Major histocompatibility complex class I-restricted alloreactive CD4+ T cells

Drug hypersensitivity and eosinophilia: The decisive role of p-i stimulation

Eosinophilia is a common finding in drug hypersensitivity reactions (DHR). Its cause is unclear, as neither antigen/allergen-driven inflammation nor clonal expansion is involved. Most delayed-DHRs are due to p-i (pharmacologic interaction of drugs with immune receptors). These are off-target activities of drugs with immune receptors that result in various types of T-cell stimulation, some of which involve excessive IL-5 production. Functional and phenotypic studies of T-cell clones and their TCR-transfected hybridoma cell lines revealed that some p-i-induced drug stimulations occur without CD4/ CD8 co-receptor engagement. The CD4/CD8 co-receptors link Lck (lymphocyte-specific protein tyrosine kinase) and LAT (linker for activation of T cells) to the TCR. Alteration of Lck or LAT can result in a TCR signalosome with enhanced IL-5 production. Thus, if a more affine TCR-[drug/peptide/HLA] interaction allows bypassing the CD4 co-receptor, a modified Lck/LAT activation may lead to a TCR signalosome with elevated IL-5 production. This "IL-5-TCR-signalosome" hypothesis could also explain eosinophilia in superantigen or allo-stimulation (graft-versus-host disease), in which evasion of CD4/CD8 co-receptors has also been described. It may open new therapeutic possibilities in certain eosinophilic diseases by directly targeting the IL-5-TCR signalosome.

A class-mismatched TCR bypasses MHC restriction via an unorthodox but fully functional binding geometry

MHC restriction, which describes the binding of TCRs from CD4⁺ T cells to class II MHC proteins and TCRs from CD8⁺ T cells to class I MHC proteins, is a hallmark of immunology. Seemingly rare TCRs that break this paradigm exist, but mechanistic insight into their behavior is lacking. TIL1383I is a prototypical class-mismatched TCR, cloned from a CD4⁺ T cell but recognizing the tyrosinase tumor antigen presented by the class I MHC HLA-A2 in a fully functional manner. Here we find that TIL1383I binds this class I target with a highly atypical geometry. Despite unorthodox binding, TCR signaling, antigen specificity, and the ability to use CD8 are maintained. Structurally, a key feature of TIL1383I is an exceptionally long CDR3β loop that mediates functions that are traditionally performed separately by hypervariable and germline loops in canonical TCR structures. Our findings thus expand the range of known TCR binding geometries compatible with normal function and specificity, provide insight into the determinants of MHC restriction, and may help guide TCR selection and engineering for immunotherapy.

Preexisting and Post-COVID-19 Immune Responses to SARS-CoV-2 in Patients with Cancer

Patients with cancer, in particular patients with hematologic malignancies, are at increased risk for critical illness upon COVID-19. We here assessed antibody as well as CD4⁺ and CD8⁺ T-cell responses in unexposed and SARS-CoV-2-infected patients with cancer to characterize SARS-CoV-2 immunity and to identify immunologic parameters contributing to COVID-19 outcome. Unexposed patients with hematologic malignancies presented with reduced prevalence of preexisting SARS-CoV-2 cross-reactive CD4⁺ T-cell responses and signs of T-cell exhaustion compared with patients with solid tumors and healthy volunteers. Whereas SARS-CoV-2 antibody responses did not differ between patients with COVID-19 and cancer and healthy volunteers, intensity, expandability, and diversity of SARS-CoV-2 T-cell responses were profoundly reduced in patients with cancer, and the latter associated with a severe course of COVID-19. This identifies impaired SARS-CoV-2 T-cell immunity as a potential determinant for dismal outcome of COVID-19 in patients with cancer. SIGNIFICANCE: This first comprehensive analysis of SARS-CoV-2 immune responses in patients with cancer reports on the potential implications of impaired SARS-CoV-2 T-cell responses for understanding pathophysiology and predicting severity of COVID-19, which in turn might allow for the development of therapeutic measures and vaccines for this vulnerable patient population.See related commentary by Salomé and Horowitz, p. 1877.This article is highlighted in the In This Issue feature, p. 1861.

T cell and antibody kinetics delineate SARS-CoV-2 peptides mediating long-term immune responses in COVID-19 convalescent individuals

Long-term immunological memory to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is crucial for the development of population-level immunity, which is the aim of vaccination approaches. Reports on rapidly decreasing antibody titers have led to questions regarding the efficacy of humoral immunity alone. The relevance of T cell memory after coronavirus disease 2019 (COVID-19) remains unclear. Here, we investigated SARS-CoV-2 antibody and T cell responses in matched samples of COVID-19 convalescent individuals up to 6 months after infection. Longitudinal analysis revealed decreasing and stable spike- and nucleocapsid-specific antibody responses, respectively. In contrast, functional T cell responses remained robust, and even increased, in both frequency and intensity. Single peptide mapping of T cell diversity over time identified open reading frame-independent, dominant T cell epitopes mediating long-term SARS-CoV-2 T cell responses. Identification of these epitopes may be fundamental for COVID-19 vaccine design.

Immunogenic SARS-CoV-2 Epitopes: In Silico Study Towards Better Understanding of COVID-19 Disease-Paving the Way for Vaccine Development

The emergence of the COVID-19 outbreak at the end of 2019, caused by the novel coronavirus SARS-CoV-2, has, to date, led to over 13.6 million infections and nearly 600,000 deaths. Consequently, there is an urgent need to better understand the molecular factors triggering immune defense against the virus and to develop countermeasures to hinder its spread. Using in silico analyses, we showed that human major histocompatibility complex (MHC) class I cell-surface molecules vary in their capacity for binding different SARS-CoV-2-derived epitopes, i.e., short sequences of 8-11 amino acids, and pinpointed five specific SARS-CoV-2 epitopes that are likely to be presented to cytotoxic T-cells and hence activate immune responses. The identified epitopes, each one of nine amino acids, have high sequence similarity to the equivalent epitopes of SARS-CoV virus, which are known to elicit an effective T cell response in vitro. Moreover, we give a structural explanation for the binding of SARS-CoV-2-epitopes to MHC molecules. Our data can help us to better understand the differences in outcomes of COVID-19 patients and may aid the development of vaccines against SARS-CoV-2 and possible future outbreaks of novel coronaviruses.

Three Types of Functional Regulatory T Cells Control T Cell Responses at the Human Maternal-Fetal Interface

During pregnancy, maternal regulatory T cells (Tregs) are important in establishing immune tolerance to invading fetal extravillous trophoblasts (EVTs). CD25^HIFOXP3+ Tregs are found at high levels in decidual tissues and have been shown to suppress fetus-specific and nonspecific responses. However, limited data are available on additional decidual Treg types and the mechanisms by which they are induced. This study investigated three distinct decidual CD4+ Treg types in healthy pregnancies with a regulatory phenotype and the ability to suppress T cell responses: CD25^HIFOXP3+, PD1^HIIL-10+, and TIGIT+FOXP3^dim. Moreover, co-culture of HLA-G+ EVTs or decidual macrophages with blood CD4+ T cells directly increased the proportions of CD25^HIFOXP3+ Tregs compared to T cells cultured alone. EVTs also increased PD1^HI Tregs that could be inhibited by HLA-C and CD3 antibodies, suggesting an antigen-specific induction. The presence of distinct Treg types may allow for the modulation of a variety of inflammatory responses in the placenta.

MHC Class I-Restricted TCR-Transgenic CD4+ T Cells Against STEAP1 Mediate Local Tumor Control of Ewing Sarcoma In Vivo

In this study we report the functional comparison of T cell receptor (TCR)-engineered major histocompatibility complex (MHC) class I-restricted CD4⁺ versus CD8⁺ T cells targeting a peptide from six transmembrane epithelial antigen of the prostate 1 (STEAP1) in the context of HLA-A*02:01. STEAP1 is a tumor-associated antigen, which is overexpressed in many cancers, including Ewing sarcoma (EwS). Based on previous observations, we postulated strong antitumor potential of tumor-redirected CD4⁺ T cells transduced with an HLA class I-restricted TCR against a STEAP1-derived peptide. We compared CD4⁺ T cell populations to their CD8⁺ counterparts in vitro using impedance-based xCELLigence and cytokine/granzyme release assays. We further compared antitumor activity of STEAP¹³⁰-TCR transgenic (tg) CD4⁺ versus CD8⁺ T cells in tumor-bearing xenografted Rag2^-/-gc^-/- mice. TCR tgCD4⁺ T cells showed increased cytotoxic features over time with similar functional avidity compared to tgCD8⁺ cells after 5-6 weeks of culture. In vivo, local tumor control was equal. Assessing metastatic organotropism of intraveniously (i.v.) injected tumors, only tgCD8⁺ cells were associated with reduced metastases. In this analysis, EwS-redirected tgCD4⁺ T cells contribute to local tumor control, but fail to control metastatic outgrowth in a model of xenografted EwS.

Multifunctional biomimetic nanoparticles loading baicalin for polarizing tumor-associated macrophages

Immunosuppression and immune tolerance lead tumor cells to evade immune system surveillance and weaken drug efficacy. The presence of various immunosuppressive cells in the tumor microenvironment, especially tumor-associated macrophages (TAMs), has been shown to be a driving force in tumor initiation and development. Reversion of the TAM phenotype is an effective way to induce a subsequent antitumor immune response. In this study, we developed baicalin-loaded poly(d,l-lactide-co-glycolide) (PLGA) nanoparticles containing an antigenic peptide (Hgp 100_25-33, Hgp) and a toll-like receptor 9 agonist (CpG). The nanoparticles were further coated with a galactose-inserted erythrocyte membrane, which actively targeted the TAMs. The TAM polarization and tumor treatment effectiveness of the nanoparticles were evaluated. The biomimetic nanoparticles showed enhanced cell uptake in vitro and targeted effects in vivo. In addition, compared with baicalin-loaded PLGA-NPs (B@NPs), the biomimetic nanoparticles, such as Hgp/B@NPs-CpG and NPs@RBC-Gala, significantly polarized the TAMs such that they changed from the M2 type to the M1 type both in vitro and in vivo. Subsequently, the infiltration of CD4⁺ T and CD8⁺ T cells into tumor sites after being induced by the biomimetic nanoparticles was greatly increased, which suggested a significant enhancement of the immune activation effect and T cell response. In addition, the activation of the T cells and induction of the CTL responses effectively suppressed melanoma tumor growth in vivo. In conclusion, the biomimetic nanoparticles effectively reversed the TAM phenotype from M2 to M1, which further improved the tumor immune microenvironment and promoted tumor immunotherapy. These results suggested that the TAM-targeted biomimetic drug delivery system had the potential to reverse the phenotypes of TAMs contributing to reverse the immunosuppressive tumor microenvironment and promote tumor treatment.

A case report of clonal EBV-like memory CD4+ T cell activation in fatal checkpoint inhibitor-induced encephalitis

Checkpoint inhibitors produce durable responses in numerous metastatic cancers, but immune-related adverse events (irAEs) complicate and limit their benefit. IrAEs can affect organ systems idiosyncratically; presentations range from mild and self-limited to fulminant and fatal. The molecular mechanisms underlying irAEs are poorly understood. Here, we report a fatal case of encephalitis arising during anti-programmed cell death receptor 1 therapy in a patient with metastatic melanoma. Histologic analyses revealed robust T cell infiltration and prominent programmed death ligand 1 expression. We identified 209 reported cases in global pharmacovigilance databases (across multiple cancer types) of encephalitis associated with checkpoint inhibitor regimens, with a 19% fatality rate. We performed further analyses from the index case and two additional cases to shed light on this recurrent and fulminant irAE. Spatial and multi-omic analyses pinpointed activated memory CD4⁺ T cells as highly enriched in the inflamed, affected region. We identified a highly oligoclonal T cell receptor repertoire, which we localized to activated memory cytotoxic (CD45RO⁺GZMB⁺Ki67⁺) CD4 cells. We also identified Epstein-Barr virus-specific T cell receptors and EBV⁺ lymphocytes in the affected region, which we speculate contributed to neural inflammation in the index case. Collectively, the three cases studied here identify CD4⁺ and CD8⁺ T cells as culprits of checkpoint inhibitor-associated immune encephalitis.

Personalized adoptive immunotherapy for patients with EBV-associated tumors and complications: Evaluation of novel naturally processed and presented EBV-derived T-cell epitopes

Morbidity and mortality of immunocompromised patients are increased by primary infection with or reactivation of Epstein-Barr virus (EBV), possibly triggering EBV⁺ post-transplant lymphoproliferative disease (PTLD). Adoptive transfer of EBV-specific cytotoxic T cells (EBV-CTLs) promises a non-toxic immunotherapy to effectively prevent or treat these complications. To improve immunotherapy and immunomonitoring this study aimed at identifying and evaluating naturally processed and presented HLA-A*03:01-restricted EBV-CTL epitopes as immunodominant targets. More than 15000 peptides were sequenced from EBV-immortalized B cells transduced with soluble HLA-A*03:01, sorted using different epitope prediction tools and eleven candidates were preselected. T2 and Flex-T peptide-binding and dissociation assays confirmed the stability of peptide-MHC complexes. Their immunogenicity and clinical relevance were evaluated by assessing the frequencies and functionality of EBV-CTLs in healthy donors (n > 10) and EBV⁺ PTLD-patients (n = 5) by multimer staining, Eli- and FluoroSpot assays. All eleven peptides elicited EBV-CTL responses in the donors. Their clinical applicability was determined by small-scale T-cell enrichment using Cytokine Secretion Assay and immunophenotyping. Mixtures of these peptides when added to the EBV Consensus pool revealed enhanced stimulation and enrichment efficacy. These EBV-specific epitopes broadening the repertoire of known targets will improve manufacturing of clinically applicable EBV-CTLs and monitoring of EBV-specific T-cell responses in patients.

Discovery of immunodominant T-cell epitopes reveals penton protein as a second immunodominant target in human adenovirus infection

Background

Human adenovirus (HAdV) infections remain a significant cause of morbidity and mortality after hematopoietic stem cell transplantation (HSCT). Efficient antiviral T-cell responses are necessary to clear infection, which is hampered by delayed immune reconstitution and medical immunosuppression after HSCT. Protective immunity may be conferred by adoptive transfer of HAdV-specific T cells. For identification of patients at risk and monitoring of treatment responses diligent assessment of anti-HAdV cellular immune responses is crucial. The HAdV-derived protein hexon has been recognized as a major immunodominant target across HAdV species. We aimed at identifying further targets of protective anti-HAdV immune response and characterizing immunogenic epitopes.

Methods

Nineteen candidate nonamers from hexon and penton proteins were identified by epitope binding prediction. Peptides were synthesized and tested for in vivo immunogenicity by screening peripheral blood mononuclear cells from healthy volunteers (n = 64) and HAdV-infected stem cell recipients (n = 26) for memory T cells recognizing the candidate epitopes in the context of most common HLA alleles.

Results

Functional CD8⁺ T cells recognizing seven epitopes were identified, among them four penton-derived and two hexon-derived peptides. The HLA-A*01-restricted penton-derived peptide STDVASLNY (A01Penton_STDV) and HLA-A*02-restricted hexon-derived peptide TLLYVLFEV (A02Hexon_TLLY) were recognized by more than half of the persons carrying the respective HLA-type.

Conclusions

Thus, the HAdV-derived penton protein is a novel major target of the anti-HAdV immune response. Identification of new immunodominant epitopes will facilitate and broaden immune assessment strategies to identify patients suitable for T-cell transfer. Knowledge of additional target structures may increase T-cell recovery in manufacturing processes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-1042-2) contains supplementary material, which is available to authorized users.

Impact of TCR reactivity and HLA phenotype on naive CD8 T cell frequency in humans

The impact of MHC phenotype on the shaping of the peripheral naive T cell repertoire in humans remains unknown. To address this, we compared the frequency and antigenic avidity of naive T cells specific for immunodominant self-, viral, and tumor Ags presented by a human MHC class I allele (HLA-A*02, referred to as A2) in individuals expressing or not this allele. Naive T cell frequencies varied from one Ag specificity to another but were restrained for a given specificity. Although A2-restricted T cells showed similar repertoire features and antigenic avidities in A2+ and A2- donors, A2 expression had either a positive, neutral, or negative impact on the frequency of A2-restricted naive CD8 T cells, depending on their fine specificity. We also identified in all donors CD4 T cells specific for A2/peptide complexes, whose frequencies were not affected by MHC class I expression, but nevertheless correlated with those of their naive CD8 T cell counterparts. Therefore, both selection by self-MHC and inherent TCR reactivity regulate the frequency of human naive T cell precursors. Moreover this study also suggests that T cell repertoire shaping by a given self-MHC allele is dispensable for generation of immunodominant T cell responses restricted by this particular allele.

HLA-B27 misfolding and spondyloarthropathies

HLA-B27 plays a central role in the pathogenesis of many spondyloarthropathies and in particular ankylosing spondylitis. The observation that the HLA-B27 heavy chain has a tendency to misfold has raised the possibility that associated diseases may belong in a rapidly expanding category of protein misfolding disorders. The synthesis of the HLA-B27 heavy chain, assembly with beta(2)m and the loading of peptide cargo, occurs in the endoplasmic reticulum (ER) before transport to the cell surface. The evidence indicates that misfolding occurs in the ER prior to beta(2)m association and peptide optimization and is manifested in the formation of aberrant inter- and intra-chain disulfide bonds and accumulation of heavy chain bound to the chaperone BiP. Enhanced accumulation of misfolded heavy chains during the induction of class I expression by cytokines, can cause ER stress resulting in activation of the unfolded protein response (UPR). Effects of UPR activation on cytokine production are beginning to emerge and may provide important missing links between HLA-B27 misfolding and spondyloarthritis. In this chapter we will review what has been learned about HLA-B27 misfolding in human cells and in the transgenic rat model of spondyloarthritis-like disease, considering it in the context of other protein misfolding disorders. These studies provide a framework to support much needed translational work assessing HLA-B27 misfolding and UPR activation in patient-derived material, its consequences for disease pathogenesis and ultimately how and where to focus intervention strategies.

HLA-B27 misfolding and spondyloarthropathies

HLA-B27 plays a central role in the pathogenesis of many spondyloarthropathies and in particular ankylosing spondylitis. The observation that the HLA-B27 heavy chain has a tendency to misfold has raised the possibility that associated diseases may belong in a rapidly expanding category of protein misfolding disorders. The synthesis of the HLA-B27 heavy chain, assembly with beta2m and the loading of peptide cargo, occurs in the endoplasmic reticulum (ER) before transport to the cell surface. The evidence indicates that misfolding occurs in the ER prior to b2m association and peptide optimization and is manifested in the formation of aberrant inter- and intra-chain disulfide bonds and accumulation of heavy chain bound to the chaperone BiP. Enhanced accumulation ofmisfolded heavy chains during the induction of class I expression by cytokines, can cause ER stress resulting in activation of the unfolded protein response (UPR). Effects of UPR activation on cytokine production are beginning to emerge and may provide important missinglinks between HLA-B27 misfolding and spondyloarthritis. In this chapter we will review what has been learned about HLA-B27 misfolding in human cells and in the transgenic rat model of spondyloarthritis-like disease, considering it in the context of other protein misfolding disorders. These studies provide a framework to support much needed translational work assessing HLA-B27 misfolding and UPR activation in patient-derived material, its consequences for disease pathogenesis and ultimately how and where to focus intervention strategies.

Ankylosing Spondylitis: A Contemporary Perspective on Diagnosis and Treatment

OBJECTIVES

In recent years, great progress has been made in the development of diagnostic tools, therapeutic approaches, and validated outcome measures in the understanding of the pathogenesis of ankylosing spondylitis (AS). The purpose of this review was to summarize these developments.

METHODS

We performed a PubMed search for the period 1978 to 2005, using the keyword, "ankylosing spondylitis," resulting in a total of 4878 publications, including 778 reviews. Articles were then selected based on their discussion of recent diagnostic tools and new treatment approaches in the pathogenesis of AS, leading to a final total of 104 articles.

RESULTS

In recent years, there have been 2 major developments in the management of AS that make earlier diagnosis possible and offer the hope of alleviating pain and preventing structural changes that result in loss of function. These developments include the use of magnetic resonance imaging to visualize the inflammatory changes in the sacroiliac joint and the axial spine, and the demonstration that tumor necrosis factor blocking agents are highly efficacious in reducing spinal inflammation and possibly in slowing radiographic progression.

CONCLUSIONS

There have been major advances in both the diagnostic tools and the therapeutic regimens available for patients with AS.

The pathogenetic role of HLA-B27 and its subtypes

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

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.

HLA-B*2704, an Allotype Associated with Ankylosing Spondylitis, Is Critically Dependent on Transporter Associated with Antigen Processing and Relatively Independent of Tapasin and Immunoproteasome for Maturation, Surface Expression, and T Cell Recognition: Relationship to B*2705 and B*2706

B*2704 is strongly associated to ankylosing spondylitis in Asian populations. It differs from the main HLA-B27 allotype, B*2705, in three amino acid changes. We analyzed the influence of tapasin, TAP, and immunoproteasome induction on maturation, surface expression, and T cell allorecognition of B*2704 and compared some of these features with B*2705 and B*2706, allotypes not associated to disease. In the tapasin-deficient .220 cell line, this chaperone significantly influenced the extent of folding of B*2704 and B*2705, but not their egress from the endoplasmic reticulum. In contrast, B*2706 showed faster folding and no accumulation in the endoplasmic reticulum in the absence of tapasin. Surface expression of B*2704 was more tapasin dependent than B*2705. However, expression of free H chain decreased in the presence of this chaperone for B*2705 but not B*2704, suggesting that more suboptimal ligands were loaded on B*2705 in the absence of tapasin. Despite its influence on surface expression, tapasin had little effect on allorecognition of B*2704. Both surface expression and T cell recognition of B*2704 were critically dependent on TAP, as established with TAP-deficient and TAP-proficient T2 cells. Both immunoproteasome and surface levels of B*2704 were induced by IFN-gamma, but this had little effect on allorecognition. Thus, except for the differential effects of tapasin on surface expression, the tapasin, TAP, and immunoproteasome dependency of B*2704 for maturation, surface expression, and T cell recognition are similar to B*2705, indicating that basic immunological features are shared by the two major HLA-B27 allotypes associated to ankylosing spondylitis in human populations.

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 role of HLA class I gene variation in autoimmune diabetes

The use of DNA-based genetic typing has enabled the identification of type 1 diabetes mellitus (T1DM) susceptible and protective major histocompatibility complex (MHC) class II alleles and haplotypes. The application of this approach has also progressed to locate MHC class I alleles that contribute to the clinicopathology of T1DM. Recent studies have shown a widespread involvement of genes from the MHC class I gene region in the clinicopathology of T1DM. These genes are shown to be involved in contributing to progression from the preclinical stage of the disease, which is characterized by the occurrence of islet-specific antibodies, to clinical disease and also to the occurrence of autoimmunity. They can either contribute directly to disease development or indirectly in concert with other susceptible MHC class II alleles or haplotypes via linkage disequilibrium. Class I alleles may also be negatively associated with T1DM. These findings are useful for the development of future strategies in designing tolerogenic approaches for the prevention or even reversal of T1DM. In this article, the latest evidence for the different kinds of participation of HLA class I genes in the etiology of T1DM is reviewed. A meta-analysis which included existing association studies was also carried out in order to re-assess the relevance of class I genes in diabetes development. The analysis of an enlarged heterogeneous sample confirmed the involvement of previously detected serotypes in the etiology of T1DM, such as A24, B8 and B18, and revealed hitherto unknown associations with B60 and B62. The analysis points out that much of the conflicting results of previous association studies originate from inadequate sample sizes and accentuate the value of future investigations of larger samples for identifying linkage in multigenic diseases.

Pathogenesis of ankylosing spondylitis and reactive arthritis

PURPOSE OF REVIEW

The hallmark of ankylosing spondylitis is acute and chronic spinal inflammation initiating in the sacroiliac joints, often coupled with enthesitis, presenting as chronic inflammation at the sites of ligamentous and tendinous insertions into bone. Peripheral joint synovitis can be a prominent feature as well. Reactive arthritis is a sterile synovitis arising after an extra-articular infection of enteric or urogenital tracts. HLA-B27 has been known for about the past 30 years to be associated with ankylosing spondylitis and reactive arthritis, but the pathogenesis of ankylosing spondylitis and reactive arthritis is still not well defined. Although the clinical manifestations of ankylosing spondylitis and reactive arthritis may differ, this update discusses the two diseases together and focuses on recent evidence in both.

RECENT FINDINGS

With respect to HLA-B27 several recent studies address arthritogenic peptides, molecular mimicry, and aberrant forms of B27. Several candidate genes in addition to B27 have been implicated in recent genetic studies. With respect to bacterial infection, recent findings in bacterial antigenicity, host response through interactions of antigen-presenting cells, T cells, and cytokines are providing new understanding of host-pathogen interactions and the pathogenesis of arthritis. Endogenous host factors such as proteoglycans may play a role as autoantigens and contribute to chronic inflammation on that basis.

SUMMARY

Recent advances provide additional new insights into distinct pathogenetic mechanisms in AS and ReA that arise from a complex interplay between genetic factors including HLA-B27 and environmental factors.

Genetic susceptibility to type 1 diabetes in the intracellular pathway of antigen processing - a subject review and cross-study comparison

Ligand binding grooves of MHC class I molecules are able to load a panel of endogenous peptides of varying length and sequence derived from self or foreign origin to activate or deactivate cytotoxic CD8(+) T cells. Peptides are assembled with class I molecules by pathways that are either dependent or independent of transport by ABC proteins (TAP) and degradation in the immunoproteasome by its subunits LMP2 and LMP7. Those peptides that require TAP and LMP treatment appear to be subject to control and optimization by TAP for proper customizing and efficient presentation. Therefore, allelic variations in the coding sequences of TAP and LMP were suspected for a long time to be responsible for improper antigen processing, interruption of self-peptide presentation and reduced cell surface expression of MHC class I molecules resulting in the activation of autoreactive CD8(+) T cells. In this article we reviewed the controversial findings regarding the role of TAP and LMP genes in autoimmune diabetes and reevaluated data of eleven separate studies in a cross-study analysis by genotype and HLA haplotype matching. We could confirm previous results by showing that TAP2*651-A/F and TAP2*687-A/A are significantly associated with disease, independently of linkage disequilibrium (LD). LMP2-R/H surprisingly seems to be primarily disease-conferring although a weak association with DR4 serotypes can be observed. Our analysis also suggests that LMP7-B/B, TAP1-A/A and TAP2*687-A/B are the protective genotypes and that these associations are not secondary to LD with DRB1. Consequently, intracellular antigen processing associated with TAP- and proteasome-dependent pathways seems to be a critical element in T cell selection for the retention of a balanced immunity.

Similar cell surface expression of β2-microglobulin-free heavy chains by HLA-B27 subtypes differentially associated with ankylosing spondylitis

OBJECTIVE

To determine whether the cell surface features of HLA-B27 subtypes reported to be differentially associated with ankylosing spondylitis (AS) differ in a way that correlates with disease susceptibility.

METHODS

Human cell transfectants expressing or lacking the transporter associated with antigen processing were used to determine the cell surface expression of B27 subtypes by flow cytometry with antibodies recognizing the B27 heterodimer or beta2-microglobulin (beta2m)-free heavy chains.

RESULTS

In lymphoid cells with an intact peptide-loading complex, all B27 subtypes, irrespective of their association with disease, showed similar ratios of free heavy chain to heterodimer, suggesting similar surface stability. A substantial decrease in dissociated heavy chains, which never reached 100%, was observed upon addition of a B27 ligand, with no significant differences among subtypes. This is compatible with similar surface expression of irreversible beta2m-free heavy chain forms among subtypes differentially associated with disease. In cells lacking the transporter associated with antigen processing, both disease-associated and non-disease-associated subtypes expressed a population of heterodimers at 26 degrees C that was less stable than the population expressed at 37 degrees C. In the presence of exogenous peptide, the expression of heterodimers increased, without a concomitant decrease in beta2m-free heavy chains. This suggests that in these cells, and for all subtypes tested, most of the dissociated heavy chains at the cell surface are in irreversible forms. At 37 degrees C, the expression of beta2m-free B27 heavy chains was very low on T2 transfectant cells.

CONCLUSION

HLA-B27 subtypes showing differential associations with AS are similar in their extent of beta2m dissociation and surface expression of free heavy chains.