Association between HLA class II genes and autoantibodies to cyclic citrullinated peptides (CCPs) influences the severity of rheumatoid arthritis

Genomic stratification by expression of HLA-DRB4 alleles identifies differential innate and adaptive immune transcriptional patterns - A strategy to detect predictors of methotrexate response in early rheumatoid arthritis

Effective drug selection is the current challenge in rheumatoid arthritis (RA). Treatment failure may follow different pathomechanisms and therefore require investigation of molecularly defined subgroups. In this exploratory study, whole blood transcriptomes of 68 treatment-naïve early RA patients were analyzed before initiating MTX. Subgroups were defined by serologic and genetic markers. Response related signatures were interpreted using reference transcriptomes of various cell types, cytokine stimulated conditions and bone marrow precursors. HLA-DRB4-negative patients exhibited most distinctive transcriptional differences. Preponderance of transcripts associated with phagocytes and bone marrow activation indicated response and transcripts of T- and B-lymphocytes non-response. HLA-DRB4-positive patients were more heterogeneous, but also linked failure to increased adaptive immune response. RT-qPCR confirmed reliable candidate selection and independent samples of responders and non-responders the functional patterning. In summary, genomic stratification identified different molecular pathomechanisms in early RA and preponderance of innate but not adaptive immune activation suggested response to MTX therapy.

Recent Advances in Defining the Genetic Basis of Rheumatoid Arthritis

Rheumatoid arthritis (RA) is the most common inflammatory arthritis and exhibits genetic overlap with other autoimmune and inflammatory disorders. Although predominant associations with the HLA-DRB1 locus have been known for decades, recent data have revealed additional insight into the likely causative variants within HLA-DRB1 as well as within other HLA loci that contribute to disease risk. In addition, more than 100 common variants in non-HLA loci have been implicated in disease susceptibility. Genetic factors are involved not only in the development of RA, but also with various disease subphenotypes, including production and circulating levels of autoantibodies and joint destruction. The major current challenge is to integrate these new data into a precise understanding of disease pathogenesis, including the critical cell types and molecular networks involved as well as interactions with environmental factors. We predict that delineating the functional effects of genetic variants is likely to drive new diagnostic and therapeutic approaches to the disease.

Decreased severity of experimental autoimmune arthritis in peptidylarginine deiminase type 4 knockout mice

Background

Peptidylarginine deiminase type 4 (PADI4) has been identified as a susceptibility gene for rheumatoid arthritis (RA) by genome-wide association studies. PADI4 is highly expressed in the bone marrow, macrophages, neutrophils, and monocytes. Peptidyl citrulline is an interesting molecule in RA because it is a target antigen for anti-citrullinated peptide antibodies, and only PADs (translated proteins from PADI genes) can provide peptidyl citrulline via the modification of protein substrates. The aim of this study was to evaluate the importance of the PADI4 gene in the progression of RA.

Methods

We generated Padi4 knockout (Padi4^−/−) DBA1J mice. The Padi4^−/− DBA1J and wild-type mice were immunized with bovine type II collagen (CII) to develop collagen-induced arthritis (CIA). The expression of various inflammatory cytokines and Padi genes in immune cells was detected by the real-time TaqMan assay. Cytokine concentrations in sera were measured by enzyme-linked immunosorbent assays. Localization of the PAD4 and PAD2 proteins was indicated by immunohistochemistry.

Results

We demonstrated that the clinical disease score was significantly decreased in the Padi4^−/− mice and Padi4 expression was induced by CII immunization. In the Padi4^−/− mice, serum anti-type II collagen (CII) immunoglobulin M (IgM), IgG, and inflammatory cytokine levels were significantly decreased compared with those in the wild-type mice. Padi2 expression was induced in the immune cells of the Padi4^−/− mice as a compensation for the defect in Padi4.

Conclusions

Padi4 affected disease severity in the CIA mice and was involved in the enhancement of the collagen-initiated inflammatory responses.

Electronic supplementary material

The online version of this article (doi:10.1186/s12891-016-1055-2) contains supplementary material, which is available to authorized users.

Have radiographic progression rates in early rheumatoid arthritis changed? A systematic review and meta-analysis of long-term cohorts

OBJECTIVE

To evaluate, firstly, all published data on baseline and annual progression rates of radiographic damage from all longitudinal observational cohorts, and secondly, the association of standard clinical and laboratory parameters with long-term radiographic joint damage.

METHODS

A comprehensive search of the literature from 1975 to 2014, using PubMed, SCOPUS and Cochrane databases, identified a total of 28 studies that investigated long-term radiographic progression, and 41 studies investigating predictors of long-term radiographic progression. This was submitted and approved by PROSPERO in February 2014 (Registration Number: CRD42014007589).

RESULTS

Meta-analysis indicated an overall baseline rate of 2.02%, and a yearly increase of 1.08% of maximum damage. Stratified analysis found that baseline radiographic scores did not differ significantly between cohorts recruiting patients pre- and post-1990 (2.01% vs 2.03%; P > 0.01); however, the annual rate of progression was significantly reduced in the post-1990 cohorts (0.68% vs 1.50%; P < 0.05). High levels of acute phase markers, baseline radiographic damage, anti-CCP and RF positivity remain consistently predictive of long-term radiographic joint damage.

CONCLUSION

Critical changes in treatment practices over the last three decades are likely to explain the reduction in the long-term progression of structural joint damage. Acute phase markers and presence of RF/anti-CCP are strongly associated with increased radiographic progression.

Periodontitis prevalence and serum antibody reactivity to periodontal bacteria in primary Sjögren's syndrome: a pilot study

AIMS

The aims of this study were as follows: (i) To assess the prevalence of periodontitis among patients with primary Sjögren's syndrome (pSS) and comparator groups of patients with rheumatoid arthritis (RA) and osteoarthritis (OA). (ii) To perform a pilot study to compare serum antibody responses to 10 oral/periodontal bacteria in these patient groups and a historical comparator group of patients with periodontitis.

MATERIALS AND METHODS

Standard clinical periodontal assessments were performed on 39 pSS, 36 RA and 23 OA patients and "In-house" antibody ELISAs for serum antibodies against 10 oral/periodontal bacteria were performed in these groups.

RESULTS

Forty-six percent of the pSS group, 64% of the RA group and 48% of the OA group had moderate/severe periodontitis. These frequencies did not reach statistical significance between groups. Raised antibody levels to Prevotella denticola were found in the pSS, RA and periodontitis groups compared to the OA group. Significant between group differences were seen for Aggregatibacter actinomycetemcomitans, Prevotella intermedia and Campylobacter showae. None of these differences were specifically associated with pSS.

CONCLUSION

This study showed no increase in periodontitis in pSS patients. Although the P. denticola data are of interest, identifying bacterial triggering factors for pSS will likely require alternative strategies including modern techniques such as microbiome analysis.

A study on FoxP3 and Tregs in paired samples of peripheral blood and synovium in rheumatoid arthritis

There is an increasing evidence suggesting the role of fork head boxP3 (FoxP3) in the development and the regulation of CD4⁺CD25⁺ Treg cells. T-cell regulatory mechanisms in rheumatoid arthritis patients were evaluated by the contributing factors such as pro-inflammatory cytokines, circulating immune complexes, HLA DR expression, ligand binding biomarkers, FoxP3 expression in paired samples of peripheral blood (PB) and synovial fluid (SF). These cellular responses were further correlated with the humoral immune responses such as anti-cyclic citrullinated peptides IgG (CCP), circulating immune complex-c1q IgG (CIC), immunoglobulin G (IgG) and immunoglobulin M (IgM) of the rheumatoid arthritis factor (RAF). The results suggest a definitive role of Tregs in the homeostatic control because there is an increase in FoxP3 (37%) and HLA-DR (45%) expression in the synovial fluid as compared to PB. Furthermore, humoral responses as a downstream effector mechanism are positively correlated with the pathogenesis of rheumatoid arthritis (RA). A positive relationship exists between quantitative anti-CCP production and the expression of HLA-DR. The study relates an increased and pivotal role of B cell activation in the synovial fluid thereby permitting the need to ablate the targeted B cell immune responses.

Monoclonal antibody against citrullinated peptides obtained from rheumatoid arthritis patients reacts with numerous citrullinated microbial and food proteins

OBJECTIVE

To investigate the reactivity of monoclonal anti-citrullinated protein antibody (ACPA) obtained from peripheral blood B cells of rheumatoid arthritis (RA) patients with human autoantigens as well as environmental proteins by determining the essential epitope for the ACPA.

METHODS

A human monoclonal ACPA (cyclic citrullinated peptide antibody 1 [CCP-Ab1]) was obtained by screening peripheral blood lymphocytes from 31 patients with RA using a novel monoclonal antibody-secreting cell (ASC) screening system, the immunospot-array assay on a chip. The essential epitope for CCP-Ab1 was determined using epitope mapping. Then, human, microbial, and plant proteins that share the essential epitope identified were searched using BLAST. Finally, representative proteins identified by the search were produced in vitro, and their reactivity with CCP-Ab1 was examined.

RESULTS

CCP-Ab1 bound CCP in a citrulline-indispensable manner. In CCP, the 6 amino acid residues required for CCP-Ab1 binding were identified. In the BLAST search, 38 human, 56 viral, 1,383 fungal, 547 bacterial, and 1,072 plant proteins were found to share the essential epitope, and CCP-Ab1 reacted with all of the recombinant citrullinated proteins tested, which included the various environmental factors, such as various plant proteins that are part of the daily diet.

CONCLUSION

Our findings demonstrate, for the first time, that a monoclonal ACPA (CCP-Ab1) derived from RA patients cross-reacts not only with various autoantigens but also with numerous plant and microbial proteins. We propose that countless environmental factors, including microbes and diet, may trigger the generation of ACPAs that then cross-react with various citrullinated human autoantigens through molecular mimicry to induce RA.

Association between ankylosing spondylitis and the miR-146a and miR-499 polymorphisms

miRNAs are small, non-coding RNAs that regulate the expression of multiple target genes at the post-transcriptional level. Single-nucleotide polymorphisms (SNPs) in miRNA sequences may alter miRNA expression and have been implicated in the pathogenesis of multiple forms of arthritis, including rheumatoid arthritis (RA) and osteoarthritis. The present study explored the association between ankylosing spondylitis (AS) and two single nucleotide polymorphisms (SNPs), miR-146a rs2910164G>C and miR-499 rs3746444T>C, in a Han Chinese population. A case-control study consisting of 102 subjects with AS and 105 healthy controls was designed. The two miRNA SNPs were identified by direct sequencing. Subsequently, their gene and genotype frequencies were compared with healthy controls. A significant difference was observed in the miR-146a rs2910164G>C SNP. The frequency of the G allele was markedly higher in the AS patients than in the healthy controls (P = 0.005, Pc = 0.01, OR = 1.787), and the frequency of the GG genotype was higher in AS patients than in controls (P = 0.014, Pc = 0.042, OR = 2.516). However, no significant association was found between the miR-499 rs3746444T>C variant and susceptibility to AS. This is the first study to address the association between the miR-146a rs2910164G>C and miR-499 rs3746444T>C polymorphisms and AS, and it suggests a potential pathogenic factor for AS. Further studies are needed to validate our findings in a larger series, as well as in other ethnic backgrounds.

Interactions between household air pollution and GWAS-identified lung cancer susceptibility markers in the Female Lung Cancer Consortium in Asia (FLCCA)

We previously carried out a multi-stage genome-wide association study (GWAS) on lung cancer among never smokers in the Female Lung Cancer Consortium in Asia (FLCCA) (6,609 cases, 7,457 controls) that identified novel susceptibility loci at 10q25.2, 6q22.2, and 6p21.32, and confirmed two previously identified loci at 5p15.33 and 3q28. Household air pollution (HAP) attributed to solid fuel burning for heating and cooking, is the leading cause of the overall disease burden in Southeast Asia, and is known to contain lung carcinogens. To evaluate the gene-HAP interactions associated with lung cancer in loci independent of smoking, we analyzed data from studies participating in FLCCA with fuel use information available (n = 3; 1,731 cases; 1,349 controls). Coal use was associated with a 30% increased risk of lung cancer (OR 1.3, 95% CI 1.0-1.6). Among the five a priori SNPs identified by our GWAS, two showed a significant interaction with coal use (HLA Class II rs2395185, p = 0.02; TP63 rs4488809 (rs4600802), p = 0.04). The risk of lung cancer associated with coal exposure varied with the respective alleles for these two SNPs. Our observations provide evidence that genetic variation in HLA Class II and TP63 may modify the association between HAP and lung cancer risk. The roles played in the cell cycle and inflammation pathways by the proteins encoded by these two genes provide biological plausibility for these interactions; however, additional replication studies are needed in other non-smoking populations.

Performance characteristics of a new automated method for measurement of anti-cyclic citrullinated peptide

Rheumatoid arthritis (RA) is a chronic inflammatory auto-immune disease affecting approximately 1%–2% of the population worldwide. RA is a potentially crippling disease since it results in malformation of the joints. RA is mostly diagnosed based on clinical manifestations but serological tests against autoantibodies, such as rheumatoid factor and anti-cyclic citrullinated peptides (aCCP), are available. The presence of aCCP antibodies is strongly associated with a more severe, destructive disease course. Recently, a new test for the measurement of aCCP antibodies on the IMMULITE 2000(XPi) platform was developed by Siemens Healthcare. In this study we investigated the performance characteristics of this new aCCP test in four different hospital laboratories and compared the new test with three different commercially available platforms.

Samples were collected from patients presented to the hospital for aCCP measurement. Serum aCCP levels were determined by aCCP (Ig)G assay for IMMULITE 2000(XPi) systems (Siemens Healthcare), ImmunoScan RA enzyme-linked immunosorbent assay (ELISA) test (Eurodiagnostica), Immunocap 250 (Thermofisher) or aCCP IgG assay on the Modular system (Roche Diagnostics). The evaluation protocol consisted of within-run imprecision (20 sequential runs), between-run imprecision (16 workdays), comparison of serum and plasma measurement and method comparison.

The within-run imprecision (n=20) for aCCP IgG assay on three different IMMULITE 2000(XPi) systems ranged from 3.0% to 6.9% at levels 3.2–171.2 U/mL. Between-run imprecision (n=16 days) ranged from 5.2% to 11% at levels of 3.2–106.9 U/mL. Method comparison showed good correlation when samples were measured on two different Immulite analyzers in two different hospital laboratories [0.21+0.96x (n=40)]. Method comparison of the IMMULITE 2000(XPi) aCCP test with aCCP on Immunoscan RA ELISA (n=112), Immunocap 250 (n=105) and the Modular system (n=289) resulted in a concordance of 90.2%, 93.3% and 94.8%, respectively. Correlation of serum versus heparin samples showed a correlation of 0.12+1.08x for the Immulite 2000(XPi) test.

The aCCP assay on the IMMULITE 2000(XPi) has good performance characteristics and shows high level of concordance with the aCCP test on Immunoscan RA ELISA test, Immunocap 250 and the Modular systems.

Genetic studies of rheumatoid arthritis

Rheumatoid arthritis (RA) is a common autoimmune disease that results in significant morbidity. As with other complex disorders, genome-wide association studies (GWASs) have greatly contributed to the current understanding of RA etiology. In this review, we describe the genetic configuration of RA as revealed primarily through GWASs and their meta-analyses. In addition, we discuss the pathologic mechanisms of RA as suggested by the findings of genetic and functional studies of individual RA-associated genes, including HLA-DRB1, PADI4, PTPN22, CCR6 and FCRL3, and the potential use of genetic information for RA treatment in clinical practice.

Epigenetic roots of immunologic disease and new methods for examining chromatin regulatory pathways

The ability to accurately quantitate and experimentally examine epigenetic modifications across the human genome has exploded in the past decade. This has given rise to a wealth of new information concerning the contributions of epigenetic regulatory networks to the pathogenesis of human disease. In particular, immunological disorders have strong developmental roots in chromatin regulatory pathways. In this review, we focus on the epigenetic signatures and new discoveries revealing the epigenetic compositions of specific immunological cancers and autoimmune diseases. We also comment on the conserved epigenetic roots among diverse immunological disorders and suggest inhibition strategies that may be relevant for future treatment. Finally, we highlight emerging experimental tools with the capability to examine the mechanisms of chromatin regulatory enzymes with a high level of temporal control. The knowledge of genetic and epigenetic defects in immunological disease combined with new experimental approaches will elucidate the contribution of individual enzymes in complex epigenetic regulatory networks. This could lead to new diagnostic and therapeutic approaches for some very diverse and difficult to treat human diseases.

RADB: a database of rheumatoid arthritis-related polymorphisms

Rheumatoid arthritis (RA) is an autoimmune disease that has a complex genetic basis. Therefore, it is important to explore the genetic background of RA. The extensive recent application of polymorphic genetic markers, especially single nucleotide polymorphisms, has presented us with a large quantity of genetic data. In this study, we developed the Database of Rheumatoid Arthritis-related Polymorphisms (RADB), to integrate all the RA-related genetic polymorphisms and provide a useful resource for researchers. We manually extracted the RA-related polymorphisms from 686 published reports, including RA susceptibility loci, polymorphisms associated with particular clinical features of RA, polymorphisms associated with drug response in RA and polymorphisms associated with a higher risk of cardiovascular disease in RA. Currently, RADB V1.0 contains 3235 polymorphisms that are associated with 636 genes and refer to 68 countries. The detailed information extracted from the literature includes basic information about the articles (e.g. PubMed ID, title and abstract), population information (e.g. country, geographic area and sample size) and polymorphism information (e.g. polymorphism name, gene, genotype, odds ratio and 95% confidence interval, P-value and risk allele). Meanwhile, useful annotations, such as hyperlinks to dbSNP, GenBank, UCSC, Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway, are included. In addition, a tool for meta-analysis was developed to summarize the results of multiple studies. The database is freely available at http://www.bioapp.org/RADB.

Database URL:http://www.bioapp.org/RADB.

Osteoprotegerin CGA haplotype protection against cerebrovascular complications in anti-CCP negative patients with rheumatoid arthritis

Introduction

Rheumatoid arthritis is an inflammatory disease with high incidence of cardiovascular disease due to accelerated atherosclerosis. Osteoprotegerin (OPG) has been associated with increased risk of atherosclerotic disease in the general population. Several polymorphisms in the OPG gene with functional effects on cardiovascular disease in non-rheumatic individuals have been described. Therefore, we aimed to analyze the effect of three of these functional OPG polymorphisms on the risk of cardiovascular disease in a large and well-characterized cohort of Spanish patients with rheumatoid arthritis.

Methods

Three OPG gene variants (rs3134063, rs2073618 and rs3134069) were genotyped by TaqMan assays in 2027 Spanish patients with rheumatoid arthritis. Anti-cyclic citrullinated peptide (anti-CCP) antibody testing was positive in 997 of 1714 tested. Also, 18.3% of the whole series had experienced cardiovascular events, including 5.4% with cerebrovascular accidents. The relationship between OPG variants and cardiovascular events was assessed using Cox regression.

Results

No association between OPG gene variants and cardiovascular disease was observed in the whole group of rheumatoid arthritis patients or in anti-CCP positive patients. Nevertheless, a protective effect of CGA haplotype on the risk of cardiovascular disease in general, and specifically in the risk of cerebrovascular complications after adjusting for sex, age at disease diagnosis and traditional cardiovascular risk factors was disclosed in anti-CCP negative patients (HR = 0.54; 95%CI: 0.31–0.95; p = 0.032 and HR = 0.17; 95%CI: 0.04–0.78; p = 0.022, respectively).

Conclusion

Our results indicate a protective effect of the OPG CGA haplotype on cardiovascular risk, mainly due to a protective effect against cerebrovascular events in anti-CCP negative rheumatoid arthritis patients.

Genetic basis of rheumatoid arthritis: a current review

Rheumatoid arthritis (RA) is one of the most common autoimmune diseases. As with other complex traits, genome-wide association studies (GWASs) have tremendously enhanced our understanding of the complex etiology of RA. In this review, we describe the genetic architecture of RA as determined through GWASs and meta-analyses. In addition, we discuss the pathologic mechanism of the disease by examining the combined findings of genetic and functional studies of individual RA-associated genes, including HLA-DRB1, PADI4, PTPN22, TNFAIP3, STAT4, and CCR6. Moreover, we briefly examine the potential use of genetic data in clinical practice in RA treatment, which represents a challenge in medical genetics in the post-GWAS era.

Association of anticyclic citrullinated peptide antibodies and/or rheumatoid factor status and clinical presentation in early arthritis: results from the ESPOIR cohort

OBJECTIVE

To compare the initial clinical, biological, and radiographic findings of early arthritis by positivity for rheumatoid factor (RF) and/or anticyclic citrullinated peptide antibodies (anti-CCP), and to validate a patient profile based on this serologic information.

METHODS

The ESPOIR cohort comprises patients presenting synovitis of at least 2 joints for 6 weeks to 6 months. Patients underwent testing for IgM rheumatoid factor (IgM-RF) and anti-CCP2 antibodies and were divided into 4 groups: RF- and anti-CCP- (group 1), RF+ and anti-CCP- (group 2), RF- and anti-CCP+ (group 3), RF+ and anti-CCP+ (group 4). We compared the groups in terms of clinical, biological, and radiographic features (baseline scores and 6-month and 12-month progression).

RESULTS

Of the 813 recruited patients, 406 (50%) were in group 1, 91 (11.2%) in group 2, 34 (4.1%) in group 3, and 281 (34.6%) in group 4. Mean baseline erythrocyte sedimentation rate and C-reactive protein were higher for anti-CCP+ groups (groups 3 and 4) than for other groups (p < 0.001), and van der Heijde-modified Sharp score for radiographs was higher for group 4 than for other groups (p < 0.001). Clinical presentation was not consistently associated with serologic profile. Radiographic progression at 1 year was higher for anti-CCP+ groups than other groups (p < 0.001).

CONCLUSION

The phenotype of patients with early arthritis with or without anti-CCP and/or RF positivity did not correspond to a particular clinical presentation. However, baseline acute-phase reactants and short-term radiographic progression were high in patients with anti-CCP positivity, which may be associated with the inflammatory process and progressive disease in patients with early arthritis.

HLA-DR/DQ Genotypes in Kurd Patients with Rheumatoid Arthritis: Relation to Disease Activity

BACKGROUND

Specific alleles present at the HLA-DR/DQ loci seem to be associated with disease activity of rheumatoid arthritis.

AIM

In the present study, our aim was to investigate the distribution of HLA-DR/DQ alleles among Kurd patients with rheumatoid arthritis and to ascertain their relationship with disease activity.

MATERIALS AND METHODS

Sixty five patients with rheumatoid arthritis (RA) and 65 apparently healthy subjects participated in the study. Diagnosis and disease activity were confirmed. Blood analyses, including those of laboratory markers of disease activity, were done. The 28 joint disease activity score (DAS-28) was calculated. HLA-DR/DQ typing was performed by polymerase chain reaction (PCR).The association between HLA-DR/DQ genotypes and disease activity was determined.

RESULTS

The most frequent alleles which were identified in RA patients were HLA-DRBI*01(23.1%) and HLA-DQBI*6(34.6%), whereas in healthy subjects, they were HLA-DRBI*11(17.7%) and HLA-DQBI*03(35.4%). Patients with active disease had high frequencies of HLA-DQBI*6 (40.0%) as compared to those with moderate disease activity (16.7%); OR=3.33. Patients with severe RA had increased frequencies of HLA-DQBI*6 (56.3%) as compared to those with mild RA (10.0%); OR = 11.57. Patients with positive rheumatoid factor (RF) and positive Anti-citrullinated peptide antibody (Anti-CCP), also had high frequencies of HLA-DQBI*06 (38.4% and 39.4%) as compared to frequencies of 11.1% and 15.4% which were seen in patients with negative rheumatoid factor and negative anti-CCP (OR= 4.98 and3.10) respectively.

CONCLUSION

HLA-DQBI*06 was found to be more common in Kurd patients and it was significantly associated with disease activity; this may indicate a high risk for developing a more progressive type of the disease.

Association of cross-reactive antibodies targeting peptidyl-arginine deiminase 3 and 4 with rheumatoid arthritis-associated interstitial lung disease

Background

A subset of rheumatoid arthritis (RA) patients have detectable antibodies directed against the peptidyl-arginine deiminase (PAD) enzyme isoforms 3 and 4. Anti-PAD3/4 cross-reactive antibodies (anti-PAD3/4XR) have been shown to lower the calcium threshold required for PAD4 activation, an effect potentially relevant to the pathogenesis of RA-associated interstitial lung disease (ILD).

Methods

RA patients underwent multi-detector computed tomography (MDCT) of the chest with interpretation by a pulmonary radiologist for ILD features. A semi-quantitative ILD Score (range 0–32) was calculated. Concurrent serum samples were assessed for antibodies against PAD by immunoprecipitation with radiolabeled PAD3 and PAD4.

Results

Among the 176 RA patients studied, any ILD was observed in 58 (33%) and anti-PAD3/4XR was detected in 19 (11%). The frequency of any ILD among those with anti-PAD3/4XR was 68% vs. 29% among those with no anti-PAD (crude OR = 5.39; p = 0.002) and vs. 27% among those with anti-PAD4 that was not cross-reactive with PAD3 (crude OR = 5.74; p = 0.001). Both associations were stronger after adjustment for relevant confounders (adjusted ORs = 7.22 and 6.61, respectively; both p-values<0.01). Among ever smokers with anti-PAD3/4XR, the adjusted frequency of any ILD was 93% vs. 17% for never smokers without the antibody (adjusted OR = 61.4; p = 0.001, p-value for the interaction of smoking with anti-PAD3/4XR<0.05).

Conclusions

The prevalence and extent of ILD was markedly higher among RA patients with anti-PAD3/4 cross-reactive antibodies, even after accounting for relevant confounders, particularly among ever smokers. These findings may suggest etiopathologic mechanisms of RA-ILD, and their clinical utility for predicting ILD warrants additional study.

Assessment of peripheral neuropathy in patients with rheumatoid arthritis who complain of neurologic symptoms

OBJECTIVE

To assess the prevalence of peripheral neuropathy in patients with rheumatoid arthritis (RA) having neuropathic symptoms, and to investigate the relationship between electrophysiological findings of peripheral neuropathy and clinical findings of RA.

METHODS

Patients with a clinical diagnosis of RA and who had tingling or burning sensation in any extremity were electrophysiologically examined for evidence of peripheral neuropathy. Study parameters, including age, gender, laboratory parameters, duration of RA, and medication, were recorded. The symptoms and signs of neuropathy were quantified with the neuropathy symptom score, and the functional statuses of these patients were assessed.

RESULTS

Out of a total of 30 RA patients, 10 (33%) had peripheral neuropathy: 2 had bilateral carpal tunnel syndrome (CTS), 5 had unilateral CTS, 1 had sensory polyneuropathy, and 2 had motor-sensory polyneuropathy. The mean ages of the patients with and without peripheral neuropathy were 69.4 and 56.5 years, respectively (p<0.05). A significant relationship was found between peripheral neuropathy and anti-cyclic citrullinated peptide (anti-CCP) antibody. However, no relationship was found between peripheral neuropathy and the type of medication, RA duration, the patients' functional status, neuropathic symptoms, erythrocyte sedimentation rate, and C-reactive protein values.

CONCLUSION

Neuropathic symptoms are common in RA patients, and it is difficult to distinguish peripheral neuropathy symptoms from those of arthritis. Patients with RA, particularly elderly patients and anti-CCP antibody positive patients who complain of neuropathic symptoms should undergo electrophysiological examination.

Gene-environmental interaction between smoking and shared epitope on the development of anti-cyclic citrullinated peptide antibodies in rheumatoid arthritis: a meta-analysis

OBJECTIVE

The aim of this study was to determine the gene-environment interactions of smoking and shared epitope (SE) both separately and combined on anti-cyclic citrullinated peptide (CCP) antibodies in patients with rheumatoid arthritis (RA).

METHODS

The literature was searched using the MEDLINE, EMBASE and Cochrane databases. A meta-analysis on the associations between tobacco exposure (TE) and/or SE and the development of anti-CCP antibodies in patients with RA was performed.

RESULTS

Eight comparison studies with 5317 RA patients were considered in this meta-analysis. The odds ratio (OR) for positive anti-CCP antibodies in TE+/SE- patients with RA was increased compared with TE-/SE- patients (OR = 1.373, 95% CI = 1.111-1.698, P = 0.003). The ORs for positive anti-CCP antibodies in TE-/SE+ patients and TE+/SE+ patients with RA were also increased compared with TE-/SE- patients (OR = 2.678, 95% CI = 2.031-3.532, P < 1.0 × 1(0-9) in TE-/SE+; OR = 4.233, 95% CI = 2.458-7.291, P = 1.9 × 10(-8) in TE+/SE+). Stratification by ethnicity indicated the same pattern as that shown in the overall group. The OR for positive anti-CCP antibodies in TE+/SE+ patients with RA was much higher than in TE-/SE- patients in Europeans and Asians (OR = 3.879, 95% CI = 2.203-6.830, P = 2.6 × 10(-7); OR = 10.504, 95% CI = 3.182-34.67, P = 1.1 × 10(-4)).

CONCLUSIONS

This meta-analysis suggests a gene-environmental interaction between smoking and SE for the development of anti-CCP antibodies.

The influence of polygenic risk scores on heritability of anti-CCP level in RA

The objective of this study was to study genetic factors that influence quantitative anticyclic citrullinated peptide (anti-CCP) antibody levels in RA patients. We carried out a genome-wide association study (GWAS) meta-analysis using 1975 anti-CCP+ RA patients from three large cohorts, the Brigham Rheumatoid Arthritis Sequential Study (BRASS), North American Rheumatoid Arthritis Consortium (NARAC) and the Epidemiological Investigation of RA (EIRA). We also carried out a genome-wide complex trait analysis (GCTA) to estimate the heritability of anti-CCP levels. GWAS-meta-analysis showed that anti-CCP levels were most strongly associated with the human leukocyte antigen (HLA) region with a P-value of 2 × 10(-11) for rs1980493. There were 112 SNPs in this region that exceeded the genome-wide significance threshold of 5 × 10(-8), and all were in linkage disequilibrium (LD) with the HLA- DRB1*03 allele with LD r(2) in the range of 0.25-0.88. Suggestive novel associations outside of the HLA region were also observed for rs8063248 (near the GP2 gene) with a P-value of 3 × 10(-7). None of the known RA risk alleles (∼52 loci) were associated with anti-CCP level. Heritability analysis estimated that 44% of anti-CCP variation was attributable to genetic factors captured by GWAS variants. In summary, anti-CCP level is a heritable trait, and HLA-DR3 and GP2 are associated with lower anti-CCP levels.

PADI4 haplotypes in association with RA Mexican patients, a new prospect for antigen modulation

Peptidyl arginine deiminase IV (PAD 4) is the responsible enzyme for a posttranslational modification called citrullination, originating the antigenic determinant recognized by anti-cyclic citrullinated peptide antibodies (ACPA). Four SNPs (single nucleotide polymorphisms) have been described in PADI4 gene to form a susceptibility haplotype for rheumatoid arthritis (RA); nevertheless, results in association studies appear contradictory in different populations. The aim of the study was to analyze if the presence of three SNPs in PADI4 gene susceptibility haplotype (GTG) is associated with ACPA positivity in patients with RA. This was a cross-sectional study that included 86 RA patients and 98 healthy controls. Polymorphisms PADI4_89, PADI4_90, and PADI4_92 in the PADI4 gene were genotyped. The susceptibility haplotype (GTG) was more frequent in RA patients; interestingly, we found a new haplotype associated with RA with a higher frequency (GTC). There were no associations between polymorphisms and high scores in Spanish HAQ-DI and DAS-28, but we did find an association between RARBIS index and PADI4_89, PADI4_90 polymorphisms. We could not confirm an association between susceptibility haplotype presence and ACPA positivity. Further evidence about proteomic expression of this gene will determine its participation in antigenic generation and autoimmunity.

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

Rheumatoid arthritis (RA) is strongly associated with the human leukocyte antigen (HLA)-DRB1 locus that possesses the shared susceptibility epitope (SE) and the citrullination of self-antigens. We show how citrullinated aggrecan and vimentin epitopes bind to HLA-DRB1*04:01/04. Citrulline was accommodated within the electropositive P4 pocket of HLA-DRB1*04:01/04, whereas the electronegative P4 pocket of the RA-resistant HLA-DRB1*04:02 allomorph interacted with arginine or citrulline-containing epitopes. Peptide elution studies revealed P4 arginine-containing peptides from HLA-DRB1*04:02, but not from HLA-DRB1*04:01/04. Citrullination altered protease susceptibility of vimentin, thereby generating self-epitopes that are presented to T cells in HLA-DRB1*04:01(+) individuals. Using HLA-II tetramers, we observed citrullinated vimentin- and aggrecan-specific CD4(+) T cells in the peripheral blood of HLA-DRB1*04:01(+) RA-affected and healthy individuals. In RA patients, autoreactive T cell numbers correlated with disease activity and were deficient in regulatory T cells relative to healthy individuals. These findings reshape our understanding of the association between citrullination, the HLA-DRB1 locus, and T cell autoreactivity in RA.

Influence of periodontal disease, Porphyromonas gingivalis and cigarette smoking on systemic anti-citrullinated peptide antibody titres

BACKGROUND

Anti-citrullinated protein antibody (ACPA) responses may precede clinical onset of rheumatoid arthritis. Porphyromonas gingivalis peptidylarginine deiminase can citrullinate proteins possibly inducing autoimmunity in susceptible individuals.

AIM

To determine whether periodontitis, carriage of P. gingivalis, smoking and periodontal therapy influence ACPA titres.

METHODS

Serum and plaque samples were collected from 39 periodontitis patients before and after non-surgical periodontal treatment, and from 36 healthy subjects. Carriage of P. gingivalis was determined by PCR of plaque DNA. ACPA was determined by anti-cyclic citrullinated peptide (CCP) enzyme-linked immunosorbent assay (ELISA). Anti-P. gingivalis titres were determined by ELISA.

RESULTS

Untreated periodontitis patients had higher anti-CCP antibody titres than healthy controls [three patients (8%) greater than manufacturer suggested assay diagnostic threshold (5 Assay Units/AU) versus none (0%); mean ± SEM: 1.37 ± 0.23 versus 0.40 ± 0.10 AU, p < 0.0001]. Periodontitis patients who smoked demonstrated lower anti-P. gingivalis (15956 ± 4385 versus 2512 ± 1290 Units/ml, p < 0.05), but similar anti-CCP than non-smoking periodontitis patients (smokers: 1.31 ± 0.35; non-smokers: 1.41 ± 0.32 AU). Healthy smokers demonstrated elevated anti-CCP titres (0.75 ± 0.19 AU), at levels between healthy non-smokers (0.15 ± 0.05 AU) and non-smoker periodontitis patients. Six months after periodontal treatment, there were significant reductions in anti-CCP (non-smokers p < 0.05) and anti-P. gingivalis (all participants p < 0.01).

CONCLUSION

In subjects with periodontitis, P. gingivalis infection may be responsible for inducing autoimmune responses that characterize rheumatoid arthritis.

Anti-citrullinated glucose-6-phosphate isomerase peptide antibodies in patients with rheumatoid arthritis are associated with HLA-DRB1 shared epitope alleles and disease activity

To identify and characterize anti-citrullinated glucose-6-phosphate isomerase (GPI) peptide antibodies in patients with rheumatoid arthritis (RA). Nine GPI arginine-bearing peptides in human GPI protein were selected and cyclic citrullinated GPI peptides (CCG-1-9) were constructed. Samples were obtained from RA (n = 208), systemic lupus erythematosus (SLE) (n = 101), Sjögren's syndrome (SS; n = 101) and healthy controls (n = 174). Antibodies against CCG-1-9 were measured, and anti-citrullinated α-enolase-1 (CEP-1), -cyclic citrullinated peptides (CCP) and -GPI proteins antibodies were also examined. Patients with RA were genotyped for HLA-DRB1. The numbers of shared epitope (SE) alleles were counted and compared with those of the autoantibodies. Rabbit GPI was citrullinated with rabbit peptidylarginine deiminase and immunoblot analysis of RA sera performed. The levels of autoantibodies were compared before and after treatment with TNF antagonists in 58 RA patients. Anti-CCG-2, -4 and -7 antibodies were detected in 25·5, 33·2 and 37·0% patients with RA, respectively, and these antibodies were very specific for RA (specificity, 98·1-99·7%). Altogether, 44·2, 86·1 and 13·9% of RA sera were positive for anti-CEP-1, -CCP and -GPI protein antibodies, respectively. Anti-CCG-2, -4 and -7 antibodies were correlated with anti-CCP and anti-CEP-1 antibodies and with the presence of HLA-DRB1 SE alleles. Citrullinated GPI protein was detected using RA sera. Treatment with tumour necrosis factor antagonists reduced significantly the levels of anti-CCG-2 and -7 but not of anti-CEP-1 antibodies. This is the first report documenting the presence of anti-CCG antibodies in RA. Anti-CCG-2 and -7 antibodies could be considered as markers for the diagnosis of RA and its disease activity.

The rheumatoid arthritis synovial fluid citrullinome reveals novel citrullinated epitopes in apolipoprotein E, myeloid nuclear differentiation antigen, and β-actin

OBJECTIVE

To generate a catalog of citrullinated proteins that are present in the synovia of patients with rheumatoid arthritis (RA) and to elucidate their relevance for the anti-citrullinated protein antibody response in RA.

METHODS

Polypeptides isolated from the synovial fluid of patients with RA were identified by mass spectrometry. Three proteins (apolipoprotein E [Apo E], myeloid nuclear differentiation antigen [MNDA], and β-actin) were studied in more detail, using immunoprecipitation and Western blotting. The presence of autoantibodies to synthetic peptides derived from these proteins in sera from patients with RA, sera from patients with other diseases, and sera from healthy control subjects was studied by enzyme-linked immunosorbent assay (ELISA).

RESULTS

RA synovial fluid samples displayed several distinct patterns of citrullinated proteins. Using mass spectrometry, (fragments of) 192 proteins were identified, including 53 citrullinated proteins, some of which contained multiple citrullinated residues. In addition to previously reported citrullinated proteins in RA synovia (e.g., vimentin and fibrinogen), a series of novel citrullinated proteins, including Apo E, MNDA, β-actin, and cyclophilin A, was identified. Immunoprecipitation experiments confirmed the citrullination of Apo E and MNDA. ELISAs demonstrated the presence of autoreactive citrullinated epitopes in Apo E, MNDA, and β-actin.

CONCLUSION

Synovial fluid samples from the inflamed joints of patients with RA contain many citrullinated proteins. Citrullinated Apo E, MNDA, and β-actin are novel antigens identified in RA synovial fluid, and only a limited number of their citrullinated epitopes are targeted by the immune system in RA.

Dendritic cells and the promise of antigen-specific therapy in rheumatoid arthritis

Rheumatoid arthritis (RA) is a systemic inflammatory disease resulting from an autoimmune response to self-antigens, leading to inflammation of synovial tissue of joints and subsequent cartilage and bone erosion. Current disease-modifying anti-rheumatic drugs and biologic inhibitors of TNF, IL-6, T cells and B cells block inflammation nonspecifically, which may lead to adverse effects, including infection. They do not generally induce long-term drug-free remission or restoration of immune tolerance to self-antigens, and lifelong treatment is usual. The development of antigen-specific strategies in RA has so far been limited by insufficient knowledge of autoantigens, of the autoimmune pathogenesis of RA and of the mechanisms of immune tolerance in man. Effective tolerance-inducing antigen-specific immunotherapeutic strategies hold promise of greater specificity, of lower toxicity and of a longer-term solution for controlling or even preventing RA. This paper reviews current understanding of autoantigens and their relationship to immunopathogenesis of RA, and emerging therapeutics that aim to leverage normal tolerance mechanisms for implementation of antigen-specific therapy in RA.

Association of anti-citrullinated vimentin and anti-citrullinated α-enolase antibodies with subsets of rheumatoid arthritis

OBJECTIVE

To determine whether the anti-citrullinated vimentin peptide 60-75 (anti-Cit-vimentin) and the immunodominant anti-citrullinated α-enolase peptide 1 (anti-CEP-1) antibodies are associated with subsets of patients with rheumatoid arthritis (RA) independently of the associations between anti-cyclic citrullinated peptide (anti-CCP) antibodies and clinical features of RA.

METHODS

The 3 antibody types were quantified by enzyme-linked immunosorbent assay (ELISA) in serum samples from 521 patients with RA and 173 healthy controls of Spanish ancestry. Genotypes for HLA-DRB1 alleles and rs2476601 in PTPN22 were available for these patients and controls plus an additional 106 healthy controls. A combined analysis of the 3 antibodies was conducted using stratified contingency tables and logistic regression models.

RESULTS

A differential, particularly strong, and independent association was observed between the presence of anti-Cit-vimentin antibodies and the presence of shared epitope (SE) alleles, specifically in patients carrying 2 SE alleles, and between the presence of anti- Cit-vimentin antibodies and the prevalence of joint erosion. Associations were observed between anti-CEP-1 positivity and the presence of HLA-DRB1 and PTPN22 risk alleles and their additive interaction. These associations were not accounted for by the anti-CCP status.

CONCLUSION

Our results indicate that the 2 antibodies against citrullinated peptides analyzed in this study add specific information beyond that obtained with the anti-CCP status. They define subgroups of patients with RA in which genetic factors have different weight and there is an observed difference in the prevalence of erosions.

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.

Consumption of water containing a high concentration of molecular hydrogen reduces oxidative stress and disease activity in patients with rheumatoid arthritis: an open-label pilot study

BACKGROUND

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by the destruction of bone and cartilage. Although its etiology is unknown, the hydroxyl radical has been suggested to be involved in the pathogenesis of RA. Recently, molecular hydrogen (H2) was demonstrated to be a selective scavenger for the hydroxyl radical. Also, the method to prepare water containing extremely high concentration of H2 has been developed. We hypothesized that H2 in the water could complement conventional therapy by reducing the oxidative stress in RA.

METHODS

Twenty patients with rheumatoid arthritis (RA) drank 530 ml of water containing 4 to 5 ppm molecular hydrogen (high H2 water) every day for 4 weeks. After a 4-week wash-out period, the patients drank the high H2 water for another 4 weeks. Urinary 8-hydroxydeoxyguanine (8-OHdG) and disease activity (DAS28, using C-reactive protein [CRP] levels) was estimated at the end of each 4-week period.

RESULTS

Drinking high H2 water seems to raise the concentration of H2 more than the H2 saturated (1.6 ppm) water in vivo. Urinary 8-OHdG was significantly reduced by 14.3% (p < 0.01) on average. DAS28 also decreased from 3.83 to 3.02 (p < 0.01) during the same period. After the wash-out period, both the urinary 8-OHdG and the mean DAS28 decreased, compared to the end of the drinking period. During the second drinking period, the mean DAS28 was reduced from 2.83 to 2.26 (p < 0.01). Urinary 8-OHdG was not further reduced but remained below the baseline value. All the 5 patients with early RA (duration < 12 months) who did not show antibodies against cyclic citrullinated peptides (ACPAs) achieved remission, and 4 of them became symptom-free at the end of the study.

CONCLUSIONS

The results suggest that the hydroxyl radical scavenger H2 effectively reduces oxidative stress in patients with this condition. The symptoms of RA were significantly improved with high H2 water.

Genetics of rheumatoid arthritis: an impressionist perspective

Rheumatoid arthritis (RA) is the most common rheumatic disease. The genetic basis of RA is supported through the identification of more than 30 susceptibility genetic variants. Each of these genes individually makes only a slight contribution to the risk of disease. Moreover, there is significant disparity in the genetic variants associated with different RA subgroups and patient ethnicities, which emphasizes the intricate nature of the disease's pathogenesis, and the complexities involved in large-scale genetic studies. This review evaluates critically the recent literature on the genetic contribution to RA and assesses the methodology used to identify these risk alleles.

Rheumatoid arthritis. Evidence for a genetic component to disease severity in RA

Rheumatoid arthritis (RA) is partly heritable; genetic and serological markers are known to confer risk of developing pathology. But given clinical heterogeneity in RA, can we predict who will develop severe disease? Substantial heritability of erosive progression rates has now been identified, but better prognostic biomarkers remain wanting.

T-cell autoreactivity to citrullinated autoantigenic peptides in rheumatoid arthritis patients carrying HLA-DRB1 shared epitope alleles

Introduction

Anti-citrullinated peptide antibodies are found in rheumatoid arthritis (RA) patients with HLA-DRβ chains encoding the shared epitope (SE) sequence. Citrullination increases self-antigen immunogenicity, through increased binding affinity to SE-containing HLA-DR molecules. To characterise T-cell autoreactivity towards citrullinated self-epitopes, we profiled responses of SE⁺ healthy controls and RA patients to citrullinated and unmodified epitopes of four autoantigens.

Methods

We compared T-cell proliferative and cytokine responses to citrullinated and native type II collagen 1,237 to 1,249, vimentin 66 to 78, aggrecan 84 to 103 and fibrinogen 79 to 91 in six SE⁺ healthy controls and in 21 RA patients with varying disease duration. Cytokine-producing cells were stained after incubation with peptide in the presence of Brefeldin-A.

Results

Although proliferative responses were low, IL-6, IL-17 and TNF were secreted by CD4⁺ T cells of SE⁺ RA patients and healthy controls, as well as IFNγ and IL-10 secreted by RA patients, in response to citrullinated peptides. Of the epitopes tested, citrullinated aggrecan was most immunogenic. Patients with early RA were more likely to produce IL-6 in response to no epitope or to citrullinated aggrecan, while patients with longstanding RA were more likely to produce IL-6 to more than one epitope. Cytokine-producing CD4⁺ T cells included the CD45RO⁺ and CD45RO^- and the CD28⁺ and CD28^- subsets in RA patients.

Conclusion

Proinflammatory cytokines were produced by CD4⁺ T cells in SE⁺ individuals in response to citrullinated self-epitopes, of which citrullinated aggrecan was most immunogenic. Our data suggest that the T-cell response to citrullinated self-epitopes matures and diversifies with development of RA.

Periodontitis, Porphyromonas, and the pathogenesis of rheumatoid arthritis

Epidemiological data indicate a link between rheumatoid arthritis (RA) and periodontal disease (PD). In vitro and in vivo studies have sought to dissect potential mechanisms by which PD may contribute to initiation and progression of RA. However, these are both multifactorial, chronic diseases, and their complex etiologies and pathogenesis themselves remain incompletely understood. Could there really be an etiological link or does this simply represent a statistical coincidence muddied by common risk factors? This review seeks to provide background on these two diseases in the context of recent discoveries suggesting that their pathogenesis may be related. In particular, the process of citrullination, a post-translational protein modification, has been highlighted as a process common to both diseases. The evidence for a relationship between the diseases is explored and its potential mechanisms discussed.

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.

Anti-citrullinated fibronectin antibodies in rheumatoid arthritis are associated with human leukocyte antigen-DRB1 shared epitope alleles

Introduction

Fibronectin is one of the most abundant proteins present in the inflamed joint. Here, we characterized the citrullination of fibronectin in the joints of rheumatoid arthritis (RA) patients and studied the prevalence, epitope specificity and human leukocyte antigen (HLA) association of autoantibodies against citrullinated fibronectin in RA.

Methods

Citrullinated residues in fibronectin isolated from RA patient synovial fluid were identified by mass spectrometry. The corresponding citrullinated and non-citrullinated peptides were synthesized and used to analyze the presence of autoantibodies to these peptides in RA sera and sera from other diseases and healthy controls by ELISA. The data were compared with risk factors like shared epitope HLA alleles and smoking, and with clinical features.

Results

Five citrullinated residues were identified in fibronectin from RA synovial fluid. RA sera reacted in a citrulline-dependent manner with two out of four citrullinated fibronectin peptides, one of which contains two adjacent citrulline residues, in contrast to non-RA sera, which were not reactive. The most frequently recognized peptide (FN-Cit_1035,1036, LTVGLTXXGQPRQY, in which × represents citrulline) was primarily targeted by anti-CCP (cyclic citrullinated peptide) 2-positive RA patients. Anti-FN-Cit_1035,1036 autoantibodies were detected in 50% of established anti-CCP2-positive RA patients and in 45% of such patients from a early arthritis clinic. These antibodies appeared to be predominantly of the immunoglobulin G (IgG) isotype and to be associated with HLA shared epitope alleles (odds ratio = 2.11).

Conclusions

Fibronectin in the inflamed synovia of RA patients can be citrullinated at least at five positions. Together with the flanking amino acids, three of these citrullinated residues comprise two epitopes recognized by RA autoantibodies. Anti-citrullinated fibronectin peptide antibodies are associated with HLA shared epitope alleles.

Production of autoantibodies against citrullinated antigens/peptides by human B cells

Autoantibodies against citrullinated protein Ags (ACPA) are associated with the development of rheumatoid arthritis (RA). This immune response against citrullinated protein Ags, which is thought to be facilitated by certain MHC HLA-DR alleles, is highly specific for this disease and has been speculated to be involved in the pathogenesis. We have previously studied cultures of B cells for the production of Abs against HLA Ags. The aim of the current study was to examine the role of B cells in the production of ACPA in patients with RA. Peripheral blood B cells from RA patients and healthy people were cultured with EL4-B5, a murine cell line expressing human CD40L, and with T cell factors to stimulate the in vitro production of Abs by B cells isolated from peripheral blood. ACPA were produced by cultured B cells from RA patients, as determined by reactivity to cyclic citrullinated peptide (CCP). The results showed that 22% of the healthy persons tested also had B cells that could produce ACPA. Patients with HLA-DR alleles carrying the RA-associated shared epitope appeared to have more B cells with autoimmune potential for CCP than those without such HLA alleles (odds ratio 8.1, p = 0.001). In healthy individuals, anti-CCP-producing B cells were also observed more frequently if the RA-associated MHC genes were present (odds ratio 8.0, p = 0.01). Analysis of B cells in cultures may shed light on the interaction of genetic and environmental factors in the development of RA.