheumatic drugs (DMARDs) in early RA, which is an unmet need in developing countries.

Patients and methods

A cohort of 140 predominantly (88.5 %) black female South African patients with early RA was treated with synthetic DMARDs, mostly methotrexate (MTX) alone, or in combination with low-dose oral corticosteroids (CS). Circulating ACPA and a panel of circulating cytokines/chemokines/growth factors were measured at baseline and after 6 months of therapy in relation to disease activity and Shared Epitope (SE).

Results

Following 6 months of therapy, the median simplified disease activity index (SDAI) declined from a baseline of 41.4 to 16.0 (p = 0.0001) for the entire cohort, which was paralleled by significant falls in median serum ACPA levels (516.6 vs. 255.7 units/ml, p = <0.0001) and several of the circulating cytokines (IL-4, IL-7, IL-8, G-CSF, VEGF; p < 0.0010 – p < 0.0001) which were most evident in the subgroup of patients treated with a combination of MTX and CS. Although biomarker concentrations decreased most notably in the low-disease activity group post-therapy, no significant correlations between these biomarkers and disease activity were observed, Baseline ACPA levels, but not SDAI or cytokines, were significantly higher in the subgroup of risk allele-positive patients (561.1 vs. 331.9 units/ml, p < 0.05), while no associations with ACPA and a smoking history were evident.

Conclusions

The use of DMARDs in RA is associated with significant decreases in ACPA and cytokines which did not correlate with changes in SDAI, precluding the utility of serial measurement of these biomarkers to monitor early responses to therapy, but may have prognostic value.

Electronic supplementary material

The online version of this article (doi:10.1186/s12891-015-0587-1) contains supplementary material, which is available to authorized users.

HLA-DRB1-associated rheumatoid arthritis risk at multiple levels in African Americans: hierarchical classification systems, amino acid positions, and residues

OBJECTIVE

To evaluate HLA-DRB1 genetic risk of rheumatoid arthritis (RA) in African Americans by 3 validated allele classification systems and by amino acid position and residue, and to compare genetic risk between African American and European ancestries.

METHODS

Four-digit HLA-DRB1 genotyping was performed on 561 autoantibody-positive African American cases and 776 African American controls. Association analysis was performed on Tezenas du Montcel (TdM), de Vries (DV), and Mattey classification system alleles and separately by amino acid position and individual residues.

RESULTS

TdM S2 and S3P alleles were associated with RA (odds ratio [95% confidence interval] 2.8 [2.0-3.9] and 2.1 [1.7-2.7], respectively). The DV (P = 3.2 × 10(-12)) and Mattey (P = 6.5 × 10(-13)) system alleles were both protective in African Americans. Amino acid position 11 (permutation P < 0.00001) accounted for nearly all variability explained by HLA-DRB1, although conditional analysis demonstrated that position 57 was also significant (0.01 ≤ permutation P ≤ 0.05). The valine and aspartic acid residues at position 11 conferred the highest risk of RA in African Americans.

CONCLUSION

With some exceptions, the genetic risk conferred by HLA-DRB1 in African Americans is similar to that in individuals of European ancestry at multiple levels: classification system (e.g., TdM), amino acid position (e.g., 11), and residue (Val11). Unlike that reported for individuals of European ancestry, amino acid position 57 was associated with RA in African Americans, but positions 71 and 74 were not. Asp11 (odds ratio 1 in European ancestry) corresponds to the 4-digit classical allele *09:01, which is also a risk allele for RA in Koreans.

Relationship between SNPs and expression level for candidate genes in rheumatoid arthritis

OBJECTIVES

The study of polymorphisms of genes differentially expressed may lead to the identification of putative causal genetic variants in multifactorial diseases such as rheumatoid arthritis (RA). Based on preceding transcriptomic results, we genotyped 10 single nucleotide polymorphisms (SNPs) belonging to six genes (S100A8, RNASE2, PGLYRP1, RUNX3, IL2RB, and LY96) showing the highest fold change (> 1.9) when level of expression was compared between RA patients and controls. These SNPs were then analysed to evaluate their role in RA.

METHOD

The relationship between gene expression and genotypes of SNPs was first investigated by Kruskal-Wallis and Mann-Whitney tests in RA patients and controls. The genetic association of these SNPs with RA were then analysed using family-based association tests in trio families.

RESULTS

We found that RNASE2 gene expression was related to rs2013109 genotypes in 14 RA patients (p = 0.030). The association study in a discovery sample of 200 French trio families revealed a significant association with RA for one SNP, PGLYRP1-rs2041992 (p = 0.019); this association was stronger in trios where RA patients carried the HLA-DRB1 shared epitope (SE) (p = 0.003). However, this association was not found in a replication sample of 240 European trio families (p = 0.6).

CONCLUSIONS

Family-based association tests did not reveal an association between RA and any SNP of the candidate genes tested. However, RNASE2 gene expression was differentially expressed in RA patients considering a sequence polymorphism. This result led us to highlight the potential disease-specific regulation for this candidate gene in RA.

Anti-citrullinated peptides as autoantigens in rheumatoid arthritis-relevance to treatment

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by the presence of rheumatoid factor (RF) and anti-citrullinated protein/peptide autoantibodies (ACPAs). Citrulline derives from arginine by peptidyl arginine deiminases, and ACPAs are directed against different citrullinated antigens, including fibrinogen, fibronectin, α-enolase, collagen type II, histones. ACPAs are present in two thirds of RA patients have higher specificity than RF for RA, and are associated with joint radiographic damage and extra-articular manifestations and they are detected years before the onset clinical arthritis. Recent studies suggest that citrullinated antigens are most likely arthritogenic autoantigens in RA. ACPA production is associated with the HLA-DRB1 shared epitope (HLA-DRB1 SE) and accounts for the well-known RA-HLA-DRB1 SE association, as T cells recognize citrullinated peptides. Smoking and periodontitis, known environmental risk factors for RA promote protein citrullination and ACPA production. Cirullinated proteins are capable of inducing arthritis in transgenic mice carrying HLA-DRB1 SE genes, and ACPAs induce macrophage TNF-α production, osteoclastogenesis and complement activation. They also induce the formation of neutrophil extracellular traps (NETs). NETs, increased in RA, are a source of citrullinated autoantigens in RA and induce fibroblast interleukin-8 production. This knowledge is likely to have therapeutic implications, as there is a need of matching therapy with patient profile. Abatacept, a T cell activation modulator, is the best therapy for ACPA(+) RA patients, although clinical data are sparse at present. Rituximab, a monoclonal antibody that depletes B cells, is also the best therapy for ACPA(+) RA patients, and clinical data support this view.

Aneurysmal lesions of patients with abdominal aortic aneurysm contain clonally expanded T cells

Abdominal aortic aneurysm (AAA) is a common disease with often life-threatening consequences. This vascular disorder is responsible for 1-2% of all deaths in men aged 65 years or older. Autoimmunity may be responsible for the pathogenesis of AAA. Although it is well documented that infiltrating T cells are essentially always present in AAA lesions, little is known about their role in the initiation and/or progression of the disease. To determine whether T cells infiltrating AAA lesions contain clonally expanded populations of T cells, we amplified β-chain TCR transcripts by the nonpalindromic adaptor-PCR/Vβ-specific PCR and/or Vβ-specific PCR, followed by cloning and sequencing. We report in this article that aortic abdominal aneurysmal lesions from 8 of 10 patients with AAA contained oligoclonal populations of T cells. Multiple identical copies of β-chain TCR transcripts were identified in these patients. These clonal expansions are statistically significant. These results demonstrate that αβ TCR(+) T lymphocytes infiltrating aneurysmal lesions of patients with AAA have undergone proliferation and clonal expansion in vivo at the site of the aneurysmal lesion, in response to unidentified self- or nonself Ags. This evidence supports the hypothesis that AAA is a specific Ag-driven T cell disease.

HLA shared epitope and ACPA: just a marker or an active player?

Autoantibody production is genetically controlled and anti-citrullinated protein/peptide antibodies (ACPA) are not an exception to the rule. ACPA are highly specific markers of rheumatoid arthritis (RA) and are also associated with a more severe disease course. The production of ACPA is almost invariably observed in HLA-shared epitope (SE) positive patients. The DRB1 alleles sharing SE are those conferring susceptibility to RA. SE alleles behave like immune response genes, controlling both the specificity and the amount of ACPA produced. These data suggest a role of SE in the presentation of citrullinated antigens. The ability of SE alleles to bind selectively to citrullinated sequences as compared to the native counterparts has been demonstrated in the case of peptides derived from several joint associated proteins (vimentin, fibrinogen and cartilage intermediate-layer protein). On the contrary, EBV-derived citrullinated peptides do not display a biologically relevant binding to SE alleles even if the immune response to VCPs is under the genetic control of these alleles (namely *0401 and *0404). Thus, the presentation of citrullinated epitopes does not represent the only molecular mechanisms underlying the HLA-DRB1 effect on ACPA production.

Genetics and epigenetics of rheumatoid arthritis

Investigators have made key advances in rheumatoid arthritis (RA) genetics in the past 10 years. Although genetic studies have had limited influence on clinical practice and drug discovery, they are currently generating testable hypotheses to explain disease pathogenesis. Firstly, we review here the major advances in identifying RA genetic susceptibility markers both within and outside of the MHC. Understanding how genetic variants translate into pathogenic mechanisms and ultimately into phenotypes remains a mystery for most of the polymorphisms that confer susceptibility to RA, but functional data are emerging. Interplay between environmental and genetic factors is poorly understood and in need of further investigation. Secondly, we review current knowledge of the role of epigenetics in RA susceptibility. Differences in the epigenome could represent one of the ways in which environmental exposures translate into phenotypic outcomes. The best understood epigenetic phenomena include post-translational histone modifications and DNA methylation events, both of which have critical roles in gene regulation. Epigenetic studies in RA represent a new area of research with the potential to answer unsolved questions.

Hierarchy of risk of childhood-onset rheumatoid arthritis conferred by HLA-DRB1 alleles encoding the shared epitope

OBJECTIVE

Associations between shared epitope (SE)-encoding HLA-DRB1 alleles and rheumatoid arthritis (RA) are well established. However, only a limited number of studies have investigated these alleles in patients with childhood-onset RA, which is defined as rheumatoid factor- and/or anti-citrullinated protein antibody-positive juvenile idiopathic arthritis. The aims of this study were to investigate the largest cohort of patients with childhood-onset RA for association with SE alleles and to determine whether there is a hierarchy of risk based on the amino acid sequence of the SE.

METHODS

High-resolution HLA-DRB1 genotypes were obtained for 204 patients with childhood-onset RA and 373 healthy control subjects. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated for different SE-encoding HLA-DRB1 alleles. In addition, genotype ORs were calculated for combinations of SE alleles classified into S(2) , S(3P) , or L alleles, based on amino acid sequences in position 70-74 of the DRβ1 chain, as proposed by Tezenas du Montcel et al.

RESULTS

We confirmed associations between HLA-DRB1 SE alleles and childhood-onset RA (76% of patients carried 1 or 2 SE alleles compared with 46% of control subjects; OR 3.81, 95% CI 2.4-6.0, P < 1 × 10(-7) ). We also observed associations between individual SE alleles (HLA-DRB1*0101, *0401, *0404, *0405, *0408, and *1001) and childhood-onset RA. Genotype-specific risk estimates suggested a hierarchy of risk, with the highest risk among individuals heterozygous for S(2) /S(3P) (OR 22.3, 95% CI 9.9-50.5, P < 0.0001).

CONCLUSION

We confirm the association between SE-encoding HLA-DRB1 alleles and susceptibility to childhood-onset RA. The excess risk conferred by carriage of the combination of S(2) and S(3P) risk alleles suggests that children with DRβ1 chains containing the KRAA and QRRAA or RRRAA sequences are especially susceptible to RA.

Association study of human leukocyte antigen-DRB1 alleles with rheumatoid arthritis in south Tunisian patients

The aim of this study is to explore relationship between HLA-DRB1 alleles and the susceptibility and clinical features of rheumatoid arthritis (RA) in the south Tunisian population. We studied 142 RA patients and 123 controls matched for age, sex, and ethnicity. HLA-DRB1 genotyping and HLA-DRB1*04 subtypes were performed using polymerase chain reaction/sequence-specific primers. Association was assessed based on the χ (2) test and odds ratio with 95% confidence interval. For multiple comparisons, p value was corrected (p (c)) with Bonferroni test. Two alleles, HLA-DRB1*04 (p=0.045, p(c)=NS) and HLA-DRB1*10 (p=0.021, p(c)=NS), were found to have increased frequencies in RA patients compared to controls. In contrast HLA-DRB1*08 allele was found to have a decreased frequency in patients compared to controls (p=0.044, p(c)=NS). Molecular subtyping of the most prevalent allele (DRB1*04) revealed increased frequencies of HLA-DRB1*04:05 in patients compared to controls (p=0.013, p(c)=NS) whereas HLA-DRB1*04:02 showed a protective effect (p=0.005, p(c)=0.04). Moreover, stratified analyses indicated statistically significant associations between HLA-DRB1*04 allele and anti-cyclic peptides antibodies positivity (ACPA(+)) and rheumatoid factor positivity (RF(+); p(c)=0.03, for both subgroups), HLA-DRBI*10 and ACPA(+) and the presence of another autoimmune disease (p(c)=0.05 and p(c)=0.007, respectively), and HLA-DRB1*04:05 and RF(+) and erosion (p(c)=0.005 and p(c)=0.049; respectively). A significant decrease in the frequency of the DRB1*04:02 allele was observed in patients with ACPA(+) and RF(+) subgroups (p(c)=0.04 and p(c)=0.02, respectively). Our results showed that there was a trend of positive association of HLA-DRB1*04 and HLA-DRB1*10 with RA as such and significant associations with the disease severity in the south Tunisian population.

HLA-DRB1 shared epitope genotyping using the revised classification and its association with circulating autoantibodies, acute phase reactants, cytokines and clinical indices of disease activity in a cohort of South African rheumatoid arthritis patients

Introduction

The revised shared epitope (SE) concept in rheumatoid arthritis (RA) is based on the presence (S) or absence (X) of the SE RAA amino acid motif at positions 72 to 74 of the third hypervariable region of the various human leucocyte antigen (HLA)-DRB1 alleles. The purpose of this study was to investigate SE subtypes on the basis of the American College of Rheumatology 1987 revised criteria for the classification of RA in a cohort of South African RA patients (n = 143) and their association with clinical and circulating biomarkers of disease activity (autoantibodies, acute phase reactants and cytokines).

Methods

Genomic DNA was analysed using high-resolution recombinant sequence-specific oligonucleotide PCR typing of the HLA-DRB1 allele. Subtypes of the SE were classified according to the amino acids at positions 72 to 74 for the RAA sequence, and further sub-divided according to the amino acids at positions 70 and 71, which either contribute to (S2, S3P), or negate (S1, S3D) RA susceptibility. Disease activity was assessed on the basis of (1) Disease Activity Score in 28 joints using C-reactive protein (CRP), (2) rheumatoid factor (RF), (3) CRP and (4) serum amyloid A by nephelometry, anticyclic citrullinated peptide antibodies (aCCP) by an immunofluorometric procedure, and cytokines by multiplex bead array technology.

Results

Of the 143 RA patients, 81 (57%) were homozygous (SS) and 50 (35%) were heterozygous (SX) for the SE alleles with significant overexpression of S2 and S3P (respective odds ratios (ORs) 5.3 and 5.8; P < 0.0001), and 12 (8%) were classified as no SE allele (XX). Both the SS and SX groups showed a strong association with aCCP positivity (OR = 10.2 and P = 0.0010, OR = 9.2 and P = 0.0028, respectively) relative to the XX group. Clinical scores and concentrations of the other biomarkers of disease activity (RF, CRP and T helper cell type 1 (Th1), Th2, macrophage and fibroblast cytokines) were also generally higher in the SS group than in the SX and XX groups.

Conclusions

RA susceptibility alleles investigated according to revised criteria for the classification of RA were significantly increased in South African RA patients and strongly associated with aCCP in particular as well as with circulating cytokines and disease severity.

A spectrum of susceptibility to rheumatoid arthritis within HLA-DRB1: stratification by autoantibody status in a large UK population

Previously-proposed rheumatoid arthritis (RA) HLA-DRB1 susceptibility and protective models were compared, based on amino acids at positions 67-74 and autoantibody combinations. 3 657 RA patients and 1 357 controls were studied using logistic regression, with secondary stratification by anti-citrullinated peptide antibodies(ACPA) and rheumatoid factor(RF). Susceptibility models were based on previously defined HLA-DRB1 shared epitope(SE) subgroups. (70)DERAA(74), D(70) and I(67) protective models were compared, adjusting for HLA-DRB1 SE. A hierarchy of risk was observed within the HLA-DRB1 SE, particularly for ACPA-positive and RF-positive RA: HLA-DRB1(*)0401∼(*)0404>(*)0101∼(*)1001 ((*)0404>(*)0101: P=0.0003). HLA-DRB1(*)0401/(*)0404 compound heterozygosity conferred a risk similar to (*)0401 homozygosity (P=0.70). Protective effects of D(70) and I(67) were similar. Predictions of the D(70) model fitted the data better than those of the I(67) model. The protective effect of D(70) showed a gene-dose effect (OR 0.82, 95% CI 0.73-0.92, P=5.8 × 10(-4)), but was only seen in RA patients positive for RF or ACPA. HLA-DRB1 SE alleles were also associated with ACPA-negative, RF-positive RA (OR 1.42 (1.15-1.76), P=0.0012). In conclusion, HLA-DRB1 SE alleles show heterogeneity in RA susceptibility; their major effect appears to be mediated by ACPA positivity, but a significant association of HLA-DRB1 SE with RF-positive, ACPA-negative RA was also observed. D(70) specifically protected against antibody-positive RA.

The HLA Region and Autoimmune Disease: Associations and Mechanisms of Action

The HLA region encodes several molecules that play key roles in the immune system. Strong association between the HLA region and autoimmune disease (AID) has been established for over fifty years. Association of components of the HLA class II encoded HLA-DRB1-DQA1-DQB1 haplotype has been detected with several AIDs, including rheumatoid arthritis, type 1 diabetes and Graves' disease. Molecules encoded by this region play a key role in exogenous antigen presentation to CD4+ Th cells, indicating the importance of this pathway in AID initiation and progression. Although other components of the HLA class I and III regions have also been investigated for association with AID, apart from the association of HLA-B*27 with ankylosing spondylitis, it has been difficult to determine additional susceptibility loci independent of the strong linkage disequilibrium (LD) with the HLA class II genes. Recent advances in the statistical analysis of LD and the recruitment of large AID datasets have allowed investigation of the HLA class I and III regions to be re-visited. Association of the HLA class I region, independent of known HLA class II effects, has now been detected for several AIDs, including strong association of HLA-B with type 1 diabetes and HLA-C with multiple sclerosis and Graves' disease. These results provide further evidence of a possible role for bacterial or viral infection and CD8+ T cells in AID onset. The advances being made in determining the primary associations within the HLA region and AIDs will not only increase our understanding of the mechanisms behind disease pathogenesis but may also aid in the development of novel therapeutic targets in the future.

Genetics of rheumatoid arthritis: GWAS and beyond

The study of complex genetics in autoimmune diseases has progressed at a tremendous pace over the last 4 years, as a direct result of the enormous gains made by genome wide association studies (GWAS). Novel genetic findings are continuously being reported alongside the rapid development of genetic technologies, sophisticated statistical analysis, and larger sample collections. It is now becoming clear that multiple genes contribute to disease risk in many complex genetic disorders including rheumatoid arthritis (RA) and that there are common genetic risk factors that underlie a spectrum of autoimmune diseases. This review details the current genetic landscape of RA, and describes what GWAS has taught us in terms of missing heritability, subsets of disease, existence of genetic heterogeneity, and shared autoimmune risk loci. Finally, this review addresses the initial challenges faced in translating the wealth of genetic findings into determining the biological mechanisms that contribute to the relationship between genotype and phenotype. Unraveling the mechanism of how genes directly influence the cause of RA will lead to a better understanding of the disease and will ultimately have a direct clinical impact, informing the development of new therapies that can be utilized in the treatment of RA.

Protection against anti-citrullinated protein antibody-positive rheumatoid arthritis is predominantly associated with HLA-DRB1*1301: a meta-analysis of HLA-DRB1 associations with anti-citrullinated protein antibody-positive and anti-citrullinated protein antibody-negative rheumatoid arthritis in four European populations

OBJECTIVE

The protective effect of HLA-DRB1 alleles on the development of rheumatoid arthritis (RA) is poorly understood. The aim of this study was to perform a meta-analysis of 4 European populations to investigate which HLA-DRB1 alleles are associated with protection in anti-citrullinated protein antibody (ACPA)-positive RA and ACPA-negative RA.

METHODS

Data for >2,800 patients and >3,000 control subjects for whom information on HLA-DRB1 typing and ACPA status was available were collected from 4 European countries: Norway, Sweden, The Netherlands, and Spain. The odds ratios (ORs) and 95% confidence intervals (95% CIs) associated with the different HLA-DRB1 alleles were analyzed in a combined meta-analysis focused on protective alleles and classifications. The analysis of ACPA-positive RA was stratified for the shared epitope (SE) alleles, to correct for skewing due to this association.

RESULTS

In ACPA-positive RA, the only alleles that conveyed protection after stratification for SE were HLA-DRB1*13 alleles (OR 0.54 [95% CI 0.38-0.77]). The protective effect of the allele classifications based on the DERAA and D70 sequences was no longer present after exclusion of DRB1*13 (for D70, OR 0.97 [95% CI 0.75-1.25]), indicating that DRB1*13, rather than the DERAA or D70 sequence as such, is associated with protection. Among the DRB1*13 alleles, only DRB1*1301 was associated with protection (OR 0.24 [95% CI 0.09-0.59]). Protection appeared to follow a north-to-south gradient, with the strongest association in northern European countries. In ACPA-negative RA, there were no robust associations with HLA-DRB1 alleles.

CONCLUSION

Our data do not support any of the classifications of protective alleles and indicate that protection against ACPA-positive RA is predominantly associated with HLA-DRB1*1301.

Pharmacogenetics of rheumatoid arthritis: Potential targets from susceptibility genes and present therapies

Rheumatoid arthritis (RA) is a chronic heterogeneous autoimmune disorder of unknown etiology resulting in inflammation in the synovium, cartilage, and bone. Genetic factors play an important role in susceptibility to RA as the heritability of RA is between 50% and 60%, with the human leukocyte antigen (HLA) locus accounting for at least 30% of overall genetic risk. Outside the major histocompatibility complex (MHC) region, six additional risk loci have been identified and validated including PTPN22, STAT4, PADI4, CTLA4, TNFAIP3-OLIG3, and TRAF1/C5. Genetic factors are also important in RA pharmacotherapy due to the gene-dependent activity of enzymes involved in the pharmacokinetics and/or pharmacodynamics of RA medications. Indeed, there is great variability in drug efficacy as well as adverse events associated with any anti-rheumatic therapy and genetics is thought to contribute significantly to this inter-individual variability in response. This review will summarize the genetic factors that have been implicated in the pathogenesis of RA, and how these determinants may factor into the potential pharmacogenetics of this disease. We will also review the therapeutic agents that are currently being utilized or presently being evaluated in the treatment of RA, along with potential pharmacogenetic markers that have been proposed for such medications.

New classification of the shared epitope in rheumatoid arthritis: impact on the production of various anti-citrullinated protein antibodies

OBJECTIVE

HLA-DR [shared epitope (SE)] alleles have recently been re-classified into S1, S2, S3P and S3D groups. S2 and S3P have been associated with increased risk for RA. We assessed the impact of S1, S2, S3P and S3D alleles on anti-citrullinated protein antibody (ACPA) production. Instead of comparing allele-carriers to non-carriers, we studied each allele group individually, using the X/X (non-SE) genotype as reference.

METHODS

Serum and genomic DNA samples of 91 RA patients and 78 healthy controls were obtained. Various ACPAs and IgM RF were determined by ELISA. HLA-DRB1 genotyping and subtyping was performed by PCR. HLA-DRB1 alleles were re-classified as described above. Correlations between SE and ACPAs were determined.

RESULTS

Not only S2 and S3P, but, to a lesser extent, S1 and S3D alleles also predisposed to anti-cyclic citrullinated peptide (CCP) production (P < 0.0001, P = 0.004, P = 0.01 and P = 0.027, respectively), with the following hierarchy of association: S2+S3P > S1+S3D > X/X. Similar associations were observed for anti-citrullinated vimentin. Anti-citrullinated fibrinogen (CF) exerted a different association pattern with the strongest correlation with S1 alleles [odds ratio (OR) 16.00; P = 0.05]. In addition, HLA-DRB1*15 alleles may represent a special predisposing effect for anti-CF antibody production. Finally, in this study, RF production was associated only with the HLA-DRB1*0401 SE allele (P = 0.04).

CONCLUSIONS

Our approach of comparing individual S allele carriers with X/X genotype patients allowed us to perform unequivocal analyses and demonstrate new associations. Thus, novel subgroups of RA could be identified with potential relevance for prognosis and therapy.

Different patterns of associations with anti-citrullinated protein antibody-positive and anti-citrullinated protein antibody-negative rheumatoid arthritis in the extended major histocompatibility complex region

OBJECTIVE

To identify additional variants in the major histocompatibility complex (MHC) region that independently contribute to risk in 2 disease subsets of rheumatoid arthritis (RA) defined according to the presence or absence of antibodies to citrullinated protein antigens (ACPAs).

METHODS

In a multistep analytical strategy using unmatched as well as matched analyses to adjust for HLA-DRB1 genotype, we analyzed 2,221 single-nucleotide polymorphisms (SNPs) spanning 10.7 Mb, from 6p22.2 to 6p21.31, across the MHC. For ACPA-positive RA, we analyzed samples from the Swedish Epidemiological Investigation of Rheumatoid Arthritis (EIRA) and the North American Rheumatoid Arthritis Consortium (NARAC) studies (totaling 1,255 cases and 1,719 controls). For ACPA-negative RA, we used samples from the EIRA study (640 cases and 670 controls). Plink and SAS statistical packages were used to conduct all statistical analyses.

RESULTS

A total of 299 SNPs reached locus-wide significance (P<2.3x10(-5)) for ACPA-positive RA, whereas surprisingly, no SNPs reached this significance for ACPA-negative RA. For ACPA-positive RA, we adjusted for known DRB1 risk alleles and identified additional independent associations with SNPs near HLA-DPB1 (rs3117213; odds ratio 1.42 [95% confidence interval 1.17-1.73], Pcombined=0.0003 for the strongest association).

CONCLUSION

There are distinct genetic patterns of MHC associations in the 2 disease subsets of RA defined according to ACPA status. HLA-DPB1 is an independent risk locus for ACPA-positive RA. We did not identify any associations with SNPs within the MHC for ACPA-negative RA.

The shared epitope hypothesis in rheumatoid arthritis: evaluation of alternative classification criteria in a large UK Caucasian cohort

OBJECTIVE

Many classification systems for the HLA-DRB1 allelic association with rheumatoid arthritis (RA) have been reported, but few have been validated in additional populations. We sought to evaluate 3 different DRB1 allele classification systems in a large cohort of Caucasian RA patients and control subjects in the UK.

METHODS

HLA-DRB1 typing was undertaken in 1,325 Caucasian RA patients and 462 healthy Caucasian controls who were residents of the UK. Logistic regression analyses were performed to investigate the different classification systems.

RESULTS

We confirmed the association between the susceptibility alleles S2 and S3P, as proposed by Tezenas du Montcel, and the presence of RA in UK Caucasians. A significant hierarchy of risk was observed within the S3P allele group. There was no evidence of a significant association between DRB1*1001 and RA. Our data did not support the hypothesis that an isoleucine at position 67 conferred protection against RA, other than in contrast to the susceptibility alleles. However, the presence of an aspartic acid at amino acid 70 did appear to confer some degree of protection.

CONCLUSION

We were unable to fully substantiate any of the 3 recent revisions of the shared epitope hypothesis in this large cohort of Caucasian RA patients and control subjects in the UK. This reinforces the importance of evaluating disease susceptibility alleles in different Caucasian populations as well as in other ethnic groups. In particular, it will be important to clarify the precise DRB1 association in a given population before DRB1 genotyping is incorporated into clinical diagnostic or treatment algorithms.

The ITGAV rs3738919-C allele is associated with rheumatoid arthritis in the European Caucasian population: a family-based study

The integrin αvβ3, whose αv subunit is encoded by the ITGAV gene, plays a key role in angiogenesis. Hyperangiogenesis is involved in rheumatoid arthritis (RA) and the ITGAV gene is located in 2q31, one of the suggested RA susceptibility loci. Our aim was to test the ITGAV gene for association and linkage to RA in a family-based study from the European Caucasian population.

Two single nucleotide polymorphisms were genotyped by PCR-restriction fragment length polymorphism in 100 French Caucasian RA trio families (one RA patient and both parents), 100 other French families and 265 European families available for replication. The genetic analyses for association and linkage were performed using the comparison of allelic frequencies (affected family-based controls), the transmission disequilibrium test, and the genotype relative risk.

We observed a significant RA association for the C allele of rs3738919 in the first sample (affected family-based controls, RA index cases 66.5% versus controls 56.7%; P = 0.04). The second sample showed the same trend, and the third sample again showed a significant RA association. When all sets were combined, the association was confirmed (affected family-based controls, RA index cases 64.6% versus controls 58.1%; P = 0.005). The rs3738919-C allele was also linked to RA (transmission disequilibrium test, 56.5% versus50% of transmission; P = 0.009) and the C-allele-containing genotype was more frequent in RA index cases than in controls (RA index cases 372 versus controls 339; P = 0.002, odds ratio = 1.94, 95% confidence interval = 1.3–2.9).

The rs3738919-C allele of the ITGAV gene is associated with RA in the European Caucasian population, suggesting ITGAV as a new minor RA susceptibility gene.

New classification of HLA-DRB1 alleles in rheumatoid arthritis susceptibility: a combined analysis of worldwide samples

Introduction

Rheumatoid arthritis (RA) is a complex polygenic disease of unknown etiology. HLA-DRB1 alleles encoding the shared epitope (SE) (RAA amino acid pattern in positions 72 to 74 of the third hypervariable region of the DRβ1 chain) are associated with RA susceptibility. A new classification of HLA-DRB1 SE alleles has been developed by Tezenas du Montcel and colleagues to refine the association between HLA-DRB1 and RA. In the present study, we used RA samples collected worldwide to investigate the relevance of this new HLA-DRB1 classification in terms of RA susceptibility across various Caucasoid and non-Caucasoid patients.

Methods

Eighteen subsamples were defined from a total number of 759 cases and 789 controls and grouped in 10 samples on the basis of their ethnic origin. HLA-DRB1 alleles were divided into five groups (S₁, S₂, S_3D, S_3P, and X) according to the new HLA-DRB1 allele classification. The whole analysis was performed by comparing carrier frequencies for the five HLA-DRB1 allele groups between RA patients and controls across the 10 Caucasoid and non-Caucasoid samples. The Mantel-Haenszel method of meta-analysis provided a global odds ratio (OR) estimate with 95% confidence interval (CI).

Results

A positive association with RA susceptibility was found for S₂ allele carriers (OR 2.15, 95% CI 1.54 to 3.00; p < 10^-5) and S_3P allele carriers (OR 2.74, 95% CI 2.01 to 3.74; p < 10^-5). A negative association was found for S₁ alleles (OR 0.60, 95% CI 0.48 to 0.76; p < 10^-4) and X alleles (OR 0.58, 95% CI 0.39 to 0.84; p = 4 × 10^-3). No significant association was highlighted for the S_3D group of alleles (OR 0.89, 95% CI 0.69 to 1.14; p = 0.89). The complementary genotype analysis fit with the genotype risk hierarchy previously reported in Caucasoid RA patients.

Conclusion

So far, the present study is the first attempt to investigate the relevance of this new HLA-DRB1 classification in terms of RA susceptibility on both Caucasoid and non-Caucasoid samples. Our results support the hypothesis of a differential role played by different HLA-DRB1 allele groups in RA susceptibility across different ethnic backgrounds and confirm the interest of such an HLA-DRB1 classification in differentiating predisposing and protective alleles.

[Toward a non-empirical treatment for rheumatoid arthritis based on its molecular pathology]

Rheumatoid arthritis (RA) is a chronic, disabbling disease that affects individuals during the productive years of their lives. Modern treatment for RA includes the so called "biologic" therapy, which is based on recombinant proteins that modify the biologic processes. These agents have potent therapeutic effects and different mechanisms of action. Nevertheless, therapeutic failure still prevails. Treatment that prevents disability in RA must be started in an early manner, before the development of complications and, ideally, with a minimum possibility of therapeutic failure. As yet, there are no clinical or laboratory criteria to identify those patients with a higher probability of responding to particular types of therapy, delaying control of RA ad affecting the prevention of incapacity. Research into gene diversity through single-nucleotide polymorphisms (SNPs) by means of microarray systems, allows the detailed analysis of gene factors associated to a given disease. SNPs have been recently applied to the study of RA, where the major polymorphisms associated to RA occur primarily in genes that code for proteins related to the initiation of an immune response and/or the control of cellular activity in the immune system, in addition to genes related to tissue repair. The specific meaning of these findings is in its initial stages of research. On the other hand, proteomics relate to the analysis of protein expression profiles at multiple levels. Both types of studies will contribute to the knowledge of patterns of gene expression in RA compared to the general population, and will allow an understanding of the pathogenesis of RA. Moreover, proteomic and genomic profiles can be employed to designs probes that identify individuals with the risk of developing RA, individually predict the response to different therapeutic modalities (pharmacogenomics) and for the follow-up of the biologic response to therapy.

A new classification of HLA-DRB1 alleles differentiates predisposing and protective alleles for autoantibody production in rheumatoid arthritis

The HLA-DRB1 gene was reported to be associated with anticitrullinated protein/peptide autoantibody (ACPA) production in rheumatoid arthritis (RA) patients. A new classification of HLA-DRB1 alleles, reshaping the shared epitope (SE) hypothesis, was recently found relevant in terms of RA susceptibility and structural severity.

We investigated the relevance of this new classification of HLA-DRB1 SE⁺ alleles in terms of rheumatoid factor (RF) and ACPA production in a sample of French RA patients.

We studied 160 early RA patients included in a prospective longitudinal cohort of French Caucasian patients with recent-onset arthritis. RF, anticyclic citrullinated peptide 2 (anti-CCP2) and antideiminated human fibrinogen autoantibodies (AhFibA) were assessed in all patients at inclusion. The HLA-DRB1 gene was typed by PCR-sequence specific oligonucleotides probes (PCR-SSOP), and SE+ alleles were classified into four groups (S1, S2, S3P, S3D) according to the new classification.

The new classification of HLA-DRB1 SE+ alleles distinguishes predisposing and protective alleles for RF, anti-CCP2 or AhFibA production. The presence of S2 or S3P alleles is associated with both RF, anti-CCP2 or AhFibA positivity, whereas the presence of S3D or S1 alleles appears to be protective for RF, anti-CCP2 or AhFibA positivity.

The new classification of HLA-DRB1 SE⁺ alleles is relevant in terms of autoantibody production in early RA patients by differentiating predisposing and protective alleles for RF or ACPA production.

Linkage proof for PTPN22, a rheumatoid arthritis susceptibility gene and a human autoimmunity gene

The tyrosine phosphatase PTPN22 allele 1858T has been associated with rheumatoid arthritis (RA) and other autoimmune diseases. RA is the most frequent of those multifactorial diseases. The RA association was usually restricted to serum rheumatoid factor positive disease (RF+). No interaction was shown with HLA-DRB1, the first RA gene. Many case-control studies replicated the RA association, showing an allele frequency increase of approximately 5% on average and large variations of population allele frequencies (2.1-15.5%). In multifactorial diseases, the final proof for a new susceptibility allele is provided by departure from Mendel's law (50% transmission from heterozygous parents). For PTPN22-1858T allele, convincing linkage proof was available only for type 1 diabetes. We aimed at providing this proof for RA. We analyzed 1,395 West European Caucasian individuals from 465 "trio" families. We replicated evidence for linkage, demonstrating departure from Mendel's law in this subset of early RA onset patients. We estimated the overtransmission of the 1858T allele in RF+ families: T = 63%, P < 0.0007. The 1858T allele frequency increased from 11.0% in controls to 17.4% in RF+ RA for the French Caucasian population and the susceptibility genotype (1858T/T or T/C) from 20.2% to 31.6% [odds ratio (OR) = 1.8 (1.2-2.8)]. In conclusion, we provided the linkage proof for the PTPN22-1858T allele and RF+ RA. With diabetes and RA, PTPN22 is therefore a "linkage-proven" autoimmunity gene. PTPN22 accounting for approximately 1% of the RA familial aggregation, many new genes could be expected that are as many leads to definitive therapy for autoimmune diseases.

What does the immunogenetic basis of rheumatoid arthritis teach us about the immunobiology of the disease?

Rheumatoid arthritis is a chronic inflammatory autoimmune disease in which, although the exact etiology is unknown, the contribution from genetic factors is approximately 60%. major histocompatibility complex alleles make the largest contribution to this genetic effect. The remainder is probably made up of an, as yet undefined, number of genes ( approximately 50-200) with low disease penetrance. Recent advances in genetic technology are now enabling us to start to identify some of these more moderate risk-conferring candidate genes. Evidence from functional studies of such genes is beginning to provide insight into the exact nature of the pathways and processes involved in disease susceptibility and expression. In this review, we will discuss how a growing number of genetic polymorphisms might underpin the immunological and molecular anomalies characteristic of rheumatoid arthritis. Specifically, we will focus on one particular pathway, T-cell activation, with an emphasis on the genetic polymorphism that influences antigen presentation and recognition in antigen-presenting cells, as well as those genes that influence the thresholds of antigen-receptor signaling in T lymphocytes.

Reshaping Cinderella's slipper: the shared epitope hypothesis

This issue of Arthritis Research and Therapy contains a succinct and elegant paper by Michou and colleagues that advances our understanding of the genetic basis of rheumatoid arthritis (RA) by reclassifying the contribution of RA susceptibility alleles according to their structure. This line of research is potentially important in our conceptualization of the mechanism of disease in RA, in predicting disease course and severity, and as a model for further studies on this topic. The author's approach to reassessing the molecular structure of the shared epitope redirects attention to using the binding properties of the major histocompatibility complex molecules associated with susceptibility to search for the peptides driving the autoimmune process underlying rheumatoid arthritis.