Enrichment of circulating interleukin-17-secreting interleukin-23 receptor-positive γ/δ T cells in patients with active ankylosing spondylitis

Subclinical enthesitis in enthesitis-related arthritis and sacroiliitis associated with familial Mediterranean fever

OBJECTIVES

In our study, we investigated the presence of subclinical enthesitis by ultrasonography (US) in asymptomatic patients with enthesitis-related arthritis (ERA) and sacroiliitis associated with familial Mediterranean fever (FMF).

METHODS

A total of 50 patients, including 35 patients with ERA and 15 with sacroiliitis associated with FMF, were included in the study. All patients were evaluated with US by a paediatric radiologist. Enthesis of seven tendons (common extensor and flexor tendons, quadriceps tendon, proximal and distal patellar tendon, Achilles tendon, and plantar fascia) was examined on both sides.

RESULTS

Subclinical enthesitis was detected in 10 ERA (28.5%) and three FMF (20%) patients. Enthesitis was radiologically diagnosed in 16 (2.3%) out of 700 evaluated entheseal sites. The most frequent sites of enthesitis were Achilles (37.5%) and quadriceps (31.3%) tendons. All patients were in clinical remission and had no active complaints, and acute phase reactants were within normal limits. Therefore, the patients were followed up without treatment change. However, disease flare-up was observed in three of these patients (23.1%) during the follow-up, and their treatments were intensified.

CONCLUSIONS

Our results showed that the US can be particularly helpful in detecting subclinical enthesitis and predicting disease flare-ups.

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

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

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.

Long-term safety of Ixekizumab in adults with psoriasis, psoriatic arthritis, or axial spondyloarthritis: a post-hoc analysis of final safety data from 25 randomized clinical trials

BACKGROUND

We report long-term, end-of-study program safety outcomes from 25 randomized clinical trials (RCTs) in adult patients with psoriasis (PsO), psoriatic arthritis (PsA), or axial spondyloarthritis (axSpA) [including ankylosing spondylitis (AS) and non-radiographic axial spondyloarthritis (nr-axSpA)] who received ≥ 1 dose of Ixekizumab (IXE) over 5 years (PsO) or up to 3 years (PsA, axSpA).

METHODS

This integrated safety analysis consists of data from patients who received any dose of IXE, across 25 RCTs (17 PsO, 4 PsA, 4 axSpA). Rates of treatment-emergent adverse events (TEAEs), serious adverse events (SAEs) and selected adverse events (AEs) of interest were analyzed for all pooled studies by years of therapy and overall, through March 2022. Results were reported as exposure-adjusted incidence rates (IRs) per 100 patient-years (PY) overall and at successive year intervals.

RESULTS

Six thousand eight hundred ninety two adult patients with PsO, 1401 with PsA, and 932 with axSpA (including AS and nr-axSpA), with a cumulative IXE exposure of 22,371.1 PY were included. The most commonly reported TEAE across indications was nasopharyngitis (IRs per 100 PY: 8.8 (PsO), 9.0 (PsA), 8.4 (axSpA)). SAEs were reported by 969 patients with PsO (IR 5.4), 134 patients with PsA (IR 6.0), and 101 patients with axSpA (IR 4.8). Forty-five deaths were reported (PsO, n = 36, IR 0.2; PsA, n = 6, IR 0.3; axSpA, n = 3, IR 0.1). TEAEs did not increase during IXE exposure: IRs per 100 PY, PsO: 88.9 to 63.2 (year 0-1 to 4-5), PsA: 87 to 67.3 (year 0-1 to 2-3), axSpA: 82.1 to 55.4 (year 0-1 to >  = 2). IRs per 100 PY of discontinuation from IXE due to AE were 2.9 (PsO), 5.1 (PsA), and 3.1 (axSpA). IRs per 100 PY of injection site reactions were 5.9 (PsO), 11.6 (PsA) and 7.4 (axSpA); Candida: 1.9 (PsO), 2.0 (PsA), and 1.2 (axSpA); depression, major adverse cerebro-cardiovascular events and malignancies: ≤ 1.6 across all indications. Adjudicated IRs per 100 PY of inflammatory bowel disease were ≤ 0.8 across indications (0.1 [PsO]; 0.1 [PsA]; 0.8 [axSpA]).

CONCLUSIONS

In this integrated safety analysis, consisting of over 22,000 PY of exposure, the long-term safety profile of IXE was found to be consistent with previous, earlier reports, with no new safety signals identified.

TRIAL REGISTRATION

NCT registration numbers for RCTs included in this integrated analysis can be found in Additional File 1.

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.

Tetrahedral Framework Nuclear Acids Can Regulate Interleukin-17 Pathway to Alleviate Inflammation and Inhibit Heterotopic Ossification in Ankylosing Spondylitis

Ankylosing spondylitis (AS) is a chronic systemic inflammatory disease that leads to serious spinal deformity and ankylosis. Persistent inflammation and progressive ankylosis lead to loss of spinal flexibility in patients with AS. Tetrahedral framework nucleic acids (tFNAs) have emerged as a one kind of nanomaterial composed of four specially designed complementary DNA single strands with outstanding biological properties. Results from in vivo experiments demonstrated that tFNAs treatment could inhibit inflammatory responses and heterotopic ossification to halt disease progression. In vitro, tFNAs were proved to influence the biological behavior of AS primary chondrocytes and inhibit the secretion of pro-inflammatory cytokines through interleukin-17 pathway. The osteogenic process of chondrocytes was as well inhibited at the transcriptional level to regulate the expression of related proteins. Therefore, we believe tFNAs had a strong therapeutic effect and could serve as a nonsurgical remedy in the future to help patients suffering from AS.

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.

The role of γδ T cells in the immunopathogenesis of inflammatory diseases: from basic biology to therapeutic targeting

The γδ T cells are lymphocytes with an innate-like phenotype that can distribute to different tissues to reside and participate in homeostatic functions such as pathogen defense, tissue modeling, and response to stress. These cells originate during fetal development and migrate to the tissues in a TCR chain-dependent manner. Their unique manner to respond to danger signals facilitates the initiation of cytokine-mediated diseases such as spondyloarthritis and psoriasis, which are immune-mediated diseases with a very strong link with mucosal disturbances, either in the skin or the gut. In spondyloarthritis, γδ T cells are one of the main sources of IL-17 and, therefore, the main drivers of inflammation and probably new bone formation. Remarkably, this population can be the bridge between gut and joint inflammation.

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.

Disrupted Neural Regeneration in Dry Eye Secondary to Ankylosing Spondylitis-With a Theoretical Link between Piezo2 Channelopathy and Gateway Reflex, WDR Neurons, and Flare-Ups

This study aimed at analyzing the corneal neural regeneration in ankylosing spondylitis patients using in vivo corneal confocal microscopy in correlation with Langerhans cell density, morphology, and dry eye parameters. Approximately 24 ankylosing spondylitis subjects and 35 age- and gender-matched control subjects were enrolled. Data analysis showed that all corneal nerve-fiber descriptives were lower in the ankylosing spondylitis group, implicating disrupted neural regeneration. Peripheral Langerhans cell density showed a negative correlation with nerve fiber descriptions. A negative correlation between tear film break-up time and corneal nerve fiber total branch density was detected. The potential role of somatosensory terminal Piezo2 channelopathy in the pathogenesis of dry eye disease and ankylosing spondylitis is highlighted in our study, exposing the neuroimmunological link between these diseases. We hypothesized earlier that spinal neuroimmune-induced sensitization due to this somatosensory terminal primary damage could lead to Langerhans cell activation in the cornea, in association with downregulated Piezo1 channels on these cells. This activation could lead to a Th17/Treg imbalance in dry eye secondary to ankylosing spondylitis. Hence, the corneal Piezo2 channelopathy-induced impaired Piezo2-Piezo1 crosstalk could explain the disrupted neural regeneration. Moreover, the translation of our findings highlights the link between Piezo2 channelopathy-induced gateway to pathophysiology and the gateway reflex, not to mention the potential role of spinal wide dynamic range neurons in the evolution of neuropathic pain and the flare-ups in ankylosing spondylitis and dry eye disease.

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.

A case report of primary biliary cholangitis combined with ankylosing spondylitis

RATIONALE

A chronic autoimmune liver disease known as primary biliary cholangitis (PBC) that selectively destructs small intrahepatic biliary epithelial cells and may result in biliary cirrhosis and eventually liver transplantation or death. PBC is associated with various other extrahepatic autoimmune diseases; however, the combination of PBC with ankylosing spondylitis has been rarely reported in the literature. Here, we reported a case of PBC with ankylosing spondylitis to improve our understanding of such coexistence and provide new ideas for the treatment of such patients.

PATIENT CONCERNS

A 54-year-old man was presented to the Department of Rheumatology because of an abnormal liver function test for 7 years, chest and back pain for 1 year, and low back pain for 2 months.

DIAGNOSES

Primary biliary cholangitis, ankylosing spondylitis, and old pulmonary tuberculosis.

INTERVENTIONS

The patient refused to use nonsteroidal anti-inflammatory drugs, conventional synthetic disease-modifying antirheumatic drugs, and biologic disease-modifying antirheumatic drugs; thus, he was treated with methylenediphosphonate (99Tc-MDP) and ursodeoxycholic acid (UDCA).

OUTCOMES

The patient achieved remission with UDCA and 99Tc-MDP therapy.

LESSONS

In the treatment of PBC combined with other disorders, the characteristics of different diseases should be considered. The patient reported herein was treated with 99Tc-MDP and UDCA, and his condition improved; thus, we consider 99Tc-MDP to be an effective treatment. Furthermore, in line with the current understanding of the pathogenesis of PBC and ankylosing spondylitis, we hypothesize that interleukin-17 inhibitor is an effective treatment for such patients.

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.

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.

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.

Deep characterization of human γδ T cell subsets defines shared and lineage-specific traits

Under non-pathological conditions, human γδ T cells represent a small fraction of CD3+ T cells in peripheral blood (1-10%). They constitute a unique subset of T lymphocytes that recognize stress ligands or non-peptide antigens through MHC-independent presentation. Major human γδ T cell subsets, Vδ1 and Vδ2, expand in response to microbial infection or malignancy, but possess distinct tissue localization, antigen recognition, and effector responses. We hypothesized that differences at the gene, phenotypic, and functional level would provide evidence that γδ T cell subpopulations belong to distinct lineages. Comparisons between each subset and the identification of the molecular determinants that underpin their differences has been hampered by experimental challenges in obtaining sufficient numbers of purified cells. By utilizing a stringent FACS-based isolation method, we compared highly purified human Vδ1 and Vδ2 cells in terms of phenotype, gene expression profile, and functional responses. We found distinct genetic and phenotypic signatures that define functional differences in γδ T cell populations. Differences in TCR components, repertoire, and responses to calcium-dependent pathways suggest that Vδ1 and Vδ2 T cells are different lineages. These findings will facilitate further investigation into the ligand specificity and unique role of Vδ1 and Vδ2 cells in early immune responses.

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.

Psoriatic Arthritis: Pathogenesis and Targeted Therapies

Psoriatic arthritis (PsA), a heterogeneous chronic inflammatory immune-mediated disease characterized by musculoskeletal inflammation (arthritis, enthesitis, spondylitis, and dactylitis), generally occurs in patients with psoriasis. PsA is also associated with uveitis and inflammatory bowel disease (Crohn's disease and ulcerative colitis). To capture these manifestations as well as the associated comorbidities, and to recognize their underlining common pathogenesis, the name of psoriatic disease was coined. The pathogenesis of PsA is complex and multifaceted, with an interplay of genetic predisposition, triggering environmental factors, and activation of the innate and adaptive immune system, although autoinflammation has also been implicated. Research has identified several immune-inflammatory pathways defined by cytokines (IL-23/IL-17, TNF), leading to the development of efficacious therapeutic targets. However, heterogeneous responses to these drugs occur in different patients and in the different tissues involved, resulting in a challenge to the global management of the disease. Therefore, more translational research is necessary in order to identify new targets and improve current disease outcomes. Hopefully, this may become a reality through the integration of different omics technologies that allow better understanding of the relevant cellular and molecular players of the different tissues and manifestations of the disease. In this narrative review, we aim to provide an updated overview of the pathophysiology, including the latest findings from multiomics studies, and to describe current targeted therapies.

Disease-specific expansion of CD29+IL-17RA+ T effector cells possessing multiple signalling pathways in spondyloarthritis

OBJECTIVES

T cells adhere to enthesis fibrocartilage via integrins and intrinsically require IL-17RA-mediated signals to maintain their effector function. We analysed CD29+IL-17RA+ T cells in inflamed lesions and peripheral blood in patients with SpA and investigated their association with disease activity and therapeutic response.

METHODS

Transcriptome analysis of synovial fluid T cells from PsA was performed using publicly available bulk cell RNA sequencing data. Blood samples were obtained from healthy controls (n = 37), RA (n = 12), IgG4-related disease (IgG4-RD; n = 12), large vessel vasculitis (LVV; n = 12) and SpA (n = 28) and were analysed by flow cytometry.

RESULTS

T cells in the inflamed joints of PsA showed CD29 and IL-17RA expression. CD29+IL-17RA+ T cells showed enriched CXCR3+CD45RA+ effector cells and activation of spleen tyrosine kinase (Syk), nuclear factor κB (NF-κB) and Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathways. The proportion of peripheral blood CD29+IL-17RA+ T cells was significantly increased in patients with SpA compared with patients with RA, IgG4-RD or LVV and in healthy controls. Based on the ASDAS-CRP scores, the proportion of CD29+IL-17RA+ T cells was positively correlated with disease activity in treatment-naïve patients with active SpA. Anti-IL-17 but not anti-TNF monoclonal antibodies reduced CD29+IL-17RA+ T cells.

CONCLUSIONS

CD29+IL-17RA+ T effector cells with enhanced Syk, NF-κB and JAK-STAT pathways were specifically increased in SpA and were correlated with disease activity, implicating a role of this newly identified T cell population in the pathogenesis. Anti-IL-17 monoclonal antibodies may be effective for patients by reducing this pathogenic T cell population.

[Psoriatic arthritis : Clinical challenges and pharmaceutical management]

Psoriatic arthritis (PsA) is a systemic immune-mediated inflammatory disease of the musculoskeletal system, which is accompanied by a chronic and progressive course. It is characterized by different clinical manifestations and can severely impair the quality of life and function of patients due to the existing heterogeneity of the manifestations. The (early) diagnosis of PsA and individualized therapeutic management in routine clinical practice are difficult due to the enormous clinical variability. In addition to the appearance of arthritis of the peripheral joints, there can be involvement of the axial skeleton, skin psoriasis, nail psoriasis, enthesitis and dactylitis. The clinical appearance, course of the disease, risk factors and pathophysiological mechanisms of PsA have been extensively researched in recent decades. With the associated better understanding of the disease, new treatment options and goals for effective treatment have also been established.

Surfing on the waves of the human γδ T cell ontogenic sea

While γδ T cells are present virtually in all vertebrates, there is a remarkable lack of conservation of the TRG and TRD loci underlying the generation of the γδ T cell receptor (TCR), which is associated with the generation of species-specific γδ T cells. A prominent example is the human phosphoantigen-reactive Vγ9Vδ2 T cell subset that is absent in mice. Murine γδ thymocyte cells were among the first immune cells identified to follow a wave-based layered development during embryonic and early life, and since this initial observation, in-depth insight has been obtained in their thymic ontogeny. By contrast, less is known about the development of human γδ T cells, especially regarding the generation of γδ thymocyte waves. Here, after providing an overview of thymic γδ wave generation in several vertebrate classes, we review the evidence for γδ waves in the human fetal thymus, where single-cell technologies have allowed the breakdown of human γδ thymocytes into functional waves with important TCR associations. Finally, we discuss the possible mechanisms contributing to the generation of waves of γδ thymocytes and their possible significance in the periphery.

Role of Th17 and IL-17 Cytokines on Inflammatory and Auto-immune Diseases

BACKGROUND

The IL-17 (interleukin 17) family consists of six structurally related pro-inflammatory cytokines, namely IL-17A to IL-17F. These cytokines have garnered significant scientific interest due to their pivotal role in the pathogenesis of various diseases. Notably, a specific subset of T-cells expresses IL-17 family members, highlighting their importance in immune responses against microbial infections.

INTRODUCTION

IL-17 cytokines play a critical role in host defense mechanisms by inducing cytokines and chemokines, recruiting neutrophils, modifying T-cell differentiation, and stimulating the production of antimicrobial proteins. Maintaining an appropriate balance of IL-17 is vital for overall health. However, dysregulated production of IL-17A and other members can lead to the pathogenesis of numerous inflammatory and autoimmune diseases.

METHOD

This review provides a comprehensive overview of the IL-17 family and its involvement in several inflammatory and autoimmune diseases. Relevant literature and research studies were analyzed to compile the data presented in this review.

RESULTS

IL-17 cytokines, particularly IL-17A, have been implicated in the development of various inflammatory and autoimmune disorders, including multiple sclerosis, Hashimoto's thyroiditis, systemic lupus erythematosus, pyoderma gangrenosum, autoimmune hepatic disorders, rheumatoid arthritis, psoriasis, psoriatic arthritis, ankylosing spondylitis, osteoarthritis, and graft-versus-host disease. Understanding the role of IL-17 in these diseases is crucial for developing targeted therapeutic strategies.

CONCLUSION

The significant involvement of IL-17 cytokines in inflammatory and autoimmune diseases underscores their potential as therapeutic targets. Current treatments utilizing antibodies against IL-17 cytokines and IL-17RA receptors have shown promise in managing these conditions. This review consolidates the understanding of IL-17 family members and their roles, providing valuable insights for the development of novel immunomodulators to effectively treat inflammatory and autoimmune diseases.

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.

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.

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.

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.

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.

Cellular and molecular diversity in spondyloarthritis

The spondyloarthritides are a cluster of inflammatory rheumatic diseases characterized by different diagnostic entities with heterogeneous phenotypes. The current classification system groups spondyloarthritis patients in two main categories, axial and peripheral spondyloarthritis, providing a framework wherein the clinical picture guides the treatment. However, the heterogeneity of the clinical manifestations of the pathologies, even when residing in the same group, highlights the importance of analyzing the smallest features of each entity to understand how different cellular subsets evolve, what the underlying mechanisms are and what biological markers can be identified and validated to evaluate the stage of disease and the corresponding efficacy of treatments. In this review, we will focus mostly on axial spondyloarthritis, report current knowledge concerning the cellular populations involved in its pathophysiology, and their molecular diversity. We will discuss the implications of such a diversity, and their meaning in terms of patients' stratification.

The gut-enthesis axis and the pathogenesis of Spondyloarthritis

Subclinical inflammation is associated with Spondylarthritis (SpA). SpA patients show features of dysbiosis, altered gut barrier function, and local expansion of innate and innate-like cells involved in type 3 immune response. The recirculation of intestinal primed immune cells into the bloodstream and, in some cases, in the joints and the inflamed bone marrow of SpA patients gave the basis of the gut-joint axis theory. In the light of the critical role of enthesis in the pathogenesis of SpA and the identification of mucosal-derived immune cells residing into the normal human enthesis, a gut-enthesis axis is also likely to exist. This work reviews the current knowledge on enthesis-associated innate immune cells' primary involvement in enthesitis development, questions their origin, and critically discusses the clues supporting the existence of a gut-enthesis axis contributing to SpA development.

IL-17A and IFN-γ are Up-regulated in CD4 and γδ T Cells in Active Behcet's Disease Patients

Involvement of γδ T cells is implicated in the pathogenesis of Behçet's disease (BD) as a bridge between innate and adaptive responses. IL-17 and IL-22 have also been shown to participate in the BD pathogenesis in addition to IFN-γ. Mainly CD4⁺ T cells are investigated previously for the production of these inflammatory cytokines. In this study, the role of γδ T cells in cytokine-related mechanisms was evaluated in BD in comparison to CD4⁺ T cells. Surface expression of markers for functional states of both CD4⁺ and γδ T cells were compared in ex vivo samples collected from patients with BD and healthy controls (HC). Sixteen active BD (a-BD), 9 inactive BD (i-BD) patients and 25 HC were investigated. The expression of CD161, CCR6 as markers for IL-17 producing cells were analyzed on γδ and CD4⁺ T cells. IFN-γ, IL-17A, IL-22, as well as CD107a (LAMP1) and CD16 (FcγRIII) were evaluated in both cell subtypes after in vitro stimulation. Only IFN-γ production was increased in γδ T cells of a-BD patients. There was no difference in increase of CD107a or decrease of CD16 surface expression on γδ T cells upon stimulation between the groups. Ex vivo IL-17A and both IL-17A/IFN-γ production and expression of CD161, CCR6 by CD4⁺ T cells were increased in a-BD. Along with CD4⁺ T cells, γδ T cells have complementary roles in cytokine production in BD. Higher IFN-γ production of γδ T cells suggests the role of an environmental triggers in BD pathogenesis, whereas IL-17 related activity is mainly provided by CD4⁺ T cells.

Inflammatory Foot Involvement in Spondyloarthritis: From Tarsitis to Ankylosing Tarsitis

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

Pathogenesis of Axial Spondyloarthritis - Sources and Current State of Knowledge

Scientific breakthroughs have culminated in the development of the spondyloarthritis (SpA) concept as a family of rheumatic diseases, distinct from rheumatoid arthritis. The demonstration of inflammatory lesions in the sacroiliac joints and spine of patients with axial symptoms of SpA who lacked radiographic features of ankylosing spondylitis (AS) helped refine the SpA concept. Axial SpA includes patients with AS and patients with axial symptoms previously categorized as undifferentiated SpA. This review examines the sources of knowledge that inform axial SpA pathogenesis, highlighting current limitations, and a basic working model of axial SpA pathogenesis.

Role of Interleukin-17 in Acute Pancreatitis

Acute pancreatitis (AP) is a leading cause of death and is commonly accompanied by systemic manifestations that are generally associated with a poor prognosis. Many cytokines contribute to pancreatic tissue damage and cause systemic injury. Interleukin-17 (IL-17) is a cytokine that may play a vital role in AP. Specifically, IL-17 has important effects on the immune response and causes interactions between different inflammatory mediators in the AP-related microenvironment. In this literature review, we will discuss the existing academic understanding of IL-17 and the impacts of IL-17 in different cells (especially in acinar cells and immune system cells) in AP pathogenesis. The clinical significance and potential mechanisms of IL-17 on AP deterioration are emphasized. The evidence suggests that inhibiting the IL-17 cytokine family could alleviate the pathogenic process of AP, and we highlight therapeutic strategies that directly or indirectly target IL-17 cytokines in acute pancreatitis.

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

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

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

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

Axial spondyloarthritis: emerging drug targets

INTRODUCTION

Axial spondyloarthritis (AxSpA) is an inflammatory disorder that affects the joints, entheses, and bone tissues and is sometimes associated with psoriasis, anterior uveitis, and gut inflammation. Its pathogenesis is not wholly understood and treatment strategies require optimization. Data concerning AxSpA pathogenesis support a critical role of abnormal CD4⁺ T cell differentiation and exacerbated type 3 immune response. This knowledge boosted the development of interleukin (IL)-17 and Janus kinase inhibitors for AxSpA treatment beyond tumor necrosis factor-α inhibition.

AREAS COVERED

Emerging drug targets in animal and cellular models and with phase-II clinical trials have been evaluated. We also reflect on key issues for preclinical and clinical research going forward.

EXPERT OPINION

Some of the most promising approaches include: (i) modulation of transforming growth factor-β family that could exert a specific role on bone formation; (ii) blockade of granulocyte-macrophage colony-stimulating factor that could reduce type 3 immune responses, and (iii) rebalancing of biased immune response by cytokines such as IL-2 or IL-27 that could favor anti-inflammatory response and sustained drug-free remission. Multiomics tools and artificial intelligence could contribute to identification of optimal targets and help stratify patients for the most appropriate treatment options.

Evolved to protect, designed to destroy: IL-17-producing γδ T cells in infection, inflammation, and cancer

T cells of the gamma delta (γδ) lineage are evolutionary conserved from jawless to cartilaginous and bony fish to mammals and represent the "swiss army knife" of the immune system capable of antigen-dependent or independent responses, memory, antigen presentation, regulation of other lymphocytes, tissue homeostasis, and mucosal barrier maintenance, to list a few. Over the last 10 years, γδ T cells that produce the cytokine IL-17 (γδT17) have taken a leading position in our understanding of how our immune system battles infection, inflicts tissue damage during inflammation, and gets rewired by the tumor microenvironment. A lot of what we know about γδT17 cells stems from mouse models, however, increasing evidence implicates these cells in numerous human diseases. Herein, we aim to give an overview of the most common mouse models that have been used to study the role of γδT17 cells in infection, inflammation, and cancer, while at the same time we will evaluate evidence for their importance in humans. We hope and believe that in the next 10 years, means to take advantage of the protective and destructive properties of γδ T and in particular γδT17 cells will be part of our standard immunotherapy toolkit.

The Impact of Programmed Cell Death on the Formation of Tertiary Lymphoid Structures

Tertiary lymphoid structures are clusters of lymphoid tissue that develop post-natally at sites of chronic inflammation. They have been described in association with infection, autoimmune disorders, cancer, and allograft rejection. In their mature stage, TLS function as ectopic germinal centers, favoring the local production of autoantibodies and cytokines. TLS formation tends to parallel the severity of tissue injury and they are usually indicative of locally active immune responses. The presence of TLS in patients with solid tumors is usually associated with a better prognosis whereas their presence predicts increased maladaptive immunologic activity in patients with autoimmune disorders or allograft transplantation. Recent data highlight a correlation between active cell death and TLS formation and maturation. Our group recently identified apoptotic exosome-like vesicles, released by apoptotic cells, as novel inducers of TLS formation. Here, we review mechanisms of TLS formation and maturation with a specific focus on the emerging importance of tissue injury, programmed cell death and extracellular vesicles in TLS biogenesis.

Imbalance of Peripheral Lymphocyte Subsets in Patients With Ankylosing Spondylitis: A Meta-Analysis

Ankylosing spondylitis is a complicated consequence of genetic predisposition and environmental factors. Enthesitis is believed to be the hallmark of ankylosing spondylitis, and the chronic inflammatory state of this disease is perpetuated by the disturbances of both the innate immune system and the acquired immune system. To clarify the alteration of immune system in patients with AS, we conducted a meta-analysis concerning the proportions of major lymphocyte subsets in the peripheral blood of AS patients. We systematically searched PubMed and China National Knowledge Infrastructure (CNKI) for articles related to this subject. A total of 95 articles involving 4,020 AS patients and 3,065 healthy controls were included in the analysis. This meta-analysis is performed on R platform using R package "meta", and Egger's tests were used to determine the presence of publication bias. Results showed that the percentages of T cells, NK cells and NKT cells were not significantly different between AS patients and healthy controls, but B cells were significantly increased. Among the subsets of T cells, the proportions of CD4+ T cells, Th17 cells, Tfh cells as well as Th1/Th2 ratio were significantly increased, while Tregs were significantly decreased. Subgroup analysis showed that the proportions of Th17 among both PBMCs, T cells and CD4+ T cells were significantly elevated, while Tregs were only significantly lower in PBMCs. Subgroup analysis also demonstrated that Tregs defined by "CD4+CD25+FoxP3+", "CD4+CD25+CD127low"or "CD4+CD25+CD127-"were significantly downregulated, indicating that the selection of markers could be critical. Further study is warranted in order to elucidate the complicated interactions between different lymphocyte subsets in AS patients. This study implied that the disequilibrium between Th17 and Tregs, as well as between Th1 and Th2 could contribute to the pathogenesis of ankylosing spondylitis, further cementing the understanding that ankylosing spondylitis is a consequence of disrupted balance of innate immune system and acquired immune system.

Inflammasome Activation in Ankylosing Spondylitis Is Associated With Gut Dysbiosis

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Ankylosing spondylitis: an autoimmune or autoinflammatory disease?

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

Circulating mature granzyme B+ T cells distinguish Crohn's disease-associated axial spondyloarthritis from axial spondyloarthritis and Crohn's disease

BACKGROUND

Axial spondyloarthritis (axSpA) has strong connections with intestinal inflammation as occurs in Crohn's disease (CD). However, the immunologic mechanisms that distinguish axSpA, CD, and those with features of both diseases (CD-axSpA) are unknown. This study aimed to address this question by initial unbiased single cell RNA-sequencing (scRNAseq) on a pilot cohort followed by validating findings using flow cytometry and ELISA in a larger cohort.

METHODS

Two individuals each with CD, axSpA, CD-axSpA, and healthy controls (HC) were recruited for a pilot discovery scRNAseq cohort, and the validation cohort consisted of 18 axSpA, 24 CD, 13 CD-axSpA, and 17 HC that was evaluated by flow cytometry on PBMCs and ELISAs for plasma cytokines.

RESULTS

Uniquely, PBMCs from subjects with CD-axSpA demonstrated a significant increase in granzyme B+ T cells of both CD4+ and CD8+ lineages by both scRNAseq and flow cytometry. T cell maturation was also greater in those with CD-axSpA, particularly the CD4+ granzyme B+ population. Pathway analysis suggested increased interferon response genes in all immune cell populations within CD-axSpA. Although IFN-γ was elevated in the plasma of a subset of subjects with CD-axSpA, IL-6 was also significantly elevated.

CONCLUSIONS

Our findings support the presence of a chronic interferonopathy in subjects with CD-axSpA characterized by interferon signaling by pathway analysis and an expansion of mature, cytotoxic T cells. These data indicate fundamental immunological differences between CD-axSpA and both of the putative "parent" conditions, suggesting that it is a distinct disease with unique natural history and treatment needs.

T2-"Low" Asthma: Overview and Management Strategies

Although the term "asthma" has been applied to all patients with airway lability and variable chest symptoms for centuries, phenotypes of asthma with distinct clinical and molecular features that may warrant different treatment approaches are well recognized. Patients with type 2 (T2)-"high" asthma are characterized by upregulation of T2 immune pathways (ie, IL-4 and IL-13 gene sets) and eosinophilic airway inflammation, whereas these features are absent in patients with T2-"low" asthma and may contribute to poor responsiveness to corticosteroid treatment. This review details definitions and clinical features of T2-"low" asthma, potential mechanisms and metabolic aspects, pediatric considerations, and potential treatment approaches. Priority research questions for T2-"low" asthma are also discussed.

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

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

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.

Regulation of Osteoblast Differentiation by Cytokine Networks

Osteoblasts, which are bone-forming cells, play pivotal roles in bone modeling and remodeling. Osteoblast differentiation, also known as osteoblastogenesis, is orchestrated by transcription factors, such as runt-related transcription factor 1/2, osterix, activating transcription factor 4, special AT-rich sequence-binding protein 2 and activator protein-1. Osteoblastogenesis is regulated by a network of cytokines under physiological and pathophysiological conditions. Osteoblastogenic cytokines, such as interleukin-10 (IL-10), IL-11, IL-18, interferon-γ (IFN-γ), cardiotrophin-1 and oncostatin M, promote osteoblastogenesis, whereas anti-osteoblastogenic cytokines, such as tumor necrosis factor-α (TNF-α), TNF-β, IL-1α, IL-4, IL-7, IL-12, IL-13, IL-23, IFN-α, IFN-β, leukemia inhibitory factor, cardiotrophin-like cytokine, and ciliary neurotrophic factor, downregulate osteoblastogenesis. Although there are gaps in the body of knowledge regarding the interplay of cytokine networks in osteoblastogenesis, cytokines appear to be potential therapeutic targets in bone-related diseases. Thus, in this study, we review and discuss our osteoblast, osteoblast differentiation, osteoblastogenesis, cytokines, signaling pathway of cytokine networks in osteoblastogenesis.

Spondyloarthritis and the Human Leukocyte Antigen (HLA)-B*27 Connection

Heritability of Spondyloarthritis (SpA) is highlighted by several familial studies and a high association with the presence of human leukocyte antigen (HLA)-B^*27. Though it has been over four decades since the association of HLA-B^*27 with SpA was first determined, the pathophysiological roles played by specific HLA-B^*27 allotypes are not fully understood. Popular hypotheses include the presentation of arthritogenic peptides, triggering of endoplasmic reticulum (ER) stress by misfolded HLA-B^*27, and the interaction between free heavy chains or heavy chain homodimers of HLA-B^*27 and immune receptors to drive IL-17 responses. Several non-HLA susceptibility loci have also been identified for SpA, including endoplasmic reticulum aminopeptidases (ERAP) and those related to the IL-23/IL-17 axes. In this review, we summarize clinical aspects of SpA including known characteristics of gut inflammation, enthesitis and new bone formation and the existing models for understanding the association of HLA-B^*27 with disease pathogenesis. We also examine newer insights into the biology of HLA class I (HLA-I) proteins and their implications for expanding our understanding of HLA-B^*27 contributions to SpA pathogenesis.

Clonorchis sinensis-Derived Protein Attenuates Inflammation and New Bone Formation in Ankylosing Spondylitis

Helminth infections and their components have been shown to have the potential to modulate and attenuate immune responses. The objective of this study was to evaluate the potential protective effects of Clonorchis sinensis-derived protein (CSp) on ankylosing spondylitis (AS). Cytotoxicity of CSp at different doses was assessed by MTS and flow cytometry before performing experiments. Peripheral blood mononuclear cells (PBMCs) and synovial fluid mononuclear cells (SFMCs) were obtained from AS patients. Inflammatory cytokine-producing cells were analyzed using flow cytometry. The levels of INF- γ , IL-17A, TNF-α, and IL-6 were measured by enzyme-linked immunosorbent assay (ELISA). SKG mice were treated with CSp or vehicles. Inflammation and new bone formation were evaluated using immunohistochemistry, positron emission tomography (PET), and micro-computed tomography (CT). Treatment with CSp resulted in no reduced cell viability of PBMCs or SFMCs until 24 h. In experiments culturing PBMCs and SFMCs, the frequencies of IFN- γ and IL-17A producing cells were significantly reduced after CSp treatment. In the SKG mouse model, CSp treatment significantly suppressed arthritis, enthesitis, and enteritis. Micro-CT analysis of hind paw revealed reduced new bone formation in CSp-treated mice than in vehicle-treated mice. We provide the first evidence demonstrating that CSp can ameliorate clinical signs and cytokine derangements in AS. In addition, such CSp treatment could reduce the new bone formation of AS.

Role of the IL-23/IL-17 Pathway in Rheumatic Diseases: An Overview

Interleukin-23 (IL-23) is a pro-inflammatory cytokine composed of two subunits, IL-23A (p19) and IL-12/23B (p40), the latter shared with Interleukin-12 (IL-12). IL-23 is mainly produced by macrophages and dendritic cells, in response to exogenous or endogenous signals, and drives the differentiation and activation of T helper 17 (Th17) cells with subsequent production of IL-17A, IL-17F, IL-6, IL-22, and tumor necrosis factor α (TNF-α). Although IL-23 plays a pivotal role in the protective immune response to bacterial and fungal infections, its dysregulation has been shown to exacerbate chronic immune-mediated inflammation. Well-established experimental data support the concept that IL-23/IL-17 axis activation contributes to the development of several inflammatory diseases, such as PsA, Psoriasis, Psoriatic Arthritis; AS, Ankylosing Spondylitis; IBD, Inflammatory Bowel Disease; RA, Rheumatoid Arthritis; SS, Sjogren Syndrome; MS, Multiple Sclerosis. As a result, emerging clinical studies have focused on the blockade of this pathogenic axis as a promising therapeutic target in several autoimmune disorders; nevertheless, a greater understanding of its contribution still requires further investigation. This review aims to elucidate the most recent studies and literature data on the pathogenetic role of IL-23 and Th17 cells in inflammatory rheumatic diseases.