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

Genetic evidence reveals a causal relationship between rheumatoid arthritis and interstitial lung disease

Background/purpose: Previous epidemiological studies have associated interstitial lung disease (ILD) with rheumatoid arthritis (RA), yet the causality of this relationship remains uncertain. This study aimed to investigate the genetic causal link between ILD and RA. Methods: Genome-wide association study (GWAS) statistics for ILD and RA were collected from public datasets. Relevant single-nucleotide polymorphisms (SNPs) were selected by executing quality control steps from the GWAS summary results. A two-sample bidirectional Mendelian randomization (MR) analysis was performed to assess the causal relationship between the two conditions. The MR analysis primarily used the inverse variance weighting (IVW), weighted median (WM), and MR-Egger regression methods. Sensitivity analyses, including MR-Egger, leave-one-out, and MR Pleiotropy RESidual Sum and Outlier (MR-PRESSO), were conducted to evaluate the heterogeneity and pleiotropy. Replication analyses using Asian datasets were also conducted to enhance the robustness of our findings. Results: In the European population, RA was found to increase the risk of ILD by 9.6% (OR: 1.096, 95% CI: 1.023-1.174, p = 0.009). Conversely, ILD was associated with a 12.8% increased risk of RA (OR: 1.128, 95% CI: 1.013-1.256, p = 0.029). Replication analyses from Asian GWAS further supported these findings, particularly the increased risk of ILD attributable to RA (OR: 1.33, 95% CI: 1.18-1.49, p-value <0.001). Conclusion: Our findings underscore the clinical importance of screening for ILD in RA patients and suggest that effective management of RA could significantly benefit ILD patients. The potential applicability of novel RA treatments to ILD warrants further exploration. Additionally, racial disparities in the manifestation of these diseases should not be overlooked, as they may offer new perspectives for targeted therapies in diverse populations.

Genetic implications in the pathogenesis of rheumatoid arthritis; an updated review

Three important factors, including genetics, environment factors and autoimmunity play a role in the pathogenesis of rheumatoid arthritis (RA). The heritability of RA has been accounted to be 50-60%, while the HLA involvement in heritability of the disease has been accounted to be 10-40%. It has been documented that shared epitope (SE) alleles, such as HLA-DRB1*01 and DRB1*04, some HLA alleles like HLA-DRB1*13 and DRB1*15 are connected to RA susceptibility. An advanced classification of SE categorizes SE alleles into four main groups namely, S1, S2, S3D, and S3P. The S2 and S3P groups have been linked to susceptibility of seropositive RA. Various genome-wide association studies (GWAS) have discovered many susceptibility loci implicated in pathogenesis of RA. Some of the important single nucleotide polymorphisms (SNPs) linked to RA are TRAF1, STAT4, CTLA4, IRF5, CCR6, PTPN22, IL23R, and PADI4. HLA and non-HLA genes may discriminate anti-cyclic citrullinated peptide (anti-CCP) antibody-positive and anti-CCP-negative RA groups. Furthermore, risk of the disease has also been linked to environmental agents, mainly cigarette smoking. Pharmacogenomics has also confirmed SNPs or genetic patterns that might be linked to drugs responses. Different aspects of genetic involvement in the pathogenesis, etiology, and RA complications are reviewed in this article.

The genetic pathogenesis, diagnosis and therapeutic insight of rheumatoid arthritis

Rheumatoid arthritis (RA) is a systemic autoimmune disease that causes chronic inflammation of the joints. RA is a heterogeneous disorder caused by an abnormal autoimmune response triggered by the complex interactions of genetic and environmental factors that contribute to RA etiology. However, its underlying pathogenic mechanisms are yet to be fully understood. In this review, I provide an overview of the pathogenesis, diagnosis and therapeutic insight in the clinical management of RA in light of the recent updates to classification criteria and recent discoveries of genetic loci associated with susceptibility for RA.

Comparison of Serological Biomarkers in Rheumatoid Arthritis and Their Combination to Improve Diagnostic Performance

Introduction

The diagnosis of rheumatoid arthritis (RA) is based on a combined approach that includes serological markers such as rheumatoid factor (RF) and anti-citrullinated peptide/protein antibodies (ACPA). The goal of this study was to evaluate the clinical performance of several RF and ACPA immunoassays for the diagnosis of RA, as well as the diagnostic value of a combinatory approach with these markers.

Methods

The study cohort included 1,655 patients from the Swiss Clinical Quality Management registry with sera from 968 patients with RA and 687 disease controls, including patients with axial spondyloarthritis (n = 450) and psoriatic arthritis (n = 237). ACPA were determined by anti-CCP2 IgG enzyme-linked immunosorbent assay (ELISA), QUANTA Flash^® CCP3 IgG [chemiluminescent immunoassay (CIA)], and QUANTA Lite^® CCP3 IgG ELISA. RF was determined by ELISA (QUANTA Lite^® RF IgM, RF IgA, and RF IgG) and with two research use only CIAs (QUANTA Flash^® RF IgM and RF IgA).

Results

All three ACPA assays showed good discrimination between RA patients and controls and good clinical performance. Overall, CCP3 performed better than CCP2. More pronounced differences were observed between the RF assays. We observed that CIA platforms for both RF IgM and RF IgA showed better performance than the ELISA platforms. Excellent and good total agreements were found between ELISA and CIA for CCP3 (total agreement 95.3%, kappa = 0.90), and between CCP2 and CCP3 ELISA (total agreement 86.6%, kappa = 0.73), respectively. RF IgM CIA and ELISA had a good qualitative agreement (86.5%, kappa = 0.73); RF IgA CIA and ELISA showed a moderate total agreement (78.5%, kappa = 0.53). When combinatory analyses were performed, the likelihood of RA increased with dual positivity and triple positivity and combining different markers resulted in higher odds ratio than the individual markers in all cases.

Conclusion

ACPA and RF showed good clinical performance in this large Swiss cohort of RA patients and controls. Overall, the performance of CCP3 was superior to CCP2. The combination of these biomarkers in an interval model represents a potential tool for the diagnosis of RA patients.

Meta-analyses of the association of HLA-DRB1 alleles with rheumatoid arthritis among Arabs

AIM

Various studies incorporating Arab populations have reported on specific associations between HLA-DRB1 variants and rheumatoid arthritis (RA). We sought to provide an overview on the association of HLA-DRB1 with RA in Arabs using meta-analysis tools.

METHODS

Data on allele counts and frequencies were compiled from the relevant literature (published before 16 February 2016) and the associations of 13 -DRB1 variants with RA were assessed; relationships were defined in terms of odds ratios (ORs) with a 95% confidence interval.

RESULTS

Based on a collection of six studies, risk conferring or protective allele associations were derived from allele counts in 475 RA patients and 1213 controls. Two HLA-DRB1 alleles (-DRB1*04, *10) significantly conferred an increased risk for RA (OR > 2; P < 0.0001). Conversely, four alleles (-DRB1*03, *07, *11 and *13) significantly conferred a protective effect against RA (OR < 1; P < 0.05). No significant associations with RA were found for seven -DRB1 variants (-DRB1*01, *08, *09, *12, *14, *15 and *16).

CONCLUSION

With increased statistical power and effect size over individual studies, we present a more robust profile on the association of HLA-DRB1 variants with RA in the Arab ethnicity, and contribute to the global geo-ethnic picture in this context.

Rheumatoid arthritis susceptibility genes: An overview

Rheumatoid arthritis (RA) is a chronic, inflammatory autoimmune disease sustained by genetic factors. Various aspects of the genetic contribution to the pathogenetics and outcome of RA are still unknown. Several genes have been indicated so far in the pathogenesis of RA. Apart from human leukocyte antigen, large genome wide association studies have identified many loci involved in RA pathogenesis. These genes include protein tyrosine phosphatase, nonreceptor type 22, Peptidyl Arginine Deiminase type IV, signal transducer and activator of transcription 4, cytotoxic T-lymphocyte-associated protein 4, tumor necrosis factor-receptor associated factor 1/complement component 5, tumor necrosis factor and others. It is important to determine whether a combination of RA risk alleles are able to identify patients who will develop certain clinical outcomes, such myocardium infarction, severe infection or lymphoma, as well as to identify patients who will respond to biological medication therapy.

Genetics of rheumatoid arthritis - a comprehensive review

The "Bermuda triangle" of genetics, environment and autoimmunity is involved in the pathogenesis of rheumatoid arthritis (RA). Various aspects of genetic contribution to the etiology, pathogenesis and outcome of RA are discussed in this review. The heritability of RA has been estimated to be about 60 %, while the contribution of HLA to heritability has been estimated to be 11-37 %. Apart from known shared epitope (SE) alleles, such as HLA-DRB1*01 and DRB1*04, other HLA alleles, such as HLA-DRB1*13 and DRB1*15 have been linked to RA susceptibility. A novel SE classification divides SE alleles into S1, S2, S3P and S3D groups, where primarily S2 and S3P groups have been associated with predisposition to seropositive RA. The most relevant non-HLA gene single nucleotide polymorphisms (SNPs) associated with RA include PTPN22, IL23R, TRAF1, CTLA4, IRF5, STAT4, CCR6, PADI4. Large genome-wide association studies (GWAS) have identified more than 30 loci involved in RA pathogenesis. HLA and some non-HLA genes may differentiate between anti-citrullinated protein antibody (ACPA) seropositive and seronegative RA. Genetic susceptibility has also been associated with environmental factors, primarily smoking. Some GWAS studies carried out in rodent models of arthritis have confirmed the role of human genes. For example, in the collagen-induced (CIA) and proteoglycan-induced arthritis (PgIA) models, two important loci - Pgia26/Cia5 and Pgia2/Cia2/Cia3, corresponding the human PTPN22/CD2 and TRAF1/C5 loci, respectively - have been identified. Finally, pharmacogenomics identified SNPs or multiple genetic signatures that may be associated with responses to traditional disease-modifying drugs and biologics.

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.

A chronic model of arthritis supported by a strain-specific periarticular lymph node in BALB/c mice

Current animal models of arthritis only partially reflect the complexity of rheumatoid arthritis and typically lack either chronicity or autoantibody formation. Here we describe a model that combines features of antigen-induced arthritis and collagen-induced arthritis, which can be efficiently induced in BALB/c and C57BL/6 mice. However, BALB/c mice generate significantly higher titres of anticollagen and anticitrullinated peptide antibodies, show a stronger progressive joint destruction, and in the chronic phase the disease spreads between joints. Concomitant to the observation of a more severe pathology, we discovered a previously undescribed small periarticular lymph node in close proximity to the knee joint of BALB/c mice, which acts as the primary draining lymph node for the synovial cavity. Our model more closely reflects the pathology of rheumatoid arthritis than classical models of arthritis and is hence particularly suitable for further studies of disease pathogenesis.

Antibodies to mutated citrullinated vimentin and anti-cyclic citrullinated peptide antibodies in inflammatory bowel disease and related arthritis

BACKGROUND

Antibodies that react with citrullinated proteins (anti-mutated citrullinated vimentin [anti-MCV] and second-generation anti-cyclic citrullinated peptide antibodies [anti-CCP2]) are markers for rheumatoid arthritis. Recent studies have demonstrated that these antibodies are present in other arthropathies including the spondyloarthritis, psoriatic arthritis, and juvenile idiopathic arthritis. Arthritis associated with inflammatory bowel disease (IBD) takes various forms, with some shared similarities with classic spondylarthropathies. Our objective was to investigate the role of anti-MCV and anti-CCP2 as potential biomarkers in IBD and related arthritis.

METHODS

In all, 125 IBD patients (71 males, 54 females) were compared to 81 age- and sex-matched healthy controls. Anti-MCV and Anti-CCP2 IgG were measured using an enzyme linked immunosorbent assay.

RESULTS

In the 125 IBD patients (mean age 32.6 ± 12.3 years), 44 (35.2%) had ulcerative colitis and 81 (64.8%) had Crohn's disease. Forty-four (35.2%) IBD patients developed arthritic manifestations. Antibody positivity was observed in 24/125 (19.2%) IBD patients and in 18/81 (22.2%) healthy subjects. The proportion of anti-MCV positivity among IBD patients and healthy individuals were similar: 16.8% vs. 16.0%, P = 0.887. Anti-CCP2 positivity among IBD patients and healthy individuals was also comparable: 6.4% vs. 6.2%, P = 0.948. Similarly, the presence of anti-MCV and anti-CCP2 antibodies was not different among IBD patients with and without arthritis. The mean titers of antibodies were low: anti-MCV (29.6 ± 7.5 U/mL) and anti-CCP2 (27.6 ± 4.0 U/mL) in IBD patients with arthritis.

CONCLUSIONS

Autoantibodies to citrullinated proteins were low in IBD-related arthritis. These findings suggest that these antibodies are not useful biomarkers in IBD to predict who may develop IBD-related arthropathy.

Association of the HLA-DRB1 epitope LA(67, 74) with rheumatoid arthritis and citrullinated vimentin binding

OBJECTIVE

Although rheumatoid arthritis (RA) has long been associated with an HLA-DRB1 shared epitope, a systematic search for other epitopes has never been conducted. In addition, the relationship between these epitopes and the binding of citrullinated autoantigens has not been investigated. We developed a program that can analyze HLA data for all possible epitopes of up to 5 amino acids and used this program to assess the shared epitope hypothesis in RA.

METHODS

We analyzed high-resolution data from the International Histocompatibility Working Group, which included a group of 488 patients with RA and a group of 448 racially and ethnically balanced control subjects, for all combinations of up to 5 amino acids among polymorphic HLA-DRB1 positions 8-93. Statistical significance was determined by chi-square and Fisher's exact tests, with a false discovery rate correction.

RESULTS

Three residues (V(11), H(13), and L(67)) were found to have the highest degree of association with RA susceptibility (P < 10(-11)), and D(70) was found to correlate best with RA resistance (P = 2 × 10(-11)). Of >2 million epitopes examined, LA(67, 74) exhibited the highest correlation with RA susceptibility (P = 2 × 10(-20); odds ratio 4.07 [95% confidence interval 3.07-5.39]). HLA alleles containing the LA(67, 74) epitope exhibited significantly greater binding to citrullinated vimentin(65-77) than did alleles containing D(70). Only 1 allele (DRB1*16:02) contained both LA(67, 74) and D(70); it bound citrullinated vimentin weakly and was not associated with RA.

CONCLUSION

The findings of these studies confirm the importance of HLA-DRB1 amino acids in pocket 4 for the binding of citrullinated autoantigens and susceptibility to RA.

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.

Anti-mutated citrullinated vimentin (anti-MCV) and anti-65 kDa heat shock protein (anti-hsp65): new biomarkers in ankylosing spondylitis

INTRODUCTION

Citrullination as well as anti-citrullinated protein/peptide antibodies (ACPA) have been implicated in the pathogenesis of rheumatoid arthritis (RA). While ACPAs are specific and sensitive markers for RA, there have been hardly any reports regarding ACPAs in ankylosing spondylitis (AS). The possible role of antibodies to Mycobacterial 65 kDa heat shock protein (hsp65) has not been characterized in AS. As new laboratory biomarkers of AS are needed, we investigated the prevalence of anti-mutated citrullinated vimentin (MCV) and anti-hsp65 antibodies in AS.

METHODS

Altogether 43 AS and 44 healthy controls were included in the study. Anti-MCV and anti-hsp65 were determined in sera by commercial and in-house ELISA, respectively. Serum autoantibody levels were correlated with ESR, CRP, HLA-B27 status, smoking habits, pain intensity, BASDAI, BASFI and BASMI indices.

RESULTS

Patients with AS had significantly higher serum anti-MCV levels (17.3 U/mL, range: 8.3-31.5 U/mL) in comparison to healthy subjects (8.9 U/mL, range: 5.4-13.3 U/mL) (p<0.01). Sixteen of the 43 AS patients (37%) and none of the 44 healthy controls (0%) were anti-MCV positive using the cut-off value recommended by the manufacturer (>20 U/mL). The mean anti-hsp65 concentration in AS sera was 124.8 AU/mL (range: 27.2-1000 AU/mL), while controls exerted significantly lower anti-hsp65 levels (mean: 51.8 AU/mL; range: 22.5-88.5 AU/mL) (p<0.001). Correlation analysis revealed that both anti-MCV positivity (r=0.613; p=0.012) and absolute serum anti-MCV levels (r=0.553; p=0.021) correlated with anti-hsp65 levels. Anti-MCV positivity also correlated with ESR (r=0.437; p=0.03).

CONCLUSIONS

Anti-MCV and anti-hsp65 may be novel biomarkers in AS.

Anti-CCP antibodies: the past, the present and the future

Rheumatoid arthritis (RA) is an autoimmune disease characterized by autoantibodies against citrullinated antigens. The importance of citrulline for the epitopes bound by these autoantibodies, referred to as ACPA (anti-citrullinated peptide/protein antibodies), was first described in 1998. In addition to citrullinated proteins, cyclic citrullinated peptides (CCP) can also be used as test substrates for detecting ACPA. The standard test for these antibodies is the second-generation CCP (CCP2) test, which is one of the best in terms of sensitivity and specificity. The generation of ACPA is an early event in the disease course, and is dependent on the presence of certain MHC class II alleles. ACPA in the inflamed synovium have been shown to associate with citrullinated antigens to form immune complexes, resulting in progression of the inflammatory process. The involvement of ACPA in the chronicity of RA is probably the reason why ACPA-positive patients have a more erosive disease course than ACPA-negative patients. The presence of ACPA has been included in the 2010 RA classification criteria. Thus, it is important to further standardize ACPA testing, for example by including an internal serum standard, which may lead to a better distinction between low and high ACPA levels.

An overview on the genetic of rheumatoid arthritis: a never-ending story

Rheumatoid arthritis (RA) is a chronic, systemic, inflammatory, multi-factorial disease sustained by environmental and genetic factors. These seem to be necessary but not sufficient in the disease development, nonetheless they can be responsible of different clinical pictures and response to therapy, and they can represent potential therapeutic targets. Several genes have been indicated so far in the pathogenesis of RA. The most important region is the Human Leukocyte Antigen (HLA) that contributes to approximately half of the genetic susceptibility for RA. The association seems to be stronger or specific for anti-citrullinated protein antibodies positive disease. Several alleles in the epitope-recognition part of the HLA molecule that show the highest association with RA susceptibility, also share a common string of amminoacid residues (the so-called shared-epitope hypothesis). Other variants in potentially pathogenic genes located in non-MHC regions have been implicated by recently performed genome wide analysis studies. These genes include PTPN22, TRAF1-C5, PADI4, STAT4. Other polymorphisms seem to be responsible for more aggressive disease phenotype such as those located at TNF, IL-1, IL-6, IL-4, IL-5, OPN, PRF1. However, still nowadays, the genetic background of RA remains to be clearly depicted, and the efforts in the post-genomic era can bring to an estimation of the real likelihood of the genetic effect on RA. Finally, the discovery of new genes associated with the disease can be relevant in finding potential biomarkers, potentially useful in disease diagnosis and treatment.

The relevance of citrullinated vimentin in the production of antibodies against citrullinated proteins and the pathogenesis of rheumatoid arthritis

Antibodies against citrullinated proteins (ACPAs) are highly specific for RA. Since the discovery of these antibodies, several of studies that focused on the presence and identity of citrullinated proteins in the joints of RA patients have been carried out. The best-known antigens that bind ACPAs are citrullinated filaggrin, Type II collagen (CII), α-enolase, fibrinogen and vimentin. This review compares citrullinated filaggrin, CII, α-enolase and fibrinogen with vimentin in their contribution to ACPA triggering, and gives an overview of the literature in which the role of citrullinated and non-citrullinated vimentin in the onset of ACPA production and the pathogenesis of RA is discussed.