Anti-citrullinated protein/peptide antibodies (ACPA) in rheumatoid arthritis: specificity and relation with rheumatoid factor

Are the cut-offs of the rheumatoid factor and anti-cyclic citrullinated peptide antibody different to distinguish rheumatoid arthritis from their primary differential diagnoses?

OBJECTIVE

Rheumatoid factor (RF) and anti-cyclic citrullinated peptide antibody (anti-CCP) are commonly used for diagnosis of rheumatoid arthritis (RA), although other rheumatic diseases with arthritis can test positive. This study aimed to determine the cutoff values for RF and anti-CCP with the best diagnostic performance in a sample of patients with RA, compared with other rheumatic diseases.

METHODS

This was a descriptive, prospective study. EUROINMMUN enzyme-linked immunosorbent assays for RF isotypes immunoglobulin (Ig) A (IgA), IgG and IgM and third-generation assay IgG for anti-CCP were used in serum samples of patients with RA, other rheumatic diseases and healthy subjects. The cutoff with the best diagnostic performance was determined by the Youden Index and receiver operating characteristic analysis Results: Three hundred and thirty-two serum samples were analysed. The cutoffs proposed in our population were for RF in RA patients versus other rheumatic diseases, and healthy subjects IgM 135 IU/mL, for each disease, compared with RA, were psoriatic arthritis (Psa) IgA 47.2 IU/mL, clinically suspicious arthralgia (CSA) IgA 39.5 IU/mL, primary Sjögren's syndrome (pSS) IgM 180.6 IU/mL, systemic lupus erythematosus (SLE) IgA 42.6 IU/mL, primary fibromyalgia (pFM) IgM 68.6 IU/mL, osteoarthritis (OA) IgM 48 IU/mL, gout IgM 117 IU/mL and healthy IgM 16.3 IU/mL. For anti-CCP, in RA patients versus other rheumatic diseases, and healthy subjects 6.95 IU/mL, for each disease, compared with RA, were Psa 6.8 IU/mL, CSA 9.95 IU/mL, pSS 20.7 IU/mL, SLE 6 IU /mL, pFM 11.8 IU/mL, OA 11.9 IU/mL, gout 5 IU/mL and healthy 5 IU/mL.

CONCLUSION

Irrespective of the manufacturer's suggested cutoff, the RA versus differential diagnosis cutoffs must be considered.

Childhood-onset rheumatoid arthritis at a tertiary hospital in Senegal, West Africa

BACKGROUND

Childhood-onset rheumatoid arthritis (CORA), known as rheumatoid factor (RF)-positive juvenile idiopathic arthritis is a type of juvenile idiopathic arthritis that shares the same genetic factors and clinical features as adult-onset rheumatoid arthritis. In Africa, CORA hasn't been the subject of a specific study.

OBJECTIVES

The aim of this study is to describe the clinical features, disease activity, functional disability, and treatment of CORA at diagnosis in Senegal and compare the findings to other CORA populations.

METHODS

We conducted a mixed cohort study by reviewing the medical records of patients diagnosed with CORA with an age of symptom onset < 18 years according to the 2019 PRINTO provisional criteria for RF-positive JIA from January 2020 to December 2022 at rheumatology department of Aristide Le Dantec Hospital in Dakar, Senegal. We collected demographic, clinical, paraclinical and therapeutic data. Disease activity score was assessed by DAS28-ESR and DAS28-CRP. Functional disability was assessed using Health Assessment Questionnaire (HAQ) or Childhood HAQ.

RESULTS

A total of 21 patients were included. Eighteen (85.7%) were Females. The mean age at symptom onset was 13.0 ± 3.0 years, and at diagnosis was 16.4 ± 4.2 years. Morning stiffness, joint swelling, and joint deformities were found in 20, 18 and 13 patients respectively. Four patients had a family history of rheumatoid arthritis. Five patients had extra-articular involvement such as rheumatoid nodules. Two patients had interstitial lung disease. The biological inflammatory syndrome was found in 90% of cases. 16 of 21 (76.2%) patients had positive RF, and 18 of 20 (90%) patients had positive Anti-CCP. Seven of 12 (58.3%) patients had positive anti-nuclear antibodies. The mean DAS28-ESR was 5.7 ± 1.0. Fifteen (71.4%) patients had high disease activity (DAS28-ESR > 5.1). The mean DAS28-CRP was 5.4 ± 1.1. The median HAQ was 2.12 with a mean HAQ of 1.9. Nineteen (90.5%) patients were treated with methotrexate, while 17 (81%) had a combination of methotrexate and hydroxychloroquine. Oral prednisone was used in 17 (81%) cases. Non-steroidal anti-inflammatory drugs were used in 4 cases (19%). After 6 months of treatment, mean DAS28-CRP was 2.9.

CONCLUSION

In our study, CORA mainly affects 13-year-old girls, characterised by high disease activity with joint deformity and significant functional impairment. Treatment is mainly based on methotrexate, prednisone and hydroxychloroquine. Further studies are needed to determine the exact clinical phenotype of this disease.

Autoantibodies in psoriatic disease

Psoriasis is an inflammatory skin disease affecting over 8 million people in the US and Canada. Approximately, a quarter of psoriasis patients have an inflammatory arthritis termed psoriatic arthritis (PsA). Psoriatic disease encompassing both psoriasis and PsA is regarded as an immune-mediated inflammatory disease, exhibiting both autoimmune and autoinflammatory features. A review of the current literature on the presence and clinical significance of autoantibodies found in psoriatic disease are presented. The frequency of several autoantibodies in psoriasis and PsA patients as well as their clinical significance regarding disease diagnosis, disease activity and treatment response are reviewed. Additionally, the basic principles of antibody assays are presented, and the methods used for each study are analyzed. Despite historically described as a rheumatoid factor negative (seronegative) disease, an array of autoantibodies has been identified in patients with psoriatic disease. This points to an autoimmune component potentially playing a role in psoriatic disease; however, additional evidence is needed to determine the clinical utility of these autoantibodies.

Cytotoxic CD8+ T cells target citrullinated antigens in rheumatoid arthritis

The immune mechanisms that mediate synovitis and joint destruction in rheumatoid arthritis (RA) remain poorly defined. Although increased levels of CD8⁺ T cells have been described in RA, their function in pathogenesis remains unclear. Here we perform single cell transcriptome and T cell receptor (TCR) sequencing of CD8⁺ T cells derived from anti-citrullinated protein antibodies (ACPA)+ RA blood. We identify GZMB⁺CD8⁺ subpopulations containing large clonal lineage expansions that express cytotoxic and tissue homing transcriptional programs, while a GZMK⁺CD8⁺ memory subpopulation comprises smaller clonal expansions that express effector T cell transcriptional programs. We demonstrate RA citrullinated autoantigens presented by MHC class I activate RA blood-derived GZMB⁺CD8⁺ T cells to expand, express cytotoxic mediators, and mediate killing of target cells. We also demonstrate that these clonally expanded GZMB⁺CD8⁺ cells are present in RA synovium. These findings suggest that cytotoxic CD8⁺ T cells targeting citrullinated antigens contribute to synovitis and joint tissue destruction in ACPA+ RA.

Platelet and Red Blood Cell Volume Indices in Patients with Rheumatoid Arthritis: A Systematic Review and Meta-Analysis

Alterations in the volume of platelets (mean platelet volume, MPV; platelet distribution width, PDW) and erythrocytes (red blood cell distribution width, RDW) have been reported in rheumatoid arthritis (RA) and might serve as diagnostic biomarkers. We conducted a systematic review and meta-analysis of the MPV, PDW, and RDW in RA patients and healthy controls. Relevant articles were searched in PubMed, Web of Science, Scopus, and Google Scholar from inception to June 2022. Risk of bias was assessed using the Joanna Briggs Institute Critical Appraisal Checklist and certainty of evidence was assessed using GRADE. In 23 studies (2194 RA patients and 1565 healthy controls), the RDW, but not MPV or PDW, was significantly higher in RA patients (standardized mean difference, SMD = 0.96, 95% CI 0.78 to 1.15, p < 0.001; moderate certainty of evidence). The substantial heterogeneity observed (I2 = 75.1%, p < 0.001) was virtually removed in a subgroup of prospective studies. In sensitivity analysis, the magnitude of the effect size was not substantially modified by sequentially removing individual studies. There was no significant publication bias. No significant associations were observed between the effect size and pre-defined study or patient characteristics. The results of our study suggest that the RDW might be a useful biomarker for the diagnosis of RA, and complement the clinical information provided by other patient characteristics and laboratory parameters (PROSPERO registration number: CRD42022349432).

An assessment of serum interleukin - 39 in rheumatoid arthritis patients from Iraq

Introduction and Aim: The pro-inflammatory cytokine IL-39, a member of the IL-12 family plays a key role in the inflammatory response by modulating immune cell activity and inflammation. A literature search shows no study undertaken for the effect of IL-39's on arthritis so far. Hence, the purpose of this study was to investigate the role of IL-39 in rheumatoid arthritis. Materials and Methods: This study involved 80 patients with rheumatoid arthritis registered at the Rheumatology Clinic at Baghdad teaching hospital. The patients were divided into three groups based on treatments received. Group 1 included patients who were not on any treatment for arthritis, Group 2 with patients on hydroxychloroquine and or prednisone treatment, and Group 3 that received Enbrel® (etanercept) and HUMIRA® (adalimumab) treatment for rheumatoid arthritis. A control group was included in the study. Patients in all groups were assessed for their serum IL-39 concentration, C - reactive protein, Anti-cyclic citrullinated peptide antibody (ACCP) and ESR.  Results: The patient age and BMI were not significantly different between the groups receiving treatment for Rheumatoid arthritis. A significant increase in the interleukin 39 concentration was observed in treatment groups (G1, G2, G3) as compared to normal healthy controls regardless of whether they were positive or negative for the anti-CCP test. Conclusion: This study showed that the serum interleukin IL-39 levels significantly increased in patients diagnosed with rheumatoid arthritis thus suggesting that IL-39 could be considered as a potential inflammatory biomarker of RA.

Peptidylarginine Deiminase 2 in Host Immunity: Current Insights and Perspectives

Peptidylarginine deiminases (PADs) are a group of enzymes that catalyze post-translational modifications of proteins by converting arginine residues into citrullines. Among the five members of the PAD family, PAD2 and PAD4 are the most frequently studied because of their abundant expression in immune cells. An increasing number of studies have identified PAD2 as an essential factor in the pathogenesis of many diseases. The successes of preclinical research targeting PAD2 highlights the therapeutic potential of PAD2 inhibition, particularly in sepsis and autoimmune diseases. However, the underlying mechanisms by which PAD2 mediates host immunity remain largely unknown. In this review, we will discuss the role of PAD2 in different types of cell death signaling pathways and the related immune disorders contrasted with functions of PAD4, providing novel therapeutic strategies for PAD2-associated pathology.

Association of particulate matter with autoimmune rheumatic diseases among adults in South Korea

OBJECTIVE

The primary objective of this study was to investigate adverse effects of ambient particulate matter of various sizes on the incidence of the prevalent autoimmune rheumatic diseases (AIRDs): RA, AS and SLE.

METHODS

We investigated 230 034 participants in three metropolitan cities of South Korea from the National Health Insurance Service-National Sample Cohort (NHIS-NSC). Starting from January 2010, subjects were followed up until the first event of prevalent AIRDs, death, or December 2013. The 2008-2009 respective averages of particulate matter2.5 (<2.5 μm) and particulate mattercoarse (2.5 μm to 10 μm) were linked with participants' administrative district codes. Adjusted hazard ratios (aHRs) and 95% CIs were estimated using Cox regression analysis in one- and two-pollutant models.

RESULTS

Adjusted for age, sex, region, and household income, in the two-pollutant model, RA incidence was positively associated with the 10 μg/m³ increment of particulate matter2.5 (aHR = 1.74, 95% CI: 1.06, 2.86), but not with particulate mattercoarse (aHR = 1.27, 95% CI: 0.87, 1.85). In the one-pollutant model, the elevated incidence rate of RA was slightly attenuated (particulate matter2.5 aHR = 1.61, 95% CI: 0.99, 2.61; particulate mattercoarse aHR = 1.13, 95% CI: 0.80, 1.61), with marginal statistical significance for particulate matter2.5. The RA incidence was also higher in the 4th quartile group of particulate matter2.5 compared with the first quartile group (aHR = 1.83, 95% CI: 1.07, 3.11). Adverse effects from particulate matter were not found for AS or SLE in either the one- or two-pollutant models.

CONCLUSION

The important components of particulate matter10 associated with RA incidence were the fine fractions (particulate matter2.5); no positive association was found between particulate matter and AS or SLE.

Identification of a Novel Serological Marker in Seronegative Rheumatoid Arthritis Using the Peptide Library Approach

Rheumatoid arthritis (RA) is a systemic autoimmune disease characterized by chronic inflammation mainly affecting the joints leading to cartilage and bone destruction. The definition of seropositive or seronegative RA is based on the presence or absence of rheumatoid factor (RF) and anti-citrullinated peptide antibodies (ACPAs). Other autoantibodies have been identified in the last decade such as antibodies directed against carbamylated antigens, peptidyl-arginine deiminase type 4 and v-Raf murine sarcoma viral oncogene homologue B. In order to identify relevant autoantigens, we screened a random peptide library (RPL) with pooled IgGs obtained from 50 patients with seronegative RA. Patients’ sera were then used in an ELISA test to identify the most frequently recognized peptide among those obtained by screening the RPL. Sera from age- and sex-matched healthy subjects were used as controls. We identified a specific peptide (RA-peptide) recognized by RA patients’ sera, but not by healthy subjects or by patients with other immune-mediated diseases. The majority of sera from seronegative and seropositive RA patients (73.8% and 63.6% respectively) contained IgG antibodies directed against the RA-peptide. Interestingly, this peptide shares homology with some self-antigens, such as Protein-tyrosine kinase 2 beta, B cell scaffold protein, Liprin-alfa1 and Cytotoxic T lymphocyte protein 4. Affinity purified anti-RA-peptide antibodies were able to cross react with these autoantigens. In conclusion, we identified a peptide that is recognized by seropositive and, most importantly, by seronegative RA patients’ sera, but not by healthy subjects, conferring to this epitope a high degree of specificity. This peptide shares also homology with other autoantigens which can be recognized by autoantibodies present in seronegative RA sera. These newly identified autoantibodies, although present also in a percentage of seropositive RA patients, may be considered as novel serum biomarkers for seronegative RA, which lacks the presence of RF and/or ACPAs.

Periodontal disease in seropositive rheumatoid arthritis: scoping review of the epidemiological evidence

The link between periodontal disease (PD) and rheumatoid arthritis (RA) has been hypothesized to lie in the anti-cyclic citrullinated protein antibody (ACPA) molecules present in seropositive RA. This review aimed to discuss how RA and specifically ACPA-positive RA link to PD, and appraise the epidemiological evidence on the relationship between ACPA-positive RA and PD. Articles were searched following the PRISMA guideline across the MEDLINE, Web of Science, Scopus and Cochrane Library databases. A total of 21 articles met the inclusion criteria of reporting the epidemiological data on the different ACPA status of the subjects with RA and PD (or periodontitis) parameters. A discrepancy is noted in the epidemiological evidence on the difference in the prevalence and severity of PD between ACPA-positive and ACPA-negative RA patients. Although the link between RA and PD is mostly discussed in terms of ACPA, reports on the different manifestations of PD between the two RA subsets remains inconclusive.

Chicken-or-egg question: Which came first, extracellular vesicles or autoimmune diseases?

Extracellular vesicles (EVs) have attracted great interest as contributors to autoimmune disease (AD) pathogenesis, owing to their immunomodulatory potential; they may also play a role in triggering tolerance disruption, by delivering auto‐antigens. EVs are released by almost all cell types, and afford paracrine or distal cell communication, functioning as biological carriers of active molecules including lipids, proteins, and nucleic acids. Depending on stimuli from the external microenvironment or on their cargo, EVs can promote or suppress immune responses. ADs are triggered by inappropriate immune‐system activation against the self, but their precise etiology is still poorly understood. Accumulating evidence indicates that lifestyle and diet have a strong impact on their clinical onset and development. However, to date the mechanisms underlying AD pathogenesis are not fully clarified, and reliable markers, which would provide early prediction and disease progression monitoring, are lacking. In this connection, EVs have recently been indicated as a promising source of AD biomarkers. Although EV isolation is currently based on differential centrifugation or density‐gradient ultracentrifugation, the resulting co‐isolation of contaminants (i.e., protein aggregates), and the pooling of all EVs in one sample, limit this approach to abundantly‐expressed EVs. Flow cytometry is one of the most promising methods for detecting EVs as biomarkers, and may have diagnostic applications. Furthermore, very recent findings describe a new method for identifying and sorting EVs by flow cytometry from freshly collected body fluids, based on specific EV surface markers.

Thioredoxin Modulates Protein Arginine Deiminase 4 (PAD4)-Catalyzed Citrullination

Protein citrullination is a post-translational modification catalyzed by the protein arginine deiminases (PADs). This modification plays a crucial role in the pathophysiology of numerous autoimmune disorders including RA. Recently, there has been a growing interest in investigating physiological regulators of PAD activity to understand the primary cause of the associated disorders. Apart from calcium, it is well-documented that a reducing environment activates the PADs. Although the concentration of thioredoxin (hTRX), an oxidoreductase that maintains the cellular reducing environment, is elevated in RA patients, its contribution toward RA progression or PAD activity has not been explored. Herein, we demonstrate that hTRX activates PAD4. Kinetic characterization of PAD4 using hTRX as the reducing agent yielded parameters that are comparable to those obtained with a routinely used non-physiological reducing agent, e.g., DTT, suggesting the importance of hTRX in PAD regulation under physiological conditions. Furthermore, we show that various hTRX mutants, including redox inactive hTRX variants, are capable of activating PAD4. This indicates a mechanism that does not require oxidoreductase activity. Indeed, we observed non-covalent interactions between PAD4 and hTRX variants, and propose that these redox-independent interactions are sufficient for hTRX-mediated PAD4 activation.

Systemic treatment with resveratrol reduces the progression of experimental periodontitis and arthritis in rats

Rheumatoid arthritis and periodontitis are chronic inflammatory diseases which has been closely associated due to the nature of immune-inflammatory imbalance response. Resveratrol is a naturall product with biological proprieties that may promote immunomodulatory effects on host response. This study investigated resveratrol continuous administration effect on experimental periodontitis and arthritis progression in rats. Thirty-five rats were assigned to the following groups: 1-experimental arthritis + experimental periodontitis + placebo (RA+EP +PL) (n = 12); 2 -RA+EP+ ibuprofen (RA+PE+IB) (n = 11); 3-RA+EP+ resveratrol (RA+PE+RSV) (n = 11). After euthanasia, the specimens were processed for morphometric analysis of bone loss, and the gingival tissue surrounding the first molar was collected for quantification of inflammatory markers using a Luminex/MAGpix assay and anti-citrullinated protein antibody (ACCPA) levels were measured by ELISA assay. Serum level of rheumatoid factor (RF) was measured by ELISA assay. Paw edema was analyzed using a plethysmometer. Higher bone loss was observed in PL group, when compared to IB and RSV groups. RSV group presented higher IL-4 concentration than PL and IB groups. Resveratrol reduced RF serum levels and both IB and RSV decreased ACCPA gingival levels. Besides, paw swelling level was significantly lower in IB and RSV groups in the 21th day and only in RSV group in the 28th day. Histological analyzes showed smooth articular surface and higher width of the subchondral cortical in RSV group. Resveratrol showed modulatory effect and seems to reduce the inflammatory signs of arthritis and articular damage throughout the time.

Distinguishing rheumatoid arthritis from psoriatic arthritis

Rheumatoid arthritis (RA) and psoriatic arthritis (PsA) have key differences in clinical presentation, radiographic findings, comorbidities and pathogenesis to distinguish between these common forms of chronic inflammatory arthritis. Joint involvement is typically, but not always, asymmetric in PsA, while it is predominantly symmetric in RA. Bone erosions, without new bone growth, and cervical spine involvement are distinctive of RA, while axial spine involvement, psoriasis and nail dystrophy are distinctive of PsA. Patients with PsA typically have seronegative test findings for rheumatoid factor (RF) and cyclic citrullinated peptide (CCP) antibodies, while approximately 80% of patients with RA have positive findings for RF and CCP antibodies. Although there is overlap in the pathogenesis of PsA and RA, differences are also present that affect the efficacy of treatment. In PsA, levels of interleukin (IL)-1β, IL-6, IL-17, IL-22, IL-23, interferon-γ and tumour necrosis factor-α (TNF-α) are elevated, and in RA, levels of IL-1, IL-6, IL-22, IL-33, TNF-α, chemokine ligand 11 and chemokine C-X-C motif ligand 13 are elevated. Differences in the pathogenesis of RA and PsA translate into some variances in the specificity and efficacy of therapies.

Levetiracetam mitigates lipopolysaccharide-induced JAK2/STAT3 and TLR4/MAPK signaling pathways activation in a rat model of adjuvant- induced arthritis

Levetiracetam (LEV), a novel anti-epileptic drug that has been demonstrated with an anti-inflammatory effect, but the exact mechanisms of its action remain to be fully defined. The present study aimed to evaluate the possible effects of LEV on lipopolysaccharides (LPS)-induced Janus kinase-signal transducers and activators of transcription (JAK/STAT) as well as toll-like receptor 4 (TLR4)/ mitogen activated protein kinase (MAPK) signaling pathways activation in adjuvant induced arthritis (AIA). Rats were allocated into normal control, three arthritic control groups: Complete Freund's Adjuvant (CFA) (0.4 ml/3days/12days), LPS (100 µg/kg/day), CFA+LPS, and three treated groups: CFA+LEV, LPS+LEV and CFA+LPS+LEV. LEV was administered in a dose 50 mg/kg/day for 15 day. After 28 days, tissue samples were collected for assessment of phosphorylated JAK2, STAT3, TLR4, MAPK and cathepsin K quantitative expression in synovium. Additionally, Serum samples were used for biochemical evaluation of interleukin-6 (IL-6), interleukin-1beta (IL-1B), LPS, anti-citrullinated protein antibody (ACPA) and 8-hydroxydeoxyguanosine (8-OHdG). Histopathological and macroscopical examinations of joints were also performed to support our study. Results indicated that LEV exerted its anti-inflammatory effect through inhibiting LPS-dependent phosphorylation of JAK2/STAT3 signaling. It significantly suppressed TLR4 and MAPK expressions, thereby decreasing release of inflammatory cytokines IL-1β, IL-6.LEV exhibited a potent inhibitory effect on cathepsin K and 8-OHdG parallel to confirmatory histopathological and macroscopical findings. In conclusion, LEV has a powerful therapeutic effect on adjuvant induced arthritis in rats and its mechanisms are strongly related to inhibiting excessive activation of JAK2-STAT3 and TLR4 pathways. This may add a new approach for treatment of RA.

Performance characteristics of rheumatoid factor and anti-cyclic citrullinated peptide antibody assays may impact ACR/EULAR classification of rheumatoid arthritis

Objectives

Rheumatoid factor (RF) and anti-cyclic citrullinated protein/peptide antibodies (ACPA) are integrated in the 2010 American College of Rheumatology/European League Against Rheumatism (ACR/EULAR) classification criteria for rheumatoid arthritis (RA). The objectives of this study were to evaluate the technical and diagnostic performance of different RF and ACPA assays and to evaluate whether differences in performance impact RA classification.

Methods

Samples from 594 consecutive patients who for the first time consulted a rheumatologist (44 of whom were diagnosed with RA) and 26 extra newly diagnosed patients with RA were analysed with six different RF assays (Menarini, Thermo Fisher, Inova, Roche, Abbott, Euroimmun) and seven different ACPA assays (Menarini, Thermo Fisher, Inova, Roche, Abbott, Euro Diagnostica, Euroimmun).

Results

We found differences in analytical performance between assays. There was poor numerical agreement between the different RF and ACPA assays. For all assays, the likelihood ratio for RA increased with increasing antibody levels. The areas under the curve of receiver operating characteristic analysis of the RF (range 0.676–0.709) and ACPA assays (range 0.672–0.769) only differed between some ACPA assays. Nevertheless, using the cut-off proposed by the manufacturer, there was a large variation in sensitivity and specificity between assays (mainly for RF). Consequently, depending on the assay used, a subgroup of patients (13% for RF, 1% for ACPA and 9% for RF/ACPA) might or might not be classified as RA according to the 2010 ACR/EULAR criteria.

Conclusion

Due to poor harmonisation of RF and ACPA assays and of test result interpretation, RA classification according to 2010 ACR/EULAR criteria may vary when different assays are used.

Anti -citrullinated peptide antibodies profiling in established rheumatoid arthritis

OBJECTIVES

Anti-citrullinated protein/peptide antibodies (ACPA) represent an important tool for the diagnosis of rheumatoid arthritis (RA) and the presence of multiple ACPA specificities is highly correlated with the evolution towards RA. However, little is known about the association of single specificities with disease manifestations and response to therapy in established RA. The aim of this work is to evaluate in a retrospective study the clinico-serological association of ACPA detected using VCP1 and VCP2 (EBV-derived citrullinated peptides) and HCP1 and HCP2 (histone-H4-derived citrulinated peptides) in established RA.

METHODS

In 413 RA patients, anti-VCP1, -VCP2, -HCP1, -HCP2 were measured by ELISA. Patients were evaluated for systemic involvement, disease activity/severity, ongoing and past therapies. Data were analyzed by cluster analysis (CA) and principal component analysis (PCA).

RESULTS

Anti-VCP1 were detected in 44% of RA patients; anti-VCP2 in 52%; anti-HCP1 in 46% and anti-HCP2 in 63%. CA and PCA independently demonstrated that ACPA levels are associated with RF positivity, and lung involvement. Subdividing patients in 5 groups according to the number of anti-peptide antibodies, mean antibody level and RF positivity, as well as the frequency of lung involvement, progressively increase in parallel with the number of ACPA specificities.

CONCLUSIONS

Higher number/levels of ACPA subtypes is associated with lung involvement but not with erosive disease. Moreover, a broader ACPA repertoire may identify patients treated with biological therapy, probably affected by a more severe disease. In conclusion, ACPA typing might be relevant for a better characterization of some disease features in established RA.

Heightened autoantibody immune response to citrullinated calreticulin in bronchiectasis: Implications for rheumatoid arthritis

Calreticulin (CRT) and citrullinated (citCRT) are implicated in rheumatoid arthritis (RA) pathology. citCRT binds to RA shared epitopes (SE) on HLA-DR molecules with high affinity and triggers pro-inflammatory events in adjacent cells. The aim of the study was to detect the presence of citCRT prior to developing RA and evaluate if citCT is a target for autoantibodies in RA cohorts with and without lung disease. Antibodies were assessed by ELISA against native CRT, citCRT and general protein citrullination, in sera from 50 RA patients without lung disease, 122 bronchiectasis (BR) patients, 52 bronchiectasis patients with RA (BRRA), 87 asthma patients and 77 healthy controls (HC). Serum citCRT was detected by immunoblotting and mass spectrometry. Genomic DNA was genotyped for HLA-DRB1 alleles. Patients were assessed for DAS28, rheumatoid factor, and anti-cyclic citrullinated peptide antibodies. Extracellular citCRT was detected in BR patients sera prior to them developing RA. A citCRT SE binding peptide GEWKPR_261citQIDNPDYK was identified. Anti-CRT antibodies were observed in 18% of BR patients with or without RA. Anti-citCRT antibodies were observed in ∼35% of BR or RA patients, increasing to 58% in BRRA patients. In the RA alone patients 7/20 (35%) who were negative for RF and anti-CCP were anti-CRT antibody positive and had higher DAS28 scores than triple negative RA alone patients. Three of the four BR patients who developed RA over 18 months were anti-citCRT+ve SE^+ve. The detection of citCRT in BR and development of anti-citCRT in BR patients suggests citCRT antigens are early targets of antigenicity in these patients, especially in SE^+ve patients prior to the onset of RA.

Periodontitis increases rheumatic factor serum levels and citrullinated proteins in gingival tissues and alter cytokine balance in arthritic rats

This study investigated some immunological features by experimental periodontitis (EP) and rheumatoid arthritis (RA) disease interact in destructive processes in arthritic rats. Rats were assigned to the following groups: EP +RA; RA; EP; and Negative Control. RA was induced by immunizations with type-II collagen and a local immunization with Complete Freund's adjuvant in the paw. Periodontitis was induced by ligating the right first molars. The serum level of rheumatoid factor (RF) and anti-citrullinated protein antibody (ACCPA) were measured before the induction of EP (T1) and at 28 days after (T2) by ELISA assay. ACCPA levels were also measured in the gingival tissue at T2. The specimens were processed for morphometric analysis of bone loss, and the gingival tissue surrounding the first molar was collected for the quantification of interleukin IL-1β, IL-4, IL-6, IL-17 and TNF-α using a Luminex/MAGpix assay. Paw edema was analyzed using a plethysmometer. Periodontitis increased the RF and ACCPA levels in the serum and in the gingival tissue, respectively. Besides, the level of paw swelling was increased by EP and remained in progress until the end of the experiment, when EP was associated with RA. Greater values of IL-17 were observed only when RA was present, in spite of PE. It can be concluded that periodontitis increases rheumatic factor serum levels and citrullinated proteins level in gingival tissues and alter cytokine balance in arthritic rats; at the same time, arthritis increases periodontal destruction, confirming the bidirectional interaction between diseases.

Association of anti-peptidyl arginine deiminase antibodies with radiographic severity of rheumatoid arthritis in African Americans

Background

Evidence suggests that the presence of peptidyl arginine deiminase type 4 (PAD4) antibodies is associated with radiographic-severity rheumatoid arthritis (RA) among Caucasian patients. The presence of anti-PAD4 antibodies that were cross-reactivity against PAD3 was associated with more aggressive erosive disease (compared with the presence of anti-PAD4 antibodies without anti-PAD3 crossreactivity) in Caucasian RA patients. The objectives of this study were to determine the prevalence of serum anti-PAD4 and anti-PAD4/PAD3 cross-reactive autoantibodies in African Americans with RA and whether these antibodies associate with radiographic severity and radiographic progression.

Methods

Serum anti-PAD4 and anti-PAD4/PAD3 antibodies were measured by immunoprecipitation, and the temporal trends in titers were analyzed. We compared total radiographic scores among anti-PAD4-positive, anti-PAD4/PAD3-positive, and anti-PAD4-negative patients and used a zero-inflated negative binomial model to determine associations between radiographic severity and antibody status. Logistic regression was used to analyze radiographic progression.

Results

Of 192 African-American patients with RA, 73 % were anti-citrullinated peptide/protein antibody (ACPA)-positive, 46 out of 192 (24 %) of whom had serum anti-PAD4 antibodies. Median (interquartile range) total Sharp van der Heijde radiographic scores were 2 (1–97.5) in ACPA-positive patients and 0 (0–3) in ACPA-negative patients (P < 0.001). Of the 46 anti-PAD4-positive patients, 20 had anti-PAD4 antibodies that cross-reacted with PAD3. In patients with early RA, anti-PAD4 and anti-PAD4/PAD3 antibody titers increased over time (P = 0.006, P = 0.001, respectively). Median (interquartile range) total radiographic scores were higher for anti-PAD4-positive than for anti-PAD4-negative patients (3 (1–115) versus 2 (0–11), respectively; P = 0.005). Median (interquartile range) total radiographic score for anti-PAD4/PAD3-positive patients was 76 (3–117) (P < 0.001) versus anti-PAD4-negative patients. Only anti-PAD4/PAD3 antibodies associated with radiographic severity (incidence rate ratio = 2.81; 95 % confidence interval 1.23, 6.43).

Conclusion

This analysis suggests that autoantibodies against PAD4 and PAD3 proteins may serve as biomarkers for identifying African-American patients with RA and higher radiographic severity.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-016-1126-7) contains supplementary material, which is available to authorized users.

Sequential high-content profiling of the IgG-autoantibody repertoire reveals novel antigens in rheumatoid arthritis

Background

The aim was to identify novel diagnostic autoantibody candidates for rheumatoid arthritis (RA) by comprehensive screening for autoreactivity.

Method

We incubated 5892 recombinant proteins coupled to fluorescent beads, with patients’ sera for the detection of IgG-autoantibodies in three independent patient cohorts: A (n = 72 patients with established RA); B/B- (n = 116 patients with early RA (B) and n = 51 CCP-negative patients with early RA from B (B-)); and C (n = 184 patients with early seronegative RA), in comparison to matched healthy controls. Intersects of significantly increased autoantibodies as determined by the Mann-Whitney test were sought.

Result

Screening of 5892 antigens in RA cohorts A and B, or the seronegative cohorts B- and C revealed intersects of 23 and 13 significantly increased autoantibodies, respectively. Reactivity to three antigens was increased in all cohorts tested: N-acetylglucosamine-1-phosphate transferase, gamma subunit (GNPTG), heterogeneous nuclear ribonucleoprotein A1-like 2 (HNRNPA1), and insulin-like growth factor binding protein 2 (IGFBP2).

Conclusions

Comprehensive sequential screening for autoantibodies reveals novel candidates for diagnostic markers in both seropositive and seronegative RA and suggests new fields of research into the pathogenesis of RA.

Immunophenotyping of rheumatoid arthritis reveals a linkage between HLA-DRB1 genotype, CXCR4 expression on memory CD4(+) T cells, and disease activity

Rheumatoid arthritis (RA) is a chronic autoimmune inflammatory disease that leads to destructive arthritis. Although the HLA class II locus is the strongest genetic risk factor for rheumatoid arthritis, the relationship between HLA class II alleles and lymphocyte activation remains unclear. We performed immunophenotyping of peripheral blood mononuclear cells on 91 HLA-DRB1-genotyped RA patients and 110 healthy donors. The frequency of memory CXCR4⁺CD4⁺ T cells, and not Th1 and Th17 cells, was significantly associated with disease severity by multiple linear regression analysis. RA patients with one or more susceptible HLA-DR haplotypes (shared epitope: SE) displayed a significantly higher frequency of memory CXCR4⁺CD4⁺ T cells. Moreover, the frequency of memory CXCR4⁺CD4⁺ T cells significantly correlated with the expression level of HLA-DR on B cells, which was elevated in RA patients with SE. In vitro analysis and transcriptomic pathway analysis suggested that the interaction between HLA-DR and T cell receptors is an important regulator of memory CXCR4⁺CD4⁺ T cells. Clinically, a higher frequency of memory CXCR4⁺CD4⁺ T cells predicted a better response to CTLA4-Ig. Memory CXCR4⁺CD4⁺ T cells may serve as a powerful biomarker for unraveling the linkage between HLA-DRB1 genotype and disease activity in RA.

B cell depletion with rituximab in patients with rheumatoid arthritis: Multiplex bead array reveals the kinetics of IgG and IgA antibodies to citrullinated antigens

The serology of patients with Rheumatoid arthritis (RA) is characterized by persistently raised levels of autoantibodies: Rheumatoid Factors (RhF) against Fc of IgG, and to citrullinated (Cit) protein/peptide sequences: ACPA, recognizing multiple Cit-sequences. B cell depletion therapy based on rituximab delivers good clinical responses in RA patients, particularly in the seropositive group, with responses sometimes lasting beyond the phase of B cell reconstitution. In general, ACPA levels fall following rituximab, but fluctuations with respect to predicting relapse have proved disappointing. In order to identify possible immunodominant specificities within either IgG- or IgA-ACPA we used a Multiplex bead-based array consisting of 30 Cit-peptides/proteins and 22 corresponding native sequences. The kinetics of the serum ACPA response to individual specificities was measured at key points (Baseline, B cell depletion phase, Relapse) within an initial cycle of rituximab therapy in 16 consecutive patients with severe, active RA. All had achieved significant decreases in Disease Activity Scores-28 and maintained B cell depletion in the peripheral blood (<5 CD19+cells/μl) for at least 3 months. At Baseline, mean fluorescence intensity shown by individual IgG- and IgA-ACPA were strongly correlated (R(2) = 0.75; p < 0.0001) but IgA-ACPA were approximately 10-fold lower. Data were Z-normalised in order to compare serial results and antibody classes. At Baseline, a total of 68 IgG- and 51 IgA-ACPA had Z-scores ≥ 1 (above population mean) were identified, with at least one Cit-antigen identified in each serum. ACPA to individual specificities subsequently fluctuated with 3 different patterns. Most 51/68 (75%) IgG- and 48/51 IgA-ACPA (94%) fell between Baseline and Depletion, of which 57% IgG- and 65% IgA-ACPA rebounded pre-Relapse. Interestingly, 17/68 IgG-ACPA (25%) and some IgA-ACPA (3/51; 6%) transiently increased from Baseline, subsequently falling pre-Relapse. Individual responses to particular Cit-epitopes were not linked to particular patterns of fluctuation, but IgG- and IgA-ACPA to individual Cit-antigens often followed similar courses. Some new IgG- and IgA-ACPA, generally to different Cit-antigens however, arose at Relapse in 4 patients. The complexities of the ACPA response after rituximab may therefore reflect its ability to deplete or modify the function of parent B cell clones, which varies between patients. Although relapse following rituximab invariably follows naïve B cell exit from the bone marrow, these studies show that interactions between both 'new' and residual autoreactive memory B cells may be key to resumption of symptoms. The lack of identification of any immunodominant specificity suggests that the process of citrullination, rather than any particular Cit-antigen drives the autoimmune response in RA patients.

Anti-cyclic citrullinated peptide and rheumatoid factor in patients with chronic hepatitis B and hepatitis B carriers

OBJECTIVE

Rheumatoid factor (RF) positivity that may occur in a number of patients with hepatitis B (HBV) infection poses challenges in terms of differential diagnosis with rheumatoid arthritis (RA). On the other hand, antibodies to cyclic citrullinated peptide (anti-CCP) may prove to be an important marker for differential diagnosis of the two conditions. This study aimed to assess anti-CCP and RF positivity among patients with hepatitis B and rheumatoid arthritis.

MATERIAL AND METHODS

Anti-CCP and RF seropositivity was assessed in 61 patients with HBV infection (32 patients with chronic hepatitis, 29 patients with inactive HBV carrier status) and 40 patients with RA as the control group.

RESULTS

RF positivity was found in 18.7% and 34.4% of the patients with chronic hepatitis B and inactive HBV carrier status, respectively. On the other hand, only one patient with chronic HBV had low positive anti-CCP. RF was positive in 24 (60%) and anti-CCP was positive in 26 (65%) patients among the 40 patients with RA.

CONCLUSION

Anti-CCP may be helpful in the differential diagnosis between RA and chronic HBV infection or inactive HBV carrier status.

Biomarkers for rheumatoid and psoriatic arthritis

Rheumatic diseases, such as rheumatoid and psoriatic arthritis are systemic inflammatory conditions characterized by a chronic form of arthritis, often leading to irreversible joint damage. Early treatment for patients with rheumatic diseases is required to reduce or prevent joint injury. However, early diagnosis can be difficult and currently it is not possible to predict which individual patient will develop progressive erosive disease or who may benefit from a specific treatment according to their clinical features at presentation. Biomarkers are therefore required to enable earlier diagnosis and predict prognosis in both rheumatoid arthritis and psoriatic arthritis. In this review we will examine the evidence and current status of established and experimental biomarkers in rheumatoid and psoriatic arthritis for three important purposes; disease diagnosis, prognosis and prediction of response to therapy.

Loss of SH3 domain-binding protein 2 function suppresses bone destruction in tumor necrosis factor-driven and collagen-induced arthritis in mice

OBJECTIVE

SH3 domain-binding protein 2 (SH3BP2) is a signaling adapter protein that regulates the immune and skeletal systems. The present study was undertaken to investigate the role of SH3BP2 in arthritis using 2 experimental mouse models, i.e., human tumor necrosis factor α-transgenic (hTNF-Tg) mice and mice with collagen-induced arthritis (CIA).

METHODS

First, Sh3bp2(-/-) and wild-type (Sh3bp2(+/+) ) mice were crossed with hTNF-Tg mice. Inflammation and bone loss were examined by clinical inspection and histologic and micro-computed tomography analysis, and osteoclastogenesis was evaluated using primary bone marrow-derived macrophage colony-stimulating factor-dependent macrophages (BMMs). Second, CIA was induced in Sh3bp2(-/-) and Sh3bp2(+/+) mice, and the incidence and severity of arthritis were evaluated. Anti-mouse type II collagen (CII) antibody levels were measured by enzyme-linked immunosorbent assay, and lymph node cell responses to CII were determined.

RESULTS

SH3BP2 deficiency did not alter the severity of joint swelling but did suppress bone erosion in the hTNF-Tg mouse model. Bone loss at the talus and tibia was prevented in Sh3bp2(-/-) /hTNF-Tg mice compared to Sh3bp2(+/+) /hTNF-Tg mice. RANKL- and TNFα-induced osteoclastogenesis was suppressed in Sh3bp2(-/-) mouse BMM cultures. NF-ATc1 nuclear localization in response to TNFα was decreased in Sh3bp2(-/-) mouse BMMs compared to Sh3bp2(+/+) mouse BMMs. In the CIA model, SH3BP2 deficiency suppressed the incidence of arthritis and this was associated with decreased anti-CII antibody production, while antigen-specific T cell responses in lymph nodes were not significantly different between Sh3bp2(+/+) and Sh3bp2(-/-) mice.

CONCLUSION

SH3BP2 deficiency prevents loss of bone via impaired osteoclastogenesis in the hTNF-Tg mouse model and suppresses the induction of arthritis via decreased autoantibody production in the CIA model. Therefore, SH3BP2 could potentially be a therapeutic target in rheumatoid arthritis.

PDL241, a novel humanized monoclonal antibody, reveals CD319 as a therapeutic target for rheumatoid arthritis

Introduction

Targeting the CD20 antigen has been a successful therapeutic intervention in the treatment of rheumatoid arthritis (RA). However, in some patients with an inadequate response to anti-CD20 therapy, a persistence of CD20^- plasmablasts is noted. The strong expression of CD319 on CD20^- plasmablast and plasma cell populations in RA synovium led to the investigation of the potential of CD319 as a therapeutic target.

Methods

PDL241, a novel humanized IgG₁ monoclonal antibody (mAb) to CD319, was generated and examined for its ability to inhibit immunoglobulin production from plasmablasts and plasma cells generated from peripheral blood mononuclear cells (PBMC) in the presence and absence of RA synovial fibroblasts (RA-SF). The in vivo activity of PDL241 was determined in a human PBMC transfer into NOD scid IL-2 gamma chain knockout (NSG) mouse model. Finally, the ability of PDL241 to ameliorate experimental arthritis was evaluated in a collagen-induced arthritis (CIA) model in rhesus monkeys.

Results

PDL241 bound to plasmablasts and plasma cells but not naïve B cells. Consistent with the binding profile, PDL241 inhibited the production of IgM from in vitro PBMC cultures by the depletion of CD319⁺ plasmablasts and plasma cells but not B cells. The activity of PDL241 was dependent on an intact Fc portion of the IgG₁ and mediated predominantly by natural killer cells. Inhibition of IgM production was also observed in the human PBMC transfer to NSG mouse model. Treatment of rhesus monkeys in a CIA model with PDL241 led to a significant inhibition of anti-collagen IgG and IgM antibodies. A beneficial effect on joint related parameters, including bone remodeling, histopathology, and joint swelling was also observed.

Conclusions

The activity of PDL241 in both in vitro and in vivo models highlights the potential of CD319 as a therapeutic target in RA.

Autoreactive T cells specific for insulin B:11-23 recognize a low-affinity peptide register in human subjects with autoimmune diabetes

Previous studies in type 1 diabetes (T1D) in the nonobese diabetic mouse demonstrated that a crucial insulin epitope (B:9-23) is presented to diabetogenic CD4 T cells by IA(g7) in a weakly bound register. The importance of antigenic peptides with low-affinity HLA binding in human autoimmune disease remains less clear. The objective of this study was to investigate T-cell responses to a low-affinity self-epitope in subjects with T1D. HLA-DQ8 tetramers loaded with a modified insulin peptide designed to improve binding the low-affinity register were used to visualize T-cell responses following in vitro stimulation. Positive responses were only detectable in T1D patients. Because the immunogenic register of B:9-23 presented by DQ8 has not been conclusively demonstrated, T-cell assays using substituted peptides and DQ8 constructs engineered to express and present B:9-23 in fixed binding registers were used to determine the immunogenic register of this peptide. Tetramer-positive T-cell clones isolated from T1D subjects that responded to stimulation by B:11-23 peptide and denatured insulin protein were conclusively shown to recognize B:11-23 bound to HLA-DQ8 in the low-affinity register 3. These T cells also responded to homologous peptides derived from microbial antigens, suggesting that their initial priming could occur via molecular mimicry. These results are in accord with prior observations from the nonobese diabetic mouse model, suggesting a mechanism shared by mouse and man through which T cells that recognize a weakly bound peptide can circumvent tolerance mechanisms and play a role in the initiation of autoimmune diseases, such as T1D.

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.

Higher levels of autoantibodies targeting mutated citrullinated vimentin in patients with psoriatic arthritis than in patients with psoriasis vulgaris

Antibodies against citrullinated proteins/peptides (ACPAs), and especially antibodies targeting mutated citrullinated vimentin (anti-MCVs), are novel biomarkers of rheumatoid arthritis (RA). Whereas ACPAs are specific and sensitive markers for RA, there have hardly been any reports relating to ACPAs in psoriatic arthritis (PsA) or in psoriasis without joint symptoms (PsO). The aim of the present study was to investigate the prevalence of anti-MCVs in PsA and PsO. Serum anti-MCV titers were measured in 46 PsA and 42 PsO patients and in 40 healthy controls by means of a commercial enzyme-linked immunosorbent assay. The potential correlations of the serum autoantibody levels with several clinical and laboratory parameters were examined. The anti-MCV levels in the PsA patients were significantly higher than those in the PsO group. Among the clinical variables, the presence of tender knee joints and nail psoriasis was significantly associated with anti-MCV positivity in the PsA patients. Higher anti-MCV titers in the PsO patients were associated with a more severe disease course and with the early onset of psoriatic skin symptoms. Our results suggest that anti-MCVs can be used as novel markers in the diagnosis of PsA and in a subset of PsO patients.

Quantification of IFNγ- and IL17-producing cells after stimulation with citrullinated proteins in healthy subjects and RA patients

Antibodies against citrullinated proteins are highly specific for rheumatoid arthritis (RA) and are currently used as a diagnostic marker. In this study, we wanted to quantify the numbers of T cells that react to a wide range of citrullinated proteins in a wide range of HLA-DR subtypes in order to investigate whether citrullination might create T-cell neo-epitopes and could initiate a universal T-cell response. Therefore, PBMCs from healthy volunteers and RA patients were stimulated with a citrullinated and non-citrullinated cell extract on IFNγ-ELISpot. We found a significantly higher number of IFNγ-secreting cells after stimulation with citrullinated proteins compared to non-citrullinated proteins in RA patients (1:14,441 cells vs. 1:32,880 cells) as well as in healthy subjects (1:6,261 reactive cells compared to 1:16,212 cells). Additionally, a higher number of IL17-secreting cells were found after stimulation with citrullinated proteins compared to their non-citrullinated counterparts. Our data indicate that citrulline-dependent T-cell response is not restricted to RA patients but that citrullination as such gives rise to a universal break in tolerance.

Modification of citrulline residues with 2,3-butanedione facilitates their detection by liquid chromatography/mass spectrometry

Citrullination is a post-translational modification (PTM) that results from the deimination of the amino acid arginine into citrulline by Peptidyl Arginine Deiminase enzymes and occurs in a wide range of proteins in health and disease. This modification causes a 1 Da mass shift, which can be used to identify citrullination sites in proteins by the use of mass spectrometry. However, other PTMs, such as deamidation from asparagine to aspartic acid or from glutamine to glutamic acid, can also cause a 1 Da mass shift, making correct interpretation of the data more difficult. We developed a chemical tagging strategy which, combined with an open source search application, allowed us to selectively pinpoint citrullinated peptides in a complex mixture after liquid chromatography/mass spectrometry (LC/MS) analysis. After incubation of a peptide mixture with 2,3 butanedione, citrulline residues were covalently modified which resulted in a 50 Da shift in singly charged mass. By comparison of the peptide mass fingerprint from a modified and an unmodified version of the same sample, our in-house search application was able to identify the citrullinated peptides in the mixture. This strategy was optimized on synthetic peptides and validated on a digest of in vitro citrullinated fibrinogen, where different proteolytic enzymes were used to augment the protein coverage. This new method results in easy detection of citrullinated residues, without the need for complex mass spectrometry equipment.

Antibodies to a new viral citrullinated peptide, VCP2: fine specificity and correlation with anti-cyclic citrullinated peptide (CCP) and anti-VCP1 antibodies

Anti-citrullinated protein/peptide antibodies (ACPA) are a hallmark of rheumatoid arthritis (RA) and can be measured using different citrullinated substrates. In this paper we describe a new viral citrullinated peptide - VCP2 - derived from the Epstein-Barr virus-encoded protein EBNA-2 and analyse its potential as substrate for ACPA detection. Analysing sera from 100 RA patients and 306 controls, anti-VCP2 immunoglobulin (Ig)G were found in 66% of RA sera, IgM in 46% and IgA in 39%, compared with less than 3% of control sera. Anti-VCP2 IgG was associated with erosive arthritis, the presence of rheumatoid factor and anti-VCP1 and anti-cyclic citrullinated peptide (CCP) antibodies. Anti-VCP2 antibodies were detected in 1% and anti-VCP1 antibodies in 4% of CCP-negative RA sera; conversely, 3% of the VCP-negative sera were CCP-positive. Taken together, these data suggest that VCP2 could offer a valuable tool for ACPA detection. Inhibition assays showed that two non-overlapping epitopes - a citrulline-glycine stretch shared between VCP1 and VCP2 and the N-terminal portion of the VCP2 sequence - were targeted by anti-VCP2 antibodies. Moreover, in some RA sera that tested positive in CCP and VCP2 assays, preincubation with VCP2 inhibited binding to CCP, whereas in other sera the binding was unaffected. Thus, the reactivity with more than one ACPA substrate might be due in some RA patients to antibody populations with different specificities, and in others to cross-reactive antibody populations. Finally, affinity-purified anti-VCP2 antibodies immunoprecipitated deiminated Epstein-Barr virus nuclear antigen (EBNA-2) from an EBNA-2-transfected cell line, suggesting that viral sequences may be involved in the generation of the ACPA response.

Anti-cyclic citrullinated peptide antibody predicts functional disability in patients with rheumatoid arthritis in a large prospective observational cohort in Japan

To clarify the clinical significance of anti-cyclic citrullinated peptide antibody (anti-CCP) in the long-term outcome of RA, we established a large observational cohort of RA patients (IORRA) in our institute beginning in 2000. Essentially all RA patients who consulted our institute were registered, and clinical parameters, including disease activity and drug use, were assessed biannually based on patient reports, physician examinations, and laboratory data. In the third phase (October 2001) of the IORRA survey, anti-CCP levels were measured in 1,226 RA patients. In a cross-sectional analysis, clinical variables were compared in anti-CCP-positive versus -negative patients and in RF-positive versus -negative patients. In a longitudinal analysis, subsequent progression of disability was analyzed in anti-CCP-positive versus -negative and in RF-positive versus -negative patients. A verified Japanese version of the Health Assessment Questionnaire (J-HAQ) was used to measure functional disability. In the cross-sectional analysis, anti-CCP-positive patients (84.2%) had a significantly longer disease duration and higher disease activity score and more frequently used corticosteroids and methotrexate compared to anti-CCP-negative patients statistically. Similar phenomena were noted between RF-positive and -negative patients. In contrast, the longitudinal analysis revealed that J-HAQ slopes-a measure of progression of functional disability-were strongly associated with anti-CCP positivity but not with RF positivity. In a linear regression model, J-HAQ scores significantly worsened in anti-CCP-positive patients compared to anti-CCP-negative patients at the third year (annual progression 0.0317, P = 0.001) and the fifth year (annual progression 0.0199, P = 0.0012); however, J-HAQ progression was not influenced by RF status. Anti-CCP is a better predictive and discriminative marker for progression of disability in the long-term outcome of RA patients compared to RF.

Relationship between rheumatoid factor isotypes and IgG anti-cyclic citrullinated peptide antibodies

OBJECTIVE

To validate in a general patient population (GPP) the clinical value of measuring rheumatoid factor (RF) isotypes in relationship to IgG anti-cyclic citrullinated peptide (CCP) antibodies (CCP2 and CCP3).

METHODS

Serum samples were obtained as follows: 1021 GPP, for whom RF was ordered for diagnosis, 137 with rheumatoid arthritis (RA), 100 healthy blood donors (HBD), and 50 with systemic lupus erythematosus. Turbidimetry and ELISA were utilized for RF screening, and individual RF isotypes and IgG anti-CCP antibodies were measured by ELISA; RF IgG was measured after pepsin digestion.

RESULTS

We validated the generally accepted 90%-98% positive predictive value (PPV) and about 68% sensitivity of the anti-CCP2 test on our diagnosed cohorts as 96% (95% CI 89-99) and 65% (95% CI 56-73), respectively. The 282 RF IgM+ specimens identified in the GPP were subdivided into 3 subsets: (1) 83 as RF IgM+ IgG+ IgA+ with 63% (95% CI 51-73) anti-CCP2+ (i.e., sensitivity similar to the RA cohort); (2) 50 as RF IgM+ IgG- IgA+ with significantly fewer anti-CCP2+ (22%; 95% CI 12-36); and (3) about half as IgM+ IgG- IgA- with just 3% (95% CI 1-8) anti-CCP2+, i.e., not significantly different from the 1% (95% CI 0-5) in HBD. Thus, the chance for a specimen in the GPP to be anti-CCP2+ (i.e., to come from an RA patient) was increased by 7- and 21-fold, respectively, by identifying RF IgA and IgG in addition to IgM. About one-third of anti-CCP- RA patients in our cohort were RF IgM+ IgG+ IgA+, reflected as 3.4% in the anti-CCP2- GPP. The agreement between anti-CCP2 and anti-CCP3 was significantly higher for RF+ RA and GPP patients, 86% (95% CI 78-93) and 83% (95% CI 73-91), respectively, than for the RF- RA (27%; 95% CI 6-61), RF- GPP (4%; 95% CI 0-19), and non-RA controls. Anti-CCP2 but not anti-CCP3 significantly distinguished the HBD from the GPP (95% CI).

CONCLUSION

Measurement of the 3 isotypes of RF may increase by 7- to 21-fold the chance of making the serologic diagnosis of RA; a testing algorithm is proposed. The anti-CCP antibody response appears significantly less peptide-specific in the presence of IgM RF than in its absence.

Relationship Between Cyclic Citrullinated Peptide Antibodies Positivity and HLA-DRB1 Shared Epitope Alleles in Patients with Rheumatoid Arthritis in Turkey

Objective: The most characteristic genetic risk factors for rheumatoid arthritis (RA), the HLA-DRB1 shared epitope (SE) alleles, encode for a common amino acid sequence in the peptide-presenting part of the HLA class II molecule. These SE alleles have been described recently to be a risk factor for the development of antibodies against citrullinated proteins in RA. The current study was performed to investigate the association between the cyclic citrullinated peptide antibodies (anti-CCP) and HLA-DR1 HLA-DRB1 shared epitope alleles in patients with RA in Turkey.

Materials and Methods: Sixty patients with RA who were newly diagnosed or under conventional treatment in our clinic and 60 healthy volunteers as controls were enrolled in the study. In patients with RA anti-CCP levels were investigated with enzyme-linked immunosorbent assay and HLA-DRB1 subtyping and SE was assessed by polymerase chain reaction. Only anti-CCP was measured in healthy volunteers.

Results: SE was positive in 50% of the patients with RA. Amongst the SE carriers, 30% of them were carrying double copy of SE. While anti-CCP was positive in 73,3% of patients with RA, this ratio was 0% in healthy volunteers. We determined that the existence of SE increases the positivity of anti-CCP (OR=4,3, 95% [CI], P=0.04 ), and a significant relationship was found between the anti-CCP positivity and the RF positivity. (OR=5,3, 95% [CI] P<0.05).

Conclusion: The results of the present study revealed that Turkish patients with RA carrying SE with HLA-DRB1 genes is significantly related with the production of anti-CCP. The diagnostic sensitivity and specificity of anti-CCP for RA is determined as 73,3% and 100% respectively. (Turk J Rheumatol 2010; 25: 12-8)

A broad screen for targets of immune complexes decorating arthritic joints highlights deposition of nucleosomes in rheumatoid arthritis

Deposits of Ig and complement are abundant in affected joints of patients with rheumatoid arthritis (RA) and in animal models of RA in which antibodies are demonstrably pathogenic. To identify molecular targets of the Igs deposited in arthritic joints, which may activate local inflammation, we used a combination of mass spectrometry (MS) and protein microarrays. Immune complexes were affinity-purified from surgically removed joint tissues of 26 RA and osteoarthritis (OA) patients. Proteins complexed with IgG were identified by proteomic analysis using tandem MS. A striking diversity of components of the extracellular matrix, and some intracellular components, copurified specifically with IgG from RA and OA tissues. A smaller set of autoantigens was observed only in RA eluates. In complementary experiments, IgG fractions purified from joint immune complexes were tested on protein microarrays against a range of candidate autoantigens. These Igs bound a diverse subset of proteins and peptides from synovium and cartilage, different from that bound by normal serum Ig. One type of intracellular protein detected specifically in RA joints (histones H2A/B) was validated by immunohistology and found to be deposited on the cartilage surface of RA but not OA joints. Thus, autoantibodies to many determinants (whether deposited as "neoantigens" or normal constituents of the extracellular matrix) have the potential to contribute to arthritic inflammation.

Autoantibodies binding to citrullinated telopeptide of type II collagen and to cyclic citrullinated peptides predict synergistically the development of seropositive rheumatoid arthritis

OBJECTIVES

To find out whether autoantibodies to citrullinated telopeptides of type I and II collagens and to cyclic citrullinated peptides (CCPs) predict the development of rheumatoid arthritis (RA).

METHODS

A case-control study (matched for sex, age and municipality) was nested within a Finnish cohort of 19072 adults who had neither arthritis nor a history of it at the baseline examination during 1973-7. 124 subjects developed RA by late 1989, and of these, 89 were positive for rheumatoid factor (RF). Preillness serum specimens were analysed for autoantibodies against arginine (A)- or citrulline (C)-containing synthetic telopeptides using a chemiluminescence method and for anti-CCPs Mark2 with an enzyme-linked immunosorbent assay method.

RESULTS

The mean levels of autoantibodies to citrulline-containing telopeptides and the C/A ratios of type I and II collagens and to CCP were higher in subjects who later developed RF-positive RA. In the highest tertiles of C/A (I), C/A (II) ratios and anti-CCPs levels, the relative risk of RF-positive RA was significantly increased. In the multifactorial model, only anti-CCPs retained its statistical significance. However, the interaction term of C/A (II) ratio and anti-CCPs proved to be statistically significant (p = 0.02). The subjects ranked into the highest tertiles of both C/A (II) ratio and anti-CCPs had an odds ratio of 20.06 (95% confidence interval, 4.37 to 92.06) of developing RF-positive RA compared with those in the lowest tertiles of these antibodies. None of the autoantibodies predicted RF-negative RA.

CONCLUSION

Autoantibodies to citrullinated telopeptides of type I and II collagen and to CCPs exert a synergistic effect on the risk of seropositive RA.