Patients' and rheumatologists' perceptions on dose reduction of rituximab in rheumatoid arthritis.

OBJECTIVE: The recommended dose of a rituximab course for the treatment of Rheumatoid Arthritis (RA) consists of two infusions of 1000 mg with a 2-week interval. Evidence is growing that a lower dose could be as effective. We aimed to investigate patients' and rheumatologists' perceptions on dose reduction of rituximab. METHODS: Patients with RA treated with rituximab, and rheumatologists were invited for a qualitative study via individual semi-structured interviews. Participants were recruited based on purposive sampling to ensure diversity. Interviews were analysed according to the principles of grounded theory and the constant comparative method. RESULTS: Sixteen patients and 13 rheumatologists were interviewed. Patients and rheumatologists perceived the benefits of rituximab dose reduction for reasons of safety and societal costs. Furthermore, available evidence for the effectiveness of lower doses was mentioned as an argument in favour, in addition to the possibility to tailor the dose based on the patients' clinical manifestations. However, patients and rheumatologists had concerns about the potential loss of effectiveness and quality of life. Moreover, some rheumatologists felt uncomfortable with dose reduction due to insufficient experience with rituximab in general. Patients and rheumatologists emphasised the importance of shared decision-making, underscoring the pivotal role of physicians in this process by explaining the reasoning behind dose reduction. CONCLUSION: Although some concerns on effectiveness were perceived, both patients and rheumatologists saw potential benefits of dose reduction in terms of safety, societal costs, and application of a personalised approach. As a result, most rheumatologists and patients showed a willingness to consider dose reduction strategies.

Classification of rheumatoid arthritis: is it time to revise the criteria?

Classification criteria have been developed for rheumatoid arthritis (RA) and other rheumatic diseases in order to gather a homogeneous patient population for clinical studies and facilitate the timely implementation of therapeutic measures. Although classification criteria are not intended to be used for diagnosis, they are frequently used to support the diagnostic process in clinical practice, including clinical decision-making. The 2010 American College of Rheumatology (ACR)/European Alliance of Associations for Rheumatology (EULAR) classification criteria for RA are capable of identifying the majority of symptomatic patients with RA already in the earliest stages of the disease who are not yet showing radiographic changes. These patients will also profit from the early implementation of therapy with disease-modifying antirheumatic drugs (DMARDs). However, the risk of misclassification is higher as compared with the former 1987 ACR criteria, which were considerably less sensitive to the recognition of patients with early RA. Of note, the presence of rheumatoid factors (RFs) and anticitrullinated protein antibodies (ACPAs) has been attributed equal weight in the 2010 ACR/EULAR criteria and may contribute up to 50% of the score needed for being classified as RA. However, while ACPAs have been proven to be the most specific serological markers of RA, the specificity of RF is moderate, especially at lower titres. This may lead to the misclassification of RF-positive patients and, consequently, the unjustified implementation of DMARD therapy. Therefore, issues arise on how comprehensive the criteria should be and whether they should be updated and adapted to findings from the past two decades that might increase both their specificity and sensitivity.

To flare or not to flare: patients' and rheumatologists' perceptions on the on-flare retreatment strategy of rituximab in rheumatoid arthritis.

Background: Several retreatment strategies exist for rituximab in rheumatoid arthritis (RA). In some countries, reimbursement criteria require a loss of disease control for rituximab retreatment. Understanding the patients' and rheumatologists' perceptions regarding this retreatment strategy would be informative in identifying the optimal treatment administration schedule. Objectives: This study aimed to uncover patients' and rheumatologists' perceptions regarding retreatment strategies of rituximab. Design: Qualitative study - semi-structured interviews. Methods: Patients with RA, treated with rituximab, and rheumatologists were invited to participate in a qualitative study consisting of individual, in-depth, semi-structured interviews. Interviews were analysed according to the Qualitative Analysis Guide of Leuven. Results: A total of 16 patients and 13 rheumatologists were interviewed. Benefits (e.g. decreased risk of overtreatment, cost savings and long-lasting effectiveness of rituximab) and barriers (e.g. fluctuating disease activity, slow mode of action and increased glucocorticoid use) of on-flare retreatment were identified. To effectively treat on-flare, flares must first be identified timely. Both stakeholder groups acknowledged that patients are capable of recognizing flares. However, the patient's ability to discriminate between inflammatory and other types of pain was perceived as difficult. Furthermore, patients and rheumatologists stressed that patients must timely seek professional help in case of a flare, followed by a swift response from the rheumatologists. Remarkably, retreatment was approached in various ways among rheumatologists, and not always adhering strictly to the on-flare reimbursement criteria. Conclusion: This study revealed that both stakeholder groups perceived the heterogeneity in recognition of and reaction to a flare as important in influencing the effectiveness of the on-flare retreatment strategy. Moreover, this study identified the benefits and barriers of treating on-flare, which could be informative for daily practice decisions.

Natural carboxyterminal truncation of human CXCL10 attenuates glycosaminoglycan binding, CXCR3A signaling and lymphocyte chemotaxis, while retaining angiostatic activity.

BACKGROUND: Interferon-γ-inducible protein of 10 kDa (IP-10/CXCL10) is a dual-function CXC chemokine that coordinates chemotaxis of activated T cells and natural killer (NK) cells via interaction with its G protein-coupled receptor (GPCR), CXC chemokine receptor 3 (CXCR3). As a consequence of natural posttranslational modifications, human CXCL10 exhibits a high degree of structural and functional heterogeneity. However, the biological effect of natural posttranslational processing of CXCL10 at the carboxy (C)-terminus has remained partially elusive. We studied CXCL10(1-73), lacking the four endmost C-terminal amino acids, which was previously identified in supernatant of cultured human fibroblasts and keratinocytes. METHODS: Relative levels of CXCL10(1-73) and intact CXCL10(1-77) were determined in synovial fluids of patients with rheumatoid arthritis (RA) through tandem mass spectrometry. The production of CXCL10(1-73) was optimized through Fmoc-based solid phase peptide synthesis (SPPS) and a strategy to efficiently generate human CXCL10 proteoforms was introduced. CXCL10(1-73) was compared to intact CXCL10(1-77) using surface plasmon resonance for glycosaminoglycan (GAG) binding affinity, assays for cell migration, second messenger signaling downstream of CXCR3, and flow cytometry of CHO cells and primary human T lymphocytes and endothelial cells. Leukocyte recruitment in vivo upon intraperitoneal injection of CXCL10(1-73) was also evaluated. RESULTS: Natural CXCL10(1-73) was more abundantly present compared to intact CXCL10(1-77) in synovial fluids of patients with RA. CXCL10(1-73) had diminished affinity for GAG including heparin, heparan sulfate and chondroitin sulfate A. Moreover, CXCL10(1-73) exhibited an attenuated capacity to induce CXCR3A-mediated signaling, as evidenced in calcium mobilization assays and through quantification of phosphorylated extracellular signal-regulated kinase-1/2 (ERK1/2) and protein kinase B/Akt. Furthermore, CXCL10(1-73) incited significantly less primary human T lymphocyte chemotaxis in vitro and peritoneal ingress of CXCR3+ T lymphocytes in mice. In contrast, loss of the four endmost C-terminal residues did not affect the inhibitory properties of CXCL10 on migration, proliferation, wound closure, phosphorylation of ERK1/2, and sprouting of human microvascular endothelial cells. CONCLUSION: Our study shows that the C-terminal residues Lys74-Pro77 of CXCL10 are important for GAG binding, signaling through CXCR3A, T lymphocyte chemotaxis, but dispensable for angiostasis.

Evaluation of discontinuation for adverse events of JAK inhibitors and bDMARDs in an international collaboration of rheumatoid arthritis registers (the 'JAK-pot' study).

BACKGROUND: In a clinical trial setting, patients with rheumatoid arthritis (RA) taking the Janus kinase inhibitor (JAKi) tofacitinib demonstrated higher adverse events rates compared with those taking the tumour necrosis factor inhibitors (TNFi) adalimumab or etanercept. OBJECTIVE: Compare treatment discontinuations for adverse events (AEs) among second-line therapies in an international real-world RA population. METHODS: Patients initiating JAKi, TNFi or a biological with another mode of action (OMA) from 17 registers participating in the 'JAK-pot' collaboration were included. The primary outcome was the rate of treatment discontinuation due to AEs. We used unadjusted and adjusted cause-specific Cox proportional hazard models to compare treatment discontinuations for AEs among treatment groups by class, but also evaluating separately the specific type of JAKi. RESULTS: Of the 46 913 treatment courses included, 12 523 were JAKi (43% baricitinib, 40% tofacitinib, 15% upadacitinib, 2% filgotinib), 23 391 TNFi and 10 999 OMA. The adjusted cause-specific hazard rate of treatment discontinuation for AEs was similar for TNFi versus JAKi (1.00, 95% CI 0.92 to 1.10) and higher for OMA versus JAKi (1.11, 95% CI 1.01 to 1.23), lower with TNFi compared with tofacitinib (0.81, 95% CI 0.71 to 0.90), but higher for TNFi versus baricitinib (1.15, 95% CI 1.01 to 1.30) and lower for TNFi versus JAKi in patients 65 or older with at least one cardiovascular risk factor (0.79, 95% CI 0.65 to 0.97). CONCLUSION: While JAKi overall were not associated with more treatment discontinuations for AEs, subgroup analyses suggest varying patterns with specific JAKi, such as tofacitinib, compared with TNFi. However, these observations should be interpreted cautiously, given the observational study design.

Patterns and determinants of response to novel therapies in juvenile and adult-onset polyarthritis.

Biologic and targeted synthetic DMARDs (b/tsDMARDs) have revolutionized the management of multiple rheumatic inflammatory conditions. Among these, polyarticular JIA (pJIA) and RA display similarities in terms of disease pathophysiology and response pattern to b/tsDMARDs. Indeed, the therapeutic efficacy of novel targeted drugs is variable among individual patients, in both RA and pJIA. The mechanisms and determinants of this heterogeneous response are diverse and complex, such that the development of true 'precision'-medicine strategies has proven highly challenging. In this review, we will discuss pathophysiological, patient-specific, drug-specific and environmental factors contributing to individual therapeutic response in pJIA in comparison with what is known in RA. Although some biomarkers have been identified that stratify with respect to the likelihood of either therapeutic response or non-response, few have proved useful in clinical practice so far, likely due to the complexity of treatment-response mechanisms. Consequently, we propose a pragmatic, patient-centred and clinically based approach, i.e. personalized instead of biomarker-based precision medicine in JIA.

Initial glucocorticoid bridging in rheumatoid arthritis: does it affect glucocorticoid use over time?

OBJECTIVES: To compare the use of glucocorticoids (GC) over time in patients with rheumatoid arthritis (RA) who were or were not treated initially with GC bridging therapy. METHODS: Data from the BeSt, CareRA and COBRA trials were combined in an individual patient data (IPD) meta-analysis. We compared GC use between bridgers and non-bridgers at 12, 18 and 24 months from baseline with mixed-effects regression analysis. Secondary outcomes were mean cumulative GC dose until 24 months after baseline with and without the bridging period, Disease Activity Score based on 28 joints (DAS28) over time and number of disease-modifying antirheumatic drug (DMARD) changes. RESULTS: 252/625 patients (40%) were randomised to GC bridging (bridgers). Excluding the period of bridging, later GC use was low in both groups and cumulative doses were similar. Mean DAS28 was similar between the groups, but bridgers improved more rapidly (p<0.001) in the first 6 months and the bridgers required significantly fewer changes in DMARDs (incidence rate ratio 0.59 (95% CI 0.38 to 0.94)). GC use was higher in the bridgers at t=12 months (OR 3.27 (95% CI 1.06 to 10.08)) and the bridging schedules resulted in a difference in cumulative GC dose of 2406 mg (95% CI 1403 to 3408) over 24 months. CONCLUSION: In randomised trials comparing GC bridging and no GC bridging, bridgers had a more rapid clinical improvement, fewer DMARD changes and similar late use of GC compared with non-bridgers. GC bridging per protocol resulted, as could be expected, in a higher cumulative GC dose over 2 years.

Patient-physician discordance impairs outcomes in early rheumatoid arthritis through less consistent treat-to-target implementation.

OBJECTIVES: We aimed to assess whether patient-physician discordance regarding disease activity affects T2T-implementation and clinical outcomes in rheumatoid arthritis (RA). METHODS: This was an analysis of the 2-year T2T-guided trial Care in early RA (CareRA). During year 1, DMARD escalations were mandated by the protocol when DAS28-CRP was >3.2. During year 2, treatment was at the rheumatologists' discretion. At each visit we assessed T2T-implementation, defined as escalating DMARDs if DAS28-CRP >3.2. Patient-physician discordance was defined by the discordance score (DS), a weighted difference between patient-reported and clinical/laboratory outcomes. Using generalised linear mixed models and multilevel mediation analysis, we studied the association between time-varying DS, T2T-implementation and the odds of remission (SDAI ≤3.3), physical functioning (HAQ-score), and radiographic progression at year 2. RESULTS: Over 2 years, 379 patients were assessed at 3129 follow-up visits. On 445 (14%) of these visits, DAS28-CRP was >3.2, and DMARDs were escalated in 217/445 (49%) of such cases. T2T-implementation declined over time and was consistently lower during the second year (year 1: 57-66%; year 2: 17-52%). Higher DS over time was negatively associated with remission and physical functioning at year 2, partly mediated by a lower proportion of T2T-adherent visits. No such association was found for radiographic progression. CONCLUSION: Even in a trial setting, T2T was applied on only around 50% of visits. T2T was less likely to be implemented with increasing patient-physician discordance regarding disease activity, which was in turn associated with less remission and worse functional outcome, but not with radiographic progression.

Viewpoint: Supporting mental health in the current management of rheumatoid arthritis: time to act!

Although clinical outcomes of RA have vastly improved in recent years, the disease's mental health impact has seemingly not decreased to the same extent. Even today, learning to live with RA is an active process involving several psychological, cognitive, behavioural and emotional pathways. Consequently, mental health disorders are more common in the context of RA than in the general population, and can be particularly detrimental both to patients' quality of life and to clinical outcomes. However, mental health is a spectrum and represents more than the absence of psychological comorbidity, and supporting patients' psychological wellbeing should thus involve a more holistic perspective than the mere exclusion or specific treatment of mental health disorders. In this viewpoint article, we build on mechanistic and historical insights regarding the relationship between RA and mental health, before proposing a practical stepwise approach to supporting patients' mental health in daily clinical practice.

Effectiveness and feasibility of a mobile health self-management intervention in rheumatoid arthritis: study protocol for a pragmatic multicentre randomised controlled trial (AEGORA).

BACKGROUND: Rheumatoid arthritis (RA) considerably impacts patients' lives. Patients' confidence in their ability to manage this impact, or self-efficacy, can be supported with self-management interventions. One approach is to use mobile health (mHealth) applications, which can additionally provide insight into disease impact by remotely monitoring patient-reported outcomes. However, user engagement with mHealth-apps is variable, and concerns exist that remote monitoring might make patients overly attentive to symptoms. METHODS: App-based Education and GOal setting in RA (AEGORA) is a multicentre, pragmatic randomised controlled trial investigating an mHealth-based self-management intervention to improve self-efficacy and remotely monitor disease impact in patients with RA. The intervention is provided via an adapted version of the application Sidekick (Sidekick Health, Reykjavik, Iceland) and consists of education, goal setting, lifestyle advice, and remote assessment of the Rheumatoid Arthritis Impact of Disease (RAID) questionnaire. Across two centres, 120 patients will be recruited and randomised (2:1:1) to usual care or intervention group A/B (study app with weekly/monthly prompts to complete the RAID, respectively). Outcomes are assessed at baseline and after 4-6 months. The primary endpoint is a clinically important improvement (≥ 5.5/110) in the Arthritis Self-Efficacy Scale in the combined intervention group compared to usual care. Secondary endpoints are (a) non-inferiority regarding pain catastrophising, as a measure of symptom hypervigilance; (b) superiority regarding the RAID, sleep quality, and physical activity; and (c) participant engagement with the study app. Finally, the relationship between engagement, prompted frequency of RAID questionnaires, and the primary and secondary outcomes will be explored. DISCUSSION: The AEGORA trial aims to study the effectiveness of mHealth-based, multicomponent self-management support to improve self-efficacy in the context of RA, while providing potentially valuable insights into temporal disease activity dynamics and the feasibility and possible negative effects of remote symptom monitoring in this population. TRIAL REGISTRATION: Clinicaltrials.gov NCT05888181. Retrospectively registered on March 23, 2023. Study inclusion started on March 3, 2023.

Ultrasonographic Presentation and Anatomic Distribution of Lung Involvement in Patients with Rheumatoid Arthritis.

BACKGROUND: Rheumatoid arthritis (RA) is a chronic auto-immune disease, typically affecting the joints, which can also present with lung involvement (pleuritis, interstitial lung disease, pulmonary nodules, etc.). Lung ultrasound (LUS) is an upcoming tool in the detection of these pulmonary manifestations. METHODS: We performed a 72-window LUS in 75 patients presenting to the outpatient rheumatology clinic and describe the abnormalities (presence of B-lines (vertical comet-tail artefacts), pleural abnormalities, pleural effusions, and subpleural nodules) on lung ultrasound. We created a topological mapping of the number of B-lines per intercostal zone. RESULTS: We observed pleural effusions, pleural abnormalities, and pleural nodules in, respectively, 1.3%, 45.3%, and 14% of patients. There were 35 (46.7%) patients who had less than 5 B-lines, 15 (20%) patients who had between 5 and 10 B-lines, 11 (14.6%) between 10 and 20, 10 (13.3%) between 20 and 50, 1 (1.3%) between 50 and 100, and 3 (4%) of patients who had more than 100 B-lines. CONCLUSIONS: LUS in patients with RA shows an array of abnormalities ranging from interstitial syndromes to pleural abnormalities, subpleural nodules, and pleural effusions. Hotspots for the presence of B-lines are situated bilaterally in the posterior subscapular regions, as well as the anterior right mid-clavicular region.

Effect of Filgotinib on Body Mass Index (BMI) and Effect of Baseline BMI on the Efficacy and Safety of Filgotinib in Rheumatoid Arthritis.

INTRODUCTION: This post hoc analysis of the phase 3 rheumatoid arthritis (RA) filgotinib clinical trial program assessed the effect of filgotinib on body mass index (BMI) in patients with RA and the impact of BMI on the efficacy and safety of filgotinib. METHODS: FINCH 1-3 were randomized, double-blind, active- or placebo-controlled phase 3 trials of filgotinib 100 and 200 mg in patients with RA (N = 3452). BMI assessments included the mean change from baseline in BMI and the proportion of patients whose BMI increased by incremental thresholds. Efficacy measures included American College of Rheumatology (ACR) 20/50/70 response and low disease activity/remission according to Disease Activity Score 28 using C-reactive protein. The exposure-adjusted incident rate (EAIR) of adverse events (AEs) was assessed by baseline BMI, using integrated data from the FINCH 1-4 and the phase 2 DARWIN 1-3 studies (total filgotinib exposure = 8085 patient-years). RESULTS: Mean change from baseline in BMI over time was similar across treatment arms. In most patients, BMI increased by ≤ 1 or 2 kg/m2 at both weeks 12 and 24, regardless of treatment group or baseline BMI; few patients had increases of ≥ 4 kg/m2. For most efficacy measures, filgotinib 200 mg was more efficacious than filgotinib 100 mg or active comparators or placebo across BMI subgroups. For the higher filgotinib dose, the EAIR of serious treatment-emergent AEs, venous thrombotic and embolic events, and major adverse cardiovascular events increased with increasing BMI. CONCLUSIONS: Filgotinib did not lead to substantial changes in BMI, and BMI did not appear to affect the efficacy of filgotinib. TRIAL REGISTRATION: ClinicalTrials.gov identifiers: NCT02889796, NCT02873936, NCT02886728, NCT03025308, NCT01888874, NCT01894516, NCT02065700.

Some rheumatoid arthritis treatments cause patients to gain weight or are less effective in patients with obesity than in patients without obesity. Also, obesity can make rheumatoid arthritis worse. Filgotinib is a rheumatoid arthritis treatment that was evaluated in seven randomized clinical studies (FINCH 1­4 and DARWIN 1­3). We investigated whether filgotinib causes changes in weight and whether body mass index (BMI) affects the efficacy or safety of filgotinib. We analyzed how the BMI of patients who participated in FINCH 1, 2, or 3 changed over time. Most patients had a small increase in BMI (around 1­2 kg/m²) after 24 weeks of filgotinib treatment. This change in BMI was not affected by patients' BMI at baseline. Baseline BMI did not impact the efficacy of filgotinib, which was assessed using standard measures of disease activity. Filgotinib was more effective than other rheumatoid arthritis treatments and placebo in all patients, regardless of BMI subgroup. Using safety data from all seven clinical studies (FINCH 1­4 and DARWIN 1­3), we found that some adverse events occurred more often in patients with obesity (a BMI of ≥ 30 kg/m²) than in those without obesity. The increased adverse events included venous thrombotic and embolic events and major adverse cardiovascular events, for which obesity is a known risk factor. These results show that filgotinib did not substantially change BMI (which increased by around 1­2 kg/m² in most patients), and that baseline BMI did not affect the efficacy of filgotinib.

Plasma cells are not restricted to the CD27+ phenotype: characterization of CD27-CD43+ antibody-secreting cells.

Circulating antibody-secreting cells are present in the peripheral blood of healthy individuals reflecting the continued activity of the humoral immune system. Antibody-secreting cells typically express CD27. Here we describe and characterize a small population of antibody-secreting class switched CD19+CD43+ B cells that lack expression of CD27 in the peripheral blood of healthy subjects. In this study, we characterized CD27-CD43+ cells. We demonstrate that class-switched CD27-CD43+ B cells possess characteristics of conventional plasmablasts as they spontaneously secrete antibodies, are morphologically similar to antibody-secreting cells, show downregulation of B cell differentiation markers, and have a gene expression profile related to conventional plasmablasts. Despite these similarities, we observed differences in IgA and IgG subclass distribution, expression of homing markers, replication history, frequency of somatic hypermutation, immunoglobulin repertoire, gene expression related to Toll-like receptors, cytokines, and cytokine receptors, and antibody response to vaccination. Their frequency is altered in immune-mediated disorders. Conclusion: we characterized CD27-CD43+ cells as antibody-secreting cells with differences in function and homing potential as compared to conventional CD27+ antibody-secreting cells.

SARS-CoV-2 infection and COVID19 vaccination across eight immune-mediated inflammatory disorders: A prospective, real-life Belgian cohort study - the BELCOMID study.

Background: The risks and impact of COVID19 disease and vaccination in patients with Immune Mediated Inflammatory Diseases (IMID) remain incompletely understood. IMID patients and particularly patients receiving immunosuppressive treatment were excluded from the original, registrational phase-3 COVID19 vaccination efficacy and safety trials. Real-world observational data can help to fill this gap in knowledge. The BELCOMID study aims to explore the interaction between IMIDs, immune-modulating treatment modalities and SARS-CoV-2 infection and vaccination in a real-life patient cohort. Methods: A multidisciplinary, prospective, observational cohort study was set up. Consecutive patients with IMIDs of the gut, joints and skin followed at two high-volume referral centers were invited. Both patients under conventional treatment or targeted immune modulating therapies were included. Patient data and serological samples were collected at 3 predefined periods (before COVID19 vaccination, before booster vaccination, after booster vaccination). Primary endpoints were positive PCR-test and SARS-CoV-2 serology reflecting previous SARS-CoV-2 infection or vaccination. Associations with IMID treatment modality and IMID disease activity were assessed. Results of the first two inclusion periods (before booster vaccination) are reported. Results: At the first inclusion period data was assessed of 2165 IMID-patients before COVID19 vaccination. At the second inclusion period, data of 2065 patients was collected of whom 1547 had received complete baseline COVID19 vaccination and 222 were partially vaccinated. SARS-CoV-2 infection rate remained low in both groups. No significant increase in IMID flare-up rate was noted in patients with prior SARS-CoV-2 infection. Multiple logistic regression analyses did not show a significant influence of IMID-treatment modality or IMID activity on SARS-CoV-2 infection risk (based on PCR positivity or N-serology). Patients treated with conventional immunomodulators, systemic steroids, and patients on advanced therapies such as biologics or small molecules, had reduced S-antibody seroconversion. S-antibody response was also lower in patients without prior SARS-CoV-2 infection and in active smokers. A subset of patients (4.1%) had no S- nor N-antibody seroconversion following complete baseline vaccination. Conclusion: The BELCOMID study results confirm the benign course of COVID19 infection and vaccination in a large real-life IMID-population. However, our results underscore the need for repeated vaccination and smoking cessation in patients with IMIDs treated with immune-modulating therapies or systemic steroids during the pandemic.

Novel method to quantify peptidylarginine deiminase activity shows distinct citrullination patterns in rheumatoid and juvenile idiopathic arthritis.

Introduction: Peptidylarginine deiminases (PADs) mediate citrullination, an irreversible posttranslational modification that converts arginine to citrulline residues in proteins. Rheumatoid arthritis (RA) is characterized by unique autoantibodies that recognize citrullinated peptides, which are highly specific for this disease. However, the mechanism preceding the anti-citrulline response remains largely unclear. PAD enzymes are known to fuel the autoimmune response by generating autoreactive epitopes, and sustain local synovial inflammation through neutrophil extracellular trap formation. Therefore, detecting endogenous PAD activity is important to understand the pathogenesis of arthritis. Methods: In this study, we improved a fluorescent in vitro assay to enable endogenous PAD activity characterization in complex samples. We combine the use of an in-house synthetic, arginine-rich substrate and a negatively charged dye molecule to visualize enzyme activity. Results: This pioneering PAD assay allowed profiling of active citrullination in leukocytes and in local and systemic samples of an arthritis cohort. Our results reveal that RA and juvenile idiopathic arthritis (JIA) synovial fluids display similar levels of PAD activity. In contrast, citrullination was limited in joints of patients suffering from gout or Lyme's disease. Interestingly, in blood, a higher level of extracellular citrullination was only found in anti-CCP-positive RA patients. Discussion: Our finding suggests that enhanced synovial PAD activity drives the loss in tolerance towards citrullinated proteins and that systemic citrullination may indicate the risk for developing citrulline-specific autoimmunity.