HLA-B27/microbial mimicry: an in vivo analysis.

The association between three major spondyloarthritic diseases, ankylosing spondylitis, Reiter's syndrome, and reactive arthritis, and the major histocompatibility complex (MHC) class 1 antigen HLA-B27 is well documented. The hypothesis of cross-reactivity between HLA-B27 and the antecedent infection-causing Gram-negative pathogens such as Salmonella, Shigella and Yersinia has been suggested by in vitro studies employing monoclonal antibodies. We have examined the possibility of such cross-reactivity in vivo using various rabbit immune sera and patient sera as the source of cross-reacting antibody. Mouse L cells were transfected with HLA-A3 or HLA-B27 and used as a source of antigen. Western blot analysis employing denatured antigen, FACS analysis employing native antigen and immunoprecipitation studies were undertaken to detect cross-reacting antibodies generated in vivo to HLA-B27 antigen. Antibodies generated in vivo by infection in patients or immunization in animals against arthritogenic bacteria did not demonstrate any cross-reactivity with HLA-B27 by any of the methods used. As defined by the humoral immune response, molecular mimicry appears unlikely to explain the role of B27 in the pathogenesis of reactive arthritis.     

The oxidative folding and misfolding of human leukocyte antigen-b27

The major histocompatibility complex class I molecule human leukocyte antigen (HLA)-B27 is strongly associated with a group of inflammatory arthritic disorders known as the spondyloarthropathies. Many autoimmune diseases exhibit associations with major histocompatibility complex molecules encoded within the class II locus with defined immune responses either mediated by T or B-lymphocytes. Despite the association being known for over 30 years, no defined immune response and target autoantigens have been characterized for the spondyloarthropathies. Thus, the mechanism and role of HLA-B27 in disease pathogenesis remains undetermined. One hypothesis that has recently received much attention has focused around the enhanced propensity for HLA-B27 to misfold and the increased tendency of the heavy chain to dimerize. The misfolding of HLA-B27 has been associated with its redox status and this is postulated to be involved in disease development. Here we discuss the impact of the redox status on HLA-B27 biosynthesis and function.     

HLA molecules, bacteria and autoimmunity

It has been well established that many diseases are linked to HLA antigens. Two of the most interesting HLA associations may provide some insight into the pathogenesis of rheumatic inflammatory conditions. In ankylosing spondylitis (AS), 96% of patients possess HLA-B27, whilst the frequency of this marker in the general population is c. 8%. In rheumatoid arthritis (RA), >90% of patients possess either HLA-DR1 or some subtypes of HLA-DR4, whilst the frequency of this marker in the general population is c. 35%. The association between HLA-B27 and reactive arthritis (ReA) has also been well established. Furthermore, it has been shown that ReA is triggered by infection via the gastrointestinal tract due to Yersinia, Salmonella or Campylobacter spp. and in the genitourinary tract due to chlamydia. In a similar way, microbiological and immunological studies have revealed an association between Klebsiella pneumoniae in AS and Proteus mirabilis in RA. This article reviews the possible pathological implications of the associations between HLA-B27, K. pneumoniae and AS, as well as HLA-DR1/DR4, P. mirabilis and RA.     

The naturally occurring polymorphism Asp116 → His116 , differentiating the ankylosing spondylitis-associated HLA-B*2705 from the non-associated HLA-B*2709 subtype,influences peptide-specific CD8 T cell recognition

HLA-B27 molecules are interesting because of their strong association with ankylosing spondylitis (AS) and reactive arthritis (ReA). A pathogenetic role for these molecules has been postulated in presenting a putative --bb--arthritogenic peptide to CD8 T cells. The HLA-B*2709 subtype, although differing by a single amino acid (His¹¹⁶ → Asp¹¹⁶ ) from the wide spread and strongly AS-associated subtype HLA-B*2705, is not found in patients. Since residue 116 interacts with the C terminus of the peptide, it is possible that the two subtypes differ in their antigen-presenting features. We show here that CD8 T cells can distinguish the two HLA-B27 subtypes when presenting a same epitope derived from Epstein-Barr virus-latent membrane protein 2. Moreover, alanine scanning mutagenesis analysis revealed that the peptide residues relevant for such recognition are different depending on whether HLA-B*2705 or -B*2709 molecules present the epitope. These results give support to the belief that functional differences determined by subtype-specific polymorphisms can have a pathogenetic relevance and open up a new scenario where subtle modifications within the peptide/HLA ligand might be responsible for the differential association between HLA-B27 subtypes and spondyloarthropathies.     

Association of ankylosing spondylitis with HLA-B27 and ERAP1: Pathogenic role of antigenic peptide

Ankylosing spondylitis (AS) is a form of seronegative inflammatory arthritis whose strong genetic association with the human leucocyte antigen (HLA)-B27 has been known for almost 4 decades. However, its mechanism remains poorly understood. Recently, with the development of genetics, further more genes have been robustly associated with the disease. Genome-wide association studies identified the association between AS and ERAP1 (endoplasmic reticulum associated aminopeptidase 1). And ERAP1 has shown the potential in trimming antigenic peptides to optimal length for binding to HLA-B27 in the ER (endoplasmic reticulum). However, the length of the peptides are strictly restricted in the process of peptide transporting, processing and presentation. A hypothesis is proposed that the abnormal mechanism of AS may related to the trimming of N-terminal sequences from antigenic precursors in the ER and the length of the antigenic peptides that are presented to the T-cell receptors.     

Characterization of HLA-Bw73 by serology and one-dimensional isoelectric focusing patterns

The HLA-Bw73 antigen has been characterized by antisera in the Ninth International Histocompatibility Workshop. The International Workshop antibodies 9w245, 9w246, and 9w247 detected HLA-B7 and one or more atingens of this group (HLA-B40, Bw22, Bw42, or Bw48) in addition to HLA-Bw73. We have serologically characterized three additional antibodies, in two family studies, which contain anti-Bw73 (two of the antisera also contain anti-B7 activity). We have performed absorption studies with the three antisera, which indicate that anti-Bw73 activity is removed by HLA-B7 positive lymphocytes in two of the antisera and that, in one case, anti-B7 activity is removed by HLA-Bw73 positive for HLA-B7 negative lymphocytes. The third antiserum is cytotoxicity negative absorption positive for HLA-B7. Neither HLA-B27 positive nor HLA-B8 positive lymphocytes removed any antibody activity. Using one-dimensional isoelectric focusing, unique bands have been characterized for over 30 Caucasian allotypes, including HLA-B7 and HLA-B27. Lymphocytes from two families carrying the HLA-Bw73 antigen were analyzed by isoelectric focusing. These two families show that HLA-Bw73 has a band migrating in the gel very close to HLA-B35 but distant from the cross-reactive group HLA-B7. These studies indicate that HLA antigens which share common epitopes (including those recently characterized, such as HLA-Bw73 and HLA-B7), can be distinguished serologically and by isoelectric focusing.     

HLA-B27: portraying immunodominant viral epitopes

Although the crystal structure of HLA-B27 has been known for a long time, only recently have X-ray diffraction studies of this molecule in complex with individual peptides become available. The report of three such structures involving viral epitopes that are immunodominant in HLA-B27-restricted T cell responses against influenza, Epstein-Barr and HIV viruses significantly improves our perception of critical aspects of the immunological and pathogenetic roles of HLA-B27, including (1) the molecular basis of its peptide-binding specificity and how this is modulated by subtype polymorphism, (2) the relationship between the structural and the antigenic features of immunodominant viral epitopes, (3) the basis for long term non-progression to AIDS of HIV-infected HLA-B27+ individuals, and (4) the structural features of microbial peptides influencing NK receptor engagement. Here, I discuss the implications of this and related studies for the relevance of HLA-B27 in host defense and as a pathogenetic molecule in spondyloarthritis.     

Molecular mimicry: Any role in the pathogenesis of spondyloarthropathies?

Ankylosing spondylitis and reactive arthritis are seronegative spondyloarthropathies, which are strongly associated with HLA-B27. Despite intensive investigation, the basis for this association is not clear. However, in recent years one favored hypothesis to explain this linkage has been that of molecular mimicry, i.e., sharing of linear or conformational epitopes common to microbial antigens and host structures. During the past few years several examples of molecular mimicry between HLA-B27 and microbial antigens have been described. Heat shock proteins, among others, have been considered as target candidates for autoimmune phenomena, because of the high degree of homology between bacterial and mammalian species. Reactive arthritis triggered byYersinia orSalmonella provides a unique model for studying the pathogenetic mechanisms underlying human inflammatory joint diseases in general, because the arthritogenic microbes are known and well-characterized. We have described two bacterial proteins that share amino acid homology with HLA-B27, namely YadA (Yersinia adhesin) and OmpH, outer surface proteins ofYersinia andSalmonella, respectively. Notably, the area of identity of these amino acid sequences is located in the same place on the HLA-B27 molecule as a hexapeptide identical betweenKlebsiella nitrogenase and HLA-B27, and a pentapeptide shared by aShigella flexneri protein and HLA-B27. We have investigated immune responses to a panel of synthetic peptides based on the HLA-B27-homologous portions of pathogen-specific antigens in patients with reactive arthritis and ankylosing spondylitis. One third of the patients have antibodies to the synthetic peptides. However, instead of recognizing the HLA-B27-homologous portion, the antibodies are directed against the flanking sequences of the synthetic peptides. The concept of the role of molecular mimicry between HLA-B27 and microbial antigens in the pathogenesis of spondyloarthropathies is discussed, with a conclusion that no convincing evidence for its significance exists at the present.     

HLA Antigens Associated with Properdin Factor B Allotype BfF1

Linkage disequilibrium has been described between HLA-B antigens and allotypes of properdin factor B (Bf). The association between HLA-B and DR antigens and the rare allotype BfF1 was investigated. In 27 HLA-A, B and DR typed individuals only one person was found who was DR3 negative but five who were B18 negative. Family studies showed that in nine cases B18, BfF1 and DR3 segregated as a haplotype; in another family which was B18 negative, BfF1 and DR3 segregated together. It is infered that the Bf locus is more strongly associated with HLA-DR than with HLA-B.     

HLA-B27 and ankylosing spondylitis in the Mexican Mestizo population

Two previous surveys of ankylosing spondylitis (AS) in Mexican Mestizos found HLA-B27 frequencies of 68.6% and 78% and a relative risk (RR) of 37.05 and 120.88, respectively. We examined an additional group of Mexican Mestizos with AS and found an HLA-B27 frequency of 80.77% and a RR of 99.24. Our results are statistically comparable to the previous studies, and they suggest that the Mexican Mestizo is similar to the Spaniard in regards to AS and HLA-B27 association.     

Microbial antigens mediate HLA-B27 diseases via TLRs

HLA-B27 positive individuals are predisposed to reactive arthritis developing 1–3 weeks after urogenital and gastrointestinal infections. Also ankylosing spondylitis (AS) associates strongly to HLA-B27, but no specific infection, Klebsiella pneumoniae excluded, has been linked to it. Before the discovery of its HLA-B27 association there were many reports suggesting a link between chronic prostatitis in men or pelvic inflammatory disease in women and AS. They have since been forgotten although HLA-B27 did not help to understand, why this disease has an axial and ascending nature. It is proposed that the urogenital organs form a source of damage (or danger)-associated molecular patterns (DAMPs), either exogenous pathogen-associated molecular patterns (PAMPs) from microbes or endogenous alarmins, such as uric acid, released from necrotic cells or urate deposits. DAMPs are slowly seeded from low-down upwards via the pelvic and spinal lymphatic pathways. They reach Toll-like receptors (TLRs) in their target mesenchymal stem cells, which are stimulated to ectopic enchondral bone formation leading to syndesmophytes and bamboo spine. At the same time inflammatory cytokines induce secondary osteoporosis of the spine. This new paradigm places microbes, HLA-B27 and TLRs in the pathogenic centre stage, but without pinpointing any (one) specific pathogen; instead, shared microbial patterns are indicated.     

Genetics and genomics of ankylosing spondylitis

Summary: Ankylosing spondylitis (AS) is a common, highly heritable arthropathy, the pathogenesis of which is poorly understood. The mechanism by which the main gene for the disease, HLA-B27, leads to AS is unknown. Genetic and genomic studies have demonstrated involvement of the interleukin-23 (IL-23) signaling pathway in AS, a finding which has stimulated much new research into the disease and has led to therapeutic trials. Several other genes and genetic regions, including further major histocompatibility complex (MHC) and non-MHC loci, have been shown to be involved in the disease, but it is not clear yet how they actually induce the condition. These findings have shown that there is a strong genetic overlap between AS and Crohn’s disease in particular, although there are also major differences in the genes involved in the two conditions, presumably explaining their different presentations. Genomic and proteomic studies are in an early phase but have potential both as diagnostic/prognostic tools and as a further hypothesis-free tool to investigate AS pathogenesis. Given the slow progress in studying the mechanism of association of HLA-B27 with AS, these may prove to be more fruitful approaches to investigating the pathogenesis of the disease.     

强直性脊柱炎遗传学研究进展

强直性脊柱炎是一种具有高度遗传倾向的血清阴性脊柱关节病。既往的研究主要报道HLA-B27基因与AS的强相关性,但近年来大量的研究提示除HLA-B27基因外,可能还存在其他的MHC类和非MHC类基因与AS相关。本文综述了强直性脊柱炎的遗传学因素的研究进展,为其诊断、预防和治疗提供新的思路。     

What is the role of HLA-B27 in spondyloarthropathies?

HLA-B27 (Human Leukocyte Antigen-B27) accounts approximately for the one third of the overall genetic susceptibility to spondylorthropathies (SpAs). Up to 70 HLA-B27 subtypes have been reported all over the world with a decreasing north-south gradient of its frequency, which is reverse to that of endemic malaria. In an attempt to explain the possible role of HLA-B27 in SpAs pathogenesis, several theories have been suggested [1. Arthritogenic peptide, 2. Misfolding, 3. Cell surface HLA-B27 homodimers, 4. β2m (β2-microglobulin) deposition, 5. β2m-free/peptide free heavy chains of HLA-I, 6. Enhanced survival of some microbes in HLA-B27 cells, 7. ERAP1/ERAP2 (endoplasmic reticulum aminopeptidases 1 and 2) and Tapasin function, 8. β2m over-expression] each of which contributes up to a point to our understanding of HLA-B27 subtypes' role in SpAs manifestation. However, reviewing all the suggested hypotheses it seems logical to pass from a puzzle of distinct hypotheses to a global theory. This review summarizes the current knowledge of HLA-B27 aiming to understand its potential use in clinical practice of SpAs diagnosis and to direct its future studies.     

Is there a common pathogenesis in aggressive periodontitis & ankylosing spondylitis in HLA-B27 patient?

HLA-B27 is having strong association to ankylosing spondylitis (AS) and other inflammatory diseases collectively known as seronegative spondyloarthropathy. In literature, although the evidence for association between AS and periodontitis as well as AS and HLA-B27 are there but the association of aggressive periodontitis in HLA-B27 positive patient with AS are not there. We hypothesize that there may be a common pathogenesis in aggressive periodontitis and ankylosing spondylitis in HLA-B27 patient. A 27-years-old female presented with the features of generalized aggressive periodontitis and difficulty in walking. On complete medical examination, ankylosing spondylitis was diagnosed with further positive HLA-B27 phenotype and negative rheumatic factor. This report may open up a new link to explore in the pathogenesis of aggressive periodontitis.     

HLA-B*27 subtypes in Northern and Northeastern Thais, Karens, and Bamars determined by a high-resolution PCR-SSP technique

Human leukocyte antigens (HLA), class I, are a group of antigens expressed on most nucleated cell surfaces. They transport endogenous peptides to the cell surface for recognition by T-cell receptors. Their functions are involved in immune responses. Many diseases are associated with HLA alleles, especially HLA-B*27 that is strongly associated with ankylosing spondylitis (AS). HLA-B*27 consists of 42 subtypes. Different subtypes of HLA-B*27 were reported in different ethnic groups of AS patients. In this study, a high-resolution polymerase chain reaction–sequence-specific primer technique has been developed to define all the HLA-B*27 subtypes with a total of 29 primer mixtures. Two of the primer mixes were used to detect the HLA-B*27 -specific group, and 27 primer mixes were used to identify 42 subtypes ( B*2701–B*2721 and B*2723–B*27 43). The HLA-B*27 -group-specific primers have been tested in unrelated healthy subjects; 846 Northeastern Thais (NET), 334 Northern Thais (NT), 264 Karens, and 310 Bamars. Sixty-three NET (phenotype frequency, PF = 7.4%), 24 NT (PF = 7.1%), 5 Karens (PF = 1.8%), and 12 Bamars (PF = 3.9%) were positive for HLA-B*27 . Only B*2704 was found in Karens, whereas B*2704 , B*2705/37/39 , B*2706 , and B*2707 were found in NET and NT. In Bamars, B*2704 , B*2705/37/39 , B*2706 , and B*2725 were found. The distribution of HLA-B*27 subtypes was compared with other studies in Asian and Caucasian populations. Significant differences of the distribution of HLA-B*27 subtypes were found in most of the populations. This study established a simple technology for HLA-B*27 subtyping and provided basic information for anthropology and further studies in disease associations.     

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.     

HLA-B*27 typing by sequence specific amplification without DNA extraction.

HLA-B27 appears to play a direct role in the pathogenesis of ankylosing spondylitis and almost all patients with this disease have HLA-B27. Therefore, a diagnosis of ankylosing spondylitis can virtually be excluded in the absence of HLA-B27. Many techniques have been used for HLA-B*27 typing. Of these, molecular methods are the most sensitive and specific but require extracted DNA as the testing material. A technique where HLA-B*27 is amplified directly from whole blood using sequence specific primers has been developed. This technique uses small sample volumes, is not restricted by choice of anticoagulant or sample age up to at least six weeks, and can be applied to other clinical polymerase chain reaction based procedures.     

HLA-B*27 typing by sequence specific amplification without DNA extraction.

HLA-B27 appears to play a direct role in the pathogenesis of ankylosing spondylitis and almost all patients with this disease have HLA-B27. Therefore, a diagnosis of ankylosing spondylitis can virtually be excluded in the absence of HLA-B27. Many techniques have been used for HLA-B*27 typing. Of these, molecular methods are the most sensitive and specific but require extracted DNA as the testing material. A technique where HLA-B*27 is amplified directly from whole blood using sequence specific primers has been developed. This technique uses small sample volumes, is not restricted by choice of anticoagulant or sample age up to at least six weeks, and can be applied to other clinical polymerase chain reaction based procedures.     

Specificity of anti-HLA-B27 cytotoxic T lymphocytes

Sub-types of HLA-B27 were detected by cytotoxic T lymphocytes (CTL) generated between HLA-A, -B- and -C-identical B27-positive individuals. We now report the specificity of six independent CTL's generated by mixed lymphocyte culture (MLC) of HLA-A, -B and -C serologically identical B27-positive responder and stimulator cells. Three CTL's recognize one sub-type, and three the other. The combined reactivity of all CTL's allows unequivocal "typing" of B27-positive cells for the two different sub-types B27K and B27W. The specificity of two CTL's was analysed by cold-target inhibition. The results indicate that (1) no further sub-types of HLA-B27 can be detected by the CTL's raised in these combinations; (2) the majority of the CTL's is directed against the B27 antigens; and (3) "extra reactions" on B27-negative cells are caused by a subset(s) of CTL's recognizing unknown antigens shared between stimulator and target cells. CTL's raised by stimulation of HLA-B27-negative responder cells with B27-positive cells of either sub-type lysed all B27-positive target cells indiscriminately. In cold-target inhibition, however, B27-positive cells, carrying the sub-type of B27 different from that of the stimulator, could not inhibit the lysis of cells bearing the stimulator sub-type of B27. This indicates the activation, in B27-negative responders, of at least two different groups of CTL clones, one directed against shared determinants of HLA-B27, and one against the HLA-B27 sub-type. Heterogeneity of the HLA-B27 antigen may have implications for studies on the well-known association between this antigen and various diseases.