Normal human enthesis harbours conventional CD4+ and CD8+ T cells with regulatory features and inducible IL-17A and TNF expression

Single-cell RNA-sequencing analysis of immune and mesenchymal cell crosstalk in the developing enthesis

Autoimmunity underlies many painful disorders, such as enthesopathies, which localize to the enthesis. From infiltration of the synovium and axial skeleton by B cells, to disturbances in the ratio of M1/M2 enthesis macrophages, to CD8 + T cell mediated inflammation, autoimmune dysregulation is becoming increasingly well characterized in enthesopathies. Tissue resident B cells, macrophages, neutrophils, and T cells have also been localized in healthy human entheses. However, the potential developmental origins, presence, and role of immune cells (ICs) in enthesis development is not known. Here, we use single-cell RNA-sequencing analysis to describe IC subtypes present in the enthesis before, during, and after mineralization, and to infer regulatory interactions between ICs and mesenchymal cells (MCs). We report the presence of nine phenotypically distinct IC subtypes, including B cells, macrophages, neutrophils, and T cells. We find that specific IC subtypes may promote MC-proliferation and differentiation, and that MCs may regulate IC phenotype and autoimmunity. Our findings suggest that bidirectional regulatory interactions between ICs and MCs may be important to enthesis mineralization, and suggest that progenitor MCs have a unique ability to limit autoimmunity during development.

GRAPPA 2023 Debate: Is Psoriatic Disease Really a Primary Enthesitis That Drives Joint Synovitis? The Enthesitis Hypothesis 25 Years On

The enthesitis hypothesis posits that enthesitis is a primary lesion and that inflammation at the enthesis initiates the musculoskeletal symptoms of psoriatic arthritis (PsA) and spondyloarthropathies (SpA). The hypothesis suggested that inflamed entheseal tissue near the synovium could trigger cytokine-mediated synovitis, that enthesis bone anchorage could explain osteitis, and that the location of entheses at the soft tissue interface could explain dactylitis. Advances in imaging techniques that allow better visualization of enthesitis lesions and the development of animal models have allowed evolution of the concept of enthesitis as a central mechanistic driver of musculoskeletal symptoms in PsA and SpA. A debate between Drs. Dennis McGonagle and Bruce Kirkham at the Group for Research on Psoriasis and Psoriatic Arthritis (GRAPPA) 2023 annual meeting discussed the data supporting and refuting this hypothesis in PsA and SpA, respectively. The major points of this debate are summarized in this article.

Dendritic epidermal T cell hydrogel induces the polarization of M2 macrophages to promote the healing of deep tissue pressure injury

Dendritic epidermal T cells (DETCs) have been shown to promote wound healing. However, the mechanisms involved need to be better understood. In the present study, we investigated the role and mechanism of DETCs in deep tissue pressure injury (DTPI). We established the DTPI model using C57BL/6 mice. Then, DTPI was evaluated and analyzed by histological staining, immunohistochemistry, real-time PCR, Western blotting, and flow cytometry in different treatment groups (DETCs, DETCs/gel, Matrigel, Saline, and Normal group). The results showed that insulin-like growth factor 1 and vascular endothelial growth factor-A expression increased after local DETCs and DETCs/gel implantation in DTPI on days 3 and 7. M1 (inducible nitric oxide synthas-marked) macrophages were predominant at 3 days after DTPI. At 7 days, M1 macrophages were decreased, and M2 (CD206-marked) macrophages were increased in the DETCs and DETCs/gel groups. In vitro, in the co-culture of DETCs and RAW264.7, CD206 expression was significantly increased in M2 macrophages. In addition, Interleukin-17A initially inhibited wound healing 1 day after injury. However, it promoted wound healing at 7, 14, and 21 days after treatment with DETCs and DETCs/gel, respectively. In conclusion, our data suggest that exogenous DETCs improve DTPI wound healing by regulating M1 to M2 macrophage polarization.

Early psoriatic arthritis: when is the right time to start advanced therapy?

Despite significant advances in the treatment of psoriatic arthritis (PsA) in the last two decades, remission remains elusive and there is no cure. Evidence from rheumatoid arthritis (RA) confirming enhanced response and outcome from earlier treatment intervention suggests the plausibility of the window of opportunity in the pathogenesis of RA. Yet, data are lacking in PsA. Although treatment response may be enhanced in shorter disease duration, it is unknown how this early intervention may impact long-term outcomes. Furthermore, it remains to be demonstrated whether there is a best treatment strategy and time of intervention. Crucially, the main hurdle when aiming for early treatment intervention is the ability to achieve a timely diagnosis that highlights the need to focus research efforts on characterizing the very early disease stages including the transition to PsA in the at-risk psoriasis population.

Lymphocyte homing and recirculation with tumor tertiary lymphoid structure formation: predictions for successful cancer immunotherapy

The capacity of lymphocytes continuously home to lymphoid structures is remarkable for cancer immunosurveillance and immunotherapy. Lymphocyte homing and recirculation within the tumor microenvironment (TME) are now understood to be adaptive processes that are regulated by specialized cytokines and adhesion molecule signaling cascades. Restricted lymphocyte infiltration and recirculation have emerged as key mechanisms contributing to poor responses in cancer immunotherapies like chimeric antigen receptor (CAR)-T cell therapy and immune checkpoint blockades (ICBs). Uncovering the kinetics of lymphocytes in tumor infiltration and circulation is crucial for improving immunotherapies. In this review, we discuss the current insights into the adhesive and migrative molecules involved in lymphocyte homing and transmigration. The potential mechanisms within the TME that restrain lymphocyte infiltration are also summarized. Advanced on these, we outline the determinates for tertiary lymphoid structures (TLSs) formation within tumors, placing high expectations on the prognostic values of TLSs as therapeutic targets in malignancies.

Investigation of the Shared Biomarkers in Heterotopic Ossification Between Ossification of the Ligamentum Flavum and Ankylosing Spondylitis

STUDY DESIGN

Bioinformatics analysis of Gene Expression Omnibus (GEO).

OBJECTIVE

Ossification of the ligamentum flavum (OLF) and ankylosing spondylitis (AS) represent intricate conditions marked by the gradual progression of endochondral ossification. This investigation endeavors to unveil common biomarkers associated with heterotopic ossification and explore the potential molecular regulatory mechanisms.

METHODS

Microarray and RNA-sequencing datasets retrieved from the Gene Expression Omnibus (GEO) repository were harnessed to discern differentially expressed genes (DEGs) within the OLF and AS datasets. Subsequently, Weighted Gene Co-expression Network Analysis (WGCNA) was implemented to pinpoint co-expression modules linked to OLF and AS. Common genes were further subjected to an examination of functional pathway enrichment. Moreover, hub intersection genes were identified using the Least Absolute Shrinkage and Selection Operator (LASSO) regression, followed by an evaluation of diagnostic performance in external OLF and AS cohorts. Lastly, an analysis of immune cell infiltration was conducted to scrutinize the correlation of immune cell presence with shared biomarkers in OLF and AS.

RESULTS

A total of 1353 and 91 Differentially Expressed Genes (DEGs) were identified in OLF and AS, respectively. Using the Weighted Gene Co-expression Network Analysis (WGCNA), 2 modules were found to be notably significant for OLF and AS. The integrative bioinformatic analysis revealed 3 hub genes (MAB21L2, MEGF10, ISLR) as shared risk biomarkers, with MAB21L2 being the central focus. Receiver Operating Characteristic (ROC) analysis exhibited a strong diagnostic potential for these hub genes. Gene Ontology (GO) analysis indicated their involvement in the positive regulation of myoblast proliferation. Notably, MAB21L2 was singled out as the optimal common biomarker for OLF and AS. Furthermore, an analysis of immune infiltration demonstrated a correlation between MAB21L2 expression and changes in immune cells. Activated CD8 T cells were identified as shared differential immune infiltrating cells significantly linked to MAB21L2 in both OLF and AS.

CONCLUSION

This study represents the first instance of identifying MAB21L2 as a prospective diagnostic marker for patients contending with OLF associated with AS. The research results indicate that the ECM-receptor interaction and the cell-cell adhesion may play a role in both disease processes. This newfound knowledge not only enhances our understanding of the pathogenesis behind spinal ligament ossification but also uncovers potential targets for therapeutic interventions.

Sequence of Events in the Pathogenesis of Axial Spondyloarthritis: A Current Review-2023 SPARTAN Meeting Proceedings

PURPOSE OF REVIEW

Over the past two decades, significant progress has been made to untangle the etiology of inflammation and new bone formation (NBF) associated with axial spondyloarthritis (axSpA). However, exact mechanisms as to how the disease initiates and develops remain elusive.

RECENT FINDINGS

Type 3 immunity, centered around the IL-23/IL-17 axis, has been recognized as a key player in the pathogenesis of axSpA. Multiple hypotheses associated with HLA-B*27 have been proposed to account for disease onset and progression of axSpA, potentially by driving downstream T cell responses. However, HLA-B*27 alone is not sufficient to fully explain the development of axSpA. Genome-wide association studies (GWAS) identified several genes that are potentially relevant to disease pathogenesis leading to a better understanding of the immune activation seen in axSpA. Furthermore, gut microbiome studies suggest an altered microbiome in axSpA, and animal studies suggest a pathogenic role for immune cells migrating from the gut to the joint. Recent studies focusing on the pathogenesis of new bone formation (NBF) have highlighted the importance of endochondral ossification, mechanical stress, pre-existing inflammation, and activated anabolic signaling pathways during the development of NBF. Despite the complex etiology of axSpA, recent studies have shed light on pivotal pieces that could lead to a better understanding of the pathogenic events in axSpA.

Patients with ankylosing spondylitis present a distinct CD8 T cell subset with osteogenic and cytotoxic potential

OBJECTIVES

Ankylosing spondylitis (AS) is a chronic inflammatory rheumatic disease affecting mainly the axial skeleton. Peripheral involvement (arthritis, enthesitis and dactylitis) and extra-musculoskeletal manifestations, including uveitis, psoriasis and bowel inflammation, occur in a relevant proportion of patients. AS is responsible for chronic and severe back pain caused by local inflammation that can lead to osteoproliferation and ultimately spinal fusion. The association of AS with the human leucocyte antigen-B27 gene, together with elevated levels of chemokines, CCL17 and CCL22, in the sera of patients with AS, led us to study the role of CCR4+ T cells in the disease pathogenesis.

METHODS

CD8+CCR4+ T cells isolated from the blood of patients with AS (n=76) or healthy donors were analysed by multiparameter flow cytometry, and gene expression was evaluated by RNA sequencing. Patients with AS were stratified according to the therapeutic regimen and current disease score.

RESULTS

CD8+CCR4+ T cells display a distinct effector phenotype and upregulate the inflammatory chemokine receptors CCR1, CCR5, CX3CR1 and L-selectin CD62L, indicating an altered migration ability. CD8+CCR4+ T cells expressing CX3CR1 present an enhanced cytotoxic profile, expressing both perforin and granzyme B. RNA-sequencing pathway analysis revealed that CD8+CCR4+ T cells from patients with active disease significantly upregulate genes promoting osteogenesis, a core process in AS pathogenesis.

CONCLUSIONS

Our results shed light on a new molecular mechanism by which T cells may selectively migrate to inflammatory loci, promote new bone formation and contribute to the pathological ossification process observed in AS.

From PsO to PsA: the role of TRM and Tregs in psoriatic disease, a systematic review of the literature

Introduction

Psoriasis (PsO) is a chronic skin condition driven by immune mediators like TNFα, INFγ, IL-17, and IL-23. Psoriatic arthritis (PsA) can develop in PsO patients. Although psoriatic lesions may apparently resolve with therapy, subclinical cutaneous inflammation may persist. The role of tissue-resident memory T-cells (TRM), and regulatory T cells (Tregs) that also contribute to chronic inflammation are being explored in this context. This systematic review explores TRM and Tregs in psoriatic disease (PsD) and its progression.

Methods

A systematic review, following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, was performed using Pubmed® and Web of Science™ databases on June 3rd 2023, using patient/population, intervention, comparison, and outcomes (PICO) criteria limited to the English language.

Results

A total of 62 reports were identified and included. In PsO, chronic inflammation is driven by cytokines including IL-17 and IL-23, and cellular mediators such as CD8+ and CD4+ T cells. TRM contributes to local inflammation, while Tregs may be dysfunctional in psoriatic skin lesions. Secukinumab and guselkumab, which target IL-17A and the IL-23p19 subunit, respectively, have different effects on CD8+ TRM and Tregs during PsO treatment. Inhibition of IL-23 may provide better long-term results due to its impact on the Treg to CD8+ TRM ratio. IL-23 may contribute to inflammation persisting even after treatment. In PsA, subclinical enthesitis is perceived as an early occurence, and Th17 cells are involved in this pathogenic process. Recent EULAR guidelines highlight the importance of early diagnosis and treatment to intercept PsA. In PsA, CD8+ TRM cells are present in synovial fluid and Tregs are reduced in peripheral blood. The progression from PsO to PsA is marked by a shift in immune profiles, with specific T-cells subsets playing key roles in perpetuating inflammation. Early intervention targeting TRM cells may hold promising, but clinical studies are limited. Ongoing studies such as IVEPSA and PAMPA aim to improve our knowledge regarding PsA interception in high-risk PsO patients, emphasizing the need for further research in this area.

Conclusion

Early intervention is crucial for PsO patients at high risk of PsA; T cells, particularly type 17 helper T cells, and CD8+ cells are key in the progression from PsO-to-PsA. Early targeting of TRM in PsD shows promise but more research is needed.

T cells in the pathogenesis of axial spondyloarthritis

Axial spondyloarthritis (axSpA) is the prototype of the spondyloarthritis spectrum. The involvement of T cells in its pathogenesis has long been suspected on the basis of the association with the major histocompatibility complex I molecule HLA-B27 and the pivotal role of interleukin 17 in the inflammatory mechanisms associated with the disease. Moreover, the presence of unconventional or "innate-like" T cells within the axial enthesis suggests an important role for these cells in the pathophysiology of the disease. In this review, we describe the characteristics and the interleukin 17 secretion capacity of the T-cell subsets identified in axSpA. We discuss the genetic and epigenetic mechanisms that support the alteration of T-cell functions and promote their activation in axSpA. We also discuss recent data on T cells that could explain the extra-articular manifestations of the SpA spectrum.

Bone Involvement in Rheumatoid Arthritis and Spondyloartritis: An Updated Review

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

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 bone marrow side of axial spondyloarthritis

Spondyloarthritis (SpA) is characterized by the infiltration of innate and adaptive immune cells into entheses and bone marrow. Molecular, cellular and imaging evidence demonstrates the presence of bone marrow inflammation, a hallmark of SpA. In the spine and the peripheral joints, bone marrow is critically involved in the pathogenesis of SpA. Evidence suggests that bone marrow inflammation is associated with enthesitis and that there are roles for mechano-inflammation and intestinal inflammation in bone marrow involvement in SpA. Specific cell types (including mesenchymal stem cells, innate lymphoid cells and γδ T cells) and mediators (Toll-like receptors and cytokines such as TNF, IL-17A, IL-22, IL-23, GM-CSF and TGFβ) are involved in these processes. Using this evidence to demonstrate a bone marrow rather than an entheseal origin for SpA could change our understanding of the disease pathogenesis and the relevant therapeutic approach.

Pathways driving tendinopathy and enthesitis: siblings or distant cousins in musculoskeletal medicine?

Tendinopathy and enthesitis share clinical, anatomical, and molecular parallels. However, their relationship is complex, presenting challenges in diagnosis and treatment. The biomechanics underlying these pathologies, together with relative immune and stromal contributions to pathology, are characterised by crucial comparative elements. However, methodologies used to study enthesitis and tendinopathy have been divergent, which could account for discrepancies in how these conditions are perceived and treated. In this Review, we summarise key clinical parallels between these two common presentations in musculoskeletal medicine and address factors that currently preclude development of more effective therapeutics. Furthermore, we describe molecular similarities and disparities that govern pathological mechanisms in tendinopathy and enthesitis, thus informing translational studies and treatment strategies.

Cytokines in Spondyloarthritis and Inflammatory Bowel Diseases: From Pathogenesis to Therapeutic Implications

Spondyloarthritis and inflammatory bowel diseases are chronic immune disorders of the joints and the gut that often coexist in the same patient, increasing the burden of each disorder, worsening patients' quality of life, and influencing therapeutic strategies. Genetic predisposition, environmental triggers, microbiome features, immune cell trafficking, and soluble factors such as cytokines contribute to the pathogenesis of both articular and intestinal inflammation. Most of the molecular targeted biological therapies developed over the last two decades were based on evidence that specific cytokines may be involved in these immune diseases. Despite pro-inflammatory cytokine pathways sharing the pathogenesis of both articular and gut diseases (i.e., tumor necrosis factor and interleukin-23), several other cytokines (i.e., interleukin-17) may be differently involved in the tissue damage process, depending on the specific disease and the organ involved in inflammation, making difficult the identification of a therapeutic plan that is efficacious for both inflammatory manifestations. In this narrative review, we comprehensively summarize the current knowledge on cytokine involvement in spondyloarthritis and inflammatory bowel diseases, underlining similarities and differences among their pathogenetic pathways; finally, we provide an overview of current and potential future treatment strategies to simultaneously target both articular and gut immune disorders.

Janus Kinase Inhibitors: A New Tool for the Treatment of Axial Spondyloarthritis

Axial spondyloarthritis (axSpA) is a chronic inflammatory disease involving the spine, peripheral joints, and entheses. This condition causes stiffness, pain, and significant limitation of movement. In recent years, several effective therapies have become available based on the use of biologics that selectively block cytokines involved in the pathogenesis of the disease, such as tumor necrosis factor-α (TNFα), interleukin (IL)-17, and IL-23. However, a significant number of patients show an inadequate response to treatment. Over 10 years ago, small synthetic molecules capable of blocking the activity of Janus kinases (JAK) were introduced in the therapy of rheumatoid arthritis. Subsequently, their indication extended to the treatment of other inflammatory rheumatic diseases. The purpose of this review is to discuss the efficacy and safety of these molecules in axSpA therapy.

How Has Molecular Biology Enhanced Our Undertaking of axSpA and Its Management

PURPOSE

This review aims at investigating pathophysiological mechanisms in spondyloarthritis (SpA). Analysis of genetic factors, immunological pathways, and abnormalities of bone metabolism lay the foundations for a better understanding of development of the axial clinical manifestations in patients, allowing physician to choose the most appropriate therapeutic strategy in a more targeted manner.

RECENT FINDINGS

In addition to the contribution of MHC system, findings emerged about the role of non-HLA genes (as ERAP1 and 2, whose inhibition could represent a new therapeutic approach) and of epigenetic mechanisms that regulate the expression of genes involved in SpA pathogenesis. Increasing evidence of bone metabolism abnormalities secondary to the activation of immunological pathways suggests the development of various bone anomalies that are present in axSpA patients. SpA are a group of inflammatory diseases with a multifactorial origin, whose pathogenesis is linked to the genetic predisposition, the action of environmental risk factors, and the activation of immune response. It is now well known how bone metabolism leads to long-term structural damage via increased bone turnover, bone loss and osteoporosis, osteitis, erosions, osteosclerosis, and osteoproliferation. These effects can exist in the same patient over time or even simultaneously. Evidence suggests a cross relationship among innate immunity, autoimmunity, and bone remodeling in SpA, making treatment approach a challenge for rheumatologists. Specifically, treatment targets are consistently increasing as new drugs are upcoming. Both biological and targeted synthetic drugs are promising in terms of their efficacy and safety profile in patients affected by SpA.

CCR2 is expressed by tendon resident macrophage and T cells, while CCR2 deficiency impairs tendon healing via blunted involvement of tendon-resident and circulating monocytes/macrophages

During tendon healing, macrophages are thought to be a key mediator of scar tissue formation, which prevents successful functional restoration of the tendon. However, macrophages are critical for successful tendon healing as they aid in wound debridement, extracellular matrix deposition, and promote fibroblast proliferation. Recent work has sought to better define the multi-faceted functions of macrophages using depletion studies, while other studies have identified a tendon resident macrophage population. To begin to delineate the functions of tendon-resident versus circulation-derived macrophages, we examined the tendon healing phenotype in Chemokine Receptor 2 (CCR2) reporter (CCR2GFP/+ ), and knockout mice. CCR2 is a chemokine receptor primarily found on the surface of circulating bone marrow-derived monocytes, with CCR2 being an important mediator of macrophage recruitment to wound environments. Surprisingly, CCR2GFP/+ cells were present in the tendon during adult homeostasis, and single-cell RNA sequencing identified these cells as tendon-resident macrophages and T cells. During both homeostasis and healing, CCR2 knockout resulted in a substantial decrease in CCR2GFP+ cells and pan-macrophages. Additionally, loss of CCR2 resulted in reduced numbers of myofibroblasts and impeded functional recovery during late healing. This study highlights the heterogeneity of tendon-resident and recruited immune cells and their contributions following injury, and establishes an important role for CCR2 in modulating both the adult tendon cell environment and tendon healing process.

Characterization of Blood Mucosal-Associated Invariant T Cells in Patients With Axial Spondyloarthritis and of Resident Mucosal-Associated Invariant T Cells From the Axial Entheses of Non-Axial Spondyloarthritis Control Patients

OBJECTIVE

The importance of interleukin-17A (IL-17A) in the pathogenesis of axial spondyloarthritis (SpA) has been demonstrated by the success of IL-17A blockade. However, the nature of the cell populations that produce this important proinflammatory cytokine remains poorly defined. We undertook this study to characterize the major IL-17A-producing blood cell populations in the peripheral blood of patients with axial SpA, with a focus on mucosal-associated invariant T (MAIT) cells, a population known to be capable of producing IL-17.

METHODS

We evaluated IL-17A production from 5 sorted peripheral blood cell populations, namely, MAIT cells, γδ T cells, CD4+ T cells, CD8+ T cells, and neutrophils, before and after stimulation with phorbol myristate acetate, the calcium ionophore A23187, and β-1,3-glucan. Expression of IL-17A transcripts and protein were determined using nCounter and ultra-sensitive Simoa technology, respectively. MAIT cells from the axial entheses of non-axial SpA control patients (n = 5) were further characterized using flow cytometric immunophenotyping and quantitative polymerase chain reaction, and the production of IL-17 was assessed following stimulation.

RESULTS

On a per-cell basis, MAIT cells from peripheral blood produced the most IL-17A compared to CD4+ T cells (P < 0.01), CD8+ T cells (P < 0.0001), and γδ T cells (P < 0.0001). IL-17A was not produced by neutrophils. Gene expression analysis also revealed significantly higher expression of IL17A and IL23R in MAIT cells. Stimulation of peripheral blood MAIT cells with anti-CD3/CD28 and IL-7 and/or IL-18 induced strong expression of IL17F. MAIT cells were present in the normal, unaffected entheses of control patients who did not have axial SpA and showed elevated AHR, JAK1, STAT4, and TGFB1 transcript expression with inducible IL-17A protein. IL-18 protein expression was evident in spinal enthesis digests.

CONCLUSION

Both peripheral blood MAIT cells and resident MAIT cells in normal axial entheses contribute to the production of IL-17 and may play important roles in the pathogenesis of axial SpA.

Cytokine competent gut-joint migratory T Cells contribute to inflammation in the joint

Although studies have identified the presence of gut-associated cells in the enthesis of joints affected by spondylarthritis (SpA), a direct link through cellular transit between the gut and joint has yet to be formally demonstrated. Using KikGR transgenic mice to label in situ and track cellular trafficking from the distal colon to the joint under inflammatory conditions of both the gut and joint, we demonstrate bona-fide gut-joint trafficking of T cells from the colon epithelium, also called intraepithelial lymphocytes (IELs), to distal sites including joint enthesis, the pathogenic site of SpA. Similar to patients with SpA, colon IELs from the TNF^ΔARE/+ mouse model of inflammatory bowel disease and SpA display heightened TNF production upon stimulation. Using ex vivo stimulation of photo-labeled gut-joint trafficked T cells from the popliteal lymph nodes of KikGR and KikGR TNF^ΔARE/+ we saw that the CD4+ photo-labeled population was highly enriched for IL-17 competence in healthy as well as arthritic mice, however in the TNF^ΔARE/+ mice these cells were additionally enriched for TNF. Using transfer of magnetically isolated IELs from TNF^+/+ and TNF^ΔARE/+ donors into Rag1 ^-/- hosts, we confirmed that IELs can exacerbate inflammatory processes in the joint. Finally, we blocked IEL recruitment to the colon epithelium using broad spectrum antibiotics in TNF^ΔARE/+ mice. Antibiotic-treated mice had reduced gut-joint IEL migration, contained fewer Il-17A and TNF competent CD4+ T cells, and lessened joint pathology compared to untreated littermate controls. Together these results demonstrate that pro-inflammatory colon-derived IELs can exacerbate inflammatory responses in the joint through systemic trafficking, and that interference with this process through gut-targeted approaches has therapeutic potential in SpA.

Bidirectional Relationship Between Osteoarthritis and Periodontitis: A Population-Based Cohort Study Over a 15-year Follow-Up

Objective

To identify the relationship between osteoarthritis and periodontitis.

Methods

144,788 periodontitis patients and 144,788 propensity score-matched controls without history of periodontitis were enrolled in this cohort study. A Cox proportional hazard model was used to estimate the risk of osteoarthritis. Survival analysis was utilized to assess the time-dependent effect of periodontitis on osteoarthritis. Age and gender were stratified to identify subgroups at risk. A symmetrical case-control analysis was designed to determine the relationship between present periodontitis and history of osteoarthritis.

Results

Patients with periodontitis had higher risk of osteoarthritis (hazard ratio, HR =1.15, 95% CI =1.12-1.17, p < 0.001) and severe osteoarthritis that led to total knee replacement or total hip replacement (TKR/THR) (HR =1.12, 95% CI =1.03-1.21, p < 0.01) than controls, which was time-dependent (log-rank test p < 0.01). The effect of periodontitis on osteoarthritis was significant in both genders and age subgroups over 30 years-old (all p < 0.001). Among them, females (HR=1.27, 95% CI = 1.13-1.42, p < 0.001) and patients aged over 51 (HR= 1.21, 95% CI =1.10-1.33, p < 0.001) with periodontitis were predisposed to severe osteoarthritis. In addition, periodontitis patients were more likely to have a history of osteoarthritis (odds ratio = 1.11, 95% CI = 1.06 - 1.17, p < 0.001).

Conclusions

These findings suggest an association between periodontitis and a higher risk of osteoarthritis, including severe osteoarthritis that led to TKR/THR. Likewise, periodontitis is more likely to develop following osteoarthritis. A bidirectional relationship between osteoarthritis and periodontitis was observed.

Molecular and cellular regulation of psoriatic inflammation

This review highlights the molecular and cellular mechanisms underlying psoriatic inflammation with an emphasis on recent developments which may impact on treatment approaches for this chronic disease. We consider both the skin and the musculoskeletal compartment and how different manifestations of psoriatic inflammation are linked. This review brings a focus to the importance of inflammatory feedback loops that exist in the initiation and chronic stages of the condition, and how close interaction between the epidermis and both innate and adaptive immune compartments drives psoriatic inflammation. Furthermore, we highlight work done on biomarkers to predict the outcome of therapy as well as the transition from psoriasis to psoriatic arthritis.

TNF inhibitors have a protective role in the risk of dementia in patients with ankylosing spondylitis: Results from a nationwide study

OBJECTIVES

Ankylosing spondylitis (AS) is a chronic progressive and debilitating form of arthritis with associated extra-articular features including uveitis, intestinal and lung apical inflammation and psoriasis. Putative associations between AS and neurologic disorders has been relatively overlooked. The purpose of this study is to assess the link between AS and major neurologic disorders and whether treatment with Tumor-Necrosis-Factor inhibitors (TNFi) has an impact on that association.

METHODS

A retrospective cross-sectional study was carried out based on the Clalit Health Services (CHS) computerized database. AS patients were compared to age- and gender-matched controls with respect to the proportion of Alzheimer's disease (AD), Parkinson's disease (PD), epilepsy, and multiple sclerosis (MS). The impact of AS therapy (biologic vs conventional therapy) was assessed as well.

RESULTS

4,082 AS patients and 20,397 age- and gender-matched controls were identified. AS was associated with a higher prevalence of AD (odds-ratio(OR) 1.46 [95%Confidence-interval(CI) 1.13-1.87], p=0.003), epilepsy (OR 2.33 [95%CI 1.75-3.09] p<0.0001) and PD (OR 2.75 [95%CI 2.04-3.72], p<0.0001), whereas no statistically significant association was found for MS. Association with PD remained significant in the multivariate analysis (OR 1.49 [95%CI 1.05- 2.13],p=0.027). Within AS patients, the use of TNFi (OR 0.10 [95%CI 0.01-0.74], p=0.024) were associated with a lowered risk of developing AD.

CONCLUSION

AS is positively associated with AD, PD, and epilepsy but not MS. AS patients treated with TNFi have lower rates of AD.

Psoriatic arthritis from a mechanistic perspective

Psoriatic arthritis (PsA) is part of a group of closely related clinical phenotypes ('psoriatic disease') that is defined by shared molecular pathogenesis resulting in excessive, prolonged inflammation in the various tissues affected, such as the skin, the entheses or the joints. Psoriatic disease comprises a set of specific drivers that promote an aberrant immune response and the consequent development of chronic disease that necessitates therapeutic intervention. These drivers include genetic, biomechanical, metabolic and microbial factors that facilitate a robust and continuous mobilization, trafficking and homing of immune cells into the target tissues. The role of genetic variants involved in the immune response, the contribution of mechanical factors triggering an exaggerated inflammatory response (mechanoinflammation), the impact of adipose tissue and altered lipid metabolism and the influence of intestinal dysbiosis in the disease process are discussed. Furthermore, the role of key cytokines, such as IL-23, IL-17 and TNF, in orchestrating the various phases of the inflammatory disease process and as therapeutic targets in PsA is reviewed. Finally, the nature and the mechanisms of inflammatory tissue responses inherent to PsA are summarized.

Tissue-Resident Immune Cells in Humans

Tissue-resident immune cells span both myeloid and lymphoid cell lineages, have been found in multiple human tissues, and play integral roles at all stages of the immune response, from maintaining homeostasis to responding to infectious challenges to resolution of inflammation to tissue repair. In humans, studying immune cells and responses in tissues is challenging, although recent advances in sampling and high-dimensional profiling have provided new insights into the ontogeny, maintenance, and functional role of tissue-resident immune cells. Each tissue contains a specific complement of resident immune cells. Moreover, resident immune cells for each lineage share core properties, along with tissue-specific adaptations. Here we propose a five-point checklist for defining resident immune cell types in humans and describe the currently known features of resident immune cells, their mechanisms of development, and their putative functional roles within various human organs. We also consider these aspects of resident immune cells in the context of future studies and therapeutics.

Bone Involvement in Patients with Spondyloarthropathies

Spondyloarthropathies (SpA) are common systemic inflammatory rheumatic diseases, in which, as in other rheumatic diseases, levels of markers of bone resorption are elevated, leading to bone loss and elevated risk of vertebral fractures. However, the diseases are also associated with new bone formation in the spine, the so-called syndesmophytes. We tried to unravel the pathogenesis of formation and growth of syndesmophytes and evaluated new diagnostic and treatment options. After a successful meeting of the Working Group on Rheumatic Diseases at the ECTS 2020, we (WL and CR) were excited about the quality of the speakers (CM, JH, AG, and GL) and their complimentary lectures. Given the relative lack of reviews on spondyloarthropathies and bone, we decided to work together on a comprehensive review that might be interesting for basic scientists and clinically relevant for clinicians. Radiographic progression in axSpA is linked to several risk factors, like male sex, smoking, HLA-B-27, increased levels of CRP, presence of syndesmophytes, and marked inflammation on MRI. The potential role of mechanical stress in the context of physically demanding jobs has been also suggested to promote structural damages. Different treatment options from NSAIDs to biologic agents like TNF inhibitors (TNFi) or IL-17inhibitors (IL-17i) result in a reduction of inflammation and symptoms. However, all these different treatment options failed to show clear and reproducible results on inhibition on syndesmophyte formation. The majority of data are available on TNFi, and some studies suggested an effect in subgroups of patients with ankylosing spondylitis. Less information is available on NSAIDs and IL-17i. Since IL-17i have been introduced quite recently, more studies are expected. IL-17 inhibitors (Il-17i) potently reduce signs and symptoms, but serum level of IL-17 is not elevated, therefore, IL-17 probably has mainly a local effect. The failure of anti-IL-23 in axSpA suggests that IL-17A production could be independent from IL-23. It may be upregulated by TNFα, resulting in lower expression of DKK1 and RANKL and an increase in osteogenesis. In active AS markers of bone resorption are increased, while bone formation markers can be increased or decreased. Bone Turnover markers and additional markers related to Wnt such as DKK1, sclerostin, and RANKL are valuable for elucidating bone metabolism on a group level and they are not (yet) able to predict individual patient outcomes. The gold standard for detection of structural lesions in clinical practice is the use of conventional radiographics. However, the resolution is low compared to the change over time and the interval for detecting changes are 2 years or more. Modern techniques offer substantial advantages such as the early detection of bone marrow edema with MRI, the fivefold increased detection rate of new or growing syndesmophytes with low-dose CT, and the decrease in 18F-fluoride uptake during treatment with TNFα-inhibitors (TNFi) in a pilot study in 12 AS patients. Detection of bone involvement by new techniques, such as low-dose CT, MRI and 18-Fluoride PET-scans, and bone turnover markers, in combination with focusing on high-risk groups such as patients with early disease, elevated CRP, syndesmophytes at baseline, male patients and patients with HLA-B27 + are promising options for the near future. However, for optimal prevention of formation of syndesmophytes we need more detailed insight in the pathogenesis of bone formation in axSpA and probably more targeted therapies.

SOX9+ enthesis cells are associated with spinal ankylosis in ankylosing spondylitis

OBJECTIVE

Although cartilage degeneration and invasion of the subchondral bone plate in entheseal lesion has been considered to consequently lead bony ankylosis in ankylosing spondylitis (AS), no evident mechanisms are known.

DESIGN

To identify histopathological and physiological changes in enthesitis-related ankylosis in AS, we performed molecular characterization of transcription factors and surface markers, and transcriptome analysis with human tissues. Entheseal tissue containing subchondral bone was obtained from the facet joints of 9 patients with AS and 10 disease controls, and assessed by using differential staining techniques. Enthesis cells were isolated, characterized, stimulated with TNF and/or IL-17A, and analysed by cell-based experimental tools.

RESULTS

We found diffusely distributed granular tissue and cartilage in the subchondral bone in AS. Co-expression of SOX9, a specific transcription factor in cartilage, and matrix metalloproteinase 13 (MMP13) was found in the granular tissues within the subchondral bone from AS patients. Intriguingly, SOX9 expression was significantly higher in AS enthesis cells than controls and correlated with TNFR1 and IL-17RA expressions, which is important for high reactivity to TNF and IL-17A cytokines. Co-stimulation by TNF and IL-17A resulted in accelerated mineralization/calcification features, and increased OCN expression in AS enthesis cells. Furthermore, SOX9 overexpression in enthesis leads to promoting mineralization feature by TNF and IL-17A stimuli. Finally, OCN expression is elevated in the destructive enthesis of advanced AS.

CONCLUSION

These findings provide insight into the links between inflammation and the mineralization of entheseal tissue as the initiation of spinal ankylosis, emphasizing the importance of SOX9⁺ enthesis cells.

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.

Hsa_circ_0000652 Aggravates Inflammation by Activation of Macrophages and Enhancement of OX40/OX40L Interaction in Ankylosing Spondylitis

Circular RNAs (circRNAs) have emerged as important roles in various inflammatory processes of rheumatic diseases. However, their expression profiles and influences in the pathogenesis of ankylosing spondylitis (AS) remain unclear. In this study, we revealed the differential expression profiles of circRNAs in peripheral blood mononuclear cells (PBMCs) in AS by circRNA sequencing. We screened the differentially expressed circRNAs in AS and verified that hsa_circ_0000652 was upregulated and had potential to be a biomarker of progression. Functionally, hsa_circ_0000652 promoted proliferation and cytokine production in macrophages and inhibited apoptosis. Through dual-luciferase assays and RNA pull-down assays, we demonstrated that hsa_circ_0000652 acted as a competing endogenous RNA (ceRNA) by binding with hsa-miR-1179 and regulated OX40L, which is characterized as a co-stimulatory molecule and found to be upregulated in AS patients. As a result, hsa_circ_0000652 aggravated the inflammation in the coculture system containing CD4⁺ T cells and macrophages via OX40/OX40L interaction. Our findings suggest that hsa_circ_0000652 was upregulated in AS patients and may serve as a pro-inflammatory factor in macrophages and a positive regulator of OX40/OX40L by sponging hsa-miR-1179.

Nail Involvement as a Predictor of Differential Treatment Effects of Secukinumab Versus Ustekinumab in Patients with Moderate to Severe Psoriasis

Introduction

Patients with plaque psoriasis may experience varying levels of treatment response to different biologics, based on phenotypic characteristics and underlying genetic factors. Nail psoriasis is a common manifestation of psoriasis (approx. 50% of patients) and has been linked to the human leukocyte antigen-C*0602 (HLA-C*0602) allele, which in turn has been associated with differential treatment responses to certain drugs. Here we investigate whether nail involvement in patients with psoriasis can predict differential skin responses to two biologics with different modes of action, namely secukinumab (anti-interleukin-17A) and ustekinumab (anti-interleukin-12/23), to ultimately guide treatment choice.

Methods

Data were pooled from the CLEAR and CLARITY studies and stratified post hoc by nail involvement status at baseline. Psoriasis Area and Severity Index (PASI) 75 and 90 responses over 52 weeks and absolute PASI ≤ 3, ≤ 1, and 0 values at weeks 16 and 52, were assessed.

Results

Based on the medical history, 30.4% (269/886) of the patients in the secukinumab arm and 29.7% (265/891) of patients in the ustekinumab arm presented with nail involvement. Nail involvement status had little to no impact on the efficacy of secukinumab, as comparable responses were achieved for patients with and without nail involvement in terms of PASI 75/90, ≤ 3, and 0 responses; slightly lower PASI ≤ 1 reponses were achieved in patients with nail involvement. In the ustekinumab arm, patients with nail involvement achieved lower responses across all endpoints.

Conclusions

These findings indicate that nail involvement can serve as an observable prognostic factor for efficacy in skin psoriasis treatment and guide the choice between secukinumab and ustekinumab.

Trial Registration

CLEAR: NCT02074982; CLARITY: NCT02826603.

Tofacitinib Blocks Entheseal Lymphocyte Activation and Modulates MSC Adipogenesis, but Does Not Directly Affect Chondro- and Osteogenesis

Entheseal spinal inflammation and new bone formation with progressive ankylosis may occur in ankylosing spondylitis (AS) and psoriatic arthritis (PsA). This study evaluated whether JAK inhibition with tofacitinib modulated the key disease associated cytokines, TNF and IL-17A, and whether tofacitinib also modulated bone marrow stromal cell-derived mesenchymal stem cell (MSCs) function, including osteogenesis, since post inflammation new bone formation occurs under these conditions. Methods: Conventional entheseal derived αβ CD4+ and CD8+ T-cells were investigated following anti-CD3/CD28 bead stimulation to determine IL-17A and TNF levels in tofacitinib treated (1000 nM) peri-entheseal bone (PEB) and peripheral blood mononuclear cells (PBMC) using ELISA. Bone marrow stromal cell-derived mesenchymal stem cell (MSC) colony forming units (CFU-F) and multi-lineage potential were evaluated using tofacitinib (dosages ranging between 100, 500, 1000 and 10,000 nM). Results: Induced IL-17A and TNF cytokine production from both entheseal CD4+ T-cells and CD8+ T-cells was effectively inhibited by tofacitinib. Tofacitinib treatment did not impact on CFU-F potential or in vitro chondro- and osteogenesis. However, tofacitinib stimulation increased MSC adipogenic potential with greater Oil Red O stained areas. Conclusion: Inducible IL-17A and TNF production by healthy human entheseal CD4+ and CD8+ T-cells was robustly inhibited in vitro by tofacitinib. However, tofacitinib did not impact MSC osteogenesis, but stimulated in vitro MSC adipogenesis, the relevance of which needs further evaluation given that the adipocytes are associated with new bone formation in SpA.

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.

Integrative Single-Cell RNA-Seq and ATAC-Seq Analysis of Peripheral Mononuclear Cells in Patients With Ankylosing Spondylitis

Objective

Genetic studies on ankylosing spondylitis (AS) have identified more than 100 pathogenic genes. Building a bridge between these genes and biologically targeted therapies is the current research hotspot.

Methods

We integrated single-cell assaying transposase-accessible chromatin sequencing (scATAC-seq) and single-cell RNA sequencing (scRNA-seq) to explore the key genes and related mechanisms associated with AS pathogenesis.

Results

We identified 18 cell types in peripheral mononuclear cells from patients with AS and normal controls and summarized the cell-type-specific abnormal genes by scRNA-seq. Interestingly, we found that the pathogenic gene NFKB involved in AS progression originated from CD8+ T cells. Moreover, we observed an abnormal tumor TNF pathway mediated by abnormal expression of TNF, NFKB, FOS, JUN, and JUNB, and scATAC-seq results confirmed the abnormal accessible binding sites of transcriptional factors FOS, JUN, and JUNB. The final magnetic bead sorting and quantitative real-time PCR(RT-qPCR) confirmed that NFKB, FOS, JUN, and JUNB in CD8+ T cells differed in the AS group.

Conclusions

Our results revealed a possible mechanism by which NFKB abnormally regulates FOS, JUN, and JUNB and drives AS progression, providing a novel perspective from a single cell point of view in AS.

Immunopathophysiology of Juvenile Spondyloarthritis (jSpA): The "Out of the Box" View on Epigenetics, Neuroendocrine Pathways and Role of the Macrophage Migration Inhibitory Factor (MIF)

Juvenile spondyloarthritis (jSpA) is a an umbrella term for heterogeneous group of related seronegative inflammatory disorders sharing common symptoms. Although it mainly affects children and adolescents, it often remains active during adulthood. Genetic and environmental factors are involved in its occurrence, although the exact underlying immunopathophysiology remains incompletely elucidated. Accumulated evidence suggests that, in affected patients, subclinical gut inflammation caused by intestinal dysbiosis, is pivotal to the future development of synovial-entheseal complex inflammation. While the predominant role of IL17/23 axis, TNF-α, and IL-7 in the pathophysiology of SpA, including jSpA, is firmly established, the role of the cytokine macrophage migration inhibitory factor (MIF) is generally overlooked. The purpose of this review is to discuss and emphasize the role of epigenetics, neuroendocrine pathways and the hypothalamic-pituitary (HPA) axis, and to propose a novel hypothesis of the role of decreased NLRP3 gene expression and possibly MIF in the early phases of jSpA development. The decreased NLRP3 gene expression in the latter, due to hypomethylation of promotor site, is (one of) the cause for inflammasome malfunction leading to gut dysbiosis observed in patients with early jSpA. In addition, we highlight the role of MIF in the complex innate, adaptive cellular and main effector cytokine network, Finally, since treatment of advanced bone pathology in SpA remains an unmet clinical need, I suggest possible new drug targets with the aim to ultimately improve treatment efficacy and long-term outcome of jSpA patients.

A review of JAK-STAT signalling in the pathogenesis of spondyloarthritis and the role of JAK inhibition

Spondyloarthritis (SpA) comprises a group of chronic inflammatory diseases with overlapping clinical, genetic and pathophysiological features including back pain, peripheral arthritis, psoriasis, enthesitis and dactylitis. Several cytokines are involved in the pathogenesis of SpA, variously contributing to each clinical manifestation. Many SpA-associated cytokines, including IL-23, IL-17, IL-6, type I/II interferon and tumour necrosis factor signal directly or indirectly via the Janus kinase (JAK)–signal transducer and activator of transcription pathway. JAK signalling also regulates development and maturation of cells of the innate and adaptive immune systems. Accordingly, disruption of this signalling pathway by small molecule oral JAK inhibitors can inhibit signalling implicated in SpA pathogenesis. Herein we discuss the role of JAK signalling in the pathogenesis of SpA and summarize the safety and efficacy of JAK inhibition by reference to relevant SpA clinical trials.

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.

The transition from enthesis physiological responses in health to aberrant responses that underpin spondyloarthritis mechanisms

PURPOSE OF REVIEW

Despite immunology and translational therapeutics advances in inflammatory arthritis over the past two decades, the enthesis, which is the epicentric of the spondyloarthritis family pathological process, retains many mysteries because of tissue inaccessibility that hampers direct immune study. As entheses are subject to almost continuous mechanical stress and spondyloarthritis is linked to microdamage or injury and joint stress, it is cardinal to understand the physiological changes occurring within the entheses not only to be able to differentiate disease from health but also to understand the transition normal physiology break down and its merges into spondyloarthritis-related disease.

RECENT FINDINGS

Imaging has played a major role in understanding the enthesis in human. Remarkable insights from enthesis functioning and microdamage in normal and with ageing including those linked to body mass index is emerging. The impact of mechanical stress and degenerative conditions on the development of the secondary entheseal vascular changes is not understood. Of note, ultrasound studies in psoriasis have shown higher power Doppler changes compared to controls pointing towards a role for vascular changes in the development of enthesitis in psoriatic arthritis.

SUMMARY

The literature pertaining to normal entheses changes with age, microdamage and vascular changes in health is providing a roadmap for understanding of the enthesis and its potential role in evolution of spondyloarthritis including psoriatic arthritis.

Tumor microenvironment: a prospective target of natural alkaloids for cancer treatment

Malignant tumor has become one of the major diseases that seriously endangers human health. Numerous studies have demonstrated that tumor microenvironment (TME) is closely associated with patient prognosis. Tumor growth and progression are strongly dependent on its surrounding tumor microenvironment, because the optimal conditions originated from stromal elements are required for cancer cell proliferation, invasion, metastasis and drug resistance. The tumor microenvironment is an environment rich in immune/inflammatory cells and accompanied by a continuous, gradient of hypoxia and pH. Overcoming immunosuppressive environment and boosting anti-tumor immunity may be the key to the prevention and treatment of cancer. Most traditional Chinese medicine have been proved to have good anti-tumor activity, and they have the advantages of better therapeutic effect and few side effects in the treatment of malignant tumors. An increasing number of studies are giving evidence that alkaloids extracted from traditional Chinese medicine possess a significant anticancer efficiency via regulating a variety of tumor-related genes, pathways and other mechanisms. This paper reviews the anti-tumor effect of alkaloids targeting tumor microenvironment, and further reveals its anti-tumor mechanism through the effects of alkaloids on different components in tumor microenvironment.

Drivers of Inflammation in Psoriatic Arthritis: the Old and the New

PURPOSE OF REVIEW

The recognition that IL-17 is produced by many lymphoid-like cells other than CD4+ T helper (Th17) cells raises the potential for new pathogenic pathways in IBD/psoriasis/SpA. We review recent knowledge concerning the role of unconventional and conventional lymphocytes expressing IL-17 in human PsA and axSpA.

RECENT FINDINGS

Innate-like lymphoid cells, namely gamma delta (γδ) T-cells, invariant natural killer T (iNKT) cells and mucosal-associated invariant T (MAIT) cells, together with innate lymphoid cells (ILCs) are found at sites of disease in PsA/SpA. These cells are often skewed to Type-17 profiles and may significantly contribute to IL-17 production. Non-IL-23 dependent IL-17 production pathways, utilising cytokines such as IL-7 and IL-9, also characterise these cells. Both conventional CD4 and CD8 lymphocytes show pathogenic phenotypes at sites of disease. A variety of innate-like lymphoid cells and conventional lymphocytes contribute towards IL-17-mediated pathology in PsA/SpA. The responses of these cells to non-conventional immune and non-immune stimuli may explain characteristic clinical features of these diseases and potential therapeutic mechanisms of therapies such as Jak inhibitors.

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.

Novel self-amplificatory loop between T cells and tenocytes as a driver of chronicity in tendon disease

OBJECTIVES

Increasing evidence suggests that inflammatory mechanisms play a key role in chronic tendon disease. After observing T cell signatures in human tendinopathy, we explored the interaction between T cells and tendon stromal cells or tenocytes to define their functional contribution to tissue remodelling and inflammation amplification and hence disease perpetuation.

METHODS

T cells were quantified and characterised in healthy and tendinopathic tissues by flow cytometry (FACS), imaging mass cytometry (IMC) and single cell RNA-seq. Tenocyte activation induced by conditioned media from primary damaged tendon or interleukin-1β was evaluated by qPCR. The role of tenocytes in regulating T cell migration was interrogated in a standard transwell membrane system. T cell activation (cell surface markers by FACS and cytokine release by ELISA) and changes in gene expression in tenocytes (qPCR) were assessed in cocultures of T cells and explanted tenocytes.

RESULTS

Significant quantitative differences were observed in healthy compared with tendinopathic tissues. IMC showed T cells in close proximity to tenocytes, suggesting tenocyte-T cell interactions. On activation, tenocytes upregulated inflammatory cytokines, chemokines and adhesion molecules implicated in T cell recruitment and activation. Conditioned media from activated tenocytes induced T cell migration and coculture of tenocytes with T cells resulted in reciprocal activation of T cells. In turn, these activated T cells upregulated production of inflammatory mediators in tenocytes, while increasing the pathogenic collagen 3/collagen 1 ratio.

CONCLUSIONS

Interaction between T cells and tenocytes induces the expression of inflammatory cytokines/chemokines in tenocytes, alters collagen composition favouring collagen 3 and self-amplifies T cell activation via an auto-regulatory feedback loop. Selectively targeting this adaptive/stromal interface may provide novel translational strategies in the management of human tendon disorders.

Perspectives on the Genetic Associations of Ankylosing Spondylitis

Ankylosing spondylitis (AS) is a common form of inflammatory spinal arthritis with a complex polygenic aetiology. Genome-wide association studies have identified more than 100 loci, including some involved in antigen presentation (HLA-B27, ERAP1, and ERAP2), some in Th17 responses (IL6R, IL23R, TYK2, and STAT3), and others in macrophages and T-cells (IL7R, CSF2, RUNX3, and GPR65). Such observations have already helped identify potential new therapies targeting IL-17 and GM-CSF. Most AS genetic associations are not in protein-coding sequences but lie in intergenic regions where their direct relationship to particular genes is difficult to assess. They most likely reflect functional polymorphisms concerned with cell type-specific regulation of gene expression. Clarifying the nature of these associations should help to understand the pathogenic pathways involved in AS better and suggest potential cellular and molecular targets for drug therapy. However, even identifying the precise mechanisms behind the extremely strong HLA-B27 association with AS has so far proved elusive. Polygenic risk scores (using all the known genetic associations with AS) can be effective for the diagnosis of AS, particularly where there is a relatively high pre-test probability of AS. Genetic prediction of disease outcomes and response to biologics is not currently practicable.

IL-17A and TNF Modulate Normal Human Spinal Entheseal Bone and Soft Tissue Mesenchymal Stem Cell Osteogenesis, Adipogenesis, and Stromal Function

Objective: The spondylarthritides (SpA) are intimately linked to new bone formation and IL-17A and TNF pathways. We investigated spinal soft tissue and bone mesenchymal stem cell (MSC) responses to IL-17A and TNF, including their osteogenesis, adipogenesis, and stromal supportive function and ability to support lymphocyte recruitment. Methods: Normal spinal peri-entheseal bone (PEB) and entheseal soft tissue (EST) were characterized for MSCs by immunophenotypic, osteogenic, chondrogenic, and adipogenic differentiation criteria. Functional and gene transcriptomic analysis was carried out on undifferentiated, adipo- differentiated, and osteo-differentiated MSCs. The enthesis C-C Motif Chemokine Ligand 20-C-C Motif Chemokine Receptor 6 (CCL20-CCR6) axis was investigated at transcript and protein levels to ascertain whether entheseal MSCs influence local immune cell populations. Results: Cultured MSCs from both PEB and EST displayed a tri-lineage differentiation ability. EST MSCs exhibited 4.9-fold greater adipogenesis (p < 0.001) and a 3-fold lower osteogenic capacity (p < 0.05). IL-17A induced greater osteogenesis in PEB MSCs compared to EST MSCs. IL-17A suppressed adipogenic differentiation, with a significant decrease in fatty acid-binding protein 4 (FABP4), peroxisome proliferator-activated receptor gamma (PPARγ), Cell Death Inducing DFFA Like Effector C (CIDEC), and Perilipin-1 (PLIN1). IL-17A significantly increased the CCL20 transcript (p < 0.01) and protein expression (p < 0.001) in MSCs supporting a role in type 17 lymphocyte recruitment. Conclusions: Normal spinal enthesis harbors resident MSCs with different in vitro functionalities in bone and soft tissue, especially in response to IL-17A, which enhanced osteogenesis and CCL20 production and reduced adipogenesis compared to unstimulated MSCs. This MSC-stromal-enthesis immune system may be a hitherto unappreciated mechanism of “fine tuning” tissue repair responses at the enthesis in health and could be relevant for SpA understanding.

Cytokine "fine tuning" of enthesis tissue homeostasis as a pointer to spondyloarthritis pathogenesis with a focus on relevant TNF and IL-17 targeted therapies

A curious feature of axial disease in ankylosing spondylitis (AS) and related non-radiographic axial spondyloarthropathy (nrAxSpA) is that spinal inflammation may ultimately be associated with excessive entheseal tissue repair with new bone formation. Other SpA associated target tissues including the gut and the skin have well established paradigms on how local tissue immune responses and proven disease relevant cytokines including TNF and the IL-23/17 axis contribute to tissue repair. Normal skeletal homeostasis including the highly mechanically stressed entheseal sites is subject to tissue microdamage, micro-inflammation and ultimately repair. Like the skin and gut, healthy enthesis has resident immune cells including ILCs, γδ T cells, conventional CD4+ and CD8+ T cells and myeloid lineage cells capable of cytokine induction involving prostaglandins, growth factors and cytokines including TNF and IL-17 that regulate these responses. We discuss how human genetic studies, animal models and translational human immunology around TNF and IL-17 suggest a largely redundant role for these pathways in physiological tissue repair and homeostasis. However, disease associated immune system overactivity of these cytokines with loss of tissue repair “fine tuning” is eventually associated with exuberant tissue repair responses in AS. Conversely, excessive biomechanical stress at spinal enthesis or peripheral enthesis with mechanically related or degenerative conditions is associated with a normal immune system attempts at cytokine fine tuning, but in this setting, it is commensurate to sustained abnormal biomechanical stressing. Unlike SpA, where restoration of aberrant and excessive cytokine “fine tuning” is efficacious, antagonism of these pathways in biomechanically related disease may be of limited or even no value.