Annals of the Rheumatic Diseases

BackgroundADP-ribosylation factor-like protein 15 (ARL15) is a rheumatoid arthritis (RA) susceptibility gene identified through GWAS. Previous studies suggested a role for ARL15 in synovial fibroblast (SF) pathogenicity, but its contribution to inflammatory arthritis remains unclear. We investigated the inflammatory role of ARL15 and its therapeutic potential in RA. MethodsARL15 was overexpressed in MH7A cells followed by bulk RNA sequencing and pathway enrichment analyses. Therapeutic relevance was evaluated in collagen-induced arthritis (CIA) mouse model using anti-ARL15 monoclonal antibodies, ARL15-targeting siRNA, or isoquinoline. Arthritis scores, histopathology, micro-CT and serum cytokines were assessed. Publicly available single-cell RNA sequencing (scRNA-seq) datasets were analyzed to determine ARL15 expression in RASF subsets. ResultsARL15 overexpression induced a pro-inflammatory transcriptional program characterized by upregulation of IL1A, IL1B, IL6, IL8, CXCL1, CXCL10, and CCL20. Gene set enrichment analysis revealed activation of IL6-JAK-STAT, TNF, interferon-response, and KRAS signaling pathways, with suppression of oxidative phosphorylation, lipid metabolism, and mTORC1 signaling. In CIA mice, ARL15 inhibition significantly reduced arthritis severity, inflammatory infiltrates, and joint destruction while preserving cartilage and bone integrity. Serum TNF-, IL-6, and IL-1{beta} levels were markedly decreased following ARL15 blockade. Combination monoclonal antibody treatment demonstrated the greatest therapeutic benefit. scRNA-seq analysis showed broad ARL15 expression across RA fibroblast populations, with enrichment in inflammatory lining and SF subsets. ConclusionsARL15 is a pro-inflammatory regulator of SF activation and arthritis progression. Integrated transcriptomic, single-cell, and in vivo analyses identify ARL15 as a therapeutic target for RA and support further translational development of ARL15 based therapies.

Background and objectivesMyasthenia gravis associated with antibodies against muscle-specific kinase (MuSK-MG) is a well-characterized IgG4-autoimmune disease, however, the mechanisms driving IgG4 predominance remain poorly understood. This study investigated whether promoter DNA methylation of cytokine genes involved in IgG4 class switching is associated with this immune response. MethodsPeripheral blood mononuclear cells were isolated from MuSK-MG patients (n=36), acetylcholine receptor myasthenia gravis (AChR-MG) patients as disease controls (n=7), and sex-matched healthy controls (n=12). Promoter DNA methylation of IL4, IL10, and IL13 was assessed by methylation-sensitive high-resolution melting and relative cytokine mRNA expression by qPCR. Associations with clinical variables, and antibody levels were subsequently evaluated. ResultsMuSK-MG patients showed lower median IL13 promoter methylation compared with healthy controls (p = 0.004). Median IL4 promoter methylation was also reduced in MuSK-MG compared with healthy controls (p < 0.001) and AChR-MG disease controls (p < 0.001), whereas no differences were observed for IL10 promoter methylation. Relative mRNA expression of IL4 (p = 0.0005), IL10 (p = 0.0462), and IL13 (p = 0.0002) was increased in MuSK-MG compared with AChR-MG. Compared with healthy controls, only IL4 expression remained significantly increased (p < 0.0001). Promoter methylation was inversely correlated with relative mRNA expression for IL4 (p < 0.0001), while IL13 showed a similar but non-significant trend (p = 0.054), no association was observed for IL10. Multivariable analysis demonstrated that treatment at sampling was independently associated with lower IL10 and IL13 promoter methylation, whereas no associations were observed with age, sex, disease phase, or disease duration. Promoter methylation did not correlate with total serum IgG4 or anti-MuSK IgG4 levels. DiscussionMuSK-MG is associated with selective hypomethylation of IL4 and IL13 promoters accompanied by increased cytokine gene expression, while IL10 promoter methylation remains unchanged. The association between treatment and IL10 and IL13 promoter methylation suggests that immunosuppressive therapy may influence epigenetic regulation in MuSK-MG. Together, these findings support a role for epigenetic dysregulation of Th2-associated cytokines in the immunological environment associated with IgG4 subclass switch. To our knowledge, this is the first study investigating IL4, IL10, and IL13 promoter DNA methylation in MuSK-MG.

Nociplastic pain features are common in systemic lupus erythematosus (SLE), yet its longitudinal trajectory remain poorly characterized. SLE patients in the FORWARD Databank were classified as Minimal, Type 1, Type 2, or Mixed using the Polysymptomatic Distress Scale (PSD[&ge;]8) and the Systemic Lupus Activity Questionnaire (SLAQ) inflammatory domain score ([&ge;]2). Cross-sectional analyses (N=372) compared clinical outcomes and medication use. Longitudinal analyses (n=301; median 3.7 years) characterized phenotype transitions using continuous-time Markov models and identified latent trajectories using joint group-based trajectory modeling (GBTM). At baseline, 29% were Minimal, 12% Type 1, 13% Type 2, and 47% Mixed. Functional impairment increased stepwise: from Minimal to Mixed, SF-36 physical component scores decreased from 49.7 to 30.0 and PROMIS Pain Interference scores increased from 46.2 to 63.6 (both p<0.001). Organ damage, depression, and opioid use were highest in Mixed. Longitudinally, Minimal and Mixed were persistent (mean duration 2.0 and 1.8 years; one-year retention 70%), while Type 1 and Type 2 were transient (~0.5 years; retention 18% and 28%). Exit trajectories were asymmetric: Type 1 moved preferentially to Minimal (49% of exits), whereas Type 2 moved to Mixed (65%; p<0.001). Population-average PSD was nearly flat (+0.014 SD/year, p=0.07); while opioid use declined to near zero in Minimal and Type 1 but remained high in Type 2 and Mixed. Joint GBTM identified four severity classes along a Minimal-to-Mixed diagonal. Nociplastic phenotypes in SLE are persistent, severity-stratified, with substantial functional, psychological, organ-damage, and opioid burdens. Transient Type 1 and Type 2 states have divergent longitudinal transitions.

Abstract Background Rheumatoid arthritis (RA) is an autoimmune inflammatory disease with complex and incompletely understood molecular mechanisms. Understanding circulating proteins associated with RA may improve understanding of disease biology and clarify its pathological links with cardiometabolic comorbidities. Methods A proteome-wide two-sample Mendelian randomisation (MR) drug target analysis was conducted using plasma proteins measured in 54,219 participants from the UK Biobank Pharma Proteomics Project as exposures and RA and cardiometabolic diseases as the outcomes. Summary statistics for RA included 53,663 cases and 1,070,200 controls. Colocalisation analysis was performed to confirm shared single causal variants and prioritise RA proteins supported by both MR and colocalisation. The prioritised proteins were then evaluated in the Accelerating Medicines Partnership RA Phase II synovial single-cell dataset for cell-type expression patterns. Druggability was then assessed followed by analysis of genetic overlap between RA-associated proteins and cardiometabolic diseases. Results 37 plasma proteins had a causal effect on RA risk, supported by combined evidence from MR and conditional colocalisation. In synovial tissue, TPPP3, RARRES2, AKAP12, and GGT5 were predominantly expressed in stromal and endothelial cell clusters. Druggability assessment identified IFNGR2, IL6R, CD40, and FCGR2B as Tier 1 targets. However, several biologically relevant proteins, including RARRES2, AKAP12, TPPP3, and SNX2, had limited available druggability data. Genetic overlap analysis demonstrated shared protein signals between RA and cardiovascular diseases, including overlap of RARRES2 and TPPP3 with coronary artery disease (CAD) and FCGR2B with atrial fibrillation (AF). To approximate the therapeutic effect of target inhibition, the direction of effect estimates for proteins showing overlap between RA-CAD and RA-AF was reversed. Conclusion This study identified circulating proteins involved in RA pathogenesis and reveals shared mechanisms between RA and cardiovascular diseases. While some proteins showed clear translational potential targets, several prioritised proteins had limited available druggability information and could not be confidently classified. Addressing these gaps may help identify new targets relevant to RA management. Future work should also use phenome-wide MR studies to evaluate potential on-target adverse effects of protein inhibition across RA-CAD and RA-AF.

Juvenile systemic sclerosis (jSSc) is a rare autoimmune disease marked by skin fibrosis and multi-organ involvement. Autologous stem cell transplantation (ASCT) is an emerging therapy for severe, treatment-refractory jSSc, but its effects on immune cell dynamics remain poorly understood. PBMCs were collected from three patients with jSSc before ASCT and at 6, 12, and 24 months post-ASCT. Patient and healthy control samples were profiled using cellular indexing of transcriptomes and epitopes by sequencing (CITE-seq). We focused on monocytes, given their role in fibrosis-promoting inflammation. To detect longitudinal trends, pseudobulked gene expression (log scale) was regressed against time since ASCT. This approach identified widespread changes in jSSc monocytes, including decreased expression of systemic sclerosis-linked genes, such as SERPINE1. On the pathway level, NF-{kappa}B-associated inflammatory signaling was elevated in jSSc monocytes at baseline relative to healthy controls and decreased progressively post-ASCT. Genes related to mitochondrial function and oxidative phosphorylation progressively increased in expression after ASCT, suggesting a shift in metabolic state. Compositional changes in monocyte subpopulations were also identified and may have contributed to longitudinal gene expression patterns. Together, these findings characterize the dynamic immune changes in jSSc following ASCT and highlight a widely applicable longitudinal modeling framework for single-cell data.

ObjectiveIn the first year after onset of the autoimmune disease RA (RA), 40-60% do not achieve remission on conventional synthetic disease-modifying anti-rheumatic drugs (csDMARDs). To understand how autoreactive T cells may contribute to unstable or non-remission, we studied CD4+ T cells, including those recognising citrullinated (Cit) vimentin in participants with RA. MethodsTwo cohorts of drug-naive new-onset participants with RA were treated with csDMARDs. Disease activity score (DAS28-CRP) and peripheral blood (PB) mononuclear cells were collected longitudinally. In HLA-DR-shared epitope+ cohort 1 (n=21), T cells were assessed with a 17-marker spectral flow panel, incorporating HLA-DRB1*04:01/01:01- VimentinCit6459-71 or HLA-DRB1*04:04-VimentinCit7166-78 tetramers. Changes in T cell subsets over time were assessed in remitting and non-remitting participants using a generalized linear mixed model with a negative binomial distribution. In cohort 2 (n=26), the transcriptome of disaggregated synovial tissue (ST) and PB CD4+ T cells were analysed at baseline, and ST biopsy spatial proteomics at baseline and 6 months. ResultsCD4CXCR5-PD1+ peripheral helper T cells (Tph), including Cit-vimentin-reactive Tph, CD4CCR7+CXCR5-PD1+ stem-like Tph and TIGIT+PD1+ Tph were increased with moderate/high DAS28-CRP at any time point. Remission outcome was associated with low CD4 follicular helper T cell (Tfh) and Cit-vimentin-reactive Tfh. In non-remitting participants, Tph/fh infiltrated germinal-centre-like ST aggregates. This decreased in remission. Circulating TIGIT+ Tph genes reflected B lymphoid activation and lymph node egress, while in ST they reflected local differentiation. ConclusionPersistently high circulating TIGIT+ Tph and Tfh, including Cit-vimentin specificities, reflecting antigen-presenting B-cell interactions, are associated with reduced response to csDMARDs in recent-onset RA. Key messagesO_ST_ABSWhat is already known on this topicC_ST_ABSO_LITph and Tfh cells interacting with B cells are implicated in active ACPA+ RA C_LIO_LICitrullinated (Cit)-vimentin is an important neutrophil extracellular trap-derived target of ACPA C_LI What this study addsO_LIHigh circulating TIGIT+ Tph, Cit-vimentin-autoreactive Tph and Tfh associate with failure to reach remission on conventional synthetic DMARDs within the first year in early HLA-DR shared-epitope+ RA C_LIO_LITph/Tfh and adjacent regulatory T cells surround follicular B-cells in lymphoid aggregates in synovial tissue in non-remission C_LIO_LICirculating TIGIT+ Tph bear a transcriptional signature of lymphoid tissue expansion and lymph node egress as compared to functional differentiation and antigen experience in synovial tissue C_LI How this study might affect research, practice or policyO_LIWhen a remission target is not achieved in HLA-DR shared-epitope+ RA patients during the first year of treatment, high circulating TIGIT+ Tph implicate autoreactive T-B-lymphoid expansion in synovial tissue. C_LI

Objective: To determine whether autoantibodies are present in giant cell arteritis (GCA) using a high-dimensional autoantibody array. Methods: Serum was collected from patients with GCA (n=20), other related vascular inflammatory diseases (Takayasu arteritis n=12, IgG4-RD n=5, Behcet's disease n=6), SLE (n=5) and healthy controls (n=12). Autoantibodies to 15,312 protein targets were measured using the GeneCopeia OmicsArray proteomic antigen microarray panel. Results: Differential abundance analysis revealed no autoantibodies significantly elevated in GCA or other related vascular inflammatory diseases. In contrast, the SLE group showed a strong and promiscuous autoantibody response, with 175 significantly associated autoantibodies (Benjamini-Hochberg-adjusted P <0.05). Conclusions: No autoantibodies were significantly elevated in GCA. We identified known and novel autoantibodies in SLE.

Fc{gamma}RIIa, encoded by FCGR2A, is a widely expressed Fc receptor implicated in autoimmunity and infectious disease susceptibility. To fine-map the rheumatoid arthritis (RA) association at the complex FCGR locus, we combined gene-specific resequencing, genetic association studies in UK and Spanish European cohorts, functional genomics, structural biology, biophysical analyses, and cellular assays. We identified a common European FCGR2A haplotype (2A.3), defined by Q27W, H131H, and the RA-associated SNP rs12746613, which showed the strongest association with RA. Multi-omics analyses demonstrated that 2A.3 is associated with reduced expression of the soluble FCGR2A splice variant and lower circulating soluble Fc{gamma}RIIa levels. Functional studies revealed altered IgG interactions and delayed Fc{gamma}RIIa signal transduction associated with Q27W, while structural analyses found no evidence for stable ectodomain dimerisation. Together, these findings identify 2A.3 as an important functional contributor to RA susceptibility and provide mechanistic insight into how FCGR2A variation may influence immune regulation and disease risk in Europeans.

Objective: Tissue-specific biomarkers that are reliable and associated with clinical manifestations of idiopathic inflammatory myopathy (IIM) are lacking. The blood circulation in individuals serves as a central conduit, allowing communication between tissues and facilitating clearance and recycling of tissue-derived proteins. Thus we applied a dual antibody-based proximity extension assay to profile the plasma proteome in subtypes of patients with IIM. Methods: Plasma samples from 201 patients diagnosed with IIM at Karolinska University Hospital were analyzed using Olink. Clinical manifestations, disease activity measurements, and laboratory results were collected. First, we evaluated differential protein abundance across IIM subtypes. Then we calculated tissue scores for each disease subtype using tissue gene expression databases. Finally, interferon (IFN) and complement pathway scores were calculated. Results: Plasma from patients with dermatomyositis was enriched for IFN signaling and skin associated proteins, anti-synthetase syndrome (ASyS) for lung associated proteins, immune-mediated necrotizing myopathy (IMNM) for muscle associated proteins, and inclusion body myositis for T cell response proteins. Patients with IMNM showed the highest tissue score for skeletal muscles, and ASyS for lung tissue score. Skeletal muscle scores correlated strongly with muscle disease activity visual analog scale scores, creatinine kinase levels, and muscle weakness score. Patients with interstitial lung disease along with and those with anti-Jo1 autoantibodies showed differential enrichment of surfactant proteins and IFN pathway activation. Conclusions: Circulatory proteome is a promising tool to capture distinct tissue-specific responses that correlate with disease activity and tissue injury in patients with IIM.

Objectives To assess the effects of 24 weeks active treatment with baricitinib, a JAK1/2 inhibitor, in adult idiopathic inflammatory myopathy (IIM). Methods Patients with active dermatomyositis (DM) or polymyositis (PM) were enrolled into a 1:1 randomized treatment delayed-start design clinical trial (NCT04208464). Participants received 24 weeks baricitinib plus 12 weeks follow-up (Immediate-start), or 12 weeks standard of care plus 24 weeks baricitinib (Delayed-start). The primary outcome was clinical response after 24 weeks active treatment, defined as minimal improvement (Total Improvement Score >20 [TIS20]). Secondary outcomes included: TIS40 (moderate), TIS60 (major) response, between-arm comparison, time to achieve response, change in clinical outcome measures. steroid-sparing and cumulative adverse events. Results 14/15 (93%) randomized participants (mean age 43.2 years [11.6 SD]; 13 DM, 2 PM; 11 female) completed the study (baseline to 36 weeks) and all achieved TIS20 at 24 weeks post-active treatment (95% exact CI 0.68-1.00). 9/15 (60%) achieved TIS40 response and 2/15 (13%) TIS60 response. At 12 weeks post-randomization, 11/15 (73%) patients achieved at least TIS20 (95%CI 0.45-0.92), including all Immediate-start arm patients and four Delayed-start arm patients. At the same time point, evidence of a difference was noted for patient global, extramuscular, CDASI skin activity, pain, fatigue and SF-36 mental/physical health scores. Two hospitalisation serious adverse events were documented, neither related to study drug. Conclusions Treatment of IIM with baricitinib resulted in improved clinical outcome after 24 weeks. Significant improvement after 12 weeks treatment was also evident. No significant safety concerns were raised. A randomized placebo-controlled trial is needed to confirm the efficacy in patients with IIM.

While progress has been made in identifying the true risk-driving single nucleotide polymorphisms (SNPS) on juvenile idiopathic arthritis (JIA) risk haplotypes, the affected cells and target genes largely remain unknown. We used data from a previously published massively parallel reporter assay (MPRA) to query human data in the Database of Immune Cell eQTLs (DICE) and the Gene-Tissue Expression (GTEx) database to identify affected cells and target genes of MPRA-identified SNPs in immune cells and relevant tissues. SNPs identified on MPRA were associated with gene expression levels in a broad range of immune cells in the DICE database, including CD4+ and CD8+ T lymphocytes, monocytes, NK cells, and B cells. MPRA-identified SNPs showed strong associations with gene expression in GTEx whole blood, spleen, and/or EBV-stimulated lymphocytes. Our data show the efficacy of combining MPRA and using human cells/tissue expression data to elucidate complex mechanisms driving genetic risk for JIA.

ObjectivesThe preferential phosphodiesterase 4B (PDE4B) inhibitor nerandomilast was recently approved for treatment of idiopathic pulmonary fibrosis (IPF) and progressive pulmonary fibrosis. Its proposed immunomodulatory, anti-fibrotic, and endothelial-stabilising actions target all three cardinal features of SSc, yet PDE4B expression has not been systematically characterised in SSc tissue. We aimed to define PDE4B expression across fibrotic organs and cellular compartments in SSc. MethodsPDE4B expression was profiled in SSc lung, peripheral blood mononuclear cells (PBMCs) and skin on the transcript level using single-cell RNA sequencing data and on the protein level using immunohistochemistry, immunofluorescence and multiplexed immunofluorescent stainings. ResultsPDE4B was consistently dysregulated in immune cells across SSc tissue and PBMCs, with compartment-specific direction and distribution. In SSc-ILD lung, expression was increased in CD8 and CD4 memory T-cells. In PBMCs, expression was increased in B cells, monocytes, and CD8 T-cells, and stratified patients into three endotypes (PDE4B//hi) not distinguishable by clinical variables. In skin, bulk RNA-seq showed a significant global increase, which localized to myeloid cells in scRNA-seq data. Approximately 90% of FAP activated fibroblasts co-expressed PDE4B at the protein level in SSc skin, identifying the activated fibroblast compartment as a candidate target for PDE4B inhibition. No PDE4B dysregulation was detected in vascular cell types. ConclusionsThis first cell-type-resolved characterisation of PDE4B in SSc demonstrates consistent immune-cell dysregulation across tissues and protein-level enrichment in activated fibroblasts. This provides a human-tissue rationale for the immunomodulatory and anti-fibrotic effects of PDE4B inhibition and supporting PDE4B as a disease-relevant therapeutic target in SSc. Key messagesO_ST_ABSWhat is already known on this topicC_ST_ABSO_LINerandomilast (BI 1015550), a PDE4B-preferential inhibitor, was approved for idiopathic pulmonary fibrosis and progressive pulmonary fibrosis. C_LIO_LIPre-clinical studies indicate that PDE4B inhibition may act on all cardinal features of SSc. C_LI What this study addsO_LIFirst cell-type-resolved characterization of PDE4B expression across SSc-affected lung, PBMCs, and skin. C_LIO_LIPBMC PDE4B expression is heterogeneous, stratifying patients into PDE4B// endotypes independent of standard clinical variables. C_LIO_LIscRNA-seq shows increased myeloid PDE4B expression in SSc skin, while [~]90% of FAP activated fibroblasts in SSc skin express PDE4B protein. C_LI How this study might affect research, practice or policyO_LIThe study strengthens the human-level evidence underpinning the target rationale for PDE4B inhibition in SSc. C_LI

Background. Tocilizumab (TCZ), a monoclonal antibody directed against the interleukin-6 receptor, is used in rheumatoid arthritis (RA) after inadequate response or secondary loss of response to conventional synthetic and biological disease-modifying antirheumatic drugs (DMARDs). Real-world data from North African cohorts remain scarce. We assessed the effectiveness and safety of TCZ in routine care and explored baseline factors associated with 6-month outcomes. Methods. We conducted a retrospective, single-centre cohort study of 44 consecutive patients with RA treated with TCZ between April 2019 and January 2024 in the Department of Rheumatology, Moulay Ismail Hospital, Meknes, Morocco. Demographic, clinical, laboratory, treatment and follow-up data were extracted from medical records using a standardised electronic form. The primary effectiveness outcome was the European Alliance of Associations for Rheumatology (EULAR) response at 6 months; DAS28-ESR remission was defined as DAS28-ESR below 2.6. Safety outcomes comprised infections, neutropenia, liver-enzyme abnormalities and lipid abnormalities. Longitudinal changes were compared with the Wilcoxon signed-rank test, and associations between baseline variables dichotomised at their median and 6-month outcomes were examined with chi-square tests, in SPSS version 29. Results. The cohort comprised 33 women (75.0%), with a median age of 57 years (range 32-82) and a mean RA duration of 12.97+/-9.1 years. Patients had received a mean of 2.5+/-1.8 previous conventional DMARDs, and 41 (93.2%) had received at least one previous biological agent, including two or more tumour necrosis factor (TNF) inhibitors in 36 (81.8%). At 6 months, outcome data were available for 34 patients: 23 (67.6%) achieved a good EULAR response, 6 (17.6%) a moderate response and 5 (14.7%) no response; 12 (35.3%) were in DAS28-ESR remission. Mean DAS28-ESR fell from 5.10+/-1.18 at baseline to 2.74+/-1.38 at 6 months and 2.45+/-1.33 at 12 months, and the mean prednisone-equivalent dose fell from 8.3+/-7.1 to 5 mg/day. Twenty-two infectious episodes were recorded, including one serious infection (purulent pleurisy) requiring hospitalisation; 5 patients (11.4%) had a temporary interruption and 1 (2.3%) a permanent discontinuation for hepatic cytolysis. A neutrophil count below 1,500/mm3 occurred in 13 patients (29.5%), with no count below 1,000/mm3, while mean neutrophils declined from 6.3+/-3.0 to 2.6+/-1.2 G/L at 12 months. Mean LDL cholesterol rose from 1.18 to 1.49 g/L and HDL cholesterol from 0.58 to 0.82 g/L. Rheumatoid-factor positivity was the only baseline variable associated with the EULAR response category (p=0.007); a baseline tender joint count above six was associated with a lower remission rate (23.5%, p=0.007), as was, borderline, a pain visual analogue scale above 65 mm (31.2%, p=0.05). Conclusions. In this heavily pretreated real-world RA cohort, TCZ was associated with a substantial and sustained reduction in disease activity and a manageable safety profile consistent with its known signals. A high baseline articular and pain burden was associated with a lower probability of remission. The small sample, incomplete 6-month follow-up, retrospective design and absence of adjusted effect estimates limit interpretation, and the reported associations should be regarded as hypothesis-generating.

Background VEXAS syndrome is a late onset autoinflammatory disease caused by somatic UBA1 mutations and characterized by heterogeneous systemic and hematologic manifestations. We aimed to describe all identified Belgian cases through a national multicenter cohort. Methods We conducted a retrospective study across four Belgian tertiary centers. Clinical, biological, genetic, therapeutic, and outcome data were collected using standardized anonymized case report forms. Analyses were descriptive. Results Twenty-one male patients were identified between January 2018 and May 2025. General symptoms such as Fatigue, weight loss and sweating occurred in 95% of cases. The most frequent manifestations were cutaneous (85.7%), hematologic (76.2%), articular (66.7%), thromboembolic (57.1%), chondritis (42.9%), ophthalmologic (38.1%), pulmonary (38.1%). Other manifestations also included vasculitis (61.9%). At diagnosis, 95% had anemia, macrocytic in 57%, and 28.6% had thrombocytopenia. Corticosteroids were the main first line therapy. Second line treatments included anti IL 6 agents (46.7%), JAK inhibitors (20%), and azacitidine (14.3%). Complete remission occurred in 50% of patients receiving anti IL 6 therapy and in 33% treated with either JAK inhibitors or azacitidine. Two patients underwent allogeneic stem cell transplantation, one died from infectious complications. Twenty six infectious episodes were recorded, including opportunistic infections. Six patients (28.6%) died during follow-up, four from infectious complications. Conclusion This first Belgian national cohort confirms the clinical heterogeneity of VEXAS syndrome and highlights substantial infectious morbidity and mortality. Access to targeted second-line therapies, particularly anti IL-6 agents and JAK inhibitors, remains challenging despite apparent clinical benefit.

Macrophages in the synovial lining are critical for the maintenance of healthy tissue while also contributing to the pathogenesis of rheumatoid arthritis (RA). However, the field currently lacks a unifying characterization of synovial macrophage heterogeneity across steady-state and inflammation. Here, we defined 4 transcriptionally distinct populations of synovial macrophages CX3CR1+MHCII- (lining); CX3CR1-MHCII- (interstitial/sublining); CX3CR1-MHCII+ (monocyte-derived); and CX3CR1+MHCII+ (infiltrating). The MHCII-populations are long-lived and derived from embryonic precursors regardless of localization while the MHCII+ populations differentiate from bone marrow (BM) progenitors dependent on CCR2. We identified conserved activation pathways between acute and chronic mouse models of inflammatory arthritis as well as novel arthritis-associated subpopulations. During peak inflammation, the influx of BM-derived cells was associated with upregulation of monocyte-related genes with concurrent down-regulation of tissue-resident genes. Our results provide a unifying schema for describing synovial macrophages across conditions and pave the way for future studies in modulating transcriptional activity in rheumatoid arthritis.

Background Pain frequently persists in rheumatoid arthritis (RA), despite effective control of inflammation. The mechanisms driving this residual pain remain poorly characterised in individual patients. Methods In 172 patients with established RA and clinically relevant pain (mean NRS 6.5/10) and 80 pain free controls, we combined indicators of inflammatory disease (CRP, joint counts, power Doppler ultrasound), centrally mediated pain (Widespread Pain Index, painDETECT), psychological distress (PHQ ADS) and quantitative sensory testing (QST). Latent profile analysis was applied without predefined thresholds. Results Four phenotypes were identified: a peripheral, low-inflammation/low-central phenotype (38%); a predominantly inflammatory phenotype (7%); and moderate (43%) and severe (12%) centrally mediated phenotypes. Centrally mediated phenotypes reported the highest pain (NRS 8.2), worst disease impact and lowest employment. DAS28 CRP was similar in both the inflammatory and severe centrally mediated phenotypes but for different reasons, swollen joints and CRP versus tender joints , and did not distinguish them. Conditioned pain modulation was impaired relative to controls (p<0.001) and most reduced in the severe centrally mediated phenotype. Psychological distress was the strongest independent predictor of pain severity (model R squared=0.33), whereas inflammatory markers were not. Principal components analysis identified swollen joint count (loading 0.63) and the tender swollen joint difference (loading 0.60) as accessible clinical markers of the inflammatory and centrally mediated phenotypes respectively. Conclusions A data driven approach identified four mechanism-based pain phenotypes in RA. This framework moves pain assessment beyond inflammation alone and provides a basis for testing analgesic strategies to target the predominant pain mechanism in individual patients.

Objective: Clonal hyperexpansion of CD4 T cells is a characteristic feature of rheumatoid arthritis (RA). Equally large T cell clones also arise in physiological ageing or latent viral infection and adopt a replicative senescence programme - a tolerance mechanism that limits immune activation by innate-like reprogramming and proliferative arrest. We aimed to characterise the senescence programme of hyperexpanded CD4 T cell clones in RA and to define their clinical associations. Methods: Hyperexpanded T cell clones were characterised by single-cell RNA and T cell receptor profiling of peripheral T cells from RA patients and healthy donors. Flow cytometric validation was performed in two cross-sectional cohorts (n=15, n=45), paired blood and synovial fluid (n=20) or synovial tissue (n=18) sampling, and a non-interventional study of co-stimulatory blockade with abatacept (n=6). Results: Hyperexpanded CD4 T cell clones exhibited a CCR7-CD27- phenotype and accumulated in RA joints. Their frequency correlated with disease activity and their surface profile was modulated by abatacept, suggesting susceptibility to therapeutic intervention. At the molecular level, hyperexpanded clones converged on a phenotype consistent with replicative senescence, characterised by natural killer (NK) cell-reminiscent cytotoxic reprogramming, loss of co-stimulatory molecules, and reduced translational activity. However, compared with healthy donor counterparts, hyperexpanded RA CD4 T cell clones showed reduced senescence-associated cytotoxic and NK cell markers, and increased IL-7 receptor signalling, indicating attenuated senescence and preserved capacity for homeostatic proliferation. Conclusion: We propose that replicative senescence insufficiently constrains hyperexpanded clones in RA, resulting in sustained antigen reactivity in autoreactive clones and perpetuation of chronic inflammation.

Objective We developed a patient- and joint-specific explant co-culture system to model active psoriatic arthritis (PsA) and capture donor-specific tissue responses to therapeutic interventions. Methods Based on convergent joint pathology between end-stage osteoarthritis (OA) and PsA, OA cartilage-bone and synovium tissues from arthroplasty patients were exposed to synovial fluid (SF) obtained from PsA and OA patients. Histological outcomes (synovitis, proteoglycan distribution), curated gene expression, soluble mediators, and proteinase activity were assessed over 7-21-days. Model responses to dexamethasone (DEX) and the anti-tumor necrosis factor antibody adalimumab (ADA) were evaluated. Results PsA SF induced distinct inflammatory and tissue remodeling responses compared to OA SF and control conditions, including altered cartilage proteoglycan distribution, increased synovitis, and tissue-specific transcriptional changes. Multivariate analyses identified distinct osteochondral and synovial transcriptional responses to PsA SF, characterized by reduced osteochondral COL2A1 expression and increased synovial expression of inflammatory and matrix-remodeling genes, including MMP1 and CXCL8. DEX and ADA elicited donor-specific responses across histological, transcriptional, and protein readouts. Among multivariable model outputs, histologic synovitis scores emerged as the most clinically aligned parameter, demonstrating associations with baseline PsA donor disease activity, active joint counts, pain, high-sensitivity C-reactive protein (hsCRP), and radiographic scores. Synovitis score changes to DEX and ADA treatments also aligned with corresponding PsA SF donor clinical improvements to corticosteroid and TNF-modifying therapies. Conclusion This osteochondral-synovial explant co-culture model captured donor-specific inflammatory and treatment-responsive features of PsA SF-induced pathology, thereby providing a clinically relevant ex vivo platform for studying patient-specific therapeutic responses in PsA.

Introduction Complement and coagulation are tightly interconnected systems that contribute to immunothrombosis and can drive inflammatory or thrombotic diseases. Leveraging this relationship and crosstalk we developed a method to functionally evaluate complement-induced coagulation activity using thromboelastometry (thermoelastometry of complement-driven immunothrombosis; TCDI). Methods To study the complement-dependent activation of coagulation, platelet-poor plasma (PPP) from patients was mixed with healthy blood in the presence or absence of the compstatin-based C3 inhibitor Cp40. PPP from healthy controls (n=10), or from patients with antiphospholipid syndrome (APS; n=6), severe COVID-19 (n=13), rheumatoid arthritis (RA; n=7), or synovial fluid (SF) from RA patients, were analyzed for their capacity to induce complement activation in healthy blood. Whole blood coagulation was analyzed by thromboelastometry and complement-driven immunothrombosis was quantified as clotting time (CT) prolongation following Cp40 treatment, expressed as fractional difference percentage (FD%). In parallel, C3a generation was measured by ELISA to monitor the C3 inhibitory activity of Cp40. Results Plasma from patients with APS and COVID-19 induced significant CT prolongation following C3 inhibition by Cp40 and increased FD% values compared with controls, indicating active complement-driven immunothrombosis. Higher TCDI levels were associated with mortality in severe COVID-19. In RA, TCDI positivity was detected in synovial fluid (SF) rather than peripheral plasma. Moreover, TCDI-positive samples treated with Cp40 exhibited significant inhibition of C3a generation, which strongly correlated with FD% values (r=0.67, p=0.0005). Conclusion The TCDI assay may provide a rapid, real-time evaluation of immunothrombotic activity in inflammatory and thrombotic disorders, which could inform timely medical prevention.

BackgroundKnee osteoarthritis (KOA) is a prevalent degenerative joint disease in which synovial inflammation and fibrosis are closely linked to pain, stiffness, and functional limitation. Growing evidence suggests that metabolic dysregulation, particularly in lipid metabolism, is involved in KOA pathogenesis, but the underlying mechanisms remain incompletely defined. MethodsSprague Dawley rats underwent bilateral anterior cruciate ligament transection to establish a KOA model; sham-operated rats served as controls. RNA sequencing of synovial tissues was performed to identify differentially expressed genes (DEGs) and enriched pathways, followed by GO/KEGG and GSEA analyses. In vivo, adeno-associated virus vectors were used to overexpress or knock down PPAR-{gamma} and phosphoenolpyruvate carboxykinase 1 (PCK1) via intra-articular injection. Ex vivo, primary rat fibroblast-like synoviocytes (FLSs) were stimulated with IL-1{beta} and transfected with PPAR-{gamma} or PCK1 siRNA/overexpression plasmids. synovitis and fibrosis were evaluated by HE, Masson, and Sirius Red staining, immunofluorescence, ELISA, RT-qPCR, and Western blotting. ResultsRNA-seq revealed 621 up-regulated and 228 down-regulated genes in KOA synovium versus sham, with DEGs significantly enriched in PPAR signaling, adipocytokine, and AMPK pathways. Metabolism-related genes including Fabp5, Plin1, Adipoq, Lep, and Pck1 were up-regulated. GSEA indicated downregulation of PPAR-{gamma} signaling in KOA synovium. In vivo and ex vivo, PPAR-{gamma} expression was reduced in KOA, whereas PCK1, FABP5, and ADIPOQ were increased. PPAR-{gamma} overexpression alleviated synovial inflammation, collagen I deposition, and fibrosis, and suppressed FABP5, ADIPOQ, and PCK1 expression; PPAR-{gamma} knockdown produced the opposite effects. Functional studies showed that PCK1 overexpression aggravated synovial inflammatory cell infiltration and fibrosis, elevated IL-1{beta}, IL-18, and TGF-{beta}, and decreased TIMP1 levels in serum, synovial tissue, and FLSs supernatants, whereas PCK1 silencing reversed these changes. ConclusionsThe PPAR-{gamma}/PCK1 metabolic axis modulates synovitis and fibrosis in KOA. Downregulation of PPAR-{gamma} and consequent upregulation of PCK1 promote synovitis and fibrotic remodeling. These findings identify the PPAR-{gamma}/PCK1 pathway as a potential therapeutic target for KOA.