Increased level of HLA-B27 expression in ankylosing spondylitis patients compared with healthy HLA-B27-positive subjects: a possible further susceptibility factor for the development of disease

Nucleotide alterations in the HLA-C class I gene can cause aberrant splicing and marked changes in RNA levels in a polymorphic context-dependent manner

Polymorphisms of HLA genes, which play a crucial role in presenting peptides with diverse sequences in their peptide-binding pockets, are also thought to affect HLA gene expression, as many studies have reported associations between HLA gene polymorphisms and their expression levels. In this study, we devised an ectopic expression assay for the HLA class I genes in the context of the entire gene, and used the assay to show that the HLA-C*03:03:01 and C*04:01:01 polymorphic differences observed in association studies indeed cause different levels of RNA expression. Subsequently, we investigated the C*03:23N null allele, which was previously noted for its reduced expression, attributed to an alternate exon 3 3' splice site generated by G/A polymorphism at position 781 within the exon 3. We conducted a thorough analysis of the splicing patterns of C*03:23N, and revealed multiple aberrant splicing, including the exon 3 alternative splicing, which overshadowed its canonical counterpart. After confirming a significant reduction in RNA levels caused by the G781A alteration in our ectopic assay, we probed the function of the G-rich sequence preceding the canonical exon 3 3' splice site. Substituting the G-rich sequence with a typical pyrimidine-rich 3' splice site sequence on C*03:23N resulted in a marked elevation in RNA levels, likely due to the enhanced preference for the canonical exon 3 3' splice site over the alternate site. However, the same substitution led to a reduction in RNA levels for C*03:03:01. These findings suggested the dual roles of the G-rich sequence in RNA expression, and furthermore, underscore the importance of studying polymorphism effects within the framework of the entire gene, extending beyond conventional mini-gene reporter assays.

Antibodies for β2-Microglobulin and the Heavy Chains of HLA-E, HLA-F, and HLA-G Reflect the HLA-Variants on Activated Immune Cells and Phases of Disease Progression in Rheumatoid Arthritis Patients under Treatment

Rheumatoid arthritis (RA) is a progressive, inflammatory, autoimmune, symmetrical polyarticular arthritis. It is characterized by synovial infiltration and activation of several types of immune cells, culminating in their apoptosis and antibody generation against “altered” autoantigens. β2-microglobulin (β2m)-associated heavy chains (HCs) of HLA antigens, also known as closed conformers (Face-1), undergo “alteration” during activation of immune cells, resulting in β2m-free structural variants, including monomeric open conformers (Face-2) that are capable of dimerizing as either homodimers (Face-3) or as heterodimers (Face-4). β2m-free HCs uncover the cryptic epitopes that can elicit antibodies (Abs). We report here the levels of IgM and IgG Abs against both β2m and HCs of HLA-E, HLA-F, and HLA-G in 74 RA patients receiving immunosuppressive drugs. Anti-β2m IgM was present in 20 of 74 patients, whereas anti-β2m IgG was found in only 8 patients. Abs against β2m would be expected if Abs were generated against β2m-associated HLA HCs. The majority of patients were devoid of either anti-β2m IgM or IgG but had Abs against HCs of different HLA-Ib molecules. The paucity of anti-β2m Abs in this cohort of patients suggests that Abs were developed against β2m-free HLA HCs, such as Face-2, Face-3, and Face-4. While 63 of 68 patients had IgG Abs against anti-HLA-F HCs, 36 and 50 patients showed IgG Ab reactivity against HLA-E and anti-HLA-G HCs, respectively. Evidently, anti-HLA-F HC Abs are the most predominant anti-HLA-Ib HC IgG Abs in RA patients. The incidence and intensity of Abs against HLA-E, HLA-F, and HLA-G in the normal control group were much higher than those observed in RA patients. Evidently, the lower level of Abs in RA patients points to the impact of the immunosuppressive drugs on these patients. These results underscore the need for further studies to unravel the nature of HLA-F variants on activated immune cells and synoviocytes of RA patients.

Comparison between qPCR and RNA-seq reveals challenges of quantifying HLA expression

Human leukocyte antigen (HLA) class I and II loci are essential elements of innate and acquired immunity. Their functions include antigen presentation to T cells leading to cellular and humoral immune responses, and modulation of NK cells. Their exceptional influence on disease outcome has now been made clear by genome-wide association studies. The exons encoding the peptide-binding groove have been the main focus for determining HLA effects on disease susceptibility/pathogenesis. However, HLA expression levels have also been implicated in disease outcome, adding another dimension to the extreme diversity of HLA that impacts variability in immune responses across individuals. To estimate HLA expression, immunogenetic studies traditionally rely on quantitative PCR (qPCR). Adoption of alternative high-throughput technologies such as RNA-seq has been hampered by technical issues due to the extreme polymorphism at HLA genes. Recently, however, multiple bioinformatic methods have been developed to accurately estimate HLA expression from RNA-seq data. This opens an exciting opportunity to quantify HLA expression in large datasets but also brings questions on whether RNA-seq results are comparable to those by qPCR. In this study, we analyze three classes of expression data for HLA class I genes for a matched set of individuals: (a) RNA-seq, (b) qPCR, and (c) cell surface HLA-C expression. We observed a moderate correlation between expression estimates from qPCR and RNA-seq for HLA-A, -B, and -C (0.2 ≤ rho ≤ 0.53). We discuss technical and biological factors which need to be accounted for when comparing quantifications for different molecular phenotypes or using different techniques.

Genetic susceptibility to autoimmunity-Current status and challenges

Autoimmune diseases (ADs) often arise from a combination of genetic and environmental triggers that disrupt the immune system's capability to properly tolerate body self-antigens. Familial studies provided the earliest insights into the risk loci of such diseases, while genome-wide association studies (GWAS) significantly broadened the horizons. A drug targeting a prominent pathological pathway can be applied to multiple indications sharing overlapping mechanisms. Advances in genomic technologies used in genetic studies provide critical insights into future research on gene-environment interactions in autoimmunity. This Review summarizes the history and recent advances in the understanding of genetic susceptibility to ADs and related immune disorders, including coronavirus disease 2019 (COVID-19), and their indications for the development of diagnostic or prognostic markers for translational applications.

HLA allele-specific expression: Methods, disease associations, and relevance in hematopoietic stem cell transplantation

Varying HLA allele-specific expression levels are associated with human diseases, such as graft versus host disease (GvHD) in hematopoietic stem cell transplantation (HSCT), cytotoxic T cell response and viral load in HIV infection, and the risk of Crohn’s disease. Only recently, RNA-based next generation sequencing (NGS) methodologies with accompanying bioinformatics tools have emerged to quantify HLA allele-specific expression replacing the quantitative PCR (qPCR) -based methods. These novel NGS approaches enable the systematic analysis of the HLA allele-specific expression changes between individuals and between normal and disease phenotypes. Additionally, analyzing HLA allele-specific expression and allele-specific expression loss provide important information for predicting efficacies of novel immune cell therapies. Here, we review available RNA sequencing-based approaches and computational tools for NGS to quantify HLA allele-specific expression. Moreover, we explore recent studies reporting disease associations with differential HLA expression. Finally, we discuss the role of allele-specific expression in HSCT and how considering the expression quantification in recipient-donor matching could improve the outcome of HSCT.

Regulation of HLA class I expression by non-coding gene variations

The Human Leukocyte Antigen (HLA) is a critical genetic system for different outcomes after solid organ and hematopoietic cell transplantation. Its polymorphism is usually determined by molecular technologies at the DNA level. A potential role of HLA allelic expression remains under investigation in the context of the allogenic immune response between donors and recipients. In this study, we quantified the allelic expression of all three HLA class I loci (HLA-A, B and C) by RNA sequencing and conducted an analysis of expression quantitative traits loci (eQTL) to investigate whether HLA expression regulation could be associated with non-coding gene variations. HLA-B alleles exhibited the highest expression levels followed by HLA-C and HLA-A alleles. The max fold expression variation was observed for HLA-C alleles. The expression of HLA class I loci of distinct individuals demonstrated a coordinated and paired expression of both alleles of the same locus. Expression of conserved HLA-A~B~C haplotypes differed in distinct PBMC's suggesting an individual regulated expression of both HLA class I alleles and haplotypes. Cytokines TNFα /IFNβ, which induced a very similar upregulation of HLA class I RNA and cell surface expression across alleles did not modify the individually coordinated expression at the three HLA class I loci. By identifying cis eQTLs for the HLA class I genes, we show that the non-coding eQTLs explain 29%, 13%, and 31% of the respective HLA-A, B, C expression variance in unstimulated cells, and 9%, 23%, and 50% of the variance in cytokine-stimulated cells. The eQTLs have significantly higher effect sizes in stimulated cells compared to unstimulated cells for HLA-B and HLA-C genes expression. Our data also suggest that the identified eQTLs are independent from the coding variation which defines HLA alleles and thus may be influential on intra-allele expression variability although they might not represent the causal eQTLs.

Upregulation of Unfolded Protein Response and ER Stress-Related IL-23 Production in M1 Macrophages from Ankylosing Spondylitis Patients

The inflammatory interleukin (IL)-23/IL-17 axis plays an important role in the pathogenesis of ankylosing spondylitis (AS), but with an unknown regulatory mechanism. This study aimed to investigate the role of endoplasmic reticulum (ER) stress and autophagy pathway in the expression of IL-23 in peripheral blood-derived macrophages in AS patients. Peripheral blood samples were obtained from 15 AS and 15 healthy control subjects. MACS was used to isolate monocytes from PBMCs. Then, M-CSF was used to differentiate monocytes to M2 macrophages. IFN-γ and/or LPS were used to activate macrophages and M2 polarization towards M1 macrophages. Thapsigargin was used to induce ER stress and 3-MA to inhibit autophagy. The purity of extracted monocytes and macrophage markers was evaluated by flow cytometry. mRNA expression of HLA-B and-B27, ER stress-related genes, autophagy-related genes, and IL-23p19 was performed using RT-qPCR. Soluble levels of IL-23p19 were measured using ELISA. Significant increase in mRNA expression of HLA-B, HLA-B27, BiP, XBP1, CHOP, and PERK mRNAs was observed in macrophages of AS patients before and after stimulation with IFN-γ and LPS. No significant change in autophagy gene expression was detected. mRNA and soluble levels of IL-23p19 demonstrated a significant increase in macrophages of AS patients compared to healthy subjects. ER stress induction led to a significant increase in IL-23p19 in macrophages. Inhibition of autophagy did not affect IL-23 expression. ER stress, unlike autophagy, is associated with increased IL-23 levels in macrophages of AS patients.Key Messages ER stress in macrophages from AS patients plays a role in the increased production of IL-23. The autophagy pathway is not involved in the modulation of IL-23 production by AS macrophages.

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).

HLA imputation and its application to genetic and molecular fine-mapping of the MHC region in autoimmune diseases

Variations of human leukocyte antigen (HLA) genes in the major histocompatibility complex region (MHC) significantly affect the risk of various diseases, especially autoimmune diseases. Fine-mapping of causal variants in this region was challenging due to the difficulty in sequencing and its inapplicability to large cohorts. Thus, HLA imputation, a method to infer HLA types from regional single nucleotide polymorphisms, has been developed and has successfully contributed to MHC fine-mapping of various diseases. Different HLA imputation methods have been developed, each with its own advantages, and recent methods have been improved in terms of accuracy and computational performance. Additionally, advances in HLA reference panels by next-generation sequencing technologies have enabled higher resolution and a more reliable imputation, allowing a finer-grained evaluation of the association between sequence variations and disease risk. Risk-associated variants in the MHC region would affect disease susceptibility through complicated mechanisms including alterations in peripheral responses and central thymic selection of T cells. The cooperation of reliable HLA imputation methods, informative fine-mapping, and experimental validation of the functional significance of MHC variations would be essential for further understanding of the role of the MHC in the immunopathology of autoimmune diseases.

Critical Review of Existing MHC I Immunopeptidome Isolation Methods

Major histocompatibility complex class I (MHC I) plays a crucial role in the development of adaptive immune response in vertebrates. MHC molecules are cell surface protein complexes loaded with short peptides and recognized by the T-cell receptors (TCR). Peptides associated with MHC are named immunopeptidome. The MHC I immunopeptidome is produced by the proteasome degradation of intracellular proteins. The knowledge of the immunopeptidome repertoire facilitates the creation of personalized antitumor or antiviral vaccines. A huge number of publications on the immunopeptidome diversity of different human and mouse biological samples-plasma, peripheral blood mononuclear cells (PBMCs), and solid tissues, including tumors-appeared in the scientific journals in the last decade. Significant immunopeptidome identification efficiency was achieved by advances in technology: the immunoprecipitation of MHC and mass spectrometry-based approaches. Researchers optimized common strategies to isolate MHC-associated peptides for individual tasks. They published many protocols with differences in the amount and type of biological sample, amount of antibodies, type and amount of insoluble support, methods of post-fractionation and purification, and approaches to LC-MS/MS identification of immunopeptidome. These parameters have a large impact on the final repertoire of isolated immunopeptidome. In this review, we summarize and compare immunopeptidome isolation techniques with an emphasis on the results obtained.

HLA transgenic mice: application in reproducing idiosyncratic drug toxicity

Various types of transgenic mice carrying either class I or II human leukocyte antigen (HLA) molecules are readily available, and reports describing their use in a variety of studies have been published for more than 30 years. Examples of their use include the discovery of HLA-specific antigens against viral infection as well as the reproduction of HLA-mediated autoimmune diseases for the development of therapeutic strategies. Recently, HLA transgenic mice have been used to reproduce HLA-mediated idiosyncratic drug toxicity (IDT), a rare and unpredictable adverse drug reaction that can result in death. For example, abacavir-induced IDT has successfully been reproduced in HLA-B*57:01 transgenic mice. Several reports using HLA transgenic mice for IDT have proven the utility of this concept for the evaluation of IDT using various HLA allele combinations and drugs. It has become apparent that such models may be a valuable tool to investigate the mechanisms underlying HLA-mediated IDT. This review summarizes the latest findings in the area of HLA transgenic mouse models and discusses the current challenges that must be overcome to maximize the potential of this unique animal model.

Fiber Optic Particle Plasmon Resonance Biosensor for Label-Free Detection of Nucleic Acids and Its Application to HLA-B27 mRNA Detection in Patients with Ankylosing Spondylitis

We developed a label-free, real-time, and highly sensitive nucleic acid biosensor based on fiber optic particle plasmon resonance (FOPPR). The biosensor employs a single-strand deoxyoligonucleotides (ssDNA) probe, conjugated to immobilized gold nanoparticles on the core surface of an optical fiber. We explore the steric effects on hybridization affinity and limit of detection (LOD), by using different ssDNA probe designs and surface chemistries, including diluent molecules of different lengths in mixed self-assembled monolayers, ssDNA probes of different oligonucleotide lengths, ssDNA probes in different orientations to accommodate target oligonucleotides with a hybridization region located unevenly in the strand. Based on the optimized ssDNA probe design and surface chemistry, we achieved LOD at sub-nM level, which makes detection of target oligonucleotides as low as 1 fmol possible in the 10-μL sensor chip. Additionally, the FOPPR biosensor shows a good correlation in determining HLA-B27 mRNA, in extracted blood samples from patients with ankylosing spondylitis (AS), with the clinically accepted real-time reverse transcription-polymerase chain reaction (RT-PCR) method. The results from this fundamental study should guide the design of ssDNA probe for anti-sense sensing. Further results through application to HLA-B27 mRNA detection illustrate the feasibility in detecting various nucleic acids of chemical and biological relevance.

Capturing Differential Allele-Level Expression and Genotypes of All Classical HLA Loci and Haplotypes by a New Capture RNA-Seq Method

The highly polymorphic human major histocompatibility complex (MHC) also known as the human leukocyte antigen (HLA) encodes class I and II genes that are the cornerstone of the adaptive immune system. Their unique diversity (>25,000 alleles) might affect the outcome of any transplant, infection, and susceptibility to autoimmune diseases. The recent rapid development of new next-generation sequencing (NGS) methods provides the opportunity to study the influence/correlation of this high level of HLA diversity on allele expression levels in health and disease. Here, we describe the NGS capture RNA-Seq method that we developed for genotyping all 12 classical HLA loci (HLA-A, HLA-B, HLA-C, HLA-DPA1, HLA-DPB1, HLA-DQA1, HLA-DQB1, HLA-DRA, HLA-DRB1, HLA-DRB3, HLA-DRB4, and HLA-DRB5) and assessing their allelic imbalance by quantifying their allele RNA levels. This is a target enrichment method where total RNA is converted to a sequencing-ready complementary DNA (cDNA) library and hybridized to a complex pool of RNA-specific HLA biotinylated oligonucleotide capture probes, prior to NGS. This method was applied to 161 peripheral blood mononuclear cells and 48 umbilical cord blood cells of healthy donors. The differential allelic expression of 10 HLA loci (except for HLA-DRA and HLA-DPA1) showed strong significant differences (P < 2.1 × 10-15). The results were corroborated by independent methods. This newly developed NGS method could be applied to a wide range of biological and medical questions including graft rejections and HLA-related diseases.

The rs75862629 minor allele in the endoplasmic reticulum aminopeptidases intergenic region affects human leucocyte antigen B27 expression and protects from ankylosing spondylitis in Sardinia

OBJECTIVES

HLA-B27 and the endoplasmic reticulum aminopeptidase 1 (ERAP1) and ERAP2 genes are predisposing factors for AS. A single nucleotide polymorphism (SNP) in the ERAP2 promoter (rs75862629) coordinates the transcription of both ERAP genes. We investigated whether this SNP associates with AS and whether it affects the expression of the two major HLA-B27 alleles present in Sardinia, the AS-associated B*2705 and the non-AS-associated B*2709.

METHODS

Four SNPs in the ERAP region were genotyped in HLA-B*2705-positive patients with AS (n = 145), B27-positive healthy subjects (n = 126) and B27-negative controls (n = 250) and the allele and haplotype frequencies were derived. The expression of ERAP1 and ERAP2 mRNAs in 36 HLA-B27-positive B lymphoblastoid cell lines was measured by quantitative PCR. An electrophoretic mobility shift assay was performed to search for a nuclear factor binding the DNA sequence encompassing rs75862629. The expression of HLA-B27 molecules related to the SNP at rs75862629 was determined by flow cytometry.

RESULTS

The minor allele G at rs75862629 was found significantly increased in B27 healthy individuals, both B*2705 and B*2709, compared with B*2705-positive patients with AS and B27-negative controls. The electrophoretic mobility shift assay indicated the lack of binding of a transcription factor as the cause of the observed reduction in the ERAP2 concomitant with a higher ERAP1 expression. Of note, this occurs with a different cell surface expression of the HLA-B*2705 and HLA-B*2709 molecules.

CONCLUSION

SNP rs75862629, by modulating simultaneously the expression of ERAP1 and ERAP2, provides protection from AS in HLA-B27-positive subjects in Sardinia. This has a functional impact on HLA-B27 expression and likely on disease onset.

Screening of underlying genetic biomarkers for ankylosing spondylitis

Genetic biomarkers for the diagnosis of ankylosing spondylitis (AS) remain unreported except for human leukocyte antigen B27 (HLA-B27). Therefore, the aim of the present study was to screen the differentially expressed genes (DEGs), and those that also possess differential single nucleotide polymorphism (SNP) loci in the whole blood of AS patients compared with healthy controls by integrating two mRNA expression profiles (GSE73754 and GSE25101) and SNP microarray data (GSE39428) collected from the Gene Expression Omnibus (GEO). Using the t-test, 1,056 and 1,073 DEGs were identified in the GSE73754 and GSE25101 datasets, respectively. Among them, 234 DEGs were found to be shared in both datasets, which were subsequently overlapped with 122 differential SNPs of genes in the GSE39428 dataset, resulting in identification of two common genes [eukaryotic translation elongation factor 1 epsilon 1 (EEF1E1) and serpin family A member 1 (SERPINA1)]. Their expression levels were significantly upregulated and the average expression log R ratios of SNP sites in these genes were significantly higher in AS patients than those in controls. Function enrichment analysis revealed that EEF1E1 was involved in AS by influencing the aminoacyl-tRNA biosynthesis, while SERPINA1 may be associated with AS by participating in platelet degranulation. However, only the genotype and allele frequencies of SNPs (rs7763907 and rs7751386) in EEF1E1 between AS and controls were significantly different between AS and the controls, but not SERPINA1. These findings suggest that EEF1E1 may be an underlying genetic biomarker for the diagnosis of AS.

HLA-B*27 subtypes and their implications in the pathogenesis of ankylosing spondylitis

Ankylosing spondylitis (AS) is a highly heritable kind of arthritis that affects the vertebral column. AS risk has been associated strongly with Human leukocyte antigen (HLA)-B*27. In fact, some HLA-B*27 subtypes have been associated with the increased disease risk, although some specific subtypes have not shown such associations. It is supposed that HLA-B*27 plays a major role in the etiopathogenesis of the disease. However, the difference in pathogenic outcomes of HLA-B*27 certain subtypes needs to be clarified. The purpose of this review article is to overview on the detailed implications of the HLA-B*27 subtypes in the etiopathogenesis of AS. Moreover, the role of ERAP1 in AS and its epistasis with HLA-B*27 have been reviewed.

Human HLA-B27 typing using the BD™ HLA-B27 kit on the BD FACSVia™ system: A multicenter study

The BD FACSVia™ system is a novel flow cytometer with improved workflow efficiencies. To evaluate the HLA‐B27 application developed on the BD FACSVia system utilizing the BD™ HLA‐B27 kit, we conducted a concordance study at three centers to compare with the BD FACSCalibur™ system. Prepared donor samples (n = 594) were analyzed on both the BD FACSVia and BD FACSCalibur for the HLA‐B27 assay. Adjudication of HLA‐B27 discordant results was performed using the reverse sequence‐specific oligonucleotide (rSSO) DNA typing method (LABType® SSO, One Lambda). On the BD FACSVia system 80 B27 positive, 499 B27 negative and 15 “Inconclusive” samples were observed. The corresponding BD FACSCalibur results were 73 B27 positive, 502 B27 negative and 19 “gray zone” samples. The overall concordance of HLA‐B27 determination was 98% between the two systems with seven more positives identified on BD FACSVia as compared to BD FACSCalibur. The equivocal zone between positive and negative on BD FACSVia (named “Inconclusive”) and on BD FACSCalibur (named “gray zone”) is due to antibody cross reactivity of HLA‐B27 clone GS145.2. One negative sample verified with the rSSO DNA method was reported as HLA‐B27 positive by the BD FACSVia system leading to a false positive result. Our study demonstrated concordance results between the BD FACSVia system and BD FACSCalibur. Intersite reproducibility of BD HLA‐B27 assay remained within the limits of acceptability. © 2018 The Authors. Cytometry Part B: Clinical Cytometry published by Wiley Periodicals, Inc. on behalf of International Clinical Cytometry Society

No evidence for a direct role of HLA-B27 in pathological bone formation in axial SpA

Objective

The strong genetic association between HLA-B27 and ankylosing spondylitis has been known for over 40 years. HLA-B27 positivity is possibly associated with severity of ankylosis. We studied the in vitro and in vivo impact of HLA-B27 in models of chondrogenesis and osteogenesis.

Methods

Different in vitro differentiation systems were used to mimic endochondral and direct bone formation. ATDC5 cells and primary human periosteum-derived cells (hPDCs) were transduced with lentiviral vectors expressing HLA-B27 or HLA-B7. These cells and limb bud cells (from HLA-B27 transgenic and wild-type (WT) mice) were cultured in micromasses. To study direct osteogenesis in hPDCs, cells were cultured as monolayers and stimulated with osteogenic media. Chondrogenesis (COL2, ACAN, COL10) and osteogenesis (OSC, ALP, RUNX2) marker expression was studied by quantitative RT-PCR. Colorimetric tests were performed to measure proteoglycans, mineralization and collagens. Collagen antibody-induced arthritis (CAIA) was induced in HLA-B27 transgenic and WT mice. Clinical scoring and µCTs were performed. Statistical analyses were performed by two-way ANOVA.

Results

There was no difference in chondrogenesis markers or in colorimetric tests between HLA-B27⁺ and HLA-B7⁺ micromasses. Expression of osteogenesis markers and Alizarin red staining was comparable in the HLA-B27⁺ and the HLA-B7⁺ hPDCs in monolayers. HLA-B27 transgenic mice showed more severe arthritis compared with WT mice in the CAIA model. µCT analysis showed no increased bone formation in HLA-B27 transgenic mice.

Conclusion

HLA-B27 seems to enhance joint inflammation in the CAIA model. We could not document a direct effect of HLA-B27 on chondrogenesis or osteogenesis.

Polymorphisms of human leukocyte antigen B*27 on clinical phenotype of spondyloarthritis in Chinese

BACKGROUND

In recent years, an ever-increasing number of alleles of human leukocyte antigen B*27 (HLA-B*27) have been identified. This study aimed to establish an updated method for HLA-B*27 subtyping, and to investigate the impact of HLA-B*27 polymorphisms on the clinical phenotype of spondyloarthritis (SpA).

METHODS

Overall, 184 SpA patients were recruited for analyzing diversity of HLA-B*27 via an updated high-resolution polymerase chain reaction amplification with sequence specific primers (PCR-SSP).

RESULTS

The prevalence of HLA-B*27 was 94.0%, and four subtypes were identified including HLA-B*2704 (77.5%), B*2705 (20.2%), B*2707 (1.7%), and B*2724 (0.6%). There was an obvious male predominance (P=.05) and markedly elevated C-reaction protein (CRP) in B*27 positive SpA (P<.01). In multivariate linear regression analysis, the elevated CRP was positively associated with HLA-B*27 positivity (regression coefficient B=46.1, P=.0003), grade of sacroiliitis (B=47.5, P=.0032), and male gender (B=20.4, P=.0041). Notably, a male predilection was also found in B*2705 positive SpA while B*2707 was associated with older age, higher positive family history, and higher prevalence of extra-articular features (all P<.05).

CONCLUSIONS

In this study, an updated PCR-SSP technique to identify increasing alleles of HLA-B*27 was developed and their different effects on clinical manifestations of SpA were demonstrated. Genotyping of HLA-B*27 would shed light on our understanding of the pathogenesis of SpA.

Detection of novel diagnostic antibodies in ankylosing spondylitis: An overview

Ankylosing spondylitis (AS) is a debilitating, chronic, rheumatic disease characterized by inflammation and new bone formation resulting in fusion of the spine and sacroiliac joints. Since early treatment is impeded by a delayed diagnosis, it is highly important to find new biomarkers that improve early diagnosis and may also contribute to a better assessment of disease activity, prognosis and therapy response in AS. Because of the absence of rheumatoid factor, AS was long assumed to have a seronegative character and antibodies are thus not considered a hallmark of the disease. However, emerging evidence suggests plasma cells and autoantibodies to be involved in the disease course. In this review, the role of B cells and antibodies in AS is discussed. Furthermore, an overview is provided of antibodies identified in AS up till now, and their diagnostic potential. Many of these antibody responses were based on small study populations and further validation is lacking. Moreover, most were identified by a hypothesis-driven approach and thus limited to antibodies against targets that are already known to be involved in AS pathogenesis. Hence, we propose an unbiased approach to identify novel diagnostic antibodies. The already successfully applied techniques cDNA phage display and serological antigen selection will be used to identify antibodies against both known and new antigen targets in AS plasma. These newly identified antibodies will enhance early diagnosis of AS and provide more insight into the underlying disease pathology, resulting in a more effective treatment strategy and eventually an improved disease outcome.

Molecular mechanism of the susceptibility difference between HLA-B*27:02/04/05 and HLA-B*27:06/09 to ankylosing spondylitis: substitution analysis, MD simulation, QSAR modelling, and in vitro assay

The human leukocyte antigen HLA-B27 is directly involved in the disease pathogenesis of ankylosing spondylitis (AS). HLA-B27 has a high degree of genetic polymorphism, with 105 currently known subtypes; the presence of aspartic acid at residue 116 (Asp116) has been found to play an essential role in AS susceptibility. Here, we systematically investigated the molecular mechanism of the susceptibility difference between the AS-associated subtypes HLA-B*27:02/04/05 and AS-unassociated subtypes HLA-B*27:06/09 to AS at sequence, structure, energetic and dynamic levels. In total seven variable residues were identified among the five studied HLA-B27 subtypes, in which Asp116 can be largely stabilized by a spatially vicinal, positively charged His114 through a salt bridge, while five other variable residues seem to have only a marginal effect on AS susceptibility. We also employed a quantitative structure-activity relationship approach to model the statistical correlation between peptide structure and affinity to HLA-B*27:05, a genetic ancestor of all other HLA-B27 subtypes and associated strongly with AS. The built regression predictor was verified rigorously through both internal cross-validation and external blind validation, and was then employed to identify potential HLA-B*27:05 binders from >20,000 cartilage-derived self-peptides. Subsequently, the binding potency of the top five antigenic peptides to HLA-B*27:05 was assayed in vitro using a FACS-based MHC stabilization experiment. Consequently, two (QRVGSDEFK and LRGAGTNEK) out of the five peptides were determined to have high affinity (BL50 = 5.5 and 15.8 nM, respectively) and, as expected, both of them possess positively charged Lys at the C-terminus.

Non-conventional forms of HLA-B27 are expressed in spondyloarthritis joints and gut tissue

Objectives

Human leukocyte antigen (HLA)-B27 (B27) is the strongest genetic factor associated with development of Ankylosing Spondylitis and other spondyloarthropathies (SpA), yet the role it plays in disease pathogenesis remains unclear. We investigated the expression of potentially pathogenic non-conventional heavy chain forms (NC) of B27 in synovial and intestinal tissues obtained from SpA patients. We also determined the presence of NC-B27 in joints, lymphoid and gastrointestinal tissue from B27 transgenic (TG¹) rats with M.tuberculosis-induced SpA.

Methods

Expression of NC-B27 in human SpA joints and gut and in (21-3 × 283-2)F₁ HLA-B27/Huβ2m rat tissue was determined by immunohistochemistry, flow cytometry and confocal microscopy analysis using HC10 and HD6 antibodies.

Results

Both HC10- and HD6-reactive HLA molecules were present in synovial tissue from SpA patients. Both NC-B27 and KIR3DL2, a ligand for NC-B27, were expressed in inflamed terminal ileal tissues in patients with early SpA. Infiltrating cells in inflamed joint tissues isolated from B27 TG¹ rats expressed high levels of NC-B27. NC-B27 were also expressed in joint-resident cells from ankle and tail joints of B27 TG¹ rats prior to clinical arthritis. The expression of NC-B27 on B27 TG¹ rat CD11b/c⁺, CD8α⁺, cells from spleens and LNs increased with animal age and disease progression.

Conclusions

Non-conventional HLA class 1 molecules are expressed on resident and infiltrating cells in both synovial and GI tissues in human SpA. NC-B27 expression in joints and lymphoid tissues from B27 TG¹ rats prior to the onset of arthritis is consistent with the hypothesis that they play a pathogenic role in SpA.

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HLA-B27 predisposes to Ankylosing Spondylitis and related Spondyloarthritis (SpA).

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Non-conventional HLA-B27 free heavy chains (NC-B27) bind innate immune receptors.

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NC HLA class I molecules are expressed in joint and gut tissues in human and rat SpA.

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B27 transgenic rats express NC-B27 prior to arthritis onset.

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These data support a pathogenic role for non-conventional B27 in SpA.

Current perspective on the role of the interleukin-23/interleukin-17 axis in inflammation and disease (chronic arthritis and psoriasis)

TH17 is a lymphocyte subset, which is characterized by its polarization to secrete interleukin (IL)-17. IL-23 is the pivotal mediator responsible for TH17 differentiation and the IL-23/IL-17 axis has been strongly implicated in the pathogenesis of several immune mediated diseases, in particular chronic arthritis and skin psoriasis. This review will summarize the basic immunology and the new monoclonal antibodies, which antagonize this pathway allowing a new therapeutic approach.

Killer-cell immunoglobulin-like receptors (KIR) and HLA-class I heavy chains in ankylosing spondylitis

HLA-B27 (B27) interactions with the killer-cell immunoglobulin-like receptors (KIR) have been implicated in the pathogenesis of ankylosing spondylitis (AS), with consistent differences among populations. KIR3DL1 and possibly KIR3DS1 interact with classical B27, whereas KIR3DL2 binds B27 heavy chain dimers. The aim of this review is to summarize data from recent studies performed in our laboratory and from the literature, which provide support for a possible role of KIR3DL2/B27 dimer interactions in the pathogenesis of AS. Recent studies in cells from AS patients and from health controls carrying the predisposing B*2705 and the nonpredisposing B*2709 haplotypes, have shown a higher percentage of positive cells and a higher surface expression of KIR3DL2 receptors on natural killer (NK) and CD4+ T cells in B*2705 AS patients compared with B*2705, B*2709 and B27-negative healthy controls. Increased expression of HC10-reactive molecules on AS monocytes was seen, supporting the possible role of the KIR3DL2/B272 pair in the pathogenesis of AS. These results underline the importance of NK cells and innate immunity, and of CD4+ T cells in the inflammatory pathogenesis of AS.

Update on ankylosing spondylitis: current concepts in pathogenesis

Ankylosing spondylitis is an insidiously progressive and debilitating form of arthritis involving the axial skeleton. The long delay in diagnosis and insufficient response to currently available therapeutics both advocate for a greater understanding of disease pathogenesis. Genome-wide association studies of this highly genetic disease have implicated specific immune pathways, including the interleukin (IL)-17/IL-23 pathway, control of nuclear factor kappa B (NF-κB) activation, amino acid trimming for major histocompatibility complex (MHC) antigen presentation, and other genes controlling CD8 and CD4 T cell subsets. The relevance of these pathways has borne out in animal and human subject studies, in particular, the response to novel therapeutic agents. Genetics and the findings of autoantibodies in ankylosing spondylitis revisit the question of autoimmune vs. autoinflammatory etiology. As environmental partners to genetics, recent attention has focused on the roles of microbiota and biomechanical stress in initiating and perpetuating inflammation. Herein, we review these current developments in the investigation of ankylosing spondylitis pathogenesis.

Increased expression of human leucocyte antigen class I free heavy chains on monocytes of patients with spondyloarthritis and cells transfected with HLA-B27

Human leucocyte antigen (HLA)-B27 expression is correlated with spondyloarthritis (SpA), but its role in disease pathogenesis remains unclear. The aim of the study was to determine whether HLA-B27 free heavy chain (FHC) contributes to SpA pathogenesis. Flow cytometry was used to analyse the FHC expression on CD3+ and CD14+ cells in the peripheral blood (PB) and synovial fluid (SF) from SpA patients, healthy controls, and rheumatoid arthritis (RA) patients. Human monocytic U937 cell lines stably expressing enhanced green fluorescence protein (EGFP)/HLA-B27, EGFP/HLA-A2 or EGFP alone were created to further investigate the relation between HLA-B27 and FHC expression. The relative FHC level on CD14+ PB cells was significantly higher in SpA patients than in controls, but lower than on the SF cells of SpA patients. No significant correlation was found for relative FHC expression with HLA-B27 or β2-microglobulin expression. HLA-B27-transfected U937 cells expressed higher FHC levels than either EGFP/HLA-A2- or EGFP-transfected cells. HLA class I FHC expression was significantly increased on monocytes of SpA patients and HLA-B27-transfected cells, implying that FHC, perhaps mostly derived from HLA-B27, plays an important role in SpA pathogenesis.

Human leukocyte antigen-b27 and disease susceptibility in vojvodina, serbia

There are numerous studies showing the role of human leukocyte antigens (HLAs) related with susceptibility or resistance to certain diseases. The aim of this study was to determine the association of HLA-B27 with ankylosing spondylitis (AS), polyarthralgia, lumboishialgia, acute anterior uveitis (AAU), psoriatic arthritis (PA), synovitis coxae and rheumatoid arthritis (RA) in patients from Vojvodina, Serbia. An HLA I class typing was performed by the serological immunomagnetic two-color fluorescence method using peripheral blood T lymphocytes in 97 patients and 224 healthy controls from the population of Vojvodina, Serbia. We calculated HLA-B27 frequencies, relative risk (RR), ethiologic fraction (EF), e.g., population attributive risk, when RR was greater than 1, while, preventive fraction (PF) was calculated when RR was lower than 1. This study revealed the strongest association of AS with HLAB27 antigen: RR = 25.0, while the EF was greater than 0.15, respectively. The χ² test showed the significant difference (p <0.05) in HLA-B27 in patients with AS in comparison to controls (χ² = 52.5). It was concluded that there is a positive association of HLA-B27 with AS and that HLA-B27 can serve as a marker for predisposition to diseases.

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.

The critical role of interleukin-23 in spondyloarthropathy

The spondyloarthropathies represent highly enigmatic conditions and although their clinical features, anatomical distribution of disease and genetic predisposing factors have been known for some time, a unified concept of the basic pathobiology underlying these illnesses has remained undefined. Recently progress has been made because numerous independent studies have converged upon IL-23 as a central cytokine in spondyloarthropathy and the mechanism and sites of action of this cytokine have now become much clearer. These findings enable the rational design of therapeutic strategies which it is hoped will profoundly modify the progression of these diseases. We will review the anatomical sites affected and the evidence for the importance of IL-23 in these conditions, before drawing these lines of investigation together to propose a model for the unified understanding of spondyloarthropathy.

Susceptibility to ankylosing spondylitis but not disease outcome is influenced by the level of HLA-B27 expression, which shows moderate variability over time

OBJECTIVE

Previous reports have highlighted the relevance of HLA-B27 expression in the pathogenesis of ankylosing spondylitis (AS). The aim of the current study was to estimate the level of HLA-B27 expression on the cell surface of ex vivo monocytes and lymphocytes by a quantitative method and to correlate this with AS disease susceptibility, disease clinical indexes, and the occurrence of acute anterior uveitis (AAU).

METHOD

We recruited 32 B27-positive patients with AS and 32 B27-positive healthy normal controls (NCs) for evaluation at different time points. The expression of HLA-B27 molecules was quantified by flow cytometry on ex vivo peripheral blood mononuclear cells (PBMCs). Patients were also evaluated by scores on the Bath AS disease activity (BASDAI), functional (BASFI), and metrology (BASMI) indexes.

RESULTS

The expression of HLA-B27 molecules was significantly higher in patients with AS than in B27-matched controls in the case of both monocytes [219K (IQR 174K-308K) vs. 137K (IQR 96K-170K), p < 0.0001] and lymphocytes [82K (IQR 58K-118K) vs. 54K (IQR 44K-61K), p < 0.0001]; AS only vs. AS with AAU: p = 0.744 in monocytes and p = 0.701 in lymphocytes. Comparisons with metrology and functional indexes were also not significant (BASMI: r = 0.05, p = 0.77; BASFI: r = -0.09, p = 0.67). The overexpression of HLA-B27 molecules was stable after 1 week of follow-up. At 3 years follow-up, the variability was moderate and did not correlate with variations in disease activity (BASDAI: r = -0.01, p = 0.92 ns).

CONCLUSIONS

The level of HLA-B27 expression in PBMCs correlates with the susceptibility to AS but not with the disease outcome, nor with the occurrence of extra-articular manifestations such as AAU.

Ankylosing spondylitis macrophage production of higher levels of interleukin-23 in response to lipopolysaccharide without induction of a significant unfolded protein response

OBJECTIVE

Previous studies of the HLA-B27-transgenic rat model of ankylosing spondylitis (AS) suggested that macrophages develop an intracellular stress response called the unfolded protein response (UPR) and, as a result, secrete increased amounts of cytokines in response to Toll-like receptor agonists such as lipopolysaccharide (LPS). Our objective was to determine whether macrophages from AS patients also undergo a UPR and secrete increased cytokines/chemokines in response to LPS.

METHODS

Peripheral blood monocytes isolated from 10 AS patients and 10 healthy controls were differentiated in vitro with macrophage colony-stimulating factor. Select samples were treated with interferon-γ (IFNγ) to up-regulate class I major histocompatibility complex (HLA-B) expression prior to stimulation with LPS for either 3 hours (for RNA) or 8-24 hours (for supernatant). UPR induction was assessed by measuring the expression of messenger RNA for ERdj4, BiP, and CCAAT/enhancer binding protein homologous protein 10 (CHOP).

RESULTS

Although IFNγ treatment up-regulated HLA-B expression (2-fold; P < 0.0001), neither IFNγ nor LPS substantially enhanced BiP or CHOP expression (<1.3-fold). ERdj4 expression increased weakly, but not significantly, in AS samples treated with IFNγ plus LPS (2.2-fold; P = 0.31). In response to LPS, AS macrophages secreted more CXCL9, interleukin-10 (IL-10), IL-12p70, IL-23, and tumor necrosis factor α than did control macrophages (P ≤ 0.025). The most striking difference was observed for IL-23 (median 265 pg/ml in AS patients versus 9 pg/ml in controls; P = 0.0007). We did not detect significant differences in IL-6, IL-8, or IFNβ production.

CONCLUSION

The greater production of IL-23 by AS patient macrophages in response to LPS provides further support for the development of Th17/IL-23-directed therapy. Since significant UPR induction was not detected in AS patient macrophages, the relationship between UPR and inflammatory cytokine production remains unclear.

Interferon-γ Contributes to HLA-B27-associated Unfolded Protein Response in Spondyloarthropathies

Objective.

HLA-B27 positivity strongly influences the susceptibility to and phenotype of spondyloarthropathies (SpA). This study was designed to screen factors that activate the promoter of HLA-B27 in U937 cells, and to assess whether these promoter-activating factors induce the unfolded protein response (UPR) in HLA-B27-expressing cells.

Methods.

Cytometric Bead Array, flow cytometry, and real-time polymerase chain reaction were used to detect the expression of cytokines and UPR-associated proteins in peripheral blood and synovial fluid of patients with SpA. The HLA-B27 promotor transfectant was incubated separately with cytokines and Toll-like receptor ligands. After interferon-γ (IFN-γ) stimulation, expressions of GRP78, CHOP, and XBP-1 were tested in HLA-B27-expressing U937 cells and peripheral blood mononuclear cell (PBMC) of patients with ankylosing spondylitis (AS). (Clinical trial registration no. ChiCTR-OCC-11001565)

Results.

Expressions of GRP78, CHOP, and XBP-1 in monocytes/macrophages of SpA peripheral blood and synovial fluid were higher than those in healthy controls and patients with osteoarthritis (OA) (p < 0.05). Tumor necrosis factor-α (TNF-α) and IFN-α, IFN-ß, and IFN-γ were found to have activated the HLA-B27 promoter in the U937 cell line (p < 0.05). Following stimulation with IFN-γ, the expressions of GRP78, CHOP and XBP-1 in HLA-B27-transfected U937 cells and PBMC of HLA-B27-positive AS patients were more intense than those in A2-U937 cells, HLA-B27-negative AS patients, or healthy controls (p < 0.05).

Conclusion.

Expressions of GRP78, CHOP, and XBP-1 were higher in monocytes/macrophages of patients with SpA than those in both OA patients and healthy controls, suggesting that UPR may participate in the pathogenesis of SpA. TNF-α and IFN-α, IFN-ß, and IFN-γ significantly activated HLA-B27 promoter in the U937 cell line, and IFN-γ, the strongest activating factor, may induce the UPR in HLA-B27-expressing cells.

The MHC Class I heavy chain structurally conserved cysteines 101 and 164 participate in HLA-B27 dimer formation

AIMS

The human leukocyte antigen (HLA)-B27 is strongly associated with a group of inflammatory arthritic disorders known as the spondyloarthropathies (SpAs). The unusual biochemistry of HLA-B27 has been proposed to participate in disease development, especially the enhanced ability of HLA-B27 to form several heavy chain-dimer populations. HLA-B27 possesses three unpaired cysteine (C) residues at position 67, 308, and 325, in addition to the four conserved cysteine residues at p101, 164, 203, and 259. C67 was proposed to participate in dimer formation of recombinant HLA-B27 protein and in vivo heavy chain-dimers. However, the structurally conserved C164 was demonstrated to participate in endoplasmic reticulum (ER) resident heavy chain-dimer formation. We therefore wanted to determine whether these aggregates involve cysteines other than C164 and the basis for the difference between the observed heavy chain-dimer species.

RESULTS

We determined that C164 and C101 can form distinct dimer structures and that the heterogenous nature of heavy chain-dimer species is due to differences in both redox status and conformation. Different HLA-B27 dimer populations can be found in physiologically relevant cell types derived from HLA-B27-positive patients with inflammatory arthritis. In addition, HLA-B27 dimer formation can be correlated with cellular stress induction.

INNOVATION

The use of both mutagenesis and manipulating cellular redox environments demonstrates that HLA-B27 dimerization requires both specific cysteine?cysteine interactions and conformations with differing redox states.

CONCLUSION

HLA-B27 heavy chain-dimerization is a complex process and these findings provide an insight into HLA-B27 misfolding and a potential contribution to inflammatory disease development.

Adaptive immunity in ankylosing spondylitis: phenotype and functional alterations of T-cells before and during infliximab therapy

Our aim was to assess the phenotype of T-cell subsets in patients with ankylosing spondylitis (AS), a chronic inflammatory rheumatic disease. In addition, we also tested short-term T-cell activation characteristics. Measurements were done in 13 AS patients before and during the intravenous therapy with anti-TNF agent infliximab (IFX). Flow cytometry was used to determine T-cell subsets in peripheral blood and their intracellular signaling during activation. The prevalence of Th2 and Th17 cells responsible for the regulation of adaptive immunity was higher in AS than in 9 healthy controls. Although IFX therapy improved patients' condition, immune phenotype did not normalize. Cytoplasmic and mitochondrial calcium responses of CD4+ and CD8+ cells to a specific activation were delayed, while NO generation was increased in AS. NO generation normalized sooner upon IFX than calcium response. These results suggest an abnormal immune phenotype with functional disturbances of CD4+ and CD8+ cells in AS.

Pathogenicity of Misfolded and Dimeric HLA-B27 Molecules

The association between HLA-B27 and the group of autoimmune inflammatory arthritic diseases, the spondyloarthropathies (SpAs) which include ankylosing spondylitis (AS) and Reactive Arthritis (ReA), has been well established and remains the strongest association between any HLA molecule and autoimmune disease. The mechanism behind this striking association remains elusive; however animal model and biochemical data suggest that HLA-B27 misfolding may be key to understanding its association with the SpAs. Recent investigations have focused on the unusual biochemical structures of HLA-B27 and their potential role in SpA pathogenesis. Here we discuss how these unusual biochemical structures may participate in cellular events leading to chronic inflammation and thus disease progression.

The Role of HLA-B27 in Spondyloarthritis

This article summarizes the proceedings of a one-day international workshop held in July 2009 on the role of HLA-B27 in the pathogenesis of ankylosing spondylitis (AS) and related disorders. HLA-B27 is found in about 90% of patients with AS, with an odds ratio of about 100, but the mechanism underlying this association is not known. There are currently 3 major mechanistic hypotheses for this association: (1) T cell recognition of one or more B27 presented peptides; (2) B27 heavy-chain misfolding that induces an unfolded protein response; and (3) innate immune recognition of cell-surface expressed B27 heavy-chain dimers. None of these hypotheses accounts for the tissue specificity of the inflammation characteristic of AS. These hypotheses were discussed in the context of known epidemiologic, biochemical, structural, and immunologic differences among HLA-B27 subtypes; data from the HLA-B27 transgenic rat model of spondyloarthritis; the growing list of other genes that have been found to be associated with AS; and other data on the pathogenesis of spondyloarthritis. Proposed directions for future research include expanded efforts to define similarities and differences among the B27 subtypes; further development of animal models; identifying the interactions of B27 with the products of other genes associated with AS; and continued investigation into the pathogenesis of spondyloarthritis.

From HLA-B27 to spondyloarthritis: a journey through the ER

Almost four decades of research into the role of human leukocyte antigen-B27 (HLA-B27) in susceptibility to spondyloarthritis has yet to yield a convincing answer. New results from an HLA-B27 transgenic rat model now demonstrate quite convincingly that CD8(+) T cells are not required for the inflammatory phenotype. Discoveries that the HLA-B27 heavy chain has a tendency to misfold during the assembly of class I complexes in the endoplasmic reticulum (ER) and to form aberrant disulfide-linked dimers after transport to the cell surface have forced the generation of new ideas about its role in disease pathogenesis. In transgenic rats, HLA-B27 misfolding generates ER stress and leads to activation of the unfolded protein response, which dramatically enhances the production of interleukin-23 (IL-23) in response to pattern recognition receptor agonists. These findings have led to the discovery of striking T-helper 17 cell activation and expansion in this animal model, consistent with results emerging from humans with spondyloarthritis and the discovery of IL23R as an additional susceptibility gene for ankylosing spondylitis. Together, these results suggest a novel link between HLA-B27 and the T-helper 17 axis through the consequences of protein misfolding and open new avenues of investigation as well as identifying new targets for therapeutic intervention in this group of diseases.

Dendritic cells from spondylarthritis-prone HLA-B27-transgenic rats display altered cytoskeletal dynamics, class II major histocompatibility complex expression, and viability

OBJECTIVE

Spondylarthritis (SpA) is characterized by spinal and peripheral joint inflammation, frequently combined with extraarticular manifestations. Despite the well-established association of SpA with the class I major histocompatibility complex (MHC) allele HLA-B27, there are still different, parallel hypotheses on the relationship between HLA-B27 and disease mechanisms. The present study was undertaken to investigate several characteristics of mature dendritic cells (DCs), which are believed to be essential for triggering disease in a model of SpA in HLA-B27-transgenic rats.

METHODS

We combined different whole-proteome approaches (2-dimensional polyacrylamide gel electrophoresis and iTRAQ) to define the most aberrant molecular processes occurring in spleen DCs. Videomicroscopy and flow cytometry were used to confirm both cytoskeletal and class II MHC expression deficiencies.

RESULTS

Our proteome studies provided evidence of up-regulation of proteins involved in class I MHC loading, and unfolded protein response, along with a striking down-regulation of several cytoskeleton-reorganizing proteins. The latter result was corroborated by findings of deficient motility, altered morphology, and decreased immunologic synapse formation. Furthermore, class II MHC surface expression was reduced in DCs from B27-transgenic rats, and this could be linked to differences in class II MHC-induced apoptotic sensitivity. Finally, we found reduced viability of the CD103+CD4- DC subpopulation, which likely exerts tolerogenic function.

CONCLUSION

Taken together, our findings have different important implications regarding the physiology of B27-transgenic rat DCs, which have a putative role in spontaneous disease in these rats. In particular, the reduced motility and viability of putatively tolerogenic CD4+ DCs could play an important role in initiating the inflammatory process, resulting in SpA.

Clinical features of ankylosing spondylitis may correlate with HLA-B27 polymorphism

The objective of this study is to investigate the relationship between clinical features of ankylosing spondylitis (AS) and HLA-B27 status or its subtypes. Clinical data and blood samples were collected with patients' informed consent. Luminex liquid array combining polymerase chain reaction-sequence specific oligonucleotide probe was used to do the low-resolution HLA-B genotype typing. Polymerase chain reaction-sequence specific primer was applied to do the high resolution HLA-B27 typing. In 98 subjects, 93 were HLA-B27 positive, of which three subtypes were detected: B*2704 (n = 76), B*2705 (n = 12), and B*2715 (n = 5). The onset age for B27 negative and positive group was 28 +/- 7.9 and 21.1 +/- 6.2 years, respectively (chi(2) = -2.047, P = 0.041). The onset age for B*2704, B*2705 and B*2715 group was 20.45 +/- 4.50, 26.67 +/- 9.95 and 17.8 +/- 11.12 years, respectively (chi(2) = 7.888, P = 0.019). No significant difference was found between B27 positive and negative group, or among three B27 subtypes groups for other clinical features. In conclusion, the clinical features of AS may be correlated with HLA-B27 status and its polymorphism.

The pathogenesis of ankylosing spondylitis

✓ Ankylosing spondylitis (AS) is a chronic inflammatory disease that can cause significant functional complications by affecting the sacroiliac joints and axial skeleton. Despite a longstanding knowledge about the familial associations of this disease, particularly among patients positive for human leukocyte antigen (HLA)–B27, the fundamental pathogenetic mechanism by which this disease arises in genetically susceptible individuals remains ill defined. Furthermore, the molecular predilection for characteristic articular site involvement remains under ongoing investigation. Current theories about the HLA-B27 association range from the presentation of novel arthritogenic peptides, to abnormal autoimmune stimulation, to anomalous microbial tolerance. The immune effectors of this damage include CD4+, CD8+, and natural killer cells, with marked heterogeneity at different sites. Biomechanical stresses may trigger this disease by exposing the body to previously immune-sequestered autoantigens or by providing a route for bacterial seeding. Environmental triggers such as infection have not been definitively established but may represent a primary pathogenic step in a molecular-mimicry process. In this article, the authors review the current literature on the origin and pathophysiology of AS, focusing on genetic and molecular associations, consequent pathomechanisms, and associated triggers. An improved understanding of the sequence of molecular events that predispose and initiate the onset of this disease will allow for more specific and targeted therapy and better avoidance of the significant side effects of systemic immunomodulation.

Open conformers: the hidden face of MHC-I molecules

A pool of MHC-I molecules present at the plasma membrane can dissociate from the peptide and/or the light chain, becoming open MHC-I conformers. Whereas peptide-bound MHC-I molecules have an important role in regulating adaptive and innate immune responses, through trans-interactions with T cell and NK cell receptors, the function of the open MHC-I conformers is less clear but seems to be related to their inherent ability to cis-associate, both with themselves and with other receptors. Here, we review data indicating the open MHC-I conformers as regulators of ligand-receptor interactions and discuss the biological implications for immune and non-immune cells. The likelihood that the MHC-I heavy chains have hidden functions that are determined by the amino acid sequence of the alpha1 and alpha2 domains are discussed.

Two HLA–B27 alleles differently associated with spondylarthritis, B*2709 and B*2705, display similar intracellular trafficking and oligomer formation

OBJECTIVE

To examine whether and to what extent the intracellular trafficking features of HLA-B*2705, which is associated with the development of spondylarthritis (SpA), differ from those of HLA-B*2709 and HLA-B*0702, which are not associated with SpA.

METHODS

HeLa cells were transfected with complementary DNA encoding for HLA-B proteins fused to Renilla luciferase or yellow fluorescent protein. The subcellular distribution of properly folded and unfolded/misfolded HLA-B proteins was examined by flow cytometry and confocal microscopy of cells labeled with ME1 and HC-10 antibodies, respectively. HLA-B/HLA-B interactions were monitored in endoplasmic reticulum (ER)- and plasma membrane-enriched subcellular fractions, by bioluminescence resonance energy transfer (BRET).

RESULTS

All 3 HLA-B alleles displayed a similar distribution pattern (properly folded heavy chain at the cell surface, unfolded/misfolded proteins only in the cytoplasm). By means of BRET, we provided evidence that both HLA-B*2705 and HLA-B*2709 formed more oligomers in the ER and the plasma membrane than did HLA-B*0702. The propensity of HLA-B*2705 to form oligomers in the ER was partly attributable to residue Cys(67) of the molecule. For all 3 alleles, increased expression of HLA-B proteins was associated with intracytoplasmic accumulation of unfolded/misfolded proteins and intracellular vesicles, probably corresponding to expanded ER-Golgi intermediate compartments, in which these proteins accumulated together with the stress sensor BiP.

CONCLUSION

Our results suggest that the difference in disease susceptibility conferred by HLA-B*2705 and HLA-B*2709 cannot be explained by their different propensity to form dimers or misfolded proteins, thus presumably implicating other, still unknown factors.

Ankylosing spondylitis is linked to Klebsiella--the evidence

Ankylosing spondylitis (AS) is a chronic inflammatory spinal and large-joint arthritic and potentially disabling condition, mainly affecting males of young age groups. Extensive literature based on the results of various genetic, microbiological, molecular and immunological studies carried out by independent research groups suggests that Klebsiella pneumoniae is the main microbial agent being implicated as a triggering and/or perpetuating factor in the etiopathogenesis of AS. Novel diagnostic markers and criteria based on the association with high anti-Klebsiella antibodies could be used in the detection of AS patients during early stages of the disease, and together with the current treatments might help in implementing the use of new therapeutic anti-microbial measures in the management of AS. Prospective longitudinal studies with the use of anti-microbial measures in patients with AS are required to establish the therapeutic benefit of this microbe-disease association.

The pathogenetic role of HLA-B27 and its subtypes

The strong association between HLA-B27 and ankylosing spondylitis has been known for more than 33 years, but the enigma of the pathogenetic role of the gene and its product has not yet been solved. Ongoing studies have produced evidence supporting different theories to explain this association, and structural and functional studies of HLA-B27 allele products at molecular level have provided information of broad and multidisciplinary value and disclosed new avenues leading to autoimmunity and immune disregulation.

Pathogenesis of ankylosing spondylitis: current concepts

More than three decades after the discovery of HLA-B27 as a major genetic clue to the origins of ankylosing spondylitis, much has been learned about pathogenesis. However, the role of this major histocompatibility complex class I allele remains undefined. Studies from animal models have demonstrated that HLA-B27 overexpression can cause inflammatory disease with spondyloarthritis features, and together with investigations of patient-derived material, both innate adaptive and immune responses have been implicated. The gastrointestinal immune response to pathogens and even normal flora, with subclinical or overt inflammation, may play a role as an environmental component of these diseases. Although there has been a large conceptual emphasis on mechanisms involving autoreactive T-cell recognition of HLA-B27 complexes displaying arthritogenic peptides, and more recently non-canonical recognition of abnormal forms of HLA-B27 free of beta(2)m (heavy-chain dimers or monomers), it remains unclear whether immunological recognition plays a role in pathogenesis. The recognition that the HLA-B27 heavy chain misfolds during assembly, and causes endoplasmic reticulum 'stress', has led to the observation that this activates the unfolded protein response. This has opened additional areas of investigation into the response of immune system cells to protein misfolding, and suggested novel alternative concepts that may explain the role of HLA-B27 in pathogenesis. This chapter will discuss available data and current concepts regarding the pathogenesis of ankylosing spondylitis.