Anticyclic Citrullinated Peptide Antibodies in Rheumatoid and Nonrheumatoid Rheumatic Disorders: Experience with 1162 Patients

The first involved joints and associated factors in patients with rheumatoid arthritis

Objectives

This study aimed to investigate the first involved joints and associated factors in Turkish patients with rheumatoid arthritis (RA).

Patients and methods

This retrospective cross-sectional study included 300 newly diagnosed and disease-modifying antirheumatic drug-naïve RA patients (240 females, 60 males; mean age: 54±1.2 years; range, 18 to 82 years). Baseline demographic, clinical, and laboratory data were evaluated between January 2022 and December 2022. The patients were divided into four groups according to autoantibody profile: antibody-negative patients (Group 1; both RF and anti-CCP were negative in this group of patients), RF-positive patients (Group 2), anti-CCP-positive patients (Group 3), and patients with dual seropositivity with RF and antiCCP (Group 4). The patients were also divided into two groups according to the size of the first affected joint: patients with SJI at diagnosis and patients without SJI involvement at diagnosis.

Results

Rheumatoid factor (RF) and anti-cyclic citrullinated peptide (CCP) antibody positivity rates were 40.3% and 35.6%, respectively. The mean lag time to diagnosis was 25±36 months. At the disease onset, 20% of patients did not have small joint involvement (SJI). Seronegative patients tended to be female (p=0.001), had longer lag time (p=0.001), and had lower levels of C-reactive protein (p=0.025), white blood count (p=0.005), and neutrophil/lymphocyte ratio (p=0.001) compared to the dual seropositive group. Patients presenting with SJI had a younger age (p=0.002), tended to be female (p=0.001), and had lower RF (p=0.034) and anti-CCP (p=0.031) positivity. Only age (p=0.005) and dual seronegativity (RF and anti-CCP; p=0.035) were the independent predictors of SJI in multivariate analysis.

Conclusion

The decreasing age and seronegative status were defined as independent risk factors of SJI at the onset of RA. Population-based, prospective studies are needed for earlier diagnosis.

A statistical symptomatic evaluation on SAPHO syndrome from 56 cases of confirmed diagnosis and 352 cases of non-SAPHO involvement

OBJECTIVE

To report a statistical evaluation of symptomatology based on 56 cases of SAPHO syndrome and 352 non-SAPHO involvement cases, to propose a symptomatic scoring system in consideration of early warning for SAPHO syndrome.

METHODS

A cohort comprising 56 subjects diagnosed with SAPHO syndrome was reported, as well as 352 non-SAPHO involvement cases, including their chief complaints, skin manifestations, radiological findings, and laboratory tests. We systematically reviewed previous published five representative huge cohorts from different countries to conclude several specific features of SAPHO by comparing with our case series. The score of each specific index is based on respective incidence and comparison of two cohorts was performed.

RESULT

In terms of complaint rates, all subjects of two cohorts suffered from osseous pain, which appeared in the anterior chest wall, spine, and limb which were calculated. In respect to dermatological lesions, SAPHO patients suffered from severe acne, and other patients (82.14%) accompanied with palmoplantar pustulosis. Having received radiological examinations, most SAPHO subjects rather than non-SAPHO involvement cases showed abnormal osteoarticular lesions under CT scanning and more detailed information under whole-body bone scintigraphy. Differences also emerged in elevation of inflammation values and rheumatic markers like HLA-B27. Based on our cases and huge cohorts documented, the early warning standard is set to be 5 scores.

CONCLUSIONS

SAPHO syndrome case series with 56 subjects were reported and an accumulative scoring system for the early reminder on SAPHO syndrome was proposed. The threshold of this system is set to be 5 points. Key Points • Fifty-six patients diagnosed by SAPHO syndrome with detailed symptoms and radiological findings were reported. • Comparison was made between the 56 SAPHO patients and 352 non-SAPHO involvement cases. • An accumulative scoring system for the early reminder on SAPHO syndrome was proposed and the threshold of this system is set to be five points.

Posttranslational modifications in psoriatic arthritis: A systematic literature review

BACKGROUND AND AIMS

Psoriatic arthritis (PsA) is an inflammatory complex condition. Posttranslational modifications influence almost all aspects of normal cell biology and pathogenesis. The aim of this systematic review was to collect all published evidence regarding posttranslational modifications in PsA, and the main outcome was to evaluate an association between disease outcomes and specific posttranslational modifications in PsA.

METHODS

A systematic electronic search was performed in Medline, PubMed, Cochrane, Virtual Health Library, and Embase databases. A total of 587 articles were identified; 59 were evaluated after removing duplicates and scanning, of which 47 were included. A descriptive analysis was conducted, with results grouped according to the type of posttranslational modification evaluated. The protocol was registered at the PROSPERO database.

RESULTS

Seven posttranslational modifications were identified: citrullination, carbamylation, phosphorylation, glycosylation, acetylation, methylation, and oxidative stress. Anti-citrullinated peptide and anti-carbamylated protein have been evaluated in rheumatoid arthritis. There is now information suggesting that these antibodies may be helpful in improving the diagnosis of PsA and that they may demonstrate a correlation with worse disease progression (erosions, polyarticular involvement, and poor treatment response). Glycosylation was associated with increased inflammation and phosphorylation products related to the expression of SIRT2 and pSTAT3 or the presence of Th17 and cytokine interleukin-22, suggesting a possible therapeutic target.

CONCLUSIONS

Posttranslational modifications often play a key role in modulating protein function in PsA and correlate with disease outcomes. Citrullination, carbamylation, phosphorylation, glycosylation, acetylation, methylation, and oxidative stress were identified as associated with diagnosis and prognosis.

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.

A retrospective analysis of the relationship between anti-cyclic citrullinated peptide antibody and interstitial lung disease in systemic sclerosis

Anti-cyclic citrullinated peptide antibody testing is used to diagnose rheumatoid arthritis and associated with interstitial lung disease in RA. Herein, we investigate the relationship between anti-CCP antibody and ILD in SSc. We performed a retrospective analysis at a tertiary medical center between 2005 and 2019. Patients with SSc, systemic lupus erythematosus, and polymyositis/dermatomyositis (PM/DM) were evaluated for anti-CCP antibody and ILD. Additionally, medical records of SSc patients with ILD were reviewed. SSc patients had the highest anti-CCP antibody positivity rate compared to those with SLE and PM/DM. The incidence of ILD was higher in SSc patients with anti-CCP antibody than in those without. The usual interstitial pneumonia (UIP) incidence was higher in the anti-CCP antibody-positive group than in the anti-CCP antibody-negative group. The DLCO was lower in the anti-CCP antibody-positive group than in the anti-CCP antibody-negative group. On multivariable analysis, factors associated with SSc-ILD were anti-CCP antibody or rheumatoid factor (β coefficient, 2.652 [95% CI 1.472 to 4.776]) and anti-Scl70 antibody (β coefficient, 4.011 [95% CI 2.142 to 7.508]). Anti-CCP antibody may be associated with a higher incidence of ILD in SSc. SSc patients with anti-CCP antibody may have more UIP pattern and lower DLCO.Trial Registration Retrospectively registered.

The Prevalence of Anticitrullinated Protein Antibodies in Older Poles-Results from a Population-Based PolSenior Study

Little is known about the occurrence of antibodies in older subjects. We analyzed the prevalence of anticitrullinated protein antibodies (anti-CCP) in a representative cohort of Polish older adults, participants of PolSenior substudy. Randomly selected 1537 serum samples of community-dwelling participants aged 65 and over. Questionnaires were completed by qualified interviewers and laboratory assessments served as a database for this analysis. The frequency of anti-CCP seropositivity (N = 50) was estimated at 3.25% (95% CI: 2.45-4.30%), being higher among women-4.05% (2.83-5.73%) than men-2.41% (1.48-3.86%). The frequency of anti-CCP seropositivity was decreasing with age from 4.29% in aged 65-74 years and 4.07% in 70-84 years to 1.50% in aged 85 years or above (p < 0.05). Hypoalbuminemia, inflammatory status (C-reactive protein >10 mg/dL or interleukin-6 ≥10 pg/mL), and female gender were associated with increased, while age ≥85 years with decreased risk of seropositivity. Multivariable logistic regression revealed that hypoalbuminemia, inflammatory status, and age ≥85 years were independently associated factors of anti-CCP seropositivity. The decreased frequency of anti-CCP seropositivity in the oldest old suggests shorter survival of the seropositive individuals who developed rheumatoid arthritis. It seems that low symptomatic RA remains frequently undiagnosed in older subjects.

Prediction of Immune-Related Adverse Events Induced by Immune Checkpoint Inhibitors With a Panel of Autoantibodies: Protocol of a Multicenter, Prospective, Observational Cohort Study

Introduction: Immune checkpoint inhibitor (ICI) therapy is markedly improving the prognosis of patients with several types of cancer. On the other hand, the growth in the use of these drugs in oncology is associated with an increase in multiple immune-related adverse events (irAEs), whose optimal prevention and management remain unclear. In this context, there is a need for reliable and validated biomarkers to predict the occurrence of irAEs in patients treated with ICIs. Thus, the main objective of this study is to evaluate the diagnostic performance of a sensitive routinely available panel of autoantibodies consisting of antinuclear antibodies, rheumatoid factor, and antineutrophil cytoplasmic antibodies to identify patients at risk of developing irAEs.

Methods and Analysis: A multicenter, prospective, observational, cohort study has been designed to be conducted in patients diagnosed with cancer amenable to ICI therapy. Considering the percentage of ICI-induced irAEs to be 25% and a loss to follow-up of 5%, it has been estimated that a sample size of 294 patients is required to detect an expected sensitivity of the autoantibody panel under study of 0.90 with a confidence interval (95%) of no less than 0.75. For 48 weeks, patients will be monitored through the oncology outpatient clinics of five hospitals in Spain. Immune-related adverse events will be defined and categorized according to CTCAE v. 5.0. All the patients will undergo ordinary blood tests at specific moments predefined per protocol and extraordinary blood tests at the time of any irAE being detected. Ordinary and extraordinary samples will be frozen and stored in the biobank until analysis in the same autoimmunity laboratory when the whole cohort reaches week 48. A predictive model of irAEs will be constructed with potential risk factors of immune-related toxicity including the autoantibody panel under study.

Ethics and Dissemination: This protocol was reviewed and approved by the Ethical Committee of the Basque Country and the Spanish Agency of Medicines and Medical Devices. Informed consent will be obtained from all participants before their enrollment. The authors declare that the results will be submitted to an international peer-reviewed journal for their prompt dissemination.

Recommendations for evaluation and diagnosis of extra-glandular manifestations of primary sjogren syndrome: results of an epidemiologic systematic review/meta-analysis and a consensus guideline from the Brazilian Society of Rheumatology (articular, pulmonary and renal)

Sjogren's Syndrome (SS) is an autoimmune disease characterized by lymphocytic infiltration of the exocrine glands and other organs, associated with sicca syndrome but also with systemic involvement with varying degrees of severity. Despite their importance, these systemic manifestations are not routinely evaluated and there is no homogenous approach to their diagnosis or evaluation. To close this gap, a panel of experts from the Brazilian Society of Rheumatology conducted a systematic review and meta-analysis on the identification of epidemiologic and clinical features of these manifestations and made recommendations based on the findings. Agreement between the experts was achieved using the Delphi method. The first part of this guideline summarizes the most important topics, and 11 recommendations are provided for the articular, pulmonary, and renal care of SS patients.

Consensus-based recommendations on the diagnosis, referral and clinical management of patients with psoriatic arthritis

Psoriatic arthritis (PsA) is a highly heterogeneous disease with complex manifestations. Limited understanding of the disease and non-availability of local guidelines pose challenges in the management of PsA in Saudi Arabia. Therefore, this expert consensus is aimed to provide recommendations on the management of patients with PsA, including referral pathway, definition of remission and treat-to-target (T2T) approach. A Delphi technique of consensus development was used involving an expert panel comprised of 10 rheumatologists, one dermatologist and one family physician. Based on the review of available published evidence and the opinions of clinical experts, key recommendations were developed. A consensus was achieved in defining the following: management guideline adaptable for Saudi Arabia, most useful screening tool, laboratory investigations, imaging tests and criteria for referring suspected PsA patients to a rheumatologist. In addition, an agreement was achieved in defining the T2T strategy and remission for the clinical management of PsA. Overall, these recommendations provide an evidence-based framework for the management of PsA patients in Saudi Arabia.

A Closer Look at the Role of Anti-CCP Antibodies in the Pathogenesis of Rheumatoid Arthritis-Associated Interstitial Lung Disease and Bronchiectasis

Rheumatoid arthritis (RA) is an articular disease with extra-articular manifestations. Pulmonary manifestations are not uncommon and can involve all compartments of the lungs with airway disease in the form of bronchiectasis or bronchiolitis, interstitial lung disease (ILD), pleural effusions and parenchymal lung nodules. The pulmonary features may present synchronously or after the articular disease, but, importantly, it may be the first presentation in 10% of patients in the absence of articular symptoms. Here we discuss the pathogenesis of RA lung involvement, particularly interstitial lung disease and bronchiectasis, focusing on the role anti-CCP antibodies (ACPAs). We highlight the complex interplay among genetic, environmental and immune factors. Furthermore, we explore the relationship of citrullination and smoking as well as the concept of interstitial pneumonia with autoimmune features (IPAF), where patients do not have evidence of another known cause of interstitial pneumonia and have incomplete features of connective tissue disease (CTD). We surmise that the frequency and titers of rheumatoid factor (RF) and ACPAs are increased in bronchiectasis and RA-bronchiectasis compared to RA patients without lung disease. ACPA is associated with more severe disease in both RA-ILD and RA-bronchiectasis even in the absence of articular symptoms. There is no clear prediction of development of articular RA with high ACPA levels in the context of positive ACPA and ILD; however, in RA-bronchiectasis, patients with positive antibodies can develop RA within a year after diagnosis of bronchiectasis. Though the primary focus of this narrative is to highlight the role of ACPA in pathogenesis and clinical practice, we also discuss the current treatment options and trials in RA-ILD and RA-bronchiectasis. Currently, there are no clear treatment guidelines. The treatments are now focusing on using a combination of immunosuppression and antifibrotic agents. Combination treatment targets both the fibrotic and inflammatory components of the disease process. Further studies are needed to identify the use of ACPA as a biomarker to tailor the treatment in RA-ILD and RA-bronchiectasis.

Antigen-specific tolerance approach for rheumatoid arthritis: Past, present and future

Rheumatoid arthritis is a chronic systemic autoimmune disease, affecting mainly the joints. It is caused by an adaptive immune reaction against self-antigens, leading to the over production of inflammatory cytokines and autoantibodies, mainly mediated by autoreactive CD4+ T cells and pathological B cell clones. The treatment options currently available rely on palliative global immunosuppression and do not restore tolerance to self-components. Here, we review antigen-specific tolerance approaches that have been developed to inhibit or delete autoreactive clones, while maintaining a potent immune system for rheumatoid arthritis. The first attempts relied on the oral ingestion of self-reactive peptides, with lukewarm results in human clinical trials. To enhance treatment efficacy, self-peptides have been engineered and combined with immunosuppressive molecules. In addition, several routes of delivery have been tested, in particular, nanoparticles carrying self-antigens and immunomodulatory molecules. More recently, transfer of immune cells, such as tolerogenic dendritic cells or regulatory T cells, has been considered to restore tolerance. Although promising results have been obtained in mouse models, the translation to humans remains highly challenging, mainly because the disease is already well developed when treatments start and because patient's specific self-antigens are often unknown. Nevertheless, these approaches hold great promises for long-term RA treatment.

Dermatologists' Role in the Early Diagnosis of Psoriatic Arthritis: Expert Recommendations

Psoriatic arthritis is a common type of inflammatory arthritis found in up to 40% of patients with psoriasis. Because skin involvement usually precedes joint involvement, dermatologists play a key role in early detection. Early diagnosis is important for reducing the risk of irreversible structural damage, attenuating the deterioration of physical function, and improving patients' quality of life. This consensus statement was drafted by a group of 9 dermatologists and 1 rheumatologist to provide simple recommendations to help dermatologists screen for psoriatic arthritis in patients with psoriasis. The experts offer consensus-based guidelines that draw on a review of available scientific evidence and on experience acquired in routine clinical practice.

Anti-cyclic citrullinated peptide antibody in psoriatic arthritis: a meta-analysis of its frequency and association with clinical features

OBJECTIVE

This study aimed to investigate the frequency of the anti-cyclic citrullinated peptide (anti-CCP) antibody in patients with psoriatic arthritis (PsA) and to assess its associations with clinical features of this disease.

METHODS

The Medline, EMBASE, and Cochrane databases were searched for studies that examined anti-CCP antibodies in patients with PsA. Meta-analyses of the frequency of the anti-CCP antibody in these patients and its association with polyarthritis, bone erosion, dactylitis, and enthesitis were then performed.

RESULTS

Fourteen studies with a combined total of 3291 patients with PsA met the inclusion criteria for this meta-analysis. The pooled overall frequency of anti-CCP antibodies was 9.8% (95% confidence interval [CI] = 7.1-13.3, p < 0.001). Stratification by ethnicity showed that the anti-CCP antibody frequency was lower in Europeans than in non-Europeans (8.5% vs. 14.0%). The meta-analysis showed a significant association of the anti-CCP antibody with polyarthritis (odds ratio [OR] = 4.390, 95% CI = 2.312-8.333, p < 0.001), bone erosion (OR = 2.800, 95% CI = 1.921-4.081, p < 0.001), and dactylitis (OR = 1.958, 95% CI = 1.340-2.861, p < 0.001). However, there was no association between this antibody and enthesitis.

CONCLUSIONS

Our meta-analysis demonstrated that the overall frequency of the anti-CCP antibody was 9.8% in patients with PsA, and its presence was associated with increased risks of polyarthritis, bone erosion, and dactylitis, but not of enthesitis.

Prevalence of anti-cyclic citrullinated peptide antibodies in patients with spondyloarthritis: A retrospective study

OBJECTIVES

Anti-cyclic citrullinated peptide (CCP) antibodies are frequently detected in the sera of patients with rheumatoid arthritis (RA). However, recent studies have revealed a potentially high prevalence rate of these antibodies in patients with other rheumatic disorders, causing confusion while diagnosing RA. Therefore, this study aimed to evaluate the positive rate of anti-CCP antibodies in other chronic arthritis diseases focusing on patients with spondyloarthritis (SpA).

METHODS

A total of 109 patients who were diagnosed with SpA at Yukioka Hospital from 1993 to 2018 were included in this retrospective analysis, including patients with ankylosing spondylitis (AS); psoriatic arthritis (PsA); synovitis, acne, pustulosis, hyperostosis, and osteitis syndrome (SAPHO); undifferentiated spondyloarthritis (uSpA); reactive arthritis (ReA); and inflammatory bowel disease-associated SpA (IBD).

RESULTS

Overall, 15.3% (16/109) of patients with SpA were positive for anti-CCP antibodies, including 2.3% (1/43) in AS, 23.1% (3/13) in SAPHO, 35.0% (7/20) in PsA, 14.8% (4/27) in uSpA, 0% (0/3) in ReA, and 33.3% (1/3) in IBD.

CONCLUSION

PsA patients have a significantly higher prevalence rate of positive anti-CCP antibodies among SpA patients, and the positive rates in SAPHO and uSpA were also high. These findings provide insight into the heterogeneity of SpA with relevance for RA differential diagnosis.

Precision medicine and management of rheumatoid arthritis

Precision medicine (PM) is a very commonly used term that implies a highly individualized and tailored approach to patient management. There are, however, many layers of precision, as for example taking an appropriate patient history, or performing additional lab or imaging tests are already helping to better tailor treatments to the right patient. All this adds to the narrower definition of PM, which implies using the unique molecular characteristics of a patient for management decisions. Big data has become an essential part of PM, including as much information as possible to improve precision of disease management, although integration of multi-source data continues to be a challenge in practical application. In research big data can identify new (sub-)phenotypes in unsupervised analyses, which ultimately advance precision by allowing new targeted therapeutic approaches. We will discuss the current status of PM in rheumatoid arthritis (RA) in the management areas of diagnosis, prognosis, selection of therapy, and decision to reduce therapy. PM markers for diagnosis of RA are usually markers of RA classification rather than diagnosis, and subtypes of RA are potentially underrecognized. Prognostic precision is well established for RA, including markers of disease activity or structure, as well as autoantibodies and genetics. The choice of the right compound in a patient identified to have a poor prognosis, however, remains widely arbitrary. Finally and most recently, the most reliable markers for a safe withdrawal of therapy continue to be lower levels of disease activity and longer presence of remission.

Measuring ACPA in the general population or primary care: is it useful?

Rheumatoid arthritis (RA) is associated with a significant disease burden and high costs for society. Because the disease has identifiable preclinical stages, screening and prevention have become a possibility in RA. Anticitrullinated peptide antibodies (ACPAs) are arguably the most likely candidate biomarker to screen for RA. This paper reviews the evidence for the use of ACPAs as a screening test in the broader general population, to identify individuals at high risk of subsequent onset of RA. We will review the diagnostic properties of the test and its positive and negative predictive value in different settings. We will discuss how ACPA testing could effectively be integrated in a broader screening strategy for RA.

Specificity of Anti-Citrullinated Protein Antibodies in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is an autoimmune disease of unknown etiology. The majority of individuals with RA are positive for the disease-specific anti-citrullinated protein antibodies (ACPAs). These antibodies are primarily of cross-reactive nature, hence, the true autoantigen to ACPA remains unidentified. In this study, we analyzed the reactivity of RA sera to several post-translationally modified epitopes, in order to further characterize the specific nature of ACPAs by immunoassays. Substituting citrulline with other amino acids, e.g., D-citrulline, homo-citrulline and methyl-arginine illustrated that ACPAs are utmost specific for citrullinated targets. Collectively, these findings support that ACPAs and citrullinated targets are specific for RA, making citrulline-containing peptide targets the most effective assays for detection of ACPAs.

Exploiting CD22 To Selectively Tolerize Autoantibody Producing B-Cells in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is an autoimmune disease that primarily affects the synovial joints and can lead to bone erosion and cartilage damage. One hallmark of RA is anticitrullinated protein autoantibodies (ACPA) and memory citrulline-specific B-cells, which have been implicated in RA pathogenesis. While depletion of B-cells with Rituximab improves clinical responses in RA patients, this treatment strategy leaves patients susceptible to infections. Here we use of Siglec-engaging Tolerance-inducing Antigenic Liposomes (STALs) to selectively target the citrulline-specific B-cells. ACPA production from purified human RA patients' B-cells in vitro was achieved through a set of stimulation conditions, which includes the following: BAFF, anti-CD40, IL-21, and LPS. In vivo generation of citrulline specific B-cells and ACPA production was accomplished by antigenic liposomes consisting of monophosphoryl lipid A (MPLA) and a cyclic citrullinated peptide (CCP) administered to SJL/J mice. We show that STALs that codisplay a high affinity CD22 glycan ligand and synthetic citrullinated antigen (CCP STALs) can prevent ACPA production from RA patients' memory B-cells in vitro. These CCP STALs were also effective in inducing tolerance to citrullinated antigens in SJL/J mice. The results demonstrate that tolerization of the B-cells responsible for ACPA can be achieved by exploiting the inhibitory receptor CD22 with high-affinity glycan ligands. Such a treatment strategy could be beneficial in the treatment of RA.

Guidelines for biomarkers in autoimmune rheumatic diseases - evidence based analysis

Autoimmune rheumatic diseases are characterised by an abnormal immune system response, complement activation, cytokines dysregulation and inflammation. In last years, despite many progresses in managing these patients, it has been shown that clinical remission is reached in less than 50% of patients and a personalised and tailored therapeutic approach is still lacking resulting in a significant gap between guidelines and real-world practice. In this context, the need for biomarkers facilitating early diagnosis and profiling those individuals at the highest risk for a poor outcome has become of crucial interest. A biomarker generally refers to a measured characteristic which may be used as an indicator of some biological state or condition. Three different types of medical biomarkers has been suggested: i. mechanistic markers; ii. clinical disease markers; iii. therapeutic markers. A combination of biomarkers from these different groups could be used for an ideal more accurate diagnosis and treatment. However, although a growing body of evidence is focused on improving biomarkers, a significant amount of this information is not integrated on standard clinical care. The overarching aim of this work was to clarify the meaning of specific biomarkers during autoimmune diseases; their possible role in confirming diagnosis, predicting outcome and suggesting specific treatments.

Prevalence and clinical correlates of rheumatoid factor and anticitrullinated protein antibodies in patients with idiopathic inflammatory myopathy

Objective

As rheumatoid factor (RF) and anticitrullinated protein antibodies (ACPAs) are not routinely tested in idiopathic inflammatory myositis (IIM), little is known about their prevalence and clinical implications in this patient group. In antisynthetase syndrome (ASS), presence of ACPA is reportedly associated with more severe and erosive arthritis. We aim to retrospectively determine the prevalence of RF and ACPA in a cross-sectional cohort of 121 patients diagnosed with IIM and to assess clinical associations.

Methods

Serum samples from 121 patients diagnosed with polymyositis (n=30), dermatomyositis (n=41), ASS (n=37), inclusion body myositis (n=1), necrotising autoimmune myopathy (n=5) or overlap myositis (n=7) were analysed. RF was evaluated by nephelometry (Immage 800, Beckman–Coulter); anti-CCP antibodies were identified using fluoro enzyme immunoassays (Immuno-Cap 250, Thermo Fisher). Values above 40 IU/mL and 7 U/mL were considered positive for RF and ACPA, respectively.

Results

The prevalence of RF and ACPA was 9.09% and 4.96%, respectively. No significant differences were observed between RF/ACPA positive versus negative patients. There was a numerical trend for RF-positive IIM patients to be older and have lower forced expiratory volume in 1 s levels.

Conclusions

RF and ACPA are prevalent in IIM, although we detected a lower prevalence than reported in previous studies. Presence of these antibodies in patients with IIM patients is not clinically relevant in our cohort.

Inflammatory arthritis in systemic sclerosis: What to do?

Musculoskeletal involvement, including arthritis and tendinopathy, is a common and important determinant of disability and impaired quality of life in systemic sclerosis. However, the treatment of arthritis in systemic sclerosis has not been studied as a primary outcome in randomized controlled trials, and arthritis-specific outcome measures for systemic sclerosis have not been sufficiently validated to date. Rheumatologists caring for patients with systemic sclerosis must address these complaints regularly despite the fact that the level of evidence for the treatment of systemic sclerosis–related inflammatory arthritis is limited. Consensus statements, based on treatments for related musculoskeletal aspects of rheumatoid arthritis, systemic lupus erythematosus, and other autoimmune diseases, support the use of methotrexate and hydroxychloroquine. Newer biologics, which have efficacy in the treatment of other autoimmune conditions, may show promise in the treatment of arthritis in systemic sclerosis. In this article, we review the current literature on the assessment and treatment of systemic sclerosis arthritis in order to address management considerations.

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

Introduction

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

Methods

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

Results

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

Conclusion

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

Autoantibodies Associated With Connective Tissue Diseases: What Meaning for Clinicians?

Connective tissue diseases (CTDs) such as systemic lupus erythematosus, systemic sclerosis, myositis, Sjögren's syndrome, and rheumatoid arthritis are systemic diseases which are often associated with a challenge in diagnosis. Autoantibodies (AAbs) can be detected in these diseases and help clinicians in their diagnosis. Actually, pathophysiology of these diseases is associated with the presence of antinuclear antibodies. In the last decades, many new antibodies were discovered, but their implication in pathogenesis of CTDs remains unclear. Furthermore, the classification of these AAbs is nowadays misused, as their targets can be localized outside of the nuclear compartment. Interestingly, in most cases, each antibody is associated with a specific phenotype in CTDs and therefore help in better defining either the disease subtypes or diseases activity and outcome. Because of recent progresses in their detection and in the comprehension of their pathogenesis implication in CTD-associated antibodies, clinicians should pay attention to the presence of these different AAbs to improve patient's management. In this review, we propose to focus on the different phenotypes and features associated with each autoantibody used in clinical practice in those CTDs.

Antibodies to a strain-specific citrullinated Epstein-Barr virus peptide diagnoses rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease. Anti-citrullinated protein antibodies (ACPA) are crucial for the serological diagnosis of RA, where Epstein-Barr virus (EBV) has been suggested to be an environmental agent in triggering the onset of the disease. This study aimed to analyse antibody reactivity to citrullinated EBV nuclear antigen-2 (EBNA-2) peptides from three different EBV strains (B95-8, GD1 and AG876) using streptavidin capture enzyme-linked immunosorbent assay. One peptide, only found in a single strain (AG876), obtained a sensitivity and specificity of 77% and 95%, respectively and showed high sequence similarity to the filaggrin peptide originally used for ACPA detection. Comparison of antibody reactivity to commercial assays found that the citrullinated peptide was as effective in detecting ACPA as highly sensitive and specific commercial assays. The data presented demonstrate that the citrullinated EBNA-2 peptide indeed is recognised specifically by RA sera and that the single peptide is able to compete with assays containing multiple peptides. Furthermore, it could be hypothesized that RA may be caused by (a) specific strain(s) of EBV.

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

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

Anti-citrullinated peptides antibodies in systemic sclerosis: Meta-analysis of frequency and meaning

OBJECTIVES

Diagnosis of systemic sclerosis (SSc) is partially determined by the presence of specific autoantibodies often associated with specific clinical features. Recent studies report the presence of ACPA in SSc. We aimed to evaluate the prevalence of ACPA in SSc and to assess their influence on clinical presentation of SSc.

METHODS

A systematic literature search was performed using PubMed and Cochrane databases' publications between 1999 and March 2017. Search terms were: "systemic sclerosis [MeSH] AND (ACPA OR anti-CCP OR rheumatoid factor OR cohort OR value diagnostic)". In a first step, we selected cohorts with >50 SSc patients with ACPA identification, for ACPA frequency determination. In a second step, we included studies that analysed clinical profiles according to ACPA status. Meta-analyses were performed when at least two studies were available.

RESULTS

First, we identified 13 observational studies with a total of 1231 SSc patients. The mean prevalence of ACPA in SSc was 9.2%. Secondly, we identified nine studies reporting clinical aspects according to ACPA status. Our meta-analyses showed a significant association between ACPA positivity and the presence of arthritis (odds ratio (OR)=22.48 [10.71-47.21]), joint erosions seen on X-rays (OR=14.79 [6.38-34.28]), pulmonary fibrosis (OR=2.75 [1.21-6.24]), oesophagus involvement (OR=2.72 [1.05-7.07]), and diffuse skin involvement (OR=2.21 [1.21-4.03]).

CONCLUSIONS

The prevalence of ACPA in scleroderma is 9.2%. Our meta-analysis shows an increased risk for erosive arthritis, pulmonary fibrosis, oesophagus involvement and diffuse skin involvement, in patients with ACPA-positive SSc. ACPA should be systematically included in SSc assessment.

The prevalence of ANA antibodies, anticentromere antibodies, and anti-cyclic citrullinated peptide antibodies in patients with primary Sjögren's syndrome compared to patients with dryness symptoms without primary Sjögren's syndrome confirmation

Objectives

Our study analyses the prevalence of ANA, anti-SS-A, anti-SS-B, and ACA and ACPA antibodies in patients with pSS and with dryness symptoms without pSS confirmation, and the association of ACPA and ACA antibodies with specific clinical symptoms.

Materials and methods

113 patients were divided into two groups: I – with diagnosed pSS (N = 75); and II – with dryness without pSS evidence (N = 38). Diagnostics: indirect immunofluorescence (IF; Hep-2 cell line) of antinuclear antibodies (ANA), anti-SS-A anti-SS-B antibodies determined with semi-quantitative method, autoantibody profile (14 antigens, ANA Profil 3 EUROLINE); basic laboratory, ophthalmic examination tests, minor salivary gland biopsy with focus score (FS), joint and lung evaluation, and ESSDAI questionnaire (pSS activity).

Results

88% of group I had ANA antibodies (1 : 320 titre), 5.3% at 1 : 160. Anti-SS-A antibodies were present in 88% of group I, including all ANA 1 : 160. Anti-SS-A antibodies positively correlated with greater and moderate activity of ESSDAI 5 (p = 0.046) and FS. The presence of SS-B antibodies significantly affected disease activity. ACPA present: group I – 13% (associated with higher arthritis incidence; p = 0.003); group II – 8%. ACA antibodies present in 4% of group I, but not in group II. No ACA association with interstitial lung changes (small ACA + group excludes full conclusions).

Conclusions

ANA antibodies should also be considered in a titre of less than 1 : 320, but the presence of anti-SS-A antibodies is still the most important immunological marker for pSS. Anti-SS-A antibodies correlate with higher disease activity (ESSDAI ≥ 5) and higher FS. The presence of the anti-SS-B antibody was significantly affected by higher activity of the disease. The incidence of arthritis was higher in patients with ACPA+ pSS compared to ACPA– (p = 0.003). There was no relationship between ACPA and arthritis in patients with dry-type syndrome without diagnosis of pSS.

Strongly positive anti-CCP antibodies in patients with sacroiliitis or reactive arthritis post-E. coli infection: A mini case-series based review

We report here on four cases of patients with strongly positive anti-citrullinated cyclic peptides (anti-CCP) antibodies and clinical features of seronegative spondyloarthritis (SpA) and reactive arthritis. The four patients had various clinical presentations: one had an initial diagnosis of seropositive rheumatoid arthritis (RA) with involvement of the sacroiliac joints (similar to previous reports of the association of two diseases); one had a clinical picture of reactive arthritis following an episode of an Escherichia coli positive urinary tract infection; and two had asymmetrical sacroiliitis (SII), but no evidence of peripheral joint involvement (never reported before). In all cases, high titers of anti-CCP antibodies were found. We present a comparison of the clinical manifestations, radiographic features and treatment regimens of these cases. Our report supports previous literature data of possible overlap existing between RA and SpA, but also presents for the first time the association of high titers of anti-CCP antibodies with SII and reactive arthritis in patients with no peripheral small joint involvement.

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.

Psoriasis in systemic lupus erythematosus: a single-center experience

The coexistence of psoriasis with systemic lupus erythematosus (SLE) has been reported in limited case series, raising hypotheses about shared pathogenetic mechanisms. Nevertheless, important differences regarding treatment do exist. The aim of the present study was to determine the prevalence and characteristics of psoriasis in a defined cohort of lupus patients. Patients with psoriasis were retrieved from the University of Toronto Lupus Clinic from its inception in 1970 up to 2015. Charts were hand-searched to collect information concerning demographic, clinical, and therapeutic variables. Patients were matched with non-psoriasis lupus patients to identify the impact of supervening psoriasis on lupus activity, damage accrual, and venous thromboembolic (VTEs) and cardiovascular events (CVEs). Psoriasis was diagnosed in 63 patients (49 females, 14 males) for a prevalence of 3.46% (63/1823). The male-to-female ratio was significantly higher in non-psoriasis patients (0.286 vs. 0.138, p = 0.017). Plaque psoriasis was the most prominent type (55/63, 87.3%) whereas three patients had pustular disease; one had psoriatic arthritis. Nine patients (14.3%) were administered systemic treatment with methotrexate (n = 5), azathioprine (n = 1), ustekinumab (n = 3), and etanercept (n = 1). Psoriasis was definitely deteriorated by hydroxychloroquine in one patient. There was no significant impact of psoriasis on disease activity, damage accrual, VTEs, and CVEs. The prevalence of psoriasis was twice as high as that of the general Canadian population in this lupus cohort. Plaque psoriasis was the most prominent subtype, and topical treatment was adequate in the majority of patients. Supervening psoriasis had no significant impact on lupus activity and damage accrual.

The Juvenile Psoriatic Arthritis Cohort in the CARRA Registry: Clinical Characteristics, Classification, and Outcomes

Objective.

Children with clinically diagnosed juvenile psoriatic arthritis (JPsA) who were enrolled in the Childhood Arthritis and Rheumatology Research Alliance (CARRA) registry (CARRA-JPsA) were classified according to pediatric International League of Associations for Rheumatology (ILAR) and adult criteria [Classification criteria for Psoriatic Arthritis (CASPAR)]. Data on demographic and clinical features at baseline and 1-year followup were analyzed and compared.

Methods.

Cross-sectional analysis was performed of CARRA-JPsA patients enrolled between May 2010 and December 2013 and stratified according to age at disease onset (≤ or > 4 yrs). Features of patients fulfilling ILAR and CASPAR criteria were compared at baseline and followup using chi square, Fisher’s exact, Mann-Whitney-McNemar, Wilcoxon signed rank, and t tests, as appropriate.

Results.

Among 361 children enrolled as CARRA-JPsA, 72.02% had symptom onset at > 4 years of age, with a male predominance and high prevalence of enthesitis. At followup, statistically significant improvements were reported in arthritis, dactylitis, enthesitis, psoriasis, sacroiliitis, and nail pitting, but not in health questionnaire (HQ) scores. Of the patients, 80.5% fulfilled ILAR criteria for JPsA. Fifty-two patients, whose disease fulfilled CASPAR criteria but had not been included in the JPsA cohort, manifested more enthesitis, sacroiliitis, inflammatory bowel disease and uveitis and less psoriasis.

Conclusion.

The data support division of patients with JPsA into 2 clinical subgroups, according to age at disease onset. Improvement in objective findings did not correlate with changes in HQ scores. Pediatric rheumatologists currently do not diagnose JPsA in all children whose disease manifestations meet CASPAR criteria. Unification of adult and pediatric PsA classification criteria warrants consideration.

Anti-citrullinated protein antibodies are linked to erosive disease in an observational study of patients with psoriatic arthritis

Objective. ACPAs are associated with bone destruction in RA. The aim of this study was to evaluate the association between ACPA and bone destruction in patients with a distinct inflammatory disorder, PsA.

Methods. We used baseline data from a large observational study of PsA patients preparing to initiate treatment with adalimumab to analyse demographic and disease characteristics by ACPA status. To ensure a homogeneous PsA study population, only patients with active psoriatic skin manifestations who met Classification of Psoriatic Arthritis criteria for PsA were included in the analyses, thereby minimizing the risk of including misdiagnosed RA patients. Multiple logistic regression analyses were used to explore potential associations between ACPA seropositivity and bone destruction.

Results. Of 1996 PsA patients who met the strict inclusion criteria, 105 (5.3%) were positive for ACPA. ACPA-positive patients had significantly higher swollen joint counts and 28-joint DAS values than ACPA-negative patients and significantly higher rates of erosive changes and dactylitis. Multiple logistic regression analysis confirmed the association of ACPA seropositivity with a 2.8-fold increase in the risk of erosive disease.

Conclusion. As has been previously shown for RA, ACPA is associated with bone destruction in PsA, suggesting that the osteocatabolic effect of ACPA is not confined to RA but is also detectable in the different pathogenetic context of a distinct disease entity.

Trial registration: ClinicalTrials.gov, NCT01111240

Assessment of the New 2012 EULAR/ACR Clinical Classification Criteria for Polymyalgia Rheumatica: A Prospective Multicenter Study

Objective.

To assess the performance of the new 2012 provisional European League Against Rheumatism (EULAR)/American College of Rheumatology (ACR) polymyalgia rheumatica (PMR) clinical classification criteria in discriminating PMR from other mimicking conditions compared with the previous 5 diagnostic criteria in a multicenter prospective study.

Methods.

Patients older than 50 years, presenting with new-onset bilateral shoulder pain with elevated acute-phase reactants (APR), were assessed for the fulfillment of the new and old classification/diagnostic criteria sets for PMR. At the end of the 1-year followup, 133 patients were diagnosed with PMR (expert opinion) and 142 with non-PMR conditions [69 rheumatoid arthritis (RA)]. Discriminating capacity, sensitivity, and specificity of the criteria sets were estimated.

Results.

Discriminating capacity of the new clinical criteria for PMR from non-PMR conditions and RA as estimated by area under the curve (AUC) were good with AUC of 0.736 and 0.781, respectively. The new criteria had a sensitivity of 89.5% and a specificity of 57.7% when tested against all non-PMR cases. When tested against all RA, seropositive RA, seronegative RA, and non-RA control patients, specificity changed to 66.7%, 100%, 20.7%, and 49.3%, respectively. Except for the Bird criteria, the 4 previous criteria had lower sensitivity and higher specificity (ranging from 83%–93%) compared with the new clinical criteria in discriminating PMR from all other controls.

Conclusion.

The new 2012 EULAR/ACR clinical classification criteria for PMR is highly sensitive; however, its ability to discriminate PMR from other inflammatory/noninflammatory shoulder conditions, especially from seronegative RA, is not adequate. Imaging and other modifications such as cutoff values for APR might increase the specificity of the criteria.

The specificity of anti-carbamylated protein antibodies for rheumatoid arthritis in a setting of early arthritis

INTRODUCTION

Anti-carbamylated protein (anti-CarP) antibodies have been described in rheumatoid arthritis (RA) and arthralgia patients at risk of developing RA. To what extent these autoantibodies are specific for RA is unknown. Therefore, we investigated the diagnostic performance of the presence of anti-CarP antibodies for RA in a setting of early arthritis.

METHODS

Anti-CarP antibodies were detected using carbamylated fetal calf serum as substrate. Anti-CCP2 antibodies were measured using enzyme-linked immunosorbent assay and immunoglobulin M (IgM) rheumatoid factor (RF) as part of routine care. Sera were derived from patients in the Leiden Early Arthritis Clinic cohort obtained at inclusion. Test characteristics were determined using the fulfillment of the 2010 RA criteria after 1 year as outcome.

RESULTS

In total 2086 early arthritis patients were studied regarding the presence of anti-CarP antibodies. We observed that the sensitivity and specificity of the presence of anti-CarP antibodies for RA were 44 % and 89 %, respectively. As a reference, sensitivity and specificity of the presence of anti-CCP2 antibodies were 54 % and 96 %, respectively, and of IgM-RF 59 % and 91 %. Patients harboring anti-CarP antibodies not classified as RA were mainly diagnosed with undifferentiated arthritis and less frequently reactive arthritis and psoriatic arthritis.

CONCLUSION

Anti-CarP antibodies are predominantly present in RA but can also be detected in other forms of arthritis.

Evaluation of anti-cyclic citrullinated peptide antibodies may be beneficial in RF-negative juvenile idiopathic arthritis patients

Despite the high diagnostic and prognostic performance in adult rheumatoid arthritis, the role of antibodies to cyclic citrullinated peptide (anti-CCP) in juvenile idiopathic arthritis (JIA) is controversial. Occurrence of anti-CCP was mainly seen in rheumatoid factor (RF)-positive polyarthritis patients. In the present study, our aim was to investigate the prevalence and significance of anti-CCP for subjects with JIA in our population. We evaluated anti-CCP reactivity in the sera of 70 patients with various subtypes of JIA in a prospective cohort study. Anti-CCP titres were correlated with the evolution of joint involvement and the presence of joint damage. Nine JIA patients were seropositive for anti-CCP with respect to the cut-off value of the test. In our cohort, 34 patients had a polyarticular joint disease, most of them being RF-negative (30/34, 88 %). All four RF-positive polyarthritis patients had high anti-CCP concentrations and an aggressive erosive disease. In the RF-negative JIA patients, anti-CCP reactivity was in lower titres but significantly associated with polyarticular joint involvement (p = 0.016) and also with the presence of joint damage (p < 0.001). Presence of anti-CCP, at both low and high concentration, was significantly associated with a more severe articular disease in our JIA patients. Investigating anti-CCP should clearly be taken into consideration even among patients with JIA subtypes other than RF-positive polyarthritis.

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.

Citrullination and autoimmunity

Autoimmune diseases are characterized by the body's own immune system attack to the self-tissues, a condition enabled, in predisposed subjects, by the reduction of self-tolerance. A central role has been recently recognized to post-translational modifications, since they can promote generation of neo-(auto)antigens and in turn an autoimmune response. During the last years great attention has been paid to citrullination, because of its role in inducing anti-citrullinated proteins/peptide antibodies (ACPA), a class of autoantibodies with diagnostic, predictive and prognostic value for Rheumatoid Arthritis (RA). Nonetheless, citrullination has been reported to be a process present in a wide range of inflammatory tissues. Indeed, citrullinated proteins have been detected also in other inflammatory arthritides and in inflammatory conditions other than arthritides (polymyositis, inflammatory bowel disease and chronic tonsillitis). Moreover, environmental exposure to cigarette smoke and nanomaterials of air pollution may be able to induce citrullination in lung cells prior to any detectable onset of inflammatory responses, suggesting that protein citrullination could be considered as a sign of early cellular damage. Accordingly, citrullination seems to be implicated in all those para-physiological processes, such as cells death pathways, in which intracellular calcium concentration raises to higher levels than in physiologic conditions: hence, peptidylarginine deiminases enzymes are activated during apoptosis, autophagy and NETosis, processes which are well-known to be implicated in autoimmunity. Taken together, these data support the hypothesis that rather than being a disease-dependent process, citrullination is an inflammatory-dependent condition that plays a central role in autoimmune diseases.