Multiorgan involvement and circulating IgG1 predict hypocomplementaemia in IgG4-related disease.

OBJECTIVES: Hypocomplementaemia is common in patients with IgG4-related disease (IgG4-RD). We aimed to determine the IgG4-RD features associated with hypocomplementaemia and investigate mechanisms of complement activation in this disease. METHODS: We performed a single-centre cross-sectional study of 279 patients who fulfilled the IgG4-RD classification criteria, using unadjusted and multivariable-adjusted logistic regression to identify factors associated with hypocomplementaemia. RESULTS: Hypocomplementaemia was observed in 90 (32%) patients. In the unadjusted model, the number of organs involved (OR 1.42, 95% CI 1.23 to 1.63) and involvement of the lymph nodes (OR 3.87, 95% CI 2.19 to 6.86), lungs (OR 3.81, 95% CI 2.10 to 6.89), pancreas (OR 1.66, 95% CI 1.001 to 2.76), liver (OR 2.73, 95% CI 1.17 to 6.36) and kidneys (OR 2.48, 95% CI 1.47 to 4.18) were each associated with hypocomplementaemia. After adjusting for age, sex and number of organs involved, only lymph node (OR 2.59, 95% CI 1.36 to 4.91) and lung (OR 2.56, 95% CI 1.35 to 4.89) involvement remained associated with hypocomplementaemia while the association with renal involvement was attenuated (OR 1.6, 95% CI 0.92 to 2.98). Fibrotic disease manifestations (OR 0.43, 95% CI 0.21 to 0.87) and lacrimal gland involvement (OR 0.53, 95% CI 0.28 to 0.999) were inversely associated with hypocomplementaemia in the adjusted analysis. Hypocomplementaemia was associated with higher concentrations of all IgG subclasses and IgE (all p<0.05). After adjusting for serum IgG1 and IgG3, only IgG1 but not IgG4 remained strongly associated with hypocomplementaemia. CONCLUSIONS: Hypocomplementaemia in IgG4-RD is not unique to patients with renal involvement and may reflect the extent of disease. IgG1 independently correlates with hypocomplementaemia in IgG4-RD, but IgG4 does not. Complement activation is likely involved in IgG4-RD pathophysiology.

Shift in perspective: autoimmunity protecting against rheumatoid arthritis.

A hallmark of rheumatoid arthritis (RA) is the increased levels of autoantibodies preceding the onset and contributing to the classification of the disease. These autoantibodies, mainly anti-citrullinated protein antibody (ACPA) and rheumatoid factor, have been assumed to be pathogenic and many attempts have been made to link them to the development of bone erosion, pain and arthritis. We and others have recently discovered that most cloned ACPA protect against experimental arthritis in the mouse. In addition, we have identified suppressor B cells in healthy individuals, selected in response to collagen type II, and these cells decrease in numbers in RA. These findings provide a new angle on how to explain the development of RA and maybe also other complex autoimmune diseases preceded by an increased autoimmune response.

The 2023 ACR/EULAR classification criteria for calcium pyrophosphate deposition disease.

OBJECTIVE: Calcium pyrophosphate deposition (CPPD) disease is prevalent and has diverse presentations, but there are no validated classification criteria for this symptomatic arthritis. The American College of Rheumatology (ACR) and EULAR have developed the first-ever validated classification criteria for symptomatic CPPD disease. METHODS: Supported by the ACR and EULAR, a multinational group of investigators followed established methodology to develop these disease classification criteria. The group generated lists of candidate items and refined their definitions, collected de-identified patient profiles, evaluated strengths of associations between candidate items and CPPD disease, developed a classification criteria framework, and used multi-criterion decision analysis to define criteria weights and a classification threshold score. The criteria were validated in an independent cohort. RESULTS: Among patients with joint pain, swelling, or tenderness (entry criterion) whose symptoms are not fully explained by an alternative disease (exclusion criterion), the presence of crowned dens syndrome or calcium pyrophosphate crystals in synovial fluid are sufficient to classify a patient as having CPPD disease. In the absence of these findings, a score>56 points using weighted criteria, comprising clinical features, associated metabolic disorders, and results of laboratory and imaging investigations, can be used to classify as CPPD disease. These criteria had a sensitivity of 92.2% and specificity of 87.9% in the derivation cohort (190 CPPD cases, 148 mimickers), whereas sensitivity was 99.2% and specificity was 92.5% in the validation cohort (251 CPPD cases, 162 mimickers). CONCLUSION: The 2023 ACR/EULAR CPPD disease classification criteria have excellent performance characteristics and will facilitate research in this field.

Novel aspects in the pathophysiology and diagnosis of glomerular diseases.

Immune deposits/complexes are detected in a multitude of tissues in autoimmune disorders, but no organ has attracted as much attention as the kidney. Several kidney diseases are characterised by the presence of specific configurations of such deposits, and many of them are under a 'shared care' between rheumatologists and nephrologists. This review focuses on five different diseases commonly encountered in rheumatological and nephrological practice, namely IgA vasculitis, lupus nephritis, cryoglobulinaemia, anti-glomerular basement membrane disease and anti-neutrophil cytoplasm-antibody glomerulonephritis. They differ in disease aetiopathogenesis, but also the potential speed of kidney function decline, the responsiveness to immunosuppression/immunomodulation and the deposition of immune deposits/complexes. To date, it remains unclear if deposits are causing a specific disease or aim to abrogate inflammatory cascades responsible for tissue damage, such as neutrophil extracellular traps or the complement system. In principle, immunosuppressive therapies have not been developed to tackle immune deposits/complexes, and repeated kidney biopsy studies found persistence of deposits despite reduction of active inflammation, again highlighting the uncertainty about their involvement in tissue damage. In these studies, a progression of active lesions to chronic changes such as glomerulosclerosis was frequently reported. Novel therapeutic approaches aim to mitigate these changes more efficiently and rapidly. Several new agents, such as avacopan, an oral C5aR1 inhibitor, or imlifidase, that dissolves IgG within minutes, are more specifically reducing inflammatory cascades in the kidney and repeat tissue sampling might help to understand their impact on immune cell deposition and finally kidney function recovery and potential impact of immune complexes/deposits.

Longitudinal gut microbiome analyses and blooms of pathogenic strains during lupus disease flares.

OBJECTIVE: Whereas genetic susceptibility for systemic lupus erythematosus (SLE) has been well explored, the triggers for clinical disease flares remain elusive. To investigate relationships between microbiota community resilience and disease activity, we performed the first longitudinal analyses of lupus gut-microbiota communities. METHODS: In an observational study, taxononomic analyses, including multivariate analysis of ß-diversity, assessed time-dependent alterations in faecal communities from patients and healthy controls. From gut blooms, strains were isolated, with genomes and associated glycans analysed. RESULTS: Multivariate analyses documented that, unlike healthy controls, significant temporal community-wide ecological microbiota instability was common in SLE patients, and transient intestinal growth spikes of several pathogenic species were documented. Expansions of only the anaerobic commensal, Ruminococcus (blautia) gnavus (RG) occurred at times of high-disease activity, and were detected in almost half of patients during lupus nephritis (LN) disease flares. Whole genome sequence analysis of RG strains isolated during these flares documented 34 genes postulated to aid adaptation and expansion within a host with an inflammatory condition. Yet, the most specific feature of strains found during lupus flares was the common expression of a novel type of cell membrane-associated lipoglycan. These lipoglycans share conserved structural features documented by mass spectroscopy, and highly immunogenic repetitive antigenic-determinants, recognised by high-level serum IgG2 antibodies, that spontaneously arose, concurrent with RG blooms and lupus flares. CONCLUSIONS: Our findings rationalise how blooms of the RG pathobiont may be common drivers of clinical flares of often remitting-relapsing lupus disease, and highlight the potential pathogenic properties of specific strains isolated from active LN patients.

Methylome and transcriptome profiling of giant cell arteritis monocytes reveals novel pathways involved in disease pathogenesis and molecular response to glucocorticoids.

OBJECTIVES: Giant cell arteritis (GCA) is a complex systemic vasculitis mediated by the interplay between both genetic and epigenetic factors. Monocytes are crucial players of the inflammation occurring in GCA. Therefore, characterisation of the monocyte methylome and transcriptome in GCA would be helpful to better understand disease pathogenesis. METHODS: We performed an integrated epigenome-and transcriptome-wide association study in CD14+ monocytes from 82 patients with GCA, cross-sectionally classified into three different clinical statuses (active, in remission with or without glucocorticoid (GC) treatment), and 31 healthy controls. RESULTS: We identified a global methylation and gene expression dysregulation in GCA monocytes. Specifically, monocytes from active patients showed a more proinflammatory phenotype compared with healthy controls and patients in remission. In addition to inflammatory pathways known to be involved in active GCA, such as response to IL-6 and IL-1, we identified response to IL-11 as a new pathway potentially implicated in GCA. Furthermore, monocytes from patients in remission with treatment showed downregulation of genes involved in inflammatory processes as well as overexpression of GC receptor-target genes. Finally, we identified changes in DNA methylation correlating with alterations in expression levels of genes with a potential role in GCA pathogenesis, such as ITGA7 and CD63, as well as genes mediating the molecular response to GC, including FKBP5, ETS2, ZBTB16 and ADAMTS2. CONCLUSION: Our results revealed profound alterations in the methylation and transcriptomic profiles of monocytes from GCA patients, uncovering novel genes and pathways involved in GCA pathogenesis and in the molecular response to GC treatment.

Multi-trait and cross-population genome-wide association studies across autoimmune and allergic diseases identify shared and distinct genetic component.

OBJECTIVES: Autoimmune and allergic diseases are outcomes of the dysregulation of the immune system. Our study aimed to elucidate differences or shared components in genetic backgrounds between autoimmune and allergic diseases. METHODS: We estimated genetic correlation and performed multi-trait and cross-population genome-wide association study (GWAS) meta-analysis of six immune-related diseases: rheumatoid arthritis, Graves' disease, type 1 diabetes for autoimmune diseases and asthma, atopic dermatitis and pollinosis for allergic diseases. By integrating large-scale biobank resources (Biobank Japan and UK biobank), our study included 105 721 cases and 433 663 controls. Newly identified variants were evaluated in 21 778 cases and 712 767 controls for two additional autoimmune diseases: psoriasis and systemic lupus erythematosus. We performed enrichment analyses of cell types and biological pathways to highlight shared and distinct perspectives. RESULTS: Autoimmune and allergic diseases were not only mutually classified based on genetic backgrounds but also they had multiple positive genetic correlations beyond the classifications. Multi-trait GWAS meta-analysis newly identified six allergic disease-associated loci. We identified four loci shared between the six autoimmune and allergic diseases (rs10803431 at PRDM2, OR=1.07, p=2.3×10-8, rs2053062 at G3BP1, OR=0.90, p=2.9×10-8, rs2210366 at HBS1L, OR=1.07, p=2.5×10-8 in Japanese and rs4529910 at POU2AF1, OR=0.96, p=1.9×10-10 across ancestries). Associations of rs10803431 and rs4529910 were confirmed at the two additional autoimmune diseases. Enrichment analysis demonstrated link to T cells, natural killer cells and various cytokine signals, including innate immune pathways. CONCLUSION: Our multi-trait and cross-population study should elucidate complex pathogenesis shared components across autoimmune and allergic diseases.

Comprehensive analysis of the major histocompatibility complex in systemic sclerosis identifies differential HLA associations by clinical and serological subtypes.

OBJECTIVE: The greatest genetic effect reported for systemic sclerosis (SSc) lies in the major histocompatibility complex (MHC) locus. Leveraging the largest SSc genome-wide association study, we aimed to fine-map this region to identify novel human leucocyte antigen (HLA) genetic variants associated with SSc susceptibility and its main clinical and serological subtypes. METHODS: 9095 patients with SSc and 17 584 controls genome-wide genotyped were used to impute and test single-nucleotide polymorphisms (SNPs) across the MHC, classical HLA alleles and their composite amino acid residues. Additionally, patients were stratified according to their clinical and serological status, namely, limited cutaneous systemic sclerosis (lcSSc), diffuse cutaneous systemic sclerosis (dcSSc), anticentromere (ACA), antitopoisomerase (ATA) and anti-RNApolIII autoantibodies (ARA). RESULTS: Sequential conditional analyses showed nine SNPs, nine classical alleles and seven amino acids that modelled the observed associations with SSc. This confirmed previously reported associations with HLA-DRB1*11:04 and HLA-DPB1*13:01, and revealed a novel association of HLA-B*08:01. Stratified analyses showed specific associations of HLA-DQA1*02:01 with lcSSc, and an exclusive association of HLA-DQA1*05:01 with dcSSc. Similarly, private associations were detected in HLA-DRB1*08:01 and confirmed the previously reported association of HLA-DRB1*07:01 with ACA-positive patients, as opposed to the HLA-DPA1*02:01 and HLA-DQB1*03:01 alleles associated with ATA presentation. CONCLUSIONS: This study confirms the contribution of HLA class II and reveals a novel association of HLA class I with SSc, suggesting novel pathways of disease pathogenesis. Furthermore, we describe specific HLA associations with SSc clinical and serological subtypes that could serve as biomarkers of disease severity and progression.

Genomic Risk Score impact on susceptibility to systemic sclerosis.

OBJECTIVES: Genomic Risk Scores (GRS) successfully demonstrated the ability of genetics to identify those individuals at high risk for complex traits including immune-mediated inflammatory diseases (IMIDs). We aimed to test the performance of GRS in the prediction of risk for systemic sclerosis (SSc) for the first time. METHODS: Allelic effects were obtained from the largest SSc Genome-Wide Association Study (GWAS) to date (9 095 SSc and 17 584 healthy controls with European ancestry). The best-fitting GRS was identified under the additive model in an independent cohort that comprised 400 patients with SSc and 571 controls. Additionally, GRS for clinical subtypes (limited cutaneous SSc and diffuse cutaneous SSc) and serological subtypes (anti-topoisomerase positive (ATA+) and anti-centromere positive (ACA+)) were generated. We combined the estimated GRS with demographic and immunological parameters in a multivariate generalised linear model. RESULTS: The best-fitting SSc GRS included 33 single nucleotide polymorphisms (SNPs) and discriminated between patients with SSc and controls (area under the receiver operating characteristic (ROC) curve (AUC)=0.673). Moreover, the GRS differentiated between SSc and other IMIDs, such as rheumatoid arthritis and Sjögren's syndrome. Finally, the combination of GRS with age and immune cell counts significantly increased the performance of the model (AUC=0.787). While the SSc GRS was not able to discriminate between ATA+ and ACA+ patients (AUC<0.5), the serological subtype GRS, which was based on the allelic effects observed for the comparison between ACA+ and ATA+ patients, reached an AUC=0.693. CONCLUSIONS: GRS was successfully implemented in SSc. The model discriminated between patients with SSc and controls or other IMIDs, confirming the potential of GRS to support early and differential diagnosis for SSc.

Functional genomics of autoimmune diseases.

For more than a decade, genome-wide association studies have been applied to autoimmune diseases and have expanded our understanding on the pathogeneses. Genetic risk factors associated with diseases and traits are essentially causative. However, elucidation of the biological mechanism of disease from genetic factors is challenging. In fact, it is difficult to identify the causal variant among multiple variants located on the same haplotype or linkage disequilibrium block and thus the responsible biological genes remain elusive. Recently, multiple studies have revealed that the majority of risk variants locate in the non-coding region of the genome and they are the most likely to regulate gene expression such as quantitative trait loci. Enhancer, promoter and long non-coding RNA appear to be the main target mechanisms of the risk variants. In this review, we discuss functional genetics to challenge these puzzles.

ß2-Glycoprotein I/IgA Immune Complexes: A Marker to Predict Thrombosis After Renal Transplantation in Patients With Antiphospholipid Antibodies.

BACKGROUND: Antiphospholipid syndrome is characterized by recurrent thrombosis and gestational morbidity in patients with antiphospholipid autoantibodies (aPLs). Predictive value of the presence of aPLs is low, and new markers are necessary to identify aPL carriers at higher risk and take preventive measures on them. The presence of circulating immune complexes of IgA bound to ß2-glycoprotein I (B2A-CIC) has been associated with occurrence of acute thrombotic events. In this work we study its possible predictive value for the appearance of acute thrombotic events in patients who are going to undergo transplant surgery, a well-known trigger of acute thrombotic events in aPL carriers. METHODS: We performed a follow-up study based on the Magnum 12+12 Cohort of patients who received a kidney transplant (n=1339). Three groups were established: group 1 patients who were positive for IgA anti-ß2-glycoprotein I (aB2GP1) and B2A-CIC (n=125); group 2 patients who were positive only for IgA aB2GP1 (n=240); and control group, patients who were negative for IgA aB2GP1 (n=974). Levels of autoantibodies and B2A-CIC were quantified immediately before the transplant surgery and patients were followed up for 6 months. RESULTS: In group 1, 46.4% of patients experienced any type of thrombosis versus 10.4% in group 2 (P<0.001) and 8.6% in the control group (P<0.001). The incidence of graft thrombosis in group 1 (31.2%) was significantly higher than that observed in group 2 (3.3%, P<0.001) and the control group (2.6%, P<0.001). In a multivariate analysis, the presence of B2A-CIC was an independent variable to experience any type of posttransplant thrombosis (hazard ratio, 6.72; 95% confidence interval, 4.81-9.37) and, prominently, for graft thrombosis (hazard ratio, 14.75; 95% confidence interval, 9.11-23.89). No significant differences were found between B2A-CIC-negative and control group patients. CONCLUSIONS: The presence of B2A-CIC is a predictor of acute thrombotic events. Patients who were positive for IgA aB2GP1 only are at risk of experiencing thrombosis if they are B2A-CIC positive. If they are B2A-CIC-negative patients, they have the same risk as the control group. Treatments to prevent acute thrombotic events should focus on B2A-CIC-positive patients.

Unraveling the immunopathogenesis of glomerular disease.

Immune-mediated damage to glomerular structures is largely responsible for the pathology associated with the majority of glomerular diseases. Therefore, a detailed understanding of the basic immune mechanisms responsible for glomerular damage is needed to inform the design of novel intervention strategies. Glomerular injury of immune origin is complex and involves both inflammatory and non-inflammatory processes driven by elements of the innate and adaptive immune system. This review summarizes the basic immune mechanisms that cause glomerular injury leading to the nephritic and nephrotic syndromes. A major focus of the review is to highlight the mechanisms by which antibodies cause glomerular injury through their interactions with glomerular cells, complement proteins, phagocytes bearing complement and Fcγ receptors, and dendritic cells expressing the neonatal receptor for IgG, FcRn.