Risk for developing type 1 (insulin-dependent) diabetes mellitus and the presence of islet 64K antibodies

Autoimmune responses in T1DM: quantitative methods to understand onset, progression, and prevention of disease

Understanding the physiological processes that underlie autoimmune disorders and identifying biomarkers to predict their onset are two pressing issues that need to be thoroughly sorted out by careful thought when analyzing these diseases. Type 1 diabetes (T1D) is a typical example of such diseases. It is mediated by autoreactive cytotoxic CD4⁺ and CD8⁺ T-cells that infiltrate the pancreatic islets of Langerhans and destroy insulin-secreting β-cells, leading to abnormal levels of glucose in affected individuals. The disease is also associated with a series of islet-specific autoantibodies that appear in high-risk subjects (HRS) several years prior to the onset of diabetes-related symptoms. It has been suggested that T1D is relapsing-remitting in nature and that islet-specific autoantibodies released by lymphocytic B-cells are detectable at different stages of the disease, depending on their binding affinity (the higher, the earlier they appear). The multifaceted nature of this disease and its intrinsic complexity make this disease very difficult to analyze experimentally as a whole. The use of quantitative methods, in the form of mathematical models and computational tools, to examine the disease has been a very powerful tool in providing predictions and insights about the underlying mechanism(s) regulating its onset and development. Furthermore, the models developed may have prognostic implications by aiding in the enrollment of HRS into trials for T1D prevention. In this review, we summarize recent advances made in determining T- and B-cell involvement in T1D using these quantitative approaches and delineate areas where mathematical modeling can make further contributions in unraveling certain aspect of this disease.

A look to the future: prediction, prevention, and cure including islet transplantation and stem cell therapy

Type 1 diabetes mellitus (T1DM) is characterized by the almost complete absence of insulin secretion, which is secondary to an autoimmune destruction or dysfunction of the insulin-producing cells of the pancreatic islets of Langerhans. Because T1DM is an autoimmune disease with a long preclinical course, the predictive testing of individuals before the clinical onset of the disease has provided a real opportunity for the identification of risk markers and the design of therapeutic intervention. With such a high degree of predictability using a combination of immunologic markers, strategies to prevent T1DM may become possible. A number of novel therapeutic strategies are under investigation in newly diagnosed T1DM patients and might ultimately be applied to prevent T1DM.

The changing faces of diabetes

As understanding about the pathophysiology of diabetes mellitus continues to evolve, it is important that its classification reflects the current state of knowledge. The eventual goal is that appreciation of the different forms of diabetes eventually will result in better treatment of hyperglycemia. Even more exciting is the fact that this appreciation is allowing us to enter the era of diabetes prediction and prevention. The current classification scheme of diabetes does not yet account for all of the types of diabetes seen in a typical diabetes clinic. Fig. 1 illustrates our current understanding of the pathophysiology of diabetes and separates the diabetes types into those used in the current classification scheme. Clearly, new classifications will be required as we learn more about the different types of diabetes.

Prognostic factors for the course of beta cell function in autoimmune diabetes

This study presents a 2-yr follow-up of 281 patients, aged 15-34 yr, diagnosed with diabetes between 1992 and 1993. At diagnosis, 224 (80%) patients were positive for at least one of the following autoantibodies: islet cell antibodies (ICAs), glutamic acid decarboxylase antibodies (GADAs), or tyrosine phosphatase antibodies (IA-2As); the remaining 57 (20%) patients were negative for all three autoantibodies. At diagnosis, C-peptide levels were lower (0. 27; 0.16-0.40 nmol/L) in autoantibody-positive patients compared with autoantibody-negative patients (0.51; 0.28-0.78 nmol/L; P: < 0. 001). After 2 yr, C-peptide levels had decreased significantly in patients with autoimmune diabetes (0.20; 0.10-0.37 nmol/L; P: = 0. 0018), but not in autoantibody-negative patients. In patients with autoimmune diabetes, a low initial level of C-peptide (odds ratio, 2. 6; 95% confidence interval, 1.7-4.0) and a high level of GADAs (odds ratio, 2.5; 95% confidence interval, 1.1-5.7) were risk factors for a C-peptide level below the reference level of 0.25 nmol/L 2 yr after diagnosis. Body mass index had a significant effect in the multivariate analysis only when initial C-peptide was not considered. Factors such as age, gender, levels of ICA or IA-2A or insulin autoantibodies (analyzed in a subset of 180 patients) had no effect on the decrease in beta-cell function. It is concluded that the absence of pancreatic islet autoantibodies at diagnosis were highly predictive for a maintained beta-cell function during the 2 yr after diagnosis, whereas high levels of GADA indicated a course of decreased beta-cell function with low levels of C-peptide. In autoimmune diabetes, an initial low level of C-peptide was a strong risk factor for a decrease in beta-cell function and conversely high C-peptide levels were protective. Other factors such as age, gender, body mass index, levels of ICA, IA-2A or IAA had no prognostic importance.

Radioimmunoassay for glutamic acid decarboxylase-65

BACKGROUND

Glutamic acid decarboxylase-65 (GAD65), the enzyme that catalyzes the formation of gamma-aminobutyric acid (GABA), is the major autoantigen in both type 1 (insulin-dependent) diabetes and stiff-man syndrome (SMS). The observation that GAD65 autoantibodies may be present for years before the clinical onset of diabetes raises the question of when GAD65 is available to initiate an immune response to allow the formation of autoantibodies. In order to address this question it will be necessary to measure GAD65 in tissue, cells, and plasma.

METHODS

A radioimmunoassay (RIA) was developed for GAD65 based on the use of a polyclonal rabbit antiserum directed to the N-terminus of GAD65.

RESULTS

Using the GAD65 RIA, we have determined the GAD65 content in a human GAD65 gene transfected cell line and in beta-cell preparations from different species. The assay detects an increase of immunoreactive GAD65 after glucose-stimulation and GAD65 that is discharged from rat beta cells after their exposure to the diabetogenic agent streptozotocin. It also measures good recovery of GAD65 added to human plasma samples.

CONCLUSIONS

The GAD65 RIA makes it possible to determine both cellular and extracellular levels of GAD65; this might be useful in investigating the mechanisms leading to the formation of GAD65 autoantibodies in type 1 diabetes and SMS patients.

Antibodies to glutamic acid decarboxylase (GAD) in non-obese Japanese diabetics without insulin therapy: a comparison of two commercial RIA kits based on recombinant and pig brain GAD

To compare the clinical usefulness of commercial radioimmunoassay (RIA) kits based on recombinant and pig brain GAD, we measured glutamic acid decarboxylase autoantibody (GADAb) titers in 125 non-obese (body mass index < 24) Japanese diabetics without insulin therapy using two commercial RIA kits based on recombinant human (rh) GAD65 (GADAb Cosmic) and purified pig brain native GAD (RIP Anti-GAD Hoechst). The frequencies of GADAb positivity using these two RIA kits (normal ranges; < 1.3 and < 4.0 U/ml, respectively) were about 4.8 (6/125) and 3.2% (4/125), respectively. The six patients found to be positive with RIA using GADAb Cosmic demonstrated significantly higher prevalence of NIDDM in their parents (P = 0.04), lower beta-cell function estimated by intravenous glucagon loading tests (P = 0.03) and higher prevalence of progression to insulin therapy (P = 0.0001). Five of these six patients slowly progressed to insulin-requiring status within 34 +/- 11 months of follow-up evaluation, and one of these five patients progressed to a completely insulin-dependent status within 30 months from the onset of diabetes. Of these six patients, two demonstrated chronic pancreatitis, three had chronic thyroiditis, and five showed HLA DR4. Interestingly, two of the six patients demonstrated very low GADAb titers (2.3 and 2.9 U/ml), while RIP Anti-GAD Hoechst showed no positivity with the same sera. Based on the binding study after pre-incubation of unlabeled GADs, these low titrated GADAb were elucidated to be true specific reactions to rh GAD65 alone. Moreover, one of the two patients with chronic thyroiditis and HLA DR4 slowly progressed to insulin-requiring status over a period of 45 months. These findings suggest that the measurement of GADAb using a commercial assay kit with rh GAD65 may be more useful to detect non-insulin-dependent type I diabetics among non-obese patients than using a commercial kit with purified pig brain native GAD, especially among those with low GADAb titers.

Prediction of insulin-dependent diabetes mellitus in siblings of children with diabetes. A population-based study. The Childhood Diabetes in Finland Study Group

An unselected population of 755 siblings of children with insulin-dependent diabetes mellitus (IDDM) was studied to evaluate the predictive characteristics of islet cell antibodies (ICA), antibodies to the IA-2 protein (IA-2A), antibodies to the 65-kD isoform of glutamic acid decarboxylase (GADA), insulin autoantibodies (IAA), and combinations of these markers. We also evaluated whether the histochemical ICA test could be replaced by the combined detection of other markers. 32 siblings progressed to IDDM within 7.7 yr of the initial sample taken at or close to the diagnosis of the index case (median follow-up, 9.1 yr). The positive predictive values of ICA, IA-2A, GADA, and IAA were 43, 55, 42, and 29%, and their sensitivities 81, 69, 69, and 25%, respectively. In contrast to the other three antibody specificities, GADA levels were not related to the risk for IDDM. The risk for IDDM in siblings with four, three, two, one, or no antibodies was 40, 70, 25, 2, and 0.8%, respectively. Combined screening for IA-2A and GADA identified 70% of all ICA-positive siblings, and all of the ICA-positive progressors were also positive for at least one of the three other markers. The sensitivity of the combined analysis of IA-2A and GADA was 81%, and the positive predictive value was 41%. In conclusion, combined screening for IA-2A and GADA may replace the ICA assay, giving comparable sensitivity, specificity, and positive predictive value. Accurate assessment of the risk for IDDM in siblings is complicated, as not even all those with four antibody specificities contract the disease, and some with only one or no antibodies initially will progress to IDDM.

Insulin-Dependent Diabetes Mellitus: Islet Changes in Relation to Etiology and Pathogenesis

Type and type II diabetes are the most common types of diabetes. The ratio of type I to type II diabetes is about 1:9. Type I diabetes is caused by absolute insulin deficiency and is therefore referred to as insulin-dependent diabetes. The disease becomes manifest clinically in childhood or adolescence ("juvenile diabetes"), though onset in adulthood is increasingly being observed. Morphologically a subtotal (>80%) to total loss of B-cells in the pancreatic islets occurs. Lymphocytic insulitis, which disappears after the B-cells have been totally destroyed, is pathogneumonic of type I diabetes. This insulitis is an expression of an autoimmune event that is triggered by a multitude of factors. An important factor appears to be a genetic predisposition (human leukocyte antigen [HLA] DR3/DR4/DQ8) in connection with as-yet-unknown environmental factors (e.g., viruses). Autoantibodies, such as islet cell cytoplasmic antibodies (ICA). insulin autoantibodies (IAA) and/or autoantibodies to the gamma-aminobutyric acid (GABA)-synthesizing enzyme glutamic acid carboxylase (GAD), are already detectable in a prediabetic phase, though it is not possible to predict the time of clinical onset. The course of the disease is dependent on age. Young children require insulin therapy sooner than juveniles or adults.

Detection of recombinant GAD65 and GAD67 antibodies using a simple radioimmunoassay

Autoantibodies to glutamic acid decarboxylase (GAD) are useful diagnostic and predictive markers for Type 1 (insulin-dependent) diabetes mellitus. In the present study we describe a development of simple, reproducible, and quantitative radioimmunoassays for detecting GAD65 and GAD67 antibodies, and compare sensitivity and specificity of these assays with native GADAb radioimmunoassay. We used in vitro transcribed and translated recombinant human islet GAD65 and GAD67 as antigens, and anti-human IgG was used to separate free from antibody-bound ligand. By using these assays, GAD65Ab and GAD67Ab were detected in 65% and 25% of recent-onset Japanese patients with Type 1 diabetes, respectively, but none of 71 healthy control subjects tested were postive for GAD65Ab and GAD67Ab. Moreover, none of 48 patients with other autoimmune disease had GAD65Ab or GAD67Ab. There was a 100% correlation between the sensitivity and specificity of GAD65Ab assay and native GADAb assay. GAD65Ab and GAD67Ab were concordant in 28% of Type 1 diabetic sera and the levels of GAD65Ab in doubly positive patients were significantly higher than those in only GAD65Ab positive patients (P < 0.01). GAD65Ab are specific markers for Type 1 diabetes, and the radioimmunoassay using in vitro translated GAD and anti-human IgG, which is sensitive, convenient and low cost for detecting GAD antibodies, will facilitate large population screening of Type 1 diabetes.

Differential beta-cell response to glucose, glucagon, and arginine during progression to type I (insulin-dependent) diabetes mellitus

Acute insulin responses to glucose (AIRG), glucagon (AIRGln), and arginine (AIRArg) were evaluated prospectively in nine subjects positive for islet-cell antibodies (ICAs) who later progressed to type I diabetes or impaired glucose tolerance (IGT) (progressors), 64 ICA-positive subjects at risk who did not develop type I diabetes, 365 ICA-negative relatives of diabetic patients who also remained free of the disease, and 89 control subjects. Seven progressors already had a low AIRG at entry into the study, and the other two became low responders 3 to 9 months before diabetes or IGT, with a progressive decline of AIRG over serial intravenous (IV) glucose tolerance tests. At entry into the study, the group of progressors displayed lower AIRG, AIRGln, and AIRArg than the other three groups (P<.001). However, AIRArg was less altered than AIRG. During the course of the prediabetic phase, there was a progressive decline in AIRG and AIRGln analyzed as a function either of time (P<.006) or of basal glycemia (P<.05), ie, two different ways of estimating worsening of the disease process. Conversely, there was no significant decrease in AIRArg with time or with increasing basal glycemia, so that AIRArg was not totally blunted in these prediabetic subjects even a few months before the onset of diabetes. The persistence of a substantial response to arginine, ie, higher than the fifth control percentile, even at a late stage, was confirmed in five of nine diabetic patients tested either at onset of the disease or during non-insulin-receiving remission. Whereas AIRG deteriorates during prediabetes, AIRArg appears to be less altered with time and increased basal glycemia, remaining substantial even at the onset of the disease. This reinforces the supposition that the prediabetic state may be associated with a glucose-specific beta-cell functional abnormality in addition to a decreasing beta-cell mass.

Radioimmunoassays for glutamic acid decarboxylase (GAD65) and GAD65 autoantibodies using 35S or 3H recombinant human ligands

Autoantibodies are an important marker of human autoimmune diseases and the development of simple, precise and reproducible immunoassays to detect autoantibodies is important to our understanding of human autoimmunity. GAD65 autoantibodies occur frequently in insulin-dependent diabetic patients and is a useful marker for IDDM. A RIA to detect immunoreactive GAD65 has not been described. In the present study we describe a semi-automated fluid-phase immunoassay for the rapid detection of GAD65 autoantibodies in human serum. We also developed a sensitive RIA to determine immunoreactive human GAD65 in biological fluids and in vitro cell systems. Using in vitro translated recombinant human GAD65 in a multiwell-adapted procedure, our GAD65Ab RIA combines high specificity and sensitivity with a high capacity to analyze a large number of samples. In this report the three critical steps in the GAD65Ab RIA, DNA preparation, in vitro translation and immunoprecipitation, have been optimized. In our RIA, GAD65Ab were detected in 116/155 (75%) new onset Swedish IDDM children and in 1/85 (1.2%) healthy controls. In an immunoassay to detect autoantibodies against the proinsulin converting enzyme 2 (PC-2) no such antibodies were detected in IDDM patients. In the GAD65 RIA the lower detection limit was 2 ng/ml (31 fmol/ml). Our data demonstrate that autoantigen radioligands produced by in vitro translation are useful in RIA for autoantibodies and autoantigens in studies of human autoimmunity.

Glutamate decarboxylase antibody levels predict rate of beta-cell decline in adult-onset diabetes

Glutamate decarboxylase autoantibodies (GAD65Ab) and beta-cell function were evaluated at and 3 years after diabetes onset in consecutive subjects over 15 years of age. At onset, 21/32 (66%) insulin-treated patients (mean age 43, range 16-79 years) had GAD65Ab; all GAD65Ab persisted 3 years later. At onset, 20/82 (24%) non-insulin-treated patients (mean age 56, range 20-79 years) had GAD65Ab. Of those with persistent GAD65Ab, 8 non-insulin-treated and 11 insulin-treated patients consented to follow-up glucose and glucagon stimulation tests. For non-insulin-treated patients, quantitative GAD65Ab index at onset correlated inversely with 1 + 3 min C-peptide response to glucose (r = -0.68, P < 0.05) and to glucagon (r = -0.79, P < 0.05) 3 years later. Those with high (> 0.50) initial GAD65Ab index had lower C-peptide (fasting, 1 + 3 min after glucose and after glucagon) 3 years later, versus those with low (< 0.50) initial GAD65Ab index (P < 0.05). In conclusion, not only did GAD65Ab presence predict future insulin dependence, but higher GAD65Ab levels may mark more rapid decline in beta-cell function in apparent non-insulin-dependent diabetes.

Relationships among 64k autoantibodies, pancreatic beta-cell function, HLA-DR antigens and HLA-DQ genes in patients with insulin-dependent diabetes mellitus in Korea

OBJECTIVES

Among autoantibodies detected in patients with insulin-dependent diabetes mellitus (IDDM), antibodies to 64,000(Mr) islet protein(64k), now recognized as glutamic acid decarboxylase(GAD), appear to be an even more predictive marker of IDDM than islet cytoplasmic antibody (ICA) or insulin autoantibody (IAA). We examined the relationships among 64k autoantibodies, pancreatic beta-cell function, HLA-DR antigens and HLA-DQ genes in patients with IDDM in Korea.

METHODS

To identify the 64k autoantibody, the immunoprecipitation method was performed for 35 patients with IDDM and 10 normal controls. In patients with IDDM, serum C-peptide levels were measured and HLA-DR typings and HLA-DQA1 and DQB1 gene typings were performed.

RESULTS

12 of 35 (34%) patients with IDDM were positive for 64k autoantibody in contrast to none of 10(0%) normal controls. There were no differences in residual pancreatic beta-cell function between 64k autoantibody positive and negative groups. 64k autoantibody was detected more frequently in patients with recent (duration < 6 months, 10/25[40%]) and young -aged(aged < 15 years, 7/18[39%]) onset of IDDM. All of 3(100%) patients with HLA-DR3/DR4 heterotypes were positive in 64k autoantibody, in contrast to 1 of 7(14%) patients without HLA-DR3 nor DR4. The frequencies of HLA-DQA1*0301, HLA-DQB1*0201, DQB1* 0302 and DQB1*0303 gene types were higher in patients with 64k autoantibody (12/12 [100%]) vs. without 64k autoantibody 18/22[81%], 5/11[45%] vs. without 64k autoantibody 5/22[23%], 5/11[45%] vs. without 64k autoantibody 8/22[36%] and 6/11 [55%] vs. without 64k autoantibody 9/22[41%].

CONCLUSIONS

There results suggest that 64k autoantibodies have some relationship with HLA-DR, DQA1 and DQB1 genes, but not with residual pancreatic beta-cell function in Korean patients with IDDM.

Isolation by anion-exchange of immunologically and enzymatically active human islet glutamic acid decarboxylase 65 overexpressed in Sf9 insect cells

The enzyme L-glutamic acid decarboxylase is a major autoantigen of the beta cell. Autoantibodies against this enzyme are observed before the onset of insulin-dependent diabetes mellitus (IDDM) in man and may be of predictive value. There is evidence that this enzyme is involved in the development of autoimmune diabetes in animals. In order to facilitate the investigation of the role of L-glutamine acid decarboxylase in IDDM, we expressed the 65 kDa isoform of human islet L-glutamic acid decarboxylase in insect cells using a baculovirus-based vector. The material was expressed at high levels (up to 50 mg/l of cells). Partially purified metabolically labelled L-glutamic acid decarboxylase bound to immunoglobulins in the sera from 20 of 49 subjects with newly-diagnosed IDDM. The enzyme was isolated in high yields (up to 26 mg/l cell culture) with fully maintained enzymatic activity by either ion-exchange chromatography or immunoaffinity chromatography. Purified L-glutamic acid decarboxylase inhibited the binding of radioactive L-glutamic acid decarboxylase, prepared by in vitro translation of mRNA, to immunoglobulins in the sera of subjects with IDDM. Recombinant human islet L-glutamic acid decarboxylase, isolated from Sf9 cells, is a suitable material for the large scale investigation of the utility of this enzyme in the prediction and prevention of autoimmune diabetes.

Heterogeneity of islet pathology in two infants with recent onset diabetes mellitus

The mechanisms by which the beta cells of pancreatic islets are destroyed in insulin-dependent diabetes mellitus (IDDM) are poorly understood. In this report the pancreatic histo- and immunopathology of two children, both HLA-DR 3/4, DQ 2/8 positive and who both died from cerebral oedema within a day of clinical diagnosis of IDDM, were investigated. Patient 1, a 14-month-old girl, had a 4-week history of polydipsia and polyuria. Patient 2, a 3-year-old boy, had 2 days of illness. Both patients had a similarly severe loss of insulin cells but differed markedly as to the extent of lymphocytic islet infiltration (insulitis). Apart from insulitis, marked islet macrophage infiltration was demonstrated in both patients with the HAM-56 monoclonal antibody. Neither patient showed aberrant expression of HLA class II antigens on insulin-immunoreactive cells, but allele-specific HLA-DQ8 expression was evident on endothelial cells. Glutamic acid decarboxylase immunoreactivity was detected in both insulin- and glucagon-immunoreactive cells. It is concluded that the heterogeneity of islet pathology, especially insulitis, may reflect different dynamics and extent rather than different pathomechanisms of immune destruction of islets in IDDM.

Genetic and immunological markers of insulin dependent diabetes in Black Americans

ICA and GAD65 autoantibody profiles and HLA-DR and DQ analysis were performed on 43 Black juvenile onset IDDM patients and 34 unrelated Black controls from Tennessee, USA. 75% of patients were positive for GAD65 autoantibodies but only 53% had ICA; 39% both ICA and GAD65 antibodies. The strongest HLA association was with the DR3 haplotype DRB1*03 DQA1*0501 DQB1*0201 (63% of patients v 12% of controls RR = 13.0, p < 0.00002). DRB1*04 DQA1*0301 DQB1*0302, associated with IDDM in Caucasians but rare in Negroids, occurred in 27% of patients and 6% of controls (RR = 5.9, p < 0.04). All patients carried DQB1*0302 or DQB1*0201. DQB1*0602 was significantly reduced in patients (2.4% v 41%, RR = 0.036, p < 0.008) and DRB1*1501 was absent in patients (0% v 35%). The frequency of GAD65 autoantibodies in Black American IDDM patients is comparable to that in Caucasians; however ICA positivity is reduced. GAD65 antibodies may therefore be a more sensitive serological test to identify individuals in the Black American general population for markers associated with increased risk of developing IDDM. Current screening methods for predicting preclinical IDDM in Caucasians relies on a combination of immune and HLA markers of IDDM; studies of these markers in the Black Americans will make it possible to extend these options to additional genetically diverse populations.

Molecular biology of IDDM

The clinical onset of insulin-dependent diabetes is associated with several autoimmune phenomena including islet cell antibodies, glutamic acid decarboxylase (the GAD65 isoform) autoantibodies (GAD65Ab) as well as insulin autoantibodies. The molecular cloning of these autoantigens has permitted the development of precise and reproducible antibody immunoassays to identify marker-positive patients and control subjects. Among patients with new-onset diabetes about 70% were GAD65Ab positive compared to 1.5% among control subjects while 46% of patients had IAA compared to 1% among control subjects. The autoreactive sites or epitopes of GAD65 and insulin remain to be determined. The disease association with HLA on chromosome 6 may help to define the epitope specificity of the autoimmune reaction. Recent data suggest that 95% of new-onset IDDM children (0-15 years of age) are positive for either DQ2, DQ8 or both compared to about 50% of healthy control subjects. HLA-DQ6 is negatively associated with the disease. Both HLA-DQ2 and DQ8 therefore seem to be necessary, but not sufficient for diabetes. Molecular modelling suggests comparable physicochemical properties of DQ2 and DQ8 but are widely different from DQ6. In 1984, the conclusion was that molecular cloning of the genes for the autoantigens, antibodies, T-cell receptors, as well as HLA class I and II molecules associated with diabetes are essential for analysing the components which control the development of pancreatic beta-cell autoimmunity. In 1994, autoantigens and HLA molecules have been cloned and recombinant reagents developed to be used in experiments aimed at testing whether it will be possible to predict IDDM.(ABSTRACT TRUNCATED AT 250 WORDS)

Islet cell antibodies predict insulin-dependent diabetes in United States school age children as powerfully as in unaffected relatives

Islet cell antibodies (ICA) in the sera of nondiabetic relatives of patients with insulin-dependent diabetes (IDD) are predictive of the disease, a finding that permits the design of intervention strategies to prevent it. However, 85% or more of patients with new onset IDD have no affected relative. We therefore screened 9,696 schoolchildren between the ages of 5 and 18 yr (mean age 10.7 yr) in Pasco County, Florida for ICA in three surveys during 1984/5, 1987/8, and 1990/1 and have followed them prospectively. Approximately 4,000 of these children have been followed for nearly 8 yr. ICA titers > or = 10 Juvenile Diabetes Foundation units on replicate tests were detected in 57 of the children (0.59%). 10 children have developed diabetes so far, and all had ICA detected beforehand. The likelihood of developing IDD among the ICA-positive children was compared with 2,959 age-matched nondiabetic first degree relatives of IDD probands who were screened for ICA by our laboratory during the same time period and also followed prospectively. Of 103 (3.5%) ICA-positive relatives, 31 have developed IDD. Life table analysis reveals no statistically significant differences in the probability of developing IDD between the ICA-positive schoolchildren and ICA-positive first degree relatives (P = 0.3). The estimated risk of developing IDD by 7 yr in the ICA-positive schoolchildren was 45% (95% confidence interval 15-74%) compared with 43% (confidence interval 22-63%) in the relatives. We conclude that ICA appear to be as predictive of IDD in low-risk schoolchildren as they are in high-risk relatives. These data suggest that it is feasible to predict IDD by screening a general population of schoolchildren for ICA and that those found to be positive could be considered, in addition to relatives, for intervention protocols to prevent the disease.

Combined analysis of islet cell antibodies which cross-react with mouse pancreas, antibodies to the M(r) 64,000 islet protein, and antibodies to glutamate decarboxylase in subjects at risk for IDDM

With regard to progression to diabetes, ICA cross-reactive with mouse pancreas, antibodies to the M(r) 64,000 islet antigen (64K), antibodies immunotrapping brain GAD activity, and IAA were analysed in 53 ICA-positive first-degree relatives of IDDM patients and 18 ICA-positive schoolchildren without a family history of diabetes. Sera from 29 (55%) relatives did not bind to mouse pancreas, whereas 24 (45%) displayed cross-species reaction. ICA titres on human and mouse pancreas were weakly correlated in the overall population (p < 0.05) but more strongly (p < 0.01) in only those subjects who displayed antibodies on tissues from both species. GAD and 64K antibodies were detected in 31% and 35% of relatives. In schoolchildren, the frequencies of cross-species reactive ICA (22%), GAD antibodies (6%), 64K antibodies (22%), and IAA (6%), were lower (p < 0.05) than in relatives. A strong correlation (p < 0.0001) was observed between GAD and 64K antibodies. GAD or 64K antibodies were strongly correlated with ICA on human pancreas (p < 0.0001) but poorly with ICA on mouse pancreas (p = 0.05). After pre-incubation of sera with brain homogenate, ICA titres were unaffected on mouse pancreas but reduced on human pancreas. ICA-positive subjects who displayed neither cross-species reactive ICA nor GAD or 64K antibodies were more frequent (p < 0.05) among schoolchildren than relatives, whereas subjects who displayed all antibody specificities were more numerous (p < 0.04) in relatives. All relatives with ICA binding only to human pancreas, as well as all schoolchildren, permanently displayed an AIRG higher than the first control percentile and remained non-diabetic.(ABSTRACT TRUNCATED AT 250 WORDS)

Importance of persistent cellular and humoral immune changes before diabetes develops: prospective study of identical twins

OBJECTIVES

To determine the pattern of cellular and humoral immune changes associated with insulin dependent diabetes before diabetes develops.

DESIGN

Prospective study over 10 years of 25 non-diabetic identical twins of patients with insulin dependent diabetes. The non-diabetic twins were followed up either till they developed diabetes or to the end of the study.

SETTING

Teaching hospital.

SUBJECTS

25 non-diabetic identical cotwins of patients with diabetes; 46 controls of the same sex and similar age tested over the same period. Of the 25 twins (total follow up 144 patient years), 10 developed diabetes (prediabetic twins); the remainder were followed up for a mean of 7.7 years.

MAIN OUTCOME MEASURES

Results of glucose tolerance tests or fasting blood glucose concentrations at each sample point. Measurements of activated T lymphocytes, expressing the HLA-DR antigen, islet cell antibodies, and insulin autoantibodies in samples.

RESULTS

All 10 prediabetic twins had both cellular and humoral changes initially and in most samples before diabetes was diagnosed (activated T lymphocytes in 39/40, islet cell antibodies in 45/47, and insulin autoantibodies to islet cells and insulin were detected infrequently (in 8/54, 6/69, and 0/69 samples, respectively). The combination of cellular and humoral (islet cell antibodies or insulin autoantibodies) immune changes were detected in all 10 of the prediabetic twins but in only one of the 15 non-diabetic twins (P < 0.001). The positive predictive value in this cohort of increased percentages of activated T cells and the presence of antibodies to islet cells or insulin on two consecutive occasions was 100%.

CONCLUSION

Most of the twins had cellular or humoral immune changes at some stage. A combination of cellular and humoral immune changes and their tendency to persist is highly predictive of insulin dependent diabetes and distinguishes twins who develop diabetes from those who do not.

A novel radioligand binding assay to determine diagnostic accuracy of isoform-specific glutamic acid decarboxylase antibodies in childhood IDDM

Insulin-dependent diabetes mellitus (IDDM) is associated with autoreactivity against GAD but the diagnostic sensitivity (positivity in disease) and specificity (negativity in health) of isoform-specific GAD antibodies have yet to be defined in assay systems suitable for screening large number of samples. One set of IDDM patient (n = 10) and control (n = 50) standard sera were used to develop quantitative antibody assays with in vitro synthesized recombinant 35S-methionine-labelled GAD65 and GAD67, respectively, and protein A-Sepharose to separate free from antibody-bound ligand. Binding levels were not normally distributed (p < 0.0001) and therefore, the diagnostic accuracy of GAD antibodies was analysed by the ROC plots in population-based, consecutively-diagnosed, recent onset, 0-14 year-old patients (n = 105), and matched, healthy control subjects (n = 157). The ROC plots showed that the diagnostic sensitivity of GAD65 antibodies was 77% and the specificity 92% compared with 8% and 98%, respectively for GAD67 antibodies. In the IDDM sera, GAD65 and GAD67 antibodies were concordant in 7% (6 of 81) and GAD65 antibodies and ICA in 89% (72 of 81) without a correlation between the autoantibody levels. Autoantibodies to recombinant human islet GAD65 are specific and sensitive markers for childhood IDDM in this immunoassay with in vitro synthesized 35S-methionine-labelled recombinant GAD.

Glutamic acid decarboxylase antibodies, autonomic nerve antibodies and autonomic neuropathy in diabetic patients

To clarify whether GAD-ab are associated with diabetic autonomic neuropathy and/or complement fixing antibodies against sympathetic ganglia, adrenal medulla, and vagus nerve, we examined 133 diabetic patients (95 with IDDM). GAD-ab were determined by a radioligand binding assay using in vitro expression of recombinant GAD-65 whereas sympathetic ganglia antibodies, adrenal medulla antibodies, vagus nerve, and ICA were evaluated by indirect immunofluorescence assays. Autonomic nerve function was evaluated by objective tests (heart rate reactions to deep breathing and to tilt). In the total material of 133 patients, GAD-ab were detected in 36 patients, all of whom had IDDM. The frequency of GAD-ab was similar (38%) in IDDM patients with and without signs of autonomic neuropathy (21 of 55 vs 15 of 40). In addition, there were no significant associations between GAD-ab and autonomic nerve antibodies; GAD-ab were detected in 9 of 21 (43%) of patients with and in 27 of 112 (24%) of patients without sympathetic ganglia antibodies, in 5 of 15 (33%) of patients with and 31 of 118 (26%) without adrenal medulla antibodies, and in 5 of 15 (33%) with and 31 of 118 (26%) of patients without vagus nerve antibodies. The frequency of ICA, however, was significantly increased in patients with sympathetic ganglia antibodies compared with those without sympathetic ganglia antibodies (10 of 21 [48%] vs 21 of 112 [19%]; p < 0.01). In conclusion, GAD-ab were neither associated with disturbed autonomic nerve function nor with antibodies against autonomic nerve structures.

Radioimmunoassay detects the frequent occurrence of autoantibodies to the Mr 65,000 isoform of glutamic acid decarboxylase in Japanese insulin-dependent diabetes

Glutamic acid decarboxylase antibodies (GAD65Ab) are common in new onset Caucasian insulin-dependent diabetic (IDDM) patients but it is unclear if this marker is also prevalent in patients of other ethnic backgrounds. We determined antibodies against human recombinant GAD in Japanese diabetic patients using a radioimmunoassay with competition between in vitro translated 35S-GAD65 and non-labelled recombinant human GAD65 (rhGAD65). GAD67 antibodies (GAD67Ab) were similarly analyzed but without antigen competition. In 73 Japanese diabetic patients, GAD65Ab were found in 11/16 (69%) of patients with short-duration (less than 5 yrs) IDDM, 6/23 (26%) with long-duration (5 or more yrs) IDDM and 10/20 (50%) with slowly progressive diabetes. High GAD65Ab levels were associated with concomitant autoimmune diseases (p = 0.021). GAD67Ab were found in 4/16 (25%) of patients with short-duration IDDM, 3/23 (13%) with long-duration IDDM and 2/20 (10%) with slowly progressive diabetes. In 14 non-insulin dependent diabetic (NIDDM) patients, GAD65Ab and GAD67Ab were not found (0/14) and 1/50 (2%) healthy controls were positive in either assay. Among the GAD67Ab-positive samples, 8/9 (88%) were also high level GAD65Ab positive, 7/9 (77%) were displaced by an excess of rhGAD65 and the antibody levels correlated (r2 = 0.573; p = 0.003). Our data are consistent with a strong association of GAD65Ab also in Japanese IDDM, and suggest that, when present, GAD67Ab are frequently directed to epitope(s) common to GAD65 and GAD67.

Autoantibodies against GAD65 rather than GAD67 precede the onset of type 1 diabetes

The enzyme glutamate decarboxylase (GAD) is considered one of the major Beta cell antigens in Type 1 diabetes mellitus. The GAD autoantibody (GAD-AAb) prevalence in newly diagnosed Type 1 diabetic patients has been described up to 80%, depending on the detection method used. The aim of this study was to evaluate a simple, specific, and sensitive radioimmunoassay (RIA) method for detection of AAb against both isoforms of the enzyme, GAD65 and GAD67, in a cross-sectional study using sera from newly diagnosed Type 1 diabetic patients and in a longitudinal study using sera from prediabetic patients and individuals at risk of developing the disease. The 125I-labelled full-length human recombinant proteins of GAD65 and GAD67 expressed in SF9 cells were used as the antigen source. The prevalence of GAD65-AAb in newly diagnosed Type 1 diabetic patients was found to be 73% (112/153), in contrast to 19% (14/72) of GAD67-AAb. Only one patient produced AAb restricted to GAD67. Furthermore, GAD65-AAb could also be detected in 73% (11/15) of prediabetic patients (up to 122 months before clinical manifestation of the disease), whereas only 27% (4/15) of them were positive for GAD67-AAb. In the group at risk of developing Type 1 diabetes, these prevalences were 77% (10/13) and 46% (6/13), respectively. In all GAD67-AAb-positive patients investigated in the longitudinal study, AAb to GAD65 were detectable. In 47% of patients positive for both GAD65-AAb and ICA, the GAD65-AAb appeared by up to 46 months before the occurrence of ICA was detected. The data illustrated that GAD65 is the main immunogenic isoform of the enzyme in the preclinical and clinical stages. The RIA detecting AAb against this isoform may facilitate the screening for individuals at risk of developing the disease.

Preventive effects of azathioprine (AZA) on the onset of diabetes mellitus in NOD mice

We have studied the effects of long-term treatment with azathioprine (AZA) vs cyclosporin A (CSA) vs placebo (PL), in three groups of 10 week old, prediabetic NOD mice. One of 8 AZA, none of 8 CSA and 7 of 11 PL treated mice developed overt diabetes (IDDM). Quantitative morphometric analysis conducted on mouse pancreatic histologic sections documented that extent and degree of islet beta-cell damage were incomparably less severe in the mice that received AZA or CSA compared to those treated with PL. Since early and prolonged treatment with AZA seems to prevent the onset of DM in NOD mice as nearly effectively as CSA, AZA, which is significantly safer than CSA, could replace the latter as a potential approach for the immunotherapy of IDDM.

Prevalence of autoantibodies to the 65- and 67-kD isoforms of glutamate decarboxylase in insulin-dependent diabetes mellitus

We investigated the presence of autoantibodies to baculovirus-expressed human recombinant 65- and 67-kD isoforms of glutamate decarboxylase (GAD65 and GAD67) in insulin-dependent diabetes mellitus (IDDM). In the immunoprecipitation test using [35S]methionine-labeled GADs antibodies to GAD65 were detected in 13/15 (87%) islet cell antibody (ICA)-positive and in 1/35 (2.9%) ICA-negative first-degree relatives of patients with IDDM, in 6/11 (54.5%) ICA-positive nondiabetic schoolchildren, and in 35/50 (70%) patients with newly diagnosed IDDM. GAD67 antibodies were positive only in five (33%) of the ICA-positive relatives (P < 0.05) and in nine (18%) IDDM patients at onset (P < 0.00001). After onset of IDDM antibodies to GAD65 and GAD67 declined but were still positive in 25 and 9.4% of subjects with long-standing IDDM (> 10 yr). In all study groups antibodies to GAD67 were only detected in GAD65 antibody-positive sera. An immunotrapping enzyme activity assay for GAD65 antibodies was positive in 64/75 (85.3%) of sera that were GAD antibody positive in the immunoprecipitation test (r = 0.870, P < 0.0001). In two (2.7%) sera GAD65 antibodies that block GAD enzyme activity were found. Our data suggest that antibodies to GAD65 but not to GAD67 represent sensitive markers for preclinical and overt IDDM. The immunotrapping assay here described represents a valuable technique for specific and sensitive screening for GAD antibodies.

Characterization of a linear epitope within the human pancreatic 64-kDa glutamic acid decarboxylase and its autoimmune recognition by sera from insulin-dependent diabetes mellitus patients

A 2.0-kb cDNA coding for the full-length 64-kDa human glutamic acid decarboxylase (GAD64) was isolated from a pancreatic carcinoma cDNA library by oligonucleotide screening, polymerase-chain-reaction amplification and subsequently characterized by sequence analysis. Five overlapping fragments of GAD64 cDNA were constructed into the vector pH6EX3, allowing the highly efficient expression of corresponding fusion proteins with a histidine hexapeptide as an affinity ligand at their N-termini in Escherichia coli. The recombinant GAD64 fragments were analysed by Western blotting using sera from patients with early onset of insulin-dependent diabetes mellitus (IDDM). We found that at least 20% of the patients with an onset of IDDM have developed autoantibodies which can specifically recognize a linear antigenic epitope within the GAD64. With a selected IDDM serum, an antigenic epitope was localized in a region of 31 amino acids located at the C-terminus of GAD64, using epitope mapping techniques, and it was characterized. The possibility of using recombinant GAD64 for the development of an immunoassay for a predictive diagnosis of IDDM is discussed.

Quantitative assay using recombinant human islet glutamic acid decarboxylase (GAD65) shows that 64K autoantibody positivity at onset predicts diabetes type

At and before onset, most insulin-dependent diabetics (IDDM) have islet GAD65 autoantibodies (GAD65Ab). Since IDDM also occurs in older patients where non-insulin-dependent diabetes is common, we studied GAD65Ab at onset to classify diabetes type. Our quantitative immunoprecipitation assay uses recombinant human islet GAD65 stably expressed in hamster fibroblasts. Electrophoretic mobility was identical to native islet GAD65. Like native antigen, recombinant GAD65 migrated as two bands during electrophoresis, but converted to one under stronger reduction. Immunoprecipitation was linear with respect to antibody or antigen concentration. In 120 population-based diabetic patients of all ages grouped by treatment at onset and after 18 mo, GAD65Ab were present in 70% on insulin (n = 37), 10% on oral agent (n = 62, P < 0.0001), 69% changing from oral agent to insulin (n = 16, P < 0.001), and 1 of 33 controls. 65% with GAD65Ab, versus 8% without, changed from oral agent to insulin (P < 0.01). The GAD65Ab quantitative index was remarkably stable, and only 2 of 32 patients changed antibody status during follow-up. Concordance between GAD65Ab and islet cell antibodies was 93%. Quantitative correlation was approximate but significant. This highly sensitive, quantitative, high capacity assay for GAD65Ab reveals treatment requirements better than clinical criteria, perhaps guiding immunomodulatory therapy.

Predictive value of islet cell and insulin autoantibodies for type 1 (insulin-dependent) diabetes mellitus in a population-based study of newly-diagnosed diabetic and matched control children

Most studies evaluating immune markers for prediction of Type 1 (insulin-dependent) diabetes mellitus have focused on first degree relatives, although only 10% of newly-diagnosed patients have an affected first degree relative. The Swedish Childhood Diabetes Register identifies 99% of all diabetic children at diagnosis. In this population-based study, islet cell antibodies and insulin autoantibodies in 0-14-year-old Swedish consecutively-diagnosed patients and control subjects were analysed to define their sensitivity and specificity. Over 16 months (1986-1987), 515 Swedish children developed diabetes. Plasma samples were obtained from 494 (96%) patients, and 420 matched control children. Among patients, the frequency of islet cell antibodies was 84% (415 of 494), insulin autoantibodies 43% (145 of 334); 40% (135 of 334) were positive for both and 88% (294 of 334) were positive for one or both. Among control children, 3% (14 of 420) had islet cell antibodies, 1% (4 of 390) insulin autoantibodies, and 4% (16 of 390) had either autoantibody marker. The predictive value of finding a patient with the disease was only 7% since 4% of the control children were antibody-positive and the cumulative incidence rate up to 15 years of age is 0.38%. None of the autoantibody-positive (n = 21) or negative control children developed diabetes during 3 to 5 years of follow-up. Longitudinal investigations of islet cell or insulin-autoantibody-positive healthy children are necessary to accurately determine the conversion rate from marker positivity to disease onset.

Antibodies to the M(r) 64,000 (64K) protein in islet cell antibody positive non-diabetic individuals indicate high risk for impaired beta-cell function

A prospective study of a normal childhood population identified 44 islet cell antibody positive individuals. These subjects were typed for HLA DR and DQ alleles and investigated for the presence of antibodies to the M(r) 64,000 (64K) islet cell antigen, complement-fixing islet cell antibodies and radiobinding insulin autoantibodies to determine their potency in detecting subjects with impaired Beta-cell function. At initial testing 64K antibodies were found in six of 44 islet cell antibody positive subjects (13.6%). The same sera were also positive for complement-fixing islet cell antibodies and five of them had insulin autoantibodies. During the follow-up at 18 months, islet cell antibodies remained detectable in 50% of the subjects studied. In all six cases who were originally positive, 64K antibodies were persistently detectable, whereas complement-fixing islet cell antibodies became negative in two of six and insulin autoantibodies in one of five individuals. HLA DR4 (p less than 0.005) and absence of asparic acid (Asp) at position 57 of the HLA DQ beta chain (p less than 0.05) were significantly increased in subjects with 64K antibodies compared with control subjects. Of 40 individuals tested in the intravenous glucose tolerance test, three had a first phase insulin response below the first percentile of normal control subjects. Two children developed Type 1 (insulin-dependent) diabetes mellitus after 18 and 26 months, respectively. Each of these subjects was non-Asp homozygous and had persistent islet cell and 64K antibodies.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative analysis of islet glutamic acid decarboxylase p64 autoantibodies in insulin-dependent diabetes mellitus

Autoantibodies against the beta-cell M(r) 64,000 protein (p64), recently identified as an isoform of glutamic acid decarboxylase (GAD), are prevalent in patients with insulin-dependent diabetes mellitus (IDDM). Dog islets were found to represent an abundant source of native p64 allowing the study of antigen-antibody interactions in IDDM. A quantitative, standardized assay for p64 antibodies based on dog islets was developed and evaluated. Utilizing dog and human islets the p64 antibodies were detected in 17/19 (89%) new onset 15-32-year-old patients, compared to 15/19 (79%) in a rat islet assay. ICA were detected in 15/19 (79%) patients and correlated with the presence of p64 antibodies (rs = 0.59, P < 0.004) but not with age at onset, sex, or C-peptide levels. Sensitivity therefore is improved with the dog islet p64 antibody assay which will allow future studies requiring native p64 antigen in larger quantities are possible based on our findings.