Anti-CCP Antibody, a Marker for the Early Detection of Rheumatoid Arthritis

Identification of autoantibodies against PsoP27 in synovial fluid derived from psoriatic arthritis and rheumatoid arthritis patients

PsoP27 is an antigen expressed in psoriatic lesions. It plays an inflammatory role in psoriasis. This study objective was to characterize antibodies (Abs) against PsoP27 in patients with psoriatic arthritis (PsA) and rheumatoid arthritis (RA). Levels of Abs against native and citrullinated PsoP27 in PsA and RA patients' synovial fluid (SF) and sera were determined by ELISA. SF of osteoarthritis (OA) patients and sera of healthy donors were used as controls. Levels of Abs against PsoP27 were correlated with disease activity scores. Abs against native and citrullinated PsoP27 levels in SF of PsA (n = 48; 0.38 ± 0.03 and 0.44 ± 0.04, respectively) and RA (n = 22; 0.57 ± 0.1 and 0.62 ± 0.09, respectively) were significantly higher than in OA patients (n = 23; 0.14 ± 0.01 and 0.15 ± 0.01, respectively) (p < .0001). For both Abs, there were no significant differences between their level in PsA and RA patients. There was no difference in the level of Abs against citrullinated PsoP27 in SF of seronegative versus seropositive RA patients. Levels of Abs against both native and citrullinated PsoP27 in the SF and level of systemic C-reactive protein in PsA correlated positively, while in RA there were no significant correlations with disease activity scores. No differences in level of Abs against PsoP27 were found in the sera of all three study groups. Abs against native and citrullinated PsoP27 are present in PsA and RA SF but not in those of OA patients, suggesting a potential role of those Abs in inflammatory joint diseases.

N-glycan in the variable region of monoclonal ACPA (CCP-Ab1) promotes the exacerbation of experimental arthritis

OBJECTIVES

The variable region of most ACPA IgG molecules in the serum of RA patients carries N-glycan (N-glycanV). To analyse the pathogenicity of N-glycanV of ACPAs, we analysed the pathogenicity of a monoclonal ACPA, CCP-Ab1, with or without N-glycanV, which had been isolated from a patient with RA.

METHODS

CCP-Ab1 with no N-glycosylation site in the variable region (CCP-Ab1 N-rev) was generated, and antigen binding, the effect on in vitro differentiation of osteoclasts from bone marrow mononuclear cells of autoimmune arthritis-prone SKG mice (the cell size of TRAP+ cells and bone resorption capacity) and the in vivo effect on the onset or exacerbation of autoimmune arthritis in SKG mice were evaluated in comparison with glycosylated CCP-Ab1.

RESULTS

Amino acid residues in citrullinated peptide (cfc1), which are essential for binding to CCP-Ab1 N-rev and original CCP-Ab1, were almost identical. The size of TRAP+ cells was significantly larger and osteoclast bone resorption capacity was enhanced in the presence of CCP-Ab1, but not with CCP-Ab1 N-rev. This enhancing activity required the sialic acid of the N-glycan and Fc region of CCP-Ab1. CCP-Ab1, but not CCP-Ab1 N-rev, induced the exacerbation of experimental arthritis in the SKG mouse model.

CONCLUSIONS

These data showed that N-glycanV was required for promoting osteoclast differentiation and bone resorption activity in both in vitro and in vivo assays. The present study demonstrated the important role of N-glycanV in the exacerbation of experimental arthritis by ACPAs.

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.

Identification of autoantigens and their potential post-translational modification in EGPA and severe eosinophilic asthma

Background

The chronic airway inflammation in severe eosinophilic asthma (SEA) suggests potential autoimmune aetiology with unidentified autoantibodies analogous to myeloperoxidase (MPO) in ANCA-positive EGPA (eosinophilic granulomatosis with polyangiitis). Previous research has shown that oxidative post-translational modification (oxPTM) of proteins is an important mechanism by which autoantibody responses may escape immune tolerance. Autoantibodies to oxPTM autoantigens in SEA have not previously been studied.

Methods

Patients with EGPA and SEA were recruited as well as healthy control participants. Autoantigen agnostic approach: Participant serum was incubated with slides of unstimulated and PMA-stimulated neutrophils and eosinophils, and autoantibodies to granulocytes were identified by immunofluorescence with anti-human IgG FITC antibody. Target autoantigen approach: Candidate proteins were identified from previous literature and FANTOM5 gene set analysis for eosinophil expressed proteins. Serum IgG autoantibodies to these proteins, in native and oxPTM form, were detected by indirect ELISA.

Results

Immunofluorescence studies showed that serum from patients with known ANCA stained for IgG against neutrophils as expected. In addition, serum from 9 of 17 tested SEA patients stained for IgG to PMA-stimulated neutrophils undergoing NETosis. Immunofluorescent staining of eosinophil slides was evident with serum from all participants (healthy and with eosinophilic disease) with diffuse cytoplasmic staining except for one SEA individual in whom subtle nuclear staining was evident. FANTOM5 gene set analysis identified TREM1 (triggering receptor expressed on myeloid cells 1) and IL-1 receptor 2 (IL1R2) as eosinophil-specific targets to test for autoantibody responses in addition to MPO, eosinophil peroxidase (EPX), and Collagen-V identified from previous literature. Indirect ELISAs found high concentrations of serum autoantibodies to Collagen-V, MPO, and TREM1 in a higher proportion of SEA patients than healthy controls. High concentrations of serum autoantibodies to EPX were evident in serum from both healthy and SEA participants. The proportion of patients with positive autoantibody ELISAs was not increased when examining oxPTM compared to native proteins.

Discussion

Although none of the target proteins studied showed high sensitivity for SEA, the high proportion of patients positive for at least one serum autoantibody shows the potential of more research on autoantibody serology to improve diagnostic testing for severe asthma.

Clinical trial registration

ClinicalTrials.gov, identifier, NCT04671446.

Current Perspectives on Periodontitis in Systemic Sclerosis: Associative Relationships, Pathogenic Links, and Best Practices

Systemic sclerosis is a chronic, autoimmune, multisystemic disease characterized by aberrant extracellular matrix protein deposition and extreme progressive microvasculopathy. These processes lead to damage within the skin, lungs, or gastrointestinal tract, but also to facial changes with physiognomic and functional alterations, and dental and periodontal lesions. Orofacial manifestations are common in SSc but are frequently overshadowed by systemic complications. In clinical practice, oral manifestations of SSc are suboptimally addressed, while their management is not included in the general treatment recommendations. Periodontitis is associated with autoimmune-mediated systemic diseases, including systemic sclerosis. In periodontitis, the microbial subgingival biofilm induces host-mediated inflammation with subsequent tissue damage, periodontal attachment, and bone loss. When these diseases coexist, patients experience additive damage, increasing malnutrition, and morbidity. The present review discusses the links between SSc and periodontitis, and provides a clinical guide for preventive and therapeutical approaches in the management of these patients.

Immunosensing for Early Detection of Rheumatoid Arthritis Biomarkers: Anti-Cyclic Citrullinated Peptide Antibodies Based on Tilted-Fiber Bragg Grating Biosensor

Rheumatoid arthritis (RA) is regarded as a chronic, immune-mediated disease that leads to the damage of various types of immune cells and signal networks, followed by inappropriate tissue repair and organ damage. RA is primarily manifested in the joints, but also manifests in the lungs and the vascular system. This study developed a method for the in vitro detection of RA through cyclic citrullinated peptide (CCP) antibodies and antigens. The diameter of a tilted-fiber Bragg grating (TFBG) biosensor was etched to 50 μm and then bonded with CCP antigens and antibodies. The small variations in the external refractive index and the optical fiber cladding were measured. The results indicated that the self-assembled layer of the TFBG biosensor was capable of detecting pre- and post-immune CCP antigen and CCP peptide concentrations within four minutes. A minimum CCP concentration of 1 ng/mL was detected with this method. This method is characterized by the sensor's specificity, ability to detect CCP reactions, user-friendliness, and lack of requirement for professional analytical skills, as the detections are carried out by simply loading and releasing the test samples onto the platform. This study provides a novel approach to medical immunosensing analysis and detection. Although the results for the detection of different concentrations of CCP antigen are not yet clear, it was possible to prove the concept that the biosensor is feasible even if the measurement is not easy and accurate at this stage. Further study and improvement are required.

iTRAQ-based proteomic analysis of differentially expressed proteins in sera of seronegative and seropositive rheumatoid arthritis patients

Objective

The diagnosis of seronegative rheumatoid arthritis (SNRA) is often difficult due to the unavailability of reliable laboratory markers. The aim of this study was to identify differentially expressed proteins in sera of SNRA, seropositive RA (SPRA), and healthy donors (HD).

Methods

A total of 32 seropositive RA patients, 32 SNRA patients, and 35 HD were enrolled in our study. Differentially expressed proteins between 3 groups were identified via isobaric tags for relative and absolute quantitation (iTRAQ)‐based proteomic analysis, and an ELISA test was used for the validation test. Correlation analysis was conducted by GraphPad Prism.

Results

Using iTRAQ quantitative proteomics, we identified 14 proteins were significantly different between SPRA and SNRA, including 4 upregulated proteins and 10 downregulated proteins. Four differentially expressed proteins were validated by ELISA test, and the results showed that SAA1 protein was significantly higher in SPRA and SNRA patients compared with HD, and PSME1 was elevated in SPRA patients. What's more, SAA1 was increased in the anti‐CCP or RF high‐level group in RA patients, and PSME1 was increased in the RF high‐level group. Alternatively, SAA1 was positively correlated with inflammation indicators in RA patients, while PSME1 showed no correlation with inflammation indicators.

Conclusions

iTRAQ proteomic approaches revealed variations in serum protein composition among SPRA patients, SNRA patients, and HD and provided new idea for advanced diagnostic methods and precision treatment of RA.

The Effect of Chinese Medicine Compound in the Treatment of Rheumatoid Arthritis on the Level of Rheumatoid Factor and Anti-Cyclic Citrullinated Peptide Antibodies: A Systematic Review and Meta-Analysis

Objectives: To evaluate the current evidence whether Chinese medicine compound (CMC) can reduce the serum levels of rheumatoid factor (RF) and anti-cyclic citrullinated peptide antibodies (anti-CCP). Methods: We comprehensively searched PubMed, Embase, the Cochrane Library, China National Knowledge Infrastructure (CNKI), the Database for Chinese Technical Periodicals (VIP), and Wanfang data. We then performed a systematic review and meta-analysis of all randomized controlled trials (RCTs) assessing the CMC therapy methods. This study is registered with PROSPERO, number CRD42020216284. Results: In total, 65 studies were eligible for inclusion, including 6099 patients. The result of the meta-analysis showed that compared with common Western medicine therapy, CMC monotherapy or combined with Western medicine was able to reduce serum RF (SMD= -0.85, 95%CI -1.04 to -0.67) and anti-CCP (SMD= -0.56, 95%CI -0.79 to -0.32) levels to some extent. In the efficacy meta-analysis, a greater number of CMC-treated patients achieved the efficacy criteria after a period of treatment, where the relative risk (RR) was 1.20 [1.08, 1.33] for achieving ACR20, 1.57 [1.38, 1.78] for ACR50, and 2.21 [1.72, 2.84] for ACR70. At the same time, there was a statistically significant difference in the effective rate of the patient's TCM symptoms (RR = 1.22, 95%CI 1.19-1.26). Conclusions: Through this meta-analysis and systematic review, we found that CMC for the treatment of RA is effective in reducing RF and anti-CCP levels and might have better clinical efficacy than Western medicine monotherapy. Some active components are responsible for this efficacy and worth further exploring.

circPTPN22 as a novel biomarker and ceRNA in peripheral blood mononuclear cells of rheumatoid arthritis

The role of circular RNAs (circRNAs) in rheumatoid arthritis (RA) remains to be elucidated. To determine the expression of circRNAs in peripheral blood mononuclear cells (PBMCs) and to identify novel biomarkers for RA and explore their potential effects in RA, the present study conducted high-throughput RNA sequencing to analyze circRNA expression profiles in PBMCs from 4 RA patients and 3 healthy controls (HCs). Reverse transcription-quantitative PCR was used to verify the expression of circPTPN22 in 42 RA patients, 44 HCs and 45 systemic lupus erythematosus (SLE) patients. In addition, bioinformatics analysis and Pearson's correlation test were conducted to assess the correlation of the relationships between circPTPN22 and RA progression. A receiver operating characteristic curve was calculated to evaluate the diagnostic value. Multilevel integrated analysis identified 41 upregulated and 30 downregulated circRNAs in RA patients compared with HCs. circPTPN22 was confirmed to be a common differentially expressed gene in RA and SLE compared with HCs. Area under the curve analysis suggested the diagnostic value of circPTPN22 expression to distinguish RA patients from both HCs and SLE patients. In addition, circPTPN22 levels in RA PBMCs were correlated with RA-IgG, RA-IgM, RA-IgA, anti-cyclic citrullinated peptide (anti-CCP), rheumatoid factor and C reactive protein levels. A total of four putative microRNAs (miRNAs or miRs), namely, hsa-miR-3074-5p, hsa-miR-373-3p, hsa-miR-766-3p and hsa-miR-34c-5p, were screened to be sponged by circPTPN22 via bioinformatics analysis and then experimentally verified to be upregulated in RA PBMCs compared with controls. The data suggested that circPTPN22 might be a novel biomarker for the diagnosis of RA and participate in RA pathogenesis through a sponge mechanism.

Combining Calcitonin and Procalcitonin and Rheumatoid Arthritis-Related Biomarkers Improve Diagnostic Outcomes in Early Rheumatoid Arthritis

Objective

To demonstrate whether procalcitonin (PCT) combined with calcitonin (CT) could provide additional diagnostic value to other clinically available rheumatoid arthritis- (RA-) related biomarkers in the early diagnosis of RA.

Method

The blood samples aseptically collected by venipuncture were centrifuged within 1 hour and frozen at -80°C. PCT and CT levels were measured using electrochemiluminescence immunoassay (ECLIA) in 260 subjects (48 patients with early RA, 34 patients with established RA, 37 patients with systemic lupus erythematosus, 30 with osteoarthritis, 31 with gouty arthritis, and 80 healthy participants). Anti-cyclic citrullinated peptide (Anti-CCP) and anti-RA33 antibodies (Anti-RA33) were analyzed by ELISA. RF was detected by transmission immunoturbidimetry. Mann-Whitney U tests and Kruskal-Wallis tests compared differences among groups. Spearman's rank correlation analysis determined the relationship between biomarkers. Receiver-operator characteristic (ROC) curves were generated, and diagnostic performance was assessed by area under the curve (AUC), as well as specificity, sensitivity, likelihood ratios (LR).

Results

Median serum PCT concentrations were significantly higher (p < 0.0001) in patients with early RA (0.065 ng/ml) when compared with healthy controls (0.024 ng/ml), and patients with osteoarthritis (0.025 ng/ml). When compared with gouty arthritis (GA) controls (0.072 ng/ml) and systemic lupus erythematosus (SLE) controls (0.093 ng/ml), median serum PCT concentrations were not significant in patients with early RA (0.065 ng/ml). Median serum CT concentrations were significantly lower (p < 0.0001) in patients with early RA (0.880 pg/ml) compared with healthy controls (3.159 pg/ml), patients with SLE (2.480 pg/ml), and patients with GA (2.550 pg/ml). When compared with osteoarthritis controls (0.586 pg/ml), median serum CT concentrations were not significant in patients with early RA (0.880 pg/ml). ROC curve analysis comparing early RA with healthy controls demonstrated that the AUC of RF, anti-CCP, and anti-RA33 were 0.66, 0.73, and 0.64, respectively; the additions of PCT and CT further improved the diagnostic ability of early RA with the AUC of 0.97, 0.98, and 0.97, respectively (p < 0.01). The sensitivities of RF, anti-CCP, and anti-RA33 for early RA were 33.33%, 44.74%, and 58.33%, respectively, and the additions of PCT and CT showed very high sensitivities of 83.33%, 92.11%, and 87.50%. The high-value groups of PCT moderately correlated with the anti-RA33 levels (r = 0.417, p < 0.05). CT had no significant correlation with disease duration, radiographic progression, or clinical/serological variables, such as ESR levels, CRP levels, RF, anti-CCP, and anti-RA33 levels in early RA.

Conclusions

Serum PCT and CT combined with clinically available RA-related biomarkers could further improve the diagnostic efficiency of early RA.

A pilot study of a machine-learning tool to assist in the diagnosis of hand arthritis

OBJECTIVE

Arthritis is a common condition, which frequently involves the hands. Patients with inflammatory arthritis have been shown to experience significant delays in diagnosis. We sought to develop and test a screening tool combining an image of a patient's hands, a short series of questions, and a single examination technique, to determine the most likely diagnosis in a patient presenting with hand arthritis. Machine learning techniques were used to develop separate algorithms for each component, which were combined to produce a diagnosis.

METHODS

280 consecutive new patients presenting to a Rheumatology practice with hand arthritis were enrolled. Each patient completed a 9-part questionnaire, had photographs taken of each hand, and had a single examination result recorded. The Rheumatologist diagnosis was recorded following a 45-minute consultation. The photograph algorithm was developed from 1000 previous hand images, and machine learning techniques were applied to the questionnaire results, training several models against the diagnosis from the Rheumatologist.

RESULTS

The combined algorithms in this study were able to predict inflammatory arthritis with an accuracy, precision, recall and specificity of 96·8%, 97·2%, 98·6% and 90·5% respectively. Similar results were found when inflammatory arthritis was subclassified into rheumatoid arthritis and psoriatic arthritis. The corresponding figures for osteoarthritis were 79·6%, 85·9%, 61·9% and 92·6%.

CONCLUSION

This study demonstrates a novel application combining image-processing and a patient questionnaire with applied machine-learning methods, to facilitate the diagnosis of patients presenting with hand arthritis. Preliminary results are encouraging for the application of such techniques in clinical practice. This article is protected by copyright. All rights reserved.

Physiologic Target, Molecular Evolution, and Pathogenic Functions of a Monoclonal Anti-Citrullinated Protein Antibody Obtained From a Patient With Rheumatoid Arthritis

OBJECTIVE

In plasma from a patient with rheumatoid arthritis (RA), we previously isolated a human monoclonal anti-citrullinated protein antibody (ACPA), CCP-Ab1, that recognizes various citrullinated antigens. In this study, we aimed to explore the physiologic target of CCP-Ab1 and the role of molecular evolution, through affinity maturation, of this ACPA in the onset and the exacerbation of RA.

METHODS

The target protein of CCP-Ab1 was identified in the plasma of a patient with RA and purified under native conditions. Germline-reverted (GL-rev) CCP-Ab1 was generated, and its reactivity was compared to that of mature CCP-Ab1. The functions of CCP-Ab1 and GL-rev CCP-Ab1 in the onset or exacerbation of autoimmune arthritis were analyzed using autoimmune arthritis-prone SKG mice.

RESULTS

CCP-Ab1 bound citrullinated fibrinogen under native conditions. In cultures with GL-rev CCP-Ab1, the binding affinity to citrullinated fibrinogen was drastically reduced (P < 0.05). The elements implicated in GL-rev CCP-Ab1 binding to a citrullinated peptide, cfc1-cyc, were almost identical to those implicated in CCP-Ab1 binding. In arthritis-prone SKG mice, CCP-Ab1, but not GL-rev CCP-Ab1, induced significant exacerbation of experimental arthritis (P < 0.05). Increased production of interleukin-6, both in the joint tissue and in the serum, was observed in SKG mice treated with CCP-Ab1 compared to those treated with GL-rev CCP-Ab1 (P < 0.05). Furthermore, the immune complex formed by CCP-Ab1 and fibrinogen was detected at higher concentrations in the synovial tissue of SKG mice administered CCP-Ab1 (P < 0.05 versus control treatment groups).

CONCLUSION

These data show that germline-encoded CCP-Ab1, which binds weakly to citrullinated fibrinogen, undergoes hypermutation through the activation of naive B cells by citrullinated peptides/proteins, thereby stimulating high reactivity to citrullinated fibrinogen. These findings deepen our understanding of the role of molecular evolution of ACPAs in the onset and exacerbation of RA.

Long-term follow-up of patients with anti-cyclic citrullinated peptide antibody-positive connective tissue disease: a retrospective observational study including information on the HLA-DRB1 allele and citrullination dependency

BACKGROUND

The anti-cyclic citrullinated peptide (CCP) antibody is a diagnostic biomarker of rheumatoid arthritis (RA). However, some non-RA connective tissue disease (CTD) patients also test positive for the anti-CCP antibody and, thus, may ultimately develop RA. We retrospectively investigated whether anti-CCP-positive non-RA CTD patients developed RA and attempted to identify factors that may differentiate RA-overlapping CTD from pure CTD.

METHODS

In total, 842 CTD patients with a primary diagnosis that was not RA were selected from our CTD database as of December 2012. Anti-CCP antibody titers were obtained from a retrospective chart review or measured using stored sera. RA was diagnosed according to the 1987 revised American College of Rheumatology classification criteria. Thirty-three anti-CCP-positive non-RA CTD patients were retrospectively followed up for the development of RA. Bone erosions on the hands and feet were assessed by X-ray. Citrullination dependency was evaluated by an in-house ELISA, the HLA-DRB1 allele was typed, and the results obtained were then compared between RA-overlapping and non-RA anti-CCP-positive CTD patients.

RESULTS

Two out of 33 anti-CCP-positive CTD patients (6.1%) developed RA during a mean follow-up period of 8.9 years. X-rays were examined in 27 out of the 33 patients, and only one (3.7%) showed bone erosions. The frequency of the HLA-DRB1 shared epitope (SE) and anti-CCP antibody titers were both significantly higher in anti-CCP-positive RA-overlapping CTD patients than in anti-CCP-positive non-RA CTD patients, while no significant differences were observed in citrullination dependency.

CONCLUSIONS

Anti-CCP-positive non-RA CTD patients rarely developed RA. HLA-DRB1 SE and anti-CCP antibody titers may facilitate the differentiation of RA-overlapping CTD from anti-CCP-positive non-RA CTD.

Restoring synovial homeostasis in rheumatoid arthritis by targeting fibroblast-like synoviocytes

Rheumatoid arthritis (RA) is a chronic immune-mediated disease that primarily affects the synovium of diarthrodial joints. During the course of RA, the synovium transforms into a hyperplastic invasive tissue that causes destruction of cartilage and bone. Fibroblast-like synoviocytes (FLS), which form the lining of the joint, are epigenetically imprinted with an aggressive phenotype in RA and have an important role in these pathological processes. In addition to producing the extracellular matrix and joint lubricants, FLS in RA produce pathogenic mediators such as cytokines and proteases that contribute to disease pathogenesis and perpetuation. The development of multi-omics integrative analyses have enabled new ways to dissect the mechanisms that imprint FLS, have helped to identify potential FLS subsets with distinct functions and have identified differences in FLS phenotypes between joints in individual patients. This Review provides an overview of advances in understanding of FLS biology and highlights omics approaches and studies that hold promise for identifying future therapeutic targets.

Current Understanding of an Emerging Role of HLA-DRB1 Gene in Rheumatoid Arthritis-From Research to Clinical Practice

Rheumatoid arthritis (RA) is an autoimmune disease with an unclear pathogenic mechanism. However, it has been proven that the key underlying risk factor is a genetic predisposition. Association studies of the HLA-DRB1 gene clearly indicate its importance in RA morbidity. This review presents the current state of knowledge on the impact of HLA-DRB1 gene, functioning both as a component of the patient’s genome and as an environmental risk factor. The impact of known HLA-DRB1 risk variants on the specific structure of the polymorphic HLA-DR molecule, and epitope binding affinity, is presented. The issues of the potential influence of HLA-DRB1 on the occurrence of non-articular disease manifestations and response to treatment are also discussed. A deeper understanding of the role of the HLA-DRB1 gene is essential to explore the complex nature of RA, which is a result of multiple contributing factors, including genetic, epigenetic and environmental factors. It also creates new opportunities to develop modern and personalized forms of therapy.

Exacerbation of symptomatic arthritis by cigarette smoke in experimental arthritis

Introduction

Epidemiologically, cigarette smoking is a well-known risk factor for the pathogenesis of rheumatoid arthritis (RA). However, there has been few plausible explanations why cigarette smoking aggravated RA. We investigated the causal effect of smoking in experimental model of arthritis development.

Methods

During induction of experimental arthritis with collagen challenge, mice were exposed to a smoking environment with 3R4F cigarettes. Generated smoke was delivered to mice through a nose-only exposure chamber (ISO standard 3308). Human cartilage pellet was challenged by cigarette smoke extract to identify citrullinating potential in vitro.

Results

Cigarette smoke exacerbated arthritis in a collagen-induced arthritis (CIA) model. Exposure to smoke accelerated the onset of arthritis by 2 weeks compared to the conventional model without smoke. Citrullination of lung tissue as well as tarsal joints were revealed in smoke-aggravated CIA mice. Interestingly, tracheal cartilage was a core organ regarding intensity and area size of citrullination. The trachea might be an interesting organ in viewpoint of sharing cartilage with joint and direct smoke exposure. Anti-CCP antibodies were barely detected in the serum of CIA mice, they were significantly elevated in cigarette smoke group. Citrullinated antigens were increased in the serum of smoke-exposed mice. Lastly, a cigarette smoke extract enhanced human cartilage citrullination in vitro.

Conclusions

Missing link of arthritic mechanism between smoke and RA could be partially explained by tracheal citrullination. To control tracheal cartilage citrullination may be beneficial for preventing arthritis development or aggravation if cigarette smoke is becoming a risk factor to pre-arthritic individual.

Aberrant dysregulated circular RNAs in the peripheral blood mononuclear cells of patients with rheumatoid arthritis revealed by RNA sequencing: novel diagnostic markers for RA

Circular RNAs (circRNAs) represent a newly identified class of non-coding RNAs that have been shown to be involved in several diseases, including autoimmune diseases. Two studies have revealed the aberrant circRNA expression profiles in the peripheral blood mononuclear cells (PBMCs) of patients with rheumatoid arthritis (RA) by microarrays. However, due to the intrinsic defects of microarrays, such as their inability to detect unidentified circRNAs, we examined the circRNA expression profiles in the PBMCs from four RA patients and three healthy controls by RNA sequencing (RNA-seq) and further explored the value of circRNAs in diagnosing RA. The results showed 71 markedly dysregulated circRNAs, including 41 upregulated and 30 downregulated circRNAs; these data included several previously unidentified candidate circRNAs. Gene Ontology and pathway annotation revealed that the most altered pathways and genes were associated with inflammation and transcriptional activity, such as the TNF pathway. The selected dysregulated circRNAs were verified by qRT-PCR in the PBMCs of 32 RA patients and 20 healthy controls, and the results indicated that hsa_circ_0000396 and hsa_circ_0130438 were downregulated in the RA group versus the healthy group, consistent with the RNA-seq data. The area under the receiver operating characteristic curve indicated the diagnostic value of both circRNAs for RA. Our results identified aberrant dysregulated circRNAs in RA patients, including several identified circRNAs, and the diagnostic value of circRNAs for RA, suggesting the superiority of RNA-seq versus microarrays for screening differentially expressed circRNAs and further strengthening the potential diagnostic value of circRNAs for the diagnosis of RA.

IL-6-PAD4 axis in the earliest phase of arthritis in knock-in gp130F759 mice, a model for rheumatoid arthritis

Objective

Animal models for human diseases are especially valuable for clarifying molecular mechanisms before or around the onset. As a model for rheumatoid arthritis (RA), we utilise knock-in mice gp130F759. They have a Y759F mutation in gp130, a common receptor subunit for interleukin 6 (IL-6) family cytokines. Definitive arthritis develops around 8 months old and the incidence reaches 100% around 1 year old. Careful examination in the clinical course revealed very subtle resistance in flexibility of joints at 5 months old. Therefore, pathophysiological changes in gp130F759 were examined to dissect molecular mechanisms for preclinical phase of RA.

Methods

Severity of arthritis in gp130F759 was evaluated with a clinical score system and histological quantification. Serum cytokines, autoantibodies and C reactive protein (CRP) were measured. Changes in the synovium were analysed by real-time PCR, flow cytometry and immunohistochemistry.

Results

Around 5 months old, various types of cytokines, rheumatoid factor (RF), anti-circular citrullinated peptide IgM and CRP increased in the sera of gp130F759. Enhancement of neovascularisation, synovial hyperplasia and fibrosis was observed. Also, increases in haematopoietic cells dominated by innate immune cells and gene expression of Il6 and Padi4 were detected in the joints. Il6 was expressed by non-haematopoietic synovial cells, whereas PAD4 protein was detected in the synovial neutrophils. Padi4 is induced in neutrophils in vitro by IL-6. Increases of phospho-STAT3 and PAD4 protein were detected in the synovium. Deletion of IL-6 in gp130F759 normalised the amount of PAD4 protein in the joints.

Conclusion

The IL-6-PAD4 axis operates in the earliest phase of arthritis in gp130F759, implicating it in early RA.

Discovery of Novel Potential Reversible Peptidyl Arginine Deiminase Inhibitor

Citrullination, a posttranslational modification, is catalyzed by peptidylarginine deiminases (PADs), a unique family of enzymes that converts peptidyl-arginine to peptidyl-citrulline. Overexpression and/or increased PAD activity is observed in rheumatoid arthritis (RA), Alzheimer’s disease, multiple sclerosis, and cancer. Moreover, bacterial PADs, such as Porphyromonas gingivalis PAD (PPAD), may have a role in the pathogenesis of RA, indicating PADs as promising therapeutic targets. Herein, six novel compounds were examined as potential inhibitors of human PAD4 and PPAD, and compared to an irreversible PAD inhibitor, Cl-amidine. Four of the tested compounds (compounds 2, 3, 4, and 6) exhibited a micromolar-range inhibition potency against PAD4 and no effect against PPAD in the in vitro assays. Compound 4 was able to inhibit the PAD4-induced citrullination of H3 histone with higher efficiency than Cl-amidine. In conclusion, compound 4 was highly effective and presents a promising direction in the search for novel RA treatment strategies.

Regulation of neutrophil pro-inflammatory functions sheds new light on the pathogenesis of rheumatoid arthritis

For more than two centuries now, rheumatoid arthritis (RA) is under investigation intending to discover successful treatment. Despite decades of scientific advances, RA is still representing a challenge for contemporary medicine. Current drug therapies allow to improve significantly the quality of life of RA patients; however, they are still insufficient to reverse tissue injury and are often generating side-effects. The difficulty arises from the considerable fluctuation of the clinical course of RA among patients, making the predictive prognosis difficult. More and more studies underline the profound influence of the neutrophil multifaceted functions in the pathogenesis of RA. This renewed interest in the complexity of neutrophil functions in RA offers new exciting opportunities for valuable therapeutic targets as well as for safe and well-tolerated RA treatments. In this review, we aim to update the recent findings on the multiple facets of neutrophils in RA, in particular their impact in promoting the RA-based inflammation through the release of the cytokine-like S100A8/A9 protein complex, as well as the importance of NETosis in the disease progression and development. Furthermore, we delve into the complex question of neutrophil heterogeneity and plasticity and discuss the emerging role of miRNAs and epigenetic markers influencing the inflammatory response of neutrophils in RA and how they could constitute the starting point for novel attractive targets in RA therapy.

MicroRNA-132, miR-146a, and miR-155 as potential biomarkers of methotrexate response in patients with rheumatoid arthritis

INTRODUCTION

Rheumatoid arthritis (RA) patients have high expression levels of hsa-miR-132-3p, hsa-miR-146a-5p, and hsa-miR-155-5p in peripheral blood. We studied if baseline blood levels of these microRNAs (miRNAs) could predict response to methotrexate (MTX).

METHODS

RA patients (the American College of Rheumatology (ACR)/European League Against Rheumatism (EULAR) criteria) with active disease (disease-modifying anti-rheumatic drug (DMARD)-naïve and Disease Activity Score 28 (DAS28) > 3.2) were enrolled. They were treated with MTX by gradually increasing dose up to 25 mg/week. After 4 months, the DAS28 score was calculated and EULAR response was assessed. The hsa-miR-132-3p, hsa-miR-146a-5p, and hsa-miR-155-5p levels were measured by real-time qPCR in whole-blood RNA at baseline and 4 months after therapy, using hsa-let-7a-5p as housekeeping gene. Results are expressed as median (interquartile range).

RESULTS

The 94 enrolled patients (81 females) had a median age of 40 (17) years, disease duration of (24) months, and DAS28 4.61 (1.11). After 4 months of therapy, 73 were classified as responders and 21 as non-responders. Baseline levels of all three miRNAs were lower in responders than non-responders, hsa-miR-132-3p (- 8.03 (0.70) versus - 7.47 (0.85), P < 0.05), hsa-miR-146a-5p (- 5.11 (0.88) versus - 4.62 (0.90), P < 0.05), and hsa-miR-155-5p (- 7.59 (1.07) versus - 7 (0.72), P = 0.002). Receiver operating characteristic curve analysis showed that all three miRNAs were also good predictors of MTX response, showing the following values: hsa-miR-132-3p (area under curve (AUC) 0.756, P < 0.05), hsa-miR-146a-5p (AUC 0.760, P < 0.05), and hsa-miR-155-5p (AUC 0.728, P = 0.002).

CONCLUSION

hsa-miR-132-3p, hsa-miR-146a-5p, and hsa-miR-155-5p are potential biomarkers of responsiveness to MTX therapy.

The impact of anti-cyclic citrullinated peptide antibody status on the management of patients with early rheumatoid arthritis: observational study results from Lithuania

Background

To provide data on the use of anti-cyclic citrullinated peptide antibody (anti-CCP) and other routinely used clinical parameters and to assess the impact of anti-CCP status on therapeutic decisions, an observational study was conducted in patients with rheumatoid arthritis (RA).

Methods

Sixty-seven adult patients with a recent diagnosis of RA were recruited from four rheumatology centres in Lithuania and were prospectively observed for 12 months. Data collection was based on the review of medical records and routine examination of patients. Patients completed the Health Assessment Questionnaire - Disability Index and Patient Global Assessment of disease activity using a visual analogue scale. Physicians were asked about the importance of the anti-CCP results and other factors important for therapeutic decisions.

Results

Of the 67 patients enrolled, 54 (80.6%) completed the study. At the beginning of the study, physicians considered anti-CCP results to be important for decision-making in 87.0% of patients. The perceived importance of anti-CCP results did not change significantly throughout the study. After one year of treatment, factors that were considered more important than the anti-CCP results included the presence of erosions, significantly increased C-reactive protein, duration of morning stiffness, multi-articular expanding, and rheumatoid factor status. For nearly half of the patients (n = 26; 48.1%), physicians would not change the treatment strategy if the patient had the opposite anti-CCP results at baseline.

Conclusions

The study revealed that decision-making in the management of RA was based on multifactorial data. The role of anti-CCP as a single test in treatment decisions needs further investigation.

Genetic polymorphism of rs9277535 in HLA-DP associated with rheumatoid arthritis and anti-CCP production in a Chinese population

HLA-II molecules are critical in triggering human immune response, especially in activating CD4+ T cells. HLA-DP, belonging to HLA-II molecules, draws increasing attention for its role in presentation of viral antigen and autoantigen to T cells. Researches reported single nucleotide polymorphism (SNP) of HLA-DP associated with HBV infection and autoimmune diseases such as SLE. However, little is known about the relationship between HLA-DP and rheumatoid arthritis (RA). Rs9277535 is located in 3' UTR region of HLA-DPB1, a subunit of HLA-DP, and was reported to affect HLA-DP mRNA expression. In the present study, we explored the relationship between gene polymorphism of rs9277535 in HLA-DPB1 and RA susceptibility and progression. Samples from 254 patients with RA and 391 age- and sex-matched healthy controls were collected and genotyped by a polymerase chain reaction-high-resolution melting (PCR-HRM) assay. Serological tests (anti-CCP, rheumatoid factor, C-reactive protein, anti-keratin antibody) were detected by laboratory assays. Strong association was observed between SNP rs9277535 in HLA-DP and RA susceptibility (allele frequency distribution: OR = 1.409, 95%CI = 1.121-1.773, P = 0.004). Further validation was provided by disease model analysis (recessive model: OR = 1.889, 95%CI = 1.194-2.990, P = 0.008; dominant model: OR = 1.464, 95%CI = 1.050-2.041, P = 0.025; additive model: OR = 2.208, 95%CI = 1.335-3.652, P = 0.003). Allele A was correlated to increased risk of RA. Serological test results demonstrated patients carrying allele A of rs9277535 had elevated serum anti-CCP antibody level. The present study provided evidence that HLA-DP gene polymorphism associated with RA susceptibility. Allele A of rs9277535 in HLA-DP correlated to increased risk of RA and elevated serum anti-CCP level.

Comorbidities in Anti-Cyclic Citrullinated Peptide Positive At-Risk Individuals Do Not Differ from Those Patients with Early Inflammatory Arthritis

Objectives

To compare comorbidities in a cohort of cyclic citrullinated peptide (CCP) antibody positive patients without or prior to onset of inflammatory arthritis (IA) to those in patients with early IA.

Methods

Baseline data from two established cohorts were used. The first recruited people at risk of IA: CCP antibody positive cases without IA (CCP Cohort, n = 296). The second cohort [the Inflammatory Arthritis CONtinuum study (IACON)] recruited patients with early IA (n = 725). Proportions of patients with given comorbidities were compared between cohorts and then logistic regression was used to determine odds ratios (OR) for the CCP cohort having specific comorbidities, compared to IACON patients. Analyses adjusted for gender, age, smoking status, and body mass index.

Results

Patients from the CCP cohort were younger (mean age 50, compared to 53 years). The proportion of patients with at least one comorbidity was higher in the IACON than the CCP cohort: (40% compared to 24%, respectively). Results of logistic regression analyses suggested the odds of hypertension, taking a lipid-lowering agent, ischemic heart disease, cerebrovascular disease, lung disease, and diabetes were not increased in either cohort. However, patients in the CCP cohort were more likely to be taking an antidepressant (OR = 1.62, 95% CI 1.03, 2.56, p = 0.037).

Conclusion

There was no significant difference in comorbidities among people with CCP antibodies but without IA, compared to those of patients with established IA.

Semisynthetic Bioluminescent Sensor Proteins for Direct Detection of Antibodies and Small Molecules in Solution

Single-step immunoassays that can be performed directly in solution are ideally suited for point-of-care diagnostics. Our group recently developed a new platform of bioluminescent sensor proteins (LUMABS; LUMinescent AntiBody Sensor) that allow antibody detection in blood plasma. Thus far, LUMABS has been limited to the detection of antibodies recognizing natural peptide epitopes. Here, we report the development of semisynthetic LUMABS sensors that recognize nonpeptide epitopes. The non-natural amino acid para-azidophenylalanine was introduced at the position of the original antibody-recognition sites as a chemical handle to enable site-specific conjugation of synthetic epitope molecules coupled to a dibenzocylcooctyne moiety via strain-promoted click chemistry. The approach was successfully demonstrated by developing semisynthetic LUMABS sensors for antibodies targeting the small molecules dinitrophenol and creatinine (DNP-LUMABS and CR-LUMABS) with affinities of 5.8 pM and 1.3 nM, respectively. An important application of these semisynthetic LUMABS is the detection of small molecules using a competitive assay format, which is demonstrated here for the detection of creatinine. Using a preassembled complex of CR-LUMABS and an anti-creatinine antibody, the detection of high micromolar concentrations of creatinine was possible both in buffer and in 1:1 diluted blood plasma. The use of semisynthetic LUMABS sensors significantly expands the range of antibody targets and enables the application of LUMABS sensors for the ratiometric bioluminescent detection of small molecules using a competitive immunoassay format.

MiR-let-7a regulates anti-citrullinated protein antibody-induced macrophage activation and correlates with the development of experimental rheumatoid arthritis

Anti-citrullinated protein antibodies (ACPAs) are a key serological marker of rheumatoid arthritis (RA). To investigate whether miR-let7a downregulated ACPA-induced macrophage activation and arthritis, miR-let7a levels were assessed in the synovial fluid from patients with RA or osteoarthritis (OA). In addition, expression of the pro-inflammatory genes HMGA2, PI3K, and IRF5 was examined in ACPA-induced macrophages and a collagen antibody-induced mouse model of arthritis. As expected, miR-let7a expression in synovial fluid macrophages was substantially lower in patients with RA than in those with OA. Moreover, ACPAs treatment (160IU/mL) suppressed miR-let7a expression in macrophages isolated from patients with RA. Mechanistic studies revealed that miR-let7a directly targets HMGA2 to suppress ACPA-induced IRF5 expression through PI3K in macrophages. Further, miR-let7a expression was markedly decreased in swollen ankle tissue and splenocytes isolated from arthritic mice, whereas HMGA2, PI3K, and IRF5 expression positively correlated with disease severity. However, injection miR-let7a agomir was unable to mitigate the development of experimental arthritis in model mice. Collectively, these data demonstrated that miR-let7a directly targets HMGA2 to downregulate ACPAs-induced macrophage activation, and correlated with experimental RA severity.

Is macrophage polarization important in rheumatoid arthritis?

Macrophages are myeloid immune cells which are strategically positioned throughout the body, where they engulf and degrade debris, dead cells, and foreign substances, and coordinating the inflammatory processes. Macrophages can be divided into two extreme subsets, classical activation (M1), and alternatively activation (M2). The symptoms and signs of rheumatoid arthritis (RA) would exacerbate with the increase in pro-inflammatory cytokines, whereas anti-inflammatory cytokines will alleviate the symptoms and signs of RA. This review, mainly discusses the effects of Notch, JNK and ERK signaling pathways on the regulation of macrophage polarization, and the effects of pro-inflammatory factors and/or anti-inflammatory cytokines produced by polarized macrophages in RA. Also, we will make an attempt to find out the importance of macrophage polarization in RA treatment as a drug target.

Cellular and molecular perspectives in rheumatoid arthritis

Synovial immunopathology in rheumatoid arthritis is complex involving both resident and infiltrating cells. The synovial tissue undergoes significant neovascularization, facilitating an influx of lymphocytes and monocytes that transform a typically acellular loose areolar membrane into an invasive tumour-like pannus. The microvasculature proliferates to form straight regularly-branching vessels; however, they are highly dysfunctional resulting in reduced oxygen supply and a hypoxic microenvironment. Autoantibodies such as rheumatoid factor and anti-citrullinated protein antibodies are found at an early stage, often before arthritis has developed, and they have been implicated in the pathogenesis of RA. Abnormal cellular metabolism and mitochondrial dysfunction thus ensue and, in turn, through the increased production of reactive oxygen species actively induce inflammation. Key pro-inflammatory cytokines, chemokines and growth factors and their signalling pathways, including nuclear factor κB, Janus kinase-signal transducer, are highly activated when immune cells are exposed to hypoxia in the inflamed rheumatoid joint show adaptive survival reactions by activating. This review attempts to highlight those aberrations in the innate and adaptive immune systems including the role of genetic and environmental factors, autoantibodies, cellular alterations, signalling pathways and metabolism that are implicated in the pathogenesis of RA and may therefore provide an opportunity for therapeutic intervention.

Epitope Specificity of Anti-Citrullinated Protein Antibodies

Anti-citrullinated protein antibodies are primarily associated with a progressive course in the autoimmune disease rheumatoid arthritis, a disease with a chronic and inflammatory nature. These antibodies do not appear to have any strict dependency for reactivity except from the presence of the non-genetically encoded amino acid citrulline, which is the result of a posttranslational modification, catalyzed by calcium-dependent peptidylarginine deiminase enzymes. Nevertheless, several amino acids surrounding the citrulline residue notably influence antibody reactivity, especially with a central-Cit-Gly-motif being essential for antibody reactivity. Most importantly, these antibodies have been proposed to be divided into two groups, based on their ability to recognize multiple citrullinated peptides. Thus, an "overlapping" antibody group, which appears to recognize several citrullinated peptides, and a "non-overlapping" antibody group, which only recognizes a limited number of citrullinated peptides, have been proposed. Based on these findings, we suggest that antibodies recognizing several citrullinated targets, also referred to as cross-reactive antibodies, primarily are backbone-dependent, whereas less cross-reactive antibodies primarily depend on the side chains of the amino acids comprising the epitopes for stable antibody-antigen interactions, which reduces the degree of cross-reactivity significantly. Clarifying the reactivity pattern of anti-citrullinated protein antibodies may contribute to determining their true nature of origin.

Physical Characteristics of a Citrullinated Pro-Filaggrin Epitope Recognized by Anti-Citrullinated Protein Antibodies in Rheumatoid Arthritis Sera

Rheumatoid arthritis (RA) is an autoimmune disease of complex etiology. A characteristic feature of a subset of RA is the presence of anti-citrullinated protein antibodies (ACPA), which correlate with a progressive disease course. In this study, we employed streptavidin capture enzyme-linked immunosorbent assay to analyze ACPA reactivity. Using the pro-filaggrin peptide HQCHQEST-Cit-GRSRGRCGRSGS, as template, we analyzed the reactivity of RA sera and healthy donor sera to various peptides in order to determine the physical characteristics of the citrullinated pro-filaggrin epitope and to examine whether biotin labelling influence antibody recognition. The full-length cyclic pro-filaggrin peptide and a linear form with a N-terminal biotin, was recognized to the same level, whereas, a notable difference in ACPA reactivity to the linear peptides with a C-terminal biotin was found, probably due to steric hindrance. Screening of linear and cyclic truncated peptides, revealed that small cyclic peptides containing 10–12 amino acids are favored over the linear. Moreover, the charged amino acids C-terminal to citrulline were found to be essential for antibody reactivity, most important was the charged amino acid in position 4 C-terminal to citrulline. Collectively, peptide structure, length, the presence of charged amino acids and biotin labelling markedly influence antibody reactivity. In relation to the clinical diagnostics of ACPA, these findings may reflect the differences in diagnostic assays used for detection of ACPA, which relates to differences in sensitivity and specificity dependent on the assay applied.

Differences in the Spectrum of Anti-Citrullinated Protein Antibody Fine Specificities Between Malaysian and Swedish Patients With Rheumatoid Arthritis: Implications for Disease Pathogenesis

Objective

Antibodies to the citrullinated protein antigens (ACPAs) are important in the diagnosis and pathogenesis of rheumatoid arthritis (RA). However, the prevalence of ACPAs with different fine specificities in different populations is unclear. This study sought to examine the fine specificity of the antibody responses toward citrullinated proteins in RA patients from Malaysia, an area where genetic and environmental determinants of RA are different from those in more frequently studied cohorts of Caucasian subjects.

Methods

A multiplex analytic microarray system was used to analyze the occurrence of antibodies to 10 different citrullinated peptides (filaggrin [fil307–324], vimentin [Vim2–17, Vim60–75], fibrinogen [Fibα563–583, Fibα580–600, Fibβ36–52, Fibβ62–81a, Fibβ62–81b], enolase [Eno5–21], and type II collagen [CitCII355–378]) in serum samples from 4,089 RA patients (1,231 Malaysian and 2,858 Swedish) and 827 healthy control subjects (249 Malaysian and 578 Swedish). The positive reaction threshold for each peptide was set separately for each population based on a specificity of 98%.

Results

Distinct differences in the frequencies of 5 ACPA fine specificities (Vim60–75, Vim2–17, Fibβ62–81b, Eno5–21, and CitCII355–378) were found between the Malaysian and Swedish RA populations, despite a nearly identical percentage of patients in each population who were positive for anti–cyclic citrullinated peptide 2 antibodies. In Malaysian RA patients compared with Swedish RA patients, the frequencies of antibodies to Vim60–75 (54% versus 44%, corrected P [P_corr] = 1.06 × 10⁻⁸) and CitCII355–378 (17% versus 13%, P_corr = 0.02) were significantly higher, while the frequencies of antibodies to Vim2–17 (25% versus 32%, P_corr = 1.91 × 10⁻⁴), Fibβ62–81b (15% versus 30%, P_corr = 2.47 × 10⁻²²), and Eno5–21 (23% versus 50%, P_corr = 3.64 × 10⁻⁵⁷) were significantly lower.

Conclusion

Serum ACPA fine specificities differ between RA patients in different populations, although the total proportions of individuals positive for ACPAs are similar. Differing patterns of ACPA fine specificity could be attributed to variations in genetic and/or environmental factors.

Synthesis of a biological active β-hairpin peptide by addition of two structural motifs

The idea of privileged scaffolds - that there seem to be more bioactive compounds found around some structures than others - is well established for small drug molecules, but has little significance for standalone peptide secondary structures whose adaptable shapes escape the definition of a 3D motif in the absence of a protein scaffold. Here, we joined two independent biological functions in a single highly restricted peptide to support the hypothesis that the β-hairpin shape is the common basis of two otherwise unrelated biological recognition processes. To achieve this, the hydrophobic cluster HWX₄LV from the decapeptide cyclic hairpin model peptide C¹-C¹⁰cyclo-CHWEGNKLVC was included in the bicyclic peptide 2. The designed β-hairpin peptide C⁴-C¹⁷, C⁸-C¹³bicyclo-KHQCHWECTZGRCRLVCGRSGS (2, Z=citrulline), serves, on the one hand, as a specific epitope for rheumatoid autoantibodies and, on the other hand, shows a not negligible antibiotic effect against the bacterial strain E. coli AS19.

Hypoxia-induced production of peptidylarginine deiminases and citrullinated proteins in malignant glioma cells

BACKGROUND

Recently, it has been reported that hypoxia highly enhances expression of peptidylarginine deiminase (PAD) 4 and production of citrullinated proteins in some tumor cells. However, little is known about malignant gliomas on this issue. Therefore, we here investigated whether expression of PADs was induced by hypoxia and whether PADs citrullinated intracellular proteins if induced using U-251 MG cells of a human malignant glioma cell line.

METHODS

Expression of PADs in U-251 MG cells, cultured under hypoxia or normoxia for 24 h, was investigated by quantitative polymerase chain reaction (qPCR). Citrullination of proteins in the cells and the cell lysates incubated for 48 h with or without Ca²⁺ was detected by western blotting. Citrullinated proteins were identified by mass spectrometry.

RESULTS

The mRNA levels of PAD1, 2, 3, and 4 were up-regulated by hypoxia in a hypoxia-inducible factor-1-dependent manner in U-251 MG cells. In spite of the increased expression, intracellular proteins were not citrullinated. However, the induced PADs citrullinated U-251 MG cell-derived proteins when the cells were lysed. Multiple proteins citrullinated by hypoxia-induced PADs were identified. In addition, the extracellular domain of vascular endothelial growth factor receptor 2 was citrullinated by human PAD2 in vitro.

CONCLUSION

Our data may contribute to understanding of pathophysiology of malignant gliomas from the aspects of protein citrullination.

FcγRIIB and autoimmunity

Autoimmune diseases are characterized by adaptive immune responses against self-antigens, including humoral responses resulting in the production of autoantibodies. Autoantibodies generate inflammation by activating complement and engaging Fcγ receptors (FcγRs). The inhibitory receptor FcγRIIB plays a central role in regulating the generation of autoantibodies and their effector functions, which include activation of innate immune cells and the cellular arm of the adaptive immune system, via effects on antigen presentation to CD4 T cells. Polymorphisms in FcγRIIB have been associated with susceptibility to autoimmunity but protection against infections in humans and mice. In the last few years, new mechanisms by which FcγRIIB controls the adaptive immune response have been described. Notably, FcγRIIB has been shown to regulate germinal center B cells and dendritic cell migration, with potential impact on the development of autoimmune diseases. Recent work has also highlighted the implication of FcγRIIB on the regulation of the innate immune system, via inhibition of Toll-like receptor- and complement receptor-mediated activation. This review will provide an update on the role of FcγRIIB in adaptive immune responses in autoimmunity, and then focus on their emerging function in innate immunity.

Cigarette Smoke Induces Immune Responses to Vimentin in both, Arthritis-Susceptible and -Resistant Humanized Mice

Rheumatoid arthritis (RA) is an autoimmune disease marked by chronic synovial inflammation and both, genetic and environmental factors are involved in its pathogenesis. Human leukocyte antigen (HLA) DRB1*0401 is associated with susceptibility to develop RA, while cigarette smoke (CS) exposure promotes seropositive disease with increased severity in DRB1*0401+ individuals. Smokers have higher levels of antibodies against citrullinated peptides. In this study, we determined whether the response to a known autoantigen, Vimentin (Vim) is shared epitope specific and how CS influences this response using transgenic-mice carrying RA-susceptible,*0401, and -resistant, *0402, genes. Following relatively brief exposure to CS, peptidyl arginine deiminase (PAD) enzyme expression was increased in murine lungs. Cigarette smoking led to production of Interferon (IFN)-γ with reduced levels of Interleukin (IL)-10 by splenocytes of *0401 mice. In contrast, CS augmented Th2 cytokines along with T-regulatory cells in *0402 mice. An increase in levels of antibodies to native and citrullinated Vim was observed in naïve mice of both strains following CS exposure. Our data showed that both arthritis-susceptible and -resistant mice can generate cellular and humoral immunity to Vim; however CS-induced modulation of host immunity is dependent on the interaction with the host HLA genes.

Spatiotemporal expression of endogenous TLR4 ligands leads to inflammation and bone erosion in mouse collagen-induced arthritis

Increased expression of endogenous Toll-like receptor 4 (TLR4) ligands (e.g., Tenascin-C, S100A8/A9, citrullinated fibrinogen (cFb) immune complexes) has been observed in patients with rheumatoid arthritis (RA). However, their roles in RA pathogenesis are not well understood. Here, we investigated the expression kinetics and role of endogenous TLR4 ligands in the murine model of collagen-induced arthritis (CIA). Tenascin-C was upregulated in blood early in CIA, and correlated positively with the clinical score at day 56. Levels of S100A8/A9 increased starting from day 28, peaking at day 42, and correlated positively with joint inflammation. Levels of anti-cFb antibodies increased during the late phase of CIA and correlated positively with both joint inflammation and cartilage damage. Blockade of TLR4 activation at the time of the first TLR4 ligand upregulation prevented clinical and histological signs of arthritis. A TLR4-dependent role was also observed for Tenascin-C and cFb immune complexes in osteoclast differentiation in vitro. Taken together, our data suggests that the pathogenic contribution of TLR4 in promoting joint inflammation and bone erosion during CIA occurs via various TLR4 ligands arising at different stages of disease. The data also suggests that Blockade of TLR4 with monoclonal antibodies is a promising strategy in RA treatment.

Anti-Citrullinated Protein Antibodies Induce Macrophage Subset Disequilibrium in RA Patients

We used samples from rheumatoid arthritis (RA) patients to examine whether Anti-citrullinated protein antibodies (ACPAs) alter macrophage subset distribution and promote RA development. Macrophage subset distributions and interferon regulatory factor 4 (IRF4) and IRF5 expressions were analyzed. ACPAs were purified by affinity column. After RA and osteoarthritis (OA) patients' macrophages were cocultured with ACPAs, macrophage subsets and IRF4 and IRF5 expressions were measured. Small interfering RNAs (siRNAs) were transfected into ACPA-activated cells to suppress IRF4 or IRF5. Fluorescence-activated cell sorting (FACS), Western blot, and immunohistochemistry were performed. Macrophage subset disequilibrium occurred in RA patient synovial fluids. IRF4 and IRF5 were all expressed in the synovial fluid and synovium. ACPAs (40 IU/ml) could induce macrophages to polarize to M1 subsets, and the percentage of increased M1/M2 ratio of RA patients was higher than that of the OA patients. ACPAs also induce IRF4 and IRF5 protein expressions. IRF5 siRNA transfection impaired ACPA activity significantly. We demonstrated that macrophage subset disequilibrium occurred in RA patients. ACPAs induced IRF5 activity and led to M1 macrophage polarization.

A Contra Capture Protein Array Platform for Studying Post-translationally Modified (PTM) Auto-antigenomes

Aberrant modifications of proteins occur during disease development and elicit disease-specific antibody responses. We have developed a protein array platform that enables the modification of many proteins in parallel and assesses their immunogenicity without the need to express, purify, and modify proteins individually. We used anticitrullinated protein antibodies (ACPAs) in rheumatoid arthritis (RA) as a model modification and profiled antibody responses to ∼190 citrullinated proteins in 20 RA patients. We observed unique antibody reactivity patterns in both clinical anticyclic citrullinated peptide assay positive (CCP+) and CCP- RA patients. At individual antigen levels, we detected antibodies against known citrullinated autoantigens and discovered and validated five novel antibodies against specific citrullinated antigens (osteopontin (SPP1), flap endonuclease (FEN1), insulin like growth factor binding protein 6 (IGFBP6), insulin like growth factor I (IGF1) and stanniocalcin-2 (STC2)) in RA patients. We also demonstrated the utility of our innovative array platform in the identification of immune-dominant epitope(s) for citrullinated antigens. We believe our platform will promote the study of post-translationally modified antigens at a breadth that has not been achieved before, by both identifying novel autoantigens and investigating their roles in disease development. The developed platforms can potentially be used to study many autoimmune disease-relevant modifications and their immunogenicity.

Autoantibodies in prediction of the development of rheumatoid arthritis among healthy relatives of patients with the disease

OBJECTIVE

Although blood bank-based studies have shown that rheumatoid arthritis (RA)-related autoantibodies are present before the onset of RA, information on their positive predictive value (PPV) for development of RA in healthy individuals is scarce. This study was undertaken to assess the 5-year PPV of serum IgM rheumatoid factor (IgM-RF) and anti-cyclic citrullinated peptide (anti-CCP) for the development of RA among healthy relatives of patients with RA.

METHODS

Healthy relatives of RA patients were invited to participate in a cohort study. At baseline, information on participants' medical history was obtained, and serum levels of IgM-RF and anti-CCP antibodies were determined (by nephelometry and second-generation anti-CCP enzyme-linked immunosorbent assay, respectively). The subjects were followed up every 4 months via a structured interview (Community Oriented Program for Control of Rheumatic Diseases [COPCORD] questionnaire). When the COPCORD questionnaire indicated possible arthritis, subjects underwent an in-office rheumatology assessment including joint count. The study end point was defined as fulfillment of the American College of Rheumatology criteria for RA.

RESULTS

Eight hundred nineteen initially healthy relatives of 252 patients with RA were included (69% female, 41% offspring, mean ± SD age 35 ± 12 years). Eleven (1.3%) were positive for both anti-CCP-2 and RF, 12 (1.5%) only for anti-CCP-2, and 16 (2%) only for RF. RA developed in 17 (2.1%) of the relatives during the 5-year followup (3,313 person-years for the seronegative group and 60.8 person-years for the anti-CCP-2-positive group). The PPV was 64% when both anti-CCP-2 and RF were positive and 58% when only anti-CCP-2 was positive. Offspring of patients with RA had an independent 3-fold increased risk of developing RA.

CONCLUSION

Results of the present study indicate that the magnitude of risk for developing RA in healthy relatives of patients with RA can be estimated using simple routine laboratory tests.

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.

Biomarkers in rheumatic diseases: how can they facilitate diagnosis and assessment of disease activity?

Serological and proteomic biomarkers can help clinicians diagnose rheumatic diseases earlier and assess disease activity more accurately. These markers have been incorporated into the recently revised classification criteria of several diseases to enable early diagnosis and timely initiation of treatment. Furthermore, they also facilitate more accurate subclassification and more focused monitoring for the detection of certain disease manifestations, such as lung and renal involvement. These biomarkers can also make the assessment of disease activity and treatment response more reliable. Simultaneously, several new serological and proteomic biomarkers have become available in the routine clinical setting--for example, a protein biomarker panel for rheumatoid arthritis and a myositis antibody panel for dermatomyositis and polymyositis. This review will focus on commercially available antibody and proteomic biomarkers in rheumatoid arthritis, systemic lupus erythematosus, systemic sclerosis (scleroderma), dermatomyositis and polymyositis, and axial spondyloarthritis (including ankylosing spondylitis). It will discuss how these markers can facilitate early diagnosis as well as more accurate subclassification and assessment of disease activity in the clinical setting. The ultimate goal of current and future biomarkers in rheumatic diseases is to enable early detection of these diseases and their clinical manifestations, and to provide effective monitoring and treatment regimens that are tailored to each patient's needs and prognosis.

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.