Value of antibodies to islet protein tyrosine phosphatase-like molecule in predicting type 1 diabetes

Clinical Significance of Diabetes-Mellitus-Associated Antibodies in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a canonical autoimmune disease that shares numerous risk factors with diabetes mellitus (DM). The production of autoantibodies is a characteristic feature in both diseases. To determine the frequency and specificity of DM-related antibodies (DMab) in RA patients and to study whether DMab associates with new DM cases in RA patients, we measured DMab defined as IgG against glutamic acid decarboxylase (GADA), tyrosine phosphatase (IA2-ab), and zinc transporter (ZnT8-ab) in a cohort of 290 RA patients (215 women and 75 men, median disease duration 11 years). Of those, 21 had a DM diagnosis at baseline. The development of new DM cases and mortality were traced in a 10-year prospective follow-up. Predictive analyses for DM and mortality were carried out by the Mantel-Cox regression. We found that 27 of the patients (9.3%) had DMab, equally often men and women. The presence of DMab was more frequent in patients with DM (p = 0.027. OR 4.01, 95%CI [1.20; 11.97]), suggesting their specificity for the disease. Men had more prevalent incidental DM at the baseline (12% vs. 5%, p = 0.030) and among the new DM cases (p = 0.012. HR 6.08, 95%CI [1.57; 25]). New DM developed equally frequently in DMab-positive and DMab-negative patients. DM, but not DMab, significantly increased the estimated mortality rate in RA patients (p = 0.021, OR 4.38 [1.2; 13.52]). Taken together, we conclude that DMab are associated with DM in RA patients, but they are not solely enough to predict disease development or mortality in those patients.

Construction of a novel vaccine by conjugating a B-cell epitope of DPP4 to peptide IA2(5)-P2-1 to significantly control type 1 diabetes in NOD mice

Type 1 diabetes is a chronic organ-specific autoimmune disease in which selective destruction of insulin-producing β cells leads to impaired glucose metabolism and its attendant complications. IA2(5)P2-1, a potent immunogenic carrier which designed by our laboratory, can induce high titer specific antibodies when carry a B cell epitope, such as B cell epitopes of DPP4, xanthine oxidase, and Urate transporter protein. In this report, we describe a novel multi-epitope vaccine composing a peptide of DPP4, an anti-diabetic B epitope of Insulinoma antigen-2(IA-2) and a Th2 epitope (P2:IPALDSLTPANED) of P277 peptide in human heat shock protein 60 (HSP60). Immunization with the multi-epitope vaccine in non-obese diabetic (NOD) mice successfully induced specific anti-DPP4 antibody, inhibited plasma DPP4 activity, and increased serum GLP-1 level. Moreover, this antibody titer was correlated with the dose of immunization (20μg, 100μg). Inoculation of this vaccine in NOD mice significantly control blood glucose level, improved glucose excursion and increased insulin level in vivo. Consistent with a lower diabetic and insulitis incidence, a induced splenic T cells proliferation and tolerance were observed. IFN-γ secretion reduced and IL-10 increased significantly in the D41-IA2(5)-P2-1 treated mice compared to P277 and control group due to the potential immunomodulatory effect of the epitope in the vaccine. Immunohistochemical analysis and cytometry showed a rebalance of Th1/Th2 in NOD mice. Our results demonstrate that this multi-epitope vaccine may serve as a promising therapeutic approach for type 1 diabetes.

Novel prokaryotic expression of thioredoxin-fused insulinoma associated protein tyrosine phosphatase 2 (IA-2), its characterization and immunodiagnostic application

Background

The insulinoma associated protein tyrosine phosphatase 2 (IA-2) is one of the immunodominant autoantigens involved in the autoimmune attack to the beta-cell in Type 1 Diabetes Mellitus. In this work we have developed a complete and original process for the production and recovery of the properly folded intracellular domain of IA-2 fused to thioredoxin (TrxIA-2_ic) in Escherichia coli GI698 and GI724 strains. We have also carried out the biochemical and immunochemical characterization of TrxIA-2_icand design variants of non-radiometric immunoassays for the efficient detection of IA-2 autoantibodies (IA-2A).

Results

The main findings can be summarized in the following statements: i) TrxIA-2_ic expression after 3 h of induction on GI724 strain yielded ≈ 10 mg of highly pure TrxIA-2_ic/L of culture medium by a single step purification by affinity chromatography, ii) the molecular weight of TrxIA-2_ic (55,358 Da) could be estimated by SDS-PAGE, size exclusion chromatography and mass spectrometry, iii) TrxIA-2_ic was properly identified by western blot and mass spectrometric analysis of proteolytic digestions (63.25 % total coverage), iv) excellent immunochemical behavior of properly folded full TrxIA-2_ic was legitimized by inhibition or displacement of [³⁵S]IA-2 binding from IA-2A present in Argentinian Type 1 Diabetic patients, v) great stability over time was found under proper storage conditions and vi) low cost and environmentally harmless ELISA methods for IA-2A assessment were developed, with colorimetric or chemiluminescent detection.

Conclusions

E. coli GI724 strain emerged as a handy source of recombinant IA-2_ic, achieving high levels of expression as a thioredoxin fusion protein, adequately validated and applicable to the development of innovative and cost-effective immunoassays for IA-2A detection in most laboratories.

Electronic supplementary material

The online version of this article (doi:10.1186/s12896-016-0309-2) contains supplementary material, which is available to authorized users.

Pathophysiologic changes in IA-2/IA-2β null mice are secondary to alterations in the secretion of hormones and neurotransmitters

IA-2 and IA-2β are transmembrane proteins of dense-core vesicles (DCV). The deletion of these proteins results in a reduction in the number of DCV and the secretion of hormones and neurotransmitters. As a result, this leads to a variety of pathophysiologic changes. The purpose of this review is to describe these changes, which are characterized by glucose intolerance, female infertility, behavior and learning abnormalities and alterations in the diurnal circadian rhythms of blood pressure, heart rate, spontaneous physical activity and body temperature. These findings show that the deletion of IA-2 and IA-2β results in multiple pathophysiologic changes and represents a unique in vivo model for studying the effect of hormone and neurotransmitter reduction on known and still unrecognized targets.

Predictive models of type 1 diabetes progression: understanding T-cell cycles and their implications on autoantibody release

Defining the role of T-cell avidity and killing efficacy in forming immunological response(s), leading to relapse-remission and autoantibody release in autoimmune type 1 diabetes (T1D), remains incompletely understood. Using competition-based population models of T- and B-cells, we provide a predictive tool to determine how these two parametric quantities, namely, avidity and killing efficacy, affect disease outcomes. We show that, in the presence of T-cell competition, successive waves along with cyclic fluctuations in the number of T-cells are exhibited by the model, with the former induced by transient bistability and the latter by transient periodic orbits. We hypothesize that these two immunological processes are responsible for making T1D a relapsing-remitting disease within prolonged but limited durations. The period and the number of peaks of these two processes differ, making them potential candidates to determine how plausible waves and cyclic fluctuations are in producing such effects. By assuming that T-cell and B-cell avidities are correlated, we demonstrate that autoantibodies associated with the higher avidity T-cell clones are first to be detected, and they reach their detectability level faster than those associated with the low avidity clones, independent of what T-cell killing efficacies are. Such outcomes are consistent with experimental observations in humans and they provide a rationale for observing rapid and slow progressors of T1D in high risk subjects. Our analysis of the models also reveals that it is possible to improve disease outcomes by unexpectedly increasing the avidity of certain subclones of T-cells. The decline in the number of β-cells in these cases still occurs, but it terminates early, leaving sufficient number of functioning β-cells in operation and the affected individual asymptomatic. These results indicate that the models presented here are of clinical relevance because of their potential use in developing predictive algorithms of rapid and slow progression to clinical T1D.

Risk factors and primary prevention trials for type 1 diabetes

Type 1 diabetes mellitus (T1DM) is a chronic autoimmune disease resulting in the designated immune destruction of insulin producing β-cells, usually diagnosed in youth, and associated with important psychological, familial, and social disorders. Once diagnosed, patients need lifelong insulin treatment and will experience multiple disease-associated complications. There is no cure for T1DM currently. The last decade has witnessed great progress in elucidating the causes and treatment of the disease based on numerous researches both in rodent models of spontaneous diabetes and in humans. This article summarises our current understanding of the pathogenesis of T1DM, the roles of the immune system, genes, environment and other factors in the continuing and rapid increase in T1DM incidence at younger ages in humans. In addition, we discuss the strategies for primary and secondary prevention trials of T1DM. The purpose of this review is to provide an overview of this disorder's pathogenesis, risk factors that cause the disease, as well as to bring forward an ideal approach to prevent and cure the disorder.

Glycotoxin and autoantibodies are additive environmentally determined predictors of type 1 diabetes: a twin and population study

In type 1 diabetes, diabetes-associated autoantibodies, including islet cell antibodies (ICAs), reflect adaptive immunity, while increased serum N(ε)-carboxymethyl-lysine (CML), an advanced glycation end product, is associated with proinflammation. We assessed whether serum CML and autoantibodies predicted type 1 diabetes and to what extent they were determined by genetic or environmental factors. Of 7,287 unselected schoolchildren screened, 115 were ICA(+) and were tested for baseline CML and diabetes autoantibodies and followed (for median 7 years), whereas a random selection (n = 2,102) had CML tested. CML and diabetes autoantibodies were determined in a classic twin study of twin pairs discordant for type 1 diabetes (32 monozygotic, 32 dizygotic pairs). CML was determined by enzyme-linked immunosorbent assay, autoantibodies were determined by radioimmunoprecipitation, ICA was determined by indirect immunofluorescence, and HLA class II genotyping was determined by sequence-specific oligonucleotides. CML was increased in ICA(+) and prediabetic schoolchildren and in diabetic and nondiabetic twins (all P < 0.001). Elevated levels of CML in ICA(+) children were a persistent, independent predictor of diabetes progression, in addition to autoantibodies and HLA risk. In twins model fitting, familial environment explained 75% of CML variance, and nonshared environment explained all autoantibody variance. Serum CML, a glycotoxin, emerged as an environmentally determined diabetes risk factor, in addition to autoimmunity and HLA genetic risk, and a potential therapeutic target.

Twin studies in autoimmune disease: genetics, gender and environment

Twin studies are powerful tools to discriminate whether a complex disease is due to genetic or environmental factors. High concordance rates among monozygotic (MZ) twins support genetic factors being predominantly involved, whilst low rates are suggestive of environmental factors. Twin studies have often been utilised in the study of systemic and organ specific autoimmune diseases. As an example, type I diabetes mellitus has been investigated to establish that that disease is largely affected by genetic factors, compared to rheumatoid arthritis or scleroderma, which have a weaker genetic association. However, large twin studies are scarce or virtually non-existent in other autoimmune diseases which have been limited to few sets of twins and individual case reports. In addition to the study of the genetic and environmental contributions to disease, it is likely that twin studies will also provide data in regards to the clinical course of disease, as well as risk for development in related individuals. More importantly, genome-wide association studies have thus far reported genomic variants that only account for a minority of autoimmunity cases, and cannot explain disease discordance in MZ twins. Future research is therefore encouraged not only in the analysis of twins with autoimmune disease, but also in regards to epigenetic factors or rare variants that may be discovered with next-generation sequencing. This review will examine the literature surrounding twin studies in autoimmune disease including discussions of genetics and gender.

Beyond the hormone: insulin as an autoimmune target in type 1 diabetes

Insulin is not only the hormone produced by pancreatic β-cells but also a key target antigen of the autoimmune islet destruction leading to type 1 diabetes. Despite cultural biases between the fields of endocrinology and immunology, these two facets should not be regarded separately, but rather harmonized in a unifying picture of diabetes pathogenesis. There is increasing evidence suggesting that metabolic factors (β-cell dysfunction, insulin resistance) and immunological components (inflammation and β-cell-directed adaptive immune responses) may synergize toward islet destruction, with insulin standing at the crossroad of these pathways. This concept further calls for a revision of the classical dichotomy between type 1 and type 2 diabetes because metabolic and immune mechanisms may both contribute to different extents to the development of different forms of diabetes. After providing a background on the mechanisms of β-cell autoimmunity, we will explain the role of insulin and its precursors as target antigens expressed not only by β-cells but also in the thymus. Available knowledge on the autoimmune antibody and T-cell responses against insulin will be summarized. A unifying scheme will be proposed to show how different aspects of insulin biology may lead to β-cell destruction and may be therapeutically exploited. We will argue about possible reasons why insulin remains the mainstay of metabolic control in type 1 diabetes but has so far failed to prevent or halt β-cell autoimmunity as an immune modulatory reagent.

Identification of type 1 diabetes-associated DNA methylation variable positions that precede disease diagnosis

Monozygotic (MZ) twin pair discordance for childhood-onset Type 1 Diabetes (T1D) is ∼50%, implicating roles for genetic and non-genetic factors in the aetiology of this complex autoimmune disease. Although significant progress has been made in elucidating the genetics of T1D in recent years, the non-genetic component has remained poorly defined. We hypothesized that epigenetic variation could underlie some of the non-genetic component of T1D aetiology and, thus, performed an epigenome-wide association study (EWAS) for this disease. We generated genome-wide DNA methylation profiles of purified CD14⁺ monocytes (an immune effector cell type relevant to T1D pathogenesis) from 15 T1D–discordant MZ twin pairs. This identified 132 different CpG sites at which the direction of the intra-MZ pair DNA methylation difference significantly correlated with the diabetic state, i.e. T1D–associated methylation variable positions (T1D–MVPs). We confirmed these T1D–MVPs display statistically significant intra-MZ pair DNA methylation differences in the expected direction in an independent set of T1D–discordant MZ pairs (P = 0.035). Then, to establish the temporal origins of the T1D–MVPs, we generated two further genome-wide datasets and established that, when compared with controls, T1D–MVPs are enriched in singletons both before (P = 0.001) and at (P = 0.015) disease diagnosis, and also in singletons positive for diabetes-associated autoantibodies but disease-free even after 12 years follow-up (P = 0.0023). Combined, these results suggest that T1D–MVPs arise very early in the etiological process that leads to overt T1D. Our EWAS of T1D represents an important contribution toward understanding the etiological role of epigenetic variation in type 1 diabetes, and it is also the first systematic analysis of the temporal origins of disease-associated epigenetic variation for any human complex disease.

Type 1 diabetes (T1D) is a complex autoimmune disease affecting >30 million people worldwide. It is caused by a combination of genetic and non-genetic factors, leading to destruction of insulin-secreting cells. Although significant progress has recently been made in elucidating the genetics of T1D, the non-genetic component has remained poorly defined. Epigenetic modifications, such as methylation of DNA, are indispensable for genomic processes such as transcriptional regulation and are frequently perturbed in human disease. We therefore hypothesized that epigenetic variation could underlie some of the non-genetic component of T1D aetiology, and we performed a genome-wide DNA methylation analysis of a specific subset of immune cells (monocytes) from monozygotic twins discordant for T1D. This revealed the presence of T1D–specific methylation variable positions (T1D–MVPs) in the T1D–affected co-twins. Since these T1D–MVPs were found in MZ twins, they cannot be due to genetic differences. Additional experiments revealed that some of these T1D–MVPs are found in individuals before T1D diagnosis, suggesting they arise very early in the process that leads to overt T1D and are not simply due to post-disease associated factors (e.g. medication or long-term metabolic changes). T1D–MVPs may thus potentially represent a previously unappreciated, and important, component of type 1 diabetes risk.

Monocyte gene-expression profiles associated with childhood-onset type 1 diabetes and disease risk: a study of identical twins

OBJECTIVE

Monocytes in childhood-onset type 1 diabetes show distinct gene expression. We hypothesize that monocyte activation in monozygotic (MZ) twin pairs discordant for childhood-onset type 1 diabetes could reflect distinct stages of the disease process including diabetes susceptibility (differences between twins, both diabetic and nondiabetic, and control subjects) and/or disease progression (differences between diabetic and nondiabetic twins).

RESEARCH DESIGN AND METHODS

We studied patterns of inflammatory gene expression in peripheral blood monocytes of MZ twin pairs (n = 10 pairs) discordant for childhood-onset type 1 diabetes, normal control twin pairs (n = 10 pairs), and healthy control subjects (n = 51) using quantitative-PCR (Q-PCR). We tested the 24 genes previously observed by whole genome analyses and verified by Q-PCR in autoimmune diabetes and performed a hierarchical cluster analysis.

RESULTS

Of 24 genes abnormally expressed in childhood-onset type 1 diabetes, we revalidated abnormal expression in 16 of them in diabetic twins including distinct sets of downregulated (P < 0.03) and upregulated (P < 0.02) genes. Of these 16 genes, 13 were abnormally expressed in nondiabetic twins, implicating these genes in diabetes susceptibility (P < 0.044 for all). Cluster analysis of monocyte gene-expression in nondiabetic twins identified two distinct, mutually exclusive clusters, while diabetic twins had a network of positively correlated genes.

CONCLUSIONS

Patients with childhood-onset type 1 diabetes show abnormal monocyte gene-expression levels with an altered gene-expression network due to gene-environment interaction. Importantly, perturbed gene-expression clusters were also detected in nondiabetic twins, implicating monocyte abnormalities in susceptibility to diabetes.

Organ specific autoantibodies in preclinical and early clinical type 1 diabetes in Turkey

Type 1 diabetes mellitus (T1D) patients (G1; n=73) and first degree relatives with islet cell antibody (ICA) values of >or=10 JDF u twice or >or=20 JDF u one and loss of FPIR (G2; n=18) were screened for two other autoantibodies, anti-glutamic acid decarboxylase (GADA) and insulin autoantibodies (IAA), and for other organ-specific autoantibodies, anti-gastric parietal cell (anti-PCA) and anti-thyroid peroxidase (anti-TPO) as well. The two control groups consisted of healthy subjects (G3; n:55 and G4; n:13). In G1, positivity of ICA, GADA, IAA, anti-TPO and anti-PCA were 63%, 75.1%, 27.4%, 17.8% and 8.2%, respectively. In G2, positivity for GADA, IAA, anti-TPO and anti-PCA were 55.6%, 11.1%, 16.7% and 11.1%, respectively. None of the anti-TPO or anti-PCA positive cases had clinical or laboratory thyroid disease or pernicious anemia. Other organ specific antibodies, in case they accompany GADAand/or IAA in high risk individuals, result in higher risk for T1D. Moreover, this condition may indicate future potential for developing thyrogastric autoimmune diseases. In conclusion; autoantibodies are markers for autoimmune destruction in T1D, and for identification of subjects at risk for disease. Even at the time of diagnosis of T1D, screening for thyrogastric autoimmunity might be recommended for early detection of the relevant diseases.

Resetting the functional capacity of regulatory T cells: a novel immunotherapeutic strategy to promote immune tolerance

Over the last few years, there has been a re-emergence of the concept of suppressor/regulatory T cells among the central players of immune mechanisms controlling a wide variety of immune responses from physiological autoreactivity (i.e., response to self-antigens) to responses to transplants, tumours and infectious antigens. Regulatory T cells are diverse in their phenotypes, antigen specificity, mode of action and immunopathological relevance. This review briefly summarises studies from the authors' group showing that specialised subsets of regulatory T cells are instrumental in the control of autoimmune diseases and more specifically of Type 1 diabetes. In addition, this review will provide evidence supporting the notion that CD3-specific monoclonal antibodies are representatives of a new category of immunotherapeutic agents that possess the unique capacity to promote immunological tolerance (an antigen-specific unresponsiveness in the absence of long-term generalised immunosuppression) through their ability to induce immunoregulatory T cells.

Identical twins discordant for type 1 diabetes show a different pattern of in vitro CD56+ cell activation

BACKGROUND

Recent studies in animal models indicate a role for natural killer (NK) cells in the protection against type 1 diabetes. In humans, a reduction of NK cell numbers has been reported in identical twins discordant for type 1 diabetes, irrespective of whether they have the disease. Here we have tested whether the activation and expansion of human NK cells with lipopolysaccharide (LPS) reveals differences between these twins.

METHODS

Proportions of CD56(+) NK cells and T-cells and Va24Vb11(+) NK-T cells from diabetic and non-diabetic twins was assessed before and after activation using flow cytometry. NK receptor usage was monitored by PCR and flow cytometry.

RESULTS

The profile of the expressed Killer Cell immunoglobulin-like receptor (KIR) repertoire (using mRNA) in freshly isolated NK cells was identical in pairs of identical twins, despite marked variation among individual twins as well as controls. Basal numbers of CD56(+) and CD94(+) (CD3(-) and CD3(+)) cells and Valpha24(+)Vbeta11(+) NK-T cells were similarly strongly correlated between identical twins (p < 0.006 for all correlations). Following LPS stimulation, the pattern of KIR mRNA expression remained unaltered in twins and the proportion of NK cells and Valpha24(+)Vbeta11(+) NK-T cells remained correlated between pairs of twins. However, there was a significant reduction in the proportion of CD56(+) cells and CD94(+) cells (whether defined as CD3(-) or CD3(+)) responding to LPS in the diabetic compared to the non-diabetic twin (p = 0.031 and 0.025, respectively).

CONCLUSION

This reduction in NK cell expansion in response to LPS in patients with type 1 diabetes is consistent with a non-genetically determined alteration in the innate immune response either predisposing to or resulting from the disease.

The effects of calcitriol and nicotinamide on residual pancreatic beta-cell function in patients with recent-onset Type 1 diabetes (IMDIAB XI)

BACKGROUND

A number of recent studies underline the importance of vitamin D in the pathogenesis of Type 1 diabetes (T1D).

AIMS

The aim of this study was to investigate whether supplementation with the active form of vitamin D (calcitriol) in subjects with recent-onset T1D protects residual pancreatic beta-cell function and improves glycaemic control (HbA(1c) and insulin requirement).

METHODS

In this open-label randomized trial, 70 subjects with recent-onset T1D, mean age 13.6 years +/- 7.6 sd were randomized to calcitriol (0.25 microg on alternate days) or nicotinamide (25 mg/kg daily) and followed up for 1 year. Intensive insulin therapy was implemented with three daily injections of regular insulin + NPH insulin at bedtime.

RESULTS

No significant differences were observed between calcitriol and nicotinamide groups in respect of baseline/stimulated C-peptide or HbA1c 1 year after diagnosis, but the insulin dose at 3 and 6 months was significantly reduced in the calcitriol group.

CONCLUSIONS

At the dosage used, calcitriol has a modest effect on residual pancreatic beta-cell function and only temporarily reduces the insulin dose.

Developments in the prediction of type 1 diabetes mellitus, with special reference to insulin autoantibodies

The prodromal phase of type 1 diabetes is characterised by the appearance of multiple islet-cell related autoantibodies (Aab). The major target antigens are islet-cell antigen, glutamic acid decarboxylase (GAD), protein-tyrosine phosphatase-2 (IA-2) and insulin. Insulin autoantibodies (IAA), in contrast to the other autoimmune markers, are the only beta-cell specific antibodies. There is general consensus that the presence of multiple Aab (> or = 3) is associated with a high risk of developing diabetes, where the presence of a single islet-cell-related Aab has usually a low predictive value. The most commonly used assay format for the detection of Aab to GAD, IA-2 and insulin is the fluid-phase radiobinding assay. The RBA does not identify or measure Aab, but merely detects its presence. However, on the basis of molecular studies, disease-specific constructs of GAD and IA-2 have been employed leading to somewhat improved sensitivity and specificity of the RBA. Serological studies have shown epitope restriction of IAA that can differentiate diabetes-related from unrelated IAA, but current assays do not distinguish between disease-predictive and non-predictive IAA or between IAA and insulin antibodies (IA). More recently, phage display technology has been successful in identifying disease-specific anti-idiotopes of insulin. In addition, phage display has facilitated the in vitro production of antibodies with high affinity. Identification of disease-specific anti-idiotopes of insulin should enable the production of a high affinity reagent against the same anti-idiotope. Such a development would form the basis of a disease-specific radioimmunoassay able to identify and measure particular idiotypes, rather than merely detect and titrate IAA.

The dense core transmembrane vesicle protein IA-2 is a regulator of vesicle number and insulin secretion

IA-2 is an enzymatically inactive member of the transmembrane protein tyrosine phosphate family located in dense core secretory vesicles and a major autoantigen in type 1 diabetes. Recent studies showed that targeted disruption of the IA-2 gene in mice resulted in impairment of insulin secretion and glucose intolerance. Insulin homeostasis, however, is a complex process involving a cascade of regulatory factors, and IA-2 is widely expressed in neuroendocrine cells throughout the body. Consequently, it is uncertain whether the impairment of insulin secretion in IA-2 knockout mice is a direct result of the knockout of IA-2 in beta cells or to counter regulatory alterations resulting from IA-2 knockout in other neuroendocrine cells. To define the function of IA-2, we studied the secretion of insulin in a single cell type, MIN-6, by overexpressing and knocking down IA-2. Our experiments showed that overexpression of IA-2 resulted in a 6-fold increase in glucose- or K+-induced insulin secretion and a approximately 3-fold increase in the number of secretory vesicles and the insulin content of cells. In contrast, knockdown of endogenous IA-2 by short interfering RNA resulted in nearly a complete loss of glucose-induced insulin secretion and a 50% decrease in basal insulin release. The half-life of insulin in cells overexpressing IA-2 was nearly twice as great as that in mock-transfected cells, suggesting that IA-2 was stabilizing the insulin-containing vesicles. From these results we conclude that in beta cells, IA-2 is an important regulator of dense core vesicle number and glucose-induced and basal insulin secretion.

Autoantibodies against IA-2, GAD, and topoisomerase II in type 1 diabetic patients

Prevalence of autoantibodies against IA-2 (IA-2A), glutamic acid decarboxylase (GADA), and type II DNA topoisomerase (TopIIA) of Taiwanese type 1 diabetes mellitus (T1DM) patients was investigated. Correlations of these autoantibodies with patients' clinical manifestations were also analyzed. Prevalence of IA-2A, GADA, and TopIIA in our patients was 23.6%, 47.1%, and 55.2%, respectively. Eighty percent of the IA-2A recognized the carboxyl terminus of the IA-2 protein tyrosine phosphatase-like domain. Average disease duration of IA-2A+ patients was significantly shorter than that of IA-2A- patients [3.76+/-0.42 vs. 4.98+/-0.34 years, p = 0.028]. Presence of GADA was correlated with the mean age of onset [10.82+/-0.76 vs. 8.38+/-0.77 years for GADA+ and GADA- patients, p = 0.026]. Patients with adolescent onset have higher GADA prevalence and better residual beta-cell functions. TopIIA and GADA are suggested to be better markers for Taiwanese T1DM patients because of their higher prevalence and persistence.

Primary biliary cirrhosis in monozygotic and dizygotic twins: genetics, epigenetics, and environment

BACKGROUND & AIMS

There is growing evidence that the interplay of genetic susceptibility and environmental factors leads to primary biliary cirrhosis (PBC). In particular, family members of an infected individual have up to a 100-fold higher risk of developing PBC. Although concordant rates for identical twins in other autoimmune diseases range between 25% and 50%, there are no such data on PBC. Accordingly, we evaluated the concordance of PBC in a genetically defined population of twin sets and evaluated the clinical characteristics between concordant subjects.

METHODS

We identified 16 pairs of twins within a 1400-family cohort followed up by several centers worldwide, evaluated the diagnosis of PBC in all individuals, and determined the zygosity of sets reported as identical by the analysis of 2 highly variable HLA class II regions and 5 short tandem repeats.

RESULTS

Eight of 16 sets of twins were monozygotic. In 5 of 8 monozygotic twin sets, both individuals had PBC (pairwise concordance rate, 0.63). Among the dizygotic twins (n = 8), no set was found to be concordant for PBC. Interestingly, the age at onset of disease was similar in 4 of 5 concordant sets of monozygotic pairs; however, there were differences in natural history and disease severity.

CONCLUSIONS

The concordance rate of PBC in identical twins is among the highest reported in autoimmunity. However, discordant pairs were identified. The data show not only the role of genetics but also emphasize that either epigenetic factors and/or environment play a critical role.

Low prevalence of autoimmune diabetes markers in a mixed ethnic population of Singaporean diabetics

BACKGROUND

Circulating antibodies to glutamic acid decarboxylase (GADab) and tyrosine phosphatase-like molecule IA-2 (IA-2ab) are major indicators for auto-immune destruction of pancreatic islet cells. They identify a majority of Caucasians with type 1 diabetes and approximately 50% of Asians, providing evidence of an idiopathic aetiology in the latter. The present study investigated these autoantibodies in a mixed ethnic group.

METHODS

Hospital clinic patients with clinically defined type 1 (n = 93) and type 2 (n = 300) diabetes and representing Singapore's major ethnic groups--Chinese, Indians and Malays--were studied. GADab and IA-2ab frequencies, and association of autoimmunity status with clinical and biochemical profiles were analysed.

RESULTS

Radio-immunoprecipitation assays detected either or both antibodies (seropositivity) in 41.9% of subjects with type 1 diabetes. GADab was detected in 36.6% and IA-2ab in 23.7% of type 1 diabetics. Prevalence of IA-2ab showed a reduction in frequency with disease duration (P = 0.026). In clinical type 2 diabetics, seropositivity was 10.0% with higher frequency in Malays (17.5%) than Chinese (9.7%) and Indians (4.5%). Multivariate analysis revealed that low fasting C-peptide was associated with seropositivity (odds ratio (OR) = 0.15; 95% confidence interval (CI) = 0.04-0.58). A significant relationship (OR = 13.5; 95% CI = 5.0-36.7) between insulin requirement and duration (>5 years) was also revealed. In patients with type 2 diabetes there was a trend of gradual progression to insulin dependency. However, there was considerable variation in body mass index between ethnic subgroups of type 2 diabetics, particularly for Chinese (mean (SD) = 26.0 (4.7)) and Malays (mean (SD) = 29.2 (5.9); P < 0.001).

CONCLUSIONS

Presence of both antibodies in our mixed ethnic group of type 1 diabetes patients was much lower than in Caucasians. Significant numbers of patients were seronegative for antibodies. Influences due to ethnicity and adiposity would require further investigations.

Humoral and Cellular Autoimmune Responses in Stiff Person Syndrome

Stiff person syndrome (SPS) is a chronic autoimmune disease associated with humoral and cellular immune responses to glutamic acid decarboxylase (GAD) 65. Another chronic autoimmune disease, type 1 diabetes (T1D), is also associated with autoimmune responses to this antigen, but T1D patients develop SPS only extremely rarely and only a third of SPS patients develop T1D (mostly mild manifestations in adulthood). In a previous study, we described important differences between T1D and SPS in the autoimmune response to GAD 65: (1) T cells of SPS patients recognize epitopes in the middle of GAD 65 (amino residues 81-171 and 313-403), whereas patients with T1D preferentially recognize another middle (161-243) and a C-terminal region (473-555); and (2) GAD antibodies (Abs) were nearly exclusively of the Th1-associated IgG1 type in T1D, whereas SPS patients had both Th1- and Th2-associated IgG4 and IgE GAD Abs. These differences were not simply related to different HLA alleles. Fine epitope mapping revealed further distinct T cell epitopes in both diseases despite similar HLA background. Therefore, a single autoantigen can elicit different immune responses causing distinct chronic autoimmune diseases possibly related to a Th1 or Th2 bias of the disease.

Evidence for a locus (IDDM16) in the immunoglobulin heavy chain region on chromosome 14q32.3 producing susceptibility to type 1 diabetes

Type 1 diabetes results from autoimmune destruction of pancreatic islet beta-cells, possibly initiated or exacerbated by viral infections. Recent studies have demonstrated that antibodies towards enterovirus and autoantibodies towards islet cell components develop in the long preclinical phase of type 1 diabetes. We therefore hypothesised that susceptibility to type 1 diabetes could be influenced by genetic factors controlling production of antiviral antibodies or autoantibodies or both. To search for evidence of linkage or association (linkage disequilibrium) between type 1 diabetes and the immunoglobulin heavy chain (IGH) region, 351 North American and British families with > or =2 diabetic children were genotyped for IGH region microsatellites. Using affected sibpair analysis, significant evidence for linkage was obtained for three markers close to the IGH gene cluster (P values 0.004, 0.002, 0.002). No evidence was found for association using family-based methods. To attempt to confirm these findings, a smaller dataset (241 families, 138 with > or =2 diabetic children) from Denmark, a more genetically-homogeneous population, was genotyped for one marker only. These families showed no linkage, but significant evidence for association (P = 0.019). This study suggests that a locus (assigned the symbol IDDM16) in the IGH region, possibly an IGH gene, influences susceptibility to type 1 diabetes.

Impact of genetic and non-genetic factors in type 1 diabetes

Type 1 insulin-dependent diabetes is due to destruction of the insulin secreting cells of the islets of Langerhans. The disease is caused by non-genetic, probably environmental, factors operating in a genetically susceptible host to initiate a destructive immune process. These unknown environmental factors may operate over a limited period either in early or later and to a variable degree, playing a particularly substantial role in adults. The environment then induces an immune process associated with destruction of the islet beta cell that can be detected in early life and persists up to disease onset. Apart from an association with the insulin gene there is no evidence that genes associated with type 1 diabetes, including HLA and CTLA4 influence the targeting of the immune response to the insulin-secreting cells. The critical period of immune activation is probably short and the process leading to diabetes probably has a long prodrome but of variable duration that determines the age at presentation with clinical disease. The amplification both of this immune response and the destructive process is in part genetically determined, involving HLA genes. The clinical spectrum of the disease process associated with type 1 diabetes is wide, encompassing insulin-dependence, non-insulin dependence and even transient impaired glucose tolerance. Type 1 diabetes presenting in adults, in contrast to children, is predominantly determined by non-genetic factors with a reduced role for protective and susceptibility HLA alleles. Thus, the evidence is that genes involved in genetic susceptibility to type 1 diabetes operate predominantly in children not adults and in both amplify the immune response and the rate of disease progression.

ICA512(IA-2) epitope specific assays distinguish transient from diabetes associated autoantibodies

ICA512/IA-2, a tyrosine phosphatase-like protein, is one of the major autoantigens in type 1 diabetes. Following phage display characterization of ICA512 autoantigenic epitopes, we developed fluid phase autoantibody radioimmunoassays for a series of ICA512 fragments (F1 [amino acids (aa): 761-964], F2A [aa 256-760], F2B [aa 761-928], and F2C [aa 929-979]). With the hypothesis that 'non-diabetes associated' ICA512 autoantibodies would differ from diabetes associated ICA512 autoantibodies in terms of epitopes recognized, we analyzed ten such serum samples (two from normal control individuals, one from a general population subject with transient ICA512 autoantibodies and seven from relatives of patients with type 1 diabetes who had single transient ICA512 positivity). All but one of the 'non-diabetes associated' ICA512 positive samples (9/10) did not react with Fragment 1 which contains the major antigenic epitopes of the molecule that were recognized by almost all (51/52) ICA512 positive new onset patient samples and pre-diabetic relatives (P< 10(-6)). The great majority of samples (44/52) from the new onset patients and pre-diabetic relatives reacted with at least two fragments and 60% (31/52) with three or more fragments. In contrast, only one sample of the ICA512 'non-diabetes associated' sera reacted with multiple fragments (P< 10(-4)). Our findings suggest that diabetes associated anti-ICA512 autoantibodies react with multiple ICA512 epitopes while non-diabetes associated ICA512 autoantibodies may usually represent reactivity of antibodies with determinants of ICA512 unrelated to type 1 diabetes. The ability to distinguish diabetes associated from non-diabetes associated anti-ICA512 autoantibodies should provide prognostic information and more importantly suggests that even with highly specific radioassays positivity may occur unrelated to type 1 diabetes.

Antibodies to SOX13 (ICA12) are associated with type 1 diabetes

SOX13 is an islet cell autoantigen (ICA12), identified by antibody screening of an islet cDNA library, using sera from patients with Type 1 diabetes. We ascertained the frequency of antibody reactivity to SOX13 and compared it with other Type 1 diabetes autoantibody reactivities. Antibodies were measured by radioimmunoprecipitation (RIP) using (35) S labelled SOX13 expressed in rabbit reticulocyte lysate. Sera from 109 subjects with Type 1 diabetes, 29 with Type 2 diabetes, 144 with other autoimmune diseases and from 201 controls were tested for anti-SOX13, and results were compared with the frequency of antibodies to glutamic acid decarboxylase (anti-GAD), islet cell antigen 512 (anti-ICA512) and islet cell cytoplasm (ICA). Anti-SOX13 were detected in 20 (18.3%) of 109 subjects with Type 1 diabetes, and more frequently in adults than in children (29% vs 10%). Anti-SOX13 usually occurred with anti-GAD but rarely with anti-ICA512. Seven sera positive for anti-SOX13 did not react with either GAD, ICA512 or islet cell cytoplasm indicating that anti-SOX13 represented a distinct population of antibodies. Reactivity to SOX13 represents a further autoantibody response in adults with Type 1 diabetes and may provide a useful disease marker in subjects in whom other autoantibody tests are negative.

Polymorphism in gene for islet autoantigen, IA-2, and type 1 diabetes in Japanese subjects

Autoantibodies against IA-2 have been detected in up to 86% of newly diagnosed patients with type 1 diabetes and appear to identify a subgroup of prediabetic subjects who rapidly progress to type 1 diabetes. We examined the association of IA-2 gene polymorphism with type 1 diabetes in Japanese subjects. A total of 276 Japanese subjects were studied for disease association and, in addition, another 53 patients were studied for association with the autoantibody status to IA-2. A microsatellite marker D2S1753E, located in the intron of the IA-2 gene, was used as a genetic marker in this study. In Japanese, two alleles (161mu and 165mu) were more frequent, and the 163mu allele was less frequent than in Caucasians (p = 0.0001). There was no significant difference in frequencies of alleles between diabetic patients and control subjects. The frequency of IA-2 gene polymorphism was not significantly different between patients stratified by age-at-onset, or between patients with and without susceptible HLA, DRB1*0405, DRB1*0802 and DRB1*0901. There was no significant difference in allele frequency of the IA-2 gene polymorphism between patients with and without autoantibody to IA-2. In conclusion, IA-2 gene polymorphism is not associated with either susceptibility to, or heterogeneity in type 1 diabetes in Japanese subjects.

Intradermal skin test with diabetes specific antigens in patients with type 1 diabetes

Cell mediated immune response in vitro to a number of antigens has been reported in patients with Type 1 diabetes. The aim of the present study was to develop an in vivo intradermal (delayed type hypersensitivity) skin test using antigens known to be recognized by lymphocytes of patients with Type 1 diabetes and to compare, where possible, the in vivo response to the in vitro T cell proliferation to the same antigens. The skin test was performed in the following group of patients: 55 with recent onset Type 1 diabetes; 16 patients with Type 1 diabetes of longer duration; 10 patients with autoimmune thyroid disease and 20 patients with Latent Autoimmune Diabetes in Adults (LADA). Type 1 diabetes specific antigens for the skin test included glutamic acid decarboxilase (GAD65), insulin and beta casein, whereas diabetes non specific antigens included tetanus toxoid, diphteria, proteus, tubercolin, streptococcus, and glycerol as control. A multitest device consisting of heads delivering intradermally 10 microl of solution containing the antigens was applied to the forearms; the specific antigens were injected in one forearm whereas the non specific antigens were injected in the other forearm. Reading of the reaction, which was considered positive in the presence of a nodule of 2 mm diameter was performed 48 h after the multitest application. The in vitro T cell response to diabetes specific antigens used in the multitest was studied using conventional proliferation assays in patients with recent onset Type 1 diabetes and in age matched normal subjects. Only recent onset Type 1 diabetes patients showed an in vivo positive response to GAD65, such response being detectable in 10 patients (18%). Two patients reacted also to beta casein and insulin, all other patient groups resulted negative but 2 patients with longer duration of Type 1 diabetes. There was no apparent link between the in vivo skin test and in vitro T cell proliferation to GAD65. We conclude that in vivo cell mediated immune reaction to GAD65, insulin and beta casein can be visualized in a minority of patients with recent onset Type 1 diabetes. Further studies are required to determine specificity and whether altering the dose can improve the sensitivity of the test.

Humoral immunity against glutamic acid decarboxylase and tyrosine phosphatase IA-2 in Lambert-Eaton myasthenic syndrome

Some beta-cell-specific autoantigens also are present in the central nervous system. Furthermore, stiff man syndrome, an autoimmune neurological disease, is frequently associated with diabetes and shares with this one an anti-GAD and IA-2 humoral immunoreactivity. We wondered whether these autoantibodies could be found in other neurological diseases with a present or supposed autoimmune origin. So, anti-GAD65 (GAD65A) and anti-IA-2 (IA-2A) autoantibodies were assayed in various neurological diseases. There was a higher prevalence of such antibodies in Lambert-Eaton myasthenic syndrome (LEMS) (GAD65A, 35%; IA-2A, 21%; double positivity, 18%) compared to amyotrophic lateral sclerosis (18%, 12%, and 12%, respectively) and multiple sclerosis (10%, 3%, and 3%, respectively). In LEMS, the humoral reaction was more frequent and/or appeared earlier in the paraneoplastic forms. The detection of such autoantibodies in patients with small-cell lung carcinoma (SCLC) without LEMS suggests that these autoantigens, GAD65 and IA-2, could be produced by SCLC tissue.

Immune reactivity to glutamic acid decarboxylase 65 in stiffman syndrome and type 1 diabetes mellitus

BACKGROUND

The immune response to an isoform of glutamic acid decarboxylase (GAD), GAD65, is associated with two clinically distinct diseases, stiff-man syndrome (SMS) and type 1 (insulin-dependent) diabetes mellitus. We sought to identify differences in the cellular and humoral immune responses to GAD in these two diseases.

METHODS

We compared T-cell responses in 14 SMS patients with axial disease and 17 patients with type 1 diabetes.

FINDINGS

Peripheral blood T cells of eight SMS patients recognised different immunodominant epitopes of GAD65 compared with T cells from 17 patients with type 1 diabetes. GAD regions 81-171 and 313-403 induced a dominant T-cell response in six of eight patients with SMS but in only one of 17 patients with type 1 diabetes (p=0.001). No SMS patients responded dominantly to GAD fragments 161-243 and 473-555 compared with ten patients with type 1 diabetes (p=0.008). GAD antibodies were detected in 11 of 14 SMS patients (seven with diabetes) and 11 of 17 patients with type 1 diabetes; IgG1 was dominant in both groups. SMS patients, however, were more likely than patients with diabetes to have isotypes other than IgG1 (p=0.03), in particular, IgG4 or IgE isotypes, which were not detected in patients with type 1 diabetes (p=0.012).

INTERPRETATION

Our findings indicate differences between patients with SMS and type 1 diabetes in cellular (epitope recognition) and humoral (isotype pattern) responses to GAD65. Thus the same autoantigen can elicit distinct immune responses in patients with SMS, even when associated with diabetes, compared with patients with type 1 diabetes.

Proliferative responses to selected peptides of IA-2 in identical twins discordant for Type 1 diabetes

BACKGROUND

The aim of the study was to define T lymphocyte reactivity to selected peptides of an islet antigen IA-2, associated with Type 1 diabetes.

METHODS

We used 10 peptides selected from the IA-2 molecule due to their predicted ability to bind to HLA-DRB1*0401, a Type 1 diabetes-associated allele. We tested 21 identical twin pairs discordant for the disease and 15 control subjects and then followed them prospectively; seven non-diabetic twins developed diabetes.

RESULTS

Twins of identical pairs tended to respond to different peptides suggesting that the T cell response is, to a degree, shaped by non-genetically determined factors (p<0. 0001). However, there was no difference in the T cell responses between diabetic twins and either their non-diabetic identical twins or control subjects and the response was heterogenous. T cell responses did not differ in those seven non-diabetic twins who developed diabetes from those twins who did not. T cell responses to peptide 11 (amino acids 502-514) was immunodominant in diabetic twins as well as their non-diabetic twins and controls; responses were not correlated with HLA, IA-2 antibodies, age or duration of disease.

CONCLUSION

We conclude that T cell responses to selected IA-2 peptides are not genetically determined, heterogeneous, not strictly HLA controlled and did not distinguish diabetic or prediabetic twins from non-diabetic twins or controls. The identification of an immunodominant T cell response to IA-2 peptide 502-514 raises the possibility that this, or similar, epitopes may be of therapeutic value in disease prevention.

Radicals and oxidative stress in diabetes

Recent evidence is reviewed indicating increased oxidative damage in Type 1 and Type 2 diabetes mellitus as well as deficits in antioxidant defence enzymes and vitamins. Mechanisms are considered whereby hyperglycaemia can increase oxidative stress, and change the redox potential of glutathione and whereby reactive oxygen species can cause hyperglycaemia. It is argued that oxygen, antioxidant defences, and cellular redox status should now be regarded as central players in diabetes and the metabolic syndrome.

T cell reactivity to human insulinoma cell line (CM) antigens in patients with type 1 diabetes

Autoimmune (type 1) diabetes mellitus results from a progressive destruction of insulin secreting beta cells operated by T lymphocytes in pancreatic islets. Circulating autoreactive T cells to specific beta cell antigens are detected in patients with type 1 diabetes. To date, several beta cell autoantigens have been identified in this disease (GAD, IA-2, 38kD secretory protein, insulin, ICA69 etc.), however, it is possible that also other unidentified self molecules contribute to trigger beta cell autoimmunity. In this study we used the human insulinoma cell line CM as source of beta cell antigens to detect reactive T lymphocytes in patients with type 1 diabetes mellitus. This cell line has been previously shown to express a number of recognized beta cell antigens. Since the expression of several beta cell antigens is affected by glucose stimulation we tested two preparations of CM cells cultured under different conditions containing low (0.8 mM) and high glucose concentration (11 mM). T cell proliferation was measured using cells from 32 patients with type 1 diabetes (19 of recent onset and 13 at 3 to 22 months from diagnosis) and 27 age-matched control subjects. A significant increase in T cell proliferation to CM cells grown in high glucose conditions (11 mM) (p < 0.05) was found in type 1 diabetic patients compared to controls. No significant differences were observed when using CM cells cultured at the low glucose concentration. Furthermore, the response to both extracts of CM cells was independent of disease duration (p = 0.6 for both CM cells cultured at 0.8 and 11 mM glucose). These data indicate that T cell reactivity to homogenates of CM cells is detectable in patients with type 1 diabetes and suggest that this human insulinoma cell line is an interesting potential source of beta cell material for immunological studies of autoimmune diabetes.

Genetic determination of islet cell autoimmunity in monozygotic twin, dizygotic twin, and non-twin siblings of patients with type 1 diabetes: prospective twin study

OBJECTIVE

To test the hypothesis that non-diabetic dizygotic and monozygotic twin siblings of patients with type 1 diabetes have a similar high prevalence of islet cell autoantibodies, thus suggesting that islet cell autoimmunity is mainly environmentally determined.

DESIGN

Prospective twin study.

SETTING

Two specialist centres for diabetes in the United States.

PARTICIPANTS

Non-diabetic monozygotic twin (n=53), dizygotic twin (n=30), and non-twin (n=149) siblings of patients with type 1 diabetes; 101 controls.

MAIN OUTCOME MEASURES

Analysis of progression to diabetes and expression of anti-islet autoantibodies.

RESULTS

Monozygotic twin siblings had a higher risk of progression to diabetes (12/53) than dizygotic twin siblings (0/30; P<0.005). At the last follow up 22 (41.5%) monozygotic twin siblings expressed autoantibodies compared with 6 (20%) dizygotic twin siblings (P<0.05), 16 (10.7%) non-twin siblings (P<0.0001), and 6 (5.9%) controls (P<0.0001). Monozygotic twin siblings expressed multiple (>/=2) antibodies more often than dizygotic twin siblings (10/38 v 1/23; P<0.05). By life table analysis the probability of developing positive autoantibodies was higher among the monozygotic twin siblings bearing the diabetes associated HLA DQ8/DQ2 genotype than in those without this genotype (64.2% (95% confidence interval 32.5% to 96%) v 23.5% (7% to 40%) at 10 years of discordance; P<0.05).

CONCLUSION

Monozygotic and dizygotic twins differ in progression to diabetes and expression of islet cell autoantibodies. Dizygotic twin siblings are similar to non-twin siblings. These two observations suggest that genetic factors play an important part in determination of islet cell autoimmunity, thus rejecting the hypothesis. In addition, there is a high penetrance of islet cell autoimmunity in DQ8/DQ2 monozygotic twin siblings.

Genomic structure and promoter sequence of the insulin-dependent diabetes mellitus autoantigen, IA-2 (PTPRN)

IA-2 is a transmembrane protein tyrosine phosphatase, expressed in neuroendocrine cells, and a major autoantigen in insulin-dependent diabetes mellitus. In the present study we elucidated the structure of the IA-2 gene (HGMW-approved symbol PTPRN) and its promoter sequence. A 40-kb genomic clone covering the whole IA-2 coding sequence and 4 kb proximal 5'-upstream sequence was isolated and mapped. The IA-2 gene encompasses approximately 20 kb with 23 exons ranging from 34 bp to more than 650 bp. The extracellular domain is encoded by exons 1-12, the transmembrane region by exon 13, and the intracellular domain by exons 14-23. The transcriptional start site(s) of the IA-2 gene was mapped by 5' rapid amplification of cDNA ends to 97 bp upstream of the translational start site. A 3-kb 5'-upstream region was sequenced, revealing a GC-rich region and TATA-less sequence containing several potential transcription-regulating sites (i.e., Sp1, CREB, GATA-1, and MZF). Functional promoter activity was confirmed by transient transfection of U87MG cells with deletion mutants linked to a luciferase reporter gene.

Identification of autoantigen epitopes in MHC class II transgenic mice

MHC class II molecules function by selective binding of antigenic peptides, thereby both shaping the T-cell receptor (TCR) repertoire in the thymus and influencing presentation of immunogenic peptides to CD4+ T cells in the periphery. The strong association between a number of human autoimmune diseases (type 1 diabetes, rheumatoid arthritis, and multiple sclerosis) and certain HLA-DR/DQ alleles suggests that it may be possible to alter pathological autoimmune responses by deliberate introduction of autoantigenic peptides in a "tolerogenic" manner. Since there are likely to be differences in epitope selection and epitope spreading in different patients over time, this approach requires identification of all the immunogenic CD4+ T-cell epitopes (dominant, subdominant, or cryptic) of an autoantigen which elicit T-cell responses restricted to the HLA-DR/DQ alleles predisposing to these autoimmune diseases. This paper describes a new approach for the identification of immunogenic peptide epitopes of human autoantigenic proteins using HLA-DR and DQ transgenic mice. These mice are engineered to select a full TCR repertoire which can identify immunogenic peptide epitopes similar or identical to human subjects of the same HLA-DR/DQ genotype. This experimental system also allows comparison of autoantigenic immune responses restricted to disease-susceptible and disease-resistant HLA-DR/DQ alleles.