T cell selection and differential activation on structurally related HLA-DR4 ligands

Carbonyl Posttranslational Modification Associated With Early-Onset Type 1 Diabetes Autoimmunity

Inflammation and oxidative stress in pancreatic islets amplify the appearance of various posttranslational modifications to self-proteins. In this study, we identified a select group of carbonylated islet proteins arising before the onset of hyperglycemia in NOD mice. Of interest, we identified carbonyl modification of the prolyl-4-hydroxylase β subunit (P4Hb) that is responsible for proinsulin folding and trafficking as an autoantigen in both human and murine type 1 diabetes. We found that carbonylated P4Hb is amplified in stressed islets coincident with decreased glucose-stimulated insulin secretion and altered proinsulin-to-insulin ratios. Autoantibodies against P4Hb were detected in prediabetic NOD mice and in early human type 1 diabetes prior to the onset of anti-insulin autoimmunity. Moreover, we identify autoreactive CD4+ T-cell responses toward carbonyl-P4Hb epitopes in the circulation of patients with type 1 diabetes. Our studies provide mechanistic insight into the pathways of proinsulin metabolism and in creating autoantigenic forms of insulin in type 1 diabetes.

Epitope Selection for HLA-DQ2 Presentation: Implications for Celiac Disease and Viral Defense

We have reported that the major histocompatibility molecule HLA-DQ2 (DQA1*05:01/DQB1*02:01) (DQ2) is relatively resistant to HLA-DM (DM), a peptide exchange catalyst for MHC class II. In this study, we analyzed the role of DQ2/DM interaction in the generation of DQ2-restricted gliadin epitopes, relevant to celiac disease, or DQ2-restricted viral epitopes, relevant to host defense. We used paired human APC, differing in DM expression (DM^null versus DM^high) or differing by expression of wild-type DQ2, versus a DM-susceptible, DQ2 point mutant DQ2α+53G. The APC pairs were compared for their ability to stimulate human CD4⁺ T cell clones. Despite higher DQ2 levels, DM^high APC attenuated T cell responses compared with DM^null APC after intracellular generation of four tested gliadin epitopes. DM^high APC expressing the DQ2α+53G mutant further suppressed these gliadin-mediated responses. The gliadin epitopes were found to have moderate affinity for DQ2, and even lower affinity for the DQ2 mutant, consistent with DM suppression of their presentation. In contrast, DM^high APC significantly promoted the presentation of DQ2-restricted epitopes derived intracellularly from inactivated HSV type 2, influenza hemagglutinin, and human papillomavirus E7 protein. When extracellular peptide epitopes were used as Ag, the DQ2 surface levels and peptide affinity were the major regulators of T cell responses. The differential effect of DM on stimulation of the two groups of T cell clones implies differences in DQ2 presentation pathways associated with nonpathogen- and pathogen-derived Ags in vivo.

Memory T cells specific to citrullinated α-enolase are enriched in the rheumatic joint

ACPA-positive rheumatoid arthritis (RA) is associated with distinct HLA-DR alleles and immune responses to many citrullinated self-antigens. Herein we investigated the T cell epitope confined within α-enolase_326-340 in the context of HLA-DRB1*04:01 and assessed the corresponding CD4⁺ T cells in both the circulation and in the rheumatic joint. Comparative crystallographic analyses were performed for the native and citrullinated α-enolase_326-340 peptides in complex with HLA-DRB1*04:01. HLA-tetramers assembled with either the native or citrullinated peptide were used for ex vivo and in vitro assessment of α-enolase-specific T cells in peripheral blood, synovial fluid and synovial tissue by flow cytometry. The native and modified peptides take a completely conserved structural conformation within the peptide-binding cleft of HLA-DRB1*04:01. The citrulline residue-327 was located N-terminally, protruding towards TCRs. The frequencies of T cells recognizing native eno_326-340 were similar in synovial fluid and peripheral blood, while in contrast, the frequency of T cells recognizing cit-eno_326-340 was significantly elevated in synovial fluid compared to peripheral blood (3.6-fold, p = 0.0150). Additionally, citrulline-specific T cells with a memory phenotype were also significantly increased (1.6-fold, p = 0.0052) in synovial fluid compared to peripheral blood. The native T cell epitope confined within α-enolase_326-340 does not appear to lead to complete negative selection of cognate CD4⁺ T cells. In RA patient samples, only T cells recognizing the citrullinated version of α-enolase_326-340 were found at elevated frequencies implicating that neo-antigen formation is critical for breach of tolerance.

Taming the TCR: antigen-specific immunotherapeutic agents for autoimmune diseases

Current treatments for autoimmune diseases are typically non-specific anti-inflammatory agents that affect not only the autoreactive cells but also the parts of the immune system that are required to maintain health. There is a need for the development of antigen-specific therapeutic agents that can effectively prevent the autoimmune attack while leaving the rest of the immune system functioning as normal. The simplest way to achieve this is using the autoantigen itself as a tolerizing agent; however, there is some risk involved with administering a potentially pathogenic antigen. In this review, we focus instead on the development and use of modified T cell receptor (TCR) ligands, in which the peptide ligand is modified to change the response by the T cell from a disease inducing to a protective response, and still retain the antigen-specificity necessary to target the autoreactive T cells. We review the use of modified TCR ligands as therapeutic agents in animal models of autoimmunity and in human autoimmune disease, and finally consider how they need to be improved in order to use them effectively in patients with autoimmune disease.

Citrulline-specific Th1 cells are increased in rheumatoid arthritis and their frequency is influenced by disease duration and therapy

OBJECTIVE

Rheumatoid arthritis (RA) is thought to be a T cell-mediated disease, based on its strong association with HLA class II alleles, clinical responsiveness to T cell-directed therapies, and the presence of CD4+ T cells in rheumatoid joints. The presence of anti-citrullinated protein antibodies (ACPAs) in RA serum and the association of these antibodies with HLA-DR4 alleles implicate citrulline-specific autoreactive T cells in the development and progression of RA. The goal of this study was to determine the characteristics and specificity of autoreactive T cell responses in RA.

METHODS

We developed a panel of HLA-DRB1*04:01 tetramers, selecting citrullinated peptides from synovial antigens and verifying their immunogenicity in DRB1*04:01-transgenic mice. Seven tetramers were used to examine the ex vivo frequency and surface phenotype of citrulline-specific (Cit-specific) T cells in patients with RA and healthy subjects with DRB1*04:01 haplotypes, using a magnetic enrichment procedure.

RESULTS

Cit-specific T cells were detectable in peripheral blood samples from both healthy subjects and RA patients. In comparison to healthy subjects, RA patients had significantly higher frequencies of Cit-specific T cells, and a greater proportion of these cells displayed a Th1 memory phenotype. Among RA patients, the frequency of Cit-specific T cells was highest within the first 5 years after diagnosis of RA and was decreased in patients taking biologic agents, irrespective of disease duration.

CONCLUSION

These findings link the presence of ACPAs in RA with Th1 cells specific for citrullinated epitopes and provide tools for disease-specific immunomonitoring of autoreactive T cells.

Correlation between human leukocyte antigen class II alleles and HAI titers detected post-influenza vaccination

Influenza is a major cause of morbidity and mortality. Despite vaccination, many elderly recipients do not develop a protective antibody response. To determine whether Human Leukocyte Antigen (HLA) alleles modulate seroprotection to influenza, a cohort of HLA class II-typed high-risk vaccine recipients was investigated. Haemagglutinin inhibition (HAI) titres were measured 14–40 days post-subunit vaccination. Seroprotection was defined as HAI titres reaching 40 or greater for all three vaccine strains. HLA-DRB1*04∶01 and HLA-DPB1*04∶01 alleles were detected at higher frequencies in seroprotected compared with non-seroprotected individuals. Thus, the presence of certain HLA class II alleles may determine the magnitude of antibody responses to influenza vaccination.

DQB1*06:02 allele-specific expression varies by allelic dosage, not narcolepsy status

The association of narcolepsy-cataplexy, a sleep disorder caused by the loss of hypocretin/orexin neurons in the hypothalamus, with DQA1*01:02-DQB1*06:02 is one of the tightest known single-allele human leukocyte antigen (HLA) associations. In this study, we explored genome-wide expression in peripheral white blood cells of 50 narcolepsy versus 47 controls (half of whom were DQB1*06:02 positive) and observed the largest differences between the groups in the signal from HLA probes. Further studies of HLA-DQ expression (mRNA and protein in a subset) in 125 controls and 147 narcolepsy cases did not reveal any difference, a result we explain by the lack of proper control of allelic diversity in Affymetrix HLA probes. Rather, a clear effect of DQB1*06:02 allelic dosage on DQB1*06:02 mRNA levels (1.65-fold) and protein (1.59-fold) could be demonstrated independent of disease status. These results indicate that allelic dosage is transmitted into changes in heterodimer availability, a phenomenon that may explain the increased risk for narcolepsy in DQB1*06:02 homozygotes versus heterozygotes.

Preclinical efficacy studies of influenza A haemagglutinin precursor cleavage loop peptides as a potential vaccine

A universal influenza vaccine that does not require annual reformulation would have clear advantages over the currently approved seasonal vaccine. In this study, we combined the mucosal adjuvant alpha-galactosylceramide (αGalCer) and peptides designed across the highly conserved influenza precursor haemagglutinin (HA(0)) cleavage loop as a vaccine. Peptides designed across the HA(0) of influenza A/H3N2 viruses, delivered to mice via the intranasal route with αGalCer as an adjuvant, provided 100 % protection following H3N2 virus challenge. Similarly, intranasal inoculation of peptides across the HA(0) of influenza A/H5N1 with αGalCer completely protected mice against heterotypic challenge with H3N2 virus. Our data suggest that these peptide vaccines effectively inhibited subsequent influenza A/H3N2 virus replication. In contrast, only 20 % of mice vaccinated with αGalCer-adjuvanted peptides spanning the HA(0) of H5N1 survived homologous viral challenge, possibly because the HA(0) of this virus subtype is cleaved by intracellular furin-like enzymes. Results of these studies demonstrated that HA(0) peptides adjuvanted with αGalCer have the potential to form the basis of a synthetic, intranasal influenza vaccine.

The analysis of the functions of human B and T cells in humanized NOD/shi-scid/gammac(null) (NOG) mice (hu-HSC NOG mice)

'Humanized mice' are anticipated to be a valuable tool for studying the human immune system, but the reconstituted human immune cells have not yet been well characterized. Here, we extensively investigated the differentiation and functions of human B and T cells in a supra-immunodeficient mouse strain, NOD/shi-scid/gammac(null) (NOG) reconstituted with CD34(+) hematopoietic stem cells obtained from umbilical cord blood. In these hu-HSC NOG mice, the development of human B cells was partially blocked, and a significant number of B-cell progenitors accumulated in the spleen. The mature CD19(+)IgM(+)IgD(+) human B cells of the hu-HSC NOG mice could produce IgG in vivo and in vitro by antigenic stimulation. In contrast, although human T cells with an apparently normal phenotype developed, most of them could neither proliferate nor produce IL-2 in response to antigenic stimulation by anti-CD3 and anti-CD28 antibodies in vitro. The positive selection of human T cells in the thymus was sufficiently functional, if not complete, and mainly mediated by mouse class II, suggesting that the human T cells lost their function in the periphery. We found that multiple mechanisms were involved in the T-cell abnormalities. Collectively, our results demonstrate that further improvements are necessary before humanized mice with a functional human immune system are achieved.

A real-time polymerase chain reaction assay for the rapid identification of the autoimmune disease-associated allele HLA-DQB1*0602

Many autoimmune diseases share a genetic association with the presence or absence of human leukocyte antigen (HLA)-DQB1*0602, including type I diabetes, multiple sclerosis, and narcolepsy. High-resolution HLA typing to determine the presence of this allele is cumbersome and expensive by currently available techniques. We present a real-time polymerase chain reaction (PCR) assay for the identification of HLA-DQB1*0602, using sequence-specific primers and probes, that provides rapid and sensitive identification of this allele, involves minimal hands-on time, and provides major cost savings compared with existing methods. The assay allows the simultaneous determination of both the presence and the number of copies of this allele. Because there is no post-PCR handling, the risk of contamination is avoided. We have validated the assay using 44 blinded and 32 unblinded samples, previously typed by standard techniques, which were identified with 100% accuracy, sensitivity, and specificity. Furthermore, using a narcolepsy cohort of 722 subjects, we demonstrated the robustness of the assay to analyze DNA isolated from buccal swabs, demonstrating the applicability of this assay as a suitable approach for population-based studies.

Class II major histocompatibility complex tetramer staining: progress, problems, and prospects

The use of major histocompatibility complex (MHC) tetramers in the detection and analysis of antigen-specific T cells has become more widespread since its introduction 11 years ago. Early challenges in the application of tetramer staining to CD4+ T cells centred around difficulties in the expression of various class II MHC allelic variants and the detection of low-frequency T cells in mixed populations. As many of the technical obstacles to class II MHC tetramer staining have been overcome, the focus has returned to uncertainties concerning how oligomer valency and T-cell receptor/MHC affinity affect tetramer binding. Such issues have become more important with an increase in the number of studies relying on direct ex vivo analysis of antigen-specific CD4+ T cells. In this review we discuss which problems in class II MHC tetramer staining have been solved to date, and which matters remain to be considered.

HLA-DRB1 alleles control allergic bronchopulmonary aspergillosis-like pulmonary responses in humanized transgenic mice

BACKGROUND

Allergic bronchopulmonary aspergillosis (ABPA) is a lung hypersensitivity disease mediated in part by CD4(+) T(H)2 cells. There is a significant association between ABPA and the HLA-DR2 genotypes DRB1(*)1501 and DRB1(*)1503, whereas resistance might be associated with HLA-DRB1(*)1502.

OBJECTIVE

We sought to elucidate the role of HLA-DR alleles in allergic inflammation in lungs.

METHODS

HLA-DR humanized transgenic mice expressing either the susceptible or resistant alleles were analyzed for the nature and extent of pulmonary inflammation after exposure to Aspergillus species antigens.

RESULTS

Exposed DRB1(*)1501 and DRB1(*)1503 transgenic mice displayed infiltrates made up prominently of eosinophils, which is consistent with the inflammation found in ABPA. The resistant DRB1(*)1502 mice, on the other hand, displayed minimal to moderate inflammation, consisting mainly of T-cell infiltrates. Significantly more mucin was produced in the DRB1(*)1503 and DRB1(*)1501 mice, and their ability to limit the number of Aspergillus species conidia within the lung parenchyma was impaired. Despite their differences, both the DRB1(*)1503 and DRB1(*)1502 strains mounted comparable T cell-proliferative responses to Aspergillus species antigens.

CONCLUSION

The HLA-DR2 alleles DRB1(*)1501 and DRB1(*)1503 play a major role in the development of allergic pulmonary inflammation. In contrast, the HLA-DR2 allele DRB1(*)1502 mediates a nonallergic T(H)1-like response to the organism, possibly explaining an ABPA resistance factor. These results are in support of our published human studies in patients with cystic fibrosis and asthma.

CLINICAL IMPLICATIONS

HLA-DR typing in patients with cystic fibrosis and asthma will aid in the identification of individuals at risk for ABPA.

A real-time PCR approach for rapid high resolution subtyping of HLA-DRB1*04

We present a real-time PCR approach for the identification and subtyping of HLA-DR4 alleles. The technique, which uses sequence-specific primers and probes in conjunction with real-time PCR for the detection and differentiation of target alleles, is rapid, involves minimal hands-on time, and is inexpensive compared to existing methods. Further, there is no post-PCR handling, so the risk of contamination is avoided. We have validated the assay using 44 blinded and 56 unblinded samples, which were identified with 100% accuracy, sensitivity, and specificity. We demonstrate the applicability of this assay as an alternative approach to traditional HLA typing methods.

Novel APC-like properties of human NK cells directly regulate T cell activation

Initiation of the adaptive immune response is dependent on the priming of naive T cells by APCs. Proteomic analysis of unactivated and activated human NK cell membrane-enriched fractions demonstrated that activated NK cells can efficiently stimulate T cells, since they upregulate MHC class II molecules and multiple ligands for TCR costimulatory molecules. Furthermore, by manipulating antigen administration, we show that NK cells possess multiple independent unique pathways for antigen uptake. These results highlight NK cell-mediated cytotoxicity and specific ligand recognition by cell surface-activating receptors on NK cells as unique mechanisms for antigen capturing and presentation. In addition, we analyzed the T cell-activating potential of human NK cells derived from different clinical conditions, such as inflamed tonsils and noninfected and CMV-infected uterine decidual samples, and from transporter-associated processing antigen 2-deficient patients. This in vivo analysis revealed that proinflammatory, but not immune-suppressive, microenvironmental requirements can selectively dictate upregulation of T cell-activating molecules on NK cells. Taken together, these observations offer new and unexpected insights into the direct interactions between NK and T cells and suggest novel APC-like activating functions for human NK cells.

HLA class II-restricted CD4+ T cell responses directed against influenza viral antigens postinfluenza vaccination

The memory T cell response is polyclonal, with the magnitude and specificity of the response controlled in part by the burst size of T cells expanded from effector/memory precursors. Sensitive assays using HLA class II multimers were used to detect low-frequency Ag-specific T cells directed against influenza viral Ags in subjects immunized with the influenza vaccine. Direct ex vivo tetramer staining of PBMC from five individuals identified frequencies of hemagglutinin (HA) 306-318 tetramer binding CD4(+) T cells in the peripheral blood ranging from 1 in 600 to 1 in 30,000 CD4(+) T cells. These frequencies were validated by counting CFSE(low), tetramer-positive T cells after in vitro expansion. Low frequency of T cells directed to other influenza epitopes, including DRA1*0101/DRB1*0401-restricted matrix protein 60-73, DRA1*0101/DRB1*0101-restricted matrix protein 18-29, DRA1*0101/DRB1*0701-restricted HA 232-244 and DRA1*0101/DRB1*0101-restricted nucleoprotein 206-217 were also determined. T cells which occurred at a frequency as low as 1 in 350,000 could be ascertained by in vitro expansion of precursors. Peripheral HA(306-318)-responsive T cells expanded 2- to 5-fold following influenza vaccination. Examination of phenotypic markers of the HA(306-318)-responsive T cells in the peripheral blood indicated that the majority were CD45RA(-), CD27(+), CD25(-), CD28(+), and CD62L(-), while T cell clones derived from this population were CD45RA(-), CD27(-), CD25(+), CD28(+), and CD62L(-).

Identification of novel immunodominant CD4+ Th1-type T-cell peptide epitopes from herpes simplex virus glycoprotein D that confer protective immunity

The molecular characterization of the epitope repertoire on herpes simplex virus (HSV) antigens would greatly expand our knowledge of HSV immunity and improve immune interventions against herpesvirus infections. HSV glycoprotein D (gD) is an immunodominant viral coat protein and is considered an excellent vaccine candidate antigen. By using the TEPITOPE prediction algorithm, we have identified and characterized a total of 12 regions within the HSV type 1 (HSV-1) gD bearing potential CD4(+) T-cell epitopes, each 27 to 34 amino acids in length. Immunogenicity studies of the corresponding medium-sized peptides confirmed all previously known gD epitopes and additionally revealed four new immunodominant regions (gD(49-82), gD(146-179), gD(228-257), and gD(332-358)), each containing naturally processed epitopes. These epitopes elicited potent T-cell responses in mice of diverse major histocompatibility complex backgrounds. Each of the four new immunodominant peptide epitopes generated strong CD4(+) Th1 T cells that were biologically active against HSV-1-infected bone marrow-derived dendritic cells. Importantly, immunization of H-2(d) mice with the four newly identified CD4(+) Th1 peptide epitopes but not with four CD4(+) Th2 peptide epitopes induced a robust protective immunity against lethal ocular HSV-1 challenge. These peptide epitopes may prove to be important components of an effective immunoprophylactic strategy against herpes.

Evolving concepts of rheumatoid arthritis

Rheumatoid arthritis is the most common inflammatory arthritis and is a major cause of disability. It existed in early Native American populations several thousand years ago but might not have appeared in Europe until the 17th century. Early theories on the pathogenesis of rheumatoid arthritis focused on autoantibodies and immune complexes. T-cell-mediated antigen-specific responses, T-cell-independent cytokine networks, and aggressive tumour-like behaviour of rheumatoid synovium have also been implicated. More recently, the contribution of autoantibodies has returned to the forefront. Based on the pathogenic mechanisms, specific therapeutic interventions can be designed to suppress synovial inflammation and joint destruction in rheumatoid arthritis.

Genetics of rheumatoid arthritis: is there a scientific explanation for the human leukocyte antigen association?

Human leukocyte antigen genes associated with rheumatoid arthritis are commonly found in the unaffected population, implying that causal mechanisms of disease involve interactions between these genes and other factors. A variety of approaches-genetic, structural, and immunologic-are used to explore possible molecular interactions that may contribute to understanding the basis for this disease association. The specific relation between human leukocyte antigen-DR4 alleles and rheumatoid arthritis remains one of the strongest and most thoroughly studied examples of human leukocyte antigen risk genes among human autoimmune disorders.