HLA-B27

Ankylosing spondylitis: From pathogenesis to therapy

Ankylosing spondylitis (AS) is an autoimmune rheumatic disease that primarily affects the axial joints, with its etiology complex and still not fully understood. The unknown pathogenesis of AS limits the development of treatment strategies, so keeping up-to-date with the current research on AS can help in searching for potential therapeutic targets. In addition to the classic HLA-B27 genetic susceptibility and Th17-related inflammatory signals, increasing research is focusing on the influence of autoantigen-centered autoimmune responses and bone stromal cells on the onset of AS. Autoantigens derived from gut microbiota and preferential TCR both exacerbate the autoimmune response in patients with AS. Furthermore, dysregulated bone metabolism also promotes pathological new bone formation in AS. Current treatments approved for AS almost focus on the management of inflammation with inconsistent treatment results due to the heterogeneity of patients. In this review, we systematically summarized various pathogenesis and management of AS, meanwhile discussed the underlying risk factors and potential therapeutic targets.

Causal relationship between ankylosing spondylitis and ocular inflammatory diseases: a Mendelian randomization study

Background

Observational studies have shown an increased risk of ocular inflammatory diseases in patients with ankylosing spondylitis (AS), but the genetically predicted association remains unclear. The aim of this study was to systematically assess the causal relationship between AS and ocular inflammatory diseases.

Methods

We conducted a two-sample Mendelian randomization (MR) analysis to investigate the causal relationship between AS and several common ocular inflammatory diseases based on genome-wide association study (GWAS) data and public health data. Five methods, namely, inverse-variance weighted (IVW), MR-Egger, weighted median, weighted mode, and simple mode, were used. Sensitivity analysis was performed using MR-Egger intercept, Mendelian Randomization Pleiotropy RESidual Sum and Outlier (MR-PRESSO), Cochran's Q test, outlier methods, leave-one-out analysis, and funnel plots.

Results

The MR analysis showed a significantly increased risk of uveitis (ORIVW = 2.825, 95%CIIVW = 1.709-4.672, and PIVW < 0.001), iridocyclitis (ORIVW = 3.806, 95%CIIVW = 2.809-5.157, and PIVW < 0.001), scleritis (ORIVW = 1.738, 95%CIIVW = 1.190-2.539, and PIVW < 0.001), and episcleritis (ORIVW = 5.113, 95%CIIVW = 2.067-12.645, and PIVW = 0.004) associated with AS. However, no correlation was found between genetically predicted AS and keratitis (ORIVW = 1.041, 95%CIIVW = 0.886-1.222, and PIVW = 0.628) and optic neuritis (ORIVW = 0.868, 95%CIIVW = 0.441-1.709, and PIVW = 0.682).

Conclusion

AS increases the genetically predicted risk for uveitis, iridocyclitis, scleritis, and episcleritis. No potential association of AS with keratitis and optic neuritis was found. It may provide clues for the prevention of AS complications.

HLA diversity unveils susceptibility and organ-specific occurrence of second primary cancers: a prospective cohort study

BACKGROUND

Up to 17% of cancer survivors have been reported to develop second primary cancers (SPC), which cause significant physical and economic distress and often complicate clinical decision-making. However, understanding of SPC remains limited and superficial. Human leukocyte antigen (HLA) is characterized by its polymorphism and has been associated with various diseases. This study aims to explore the role of HLA diversity in SPC incidence.

METHODS

We analyzed a cohort of 47,550 cancer patients from the UK Biobank. SNP-derived HLA alleles were used and SPC-related HLA alleles were identified using logistic regression, followed by stepwise filtering based on the Akaike information criterion (AIC) and permutation tests. Additionally, we examined the association between extragenetic factors and the risk of SPC in patients carrying hazardous HLA alleles.

RESULTS

During a median follow-up of 3.11 years, a total of 2894 (6.09%) participants developed SPC. We identified three protective HLA alleles (DRB1*04:03 and DPA1*02:02 for males and DRB5*01:01 for females) and two hazardous alleles (A*26:01 for males and DPB1*11:01 for females) about SPC. The presence of the protective alleles was associated with a reduced SPC risk (males: hazard ratio [HR] 0.72, 95% confidence interval [CI] 0.59-0.89; females: HR 0.81, 95% CI 0.70-0.93), while the hazardous alleles were linked to an increased risk (males: HR 1.27, 95% CI 1.03-1.56; females: HR 1.35, 95% CI 1.07-1.70). The hazardous allele A*26:01 indicated skin-lung organ-specific SPC occurrence in males. Animal fat and vitamin C were associated with SPC risk in males carrying the hazardous alleles, while free sugar and vegetable fat were linked to SPC risk in females.

CONCLUSIONS

These results suggest that HLA alleles may serve as biomarkers for the susceptibility and organ-specific occurrence of SPC, while dietary modulation may mitigate hazardous alleles-related SPC risk, potentially aiding in the early prediction and prevention of SPC.

Precision medicine in axial spondyloarthritis: current opportunities and future perspectives

Axial spondyloarthritis (axSpA) is a complex disease characterized by a diverse range of clinical presentations. The primary manifestation is inflammatory lower back pain, often accompanied by other clinical manifestations such as peripheral arthritis, enthesitis, uveitis, psoriasis, and inflammatory bowel disease. However, the presentation of axSpA can vary widely among patients. Despite extensive research, the precise pathogenesis of axSpA remains largely unknown. The lack of complete understanding poses challenges in subgrouping the disease, developing specific treatment approaches, and predicting treatment response. In this review, we will explore the limitations in diagnosing and treating axSpA. In addition, we will examine the current knowledge and potential opportunities provided by various omics and technological advancements in enhancing the diagnosis and personalized treatment of axSpA.

Complex Interactions between the Human Major Histocompatibility Complex (MHC) and Microbiota: Their Roles in Disease Pathogenesis and Immune System Regulation

The relationship between microbiota and the immune system is complex and characterized by the ways in which microbiota directs immune function interactions, both innate and acquired and also keeps activating the immune system throughout an individual's life. In this respect, the human Major Histocompatibility Complex (MHC, referred to as HLA in humans) plays a crucial role and is also established in self-defense against microbes by presenting microbial-derived peptides to the immune cells. However, this assumption has some unclear aspects that should be investigated. For example, how is the microbiota shaped by microbe species diversity, quantity and functions of the immune system, as well as the role and molecular mechanisms of the HLA complex during this process. There are autoimmune diseases related to both HLA and specific microbiota changes or alterations, many of which are mentioned in the present review. In addition, the HLA peptide presenting function should be put in a framework together with its linkage to diseases and also with HLA compatibility necessary for transplants to be successful. These are still quite an enigmatically statistical and phenomenological approach, but no firm pathogenic mechanisms have been described; thus, HLA's real functioning is still to be fully unveiled. After many years of HLA single-genes studies, firm pathogenesis mechanisms underlying disease linkage have been discovered. Finally, microbiota has been defined as conformed by bacteria, protozoa, archaea, fungi, and viruses; notwithstanding, endogenous viral sequences integrated into the human genome and other viral particles (obelisks) recently found in the digestive mucosa should be taken into account because they may influence both the microbiome and the immune system and their interactions. In this context, we propose to integrate these microbial-genetic particle components into the microbiome concept and designate it as "microgenobiota".

Emerging biochemical, microbial and immunological evidence in the search for why HLA-B∗27 confers risk for spondyloarthritis

The strong association of the human leukocyte antigen B∗27 alleles (HLA-B∗27) with spondyloarthritis and related rheumatic conditions has long fascinated researchers, yet the precise mechanisms underlying its pathogenicity remain elusive. Here, we review how interplay between the microbiome, the immune system, and the enigmatic HLA-B∗27 could trigger spondyloarthritis, with a focus on whether HLA-B∗27 presents an arthritogenic peptide. We propose mechanisms by which the unique biochemical characteristics of the HLA-B∗27 protein structure, particularly its peptide binding groove, could dictate its propensity to induce pathological T cell responses. We further provide new insights into how TRBV9+ CD8+ T cells are implicated in the disease process, as well as how the immunometabolism of T cells modulates tissue-specific inflammatory responses in spondyloarthritis. Finally, we present testable models and suggest approaches to this problem in future studies given recent advances in computational biology, chemical biology, structural biology, and small-molecule therapeutics.

A Cost-Effective and Labor-Saving Method for Detecting Human Leukocyte Antigen B27 Status via Sequence-Encoded Fluorescence Amplification Assay

Identification of human leukocyte antigen B27 (HLA-B27) by flow cytometry (FCM) has been widely applied in clinical practice for auxiliary diagnosis of ankylosing spondylitis (AS). However, FCM requires freshly prepared samples and relies on expensive equipment, reagents, and an experienced operator. To provide a cheaper and more convenient method for HLA-B27 detection, we proposed a new method termed sequence-encoded fluorescence amplification assay (SEFA), which specially recognized sequences of HLA-B27 gene (HLA-B∗27) covering current common subtypes in a single closed tube. SEFA could detect as low as 10 pg (equal to 3 copies) genomic DNA per reaction and distinguish HLA-B∗27 from other HLA-B alleles with highly similar sequences. A total of 288 clinical samples were tested by SEFA, including 181 patients with AS and 107 healthy controls. Compared with the detection results from FCM, two controversial samples of patients with AS were obtained and further confirmed to be consistent with SEFA by Sanger sequencing, indicating that this method was more accurate than FCM. Moreover, SEFA could detect HLA-B27 status by using supernatant from crude extract of 10-μL blood without commercial reagents. Overall, SEFA has the potential to be an alternative for HLA-B27 identification with the advantage of convenience and low cost, especially suitable for early diagnosis of AS in areas with limited medical resources.

Association between specific human leukocyte antigen alleles and development of thyroid immune-related adverse event

Aim: Inherent variations in human leukocyte antigen (HLA) alleles have been revealed epidemiologically to influence the development of autoimmune diseases. HLA alleles may thus also be associated with the development of immune-related adverse events (irAEs), such as thyroid irAE.Materials & methods: In this case-control study, 71 cancer patients who received immune checkpoint inhibitors were enrolled and HLA-genotyped and the frequency of HLA alleles was compared.Results: A*26:01, DPA1*01:03 and DPB1*02:01 were significantly more frequent in patients with thyroid irAE than in patients without any irAEs (35.0 vs 3.2% [p = 0.004], 80.0 vs 45.2% [p = 0.020] and 55.0 vs 25.8% [p = 0.044], respectively).Conclusion: A*26:01, DPA1*01:03 and DPB1*02:01 appear to be associated with thyroid irAE.

Exploring the Pathogenesis of Spondylarthritis beyond HLA-B27: A Descriptive Review

Spondylarthritis (SpA) is a chronic inflammatory condition that encompasses damage to the axial or peripheral skeleton, accompanied by specific extra-articular symptoms. Within this group, Ankylosing Spondylitis stands out as the hallmark member. Although the heritability of Ankylosing Spondylitis is estimated to be over 95%, only a portion of the heritability has been explained, with HLA-B27 accounting for 20.1% of it; therefore, ongoing research endeavors are currently concentrated on investigating the potential participation of different entities in the development of the disease. Genome-wide association studies have led to significant advances in our understanding of the genetics of SpA. In this descriptive review, we delve into the pathogenesis of Spondylarthritis beyond HLA-B27. We summarize the latest research on the potential participation of various entities in the development of the disease, including other genetic loci, immune dysregulation, microbiota, and environmental factors. The multifactorial nature of SpA and the complex interplay of genetic, immunological, and environmental factors are being increasingly recognized; therefore, it is of paramount importance to consider a holistic approach to comprehend the pathogenesis of SpA in order to identify novel therapeutic targets.

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.

Evaluation of HLA typing content of next-generation sequencing datasets from family trios and individuals of arab ethnicity

Introduction: HLA typing is a critical tool in both clinical and research applications at the individual and population levels. Benchmarking studies have indicated HLA-HD as the preferred tool for accurate and comprehensive HLA allele calling. The advent of next-generation sequencing (NGS) has revolutionized genetic analysis by providing high-throughput sequencing data. This study aims to evaluate, using the HLA-HD tool, the HLA typing content of whole exome, whole genome, and HLA-targeted panel sequence data from the consanguineous population of Arab ethnicity, which has been underrepresented in prior benchmarking studies. Methods: We utilized sequence data from family trios and individuals, sequenced on one or more of the whole exome, whole genome, and HLA-targeted panel sequencing technologies. The performance and resolution across various HLA genes were evaluated. We incorporated a comparative quality control analysis, assessing the results obtained from HLA-HD by comparing them with those from the HLA-Twin tool to authenticate the accuracy of the findings. Results: Our analysis found that alleles across 29 HLA loci can be successfully and consistently typed from NGS datasets. Clinical-grade whole exome sequencing datasets achieved the highest consistency rate at three-field resolution, followed by targeted HLA panel, research-grade whole exome, and whole genome datasets. Discussion: The study catalogues HLA typing consistency across NGS datasets for a large array of HLA genes and highlights assessments regarding the feasibility of utilizing available NGS datasets in HLA allele studies. These findings underscore the reliability of HLA-HD for HLA typing in underrepresented populations and demonstrate the utility of various NGS technologies in achieving accurate HLA allele calling.

Single-cell transcriptome revealed dysregulated RNA-binding protein expression patterns and functions in human ankylosing spondylitis

Objective

To explore the expression characteristics and regulatory patterns of RBPs in different immune cell types of AS, and to clarify the potential key role of RBPs in the occurrence and development of AS disease.

Methods

PBMC sample data from scRNA-seq (HC*29, AS*10) and bulk RNA-seq (NC*3, AS*5) were selected for correlation analysis.

Results

(1) Compared with the HC group, the numbers of B, DC (dendritic cells), CD14+ Mono and CD8+ T cells were increased in AS group, while the numbers of platelet (platelets), CD8+ NKT, CD16+ Mono (non-classical monocytes), Native CD4+ T and NK were decreased. (2) Through the analysis of RBP genes in B cells, some RBPs were found to play an important role in B cell differentiation and function, such as DDX3X, SFPQ, SRRM1, UPF2. (3) It may be related to B-cell receptor, IgA immunity, NOD-like receptor and other signaling pathways; Through the analysis of RBP genes in CD8+ T cells, some RBPs that play an important role in the immune regulation of CD8+ T were found, such as EIF2S3, EIF4B, HSPA5, MSL3, PABPC1 and SRSF7; It may be related to T cell receptor, TNF, IL17 and other signaling pathways. (4) Based on bulk RNA-seq, it was found that compared with HC and AS patients, differentially expressed variable splicing genes (RASGs) may play an important role in the occurrence and development of AS by participating in transcriptional regulation, protein phosphorylation and ubiquitination, DNA replication, angiogenesis, intracellular signal transduction and other related pathways.

Conclusion

RBPs has specific expression characteristics in different immune cell types of AS patients, and has important regulatory functions. Its abnormal expression and regulation may be closely related to the occurrence and development of AS.

Phenomic landscape and pharmacogenomic implications for HLA region in a Taiwan Han Chinese population

BACKGROUND

The human leukocyte antigen (HLA) genes, exhibiting significant genetic diversity, are associated with susceptibility to various clinical diseases and diverse in drug responses. High costs of HLA sequencing and the population-specific architecture of this genetic region necessitate the establishment of a population-specific HLA imputation reference panel. Moreover, there is a lack of understanding about the genetic and phenotypic landscape of HLA variations within the Taiwanese population.

METHODS

We created models for a Taiwanese-specific HLA imputation reference panel. These models were trained with the array genotype data and HLA sequencing data from 845 Taiwanese subjects. HLA imputation was applied for 59,448 Taiwanese subjects to characterize the HLA allele and haplotype frequencies. Additionally, a phenome-wide association study (PheWAS) was conducted to identify the phenotypes associated with HLA variations. The association of the biallelic HLA variants with the binary and quantitative traits were evaluated with additive logistic and linear regression models, respectively. Furthermore, an omnibus test with likelihood-ratio test was applied for each HLA amino acid position in the multiallelic HLA amino acid polymorphisms to compare the difference between a fitted model and a null model following a χ2 distribution of n-1 degree of freedom at a position with n residues. Finally, we estimated the prevalence of adverse drug reactions (ADR)-related HLA alleles in the Taiwanese population.

RESULTS

In this study, the reference panel models displayed remarkable accuracy, with averages of 99.3%, 98.9%, and 99.1% for 2-, 4-, 6-digit alleles of the eight classical HLA genes, respectively. For PheWAS, a total of 18,136 significant associations with HLA variants across 26 phenotypes are identified (p < 5×10-8), highlighting the pleiotropy feature of the HLA region. Among the independent signals, 15 are novel, including the association of HLA-B pos 138 variation with ankylosing spondylitis (AS), and rs9266290 and rs9266292 with allergy. Through an analysis spanning the entire HLA region, we identified clusters of phenotype correlations. Finally, the carriers of pharmacogenomic related HLA alleles, including HLA-C*01:02 (35.86%), HLA-B*58:01 (20.9%), and HLA-B*15:02 (8.38%), were characterized in the Taiwanese general population.

CONCLUSIONS

We successfully delivered the HLA imputation for 59,448 Taiwanese subjects and characterized the genetic and phenotypic landscapes of the HLA variations. In addition, we quantified the estimated prevalence of the ADR-related HLA alleles in the Taiwanese population. The developed HLA imputation reference panel could be used for estimation of population HLA allele frequencies, which can facilitate further studies in the role of HLA variants in a wider range of phenotypes in the population.

Biology of HLA class I associated inflammatory diseases

Human leukocyte antigen (HLA) class I association is a well-established feature of common and uncommon inflammatory diseases, but it is unknown whether it impacts the pathogenesis of these disorders. The "arthritogenic peptide" hypothesis proposed initially for HLA-B27-associated ankylosing spondylitis (AS) seems the most intuitive to serve as a model for other HLA class I-associated diseases, but evidence supporting it has been scarce. Recent technological advances and the discovery of epistatic relationships between disease-associated HLA class I and endoplasmic reticulum aminopeptidase (ERAP) coding variants have led to the generation of new data and conceptual approaches to the problem requiring its re-examination. Continued success in these endeavors holds promise to resolve a Gordian Knot in human immunobiology. It may ultimately benefit patients by enabling the development of new therapies and precision tools for assessing disease risk and predicting treatment responses.

The impact of micropolymorphism in Anpl-UAA on structural stability and peptide presentation

Micropolymorphism significantly shapes the peptide-binding characteristics of major histocompatibility complex class I (MHC-I) molecules, affecting the host's resistance to pathogens, which is particularly pronounced in avian species displaying the "minimal essential MHC" expression pattern. In this study, we compared two duck MHC-I alleles, Anpl-UAA*77 and Anpl-UAA*78, that exhibit markedly different peptide binding properties despite their high sequence homology. Through mutagenesis experiments and crystallographic analysis of complexes with the influenza virus-derived peptide AEAIIVAMV (AEV9), we identified a critical role for the residue at position 62 in regulating hydrogen-bonding interactions between the peptide backbone and the peptide-binding groove. This modulation affects the characteristics of the B pocket and the stability of the loop region between the 310 helix and the α1 helix, leading to significant changes in the structure and stability of the peptide-MHC-I complex (pMHC-I). Moreover, the proportion of different residues at position 62 among Anpl-UAAs may reflect the correlation between pAnpl-UAA stability and duck body temperature. This research not only advances our understanding of the Anpl-UAA structure but also deepens our insight into the impact of MHC-I micropolymorphism on peptide binding.

miRNAs dysregulation in ankylosing spondylitis: A review of implications for disease mechanisms, and diagnostic markers

Epigenetic processes, including non-coding RNA, histone modifications, and DNA methylation, play a vital role in connecting the environment to the development of a disorder, especially when there is a favorable genetic background. Ankylosing Spondylitis (AS) is a chronic type of spinal arthritis that highlights the significance of epigenetics in diseases related to autoimmunity and inflammation. MicroRNAs (miRNAs) are small non-coding RNAs that are involved in both normal and aberrant pathological and physiological gene expression. This study focuses on the pathophysiological pathways to clarify the role of miRNAs in AS. We have conducted a thorough investigation of the involvement of miRNAs in several processes, including inflammation, the production of new bone, T-cell activity, and the regulation of pathways such as BMP, Wnt, and TGFβ signaling. Undoubtedly, miRNAs play a crucial role in enhancing our comprehension of the pathophysiology of AS, and their promise as a therapeutic strategy is quickly expanding.

A statistical symptomatic evaluation on SAPHO syndrome from 56 cases of confirmed diagnosis and 352 cases of non-SAPHO involvement

OBJECTIVE

To report a statistical evaluation of symptomatology based on 56 cases of SAPHO syndrome and 352 non-SAPHO involvement cases, to propose a symptomatic scoring system in consideration of early warning for SAPHO syndrome.

METHODS

A cohort comprising 56 subjects diagnosed with SAPHO syndrome was reported, as well as 352 non-SAPHO involvement cases, including their chief complaints, skin manifestations, radiological findings, and laboratory tests. We systematically reviewed previous published five representative huge cohorts from different countries to conclude several specific features of SAPHO by comparing with our case series. The score of each specific index is based on respective incidence and comparison of two cohorts was performed.

RESULT

In terms of complaint rates, all subjects of two cohorts suffered from osseous pain, which appeared in the anterior chest wall, spine, and limb which were calculated. In respect to dermatological lesions, SAPHO patients suffered from severe acne, and other patients (82.14%) accompanied with palmoplantar pustulosis. Having received radiological examinations, most SAPHO subjects rather than non-SAPHO involvement cases showed abnormal osteoarticular lesions under CT scanning and more detailed information under whole-body bone scintigraphy. Differences also emerged in elevation of inflammation values and rheumatic markers like HLA-B27. Based on our cases and huge cohorts documented, the early warning standard is set to be 5 scores.

CONCLUSIONS

SAPHO syndrome case series with 56 subjects were reported and an accumulative scoring system for the early reminder on SAPHO syndrome was proposed. The threshold of this system is set to be 5 points. Key Points • Fifty-six patients diagnosed by SAPHO syndrome with detailed symptoms and radiological findings were reported. • Comparison was made between the 56 SAPHO patients and 352 non-SAPHO involvement cases. • An accumulative scoring system for the early reminder on SAPHO syndrome was proposed and the threshold of this system is set to be five points.

[The role of HLA-B27 in the pathogenesis and diagnosis of axial spondyloarthritis : 50 years after discovery of the strong genetic association]

BACKGROUND

The association of the human lymphocyte antigen B27 (HLA-B27) with ankylosing spondylitis (AS), also now called axial spondylarthritis (axSpA), was first described 50 years ago.

OBJECTIVE

This article gives an overview of the available knowledge on the topic.

MATERIAL AND METHODS

This is a narrative review based on the experience of the authors.

RESULTS

The HLA-B27 is a member of the HLA class I family of genes of the major histocompatibility complex (MHC). The prevalence of HLA-B27 in the central European population is approximately 8 %, i.e., the vast majority of carriers of HLA-B27+ remain healthy. The frequency of HLA-B27 shows a decline from north to south. The HLA-B27 explains only 30 % of the genetic burden of axSpA. The prevalence of the disease correlates with the frequency of HLA-B27 in the population, i.e., there are geographic differences. Approximately 60-90 % of patients with axSpA worldwide are HLA-B27+. Some 200 subtypes of HLA-B27 can be differentiated using the polymerase chain reaction (PCR). In Thailand and Sardinia two subtypes were found that are not associated with axSpA. The physiological function of HLA class I molecules is the defence of the organism against microbes. Microbial peptides are presented to the immune system, which can be specifically attacked by CD8+ T‑cells. Genetic polymorphisms of the enzyme endoplasmic reticulum aminopeptidase 1 (ERAP1), which breaks down peptides in the endoplasmic reticulum, are associated only with HLA-B27+ diseases.

DISCUSSION

The pathogenesis of axSpA is unclear but a major hypothesis is that of the arthritogenic peptides. In this it is assumed that potentially pathogenic foreign or autologous peptides can be presented by HLA-B27. If nothing else, HLA-B27 plays an important role in the diagnosis, classification and determination of the severity of axSpA.

Reactive Arthritis in Children: Case Report, Narrative Review and Proposed Therapy

Reactive arthritis is an acute inflammatory aseptic arthritis that is preceded by an infectious process in genetically predisposed individuals. It has been associated with gastrointestinal or genitourinary infection. Reactive arthritis is rare in children. In this review, we present two index cases that need biologic treatment followed by a thorough review of reactive arthritis in children and adolescents with proposed treatment algorithm.

Disease characteristics, pathogenesis, and treatment controversies of axial psoriatic arthritis

Axial psoriatic arthritis (axPsA) has considerable overlap with axial spondyloarthritis (axSpA) but has some unique features that sometimes preclude classification into axSpA. It has some clinical and radiographic differences compared to axSpA. Imaging typically shows asymmetric syndesmophytes, mainly in the cervical spine, with less frequent sacroiliitis. It more commonly presents later in life and is associated with less severe inflammatory back pain than axSpA. The interleukin (IL) IL-23/IL-17 axis is central to the pathogenesis of both diseases. However, the response to therapies targeting these cytokines has been different. IL-23 inhibitors are ineffective in axSpA but may be effective in psoriatic arthritis (PsA). Recent post hoc analyses of clinical trial data with IL-23 inhibitors in PsA have raised the possibility of their efficacy in axPsA and need evaluation in future clinical trials. Moreover, there is a need for classification criteria for axPsA and better tools to assess therapeutic response.

HLA-B*27 and Ankylosing Spondylitis: 50 Years of Insights and Discoveries

PURPOSE OF REVIEW

To commemorate the 50th anniversary of the groundbreaking discovery of a remarkably strong association between HLA-B*27 and ankylosing spondylitis (AS).

RECENT FINDINGS

In addition to HLA-B*27, more than 116 other recognized genetic risk variants have been identified, while epigenetic factors largely remain unexplored in this context. Among patients with AS who carry the HLA-B*27 gene, clonally expanded CD8 + T cells can be found in their bloodstream and within inflamed tissues. Moreover, the α and β chain motifs of these T-cell receptors demonstrate a distinct affinity for certain self- and microbial-derived peptides, leading to an autoimmune response that ultimately results in the onset of the disease. These distinctive peptide-binding and presentation characteristics are a hallmark of the disease-associated HLA-B*27:05 subtype but are absent in HLA-B*27:09, a subtype not associated with the disease, differing by only a single amino acid. This discovery represents a significant advancement in unraveling the 50-year-old puzzle of how HLA-B*27 contributes to the development of AS. These findings will significantly accelerate the process of identifying peptides, both self- and microbial-derived, that instigate autoimmunity. This, in return, will pave the way for the development of more accurate and effective targeted treatments. Moreover, the discovery of improved biomarkers, in conjunction with the emerging technology of electric field molecular fingerprinting, has the potential to greatly bolster early diagnosis capabilities. A very recently published groundbreak paper underscores the remarkable effectiveness of targeting and eliminating disease-causing T cells in a HLA-B*27 patients with AS. This pivotal advancement not only signifies a paradigm shift but also bolsters the potential for preventing the disease in individuals carrying high-risk genetic variants.

Targeted depletion of TRBV9+ T cells as immunotherapy in a patient with ankylosing spondylitis

Autoimmunity is intrinsically driven by memory T and B cell clones inappropriately targeted at self-antigens. Selective depletion or suppression of self-reactive T cells remains a holy grail of autoimmune therapy, but disease-associated T cell receptors (TCRs) and cognate antigenic epitopes remained elusive. A TRBV9-containing CD8+ TCR motif was recently associated with the pathogenesis of ankylosing spondylitis, psoriatic arthritis and acute anterior uveitis, and cognate HLA-B*27-presented epitopes were identified. Following successful testing in nonhuman primate models, here we report human TRBV9+ T cell elimination in ankylosing spondylitis. The patient achieved remission within 3 months and ceased anti-TNF therapy after 5 years of continuous use. Complete remission has now persisted for 4 years, with three doses of anti-TRBV9 administered per year. We also observed a profound improvement in spinal mobility metrics and the Bath Ankylosing Spondylitis Metrology Index (BASMI). This represents a possibly curative therapy of an autoimmune disease via selective depletion of a TRBV-defined group of T cells. The anti-TRBV9 therapy could potentially be applicable to other HLA-B*27-associated spondyloarthropathies. Such targeted elimination of the underlying cause of the disease without systemic immunosuppression could offer a new generation of safe and efficient therapies for autoimmunity.

PRICKLE1 gene methylation and abnormal transcription in Chinese patients with ankylosing spondylitis

BACKGROUND

Ankylosing spondylitis (AS) is a common inflammatory arthritis without a reliable biomarker. The role of methylation and mRNA expression of PRICKLE1 promoter in the pathogenesis of ankylosing spondylitis remains unclear.

METHODS

A two-stage case-control design was used to detect the characteristics of methyl group and transcriptome of PRICKLE1 gene in Ankylosing spondylitis. The methylation degree of PRICKLE1 gene promoter region was tested by phosphate-sequencing, and further analyzed whether there was significant difference in methylation level of PRICKLE1 gene. The expression levels of PRICKLE1 mRNA in 50 AS patients and 50 healthy controls were detected by real-time quantitative PCR (RT-qPCR).

RESULTS

Compared with healthy control group, the intensity of methylation in 4 ponds of PRICKLE1 in patients with Ankylosing spondylitis was low, and the mRNA levels were overexpressed (P = 0.017). ROC results showed that the sensitivity of PRICKLE1 was 68.67% and specificity was 71.43%.

CONCLUSION

There is a significant change in the concentration of serum PRICKLE1 mRNA​in patients with Ankylosing spondylitis, and the degree of gene methylation is significantly reduced, suggesting that PRICKLE1 gene maybe involved in the pathogenesis of Ankylosing spondylitis, which may be useful for predicting the occurrence of AS and finding new early screening indicators.

Bone Involvement in Rheumatoid Arthritis and Spondyloartritis: An Updated Review

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

Development and validation of a machine learning-based nomogram for predicting HLA-B27 expression

BACKGROUND

HLA-B27 positivity is normal in patients undergoing rheumatic diseases. The diagnosis of many diseases requires an HLA-B27 examination.

METHODS

This study screened totally 1503 patients who underwent HLA-B27 examination, liver/kidney function tests, and complete blood routine examination in First Affiliated Hospital of Guangxi Medical University. The training cohort included 509 cases with HLA-B27 positivity whereas 611 with HLA-B27 negativity. In addition, validation cohort included 147 cases with HLA-B27 positivity whereas 236 with HLA-B27 negativity. In this study, 3 ML approaches, namely, LASSO, support vector machine (SVM) recursive feature elimination and random forest, were adopted for screening feature variables. Subsequently, to acquire the prediction model, the intersection was selected. Finally, differences among 148 cases with HLA-B27 positivity and negativity suffering from ankylosing spondylitis (AS) were investigated.

RESULTS

Six factors, namely red blood cell count, human major compatibility complex, mean platelet volume, albumin/globulin ratio (ALB/GLB), prealbumin, and bicarbonate radical, were chosen with the aim of constructing the diagnostic nomogram using ML methods. For training queue, nomogram curve exhibited the value of area under the curve (AUC) of 0.8254496, and C-value of the model was 0.825. Moreover, nomogram C-value of the validation queue was 0.853, and the AUC value was 0.852675. Furthermore, a significant decrease in the ALB/GLB was noted among cases with HLA-B27 positivity and AS cases.

CONCLUSION

To conclude, the proposed ML model can effectively predict HLA-B27 and help doctors in the diagnosis of various immune diseases.

Impact of early antiretroviral therapy, early life immunity and immune sex differences on HIV disease and posttreatment control in children

PURPOSE OF REVIEW

To review recent insights into the factors affecting HIV disease progression in children living with HIV, contrasting outcomes: following early ART initiation with those in natural, antiretroviral therapy (ART)-naive infection; in children versus adults; and in female individuals versus male individuals.

RECENT FINDINGS

Early life immune polarization and several factors associated with mother-to-child transmission of HIV result in an ineffective HIV-specific CD8+ T-cell response and rapid disease progression in most children living with HIV. However, the same factors result in low immune activation and antiviral efficacy mediated mainly through natural killer cell responses in children and are central features of posttreatment control. By contrast, rapid activation of the immune system and generation of a broad HIV-specific CD8+ T-cell response in adults, especially in the context of 'protective' HLA class I molecules, are associated with superior disease outcomes in ART-naive infection but not with posttreatment control. The higher levels of immune activation in female individuals versus male individuals from intrauterine life onwards increase HIV infection susceptibility in females in utero and may favour ART-naive disease outcomes rather than posttreatment control.

SUMMARY

Early-life immunity and factors associated with mother-to-child transmission typically result in rapid HIV disease progression in ART-naive infection but favour posttreatment control in children following early ART initiation.

Fifty years after the discovery of the association of HLA B27 with ankylosing spondylitis

The human lymphocyte antigen B27 (HLA B27) is a member of the HLA class I family of genes in the major histocompatibility complex whose name goes back to its discovery in studies of transplanted tissue compatibility. Its prevalence in the mid-European population is about 8%. The association of HLA B27 alleles with ankylosing spondylitis (AS), a highly heritable disease, which is part of the spectrum of axial spondyloarthritis (axSpA), was discovered 50 years ago. HLA B27 explains less than 30% of the total genetic load. About 60%-90% of axSpA patients worldwide carry HLA B27. The prevalence of the disease is linked to the frequency of HLA B27 in the population which implies that there are relevant differences. Among the roughly 200 subtypes known there are two which are not disease associated. The function of HLA class I molecules is to present peptides to the immune system to defend the organism against microbes targeted by CD8+T cells. This is much supported by the role of the endoplasmic reticulum aminopeptidase 1 (ERAP 1) in AS, an enzyme that is responsible for the intracellular trimming of peptides, since polymorphisms of this gene are only associated with HLA-B27+ disease. The arthritogenic peptide hypothesis trying to explain the pathogenesis of AS is based on that very immune function assuming that also self peptides can be presented. HLA-B27 also plays an important role in classification, diagnosis and severitiy of axSpA.

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 study of the effect of HLA-B27 on THP-1 monocytic cells survival and its mechanism

OBJECTIVE

Previous studies have shown that human leukocyte antigen (HLA)-B27 induces the accumulation of unfolded proteins in the endoplasmic reticulum (ER) to cause ER stress, resulting in the unfold protein response (UPR), apoptosis and autophagy. However, it is still unknown whether it affects the survival of monocytes. In this study, we attempted to examine the effect of HLA-B27 gene knockout on the proliferation and apoptosis of THP-1 monocytic cell line and its potential mechanism.

METHODS

HLA-B27 gene knockout THP-1 cell line was constructed by lentivirus infection, and knockout efficiency was detected by immunofluorescence, quantitative reverse transcription - polymerase chain reaction (qRT-PCR) and western blot. Cell Counting Kit-8 (CCK-8) method and Annexin-V/PI double staining were used to detect the proliferation and apoptosis of the constructed THP-1 cell line, respectively. qRT-PCR was used to detect the effect of HLA-B27 inhibition on the expressions of ER molecular chaperone binding immunoglobulin protein (BiP) and genes about the UPR pathway. The proliferation rate of human BiP protein-stimulated THP-1 cells was detected by CCK-8 method.

RESULTS

HLA-B27 gene knockout THP-1 cells were successfully constructed by lentivirus infection. Knockout of HLA-B27 effectively promoted the proliferation of THP-1 cells and inhibited the apoptosis induced by cisplatin. qRT-PCR showed that BiP was synchronously increased, while activation of UPR pathway was inhibited. Stimulation with human BiP promoted the proliferation of THP-1 cells in a concentration-dependent manner.

CONCLUSIONS

HLA-B27 inhibition can promote the proliferation and inhibit the apoptosis of THP-1 cells. The inhibition function may be achieved through promotion of BiP and inhibition of UPR pathway activation.

Identification of potential biomarkers for ankylosing spondylitis based on bioinformatics analysis

OBJECTIVE

The aim of this study was to search for key genes in ankylosing spondylitis (AS) through comprehensive bioinformatics analysis, thus providing some theoretical support for future diagnosis and treatment of AS and further research.

METHODS

Gene expression profiles were collected from Gene Expression Omnibus (GEO, http://www.ncbi.nlm.nih.gov/geo/ ) by searching for the term "ankylosing spondylitis". Ultimately, two microarray datasets (GSE73754 and GSE11886) were downloaded from the GEO database. A bioinformatic approach was used to screen differentially expressed genes and perform functional enrichment analysis to obtain biological functions and signalling pathways associated with the disease. Weighted correlation network analysis (WGCNA) was used to further obtain key genes. Immune infiltration analysis was performed using the CIBERSORT algorithm to conduct a correlation analysis of key genes with immune cells. The GWAS data of AS were analysed to identify the pathogenic regions of key genes in AS. Finally, potential therapeutic agents for AS were predicted using these key genes.

RESULTS

A total of 7 potential biomarkers were identified: DYSF, BASP1, PYGL, SPI1, C5AR1, ANPEP and SORL1. ROC curves showed good prediction for each gene. T cell, CD4 naïve cell, and neutrophil levels were significantly higher in the disease group than in the paired normal group, and key gene expression was strongly correlated with immune cells. CMap results showed that the expression profiles of ibuprofen, forskolin, bongkrek-acid, and cimaterol showed the most significant negative correlation with the expression profiles of disease perturbations, suggesting that these drugs may play a role in AS treatment.

CONCLUSION

The potential biomarkers of AS screened in this study are closely related to the level of immune cell infiltration and play an important role in the immune microenvironment. This may provide help in the clinical diagnosis and treatment of AS and provide new ideas for further research.

HLA-B27 as a predictor of effectiveness of treatment with TNF inhibitors in axial spondyloarthritis: data from the Swiss Clinical Quality Management Registry

OBJECTIVE

To explore the impact of the human leucocyte antigen (HLA)-B27 on the effectiveness of tumor necrosis factor inhibitors (TNFi) in patients with axial spondyloarthritis (axSpA).

METHODS

A total of 1109 patients with available HLA-B27 status (831 B27+ patients and 278 B27- patients) fulfilling the Assessment of Spondyloarthritis international Society classification criteria for axSpA from the prospective Swiss Clinical Quality Management Registry initiating a first TNFi were included. Drug retention was investigated with multiple adjusted Cox proportional hazard models with imputation of missing values. Multiple-adjusted logistic regression analyses were used to assess the proportion of patients reaching 50% reduction in the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI50) at 1 year.

RESULTS

B27+ and B27- patients differed with regard to age, sex, BASDAI, C-reactive protein (CRP), body mass index, enthesitis, uveitis, and classification status. After adjustment for potential confounders for the relationship between HLA-B27 and drug effectiveness (sex and family history of spondyloarthritis), a higher risk of drug discontinuation was found in B27- patients (HR 1.53, 95% CI 1.27-1.83). This difference decreased after additional adjustment for parameters which may act as mediators (HR 1.30, 95% CI 1.30-1.55). Male sex and elevated C-reactive protein (CRP) levels were consistently associated with longer retention. Comparable results were obtained for BASDAI50 responses.

CONCLUSION

The HLA-B27 genotype is an important predictor of treatment effectiveness. Male sex and CRP seem, however, to better describe variability of response in individual patients. This data may help avoiding potential discrimination of B27- individuals with regard to TNFi initiation. Key Points • HLA-B27 is a predictor of effectiveness of TNF inhibitors in axial spondyloarthritis. • Variability of response in individual patients is better defined by sex and objective markers of disease activity, such as C-reactive protein.

Immune-mediated lung diseases: A narrative review

The role of immunity in the pathogenesis of various pulmonary diseases, particularly interstitial lung diseases (ILDs), is being increasingly appreciated as mechanistic discoveries advance our knowledge in the field. Immune-mediated lung diseases demonstrate clinical and immunological heterogeneity and can be etiologically categorized into connective tissue disease (CTD)-associated, exposure-related, idiopathic, and other miscellaneous lung diseases including sarcoidosis, and post-lung transplant ILD. The immunopathogenesis of many of these diseases remains poorly defined and possibly involves either immune dysregulation, abnormal healing, chronic inflammation, or a combination of these, often in a background of genetic susceptibility. The heterogeneity and complex immunopathogenesis of ILDs complicate management, and thus a collaborative treatment team should work toward an individualized approach to address the unique needs of each patient. Current management of immune-mediated lung diseases is challenging; the choice of therapy is etiology-driven and includes corticosteroids, immunomodulatory drugs such as methotrexate, cyclophosphamide and mycophenolate mofetil, rituximab, or other measures such as discontinuation or avoidance of the inciting agent in exposure-related ILDs. Antifibrotic therapy is approved for some of the ILDs (e.g., idiopathic pulmonary fibrosis) and is being investigated for many others and has shown promising preliminary results. A dire need for advances in the management of immune-mediated lung disease persists in the absence of standardized management guidelines.

Inhibition of ERAP1 represses HLA-B27 free heavy chains expression on polarized macrophages and interrupts NK cells activation and function from ankylosing spondylitis

BACKGROUND

We aimed to assess if Endoplasmic reticulum aminopeptidase 1 (ERAP1) polymorphisms might impress Human leukocyte antigen (HLA)-B27-free heavy chains (FHCs) expression on macrophages and eventually NK cell activation in Ankylosing spondylitis (AS).

METHODS

Blood samples were obtained from 10 HLAB27⁺ patients with protective and 10 HLAB27⁺ patients with non-protective genotype. Monocytes were isolated and polarized toward M1 and M2 macrophages. ERAP1 was inhibited in macrophages, which were then co-cultured with autologous NK cells.

RESULTS

Expression of HLA-B27-FHCs on M1 and M2 macrophages was reduced in patients with protective ERAP1 genotype. Co-culturing ERAP1-inhibited M1 macrophages and NK cells from patients with protective genotype resulted in downmodulation of CD69 and CD107a markers on NK cells and reduced number of IFN-γ⁺ NK cells compared to that of patients with non-protective genotypes.

CONCLUSION

Inhibition of ERAP1 activity, by diminishing NK activation, may have therapeutic value in treating AS patients.

Air pollution exposure and auto-inflammatory and autoimmune diseases of the musculoskeletal system: a review of epidemiologic and mechanistic evidence

Auto-inflammatory and autoimmune diseases of the musculoskeletal system can be perceived as a spectrum of rheumatic diseases, with the joints and connective tissues are eroded severely that progressively develop chronic inflammation and lesion. A wide range of risk factors represented by genetic and environmental factors have been uncovered by population-based surveys and experimental studies. Lately, the exposure to air pollution has been found to be potentially involved in the mechanisms of occurrence or development of such diseases, principally manifest in oxidative stress, local and systemic inflammation, and epigenetic modifications, as well as the mitochondrial dysfunction, which has been reported to participate in the intermediate links. The lungs might serve as a starting area of air pollutants, which would cause oxidative stress-induced bronchial-associated lymphoid tissue (iBALT) to further to influence T, B cells, and the secretion of pro-inflammatory cytokines. The binding of aromatic hydrocarbon receptor (AhR) to the corresponding contaminant ligands tends to regulate the reaction of Th17 and Tregs. Furthermore, air pollution components might spur on immune and inflammatory responses by damaging mitochondria that could interact with and exacerbate oxidative stress and pro-inflammatory cytokines. In this review, we focused on the association between air pollution and typical auto-inflammatory and autoimmune diseases of the musculoskeletal system, mainly including osteoarthritis (OA), rheumatoid arthritis (RA), spondyloarthritis (SpA) and juvenile idiopathic arthritis (JIA), and aim to collate the mechanisms involved and the potential channels. A complete summary and in-depth understanding of the autoimmune and inflammatory effects of air pollution exposure should hopefully contribute new perspectives on how to formulate better public health policies to alleviate the adverse health effects of air pollutants.

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.

The microbiome in HLA-B27-associated disease: implications for acute anterior uveitis and recommendations for future studies

The pathogenesis of human leukocyte antigen (HLA)-B27-associated diseases such as acute anterior uveitis (AAU) and ankylosing spondylitis (AS) remains poorly understood, though Gram-negative bacteria and subclinical bowel inflammation are strongly implicated. Accumulating evidence from animal models and clinical studies supports several hypotheses, including HLA-B27-dependent dysbiosis, altered intestinal permeability, and molecular mimicry. However, the existing literature is hampered by inadequate studies designed to establish causation or uncover the role of viruses and fungi. Moreover, the unique disease model afforded by AAU to study the gut microbiota has been neglected. This review critically evaluates the current literature and prevailing hypotheses on the link between the gut microbiota and HLA-B27-associated disease. We propose a new potential role for HLA-B27-driven altered antibody responses to gut microbiota in disease pathogenesis and outline recommendations for future well-controlled human studies, focusing on AAU.

Vesicular traffic-mediated cell-to-cell signaling at the immune synapse in Ankylosing Spondylitis

The chronic inflammatory disease ankylosing spondylitis (AS) is marked by back discomfort, spinal ankylosis, and extra-articular symptoms. In AS, inflammation is responsible for both pain and spinal ankylosis. However, the processes that sustain chronic inflammation remain unknown. Despite the years of research conducted to decipher the intricacy of AS, little progress has been made in identifying the signaling events that lead to the development of this disease. T cells, an immune cell type that initiates and regulates the body's response to infection, have been established to substantially impact the development of AS. T lymphocytes are regarded as a crucial part of adaptive immunity for the control of the immune system. A highly coordinated interaction involving antigen-presenting cells (APCs) and T cells that regulate T cell activation constitutes an immunological synapse (IS). This first phase leads to the controlled trafficking of receptors and signaling mediators involved in folding endosomes to the cellular interface, which allows the transfer of information from T cells to APCs through IS formation. Discrimination of self and nonself antigen is somatically learned in adaptive immunity. In an autoimmune condition such as AS, there is a disturbance of self/nonself antigen discrimination; available findings imply that the IS plays a preeminent role in the adaptive immune response. In this paper, we provide insights into the genesis of AS by evaluating recent developments in the function of vesicular trafficking in IS formation and the targeted release of exosomes enriched microRNAs (miRNA) at the synaptic region in T cells.

MicroRNA-155 acts as a potential prognostic and diagnostic factor in patients with ankylosing spondylitis by modulating SOCS3

BACKGROUND

Ankylosing spondylitis (AS) is a progressive inflammatory disease. Our primary objective was to explore the role of miR-155 and its targeted factors in AS pathogenesis.

METHODS AND RESULTS

PBMCs were isolated from 30 AS patients and 30 healthy individuals using the Ficoll-hypaque isolation approach. The expression of miR-155 and its associated targets, including Suppressor Of Cytokine Signaling 3 (SOCS3), STAT3, and IL-21, were determined using qT-qPCR. Then, PBMCs were cultured, and the effect of miR-155, SOCS3 siRNA (to suppress its expression), pEFSOCS3 (enforced expression), and their combination were investigated by qRT-PCR and western blotting. We also treated the cultured PBMCs with Brefeldin A, a potent inhibitor of cytokine secretion, to determine its effect on IL-21 expression and secretion. In addition, the association between miR-155 and patients' clinicopathological features was examined. The results showed that miR-155, IL-21, and STAT3 were increased in patients with AS, while SOCS3 had decreasing expression trend. It was also determined that miR-155 alleviates SOCS3 expression and increases IL-21 and STAT3 expression; it had a prominent effect when combined with SOCS3 siRNA. Besides, we showed that simultaneous transfection of miR-155 and pEFSOCS3 had no significant effect on IL-21 and STAT3 expression, revealing that miR-155 could alleviate the enforced expression of SOCS3. It was also proven that Brefledine A led to IL-21 up-regulation or accumulation while relieving its secretion. Also, a significant correlation between miR-155 and pathological features of AS patients was found.

CONCLUSION

miR-155 acts as a potential prognostic and diagnostic biomarker. Its up-regulation leads to the down-regulation of SOCS3 and increased expression of IL-21 and STAT3 as characteristic of TH-17 lymphocytes, leading to worsening inflammatory conditions in patients with AS.

Autoimmunity-associated T cell receptors recognize HLA-B*27-bound peptides

Human leucocyte antigen B*27 (HLA-B*27) is strongly associated with inflammatory diseases of the spine and pelvis (for example, ankylosing spondylitis (AS)) and the eye (that is, acute anterior uveitis (AAU))1. How HLA-B*27 facilitates disease remains unknown, but one possible mechanism could involve presentation of pathogenic peptides to CD8+ T cells. Here we isolated orphan T cell receptors (TCRs) expressing a disease-associated public β-chain variable region-complementary-determining region 3β (BV9-CDR3β) motif2-4 from blood and synovial fluid T cells from individuals with AS and from the eye in individuals with AAU. These TCRs showed consistent α-chain variable region (AV21) chain pairing and were clonally expanded in the joint and eye. We used HLA-B*27:05 yeast display peptide libraries to identify shared self-peptides and microbial peptides that activated the AS- and AAU-derived TCRs. Structural analysis revealed that TCR cross-reactivity for peptide-MHC was rooted in a shared binding motif present in both self-antigens and microbial antigens that engages the BV9-CDR3β TCRs. These findings support the hypothesis that microbial antigens and self-antigens could play a pathogenic role in HLA-B*27-associated disease.

Novel peripheral blood diagnostic biomarkers screened by machine learning algorithms in ankylosing spondylitis

Background: Ankylosing spondylitis (AS) is a chronic inflammatory disorder of unknown etiology that is hard to diagnose early. Therefore, it is imperative to explore novel biomarkers that may contribute to the easy and early diagnosis of AS. Methods: Common differentially expressed genes between normal people and AS patients in GSE73754 and GSE25101 were screened by machine learning algorithms. A diagnostic model was established by the hub genes that were screened. Then, the model was validated in several data sets. Results: IL2RB and ZDHHC18 were screened using machine learning algorithms and established as a diagnostic model. Nomograms suggested that the higher the expression of ZDHHC18, the higher was the risk of AS, while the reverse was true for IL2RB in vivo. C-indexes of the model were no less than 0.84 in the validation sets. Calibration analyses suggested high prediction accuracy of the model in training and validation cohorts. The area under the curve (AUC) values of the model in GSE73754, GSE25101, GSE18781, and GSE11886 were 0.86, 0.84, 0.85, and 0.89, respectively. The decision curve analyses suggested a high net benefit offered by the model. Functional analyses of the differentially expressed genes indicated that they were mainly clustered in immune response-related processes. Immune microenvironment analyses revealed that the neutrophils were expanded and activated in AS while some T cells were decreased. Conclusion: IL2RB and ZDHHC18 are potential blood biomarkers of AS, which might be used for the early diagnosis of AS and serve as a supplement to the existing diagnostic methods. Our study deepens the insight into the pathogenesis of AS.

Resistance to unfolding by acidic pH and resistance to lysosomal degradation explains disease-association of HLA-B27 subtypes

Several hypotheses have been proposed to explain the high rate of disease association of HLA-B27 with ankylosing spondylitis (AS), including formation of disulfide-bonded dimers and misfolding of the heavy chain (HC), involving formation of high molecular weight (HMW) multimers. Recently, we have shown that the HMW entities of non-disease associated (non-DA) subtypes cause activation of endosomal-lysosomal pathways, while disease-associated (DA) subtypes of HLA-B27 cause activation of autophagy and unfolded protein response (UPR) pathways. In this paper, we seek an explanation for the failure of these pathways to degrade the HMW entities of DA subtypes of HLA-B27, using a combination of in vitro assays, using extracellular domains of heavy chains (EDHC), as well as in vivo assays, using stable transfectants of the full lengths of heavy chains (FLHC) of DA and non-DA subtypes. Our data shows that both DA and non-DA subtypes form HMW entities. However, non-DA HMW entities display far greater levels of degradation than DA HMW species. Non-DA EDHC display greater loss of structure at lysosomal pH in vitro. This was confirmed by experiments showing that (i) DA FLHCs co-localize with LAMP1, and (ii) induction of autophagy by rapamycin causes significant decrease in levels of non-DA HMW entities, but not that of DA HMW entities. These results point towards lack of facile lysosomal clearance of FLHCs of DA subtypes, suggesting that disease association of HLA-B27 subtypes is correlated with higher persistence of HMW entities in the low pH of lysosomes, with higher potential to trigger immune response.

Survivin; a novel therapeutic target that correlates with survival of autoreactive T lymphocytes obtained from patients with ankylosing spondylitis

Ankylosing spondylitis (AS) is progressive immune-mediated arthritis. Persistent autoreactivity of T cells with an up-regulated Survivin expression is strongly implicated in AS immunopathogenesis. Besides, Survivin can inhibit proapoptotic caspase 9 activations. Moreover, microRNAs are small non-coding RNAs that are dysregulated in various diseases, in which their altered expression could modulate Survivin expression. The primary goal of this study was to assess the role of Survivin and its-targeting microRNAs in the immunopathogenesis of AS disease. For this aim, peripheral blood mononuclear cells (PBMCs) were isolated from 15 patients with AS and healthy matched controls using Ficoll-Hypaque. T cells were obtained using the magnetic-activated cell sorting (MACS) method. After that, the expression levels of Survivin, Caspase 9, and specific miRNAs were determined using qT-qPCR. Also, the expression of Survivin and Caspase 9 at protein levels was determined by western blotting. Then, the isolated T cells were co-cultured with interleukin (IL)-2 and muromonab-CD3 (OKT-3) for active-induced cell death (AICD) induction, Survivin siRNA for inhibition of Survivin expression, and their combination to assess the implication of Survivin expression in autoreactive T lymphocytes' resistance to apoptosis by determining the rate of apoptosis by Flowcytometry assay. The results showed that Survivin was up-regulated while Caspase 9 was downregulated in patients with AS. It was also revealed that microRNAs that directly or indirectly target the Survivin mRNA were dysregulated in patients with AS. It was also revealed that T cells obtained from AS patients were more resistant to apoptosis induction than those obtained from healthy people. In summary, the results obtained from this study showed that dysregulation of Survivin and Survivin-targeting miRNAs in T lymphocytes obtained from AS patients contribute to their resistance to apoptosis, suggesting the future development of targeted therapies for AS.

Behçet's disease risk-variant HLA-B51/ERAP1-Hap10 alters human CD8 T cell immunity

OBJECTIVES

The endoplasmic reticulum aminopeptidase (ERAP1) haplotype Hap10 encodes for a variant allotype of the endoplasmic reticulum (ER)-resident peptide-trimming aminopeptidase ERAP1 with low enzymatic activity. This haplotype recessively confers the highest risk for Behçet's diseases (BD) currently known, but only in carriers of HLA-B*51, the classical risk factor for the disease. The mechanistic implications and biological consequences of this epistatic relationship are unknown. Here, we aimed to determine its biological relevance and functional impact.

METHODS

We genotyped and immune phenotyped a cohort of 26 untreated Turkish BD subjects and 22 healthy donors, generated CRISPR-Cas9 ERAP1 KOs from HLA-B*51 ⁺ LCL, analysed the HLA class I-bound peptidome for peptide length differences and assessed immunogenicity of genome-edited cells in CD8 T cell co-culture systems.

RESULTS

Allele frequencies of ERAP1-Hap10 were similar to previous studies. There were frequency shifts between antigen-experienced and naïve CD8 T cell populations of carriers and non-carriers of ERAP1-Hap10 in an HLA-B*51 background. ERAP1 KO cells showed peptidomes with longer peptides above 9mer and significant differences in their ability to stimulate alloreactive CD8 T cells compared with wild-type control cells.

CONCLUSIONS

We demonstrate that hypoactive ERAP1 changes immunogenicity to CD8 T cells, mediated by an HLA class I peptidome with undertrimmed peptides. Naïve/effector CD8 T cell shifts in affected carriers provide evidence of the biological relevance of ERAP1-Hap10/HLA-B*51 at the cellular level and point to an HLA-B51-restricted process. Our findings suggest that variant ERAP1-Hap10 partakes in BD pathogenesis by generating HLA-B51-restricted peptides, causing a change in immunodominance of the ensuing CD8 T cell response.

Altered cerebral blood flow patterns in ankylosing spondylitis: A three-dimensional pseudo-continuous arterial spin labeling study

Objective

This study aimed to detect the cerebral blood flow (CBF) values changes in patients with ankylosing spondylitis (AS) and to evaluate the correlation between the CBF values and the specific clinical characteristics.

Materials and methods

Forty-eight patients with AS (43 male and 5 female) and 42 healthy controls (HCs) (38 male and 4 female) were recruited. Three-dimensional pseudo-continuous arterial spin labeling (3D-pCASL) was performed on a 3.0T magnetic resonance imaging (MRI). CBF values were obtained on the Philips post-processing workstation based on arterial spin labeling (ASL) data. The two-sample t-test was used to compare CBF differences. The correlation between CBF values and specific clinical characteristics of AS was evaluated.

Results

The AS group showed increased CBF values in the right precentral gyrus, the left inferior frontal gyrus, and the left temporal pole compared with HCs the AS group also showed decreased CBF values in the left precuneus and the left superior occipital gyrus compared with HCs. There were no significant correlations between the CBF values and the clinical characteristics including total back pain (TBP), erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP).

Conclusion

Patients with AS displayed CBF changes compared with HCs using 3D-PCASL. These results may enhance our understanding of the neural substrates of AS and provide evidence of AS-related neurological impairment.

New Insights into the Regulatory Role of Ferroptosis in Ankylosing Spondylitis via Consensus Clustering of Ferroptosis-Related Genes and Weighted Gene Co-Expression Network Analysis

Background: The pathogenesis of ankylosing spondylitis (AS) remains undetermined. Ferroptosis is a newly discovered form of regulated cell death involved in multiple autoimmune diseases. Currently, there are no reports on the connection between ferroptosis and AS. Methods: AS samples from the Gene Expression Omnibus were divided into two subgroups using consensus clustering of ferroptosis-related genes (FRGs). Weighted gene co-expression network analysis (WGCNA) of the intergroup differentially expressed genes (DEGs) and protein–protein interaction (PPI) analysis of the key module were used to screen out hub genes. A multifactor regulatory network was then constructed based on hub genes. Results: The 52 AS patients in dataset GSE73754 were divided into cluster 1 (n = 24) and cluster 2 (n = 28). DEGs were mainly enriched in pathways related to mitochondria, ubiquitin, and neurodegeneration. Candidate hub genes, screened by PPI and WGCNA, were intersected. Subsequently, 12 overlapping genes were identified as definitive hub genes. A multifactor interaction network with 45 nodes and 150 edges was generated, comprising the 12 hub genes and 32 non-coding RNAs. Conclusions: AS can be divided into two subtypes according to FRG expression. Ferroptosis might play a regulatory role in AS. Tailoring treatment according to the ferroptosis status of AS patients can be a promising direction.

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

OBJECTIVES

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

METHOD

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

RESULTS

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

CONCLUSIONS

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

SAPHO Syndrome Complicated by Ankylosing Spondylitis Successfully Treated With Tofacitinib: A Case Report

Synovitis, acne, pustulosis, hyperostosis, and osteitis (SAPHO) syndrome, a type of chronic inflammatory disease, is rare and difficult to treat. Osteoarthropathy with skin involvement is the primary clinical manifestation of SAPHO syndrome. The unknown pathogenesis of SAPHO syndrome is speculated to be related to individual genetic differences, immune levels, microorganisms, and environmental factors. Tofacitinib, a novel small-molecule Janus kinase (JAK) inhibitor, has been used to treat rheumatoid arthritis. However, it also has great potential for the treatment of other immune diseases, including SAPHO syndrome. A 36-year-old man with chest and back pain for more than two months was admitted to our hospital. After admission, the patient developed a pustular rash and enteritis. SAPHO syndrome was diagnosed based on the above clinical manifestations, computed tomography (CT), and bone scintigraphy findings. Notably, the patient also had ankylosing spondylitis. Tofacitinib significantly improved the patient’s skin symptoms while preventing worsening of chest and back pain when adalimumab was discontinued. We report the first case of ankylosing spondylitis with SAPHO syndrome. In addition, it is also the first successful treatment thereof with tofacitinib. We hope to provide valuable information regarding the pathogenesis and treatment of SAPHO syndrome in this case.

Increased proportions of inflammatory T cells and their correlations with cytokines and clinical parameters in patients with ankylosing spondylitis from northern Sweden

Ankylosing spondylitis (AS) is an autoimmune disease affecting parts of the skeletal structure in particular. Previously increased levels of the inflammatory cell types Th17, Th22, Tc17 and Tc22 cells have been shown to be associated with AS. Here, we analysed the levels of inflammatory T cell subsets, related cytokines and clinical characteristics of AS patients vs controls from northern Sweden. Peripheral blood mononuclear cells (PBMCs) obtained from 50 AS patients and 50 matched controls were short term stimulated with PMA/Ionomycin, stained and analysed by flow cytometry. Plasma levels of Interleukin (IL)‐17, IL‐22, IL‐10 as well as clinically relevant markers were determined. Compared to male controls, male AS patients showed 1.5‐ to 2‐fold increases of Th17 (P = .013), Th22 (P = .003) and Tc22 (P = .024) among CD45⁺CD3⁺ lymphocytes. Plasma IL‐22 levels correlated with the Tc17 proportion in male patients (R_s = 0.499, P = .003) and plasma IL‐10 levels were inversely correlated with Tc17 among all patients (R_s = −0.276, P = .05). Male patients with syndesmophytes showed significantly higher Th17 proportions (P = .038). In female AS patients, Tc22 was negatively correlated with C‐reactive protein (high sensitivity) (hsCRP) (R_s = −0.573, P = .016). We confirmed increased proportions of inflammatory T cells and correlations with relevant cytokines from male AS patients. The correlation between Th17 and syndesmophytes supports a role of Th17 in the pathogenic process.