The IL-23/IL-17 axis in psoriatic arthritis

Interleukin 23 regulates the functions of human decidual immune cells during early pregnancy

BACKGROUND

This study investigated the effects of interleukin 23 (IL-23) on the production of cytokines (IL-1, IL-4, IL-10, and IL-17), the differentiation of Treg/Th17 and STAT3 (i.e., signal transducer and activator of transcription 3) in human decidual immune cells (DICs) during early pregnancy.

METHODS

DICs were treated with recombinant human IL-23 and an antibody against IL-23 subunit p19. The differentiation of Treg and Th17 cells was detected by flow cytometry. Levels of IL-23 receptor (IL-23R), STAT3, and phosphorylated STAT3 (pSTAT3) was examined by Western blot. The production of IL1, IL4, IL10, and IL-17 in DICs was measured by ELISA.

RESULTS

Exogenous recombinant human IL-23 significantly promoted the differentiation of Th17 cells from DICs, while anti-IL-23 antibody significantly promoted the differentiation of Treg cells from DICs. Consistent with the differentiation of Th17 and Tregs cells, levels of IL-1β and IL-17 correlated positively with IL-23 treatment, and anti-IL-23 antibody increased the secretion of IL-4 and IL-10 from DICs. Levels of pSTAT3, but not STAT3 or IL-23R, were significantly elevated by recombinant IL-23 treatment; anti-IL-23 antibody significantly decreased the levels of pSTAT3 and IL-23R in DICs.

CONCLUSIONS

IL-23 mediates the differentiation of Th17 and Treg cells and the production of associated cytokines in DICs. The potential mechanism likely involves the STAT3 pathway.

Emerging biomarkers in psoriatic arthritis

Psoriasis is an immune-mediated skin disease which affects 2-4% of the worldwide population. Approximately 20-30% of patients with psoriasis develop psoriatic arthritis (PsA), a frequently destructive and disabling condition. As skin manifestations precede joint symptoms in nearly all patients with PsA, identification of biomarkers for early prediction of joint damage is an important clinical need. Because not all patients with PsA respond to treatment in the same fashion, identification of biomarkers capable of predicting therapeutic response is also imperative. Here, we review existing literature and discuss current investigations to identify potential biomarkers for PsA disease activity, with particular emphasis on microRNAs as novel markers of interest. Serum (soluble) biomarkers, peripheral osteoclast precursor as cellular biomarkers, and genetic loci associated with skin and joint disease are also reviewed.

Therapeutic Targeting of IL-17 and IL-23 Cytokines in Immune-Mediated Diseases

The discovery of the biological functions of the interleukin-23/-17 axis led to the identification of IL-23 and IL-17 as important participants in the pathogenesis of several immune-mediated diseases. Therapeutic agents targeting these cytokines and/or their receptors have now been developed as potential treatment strategies for common immune-mediated diseases. Anti-IL-17 and anti-IL-12/-23 regimens appear particularly effective in psoriasis, with promising results in spondyloarthropathies also emerging. Overall, these agents appear well tolerated, with adverse-event rates that are commensurate with those in other biologic treatment programs. The strategic utility of these new agents, however, remains uncertain, and further studies will be required to determine their place in the context of existing conventional and biologic immune-modifying agents.

Metabolic syndrome and its relationship with the achievement of minimal disease activity state in psoriatic arthritis patients: an observational study

The aim of the study was to evaluate the influence of metabolic syndrome (MetS) on achieving minimal disease activity (MDA) in psoriatic arthritis (PsA) patients treated with anti-tumor necrosis factor (TNF)-α with a follow-up period of 24 months. A cohort of PsA patients was assessed at the University Federico II of Naples and at University of Padova. For the aim of the present study, patients' data were collected at baseline (T0), at 12 months (T1) and at 24 months (T2). Assessment of metabolic and disease activity parameters was performed at each visit. The NCEP-ACT III criteria were used to identify subjects with MetS and the MDA criteria to evaluate the disease activity. On the basis of the exclusion and inclusion criteria, 330 subjects were included in the study; 134 patients (40.7%) were classified as not having MetS and 196 (59.3%) as having MetS. An inverse association was found between presence of metabolic syndrome and the probability of achieving MDA. Univariate analysis indicated that patients with metabolic syndrome were less likely to achieve MDA than patients without metabolic syndrome (OR 0.45, p < 0.001). This inverse association remained statistically significant in the multivariate regression model (OR 0.56, p < 0.001). Metabolic syndrome is associated with a lower probability of achieving MDA in PsA patients in therapy with anti-TNF-α.

Biologic Therapy for Psoriatic Arthritis

Biologic medications, therapeutic proteins that inhibit or modulate proinflammatory immune cells and cytokines, have significantly altered clinicians' ability to effectively treat psoriatic arthritis (PsA). The first widely used biologics have been those targeting tumor necrosis factor alpha. Five agents (etanercept, infliximab, adalimumab, golimumab, and certolizumab) have shown significant benefit in all clinical domains of PsA as well as inhibiting progressive joint destruction. Treatment strategies such as treating PsA early in the disease course, treating to target and tight control, use of background methotrexate to reduce immunogenicity, and various cost-saving strategies are all being tested with biologic medicines for PsA.

Differential effects of anti-TNF-α and anti-IL-12/23 agents on human leukocyte-endothelial cell interactions

Enhanced leukocyte recruitment is an inflammatory process that occurs during early phases of the vascular dysfunction that characterises atherosclerosis. We evaluated the impact of anti-TNF-α (adalimumab, infliximab and etanercept) and anti-IL-12/23 (ustekinumab) on interactions between human leukocytes and endothelial cells in a flow chamber that reproduced in vivo conditions. Clinical concentrations of anti-TNF-α were evaluated on the leukocyte recruitment induced by a variety of endothelial (TNF-α, interleukin-1β, lymphotoxin-α and angiotensin-II) and leukocyte (PAF, IL-12 and IL-23) stimuli related to inflammation and atherosclerosis. Treatment with anti-TNF-α, even before or after establishing the inflammatory situation induced by TNF-α, diminished leukocyte-endothelial cell interactions induced by this stimuli. Our results also implicated adhesion molecules (ICAM-1, VCAM-1 and E-selectin) in the actions of anti-TNF-α in terms of leukocyte adhesion to endothelium. However, anti-TNF-α drugs did not influence the actions of interleukin-1β, but prevented those of lymphotoxin-α and angiotensin-II. However, once established, inflammatory response elicited by the latter three stimuli could not be reversed. Pre-treatment with anti-TNF-α, also prevented leukocyte actions induced by IL-23 on PBMC rolling flux and rolling velocity and by IL-12 on PMN adhesion. Ustekinumab exhibited a more discreet profile, having no effect on leukocyte recruitment induced by any of the endothelial stimuli, while blocking the effects of IL-23 on leukocyte activation and those of IL-12 on PMN adhesion and PAF on PBMC rolling velocity. These findings endorse the idea that biological anti-inflammatory drugs, in particular anti-TNF-α, have the capacity to influence cardiovascular risk accompanying psoriasis and rheumatoid arthritis by ameliorating vascular inflammation.

New treatments for inflammatory rheumatic disease

As our understanding of the pathogenesis of autoimmune diseases is growing, new therapies are being developed to target disease-specific pathways. Since the introduction of etanercept in 1998, several biotechnological agents have been developed, most of them indicated in the treatment of rheumatoid arthritis, but also psoriatic arthritis. Most currently available molecules target TNF-alfa with different strategies (i.e., etanercept, infliximab, adalimumab, golimumab, and certolizumab pegol), IL-6 (tocilizumab), CTLA-4 (abatacept), and B cells (rituximab, belimumab) as they are key mediators in the cascade of inflammation. Further, small molecules have been recently developed to target intracellular signaling, such as Janus Kinases for tofacitinib, the first FDA-approved small molecule for rheumatoid arthritis. Most novel treatments are being developed for arthritis with specific differences between rheumatoid and psoriatic arthritis, as well as for systemic lupus erythematosus, following the approval of belimumab. Finally, biologic therapies are effective also in gout, mainly targeting interleukin-1 to block the inflammasome. This review article describes the new and upcoming treatment options for rheumatoid arthritis, psoriatic arthritis, systemic lupus erythematosus, and gout to dissect what we should be aware of when discussing these new and promising molecules.

The immunogenetics of Psoriasis: A comprehensive review

Psoriasis vulgaris is a common, chronic inflammatory skin disease with a complex etiology involving genetic risk factors and environmental triggers. Here we describe the many known genetic predispositions of psoriasis with respect to immune genes and their encoded pathways in psoriasis susceptibility. These genes span an array of functions that involve antigen presentation (HLA-Cw6, ERAP1, ERAP2, MICA), the IL-23 axis (IL12Bp40, IL23Ap19, IL23R, JAK2, TYK2), T-cell development and T-cells polarization (RUNX1, RUNX3, STAT3, TAGAP, IL4, IL13), innate immunity (CARD14, c-REL, TRAF3IP2, DDX58, IFIH1), and negative regulators of immune responses (TNIP1, TNFAIP3, NFKBIA, ZC3H12C, IL36RN, SOCS1). The contribution of some of these gene products to psoriatic disease has also been revealed in recent years through targeting of key immune components, such as the Th17/IL-23 axis which has been highly successful in disease treatment. However, many of the genetic findings involve immune genes with less clear roles in psoriasis pathogenesis. This is particularly the case for those genes involved in innate immunity and negative regulation of immune specific pathways. It is possible that risk alleles of these genes decrease the threshold for the initial activation of the innate immune response. This could then lead to the onslaught of the pathogenic adaptive immune response known to be active in psoriatic skin. However, precisely how these various genes affect immunobiology need to be determined and some are speculated upon in this review. These novel genetic findings also open opportunities to explore novel therapeutic targets and potentially the development of personalized medicine, as well as discover new biology of human skin disease.

Elevated serum prolactin levels as a marker of inflammatory arthritis in psoriasis vulgaris

BACKGROUND AND AIMS

Psoriasis vulgaris (PV) is complicated in up to 40% patients by the inflammatory joint disease psoriatic arthritis (PsA). Neither the aetiology of the arthritis nor specific laboratory markers for its disease activity have been clearly elucidated. Prolactin (PRL) acts as a cytokine with immunomodulatory functions and plays a role in skin and joint biology. The results on PRL however as a marker are unclear. The aim of this study was to confirm whether serum PRL levels reflect systemic complications of PV, like inflammatory joint disease and/or can serve as a marker of disease activity in both cases.

METHODS

A total of 70 patients with PV without arthritis and 40 patients suffering from PsA were included. In all patients, we determined skin disease activity according to the PASI index and in PsA, active disease assessed as swollen or tender joints. The control group included 27 age and sex matched healthy individuals. The concentration of PRL in the serum was measured by immunoradiometric assays.

RESULTS

The PRL serum levels were significantly increased in PsA patients (299.2±28.29 mIU/L) compared to PV only patients (201.4.2±11.72 mIU/L), P = 0.0003 and healthy individuals (198.2±15.31 mIU/L), P = 0.007. The serum PRL levels in PsA with active disease 336.8±42.50 (mIU/L) were higher than in PV and controls, P < 0.0001 and P = 0.002 respectively. In PV only patients, there was no correlation between PASI and PRL levels.

CONCLUSION

Our results showed that PRL serum levels are a marker of active arthritis in PsA and reflects systemic complication rather than local skin activity.

Gene Expression Profiling in Peripheral Blood Cells and Synovial Membranes of Patients with Psoriatic Arthritis

Background

Psoriatic arthritis (PsA) is an inflammatory arthritis whose pathogenesis is poorly understood; it is characterized by bone erosions and new bone formation. The diagnosis of PsA is mainly clinical and diagnostic biomarkers are not yet available. The aim of this work was to clarify some aspects of the disease pathogenesis and to identify specific gene signatures in paired peripheral blood cells (PBC) and synovial biopsies of patients with PsA. Moreover, we tried to identify biomarkers that can be used in clinical practice.

Methods

PBC and synovial biopsies of 10 patients with PsA were used to study gene expression using Affymetrix arrays. The expression values were validated by Q-PCR, FACS analysis and by the detection of soluble mediators.

Results

Synovial biopsies of patients showed a modulation of approximately 200 genes when compared to the biopsies of healthy donors. Among the differentially expressed genes we observed the upregulation of Th17 related genes and of type I interferon (IFN) inducible genes. FACS analysis confirmed the Th17 polarization. Moreover, the synovial trascriptome shows gene clusters (bone remodeling, angiogenesis and inflammation) involved in the pathogenesis of PsA. Interestingly 90 genes are modulated in both compartments (PBC and synovium) suggesting that signature pathways in PBC mirror those of the inflamed synovium. Finally the osteoactivin gene was upregulared in both PBC and synovial biopsies and this finding was confirmed by the detection of high levels of osteoactivin in PsA sera but not in other inflammatory arthritides.

Conclusions

We describe the first analysis of the trancriptome in paired synovial tissue and PBC of patients with PsA. This study strengthens the hypothesis that PsA is of autoimmune origin since the coactivity of IFN and Th17 pathways is typical of autoimmunity. Finally these findings have allowed the identification of a possible disease biomarker, osteoactivin, easily detectable in PsA serum.

The Assessment of Selected Bone and Cartilage Biomarkers in Psoriatic Patients from Poland

Background. Psoriasis is an inflammatory disease in which joints involvement may be insidious and difficult to detect. Bone and cartilage biomarkers may be helpful in screening patients with psoriasis for psoriatic arthritis (PsA). Objectives. To assess bone and cartilage serum biomarkers in psoriasis. Methods. The study was conducted in 2014 and included 61 psoriatic patients and 30 healthy individuals. In both groups, the serum concentrations of soluble receptor activator of nuclear factor-κB ligand (sRANKL), cartilage oligomeric matrix protein (COMP), osteoprotegerin (OPG), and interleukin-20 (IL-20) were examined. Severity of skin lesions was assessed by Psoriasis Area and Severity Index (PASI), body surface area (BSA), and Physician Global Assessment (PGA) scores. Results. The duration of psoriasis was from 1 year to 45 years. 22 patients suffered from concomitant PsA. The mean value of PASI was 23.1 ± 12.0 and BSA was 27.6 ± 20.6%. COMP, OPG, and IL-20 concentrations in psoriatic patients were significantly higher than in the control group. OPG/sRANKL ratio was significantly lower in PsA patients than in psoriatic patients without arthritis. Conclusions. Results of the conducted study suggest that COMP, OPG, IL-20, and OPG/sRANKL ratio may appear useful biomarkers of bone and cartilage involvement in psoriasis.

Measuring psoriatic disease in clinical practice. An expert opinion position paper

Psoriasis is a common, immune-mediated chronic inflammatory disease with a primary involvement of skin and joints, affecting approximately 2% of the population worldwide. Up to one third of patients with psoriasis are diagnosed with psoriatic arthritis (PsA). Psoriasis and PsA are heterogeneous diseases whose severity depends on a number of clinical factors, such as areas affected and pattern of involvement, and are associated with a range of comorbid diseases and risk factors, including obesity, metabolic syndrome, cardiovascular disease and liver disease. Thus measuring the severity of psoriatic disease needs to take into account the multidimensional aspects of the disease. Subjective measures including the impairment in quality of life or in daily living activities as well as the presence of cardio-metabolic comorbidities, are important for the outcome and add further levels of complexity that, to a certain extent, need to be assessed. Because of the wide range of comorbid conditions associated with psoriasis, comprehensive screening and treatment must be implemented for a most effective managing of psoriasis patients. A joint dermatologist-rheumatologist roundtable discussion was convened to share evidence on the real-life use of methods for measuring psoriasis severity comprehensively. Our objective was to provide an expert position on which clinical variables are to be taken into account when considering patients affected by psoriasis and/or PsA globally and on the assessment tools more suitable for measuring disease activity and/or severity in clinical practice.

The IL-23-IL-17 axis in inflammatory arthritis

The discovery that the IL-23-IL-17 immune pathway is involved in many models of autoimmune disease has changed the concept of the role of T-helper cell subsets in the development of autoimmunity. In addition to TH17 cells, IL-17 is also produced by other T cell subsets and innate immune cells; which of these IL-17-producing cells have a role in tissue inflammation, and the timing, location and nature of their role(s), is incompletely understood. The current view is that innate and adaptive immune cells expressing the IL-23 receptor become pathogenic after exposure to IL-23, but further investigation into the role of IL-23 and IL-17 at different stages in the development and progression of chronic (destructive) inflammatory diseases is needed. Rheumatoid arthritis (RA) and spondyloarthritis (SpA) are the two most common forms of chronic immune-mediated inflammatory arthritis, and the IL-23-IL-17 axis is thought to have a critical role in both. This Review discusses the basic mechanisms of these cytokines in RA and SpA on the basis of findings from disease-specific animal models as well as human ex vivo studies. Promising therapeutic applications to modulate this immune pathway are in development or have already been approved. Blockade of IL-17 and/or TH17-cell activity in combination with anti-TNF therapy might be a successful approach to achieving stable remission or even prevention of chronic immune-mediated inflammatory diseases.

Endothelial-binding, proinflammatory T cells identified by MCAM (CD146) expression: Characterization and role in human autoimmune diseases

A subset of T cells defined by the cell surface expression of MCAM (CD146) has been identified in the peripheral circulation of healthy individuals. These cells comprise approximately 3% of the pool of circulating T cells, have an effector memory phenotype, and are capable of producing several cytokines. Notably, the MCAM positive cells are enhanced for IL-17 production compared to MCAM negative effector memory T cells. These cells are committed to IL-17 production and do not require in vitro polarization with exogenous cytokines. MCAM positive T cells also demonstrate an increased ability to bind to endothelial monolayers. In numerous autoimmune diseases these cells are found at increased proportions in the peripheral circulation, and at the sites of active inflammation in patients with autoimmune disease, these cells appear in large numbers and are major contributors to IL-17 production. Studies to date have been performed with human subjects and it is uncertain if appropriate mouse models exist for this cell type. These cells could represent early components of the adaptive immune response and serve as targets of therapy in these diseases, although much work remains to be performed in order to discern the exact nature and function of these cells.

Emerging drugs for the treatment of axial and peripheral spondyloarthritis

INTRODUCTION

The topic under discussion is of strong relevance to the field of spondyloarthritis (SpA) because, in addition to established biological, there are new promising compounds. The reason for the review is to put all available data together to allow for an overview on recent developments and to especially inform readers about emerging drugs, biologics and small molecules in the field of SpA.

AREAS COVERED

This review on new therapies in axial and peripheral SpA comprising psoriatic arthritis (PsA) shows, that, in addition to the established anti-TNF agents infliximab, etanercept, adalimumab, golimumab, certolizumab and the first biosimilar approved in the EU, there are at least two emerging biologics in the field of SpA: ustekinumab, a compound targeting IL12/IL-23 via the p40 subunit of both cytokines works for psoriasis and PsA and probably also for Crohn's disease, and the anti-IL-17 antibody secukinumab which has also been shown to work in psoriasis, both compounds seem to also work in ankylosing spondylitis. In addition, the potential of two small molecules, apremilast a phoshodiesterase4 inhibitor and tofacitinib, a januskinase inhibitor is discussed.

EXPERT OPINION

Since, in contrast to rheumatoid arthritis, the therapeutic array in SpA is currently limited to TNF-blockers, and since there is still an unmet need because some patients do not respond to anti-TNF therapy at all or they loose response, new agents with a different mechanism of action are eagerly awaited.

T cell responses in psoriasis and psoriatic arthritis

According to the current view the histological features of psoriasis arise as a consequence of the interplay between T cells, dendritic cells and keratinocytes giving rise to a self-perpetuating loop that amplifies and sustains inflammation in lesional skin. In particular, myeloid dendritic cell secretion of IL-23 and IL-12 activates IL-17-producing T cells, Th22 and Th1 cells, leading to the production of inflammatory cytokines such as IL-17, IFN-γ, TNF and IL-22. These cytokines mediate effects on keratinocytes thus establishing the inflammatory loop. Unlike psoriasis the immunopathogenic features of psoriatic arthritis are poorly characterized and there is a gap in the knowledge of the pathogenic link between inflammatory T cell responses arising in the skin and the development of joint inflammation. Here we review the knowledge accumulated over the years from the early evidence of autoreactive CD8 T cells that was studied mainly in the years 1990s and 2000s to the recent findings of the role of Th17, Tc17 cells and γδ T cells in psoriatic disease pathogenesis. The review will also focus on common and distinguishing features of T cell responses in psoriatic plaques and in synovial fluid of patients with psoriatic arthritis. The integration of this information could help to distinguish the role played by T cells in the initiation phase of the disease from the role of T cells as downstream effectors sustaining inflammation in psoriatic plaques and potentially leading to disease manifestation in distant joints.

The intestinal microbiota and microenvironment in liver

The intestinal microbiome plays a significant role in the development of autoimmune diseases, in particular, inflammatory bowel diseases. But the interplay between the intestinal tract and the liver may explain the increased association with autoimmune liver diseases and inflammatory bowel diseases. The gut-liver axis involves multiple inflammatory cell types and cytokines, chemokines and other molecules which lead to the destruction of normal liver architecture. Triggers for the initiation of these events are unclear, but appear to include multiple environmental factors, including pathogenic or even commensal microbial agents. The variation in the gut microbiome has been cited as a major factor in the pathogenesis of autoimmune liver disease and even other autoimmune diseases. The unique positioning of the liver at the juncture of the peripheral circulation and the portal circulation augments the interaction between naïve T cells and other hepatic cells and leads to the disruption in the development of tolerance to commensal bacteria and other environmental agents. Finally, the innate immune system and in particular toll-like receptors play a significant role in the pathogenesis of autoimmune liver disease.

From defining antigens to new therapies in multiple sclerosis: honoring the contributions of Ruth Arnon and Michael Sela

Ruth Arnon and Michael Sela profoundly influenced the development of a model system to test new therapies in multiple sclerosis (MS). Their application of the animal model, known as experimental autoimmune encephalomyelitis (EAE), for the discovery of Copaxone, opened a new path for testing of drug candidates in MS. By measuring clinical, pathologic, and immunologic outcomes, the biological implications of new drugs could be elucidated. Using EAE they established the efficacy of Copaxone as a therapy for preventing and reducing paralysis and inflammation in the central nervous system without massive immune suppression. This had a huge impact on the field of drug discovery for MS. Much like the use of parabiosis to discover soluble factors associated with obesity, or the replica plating system to probe antibiotic resistance in bacteria, the pioneering research on Copaxone using the EAE model, paved the way for the discovery of other therapeutics in MS, including Natalizumab and Fingolimod. Future applications of this approach may well elucidate novel therapies for the neurodegenerative phase of multiple sclerosis associated with disease progression.

The effect of the novel tellurium compound AS101 on autoimmune diseases

Tellurium is a rare element, which has been regarded as a non-essential trace element despite its relative abundance in the human body. The chemistry of tellurium supports a plethora of activities, but its biochemistry is not clearly established to date. The small tellurium(IV) compound, ammonium trichloro (dioxoethylene-o,o')tellurate (AS101) developed and initially investigated by us, is currently being evaluated in Phase II clinical trials in psoriasis patients. AS101 is the first tellurium compound to be tested for clinical efficacy. This compound is a potent immunomodulator both in vitro and in vivo with a variety of potential therapeutic applications. The present review will focus on the immunomodulatory properties of AS101, and specifically, its effects in mitigating autoimmune diseases. AS101 has several activities that act on the immune system, including: 1) its ability to reduce IL-17 levels and to inhibit the function of Th17 cells; 2) its specific unique redox-modulating activities enabling the inhibition of specific leukocyte integrins such as α4β1 and α4β7, that are pivotal for diapedesis of macrophages and CD4(+) T inflammatory/auto-reactive cells into the autoimmune tissues; and 3) its ability to enhance the activity of regulatory T cells (Treg). These activities coupled with its excellent safety profile suggest that AS101 may be a promising candidate for the management of autoimmune diseases.

Immunopathogenesis of reactive arthritis: Role of the cytokines

Reactive arthritis (ReA), also known as sterile postinfectious arthritis, belongs to the group of related arthropathies known as spondyloarthritis (SpA). ReA can arise 1-4 wk after a gastrointestinal or genitourinary infection, but once arthritis develops, the microorganism is not found in the joint. The classical microbes associated with ReA development include Gram-negative aerobic or microaerophilic bacteria containing LPS in their outer membrane. The immunopathogenic mechanisms involved in ReA development are still unknown. A hypothesis suggested that the bacteria probably persist outside the joint, at sites such as gut mucosa or lymph nodes, and bacterial antigens might then be transported to the joints. On the other hand, an altered immune response and the unbalanced production of cytokines have been reported in subjects with ReA. Currently, there is increased evidence to suggest that both mechanisms would operate in the immunopathogenesis of ReA. In this review we highlight recent advances on the role of cytokines in the ReA. Particularly, we discuss the roles of some pro- and anti-inflammatory cytokines involved in the immunopathogenesis of ReA.