Interleukin-23 mediates the intestinal response to microbial β-1,3-glucan and the development of spondyloarthritis pathology in SKG mice

Exploring effects of gut microbiota on tertiary lymphoid structure formation for tumor immunotherapy

Anti-tumor immunity, including innate and adaptive immunity is critical in inhibiting tumorigenesis and development of tumor. The adaptive immunity needs specific lymph organs such as tertiary lymphoid structures (TLSs), which are highly correlated with improved survival outcomes in many cancers. In recent years, with increasing attention on the TLS in tumor microenvironment, TLSs have emerged as a novel target for anti-tumor therapy. Excitingly, studies have shown the contribution of TLSs to the adaptive immune responses. However, it is unclear how TLSs to form and how to more effectively defense against tumor through TLS formation. Recent studies have shown that the inflammation plays a critical role in TLS formation. Interestingly, studies have also found that gut microbiota can regulate the occurrence and development of inflammation. Therefore, we here summarize the potential effects of gut microbiota- mediated inflammation or immunosuppression on the TLS formation in tumor environments. Meanwhile, this review also explores how to manipulate mature TLS formation through regulating gut microbiota/metabolites or gut microbiota associated signal pathways for anti-tumor immunity, which potentially lead to a next-generation cancer immunotherapy.

Clonorchis sinensis excretory/secretory proteins ameliorate inflammation in rheumatoid arthritis and ankylosing spondylitis

BACKGROUND

We aimed to investigate whether substances secreted by Clonorchis sinensis excretory/secretory protein (CS-ESP) have an effect on the inflammation of rheumatoid arthritis (RA) and ankylosing spondylitis (AS) and to identify specific peptides through related proteomic analysis to determine which proteins exhibit anti-inflammatory effects more specifically.

METHODS

Peripheral blood mononuclear cells (PBMCs) were obtained from healthy controls (HCs), RA and AS patients. Cytotoxicity of CS-ESP at different doses was assessed by MTS and flow cytometry before performing experiments. Inflammatory cytokine producing cells were analyzed using flow cytometry. To determine the effect of CS-ESP in an arthritis mouse model, 8-week-old SKG mice were injected intraperitoneally with curdlan and treated with CS-ESP; body weight and paw swelling were checked twice a week. Inflammation was evaluated using immunohistochemistry. We conducted proteomic analysis on CS-ESP and identified specific Cs-GT and Cs-Severin proteins. In vitro effect of coculture with Cs-GT and Cs-Severin was determined by inflammatory cytokine measurements.

RESULT

Treatment with CS-ESP resulted in no reduced cell viability of PBMCs. In experiments culturing PBMCs, the frequencies of IL-17A and GM-CSF producing cells were significantly reduced after CS-ESP treatment. In the SKG mouse model, CS-ESP treatment significantly suppressed clinical score, arthritis and enthesitis. Treatment with Cs-GT and Cs-Severin resulted in no reduced cell viability of HC PBMCs. After Cs-GT and Cs-Severin treatment of HC PBMC, the frequencies of IL-17A and GM-CSF producing cells were significantly reduced.

CONCLUSIONS

We provide evidence showing that CS-ESP, Cs-GT and Cs-Severin can ameliorate clinical signs and cytokine derangements in AS.

Pathogenesis of psoriatic arthritis: new insights from a bone marrow perspective

PURPOSE OF REVIEW

Psoriatic arthritis is an immune-mediated disease that primarily affects the skin and joints. It falls under the umbrella term of rheumatic diseases, which describes a group of closely related yet distinct disorders with many common underlying molecular pathways. Despite the distinct clinical manifestation of each disorder, the shared therapeutic strategies attest to the commonality of cellular and molecular underpinnings. Herein we provide a concise yet comprehensive overview of the interleukin (IL)-23/IL-17 axis and its involvement in mechanistic pathways leading to the pathogenesis of this dual skin and joint clinical manifestation which is characteristic of psoriatic arthritis and other rheumatic diseases.

RECENT FINDINGS

The interconnection between activated innate immune cells and adaptive immunity has transformed current thinking to include other organs such as the bone marrow as potential tissue of disease origin. A plethora of animal models and genetic studies converge on the critical role of IL-23/IL-17 axis, and highlight the importance of myeloid cell activation as common pathways between autoinflammatory and autoimmune diseases and chronic inflammation. These findings underscore the intricate immune mechanisms involved in inflammatory arthritis and highlight molecular mechanisms in disease pathogenesis.

SUMMARY

These insights pave the way for the development of novel diagnostic and therapeutic strategies, with a focus on translating these findings into improved clinical practice.

Targeting osteoclast-derived DPP4 alleviates inflammation-mediated ectopic bone formation in ankylosing spondylitis

BACKGROUND

Ankylosing spondylitis (AS) is a chronic inflammatory disease characterized by ectopic bone formation. The anti-inflammatory function of dipeptidyl peptidase-4 (DPP4) inhibitor has been reported in bone metabolism, but its utility in AS has not previously been investigated.

METHODS

We assessed DPP4 level in serum, synovial fluid, and facet joint tissue of AS patients. Additionally, we investigated the effect of a DPP4 inhibitor in an experimental AS model using curdlan-injected SKG mice. Following curdlan injection, SKG mice were orally administered a DPP4 inhibitor three times per week for 5 weeks and observed clinical arthritis scores, and analyzed by micro-CT. Furthermore, osteoclast precursor cells (OPCs) from curdlan-injected SKG mice were treated with DPP4 inhibitor and evaluated the inhibitory effects of this treatment in vitro.

RESULTS

Soluble DPP4 level was elevated in the serum and synovial fluid of patients with AS compared to those in the control group. Expression of DPP4 increased gradually during human osteoclastogenesis and was high in mature osteoclasts. Oral administration of a DPP4 inhibitor resulted in a decrease in thickness of the hind paw, clinical arthritis scores, and enthesitis at the ankle in curdlan-injected SKG mice compared to the vehicle group. Micro-CT data revealed a significant reduction in inflammation-induced low bone density in the DPP4 inhibitor group. Moreover, treatment with a DPP4 inhibitor significantly reduced osteoclast differentiation of OPC in addition to decreasing expression of osteoclast differentiation markers.

CONCLUSION

Our findings suggest that inhibiting DPP4 may have a therapeutic effect on inflammation-mediated ectopic bone formation in AS patients.

Persistent articular infection and host reactive response contribute to Brucella -induced spondyloarthritis in SKG mice

Brucellosis, one of the most prevalent zoonotic diseases worldwide, often results in osteoarticular complications including large joint and axial arthritis mimicking spondyloarthritis. To model this chronic manifestation, we infected autoimmunity-prone SKG mice containing a mutation in the T-cell adaptor ZAP-70 with Brucella species. B. melitensis infection resulted in a fully penetrant, readily scoreable disease involving large joint wrist and foot arthritis, peri-ocular inflammation, and less frequent scaly paw rash. Infection with B. abortus resulted in delayed arthritis onset, and B. neotomae revealed sex differences, with more severe disease and a dose response in females. Heat-killed Brucella did not induce arthritis, evincing a requirement for viable infection. Across species, splenic CFU correlated well with final clinical score at 12 weeks (ρ=0.79 and p<0.001). In vivo imaging using luminescent B. neotomae revealed rapid colonization of the paws by one-week post-infection, more than a month prior to arthritis onset. Paw luminescence levels decreased after 2 weeks and then remained relatively static, even as clinical scores increased. Thus, the degree of arthritis did not strictly correlate with degree of paw infection but suggested an additional reactive component. Further, in examining a Brucella Δ tcpB mutant lacking a Type IV secretion system-dependent mediator, mice displayed an intermediate phenotype without significant differences in splenic CFU. Together these data suggest Brucella induced spondyloarthritis reflects both persistent colonization as well as excess host reactivity. Moreover, the sensitivity of the SKG model to different species and mutants will provide new opportunities for dissecting correlates of Brucella virulence and host immunity.

Importance

Brucellosis, a bacterial infection acquired from herd animals, remains one of the most common zoonotic diseases worldwide. Chronic infection often results in spondyloarthritis-like complications. Investigation into pathogenesis has been limited by the lack of overt disease in standard lab mice. We addressed this issue using spondyloarthritis-susceptible SKG mice. Upon infection with B. melitensis , SKG mice develop robust, fully penetrant large joint arthritis. Arthritis development required viable bacteria. Moreover, studies of colonization, gene expression and anatomic distribution using bioluminescent bacteria revealed active persistent infection in the mouse paws. However, peak paw infection occurred much earlier than arthritis onset, suggesting an added immune reactive component. Disease onset, severity and manifestations varied upon infection with different Brucella species and mutants. Together these results suggest this new model will be very useful to the scientific community for determining correlates of bacterial virulence leading to clinical disease.

Type 17 immunity: novel insights into intestinal homeostasis and autoimmune pathogenesis driven by gut-primed T cells

The IL-23 signaling pathway in both innate and adaptive immune cells is vital for orchestrating type 17 immunity, which is marked by the secretion of signature cytokines such as IL-17, IL-22, and GM-CSF. These proinflammatory mediators play indispensable roles in maintaining intestinal immune equilibrium and mucosal host defense; however, their involvement has also been implicated in the pathogenesis of chronic inflammatory disorders, such as inflammatory bowel diseases and autoimmunity. However, the implications of type 17 immunity across diverse inflammation models are complex. This review provides a comprehensive overview of the multifaceted roles of these cytokines in maintaining gut homeostasis and in perturbing gut barrier integrity, leading to acute and chronic inflammation in various models of gut infection and colitis. Additionally, this review focuses on type 17 immunity interconnecting multiple organs in autoimmune conditions, with a particular emphasis on the pathogenesis of autoimmune arthritis and neuroinflammation driven by T cells primed within the gut microenvironment.

IL-17 inhibitors in axial spondyloarthritis. An overview

INTRODUCTION

The therapeutic armamentarium for spondyloarthritis has expanded considerably in recent years, and there is growing evidence to support the increasing use of IL-17 inhibitors (IL-17i) in axial spondyloarthritis (axSpA).

AREAS COVERED

This literature review provides an update on the role of IL-17 in the pathogenesis of axSpA, efficacy and safety from clinical trials and real-life studies on the use of IL17i in axSpA. We also review the impact of extra-musculoskeletal manifestations on the decision to treat with IL17i and the efficacy of IL17i on structural progression.

EXPERT OPINION

There are still some unanswered questions concerning the use of IL-17i in axSpA in clinical practice such as their respective place in the management of axSpA compared to TNFα inhibitors (TNFi). Their main differences rely on their specific efficacy in extra-articular manifestations such as psoriasis, uveitis, and inflammatory bowel diseases leading to the choice of the best treatment in a given patient. Regarding their real impact on structural progression, the rate of progression under IL-17i appears to be low and presumably similar to TNFi. One final question is the advantage of blocking the two IL-17 isoforms A and F compared to the single inhibition of IL-17A.

Swimming exercise alleviates pathological bone features in curdlan-injected SKG mice by inducing irisin expression

This study assessed the therapeutic potential of swimming exercise in the curdlan-injected SKG mouse model and investigated the modulatory effects of irisin on inflammation. Curdlan-injected SKG were randomly assigned to either a home-cage group or a swimming group for 6 weeks. Changes in clinical arthritis scores and ankle thickness were measured weekly. Post-swimming program, mice were anesthetized for collection of vastus lateralis muscle and blood, which was followed by histological analysis, micro-CT imaging of the ankle joints, and the measurement of pro-inflammatory cytokines and irisin levels. Additionally, curdlan-injected SKG mice were intravenously injected with recombinant irisin protein and observed. Finally, serum levels of irisin in healthy control and ankylosing spondylitis (AS) patient groups were measured by ELISA. The swimming group of curdlan-injected SKG mice exhibited significant improvements in arthritis and enthesitis compared to the home-cage group. In particular, micro-CT and histological analyses revealed a notable reduction in pathological bone features in the swimming group compared to the home-cage group. Muscle endurance was also enhanced in the swimming group compared to the home-cage group, as determined by the wire-hanging test. Intriguingly, irisin levels not only were statistically increased in the swimming group but, also, TNF-α, IL-1β, and IL-6 levels were decreased. Additionally, injection of irisin protein slightly attenuated both arthritis and enthesitis in curdlan-injected SKG mice. Meanwhile, irisin serum levels were declined in AS patients. Overall, we found that swimming exercise attenuated pathological bone features in an AS animal model, potentially mediated by increased irisin serum levels with associated anti-inflammatory effects.

The management of axial spondyloarthritis with cutting-edge therapies: advancements and innovations

INTRODUCTION

Axial involvement in spondyloarthritis has significantly evolved from the original 1984 New York criteria for ankylosing spondylitis, leading to an improved understanding of axial spondyloarthritis (axSpA) as a disease continuum encompassing non- radiographic axSpA (nr-axSpA) and radiographic axSpA (r-axSpA). A clear definition for early axSpA has been established, underscoring the need for early intervention with biological and targeted synthetic drugs to mitigate pain, reduce functional impairment, and prevent radiographic progression.

AREAS COVERED

This review explores therapeutic strategies in axSpA management, focusing on biological and targeted synthetic therapies and recent advancements. Biologics targeting TNFα or IL-17 and targeted synthetic disease-modifying antirheumatic drugs (DMARDs) are primary treatment options. These therapies significantly impact clinical outcomes, radiographic progression, and patient-reported functional improvement.

EXPERT OPINION

AxSpA treatment has evolved significantly, offering various therapeutic options. Biological DMARDs, particularly TNFα inhibitors, have transformed treatment, significantly enhancing patient outcomes. However, challenges persist for patients unresponsive or intolerant to existing therapies. Emerging therapeutic targets promise to address these challenges. Comprehensive management strategies and personalized approaches, considering extra-articular manifestations and individual patient factors, are crucial for achieving optimal outcomes in axSpA management.

HIF-1α and MIF enhance neutrophil-driven type 3 immunity and chondrogenesis in a murine spondyloarthritis model

The hallmarks of spondyloarthritis (SpA) are type 3 immunity-driven inflammation and new bone formation (NBF). Macrophage migration inhibitory factor (MIF) was found to be a key driver of the pathogenesis of SpA by amplifying type 3 immunity, yet MIF-interacting molecules and networks remain elusive. Herein, we identified hypoxia-inducible factor-1 alpha (HIF1A) as an interacting partner molecule of MIF that drives SpA pathologies, including inflammation and NBF. HIF1A expression was increased in the joint tissues and synovial fluid of SpA patients and curdlan-injected SKG (curdlan-SKG) mice compared to the respective controls. Under hypoxic conditions in which HIF1A was stabilized, human and mouse neutrophils exhibited substantially increased expression of MIF and IL-23, an upstream type 3 immunity-related cytokine. Similar to MIF, systemic overexpression of IL-23 induced SpA pathology in SKG mice, while the injection of a HIF1A-selective inhibitor (PX-478) into curdlan-SKG mice prevented or attenuated SpA pathology, as indicated by a marked reduction in the expression of MIF and IL-23. Furthermore, genetic deletion of MIF or HIF1A inhibition with PX-478 in IL-23-overexpressing SKG mice did not induce evident arthritis or NBF, despite the presence of psoriasis-like dermatitis and blepharitis. We also found that MIF- and IL-23-expressing neutrophils infiltrated areas of the NBF in curdlan-SKG mice. These neutrophils potentially increased chondrogenesis and cell proliferation via the upregulation of STAT3 in periosteal cells and ligamental cells during endochondral ossification. Together, these results provide supporting evidence for an MIF/HIF1A regulatory network, and inhibition of HIF1A may be a novel therapeutic approach for SpA by suppressing type 3 immunity-mediated inflammation and NBF.

Elevated type-17 cytokines are present in axial spondyloarthritis stool

Axial spondyloarthritis (axSpA) is characterized by type-17 immune-driven joint inflammation, and intestinal inflammation is present in around 70% of patients. In this study, we asked whether axSpA stool contained Th17-associated cytokines and whether this related to systemic Th17 activation. We measured stool cytokine and calprotectin levels by ELISA and found that patients with axSpA have increased stool IL-17A, IL-23, GM-CSF, and calprotectin. We further identified increased levels of circulating IL-17A+ and IL-17F+ T-helper cell lymphocytes in patients with axSpA compared to healthy donors. We finally assessed stool metabolites by unbiased nuclear magnetic resonance spectroscopy and found that multiple stool amino acids were negatively correlated with stool IL-23 concentrations. These data provide evidence of type-17 immunity in the intestinal lumen, and suggest its association with microbial metabolism in the intestine.

The complement factor H-related protein-5 (CFHR5) exacerbates pathological bone formation in ankylosing spondylitis

Ankylosing spondylitis (AS) is a chronic inflammatory disease, characterized by excessive new bone formation. We previously reported that the complement factor H-related protein-5 (CFHR5), a member of the human factor H protein family, is significantly elevated in patients with AS compared to other rheumatic diseases. However, the pathophysiological mechanism underlying new bone formation by CFHR5 is not fully understood. In this study, we revealed that CFHR5 and proinflammatory cytokines (TNF, IL-6, IL-17A, and IL-23) were elevated in the AS group compared to the HC group. Correlation analysis revealed that CFHR5 levels were not significantly associated with proinflammatory cytokines, while CFHR5 levels in AS were only positively correlated with the high CRP group. Notably, treatment with soluble CFHR5 has no effect on clinical arthritis scores and thickness at hind paw in curdlan-injected SKG, but significantly increased the ectopic bone formation at the calcaneus and tibia bones of the ankle as revealed by micro-CT image and quantification. Basal CFHR5 expression was upregulated in AS-osteoprogenitors compared to control cells. Also, treatment with CFHR5 remarkedly induced bone mineralization status of AS-osteoprogenitors during osteogenic differentiation accompanied by MMP13 expression. We provide the first evidence demonstrating that CFHR5 can exacerbate the pathological bone formation of AS. Therapeutic modulation of CFHR5 could be promising for future treatment of AS. KEY MESSAGES: Serum level of CFHR5 is elevated and positively correlated with high CRP group of AS patients. Recombinant CFHR5 protein contributes to pathological bone formation in in vivo model of AS. CFHR5 is highly expressed in AS-osteoprogenitors compared to disease control. Recombinant CFHR5 protein increased bone mineralization accompanied by MMP13 in vitro model of AS.

A potential role of protein extractions from Metagonimus yokogawai in amelionating inflammation in patients with ankylosing spondylitis

Helminth infections and their components has been recognized to have a positive impact on the immune system. This study aimed to investigate the potential of Metagonimus yokogawai-derived proteins (MYp) to provide protection against ankylosing spondylitis (AS) through modulation of immune responses. The cytotoxicity of MYp at various doses was first assessed using MTS and flow cytometry. Peripheral blood mononuclear cells (PBMCs) were collected from AS patients, and the production of inflammatory cytokines was analyzed through flow cytometry. In the experiments with SKG mice, MYp or vehicle was administered and inflammation was evaluated through immunohistochemistry and enzyme-linked immunosorbent assay. The results showed that MYp did not decrease cell viability of PBMCs even after 48 h. Additionally, the frequencies of IFN-γ and IL-17A producing cells were significantly reduced after MYp treatment in the PBMC cultures. Furthermore, MYp treatment significantly suppressed arthritis and enthesitis in the SKG mouse model. The results suggest the first evidence that MYp can effectively alleviate clinical symptoms and restore cytokine balance in patients with AS.

The Efficacy and Safety of Biologics in Treating Ankylosing Spondylitis and Their Impact on Quality of Life and Comorbidities: A Literature Review

Ankylosing spondylitis (AS) is a chronic inflammatory arthritis that affects the axial skeleton, causing intense pain, progressive joint destruction, and a gradual reduction in physical function. Additionally, AS can result in extra-musculoskeletal manifestations including inflammatory bowel disease (IBD), psoriasis, and acute anterior uveitis (AAU) affecting patients' quality of life (QoL). Furthermore, AS association with neurological and cardiovascular events has been documented. With the advent of biologics, treating AS has dramatically changed due to their high efficacy and tolerable safety. Nevertheless, there are differences in traits, including rapidity of onset, long-term efficacy, safety profile, and influence on comorbidities. A better understanding of such traits enables clinicians to make the best decision for each patient, increasing persistence, extending medication survival, enhancing patient satisfaction, and reducing the disease effect of AS. A review of the literature published in English in PubMed and Google Scholar databases from 2010 to 2023 was conducted. All relevant results fitting the scope of the topic were included. In this article, we emphasize biologics' efficacy and safety profile in patients with AS. In addition, we discuss the impact of biologics on comorbidities and health-related quality of life (HRQoL).

Current insights on the roles of gut microbiota in inflammatory bowel disease-associated extra-intestinal manifestations: pathophysiology and therapeutic targets

Inflammatory bowel disease (IBD) is a chronic, recurrent inflammatory disease of the gastrointestinal tract. In addition to digestive symptoms, patients with IBD may also develop extra-intestinal manifestations (EIMs), the etiology of which remains undefined. The gut microbiota has been reported to exert a critical role in the pathogenesis of IBD, with a similar pattern of gut dysbiosis observed between patients with IBD and those with EIMs. Therefore, it is hypothesized that the gut microbiota is also involved in the pathogenesis of EIMs. The potential mechanisms are presented in this review, including: 1) impaired gut barrier: dysbiosis induces pore formation in the intestinal epithelium, and activates pattern recognition receptors to promote local inflammation; 2) microbial translocation: intestinal pathogens, antigens, and toxins translocate via the impaired gut barrier into extra-intestinal sites; 3) molecular mimicry: certain microbial antigens share similar epitopes with self-antigens, inducing inflammatory responses targeting extra-intestinal tissues; 4) microbiota-related metabolites: dysbiosis results in the dysregulation of microbiota-related metabolites, which could modulate the differentiation of lymphocytes and cytokine production; 5) immunocytes and cytokines: immunocytes are over-activated and pro-inflammatory cytokines are excessively released. Additionally, we summarize microbiota-related therapies, including probiotics, prebiotics, postbiotics, antibiotics, and fecal microbiota transplantation, to promote better clinical management of IBD-associated EIMs.

The Expression of the Alpha7 Nicotinic Acetylcholine Receptor and the Effect of Smoking in Curdlan-Administered SKG Mice

Nicotine, an abundant molecule in tobacco, has immunomodulatory effects on inflammatory diseases, primarily due to the activation of alpha7 nicotinic acetylcholine receptor (α7 nAChR). We aim to evaluate the expression of the α7 nAChR+ cells in joint tissue and the effect of smoking on immune cells and peripheral arthritis in curdlan-administered SKG mice, a murine model of spondyloarthropathy (SpA). The SKG mice were injected with curdlan two times at 2-week intervals and were divided into two groups; one exposed to cigarette smoke and the other not exposed. We found that the α7 nAChR+ cells increased in the joint tissue of curdlan-administered SKG mice compared to in the wild type. Furthermore, the peripheral arthritis scores and histological scores for synovial inflammation were lower in smoke-exposed curdlan-administered SKG mice than in mice not exposed to smoke. Immunofluorescence staining of the α7 nAChR+ and IL-17A+ cells was lower in the synovia of smoke-exposed mice than the control mice. The proportions of α7 nAChR+IL-17A+ and α7 nAChR+IL-17A+FOXP3+ cells also decreased in the synovia of smoke-exposed mice compared with the controls. We observed an increase in the α7 nAChR+ cells within the joint tissue of curdlan-administered SKG mice and that cigarette smoke had an influence on both peripheral arthritis and immune cell population, especially α7 nAChR+ cells. Thus, exposure to cigarette smoke after arthritogenic stimuli may have an anti-arthritogenic effect in curdlan-administered SKG mice.

Pathophysiology and immunolgical basis of axial spondyloarthritis

Over the recent years the wider availability and application of state-of-the-art immunological technologies greatly advanced the insight into the mechanisms that play an important role in axial spondyloarthritis (axSpA) pathophysiology. This increased understanding has facilitated the development of novel treatments that target disease relevant pathways, hereby improving outcome for axSpA patients. In axSpA pathophysiology genetic and environmental factors as well as immune activation by mechanical or bacterial stress resulting in a chronic inflammatory response have a central role. The TNF and IL-23/IL-17 immune pathways play a pivotal role in these disease mechanisms. This review provides an outline of the immunological basis of axSpA with a focus on key genetic risk factors and their link to activation of the pathological immune response, as well as on the role of the gut and entheses in the initiation of inflammation with subsequent new bone formation in axSpA.

The Conundrum of Psoriatic Arthritis: a Pathogenetic and Clinical Pattern at the Midpoint of Autoinflammation and Autoimmunity

Psoriatic arthritis (PsA) is a chronic inflammatory condition characterized by psoriasis, synovitis, enthesitis, spondylitis, and the possible association with other extra-articular manifestations and comorbidities. It is a multifaceted and systemic disorder sustained by complex pathogenesis, combining aspects of autoinflammation and autoimmunity. Features of PsA autoinflammation include the role of biomechanical stress in the onset and/or exacerbation of the disease; the evidence of involvement of the innate immune response mediators in the skin, peripheral blood and synovial tissue; an equal gender distribution; the clinical course which may encounter periods of prolonged remission and overlapping features with autoinflammatory syndromes. Conversely, the role of autoimmunity is evoked by the association with class I major histocompatibility complex alleles, the polyarticular pattern of the disease which sometimes resembles rheumatoid arthritis and the presence of serum autoantibodies. Genetics also provide important insights into the pathogenesis of PsA, particularly related to class I HLA being associated with psoriasis and PsA. In this review, we provide a comprehensive review of the pathogenesis, genetics and clinical features of PsA that endorse the mixed nature of a disorder at the crossroads of autoinflammation and autoimmunity.

Challenges and opportunities in animal models of psoriatic arthritis

OBJECTIVE

To review the preparation, characteristics and research progress of different PsA animal models.

METHODS

Computerized searches were conducted in CNKI, PubMed and other databases to classify and discuss the relevant studies on PsA animal models. The search keywords were "PsA and animal model(s), PsA and animal(s), PsA and mouse, PsA and mice, PsA and rat(s), PsA and rabbit(s), PsA and dog(s)" RESULTS: The experimental animals currently used to study PsA are mainly rodents, including mice and rats. According to the different methods of preparing the models, the retrieved animal models were classified into spontaneous or genetic mutation, transgenic and induced animal models. These PsA animal models involve multiple pathogenesis, some experimental animals' lesions appear in a short and comprehensive cycle, some have a high success rate in molding, and some are complex and less reproducibility. This article summarizes the preparation methods, advantages and disadvantages of different models.

CONCLUSIONS

The animal models of PsA aim to mimic the clinicopathological alterations of PsA patients through gene mutation, transgenesis or targeted proinflammatory factor and to reveal new pathogenic pathways and therapeutic targets by exploring the pathological features and clinical manifestations of the disease. This work will have very far-reaching implications for the in-depth understanding of PsA and the development of new drugs.

Uncovering the Underworld of Axial Spondyloarthritis

Axial spondyloarthritis (axial-SpA) is a multifactorial disease characterized by inflammation in sacroiliac joints and spine, bone reabsorption, and aberrant bone deposition, which may lead to ankylosis. Disease pathogenesis depends on genetic, immunological, mechanical, and bioenvironmental factors. HLA-B27 represents the most important genetic factor, although the disease may also develop in its absence. This MHC class I molecule has been deeply studied from a molecular point of view. Different theories, including the arthritogenic peptide, the unfolded protein response, and HLA-B27 homodimers formation, have been proposed to explain its role. From an immunological point of view, a complex interplay between the innate and adaptive immune system is involved in disease onset. Unlike other systemic autoimmune diseases, the innate immune system in axial-SpA has a crucial role marked by abnormal activity of innate immune cells, including γδ T cells, type 3 innate lymphoid cells, neutrophils, and mucosal-associated invariant T cells, at tissue-specific sites prone to the disease. On the other hand, a T cell adaptive response would seem involved in axial-SpA pathogenesis as emphasized by several studies focusing on TCR low clonal heterogeneity and clonal expansions as well as an interindividual sharing of CD4/8 T cell receptors. As a result of this immune dysregulation, several proinflammatory molecules are produced following the activation of tangled intracellular pathways involved in pathomechanisms of axial-SpA. This review aims to expand the current understanding of axial-SpA pathogenesis, pointing out novel molecular mechanisms leading to disease development and to further investigate potential therapeutic targets.

Genetically encoded Runx3 and CD4+ intestinal epithelial lymphocyte deficiencies link SKG mouse and human predisposition to spondyloarthropathy

Disturbances in immune regulation, intestinal dysbiosis and inflammation characterize ankylosing spondylitis (AS), which is associated with RUNX3 loss-of-function variants. ZAP70^W163C mutant (SKG) mice have reduced ZAP70 signaling, spondyloarthritis and ileitis. In small intestine, Foxp3⁺ regulatory T cells (Treg) and CD4⁺CD8αα⁺TCRαβ⁺ intraepithelial lymphocytes (CD4-IEL) control inflammation. TGF-β and retinoic acid (RA)-producing dendritic cells and MHC-class II⁺ intestinal epithelial cells (IEC) are required for Treg and CD4-IEL differentiation from CD4⁺ conventional or Treg precursors, with upregulation of Runx3 and suppression of ThPOK. We show in SKG mouse ileum, that ZAP70^W163C or ZAP70 inhibition prevented CD4-IEL but not Treg differentiation, dysregulating Runx3 and ThPOK. TGF-β/RA-mediated CD4-IEL development, T-cell IFN-γ production, MHC class-II⁺ IEC, tissue-resident memory T-cell and Runx3-regulated genes were reduced. In AS intestine, CD4-IEL were decreased, while in AS blood CD4⁺CD8⁺ T cells were reduced and Treg increased. Thus, genetically-encoded TCR signaling dysfunction links intestinal T-cell immunodeficiency in mouse and human spondyloarthropathy.

Bibliometric analysis of publications on enthesitis in spondyloarthritis in 2012-2021 based on web of science core collection databases

Enthesitis, a characteristic of spondyloarthritis, has been paid considerable attention by researchers, and numerous enthesitis-related studies have been published in recent years. However, no study has been conducted to analyze enthesitis-related researches with bibliometric methods. This study aimed to provide a broad understanding of enthesitis-related researches and explore the direction of hot topics and future research trends from a bibliometric perspective. The global literatures on enthesitis published from 2012 to 2021 were scanned in the Web of Science Core Collection databases. Visualization and bibliometric analyses were generated by an online bibliometric platform and VOSviewer software to explore the hot topics and research trends. A total of 1,181 documents were included in this study. Publications were mainly from these countries in North America and Western Europe. Among these countries, the United States was the leading country with the maximum publication counts (210), highest h-index (47), and largest collaboration network as of June 29, 2022. The most influential journal and powerful author were Journal of Rheumatology and Professor Mease PJ, respectively. Co-occurrence analysis of keywords identified that "axial spondyloarthritis", "interleukin 23", and "secukinumab" might be the future hotspots. More and more attention had been paid to enthesitis in the past 10 years. Present studies focused on the effect of inflammatory cytokines involved in the pathogenesis and the development of antibodies against these factors. These studies played a key role in understanding the research direction and subsequent management of enthesitis, and helped researchers extract hidden valuable information for further study.

Oral dextran sulfate sodium administration induces peripheral spondyloarthritis features in SKG mice accompanied by intestinal bacterial translocation and systemic Th1 and Th17 cell activation

BACKGROUND

Spondyloarthritis (SpA) is an autoimmune and autoinflammatory musculoskeletal disease characterised by systemic enthesitis. Recent research has focused on subclinical inflammatory bowel disease (IBD) in SpA pathogenesis. SKG mice, harbouring the Zap70 W163C mutation, increase autoreactive Th17 cells intrinsically, and in a conventional environment, they exhibit spontaneous arthritis with fungal factors. Under SPF conditions, they show SpA features, including enteritis, after peritoneal injection of β-1,3-glucan. This study aimed to clarify whether oral dextran sulfate sodium (DSS) administration, utilised in IBD model mice, can provoke SpA features in SKG mice under SPF conditions, focusing on the relationship between gut microorganisms and SpA pathogenesis.

METHODS

BALB/c and SKG mice were administered oral DSS, and their body weights, arthritis, and enthesitis scores were recorded. In another cohort, antibiotics (meropenem and vancomycin) or an anti-fungal agent (amphotericin B) was administered orally before DSS administration. The splenic Th1 and Th17 cell populations were examined before and after DSS administration using flow cytometry. Furthermore, the amount of circulating bacterial DNA in whole blood was measured by absolute quantitative polymerase chain reaction (qPCR), and the number and characteristics of bacterial species corresponding to these circulating DNA were analysed by next-generation sequencing (NGS).

RESULTS

Ankle enthesitis as a peripheral SpA feature was elicited in half of DSS-administered SKG mice, and none of the BALB/c mice. Pre-administration of antibiotics suppressed enthesitis, whilst an anti-fungal agent could not. Th1 and Th17 cell levels in the spleen increased after DSS administration, and this was suppressed by pre-administration of antibiotics. SKG mice have a larger amount of bacterial DNA in whole blood than BALB/c mice before and 1 day after the initiation of DSS administration. The number of bacterial species in whole blood increased after DSS administration in BALB/c and SKG mice. Some genera and species significantly specific to the DSS-treated SKG mouse group were also detected.

CONCLUSION

Oral DSS administration alone elicited peripheral enthesitis in SKG mice with bacterial translocation accompanied by increased splenic Th1 and Th17 cell levels. Pre-administration of antibiotics ameliorated these DSS-induced SpA features. These findings suggest that intestinal bacterial leakage plays a pivotal role in SpA pathogenesis.

Optimal Biologic Drugs for the Treatment of Ankylosing Spondylitis: Results from a Network Meta-Analysis and Network Metaregression

Background

Ankylosing spondylitis (AS) is a common immune-related systemic chronic inflammatory osteoarthropathy. Previous studies have proven that biologic agents, including IL-17A inhibitors (IL17Ai), TNF-α inhibitor FC fusion protein (TNFiFCP), or fully human monoclonal antibody (TNFiNMA) and JAK inhibitor (JAKi), are effective for AS treatment. Our study is aimed at comparing the clinical efficacy, tolerability, and safety of different biological agents, including novel IL-6 inhibitor (IL6i), IL-23 inhibitor (IL23i), and IL-17 A/F dual variable domain inhibitor (IL17AFi) in AS.

Method

PubMed, Scopus, Embase, CNKI, and the Cochrane Library were systematically searched. A frequentist framework network meta-analysis with a random-effects model was performed. Ranking effects were calculated by surface under the cumulative ranking analysis (SUCRA) and cluster-rank analysis.

Results

IL17AFi reported both the highest ASAS40 (SUCRA = 91.4%) and ASAS20 (SUCRA = 92.5%) response, while IL6i and IL23i reported the lowest responses (SUCRA = 6.6% and 19.9%, respectively). With the exceptions of IL6i (RR 0.60, 95% CI (0.22 to 1.67) for ASAS40 and 1.36 (0.71 to 2.58) for ASAS20) and IL23i (0.98 (0.68 to 1.40) for ASAS40 and 0.91 (0.70 to 1.19) for ASAS20), all biological drugs demonstrated statistically superior ASAS responses than placebo. TNFiFMA performed best in the suppression of disease activity (SUCRA = 77.4%, SMD 2.35, and 95% CI (1.11 to 3.59)) and functional improvement (SUCRA = 68.8%, SMD 1.67, and 95% CI (0.59 to 2.74)). There were no significant differences in tolerability or safety between biologic drugs and placebo.

Conclusions

The novel IL-17 A/F dual variable domain inhibitor, bimekizumab, may be an ideal future treatment choice for AS, while IL-23 and IL-6 inhibitors demonstrate little potential in the treatment of AS. For patients with rapid disease progression and severe functional limitation, TNF-α inhibitors, especially infliximab, are safe and effective and could be a first-line treatment choice.

Bone marrow mesenchymal stem cells-derived exosomes suppress miRNA-5189-3p to increase fibroblast-like synoviocyte apoptosis via the BATF2/JAK2/STAT3 signaling pathway

Ankylosing spondylitis (AS) is characterized by inflammation of the sacroiliac joint and the attachment point of the spine. Herein, we aimed to investigate the effect of bone marrow mesenchymal stem cells (BMSCs)-derived exosomes on apoptosis of fibroblast-like synoviocytes (FLSs) and explored its molecular mechanism. Exosomes were isolated from BMSCs and verified by transmission electron microscope and nanoparticle tracking analysis. FLSs were isolated and co-incubated with BMSC exosomes. Cell apoptosis was assessed using terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling analysis and flow cytometry. The results showed that BMSC exosomes increased apoptosis of FLSs. MiR-5189-3p was downregulated, while basic leucine zipper transcription factor ATF-like 2 (BATF2) was upregulated in FLSs by treatment of BMSC exosomes. As a direct target of miR-5189-3p, BATF2 inactivates the JAK2/STAT3 pathway. MiR-5189-3p suppressed apoptosis of FLSs and BATF2 exerted an opposite effect. In conclusion, BMSCs-derived exosomes suppress miR-5189-3p to facilitate the apoptosis of FLSs via the BATF2/JAK2/STAT3 signaling pathway, which facilitates the understanding of the therapeutic effect of BMSCs on AS and the underlying molecular mechanism.

The Potential Role of Genetics, Environmental Factors, and Gut Dysbiosis in the Aberrant Non-Coding RNA Expression to Mediate Inflammation and Osteoclastogenic/Osteogenic Differentiation in Ankylosing Spondylitis

Ankylosing spondylitis (AS) or radiographic axial spondyloarthritis is a chronic immune-mediated rheumatic disorder characterized by the inflammation in the axial skeleton, peripheral joints, and soft tissues (enthesis, fascia, and ligament). In addition, the extra-skeletal complications including anterior uveitis, interstitial lung diseases and aortitis are found. The pathogenesis of AS implicates an intricate interaction among HLA (HLA-B27) and non-HLA loci [endoplasmic reticulum aminopeptidase 1 (ERAP1), and interleukin-23 receptor (IL23R), gut dysbiosis, immune plasticity, and numerous environmental factors (infections, heavy metals, stress, cigarette smoking, etc.) The latter multiple non-genetic factors may exert a powerful stress on epigenetic regulations. These epigenetic regulations of gene expression contain DNA methylation/demethylation, histone modifications and aberrant non-coding RNAs (ncRNAs) expression, leading to inflammation and immune dysfunctions. In the present review, we shall discuss these contributory factors that are involved in AS pathogenesis, especially the aberrant ncRNA expression and its effects on the proinflammatory cytokine productions (TNF-α, IL-17 and IL-23), T cell skewing to Th1/Th17, and osteoclastogenic/osteogenic differentiation. Finally, some potential investigatory approaches are raised for solving the puzzles in AS pathogenesis.

A role for neutrophils in early enthesitis in spondyloarthritis

Background

Neutrophils are present in the early phases of spondyloarthritis-related uveitis, skin and intestinal disease, but their role in enthesitis, a cardinal musculoskeletal lesion in spondyloarthritis, remains unknown. We considered the role of neutrophils in the experimental SKG mouse model of SpA and in human axial entheses.

Methods

Early inflammatory infiltrates in the axial and peripheral entheseal sites in SKG mice were evaluated using immunohistochemistry and laser capture microdissection of entheseal tissue. Whole transcriptome analysis was carried out using Affymetrix gene array MTA 1.0, and data was analyzed via IPA. We further isolated neutrophils from human peri-entheseal bone and fibroblasts from entheseal soft tissue obtained from the axial skeleton of healthy patients and determined the response of these cells to fungal adjuvant.

Results

Following fungal adjuvant administration, early axial and peripheral inflammation in SKG mice was characterized by prominent neutrophilic entheseal inflammation. Expression of transcripts arising from neutrophils include abundant mRNA for the alarmins S100A8 and S100A9. In normal human axial entheses, neutrophils were present in the peri-entheseal bone. Upon fungal stimulation in vitro, human neutrophils produced IL-23 protein, while isolated human entheseal fibroblasts produced chemokines, including IL-8, important in the recruitment of neutrophils.

Conclusion

Neutrophils with inducible IL-23 production are present in uninflamed human entheseal sites, and neutrophils are prominent in early murine spondyloarthritis-related enthesitis. We propose a role for neutrophils in the early development of enthesitis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-021-02693-7.

Integrating imaging and biomarker assessment to better define psoriatic arthritis and predict response to biologic therapy

The treatment options for PsA have substantially expanded over the last decade. Approximately 40% of patients will not respond to first-line anti-TNF-α therapies. There is limited data to help clinicians select the most appropriate biologic therapy for PsA patients, including guidance for decisions on biologic therapy switching. In this review we will examine the current understanding of predictors of response to treatment. Imaging technology has evolved to allow us to better study psoriatic disease and define disease activity, including synovitis and enthesitis. Enthesitis is implicated in the pathogenesis, diagnosis and prognosis of PsA. It appears to be a common thread among all of the various PsA clinical presentations. Enthesitis mainly manifests as tenderness, which is difficult to distinguish from FM, chronic pain and mechanically associated enthesopathy, and it might be relevant for understanding the apparent 40% failure of existing therapy. Excess adipose tissue makes if more difficult to detect joint swelling clinically, as many PsA patients have very high BMIs. Integrating imaging and clinical assessment with biomarker analysis could help to deliver stratified medicine in PsA and allow better treatment decision making. This could include which patients require ongoing biologic therapy, which class of biologic therapy that should be, and who alternatively requires management of non-inflammatory disease.

Unexpected connections of the IL-23/IL-17 and IL-4/IL-13 cytokine axes in inflammatory arthritis and enthesitis

The IL-23/IL-17 cytokine axis is related to spondyloarthropathy (SpA) pattern diseases that target the skin, eye, gut and joints. These share overlapping target tissues with Th2 type or allergic diseases, including the skin, eye and gut but SpA diseases exhibit distinct microanatomical topography, molecular characteristics, and clinical features including uveitis, psoriasis, apical pulmonary involvement, lower gastrointestinal involvement with colitis, and related arthritides including psoriatic arthritis and ankylosing spondylitis. Inflammatory arthritis is conspicuously absent from the Th2 diseases which are characterised IL-4/IL-13 dependent pathway activation including allergic rhino-conjunctivitis, atopic eczema, allergic asthma and food allergies. This traditional understanding of non-overlap of musculoskeletal territory between that atopic diseases and the IL-17 -mediated SpA diseases is undergoing a critical reappraisal with the recent demonstration of IL-4/IL-13 blockade, may be associated with the development of SpA pattern arthritis, psoriasiform skin disease and occasional anterior uveitis. Given the known plasticity within Th paradigm pathways, these findings suggest dynamic Th2 cytokine and Th17 cytokine counter regulation in vivo in humans. Unexpected, this is the case in peripheral enthesis and when the IL-4/13 immunological brake on IL-23/17 cytokines is removed, a SpA phenotype may emerge. We discuss hitherto unexpected observations in SpA, showing counter regulation between the Th17 and Th2 pathways at sites including the entheses that collectively indicate that the emergent reverse translational therapeutic data is more than coincidental and offers new insights into the "Th paradigms" in atopy and SpA.

Targeting GM-CSF in inflammatory and autoimmune disorders

Granulocyte macrophage-colony stimulating factor (GM-CSF) was originally identified as a growth factor for its ability to promote the proliferation and differentiation in vitro of bone marrow progenitor cells into granulocytes and macrophages. Many preclinical studies, using GM-CSF deletion or depletion approaches, have demonstrated that GM-CSF has a wide range of biological functions, including the mediation of inflammation and pain, indicating that it can be a potential target in many inflammatory and autoimmune conditions. This review provides a brief overview of GM-CSF biology and signaling, and summarizes the findings from preclinical models of a range of inflammatory and autoimmune disorders and the latest clinical trials targeting GM-CSF or its receptor in these disorders.

Inflammatory Foot Involvement in Spondyloarthritis: From Tarsitis to Ankylosing Tarsitis

Spondyloarthritis (SpA) is a group that includes a wide spectrum of clinically similar diseases manifested by oligoarticular arthritis and axial or peripheral ankylosis. Although axial SpA is predominant in Caucasians and adult-onset patients, juvenile-onset and Latin American patients are characterized by severe peripheral arthritis and particularly foot involvement. The peripheral involvement of SpA can vary from tarsal arthritis to the most severe form named ankylosing tarsitis (AT). Although the cause and etiopathogenesis of axSpA are often studied, the specific characteristics of pSpA are unknown. Several animal models of SpA develop initial tarsitis and foot ankylosis as the main signs, emphasizing the role of foot inflammation in the overall SpA spectrum. In this review, we attempt to highlight the clinical characteristics of foot involvement in SpA and update the knowledge regarding its pathogenesis, focusing on animal models and the role of mechanical forces in inflammation.

Treatment of Connective Tissue Disease-Related Intractable Disease with Biological Therapeutics

The treatment of connective tissue disease (CTD) and CTD-related intractable diseases (CTD-IDs) currently depends on the use of steroid therapy. Approximately 20 years have passed since the approval of infliximab for rheumatoid arthritis in 2003. Since then, several biological therapeutics have been marketed and adapted for many CTDs and CTD-IDs other than rheumatoid arthritis. Although conventional treatment for patients with these diseases is rarely used because of their poor prognosis, these cases may benefit from biological therapeutics. However, choosing biological therapeutics is difficult because they have different target molecules compared with conventional therapeutics. In this review, we address the current situation of biological therapeutics for CTD-IDs including Behcet's disease, psoriatic arthritis, ankylosing spondylitis, anti-neutrophil cytoplasmic antibody-related arthritis, and adult Still's disease, as well as the choice of biological therapeutics in clinical practice.

Paradoxical Augmentation of Experimental Spondyloarthritis by RORC Inhibition in HLA-B27 Transgenic Rats

Objective

IL-17A plays a major role in the pathogenesis of spondyloarthritis (SpA). Here we assessed the impact of inhibition of RAR related orphan receptor-γ (RORC), the key transcription factor controlling IL-17 production, on experimental SpA in HLA-B27 transgenic (tg) rats.

Methods

Experimental SpA was induced by immunization of HLA-B27 tg rats with heat-inactivated Mycobacterium tuberculosis. Splenocytes obtained at day 7, 14 and 21 after immunization were restimulated ex vivo to assess the induction of pro-inflammatory cytokines. Rats were then prophylactically treated with a RORC inhibitor versus vehicle control. The biologic effect of RORC inhibition was assessed by pro-inflammatory cytokine expression in draining lymph nodes. Arthritis and spondylitis were monitored clinically, and the degree of peripheral and axial inflammation, destruction and new bone formation was confirmed by histology.

Results

Ex vivo mRNA and protein analyses revealed the rapid and selective induction of IL-17A and IL-22 production by a variety of lymphocyte subsets upon disease induction in HLA-B27 tg rats. Prophylactic RORC inhibition in vivo suppressed the expression of IL-17A, IL17F, and IL-22 without affecting the expression of other T helper cell subset related genes. This biological effect did not translate into clinical efficacy as RORC inhibition significantly accelerated the onset of arthritis and spondylitis, and aggravated the clinical severity of arthritis. This worsening of experimental SpA was confirmed by histopathological demonstration of increased inflammation, destruction, and new bone formation.

Conclusion

Despite a significant suppression of the IL-17 axis, RORC inhibitor treatment accelerates and aggravates experimental SpA in the HLA-B27 tg rat model.

Targeting the Interleukin-23/Interleukin-17 Inflammatory Pathway: Successes and Failures in the Treatment of Axial Spondyloarthritis

The IL-23/IL-17 pathway has been implicated in the etiopathogenesis of axial spondyloarthritis through studies of genetic polymorphisms associated with disease, an animal model with over-expression of IL-23 that resembles human disease, and observations that cytokines in this pathway can be found at the site of disease in both humans and animal models. However, the most direct evidence has emerged from clinical trials of agents targeting cytokines in this pathway. Monoclonal antibodies targeting IL-17A have been shown to ameliorate signs and symptoms, as well as MRI inflammation in the spine and sacroiliac joints, in patients with radiographic and non-radiographic axial spondyloarthritis. This was evident in patients refractory to non-steroidal anti-inflammatory agents as well as patients failing treatment with tumor necrosis factor inhibitor therapies. Treatment with a bispecific antibody targeting both IL-17A and IL-17F was also effective in a phase II study. Post-hoc analyses have even suggested a potential disease-modifying effect in reducing development of spinal ankylosis. However, benefits for extra-articular manifestations were limited to psoriasis and did not extend to colitis and uveitis. Conversely, trials of therapies targeting IL-23 did not demonstrate any significant impact on signs, symptoms, and MRI inflammation in axial spondyloarthritis. These developments coincide with recent observations that expression of these cytokines is evident in many different cell types with roles in innate as well as adaptive immunity. Moreover, evidence has emerged for the existence of both IL-23-dependent and IL-23-independent pathways regulating expression of IL-17, potentially associated with different roles in intestinal and axial skeletal inflammation.

Complexity of enthesitis and new bone formation in ankylosing spondylitis: current understanding of the immunopathology and therapeutic approaches

Despite increasing availability of treatments for spondyloarthritis (SpA) including tumour necrosis factor (TNF) and interleukin-17 (IL-17) inhibitors, there is no established treatment that abates new bone formation (NBF) in ankylosing spondylitis (AS), a subset of SpA. Recent research on TNF has revealed the increased level of transmembrane TNF in the joint tissue of SpA patients compared to that of rheumatoid arthritis patients, which appears to facilitate TNF-driven osteo-proliferative changes in AS. In addition, there is considerable interest in the central role of IL-23/IL-17 axis in type 3 immunity and the therapeutic potential of blocking this axis to ameliorate enthesitis and NBF in AS. AS immunopathology involves a variety of immune cells, including both innate and adoptive immune cells, to orchestrate the immune response driving type 3 immunity. In response to external stimuli of inflammatory cytokines, local osteo-chondral progenitor cells activate intra-cellular anabolic molecules and signals involving hedgehog, bone morphogenetic proteins, receptor activator of nuclear factor kappa-B ligand, and Wnt pathways to promote NBF in AS. Here, we provide an overview of the current immunopathology and future directions for the treatment of enthesitis and NBF associated with AS.

STAT3 phosphorylation inhibition for treating inflammation and new bone formation in ankylosing spondylitis

OBJECTIVE

AS is a rheumatic disease characterized by chronic inflammation and bony ankylosis. This study was to evaluate whether a signal transducer and activator of transcription 3 phosphorylation inhibitor (stat3-p Inh) could treat both chronic inflammation and bone formation in AS.

METHODS

Primary AS osteoprogenitor cells and spinal entheseal cells were examined for osteogenic differentiation. SF mononuclear cells (SFMCs) and lamina propria mononuclear cells (LPMCs) were obtained from AS patients. Inflammatory cytokine-producing cells were analysed using flow cytometry and ELISA. Female SKG mice were treated with stat3-p Inh, IL-17A blocker or vehicle. Inflammation and new bone formation were evaluated using immunohistochemistry, PET and micro-CT.

RESULTS

In the SKG mouse model, stat3-p Inh significantly suppressed arthritis, enthesitis, spondylitis and ileitis. In experiments culturing SFMCs and LPMCs, the frequencies of IFN-γ-, IL-17A- and TNF-α-producing cells were significantly decreased after stat3-p Inh treatment. When comparing current treatments for AS, stat3-p Inh showed a comparable suppression effect on osteogenesis to Janus kinase inhibitor or IL-17A blocker in AS-osteoprogenitor cells. Stat3-p Inh suppressed differentiation and mineralization of AS-osteoprogenitor cells and entheseal cells toward osteoblasts. Micro-CT analysis of hind paws revealed less new bone formation in stat3-p Inh-treated mice than vehicle-treated mice (P = 0.005). Hind paw and spinal new bone formation were similar between stat3-p Inh- and anti-IL-17A-treated SKG mice (P = 0.874 and P = 0.117, respectively).

CONCLUSION

Stat-3p inhibition is a promising treatment for both inflammation and new bone formation in AS.

Ixekizumab: an IL-17A inhibitor for the treatment of axial Spondylarthritis

INTRODUCTION

Axial spondyloarthritis (axSpA) is an inflammatory arthritis which affects primarily the entheses of the spine and sacroiliac joints with peripheral joint synovitis and extra-articular manifestations. In 2017, the first IL-17A inhibitor (IL-17Ai) secukinumab was approved for the treatment of radiographic axSpA not responding adequately to conventional therapies, and this was followed in 2019 by a second IL-17Ai, ixekizumab. These agents represent the first alternative class of biological treatments after the TNF inhibitor which dominated the therapeutic landscape of axSpA for over a decade.

AREAS COVERED

This review discusses the role of IL-17Ais in the treatment in axSpA focusing on the newest IL-17Ai ixekizumab. It provides a detailed overview of the drug pharmacodynamic, pharmacokinetics, and clinical trial data, including areas of future research needed in the post-marketing era.

EXPERT OPINION

Early trials of ixekizumab for axSpA have shown encouraging results and an acceptable safety profile. Future phase IV trials should focus on direct head-to-head comparisons between ixekizumab and other biologic drugs, and stratify patients according to important disease characteristics known to affect treatment response including sex, HLA-B27 status, presence of MRI bone marrow edema at baseline, disease duration and any extra-articular manifestations.

Inflammasome Activation in Ankylosing Spondylitis Is Associated With Gut Dysbiosis

OBJECTIVE

We undertook this study to evaluate the activation and functional relevance of inflammasome pathways in ankylosing spondylitis (AS) patients and rodent models and their relationship to dysbiosis.

METHODS

An inflammasome pathway was evaluated in the gut and peripheral blood from 40 AS patients using quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR), immunohistochemistry (IHC), flow cytometry, and confocal microscopy, and was compared to that of 20 healthy controls and 10 patients with Crohn's disease. Bacteria was visualized using silver stain in human samples, and antibiotics were administered to HLA-B27-transgenic rats. The NLRP3 inhibitor MCC950 was administered to SKG mice, and ileal and joint tissues were assessed by IHC analysis and real-time qRT-PCR. The role of inflammasome in modulating the interleukin-23 (IL-23)/IL-17 axis was studied ex vivo.

RESULTS

Expression levels of Nlrp3, Nlrc4, and Aim2 were increased in the gut of HLA-B27-transgenic rats and reduced by antibiotic treatment (P < 0.05). In curdlan-treated SKG mice, NLRP3 blockade prevented ileitis and delayed arthritis onset (P < 0.05). Compared to healthy controls, AS patients demonstrated overexpression of NLRP3 (fold induction 2.33 versus 22.2; P < 0.001), NLRC4 (fold induction 1.90 versus 6.47; P < 0.001), AIM2 (fold induction 2.40 versus 20.8; P < 0.001), CASP1 (fold induction 2.53 versus 24.8; P < 0.001), IL1B (fold induction 1.07 versus 10.93; P < 0.001), and IL18 (fold induction 2.56 versus 15.67; P < 0.001) in the ileum, and caspase 1 activity was increased (P < 0.01). The score of adherent and invasive mucosa-associated bacteria was higher in AS (P < 0.01) and correlated with the expression of inflammasome components in peripheral blood mononuclear cells (P < 0.001). NLRP3 expression was associated with disease activity (the Ankylosing Spondylitis Disease Activity Score using the C-reactive protein level) (r² = 0.28, P < 0.01) and with IL23A expression (r² = 0.34, P < 0.001). In vitro, inflammasome activation in AS monocytes was paralleled by increased serum levels of IL-1β and IL-18. Induction of IL23A, IL17A, and IL22 was IL-1β-dependent.

CONCLUSION

Inflammasome activation occurs in rodent models of AS and in AS patients, is associated with dysbiosis, and is involved in triggering ileitis in SKG mice. Inflammasomes drive type III cytokine production with an IL-1β-dependent mechanism in AS patients.

The Role of the IL-23/IL-17 Axis in Disease Initiation in Spondyloarthritis: Lessons Learned From Animal Models

Spondyloarthritis (SpA) is a spectrum of chronic inflammatory joint diseases that frequently presents with inflammation of the axial skeleton, peripheral joints, entheses, skin, and gut. Understanding SpA pathogenesis has been proven challenging due to the limited availability of human target tissues. In recent years, the interleukin (IL)-23/IL-17 pathway has been implicated in the pathogenesis of SpA, in addition to the Tumor Necrosis Factor Alpha (TNF-α) cytokine. The underlying molecular mechanisms by which the IL-23/IL-17 pathway triggers disease initiation, both in the joints as well as at extra-musculoskeletal sites, are not precisely known. Animal models that resemble pathological features of human SpA have provided possibilities for in-depth molecular analyses of target tissues during various phases of the disease, including the pre-clinical initiation phase of the disease before arthritis and spondylitis are clinically present. Herein, we summarize recent insights gained in SpA animal models on the role of the IL-23/IL-17 pathway in immune activation across affected sites in SpA, which include the joint, entheses, gut and skin. We discuss how local activation of the IL-23/IL-17 axis may contribute to the development of tissue inflammation and the onset of clinically manifest SpA. The overall aim is to provide the reader with an overview of how the IL-23/IL-17 axis could contribute to the onset of SpA pathogenesis. We discuss how insights from animal studies into the initiation phase of disease could instruct validation studies in at-risk individuals and thereby provide a perspective for potential future preventive treatment.

Ankylosing spondylitis: an autoimmune or autoinflammatory disease?

Ankylosing spondylitis (AS) is a chronic inflammatory disorder of unknown aetiology. Unlike other systemic autoimmune diseases, in AS, the innate immune system has a dominant role characterized by aberrant activity of innate and innate-like immune cells, including γδ T cells, group 3 innate lymphoid cells, neutrophils, mucosal-associated invariant T cells and mast cells, at sites predisposed to the disease. The intestine is involved in disease manifestations, as it is at the forefront of the interaction between the mucosal-associated immune cells and the intestinal microbiota. Similarly, biomechanical factors, such as entheseal micro-trauma, might also be involved in the pathogenesis of the articular manifestation of AS, and sentinel immune cells located in the entheses could provide links between local damage, genetic predisposition and the development of chronic inflammation. Although these elements might support the autoinflammatory nature of AS, studies demonstrating the presence of autoantibodies (such as anti-CD74, anti-sclerostin and anti-noggin antibodies) and evidence of activation and clonal expansion of T cell populations support an autoimmune component to the disease. This Review presents the evidence for autoinflammation and the evidence for autoimmunity in AS and, by discussing the pathophysiological factors associated with each, aims to reconcile the two hypotheses.

[Update: enterogenic spondylarthritis]

Spondylarthritis (SpA) is one of the most frequent extraintestinal manifestations of chronic inflammatory bowel disease (IBD). Several arthritogenic enterobacterial infections can induce sequelae such as reactive SpA. Studies on the gut-synovium axis in view of genetic, immunological, clinical and therapeutic aspects has made enterogenic SpA a model disease of all forms of SpA. The same applies for investigating IBD, as subclinical gut inflammation seen in SpA patients has provided significant evidence for a better understanding of mucosa-associated early immune events in Crohn's disease (CD). This article summarizes the pathognomonic clinical features, diagnostic steps, differential diagnosis and current pathogenetic models of enterogenic SpA. Knowledge of pathogenetic contexts leads to concrete treatment recommendations. These vary individually depending on the underlying IBD, on the inflammatory intestinal or rheumatic activity and on the rheumatological manifestation pattern.

Anti-IL-17 Agents in the Treatment of Axial Spondyloarthritis

Axial spondyloarthritis (axSpA) describes a group of chronic inflammatory rheumatic diseases primarily involving the axial skeleton. IL-17 is involved in the pathogenesis of numerous inflammatory diseases, including inflammatory arthritis. Until a few years ago, the only biological agents licensed for the treatment of axSpA and nr-axSpA were TNF inhibitors. However, as some patients did not respond to TNF inhibition or experienced secondary failure, the introduction of the first two IL-17 inhibitors (secukinumab [SEC] and ixekizumab [IXE]) has extended the treatment options, and there are now three others (bimekizumab, brodalumab and netakimab) in various stages of clinical development. The last ten years have seen the development of a number of therapeutic recommendations that aimed at improving the management of axSpA patients. The aim of this narrative review of the published literature concerning the role of IL-17 in the pathogenesis of SpA, and the role of IL-17 inhibitors in the treatment of axSpA, is to provide a comprehensive picture of the clinical efficacy and safety of the drugs themselves, and the treatment strategies recommended in the international guidelines.

Streptococcus species enriched in the oral cavity of patients with RA are a source of peptidoglycan-polysaccharide polymers that can induce arthritis in mice

OBJECTIVES

Analysis of oral dysbiosis in individuals sharing genetic and environmental risk factors with rheumatoid arthritis (RA) patients may illuminate how microbiota contribute to disease susceptibility. We studied the oral microbiota in a prospective cohort of patients with RA, first-degree relatives (FDR) and healthy controls (HC), then genomically and functionally characterised streptococcal species from each group to understand their potential contribution to RA development.

METHODS

After DNA extraction from tongue swabs, targeted 16S rRNA gene sequencing and statistical analysis, we defined a microbial dysbiosis score based on an operational taxonomic unit signature of disease. After selective culture from swabs, we identified streptococci by sequencing. We examined the ability of streptococcal cell walls (SCW) from isolates to induce cytokines from splenocytes and arthritis in ZAP-70-mutant SKG mice.

RESULTS

RA and FDR were more likely to have periodontitis symptoms. An oral microbial dysbiosis score discriminated RA and HC subjects and predicted similarity of FDR to RA. Streptococcaceae were major contributors to the score. We identified 10 out of 15 streptococcal isolates as S. parasalivarius sp. nov., a distinct sister species to S. salivarius. Tumour necrosis factor and interleukin 6 production in vitro differed in response to individual S. parasalivarius isolates, suggesting strain specific effects on innate immunity. Cytokine secretion was associated with the presence of proteins potentially involved in S. parasalivarius SCW synthesis. Systemic administration of SCW from RA and HC-associated S. parasalivarius strains induced similar chronic arthritis.

CONCLUSIONS

Dysbiosis-associated periodontal inflammation and barrier dysfunction may permit arthritogenic insoluble pro-inflammatory pathogen-associated molecules, like SCW, to reach synovial tissue.

Recent Updates in the Immunopathology of Type 3 Immunity-Mediated Enthesitis

PURPOSE OF REVIEW

Enthesitis is a cardinal feature of spondyloarthritis (SpA). Despite increasing available treatments, challenges remain in adequately controlling inflammation and subsequent new bone formation (NBF) in entheses; thus, a better understanding of the immunopathogenesis is warranted.

RECENT FINDINGS

Increasing evidence has identified immune cells playing key roles in enthesitis such as γδ T cells and group 3 innate lymphoid cells (ILC3), possibly with site-specific regulatory systems. The presence of T cells producing interleukin (IL)-17 independent of IL-23 in human spinal entheses was recently reported, which may corroborate the discrepancy between recent clinical trials and pre-clinical studies. In addition, the contribution of myeloid cells has also been focused in both human and pre-clinical SpA models. Moreover, not only the IL-23/IL-17 signaling, but other key type 3 immunity mediators, such as IL-22 and granulocyte-macrophage colony-stimulating factor (GM-CSF), have been reported as pivotal cytokines in inflammation and NBF of entheses. Immune cells demonstrating distinct features orchestrate entheses, leading to the complex landscape of enthesitis. However, recent advances in understanding the immunopathogenesis may provide new therapeutic targets and future research directions.

Alterations of the Skin and Gut Microbiome in Psoriasis and Psoriatic Arthritis

Numerous scientific studies in recent years have shown significant skin and gut dysbiosis among patients with psoriasis. A significant decrease in microbiome alpha-diversity (abundance of different bacterial taxa measured in one sample) as well as beta-diversity (microbial diversity in different samples) was noted in psoriasis skin. It has been proven that the representation of Cutibacterium, Burkholderia spp., and Lactobacilli is decreased and Corynebacterium kroppenstedii, Corynebacterium simulans, Neisseria spp., and Finegoldia spp. increased in the psoriasis skin in comparison to healthy skin. Alterations in the gut microbiome in psoriasis are similar to those observed in patients with inflammatory bowel disease. In those two diseases, the F. prausnitzii, Bifidobacterium spp., Lactobacillus spp., Parabacteroides and Coprobacillus were underrepresented, while the abundance of Salmonella sp., Campylobacter sp., Helicobacter sp., Escherichia coli, Alcaligenes sp., and Mycobacterium sp. was increased. Several research studies provided evidence for the significant influence of psoriasis treatments on the skin and gut microbiome and a positive influence of orally administered probiotics on the course of this dermatosis. Further research is needed to determine the influence of the microbiome on the development of inflammatory skin diseases. The changes in microbiome under psoriasis treatment can serve as a potential biomarker of positive response to the administered therapy.

The arthritis connection to inflammatory bowel disease (IBD): why has it taken so long to understand it?

Inflammatory bowel disease (IBD) associated arthritis is a subgroup of spondyloarthritis (SpA) that has suffered from lack of recognition in rheumatology clinical and research circles for over 100 years. Although clinically distinguishable from rheumatoid arthritis and ankylosing spondylitis, it took advances in detection systems in the middle of the last century (rheumatoid factor, HLA-B27) to convincingly make the final separations. We now know that significant numbers of patients with SpA have associated clinical IBD and almost half of them show subclinical gut inflammation, yet the connection between the gut and the musculoskeletal system has remained a vexing problem. Two publications from Nathan Zvaifler (one in 1960, the other in 1975) presciently described the relationship between the gut and the spine/peripheral joints heralding much of the work present today in laboratories around the world trying to examine basic mechanisms for the connections (there are likely to be many) between the gut, the environment (presumably our intestinal flora) and the downstream effect on the musculoskeletal system. The role of dysregulated microbiome along with microbiome-driven T helper 17 cell expansion and immune cell migration to the joints has been recognised, all of which occur in the appropriate context of genetic background inside and outside of the human leucocyte antigen system. Moreover, different adhesion molecules that mediate immune cells homing to the gut and joints have been noted. In this review, we studied the origins and evolution of IBD-arthritis, proposed pathogenic mechanisms and the current gaps that need to be filled for a complete understanding of IBD-arthritis.

Why Inhibition of IL-23 Lacked Efficacy in Ankylosing Spondylitis

The term spondyloarthritis pertains to both axial and peripheral arthritis including ankylosing spondylitis (AS) and psoriatic arthritis (PsA), which is strongly linked to psoriasis and also the arthritis associated with inflammatory bowel disease. The argument supporting the role for IL-23 across the spectrum of SpA comes from 4 sources. First, genome wide associated studies (GWAS) have shown that all the aforementioned disorders exhibit IL-23R pathway SNPs, whereas HLA-B27 is not linked to all of these diseases-hence the IL-23 pathway represents the common genetic denominator. Secondly, experimental animal models have demonstrated a pivotal role for the IL-23/IL-17 axis in SpA related arthropathy that initially manifests as enthesitis, but also synovitis and axial inflammation and also associated aortic root and cutaneous inflammation. Thirdly, the emergent immunology of the human enthesis also supports the presence of IL-23 producing myeloid cells, not just at the enthesis but in other SpA associated sites including skin and gut. Finally, drugs that target the IL-23 pathway show excellent efficacy for skin disease, efficacy for IBD and also in peripheral arthropathy associated with SpA. The apparent failure of IL-23 blockade in the AS which is effectively a spinal polyenthesitis but evidence for efficacy of IL-23 inhibition for peripheral enthesitis in PsA and preliminary suggestions for benefit in axial PsA, raises many questions. Key amongst these is whether spinal inflammation may exhibit entheseal IL-17A production independent of IL-23 but peripheral enthesitis is largely dependent on IL-23 driven IL-17 production. Furthermore, IL-23 blocking strategies in animal models may prevent experimental SpA evolution but not prevent established disease, perhaps pointing towards a role for IL-23 in innate immune disease initiation whereas persistent disease is dependent on memory T-cell responses that drive IL-17A production independently of IL-23, but this needs further study. Furthermore, IL-12/23 posology in inflammatory bowel disease is substantially higher than that used in AS trials which merits consideration. Therefore, the IL-23 pathway is centrally involved in the SpA concept but the nuances and intricacies in axial inflammation that suggest non-response to IL-23 antagonism await formal definition. The absence of comparative immunology between the different skeletal sites renders explanations purely hypothetical at this juncture.

IL-33 promotes anemia during chronic inflammation by inhibiting differentiation of erythroid progenitors

An important comorbidity of chronic inflammation is anemia, which may be related to dysregulated activity of hematopoietic stem and progenitor cells (HSPCs) in the bone marrow (BM). Among HSPCs, we found that the receptor for IL-33, ST2, is expressed preferentially and highly on erythroid progenitors. Induction of inflammatory spondyloarthritis in mice increased IL-33 in BM plasma, and IL-33 was required for inflammation-dependent suppression of erythropoiesis in BM. Conversely, administration of IL-33 in healthy mice suppressed erythropoiesis, decreased hemoglobin expression, and caused anemia. Using purified erythroid progenitors in vitro, we show that IL-33 directly inhibited terminal maturation. This effect was dependent on NF-κB activation and associated with altered signaling events downstream of the erythropoietin receptor. Accordingly, IL-33 also suppressed erythropoietin-accelerated erythropoiesis in vivo. These results reveal a role for IL-33 in pathogenesis of anemia during inflammatory disease and define a new target for its treatment.