Type 3 innate lymphoid cells producing IL-17 and IL-22 are expanded in the gut, in the peripheral blood, synovial fluid and bone marrow of patients with ankylosing spondylitis

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.

Alterations in peripheral T-cell and B-cell subsets in the ankylosing spondylitis patients with gut inflammation

AIM

This study investigates changes in immune cell subsets in peripheral blood of ankylosing spondylitis (AS) patients with colitis or terminal ileitis. It aims to explore the connection between changes in lymphocyte subsets and gut inflammation, providing insights for early detection.

METHODS

Overall, 50 AS patients undergoing colonoscopy were enrolled. Flow cytometry was employed to analyze lymphocyte subsets, including T and B cells, in peripheral blood. Disease activity was assessed using CRP, ESR, BASDAI, ASDAS-CRP, and ASDAS-ESR.

RESULTS

Compared to AS patients without gut inflammation, those with colorectal inflammation showed a significant increase in total T cells (p < .05), an increase in exhausted CD4+ T cells (p < .05), and a decrease in Th2 cells and total Tc cells (p < .05). Notably, in AS patients with terminal ileitis, there was an increase in total B cells and classic switched B cells (p < .05), with a decrease in double-positive T cells (p < .05). However, no significant differences were observed in the distribution of Tfh-cell subpopulations (Tfh1, Tfh2, Tfh17) and Tc-cell subpopulations (Tc1, Tc2, Tc17) between AS patients with either colorectal inflammation or terminal ileitis (p > .05). We explored the relationship between disease activity scores, ESR, CRP, and lymphocyte subsets, but found no statistically significant correlation between them.

CONCLUSION

Distinct immune patterns may exist in AS with different types of intestinal inflammation. Colitis in AS is primarily characterized by a significant increase in exhausted CD4+ T cells, along with a decrease in Th2 cells. In contrast, terminal ileum inflammation in AS is marked by an increase in total B cells and classic switched B cells. These findings offer new insights for early detection and therapeutic intervention.

The impact of vedolizumab therapy on extraintestinal manifestations in patients with inflammatory bowel disease: A systematic review and meta-analysis

BACKGROUND AND AIM

Extraintestinal manifestations (EIMs) pose a significant threat in inflammatory bowel disease (IBD) patients. Vedolizumab (VDZ) primarily affects the gastrointestinal tract. However, its impact on EIMs remains uncertain. Therefore, we conducted this meta-analysis to examine the effects of VDZ on EIMs during treatment.

METHODS

Relevant studies were identified by conducting thorough searches across electronic databases, including PubMed, Ovid Embase, Medline, and Cochrane CENTRAL. Primary outcomes focused on the proportion of patients with resolution for pre-existing EIMs in IBD patients receiving VDZ. Secondary outcomes included the proportion of patients with EIM exacerbations and new onset EIMs during VDZ treatment.

RESULTS

Our meta-analysis encompassed 21 studies. The proportion of patients with resolution of pre-existing EIMs in VDZ-treated IBD patients was 39% (150/386; 95% confidence interval [CI] 0.31-0.48). The proportion of patients with EIM exacerbations occurred at a rate of 28% (113/376; 95% CI 0.05-0.50), while new onset EIMs had a rate of 15% (397/2541; 95% CI 0.10-0.20). Subgroup analysis revealed a 40% (136/337) proportion of patients with resolution for articular-related EIMs and a 50% (9/18) rate for erythema nodosum. Exacerbation rates for arthritis/arthralgia, erythema nodosum/pyoderma gangrenosum, and aphthous stomatitis during VDZ use were 28% (102/328), 18% (7/38), and 11% (3/28), respectively. The incidence rate of newly developed EIMs during treatment was 11% (564/4839) for articular-related EIMs, with other EIMs below 2%.

CONCLUSION

VDZ demonstrates efficacy in skin-related EIMs like erythema nodosum and joint-related EIMs including arthritis, arthralgia, spondyloarthritis, and peripheral joint diseases. Some joint and skin-related EIMs may experience exacerbation during VDZ therapy.

Contribution of gut-derived T cells to extraintestinal autoimmune diseases

The mammalian intestine harbors abundant T cells with high motility, where these cells can affect both intestinal and extraintestinal disorders. Growing evidence shows that gut-derived T cells migrate to extraintestinal organs, contributing to the pathogenesis of certain autoimmune diseases, including type 1 diabetes (T1D) and multiple sclerosis (MS). However, three key questions require further elucidation. First, how do intestinal T cells egress from the intestine? Second, how do gut-derived T cells enter organs outside the gut? Third, what is the pathogenicity of gut-derived T cells and their correlation with the gut microenvironment? In this Opinion, we propose answers to these questions. Understanding the migration and functional regulation of gut-derived T cells might inform precise targeting for achieving safe and effective approaches to treat certain extraintestinal autoimmune diseases.

Exploring the pathogenesis of RA through the gut-articular axis-dysbiosis a potential factor

Rheumatoid arthritis (RA) is a chronic autoimmune disease with a complex etiology. It has been suggested that the pathogenesis of RA begins in the mucosa and then transitions to the joints when many factors interact, including microbial dysbiosis, inflammatory responses, and immune abnormalities at the mucosal site. Data from RA animals and patients suggest there are changes in the mucosal microflora before the onset of RA, and that dysbiosis of the mucosal ecology continues to play a role in the development of arthritis. Microbial dysbiosis of the mucosa reduces the normal barrier function of the intestinal tract, promotes inflammatory reactions in the mucosal areas of the intestines, and then activates the intestinal immune cells abnormally to produce a large number of auto-reactive antibodies that exacerbate arthritis. Current findings do not clarify whether dysbiosis is only a potential trigger for the development of RA. If it is possible to intervene in such microbial changes before the onset of RA, could the clinical symptoms of arthritis be prevented or reduced? Finding new ways to regulate gut flora composition to maintain gut barrier function is an ongoing challenge for the prevention and treatment of RA.

Enhanced Type 1 Interferon Signature in Axial Spondyloarthritis Patients Unresponsive to Secukinumab Treatment

OBJECTIVE

Axial spondyloarthritis (axSpA) is an inflammatory disease in which overactive interleukin (IL)-17A-producing cells are implicated in a central role. Therapeutically, biologics that target IL-17A, such as secukinumab, have demonstrated improved clinical outcomes. Despite this translational success, there is a gap in understanding why some patients with axSpA do not respond to IL-17A-blocking therapy. Our study aims to discriminate immune profiles between secukinumab responders (SEC-R) and nonresponders (SEC-NR).

METHODS

Peripheral blood mononuclear cells were collected from 30 patients with axSpA before and 24 weeks after secukinumab treatment. Frequency of CD4+ subsets were compared between SEC-R and SEC-NR using flow cytometry. Mature CD45RO+CD45RA-CD4+ T cells were fluorescent-activated cell sorting sorted, and RNA was measured using NanoString analysis.

RESULTS

SEC-NR had an increased frequency of IL-17A-producing RORγt+CD4+ T cells compared to healthy controls before secukinumab treatment (P < 0.01). SEC-NR had a significant increase of CXCR3+ CD4+ T cells before secukinumab treatment compared to SEC-R (P < 0.01). Differentially expressed gene analysis revealed up-regulation of type 1 interferon (IFN)-regulated genes in SEC-NR patients compared to SEC-R patients after receiving the biologic. SEC-R patients had an up-regulated cytotoxic CD4+ T cell gene signature before receiving secukinumab treatment compared to SEC-NR patients.

CONCLUSION

The increased frequency of IL-17A-producing cells in SEC-NR patients suggests a larger inflammatory burden than SEC-R patients. With treatment, SEC-NR patients have a more pronounced type 1 IFN signature than SEC-R patients, suggesting a mechanism contributing to this larger inflammatory burden. The results point toward more immune heterogeneity in axSpA than has been recognized and highlights the need for precision therapeutics in this disease.

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.

Causal relationship between gut microbiota and ankylosing spondylitis and potential mediating role of inflammatory cytokines: A mendelian randomization study

Associations between gut microbiota and ankylosing spondylitis have been discovered in previous studies, but whether these associations reflect a causal relationship remains inconclusive. Aiming to reveal the bidirectional causal associations between gut microbiota and ankylosing spondylitis, we utilized publicly available genome wide association study summary data for 211 gut microbiota (GM) taxa and ankylosing spondylitis (AS) to conduct two sample mendelian randomization analyses. Mediation analysis was performed to explore mediating inflammatory cytokines. We found that genetically predicted higher abundance of Lactobacillaceae family, Rikenellaceae family and Howardella genus had suggestive associations with decreased risk of ankylosing spondylitis while genetic proxied higher abundance of Actinobacteria class and Ruminococcaceae_NK4A214_group genus was associated with increased risk of ankylosing spondylitis. IL23 and IFN-γ were potential mediating cytokines for GM dysbiosis, especially for Actinobacteria class, leading to AS. Our study provided a new exploration direction for the treatment of AS. Lactobacillaceae family, Rikenellaceae family, Howardella genus, Actinobacteria class and Ruminococcaceae_NK4A214_group genus are expected to become new therapeutic targets and monitoring indicators for AS.

Gut microbiota in axial spondyloarthritis : genetics, medications and future treatments

Axial spondyloarthritis, also referred to as ankylosing spondylitis, is a chronic inflammatory condition that predominantly affects the axial spine but may also present with peripheral arthritis. It falls within the umbrella of disorders known as spondyloarthropathies. In addition to axial spondyloarthritis, this group includes psoriatic arthritis, enteropathic arthritis, reactive arthritis, and undifferentiated spondyloarthropathy, with axial spondyloarthritis being one of the most common. The overall mechanisms underlying the development of axial spondyloarthritis are complex and multifactorial. There is a significant and well-recognized association between axial spondyloarthritis and the HLA-B27 gene, but there have also been non-HLA genes identified in the disease process, as well as certain inflammatory cytokines that play a role in the inflammatory process, such as tumor necrosis factor (TNF). More recently, there has been research and new evidence linking changes in the gut microbiota to the disease process of axial spondyloarthritis. Research into the role of the gut microbiota and gut dysbiosis is a large, ever-growing field. It has been associated with a multitude of conditions, including axial spondyloarthritis. This mini-review highlights the symbiotic relationship of the gut microbiota with the pathogenesis, therapeutic agents and future treatments of axial spondyloarthritis.

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.

Identification and bioinformatics analysis of lncRNAs in serum of patients with ankylosing spondylitis

OBJECTIVES

The aim of this study was to explore the long non-coding RNA (lncRNA) expression profiles in serum of patients with ankylosing spondylitis (AS). The role of these lncRNAs in this complex autoimmune situation needs to be evaluated.

METHODS

We used high-throughput whole-transcriptome sequencing to generate sequencing data from three patients with AS and three normal controls (NC). Then, we performed bioinformatics analyses to identify the functional and biological processes associated with differentially expressed lncRNAs (DElncRNAs). We confirmed the validity of our RNA-seq data by assessing the expression of eight lncRNAs via quantitative reverse transcription polymerase chain reaction (qRT-PCR) in 20 AS and 20 NC samples. We measured the correlation between the expression levels of lncRNAs and patient clinical index values using the Spearman correlation test.

RESULTS

We identified 72 significantly upregulated and 73 significantly downregulated lncRNAs in AS patients compared to NC. qRT-PCR was performed to validate the expression of selected DElncRNAs; the results demonstrated that the expression levels of MALAT1:24, NBR2:9, lnc-DLK1-35:13, lnc-LARP1-1:1, lnc-AIPL1-1:7, and lnc-SLC12A7-1:16 were consistent with the sequencing analysis results. Enrichment analysis showed that DElncRNAs mainly participated in the immune and inflammatory responses pathways, such as regulation of protein ubiquitination, major histocompatibility complex class I-mediated antigen processing and presentation, MAPkinase activation, and interleukin-17 signaling pathways. In addition, a competing endogenous RNA network was constructed to determine the interaction among the lncRNAs, microRNAs, and mRNAs based on the confirmed lncRNAs (MALAT1:24 and NBR2:9). We further found the expression of MALAT1:24 and NBR2:9 to be positively correlated with disease severity.

CONCLUSION

Taken together, our study presents a comprehensive overview of lncRNAs in the serum of AS patients, thereby contributing novel perspectives on the underlying pathogenic mechanisms of this condition. In addition, our study predicted MALAT1 has the potential to be deeply involved in the pathogenesis of AS.

Advances in the study of tertiary lymphoid structures in the immunotherapy of breast cancer

Breast cancer, as one of the most common malignancies in women, exhibits complex and heterogeneous pathological characteristics across different subtypes. Triple-negative breast cancer (TNBC) and HER2-positive breast cancer are two common and highly invasive subtypes within breast cancer. The stability of the breast microbiota is closely intertwined with the immune environment, and immunotherapy is a common approach for treating breast cancer.Tertiary lymphoid structures (TLSs), recently discovered immune cell aggregates surrounding breast cancer, resemble secondary lymphoid organs (SLOs) and are associated with the prognosis and survival of some breast cancer patients, offering new avenues for immunotherapy. Machine learning, as a form of artificial intelligence, has increasingly been used for detecting biomarkers and constructing tumor prognosis models. This article systematically reviews the latest research progress on TLSs in breast cancer and the application of machine learning in the detection of TLSs and the study of breast cancer prognosis. The insights provided contribute valuable perspectives for further exploring the biological differences among different subtypes of breast cancer and formulating personalized treatment strategies.

Innate lymphoid cells: New players in osteoimmunology

Innate lymphoid cells (ILCs) are the most recently identified immune cell types existing in lymphoid and nonlymphoid organs. Albeit they lack the expression of antigen receptors, ILCs play vital roles in innate immune responses by producing multiple effector cytokines. The ILC family includes conventional natural killer cells and cytokine-producing ILCs, which are divided into group 1, group 2, and group 3 ILCs based on their effector cytokines and developmental requirements. Emerging evidence has indicated that ILCs are essential immune regulators of bone homeostasis, playing a critical role in osteoimmunology. In this mini-review, we discuss recent advances in the understanding of ILC functions in bone homeostasis under physiological and pathological conditions, with an emphasis on the communication between ILCs and bone cells including osteoclasts and osteoblasts, as well as the underlying immunoregulatory networks involving ILC-derived cytokines and growth factors. This review also discusses future research directions and the potential of targeting ILCs for the treatment of inflammation-associated bone disorders.

All-trans retinoic acid alleviates collagen-induced arthritis and promotes intestinal homeostasis

All-trans retinoic acid (ATRA) has emerged as a promising adjunctive treatment for rheumatoid arthritis. However, the mechanism by which ATRA mitigates arthritis remains unclear. In this study, we aimed to explore ATRA alleviation of arthritis and the role of ATRA in regulating intestinal homeostasis. Thus, we established a collagen-induced arthritis (CIA) model in Wistar rats. After 6 weeks of ATRA treatment, the arthritis index of CIA rats decreased, synovial inflammation was alleviated, and the disruption of Th17/Treg differentiation in peripheral blood was reversed. Additionally, the Th17/Treg ratio in the mesenteric lymph nodes decreased and the expression of Foxp3 mRNA increased and that of IL-17 mRNA decreased in the colon and ileum. Microscopically, we observed reduced intestinal inflammation. Transmission electron microscopy revealed that ATRA could repair tight junctions, which was accompanied by an increase in the expression of Claudin-1, Occludin and ZO-1. Moreover, ATRA regulated the composition of the gut microbiota, as was characterized based on the reduced abundance of Desulfobacterota and the increased abundance of Lactobacillus. In conclusion, ATRA demonstrates the potential to alleviate arthritis in CIA rats, which might be correlated with modulating the gut microbiota and regulating the intestinal immune response. Our findings provide novel insights into ATRA-mediated alleviation of arthritis.

Gut microbiota does not play a mediating role in the causal association between inflammatory bowel disease and several its associated extraintestinal manifestations: a Mendelian randomization study

Background and objectives

Observational study has found inflammatory bowel disease to be associated with multiple extraintestinal manifestations. To this end, we characterized the causal association between inflammatory bowel disease and extraintestinal manifestations through a Mendelian randomization study and further explored the role of intestinal flora in inflammatory bowel disease and the extraintestinal manifestations associated with it.

Materials and methods

We genetically predicted the causal relationship between inflammatory bowel disease and twenty IBD-related extraintestinal manifestations (including sarcoidosis, iridocyclitis, interstitial lung disease, atopic dermatitis, ankylosing spondylitis, psoriatic arthropathies, primary sclerosing cholangitis, primary biliary cholangitis). We used the full genome-wide association study (GWAS) summary statistics on gut microbiota in 18,340 participants from 24 cohorts to explore its role in the casual relationships between IBD and IBD-related extraintestinal manifestations. Inverse variance weighting (IVW) was used as the main analytical method to assess the causal associations. We performed Cochran's Q test to examine the heterogeneity. To assess the robustness of the IVW results, we further performed sensitivity analyses including the weighted median method, MR-Egger regression, and Mendelian Randomization Pleiotropy RESidual Sum and Outlier (MR-PRESSO) test. The leave-one-out sensitivity analysis was further performed to monitor if significant associations were dominated by a single nucleotide polymorphism (SNP).

Result

A total of eight extraintestinal manifestations were found to be at elevated risk of development due to inflammatory bowel diseases. A total of 11 causal relationships were found between IBD and gut microbiota, four of which were stable. Between gut microbiota and these eight extraintestinal manifestations, a total of 67 nominal causal associations were identified, of which 13 associations were stable, and notably 4 associations were strongly correlated.

Conclusion

Through the two-sample MR analysis, we identified extraintestinal manifestations that were causally associated with inflammatory bowel disease and obtained multiple associations from inflammatory bowel disease and gut microbiota, and gut microbiota and extraintestinal manifestations in further analyses. These associations may provide useful biomarkers and potential targets for pathogenesis and treatment.

Microbiota-dependent indole production stimulates the development of collagen-induced arthritis in mice

Altered tryptophan catabolism has been identified in inflammatory diseases like rheumatoid arthritis (RA) and spondyloarthritis (SpA), but the causal mechanisms linking tryptophan metabolites to disease are unknown. Using the collagen-induced arthritis (CIA) model, we identified alterations in tryptophan metabolism, and specifically indole, that correlated with disease. We demonstrated that both bacteria and dietary tryptophan were required for disease and that indole supplementation was sufficient to induce disease in their absence. When mice with CIA on a low-tryptophan diet were supplemented with indole, we observed significant increases in serum IL-6, TNF, and IL-1β; splenic RORγt+CD4+ T cells and ex vivo collagen-stimulated IL-17 production; and a pattern of anti-collagen antibody isotype switching and glycosylation that corresponded with increased complement fixation. IL-23 neutralization reduced disease severity in indole-induced CIA. Finally, exposure of human colonic lymphocytes to indole increased the expression of genes involved in IL-17 signaling and plasma cell activation. Altogether, we propose a mechanism by which intestinal dysbiosis during inflammatory arthritis results in altered tryptophan catabolism, leading to indole stimulation of arthritis development. Blockade of indole generation may present a unique therapeutic pathway for RA and SpA.

Group 3 Innate Lymphoid Cells Exacerbate Lupus Nephritis by Promoting B Cell Activation in Kidney Ectopic Lymphoid Structures

Group 3 innate lymphoid cells (ILC3s) represent a new population in immune regulation, yet their role in lupus nephritis (LN) remains elusive. In the present work, systemic increases in ILC3s, particularly in the kidney, are observed to correlate strongly with disease severity in both human and murine LN. Using MRL/lpr lupus mice and a nephrotoxic serum-induced LN model, this study demonstrates that ILC3s accumulated in the kidney migrate predominantly from the intestine. Furthermore, intestinal ILC3s accelerate LN progression, manifested by exacerbated autoimmunity and kidney injuries. In LN kidneys, ILC3s are located adjacent to B cells within ectopic lymphoid structures (ELS), directly activating B cell differentiation into plasma cells and antibody production in a Delta-like1 (DLL1)/Notch-dependent manner. Blocking DLL1 attenuates ILC3s' effects and protects against LN. Altogether, these findings reveal a novel pathogenic role of ILC3s in B cell activation, renal ELS formation and autoimmune injuries during LN, shedding light on the therapeutic value of targeting ILC3s for LN.

Beyond the horizon: Innovations and future directions in axial-spondyloarthritis

Axial spondyloarthritis (axSpA) is a chronic inflammatory disease of the spine and sacroiliac joints. This review discusses recent advances across multiple scientific fields that promise to transform axSpA management. Traditionally, axSpA was considered an immune-mediated disease driven by human leukocyte antigen B27 (HLA-B27), interleukin (IL)-23/IL-17 signaling, biomechanics, and dysbiosis. Diagnosis relies on clinical features, laboratory tests, and imaging, particularly magnetic resonance imaging (MRI) nowadays. Management includes exercise, lifestyle changes, non-steroidal anti-inflammatory drugs and if this is not sufficient to achieve disease control also biological and targeted-synthetic disease modifying anti-rheumatic drugs. Beyond long-recognized genetic risks like HLA-B27, high-throughput sequencing has revealed intricate gene-environment interactions influencing dysbiosis, immune dysfunction, and aberrant bone remodeling. Elucidating these mechanisms promises screening approaches to enable early intervention. Advanced imaging is revolutionizing the assessment of axSpA's hallmark: sacroiliac bone-marrow edema indicating inflammation. Novel magnetic resonance imaging (MRI) techniques sensitively quantify disease activity, while machine learning automates complex analysis to improve diagnostic accuracy and monitoring. Hybrid imaging like synthetic MRI/computed tomography (CT) visualizes structural damage with new clarity. Meanwhile, microbiome analysis has uncovered gut ecosystem alterations that may initiate joint inflammation through HLA-B27 misfolding or immune subversion. Correcting dysbiosis represents an enticing treatment target. Moving forward, emerging techniques must augment patient care. Incorporating patient perspectives will be key to ensure innovations like genetics, microbiome, and imaging biomarkers translate into improved mobility, reduced pain, and increased quality of life. By integrating cutting-edge, multidisciplinary science with patients' lived experience, researchers can unlock the full potential of new technologies to deliver transformative outcomes. The future is bright for precision diagnosis, tightly controlled treatment, and even prevention of axSpA.

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.

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.

Distinct regulatory machineries underlying divergent chromatin landscapes distinguish innate lymphoid cells from T helper cells

Innate lymphoid cells (ILCs), as the innate counterpart of CD4+ T helper (Th) cells, play crucial roles in maintaining tissue homeostasis. While the ILC subsets and their corresponding Th subsets demonstrate significant similarities in core programming related to effector function and regulatory mechanisms, their principal distinctions, given their innate and adaptive lymphocyte nature, remain largely unknown. In this study, we have employed an integrative analysis of 294 bulk RNA-sequencing results across all ILC and Th subsets, using scRNA-seq algorithms. Consequently, we identify two genesets that predominantly differentiate ILCs from Th cells, as well as three genesets that distinguish various immune responses. Furthermore, through chromatin accessibility analysis, we find that the ILC geneset tends to rely on specific transcriptional regulation at promoter regions compared with the Th geneset. Additionally, we observe that ILCs and Th cells are under differential transcriptional regulation. For example, ILCs are under stronger regulation by multiple transcription factors, including RORα, GATA3, and NF-κB. Otherwise, Th cells are under stronger regulation by AP-1. Thus, our findings suggest that, despite the acknowledged similarities in effector functions between ILC subsets and corresponding Th subsets, the underlying regulatory machineries still exhibit substantial distinctions. These insights provide a comprehensive understanding of the unique roles played by each cell type during immune responses.

Unravelling the immunobiology of innate lymphoid cells (ILCs): Implications in health and disease

Innate lymphoid cells (ILCs), a growing class of immune cells, imitate the appearance and abilities of T cells. However, unlike T cells, ILCs lack acquired antigen receptors, and they also do not undergo clonal selection or proliferation in response to antigenic stimuli. Despite lacking antigen-specific receptors, ILCs respond quickly to signals from infected or damaged tissues and generate an array of cytokines that regulate the development of adaptive immune response. ILCs can be categorized into four types based on their signature cytokines and transcription factors: ILC1, ILC2, ILC3 (including Lymphoid Tissue inducer- LTi cells), and regulatory ILCs (ILCregs). ILCs play key functions in controlling and resolving inflammation, and variations in their proportion are linked to various pathological diseases including cancer, gastrointestinal, pulmonary, and skin diseases. We highlight current advancements in the biology and classification of ILCs in this review. Additionally, we provide a thorough overview of their contributions to several inflammatory bone-related pathologies, including osteoporosis, rheumatoid arthritis, periodontitis, and ankylosing spondylitis. Understanding the multiple functions of ILCs in both physiological and pathological conditions will further mobilize future research towards targeting ILCs for therapeutic purposes.

Gut Inflammation in Axial Spondyloarthritis Patients is Characterized by a Marked Type 17 Skewed Mucosal Innate-like T Cell Signature

OBJECTIVE

Patients with spondyloarthritis (SpA) often present with microscopic signs of gut inflammation, a risk factor for progressive disease. We investigated whether mucosal innate-like T cells are involved in dysregulated interleukin-23 (IL-23)/IL-17 responses in the gut-joint axis in SpA.

METHODS

Ileal and colonic intraepithelial lymphocytes (IELs), lamina propria lymphocytes (LPLs), and paired peripheral blood mononuclear cells (PBMCs) were isolated from treatment-naive patients with nonradiographic axial SpA with (n = 11) and without (n = 14) microscopic gut inflammation and healthy controls (n = 15) undergoing ileocolonoscopy. The presence of gut inflammation was assessed histopathologically. Immunophenotyping of innate-like T cells and conventional T cells was performed using intracellular flow cytometry. Unsupervised clustering analysis was done by FlowSOM technology. Serum IL-17A levels were measured via Luminex.

RESULTS

Microscopic gut inflammation in nonradiographic axial SpA was characterized by increased ileal intraepithelial γδ-hi T cells, a γδ-T cell subset with elevated γδ-T cell receptor expression. γδ-hi T cells were also increased in PBMCs of patients with nonradiographic axial SpA versus healthy controls and were strongly associated with Ankylosing Spondylitis Disease Activity Score. The abundance of mucosal-associated invariant T cells and invariant natural killer T cells was unaltered. Innate-like T cells in the inflamed gut showed increased RORγt, IL-17A, and IL-22 levels with loss of T-bet, a signature that was less pronounced in conventional T cells. Presence of gut inflammation was associated with higher serum IL-17A levels. In patients treated with tumor necrosis factor blockade, the proportion of γδ-hi cells and RORγt expression in blood was completely restored.

CONCLUSION

Intestinal innate-like T cells display marked type 17 skewing in the inflamed gut mucosa of patients with nonradiographic axial SpA. γδ-hi T cells are linked to intestinal inflammation and disease activity in SpA.

ILC3: a case of conflicted identity

Innate lymphoid cells type 3 (ILC3s) are the first line sentinels at the mucous tissues, where they contribute to the homeostatic immune response in a major way. Also, they have been increasingly appreciated as important modulators of chronic inflammatory and autoimmune responses, both locally and systemically. The proper identification of ILC3 is of utmost importance for meaningful studies on their role in immunity. Flow cytometry is the method of choice for the detection and characterization of ILC3. However, the analysis of ILC3-related papers shows inconsistency in ILC3 phenotypic definition, as different inclusion and exclusion markers are used for their identification. Here, we present these discrepancies in the phenotypic characterization of human and mouse ILC3s. We discuss the pros and cons of using various markers for ILC3 identification. Furthermore, we consider the possibilities for the efficient isolation and propagation of ILC3 from different organs and tissues for in-vitro and in-vivo studies. This paper calls upon uniformity in ILC3 definition, isolation, and propagation for the increased possibility of confluent interpretation of ILC3's role in immunity.

Microbiota-dependent indole production is required for the development of collagen-induced arthritis

Altered tryptophan catabolism has been identified in inflammatory diseases like rheumatoid arthritis (RA) and spondyloarthritis (SpA), but the causal mechanisms linking tryptophan metabolites to disease are unknown. Using the collagen-induced arthritis (CIA) model we identify alterations in tryptophan metabolism, and specifically indole, that correlate with disease. We demonstrate that both bacteria and dietary tryptophan are required for disease, and indole supplementation is sufficient to induce disease in their absence. When mice with CIA on a low-tryptophan diet were supplemented with indole, we observed significant increases in serum IL-6, TNF, and IL-1β; splenic RORγt+CD4+ T cells and ex vivo collagen-stimulated IL-17 production; and a pattern of anti-collagen antibody isotype switching and glycosylation that corresponded with increased complement fixation. IL-23 neutralization reduced disease severity in indole-induced CIA. Finally, exposure of human colon lymphocytes to indole increased expression of genes involved in IL-17 signaling and plasma cell activation. Altogether, we propose a mechanism by which intestinal dysbiosis during inflammatory arthritis results in altered tryptophan catabolism, leading to indole stimulation of arthritis development. Blockade of indole generation may present a novel therapeutic pathway for RA and SpA.

The role of inflammation in autoimmune disease: a therapeutic target

Autoimmune diseases (AIDs) are immune disorders whose incidence and prevalence are increasing year by year. AIDs are produced by the immune system's misidentification of self-antigens, seemingly caused by excessive immune function, but in fact they are the result of reduced accuracy due to the decline in immune system function, which cannot clearly identify foreign invaders and self-antigens, thus issuing false attacks, and eventually leading to disease. The occurrence of AIDs is often accompanied by the emergence of inflammation, and inflammatory mediators (inflammatory factors, inflammasomes) play an important role in the pathogenesis of AIDs, which mediate the immune process by affecting innate cells (such as macrophages) and adaptive cells (such as T and B cells), and ultimately promote the occurrence of autoimmune responses, so targeting inflammatory mediators/pathways is one of emerging the treatment strategies of AIDs. This review will briefly describe the role of inflammation in the pathogenesis of different AIDs, and give a rough introduction to inhibitors targeting inflammatory factors, hoping to have reference significance for subsequent treatment options for AIDs.

Concurrent Brain Subregion Microgliosis in an HLA-II Mouse Model of Group A Streptococcal Skin Infection

The broad range of clinical manifestations and life-threatening infections caused by the Gram-positive bacterium, Streptococcus pyogenes or Group A Streptococcus (GAS), remains a significant concern to public health, with a subset of individuals developing neurological complications. Here, we examined the concurrent neuroimmune effects of subcutaneous GAS infections in an HLA-Class II (HLA) transgenic mouse model of subcutaneous GAS infection. To investigate changes in the skin-brain axis, HLA-DQ8 (DQA1*0301/DQB1*0302) mice (DQ8) were randomly divided into three groups: uninfected controls (No Inf), GAS infected and untreated (No Tx), and GAS infected with a resolution by clindamycin (CLN) treatment (CLN Tx) (10 mg/kg/5 days) and were monitored for 16 days post-infection. While the skin GAS burden was significantly reduced by CLN, the cortical and hippocampal GAS burden in the male DQ8 mice was not significantly reduced with CLN. Immunoreactivity to anti-GAS antibody revealed the presence of GAS bacteria in the vicinity of the neuronal nucleus in the neocortex of both No Tx and CLN Tx male DQ8 mice. GAS infection-mediated cortical cytokine changes were modest; however, compared to No Inf or No Tx groups, a significant increase in IL-2, IL-13, IL-22, and IL-10 levels was observed in CLN Tx females despite the lack of GAS burden. Western blot analysis of cortical and hippocampal homogenates showed significantly higher ionized calcium-binding adaptor-1 (Iba-1, microglia marker) protein levels in No Tx females and males and CLN Tx males compared to the No Inf group. Immunohistochemical analysis showed that Iba-1 immunoreactivity in the hippocampal CA3 and CA1 subregions was significantly higher in the CLN Tx males compared to the No Tx group. Our data support the possibility that the subcutaneous GAS infection communicates to the brain and is characterized by intraneuronal GAS sequestration, brain cytokine changes, Iba-1 protein levels, and concurrent CA3 and CA1 subregion-specific microgliosis, even without bacteremia.

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 paradigm of IL-23-independent production of IL-17F and IL-17A and their role in chronic inflammatory diseases

Interleukin-17 family (IL-17s) comprises six structurally related members (IL-17A to IL-17F); sequence homology is highest between IL-17A and IL-17F, displaying certain overlapping functions. In general, IL-17A and IL-17F play important roles in chronic inflammation and autoimmunity, controlling bacterial and fungal infections, and signaling mainly through activation of the nuclear factor-kappa B (NF-κB) pathway. The role of IL-17A and IL-17F has been established in chronic immune-mediated inflammatory diseases (IMIDs), such as psoriasis (PsO), psoriatic arthritis (PsA), axial spondylarthritis (axSpA), hidradenitis suppurativa (HS), inflammatory bowel disease (IBD), multiple sclerosis (MS), and asthma. CD4+ helper T cells (Th17) activated by IL-23 are well-studied sources of IL-17A and IL-17F. However, other cellular subtypes can also produce IL-17A and IL-17F, including gamma delta (γδ) T cells, alpha beta (αβ) T cells, type 3 innate lymphoid cells (ILC3), natural killer T cells (NKT), or mucosal associated invariant T cells (MAIT). Interestingly, the production of IL-17A and IL-17F by innate and innate-like lymphocytes can take place in an IL-23 independent manner in addition to IL-23 classical pathway. This would explain the limitations of the inhibition of IL-23 in the treatment of patients with certain rheumatic immune-mediated conditions such as axSpA. Despite their coincident functions, IL-17A and IL-17F contribute independently to chronic tissue inflammation having somehow non-redundant roles. Although IL-17A has been more widely studied, both IL-17A and IL-17F are overexpressed in PsO, PsA, axSpA and HS. Therefore, dual inhibition of IL-17A and IL-17F could provide better outcomes than IL-23 or IL-17A blockade.

The Underappreciated Role of Secretory IgA in IBD

Eighty percent of antibody secreting cells (ASCs) are found in the intestine, where they produce grams of immunoglobulin (Ig) A daily. immunoglobulin A is actively transcytosed into the lumen, where it plays a critical role in modulating the gut microbiota. Although loss of immune tolerance to bacterial antigens is the likely trigger of the dysregulated immune response that characterizes inflammatory bowel disease (IBD), little effort has been placed on understanding the interface between B cells, IgA, and the microbiota during initiation or progression of disease. This may be in part due to the misleading fact that IgA-deficient humans are mostly asymptomatic, likely due to redundant role of secretory (S) IgM. Intestinal B cell recruitment is critically dependent on integrin α4β7-MAdCAM-1 interactions, yet antibodies that target α4β7 (ie, vedolizumab), MAdCAM-1 (ie, ontamalimab), or both β7 integrins (α4β7 and αE [CD103] β7; etrolizumab) are in clinical use or development as IBD therapeutics. The effect of such interventions on the biology of IgA is largely unknown, yet a single dose of vedolizumab lowers SIgA levels in stool and weakens the oral immunization response to cholera vaccine in healthy volunteers. Thus, it is critical to further understand the role of these integrins for the migration of ASC and other cellular subsets during homeostasis and IBD-associated inflammation and the mode of action of drugs that interfere with this traffic. We have recently identified a subset of mature ASC that employs integrin αEβ7 to dock with intestinal epithelial cells, predominantly in the pericryptal region of the terminal ileum. This role for the integrin had not been appreciated previously, nor the αEβ7-dependent mechanism of IgA transcytosis that it supports. Furthermore, we find that B cells more than T cells are critically dependent on α4β7-MAdCAM-1 interactions; thus MAdCAM-1 blockade and integrin-β7 deficiency counterintuitively hasten colitis in interleukin-10-deficient mice. In both cases, de novo recruitment of IgA ASC to the intestinal lamina propria is compromised, leading to bacterial overgrowth, dysbiosis, and lethal colitis. Thus, despite the safe and effective use of anti-integrin antibodies in patients with IBD, much remains to be learned about their various cell targets.

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.

Triggers and regulation: the gut microbiome in rheumatoid arthritis

INTRODUCTION

Rheumatoid arthritis is a chronic inflammatory disease marked by systemic symptoms and joint degeneration. Interestingly, the development and progression of rheumatoid arthritis have been linked to the microbiome, notably the gut microbiome. Dysbiosis, an alteration in the gut microbiome, has been connected to the etiology and pathogenesis of rheumatoid arthritis. For instance, dysbiosis increases intestinal permeability and promotes the movement of bacteria and their products, which in turn triggers and aggravates systemic inflammation.

AREAS COVERED

The correlation between the gut microbiome and RA. Triggers of RA including dysbiosis. The therapeutic potential of the gut microbiome in RA due to its critical function in influencing the immune response. The fecal microbiota transplantation (FMT), a therapeutic strategy that involves the transfer of healthy fecal microbiota from a donor to a recipient, has produced encouraging results in the treatment of several autoimmune illnesses, including rheumatoid arthritis.

EXPERT OPINION

The role of the gut microbiome in RA is critical and serves as a basis for etiology and pathogenesis, as well as having therapeutic implications. In our opinion, FMT is an excellent example of this correlation. Still, more investigations and well-designed studies are needed in order to make firm conclusions and recommendations.

Evidence in support of the bone marrow as the primary lesion in axial spondyloarthritis

PURPOSE OF REVIEW

Over the past several decades, the concept that the primary lesion accounting for the development of axSpA is an enthesopathy has been widely accepted. However, the hallmark abnormality of axSpA occurs in the sacroiliac joint at the interface of cartilage and bone at a location remote from any anatomical enthesis. Both imaging and histopathological data from the sacroiliac joint point to immunopathogenetic events in the bone marrow as being of primary importance. Here, we discuss new developments in our understanding of immune events in the bone marrow relevant to axSpA that reinforce the need for a change in our conceptual paradigm for the pathogenesis of axSpA.

RECENT FINDINGS

Human spinal enthesis samples contain myeloperoxidase-expressing cells, a marker of neutrophils, and mucosal-associated invariant T cells in the perientheseal bone marrow, which may be activated by stromal cells and circulating microbial products to express IL-17A and IL-17F and tumor necrosis factor (TNF). Evaluation of transcriptomes of monocytes from patients with axSpA demonstrates a lipopolysaccharide/TNF signature characterized by the expression of genes associated with granulocytopoietic bone marrow cells. This neutrophil-like phenotype is more evident in established and more severe axSpA and may be activated by microbial products from the gut. A similar expansion of granulocyte-monocyte progenitor-driven hematopoiesis occurs in the SKG mouse driven by granulocyte-macrophage colony-stimulating factor. Mesenchymal stem cells (MSCs) from ankylosing spondylitis patients are more likely to exhibit osteogenic differentiation than MSCs from healthy donors, which may be mediated by the formation of specific clusters of transcriptional factors, super enhancers, regulated by axSpA-associated single nucleotide polymorphisms located mostly in noncoding regions. TNF-α may enhance directional migration of AS-MSC compared with MSC from healthy controls from the bone marrow to entheseal soft tissue, which is mediated by increased expression of engulfment and cell motility protein 1 (ELMO1). TNF and IL-17A display differential effects on adipogenesis and osteogenesis of MSC in perientheseal bone marrow and soft tissue.

SUMMARY

Bone marrow has the capacity to undergo rapid adaptation in terms of cell composition, differentiation, and immune function, resulting in inflammation and osteogenesis in axSpA.

Spondyloarthritis with inflammatory bowel disease: the latest on biologic and targeted therapies

Spondyloarthritis (SpA) encompasses a heterogeneous group of chronic inflammatory diseases that can affect both axial and peripheral joints, tendons and entheses. Among the extra-articular manifestations, inflammatory bowel disease (IBD) is associated with considerable morbidity and effects on quality of life. In everyday clinical practice, treatment of these conditions requires a close collaboration between gastroenterologists and rheumatologists to enable early detection of joint and intestinal manifestations during follow-up and to choose the most effective therapeutic regimen, implementing precision medicine for each patient's subtype of SpA and IBD. The biggest issue in this field is the dearth of drugs that are approved for both diseases, as only TNF inhibitors are currently approved for the treatment of full-spectrum SpA-IBD. Janus tyrosine kinase inhibitors are among the most promising drugs for the treatment of peripheral and axial SpA, as well as for intestinal manifestations. Other therapies such as inhibitors of IL-23 and IL-17, phosphodiesterase 4 inhibitor, α4β7 integrin blockers and faecal microbiota transplantation seem to only be able to control some disease domains, or require further studies. Given the growing interest in the development of novel drugs to treat both conditions, it is important to understand the current state of the art and the unmet needs in the management of SpA-IBD.

Pathogenic Role of IL-17 and Therapeutic Targeting of IL-17F in Psoriatic Arthritis and Spondyloarthropathies

The interleukin 17 (IL-17) family, a subset of cytokines consisting of IL-17A-F, plays crucial roles in host defence against microbial organisms and the development of inflammatory diseases, including psoriasis (PsO), axial spondyloarthritis (axSpA), and psoriatic arthritis (PsA). IL-17A is the signature cytokine produced by T helper 17 (Th17) cells and is considered the most biologically active form. The pathogenetic involvement of IL-17A in these conditions has been confirmed, and its blockade with biological agents has provided a highly effective therapeutical approach. IL-17F is also overexpressed in the skin and synovial tissues of patients with these diseases, and recent studies suggest its involvement in promoting inflammation and tissue damage in axSpA and PsA. The simultaneous targeting of IL-17A and IL-17F by dual inhibitors and bispecific antibodies may improve the management of Pso, PsA, and axSpA, as demonstrated in the pivotal studies of dual specific antibodies such as bimekizumab. The present review focuses on the role of IL-17F and its therapeutic blockade in axSpA and PsA.

Cytokines and intestinal epithelial permeability: A systematic review

BACKGROUND

The intestinal mucosa is composed of a well-organized epithelium, acting as a physical barrier to harmful luminal contents, while simultaneously ensuring absorption of physiological nutrients and solutes. Increased intestinal permeability has been described in various chronic diseases, leading to abnormal activation of subepithelial immune cells and overproduction of inflammatory mediators. This review aimed to summarize and evaluate the effects of cytokines on intestinal permeability.

METHODS

A systematic review of the literature was performed in the Medline, Cochrane and Embase databases, up to 01/04/2022, to identify published studies assessing the direct effect of cytokines on intestinal permeability. We collected data on the study design, the method of assessment of intestinal permeability, the type of intervention and the subsequent effect on gut permeability.

RESULTS

A total of 120 publications were included, describing a total of 89 in vitro and 44 in vivo studies. TNFα, IFNγ or IL-1β were the most frequently studied cytokines, inducing an increase in intestinal permeability through a myosin light-chain-mediated mechanism. In situations associated with intestinal barrier disruption, such as inflammatory bowel diseases, in vivo studies showed that anti-TNFα treatment decreased intestinal permeability while achieving clinical recovery. In contrast to TNFα, IL-10 decreased permeability in conditions associated with intestinal hyperpermeability. For some cytokines (e.g. IL-17, IL-23), results are conflicting, with both an increase and a decrease in gut permeability reported, depending on the study model, methodology, or the studied conditions (e.g. burn injury, colitis, ischemia, sepsis).

CONCLUSION

This systematic review provides evidence that intestinal permeability can be directly influenced by cytokines in numerous conditions. The immune environment probably plays an important role, given the variability of their effect, according to different conditions. A better understanding of these mechanisms could open new therapeutic perspectives for disorders associated with gut barrier dysfunction.

Immune cells and their related genes provide a new perspective on the common pathogenesis of ankylosing spondylitis and inflammatory bowel diseases

Background

The close relationship between ankylosing spondylitis (AS) and inflammatory bowel diseases (IBD) has been supported by many aspects, including but not limited to clinical manifestations, epidemiology and pathogenesis. Some evidence suggests that immune cells actively participated in the pathogenesis of both diseases. However, information on which cells are primarily involved in this process and how these cells mobilize, migrate and interact is still limited.

Methods

Datasets were downloaded from Gene Expression Omnibus (GEO) database. Common differentially expressed genes (coDEGs) were identified by package “limma”. The protein-protein interaction (PPI) network and Weighted Gene Co-Expression Network Analysis (WGCNA) were used to analyze the interactions between coDEGs. KEGG pathway enrichment analysis and inverse cumulative distribution function were applied to identify common differential pathways, while Gene Set Enrichment Analysis (GSEA) was used to confirm the significance. Correlation analysis between coDEGs and immune cells led to the identification of critical immune-cell-related coDEGs. The diagnostic models were established based on least absolute shrinkage and selection operator (LASSO) regression, while receiver operating characteristic (ROC) analysis was used to identify the ability of the model. Validation datasets were imported to demonstrate the significant association of coDEGs with specific immune cells and the capabilities of the diagnostic model.

Results

In total, 67 genes were up-regulated and 185 genes were down-regulated in both diseases. Four down-regulated pathways and four up-regulated pathways were considered important. Up-regulated coDEGs were firmly associated with neutrophils, while down-regulated genes were significantly associated with CD8+ T−cells and CD4+ T−cells in both AS and IBD datasets. Five up-regulated and six down-regulated key immue-cell-related coDEGs were identified. Diagnostic models based on key immue-cell-related coDEGs were established and tested. Validation datasets confirmed the significance of the correlation between coDEGs and specific immune cells.

Conclusion

This study provides fresh insights into the co-pathogenesis of AS and IBD. It is proposed that neutrophils and T cells may be actively involved in this process, however, in opposite ways. The immue-cell-related coDEGs, revealed in this study, may be relevant to their regulation, although relevant research is still lacking.

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.

Phenotypic heterogeneity in psoriatic arthritis: towards tissue pathology-based therapy

Psoriatic arthritis (PsA) is a heterogeneous disease involving multiple potential tissue domains. Most outcome measures used so far in randomized clinical trials do not sufficiently reflect this domain heterogeneity. The concept that pathogenetic mechanisms might vary across tissues within a single disease, underpinning such phenotype diversity, could explain tissue-distinct levels of response to different therapies. In this Review, we discuss the tissue, cellular and molecular mechanisms that drive clinical heterogeneity in PsA phenotypes, and detail existing tissue-based research, including data generated using sophisticated interrogative technologies with single-cell precision. Finally, we discuss how these elements support the need for tissue-based therapy in PsA in the context of existing and new therapeutic modes of action, and the implications for future PsA trial outcomes and design.

Therapeutic potential of targeting IL-17 and its receptor signaling in neuroinflammation

T helper 17 cells are thought to significantly contribute to the neuroinflammation process during neurogenerative diseases via their signature cytokine, interleukin (IL)-17. Recently, an emerging key role of IL-17 and its receptors has been documented in inflammatory and autoimmune diseases. The clinical studies conducted on patients with neurodegenerative disease have also shown an increase in IL-17 levels in serum as well as cerebrospinal fluid samples. Therapeutic targeting of either IL-17 receptors or direct IL-17 neutralizing antibodies has shown a promising preclinical and clinical proof of concept for treating chronic autoimmune neurodegenerative diseases such as multiple sclerosis. Thus, IL-17 and its receptors have a central role in regulation of neuroinflammation and can be considered as one of the major therapeutic targets in chronic neuroinflammatory diseases.

Reduced type 3 innate lymphoid cells related to worsening kidney function in renal dysfunction

Intestinal mucosa barrier injury and immunity imbalance contribute to chronic kidney disease (CKD) progression. Type 3 innate lymphoid cells (ILC3s) are essential for normal intestinal homeostasis. Nevertheless, the relationship between ILC3s and CKD remains largely unknown. The aim of this study was to investigate the relationship linking ILC3s to clinical indicators among patients with renal dysfunction. The levels of circulating ILC3s and dendritic cells, as well as their subsets, in patients with renal dysfunction and healthy controls were determined through flow cytometry. The levels of human plasma granulocyte-macrophage colony-stimulating factor (GM-CSF) were measured using enzyme-linked immunosorbent assay. Renal function was evaluated by measuring the estimated glomerular filtration rate (eGFR), as well as the levels of serum creatinine, blood urea nitrogen (BUN), and uric acid. The results revealed that the proportion of peripheral ILC3s was significantly decreased in patients with renal dysfunction. This reduction was positively associated with the levels of eGFR, and inversely associated with the levels of BUN and uric acid. Similarly, the percentage of circulating C-C motif chemokine receptor 6-positive (CCR6 ⁺) ILC3s was also obviously reduced, and demonstrated positive and negative associations with the levels of eGFR and BUN, respectively. Furthermore, the levels of CCR6 ⁺ ILC3s correlated positively with those of GM-CSF, as well as type 1 conventional dendritic cells (cDC1s), which also decreased in parallel with kidney function. Thus, the reduction of ILC3s, particularly CCR6 ⁺ ILC3s, was related to worsening kidney function in patients with renal dysfunction. This effect may delay renal function impairment by regulating cDC1s via the secretion of GM-CSF, indicating that CCR6 ⁺ ILC3s may serve as efficient biomarkers for evaluating kidney function.

Unmet need in rheumatology: reports from the Advances in Targeted Therapies meeting, 2022

To detail the unmet clinical and scientific needs in the field of rheumatology. After a 2-year hiatus due to the SARS-CoV-2 pandemic, the 22nd annual international Advances in Targeted Therapies meeting brought together more than 100 leading basic scientists and clinical researchers in rheumatology, immunology, epidemiology, molecular biology and other specialties. Breakout sessions were convened with experts in five rheumatological disease-specific groups including: rheumatoid arthritis (RA), psoriatic arthritis, axial spondyloarthritis, systemic lupus erythematosus and connective tissue diseases (CTDs). In each group, experts were asked to identify and prioritise current unmet needs in clinical and translational research, as well as highlight recent progress in meeting formerly identified unmet needs. Clinical trial design innovation was emphasised across all disease states. Within RA, developing therapies and trials for refractory disease patients remained among the most important identified unmet needs and within lupus and spondyloarthritis the need to account for disease endotypes was highlighted. The RA group also identified the need to better understand the natural history of RA, pre-RA states and the need ultimately for precision medicine. In CTD generally, experts focused on the need to better identify molecular, cellular and clinical signals of early and undifferentiated disease in order to identify novel drug targets. There remains a strong need to develop therapies and therapeutic strategies for those with treatment-refractory disease. Increasingly it is clear that we need to better understand the natural history of these diseases, including their 'predisease' states, and identify molecular signatures, including at a tissue level, which can facilitate disease diagnosis and treatment. As these unmet needs in the field of rheumatic diseases have been identified based on consensus of expert clinicians and scientists in the field, this document may serve individual researchers, institutions and industry to help prioritise their scientific activities.

Gut immune cell trafficking: inter-organ communication and immune-mediated inflammation

Immune cell trafficking is a complex and tightly regulated process that is indispensable for the body's fight against pathogens. However, it is also increasingly acknowledged that dysregulation of cell trafficking contributes to the pathogenesis of immune-mediated inflammatory diseases (IMIDs) in gastroenterology and hepatology, such as inflammatory bowel disease and primary sclerosing cholangitis. Moreover, altered cell trafficking has also been implicated as a crucial step in the immunopathogenesis of other IMIDs, such as rheumatoid arthritis and multiple sclerosis. Over the past few years, a central role of the gut in mediating these disorders has progressively emerged, and the partly microbiota-driven imprinting of particular cell trafficking phenotypes in the intestine seems to be crucially involved. Therefore, this Review highlights achievements in understanding immune cell trafficking to, within and from the intestine and delineates its consequences for immune-mediated pathology along the gut-liver, gut-joint and gut-brain axes. We also discuss implications for current and future therapeutic approaches that specifically interfere with homing, retention, egress and recirculation of immune cells.

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.

Features of Peripheral Blood Th-Cell Subset Composition and Serum Cytokine Level in Patients with Activity-Driven Ankylosing Spondylitis

Th cells may exhibit pathological activity depending on the regulatory and functional signals sensed under a wide range of immunopathological conditions, including ankylosing spondylitis (AS). The relationship between Th cells and cytokines is important for diagnoses and for determining treatment. Accordingly, the aim of this study was to investigate the relationship between Th-cell subset composition and serum cytokine profile for patients with activity-driven AS. In our study, patients were divided into two groups according to disease activity: low-activity AS (ASDAS-CRP < 2.1) and high-activity AS (ASDAS-CRP > 2.1). The peripheral blood Th cell subset composition was studied by flow cytometry. Using multiplex analysis, serum cytokine levels were quantified and investigated. It was found that only patients with high-activity AS had reduced central memory (CM) Th1 cells (p = 0.035) but elevated numbers of CM (p = 0.014) and effector memory (EM) Th2 cells (p < 0.001). However, no activity-driven change in the Th17 cell subset composition was observed in AS patients. Moreover, low-AS activity patients had increased numbers of Tfh17 EM cells (p < 0.001), whereas high-AS activity was associated with elevated Tfh2 EM level (p = 0.031). The serum cytokine profiles in AS patients demonstrated that cues stimulating cellular immunity were increased, but patients with high-AS activity reveled increased IL-5 level (p = 0.017). Analyzing the data obtained from AS patients allowed us to conclude that Th cell subset differentiation was mainly affected during the CM stage and characterized the IL-23/IL-17 regulatory axis, whereas increased humoral immunity was observed in the high-AS activity group.

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.

Joint together: The etiology and pathogenesis of ankylosing spondylitis

Spondyloarthritis (SpA) refers to a group of diseases with inflammation in joints and spines. In this family, ankylosing spondylitis (AS) is a rare but classic form that mainly involves the spine and sacroiliac joint, leading to the loss of flexibility and fusion of the spine. Compared to other diseases in SpA, AS has a very distinct hereditary disposition and pattern of involvement, and several hypotheses about its etiopathogenesis have been proposed. In spite of significant advances made in Th17 dynamics and AS treatment, the underlying mechanism remains concealed. To this end, we covered several topics, including the nature of the immune response, the microenvironment in the articulation that is behind the disease's progression, and the split between the hypotheses and the evidence on how the intestine affects arthritis. In this review, we describe the current findings of AS and SpA, with the aim of providing an integrated view of the initiation of inflammation and the development of the disease.

Role of the microbiome and its metabolites in ankylosing spondylitis

Ankylosing spondylitis (AS), a chronic condition that commonly influences the spine and sacroiliac joints, usually progresses to stiffness and progressive functional limitation. Its fundamental etiology and pathogenesis are likely multifactorial and remain elusive. As environmental factors, gut microbiota performs critical functions in the pathogenesis of AS through various mechanisms, including interacting with genes, enhancing intestinal permeability, activating the gut mucosa immune system, and affecting the intestinal microbiota metabolites. This review provides an overview of recent advances in investigating gut microbiota in AS pathogenesis and discusses potential methods for future therapeutic intervention.

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.

Role of macrophage-associated chemokines in the assessment of initial axial spondyloarthritis

OBJECTIVES

To identify biomarkers that reflect disease activity scores and to investigate the role of macrophage-associated chemokines in initial axial spondyloarthritis (axSpA).

METHOD

Patients with axSpA were enrolled. The SpondyloArthritis Research Consortium of Canada (SPARCC) method was used to score bone marrow oedema (BMO) in the inflammatory lesions on magnetic resonance imaging (MRI). Radiographic assessment of the spine was performed using the modified Stoke Ankylosing Spondylitis Spine Score (mSASSS). Clinical variables, including inflammatory markers, serum CC chemokine ligand 2 (CCL2), CCL3, CCL7, CCL8 and C-X3-C motif ligand 1 (CX3CL1), were measured. Correlation analysis between serum levels of these macrophage-associated chemokines and clinical data was performed.

RESULTS

There were no significant differences between the axSpA group and the healthy control group in terms of serum levels of CCL2, CCL3 or CCL8. Compared to the healthy control group, the serum levels of CCL7 and CX3CL1 were significantly higher in ankylosing spondylitis (AS) (p = 0.045, p = 0.017, respectively). In the AS subgroup, the serum level of CX3CL1 had a positive correlation with SPARCC scores.

CONCLUSIONS

In AS, serum CCL7 and CX3CL1 levels are elevated. The serum level of CX3CL1 is associated with MRI-determined oedema in AS. CX3CL1 may be useful as a biomarker to predict active inflammation in the sacroiliac joint (SIJ) in AS. Key Points • Serum levels of CX3CL1 are associated with MRI-determined oedema in AS. • CX3CL1 may be a useful biomarker to predict active inflammation in the sacroiliac joint in AS.