Identification of HLA-B27-restricted peptides from the Chlamydia trachomatis proteome with possible relevance to HLA-B27-associated diseases

Targeted therapies for uveitis in spondyloarthritis: A narrative review

Spondyloarthritis (SpA) encompasses a group of chronic inflammatory disorders of the joints frequently associated with uveitis in almost a quarter of cases. SpA-related uveitis typically affects the eye anterior chamber with sudden onset, causing pain, redness, photophobia, and blurred vision. Ophthalmologists will describe an acute anterior unilateral uveitis. Most patients present with episodic acute anterior non-granulomatous uveitis and retain excellent visual acuity. However, systemic treatments are recommended in the event of frequent relapses (2-3/year) or in rare cases of sight-threatening with ocular complications. The improved understanding of the pathogenesis of SpA has led to the management of this disease by biologics. Here, we review the main data regarding the opportunity to target specific components in inflammatory pathways for the treatment of SpA-related uveitis. These therapies are recommended for long-term control when uveitis relapses occur too frequently despite conventional systemic treatments. Significant benefits have been obtained with the tumor necrosis factor-α inhibitors (TNFis), particularly infliximab and adalimumab. Paradoxically, a high number of uveitis occurrences have been shown on etanercept. Mixed results have been demonstrated with interleukin-17 antagonists (secukinumab) and interleukin-12/interleukin-23 antagonists (ustekinumab) in cases of failure of TNFis. JAK inhibitors seem to be a valuable class of medications for these patients in the future. Although SpA-related uveitis is typically managed with conventional local and/or systemic treatments, these biological/targeted therapies may provide avenues to control both the underlying SpA and uveitis manifestations. Thus, a close collaboration between patients, rheumatologists, internists, and ophthalmologists is needed to optimally manage ocular inflammation in SpA.

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

BACKGROUND

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

OBJECTIVE

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

MATERIAL AND METHODS

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

RESULTS

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

DISCUSSION

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

Analysis of Peripapillary Retinal Nerve Fiber Layer Thickness in Acute Anterior Uveitis among Children with HLA-B27-Positive Juvenile Idiopathic Arthritis

PURPOSE

The aim of this study was to evaluate changes in the thickness of the peripapillary retinal nerve fiber layer (pRNFL) in children with a diagnosis of juvenile idiopathic arthritis (JIA) who were positive for human leukocyte antigen (HLA)-B27, treated for the first episode of unilateral acute anterior uveitis (AAU).

MATERIALS AND METHODS

This retrospective study included 41 children (aged 5 to 14 years; mean age 8.32 ± 2.4 years) with HLA-B27 positivity and unilateral JIA-AAU, and 40 healthy children. Optical coherence tomography (OCT) imaging was performed during active inflammation and subsequent noninflammatory phases (6 months after the resolution of inflammatory symptoms in the anterior segment of the eye).

RESULTS

There was a marked difference in mean pRNFL thickness between eyes with AU in the active phase, unaffected fellow eyes and the control group (110.22 ± 5.95 μm, 102.39 ± 4.39 μm and 95.83 ± 8.84 μm, respectively; p < 0.001). The thickness of pRNFL in eyes with AU in the active phase in all sectors was greater compared to unaffected fellow eyes (p < 0.001) and normal eyes (p < 0.001). In addition, it was demonstrated that pRNFL thickness was significantly increased in the superior and temporal sectors in the unaffected fellow eyes compared to the control group (128.73 ± 13.16 μm vs. 121.48 ± 13.35 μm and 71.37 ± 4.02 μm vs. 64.98 ± 9.12 μm, respectively). Even during the inactive phase, eyes with AU, compared to the healthy control group, had significantly greater pRNFL thickness in the inferior sector (129.78 ± 11.98 μm vs. 122.3 ± 14.59 μm; p = 0.018), along with the temporal sector (70.88 ± 5.48 μm vs. 64.98 ± 9.12 μm; p = 0.001).

CONCLUSIONS

An increase in pRNFL thickness in children with unilateral JIA-AAU who were positive for HLA-B27 antigen can be observed in both eyes compared to healthy controls, and this change may persist even after the inflammatory symptoms have resolved. Measurements of pRNFL thickness resulting from JIA-AU-associated glaucoma should be performed during quiescent periods to avoid subclinical changes in pRNFL thickness caused by inflammation. However, when reviewing the results, it should be noted that changes in pRNFL parameters may be present despite evidence of a resolution of inflammation.

Four Faces of Cell-Surface HLA Class-I: Their Antigenic and Immunogenic Divergence Generating Novel Targets for Vaccines

Leukocyte cell-surface HLA-I molecules, involved in antigen presentation of peptides to CD8+ T-cells, consist of a heavy chain (HC) non-covalently linked to β2-microglobulin (β2m) (Face-1). The HC amino acid composition varies across all six isoforms of HLA-I, while that of β2m remains the same. Each HLA-allele differs in one or more amino acid sequences on the HC α1 and α2 helices, while several sequences among the three helices are conserved. HCs without β2m (Face-2) are also observed on human cells activated by malignancy, viral transformation, and cytokine or chemokine-mediated inflammation. In the absence of β2m, the monomeric Face-2 exposes immunogenic cryptic sequences on these cells as confirmed by HLA-I monoclonal antibodies (LA45, L31, TFL-006, and TFL-007). Furthermore, such exposure enables dimerization between two Face-2 molecules by SH-linkage, salt linkage, H-bonding, and van der Waal forces. In HLA-B27, the linkage between two heavy chains with cysteines at position of 67 of the amino acid residues was documented. Similarly, several alleles of HLA-A, B, C, E, F and G express cysteine at 67, 101, and 164, and additionally, HLA-G expresses cysteine at position 42. Thus, the monomeric HC (Face-2) can dimerize with another HC of its own allele, as homodimers (Face-3), or with a different HC-allele, as heterodimers (Face-4). The presence of Face-4 is well documented in HLA-F. The post-translational HLA-variants devoid of β2m may expose several cryptic linear and non-linear conformationally altered sequences to generate novel epitopes. The objective of this review, while unequivocally confirming the post-translational variants of HLA-I, is to highlight the scientific and clinical importance of the four faces of HLA and to prompt further research to elucidate their functions and their interaction with non-HLA molecules during inflammation, infection, malignancy and transplantation. Indeed, these HLA faces may constitute novel targets for passive and active specific immunotherapy and vaccines.

Immunopathophysiology and clinical impact of uveitis in inflammatory rheumatic diseases: An update

BACKGROUND

Uveitis is one of the most frequent ophthalmologic manifestations in rheumatology. Uveal inflammation can underlie a systemic inflammatory rheumatic disease (SIRD) in approximately 30% of cases with a significant burden on the quality of life since it represents a cause of blindness in up to 20% of cases in Western countries.

METHODS

In this review, we provide a comprehensive overview of the pathophysiology of uveitis associated with SIRDs. According to our literature survey on the epidemiology of uveitis among SIRDs, spondyloarthritides, Behçet's disease and sarcoidosis get the major impact.

RESULTS

In Behçet's uveitis, the key players are highly polarized Th1 and Th17 lymphocytes, natural killer T cells and γδ T cells. All contribute to a great destructive inflammatory environment with the most serious visual damage resulting from the involvement of the posterior segment of the eye. In contrast, spondyloarthritides-related uveitis derives from a complex interaction between genetic background and extra-ocular inflammatory mediators originating from enthesitis, arthritis, psoriatic lesions and microbiome pro-inflammatory alterations. In such conditions, the immune infiltration of CD4+ T cells, Th17 and natural killer cells along with pro-inflammatory cytokines, TNF-α among all, leads to intraocular inflammation. Lastly, granuloma formation represents the primary hallmark lesion in sarcoid uveitis. This suggests a profound link between the innate system that mainly recruits activated macrophages and adaptive system involving by Th1, Th17 and Th17.1 cells.

CONCLUSIONS

Awareness among rheumatologists of a potential severe ocular involvement generates new insights into targeted therapeutic approaches and personalized treatments for each patient.

Ankylosing spondylitis: an autoimmune or autoinflammatory disease?

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

Recent Developments in HLA B27 Anterior Uveitis

There has been steady progress in understanding the pathogenesis, clinical features, and effective treatment of acute anterior uveitis (AU) over the past 5 years. Large gene wide association studies have confirmed that AU is a polygenic disease, with overlaps with the seronegative arthropathies and inflammatory bowel diseases, associations that have been repeatedly confirmed in clinical studies. The role of the microbiome in AU has received increased research attention, with recent evidence indicating that human leukocyte antigen B27 (HLA B27) may influence the composition of the gut microbiome in experimental animals. Extensive clinical investigations have confirmed the typical features of acute AU (AAU) and its response to topical, regional and systemic immunosuppressive treatment. Increased understanding of the role of cytokines has resulted in studies confirming the value of anti-cytokine therapy [anti-tumor necrosis factor (anti-TNF) and interleukin 6 (IL-6) therapy] in severe and recurrent cases of AAU, particularly in subjects with an associated spondyloarthopathy (SpA) and in juvenile idiopathic arthritis (JIA)-associated AAU.

Understanding the Pathogenesis of Spondyloarthritis

Spondyloarthritis comprises a group of inflammatory diseases of the joints and spine, with various clinical manifestations. The group includes ankylosing spondylitis, reactive arthritis, psoriatic arthritis, arthritis associated with inflammatory bowel disease, and undifferentiated spondyloarthritis. The exact etiology and pathogenesis of spondyloarthritis are still unknown, but five hypotheses explaining the pathogenesis exist. These hypotheses suggest that spondyloarthritis is caused by arthritogenic peptides, an unfolded protein response, HLA-B*27 homodimer formation, malfunctioning endoplasmic reticulum aminopeptidases, and, last but not least, gut inflammation and dysbiosis. Here we discuss the five hypotheses and the evidence supporting each. In all of these hypotheses, HLA-B*27 plays a central role. It is likely that a combination of these hypotheses, with HLA-B*27 taking center stage, will eventually explain the development of spondyloarthritis in predisposed individuals.

Uveitis in spondyloarthritis

Uveitis is the most frequent extra-articular manifestation of axial spondyloarthritis (SpA), occurring in up to one-third of the patients. In the majority of patients, uveitis is acute, anterior and unilateral and presents with photosensitivity, sudden onset of pain and blurred vision. Topical steroids are an effective treatment; however, recurrent or refractory cases may need conventional disease-modifying antirheumatic drugs or biological treatment with monoclonal tumor necrosis factor (TNF) inhibitors, thus also influencing treatment strategy of the underlying SpA. Though the exact pathogenesis of SpA and uveitis remains unknown, both seem to result from the interaction of a specific, mostly shared genetical background (among other HLA-B27 positivity), external influences such as microbiome, bacterial infection or mechanical stress and activation of the immune system resulting in inflammation. Up to 40% of patients presenting with acute anterior uveitis (AAU) have an undiagnosed SpA. Therefore, an effective referral strategy for AAU patients is needed to shorten the diagnostic delay of SpA and enable an early effective treatment. Further, the risk for ophthalmological manifestations increases with the disease duration in SpA; and patients presenting with ocular symptoms should be referred to an ophthalmologist. Thus, a close collaboration between patient, rheumatologist and ophthalmologist is needed to optimally manage ocular inflammation in SpA.

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.

HLA-B27 Anterior Uveitis: Immunology and Immunopathology

Acute anterior uveitis (AAU) is the commonest type of uveitis and HLA-B27 AAU is the most frequently recognized type of acute anterior uveitis and anterior uveitis overall. Recent evidence indicates that acute anterior uveitis is a heterogenous disease, is polygenic and is frequently associated with the spondyloarthropathies (SpA). Studies of patients with AAU and animal models of disease indicate a role for innate immunity, the IL-23 cytokine pathway and exogenous factors, in the pathogenesis of both SpA and acute anterior uveitis. Recently described genetic associations cluster around immunologic pathways, including the IL-17 and IL-23 pathways, antigen processing and presentation, and lymphocyte development and activation. Patients with ankylosing spondylitis (AS) and AAU share other genetic markers, such as ERAP-1, which show strong evidence of gene-gene interaction and point to new mechanisms of disease pathogenesis. These observations have major implications for understanding the pathogenesis of HLA-B27 diseases, such as AAU, and may lead to the development of more specific therapy for AAU. Received 6 January 2016; revised 6 February 2016; accepted 18 February 2016; published online 31 May 2016.

Recombinant Salmonella typhimurium outer membrane protein A is recognized by synovial fluid CD8 cells and stimulates synovial fluid mononuclear cells to produce interleukin (IL)-17/IL-23 in patients with reactive arthritis and undifferentiated spondyloarthropathy

In developing countries, one-third of patients with reactive arthritis (ReA) and undifferentiated spondyloarthropathy (uSpA) are triggered by Salmonella typhimurium. Synovial fluid mononuclear cells (SFMCs) of patients with ReA and uSpA proliferate to low molecular weight fractions (lmwf) of outer membrane proteins (Omp) of S. typhimurium. To characterize further the immunity of Omp of Salmonella, cellular immune response to two recombinant proteins of lmwf, OmpA and OmpD of S. typhimurium (rOmpA/D-sal) was assessed in 30 patients with ReA/uSpA. Using flow cytometry, 17 of 30 patients' SF CD8(+) T cells showed significant intracellular interferon (IFN)-γ to Omp crude lysate of S. typhimurium. Of these 17, 11 showed significantly more CD8(+) CD69(+) IFN-γ T cells to rOmpA-sal, whereas only four showed reactivity to rOmpD-sal. The mean stimulation index was significantly greater in rOmpA-sal than rOmpD-sal [3·0 (1·5-6·5) versus 1·5 (1·0-2·75), P < 0·005]. Similarly, using enzyme-linked immunospot (ELISPOT) in these 17 patients, the mean spots of IFN-γ-producing SFMCs were significantly greater in rOmpA-sal than rOmpD-sal [44·9 (3·5-130·7) versus 19·25 (6-41), P < 0·05]. SFMCs stimulated by rOmpA-sal produced significantly more proinflammatory cytokines than rOmpD-sal: IFN-γ [1·44 (0·39-20·42) versus 0·72 (0·048-9·15) ng/ml, P < 0·05], interleukin (IL)-17 [28·60 (6·15-510·86) versus 11·84 (6·83-252·62) pg/ml, P < 0·05], IL-23 [70·19 (15-1161·16) versus 28·25 (> 15-241·52) pg/ml, P < 0·05] and IL-6 [59·78 (2·03-273·36) versus 10·17 (0·004-190·19) ng/ml, P < 0·05]. The rOmpA-sal-specific CD8(+) T cell response correlated with duration of current synovitis (r = 0·53, P < 0·05). Thus, OmpA of S. typhimurium is a target of SF CD8(+) T cells and drives SFMC to produce increased cytokines of the IL-17/IL-23 axis which contribute to the pathogenesis of Salmonella-triggered ReA.

Enhanced Direct Major Histocompatibility Complex Class I Self-Antigen Presentation Induced by Chlamydia Infection

The direct major histocompatibility complex (MHC) class I antigen presentation pathway ensures intracellular peptides are displayed at the cellular surface for recognition of infected or transformed cells by CD8(+) cytotoxic T lymphocytes. Chlamydia spp. are obligate intracellular bacteria and, as such, should be targeted by CD8(+) T cells. It is likely that Chlamydia spp. have evolved mechanisms to avoid the CD8(+) killer T cell responses by interfering with MHC class I antigen presentation. Using a model system of self-peptide presentation which allows for posttranslational control of the model protein's stability, we tested the ability of various Chlamydia species to alter direct MHC class I antigen presentation. Infection of the JY lymphoblastoid cell line limited the accumulation of a model host protein and increased presentation of the model-protein-derived peptides. Enhanced self-peptide presentation was detected only when presentation was restricted to defective ribosomal products, or DRiPs, and total MHC class I levels remained unaltered. Skewed antigen presentation was dependent on a bacterial synthesized component, as evidenced by reversal of the observed phenotype upon preventing bacterial transcription, translation, and the inhibition of bacterial lipooligosaccharide synthesis. These data suggest that Chlamydia spp. have evolved to alter the host antigen presentation machinery to favor presentation of defective and rapidly degraded forms of self-antigen, possibly as a mechanism to diminish the presentation of peptides derived from bacterial proteins.

Role of genetics in infection-associated arthritis

Genetic discoveries in arthritis and their associated biological pathways spanning the innate and adaptive immune system demonstrate the strong association between susceptibility to arthritis and control of exogenous organisms. The canonical theory of the aetiology of immune-mediated arthritis and other immune-mediated diseases is that the introduction of exogenous antigenic stimuli to a genetically susceptible host sets up the environment for an abnormal immune response manifesting as disease. A disruption in host-microbe homeostasis driven by disease-associated genetic variants could ultimately provide the source of exogenous antigen triggering disease development. We discuss genetic variants impacting the innate and adaptive arms of the immune system and their relationship to microbial control and arthritic disease. We go on to consider the evidence for a relationship between HLA-B27, infection and arthritis, and then emerging evidence for an interaction between microbiota and rheumatoid arthritis.

Mucosal immune responses to microbiota in the development of autoimmune disease

The etiology of most systemic autoimmune diseases remains unknown. There is often a preclinical period of systemic autoimmunity prior to the onset of clinically classifiable disease; established and emerging data suggest that dysregulated immune interactions with commensal microbiota may play a role in the initial generation of autoimmunity in this preclinical period. This article reviews potential mechanisms by which alterations of healthy microbiota may induce autoimmunity as well as mucosal microbial associations with autoimmune diseases. If mucosal microbiota lead to the development of autoimmunity, these mucosal sites, microorganisms, and immunologic mechanisms can be targeted to prevent the onset of systemic autoimmune disease.

Genetics, environment, and gene-environment interactions in the development of systemic rheumatic diseases

Rheumatic diseases offer distinct challenges to researchers because of heterogeneity in disease phenotypes, low disease incidence, and geographic variation in genetic and environmental factors. Emerging research areas, including epigenetics, metabolomics, and the microbiome, may provide additional links between genetic and environmental risk factors in the pathogenesis of rheumatic disease. This article reviews the methods used to establish genetic and environmental risk factors and studies gene-environment interactions in rheumatic diseases, and provides specific examples of successes and challenges in identifying gene-environment interactions in rheumatoid arthritis, systemic lupus erythematosus, and ankylosing spondylitis. Emerging research strategies and future challenges are discussed.

Endoplasmic reticulum aminopeptidase-1 alleles associated with increased risk of ankylosing spondylitis reduce HLA-B27 mediated presentation of multiple antigens

Ankylosing spondylitis (AS) is a chronic systemic arthritic disease that leads to significant disability and loss of quality of life in the ∼0.5% of the worldwide human population it affects. There is currently no cure for AS and mechanisms underlying its pathogenesis remain unclear. AS is highly genetic, with over 70% of the genetic risk being associated with the presence of HLA-B27 and endoplasmic reticulum aminopeptidase-1 (ERAP1) alleles. Furthermore, gene-gene interactions between HLA-B27 and ERAP1 AS risk alleles have recently been confirmed. Here, we demonstrate that various ERAP1 alleles can differentially mediate surface expression of antigens presented by HLA-B27 on human cells. Specifically, for all peptides tested, we found that an ERAP1 variant containing high AS risk SNPs reduced the amount of the peptide presented by HLA-B27, relative to low AS risk ERAP1 variants. These results were further validated using peptide catalysis assays in vitro, suggesting that high AS risk alleles have an enhanced catalytic activity that more rapidly destroys many HLA-B27-destined peptides, a result that correlated with decreased HLA-B27 presentation of the same peptides. These findings suggest that one mechanism underlying AS pathogenesis may involve an altered ability for AS patients harboring both HLA-B27 and high AS risk ERAP1 alleles to correctly display a variety of peptides to the adaptive arm of the immune system, potentially exposing such individuals to higher AS risk due to abnormal display of pathogen or self-derived peptides by the adaptive immune system.

Novel HLA-B27-restricted epitopes from Chlamydia trachomatis generated upon endogenous processing of bacterial proteins suggest a role of molecular mimicry in reactive arthritis

Reactive arthritis (ReA) is an HLA-B27-associated spondyloarthropathy that is triggered by diverse bacteria, including Chlamydia trachomatis, a frequent intracellular parasite. HLA-B27-restricted T-cell responses are elicited against this bacterium in ReA patients, but their pathogenetic significance, autoimmune potential, and relevant epitopes are unknown. High resolution and sensitivity mass spectrometry was used to identify HLA-B27 ligands endogenously processed and presented by HLA-B27 from three chlamydial proteins for which T-cell epitopes were predicted. Fusion protein constructs of ClpC, Na(+)-translocating NADH-quinone reductase subunit A, and DNA primase were expressed in HLA-B27(+) cells, and their HLA-B27-bound peptidomes were searched for endogenous bacterial ligands. A non-predicted peptide, distinct from the predicted T-cell epitope, was identified from ClpC. A peptide recognized by T-cells in vitro, NQRA(330-338), was detected from the reductase subunit. This is the second HLA-B27-restricted T-cell epitope from C. trachomatis with relevance in ReA demonstrated to be processed and presented in live cells. A novel peptide from the DNA primase, DNAP(211-223), was also found. This was a larger variant of a known epitope and was highly homologous to a self-derived natural ligand of HLA-B27. All three bacterial peptides showed high homology with human sequences containing the binding motif of HLA-B27. Molecular dynamics simulations further showed a striking conformational similarity between DNAP(211-223) and its homologous and much more flexible human-derived HLA-B27 ligand. The results suggest that molecular mimicry between HLA-B27-restricted bacterial and self-derived epitopes is frequent and may play a role in ReA.

Protein damage, repair and proteolysis

Proteins are continuously affected by various intrinsic and extrinsic factors. Damaged proteins influence several intracellular pathways and result in different disorders and diseases. Aggregation of damaged proteins depends on the balance between their generation and their reversal or elimination by protein repair systems and degradation, respectively. With regard to protein repair, only few repair mechanisms have been evidenced including the reduction of methionine sulfoxide residues by the methionine sulfoxide reductases, the conversion of isoaspartyl residues to L-aspartate by L-isoaspartate methyl transferase and deglycation by phosphorylation of protein-bound fructosamine by fructosamine-3-kinase. Protein degradation is orchestrated by two major proteolytic systems, namely the lysosome and the proteasome. Alteration of the function for both systems has been involved in all aspects of cellular metabolic networks linked to either normal or pathological processes. Given the importance of protein repair and degradation, great effort has recently been made regarding the modulation of these systems in various physiological conditions such as aging, as well as in diseases. Genetic modulation has produced promising results in the area of protein repair enzymes but there are not yet any identified potent inhibitors, and, to our knowledge, only one activating compound has been reported so far. In contrast, different drugs as well as natural compounds that interfere with proteolysis have been identified and/or developed resulting in homeostatic maintenance and/or the delay of disease progression.

The link between HLA-B27 and SpA--new ideas on an old problem

The strong association of the HLA-B27 with AS was first discovered independently by groups in London and California in 1972 and has recently been confirmed beyond reasonable doubt by fine mapping in the latest and most sophisticated genome-wide association study (GWAS) published this July. Yet, despite nearly four decades of extensive research, the exact role that HLA-B27 plays in pathogenesis remains unknown. However, we believe that recent developments in three fields have allowed us to view this conundrum in a new light and to propose coherent theories of disease pathogenesis. These areas are as follows: (i) GWASs, (ii) studies of B27 biology and (iii) lessons from biologic therapies. In this review we will discuss these recent advances before discussing the current models of AS pathogenesis under investigation.

CD154, a marker of antigen-specific stimulation of CD4 T cells, is associated with response to treatment in patients with chronic HCV infection

CD4 T-cell function is crucial for the eradication of HCV, and insufficient function is observed in chronic carriers. The monitoring of T-cell responses is complicated by the scarcity of antigen-specific T cells and the relative inefficiency of virus-specific T cells to produce effector cytokines. CD154 is a marker of activation expressed on T cells induced through their T-cell receptor. We analysed CD4 T-cell responses in 72 patients with chronic or resolved HCV infection (23 treatment naïve, 49 treatment experienced, including 16 who had achieved a sustained response). In an additional prospective protocol, 20 of the chronically infected patients were analysed before and after 8-12 weeks of combination therapy with peg-interferon-α and ribavirin. T-cell responses were measured by detecting the expression of CD154 and Th1 cytokines after stimulation with recombinant HCV proteins and were correlated with pretreatment status and outcome of therapy. Broader T-cell responses were observed in treatment naïve than in experienced patients, while the outcome of a preceding therapy regimen did not influence T-cell responses. In the prospective cohort, an on-treatment increase in CD154+ cytokine- T-cell activity was associated with response to treatment, while a decrease was observed in nonresponders. Stronger antigen-independent activity of CD154+ cytokine+ T cells was observed in responders than in nonresponders. Our data indicate that CD154 as a marker of activation of CD4 T cells is a suitable tool for the analysis of T-cell responses in patients with HCV infection.

Ankylosing spondylitis monocytes show upregulation of proteins involved in inflammation and the ubiquitin proteasome pathway

OBJECTIVES

To determine if peripheral blood monocytes from patients with ankylosing spondylitis (AS) differed in protein expression compared to rheumatoid arthritis (RA) and healthy controls (HC).

METHODS

Monocyte protein expression was characterised by 2D gel electrophoresis and by label-free quantitative expression profiling, using nano-ultra performance liquid chromatography coupled to electrospray ionisation mass spectrometry (ESI-MS(E), where (E) refers to low/high collision energy switching). Data sets were analysed using the Waters expression profiling system and Ingenuity pathway analysis (IPA).

RESULTS

Two-dimensional gel electrophoresis showed upregulation of proteasomal constituents in AS monocytes, including the beta subunit of proteasome activator (PA)28. Monocyte expression profiling and IPA showed that significant changes in protein expression within the ubiquitin proteasome pathway (UPP) were restricted to AS monocytes. Statistically significant differences in protein expression involving the leucocyte extravasation, vascular endothelial growth factor, integrin and Toll-like receptor signalling pathways were seen in AS and RA monocytes compared to healthy controls. No evidence of upregulation of proteins involved in the endoplasmic reticulum stress response pathway was found in either AS or RA monocytes. Finally, the PA28 complex was shown to increase the generation of human leucocyte antigen (HLA)-B27 antigenic epitopes by the proteasome in vitro.

CONCLUSIONS

Our proteomic analyses support the hypothesis that monocytes play an important role in the pathogenesis of AS and RA, and further suggest a specific role in AS for the UPP. Quantitative proteomic expression profiling constitutes a powerful new tool for rheumatology research.

Two MHC class I molecules associated with elite control of immunodeficiency virus replication, Mamu-B*08 and HLA-B*2705, bind peptides with sequence similarity

HLA-B27- and -B57-positive HIV-infected humans have long been associated with control of HIV replication, implying that CD8(+) T cell responses contribute to control of viral replication. In a similar fashion, 50% of Mamu-B*08-positive Indian rhesus macaques control SIVmac239 replication and become elite controllers with chronic-phase viremia <1000 viral RNA copies/ml. Interestingly, Mamu-B*08-restricted SIV-derived epitopes appeared to match the peptide binding profile for HLA-B*2705 in humans. We therefore defined a detailed peptide-binding motif for Mamu-B*08 and investigated binding similarities between the macaque and human MHC class I molecules. Analysis of a panel of approximately 900 peptides revealed that despite substantial sequence differences between Mamu-B*08 and HLA-B*2705, the peptide-binding repertoires of these two MHC class I molecules share a remarkable degree of overlap. Detailed knowledge of the Mamu-B*08 peptide-binding motif enabled us to identify six additional novel Mamu-B*08-restricted SIV-specific CD8(+) T cell immune responses directed against epitopes in Gag, Vpr, and Env. All 13 Mamu-B*08-restricted epitopes contain an R at the position 2 primary anchor and 10 also possess either R or K at the N terminus. Such dibasic peptides are less prone to cellular degradation. This work highlights the relevance of the Mamu-B*08-positive SIV-infected Indian rhesus macaque as a model to examine elite control of immunodeficiency virus replication. The remarkable similarity of the peptide-binding motifs and repertoires for Mamu-B*08 and HLA-B*2705 suggests that the nature of the peptide bound by the MHC class I molecule may play an important role in control of immunodeficiency virus replication.

Endogenous processing and presentation of T-cell epitopes from Chlamydia trachomatis with relevance in HLA-B27-associated reactive arthritis

Chlamydia trachomatis triggers reactive arthritis, a spondyloarthropathy linked to the human major histocompatibility complex molecule HLA-B27, through an unknown mechanism that might involve molecular mimicry between chlamydial and self-derived HLA-B27 ligands. Chlamydia-specific CD8(+) T-cells are found in reactive arthritis patients, but the immunogenic epitopes are unknown. A previous screening of the chlamydial genome for putative HLA-B27 ligands predicted multiple peptides that were recognized in vitro by CD8(+) T-lymphocytes from patients. Here stable transfectants expressing bacterial fusion proteins in human cells were generated to investigate the endogenous processing and presentation by HLA-B27 of two such epitopes through comparative immunoproteomics of HLA-B27-bound peptide repertoires. A predicted T-cell epitope, from the CT610 gene product, was presented by HLA-B27. This is, to our knowledge, the first endogenously processed epitope involved in HLA-B27-restricted responses against C. trachomatis in reactive arthritis. A second predicted epitope, from the CT634 gene product, was not detected. Instead a non-predicted nonamer from the same protein was identified. Both bacterial peptides showed very high homology with human sequences containing the HLA-B27 binding motif. Thus, expression and intracellular processing of chlamydial proteins into human cells allowed us to identify two bacterial HLA-B27 ligands, including the first endogenous T-cell epitope from C. trachomatis involved in spondyloarthropathy. That human proteins contain sequences mimicking chlamydial T-cell epitopes suggests a basis for an autoimmune component of Chlamydia-induced HLA-B27-associated disease.

Role of CD8(+)T cells in the host response to Chlamydia

Chlamydia infections constitute a major public health problem. Although multiple arms of the immune system participate in the control of Chlamydia in infected hosts, T lymphocytes are essential. This review focuses on the roles that CD8(+)T cells may play in immunoprotection and immunopathology following recognition of Chlamydia-infected cells.

A review of pediatric uveitis: part II. Autoimmune diseases and treatment modalities

Uveitis is a manifestation of complex processes that can represent an infectious process or a dysfunction of the immune system that may have grave effects on the eye. Although infectious causes, once properly identified, may be successfully treated by addressing the inciting organism with recognized interventions, the immune-modulated chronic forms of uveitis often provide more complex challenges in management. Recent strides in understanding the inflammatory pathway and better bioengineering capabilities have resulted in some new modalities of treatment.

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.

Identification of human T cell targets recognized during Chlamydia trachomatis genital infection

The specificity of the human T cell response to Chlamydia trachomatis was investigated by stimulating lymphocytes from 16 case patients with urogenital infection by use of a size-fractionated serovar D lysate. Considerable heterogeneity was found among case patients, and multiple protein fractions were recognized in each specimen. Mass spectrometry analysis of the 30-42-kDa T cell-stimulating region identified 10 C. trachomatis proteins. Of these, CT583, CT603, and CT610 were identified as strong antigens that induced significantly higher levels of IFN- gamma secretion in PBMCs from case patients, compared with PBMCs from control donors. All 3 proteins were recognized in specimens from case patients infected with serovars D-F, the most prevalent serovars. McDonald-Kreitman and Tajima's D tests involving clinical isolates from the same samples showed evidence for frequency-dependent selection on ct583. We predict that CT583 is a target of acquired protective immune responses in humans.

Th1/Th17 cytokine profiles in patients with reactive arthritis/undifferentiated spondyloarthropathy

OBJECTIVE

Data on synovial fluid (SF) cytokine concentrations in patients with reactive arthritis (ReA) or undifferentiated spondyloarthropathy (uSpA) are limited and contradictory. We measured levels of several proinflammatory and immunoregulatory cytokines in SF and sera from patients with ReA/uSpA.

METHODS

Interleukin 17 (IL-17), IL-6, interferon-g (IFN-g), and IL-12p40, and immunoregulatory cytokines IL-10 and transforming growth factor-beta (TGF-beta) were assayed using ELISA in SF specimens from 51 patients with ReA/uSpA (ReA 21, uSpA 30), 40 patients with rheumatoid arthritis (RA), and 11 patients with osteoarthritis (OA). IL-17, IL-6, IFN-g, and IL-10 levels were also measured in paired sera samples from patients with ReA/uSpA.

RESULTS

SF concentrations of IL-17, IL-6, TGF-beta, and IFN-g were significantly higher in patients with ReA/uSpA as compared to RA patients (for IL-17 median 46 pg/ml, range < 7.8-220 vs median < 7.8 pg/ml, range < 7.8-136, p < 0.05; for TGF-beta median 4.2 ng/ml, range 1.32-12 vs median 3.01 ng/ml, range 0.6-9.6, p < 0.01; for IL-6 median 58 ng/ml, range 2-540 vs median 34.5 ng/ml, range < 0.009-220, p < 0.05; for IFN-g median 290 pg/ml, range < 9.4-1600 vs median 100 pg/ml, range < 9.4-490, p < 0.05). SF levels of IL-10 were comparable but the ratio of IFN-g/IL-10 was significantly higher in ReA/uSpA patients than RA patients (median 3.18, range 0.06-200 for ReA/uSpA vs median 1.0, range 0.03-26.9 for RA; p < 0.05). IL-17, IL-6, IL-10, and IFN-g SF levels were significantly higher than paired serum levels in ReA/uSpA patients (p < 0.01 for IL-17, p < 0.0001 for IL-6, p < 0.0001 for IL-10, and p < 0.001 for IFN-g).

CONCLUSION

Increased IL-17, IL-6, TGF-beta, and IFN-g concentrations in ReA/uSpA than in RA suggest that Th1 and Th17 cells could be the major agents in inflammation in ReA/uSpA.

Identification of endogenously presented peptides from Chlamydia trachomatis with high homology to human proteins and to a natural self-ligand of HLA-B27

A strategy for the stable expression of proteins, or large protein fragments, from Chlamydia trachomatis into human cells was designed to identify bacterial epitopes endogenously processed and presented by HLA-B27. Fusion protein constructs in which the green fluorescent protein gene was placed at the 5'-end of the bacterial DNA primase gene or some of its fragments were transfected into B*2705-C1R cells. One of these constructs, including residues 90-450 of the bacterial protein, was stably and efficiently expressed. Mass spectrometry-based comparative analysis of HLA-B27-bound peptide pools led to identification of three HLA-B27 ligands differentially presented in the transfectant cells. Sequencing of these peptides confirmed that they were derived from the bacterial DNA primase. One of them, spanning residues 211-221, showed 55% sequence identity with a known self-ligand of HLA-B27 derived from its own molecule. The other two bacterial ligands, P-(112-121) and P-(112-122), were derived from the same region and differed in length by one residue at the C terminus. Both peptides showed >50% identity with multiple human protein sequences that possessed the optimal peptide motifs for HLA-B27 binding. Thus, expression of proteins from arthritogenic bacteria in HLA-B27-positive human cells allows identifying bacterial peptides that are endogenously processed and presented by HLA-B27 and show molecular mimicry with known self-ligands of this molecule and human proteins.

The intimate relationship between gut and joint in spondyloarthropathies

PURPOSE OF REVIEW

The aim of this article is to highlight recent progress in the combined joint and gut disease in spondyloarthropathies.

RECENT FINDINGS

A set of genes has been identified that are differentially expressed in the colon of spondyloarthropathy and Crohn's disease patients. Reduction of human leukocyte antigen B27 (HLA B27) misfolding by additional beta2-microglobulin in HLA B27 transgenic rats unexpectedly increased disease severity, with more similarities to spondyloarthropathies. By contrast, colitis disappeared.

SUMMARY

Human genomic studies combined with animal model research provide new clues concerning the common pathogenesis of spondyloarthropathy and Crohn's disease, further substantiating the unique relationship between gut and joint inflammation.

HLA-B27 and the pathogenesis of spondyloarthropathies

The association of HLA-B27 with ankylosing spondylitis, a chronic inflammatory disease of the axial skeleton, and other spondyloarthropathies, is among the strongest of an MHC antigen and any disease. Yet, the basis for this association remains unknown. In this review the main current hypotheses concerning the pathogenetic role of HLA-B27 will be discussed. They focus on three molecular properties of the molecule: (1) its peptide-presenting specificity, (2) its slow folding and tendency to misfold, and (3) its capacity to form covalent heavy chain homodimers amenable to recognition by leukocyte receptors. On the basis of the peptide specificity spondyloarthropathies would be triggered through T-cell autoimmunity against a self-ligand of HLA-B27 elicited by a cross-reactive foreign antigen. HLA-B27 misfolding would trigger disease through activation of inflammatory pathways following induction of endoplasmic reticulum stress, thus independently of antigen presentation. Recognition of heavy chain homodimers by leukocyte receptors might be involved in disease through immunomodulation of both innate and adaptive responses to arthritogenic pathogens. None of these hypotheses can yet satisfactorily account for the pathogenesis of spondyloarthritides. It is proposed that the pathogenetic role of HLA-B27 will eventually be explained through a global understanding of its biology, in which the various features of this molecule are envisaged as inter-dependent in their contribution to disease.

Ankylosing spondylitis and bowel disease

Between 5 and 10% of cases of ankylosing spondylitis (AS) are associated with inflammatory bowel disease (IBD), either Crohn's disease or ulcerative colitis. A much larger percentage of AS patients have subclinical gut inflammation manifested either by endoscopic findings or by histology. The association with HLA-B27 is less strong in IBD-associated AS than in idiopathic AS, and there is evidence for an association between gut inflammation in AS with the Crohn's-disease-related CARD15 mutations. Despite the different genetics, the immunopathology suggests common inflammatory pathways in gut and joint inflammation in AS, and in gut inflammation in AS and IBD. Although this observation is of interest to unravel the pathophysiology of the disease, systematic screening of AS patients by ileocolonoscopy is not indicated in the absence of gut symptomatology as only a small proportion of AS patients with subclinical gut inflammation will develop overt IBD over time. Treatment of AS associated with IBD with non-steroidal anti-inflammatory drugs (NSAIDs) is problematic because of concerns of potential re-activation of IBD by NSAIDs. Major advances have been made in recent years with the establishment of anti-tumour necrosis factor (TNF) therapy in AS, the other spondyloarthritides and IBD. Anti-TNF agents are of particular relevance to AS patients with concomitant IBD who are at risk of exacerbation of the underlying bowel disease when treated with NSAIDs. In IBD, infliximab, unlike etanercept, is effective in treating clinical symptoms, inducing and maintaining remission, and mucosal healing. Adalimumab appears to be effective in treating both AS and IBD; however, official approval is pending. Currently, infliximab is the drug of choice for the treatment of patients with active AS associated with IBD.

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.

Mechanisms of disease: infection and spondyloarthritis

There is compelling evidence that some infections can initiate a chronic nonseptic arthritis. This has proved to be an important area of investigation into gene-environment interactions, particularly since HLA-B27 confers increased susceptibility to reactive arthritis. This research has investigated the microbiology of these events, and the strategies used by pathogens to induce chronic joint inflammation. Insights into the HLA-orchestrated immune response in this context have also shed light on the impact of HLA-B27 on immunity, which might provide insights into the mechanism of other HLA-B27-associated diseases. Despite the genetic link to reactive arthritis, there is no proven relationship between ankylosing spondylitis and an inciting infection. In general, most trials have found antibiotics to be ineffective in modifying the course of spondyloarthritis.

Spondyloarthropathy: disease at the crossroads of immunity

Up until recently, the prevailing paradigm relating to spondyloarthropathy (SpA) pathogenesis was that they were human leukocyte antigen (HLA)-associated, T-cell-driven autoimmune diseases. This view is now being questioned. Careful studies of well-characterised cohorts of patients with SpA, including detailed analysis of involved tissue, together with clinical trials of targeted treatments, in particular anti-tumour necrosis factor (TNF) therapies, have contributed enormously to both interest in and understanding of disease pathogenesis. In this chapter, our current knowledge and understanding of the relative contributions of the components of the innate and adaptive arms of the immune response to SpA pathogenesis is reviewed. It is clear that both arms of the immune response are involved and inter-dependent in SpA. With continued emphasis on discovery research, including detailed analysis of novel therapeutic interventions, significant additional breakthroughs in SpA are likely to be forthcoming.

The genetic basis of ankylosing spondylitis

PURPOSE OF REVIEW

Genetic factors provide over 90% of the overall susceptibility to ankylosing spondylitis, with about half of the genetic contribution attributed to HLA-B27 and other major histocompatibility complex genes. Recent studies have focused on non-major histocompatibility complex genes. This review is aimed at summarizing the status of major histocompatibility complex and non-major histocompatibility complex genes in ankylosing spondylitis susceptibility, and suggests areas for future studies.

RECENT FINDINGS

A recent meta-analysis of published scans of ankylosing spondylitis susceptibility has confirmed sites on chromosomes 3q, 6p (the major histocompatibility complex), 10q, 16q and 19q in ankylosing spondylitis susceptibility. Non-major histocompatibility complex candidate gene analyses have confirmed a role for the IL-1 gene complex. The search for other non-major histocompatibility complex candidate genes, however, has been complicated by inadequate power in most previous studies. Innovations in genetic methodologies will allow thorough genome wide linkage disequilibrium mapping studies in large cohorts of patients that will result in the dissection of the genetic susceptibility to ankylosing spondylitis.

SUMMARY

Nearly half of the susceptibility to ankylosing spondylitis is provided by major histocompatibility complex genes. Non-major histocompatibility complex genes, most notably the IL-1 gene complex, have been identified and novel technologies promise that a more thorough examination of the rest of the genome will soon elucidate the genetic basis of this disease.

The frequency of Chlamydia trachomatis major outer membrane protein-specific CD8+ T lymphocytes in active trachoma is associated with current ocular infection

Chlamydia-specific cytotoxic T lymphocytes are able to control model infections but may be implicated in disease pathogenesis. HLA-A2 peptide tetramers to Chlamydia trachomatis major outer membrane protein 258-266 (MOMP258-266) and MOMP260-268 were used to characterize HLA class I-restricted CD8+ T cells in Gambian children aged 4 to 15 years with clinical signs of active trachoma and/or infection with C. trachomatis. The frequencies of circulating HLA-A2 tetramer binding cells (TBC) were determined in whole blood samples by flow cytometric analysis. Initial screening of subjects with an anti-HLA-A2 antibody confirmed the presence of either HLA-A2 or HLA-A28. These were subsequently further divided by molecular subtyping. The C. trachomatis-specific HLA-A2 peptide tetramers were able to bind T cells with receptors from subjects which were restricted by either the HLA-A2 or the HLA-A28 restriction element. In this population, the median value of C. trachomatis-specific CD8+ T cells was 0.02%, with frequencies of up to 3.71% of CD8+ T cells reactive with a single tetramer in a minority of subjects. TBC were detected more often in subjects who were infected at the ocular surface, and their presence was associated with infection episodes of longer duration. Detection of C. trachomatis-specific TBC was not associated with the presence of disease or with the estimated load of ocular C. trachomatis infection at the time of sample collection. High frequencies of C. trachomatis-specific cells did not predict subsequent appearance or resolution of the clinical disease signs of active trachoma.

Resistance to chlamydial lung infection is dependent on major histocompatibility complex as well as non-major histocompatibility complex determinants

Our previous work has shown that C3H/HeN and C57BL/6 mice have differential susceptibility to Chlamydia trachomatis mouse pneumonitis (C. muridarum) lung infection. C3H/HeN (H-2(k)) mice were found to be highly susceptible to C. muridarum infection with higher mortality and more severe morbidity compared to C57BL/6 (H-2(b)) mice. To examine the role of major histocompatibility complex (MHC) genes on host resistance to chlamydial lung infection, we compared MHC congenic mice, B6.H2k [C57BL/6 background, C3H MHC (H-2(k))] and C3H.H2b [C3H/HeN background, C57BL/6 MHC (H-2(b))] and their corresponding wild type C57BL/6 mice and C3H/HeN mice, respectively, in susceptibility to C. muridarum infection. We found that B6.H2k, C3H.H2b and C3H/HeN mice are more susceptible to chlamydial lung infection compared to the wild type C57BL/6 mice by showing more serious body weight loss, higher in vivo chlamydial growth and more severe pathologic changes. Congenic B6.H2k mice showed significantly lower levels of IL-12 and IFN-gamma production compared to C57BL/6 as well as C3H/HeN and C3H.H2b mice. One the other hand, although congenic C3H.H2b mice displayed similar cytokine response to C57BL/6 mice, they were highly susceptible to C. muridarum infection. Overall, the results suggest that protection against chlamydial lung infection is both MHC and non-MHC gene dependent, and that the interaction between MHC and non-MHC elements may contribute to host resistance to chlamydial infection.

Chlamydia pneumoniae genome sequence analysis and identification of HLA-A2-restricted CD8+ T cell epitopes recognized by infection-primed T cells

In the present study, we performed in silico analysis of Chlamydia pneumoniae genome sequence to identify human HLA-A2-restricted T cell epitopes. Thirty-one Chlamydia-specific protein antigens were selected and peptides were derived thereof using an HLA-A2 epitope predictive algorithm. Firstly, we tested binding of 55 selected 9mer peptides to HLA-A2 in vitro. Next, infection of HLA-A2 transgenic mice with C. pneumoniae elementary bodies and assessment of effector CD8+ T cells allowed us to identify which of the epitopes binding to HLA-A2 in vitro were recognized by C. pneumoniae infection-primed CD8+ T cells. Finally, we could confirm that CD8+ T cells in association with HLA-A2 recognized the most reactive peptides when the corresponding full-length genes were used to DNA-immunize HLA-A2 transgenic mice. By using this approach, a novel HLA-A2-restricted epitope in the outer membrane protein A (OmpA) of C. pneumoniae was identified, which proved to mediate specific lysis of peptide-loaded target cells.

Spondyloarthritis: update on pathogenesis and management

A great deal of progress has occurred in the past few years in elucidating the causes and designing new treatments for ankylosing spondylitis and other types of spondyloarthritis. In addition to the human leukocyte antigen (HLA)-B27 and other major histocompatibility complex (MHC) genes, chromosomal regions and genes elsewhere in the genome are being implicated both in disease susceptibility and severity. The various ways HLA-B27 may function in causing spondyloarthritis now are better understood to encompass not only antigen presentation but also other mechanisms, possibly all being operative in pathogenesis (misfolding of the HLA-B27 molecule, impaired intracellular killing of bacteria, and HLA-B27 itself serving as an autoantigen). Specific enteric and sexually acquired infections can trigger reactive arthritis, though no specific microbe has been identified in other forms of spondyloarthritis. Intestinal inflammation with impairment of the gut:blood barrier may be operative in driving ankylosing spondylitis and enteropathic arthritis. A number of treatments have been tried in spondyloarthritis, including older agents such as methotrexate and sulfasalazine but also newer drugs such as pamindronate. The recent introduction of tumor necrosis factor (TNF) blockers in the treatment of spondyloarthritis has offered the most hope in not only relieving symptoms and signs of both peripheral arthritis and enthesitis but also spinal disease, which often has been refractory to other agents. Their high cost and considerable side effect profile, however, have necessitated the establishment of guidelines for their use in these diseases in order to target the patient in whom they are likely to have the most benefit.

[Chlamydia trachomatis urogenital infections in women. Best diagnostic approaches]

Chlamydiae are obligate intracellular bacteria. Chlamydia trachomatis is the most common sexually transmitted disease (STD). The C. trachomatis damaging disease sequelae such as sterility is based on intense and chronic inflammation elicited and maintained by reinfection or persistent infection. The high prevalence of C. trachomatis infection reflects the long and successful adaptation of these organisms to persist in their human host population. The large group of asymptomatically infected persons is not only at risk of serious long-term sequelae but also sustains transmission within communities. C. trachomatis acute infections have been diagnosed by cell culture, direct immunofluorescence, enzyme immunoassay, direct DNA hybridization, and more recently by nucleic acid amplification tests (NAATs). In chronic or persistent chlamydial infections, the level of Chlamydia is very low and bacteria are often not viable. Such infections would be characterized by continuing positive NAATs but only intermittent isolation of viable Chlamydia and positive assays for chlamydial protein antigen. The development of NAATs has been a major advance in the field of chlamydial diagnosis. The use of NAATs associated with serology test is the best diagnosis. The introduction of assays based on amplification of genetic material has subsequently increased the sensitivity of detecting chlamydial infections and offers the opportunity to use non-invasive sampling techniques to screen for infections in asymptomatic subjects. In this article, it was proposed the best diagnosis approaches for detection of acute and chronic infections.

Analysis of the CD8+ T cell response to the G1 domain of aggrecan in ankylosing spondylitis

BACKGROUND

CD4+ T cell responses to the G1 domain of aggrecan in patients with ankylosing spondylitis (AS) were recently reported. Whether such an immune response can be seen in the CD8+ subpopulation has not yet been determined.

OBJECTIVE

To determine if HLA-B27 restricted G1-specific CD8+ T cells are present in AS and to analyse immunodominant CD8+ T cell epitopes.

METHODS

Peripheral blood mononuclear cells of 45 patients with AS were stimulated with overlapping 18-mer peptides covering the whole G1 protein. Results were compared with those for patients with rheumatoid arthritis (RA) and healthy controls. For epitope analysis, G1-specific interferon gamma positive (IFNgamma+) T cells were isolated by magnetic activated cell sorting. After in vitro expansion, CD8+ T cells were restimulated with 14 subpools of G1 peptides. T cells responding to G1 peptide subpools were quantified by flow cytometry according to IFNgamma secretion. Predicted peptides were subsequently confirmed by stimulation with single peptides.

RESULTS

G1-specific CD8+ T cell responses were found in 29/45 (64%) patients with AS, 18/35 (51%) patients with RA, but not in healthy controls. Five CD8+ T cell epitopes were identified as immunodominant in five patients. However, the T cell response was not HLA-B27 restricted. Nonamer peptides with an HLA-B27 binding motif did not induce a T cell response.

CONCLUSION

A G1 peptide-specific CD8+ T cell response is present in AS but also in patients with RA. It does not seem to be HLA-B27 restricted. Whether such a response has a role in the pathogenesis of AS needs clarification.

The proteasome and MHC class I antigen processing

By generating peptides from intracellular antigens, which are then presented to T cells, the ubiquitin/26S proteasome system plays a central role in the cellular immune response. Under the control of interferon-gamma the proteolytic properties of the proteasome are adapted to the requirements of the immune system. Interferon-gamma induces the formation of immunoproteasomes and the synthesis of the proteasome activator PA28. Both alter the proteolytic properties of the proteasome complex and enhance proteasomal function in antigen presentation. Thus, a combination of several of regulatory events tunes the proteasome system for maximal efficiency in the generation of MHC class I antigens.

HLA-B27-restricted CD8+ T cell response to cartilage-derived self peptides in ankylosing spondylitis

OBJECTIVE

Several hypotheses have been proposed to explain the strong association between HLA-B27 and ankylosing spondylitis (AS). Among these, the arthritogenic peptide theory proposes that certain B27 subtype alleles bind specific arthritogenic peptide(s) due to their unique amino acid anchor residues. Cartilage antigens have been discussed as candidate targets for the immune response in AS. The recognition of HLA-B27-peptide complexes by self-reactive CD8+ T cells might contribute to joint-specific tissue damage. Therefore, we investigated the presence of autoreactive CD8+ T cells specific for cartilage-derived peptides in patients with AS.

METHODS

An HLA-B27-binding prediction program and a proteasome-cutting prediction program for the human 20S proteasome were used to screen 18 human cartilage proteins for potentially immunogenic nonamer peptides. The peptides identified were used to stimulate peripheral blood mononuclear cells from 20 HLA-B27-positive patients with AS and synovial fluid (SF) mononuclear cells from 7 HLA-B27-positive patients with AS. Activation of T cells was measured by antigen-specific intracellular cytokine staining and quantified by flow cytometry.

RESULTS

From the screening analysis, we identified 121 nonamer peptides. Of these, 1 peptide derived from type II collagen and 1 from type VI collagen were stimulatory for peripheral blood CD8+ T cells in only 1 of 20 patients. However, in 4 of 7 SF samples the same type VI collagen-derived nonamer peptide stimulated SF CD8+ T cells, but none of the other peptides was stimulatory. This CD8+ T cell response could be blocked by an anti-HLA-B27 antibody, confirming an HLA-B27-restricted immune response.

CONCLUSION

Our findings suggest that cartilage-directed cellular autoimmunity might play an important role in joint-specific tissue damage in patients with AS. Future research is necessary to determine whether the identified peptide is of pathogenetic relevance.