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Immune responses to autoantigens are in part controlled by deletion of autoreactive cells through genetically regulated selection mechanisms. We have directly analyzed peripheral CD4+ proinsulin (PI) 76–90 (SLQPLALEGSLQKRG)-specific T cells using soluble fluorescent major histocompatibility complex class II tetramers. Subjects with type I diabetes and healthy controls with high levels of peripheral proinsulin-specific T cells were characterized by the presence of a disease-susceptible polymorphism in the insulin variable number of tandem repeats (INS-VNTR) gene. Conversely, subjects with a ‘protective’ polymorphism in the INS-VNTR gene had nearly undetectable levels of proinsulin tetramer-positive T cells. These results strongly imply a direct relationship between genetic control of autoantigen expression and peripheral autoreactivity, in which proinsulin genotype restricts the quantity and quality of the potential T-cell response. Using a modified tetramer to isolate low-avidity proinsulin-specific T cells from subjects with the susceptible genotype, transcript arrays identified several induced pro-apoptotic genes in the control, but not diabetic subjects, likely representing a second peripheral mechanism for maintenance of tolerance to self antigens. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We investigated whether beta cell neoformation occurs in the transplanted pancreas in patients with type 1 diabetes who had received a simultaneous pancreas–kidney transplant (SPK) and later developed recurrence of autoimmunity. We examined pancreas transplant biopsies from nine SPK patients with or without recurrent autoimmunity or recurrent diabetes and from 16 non-diabetic organ donors. Tissues were analysed by immunohistochemistry and immunofluorescence. Numerous cytokeratin-19 (CK-19)+ pancreatic ductal cells stained for insulin in six SPK recipients with recurrent autoimmunity, in five of whom diabetes requiring insulin therapy recurred. These cells also stained for the transcription factor pancreatic-duodenal homeobox-1 (Pdx-1), which is implicated in pancreatic development and beta cell differentiation. The number of insulin+ ductal cells varied, being highest in the patient with the most severe beta cell loss and lowest in the normoglycaemic patient. In the patient with the most severe beta cell loss, we detected insulin+CK-19+Pdx-1+ cells staining for the proliferation-related Ki-67 antigen (Ki-67), indicating proliferation. We were unable to detect Ki-67+ beta cells within the islets in any SPK patient. Some insulin+CK-19– ductal cells contained chromogranin A, suggesting further endocrine differentiation. Insulin+ cells were rarely noted in the pancreas transplant ducts in three SPK patients without islet autoimmunity and in six of 16 non-diabetic organ donors; these insulin+ cells were never CK-19+. Insulin+ pancreatic ductal cells, some apparently proliferating, were found in the transplanted pancreas with recurrent islet autoimmunity/diabetes. Replicating beta cells were not detected within islets. The observed changes may represent attempts at tissue remodelling and beta cell regeneration involving ductal cells in the human transplanted pancreas, possibly stimulated by hyperglycaemia and chronic inflammation. [ABSTRACT FROM AUTHOR]

Human CD4 T cell responses to an epitope of hGAD65 (GAD = glutamic acid decarboxylase), residues 555–567, are modulated by interaction with an altered peptide ligand containing modifications at TCR contact residues. Using different HLA-DR4 molecules with polymorphisms at sites corresponding to peptide binding pockets p1 and p9, we tested the effect of additional modifications in the altered peptide ligand (APL) designed to increase the avidity of the MHC–peptide interaction and therefore the efficiency of TCR signaling. Modification of the peptide or the MHC molecule which enhanced the p1 interaction also enhanced the antagonist activity of the modified APL. In contrast, modifications at p9 led to a reversal in APL function, resulting in agonist activity. Molecular homology modeling of these MHC–peptide interactions suggests a structural basis for this functional dichotomy in which topographically remote variations lead to unique interaction effects. [ABSTRACT FROM AUTHOR]

GAD65 autoantibodies (GAD65Ab) are highly prevalent in type 1 diabetes, but their functional role in the pathogenesis of the disease and their relationship to T-cell reactivity to GAD65 is still unclear. We tested the hypothesis that GAD65Ab modulate presentation of GAD65 to T-cells. T-cell hybridoma T33.1, which recognizes the GAD65 274-286 epitope in the context of HLA-DRB 1*0401, was incubated with antigen-presenting cells exposed to recombinant human GAD65 alone or complexed with GAD65Ab' or GAD65Ab- sera. Stimulation of the T33.1 hybridoma was greatly enhanced by multiple GAD65Ab+ sera. The enhancement effect was most prominent with sera from patients with high GAD65 autoantibody levels. Sera from GAD65Ab- subjects had no effect. The correlation between T-cell stimulation and GAD65Ab levels was not absolute, suggesting that other variables such as autoantibody recognition of different regions of GAD65 and variable effects on processing of the 274-286 epitope may contribute. Uptake of antibody-complexed GAD65 was Fc receptor (FcR)-mediated because the enhancement of presentation was inhibited by monoclonal antibodies against FcR. Our results support the hypothesis that GAD65Ab modulate presentation of GAD65 to T-cells. Increased antigen uptake and heterogeneity in the autoantibody specificity may provide a mechanism for antibody-facilitated T-cell response influencing the progression of type 1 diabetes. [ABSTRACT FROM AUTHOR]

Sydenham’s chorea (SC) may occur in rheumatic fever (RF) patients without arthritis and carditis. In this study we typed HLA antigens and alleles in patients presenting with the distinct major clinical manifestations of RF, i.e., chorea, carditis, or arthritis, in population and family studies. We evaluated 91 patients with RF for HLA-A, HLA-B, and HLA-DR antigens; of these, 33 had pure chorea, 26 pure carditis, 16 pure arthritis, and 16 carditis plus arthritis. We also typed 24 SC patients and their unaffected siblings for HLA-DRB1 and HLA-DQB1 alleles using molecular methods. HLA-B49 and HLA-DR1 antigens were overrepresented in the total group of patients with RF and in all the subgroups studied, excluding the SC subgroup in which the frequency of HLA-DR1 antigen was not increased. The frequencies of the HLA-DRB1 and HLA-DQB1 alleles in patients with pure chorea were not significantly different from those observed in controls. Similarly, the frequencies of HLA class II alleles in SC patients did not differ significantly from those observed in unaffected siblings. These findings show that immunogenetic susceptibility to RF varies according to the major clinical manifestation presented by the patient. [ABSTRACT FROM AUTHOR]

Autoimmune diabetes is the clinical end point for a sequential cascade of immunologic events that occur in a genetically susceptible individual. Structural and functional analysis of the HLA class II susceptibility genes in IDDM suggests likely molecular mechanisms for several of the key steps in this cascade of autoimmune events. We outline a pathway in which the HLA-DQ genes associated with IDDM bias the immunologic repertoire toward autoimmune specificities, creating an autoimmune-prone individual, followed by amplification and triggering events that promote subsequent immune activation. There are several direct links between genetics and autoimmune disease in this pathway: the developmental maturation of T-cells in a genetically susceptible individual occurs through molecular interactions between the T-cell receptor and the HLA-peptide complex. Selection of T-cells with receptors likely to contribute to autoreactivity may preferentially occur in the context of specific HLA-DQ alleles that are diabetes prone, because of inefficiencies in the peptide-MHC structural interactions of these molecules. Subsequent activation of these T-cells in the context of recognizing islet-associated antigens can trigger a poorly regulated immune response that results in progressive islet destruction. These subsequent diabetes-specific events are also directed by specific HLA genes, most prominently by the binding of specific antigenic peptides by the disease-associated HLA molecules. In this sequential cascade, opportunities for environmental influences and modulation by non-HLA genes are identified that likely act in concert with the predominant genetic susceptibility contributed by the HLA molecules themselves. Clarification of the steps in this pathway extends our understanding of the prevailing role of HLA genes in IDDM pathogenesis and suggests opportunities to intervene at discrete initiating, disease-promoting, or regulatory steps in IDDM development. [ABSTRACT FROM AUTHOR]

There are many parallels between T cell-mediated suppression of tumor immunity and suppression of immune responses to haptens and polypeptides. We propose a cell interaction model which takes this into account and outlines a regulatory pathway for suppression of immunity to tumor antigens. Free antigen or antigen/antibody complexes trigger an inducer T cell subset, Ts, which is tumor-specific. This cell activates a non-immune T cell population, pre Ts, to generate effector suppressor cells, Ts. The Ts are specific for either the idiotype of Ts or for antigen complexed with a soluble factor made by the Ts, but the suppression they mediate is antigenically nonspecific. Tumor antigen-specific suppressor factors, TsF, play a major role in the communication between different suppressor cells. Characterization of polyclonal and monoclonal factors produced by Ts, called TsF, indicates that they both bind to tumor antigen and contain tumor-specific (idiotypic?) determinants. [ABSTRACT FROM AUTHOR]

A shared amino-acid sequence on the α helix of certain DRβ1 chains is predicted to generate a 'shared epitope' that is implicated in susceptibility to the development of rheumatoid arthritis (RA). Different relative risks (RR) for disease susceptibility and severity conferred by these DRβ1 chains suggest that their 'shared epitopes' are not equivalent. A set of monoclonal antibodies (MoAb) that map to the critical region, and for which optimal binding depends on DR context and cell lineage, was used to test this idea. Mapping experiments using mutated DRβ1* molecules showed that the antibody-binding epitopes are overlapping; residue 70Q is pivotal for each, but neighbouring residues on the α helix and on the floor of the groove are also involved. Importantly, these epitopes are profoundly modified by peptide loading of DRβ1*0401 molecules. These data suggest that 'shared epitopes' on DR molecules that are associated with RA are influenced by their context; such structural modifications may be the basis for the varying susceptibilities conferred by these DR molecules for the development of RA. [ABSTRACT FROM AUTHOR]

HLA class II (HLA-DR) frequencies were examined in relation to incidence of acute arthralgia or arthritis in 283 white women who had received RA27/3 rubella vaccine (n = 146) or placebo (n = 137) postpartum. Leukocyte DNA was molecularly typed for HLA-DRB1 gene expression. Univariate analysis revealed higher frequencies of DR2 (odds ratio [OR], 4.8; 95% confidence interval [CI], 1.2–18.8) and DR5 (OR, 7.5; 95% CI, 1.5–37.5) but lower frequencies of DR4 (OR, 2.3; 95% CI, 1.1–4.9) and DR6 (OR, 2.8; 95% CI, 1.4–5.8), in rubella vaccinees compared with placebo recipients with arthropathy. Logistic regression modelling of DR, treatment, age, time postpartum, and arthropathy revealed that the odds of developing arthropathy was 1.9 times greater (95% CI, 1.07–3.44) after rubella vaccine than placebo. Risk for arthropathy (regardless of rubella vaccination) was also influenced by DR interactions: odds were 8 times greater in individuals with both DR1 and DR4 (95% CI, 1.45–44.02) and 7.1 times greater with both DR4 and DR6 present (95% CI, 1.85–27.52]), suggesting that coexpression of these specificities may predispose to postpartum arthropathy. [ABSTRACT FROM PUBLISHER]