Arthritis & Rheumatology

Systemic sclerosis (SSc) is a rare, heterogeneous autoimmune disease characterized by immune dysregulation, vasculopathy and fibrosis. While typically sporadic, SSc can in a minority of cases show familial clustering. Whole exome sequencing (WES), performed on six families with two affected members each, identified a total of 253 genes with rare, disease co-segregating variants predicted to affect protein function. Of these, we prioritized PRKD2, one of only three genes identified in two families. PRKD2 encodes Protein kinase D2: an intracellular serine-threonine kinase that amplifies T cell receptor (TCR) signaling. Both familial SSc-associated PRKD2 missense variants increased kinase activation, exerting overlapping, activating effects on TCR signaling in heterozygous knock-in Jurkat cells. A pan-PRKD inhibitor suppressed T cell activation in peripheral blood mononuclear cells from both familial SSc cases and controls. The enrichment of PRKD2 rare variants in a sporadic SSc cohort provides further support for its relevance to SSc pathogenesis. Together, these findings identify PRKD2 rare variants as potential genetic contributors to SSc, and PRKD2-mediated TCR signaling as a candidate disease-relevant and potentially targetable pathway.

Systemic sclerosis (SSc) is an autoimmune connective tissue disease characterized by symmetric fibrosis of the skin and multiple internal organs. The mechanisms that trigger early fibrotic changes remain unclear. Mast cells are known to infiltrate human SSc lesional skin in early disease stages, yet the role of mast cells in initiating fibrosis and pruritus in SSc remains debated, in part due to unclear pathways of mast cell activation. Here, we show that mast cells, via the receptor Mrgprb2, contribute to fibrosis in the bleomycin (BLM)-induced skin fibrosis mouse model. Mast cells accumulate in the skin of BLM-treated wild-type (WT) but not Mrgprb2-knockout (Mrgprb2-/-) mice. Mrgprb2-/- mice show attenuated disease severity, with reduced collagen deposition and lower expression of matrix metalloproteinases and inflammatory markers associated with fibrosis. BLM treatment also increases pruritus in WT mice in the early stages of the model; an effect reduced in Mrgprb2-/- mice. This is the first report of itch in this model of skin fibrosis, further linking it to clinical SSc, where pruritus is an early and prevalent symptom affecting nearly half of patients. In a parallel human cohort, lesional SSc skin harbors significantly more mast cells than paired non-lesional skin from the same patients, demonstrating that mast cell accumulation is specific to affected tissue. Lesional mast cell counts also track with skin disease severity, correlating with modified Rodnan skin score and patient-reported skin tightness. Together, these findings implicate Mrgprb2-mediated mast cell activity in both fibrosis and pruritus in SSc, highlighting mast cells as a candidate therapeutic target in this understudied disease process.

Objective: The principal diagnostic test for rheumatoid arthritis (RA) relies on the detection of anti-cyclic citrullinated peptide (CCP) antibodies. The CCP test exhibits moderate sensitivity and specificity but does not adequately detect a high proportion of cases or effectively distinguish RA from related conditions such as systemic lupus erythematosus (SLE). To discover improved diagnostic biomarkers for RA, we performed a comprehensive proteomic analysis of antibody-bound antigens present in RA, SLE, and healthy control (HC) sera and identified proteins associated with transforming growth factor-beta-1 (TGF-beta-1) signaling and assessed the sensitivity and specificity of antibodies against these antigens in comparison to CCP. Methods: Total antibodies were immunoprecipitated from pooled sera of HC individuals (n=3) and patients with clinically diagnosed RA (n=3) or SLE (n=3). Antibody-bound antigens were identified using multidimensional protein identification technology (MudPIT) shotgun proteomics. Candidate antigens associated with TGF-beta-1 signaling were selected for evaluation, and corresponding serum autoantibodies were assessed for their ability to classify RA using a POC lateral-flow immunochromatographic format. Results: Proteins present in antibody immunoprecipitations included TGF-beta-1-induced protein (TGFBI), thrombospondin 1 (TSP1), serum amyloid A1 (SAA), and fibronectin (FN). POC assays using these candidates, as well as TGF-beta-1 itself, as capture antigens were used to detect corresponding serum autoantibodies in 107 subjects with clinically diagnosed RA, 42 subjects with other rheumatic diseases (non-RA), and 121 HC subjects. Receiver operating characteristic curves were constructed using RA and HC groups to assess diagnostic performance, and optimal cutpoints identified using the Youden Index (maximizing the sum of sensitivity and specificity). CCP test results were determined using previously established thresholds. Using an analysis et of 169 subjects in the HC and RA groups who had values for TGFBI, SAA, and CCP, TGFBI autoantibodies achieved a sensitivity of 82%, specificity of 98.8%, positive likelihood ratio (PLR) of 65.6, and NLR of 0.2. SAA autoantibodies achieved a sensitivity of 92.1%, specificity of 85%, PLR of 6.1, and NLR of 0.1. Both outperformed CCP (sensitivity of 68.5%, specificity of 95%, PLR of 13.7, and NLR of 0.3). Using an analysis set of 120 subjects in the RA and non-RA groups who had values for TGFBI, SAA, and CCP, TGFBI and SAA autoantibodies exhibited sensitivities and specificities of 82 and 92.1% and 74.2 and 45.2%, respectively, compared to 68.5 and 74.2% for CCP. Autoantibodies to TGF-beta-1, TSP1, and FN exhibited only modest diagnostic performance. Conclusion: RA sera contain autoantibodies targeting multiple proteins associated with the TGF-beta-1 signaling pathway that is implicated in inflammatory processes in RA. Among the candidates tested, TGFBI and SAA autoantibodies exhibited the highest diagnostic performance in a POC lateral-flow format, supporting their potential utility as biomarkers for RA diagnosis. These findings also support further investigation of the TGF-beta-1 signaling pathway as a potential therapeutic target in RA.

Giant cell arteritis (GCA) is an immune-mediated vasculitis that can cause serious morbidity including sight loss, stroke and aortic aneurysm. There is an unmet need for blood-based biomarkers and novel therapeutics. We measured plasma protein levels using the SomaScan v4.1 platform, comprising 7,273 protein measurements (SOMAmers) reflecting 6,596 unique protein targets. We profiled the proteome in 113 patients who presented acutely with possible GCA. 56 had biopsy-proven GCA and 57 did not have GCA (non-GCA). We found 144 SOMAmers increased and 151 reduced in GCA. Dysregulated biological pathways included IL6-JAK-STAT3 signalling, chemokines for both myeloid (e.g. CXCL2, CXCL3, CCL18, CCL23) and lymphoid cells (e.g. CXCL9, CXCL13), and the complement system (e.g. C9, CFHR5, C5a, Factor B). Enzyme-Linked Immunosorbent Assays (ELISAs) confirmed elevated plasma levels of C5a, the terminal complement complex, Factor B and CFHR5 in GCA. We developed a 26-protein signature that distinguished GCA from non-GCA (area-under-the curve, AUC, 0.93) and validated the diagnostic signature in external datasets. Our data implicate terminal complement pathway activation in GCA, raising the possibility of complement-directed therapies. We show proof-of-principle that a multiplex protein biomarker could be used as a diagnostic adjunct in suspected GCA.

Objective: To assess the accuracy of codes and algorithms used to identify selected connective tissue diseases (CTDs) in electronic health records (EHRs) and administrative databases. Methods: We searched MEDLINE, Embase, and CENTRAL databases for studies that validated case definitions in EHRs against a reference standard, including rheumatologist-confirmed diagnosis or clinical classification criteria. Title/abstract screening, full-text review, data extraction, and quality appraisal were independently performed in duplicate. Findings were synthesised narratively and through a bivariate random-effects meta-analysis of sensitivity and specificity. Results: A total of 38 studies were included. Systemic lupus erythematosus (SLE) was the most frequently studied disease, followed by systemic sclerosis (SSc). Across diseases, progressively restrictive algorithms generally improved positive predictive value (PPV), although the optimal strategy varied by disease. In SLE, multiple diagnostic codes provided the most favorable overall performance, whereas adding clinical data provided limited incremental benefit. In SSc, disease-specific clinical features, particularly Raynaud's phenomenon, improved case identification, while specialist or inpatient-based algorithms performed better for polymyositis/dermatomyositis, although evidence was limited. For SLE, meta-analysis yielded pooled sensitivity of 0.90 (95% Cis 0.70-0.97), specificity of 0.83 (95% CIs 0.54-0.95), and PPV of 0.75 (95% CIs 0.59-0.86). Evidence for Sjogren's Disease was limited to one study, and no studies evaluated MCTD/UCTD. Conclusions: Optimal EHR case-identification strategies vary by disease and should be tailored to disease-specific clinical and diagnostic characteristics rather than algorithm complexity alone. Future research should develop and externally validate robust, standardised algorithms in representative populations, using rigorous validation methods, and assess the added value of longitudinal EHR data, biomarkers, and computational phenotyping approaches.

Osteoarthritis (OA) and systemic sclerosis (SSc) are diseases with distinct etiologies but similar disease phenotypes, most prominently fibrosis, a process governed by the pathological activation of fibroblasts. Mechanisms underpinning fibrosis in these diseases are widely studied, though have yet to be directly compared. We employed single-cell RNA-seq and high-resolution spatial transcriptomics to describe the functional plasticity and the range of fibroblast activation states in both diseases. We identified disease-enriched fibroblast subsets conserved in both diseases, including fibrogenic myofibroblast-like cells, chemokine- and cytokine-expressing inflammatory fibroblasts, and lining-like fibroblasts. These subsets exhibited convergent fibrotic programs also observed in idiopathic pulmonary fibrosis, as well as overlapping osteochondral transcriptional programs. Xenium 5K spatial transcriptomics revealed that conserved, disease-associated fibroblasts reside in highly similar anatomic niches in OA synovium and SSc skin. These consisted of a fibrotic ECM-rich niche harboring myofibroblast-like cells and an inflammatory niche containing inflammatory fibroblasts adjacent to infiltrating immune cells. Disease-associated transcriptional remodeling converged on shared functional pathways and common putative upstream molecular regulators. These findings identify conserved cellular states, spatial niches, and regulatory programs across OA and SSc, suggesting that fibrotic disease is underpinned by shared pathogenic stromal states and candidate targets for therapeutic strategies are applicable across both diseases.

Objective: Autoantibodies are central for pathology of rheumatoid arthritis (RA) and diabetes mellitus (DM) carrying high predictive and diagnostic value. Here, we explore the frequency and functional potential of DM-related antibodies (DMab) in RA. Methods: DMab targeting glutamic acid decarboxylase (GAD65ab), tyrosine phosphatase-like islet antigen 2 (IA2ab) and zinc transporter 8 (ZnT8ab) were measured in 326 DM-free RA patients (260 females, 66 males), using specific ELISAs. The DMab profile was analysed in relation to 30 clinical and serological variables. ZnT8+ cells were detailed by a public single-cell transcriptome in RA synovial tissue. Results: DMab production was more frequent in females, dominated by ZnT8ab (86%), followed by GAD65ab (26.4%) and IA2ab (7.0%). DMab-positive patients, and specifically ZnT8ab-positive women, had higher levels of insulin and HOMA-IR index and lower serum IL-6, IFN{gamma}, and IL-9. Multivariable logistic regression estimating ZnT8ab, IA2ab, GAD65ab production revealed that BDNF, insulin and DAS28 were positive predictors of ZnT8ab. Increasing ZnT8ab levels were inversely related to RAab in the mixed interaction model. CD14+ cell transcriptome identified association between an activated secretory cell type and increasing ZnT8ab levels. Additionally, ZnT8ab levels were in direct proportion with ZnT8 production in RA CD4+ T cells. Single-cell transcriptome of RA synovial tissue revealed ZnT8+ cells among the lubricin producing lining layer fibroblasts programmed for invasive behaviour. Conclusion: This study reveals frequent production of ZnT8ab in non-diabetic RA patients and identifies their antigenic target expressed in lining synovial fibroblasts of RA joints.

Multiple sclerosis (MS) is approximately three times more common in females than in males, but sex-linked epigenetic mechanisms remain incompletely understood. We tested whether X-chromosome DNA methylation differs in females with MS and whether associated sites preferentially map to genes normally subject to X-chromosome inactivation (XCI). An X-chromosome-focused epigenome-wide association study was performed in whole blood from three datasets comprising 496 females with MS and 509 female controls, with independent evaluation in isolated CD4+ T cells (80 cases, 76 controls). At FDR < 0.01, 3 182 X-chromosome CpGs were hypomethylated in MS (mean {Delta}{beta} = -0.035). Hypomethylated CpGs were strongly enriched in non-escape genes normally subject to XCI relative to escape genes (OR 6.77; p = 1.55x10-57) and mapped to immune and chromatin-related processes. Exploratory cis-mQTL analysis identified strong local genetic effects at a small subset of loci, including WAS, IRAK1 and TLR7. In CD4+ T cells, 2 080 of the 3,182 whole-blood hypomethylated CpGs (65.4%) were also significantly hypomethylated. These findings identify a reproducible X-chromosome hypomethylation signature in female MS and support direct investigation of inactive-X regulation, XCI escape and X-linked immune gene dosage.

While the immune reset induced by CD19 CAR T therapies has shown striking promise in systemic lupus erythematosus (SLE), the nature and duration of benefit mediated by B cell depletion remains unclear. Loss of tolerance in SLE is driven by extrafollicular and germinal center interactions between dendritic cells and self-reactive T and B cells. We hypothesized that CD19 CAR-engineered regulatory T cells (CAR19 EngTreg), capable of suppressing multiple autoimmune effector cell types, might promote long-term tolerance without producing high-levels of inflammatory mediators. To generate CAR19 EngTreg, we combined CD19 CAR delivery with homology directed repair at the FOXP3 locus to drive constitutive, stable FOXP3 expression in CD4 T cells. CAR19 EngTreg expressed canonical Treg markers; exhibited minimal inflammatory cytokine production; and blocked human B cell differentiation into antibody secreting plasma cells. In humanized mouse models, transfer of CAR19 EngTreg led to a reduction in B cell numbers with low inflammatory cytokine production relative to CD19 CAR Teff, and reduced tissue inflammation. In a short-term, in vivo imiquimod-induced inflammatory model, murine CAR19 EngTreg reduced skin pathology, spleen size, and inflammatory cytokines. Finally, in two distinct mouse models of lupus, CAR19 EngTreg persisted for >4 months leading to reduced autoimmune T and B effector populations, sustained reduction in multiple autoantibodies and improved renal function and histopathology. Thus, CAR19 EngTreg may offer a promising and durable therapeutic avenue for B cell-mediated autoimmune disorders capable of long-term regulation of both autoreactive B and T cells.

Objectives: Patients with pediatric acute-onset neuropsychiatric syndrome (PANS) frequently report pain and fatigue. While some patients experience resolution of pain and fatigue following improvement in psychiatric symptoms, others develop persistent symptoms resembling fibromyalgia. Understanding these trajectories is critical for early identification and intervention in patients at risk for chronic pain or fatigue. In this study we characterize fibromyalgia symptoms in PANS and identify predictors of symptom progression following a PANS flare. Design: Prospective observational cohort study. Setting: Stanford University Immune Behavioral Health (IBH) Clinic in Menlo Park, California, USA. Participants: 204 consecutive patients with PANS evaluated by the IBH Clinic. The average (SD) age at first neuropsychiatric deterioration was 8.2 (3.3) years. Main outcome measures: We prospectively collected data on pain, fatigue, and other fibromyalgia symptoms using the 2016 American College of Rheumatology (ACR) Fibromyalgia Survey Questionnaire (FSQ), which includes the Widespread Pain Index (WPI) and Symptom Severity Scale (SSS). For the reference standard, clinician-documented diagnoses of pain syndromes were ascertained through a retrospective review of participants' electronic medical records. We report the prevalence of these symptoms in PANS patients and controls and evaluate factors associated with time to meeting ACR fibromyalgia criteria threshold scores following clinic presentation using a Cox proportional hazards model. Results: Among 204 patients with PANS (110 boys [54%]), eighty-five (42%) met ACR fibromyalgia criteria threshold scores at least once during follow-up (95% CI at 10 years follow-up time: 60.5 [46.7-74.5]). Twenty-eight of these 85 patients (13.7% of total cohort) progressed to meet full ACR fibromyalgia criteria (95% CI at 10 years follow-up time: 24.1 [15.6-36.2]). Compared with controls, patients with PANS reported substantially elevated rates of pain, daytime fatigue, waking unrefreshed, and cognitive symptoms (brain fog). Higher scores on the WPI and SSS at presentation were associated with a higher hazard of subsequently meeting ACR fibromyalgia criteria threshold scores. Conclusions: Fibromyalgia symptoms were common in this PANS cohort, with a notable subset developing symptoms meeting full ACR fibromyalgia criteria. These findings suggest that pain and fatigue may represent post-inflammatory sequelae of PANS and may overlap mechanistically with other post-infectious conditions. Recognizing these symptom patterns may inform clinical management, development of outcome measures, and future clinical trials in these patients, as well as support investigation into shared neuroimmune mechanisms underlying post-infectious pain and fatigue syndromes.

Systemic lupus erythematosus (SLE) is the prototypical systemic autoimmune disease defined by the production of autoantibodies directed against diverse self-antigens. Antinuclear antibodies (ANA) are central to SLE diagnosis, and anti-double-stranded DNA (anti-dsDNA) antibodies are clinically used to track disease activity. However, these biomarkers provide only partial insight into the full spectrum of autoimmune changes in patients. To expand the known landscape of SLE autoreactivity shared among patients and associated with disease activity, we performed an unbiased characterization of 1,268 SLE plasma samples from 695 SLE patients and 301 healthy controls using phage immunoprecipitation and sequencing (PhIP-seq). This technique preferentially displays linear epitopes, and thus provides a complementary set of autoreactivities to previously discovered autoreactive targets. Despite the marked clinical heterogeneity of SLE, machine learning applied to this data surfaced a shared, reproducible signature that robustly discriminates between SLE and healthy controls in two validation cohorts. Autoreactivities in SLE were significantly enriched for RNA-binding protein targets. Autoreactive proteins containing Basic Acidic Dipeptides (BAD) repeat domains, features associated with biomolecular condensate formation, distinguished patients with high disease activity (by SLEDAI score) from patients with no disease activity. Among all shared autoreactivities, a peptide derived from YTHDF2 emerged as the most prevalent target across SLE cohorts occurring in ~25% of SLE patients and displayed striking sequence similarity to a peptide derived from the Epstein Barr virus (EBV) lytic switch protein BZLF1. Competition assays demonstrated higher-affinity binding to the viral peptide, supporting a model in which antiviral humoral responses to EBV may drive secondary epitope spreading toward molecularly mimicked self-antigens. Remarkably, orthogonal validation using the Luminex bead platform containing a panel of only 10 peptides, including BZLF1, demonstrated strong discrimination between SLE and healthy controls (AUC = 0.95). Together, these findings identify a rich, greatly expanded landscape of autoreactivities in SLE, candidate biomarkers associated with high disease activity, and provide mechanistic insight linking EBV-driven immunity to epitope-specific autoimmunity in lupus.

CD11c+CD21- B cells are overrepresented in rheumatoid arthritis (RA). Here we delineate their functional state at site of inflammation and its molecular basis. Phenotypic profiling of paired blood and synovial fluid from patients with anti-citrullinated protein antibody (ACPA) seropositive RA (N=12), seronegative RA (N=10) and spondyloarthritis (N=8), demonstrated a striking enrichment of CD11c+CD21- B cells in synovial fluid in all three diseases (average of CD19+ cells: 67%, 49% and 51%). In ACPA-positive RA we identified increased proportions of CD11c+IgG+CD27low cells and several stages of pre-plasmablasts. The CD11c+CD21- cells had a phenotype indicating BCR activation, proliferation, and antigen presentation. This B-cell profile was mirrored by a LAG3+CTLA4+TIGIT+ peripheral helper T-cell program in ACPA-positive RA, contrasting a CCR6+ Th17-skewing in seronegative RA. Single-cell spatial proteomics revealed a unique CD11chighCD21 low B-cell surface architecture including a BCR co-receptor-tetraspanin signature with CD72-CD81 co-localization, which was elevated in RA. CD11c+ cells also displayed CD44-CD52/CD59 and MHCII-CD40/CD84 immune-modules absent in other B-cell subsets. In summary, CD11c+CD21- B cells are highly diverse, and while an activated antigen-experienced synovial profile was shared between disease groups, ACPA+ RA showed evidence of increased extrafollicular plasmablast differentiation. Surface receptor organization implicated a favoured BCR responsiveness, complement resistance and antigen presentation.

Objectives. Before-and-after transcriptomics in rheumatic disease often yields no reproducible treatment signal, though disease-state stratification is robust. We asked whether exposure and response-prediction labels fall below the detection floor of the designs defining them, while matched disease-state labels do not. Methods. Eight public datasets were analysed (paired juvenile dermatomyositis n = 10; RA before/after methotrexate, n = 28 pairs; lupus nephritis n = 10; controlled exposures; a single-cell dose series). Response labels in current use (one benchmark trajectory, five published signatures) were audited in every analysable source cohort, using effect sizes (dz) against each design's exact minimum detectable effect. Results. Disease-state labels were detectable: the interferon signature declined in 10/10 juvenile dermatomyositis patients (p = 0.002; 59.5% of score variance). No exposure label cleared its design floor in any clinical cohort; a drug-matched methotrexate prior was nominally significant in juvenile dermatomyositis yet did not clear its floor (dz = -0.80; CI spanning it). Exposure became detectable only where prior-context and intensity were jointly favourable (multi-day target tissue dz = 1.24, q = 0.018; well-level pseudobulk dz = +3.70, floor 1.80). Audited response labels failed in 14 of 15 cohorts (93%; descriptive binomial 95% CI 68-100): eleven below their floors, three sign-reversed; the largest training cohort pooled to zero (dz = +0.07; I2 = 69%). Effect size ordered reported AUCs monotonically. Conclusion. Under conventional treatment intensities, exposure and response-prediction labels are either undetectable below the design floor or detected with a sign that does not replicate; disease-state labels are detectable. Part of the negative literature reflects a design floor.

Introduction: Across major phases of the COVID-19 pandemic (March 2020-April 2023), we compared the burden of severe COVID-19 among individuals with systemic autoimmune rheumatic diseases (SARDs) versus immunocompetent individuals with and without comorbidities. Methods: This population-based cohort study used administrative datasets to estimate crude and age- and sex-standardized SARS-CoV-2 and severe COVID-19 incidences among adults >18 years with SARDs, chronic comorbidities, or no comorbidities. Relative to the latter, we used Cox models to derive adjusted hazard ratios (aHRs) for infection, hospitalization, and intensive care unit admission or death (ICU/death) during the pre-vaccination (March-December 2020), vaccination pre-Omicron (December 2020-December 2021), and Omicron (December 2021-April 2023) periods. Results: We included 81,434 adults with SARDs, and 2,020,356 with comorbidities versus 3,144,700 without comorbidities. Despite similar adjusted infection rates, the SARDS cohort had higher risks of hospitalization and ICU/death during the pre-vaccination period (aHRs: 3.4, 95%CI:2.8-4.1; and 4.0, 95%CI:2.8-5.7, respectively), persisting through the Omicron period (aHRs: 4.5, 95%CI:4.0-4.9; and 4.4, 95%CI:3.6-5.4, respectively). Among SARDS, rheumatoid arthritis, psoriatic arthritis and systemic lupus erythematosus contributed highest burden, with comparable hospitalization and mortality rates among younger rheumatoid arthritis versus healthy older adults. Highly immunosuppressive rituximab- or mycophenolate-treated patients had highest hospitalization and ICU/death risks, particularly during the Omicron period (aHRs: 11.9, 95%CI:9.9-14.3; and 17.6, 95%CI:13.0-23.9, respectively). Conclusion: Individuals with SARDs, especially receiving highly immunosuppressive therapies, experienced elevated COVID-19 burden and severe outcome risks throughout the pandemic, warranting their prioritized consideration during future public health emergencies.

Purpose: To determine whether a cobalt-chrome genetic reactivity (CoGR) score - originally developed to identify patients at greater risk of developing adverse reaction to metal-on-metal hips - is associated with poorer patient-reported outcomes after knee arthroplasty (KA). Methods: In a prospective multicentre study, patients at a minimum two years post all cobalt-chrome KA were invited to research clinics. Participants provided samples for blood metal ion measurements and DNA sequencing and completed Forgotten Joint Scores (FJS). Component alignment was assessed on AP and lateral plain radiographs. The association between CoGR and FJS was assessed using regression adjusted for time since surgery, age, gender, BMI and tested for modification by blood cobalt. In a case-control analysis, CoGR scores of revised patients with histologically confirmed adverse reactions to metal debris (and specifically aseptic lymphocyte-dominated vasculitis-associated lesions (ALVAL)) were compared with controls (revised patients with no signs of ARMD and unrevised patients with FJS of 75 or more) using Firth logistic regression. Results: 376 patients were included: 312 unrevised patients and 64 patients who underwent revision. Each one-unit increase in CoGR score was associated with a 9.8 point lower FJS (95% confidence interval (CI) 4.2 to 15.4 points; p < 0.001). This increased to a 17.5 (9.4 to 25.5) point reduction per CoGR score unit in patients with blood cobalt above the median level. Comparing 28 ARMD cases (12 with ALVAL) with 177 controls, each one-unit CoGR increase was associated with odds ratios of 1.90 (CI 1.34 to 2.75) for ARMD and 3.05 (CI 1.89 to 5.34) for ALVAL. Conclusions: A higher CoGR score was associated with worse patient-reported outcome and higher odds of histologically confirmed adverse reaction to metal debris at revision. Adverse immune responses may be a more significant factor in unexplained pain after KA than is generally recognised.

Background: Giant cell arteritis (GCA), traditionally considered T cell-driven, exhibits vascular B/plasma-cell infiltrates and altered circulating B-cell homeostasis, suggesting a pathogenic role for B cells. Relapse is common in newly diagnosed GCA (nGCA), yet predictive biomarkers remain elusive. Objective: To characterize circulating B-cell subpopulations in nGCA and assess their association with 12-month relapse. Methods: Baseline multiparametric flow cytometry was performed on peripheral blood samples from consecutive patients with nGCA and sex/age-matched healthy controls (HC). Patients received standard treatment per 2018 EULAR recommendations and were followed longitudinally. Results: 102 patients with nGCA and 102 matched HC were included. One-year outcome data were available for 55 patients, of whom 34 relapsed and 21 remained relapse-free. Baseline B-cell homeostasis differed by disease course. Non-relapsers showed reduced total CD19+ B-cell counts and contraction of most B-cell subsets, while CD27-IgD-double-negative (DN) B-cell counts remained comparable to HC. Conversely, relapsers maintained total B-cell numbers above HC despite reduced memory compartments, driven by expanded naive and DN B cells, alongside preserved plasmablast and transitional B-cell counts. At 6 months, total B-cell counts increased only in non-relapsers. DN B cells showed the greatest divergence between groups and independently predicted relapse. DN B-cell counts also correlated with circulating T peripheral helper cell numbers, supporting extrafollicular immune pathway activation. Conclusion: nGCA is characterized by outcome-dependent disturbances in B-cell homeostasis. Expansion of the DN B-cell compartment identifies a relapse-prone immunophenotype and represents a clinically relevant biomarker for early risk stratification.

Thrombotic thrombocytopenic purpura (TTP) is a rare, life-threatening thrombotic microangiopathy caused by a severe deficiency of the ADAMTS13 protease. We performed the first large-scale genome-wide association study (GWAS) of TTP in 1,344 individuals of Han Chinese ancestry, comprising a discovery cohort (n = 913) and a validation cohort (n = 431). We identified two independent susceptibility loci, including the known locus 6p21 and the novel locus 14q32. At the known locus 6p21, the lead signal rs2187668 is near HLA-DQA1 and strongly associated with TTP risk (P = 5.35e-10; Odds Ratio [OR] = 3.94). At the novel locus 14q32, the lead SNP rs1024350 (P = 1.01e-10; OR = 1.90) is located between LINC00221 and MIR5195. Fine-mapping prioritized rs2187668 as the leading signal at 6p21, whereas HLA imputation and stepwise conditional analysis further pinpointed amino acid position 74 of HLA-DRB1 as the primary driver of the broader MHC association (P = 2.28e-10), superseding classical allele-based models. Structural analysis revealed that position 74 lines pocket 4 of the HLA-DRB1 peptide-binding groove; the risk-conferring Leu/Arg residues at this position carried by HLA-DRB1*08:03 and DRB1*03 may favour presentation of ADAMTS13-derived autoantigenic peptides, whereas the common Ala residue is protective. In summary, we reconstructed the genetic architecture of TTP in East Asians and identified structural gatekeepers of autoimmunity, providing novel targets for precision medicine and ethnic-specific risk stratification.

Despite its relative anti-inflammatory nature, IgG4 is involved in a variety of pathological conditions such as autoimmune disease and cancer. To investigate whether the IgG4 repertoire presents any abnormalities in diseases where IgG4 autoantibodies predominate, we charted longitudinal IgG4 repertoires in health, in an IgG4-mediated autoimmune disease (AID; muscle-specific kinase myasthenia gravis (MuSK MG)), and in IgG1/IgG3 mediated AIDs (acetylcholine receptor (AChR) MG and Lambert-Eaton myasthenic syndrome (LEMS). In total, we assessed 218 samples of 69 donors using mass spectrometry-based antibody repertoire analysis, covering a timespan of up to eight years. Despite being superficially inconspicuous in clonal diversity and abundances, we detected a slightly elevated number of IgG4 clones in MuSK MG patients compared to healthy donors. Notably, this observation did not coincide with drastic repertoire changes during treatment, suggesting that a large portion of the IgG4 repertoire is not significantly affected by common MuSK MG treatment regimens. Comparing the IgG4 antibody repertoires of all donors, we found that they were exceptionally unique for each individual. Against what would be expected in the case of a constantly adapting antibody repertoire, a large portion of the IgG4 clones remained stable without any further maturation. This observation even extended to patients receiving B cell depleting or IgG modulating treatments. Our findings suggest that a dominating fraction of the IgG4 pool may be produced by long-lived plasma cells, which are unaffected by disease or medical interventions.

Background. Short telomeres are an established cause of idiopathic pulmonary fibrosis (IPF), but the genetic evidence rests on seven instruments, six of which lie at telomere-maintenance loci, and so cannot separate an effect of telomere length from an effect of the telomerase pathway itself - a distinction that determines whether telomere length is a tractable target or only a marker of the pathway. Whether other measures of biological ageing share the effect, and whether accelerated ageing causes immune-mediated disease more generally, has not been tested systematically. Methods. Two-sample Mendelian randomisation of six ageing measures - GrimAge, PhenoAge, Hannum-age and intrinsic epigenetic age acceleration, proteomic age acceleration, and leukocyte telomere length - against six immune-mediated diseases in FinnGen R12: giant cell arteritis (GCA), polymyalgia rheumatica, primary Sjoegren's disease, interstitial lung disease (ILD), Crohn's disease and ulcerative colitis. All 36 pairs were analysed in both directions using inverse-variance weighted (IVW), MR-Egger, weighted-median and weighted-mode estimators, with Cochran's Q, I2, leave-one-out and single-variant diagnostics, a pre-specified analysis excluding HLA-region instruments, and iterative Q-based outlier removal. Instruments were annotated against telomere-maintenance and pulmonary-fibrosis loci and that class excluded. Minimum detectable effects were computed for every pair before estimates were examined. Any pair surviving correction was re-estimated in two independent IPF case-control datasets. A two-step analysis tested mediation of ILD risk by seven gut microbial taxa acting through telomere length. Results. One of 36 forward pairs survived correction. Longer telomeres reduced ILD risk: outlier-robust IVW odds ratio (OR) 0.59 per standard deviation (SD), 95% CI 0.49-0.71, p = 2.7 x 10^-8, on 77 instruments, with no residual heterogeneity (I2 = 6%) and concordance across estimators. Four pleiotropic instruments - in TERT, TERC, APOE and ATM - inflated the unfiltered estimate to OR 0.46 (0.37-0.57) and accounted for all of its heterogeneity. The effect was reproduced in 5,159 clinician-diagnosed European IPF cases (OR 0.18, 0.12-0.25, p = 5.0 x 10^-23) and in 1,210 East Asian cases (OR 0.54, 0.35-0.83, p = 0.005). Excluding every telomere-maintenance and pulmonary-fibrosis locus left OR 0.26 (0.17-0.40), p = 1.6 x 10^-9, on 72 instruments, establishing that the effect does not depend on TERT or TERC. The effect was three times larger for clinically defined IPF than for the broad registry ILD endpoint (p = 1.8 x 10^-9), consistent with dilution of a fibrosis-specific mechanism by case mix. No methylation clock and no proteomic age measure affected any disease; smallest detectable ORs ranged from 1.29 to 5.24 per SD, so these nulls exclude only large effects. The reverse direction could not be tested at informative precision. One apparent clock-autoimmunity association was produced entirely by a single HLA-region instrument. Mediation was null at its first step. Conclusions. Telomere attrition causally increases fibrotic lung disease risk, with an effect that concentrates in clinically defined IPF and that survives removal of every telomere-maintenance locus - shown here for the first time - and is therefore attributable to telomere length rather than to the telomerase genes that dominate conventional instrument sets. Four methylation clocks and proteomic age acceleration show no such effect, so these measures cannot be treated as interchangeable proxies for biological ageing.

Pulmonary hypertension (PH) is a progressive and fatal disease characterized by pulmonary vascular remodeling, inflammation, and immune dysregulation. Myeloid-derived suppressor cells (MDSCs) and macrophages contribute to PAH pathobiology; however, the molecular regulators of their pathological activation remain poorly defined. The triggering receptor expressed on myeloid cells 2 (TREM2) is an immunomodulatory receptor that shapes myeloid cell metabolism, survival, and immunosuppressive function, yet its role in PH has not been investigated. Methods: Single-cell RNA sequencing (scRNA-seq) data from human pulmonary artery tissue (GSE210248; n=3 PAH, n=3 donors) were analyzed to characterize TREM2 expression across cell populations. Wild-type (WT) and global TREM2 knockout (TREM2 KO) mice were exposed to chronic hypoxia (10% FiO2, 28 days). Hemodynamic, histological, flow cytometric, and ex vivo functional assessments were performed. TREM2 expression was measured by flow cytometry in circulating MDSCs from PAH patients (n=22) and healthy controls (n=13). Results: TREM2 was markedly enriched in monocyte/macrophage populations in PH pulmonary arteries and TREM2-high immune cells exhibited transcriptional downregulation of chemotaxis programs and upregulation of antigen processing and MHC II presentation pathways. TREM2 deficiency significantly attenuated hypoxia-induced RVSP increase, right ventricular dysfunction, pulmonary inflammation, and vascular remodeling. MDSCs from TREM2 KO mice exerted significantly less suppression of CD4+ and CD8+ T cell proliferation. TREM2 was significantly elevated in circulating MDSCs from PAH patients and showed a directional association with hemodynamic severity. Conclusions: TREM2 is a novel regulator of myeloid-driven immunosuppression and vascular remodeling in PAH and warrants investigation as a therapeutic target and biomarker.