Inflammatory disease in HLA-B27 transgenic rats

CHOP-mediated IL-23 overexpression does not drive colitis in experimental spondyloarthritis

HLA-B27 is a major risk factor for spondyloarthritis (SpA), yet the underlying mechanisms remain unclear. HLA-B27 misfolding-induced IL-23, which is mediated by endoplasmic reticulum (ER) stress has been hypothesized to drive SpA pathogenesis. Expression of HLA-B27 and human β2m (hβ2m) in rats (HLA-B27-Tg) recapitulates key SpA features including gut inflammation. Here we determined whether deleting the transcription factor CHOP (Ddit3-/-), which mediates ER-stress induced IL-23, affects gut inflammation in HLA-B27-Tg animals. ER stress-mediated Il23a overexpression was abolished in CHOP-deficient macrophages. Although CHOP-deficiency also reduced Il23a expression in immune cells isolated from the colon of B27+ rats, Il17a levels were not affected, and gut inflammation was not reduced. Rather, transcriptome analysis revealed increased expression of pro-inflammatory genes, including Il1a, Ifng and Tnf in HLA-B27-Tg colon tissue in the absence of CHOP, which was accompanied by higher histological Z-scores. RNAScope localized Il17a mRNA to the lamina propria of the HLA-B27-Tg rats and revealed similar co-localization with Cd3e (CD3) in the presence and absence of CHOP. This demonstrates that CHOP-deficiency does not improve, but rather exacerbates gut inflammation in HLA-B27-Tg rats, indicating that HLA-B27 is not promoting gut disease through ER stress-induced IL-23. Hence, CHOP may protect rats from more severe HLA-B27-induced gut inflammation.

Opposing diet, microbiome, and metabolite mechanisms regulate inflammatory bowel disease in a genetically susceptible host

Inflammatory bowel diseases (IBDs) are chronic conditions characterized by periods of spontaneous intestinal inflammation and are increasing in industrialized populations. Combined with host genetics, diet and gut bacteria are thought to contribute prominently to IBDs, but mechanisms are still emerging. In mice lacking the IBD-associated cytokine, interleukin-10, we show that a fiber-deprived gut microbiota promotes the deterioration of colonic mucus, leading to lethal colitis. Inflammation starts with the expansion of natural killer cells and altered immunoglobulin-A coating of some bacteria. Lethal colitis is then driven by Th1 immune responses to increased activities of mucin-degrading bacteria that cause inflammation first in regions with thinner mucus. A fiber-free exclusive enteral nutrition diet also induces mucus erosion but inhibits inflammation by simultaneously increasing an anti-inflammatory bacterial metabolite, isobutyrate. Our findings underscore the importance of focusing on microbial functions-not taxa-contributing to IBDs and that some diet-mediated functions can oppose those that promote disease.

HLA-B27 did not protect against COVID-19 in patients with axial spondyloarthritis - data from the ReumaCov-Brasil Registry

BACKGROUND

Some studies have suggested the HLA-B27 gene may protect against some infections, as well as it could play a benefit role on the viral clearance, including hepatitis C and HIV. However, there is lack of SARS-CoV-2 pandemic data in spondyloarthritis (SpA) patients.

AIM

To evaluate the impact of HLA-B27 gene positivity on the susceptibility and severity of COVID-19 and disease activity in axial SpA patients.

METHODS

The ReumaCoV-Brasil is a multicenter, observational, prospective cohort designed to monitor immune-mediated rheumatic diseases patients during SARS-CoV-2 pandemic in Brazil. Axial SpA patients, according to the ASAS classification criteria (2009), and only those with known HLA-B27 status, were included in this ReumaCov-Brasil's subanalysis. After pairing them to sex and age, they were divided in two groups: with (cases) and without (control group) COVID-19 diagnosis. Other immunodeficiency diseases, past organ or bone marrow transplantation, neoplasms and current chemotherapy were excluded. Demographic data, managing of COVID-19 (diagnosis, treatment, and outcomes, including hospitalization, mechanical ventilation, and death), comorbidities, clinical details (disease activity and concomitant medication) were collected using the Research Electronic Data Capture (REDCap) database. Data are presented as descriptive analysis and multiple regression models, using SPSS program, version 20. P level was set as 5%.

RESULTS

From May 24th, 2020 to Jan 24th, 2021, a total of 153 axial SpA patients were included, of whom 85 (55.5%) with COVID-19 and 68 (44.4%) without COVID-19. Most of them were men (N = 92; 60.1%) with mean age of 44.0 ± 11.1 years and long-term disease (11.7 ± 9.9 years). Regarding the HLA-B27 status, 112 (73.2%) patients tested positive. There were no significant statistical differences concerning social distancing, smoking, BMI (body mass index), waist circumference and comorbidities. Regarding biological DMARDs, 110 (71.8%) were on TNF inhibitors and 14 (9.15%) on IL-17 antagonists. Comparing those patients with and without COVID-19, the HLA-B27 positivity was not different between groups (n = 64, 75.3% vs. n = 48, 48%, respectively; p = 0.514). In addition, disease activity was similar before and after the infection. Interestingly, no new episodes of arthritis, enthesitis or extra-musculoskeletal manifestations were reported after the COVID-19. The mean time from the first symptoms to hospitalization was 7.1 ± 3.4 days, and although the number of hospitalization days was numerically higher in the B27 positive group, no statistically significant difference was observed (5.7 ± 4.11 for B27 negative patients and 13.5 ± 14.8 for B27 positive patients; p = 0.594). Only one HLA-B27 negative patient died. No significant difference was found regarding concomitant medications, including conventional or biologic DMARDs between the groups.

CONCLUSIONS

No significant difference of COVID-19 frequency rate was observed in patients with axial SpA regarding the HLA-B27 positivity, suggesting a lack of protective effect with SARS-CoV-2 infection. In addition, the disease activity was similar before and after the infection.

TRIAL REGISTRATION

This study was approved by the Brazilian Committee of Ethics in Human Research (CONEP), CAAE 30186820.2.1001.8807, and was registered at the Brazilian Registry of Clinical Trials - REBEC, RBR-33YTQC. All patients read and signed the informed consent form before inclusion.

Cell Surface B2m-Free Human Leukocyte Antigen (HLA) Monomers and Dimers: Are They Neo-HLA Class and Proto-HLA?

Cell surface HLA-I molecules (Face-1) consist of a polypeptide heavy chain (HC) with two groove domains (G domain) and one constant domain (C-domain) as well as a light chain, B2-microglobulin (B2m). However, HCs can also independently emerge unfolded on the cell surface without peptides as B2m-free HC monomers (Face-2), B2m-free HC homodimers (Face 3), and B2m-free HC heterodimers (Face-4). The transport of these HLA variants from ER to the cell surface was confirmed by antiviral antibiotics that arrest the release of newly synthesized proteins from the ER. Face-2 occurs at low levels on the normal cell surface of the lung, bronchi, epidermis, esophagus, breast, stomach, ilium, colorectum, gall bladder, urinary bladder, seminal vesicles ovarian epithelia, endometrium, thymus, spleen, and lymphocytes. They are upregulated on immune cells upon activation by proinflammatory cytokines, anti-CD3 antibodies, antibiotics (e.g., ionomycin), phytohemagglutinin, retinoic acid, and phorbol myristate acetate. Their density on the cell surface remains high as long as the cells remain in an activated state. After activation-induced upregulation, the Face-2 molecules undergo homo- and hetero-dimerization (Face-3 and Face-4). Alterations in the redox environment promote dimerization. Heterodimerization can occur among and between the alleles of different haplotypes. The glycosylation of these variants differ from that of Face-1, and they may occur with bound exogenous peptides. Spontaneous arthritis occurs in HLA-B27+ mice lacking B2m (HLA-B27+ B2m-/-) but not in HLA-B27+ B2m+/- mice. The mice with HLA-B27 in Face-2 spontaneous configuration develop symptoms such as changes in nails and joints, hair loss, and swelling in paws, leading to ankyloses. Anti-HC-specific mAbs delay disease development. Some HLA-I polyreactive mAbs (MEM series) used for immunostaining confirm the existence of B2m-free variants in several cancer cells. The upregulation of Face-2 in human cancers occurs concomitantly with the downregulation of intact HLAs (Face-1). The HLA monomeric and dimeric variants interact with inhibitory and activating ligands (e.g., KIR), growth factors, cytokines, and neurotransmitters. Similarities in the amino acid sequences of the HLA-I variants and HLA-II β-chain suggest that Face-2 could be the progenitor of both HLA classes. These findings may support the recognition of these variants as a neo-HLA class and proto-HLA.

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.

Preclinical study models of psoriasis: State-of-the-art techniques for testing pharmaceutical products in animal and nonanimal models

Local and systemic treatments exist for psoriasis, but none can do more than control its symptoms because of its numerous unknown mechanisms. The lack of validated testing models or a defined psoriatic phenotypic profile hinders antipsoriatic drug development. Despite their intricacy, immune-mediated diseases have no improved and precise treatment. The treatment actions may now be predicted for psoriasis and other chronic hyperproliferative skin illnesses using animal models. Their findings confirmed that a psoriasis animal model could mimic a few disease conditions. However, their ethical approval concerns and inability to resemble human psoriasis rightly offer to look for more alternatives. Hence, in this article, we have reported various cutting-edge techniques for the preclinical testing of pharmaceutical products for the treatment of psoriasis.

Paradoxical Effects of Endoplasmic Reticulum Aminopeptidase 1 Deficiency on HLA-B27 and Its Role as an Epistatic Modifier in Experimental Spondyloarthritis

OBJECTIVE

We undertook this study to examine the functional basis for epistasis between endoplasmic reticulum aminopeptidase 1 (ERAP1) and HLA-B27 in experimental spondyloarthritis (SpA).

METHODS

ERAP1-knockout rats were created using genome editing and bred with HLA-B27/human β2 -microglobulin-transgenic (HLA-B27-Tg) rats and HLA-B7-Tg rats. The effects of ERAP1 deficiency on HLA allotypes were determined using immunoprecipitation and immunoblotting, flow cytometry, allogeneic T cell proliferation assays, and gene expression analyses. Animals were examined for clinical features of disease, and tissue was assessed by histology.

RESULTS

ERAP1 deficiency increased the ratio of folded to unfolded (β2 m-free) HLA-B27 heavy chains, while having the opposite effect on HLA-B7. Furthermore, in rats with ERAP1 deficiency, HLA-B27 misfolding was reduced, while free HLA-B27 heavy chain dimers on the cell surface and monomers were increased. The effects of ERAP1 deficiency persisted during up-regulation of HLA-B27 and led to a reduction in endoplasmic reticulum stress. ERAP1 deficiency reduced the prevalence of arthritis in HLA-B27-Tg rats by two-thirds without reducing gastrointestinal inflammation. Dendritic cell abnormalities attributed to the presence of HLA-B27, including reduced allogeneic T cell stimulation and loss of CD103-positive/major histocompatibility complex class II-positive cells, were not rescued by ERAP1 deficiency, while excess Il23a up-regulation was mitigated.

CONCLUSION

ERAP1 deficiency reduced HLA-B27 misfolding and improved folding while having opposing effects on HLA-B7. The finding that HLA-B27-Tg rats had partial protection against SpA in this study is consistent with genetic evidence that loss-of-function and/or reduced expression of ERAP1 reduces the risk of ankylosing spondylitis. Functional studies support the concept that the effects of ERAP1 on HLA-B27 and SpA may be a consequence of how peptides affect the biology of this allotype rather than their role as antigenic determinants.

Effects of intestinal microbes on rheumatic diseases: A bibliometric analysis

Background

Rheumatic diseases (RD) are a group of multi-system inflammatory autoimmune diseases whose causes are still under study. In the past few decades, researchers have found traces of the association between rheumatic diseases and intestinal microbiota, which can partially explain the pathogenesis of rheumatic diseases. We aimed to describe the research trend and main divisions on how gut flora interreacts with rheumatic diseases, and discussed about the possible clinical applications.

Methods

We analyzed bibliometric data from the Web of Science core collection (dated 15th May 2022). Biblioshiny R language software packages (bibliometrix) were used to obtain the annual publication and citations, core sources according to Bradford's law, and country collaboration map. We designed and verified the keyword co-occurrence network and strategic diagram with the help of VOSviewer and CiteSpace, subdivided the research topic into several themes and identified research dimensions. The tables of most local cited documents and core sources were processed manually. Furthermore, the Altmetric Attention Score and the annual Altmetric Top 100 were applied to analyze the annual publication and citation.

Results

From a total of 541 documents, we found that the overall trend of annual publication and citation is increasing. The major research method is to compare the intestinal microbial composition of patients with certain rheumatic disease and that of the control group to determine microbial alterations related to the disease's occurrence and development. According to Bradford's law, the core sources are Arthritis and Rheumatology, Annals of the Rheumatic Diseases, Current Opinion in Rheumatology, Nutrients, Rheumatology, and Journal of Rheumatology. Since 1976, 101 countries or regions have participated in studies of rheumatology and intestinal microbes. The United States ranks at the top and has the broadest academic association with other countries. Five themes were identified, including the pivotal role of inflammation caused by intestinal bacteria in the rheumatic pathogenesis, the close relationship between rheumatic diseases and inflammatory bowel disease, immunoregulation mechanism as a mediator of the interaction between rheumatic diseases and gut flora, dysbiosis and decreased diversity in intestine of patients with rheumatic diseases, and the influence of oral flora on rheumatic diseases. Additionally, four research dimensions were identified, including pathology, treatment, disease, and experiments.

Conclusion

Studies on rheumatic diseases and the intestinal microbiota are growing. Attention should be paid to the mechanism of their interaction, such as the microbe-immune-RD crosstalk. Hopefully, the research achievements can be applied to diseases' prevention, diagnosis, and treatment, and our work can contribute to the readers' future research.

A brief human history of ankylosing spondylitis: A scoping review of pathogenesis, diagnosis, and treatment

Background:

Ankylosing spondylitis (AS) is a chronic, progressive, inflammatory disease of the spine and SI joints. Diagnostic criteria and treatments have continued to evolve, necessitating a historical compendium of AS and its management. This paper aims to review the historical context underlying the discovery of AS, as well as the major diagnostic and therapeutic discoveries in the last two centuries.

Methods:

A scoping review of the literature pertaining to AS was performed via the Pubmed, Scopus, and Web of Science databases. Future directions of AS treatments were assessed by querying the clinicaltrials.gov website.

Results:

The history of AS can be traced as far back as ancient Egypt (as evidenced by the discovery of its presence in ancient Egyptian mummies) to the late 20^th century, when the inherited nature of AS was linked to a genetic factor, HLA-B27. Each discovery made throughout the years led to further investigations into the pathophysiology, diagnosis, and treatment of AS. The criteria to differentiate AS from rheumatoid arthritis were first reported in 1893. Since then, diagnostic criteria for AS have undergone a series of changes before the present-day diagnostic criteria for AS were ultimately determined in 2009 by the Assessment of Spondyloarthritis International Society.

Conclusion:

As the pathophysiology of AS is better understood, healthcare providers are able to diagnose and treat the condition more effectively. In particular, earlier diagnosis and multiple treatment options have facilitated efficient and more effective treatment.

A Potential New Mouse Model of Axial Spondyloarthritis Involving the Complement System

Many mouse models of rheumatoid arthritis have been identified, but only a limited number are present for axial spondyloarthritis (AxSpA). Collagen Ab-induced arthritis (CAIA) is one of the most widely used mouse models of arthritis, and it is complement-dependent. We found that mice developing CAIA also developed spinal lesions similar to those found in AxSpA. To induce CAIA, mice were injected intraperitoneally at day 0 with anti-collagen Abs, followed by LPS injection at day 3. CAIA mice demonstrated a significant kyphosis through the spine, as well as hypertrophic cartilage and osseous damage of the intravertebral joints. Immunohistochemical staining of the kyphotic area revealed increased complement C3 deposition and macrophage infiltration, with localization to the intravertebral joint margins. Near Infrared (NIR) in vivo imaging showed that anti-collagen Abs conjugated with IRDye^® 800CW not only localized to cartilage surface in the joints but also to the spine in arthritic mice. We report here a novel preclinical mouse model in which, associated with the induction of CAIA, mice also exhibited salient features of AxSpA; this new experimental model of AxSpA may allow investigators to shed light on the local causal mechanisms of AxSpA bone and soft tissue changes as well as treatment.

Spondyloarthritides: Theories and beyond

Spondyloarthritides (SpA) are a family of interrelated rheumatic disorders with a typical disease onset ranging from childhood to middle age. If left untreated, they lead to a severe decrease in patients' quality of life. A succesfull treatment strategy starts with an accurate diagnosis which is achieved through careful analysis of medical symptoms. Classification criterias are used to this process and are updated on a regular basis. Although there is a lack of definite knowledge on the disease etiology of SpA, several studies have paved the way for understanding plausible risk factors and developing treatment strategies. The significant increase of HLA-B27 positivity in SpA patients makes it a strong candidate as a predisposing factor and several theories have been proposed to explain HLA-B27 driven disease progression. However, the presence of HLA-B27 negative patients underlines the presence of additional risk factors. The current treatment options for SpAs are Non-Steroidal Anti-Inflammatory Drugs (NSAIDs), TNF inhibitors (TNFis), Disease-Modifying Anti-Rheumatic Drugs (DMARDs) and physiotherapy yet there are ongoing clinical trials. Anti IL17 drugs and targeted synthetic DMARDs such as JAK inhibitors are also emerging as treatment alternatives. This review discusses the current diagnosis criteria, treatment options and gives an overview of the previous findings and theories to clarify the possible contributors to SpA pathogenesis with a focus on Ankylosing Spondylitis (AS) and enthesitis-related arthritis (ERA).

Intestinal microbiota changes induced by TNF-inhibitors in IBD-related spondyloarthritis

Background

The close relationship between joints and gut inflammation has long been known and several data suggest that dysbiosis could link spondyloarthritis (SpA) to inflammatory bowel diseases (IBD). The introduction of biological drugs, in particular tumour necrosis factor inhibitors (TNFi), revolutionised the management of both these diseases. While the impact of conventional drugs on gut microbiota is well known, poor data are available about TNFi.

Aim

To investigate the impact of TNFi on gut microbiota.

Methods

We evaluated 20 patients affected by enteropathic arthritis, naïve for biological drugs, treated with TNFi at baseline and after 6 months of therapy. All patients followed a Mediterranean diet. Patients performed self-sampling of a faecal sample at baseline and after 6 months of therapy. NGS-based ITS and 16S rRNA gene sequencing was performed, followed by the taxonomic bioinformatics analysis.

Results

After 6 months of therapy, we detected a remarkable increase in Lachnospiraceae family (Δ +10.3, p=0.04) and Coprococcus genus (Δ +2.8, p=0.003). We also noted a decreasing trend in Proteobacteria (Δ −8.0, p=0.095) and Gammaproteobacteria (Δ −9, p=0.093) and an increasing trend in Clostridia (Δ +8.2, p=0.083). We did not find differences between TNFi responders (SpA improvement or IBD remission achieved) and non-responders in terms of alpha and beta diversity.

Conclusions

Our findings are consistent with the hypothesis that TNFi therapy tends to restore the intestinal eubiosis.

EANM recommendations based on systematic analysis of small animal radionuclide imaging in inflammatory musculoskeletal diseases

Inflammatory musculoskeletal diseases represent a group of chronic and disabling conditions that evolve from a complex interplay between genetic and environmental factors that cause perturbations in innate and adaptive immune responses. Understanding the pathogenesis of inflammatory musculoskeletal diseases is, to a large extent, derived from preclinical and basic research experiments. In vivo molecular imaging enables us to study molecular targets and to measure biochemical processes non-invasively and longitudinally, providing information on disease processes and potential therapeutic strategies, e.g. efficacy of novel therapeutic interventions, which is of complementary value next to ex vivo (post mortem) histopathological analysis and molecular assays. Remarkably, the large body of preclinical imaging studies in inflammatory musculoskeletal disease is in contrast with the limited reports on molecular imaging in clinical practice and clinical guidelines. Therefore, in this EANM-endorsed position paper, we performed a systematic review of the preclinical studies in inflammatory musculoskeletal diseases that involve radionuclide imaging, with a detailed description of the animal models used. From these reflections, we provide recommendations on what future studies in this field should encompass to facilitate a greater impact of radionuclide imaging techniques on the translation to clinical settings.

Effects of a low-dose IL-2 treatment in HLA-B27 transgenic rat model of spondyloarthritis

Abstract

Introduction/Aim

HLA-B27/human β2m transgenic rats (B27-rats) develop an inflammatory disorder resembling spondyloarthritis (SpA) with dysregulated IL-10/IL-17 production by regulatory T cells (Treg). Treg plays a major role in controlling pathogenic inflammatory processes. Interleukin 2 (IL-2), a cytokine which promotes Treg cell survival and function, may thus have therapeutic efficacy in SpA. Here, we tested this hypothesis using a low dose of IL-2 treatment in B27-rat.

Material and methods

B27-rats aged 4 weeks (before disease onset) and nontransgenic (NTG) littermates were administered intraperitoneally recombinant human IL-2 (Sanofi®; 2,000IU/injection) or PBS, 3 days per week during 6 weeks. Assessment of treatment effect was performed, based on clinical (weight, diarrhea, arthritis), histological (proximal and distal colon, caecum, ileum and tarsal/ankle joint) scores, and frequency of Treg in the spleen and lymph nodes (LN).

Results

IL-2 administration had no effect on weight gain, either in B27- or NTG-rats. Over the 6 weeks of treatment, the clinical disease score worsened similarly in both IL-2-treated and control groups of B27-rats. The macroscopic and histological evaluation of gut and joints showed marked inflammation in B27-rats; however, no change related to IL-2 treatment was observed. In the B27-rats, the percentage of Treg was moderately increased after IL-2 treatment in the spleen, but neither in mesenteric nor peripheral LN in those rats.

Conclusion

Our data demonstrate that a low dose of IL-2 administered before disease onset was moderately effective for boosting Treg but failed to prevent SpA development in B27-rat.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-021-02559-y.

The enigmatic role of HLA-B*27 in spondyloarthritis pathogenesis

Establishing a clear role for HLA-B*27 in the pathogenesis of spondyloarthritis continues to be challenging. Aberrant properties of the heavy chain as well as a potential role presenting arthritogenic peptides continue to be pursued as plausible mechanisms. Recent studies implicate HLA-B*27 in aberrant bone formation. An unanticipated cell surface interaction between HLA-B*27 and the bone morphogenetic protein pathway receptor subunit ALK2 may augment TGFβ superfamily signaling pathways, increasing responsiveness to Activin A and TGFβ. This has the potential to increase bone formation as well as Th17 T cell development, presenting an attractive model to explain several aspects of axial and peripheral spondyloarthritis. In a separate study, intracellular effects of misfolded HLA-B*27 implicate this mechanism in increased osteoblast mineralization and bone formation. HLA-B*27 expression in early osteoblasts activates unfolded protein response-mediated X-box binding protein-1 mRNA splicing and induction of the retinoic acid receptor-β gene, with downstream increases in expression of tissue non-specific alkaline phosphatase. Increased TNAP expression in osteoblasts was linked to increased mineralization in vitro and bone formation in vivo. In the ongoing search for evidence of arthritogenic peptides, high-throughput TCR (T cell receptor) sequencing has provided evidence for reduced clonal expansion and increased TCR diversity in ankylosing spondylitis. In addition to two common CD8+ TCR sequences identified in one study, similar CD8 and CD4 TCR motifs were found in another study. Further work will be needed to shed light on the nature of the peptide-HLA class I complex recognized by these T cells and its role in disease.

Lessons on SpA pathogenesis from animal models

Understanding the complex mechanisms underlying a disorder such as spondyloarthritis (SpA) may benefit from studying animal models. Several suitable models have been developed, in particular to investigate the role of genetic factors predisposing to SpA, including HLA-B27, ERAP1, and genes related to the interleukin (IL)-23/IL-17 axis. One of the best examples of such research is the HLA-B27 transgenic rat model that fostered the emergence of original theories regarding HLA-B27 pathogenicity, including dysregulation of innate immunity, contribution of the adaptive immune system to chronic inflammation, and influence of the microbiota on disease development. Very recently, a new model of HLA-B27 transgenic Drosophila helped to expand further some of those theories in an unexpected direction involving the TGFβ/BMP family of mediators. On the other hand, several spontaneous, inducible, and/or genetically modified mouse models-including SKG mouse, TNF^ΔARE mouse and IL-23-inducible mouse model of SpA-have highlighted the importance of TNFα and IL-23/IL-17 axis in the development of SpA manifestations. Altogether, those animal models afford not only to study disease mechanism but also to investigate putative therapeutic targets.

GlutenSpA trial: protocol for a randomised double-blind placebo-controlled trial of the impact of a gluten-free diet on quality of life in patients with axial spondyloarthritis

INTRODUCTION

Subclinical intestinal inflammation and gut dysbiosis have been reported in patients with spondyloarthritis (SpA). In common practice, rheumatologists are increasingly confronted with patients with inflammatory rheumatism who are on gluten-free diets (GFDs), despite the lack of reliable data from controlled studies. This study aims to determine the impact of a GFD on the quality of life of patients with axial SpA.

METHODS AND ANALYSIS

The GlutenSpA study is a 24-week, randomised, double-blinded, placebo-controlled, multicentre trial. Patients with axial SpA (n=200) will follow a 16-week GFD and be randomly assigned (1:1) to an experimental or control arm. In the experimental arm with receive at least 6 gluten-free breads per day + 200 g of gluten-free penne pasta per week + 6 rice flavour capsules per day. The control arm will receive at least 6 gluten-containing breads per day + 200 g of gluten-containing penne pasta per week + 6 vital gluten-containing capsules per day. The primary end-point is the variation in Assessment of SpondyloArthritis International Society-Health Index (ASAS-HI) questionnaire between week 16 and baseline. A second open-label period of 8 weeks will follow the intervention period, during which the patient will be free to decide whether they will follow the GFD. The secondary outcomes comprise several patient-reported outcomes (SpA activity (Bath Ankylosing Spondylitis Disease Activity Index)), fatigue (Functional Assessment of Chronic Illness Therapy), depression (Hospital Anxiety and Depression Scale), functional disability index (Bath Ankylosing Spondylitis Functional Index)), variations in body mass index and Homeostasis Model Assessment Index and variations in the abundance and type of bacterial species found in the gut microbiota for a subgroup of patients (n=40). The data will be analysed using the intention-to-treat principle.The regional ethics committee (CPP Nord-ouest IV) has approved the study (IDRCB 2018-A00309-46). The results of the trial will be submitted for publication in peer-reviewed journals. The authors have no relationship that may have influenced the submitted work.

TRIAL REGISTRATION NUMBER

NCT04274374.

The microbiome in spondyloarthritis

A causal link between the wealth of microbes that populate our body surfaces, designated as microbiota, and inflammatory disorders, including ankylosing spondylitis and the related spondyloarthritis (SpA) has been suspected for decades. This specially concerns the gut microbiota that became only recently accessible to thorough description thanks to massive sequencing methods or metagenomics. Here, we review evidences supporting the existence of microbiota imbalance or dysbiosis in the context of SpA. We also discuss currently existing evidences for a causal relationship between such dysbiosis and disease development, as well as putative therapeutic implications.

Mechanisms Underlying Bone Loss Associated with Gut Inflammation

Patients with gastrointestinal diseases frequently suffer from skeletal abnormality, characterized by reduced bone mineral density, increased fracture risk, and/or joint inflammation. This pathological process is characterized by altered immune cell activity and elevated inflammatory cytokines in the bone marrow microenvironment due to disrupted gut immune response. Gastrointestinal disease is recognized as an immune malfunction driven by multiple factors, including cytokines and signaling molecules. However, the mechanism by which intestinal inflammation magnified by gut-residing actors stimulates bone loss remains to be elucidated. In this article, we discuss the main risk factors potentially contributing to intestinal disease-associated bone loss, and summarize current animal models, illustrating gut-bone axis to bridge the gap between intestinal inflammation and skeletal disease.

Fecal microbiota in patients with ankylosing spondylitis: Correlation with dietary factors and disease activity

BACKGROUND

We investigated the characterization of the gut microbiome in Chinese patients with ankylosing spondylitis (AS) and healthy controls (HCs) and to explore the association ofbacteria communities with dietary factors and disease activity.

METHODS

16S ribosomal RNA gene sequencing was performed on fecal DNA isolated from stool samples in consecutive cross-sectional cohorts. Alpha and beta diversities were assessed using QIIME, and comparisons were performed using one-way ANOVA, Student's t-test, and SKN multiple range comparisons to examine differences between groups and a correlation network analysis was performed.

RESULTS

We investigated 207 samples from 103 AS patients and 104 HCs. Alpha diversity was not significant difference in AS compared with HCs. For the community structure, Bacteroidetes was the most represented class. Megamonas, Dorea, and Blautia were significantly greater in AS than in HCs, whereas the abundance of Lachnospira, Ruminococcus, and Clostridium_XlVb was significantly lower in AS than in HCs. In addition, Specific gut microbiome was significantly correlated with disease activity and dietary factors.

CONCLUSIONS

Our results suggest that the human gut microbiome of AS patients was clearly different from that of HCs and bacteria communities are associated with dietary factors and disease activity.

The correlation between intestinal dysbiosis and the development of ankylosing spondylitis

The pathogenesis and development of ankylosing spondylitis (AS) is concealed and complicated. In recent years, alterations in gut microbiota of AS patients have been largely investigated, although the underlying mechanisms remain unclear. This article reviews the recent studies on changes of gut microbiota in AS patients, and discusses the possible correlation between intestinal dysbiosis and AS development from aspects including genetic factor HLA-B27, mucosal immune responses and the depression accompanying AS.

The Role of Autophagy in the Degradation of Misfolded HLA-B27 Heavy Chains

OBJECTIVE

To determine whether autophagy is involved in the degradation of misfolded HLA-B27 in experimental spondyloarthritis.

METHODS

Bone marrow-derived macrophages from HLA-B27/human β2 -microglobulin (hβ2 m)-transgenic rats were incubated in the presence or absence of interferon-γ and proteasome or autophagy inhibitors. Immunoprecipitation, immunoblotting, and immunofluorescence analysis were used to measure HLA-B27 heavy chains and autophagy. Autophagy was induced using rapamycin. Macrophages from HLA-B7/hβ2 m-transgenic and wild-type rats were used as controls.

RESULTS

HLA-B27-expressing macrophages showed phosphatidylethanolamine-conjugated microtubule-associated protein 1 light chain 3B levels similar to those in both control groups, before and after manipulation of autophagy. Blocking autophagic flux with bafilomycin resulted in the accumulation of misfolded HLA-B27 dimers and oligomers as well as monomers, which was comparable with the results of blocking endoplasmic reticulum-associated degradation (ERAD) with the proteasome inhibitor bortezomib. HLA-B7 monomers also accumulated after blocking each degradation pathway. The ubiquitin-to-heavy chain ratio was 2-3-fold lower for HLA-B27 than for HLA-B7. Activation of autophagy with rapamycin rapidly eliminated ~50% of misfolded HLA-B27, while folded HLA-B27 or HLA-B7 monomeric heavy chains were minimally affected.

CONCLUSION

This study is the first to demonstrate that both autophagy and ERAD play roles in the elimination of excess HLA class I heavy chains expressed in transgenic rats. We observed no evidence that HLA-B27 expression modulated the autophagy pathway. Our results suggest that impaired ubiquitination of HLA-B27 may play a role in the accumulation of misfolded disulfide-linked dimers, the elimination of which can be enhanced by activation of autophagy. Manipulation of the autophagy pathway should be further investigated as a potential therapeutic target in spondyloarthritis.

Effects of HLA-B27 on Gut Microbiota in Experimental Spondyloarthritis Implicate an Ecological Model of Dysbiosis

OBJECTIVE

To investigate whether HLA-B27-mediated experimental spondyloarthritis (SpA) is associated with a common gut microbial signature, in order to identify potential drivers of pathogenesis.

METHODS

The effects of HLA-B27 on 3 genetic backgrounds, dark agouti (DA), Lewis, and Fischer, were compared, using wild-type littermates and HLA-B7-transgenic Lewis rats as controls. Cecum and colon tissue specimens or contents were collected from the rats at 2, 3-4, and 6-8 months of age, and histologic analysis was performed to assess inflammation, RNA sequencing was used to determine gene expression differences, and 16S ribosomal RNA gene sequencing was used to determine microbiota differences.

RESULTS

Both HLA-B27-transgenic Lewis rats and HLA-B27-transgenic Fischer rats developed gut inflammation, while DA rats were resistant to the effects of HLA-B27, and HLA-B7-transgenic rats were not affected. Immune dysregulation was similar in affected Lewis and Fischer rats and was dominated by activation of interleukin-23 (IL-23)/IL-17, interferon, tumor necrosis factor, and IL-1 cytokines and pathways in the colon and cecum, while DA rats exhibited low-level cytokine dysregulation without inflammation. Gut microbial changes in HLA-B27-transgenic rats were strikingly divergent on the 3 different host genetic backgrounds, including different patterns of dysbiosis in HLA-B27-transgenic Lewis and HLA-B27-transgenic Fischer rat strains, with some overlap. Interestingly, DA rats lacked segmented filamentous bacteria that promote CD4+ Th17 cell development, which may explain their resistance to disease.

CONCLUSION

The effects of HLA-B27 on gut microbiota and dysbiosis in SpA are highly dependent on the host genetic background and/or environment, despite convergence of dysregulated immune pathways. These results implicate an ecological model of dysbiosis, with the effects of multiple microbes contributing to the aberrant immune response, rather than a single or small number of microbes driving pathogenesis.

Accumulation of HLA-DR4 in Colonic Epithelial Cells Causes Severe Colitis in Homozygous HLA-DR4 Transgenic Mice

BACKGROUND

Homozygous HLA-DR4/I-E transgenic mice (tgm) spontaneously developed colitis similar to human ulcerative colitis. We explored whether endoplasmic reticulum stress in colonic epithelial cells due to overexpression of HLA-DR4/I-E was involved in the pathogenesis of colitis.

METHODS

Major histocompatibility complex class II transactivator-knockout (CIITAKO) background tgm were established to test the involvement of HLA-DR4/I-E expression in the pathogenesis of colitis. Histological and cellular analyses were performed and the effect of oral administration of the molecular chaperone tauroursodeoxycholic acid (TUDCA) and antibiotics were investigated. IgA content of feces and serum and presence of IgA-coated fecal bacteria were also investigated.

RESULTS

Aberrantly accumulated HLA-DR4/I-E molecules in colonic epithelial cells were observed only in the colitic homozygous tgm, which was accompanied by upregulation of the endoplasmic reticulum stress marker Binding immunoglobulin protein (BiP) and reduced mucus. Homozygous tgm with CIITAKO, and thus absent of HLA-DR4/I-E expression, did not develop colitis. Oral administration of TUDCA to homozygotes reduced HLA-DR4/I-E and BiP expression in colonic epithelial cells and restored the barrier function of the intestinal tract. The IgA content of feces and serum, and numbers of IgA-coated fecal bacteria were higher in the colitic tgm, and antibiotic administration suppressed the expression of HLA-DR4/I-E and colitis.

CONCLUSIONS

The pathogenesis of the colitis observed in the homozygous tgm was likely due to endoplasmic reticulum stress, resulting in goblet cell damage and compromised mucus production in the colonic epithelial cells in which HLA-DR4/I-E molecules were heavily accumulated. Commensal bacteria seemed to be involved in the accumulation of HLA-DR4/I-E, leading to development of the colitis.

Intestinal Metabolites Are Profoundly Altered in the Context of HLA-B27 Expression and Functionally Modulate Disease in a Rat Model of Spondyloarthritis

OBJECTIVE

HLA-B27-associated spondyloarthritides are associated with an altered intestinal microbiota and bowel inflammation. We undertook this study to identify HLA-B27-dependent changes in both host and microbial metabolites in the HLA-B27/β2 -microglobulin (β2 m)-transgenic rat and to determine whether microbiota-derived metabolites could impact disease in this major model of spondyloarthritis.

METHODS

Cecal contents were collected from Fischer 344 33-3 HLA-B27/β2 m-transgenic rats and wild-type controls at 6 weeks (before disease) and 16 weeks (with active bowel inflammation). Metabolomic profiling was performed by high-throughput gas and liquid chromatography-based mass spectrometry. HLA-B27/β2 m-transgenic rats were treated with the microbial metabolites propionate or butyrate in drinking water for 10 weeks, and disease activity was subsequently assessed.

RESULTS

Our screen identified 582 metabolites, of which more than half were significantly altered by HLA-B27 expression at 16 weeks. Both microbial and host metabolites were altered, with multiple pathways affected, including those for amino acid, carbohydrate, xenobiotic, and medium-chain fatty acid metabolism. Differences were even observed at 6 weeks, with up-regulation of histidine, tyrosine, spermidine, N-acetylmuramate, and glycerate in HLA-B27/β2 m-transgenic rats. Administration of the short-chain fatty acid propionate significantly attenuated HLA-B27-associated inflammatory disease, although this was not associated with increased FoxP3+ T cell induction or with altered expression of the immunomodulatory cytokines interleukin-10 (IL-10) or IL-33 or of the tight junction protein zonula occludens 1. HLA-B27 expression was also associated with altered host expression of messenger RNA for the microbial metabolite receptors free fatty acid receptor 2 (FFAR2), FFAR3, and niacin receptor 1.

CONCLUSION

HLA-B27 expression profoundly impacts the intestinal metabolome, with changes evident in rats even at age 6 weeks. Critically, we demonstrate that a microbial metabolite, propionate, attenuates development of HLA-B27-associated inflammatory disease. These and other microbiota-derived bioactive mediators may provide novel treatment modalities in HLA-B27-associated spondyloarthritides.

Genetics and the Causes of Ankylosing Spondylitis

Ankylosing spondylitis (AS) is a common inflammatory arthritis in which genetic factors are the primary determinants of disease risk and severity. Substantial progress has been made in identifying genetic pathways involved in the disease, and in translating those discoveries to drug discovery programs. Recently discovered novel disease pathways include those involved in control of DNA methylation, bacterial sensing, and mucosal immunity. Additional pathways are likely to be identified as a higher proportion of the genetic risk of AS is determined.

Polymorphisms in the F Pocket of HLA-B27 Subtypes Strongly Affect Assembly, Chaperone Interactions, and Heavy-Chain Misfolding

OBJECTIVE

HLA-B27 is associated with the inflammatory spondyloarthritides (SpA), although subtypes HLA-B*27:06 and HLA-B*27:09 are not. These subtypes differ from the HLA-B*27:05 disease-associated allele primarily at residues 114 and 116 of the heavy chain, part of the F pocket of the antigen-binding groove. Dimerization of HLA-B27 during assembly has been implicated in disease onset. The purpose of this study was to investigate the factors that influence differences in dimerization between disease-associated and non-disease-associated HLA-B27 alleles.

METHODS

HLA-B*27:05 and mutants resembling the HLA-B*27:06 and 09 subtypes were expressed in the rat C58 T cell line, the human CEM T cell line and its calnexin-deficient variant CEM.NKR. Immunoprecipitation, pulse-chase experiments, flow cytometry, and immunoblotting were performed to study the assembly kinetics, heavy-chain dimerization, and chaperone associations.

RESULTS

By expressing HLA-B*27:05, 06-like, and 09 alleles on a restrictive rat transporter associated with antigen processing background, we demonstrate that a tyrosine expressed at p116, either alone or together with an aspartic acid residue at p114, inhibited HLA-B27 dimerization and increased the assembly rate. F-pocket residues altered the associations with chaperones of the early major histocompatibility complex class I folding pathway. Calnexin was demonstrated to participate in endoplasmic reticulum (ER) stress-mediated degradation of dimers, whereas the oxidoreductase ERp57 does not appear to influence dimerization.

CONCLUSION

Residues within the F pocket of the peptide-binding groove, which differ between disease-associated and non-disease-associated HLA-B27 subtypes, can influence the assembly process and heavy-chain dimerization, events which have been linked to the initiation of disease pathogenesis.

Perturbed Mucosal Immunity and Dysbiosis Accompany Clinical Disease in a Rat Model of Spondyloarthritis

OBJECTIVE

The HLA-B27/β2 -microglobulin (β2 m)-transgenic (Tg) rat is a leading model of B27-associated spondyloarthritis (SpA), and the disease is dependent on the presence of intestinal bacteria. Previous studies have shown that adult HLA-B27/β2 m-Tg rats have an altered intestinal microbiota. This study sought to better define the age-dependent changes to both mucosal immune function and dysbiosis in this rat model of SpA.

METHODS

Intestinal contents were collected from wild-type and HLA-B27/β2 m-Tg rats postweaning (ages 3 and 6 weeks), at disease onset (age 10 weeks), and after the establishment of disease (ages ≥16 weeks). The microbial community structure was determined by 16S ribosomal RNA sequencing and quantitative reverse transcription-polymerase chain reaction (qRT-PCR). Mucosal and systemic Th1, Th17, and Treg cell responses were analyzed by flow cytometry, as was the frequency of IgA-coated intestinal bacteria. Intestinal expression of inflammatory cytokines and antimicrobial peptides (AMPs) was determined by qRT-PCR.

RESULTS

An inflammatory cytokine signature and elevated AMP expression during the postweaning period preceded the development of clinical bowel inflammation and dysbiosis in HLA-B27/β2 m-Tg rats. An early and sustained expansion of the Th17 cell pool was specifically observed in the cecal and colonic mucosa of HLA-B27/β2 m-Tg rats. Strongly elevated intestinal colonization of Akkermansia muciniphila and an increased frequency of IgA-coated fecal bacteria were significantly associated with expression of HLA-B27 and arthritis development.

CONCLUSION

HLA-B27/β2 m expression in this rat model renders the host hyperresponsive to microbial antigens from infancy. Early activation of innate immunity and expansion of a mucosal Th17 signature are soon followed by dysbiosis in HLA-B27/β2 m-Tg animals. The pathologic processes of perturbed mucosal immunity and dysbiosis strongly merit further study in both prediseased and diseased populations of patients with SpA.

Faecal microbiota study reveals specific dysbiosis in spondyloarthritis

OBJECTIVE

Altered microbiota composition or dysbiosis is suspected to be implicated in the pathogenesis of chronic inflammatory diseases, such as spondyloarthritis (SpA) and rheumatoid arthritis (RA).

METHODS

16S ribosomal RNA gene sequencing was performed on faecal DNA isolated from stool samples in two consecutive cross-sectional cohorts, each comprising three groups of adult volunteers: SpA, RA and healthy controls (HCs). In the second study, HCs comprised a majority of aged-matched siblings of patients with known HLA-B27 status. Alpha and beta diversities were assessed using QIIME, and comparisons were performed using linear discriminant analysis effect size to examine differences between groups.

RESULTS

In both cohorts, dysbiosis was evidenced in SpA and RA, as compared with HCs, and was disease specific. A restriction of microbiota biodiversity was detected in both disease groups. The most striking change was a twofold to threefold increased abundance of Ruminococcus gnavus in SpA, as compared with both RA and HCs that was significant in both studies and positively correlated with disease activity in patients having a history of inflammatory bowel disease (IBD). Among HCs, significant difference in microbiota composition were also detected between HLA-B27+ and HLA-B27 negative siblings, suggesting that genetic background may influence gut microbiota composition.

CONCLUSION

Our results suggest that distinctive dysbiosis characterise both SpA and RA and evidence a reproducible increase in R. gnavus that appears specific for SpA and a marker of disease activity. This observation is consistent with the known proinflammatory role of this bacteria and its association with IBD. It may provide an explanation for the link that exists between SpA and IBD.

The Human Leukocyte Antigen (HLA)-B27 Peptidome in Vivo, in Spondyloarthritis-susceptible HLA-B27 Transgenic Rats and the Effect of Erap1 Deletion

HLA-B27 is a class I major histocompatibility (MHC-I) allele that confers susceptibility to the rheumatic disease ankylosing spondylitis (AS) by an unknown mechanism. ERAP1 is an aminopeptidase that trims peptides in the endoplasmic reticulum for binding to MHC-I molecules. ERAP1 shows genetic epistasis with HLA-B27 in conferring susceptibility to AS. Male HLA-B27 transgenic rats develop arthritis and serve as an animal model of AS, whereas female B27 transgenic rats remain healthy. We used large scale quantitative mass spectrometry to identify over 15,000 unique HLA-B27 peptide ligands, isolated after immunoaffinity purification of the B27 molecules from the spleens of HLA-B27 transgenic rats. Heterozygous deletion of Erap1, which reduced the Erap1 level to less than half, had no qualitative or quantitative effects on the B27 peptidome. Homozygous deletion of Erap1 affected approximately one-third of the B27 peptidome but left most of the B27 peptidome unchanged, suggesting the possibility that some of the HLA-B27 immunopeptidome is not processed in the presence of Erap1. Deletion of Erap1 was permissive for the AS-like phenotype, increased mean peptide length and increased the frequency of C-terminal hydrophobic residues and of N-terminal Ala, Ser, or Lys. The presence of Erap1 increased the frequency of C-terminal Lys and Arg, of Glu and Asp at intermediate residues, and of N-terminal Gly. Several peptides of potential interest in AS pathogenesis, previously identified in human cell lines, were isolated. However, rats susceptible to arthritis had B27 peptidomes similar to those of non-susceptible rats, and no peptides were found to be uniquely associated with arthritis. Whether specific B27-bound peptides are required for AS pathogenesis remains to be determined. Data are available via ProteomeXchange with identifier PXD005502.

Sex differences in autoimmune disease

Female/male ratios of autoimmune diseases range from 10: 1 to 1: 3, with similar severity between the sexes. Men and women respond similarly to the infection and to vaccination, arguing against intrinsic sex differences in immune response. In autoimmune-like illnesses caused by environmental agents sex discrepancy is explained by differences in exposure. Endogenous hormones could cause sex discrepancy if their effect is a threshold off-on switch rather than quantitatively variable. X-inactivation and imprinting could cause sex discrepancy. Other possibilities include chronobiologic differences and pregnancy and menstruation biologies in which men differ from women.

Gut microbiota and inflammatory joint diseases

In most chronic inflammatory diseases, the cause remains unknown. Chronic infection is, however, among the current hypotheses. Recent technological advances have allowed in-depth studies of the gut microflora, or microbiota, which contains a vast array of organisms, most of which cannot be cultured. Inflammatory bowel disease has been associated with distinctive changes in the gut microbiota, which persist between disease flares and may play a pathogenic role. Links have been demonstrated between the gut microbiota and joint inflammation in murine models of arthritis but have received little attention in human patients. Recent work has nevertheless demonstrated substantial alterations in the gut microbiota in patients with rheumatoid arthritis, psoriatic arthritis, or spondyloarthritis, with differences across diagnoses and studies. Interestingly, some of these alterations resemble those now firmly established in inflammatory bowel disease; examples include decreased microbial diversity and lower frequencies of bacterial groups belonging to the Firmicutes phylum known to have immunoregulatory properties. These new findings open up important new horizons both for understanding disease and for developing novel biomarkers and treatment strategies.

The intestinal microbiome in spondyloarthritis

PURPOSE OF REVIEW

Microbial dysbiosis in the gut is emerging as a common component in various inflammatory disorders including spondyloarthritis (SpA). The depth of this influence has begun to be realized with next-generation sequencing of the gut microbiome providing unbiased assessment of previously uncharted bacterial populations.

RECENT FINDINGS

Decreased numbers of Firmicutes, a major phyla of gut commensals, especially the species Faecalibacterium prausnitzii and Clostridium leptum have been found in various inflammatory disorders including SpA and inflammatory bowel disease (IBD), and could be an important link between SpA and gut inflammation. Multiple studies in ankylosing spondylitis, psoriatic arthritis, juvenile SpA, and animal models of SpA are revealing common bacterial associations among these diseases as well as IBD.

SUMMARY

We are beginning to appreciate the complex relationship between the gut microbiome and host immune regulation and dysregulation in health and disease. Potentially important differences have been revealed in SpA, but cause and effect relationships remain far from established. Many critical questions remain to be answered before we can apply new knowledge to improve therapeutics in SpA.

Sulfasalazine Treatment Suppresses the Formation of HLA-B27 Heavy Chain Homodimer in Patients with Ankylosing Spondylitis

Human leukocytic antigen-B27 heavy chain (HLA-B27 HC) has the tendency to fold slowly, in turn gradually forming a homodimer, (B27-HC)₂ via a disulfide linkage to activate killer cells and T-helper 17 cells and inducing endoplasmic reticulum (ER) stress to trigger the IL-23/IL-17 axis for pro-inflammatory reactions. All these consequences lead to the pathogenesis of ankylosing spondylitis (AS). Sulfasalazine (SSA) is a common medication used for treatment of patients with AS. However, the effects of SSA treatment on (B27-HC)₂ formation and on suppression of IL-23/IL-17 axis of AS patients remain to be determined. In the current study, we examine the (B27-HC)₂ of peripheral blood mononuclear cells (PBMC), the mean grade of sarcoiliitis and lumbar spine Bath Ankylosing Spondylitis Radiology Index (BASRI) scores of 23 AS patients. The results indicated that AS patients without (B27-HC)₂ on PBMC showed the lower levels of mean grade of sarcoiliitis and the lumbar spine BASRI scores. In addition, after treatment with SSA for four months, the levels of (B27-HC)₂ on PBMCs were significantly reduced. Cytokines mRNA levels, including TNFα, IL-17A, IL-17F and IFNγ, were also significantly down-regulated in PBMCs. However, SSA treatment did not affect the levels of IL-23 and IL-23R mRNAs.

Loss of bone strength in HLA-B27 transgenic rats is characterized by a high bone turnover and is mainly osteoclast-driven

OBJECTIVE

Although osteopenia is frequent in spondyloarthritis (SpA), the underlying cellular mechanisms and association with other symptoms are poorly understood. This study aimed to characterize bone loss during disease progression, determine cellular alterations, and assess the contribution of inflammatory bowel disease (IBD) to bone loss in HLA-B27 transgenic rats.

METHODS

Bones of 2-, 6-, and 12-month-old non-transgenic, disease-free HLA-B7 and disease-associated HLA-B27 transgenic rats were examined using peripheral quantitative computed tomography, μCT, and nanoindentation. Cellular characteristics were determined by histomorphometry and ex vivo cultures. The impact of IBD was determined using [21-3 x 283-2]F1 rats, which develop arthritis and spondylitis, but not IBD.

RESULTS

HLA-B27 transgenic rats continuously lost bone mass with increasing age and had impaired bone material properties, leading to a 3-fold decrease in bone strength at 12 months of age. Bone turnover was increased in HLA-B27 transgenic rats, as evidenced by a 3-fold increase in bone formation and a 6-fold increase in bone resorption parameters. Enhanced osteoclastic markers were associated with a larger number of precursors in the bone marrow and a stronger osteoclastogenic response to RANKL or TNFα. Further, IBD-free [21-3 x 283-2]F1 rats also displayed decreased total and trabecular bone density.

CONCLUSIONS

HLA-B27 transgenic rats lose an increasing amount of bone density and strength with progressing age, which is primarily mediated via increased bone remodeling in favor of bone resorption. Moreover, IBD and bone loss seem to be independent features of SpA in HLA-B27 transgenic rats.

Increased production of interleukin-17 over interleukin-10 by treg cells implicates inducible costimulator molecule in experimental spondyloarthritis

OBJECTIVE

HLA-B27/human β2 -microglobulin (hβ2 m)-transgenic (B27-transgenic) rats develop an inflammatory disorder resembling spondyloarthritis, with accumulation of proinflammatory Th17 cells. Because Treg cells and Th17 cells have opposing effects in inflammatory disorders, we sought to determine whether biased expansion of Th17 cells could result from altered Treg cell frequency and/or function in B27-transgenic rats.

METHODS

We characterized the phenotype and function of Treg cells from B27-transgenic rats in comparison with those from control rats, by examining their expression of cell surface markers, suppressive activity, cytokine production, and differentiation pattern.

RESULTS

In B27-transgenic rats, the preferential accumulation of CD4+ Teff cells over Treg cells was not associated with a defect in Treg cell differentiation or suppressive activity. The expression of Treg cell markers was similar between B27-transgenic and control rats, with the exception of the inducible costimulator (ICOS) molecule, which was overexpressed in B27-transgenic rats. High levels of ICOS are considered to be a hallmark of Treg cells with heightened suppressive activity and interleukin-10 (IL-10) expression. Paradoxically, the production of IL-10 by Treg cells was reduced in B27-transgenic rats, whereas the production of IL-17 was enhanced. Moreover, the addition of anti-ICOS monoclonal antibodies during Treg cell differentiation in the presence of dendritic cells from B27-transgenic rats reversed this cytokine profile, restoring the balance between IL-10 and IL-17 in Treg cells from B27-transgenic rats.

CONCLUSION

We observed dysregulated production of IL-10 and IL-17 by Treg cells from B27-transgenic rats, which may contribute to disease development. Moreover, our data highlight a key role for ICOS signaling in the generation of imbalanced production of IL-10 and IL-17 by Treg cells in this experimental model of spondyloarthritis.

Reverse interferon signature is characteristic of antigen-presenting cells in human and rat spondyloarthritis

OBJECTIVE

In HLA-B27-transgenic rats, the development of a disorder that mimics spondyloarthritis (SpA) is highly correlated with dendritic cell (DC) dysfunction. The present study was undertaken to analyze the underlying mechanisms of this via transcriptome analysis.

METHODS

Transcriptome analysis of ex vivo-purified splenic CD103+CD4+ DCs from B27-transgenic rats and control rats was performed. Transcriptional changes in selected genes were confirmed by quantitative reverse transcriptase-polymerase chain reaction. A meta-analysis of our rat data and published data on gene expression in macrophages from ankylosing spondylitis (AS) patients was further performed.

RESULTS

Interferon (IFN) signaling was the most significantly affected pathway in DCs from B27-transgenic rats; the majority of genes connected to IFN were underexpressed in B27-transgenic rats as compared to controls. This pattern was already present at disease onset, persisted over time, and was conserved in 2 disease-prone B27-transgenic rat lines. In DCs from B27-transgenic rats, we further found an up-regulation of suppressor of cytokine signaling 3 (which may account for reverse IFN signaling) and a down-regulation of interleukin-27 (a cytokine that opposes Th17 differentiation and promotes Treg cells). The meta-analysis of data on conventional DCs from rats and data on monocyte-derived macrophages from humans revealed 7 IFN-regulated genes that were negatively regulated in both human and rat SpA (i.e., IRF1, STAT1, CXCL9, CXCL10, IFIT3, DDX60, and EPSTI1).

CONCLUSION

Our results suggest that expression of HLA-B27 leads to a defect in IFNγ signaling in antigen-presenting cells in both B27-transgenic rats and SpA patients, which may result in Th17 expansion and Treg cell alteration (as shown in B27-transgenic rats) and contribute to disease pathogenesis.

HLA-B27 alters the response to tumor necrosis factor α and promotes osteoclastogenesis in bone marrow monocytes from HLA-B27-transgenic rats

OBJECTIVE

To determine whether HLA-B27 expression alters the response of bone marrow monocytes from HLA-B27/human β2 -microglobulin-transgenic (B27-Tg) rats to tumor necrosis factor α (TNFα) and, if so, whether this affects the cells involved in bone homeostasis.

METHODS

Bone marrow monocytes were treated with RANKL or with TNFα to promote osteoclast formation. Osteoclasts were quantified by counting. Gene expression was measured using quantitative polymerase chain reaction analysis, and protein was detected by enzyme-linked immunosorbent assay, immunoblotting, or immunofluorescence. Effects of endogenously produced cytokines on osteoclast formation were determined with neutralizing antibodies.

RESULTS

TNFα treatment enhanced osteoclast formation 2.5-fold in HLA-B27-expressing cells as compared to wild-type or to HLA-B7/human β2 -microglobulin-expressing monocytes. TNFα induced ∼4-fold up-regulation of HLA-B27, which was associated with the accumulation of misfolded heavy chains, binding of the endoplasmic reticulum (ER) chaperone BiP, and activation of an ER stress response, which was not seen with HLA-B7. No differences were seen with RANKL-induced osteoclastogenesis. Enhanced interleukin-1α (IL-1α) production from ER-stressed bone marrow monocytes from B27-Tg rats was found to be necessary and sufficient for enhanced osteoclast formation. However, bone marrow monocytes from B27-Tg rats also produced more interferon-β (IFNβ), which attenuated the effect of IL-1α on osteoclast formation.

CONCLUSION

HLA-B27-induced ER stress alters the response of bone marrow monocytes from B27-Tg rats to TNFα, which is associated with enhanced production of IL-1α and IFNβ, cytokines that exhibit opposing effects on osteoclast formation. The altered response of cells expressing HLA-B27 to proinflammatory cytokines suggests that this class I major histocompatibility complex allele may contribute to the pathogenesis of spondyloarthritis and its unique phenotype through downstream effects involving alterations in bone homeostasis.

HLA-B27 misfolding and ankylosing spondylitis

Understanding how HLA-B27 contributes to the pathogenesis of spondyloarthritis continues to be an important goal. Current efforts are aimed largely on three areas of investigation; peptide presentation to CD8T cells, abnormal forms of the HLA-B27 heavy chain and their recognition by leukocyte immunoglobulin-like receptors on immune effector cells, and HLA-B27 heavy chain misfolding and intrinsic biological effects on affected cells. In this chapter we review our current understanding of the causes and consequences of HLA-B27 misfolding, which can be defined biochemically as a propensity to oligomerize and form complexes in the endoplasmic reticulum (ER) with the chaperone BiP (HSPA5/GRP78). HLA-B27 misfolding is linked to an unusual combination of polymorphisms that identify this allele, and cause the heavy chain to fold and load peptides inefficiently. Misfolding can result in ER-associated degradation (ERAD) of heavy chains, which is mediated in part by the E3 ubiquitin ligase HRD1 (SYVN1), and the ubiquitin conjugating enzyme UBE2JL. Upregulation of HLA-B27 and accumulation of misfolded heavy chains can activate ER stress signaling pathways that orchestrate the unfolded protein response. In transgenic rats where HLA-B27 is overexpressed, UPR activation is prominent. However, it is specific for heavy chain misfolding, since overexpression of HLA-B7, an allele that does not misfold, fails to generate ER stress. UPR activation has been linked to cytokine dysregulation, promoting lL-23, IFNβ, and lL-1α production, and may activate the IL-23/IL-17 axis in these rats. IL-1α and IFNβ are pro- and anti-osteoclastogenic cytokines, respectively, that modulate osteoclast development in HLA-B27-expressing transgenic rat monocytes. Translational studies of patient derived cells expressing HLA-B27 at physiologic levels have provided evidence that ER stress and UPR activation can occur in peripheral blood, but this has not been reported to date in isolated macrophages. Inflamed gastrointestinal tissue reveals evidence for HLA-B27 misfolding, ERAD, and autophagy, without acute UPR activation. A more complete picture of conditions that impact HLA-B27 folding and misfolding, the full spectrum and time course of consequences of ER stress, and critical cell types involved is needed to understand the role of HLA-B27 misfolding in spondyloarthritis pathogenesis.

Expression of aberrant HLA-B27 molecules is dependent on B27 dosage and peptide supply

OBJECTIVES

Cellular expression of non-classical forms of human leukocyte antigen (HLA)-B27 (NC-B27) may be involved in spondyloarthritis (SpA) pathogenesis. We used a novel B27-specific monoclonal antibody, HD6, to ask if B27 transgenic (TG) rat splenocytes express these NC-B27 molecules. We also investigated whether B27-binding peptides could affect the expression and functional immune recognition of HD6-reactive B27 molecules.

METHODS

Splenocytes from B27-TG, B7-TG and non-transgenic rats, and HLA-B27+ cell lines were stained with monoclonal antibodies recognising classical (ME-1, HLA-ABC-m1) and non-classical (HD6, HC10) B27. Cells were further cultured in the presence of HLA-B27-binding peptides, or subjected to brief low pH treatment prior to mAb staining and/or immunoprecipitation or co-culture with KIR3DL2-CD3ε-expressing Jurkat reporter cells.

RESULTS

HD6-reactive molecules were detected in the majority of adult B27-TG rat splenocyte cell subsets, increasing with age and concomitant increased B27 expression. HD6 staining was inhibited by incubation with B27-binding peptides and induced by low pH treatment. HD6 staining correlated with KIR3DL2-CD3ε-expressing Jurkat reporter cell activity. Thus, IL-2 production was decreased when B27-expressing antigen-presenting cells were preincubated with B27-binding peptides, but increased following pretreatment with low pH buffer.

CONCLUSIONS

Surface expression of HD6-reactive B27 molecules on B27-TG rat splenocytes is consistent with a pathogenic role for NC-B27 in SpA. Interaction of NC-B27 with innate immune receptors could be critical in SpA pathogenesis, and we show that this may be influenced by the availability and composition of the B27-binding peptide pool.

Spondyloarthropathies

Spondyloarthropathies (SpA) are a group of common inflammatory rheumatic disorders characterised by axial and or peripheral arthritis, associated with enthesitis, dactylitis and potential extra-articular manifestations such as uveitis and skin rash. The diseases, which comprise the group, share a common genetic predisposition, the HLA-B27 gene; however, this association varies markedly among the various SpAs and among different ethnic groups. Environmental factors seem to be triggering the diseases in the genetically predisposed individuals. The radiographic hallmark of the group is sacroiliitis, which when present is of help in the diagnosis. Various sets of diagnostic and classification criteria were developed over the years including the European Spondyloarthropathy Study Group (ESSG) criteria which were until recently the most widely used. The new Assessment in SpondyloArthritis international Society (ASAS) international working group has recently proposed a new set of diagnostic criteria that would enable identification of SpA before structural changes develop in the spine. Magnetic resonance imaging (MRI) changes have now been included in the new classification criteria of early axial SpA and are now considered as a major tool in the diagnosis. Until recently, there were no real disease-modifying anti-rheumatic drugs which were able to halt the disease progression. Over the past decade, tumour necrosis factor (TNF)-alfa-blocking agents have been extensively investigated and became the mainstream of therapy providing the patients an effective treatment option.

Relationship between inflammation, bone destruction, and osteoproliferation in the HLA-B27/human β2 -microglobulin-transgenic rat model of spondylarthritis

OBJECTIVE

Inhibition of inflammation and destruction, but not of osteoproliferation, in patients with spondylarthritis (SpA) treated with anti-tumor necrosis factor raises the question of how these three processes are interrelated. This study was undertaken to analyze this relationship in a rat model of SpA.

METHODS

Histologic spine and joint samples from HLA-B27/human β(2) -microglobulin (hβ(2) m)-transgenic rats were analyzed for signs of spondylitis and destructive arthritis and semiquantitatively scored as showing mild, moderate, or severe inflammation.

RESULTS

In rats exhibiting spondylitis, mildly inflamed sections displayed lymphocyte infiltration in connective tissue adjacent to the junction of the anulus fibrosus and vertebral bone but not at the enthesis. Moderately inflamed tissue samples contained osteoclasts eroding bone outside the cartilage end plate. In sections from rats with severe inflammation, the cartilage end plate and underlying bone marrow were also affected. End-stage disease was characterized by complete destruction of the intervertebral disc and vertebrae, with ongoing infiltration. Osteoproliferation was not observed in samples from rats with no or mild inflammation, but was present at the edge of the vertebrae in sections with moderate inflammation and persisted during severe inflammation and end-stage destruction. Osteoproliferation occurred at the border of inflammation, at a distance from bone destruction. A strong correlation between the extent of inflammation, destruction, and osteoproliferation was observed. Sections from rats with arthritis displayed a similar pattern of synovial inflammation associated with bone destruction, and simultaneous but topographically distinct osteoproliferation starting from the periosteum.

CONCLUSION

SpA in B27/hβ(2) m-transgenic rats is characterized by destructive inflammatory pannus tissue rather than by enthesitis or osteitis. Destruction and osteoproliferation occur simultaneously but at distinct sites in joints with moderate to severe inflammation.

The interplay between fiber and the intestinal microbiome in the inflammatory response

Fiber intake is critical for optimal health. This review covers the anti-inflammatory roles of fibers using results from human epidemiological observations, clinical trials, and animal studies. Fiber has body weight-related anti-inflammatory activity. With its lower energy density, a diet high in fiber has been linked to lower body weight, alleviating obesity-induced chronic inflammation evidenced by reduced amounts of inflammatory markers in human and animal studies. Body weight-unrelated anti-inflammatory activity of fiber has also been extensively studied in animal models in which the type and amount of fiber intake can be closely monitored. Fermentable fructose-, glucose-, and galactose-based fibers as well as mixed fibers have shown systemic and local intestinal anti-inflammatory activities when plasma inflammatory markers and tissue inflammation were examined. Similar anti-inflammatory activities have also been demonstrated in some human studies that controlled total fiber intake. The anti-inflammatory activities of synbiotics (probiotics plus fiber) were reviewed as well, but there was no convincing evidence indicating higher efficacy of synbiotics compared with that of fiber alone. Adverse effects have not been observed with the amount of fiber intake or supplementation used in studies, although patients with Crohn's disease may be more sensitive to inulin intake. Several possible mechanisms that may mediate the body weight-unrelated anti-inflammatory activity of fibers are discussed based on the in vitro and in vivo evidence. Fermentable fibers are known to affect the intestinal microbiome. The immunomodulatory role of the intestinal microbiome and/or microbial metabolites could contribute to the systemic and local anti-inflammatory activities of fibers.