Immune complexes from rheumatoid arthritis synovial fluid induce FcgammaRIIa dependent and rheumatoid factor correlated production of tumour necrosis factor-alpha by peripheral blood mononuclear cells

The Contribution of Macrophage Plasticity to Inflammatory Arthritis and Their Potential as Therapeutic Targets

Inflammatory arthritis are common chronic inflammatory autoimmune diseases characterised by progressive, destructive inflammation of the joints leading to a loss of function and significant comorbidities; importantly, there are no cures and only 20% of patients achieve drug-free remission for over 2 years. Macrophages play a vital role in maintaining homeostasis, however, under the wrong environmental cues, become drivers of chronic synovial inflammation. Based on the current "dogma", M1 macrophages secrete pro-inflammatory cytokines and chemokines, promoting tissue degradation and joint and bone erosion which over time lead to accelerated disease progression. On the other hand, M2 macrophages secrete anti-inflammatory mediators associated with wound healing, tissue remodelling and the resolution of inflammation. Currently, four subtypes of M2 macrophages have been identified, namely M2a, M2b, M2c and M2d. However, more subtypes may exist due to macrophage plasticity and the ability for repolarisation. Macrophages are highly plastic, and polarisation exists as a continuum with diverse intermediate phenotypes. This plasticity is achieved by a highly amenable epigenome in response to environmental stimuli and shifts in metabolism. Initiating treatment during the early stages of disease is important for improved prognosis and patient outcomes. Currently, no treatment targeting macrophages specifically is available. Such therapeutics are being investigated in ongoing clinical trials. The repolarisation of pro-inflammatory macrophages towards the anti-inflammatory phenotype has been proposed as an effective approach in targeting the M1/M2 imbalance, and in turn is a potential therapeutic strategy for IA diseases. Therefore, elucidating the mechanisms that govern macrophage plasticity is fundamental for the success of novel macrophage targeting therapeutics.

Fcγ-receptor-IIIA bioactivity of circulating and synovial immune complexes in rheumatoid arthritis

OBJECTIVE

Previous technical limitations prevented the proof of Fcγ-receptor (FcγR)-activation by soluble immune complexes (sICs) in patients. FcγRIIIa (CD16) is a risk factor in rheumatoid arthritis (RA). We aimed at determining the presence of CD16-activating sICs in RA and control diseases.

METHODS

Sera from an exploratory cohort (n=50 patients with RA) and a validation cohort (n=106 patients with RA, 20 patients with psoriasis arthritis (PsA), 22 patients with systemic lupus erythematosus (SLE) and 31 healthy controls) were analysed using a new reporter cell assay. Additionally, 26 synovial fluid samples were analysed, including paired serum/synovial samples.

RESULTS

For the first time using a reliable and sensitive functional assay, the presence of sICs in RA sera was confirmed. sICs possess an intrinsic capacity to activate CD16 and can be found in both synovial fluid and in blood. In low experimental dilutions, circulating sICs were also detected in a subset of healthy people and in PsA. However, we report a significantly increased frequency of bioactive circulating sICs in RA. While the bioactivity of circulating sICs was low and did not correlate with clinical parameters, synovial sICs were highly bioactive and correlated with serum autoantibody levels. Receiver operator curves indicated that sICs bioactivity in synovial fluid could be used to discriminate immune complex-associated arthritis from non-associated forms. Finally, circulating sICs were more frequently found in SLE than in RA. The degree of CD16 bioactivity showed strong donor-dependent differences, especially in SLE.

CONCLUSIONS

RA is characterised by the presence of circulating and synovial sICs that can engage and activate CD16.

Immune Thrombosis: Exploring the Significance of Immune Complexes and NETosis

Neutrophil extracellular traps (NETs) are major contributors to inflammation and autoimmunity, playing a key role in the development of thrombotic disorders. NETs, composed of DNA, histones, and numerous other proteins serve as scaffolds for thrombus formation and promote platelet activation, coagulation, and endothelial dysfunction. Accumulating evidence indicates that NETs mediate thrombosis in autoimmune diseases, viral and bacterial infections, cancer, and cardiovascular disease. This article reviews the role and mechanisms of immune complexes in NETs formation and their contribution to the generation of a prothrombotic state. Immune complexes are formed by interactions between antigens and antibodies and can induce NETosis by the direct activation of neutrophils via Fc receptors, via platelet activation, and through endothelial inflammation. We discuss the mechanisms by which NETs induced by immune complexes contribute to immune thrombotic processes and consider the potential development of therapeutic strategies. Targeting immune complexes and NETosis hold promise for mitigating thrombotic events and reducing the burden of immune thrombosis.

Bone Involvement in Rheumatoid Arthritis and Spondyloartritis: An Updated Review

Several rheumatologic diseases are primarily distinguished by their involvement of bone tissue, which not only serves as a mere target of the condition but often plays a pivotal role in its pathogenesis. This scenario is particularly prominent in chronic inflammatory arthritis such as rheumatoid arthritis (RA) and spondyloarthritis (SpA). Given the immunological and systemic nature of these diseases, in this review, we report an overview of the pathogenic mechanisms underlying specific bone involvement, focusing on the complex interactions that occur between bone tissue's own cells and the molecular and cellular actors of the immune system, a recent and fascinating field of interest defined as osteoimmunology. Specifically, we comprehensively elaborate on the distinct pathogenic mechanisms of bone erosion seen in both rheumatoid arthritis and spondyloarthritis, as well as the characteristic process of aberrant bone formation observed in spondyloarthritis. Lastly, chronic inflammatory arthritis leads to systemic bone involvement, resulting in systemic bone loss and consequent osteoporosis, along with increased skeletal fragility.

CD64 as novel molecular imaging marker for the characterization of synovitis in rheumatoid arthritis

BACKGROUND

Rheumatoid arthritis (RA) is one of the most prevalent and debilitating joint diseases worldwide. RA is characterized by synovial inflammation (synovitis), which is linked to the development of joint destruction. Magnetic resonance imaging and ultrasonography are widely being used to detect the presence and extent of synovitis. However, these techniques do not reveal the activation status of inflammatory cells such as macrophages that play a crucial role in synovitis and express CD64 (Fc gamma receptor (FcγR)I) which is considered as macrophage activation marker.

OBJECTIVES

We aimed to investigate CD64 expression and its correlation with pro-inflammatory cytokines and pro-damaging factors in human-derived RA synovium. Furthermore, we aimed to set up a molecular imaging modality using a radiolabeled CD64-specific antibody as a novel imaging tracer that could be used to determine the extent and phenotype of synovitis using optical and nuclear imaging.

METHODS

First, we investigated CD64 expression in synovium of early- and late-stage RA patients and studied its correlation with the expression of pro-inflammatory and tissue-damaging factors. Next, we conjugated an anti-CD64 antibody with IRDye 800CW and diethylenetriamine penta-acetic acid (DTPA; used for 111In labeling) and tested its binding on cultured THP1 cells, ex vivo RA synovium explants and its imaging potential in SCID mice implanted with human RA synovium explants obtained from RA patients who underwent total joint replacement.

RESULTS

We showed that CD64 is expressed in synovium of early and late-stage RA patients and that FCGR1A/CD64 expression is strongly correlated with factors known to be involved in RA progression. Combined, this makes CD64 a useful marker for imaging the extent and phenotype of synovitis. We reported higher binding of the [111In]In-DTPA-IRDye 800CW anti-CD64 antibody to in vitro cultured THP1 monocytes and ex vivo RA synovium compared to isotype control. In human RA synovial explants implanted in SCID mice, the ratio of uptake of the antibody in synovium over blood was significantly higher when injected with anti-CD64 compared to isotype and injecting an excess of unlabeled antibody significantly reduced the antibody-binding associated signal, both indicating specific receptor binding.

CONCLUSION

Taken together, we successfully developed an optical and nuclear imaging modality to detect CD64 in human RA synovium in vivo.

Transforming mutations in the development of pathogenic B cell clones and autoantibodies

Autoimmune diseases are characterized by serum autoantibodies, some of which are pathogenic, causing severe manifestations and organ injury. However, autoantibodies of the same antigenic reactivity are also present in the serum of asymptomatic people years before they develop any clinical signs of autoimmunity. Autoantibodies can arise during multiple stages of B cell development, and various genetic and environmental factors drive their production. However, what drives the development of pathogenic autoantibodies is poorly understood. Advances in single-cell technology have enabled the deep analysis of rare B cell clones producing pathogenic autoantibodies responsible for vasculitis in patients with primary Sjögren's syndrome complicated by mixed cryoglobulinaemia. These findings demonstrated a cascade of genetic events involving stereotypic immunoglobulin V(D)J recombination and transforming somatic mutations in lymphoma genes and V(D)J regions that disrupted antibody quality control mechanisms and decreased autoantibody solubility. Most studies consider V(D)J mutations that enhance autoantibody affinity to drive pathology; however, V(D)J mutations that increase autoantibody propensity to form insoluble complexes could be a major contributor to autoantibody pathogenicity. Defining the molecular characteristics of pathogenic autoantibodies and failed tolerance checkpoints driving their formation will improve prognostication, enabling early treatment to prevent escalating organ damage and B cell malignancy.

Fc receptors gone wrong: A comprehensive review of their roles in autoimmune and inflammatory diseases

Systemic autoimmune and inflammatory diseases have a complex and only partially known pathophysiology with various abnormalities involving all the components of the immune system. Among these components, antibodies, and especially autoantibodies are key elements contributing to autoimmunity. The interaction of antibody fragment crystallisable (Fc) and several distinct receptors, namely Fc receptors (FcRs), have gained much attention during the recent years, with possible major therapeutic perspectives for the future. The aim of this review is to comprehensively describe the known roles for FcRs (activating and inhibitory FcγRs, neonatal FcR [FcRn], FcαRI, FcεRs, Ro52/tripartite motif containing 21 [Ro52/TRIM21], FcδR, and the novel Fc receptor-like [FcRL] family) in systemic autoimmune and inflammatory disorders, namely rheumatoid arthritis, Sjögren's syndrome, systemic lupus erythematosus, systemic sclerosis, idiopathic inflammatory myopathies, mixed connective tissue disease, Crohn's disease, ulcerative colitis, immunoglobulin (Ig) A vasculitis, Behçet's disease, Kawasaki disease, IgG4-related disease, immune thrombocytopenia, autoimmune hemolytic anemia, antiphospholipid syndrome and heparin-induced thrombocytopenia.

Monocytes Exposed to Immune Complexes Reduce pDC Type 1 Interferon Response to Vidutolimod

Vidutolimod, also known as CMP-001, is a virus-like particle composed of the Qβ bacteriophage coat protein encasing a TLR9 agonist. Vidutolimod injected intratumorally is showing promise in early phase clinical trials based on its ability to alter the tumor microenvironment and induce an anti-tumor immune response. We previously demonstrated that the in vivo efficacy of vidutolimod is dependent on the presence of anti-Qβ antibodies that enhance opsonization and uptake of vidutolimod by TLR9-expressing plasmacytoid dendritic cells (pDCs). Here, we evaluated the effect of immune complexes, including anti-Qβ-coated vidutolimod, on induction of Type 1 Interferon production by peripheral blood mononuclear cells in response to vidutolimod and soluble TLR9 agonists. Immune complexes, including but not limited to anti-Qβ-coated vidutolimod, indirectly suppressed TLR9-mediated Type 1 Interferon production by pDCs in a monocyte-dependent manner. These findings indicate that anti-Qβ-coated vidutolimod has effects in addition to those mediated by TLR9 that could have important clinical implications for understanding the mechanism of action of this exciting new approach to in situ immunization and cancer immunotherapy.

Immunomodulatory Effects of Curcumin in Rheumatoid Arthritis: Evidence from Molecular Mechanisms to Clinical Outcomes

Rheumatoid arthritis (RA) is a chronic immune-mediated inflammatory disorder characterized by the destruction of the joint and bone resorption. The production of pro-inflammatory cytokines and chemokines, dysregulated functions of three important subtypes of T helper (T_H) cells including T_H1, T_H17, and regulator T (Treg) cells are major causes of the initiation and development of RA. Moreover, B cells as a source of the production of several autoantibodies play key roles in the pathogenesis of RA. The last decades have seen increasingly rapid advances in the field of immunopharmacology using natural origin compounds for the management of various inflammatory diseases. Curcumin, a main active polyphenol compound isolated from turmeric, curcuma longa, possesses a wide range of pharmacologic properties for the treatment of several diseases. This review comprehensively will assess beneficial immunomodulatory effects of curcumin on the production of pro-inflammatory cytokines and also dysregulated functions of immune cells including T_H1, T_H17, Treg, and B cells in RA. We also seek the clinical efficacy of curcumin for the treatment of RA in several recent clinical trials. In conclusion, curcumin has been found to ameliorate RA complications through modulating inflammatory and autoreactive responses in immune cells and synovial fibroblast cells via inhibiting the expression or function of pro-inflammatory mediators, such as nuclear factor-κB (NF-κB), activated protein-1 (AP-1), and mitogen-activated protein kinases (MAPKs). Of note, curcumin treatment without any adverse effects can attenuate the clinical symptoms of RA patients and, therefore, has therapeutic potential for the treatment of the diseases.

Gut Commensal Segmented Filamentous Bacteria Fine-Tune T Follicular Regulatory Cells to Modify the Severity of Systemic Autoimmune Arthritis

Autoantibodies play a major pathogenic role in rheumatoid arthritis. T follicular helper (Tfh) cells promote germinal center B cell and Ab responses. Excessive Tfh cell responses lead to autoimmunity, and therefore, counterregulation is crucial. T follicular regulatory (Tfr) cells, mainly differentiated from T regulatory cells, can negatively regulate Tfh and germinal center B cells. Dysbiosis is involved in rheumatoid arthritis's pathogenesis. We previously demonstrated that the gut microbiota, segmented filamentous bacteria (SFB), promote autoimmune arthritis by inducing Tfh cells. However, little is known regarding whether gut microbiota influence systemic (nongut) Tfr cells, impacting gut-distal autoimmunity. In this study, using SFB in autoimmune arthritic K/BxN mice, we demonstrated that SFB-induced arthritis is linked to the reduction of Tfr cells' CTLA-4, the key regulatory molecule of Tfr cells. This SFB-mediated CTLA-4 reduction is associated with increased Tfr glycolytic activity, and glycolytic inhibition increases Tfr cells' CTLA-4 levels and reduces arthritis. The surface expression of CTLA-4 is tied to TCR signaling strength, and we discovered that SFB-reduced CTLA-4 is associated with a reduction of Nur77, an indicator of TCR signaling strength. Nur77 is known for repressing glycolytic activity. Using a loss-of-function study, we demonstrated that Nur77+/- haplodeficiency increases glycolysis and reduces CTLA-4 on Tfr cells, which is associated with increased arthritis and anti-glucose-6-phosphate isomerase titers. Tfr-specific deletion (KRN.Foxp3CreBcl-6fl/fl) in autoimmune condition reveals that Tfr cells repress arthritis, Tfh cells, and autoantibody responses and that SFB can mitigate this repression. Overall, these findings demonstrated that gut microbiota distally impact systemic autoimmunity by fine-tuning Tfr cells.

A proteomics-based method for identifying antigens within immune complexes

A novel approach to recover and identify immune complexes (ICs) was developed using size exclusion chromatography (SEC) and affinity chromatography on immunoglobulin binding columns (HiTrap Protein G). The purification process was monitored by 1D SDS-PAGE, protein staining, Western blotting and, finally, liquid chromatography tandem mass spectrometry (LC MS/MS) was used to identify the recovered antigens. This approach was applied to serum with artificially created immune complexes (ICs) comprising vaccine antigen (influenza) and antibody, which led to recovery and identification of influenza peptides within the recovered ICs. This approach was compared with the established method for IC detection and recovery, polyethylene glycol (PEG) precipitation, followed by LC MS/MS. Both approaches successfully enabled capture, recovery and characterization of immunoglobulins and influenza antigen(s) in complex with the immunoglobulins. However, PEG precipitation has the advantage of simplicity and is more suited for large scale studies.

Identification of Common Differentially Expressed Genes and Potential Therapeutic Targets in Ulcerative Colitis and Rheumatoid Arthritis

Ulcerative colitis (UC) and rheumatoid arthritis (RA) are immune-mediated inflammatory diseases (IMIDs) with similar symptoms and common genomics. However, the relationship between UC and RA has not been investigated thoroughly. Therefore, this study aimed to establish the differentially expressed genes (DEGs) and potential therapeutic targets in UC and RA. Three microarray datasets (GSE38713, GSE1919, and GSE12251) were selected from the Gene Expression Omnibus (GEO) database for analysis. We used R software to identify the DEGs and performed enrichment analyses. Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) and Cytoscape software were used to construct the protein-protein interaction (PPI) network and identify the hub genes. A regulatory network based on the constructed PPI was generated using StarBase and PROMO databases. We identified a total of 1542 and 261 DEGs in UC and RA. There were 169 common DEGs identified in both UC and RA, including 63 upregulated genes (DEGs1) and nine downregulated genes (DEGs2). The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses of DEGs1 and DEGs2 in the PPI network revealed that the genes enriched were involved in immunity. A total of 45 hub genes were selected based on high scores of correlation; three hub genes (SRGN, PLEK, and FCGR3B) were found to be upregulated in UC and RA, and downregulated in UC patients with response to infliximab treatment. The identification of novel DEGs and hub genes in the current study contributes to a novel perception for latent functional mechanisms and presents potential prognostic indicators and therapeutic targets in UC and RA.

Neutrophil extracellular traps mediate articular cartilage damage and enhance cartilage component immunogenicity in rheumatoid arthritis

Rheumatoid arthritis (RA) is characterized by synovial joint inflammation, cartilage damage, and dysregulation of the adaptive immune system. While neutrophil extracellular traps (NETs) have been proposed to play a role in the generation of modified autoantigens and in the activation of synovial fibroblasts, it remains unknown whether NETs are directly involved in cartilage damage. Here, we report a new mechanism by which NET-derived elastase disrupts cartilage matrix and induces release of membrane-bound peptidylarginine deiminase-2 by fibroblast-like synoviocytes (FLSs). Cartilage fragments are subsequently citrullinated, internalized by FLSs, and then presented to antigen-specific CD4+ T cells. Furthermore, immune complexes containing citrullinated cartilage components can activate macrophages to release proinflammatory cytokines. HLA-DRB1*04:01 transgenic mice immunized with NETs develop autoantibodies against citrullinated cartilage proteins and display enhanced cartilage damage. Inhibition of NET-derived elastase rescues NET-mediated cartilage damage. These results show that NETs and neutrophil elastase externalized in these structures play fundamental pathogenic roles in promoting cartilage damage and synovial inflammation. Strategies targeting neutrophil elastase and NETs could have a therapeutic role in RA and in other inflammatory diseases associated with inflammatory joint damage.

Mouse Models of Rheumatoid Arthritis for Studies on Immunopathogenesis and Preclinical Testing of Fc Receptor-Targeting Biologics

<b><i>Background:</i></b> Rheumatoid arthritis (RA) is a chronic autoimmune disease that causes inflammation, swelling, and pain in the joints and involves systemic complications. Mouse models of RA have been extensively used to model the pathogenesis of RA and to develop effective therapies. Although many components of the immune system have been studied in these models, the role of crystallizable fragment (Fc) gamma receptors (FcγRs) in RA has been sorely neglected. The aim of this review was to introduce the different mouse models of RA and to describe the different drug development strategies that have been tested in these models to target FcγR function, with the focus being on drugs that have been made from the Fc of immunoglobulin G (IgG). <b><i>Summary:</i></b> Evidence suggests that FcγRs play a major role in immune complex-induced inflammation in autoimmune diseases, such as RA. However, there is limited knowledge on the importance of FcγRs in the human disease even though there has been extensive work in mouse models of RA. Numerous mouse models of RA are available, with each model depicting certain aspects of the disease. Induced models of RA have nonspecific immune activation with cartilage-directed autoimmunity, whereas spontaneous models of RA develop without immunization, which results in a more chronic form of arthritis. These models have been used to test FcγR-targeting monoclonal antibodies, intravenous immunoglobulin (IVIg), subcutaneously administered IVIg, and recombinant Fcs for their ability to interact with and modify FcγR function. Recombinant Fcs avidly bind FcγRs and exhibit enhanced therapeutic efficacy in mouse models of RA. <b><i>Key Message:</i></b> The therapeutic utility of targeting FcγRs with recombinant Fcs is great and should be explored in human clinical trials for autoimmune diseases, such as RA.

Clinical Proteomics Profiling for Biomarker Identification Among Patients Suffering With Indian Post Kala Azar Dermal Leishmaniasis

Background: Post Kala Azar Dermal Leishmaniasis (PKDL) is a non-fatal dermal sequel of Visceral Leishmaniasis (VL), affecting individuals worldwide. Available diagnostic tools lack sensitivity and specificity toward identifying macular (MAC) PKDL patients, due to low parasite load in patients' sample. Confirmatory test like punch biopsy are invasive and painful. Considering the rural nature of this disease and the prevailing situation of diagnostic scenario, PKDL patients mostly remains unattended from receiving proper medical care. They in turn act as “mobile parasite reservoir,” responsible for VL transmission among healthy individuals (HI). This study aims to identify PKDL disease specific glycated protein biomarkers, utilizing the powerful LC-MS/MS technology, which is the tool of choice to efficiently identify and quantify disease specific protein biomarkers. These identified PKDL disease specific novel glycoproteins could be developed in future as immunochromatographic based assay for efficient case detection.

Methodology: Previously our lab had identified importance of glycated (Circulating Immune Complexes) CICs, among PKDL patients. This study aims to further characterize disease specific glycated protein biomarkers, among MAC PKDL patients for both diagnostic and prognostic evaluation of the disease. LC-MS/MS based comparative spectral count analysis of MAC PKDL to polymorphic (POLY) PKDL, HI, and Cured (CR) individuals were performed. Proteins level alterations among all study groups were confirmed by Western blot and enzyme-linked immunosorbant Assay (ELISA).

Results: Among MAC PKDL patients 43, 60, 90 proteins were altered compared to POLY PKDL, HI, and CR groups, respectively. Filtering for the most significant proteins, Plasminogen (PLG) and Vitronectin (VTN) were identified which promisingly identified MAC PKDL cases. Active surveillance results from endemic districts of West Bengal revealed drastic rise of MAC PKDL cases, alarming the urgency for field adaptive efficient biomarker.

Conclusion: This current study aims to establish PLG and VTN as novel diagnostic and prognostic protein biomarker for MAC and POLY PKDL cases management.

Autoantibody and Cytokine Profiles during Treatment with Belimumab in Patients with Systemic Lupus Erythematosus

We investigated whether belimumab treatment impacts on levels of autoantibodies and cytokines of interest in systemic lupus erythematosus (SLE). Longitudinally collected serum samples from 78 belimumab-treated Swedish SLE patients were analysed. Serum cytokine levels were determined using Luminex xMAP technology, and nuclear antigen autoantibody specificities using addressable laser bead immunoassay. In patients with detectable levels at baseline, interferon (IFN)-α2 levels were lower at month 6 (median; interquartile range (IQR): 8.9; 1.5-54.9 pg/mL) versus baseline (28.4; 20.9-100.3 pg/mL; p = 0.043). Interleukin (IL)-6 (baseline: 7.1; 2.9-16.1 pg/mL) decreased from month 6 (0.5; 0.5-6.3 pg/mL; p = 0.018) and throughout a 24 month follow-up. IL-10 (baseline: 12.6; 2.8-29.7 pg/mL) showed more rapid decreases from month 3 (1.8; 0.6-9.1 pg/mL; p = 0.003). Levels of anti-dsDNA (p < 0.001), anti-Smith antigen (Sm) (p = 0.002), anti-U1 small nuclear ribonucleoprotein (U1RNP) (p < 0.001), anti-Sm-U1RNP complex (p = 0.028), and anti-ribosomal P (p = 0.012) antibodies decreased from month 3 and remained decreased. Anti-Sm positivity at baseline was associated with higher probability and/or shorter time to achieve sustained SLE responder index-4 response (hazard ratio (HR): 2.52; 95% CI: 1.20-5.29; p = 0.015), independently of other factors. Decline of IL-6 levels through month 3 was greater in responders. In summary, belimumab treatment lowered IFN-α2, IL-6, and IL-10 levels, as well as levels of multiple autoantibodies, however after different time spans. Notably, anti-Sm positivity and early decline in IL-6 levels were associated with favorable treatment outcome.

Fc-gamma receptors and S100A8/A9 cause bone erosion during rheumatoid arthritis. Do they act as partners in crime?

Bone erosion is one of the central hallmarks of RA and is caused by excessive differentiation and activation of osteoclasts. Presence of autoantibodies in seropositive arthritis is associated with radiographic disease progression. ICs, formed by autoantibodies and their antigens, activate Fcγ-receptor signalling in immune cells, and as such stimulate inflammation-mediated bone erosion. Interestingly, ICs can also directly activate osteoclasts by binding to FcγRs on their surface. Next to autoantibodies, high levels of alarmins, among which is S100A8/A9, are typical for RA and they can further activate the immune system but also directly promote osteoclast function. Therefore, IC-activated FcγRs and S100A8/A9 might act as partners in crime to stimulate inflammation and osteoclasts differentiation and function, thereby stimulating bone erosion. This review discusses the separate roles of ICs, FcγRs and alarmins in bone erosion and sheds new light on the possible interplay between them, which could fuel bone erosion.

Germinal centers and autoantibodies

Preventing self-reactive lymphocytes from participating in effector responses is fundamental to maintaining immunological self-tolerance and circumventing autoimmunity. A range of complementary mechanisms are known to act upon the primary B- and T-cell repertoires to this effect, eliminating or silencing lymphocytes expressing self-reactive antigen receptors generated through V(D)J recombination in early lymphoid precursors. In the case of B cells, secondary diversification of antigen receptor repertoire by somatic hypermutation (SHM) provides an additional challenge, especially because this occurs in germinal center (GC) B cells that are actively responding to antigen and primed for differentiation into antibody-producing plasma cells. While it is clear that self-tolerance mechanisms do act to prevent antibody production by self-reactive GC B cells, it is also apparent that most pathogenic autoantibodies carry somatic mutations and so have derived from a GC response. Recent advances in the analysis of autoantibody-producing cells associated with human autoimmune diseases together with insights gained from animal models have increased our understanding of the relationships between GCs, SHM and autoantibody production. Here we discuss these developments and focus in particular on how they have illuminated the genesis and pathogenesis of one archetypal autoantibody, rheumatoid factor.

Longitudinal relationships between rheumatoid factor and cytokine expression by immunostimulated peripheral blood lymphocytes from patients with rheumatoid arthritis: New insights into B-cell activation

To identify associations between immunostimulated cytokine production and disease characteristics, peripheral blood lymphocytes were collected from 155 adult patients with rheumatoid arthritis (RA) before and after a 5-year interval. The lymphocytes were activated in vitro with T-cell stimulants, cytosine-phosphate-guanine (CpG) oligonucleotide, and medium alone (negative control). Expression of 17 cytokines was evaluated with immunoassays, and factor analysis was used to reduce data complexity and identify cytokine combinations indicative of cell types preferentially activated by each immunostimulant. The findings showed that the highest numbers of correlations were between cytokine levels and rheumatoid factor (RF) positivity and between cytokine levels and disease duration. Scores for cytokines driven by CpG and medium alone were negatively associated with RF positivity and disease duration at baseline but positively associated with both at 5 years. Our findings suggest that RF expression sustained over time increases activation of B cells and monocytes without requirements for T-cell functions.

IL-4 controls activated neutrophil FcγR2b expression and migration into inflamed joints

Neutrophils are the most abundant immune cells found in actively inflamed joints of patients with rheumatoid arthritis (RA), and most animal models for RA depend on neutrophils for the induction of joint inflammation. Exogenous IL-4 and IL-13 protect mice from antibody-mediated joint inflammation, although the mechanism is not understood. Neutrophils display a very strong basal expression of STAT6, which is responsible for signaling following exposure to IL-4 and IL-13. Still, the role of IL-4 and IL-13 in neutrophil biology has not been well studied. This can be explained by the low neutrophil surface expression of the IL-4 receptor α-chain (IL-4Rα), essential for IL-4- and IL-13-induced STAT6 signaling. Here we identify that colony stimulating factor 3 (CSF3), released during acute inflammation, mediates potent STAT3-dependent neutrophil IL-4Rα up-regulation during sterile inflammatory conditions. We further demonstrate that IL-4 limits neutrophil migration to inflamed joints, and that CSF3 combined with IL-4 or IL-13 results in a prominent neutrophil up-regulation of the inhibitory Fcγ receptor (FcγR2b). Taking these data together, we demonstrate that the IL-4 and CSF3 pathways are linked and play important roles in regulating proinflammatory neutrophil behavior.

The etiology of rheumatoid arthritis

Rheumatoid arthritis is a heterogeneous disease, which can be, based on data combining genetic risk factors and autoantibodies, sub-classified into ACPA-positive and -negative RA. Presence of ACPA and RF as well as rising CRP-levels in some patients years before onset of clinical symptoms indicate that relevant immune responses for RA development are initiated very early. ACPA are highly specific for RA, whereas RF can also be found among healthy (elderly) individuals and patients with other autoimmune diseases or infection. The most important genetic risk factor for RA development, the shared epitope alleles, resides in the MHC class II region. Shared epitope alleles, however, only predispose to the development of ACPA-positive RA. Smoking is thus far the most important environmental risk factor associated with the development of RA. Studies on synovitis have shown the importance not only of adaptive but also of innate immune responses. In summary of the various results from immunological changes in blood and synovial tissue, the extension of the immune response from a diffuse myeloid to a lympho-myeloid inflammation appears to be associated with a more successful therapeutic response to biologics. With respect to advances in synovitis research, new targets for treatment against pathological subsets of immune cells or fibroblasts are already on the horizon. However, alternative strategies involving the microbiome may play an important role as well and research in this field is growing rapidly.

Autoantibodies and B Cells: The ABC of rheumatoid arthritis pathophysiology

Rheumatoid arthritis (RA) is an autoimmune disease characterized by joint inflammation. In the last few decades, new insights into RA‐specific autoantibodies and B cells have greatly expanded our understanding of the disease. The best‐known autoantibodies in RA—rheumatoid factor (RF) and anti‐citrullinated protein antibodies (ACPA)—are present long before disease onset, and both responses show signs of maturation around the time of the first manifestation of arthritis. A very intriguing characteristic of ACPA is their remarkably high abundance of variable domain glycans. Since these glycans may convey an important selection advantage of citrulline‐reactive B cells, they may be the key to understanding the evolution of the autoimmune response. Recently discovered autoantibodies targeting other posttranslational modifications, such as anti‐carbamylated and anti‐acetylated protein antibodies, appear to be closely related to ACPA, which makes it possible to unite them under the term of anti‐modified protein antibodies (AMPA). Despite the many insights gained about these autoantibodies, it is unclear whether they are pathogenic or play a causal role in disease development. Autoreactive B cells from which the autoantibodies originate have also received attention as perhaps more likely disease culprits. The development of autoreactive B cells in RA largely depends on the interaction with T cells in which HLA “shared epitope” and HLA DERAA may play an important role. Recent technological advances made it possible to identify and characterize citrulline‐reactive B cells and acquire ACPA monoclonal antibodies, which are providing valuable insights and help to understand the nature of the autoimmune response underlying RA. In this review, we summarize what is currently known about the role of autoantibodies and autoreactive B cells in RA and we discuss the most prominent hypotheses aiming to explain the origins and the evolution of autoimmunity in RA.

Disordered Antigens and Epitope Overlap Between Anti-Citrullinated Protein Antibodies and Rheumatoid Factor in Rheumatoid Arthritis

OBJECTIVE

Anti-citrullinated protein antibodies (ACPAs) and rheumatoid factor (RF) are commonly present in rheumatoid arthritis (RA) without a clear rationale for their coexistence. Moreover, autoantibodies develop against proteins with different posttranslational modifications and native proteins without obvious unifying characteristics of the antigens. We undertook this study to broadly evaluate autoantibody binding in seronegative and seropositive RA to identify novel features of reactivity.

METHODS

An array was created using a total of 172,828 native peptides, citrulline-containing peptides, and homocitrulline-containing peptides derived primarily from proteins citrullinated in the rheumatoid joint. IgG and IgM binding to peptides were compared between cyclic citrullinated peptide (CCP)-positive RF+, CCP+RF-, CCP-RF+, and CCP-RF- serum from RA patients (n = 48) and controls (n = 12). IgG-bound and endogenously citrullinated peptides were analyzed for amino acid patterns and predictors of intrinsic disorder, i.e., unstable 3-dimensional structure. Binding to IgG-derived peptides was specifically evaluated. Enzyme-linked immunosorbent assay confirmed key results.

RESULTS

Broadly, CCP+RF+ patients had high citrulline-specific IgG binding to array peptides and CCP+RF- and CCP-RF+ patients had modest citrulline-specific IgG binding (median Z scores 3.02, 1.42, and 0.75, respectively; P < 0.0001). All RA groups had low homocitrulline-specific binding. CCP+RF+ patients had moderate IgG binding to native peptides (median Z score 2.38; P < 0.0001). The highest IgG binding was to citrulline-containing peptides, irrespective of protein identity, especially if citrulline was adjacent to glycine or serine, motifs also seen in endogenous citrullination in the rheumatoid joint. Highly bound peptides had multiple features predictive of disorder. IgG from CCP+RF+ patients targeted citrulline-containing IgG-derived peptides.

CONCLUSION

Disordered antigens, which are frequently citrullinated, and common epitopes for ACPAs and RF are potentially unifying features for RA autoantibodies.

Increased levels of anti-dsDNA antibodies in immune complexes before treatment with belimumab associate with clinical response in patients with systemic lupus erythematosus

INTRODUCTION

Immune complexes are of importance in systemic lupus erythematosus pathogenesis, and autoantibodies are believed to participate in immune complex formation. Quantification of autoantibody levels in circulating IC might be of prognostic value.

METHODS

A C1q-binding-eluting technique was applied to purify immune complexes from 55 belimumab-treated systemic lupus erythematosus patients during a 24-month follow-up. Autoantibodies in serum and in solubilized immune complexes were quantified using addressable laser bead immunoassay. We investigated whether levels of autoantibodies in immune complexes associate with disease activity and response to belimumab treatment.

RESULTS

High baseline anti-double-stranded DNA and anti-histone levels in immune complexes associated with attainment of zero scores in clinical systemic lupus erythematosus disease activity index 2000 during the 24-month follow-up (p = 0.003 and p = 0.048, respectively). Low complement levels associated with high serum anti-double-stranded DNA and anti-ribosomal P levels (p = 0.003 and p = 0.008, respectively) and high anti-double-stranded DNA (p = 0.002) but not anti-ribosomal P levels in immune complexes. Anti-SSA/SSB serum levels were lower in patients attaining lupus low disease activity state at month 6; these associations were stronger for corresponding immune complex levels. Serum levels of most autoantibodies had declined at month 3, whereas autoantibody levels in immune complexes, except for anti-double-stranded DNA, showed a more gradual decline over 1-2 years. Serum anti-double-stranded DNA levels decreased in all patients irrespective of systemic lupus erythematosus disease activity index 2000=0 attainment, whereas immune complex levels decreased only in achievers.

CONCLUSION

Immune complex levels of autoantibodies against double-stranded DNA and the SSA/SSB complex show more specific associations with treatment outcome compared with serum levels in belimumab-treated systemic lupus erythematosus patients. Characterization of autoantibody content in circulating immune complexes could prove useful in treatment evaluation in systemic lupus erythematosus and other immune complex-associated diseases.

Steroid hormone-related polymorphisms associate with the development of bone erosions in rheumatoid arthritis and help to predict disease progression: Results from the REPAIR consortium

Here, we assessed whether 41 SNPs within steroid hormone genes associated with erosive disease. The most relevant finding was the rheumatoid factor (RF)-specific effect of the CYP1B1, CYP2C9, ESR2, FcγR3A, and SHBG SNPs to modulate the risk of bone erosions (P = 0.004, 0.0007, 0.0002, 0.013 and 0.015) that was confirmed through meta-analysis of our data with those from the DREAM registry (P = 0.000081, 0.0022, 0.00074, 0.0067 and 0.0087, respectively). Mechanistically, we also found a gender-specific correlation of the CYP2C9_rs1799853T/T genotype with serum vitamin D3 levels (P = 0.00085) and a modest effect on IL1β levels after stimulation of PBMCs or blood with LPS and PHA (P = 0.0057 and P = 0.0058). An overall haplotype analysis also showed an association of 3 ESR1 haplotypes with a reduced risk of erosive arthritis (P = 0.009, P = 0.002, and P = 0.002). Furthermore, we observed that the ESR2, ESR1 and FcγR3A SNPs influenced the immune response after stimulation of PBMCs or macrophages with LPS or Pam3Cys (P = 0.002, 0.0008, 0.0011 and 1.97•10⁻⁷). Finally, we found that a model built with steroid hormone-related SNPs significantly improved the prediction of erosive disease in seropositive patients (P_RF+ = 2.46•10⁻⁸) whereas no prediction was detected in seronegative patients (P_RF− = 0.36). Although the predictive ability of the model was substantially lower in the replication population (P_RF+ = 0.014), we could confirm that CYP1B1 and CYP2C9 SNPs help to predict erosive disease in seropositive patients. These results are the first to suggest a RF-specific association of steroid hormone-related polymorphisms with erosive disease.

Fra1 Controls Rheumatoid Factor Autoantibody Production by Bone Marrow Plasma Cells and the Development of Autoimmune Bone Loss

Next to proinflammatory cytokines, autoimmunity has been identified as a key trigger for osteoclast activation and bone loss. IgG-rheumatoid factor (IgG-RF) immune complexes, which are present in patients with rheumatoid arthritis, were shown to boost osteoclast differentiation. To date, the regulation of IgG-RF production in the absence of inflammatory triggers is unknown. Herein, we describe Fra1 as a key checkpoint that controls IgG-RF production by plasma cells and regulates autoimmune-mediated bone loss. Fra1 deficiency in B cells (Fra1^ΔBcell ) led to increased IgG1-producing bone marrow plasma cells, enhanced IgG-RF production, and increased bone loss associated with elevated osteoclast numbers after immunization. The effect of IgG-RF on osteoclasts in vitro and on osteoclasts associated with bone loss in vivo was dependent on FcγR, especially FcγR3. Furthermore, immunization of WT mice with T-cell-dependent antigens induced a significant and robust decrease in Fra1 expression in bone marrow B cells, which was followed by increased IgG1 production and the induction of osteoclast-mediated bone loss. Overall, these data identify Fra1 as a key mediator of IgG-RF production and autoimmune-mediated bone loss. © 2019 American Society for Bone and Mineral Research.

Kawasaki Disease: The Role of Immune Complexes Revisited

Kawasaki disease (KD) is an inflammatory disease in children associated with vasculitis affecting predominantly the coronary arteries and is now the most common cause of acquired heart disease in children in developed countries. The etiology of KD is unknown but epidemiological studies implicate an infectious agent or toxin, which causes disease in genetically predisposed individuals. The presence of immune complexes (ICs) in the serum of children with KD was established in numerous studies during the 1970s and 80s. More recent genetic studies have identified variation in Fcγ receptors and genes controlling immunoglobulin production associated with KD. In this review we link the genetic findings and IC studies and suggest a key role for their interaction in pathophysiology of the disease.

P2RX7 Deletion in T Cells Promotes Autoimmune Arthritis by Unleashing the Tfh Cell Response

Rheumatoid arthritis (RA) is an autoimmune disease that affects ~1% of the world's population. B cells and autoantibodies play an important role in the pathogenesis of RA. The P2RX7 receptor is an ATP-gated cation channel and its activation results in the release of pro-inflammatory molecules. Thus, antagonists of P2RX7 have been considered to have potential as novel anti-inflammatory therapies. Although originally identified for its role in innate immunity, P2RX7 has recently been found to negatively control Peyer's patches (PP) T follicular helper cells (Tfh), which specialize in helping B cells, under homeostatic conditions. We have previously demonstrated that PP Tfh cells are required for the augmentation of autoimmune arthritis mediated by gut commensal segmented filamentous bacteria (SFB). Thus, we hypothesized that P2RX7 is required to control autoimmune disease by keeping the Tfh cell response in check. To test our hypothesis, we analyzed the impact of P2RX7 deficiency in vivo using both the original K/BxN autoimmune arthritis model and T cell transfers in the K/BxN system. We also examined the impact of P2RX7 ablation on autoimmune development in the presence of the gut microbiota SFB. Our data illustrate that contrary to exerting an anti-inflammatory effect, P2RX7 deficiency actually enhances autoimmune arthritis. Interestingly, SFB colonization can negate the difference in disease severity between WT and P2RX7-deficient mice. We further demonstrated that P2RX7 ablation in the absence of SFB caused reduced apoptotic Tfh cells and enhanced the Tfh response, leading to an increase in autoantibody production. It has been shown that activation of TIGIT, a well-known T cell exhaustion marker, up-regulates anti-apoptotic molecules and promotes T cell survival. We demonstrated that the reduced apoptotic phenotype of P2rx7^−/− Tfh cells is associated with their increased expression of TIGIT. This suggested that while P2RX7 was regulating the Tfh population by promoting cell death, TIGIT may have been opposing P2RX7 by inhibiting cell death. Together, these results demonstrated that systemic administration of general P2RX7 antagonists may have detrimental effects in autoimmune therapies, especially in Tfh cell-dependent autoimmune diseases, and cell-specific targeting of P2RX7 should be considered in order to achieve efficacy for P2RX7-related therapy.

The Human FcγRII (CD32) Family of Leukocyte FcR in Health and Disease

FcγRs have been the focus of extensive research due to their key role linking innate and humoral immunity and their implication in both inflammatory and infectious disease. Within the human FcγR family FcγRII (activatory FcγRIIa and FcγRIIc, and inhibitory FcγRIIb) are unique in their ability to signal independent of the common γ chain. Through improved understanding of the structure of these receptors and how this affects their function we may be able to better understand how to target FcγR specific immune activation or inhibition, which will facilitate in the development of therapeutic monoclonal antibodies in patients where FcγRII activity may be desirable for efficacy. This review is focused on roles of the human FcγRII family members and their link to immunoregulation in healthy individuals and infection, autoimmunity and cancer.

Fc-binding proteins enhance autoantibody-induced BP180 depletion in pemphigoid

Immunoglobulins (Igs) consist of two antigen-binding regions (Fab) and one constant region (Fc). Protein A and protein G are bacterial proteins used for the purification of IgG by virtue of their high affinities for the Fc fragment. Rheumatoid factors are autoantibodies against IgG Fc fragments, which are present in the body under physiological conditions. Little is known about the influence of Fc-binding proteins on the pathogenicity of antibody-induced autoimmune diseases. Pemphigoid diseases are a group of autoimmune subepidermal blistering disorders that includes bullous pemphigoid and mucous membrane pemphigoid. IgGs targeting the non-collagenous NC16A domain of the 180-kDa bullous pemphigoid antigen (BP180) are known to induce skin fragility in mice and the depletion of BP180 in keratinocytes. In this study, mAb against NC16A in combination with Fc-binding proteins was found to enhance BP180 depletion. Although mAb against the C-terminus of BP180 does not show pathogenicity in vivo or in vitro, mAb treatment with Fc-binding proteins clearly induced skin fragility in mice and BP180 depletion in keratinocytes. Anti-BP180 mAbs and Fc-binding proteins were colocalized in the cytoplasm and at the basement membrane zone. Cell adhesion strengths were decreased in parallel with BP180 amounts. Clinically, bullous pemphigoid patients had higher rheumatoid factor titers than controls. Anti-BP180 mAb in combination with high-titer rheumatoid factor serum was found to enhance BP180 depletion. Furthermore, saliva from mucous membrane pemphigoid patients contained larger quantities of bacteria and Fc-binding proteins than controls. Our results suggest that Fc-binding proteins (rheumatoid factor or protein G) may enhance the pathogenicity of autoantibodies in pemphigoid diseases. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Pathogenic effects of anti-citrullinated protein antibodies in rheumatoid arthritis - role for glycosylation

The identification in 1998 of the main antigenic substrate recognized by autoantibodies was a dramatic turning point in our understanding of rheumatoid arthritis (RA) biology. Now, two decades later, antibodies to citrullinated proteins are viewed no longer as mere biomarkers for RA, but also as major pathophysiological factors involved in the development of bone loss and joint pain. These pathogenic effects are ascribable to abnormal autoantibody glycosylation via a pathway involving the Th17T cells. In the future, abnormal autoantibody glycosylation may serve as a disease activity biomarker and suggest novel treatment strategies.

Impact of gut microbiota on gut-distal autoimmunity: a focus on T cells

The immune system is essential for maintaining a delicate balance between eliminating pathogens and maintaining tolerance to self-tissues to avoid autoimmunity. An enormous and complex community of gut microbiota provides essential health benefits to the host, particularly by regulating immune homeostasis. Many of the metabolites derived from commensals can impact host health by directly regulating the immune system. Many autoimmune diseases arise from an imbalance between pathogenic effector T cells and regulatory T (Treg) cells. Recent interest has emerged in understanding how cross-talk between gut microbiota and the host immune system promotes autoimmune development by controlling the differentiation and plasticity of T helper and Treg cells. At the molecular level, our recent study, along with others, demonstrates that asymptomatic colonization by commensal bacteria in the gut is capable of triggering autoimmune disease by molecular mimicking self-antigen and skewing the expression of dual T-cell receptors on T cells. Dysbiosis, an imbalance of the gut microbiota, is involved in autoimmune development in both mice and humans. Although it is well known that dysbiosis can impact diseases occurring within the gut, growing literature suggests that dysbiosis also causes the development of gut-distal/non-gut autoimmunity. In this review, we discuss recent advances in understanding the potential molecular mechanisms whereby gut microbiota induces autoimmunity, and the evidence that the gut microbiota triggers gut-distal autoimmune diseases.

Autoantibodies in the Pathogenesis, Diagnosis, and Prognosis of Juvenile Idiopathic Arthritis

Autoantibody production occurs in juvenile idiopathic arthritis (JIA) and numerous other autoimmune diseases. In some conditions, the autoantibodies are clearly pathogenic, whereas in others the roles are less defined. Here we review various autoantibodies associated with JIA, with a particular focus on antinuclear antibodies and antibodies recognizing citrullinated self-antigens. We explore potential mechanisms that lead to the development of autoantibodies and the use of autoantibody testing in diagnosis and prognosis. Finally, we compare and contrast JIA-associated autoantibodies with those found in adults with rheumatoid arthritis (RA).

Humanised effector-null FcγRIIA antibody inhibits immune complex-mediated proinflammatory responses

Objective

Immune complexes (ICs) play a critical role in the pathology of autoimmune diseases. The aim of this study was to generate and characterise a first-in-class anti-FcγRIIA antibody (Ab) VIB9600 (previously known as MEDI9600) that blocks IgG immune complex-mediated cellular activation for clinical development.

Methods

VIB9600 was humanised and optimised from the IV.3 Ab. Binding affinity and specificity were determined by Biacore and ELISA. Confocal microscopy, Flow Cytometry-based assays and binding competition assays were used to assess the mode of action of the antibody. In vitro cell-based assays were used to demonstrate suppression of IC-mediated inflammatory responses. In vivo target suppression and efficacy was demonstrated in FcγRIIA-transgenic mice. Single-dose pharmacokinetic (PK)/pharmacodynamic study multiple dose Good Laboratory Practice (GLP) toxicity studies were conducted in non-human primates.

Results

We generated a humanised effector-deficient anti-FcγRIIA antibody (VIB9600) that potently blocks autoantibody and IC-mediated proinflammatory responses. VIB9600 suppresses FcγRIIA activation by blocking ligand engagement and by internalising FcγRIIA from the cell surface. VIB9600 inhibits IC-induced type I interferons from plasmacytoid dendritic cells (involved in SLE), antineutrophil cytoplasmic antibody (ANCA)-induced production of reactive oxygen species by neutrophils (involved in ANCA-associated vasculitis) and IC-induced tumour necrosis factor α and interleukin-6 production (involved in rheumatoid arthritis). In FcγRIIA transgenic mice, VIB9600 suppressed antiplatelet antibody-induced thrombocytopaenia, acute anti-GBM Ab-induced nephritis and anticollagen Ab-induced arthritis. VIB9600 also exhibited favourable PK and safety profiles in cynomolgus monkey studies.

Conclusions

VIB9600 is a specific humanised antibody antagonist of FcγRIIA with null effector function that warrants further clinical development for the treatment of IC-mediated diseases.

Number of individual ACPA reactivities in synovial fluid immune complexes, but not serum anti-CCP2 levels, associate with inflammation and joint destruction in rheumatoid arthritis

Introduction

Individual patients with rheumatoid arthritis (RA) show divergent specific anti-citrullinated protein/peptide antibodies (ACPA) patterns, but hitherto no individual ACPA specificity has consistently been linked to RA pathogenesis. ACPA are also implicated in immune complexes (IC)-associated joint pathology, but until now, there has been no method to investigate the role of individual ACPA in RA IC formation and IC-associated pathogenesis.

Methods

We have developed a new technique based on IC binding to C1q-coated magnetic beads to purify and solubilise circulating IC in sera and synovial fluids (SF) from 77 patients with RA. This was combined with measurement of 19 individual ACPA in serum, SF and in the IC fractions from serum and SF. We investigated whether occurrence of individual ACPA as well as number of ACPA in these compartments was related to clinical and laboratory measures of disease activity and inflammation.

Results

The majority of individual ACPA reactivities were enriched in SF as compared with in serum, and levels of ACPA in IC were regulated independently of levels in serum and SF. No individual ACPA reactivity in any compartment showed a dominating association to clinical and laboratory measures of disease activity and severity. Instead, the number of individual ACPA reactivities in the IC fraction from SF associated with a number of markers of joint destruction and inflammation.

Conclusions

Our data highlight the polyclonality of ACPA in joint IC and the possibility that a broad ACPA repertoire in synovial fluid IC might drive the local inflammatory and matrix-degrading processes in joints, in analogy with antibody-induced rodent arthritis models.

Formation of Immune Complexes with a Tetanus-Derived B Cell Epitope Boosts Human T Cell Responses to Covalently Linked Peptides in an Ex Vivo Blood Loop System

Enhancing T cell responses against both viral and tumor Ags requires efficient costimulation and directed delivery of peptide Ags into APCs. Long peptide vaccines are considered favorable vaccine moieties from a clinical perspective, as they can harbor more than one immunogenic epitope enabling treatment of a broader target population. In addition, longer peptides are not extracellularly loaded on MHC class I; rather, they require intracellular processing and will thereby be presented to T cells mainly by professional APCs, thereby avoiding the risk of tolerance induction. The drawback of peptide vaccines regardless of peptide length is that naked peptides are not actively targeted to and taken up by APCs, and the standard nonconjugated adjuvant-peptide mixtures do not ensure cotargeting of the two to the same APC. We have identified a tetanus toxin-derived B cell epitope that can mediate the formation of immune complexes in the presence of circulating Abs. In this study, we show that these immune complexes improve both Ag uptake by APCs (blood monocytes and CD1c⁺ dendritic cells) and consequently improve CD8⁺ T cell recall responses in a human ex vivo blood loop system. The uptake of the peptide conjugate by blood monocytes is dependent on Abs and the complement component C1q. We envision that this strategy can be used to facilitate active uptake of Ags into APCs to improve T cell responses against pathogens or cancer.

The Role of Autoantibodies in Bone Metabolism and Bone Loss

Many autoimmune diseases are associated with deranged bone metabolism. The resulting localized or systemic bone loss can compromise the quality of life of patients by causing local bone deformities or fragility fractures. There is emerging evidence that antibodies have a direct impact on key players of bone homeostasis, in particular osteoclasts. Clinical and pre-clinical studies provide insight into the function of autoantibodies related to Rheumatoid Arthritis (rheumatoid factor, anti-citrullinated protein antibodies, and anti-carbamylated protein antibodies) and their inflammation-independent interaction with bone cells. Furthermore, we summarize the current knowledge about neutralizing antibodies to the antiresorptive protein osteoprotegerin, which have been described in patients with Coeliac Disease, Rheumatoid Arthritis, and Spondyloarthritis.

Bone Loss in Rheumatoid Arthritis: Basic Mechanisms and Clinical Implications

Patients with rheumatoid arthritis (RA) have historically developed progressive damage of articular bone and cartilage, which correlates with disability over time. In addition, these patients are prone to periarticular and systemic bone loss, carrying additional morbidity. In contrast to what is seen in many other rheumatic diseases, the impact of inflammation on bone in RA is uniquely destructive. Loss of articular bone (erosions) and periarticular bone (demineralization) is a result of excessive bone resorption and markedly limited bone formation. There has been tremendous progress in preventing net bone loss in RA with the advent of disease-modifying agents, including biologic agents and small molecules, that both limit inflammation and may have a direct impact on the prevention of cytokine- and antibody-driven osteoclastogenesis. However, repair of existing bone erosions, although feasible, is observed infrequently. Lack of repair is a consequence of suppression of osteoblast function and bone formation by some of the same mechanisms that promote osteoclastogenesis and bone resorption. As new agents are introduced to control inflammation in RA, and novel mechanisms to target synovitis are identified, it may be possible in the future to fully repair damaged bone.

The role of ACPAs in at-risk individuals: Early targeting of the bone and joints

Autoimmunity precedes inflammation in patients with rheumatoid arthritis (RA), opening the possibility to search for early changes in the tissue preceding the onset of systemic inflammation. Autoantibodies are important and early drivers of bone damage in RA. This article summarizes current evidence for the role of RA-related autoantibodies in mediating bone loss. Rheumatoid factor (RF) and antibodies recognizing modified (citrullinated) proteins have been used as diagnostic markers for RA over many years. Their role as pathogenic players, however, has long been unrecognized. Recently, several pieces of evidence suggested that bone-resorbing osteoclasts are highly responsive to RA-related autoantibodies, providing a novel association between autoimmunity and bone. These developments have allowed the unraveling of the underlying mechanisms, which are responsible for the well-known clinical observation that anti-citrullinated protein antibodies and RF are associated with a more severe disease course. Furthermore, these mechanisms also explain the onset of inflammation in the joints of RA patients.

Postmenopausal osteoporosis in rheumatoid arthritis: The estrogen deficiency-immune mechanisms link

Rheumatoid arthritis (RA) is characterized, among other factors, by systemic bone loss, reaching ~50% prevalence of osteoporosis in postmenopausal women. This is roughly a doubled prevalence in comparison with age-matched non-RA women. Postmenopausal RA women are more likely to be sero-positive for the anti-citrullinated peptide antibody (ACPA). Our extensive review of recent scientific literature enabled us to propose several mechanisms as responsible for the accelerated bone loss in ACPA(+) RA postmenopausal women. Menopause-associated estrogen deficiency plays a major role in these pathological mechanisms, as follows.

Cellular and molecular pathways of structural damage in rheumatoid arthritis

Structural damage of cartilage and bone tissue is a hallmark of rheumatoid arthritis (RA). The resulting joint destruction constitutes one of the major disease consequences for patients and creates a significant burden for the society. The main cells executing bone and cartilage degradation are osteoclasts and fibroblast-like synoviocytes, respectively. The function of both cell types is heavily influenced by the immune system. In the last decades, research has identified several mediators of structural damage, ranging from infiltrating immune cells and inflammatory cytokines to autoantibodies. These factors result in an inflammatory milieu in the affected joints which leads to an increased development and function of osteoclasts and the transformation of fibroblast-like synoviocytes towards a highly migratory and destructive phenotype. In addition, repair mechanisms mediated by osteoblasts and chondrocytes are strongly impaired by the presence of pro-inflammatory cytokines. This article will review the current knowledge on the mechanisms of joint inflammation and the destruction of bone and cartilage.

Accumulation of immunoglobulin G against Dermatophagoides farinae tropomyosin in dorsal root ganglia of NC/Nga mice with atopic dermatitis-like symptoms

Atopic dermatitis (AD), a chronic inflammatory skin disease, manifests as intractable itch, but its underlying mechanisms are poorly understood. This study assessed the relationship between immunoglobulin G (IgG) and dorsal root ganglia (DRG) in NC/Nga mice, a model of AD that manifests AD-like symptoms including itch. Immunohistochemical analysis showed large amounts of IgG in DRG extracts of NC/Nga mice with AD-like dermatitis, with a large fraction of the IgG distributed in satellite glial cells of the DRG. Proteomic analysis showed that this IgG was reactive against tropomyosin of Dermatophagoides farinae. These findings indicate that the accumulation of anti-tropomyosin IgG in DRG of atopic NC/Nga mice may be associated with the pathogenesis of AD-like symptoms, including itch.

Bone as a Target Organ in Rheumatic Disease: Impact on Osteoclasts and Osteoblasts

Dysregulated bone remodeling occurs when there is an imbalance between bone resorption and bone formation. In rheumatic diseases, including rheumatoid arthritis (RA) and seronegative spondyloarthritis, systemic and local factors disrupt the process of physiologic bone remodeling. Depending upon the local microenvironment, cell types, and local mechanical forces, inflammation results in very different effects on bone, promoting bone loss in the joints and in periarticular and systemic bone in RA and driving bone formation at enthesial and periosteal sites in diseases such as ankylosing spondylitis (AS), included within the classification of axial spondyloarthritis. There has been a great deal of interest in the role of osteoclasts in these processes and much has been learned over the past decade about osteoclast differentiation and function. It is now appreciated that osteoblast-mediated bone formation is also inhibited in the RA joint, limiting the repair of erosions. In contrast, osteoblasts function to produce new bone in AS. The Wnt and BMP signaling pathways have emerged as critical in the regulation of osteoblast function and the outcome for bone in rheumatic diseases, and these pathways have been implicated in both bone loss in RA and bone formation in AS. These pathways provide potential novel approaches for therapeutic intervention in diseases in which inflammation impacts bone.

A specific anti-citrullinated protein antibody profile identifies a group of rheumatoid arthritis patients with a toll-like receptor 4-mediated disease

BACKGROUND

Increased expression of toll-like receptor 4 (TLR4) and its endogenous ligands, is characteristic of rheumatoid arthritis (RA) synovitis. In this study, we evaluated how these TLR4 ligands may drive pathogenic processes and whether the fine profiling of anti-citrullinated protein antibodies (ACPA) based on their target specificity might provide a simple means to predict therapeutic benefit when neutralizing TLR4 in this disease.

METHODS

The capacity of RA synovial fluids (RASF) to stimulate cytokine production in monocytes from patients with RA was analyzed by ELISA. The presence of TLR4 activators in RASF was determined by measuring the levels of ACPA, ACPA subtypes with reactivity to specific citrullinated peptides and other TLR4 ligands. Neutralization of TLR4 signaling was investigated using NI-0101, a therapeutic antibody that targets TLR4.

RESULTS

RASF exhibited a heterogeneous capacity to induce production of proinflammatory cytokines by monocytes isolated from patients with RA. Such cytokine responses were significantly modified by TLR4 blockade achieved using NI-0101. The analysis of the content of RASF and matched sera demonstrated that ACPA fine specificities in patient samples predict cellular response to anti-TLR4 exposure in vitro.

CONCLUSION

TLR4 represents a possible therapeutic target in RA. Our study demonstrates that TLR4 inhibition in an ex vivo model of RA pathogenesis can significantly modulate cytokine release and does so in specific subgroups of RA patient-derived samples. It also suggests that ACPA fine profiling has the potential to identify RA patients with a predominantly TLR4-driven pathotype that could be used to predict preferential response to TLR4 antagonism.

Granulocyte-augmented chemokine production induced by type II collagen containing immune complexes is mediated via TLR4 in rheumatoid arthritis patients

Rheumatoid arthritis (RA) patients with early elevations of antibodies against collagen type II (CII) have a distinct acute onset phenotype, associated with cytokine induction by surface‐bound anti‐CII‐containing immune complexes (ICs) and high C‐reactive protein (CRP) and erythrocyte sedimentation rate (ESR). Polymorphonuclear granulocytes (PMNs) and peripheral blood mononuclear cells (PBMCs) are abundant in the vicinity of CII in RA joints, and both PMN and PBMC reactivity against anti‐CII IC individually relate to early joint destruction and early elevation of CRP and ESR in RA. We searched for CII‐dependent mechanisms that might attract PMNs and PBMCs to RA joints. Human PBMCs and PMNs were stimulated with anti‐CII ICs and control ICs, either individually or in cocultures. Cocultured PMNs and PBMCs stimulated with anti‐CII ICs synergistically augmented production of the chemokines CXCL8, RANTES and MCP‐1, whereas downregulation was seen with control IC. This upregulation was unique to chemokines, as TNF‐α, IL‐1β, and GM‐CSF were downregulated in anti‐CII IC‐stimulated cocultures. The coculture‐associated chemokine upregulation depended on endogenous TLR4 ligand(s) and functionally active PMN enzymes, and was partially mediated by GM‐CSF. As anti‐CII levels peak around the time of RA diagnosis, this mechanism can attract inflammatory cells to joints in early RA and intensify the anti‐CII‐associated acute onset RA phenotype.

Historical observations contributing insights on etiopathogenesis of rheumatoid arthritis and role of rheumatoid factor

When studies on rheumatoid arthritis (RA) that were made many decades ago and could be considered "historical" in nature are analyzed in the context of recent observations, important insights on RA and on the function of rheumatoid factor (RF) become apparent. RF in the role of antibody to immune complexes (ICs) appears to be involved in activation of the complement system and in the production of chemotactic and inflammatory mediators, creating a condition that can be sustained and reinitiated. In the synovial cavity, a state of nonresolving inflammation is produced with the formation of citrullinated protein antigen-antibody complexes or other forms of ICs. This is followed by a second wave of IC production in the form of RF acting as antibody reactive with the initial ICs. Both of these processes are associated with complement consumption and production of inflammatory mediators. We present a model of an initiation phase of RA that might represent an example of repetitive formation of ICs and complement-mediated inflammation. Targeting therapy at this phase of RA to break the cycles of recurrent inflammation might be a novel approach to aid in further control of the disease.