IA-2, a transmembrane protein of the protein tyrosine phosphatase family, is a major autoantigen in insulin-dependent diabetes mellitus

Prediabetes in children: natural history, diagnosis, and preventive strategies

The clinical manifestation of type 1 diabetes mellitus is preceded by an asymptomatic prodromal period called prediabetes or preclinical diabetes. It may last from a few months to several years, during which the autoimmune destruction of the insulin-producing beta-cells in the pancreas progresses. The genes on the human leukocyte antigen (HLA) and insulin gene region are major genetic determinants for genetic disease susceptibility, while dietary compounds and viral infections are the most likely environmental factors contributing to the etiopathogenesis. T cells are thought to be the effector cells for the beta-cell destruction, and glutamic acid decarboxylase, insulinoma-associated protein 2 and insulin represent the three major autoantigens. Autoantibodies are early detectable markers of an ongoing disease process and are used to diagnose prediabetes. Among first-degree relatives of patients with type 1 diabetes, the risk for clinical disease can be graded from <5% in those with one or no antibodies to >90% in individuals who carry the HLA-DQB1*02/0302 risk genotype and are positive for multiple autoantibodies. beta-Cell function may also be tested in autoantibody-positive individuals and low first-phase insulin response is highly predictive for rapid progression to the clinical disease. However, dynamic course and individual variation of the disease process complicates the disease prediction, and it is not known whether all individuals with signs of prediabetes will inevitably progress to clinical type 1 diabetes. Until clinically applicable prevention for the condition exists, the screening for the risk markers of type 1 diabetes should actively be undertaken only in the context of research projects. Several major national and international multicenter studies are ongoing to test the potential of various agents (e.g. insulin and nicotinamide) or early elimination of dietary compounds (e.g. cow's milk proteins) to delay or prevent the onset of clinical type 1 diabetes.

Harnessing the Immunomodulatory Properties of Sertoli Cells to Enable Xenotransplantation in Type I Diabetes

Islet transplantation has emerged as a viable long-term means of treating type I diabetes. This is largely due to the success of the "Edmonton protocol" which has produced insulin independence in 85% of patients 1 year after transplantation of allogeneic islets together with a non-steroid immunosuppressive regimen. While these data provide a clear and unequivocal demonstration that islet transplantation is a viable treatment strategy, the shortage of suitable donor tissue together with the debilitating consequences of life-long immunosuppression necessitate the development of novel means to enable transplantation of all type 1 diabetics including the young juvenile diabetics. One potential means of enabling islet transplantation takes advantage of the ability of Sertoli cells to provide local immunoprotection to co-grafted islets, including those from xenogeneic sources. Sertoli cells are normally found in the testes where one of their functions is to provide local immunologic protection to developing germ cells. In animal models, allogeneic and xenogeneic islets survive and function for extended periods of time when grafted into the testes. Moreover, isolated Sertoli cells protect co-grafted allogeneic and xenogeneic islets from immune destruction and reverse diabetes in immunocompetent and autoimmune animals. These benefits are discussed in the context of several potential underlying biological mechanisms.

Addressing parents' concerns: do vaccines cause allergic or autoimmune diseases?

Anecdotal case reports and uncontrolled observational studies in the medical literature claim that vaccines cause chronic diseases such as asthma, multiple sclerosis, chronic arthritis, and diabetes. Several biological mechanisms have been proposed to explain how vaccines might cause allergic or autoimmune diseases. For example, allergic diseases might be caused by prevention of early childhood infections (the "hygiene hypothesis"), causing a prolongation of immunoglobulin E-promoting T-helper cell type 2-type responses. However, vaccines do not prevent most common childhood infections, and large well-controlled epidemiologic studies do not support the hypothesis that vaccines cause allergies. Autoimmune diseases might occur after immunization because proteins on microbial pathogens are similar to human proteins ("molecular mimicry") and could induce immune responses that damage human cells. However, wild-type viruses and bacteria are much better adapted to growth in humans than vaccines and much more likely to stimulate potentially damaging self-reactive lymphocytes. Consistent with critical differences between natural infection and immunization, well-controlled epidemiologic studies do not support the hypothesis that vaccines cause autoimmunity. Flaws in proposed biological mechanisms that explain how vaccines might cause chronic diseases are consistent with the findings of many well-controlled large epidemiologic studies that fail to show a causal relationship.

Effect of proinflammatory cytokines on gene expression of the diabetes-associated autoantigen IA-2 in INS-1 cells

Cytokines released from activated antigen-presenting cells and T-lymphocytes are crucially involved in the pathogenesis of type 1 diabetes. Previous studies have shown that proinflammatory cytokines play an important role in the induction of autoimmunity and beta-cell damage. Inhibition of insulin expression has been described, but their effects on other major target autoantigens, such as the tyrosine phosphatase-like protein IA-2, is not known. In the present study, we established sensitive real-time RT-PCR to measure IA-2, insulin, and inducible nitric oxide (NO) synthase (iNOS) mRNA expression. Rat insulinoma INS-1 cells were stimulated with IL-1beta, TNF-alpha, interferon (IFN)-gamma, and IL-2 as well as with two combinations of these cytokines (C1: IL-1beta + TNF-alpha + IFN-gamma; C2: TNF-alpha + IFN-gamma). Treatment with IL-1beta, TNF-alpha, or IFN-gamma alone caused a significant down-regulation of IA-2 and insulin mRNA levels in a time and dose-dependent manner, whereas IL-2 had no effect. Exposure to cytokine combinations strongly potentiates the inhibitory effects. Incubation of cells with C1 and C2 for 24 h induces a significant inhibition of IA-2 mRNA levels by 78% and 58%, respectively. Under these conditions, an up to 5 x 10(4)-fold increase of iNOS gene expression was observed. The hypothesis that the formation of NO is involved in IA-2 regulation was confirmed by the finding that the coincubation of C1 with 4 mM L-N(G)-monomethyL-L-arginine, an inhibitor of the iNOS, partly reversed the down-regulation of IA-2. Further, incubation with the synthetic NO-donor S-nitroso-N-acetyl-D-L-penicillamine significantly decreased IA-2 mRNA level to 51% of basal levels. In conclusion, we have demonstrated for the first time that IL-1beta, TNF-alpha, and IFN-gamma exert a strong inhibitory effect on expression of the diabetes autoantigen IA-2. The action of IL-1beta may be partly mediated by the activation of the NO pathway.

T-cell reactivity to glutamic acid decarboxylase in stiff-man syndrome and cerebellar ataxia associated with polyendocrine autoimmunity

Antibodies to glutamic acid decarboxilase (GAD-Abs) are present in the serum of 60-80% of newly diagnosed type 1 diabetes (DM1) patients and patients with autoimmune polyendocrine syndrome (APS) associated with DM1. Higher titre of GAD-Abs are also present in the serum of 60% of patients with stiff-man syndrome (SMS) and all reported patients with cerebellar ataxia associated with polyendocrine autoimmunity (CAPA). Several studies suggest that GAD-Abs may play a critical role in the pathogenesis of SMS and CAPA but little is known about T-cell responsiveness to GAD-65 in these neurological diseases. To analyse cell-mediated responses to GAD, we studied the peripheral blood lymphocyte proliferation and cytokine responses to recombinant human GAD-65 in 5 patients with SMS, 6 with CAPA, 9 with DM1, 8 with APS and 15 control subjects. GAD-65-specific cellular proliferation was significantly higher in SMS than in CAPA, DM1, APS or controls. In contrast, only T cells from CAPA patients showed a significantly high production of interferon-gamma after GAD stimulation, compared to all other patients and controls. No differences were found for IL-4 production. These results suggest that, despite similar humoral autoreactivity, cellular responses to GAD are different between SMS and CAPA, with a greater inflammatory response in CAPA, and this difference may be relevant to the pathogenesis of these diseases.

Targeted disruption of the protein tyrosine phosphatase-like molecule IA-2 results in alterations in glucose tolerance tests and insulin secretion

IA-2 is a major autoantigen in type 1 diabetes. Autoantibodies to IA-2 appear years before the development of clinical disease and are being widely used as predictive markers to identify individuals at risk for developing type 1 diabetes. IA-2 is an enzymatically inactive member of the transmembrane protein tyrosine phosphatase family and is an integral component of secretory granules in neuroendocrine cells. To study its function, we generated IA-2-deficient mice. Northern and Western blot analysis showed that neither IA-2 mRNA nor protein was expressed. Physical examination of the IA-2(- /-) animals and histological examination of tissues failed to reveal any abnormalities. Nonfasting blood glucose levels, measured over 6 months, were slightly elevated in male IA-2(-/-) as compared to IA-2(+ /+) littermates, but remained within the nondiabetic range. Glucose tolerance tests, however, revealed statistically significant elevation of glucose in both male and female IA-2(-/-) mice and depressed insulin release. In vitro glucose stimulation of isolated islets showed that male and female mice carrying the disrupted gene released 48% (P < 0.001) and 42% (P < 0.01) less insulin, respectively, than mice carrying the wild-type gene. We concluded that IA-2 is involved in glucose-stimulated insulin secretion.

Patterns of gene expression in the developing adult sea urchin central nervous system reveal multiple domains and deep-seated neural pentamery

The adult sea urchin central nervous system (CNS) is composed of five radial nerve cords connected to a circular nerve ring. Although much is known about the molecular mechanisms underlying the development and function of the nervous systems of many invertebrate and vertebrate species, virtually nothing is known about these processes in echinoderms. We have isolated a set of clones from a size-selected cDNA library prepared from the nervous system of the sea urchin Heliocidaris erythrogramma for use as probes. A total of 117 expressed sequence clones were used to search the GenBank database. Identified messages include genes that encode signaling proteins, cytoskeletal elements, cell surface proteins and receptors, cell proliferation and differentiation factors, transport and channel proteins, and a RNA DEAD box helicase. Expression was analyzed by RNA gel blot hybridization to document expression through development. Many of the genes have apparently neural limited expression and function, but some have been co-opted into new roles, notably associated with exocytotic events at fertilization. Localization of gene expression by whole-mount in situ hybridization shows that the morphologically simple sea urchin radial CNS exhibits complex organization into localized transcriptional domains. The transcription patterns reflect the morphological pentamery of the echinoderm CNS and provide no indication of an underlying functional bilateral symmetry in the CNS.

Guidelines and Recommendations for Laboratory Analysis in the Diagnosis and Management of Diabetes Mellitus

Background: Multiple laboratory tests are used in the diagnosis and management of patients with diabetes mellitus. The quality of the scientific evidence supporting the use of these assays varies substantially.

Approach: An expert committee drafted evidence-based recommendations for the use of laboratory analysis in patients with diabetes. An external panel of experts reviewed a draft of the guidelines, which were modified in response to the reviewers’ suggestions. A revised draft was posted on the Internet and was presented at the AACC Annual Meeting in July, 2000. The recommendations were modified again in response to oral and written comments. The guidelines were reviewed by the Professional Practice Committee of the American Diabetes Association.

Content: Measurement of plasma glucose remains the sole diagnostic criterion for diabetes. Monitoring of glycemic control is performed by the patients, who measure their own plasma or blood glucose with meters, and by laboratory analysis of glycated hemoglobin. The potential roles of noninvasive glucose monitoring, genetic testing, autoantibodies, microalbumin, proinsulin, C-peptide, and other analytes are addressed.

Summary: The guidelines provide specific recommendations based on published data or derived from expert consensus. Several analytes are of minimal clinical value at the present time, and measurement of them is not recommended.

Type 1 diabetes islet autoantibody markers

The diagnosis of type 1 diabetes versus other forms of diabetes such as type 2 diabetes is paramount to guiding proper therapy. Several islet autoantibodies have been identified that serve to diagnose immune-mediated, type 1a diabetes in clinically ambiguous cases. These autoantibodies also serve to predict type 1 diabetes in nondiabetic individuals. The most useful islet autoantibodies include islet cell cytoplasmic autoantibodies, insulin autoantibodies, glutamic acid decarboxylase autoantibodies, and insulinoma-associated-2 autoantibodies. Once type 1 diabetes can be safely and reliably prevented, large-scale islet autoantibody screening programs of the general pediatric population may be warranted. It is controversial whether islet autoantibodies influence the course of type 1 diabetes following diagnosis.

Autoantibodies to GAD, IA-2 and insulin in ICA-positive first-degree relatives of children with type 1 diabetes: a comparison between parents and siblings

BACKGROUND

Islet cell antibodies (ICA) represent a heterogenous group of autoantibodies to diabetes-associated antigens, including glutamic acid decarboxylase (GAD) and the IA-2 protein. The objectives of the present study were to compare the prevalence of autoantibodies to known biochemically characterized autoantigens between ICA-positive non-diabetic parents and siblings of children with type 1 diabetes and to evaluate how such antibodies explain ICA reactivity.

METHODS

The presence and levels of GAD antibodies (GADA), IA-2 antibodies (IA-2A) and insulin autoantibodies (IAA) were analyzed in the sera of 184 ICA-positive first-degree relatives (79 parents and 105 siblings).

RESULTS

The prevalences of GADA (61.9% in siblings vs 32.9% in parents), IA-2A (55.2% vs 15.2%) and IAA (41.0% vs 0%) were increased among ICA-positive siblings relative to ICA-positive parents (p<0.001). The siblings had higher ICA titers (p<0.001) than the parents but tended to have lower GADA levels (p=0.12). IA-2A levels did not differ between the two groups. IA-2A levels explained a higher proportion of the ICA reactivity in the siblings than in the parents (44% vs 12%, p=0.004), and GADA levels had the same tendency (27% vs 10%, p=0.11). In a multiple regression analysis, GADA and IA-2A were found to explain together 16% of the ICA reactivity in parents and 49% in siblings (p=0.003 for the difference).

CONCLUSIONS

These results indicate that the increased frequency of additional diabetes-associated autoantibodies in ICA-positive siblings when compared to their ICA-positive parents may reflect the increased risk of progression to clinical type 1 diabetes previously reported in young ICA-positive relatives. We conclude that ICA immunofluorescence is not only due to GADA and IA-2A, but there are other additional antigens contributing to the ICA reactivity. Antibodies to such antigens appear to be more common among adults than in children.

Analysis of the coding and promoter regions of the autoantigen IA-2 in subjects with and without autoantibodies to IA-2

Despite extensive studies on HLA polymorphism, there have been few, if any, studies on allelic forms or mutations in proteins that serve as autoantigens. The present experiments were designed to look for alterations in the coding and promoter regions of the autoantigen IA-2 in type one (insulin-dependent) diabetic patients with autoantibodies to IA-2 as compared with siblings without diabetes or autoantibodies to IA-2. Genomic DNA was used as a template and was amplified by polymerase chain reaction, with pairs of primers encompassing the promoter region and the 23 exons of the coding region of IA-2. A total of nine nucleotide changes were found in the coding region of the six type 1 diabetic patients; four were silent and five were missense changes, but all occurred in the extracellular domain of IA-2 to which autoantibodies are not directed. Few, if any, changes were found in the 5' upstream (-706 to +135) promoter region. The results of the experiments support the null hypothesis that differences among individuals in the nucleotide and amino acid sequences of the promoter and coding regions of IA-2, respectively, do not account for why some individuals develop autoantibodies to IA-2 and others do not.

Islet cell autoimmunity in youth onset diabetes mellitus in Northern India

We characterised a consecutive cohort of 132 youth onset diabetic individuals (age at onset<30 years, mean duration of disease 5.5+/-6.0 years) from North India, by serological determination of the determination of the islet cell autoantibodies, GAD(65) and IA2, and clinically for coexisting autoimmune thyroid disease, malnutrition and pancreatic calcification. Five types of diabetes were delineated: Type 1 (37%), ketosis resistant (32%), Type 2 (13%), fibrocalculous pancreatopathy (11%) and autoimmune polyglandular syndrome (7%). C-peptide response to glucagon was assessed in a representative subset of 50 patients with Type 1, ketosis resistant, and autoimmune polyglandular syndrome. A total of 22.4% of Type 1 and 30% of autoimmune polyglandular syndrome subjects showed both GAD(65) plus IA-2 autoantibody positivity, significantly more than the 4.7% positivity shown by the ketosis resistant type. However, GAD(65) antibody positivity alone was seen in 38% of ketosis resistant subjects which was significantly more than the 14.2 and 10% positivity seen in Type 1 and autoimmune polyglandular groups, respectively. The fibrocalculous pancreatopathy group showed GAD(65) plus IA-2 autoantibody positivity in 14.2% and GAD(65) autoantibody alone positivity in 7.1%. 26 and 60%, respectively, of the Type 1 and autoimmune polyglandular syndrome groups had thyroid microsomal autoantibody positivity. Type 1 showed significantly less C-peptide response to glucagon when compared to the ketosis resistant and autoimmune polyglandular syndrome groups. The controls and Type 2 diabetic individuals tested negative for islet cell autoimmunity markers. These findings demonstrate a role of islet cell autoimmunity in the pathogenesis of four out of the five clinical types of youth onset diabetes seen in North India.

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.

Differential splicing of the IA-2 mRNA in pancreas and lymphoid organs as a permissive genetic mechanism for autoimmunity against the IA-2 type 1 diabetes autoantigen

Type 1 diabetes results from the autoimmune destruction of pancreatic beta-cells in genetically susceptible individuals. Growing evidence suggests that genetically determined variation in the expression of self-antigens in thymus may affect the shaping of the T-cell repertoire and susceptibility to autoimmunity. For example, both allelic variation and parent-of-origin effects influence the thymic expression of insulin (a known type 1 diabetes autoantigen), and insulin gene transcription levels in thymus inversely correlate with susceptibility in both humans and transgenic models. It is unclear why patients lose tolerance to IA-2 (insulinoma-associated tyrosine phosphatase-like protein, or islet cell antigen 512 [ICA512]), especially because IA-2 polymorphisms are not associated with type 1 diabetes. We report that alternative splicing determines differential IA-2 expression in islets compared with thymus and spleen. Islets express full-length mRNA and two alternatively spliced transcripts, whereas thymus and spleen exclusively express an alternatively spliced transcript lacking exon 13. This encodes for the transmembrane (TM) and juxta-membrane (JM) domains that comprise several type 1 diabetes target epitopes, supporting the concept that tolerance to IA-2 epitopes not expressed in lymphoid organs may not be achieved. We propose differential splicing as a regulatory mechanism of gene expression playing a permissive role in the development of autoimmune responses to IA-2. Our findings also show that candidate gene expression studies can help in dissecting the complex genetic determinants of a multifactorial disease such as type 1 diabetes.

Neither B lymphocytes nor antibodies directed against self antigens of the islets of Langerhans are required for development of virus-induced autoimmune diabetes

We evaluated the role of the humoral arm of the immune response in causing or contributing to virus-induced diabetes. Transgenic mice expressing the nucleoprotein (NP) or glycoprotein (GP) of the lymphocytic choriomeningitis virus (LCMV) under control of the rat insulin promoter (RIP) in pancreatic beta cells (RIP-LCMV) and RIP-LCMV mice with genetic dysfunction of B cells (RIP-LCMV x microMT/microMT) were compared for development of diabetes after challenge with LCMV. After inoculation with LCMV, B and T lymphocytes and macrophages infiltrated into pancreatic islets in RIP-LCMV mice, and over 50% of these mice generated Abs against host insulin or glutamate decarboxylase. However, neither B cells nor the autoantibodies played a direct role in the initiation, kinetics, or severity of the virus-induced diabetes as judged by comparing disease in RIP-LCMV mice to littermates whose functional B cells were genetically eliminated. Furthermore, the quality and quantity of T lymphocyte and macrophage infiltration was similar in the B cell-deficient and non-B cell-deficient RIP-LCMV mice. Although the development of autoantibodies to islet Ags had no direct influence on the pathogenesis of insulin-dependent (type 1) diabetes mellitus, it served as a prediabetes marker, as such autoantibodies were often elevated before the onset of disease. Hence, the RIP-LCMV model is not only useful for understanding the pathogenetic mechanisms of how islets are destroyed and spared but also for evaluating therapeutic strategies before onset of clinical diabetes.

The receptor tyrosine phosphatase-like protein ICA512 binds the PDZ domains of beta2-syntrophin and nNOS in pancreatic beta-cells

Islet cell autoantigen (ICA) 512 of type I diabetes is a receptor tyrosine phosphatase-like protein associated with the secretory granules of neurons and endocrine cells including insulin-secreting beta-cells of the pancreas. Here we show that in a yeast two-hybrid assay its cytoplasmic domain binds beta2-syntrophin, a modular adapter which in muscle cells interacts with members of the dystrophin family including utrophin, as well as the signaling molecule neuronal nitric oxide synthase (nNOS). The cDNA isolated by two-hybrid screening corresponded to a novel beta2-syntrophin isoform with a predicted molecular mass of 28 kDa. This isoform included the PDZ domain, but not the C-terminal region, which in full-length beta2-syntrophin is responsible for binding dystrophin-related proteins. In vitro binding of the beta2-syntrophin PDZ domain to ICA512 required both ICA512's C-terminal region and an internal polypeptide preceding its tyrosine phosphatase-like domain. Immunomicroscopy and co-immunoprecipitations from insulinoma INS-1 cells confirmed the occurrence of ICA512-beta2-syntrophin complexes in vivo. ICA512 also interacted in vitro with the PDZ domain of nNOS and ICA512-nNOS complexes were co-immunoprecipitated from INS-1 cells. Finally, we show that INS-1 cells, like muscle cells, contain beta2-syntrophin-utrophin oligomers. Thus, we propose that ICA512, through beta2-syntrophin and nNOS, links secretory granules with the actin cytoskeleton and signaling pathways involving nitric oxide.

Identity of mouse IA-2 and PTP35 genes of the tyrosine phosphatase family, and their expression in neuroendocrine tissues

Recently, IA-2, one of the major diabetic autoantigens, and PTP35 cDNA were independently isolated by subtraction cloning using insulinoma cells and a polymerase chain reaction (PCR)-based search for conserved sequences using NIH3T3 fibroblast cell line, respectively. By Southern blot analysis and nucleotide sequence determination of reverse transcription PCR products, we showed that IA-2 and PTP35 are identical and exist as a single gene in a mouse genome. The expression of IA-2/PTP35 messages was detected by northern blot analysis in MIN6N8 cells, an insulinoma cell line derived from non-obese diabetic mice, but its expression level was not affected by the ambient glucose level, phorbol-12-myristate 13-acetate or tumour necrosis factor-alpha. We also generated polyclonal antibodies to murine IA-2/PTP35 by immunization with recombinant proteins. Subsequent immunohistochemical analysis using these polyclonal antibodies disclosed that IA-2/PTP35 is strongly expressed in mouse neuroendocrine tissues such as pancreatic islets and the hypothalamus-pituitary gland. These results suggest that IA-2/PTP35 functions primarily in neuroendocrine tissues.

Clinical evaluation of a radioimmunoprecipitation assay for IA-2 antibody and comparison of GAD antibody in type 1 diabetes mellitus

We evaluated a insulinoma-associated protein (IA-2) antibody assay kit using 125I-labelled recombinant IA-2. IA-2 antibodies were present in patients with early-onset type 1 diabetes mellitus (DM) at frequencies of 74%, 67%, 57%, and 50% for respective periods <1 year, 1 < or =years<2, 2< or =years<3, and 3< or =years<4 after onset. IA-2 antibody frequency was low throughout the DM course as compared with glutamic acid decarboxylase (GAD) antibody frequency. No one had IA-2 antibody, but 29% still had positive GAD antibody titers after 11 years. Of the patients with 0<years<7 duration, 42% had IA-2 Ab+/GAD Ab+, 9% IA-2 Ab+/GAD Ab-, and 24% IA-2 Ab-/GAD Ab+. Prevalence of IA-2 and GAD antibody in 1243 patients with type 2 DM were 1.5% and 3.1%, respectively, and 1.1% had both. This new IA-2 antibody kit is easy to use and provides a specific, sensitive method for making routine assays. Furthermore, the combined analysis of GAD antibody provides high detection of type 1 DM.

Autoantibodies predicting diabetes mellitus type I in celiac disease

Celiac disease (CD) and diabetes mellitus type I (DM-I) are both autoimmune diseases. Abnormal first-phase insulin response (FPIR) is associated with the prediabetic phase. Glutamic acid decarboxylase (GAD) and islet cell antibodies (ICAs) - especially the tyrosine phosphatase-like protein IA-2 antibodies - are considered to be serological markers of DM-I future development. The aim of this study is to investigate the presence of autoantibodies (GAD, IA-2) in individuals with CD, on a gluten-free diet, who have normal intestinal morphology. Thirty patients with CD (4-22, mean 15 years), 30 newly diagnosed diabetic children (2.5-16, mean 10 years) and 30 healthy subjects (7-35, mean 18 years) were investigated. Serum GAD and IA-2 autoantibodies were assessed by a quantitative enzyme-linked immunosorbent assay (ELISA) method in all patients and controls. Seven CD patients (23%), 28 diabetic children (93%) and none in the control group had positive GAD and IA-2 antibodies. The FPIR was normal in CD patients (>/=46 mU/l).

CONCLUSIONS

GAD and IA-2 antibodies are detected in 23% of patients with CD. These patients may be at risk to develop DM-I. Regular follow-up and determination of FPIR for the early diagnosis of the prediabetic phase in patients with CD having circulating autoantibodies is recommended.

Autoantibodies to IA-2 in insulin-dependent diabetes mellitus. Measurements with a new immunoprecipitation assay

An immunoprecipitation assay for autoantibodies (Abs) to the human islet cell antigen IA-2 has been developed using 125I-labelled recombinant IA-2 expressed in E. coli. With this assay IA-2 Abs were detected in 103/217 (47%) of IDDM patients of different ages and with different disease duration. IA-2 Ab prevalence was higher in younger patients (at the age of 15 years or below) with the recent onset IDDM (64/113; 57%) compared to patients above the age of 15 years (11/25; 44%). One of 40 (2.5%) Graves' disease patients and five of 204 (2.5%) of NIDDM patients were also positive. IA-2 Abs were not detected in sera from patients with Hashimoto's thyroiditis (n=32), myasthenia gravis (n=20) or systemic lupus erythematosus (n=10). IA-2 Ab measurements based on 125I-labelled IA-2 showed a good correlation with the results of an immunoprecipitation assay based on 35S-labelled IA-2 produced in the in vitro transcription/translation system (r=0.78; n=113; p<0.001). Out of 217 IDDM sera which were tested for IA-2 Abs, 140 (65%) were positive for Abs to glutamic acid decarboxylase (GAD) and 166 (76%) were positive for Abs to IA-2 and/or Abs to GAD. In addition, Abs to IA-2, to GAD and to insulin were analysed in sera from recent onset IDDM patients who had not been treated with insulin (n=117). In all, 76/117 (65%) of these sera were positive for GAD Abs, 66/117 (56%) for IA-2 Abs, 45/117 (38%) for insulin Abs. However, 98/117 (84%) were positive for at least one of the three Abs confirming earlier observations on the complementarity of Ab testing in IDDM. Overall, the IA-2 Ab assay based on 125I-labelled recombinant IA-2 showed good sensitivity, precision and specificity which, combined with an easy and convenient protocol, makes it attractive for routine use.

Serological markers of recurrent beta cell destruction in diabetic patients undergoing pancreatic transplantation

BACKGROUND

Besides alloimmunity to transplanted pancreatic tissue, recurrent autoimmune beta cell destruction is an additional limitation to successful clinical pancreatic allografts in type 1 diabetic patients.

METHODS

We studied the prevalence of autoantibodies to glutamate decarboxylase (GAD) 65 and tyrosine phosphatase (IA-2) in 68 C-peptide-negative diabetic patients receiving pancreatic allografts. Sera from patients were obtained immediately before grafting. A second blood sample was analyzed at the time of graft failure in patients who returned to hyperglycemia and during the same follow-up period in those who experienced a functional pancreatic allograft. Patients were classified according to clinical outcome into chronic graft failure (group A, n=20), acute graft failure and/or arterial thrombosis (n=7), or functional pancreatic graft (group C, n=41). Sera from patients were screened for the presence of specific autoantibodies using an islet cell autoantibody assay, a combi-GAD and IA-2 test, and individual GAD and IA-2 assays.

RESULTS

Patients from group A had significantly higher combi-test values than patients from group C (13+/-16 vs. 4.5+/-12 units, P<0.02) and higher anti-GAD65 antibody (Ab) levels (0.19+/-0.3 vs. 0.04+/-0.13 units, P<0.01) immediately before grafting. After graft failure in group A, both anti-GAD65 and anti-IA-2 Ab levels increased from baseline, but only the increase in anti-IA-2 Ab levels reached statistical significance (0.28+/-0.12 vs. 15+/-34, P=0.03). When compared with group C, patients from group A had higher anti-GAD65 Abs (0.29+/-0.35 vs. 0.05+/-0.16, P<0.001) after graft failure. Interestingly, the number of double-Ab-positive patients rose from 5% to 35% in group A, whereas it remained at 5% in group C. In pancreatic transplants with bladder drainage, the presence of anti-GAD65 and/or anti-IA2 Abs was not associated with a reduction in urinary amylase levels. This suggests that a loss of endocrine function was not associated with exocrine failure in patients from group A.

CONCLUSIONS

We can conclude from the present study that peripheral autoimmune markers are useful in diabetic patients receiving pancreatic allografts.

Molecular cloning, chromosomal mapping, and developmental expression of a novel protein tyrosine phosphatase-like gene

Protein tyrosine phosphatases (PTPs) mediate the dephosphorylation of phosphotyrosine. PTPs are known to be involved in many signal transduction pathways leading to cell growth, differentiation, and oncogenic transformation. We have cloned a new family of novel protein tyrosine phosphatase-like genes, the Ptpl (protein tyrosine phosphatase-like; proline instead of catalytic arginine) gene family. This gene family is composed of at least three members, and we describe here the developmental expression pattern and chromosomal location for one of these genes, Ptpla. In situ hybridization studies revealed that Ptpla expression was first detected at embryonic day 8.5 in muscle progenitors and later in differentiated muscle types: in the developing heart, throughout the liver and lungs, and in a number of neural crest derivatives including the dorsal root and trigeminal ganglia. Postnatally Ptpla was expressed in a number of adult tissues including cardiac and skeletal muscle, liver, testis, and kidney. The early expression pattern of this gene and its persistent expression in adult tissues suggest that it may have an important role in the development, differentiation, and maintenance of a number of different tissue types. The human homologue of Ptpla (PTPLA) was cloned and shown to map to 10p13-p14.

Cellular and molecular roles of beta cell autoantigens, macrophages and T cells in the pathogenesis of autoimmune diabetes

Type I diabetes, also known as insulin-dependent diabetes mellitus (IDDM) results from the destruction of insulin-producing pancreatic beta cells by a progressive beta cell-specific autoimmune process. The pathogenesis of autoimmune IDDM has been extensively studied for the past two decades using animal models such as the non-obese diabetic (NOD) mouse and the BioBreeding (BB) rat. However, the initial events that trigger the immune responses leading to the selective destruction of the beta cells are poorly understood. It is thought that beta cell autoantigens are involved in the triggering of beta cell-specific autoimmunity. Among a dozen putative beta cell autoantigens, glutamic acid decarboxylase (GAD) has been proposed as perhaps the strongest candidate in both humans and the NOD mouse. In the NOD mouse, GAD, as compared with other beta cell autoantigens, provokes the earliest T cell proliferative response. The suppression of GAD expression in the beta cells results in the prevention of autoimmune diabetes in NOD mice. In addition, the major populations of cells infiltrating the islets during the early stage of insulitis in BB rats and NOD mice are macrophages and dendritic cells. The inactivation of macrophages in NOD mice results in the prevention of T cell mediated autoimmune diabetes. Macrophages are primary contributors to the creation of the immune environment conducive to the development and activation of beta cell-specific Th1-type CD4+ T cells and CD8+ cytotoxic T cells that cause autoimmune diabetes in NOD mice. CD4+ and CD8+ T cells are both believed to be important for the destruction of beta cells. These cells, as final effectors, can kill the insulin-producing beta cells by the induction of apoptosis. In addition, CD8+ cytotoxic T cells release granzyme and cytolysin (perforin), which are also toxic to beta cells. In this way, macrophages, CD4+ T cells and CD8+ T cells act synergistically to kill the beta cells in conjunction with beta cell autoantigens and MHC class I and class II antigens, resulting in the onset of autoimmune type I diabetes.

Production of the islet cell antigen ICA69 (p69) with baculovirus expression system: analysis with a solid-phase time-resolved fluorescence method of sera from patients with IDDM and rheumatoid arthritis

Islet cell antigen 69 (ICA69), previously implicated as an autoantigen in autoimmune insulin-dependent diabetes mellitus (IDDM), was produced using baculovirus-mediated expression in Spodopterafrugiperda (Sf9) insect cells. In these cells the protein was effectively expressed and ICA69 carrying C-terminal histidine-hexapeptide could be efficiently purified using immobilized metal chelate affinity chromatography. Screening of patient and control sera using this protein as an antigen in time-resolved fluoroimmunoassay (TR-FIA) identified 4/50 of patients with IDDM and 6/73 of patients with rheumatoid arthritis (RA) to be positive for ICA69 antibodies. The number of positives did not differ significantly between patients and control subjects but the level of binding was higher in sera from RA patients compared to that of control sera (P = 0.003). The results show that some subjects have specific autoreactive antibodies against the ICA69 protein produced with recombinant technology.

Post-translational modifications of ICA512, a receptor tyrosine phosphatase-like protein of secretory granules

The autoantigen of type I diabetes ICA512 is a receptor tyrosine phosphatase-like protein enriched in the secretory granule membranes of neurons and peptide secreting endocrine cells. While the function of ICA512 remains unknown, it is thought to link regulated neuropeptide and peptide hormone secretion with signal transduction pathways involving tyrosine phosphorylation/dephosphorylation. To characterize further its biochemical properties, we conducted studies in the bovine pituitary, an abundant source of native ICA512, as well as in fibroblasts transfected with various human ICA512 cDNA constructs. Based on these studies we have established that the signal peptide of ICA512 encompasses residues 1-34 and that the ectodomain of ICA512 undergoes multiple post-translation modifications, including N-glycosylation. Newly synthesized ICA512 appears first as a pro-protein of 110 kDa that is then converted by post-translational modifications into a 130-kDa species. Cleavage of pro-ICA512 at a consensus for furin-like convertases generates a 60-66-kDa ICA512 transmembrane fragment (amino acids 449-979). Such processing ICA512 is not restricted to neuroendocrine cells, as it can also occur in transfected fibroblasts. Finally, the predicted N-terminal fragment of ICA512 resulting from this cleavage (amino acids 35-448) or parts thereof are present in the neurosecretosomes of posterior pituitary, raising the possibility that they may be secreted upon exocytosis of secretory granules.

Treatment of an autoimmune disease with "classical" T cell veto: a proposal

Immune responses protect against infectious diseases and cancers. In normal circumstances, the immune system is tolerant to self. However, under certain conditions this tolerance is broken. The immune system attacks otherwise normal tissue. An autoimmune disease ensues. Strategies are now being sought that remove the pathogenic T cells without affecting other immune functions. "Classical" veto has been described as an immune suppressive mechanism able to remove T cells in a highly specific and effective manner. The present article briefly reviews the current knowledge on the development of autoreactive T cells and their regulation in the periphery. It describes "classical" veto, its mechanisms, and its novel applications. Finally, it argues that "classical" veto can be adapted to treat an autoimmune disease, such as type I diabetes mellitus.

Stiff-man syndrome: from the bedside to the bench

The study of SMS, a rare disease, has resulted in a better understanding of a more common disorder, IDDM, and has allowed investigators to gain insights into the molecular mechanisms of autoimmunity. Many unanswered questions remain, such as the specific site of disease activity in SMS, both at the bedside (cortex, brain stem, or spinal cord) and at the bench (neuronal cytoplasma or synapse). The association of SMS with neoplastic disease and the development of autonomicdysfunction are not understood. The next decade may provide answers to these puzzling issues.

Only multiple autoantibodies to islet cells (ICA), insulin, GAD65, IA-2 and IA-2beta predict immune-mediated (Type 1) diabetes in relatives

We report here our prospective study of 15,224 non-diabetic, first-degree relatives of probands with immune-mediated (type 1) diabetes (IMD), of which 135 were found to eventually develop diabetes. We determined islet cell, insulin, GAD65, insulinoma-associated antigen-2 and 2beta autoantibodies (ICA, IAA, GAD65A, IA-2A and IA-2betaA), on the first available serum samples. The latter three autoantibodies were however assayed on subsets of the relatives with and without ICA, IAA and/or GAD65A, plus most of the relatives who developed diabetes. Of the relatives who progressed to diabetes, 94% had at least one of these autoantibodies on the first screening, while ICA proved to be the most sensitive single marker (sensitivity 74%). Risk of diabetes was however negligible when ICA was found in the absence of the others (5-year risk=5.3%), but increased dramatically whenever two or more autoantibodies were present (5-year risk=28.2% and 66.2%, respectively). The most predictive combination of markers was ICA plus IA-2A and/or IA-2beta A. Loss of first phase insulin release to IVGTT also occurred only in those ICA-positive relatives who had one or more of the other autoantibodies. The data suggests that significant beta-cell damage is seen only when the underlying autoimmunity has spread to multiple antigenic islet cell determinants. Combinations of the autoantibodies occurred most often in relatives with the highest risk HLA-DR/DQ phenotypes. These data document that only relatives positive for at least two or more of these five autoantibodies are at significant risk of diabetes themselves. Intervention trials for the prevention of type 1 diabetes could be designed based on testing for these autoantibodies alone, without the need for HLA typing and IVGTT testing.

Type 1 1/2 diabetes: myth or reality?

The disease process in classical Type 1 diabetes patients (IDDM) is believed to be autoimmune. In contrast, the disease process in classical Type 2 diabetes patients (NIDDM) is not autoimmune and a decreased sensitivity to insulin action is the main abnormality. The clinical distinction of Type 1 diabetes versus Type 2 diabetes is recognized to be imperfect and has limitations. There is a group of individuals (Type 1 1/2 diabetes), who present like typical NIDDM, but have some of the immunological and clinical features of IDDM. We review the current medical literature on Type 1 1/2 diabetes with special reference to its clinical characteristics, natural history and pathophysiology. Since the distinction between these two forms of diabetes may have important therapeutic implications especially with regards to the benefits of insulin therapy in patients with Type 1 1/2 diabetes and because of the need for uniformity in its diagnosis we recommend that both clinical plus biochemical criteria (the presence of ICA and/or GAD Ab, HLA typing and tests to quantify beta cell function) be used to make a diagnosis. Comparative studies in the area of cytokine production, T cell reactivity and autoantibody clustering between classic Type 1 diabetes and Type 1 1/2 diabetes patients are needed as are studies with the animal model of Type 1 1/2 diabetes, Psammomys obesus.

Young age and HLA markers enhance the risk of progression to type 1 diabetes in antibody-positive siblings of diabetic children

The contribution of autoantibodies, HLA markers and age to long-term estimates of risk of type 1 diabetes were examined after a median of 11 years (range 7.5-14) during the follow-up in a cohort of 234 siblings (aged 2-29 years) of French children with recent-onset type 1 diabetes, of whom 12 (5.1%) developed diabetes. We evaluated islet cell antibodies (ICA) by indirect immunofluorescence and autoantibodies to insulin (IAA), to the 65 kDa isoform of glutamic acid decarboxylase (GADA) and to the IA-2 protein (IA-2A) by radioligand assay in sequential serum samples. Among the 234 siblings of type 1 diabetic patients screened, 27 were positive for at least one antibody, 11 of whom progressed to develop type 1 diabetes during the follow-up (sensitivity, 92%, predictive value, 41%). Among the four antibodies tested individually, ICA had the highest sensitivity (83%) but a poor predictive value (59%) and IA-2A the highest predictive value (70%). IAA and GADA both exhibited poor sensitivity and predictive value. Combinations of antibodies achieved better predictive values than antibodies tested individually. Satisfactory predictive values were obtained for the combination of GADA with IA-2A (83%), for any combination of at least two antibodies other than ICA (70%) and for the combination of ICA with at least one other antibody (69%). The risk estimates were highest in the presence of three or four antibodies, whether comprising ICA or not, but with a concomitant loss of sensitivity. For most antibody combinations, cumulative risks showed progression from approximately 50% after 5 years to 100% after 13 years. HLA-DR3/4 was significantly more frequent in siblings developing type 1 diabetes than in non-diabetic siblings (9/12 vs. 39/217, relative risk (RR)=14, P</=0.0001). The predictive value of HLA-DR3/4 was low (19%); however, taking into account the presence of HLA-DR3/4 in subjects who were positive for more than one antibody resulted in a higher predictive value (67%, vs. 20% in non-DR3/4 subjects, P</=0.02). In addition, siblings developing diabetes were younger at entry than those who did not (mean =7.5 +/-1.23 vs. 12.5 +/-0.39 years, respectively; P</=0.01). Ten of 12 were aged less than 10 years compared with 106/222 non-diabetic siblings (RR =5.4, P</=0.03). Moreover, younger age was associated with a more rapid development of type 1 diabetes. In conclusion, our results show that the combination of IAA, GADA and IA-2A autoantibodies in sequential serum samples is satisfactory for the identification of subjects at risk of developing type 1 diabetes. Additional factors such as younger age and HLA-DR3/4 as markers of progression to disease may contribute to more efficient prediction in antibody positive subjects.

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.

Expression, characterization, processing and immunogenicity of an insulin-dependent diabetes mellitus autoantigen, IA-2, in Sf-9 cells

Autoantibodies to a 64-kD protein and a 40-kD tryptic fragment from pancreatic islets have been detected at high frequency in the sera of patients with insulin-dependent diabetes mellitus (IDDM). IA-2, a newly isolated transmembrane protein tyrosine phosphatase, is a major islet cell autoantigen in IDDM and the precursor of a 40-kD tryptic fragment. To express large quantities of recombinant IA-2 protein and analyse post-translational modifications we expressed full-length human IA-2 in baculovirus-infected Sf-9 cells. IA-2 expression was analysed by Western blot and by immunoprecipitation of 35S-methionine-radiolabelled proteins with rabbit antisera or IDDM sera. A 120-kD IA-2 protein was detected during the early, but not the late, phase of the infection. Pulse-chase experiments showed that the 120-kD protein was processed into fragments of 64 kD and smaller fragments of approximately 50 kD, 38 kD and 32 kD. The 64-kD fragment appeared as a doublet. Tunicamycin and PNGase F treatment down-shifted the 120-kD protein and the 64-kD doublet into lower molecular weight bands, suggesting that both were glycosylated. Trypsin treatment converted the 120-kD protein and the 64-kD doublet into a 40-kD fragment. Baculovirus-expressed IA-2 was as sensitive or slightly more sensitive than in vitro translated IA-2 in detecting autoantibodies to IA-2: 66% of sera from newly diagnosed IDDM patients reacted with baculovirus-expressed IA-2 compared with 59% of the same sera which reacted with in vitro translated IA-2. It is concluded that baculovirus-expressed IA-2 is a good source of autoantigen and that a number of lower molecular weight fragments with which IDDM autoantibodies react are derived from the 120-kD full-length IA-2 molecule.

Characterization and chromosomal localization of PTP-NP-2, a new isoform of protein tyrosine phosphatase-like receptor, expressed on synaptic boutons

Recently, there have been several reports describing the cloning and characterization of the novel family of protein tyrosine phosphatase-like receptor molecules (known as IA-2 and PTP-NP/PTP-IAR/IA-2beta/phogrin), which may act as autoantigens in diabetes. Here, we report the molecular characterization and chromosomal localization of a new isoform of this family in brain termed PTP-NP-2 (for PTP-NP tyrosine phosphatase isoform), and its function in rat primary hippocampal neurons. PTP-NP-2 has 48% identity to IA-2. The principal difference between PTP-NP-2 and PTP-NP is a 17-amino-acid insert near the N-terminus of PTP-NP that is absent in PTP-NP-2. Genomic DNA analysis indicates that the 17-amino-acid insert is coded by a separate exon, suggesting that both IA-2beta and PTP-NP-2 are isoforms arising by alternate splicing of the same gene. Reverse transcriptase-PCR revealed that both isoforms are present in human SH-SY5Y neuroblastoma cells. PTP-NP-2 mRNA expression is highly restricted, with a 5.5-kb specific transcript in human fetal and adult brain and 5.5 and 3. 8 kb in human adult pancreas. SH-SY5Y neuroblastoma and U87-MG glioblastoma cells showed specific transcripts of 5.5 and 3.8<HSP SP = "0.25">kb, respectively, indicating the existence of several isoforms of this molecule in the nervous system. The human gene encoding PTP-NP-2 was assigned to human chromosome 7q22-qter using Southern blot analysis of genomic DNAs from rodent/human somatic hybrid cell lines. Confocal microscopy analyses of rat primary hippocampal neurons revealed that PTP-NP-2 is abundantly expressed on synaptic boutons in primary neurons. Wild-type PTP-NP-2 showed no measurable tyrosine phosphatase activity using an in-vitro pNPP assay. Examination of the PTP-NP-2 catalytic consensus sequence revealed that this sequence differed from the typical tyrosine phosphatase-domain consensus sequence by an alanine to aspartate change (amino acid 930). Mutation of aspartate 930 to alanine produced a catalytically active enzyme, suggesting that native PTP-NP and its isoform PTP-NP-2 are catalytically inactive receptor protein tyrosine phosphatase homologues. Taken together, these results indicate that the tyrosine phosphatase PTP-NP-2 is a new isoform of PTP-NP tyrosine phosphatase, is expressed on synaptic boutons and may participate in the regulation of synaptic bouton endocytosis.

Molecular cloning and characterization of a highly basic protein, IA-4, expressed in pancreatic islets and brain

A substraction library was constructed from mouse insulinoma (betaTC-1) and glucagonoma (alphaTC-1) cell lines. Differential screening and sequencing revealed a novel cDNA clone, IA-4, which was expressed in the islets of Langerhans and the brain. IA-4 cDNA is 1,007 bp in length and predicts a protein of 187 amino acids with a molecular mass of 19,940 D. Examination of the amino acid sequence showed a high content of arginine (18.7%), proline (14.4%), alanine (16.0%), leucine (13.4%) and glycine (9.6%). The deduced pI value is 12.5 indicating a highly basic protein. Northern blot analysis revealed a 1-kb mRNA highly expressed in brain, trigeminal ganglia and cell lines of neuroendocrine origin. Rabbit polyclonal antiserum raised against a synthetic IA-4 peptide, designated Pep-1, not only reacted with IA-4 recombinant protein, but also immunostained the islets of Langerhans and large neurons of the hippocampus, cerebral cortex, spinal cord, dorsal ganglia and Purkinje cells of the cerebellum. The high expression of IA-4 protein in neuroendocrine cells and its unique amino acid sequence suggest that IA-4 may have an important, but still undetermined, function in these special cell types.

Combined analysis of GAD65 and ICA512(IA-2) autoantibodies in organ and non-organ-specific autoimmune diseases confers high specificity for insulin-dependent diabetes mellitus

There is evidence that insulin-dependent diabetes mellitus (IDDM) may develop in association with other non-beta-cell-specific autoimmune diseases. We aimed to assess whether autoantibodies to the islet cell antigens glutamic acid decarboxylase (Mr 65,000 isoform) (GAD65) and ICA512(IA-2), present alone or in combination, are limited to IDDM or also occur in other organ- or non-organ-specific autoimmune disorders. We determined the frequency of these autoantibodies by radioimmunoassay in 199 sera from patients with autoimmune thyroid diseases (AITD), rheumatoid arthritis (RA), systemic lupus erythematosus (SLE) and primary biliary cirrhosis (PBC), and compared the results with those from 507 newly diagnosed patients with IDDM and 280 healthy controls. ICA512(IA-2) autoantibodies were detected exclusively in AITD with concurrent IDDM, but not in other autoimmune diseases without IDDM, whereas GAD65 autoantibodies exceeded the limit of normal in 67.7% (21 of 31) of patients with AITD who also had IDDM and in 5.5% (three of 55) of patients with PBC. The frequency of either GAD65 and/or ICA512(IA-2) autoantibodies was significantly higher in patients with AITD who also had IDDM (27 of 31, 87.1%) than in those with AITD alone (one of 53, 1.9%; P<10(-6)), but was not significantly different from those patients with newly diagnosed IDDM (418 of 507, 82.4%). Neither patients with organ- or non-organ-specific autoimmune diseases without IDDM nor healthy controls had autoantibodies against both GAD65 and ICA512(IA-2). Despite the fact that one of the two autoantibodies was occasionally detected in patients with non-beta-cell-specific autoimmune diseases without IDDM, combined determination of GAD65 and ICA512(IA-2) autoantibodies specifically identified IDDM in the majority of patients with AITD. In conclusion, because of the strong association of IDDM with AITD, testing for multiple islet autoanti-bodies could be useful as a predictive marker for risk of progression to IDDM onset amongst patients with autoimmune thyroid disorders.

Antibodies to the tyrosine phosphatase-like protein IA-2 are highly associated with IDDM, but not with autoimmune endocrine diseases or stiff man syndrome

Antibodies to the 40 kD antigen (identified as tyrosine phosphatase IA-2) and glutamate decarboxylase (GAD65) are strongly associated with insulin dependent diabetes mellitus (IDDM). However, antibodies to GAD (GADA) can appear in the absence of IDDM, particularly in stiff man syndrome (SMS) and in some individuals with autoimmune polyendocrine syndrome type II (APS II) and organ specific autoimmune diseases. The aim of this study was to compare the specificity of IA-2 antibodies (IA-2A) and GADA for IDDM by determining their frequency in different patient groups. IA-2A were present in 64/114 (56%) IDDM patients and 9/19 (47%) APS II patients with IDDM but in only 4/28 (14%) SMS patients. 1/24 (4%) APS II patients without IDDM and 1/113 (0.9%) patients with organ specific autoimmune disease had low level IA-2A. In contrast GADA were present in 77/114 (68%) IDDM patients and 17/19 (89%) APS II patients with IDDM, but also in 25/28 (89%) SMS patients, 5/24 (21%) APS II patients without IDDM and 22/113 (19%) patients with organ specific autoimmune diseases. Furthermore, within the group of new onset IDDM, IA-2A seemed to be associated with ICA and age: 63% of ICA positive IDDM patients had IA-2A (74% had GADA) increasing to 77% in the group below 20 years of age (69% for GADA). Our results demonstrate that IA-2A may be more specific for IDDM than GADA, as the latter are also present in patients with SMS, APS II without IDDM and organ specific autoimmune diseases. IA-2A were less frequent in older patients with IDDM than GADA or ICA. A combination of IA-2A and GADA detected 84% of total and 93% of ICA positive IDDM patients.

Antibody screening in a population of children

The first large-scale (secondary) intervention trials have been initiated in first-degree family members of patients with insulin-dependent diabetes mellitus (IDDM). Within a few years, data from these studies may suggest that intervention is possible, thereby opening similar approaches in the general population. However, before large-scale intervention studies can be initiated, several problems need to be solved. One of these problems is the lack of knowledge on the natural course of beta-cell autoimmunity. This review analyses this and other issues related to population-based prediction for IDDM. At present, no long-term follow-up studies are available in large-sized populations, but data show that prediction in the general population is both technically feasible and likely to have sufficient power to be useful in prevention trials. More data need to be generated, not only to determine which markers are most likely to give good prediction but also to obtain knowledge on the natural course, psychosocial impact and cost-effectiveness of screening.

Immunization therapies in the prevention of diabetes

Insulin-dependent diabetes (IDD), being an autoimmune disease, offers several opportunities for immunological interventions that may result either in the reduction of disease severity or in delaying diabetes onset. Among the various experimental preventative approaches, parenteral immunization with islet-specific autoantigens appears to be practically simpler and promising. We have previously shown that immunization with insulin, insulin B chain and B chain epitope (p9-23), but not insulin A chain, in incomplete Freund's adjuvant (IFA) and in alum (with B chain) delayed/prevented diabetes onset in NOD mice. Here we demonstrate the protective efficacy of affinity purified GAD65 in IFA. While both insulin B chain and GAD65 significantly delayed the onset of diabetes (P=0.001), a recently described tyrosine phosphatase (IA-2) antigen did not (P=0.38). Interestingly, B chain immunization reduced the incidence of cyclophosphamide (CY)-accelerated diabetes by about 50-55%. We also provide further evidence that B chain, upon increased adsorption to alum, could improve on its protective capacity in NOD mice.

Comparison of IA-2 with IA-2beta and with six other members of the protein tyrosine phosphatase family: recognition of antigenic determinants by IDDM sera

To study the expression of protein tyrosine phosphatases (PTPs) in pancreatic islets, a cDNA library from islet cells was constructed and analysed. Twenty-one different PTPs were found to be expressed in islet cells, including three previously unknown PTPs. One of these, IA-2beta, was cloned, sequenced, and found to be related to IA-2, a major autoantigen in insulin-dependent diabetes mellitus (IDDM). The intracellular and extracellular domains of IA-2beta were 74 and 27% identical, respectively, to the intracellular and extracellular domains of IA-2. Approximately 70 and 45% of sera from patients with IDDM had autoantibodies that immunoprecipitated recombinant IA-2 and IA-2beta, respectively. By use of deletion mutants, we were able to show that the autoantibodies reacted with the intracellular, and not the extracellular, domains of IA-2 and IA-2beta, and that the major antigenic determinants resided within the COOH-terminus of the intracellular domains. Further studies revealed that approximately 97% of the IDDM sera that reacted with IA-2beta also reacted with IA-2, whereas only 50% of IDDM sera that reacted with IA-2 also reacted with IA-2beta. In contrast to the reactivity of IDDM sera with the IA-2 and IA-2beta, IDDM sera did not react with six other members of the PTP family. It is concluded that many members of the PTP family are expressed in pancreatic islets, but thus far only IA-2 and IA-2beta appear to be recognized as autoantigens by IDDM sera.