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

Non-HLA type 1 diabetes genes modulate disease risk together with HLA-DQ and islet autoantibodies

The possible interrelations between HLA-DQ, non-HLA single nucleotide polymorphisms (SNPs) and islet autoantibodies were investigated at clinical onset in 1-34 year old type 1 diabetes (T1D) patients (n=305) and controls (n=203). Among the non-HLA SNPs reported by the Type 1 Diabetes Genetics Consortium, 24% were supported in this Swedish replication set including that the increased risk of minor PTPN22 allele and high risk HLA was modified by GAD65 autoantibodies. The association between T1D and the minor AA+AC genotype in ERBB3 gene was stronger among IA-2 autoantibody-positive patients (comparison p=0.047). The association between T1D and the common insulin (AA) genotype was stronger among insulin autoantibody (IAA)-positive patients (comparison p=0.008). In contrast, the association between T1D and unidentified 26471 gene was stronger among IAA-negative (comparison p=0.049) and IA-2 autoantibody-negative (comparison p=0.052) patients. Finally, the association between IL2RA and T1D was stronger among IAA-positive than among IAA-negative patients (comparison p=0.028). These results suggest that the increased risk of T1D by non-HLA genes is often modified by both islet autoantibodies and HLA-DQ. The interactions between non-HLA genes, islet autoantibodies and HLA-DQ should be taken into account in T1D prediction studies as well as in prevention trials aimed at inducing immunological tolerance to islet autoantigens.

A comparative analysis of recombinant protein expression in different biofactories: bacteria, insect cells and plant systems

Plant-based systems are considered a valuable platform for the production of recombinant proteins as a result of their well-documented potential for the flexible, low-cost production of high-quality, bioactive products. In this study, we compared the expression of a target human recombinant protein in traditional fermenter-based cell cultures (bacterial and insect) with plant-based expression systems, both transient and stable. For each platform, we described the set-up, optimization and length of the production process, the final product quality and the yields and we evaluated provisional production costs, specific for the selected target recombinant protein. Overall, our results indicate that bacteria are unsuitable for the production of the target protein due to its accumulation within insoluble inclusion bodies. On the other hand, plant-based systems are versatile platforms that allow the production of the selected protein at lower-costs than Baculovirus/insect cell system. In particular, stable transgenic lines displayed the highest-yield of the final product and transient expressing plants the fastest process development. However, not all recombinant proteins may benefit from plant-based systems but the best production platform should be determined empirically with a case-by-case approach, as described here.

A downstream process allowing the efficient isolation of a recombinant amphiphilic protein from tobacco leaves

The 65-kDa isoform of human glutamic acid decarboxylase (hGAD65) is a major autoantigen in autoimmune diabetes. The heterologous production of hGAD65 for diagnostic and therapeutic applications is hampered by low upstream productivity and the absence of a robust and efficient downstream process for product isolation. A tobacco-based platform has been developed for the production of an enzymatically-inactive form of the protein (hGAD65mut), but standard downstream processing strategies for plant-derived recombinant proteins cannot be used in this case because the product is amphiphilic. We therefore evaluated different extraction buffers and an aqueous micellar two-phase system (AMTPS) to optimize the isolation and purification of hGAD65mut from plants. We identified the extraction conditions offering the greatest selectivity for hGAD65mut over native tobacco proteins using a complex experimental design approach. Under our optimized conditions, the most efficient initial extraction and partial purification strategy achieved an overall hGAD65mut yield of 92.5% with a purification factor of 12.3 and a concentration factor of 23.8. The process also removed a significant quantity of phenols, which are major contaminants present in tobacco tissue. This is the first report describing the use of AMTPS for the partial purification of an amphiphilic recombinant protein from plant tissues and our findings could also provide a working model for the initial recovery and partial purification of hydrophobic recombinant proteins from transgenic tobacco plants.

Comparative analysis of different biofactories for the production of a major diabetes autoantigen

The 65-kDa isoform of human glutamic acid decarboxylase (hGAD65) is a major diabetes autoantigen that can be used for the diagnosis and (more recently) the treatment of autoimmune diabetes. We previously reported that a catalytically-inactive version (hGAD65mut) accumulated to tenfold higher levels than its active counterpart in transgenic tobacco plants, providing a safe and less expensive source of the protein compared to mammalian production platforms. Here we show that hGAD65mut is also produced at higher levels than hGAD65 by transient expression in Nicotiana benthamiana (using either the pK7WG2 or MagnICON vectors), in insect cells using baculovirus vectors, and in bacterial cells using an inducible-expression system, although the latter system is unsuitable because hGAD65mut accumulates within inclusion bodies. The most productive of these platforms was the MagnICON system, which achieved yields of 78.8 μg/g fresh leaf weight (FLW) but this was substantially less than the best-performing elite transgenic tobacco plants, which reached 114.3 μg/g FLW after six generations of self-crossing. The transgenic system was found to be the most productive and cost-effective although the breeding process took 3 years to complete. The MagnICON system was less productive overall, but generated large amounts of protein in a few days. Both plant-based systems were therefore advantageous over the baculovirus-based production platform in our hands.

Interaction of onset and duration of diabetes on the percent of GAD and IA-2 antibody-positive subjects in the type 1 diabetes genetics consortium database

OBJECTIVE

GAD antibodies (GADA) are more common in type 1 diabetic subjects diagnosed at an older age, whereas insulinoma-antigen 2 antibodies (IA-2A) are more common in subjects with younger onset. The prevalence of both antibodies decreases with longer duration of type 1 diabetes. We evaluated the interaction between age of diagnosis (onset) and duration of diabetes on the percentage of GADA- and IA-2A-positive subjects.

RESEARCH DESIGN AND METHODS

Data were used from 5,020 individuals with type 1 diabetes obtained from the Type 1 Diabetes Genetics Consortium dataset. The percentages of GADA- and IA-2A-positive subjects were modeled with duration as the continuous independent variable using a modified spline.

RESULTS

Within the first 5 years from diagnosis, 19.4% of individuals (median age 13 years) had neither GADA nor IA-2A, and by 6 to 13 years after diagnosis (median age 18 years), 31.7% were antibody-negative. There was no significant interaction between onset of disease and duration of diabetes for IA-2A (P = 0.30). The interaction was significant for GADA (P = 0.0002), resulting from differences in subjects diagnosed at or older than age 14. For these individuals, there was no apparent effect of duration of disease on the percentage of GADA-positive subjects within the first 5 years of diagnosis.

CONCLUSIONS

Onset and duration of diabetes both have an important effect on antibody status. The interaction of onset and duration on GADA positivity, but not on IA-2A, suggests differences in biology. These data provide a context for clinicians to interpret results of autoantibody testing in clinical practice.

The association between the PTPN22 1858C>T variant and type 1 diabetes depends on HLA risk and GAD65 autoantibodies

The single nucleotide polymorphism 1858C>T in the PTPN22 gene is associated with type 1 diabetes (T1D) in several populations. Earlier reports have suggested that the association may be modified by human leukocyte antigen (HLA), as well as by islet autoantibodies. In a large case-control study of Swedish incident T1D patients and controls, 0-34 years of age, we tested whether the odds ratio (OR) measure of association was dependent on HLA or autoantibodies against the islet autoantigens glutamic acid decarboxylase 65 kDa autoantibodies (GADA), insulin, islet antigen-2, or islet cell. The association between the carrier status of 1858C>T allele in PTPN22 (PTPN22(CT+TT)) and T1D was modified by HLA. In addition, in GADA-positive T1D, the OR was 2.83 (2.00, 3.99), whereas in GADA-negative T1D, the OR was 1.41 (0.98, 2.04) (P for comparison=0.007). The OR of association between PTPN22(CT+TT) and GADA-positive T1D declined with increasing HLA-risk category from 6.12 to 1.54 (P=0.003); no such change was detected in GADA-negative T1D (P=0.722) (P for comparison=0.001). However, the absolute difference in risk between PTPN22(CC) and PTPN22(CT+TT) subjects with high-risk HLA was five times higher than that for subjects with low-risk HLA. We hypothesize that the altered T-cell function because of the PTPN22(1858C>T) polymorphism is exclusively associated with GADA-positive T1D at diagnosis.

Insulin receptor autoimmunity and insulin resistance

The frequency of insulin receptor autoantibodies (IR-ab) was determined among adolescents and young adults with documented insulin resistance syndrome (IRS) with and without concomitant autoimmunity. The study population was comprised of 61 patients with obesity, acanthosis nigricans and insulin resistance (simple IRS); 12 with IRS and other autoimmune problems (lupus erythematosus, rheumatoid arthritis, dermatomyositis) (type B insulin resistance); six with autoimmune polyglandular syndrome type 2; and 40 healthy controls. Using our newly developed radiobinding assay system, we found no control positive while 25% of the patients with type B IRS (3/12) were positive, as expected. However, we found that 9.8% of the patients with simple IRS (6/61) were also reproducibly positive. All the latter patients with positive IR-ab were female with ovarian hyperandrogenism. The phenotype of those affected was otherwise unremarkably different from those without IR-ab. Our findings suggest that autoimmunity to insulin receptors may be causal in IRS especially for females with ovarian hyperandrogenism, and that IR-ab may be found in IRS besides those previously defined by the type B phenotype. Determining the level of IR-ab in childhood onset IRS may provide mechanistic insights into the genesis of insulin resistance and lead to novel treatment approaches.

Autoantibody epitopes to the smaller isoform of glutamate decarboxylase do not differ in Swedish and Japanese type 1 diabetes patients and may be associated with high-risk human leucocyte antigen class II alleles

Type 1 diabetes (T1D) is an autoimmune disease with a strong human leucocyte antigen (HLA) class II association. Depending on geographic locations, the disease-associated HLA class II alleles vary. We evaluated the beta cell-specific autoimmunity reflected in autoantibodies directed to the smaller isoform of glutamate decarboxylase (GAD65) in Japanese and Swedish T1D patients. GAD65Ab epitope specificities were assessed using GAD65-specific recombinant Fab. GAD65Ab epitope specificities did not differ between Swedish and Japanese patients. Only recognition of the MICA-4-defined middle epitope was significantly stronger in the Japanese T1D patient group compared to the Swedish T1D patients (P = 0.001). Binding to the b96.11-defined middle epitope was substantial in both groups and showed significant associations with high-risk HLA class II haplotypes. In the Japanese T1D group the association was with haplotype DRB1*0802-DQB1*0302 (P = 0.0008), while in the Swedish T1D patients binding to the b96.11-defined epitope as associated with the presence of high-risk HLA genotypes DR3-DQB1*0201 and/or DR4-DQB1*0302 (P = 0.02). A significant association between reduction in binding in the presence of recombinant Fab (rFab) DPD and high-risk allele DQB1*0201 was found (P = 0.008) in the Swedish T1D patients only. We hypothesize that epitope-specific autoantibodies effect the peptide presentation on HLA class II molecules by modulating antigen uptake and processing. Molecular modelling of the high-risk HLA class II molecules will be necessary to test whether these different molecules present similar peptide-binding specificities.

IA-2 autoantibodies in incident type I diabetes patients are associated with a polyadenylation signal polymorphism in GIMAP5

In a large case-control study of Swedish incident type I diabetes patients and controls, 0-34 years of age, we tested the hypothesis that the GIMAP5 gene, a key genetic factor for lymphopenia in spontaneous BioBreeding rat diabetes, is associated with type I diabetes; with islet autoantibodies in incident type I diabetes patients or with age at clinical onset in incident type I diabetes patients. Initial scans of allelic association were followed by more detailed logistic regression modeling that adjusted for known type I diabetes risk factors and potential confounding variables. The single nucleotide polymorphism (SNP) rs6598, located in a polyadenylation signal of GIMAP5, was associated with the presence of significant levels of IA-2 autoantibodies in the type I diabetes patients. Patients with the minor allele A of rs6598 had an increased prevalence of IA-2 autoantibody levels compared to patients without the minor allele (OR=2.2; Bonferroni-corrected P=0.003), after adjusting for age at clinical onset (P=8.0 x 10(-13)) and the numbers of HLA-DQ A1*0501-B1*0201 haplotypes (P=2.4 x 10(-5)) and DQ A1*0301-B1*0302 haplotypes (P=0.002). GIMAP5 polymorphism was not associated with type I diabetes or with GAD65 or insulin autoantibodies, ICA, or age at clinical onset in patients. These data suggest that the GIMAP5 gene is associated with islet autoimmunity in type I diabetes and add to recent findings implicating the same SNP in another autoimmune disease.

Longitudinal changes in epitope recognition of autoantibodies against glutamate decarboxylase 65 (GAD65Ab) in prediabetic adults developing diabetes

We analysed the beta cell-specific autoimmunity reflected in autoantibodies to the smaller isoform of glutamate decarboxylase (GAD65Ab) in the prediabetic period of GAD65Ab-positive healthy adults who developed Type 2 diabetes (T2D) during a follow-up period of 10 years. We found that of the adults that tested GAD65Ab-positive at baseline (n=25), six developed T2D and one developed Type 1 diabetes (T1D). Of the subjects that tested GAD65Ab-negative at baseline (n=2209), 81 developed T2D, one developed T1D and four developed unclassified diabetes, indicating that the risk for GAD65Ab-positive healthy adults to develop diabetes is increased sixfold. The GAD65Ab epitopes were characterized in a competition radioligand binding assay using recombinant Fab derived of GAD65-specific monoclonal antibodies. We observed that the GAD65Ab epitope specificities in the prediabetic period changed dynamically. Specifically, the binding to a middle and a C-terminal epitope increased during the follow-up period (P=0 x 03), causing a significant increase in the number of epitopes recognized (P=0 x 03). These findings are similar to previous observations of dynamic changes in the prediabetic period of schoolchildren at high risk for T1D development. However, the character of the epitopes differs between the two populations, suggesting differences in the beta cell-specific autoimmune response in the prediabetic period of patients with latent autoimmune diabetes in adults (LADA) and T1D.

Pituitary autoantibodies in autoimmune polyendocrine syndrome type 1

Autoimmune polyendocrine syndrome type 1 (APS1) is a rare autosomal recessive disorder caused by mutations in the autoimmune regulator (AIRE) gene. High titer autoantibodies (Aabs) toward intracellular enzymes are a hallmark for APS1 and serve as diagnostic markers and predictors for disease manifestations. In this study, we aimed to identify pituitary autoantigens in patients with APS1. A pituitary cDNA expression library was screened with APS1 sera and a tudor domain containing protein 6 (TDRD6) cDNA clone was isolated. Positive immunoreactivity against in vitro translated TDRD6 fragments was shown in 42/86 (49%) APS1 patients but not in patients with other autoimmune diseases or in healthy controls. By using immunohistochemistry, sera from 3/6 APS1 patients with growth hormone (GH) deficiency showed immunostaining of a small number of guinea pig anterior pituitary cells, and 40-50% of these cells were GH-positive. No such immunostaining was seen with sera from healthy controls. The APS1 Aab-positive, GH-negative cells may represent a novel subpopulation of anterior pituitary cells. In addition, 4/6 patient sera showed staining of a fiber-plexus in the pituitary intermediate lobe recognizing enzymes of monoamine and GABA synthesis. Thus, we have identified TDRD6 as a major autoantigen in APS1 patients and shown that several sera from GH-deficient patients stain specific cell populations and nerves in the pituitary gland.

MHC Class I Chain-Related Gene-A Is Associated with IA2 and IAA but Not GAD in Swedish Type 1 Diabetes Mellitus

In type 1 diabetes mellitus (T1DM), the frequency of antibodies against insulin (IAA), glutamic acid decarboxylase-65 (GAD65), ICA512/IA2 (IA2), and islet cell antigens (ICA) vary with human leukocyte antigen (HLA) composition of the patient. IAA, IA2 autoantibodies, and ICA are increased in DQ8 positives; GAD65 antibodies are increased in DQ2 positives. MHC class I chain-related gene-A (MICA) is another genetic marker that has been proposed to be associated with T1DM. In this article, we looked at microsatellite polymorphism of MICA and its association with autoantibodies (IAA, IA2, and GAD65) in Swedish T1DM patients and if the association explains its importance in early events in autoimmune response. We studied 635 T1DM patients between 0-35 years. Frequency of MICA5/5 was positively associated with the formation of IAA and IA2 antibodies considered individually or in combination (odds ratio [OR], 95% CI, Pc: [IAA+ versus IAA-]: 4.94, 2.09-11.62, <0.0005; [IA2+ versus IA2-]: 2.65, 1.52-4.59, 0.0015; [IAA and/or IA2+ versus rest]: 9.83, 2.37-40.78, <0.0015; [IAA and IA2+ versus rest]: 3.51, 2.01-6.15, <0.0015). Also, -5.1/5.1 was increased in IAA+ patients compared to IAA- patients (2.82, 1.64-4.83, <0.0005). All patients positive for -5/5 developed at least one of the three antibodies. Frequency of MICA5.1 was decreased in IAA+ (0.54, 0.36-0.81, 0.017), in IA2A+ (0.63, 0.45-0.88, 0.04), in IAA and/or IA2A+ (0.52, 0.33-0.84, 0.044), and in IAA and IA2A+ (0.55, 0.39-0.78, 0.0055) patients when compared with patients negative for corresponding antibodies. Frequency of MICA9, 5/5.1, and 5.1/9 was decreased in IAA+ compared to IAA- patients (0.51, 0.32-0.79, 0.021; 0.22, 0.11-0.44, <0.005; and 0.39, 0.22-0.69, 0.026, respectively). Frequency of MICA9 and -5.1/9 was also decreased in IAA and/or IA2 antibody-positive patients while MICA5/5.1 decreased in patients positive for IAA and IA2 antibody both together. IAA and IA2 antibodies are believed to appear early during the autoimmune reaction against beta cells. Thus, according to our data, MICA-5/5 and -5.1/5.1 is associated with early autoimmunity in T1DM patients. Our study suggests that MICA gene polymorphism is associated with autoantibody formation and that the polymorphism especially MICA5/5 and -5.1/5.1 are important in early events of autoimmune reaction.

Glutathione-s-transferase M1 and T1 polymorphisms and associations with type 1 diabetes age-at-onset

Type 1 diabetes (T1D) is an autoimmune disease characterized by pancreatic beta cell destruction involving auto-reactive T-cells, pro-inflammatory cytokines, reactive oxygen species (ROS) and loss of insulin. Monozygotic twin studies show a 20-60% concordance with T1D indicating there may be an environmental component to the disease. Glutathione (GSH) is the major endogenous antioxidant produced by the cell. GSH participates directly in the neutralization of free radicals and plays a role in the immune response. Glutathione-s-transferases (GSTs) conjugate GSH to free-radicals or xenobiotics. GST activity depletes GSH levels and may either detoxify or enhance the toxicity of a compound. Glutathione-s-transferase mu 1 (GSTM1) and glutathione-s-transferase theta 1 (GSTT1) have polymorphic homozygous deletion (null) genotypes resulting in complete absence of enzyme activity. GSTM1 and GSTT1 null genotypes in Caucasian populations have frequencies of approximately 40-60% and 15-20%, respectively. GST null genotypes have been associated with susceptibility to cancer and protection against chronic pancreatitis. The aim of this study was to investigate associations with GSTM1 and GSTT1 polymorphisms in a group T1D patients and control subjects 0-35 years old who participated in the Combined Swedish Childhood Diabetes Registry and Diabetes Incidence Study (1986-1988). Results show that the presence of the GSTM1 and not the null genotype (OR, 2.13 95% CI, 1.23-3.70, p-value, 0.007, Bonferroni corrected p-value, 0.035) may be a susceptibility factor in T1D 14-20 years old. These results suggest that the GSTM1 null genotype is associated with T1D protection and T1D age-at-onset and that susceptibility to T1D may involve GST conjugation.

Subtle hyperproinsulinaemia characterises the defective insulin secretory capacity in offspring of glutamic acid decarboxylase antibody-positive patients with latent autoimmune diabetes mellitus in adults

OBJECTIVE

We set out to assess whether hyperproinsulinaemia is an early finding in latent autoimmune diabetes in adults (LADA).

RESEARCH DESIGN AND METHODS

We measured plasma proinsulin and C-peptide responses during a 2-h oral glucose tolerance test (OGTT) and in the hyperglycaemic clamp in 21 normoglycaemic offspring of LADA patients testing positive for glutamic acid decarboxylase antibodies (GADA) or islet cell antibodies (ICA), and in 17 healthy control subjects without a family history of diabetes.

RESULTS

The study groups had comparable areas under the curves of blood glucose, plasma proinsulin, C-peptide and proinsulin/C-peptide in the OGTT. However, the offspring of LADA patients had higher proinsulin/C-peptide in the hyperglycaemic clamp (P < 0.01 versus the control group). The offspring of GADA-positive LADA patients (n = 9) had higher proinsulin and proinsulin/C-peptide than did the control group in the OGTT (P < 0.05 for both comparisons) and in the hyperglycaemic clamp (P < 0.001 and P < 0.05 respectively). They also had higher proinsulin than the offspring of ICA-positive LADA patients (n = 12) (P < 0.001) in the hyperglycaemic clamp. The offspring of ICA-positive LADA patients did not clearly show hyperproinsulinaemia during the tests, but they had lower maximal glucose-stimulated insulin secretory capacity than the control group (P < 0.05) and the offspring of GADA-positive LADA patients (P < 0.05) in the hyperglycaemic clamp.

CONCLUSIONS

These results suggested that insulin secretion in the offspring of GADA-positive LADA patients is characterised by subtle defects in the processing of insulin precursors. Furthermore, various proinsulin responses among the offspring of LADA patients with different autoimmune markers provided further evidence that LADA is a heterogeneous disorder.

Comparison of nucleotide sequence of p2C region in diabetogenic and non-diabetogenic Coxsacie virus B5 isolates

Enteroviruses are environmental triggers in the pathogenesis of type 1 diabetes mellitus (DM). A sequence of six identical amino acids (PEVKEK) is shared by the 2C protein of Coxsackie virus B and the glutamic acid decarboxylase (GAD) molecules. Between 1995 and 2002, we investigated 22 Coxsackie virus B5 (CVB5) isolates from southern Taiwan. Four of these isolates were obtained from four new-onset type 1 DM patients with diabetic ketoacidosis. We compared a 300 nucleotide sequence in the 2C protein gene (p2C) in 24 CVB5 isolates (4 diabetogenic, 18 non-diabetogenic and 2 prototype). We found 0.3-10% nucleotide differences. In the four isolates from type 1 DM patients, there was only 2.4-3.4% nucleotide difference, and there was only 1.7-7.1% nucleotide difference between type 1 DM isolates and non-diabetogenic isolates. Comparison of the nucleotide sequence between prototype virus and 22 CVB5 isolates revealed 18.4-24.1% difference. Twenty-one CVB5 isolates from type 1 DM and non-type 1 DM patients contained the PEVKEK sequence, as shown by the p2C nucleotide sequence. Our data showed that the viral p2C sequence with homology with GAD is highly conserved in CVB5 isolates. There was no difference between diabetogenic and non-diabetogenic CVB5 isolates. All four type 1 DM patients had at least one of the genetic susceptibility alleles HLA-DR, DQA1, DQB1. Other genetic and autoimmune factors such as HLA genetic susceptibility and GAD may also play important roles in the pathogenesis in type 1 DM.

HLA-DRB1, -DQA1, and -DQB1 subtypes or ACE gene polymorphisms do not seem to be risk markers for severe retinopathy in younger Type 1 diabetic patients

The aim of this study was to test the hypothesis that HLA-DRB1, -DQA1, and -DQB1 subgroups or angiotensin-converting enzyme (ACE) gene polymorphisms are associated with severe retinopathy in younger Type 1 diabetic patients. Twenty-four Type 1 diabetic patients who had received panretinal photocoagulation for severe nonproliferative or proliferative diabetic retinopathy were compared with 24 Type 1 diabetic patients (participating in a photographic screening program with regular fundus examinations) with no or minimal retinopathy, matched for age at onset and duration of diabetes. The HLA-DRB1-DQA1-B1 haplotype 04-03-0302 represented 22/48 (46%) in the severe and 21/48 (44%) in the no/minimal retinopathy group, respectively (n.s.). The most common genotype, 03-0501-0201/04-03-0302, occurred in 8/24 (33%) with severe and 10/24 (42%) with no/minimal retinopathy, respectively (n.s.). There were no statistical differences between patients with severe and no/minimal retinopathy whether DRB1, DQA1, or DQB1 alleles, haplotypes, or genotypes were analysed. The ACE gene polymorphism was almost identical between patients with severe and no/minimal retinopathy, and serum ACE levels did not differ. Thus, in the present study on a small group with carefully characterised diabetic retinopathy phenotypes, there was no indication that HLA-DRB1, -DQA1, and -DQB1 subtypes or ACE gene polymorphisms were associated with severe retinopathy in younger Type 1 diabetic patients.

Expression of endocrine autoantibodies in chronic hepatitis C, before and after interferon-alpha therapy

Interferon-alpha (IFN-alpha) treatment for chronic hepatitis C (CHC) has been associated with thyroid autoimmunity and/or dysfunction. Only a few data concerning the prevalence of islet-cell or adrenal cortex autoantibodies in IFN-alpha-treated subjects are currently available. The aims of our study were to evaluate in CHC, 1) the prevalence and association of thyroid, islet-cell and adrenal autoantibodies, and 2) the appearance of endocrine dysfunction, before and after a 6 month IFN-alpha treatment. We analyzed serum samples from 203 adult patients at the time of clinical diagnosis of CHC and showed that the prevalence of thyroperoxidase (TPOAb), thyroglobulin (TGAb), TSH-receptor (TRAb), glutamic acid decarboxylase (GAD65Ab), IA-2/ICA512 (IA-2/ICA512Ab) and 21-hydroxylase (21OHAb) autoantibodies was similar to that observed among healthy control subjects of similar age and sex distribution. Among 99 patients with follow-up serum samples, 83 accepted and 16 refused IFN-alpha treatment. The IFN-alpha treatment was associated with increase of TPOAb levels in 3 subjects already positive at baseline, with progression to overt hypothyroidism in 2 of them. The de novo appearance of autoantibodies was observed in 5/80 (6%) cases for TPOAb, 1/81 (1.2%) for GAD65Ab and 2/81 (2.5%) for IA-2/ICA512Ab. Clinical or subclinical signs of either hyperthyroidism or hypothyroidism were demonstrated in 3/5 cases with de novo appearance of TPOAb. Four subjects, initially positive for either GAD65Ab or IA2/ICA512Ab, were all found negative after IFN-alpha-treatment. No subjects showed positivity for 21OHAb either at baseline or after the follow-up period. Our study suggests that, in CHC untreated patients, the prevalence of endocrine autoantibodies is similar to that observed in the general population. Furthermore, we demonstrate that IFN-alpha treatment is associated with the induction or enhancement of thyroid, but not of islet-cell or adrenal cortex autoimmunity.

Genetic effects on age-dependent onset and islet cell autoantibody markers in type 1 diabetes

Age-dependent associations between type 1 diabetes risk genes HLA, INS VNTR, and CTLA-4 and autoantibodies to GAD65 (GADAs), ICA512/IA-2, insulin, and islet cells were determined by logistic regression analysis in 971 incident patients with type 1 diabetes and 702 control subjects aged 0-34 years. GADAs were associated with HLA-DQ2 in young but not in older patients (P = 0.009). Autoantibodies to insulin were negatively associated with age (P < 0.0001) but positively associated with DQ8 (P = 0.03) and with INS VNTR (P = 0.04), supporting possible immune tolerance induction. ICA512/IA-2 were negatively associated with age (P < 0.0001) and with DQ2 (P < 0.0001) but positively associated with DQ8 (P = 0.04). Males were more likely than females to be negative for GADA (P < 0.0001), autoantibodies to islet cells (P = 0.04), and all four autoantibody markers (P = 0.004). The CTLA-4 3' end microsatellite marker was not associated with any of the autoantibodies. We conclude that age and genetic factors such as HLA-DQ and INS VNTR need to be combined with islet autoantibody markers when evaluating the risk for type 1 diabetes development.

Insulin intervention to preserve beta cells in slowly progressive insulin-dependent (type 1) diabetes mellitus

Slowly progressive insulin-dependent (type 1) diabetes mellitus (SPIDDM) is characterized by (1) late age of onset, with initial features of NIDDM and subsequent progression to insulin-dependent stage; (2) high predictive value of autoantibodies against glutamic acid decarboxylase (GADAb) and islet cell antibodies (ICA) for progression of beta cell failure; (3) less predominant T cell response, which may attack and eventually destroy beta-cells in affected pancreas. These findings may suggest a rationale for intervention to prevent slowly progressive beta cell dysfunction in this type of diabetes. We identified three independent risk factors for progression of beta cell failure in SPIDDM: (1) sulfonylurea treatment; (2) ICA-positive periods; and (3) initial body weight. We hypothesized that removal of the risk factors for further progression of beta cell dysfunction will have beneficial effects on intervention strategy in treating SPIDDM. In our pilot study, we used a small dose of insulin instead of sulfonylurea in the early stage of treatment of patients with SPIDDM. Insulin-treated SPIDDM patients had a sustained C peptide response (CPR), while most of sulfonylurea-treated patients progressed to an insulin-dependent state. We organized a randomized multicenter clinical trial to study early treatment to prevent the progression of beta cell dysfunction in SPIDDM (the Tokyo Study). It was demonstrated that early intervention with insulin therapy is an effective treatment modality in the early stage of SPIDDM patients who had preserved beta cell function at entry (integrated value of serum C peptide values at 0, 30, 60, 90, and 120 minutes; Sigma CPR >or= 10 ng/mL) and high GADAb (>10 U/mL). Preventive insulin treatment was ineffective in the patients who had diminished insulin reserve at entry (Sigma CPR < 10 ng/mL). Insulin intervention to preserve beta cell dysfunction in SPIDDM is effective and safe in patients with preserved beta cell function and high GADAb titers at the initiation of insulin.

Molecular mechanisms involved in the etiopathogenesis of malnutrition-modulated diabetes mellitus

MMDM patients are typically young at onset with low body mass index, require insulin treatment for glycemic control, have insulin resistance, and do not develop ketosis on withdrawal of insulin. WHO's revised classification in 1999, based on the etiopathogenesis of the disease, identifies only two categories: type 1 diabetes and type 2 diabetes. MMDM could be considered as type 1b diabetes. Genetic and immunological studies were done on MDDM patients (n = 72) from Cuttack and healthy controls to understand and to justify its inclusion in the category of type 1b diabetes. Antibodies (Abs) to tyrosine pyrophosphatase (IA2-Abs), glutamate decarboxylase 65 (GAD65-Abs), and other minor markers like ICA12 Abs and tissue transglutaminase Abs (TTG-Abs) were studied. HLA-DR and DQ were studied for the genetic markers. Of the MMDM patients 30% were positive for either GAD65 or IA-2 antibodies, and 14% were positive for ICA12 antibodies. All three antibody markers together accounted for 39% of PDDM patients, as some patients were positive for more than one autoantibody. TTG antibodies (specific for Celiac disease) were present in 14/71 (20%) of MMDM patients compared to 3/122 (2%) controls. All four autoantibodies accounted for 53% of PDDM patients, leaving 47% of patients free of known autoantibodies. The autoantibody-negative PDDM patients were analyzed for HLA and MICA markers, showing that DR7-DQ9 and MICA allele 9 are increased in this group compared to healthy controls, which suggests an autoimmune response to an unknown dietary autoantigen. We conclude from our data that an autoimmune mechanism is involved in the etiology of MMDM. In addition, the presence of silent celiac disease seen with MMDM patients, which has not yet been reported, is significant. It is important to note that subclinical celiac disease exists with diabetes mellitus and must be considered in the diagnosis of MMDM.

Antibodies to new beta cell antigen ICA12 in Latvian diabetes patients

In Latvia diabetes mellitus is diagnosed using the WHO's clinical criteria, and assays for the detection of autoantibodies are not available. In consequence, slowly progressive autoimmune diabetes or LADA is likely to be missed. Antibodies to GAD65 and IA-2 are the major immunological markers in autoimmune diabetes. Recently, a new beta cell antigen, called ICA12, has been identified, which has a homology to the SOX family of transcription factors. The aim of the study was to analyze the prevalence of ICA12 antibodies in diabetes mellitus patients and controls from Latvia and to see whether this antigen is important in revealing autoimmunity when antibodies against major antigens are not present. We studied 88 IDDM patients and 100 NIDDM patients as well as controls for the prevalence of GAD65, IA-2, and ICA12 antibodies by radioligand binding assay (RIA) using (35)S-labeled islet antigens. We found ICA12Abs in 26 of 88 IDDM patients (30%) vs. 4% in healthy controls (4/100) and in 9 of 100 NIDDM patients (9%) vs. 2% controls (2/100). ICA12Abs alone are present in only 3% (3/88) of the patients with IDDM and 1% (1/100) of the NIDDM patients. We conclude that ICA12 represents the minor antigens in autoimmune diabetes and that, as a minor antigen, ICA12 alone does not contribute significantly in revealing new cases of autoimmunity.

GAD65 antibody prevalence and association with thyroid antibodies, HLA-DR in Chinese children with type 1 diabetes mellitus

Persistent humoral autoimmunity to the enzyme glutamic acid decarboxylase (GAD) has been described in a substantial proportion of patients with type 1 diabetes mellitus. Higher prevalence of GAD antibody in diabetes patients using a new radioligand-binding assay with recombinant human GAD65 antibodies (GAD65Ab) has been seen in several studies. Using this method, we have reassessed the prevalence of GAD65Ab and investigated the association of GAD65Ab with HbA1C values, C-peptide values, HLA-DR typing and thyroid autoimmune antibody in 70 Chinese children with type 1 diabetes mellitus (mean age of onset 8.21+/-3.84 years, mean duration 3.39+/-2.54 years). Our result revealed that GAD65 antibodies were present in 54.3% (38/70) of diabetes children. There was no significant difference in gender, diabetes onset and duration, HbA1c, C-peptide concentration and frequencies of HLA DR3, DR4, DR9, DR3/DR4, DR3/DR9 and DR4/DR9 genotypes between GAD65Ab+ and GAD65Ab- groups. There was no negative correlation between GAD65Ab values and duration of diabetes in those with GAD65Ab positivity (r=-0.239, P>0.05). The frequencies of antimicrosomal and anti-thyroglobulin antibodies in GAD65Ab+ (13.5,8.1%, respectively) were not different from GAD65- patients (9.4,12.5%, respectively).

Human fibroblasts ubiquitously express glutamic acid decarboxylase 65 (GAD 65): possible effects of connective tissue inflammation on GAD antibody titer

BACKGROUND

Type 1 diabetes is caused by a destruction of pancreatic beta cells due to autoimmunity. Autoantibody against glutamic acid decarboxylase (GAD) 65 expressed in pancreatic beta cells is widely used as a predictive marker for pancreatic destruction. In this study, we hypothesized that if certain cells in periodontal tissues could express GAD, then it may influence GAD antibody titer.

METHODS

We used: 1) reverse transcription-polymerase chain reaction (PCR) analysis to detect GAD 65 mRNA in various cells; 2) nucleotide sequencing analysis to confirm that amplified PCR product is the gene encoding GAD; and 3) Western blotting to determine the expression of GAD 65 protein in human gingival fibroblasts. Immunohistochemical staining of GAD 65 protein in normal and inflamed gingiva was performed to examine the potential influence of periodontal inflammation on GAD 65 expression. GAD antibody titer in sera of periodontal patients as well as healthy subjects was measured to determine if periodontal patients could develop autoantibody against GAD 65.

RESULTS

Cultured human gingival, periodontal, and dermal fibroblasts and mesangial cells expressed GAD mRNA. Nucleotide sequencing analyses confirmed the amplified PCR product as GAD 65. Western immunoblotting analyses and immunohistochemical staining revealed that the GAD 65 protein was expressed in vitro and in vivo. The expression of GAD 65 in inflamed tissue was higher than that in normal tissues. Two of 62 periodontal patients without diabetes showed an increased antibody titer against GAD 65, while none of the systemically healthy subjects showed an increased antibody titer against this antigen.

CONCLUSIONS

We concluded that periodontal inflammation may result in higher levels of GAD and influence GAD antibody titer, and, hence, affect diabetic diagnosis based upon GAD antibody production.

Site-directed mutagenesis of K396R of the 65 kDa glutamic acid decarboxylase active site obliterates enzyme activity but not antibody binding

The role of K396 in the enzymatic catalysis and the antigenicity of the 65 kDa isoform of glutamate decarboxylase (GAD65) was analyzed using the K396R GAD65 mutant. GAD65 is a major autoantigen in Type 1 diabetes and autoantibodies directed to GAD65 are widely used markers for this disease. We found that (1) recombinant human GAD65 is fully enzymatically active; (2) the K396R mutation abolished GAD65 activity; and (3) the K396R mutant retained full antigenicity to GAD65 autoantibodies in serum from Type 1 diabetes patients, but not to polyclonal antibodies raised to the catalytic domain.

Recognition of glutamic acid decarboxylase (GAD) by autoantibodies from different GAD antibody-positive phenotypes

Autoantibodies against the smaller isoform of glutamic acid decarboxylase (GAD) are markers for Type 1 diabetes. GAD65 autoantibody (GAD65Ab)-positive individuals in the general population are, however, mostly at low risk of developing Type 1 diabetes, suggesting that GAD65Ab phenotypes may be associated with different underlying pathogenic processes. The aim of this study was to test the hypothesis that Type 1 diabetes patients (n = 243; group I), GAD65Ab-positive healthy individuals (n = 28; group II), and healthy first-degree relatives of Type 1 diabetes patients (n = 41; group III) have antibody phenotypes that recognize different GAD65 epitopes. Sera from groups I-III were tested for their binding to GAD65 and GAD67, as well as six different GAD65/67 fusion proteins. Regardless of group, sera reactive to both GAD65 and GAD67 showed broader epitope reactivity than GAD65-specific sera. Furthermore, Type 1 diabetes patients showed a more restricted epitope binding than healthy individuals and first-degree relatives, demonstrating significantly less binding to the N-terminal part of GAD65 and to GAD67. Our analysis demonstrates that the N-terminal part is essential for full antibody binding to GAD65, in particular, to the middle epitope. It is suggested that Type 1 diabetes is associated with restricted GAD65Ab epitope specificity.

Autoantibodies to the flavoprotein subunit of succinate dehydrogenase: analysis of specificity in autoimmune thyroid disease

OBJECTIVE

Thyroid-associated ophthalmopathy is a progressive eye disorder affecting the extraocular muscle and orbital connective tissue and is considered to have an autoimmune aetiology. A recent study reported a close relationship between serum antibodies against the flavoprotein subunit of succinate dehyhdrogenase (SDHFp) and active thyroid-associated ophthalmopathy involving eye muscle damage. The aim of the present study was to develop a sensitive and quantitative radiobinding assay for the detection of antibodies to the flavoprotein subunit of succinate dehydrogenase and to use this to determine the distribution of antibodies in different patient groups.

DESIGN AND PATIENTS

Serum samples from the following patient groups were analysed: 20 systemic lupus erythematosus; 20 Addison's disease; 26 autoimmune hypothyroidism; 28 Graves' hyperthyroidism; 12 pretibial myxoedema; 25 thyroid-associated ophthalmopathy. Sera from 20 healthy subjects were used as controls. [35S]-labelled succinate dehydrogenase flavoprotein was produced in an in vitro transcription-translation system and subsequently used in immunoprecipitation experiments with sera from patient and control groups to test for the presence of antibodies to the flavoprotein.

RESULTS

Succinate dehydrogenase flavoprotein antibodies were detected in five of the 20 (25%) patients with Addison's disease, six of the 20 (30%) with systemic lupus erythematosus, five of the 26 (19%) with autoimmune hypothyroidsm, six of the 28 (21%) with Graves' hyperthyroidism, two of the 12 (17%) with pretibial myxoedema and three of the 25 (12%) with thyroid-associated ophthalmopathy. The frequencies of flavoprotein antibodies were significantly greater than controls (P-value < 0.05) for patients with systemic lupus erythematosus (P = 0.02), but not for patients with either Addison's disease (P = 0.05), pretibial myxoedema (P = 0.13), Graves' hyperthyroidism (P = 0.07), autoimmune hypothyroidism (P = 0.06) or thyroid-associated ophthalmopathy (P = 0.24). For the patients with thyroid-associated ophthalmopathy, the frequency of SDHFp antibodies did not appear to be related to the length of time from diagnosis: the group containing samples taken less than one year from diagnosis showed no increased frequency of SDHFp antibodies when compared to controls (P = 0.10), with three of the 18 (17%) patients being positive. With respect to seven patients with thyroid-associated ophthalmopathy diagnosed for more than a year, SDHFp antibodies were not detected in any of their serum samples. In addition, the clinical severity of the disease, as recorded by the NOSPECS classification, did not correlate with the frequency of SDHFp antibodies: P = 0.13, 0.33 and 0.38, respectively, for patients with Grade II, III and IV ophthalmopathy. Similar results were also found in the case of patients with pretibial myxoedema and eye disease: P = 0.06 for patients with Grade III ophthalmopathy and, SDHFp antibodies were not detected in any of the sera taken from patients with Grade IV ophthalmopathy. In addition, no association was found between disease duration and the frequency of antibodies to the flavoprotein in this patient group.

CONCLUSIONS

Our results indicate that succinate dehydrogenase flavoprotein antibodies are not a suitable marker for thyroid-associated ophthalmopathy, at least with the assay system used, as they can be found in patients who do not have eye disease and therefore lack the disease specificity required of a diagnostic tool.

Increased risk for endocrine autoimmunity in Italian type 2 diabetic patients with GAD65 autoantibodies

OBJECTIVE

Glutamic acid decarboxylase (GAD)65 autoantibodies (GAD65Ab) in type 2 diabetic subjects with secondary failure to sulphonylurea treatment identify the so-called latent autoimmune diabetes of the adult (LADA). The aim of our study was to estimate the risk for endocrine autoimmunity in type 2 diabetic subjects with GAD65Ab.

DESIGN AND PATIENTS

We analysed serum samples from 600 adult subjects with a clinical diagnosis of type 2 diabetes mellitus for the presence and levels of GAD65Ab and antibodies directed against the islet autoantigen IA-2/ICA512 (IA-2/ICA512Ab). All the patients had been treated initially with hypoglycaemic agents and/or diet for at least 1 year. GAD65Ab+ subjects were studied for the presence of thyroid peroxidase autoantibodies (TPOAb), 21 hydroxylase autoantibodies (21OHAb) and frequency of HLA class II haplotypes.

RESULTS

GAD65Ab were found in 67/600 (11%) and IA-2/ICA512Ab in 12/600 (2%) subjects (P < 0.0001). The presence of GAD65Ab, but not that of IA-2/ICA512Ab, was significantly associated with insulin therapy, low BMI (P < 0.0001) and low basal C-peptide (P < 0.01). Islet-cell antibodies (ICA) were detected in 43/67 (64%) GAD65Ab+ and in 10/12 (83%) IA-2/ICA512Ab + subjects. TPOAb occurred more frequently in GAD65Ab+ (16/67, 24%) than in GAD65Ab-subjects (9/174, 5%) (P < 0.0001). 21OHAb were detected only in GAD65Ab+ subjects (3/67, 4.5%) (P = 0.03 vs. GAD65Ab-subjects). None of the 21OHAb+ subjects had metabolic or clinical signs of adrenal dysfunction. HLA-DRB1*03-DQA1*0501-DQB1*0201 (DR3-DQ2) was significantly more frequent in GAD65Ab+ subjects than in healthy controls (OR = 5.42, corrected P < 0.0026). The presence of TPOAb was significantly associated with DR3-DQ2 (P = 0.024).

CONCLUSIONS

Our study demonstrates that the presence of GAD65Ab identifies a subgroup of type 2 diabetic patients with high risk for thyroid and adrenal autoimmunity, and that both GAD65Ab and TPOAb are associated with the presence of HLA-DR3-DQ2, in these patients.

The role of sulphonylurea in combination therapy assessed in a trial of sulphonylurea withdrawal. Scandinavian Insulin-Sulphonylurea Study Group Research Team

AIMS

To evaluate the effect of adding insulin to sulphonylurea (SU) and the effect of SU withdrawal on glycaemic control in Type 2 diabetic patients who failed on treatment with SU alone.

METHOD

One hundred and seventy-five patients were included in a placebo-controlled multicentre study. During phase I (4 months), premixed insulin was added to glibenclamide therapy; during phase II (1-4 months, depending on response) the insulin dose was fixed, while placebo or glibenclamide replaced the open SU therapy. Insulin sensitivity (KITT), beta-cell function (C-peptide) and metabolic control (HbA1c) were monitored.

RESULTS

HbA1c improved from 9.65% to 7.23% (P < 0.0001) during phase I. A high HbA1c value (P < 0.0001) and a high KITT-value (P = 0.045) at baseline were associated with a beneficial response to combination treatment. During phase II, glycaemic control was unchanged in the control (glibenclamide) group. In the placebo group, after SU withdrawal, fasting blood glucose (FBG) increased by 10% or more within 4 weeks in 79% of the patients. Patients (67 of 112) with an FBG increase > or =40% during phase II were defined as 'SU responders' by protocol. In a multivariate analysis only a long duration of diabetes was associated with SU response. There were more GAD-antibody-positive patients among non-responders (18% vs. 4%, P = 0.0263).

CONCLUSIONS

Poor glycaemic control in combination with preserved insulin sensitivity and lack of GAD antibodies predicts a beneficial response to combination therapy, which can be achieved in 75% of patients with SU failure.

Appearance of islet cell autoantibodies after clinical diagnosis of diabetes mellitus

Islet cell antibodies (ICA) and glutamic acid decarboxylase antibodies (GAD65Ab) are often present at diagnosis of insulin dependent diabetes mellitus (type I diabetes) and are supposed to decline in level and frequency during the first years of disease. We have analysed ICA and GAD65Ab at onset and after one year in 395 population based randomly selected 15-34 year old patients newly diagnosed with diabetes mellitus, to study how these autoantibodies persist, disappear and appear and their relation to C-peptide levels. Of the 395 samples 212 (54%) were positive for ICA, 250 (63%) were positive for GAD65Ab and 170 (43%) were positive for both. At follow up after one year, 27/183 (15%) of the ICA negative patients and 25/145 (17%) of the GAD65Ab negative patients had converted to positivity. Among the 103 patients negative for both ICA and GAD65Ab, 16 turned positive for one or both antibodies after one year. Patients converting to positivity for one or the other antibody after one year, had lower C-peptide levels after one year than patients who initially were and remained negative, supporting the hypothesis that these patients have a genuine type I diabetes. In conclusion, newly diagnosed patients may be negative for autoantibodies at diagnosis but develop these antibodies later on during the disease.

Autoantibodies to human melanocyte-specific protein pmel17 in the sera of vitiligo patients: a sensitive and quantitative radioimmunoassay (RIA)

In the present study we describe the in vitro transcription-translation of human melanocyte-specific protein Pmel17 cDNA and subsequent use of the resulting 35S-labelled Pmel17 in an RIA to analyse vitiligo sera for the presence of Pmel17 antibodies. Of 53 vitiligo sera examined in the assay, three (5.9%) were found to be positive for Pmel17 antibodies. In contrast, sera from 20 healthy controls, 10 patients with Hashimoto's thyroiditis and 10 patients with Graves' disease (GD) were all negative for Pmel17 antibodies. All three patients positive for Pmel17 antibodies (aged 50-63 years) had had vitiligo of the symmetrical type for > 1 year and all of them also had an associated autoimmune disorder: GD in one and autoimmune hypothyroidism in two. In addition, all three patients had antibodies to the melanogenic enzymes tyrosinase, tyrosinase-related protein-1 (TRP-1) and tyrosinase-related protein-2 (TRP-2) in their serum. Absorption studies indicated that preincubation with COS-7 cell extract containing expressed Pmel17 absorbed out the immunoreactivity of the three sera positive in the RIA, confirming the anti-Pmel17 reactivity of the sera from these patients. In contrast, COS-7 cell extracts containing either expressed tyrosinase, TRP-1 or TRP-2 did not remove the anti-Pmel17 reactivity of the three sera in the RIA. This lack of cross-reactivity suggests that the humoral response to Pmel17 in these patients is specific and independent of the antibody reactivity to tyrosinase, TRP-1 and TRP-2.

Autoantibodies to tyrosinase-related protein-1 detected in the sera of vitiligo patients using a quantitative radiobinding assay

In the present study, we describe the in vitro transcription-translation of human tyrosinase-related protein-1 (TRP-1) cDNA and subsequent use of the resulting 35S-labelled TRP-1 in a radioimmunoassay to analyse vitiligo sera for the presence of TRP-1 antibodies. Of 53 vitiligo sera examined in the assay, three (5.7%) were found to be positive for TRP-1 antibodies. In contrast, sera from 20 controls, 10 patients with Hashimoto's thyroiditis and 10 patients with Graves' disease were all negative for TRP-1 antibodies. Although glycosylation of the labelled protein was necessary for its immunoprecipitation by TRP-1-specific monoclonal antibody TA99, this post-translational processing did not affect the binding of any of the sera tested. All three patients positive for TRP-1 antibodies (aged 50-63 years) had had vitiligo of the symmetrical type for more than 1 year, and all of them also had an associated autoimmune disorder: Graves' disease in one and autoimmune hypothyroidism in two. In addition, antibodies to the melanogenic enzymes tyrosinase and tyrosinase-related protein-2 (TRP-2) were present in their serum. Absorption studies indicated that preincubation with COS-7 cell extract containing either expressed TRP-1, tyrosinase or TRP-2 absorbed out the immunoreactivity of the three sera positive in the radioimmunoassay (RIA) with [35S]TRP-1. The results indicate that autoantibodies to TRP-1 cross-react with tyrosinase and TRP-2, suggesting one or more common epitopes between the three proteins.

A simple and rapid microSepharose assay for GAD65 and ICA512 autoantibodies in diabetes. Diabetes Incidence Study in Sweden (DISS)

GAD65Ab and ICA512Ab are strongly associated with insulin-dependent (Type 1) diabetes mellitus. A novel, simple radio-antigen binding assay with microSepharose conjugated with monoclonal antibodies specific for human immunoglobulin light chains was developed to provide diagnostic sensitivity and specificity of GAD65Ab and ICA512Ab for Type 1 diabetes. The Receiver Operating Characteristic (ROC) curve was used to determine the upper level of Normal in 583 new onset Type 1 diabetic patients and in 829 matched controls. The sensitivity of GAD65Ab and ICA512Ab was 66% (384/583) and 41% (211/520), respectively, and the diagnostic specificity was 96% for both autoantibodies. Levels, but not frequency, of GAD65Ab were higher among female Type 1 diabetes patients, whereas ICA512Ab levels did not differ between males and females. Positivity for GAD65Ab. ICA512Ab or both showed a sensitivity of 74% and a specificity of 92% for Type 1 diabetes. This simple, one-step centrifugation, high-capacity radio-antigen binding assay has a high precision and reproducibility to accurately detect both GAD65Ab and ICA512Ab. This assay should also prove useful in other autoantibody assays against conformation-sensitive autoantigens.

Inverse relationship between GAD65 antibody levels and severe retinopathy in younger type 1 diabetic patients

Several risk factors for severe non-proliferative and proliferative retinopathy in type 1 diabetes mellitus have been proposed without explaining the rapid progression of retinopathy in some patients. Since GAD65 autoantibodies (GAD65Abs) are detected against glutamic acid decarboxylase (GAD), which is mainly expressed in islets and nervous tissue in type 1 diabetic patients, the aim of the present investigation was to test the hypothesis whether GAD65Abs are associated with rapidly progressing severe retinopathy. Patients with severe non-proliferative or proliferative retinopathy (n = 27) were compared with another group, which in spite of long diabetes duration had no or only mild signs of retinopathy (n = 28). GAD65Abs were analysed in a radioimmunoassay using in vitro translated human GAD65, and the levels were expressed as an index in relation to positive and negative reference samples. Using a cut-off level representing the 99th percentile of normals, 6/27 (22%) with and 9/28 (32%) without severe retinopathy were considered GAD65Ab positive. Although there was no difference in the number of GAD65Ab positive patients, the GAD65Ab levels were lower in patients with (0.30; 0.11-0.64) than without (0.68; 0.34-1.12) severe retinopathy (P = 0.03). The patients were also subjected to HLA-DR and DQ typing by PCR and hybridization with oligospecific probes. DQ2/8 was more common in patients with (56%) than without (29%) severe retinopathy (P = 0.05), but DQ2/8 could not account for the lower GAD65Ab levels in patients with severe retinopathy. It is concluded that GAD65Ab levels are inversely correlated with severe retinopathy in young type 1 diabetic patients.

A new solid-phase radioimmunoassay to detect anti-GAD65 autoantibodies

This paper describes a simple, rapid, routine method to detect anti-GAD65 autoantibodies by a solid-phase radioimmunoassay using human recombinant GAD65 coated microwells and 125I-protein A to reveal antibody binding. Both recombinant and radiolabelled proteins are commercially available. This new method was validated by investigating the presence of GAD65 autoantibodies in two different studies (A and B); the first including subjects originating from our own case histories (group A sera), the second made up of recoded subjects and standards sent to our lab by the Second International GAD Antibody Workshop organizers (group B sera). In study A we tested sera from 52 normal subjects, 25 newly diagnosed type 1 diabetics and 3 stiff man syndrome (SMS) subjects detecting GAD65 autoantibodies in 72% of IDDM and 100% of SMS patients. In study B we tested (in blind fashion) 89 recoded sample sera or standards that were part of the larger group used in the Second International GAD Antibody Workshop, finding GAD65 autoantibodies in 3.3% of healthy control subjects (1/30), 60% of IDDM patients (18/30), 100% of ICA + nondiabetic subjects (3/3) but in none of 4 nondiabetic patients with Graves disease. Comparing our solid-phase RIA results with those published for the same sera from the Second International GAD Antibody Workshop we obtained for our method a sensitivity of 85.7%, a specificity of 93.9% and a consistency of 100%. These result indicate that our assay, which is based on commercially available reagents, should be a useful tool for the detection of GAD65 autoantibodies in large scale studies.

Detection of tyrosinase autoantibodies in patients with vitiligo using 35S-labeled recombinant human tyrosinase in a radioimmunoassay

Tyrosinase antibodies recently have been reported to occur frequently in patients with vitiligo. We describe the detection of tyrosinase antibodies in vitiligo patients using in vitro 35S-labeled human tyrosinase in a radioimmunoassay. Of 46 vitiligo sera examined in the assay, five (10.9%) were found to be positive for tyrosinase antibodies. In contrast, 20 control sera and sera from 10 patients with Hashimoto's thyroiditis were negative. Four of the sera positive in the radioimmunoassay were also positive in an ELISA using mushroom tyrosinase as antigen. Absorption studies indicated that pre-incubation with mushroom tyrosinase absorbed out the immunoreactivity of the positive sera in the radioimmunoassay, suggesting cross-reactivity, but this absorption was never complete, indicating that there are tyrosinase antibodies in human sera that do not react with the mushroom protein. There was no obvious association between the presence of tyrosinase antibodies and the age of the patients (range: 22-62 y), their duration of disease (range: 5-20 y), or the type of vitiligo (one segmental, one symmetrical/periorificial, three symmetrical), although the three patients with the highest antibody levels also had an associated autoimmune disorder (one with Graves' disease; two with autoimmune hypothyroidism). The results confirm that tyrosinase autoantibodies are present in the sera of vitiligo patients but at a low frequency. The technique described is sensitive and quantitative and allows the detection of conformational epitopes. It will be useful in longitudinal studies to determine the relation between the clinical features of vitiligo and tyrosinase antibody levels.

Association between HLA and islet cell antibodies in diabetic patients with a mitochondrial DNA mutation at base pair 3243

Islet cell antibodies (ICA), autoantibodies to glutamic acid decarboxylase (GAD) and HLA genotypes were examined in 31 patients with diabetes and a mitochondrial gene mutation located at base pair 3243 (mtDNA 3243 mutation). ICA was detected in 42% (13/31) of these patients compared to 0 of 90 among healthy control subjects. The ICA showed a "non-restricted" pattern of staining in all 13 ICA-positive patients. In a sensitive radioligand assay only 2 of 31 (6%) diabetic patients with the mutation were positive for both GAD65 autoantibodies and ICA, while the remaining 29 patients were GAD65 antibody negative. The ICA-positive patients had an increased frequency of the HLA-DQA1*0301 allele compared to control subjects (p < 0.05). Of the diabetic patients with the mutation 45% (14/31) had progressive clinical course of beta-cell failure. These results indicate that patients with an mtDNA 3243 mutation may develop islet autoimmunity associated with ICA and GAD autoantibodies. We hypothesize that the presence of HLA-DQA1*0301 in individuals with the mtDNA 3243 mutation increases the risk for diabetes and associated autoantibodies against islet cell antigens.

Diagnostic sensitivity of immunodominant epitopes of glutamic acid decarboxylase (GAD65) autoantibodies in childhood IDDM

The prevalence and titre of epitope-specific autoantibodies to glutamic acid decarboxylase (GAD65) in 155 insulin-dependent diabetic (IDDM) and 9 GAD65 antibody (Ab)-positive healthy children were determined using four GAD65/67 chimaeric molecules which discriminate among the N-terminal (N), middle (M) and C-terminal (C) epitopes of GAD65. Radioligand binding assays for IgGAb used immunoprecipitation of in vitro translated 35S-GAD. We found autoantibodies to GAD65 in 116 of 155 (75%), to GAD67 in 19 of 155 (12%) (p < 0.0001) and to the GAD65-N-67 chimaera in 25 of 155 (16%) (p < 0.0001) IDDM sera. GAD67Ab were found almost exclusively (17 of 19, 89%) in GAD65Ab-positive sera and the levels of GAD67Ab correlated with those of GAD65Ab (r2 = 0.5913; p = 0.009). GAD65Ab directed to GAD65-M were found in 104 of 155 (67%), to GAD65-C in 104 of 155 (67%) and to GAD65-M + C in 116 of 155 (75%) of IDDM sera, and indicated reactivity to at least two distinct epitopes. Among the nine GAD65Ab-positive healthy children, two (22%) were also positive with GAD67, nine (100%) with GAD65-M + C, seven (78%) with GAD65-M, eight (89%) with GAD65-C and two (22%) with GAD65-N-67. Titres of GAD65Ab (p = 0.007), GAD65-C-Ab (p = 0.002) and GAD65-C + M-Ab (p = 0.003), but not of GAD65-M-Ab (p = 0.101) were significantly higher in IDDM than in healthy children. We conclude that GAD65Ab in IDDM and healthy children are directed to middle and C-terminal epitopes, and propose that levels of antibodies specifically directed to the carboxy-terminal end of GAD65 may distinguish IDDM from healthy children.

HLA class II is associated with the frequency of glutamic acid decarboxylase M(r) 65,000 autoantibodies in Japanese patients with insulin-dependent diabetes mellitus

Autoantibodies to glutamic acid decarboxylase (GAD65Ab) are common in both caucasian and Japanese patients with insulin-dependent diabetes mellitus (type 1), while the type 1-associated HLA haplotypes differ. In the present study, we analyzed GAD65Ab in relation to HLA-DQ and -DR alleles in Japanese type 1 patients. GAD65Ab were found in 58% short-duration (less than 5 years) type 1, 23% long-duration type 1, 56% slowly progressive type 1, 3% type 2 patients, and 1.7% healthy individuals. In 75 HLA-typed type 1 patients, the GAD65Ab frequency was higher in short-duration patients with DRB1*08 allele (100%, Pc < 0.05). GAD65Ab frequencies in DQB1*0302, DQB1*0303, and DRB1*09-positive, long-duration type 1 patients were lower than those in short-duration type 1 patients (14%, 19%, and 20%, Pc < 0.02 compared with short-duration type 1, 90%, 75%, and 71%, respectively), while the frequency varied less in DQB1*04 individuals (44% and 30% in short- and long-duration type 1 patients, respectively). These findings were also observed among patients with DRB1*04, i.e., the haplotype DRB1*0405-DQB1*0401 showed less variation in frequency of GAD65Ab (44% and 35% in short- and long-duration type 1 patients, respectively), while DRB1*04xx-DQB1*0302 showed lower frequency in long-duration type 1 than short-duration (13% and 100%, respectively). Thus, HLA class II is associated with frequency GAD65Ab, and this association might be affected by disease duration in Japanese type 1 patients.

Sexual dimorphism in transmission of expression of islet autoantibodies to offspring

To help elucidate the mode of inheritance of insulin-dependent diabetes mellitus (IDDM), we measured GAD (glutamic acid decarboxylase) autoantibodies (GAD65Ab), insulin autoantibodies (IAA), and cytoplasmic islet cell autoantibodies (ICA) in 292 sequentially screened non-diabetic offspring of patients with IDDM. The prevalence of these islet autoantibodies was higher in offspring of diabetic fathers than in offspring of diabetic mothers. The prevalences of GAD65Ab, IAA, and ICA in the offspring of diabetic fathers were 11.5%, 10.8%, and 8.1% vs 2.1%, 1.4%, and 2.8%, respectively in the offspring of diabetic mothers (p < 0.002, p < 0.001, and p = 0.06 NS). Amongst autoantibody-positive relatives the IAA and ICA levels were significantly higher in offspring of diabetic fathers than of diabetic mothers (p < 0.002 and p < 0.01, respectively). The frequencies of these autoantibodies were equal in male and female offspring. We conclude that IDDM mothers transmitted islet autoimmunity less frequently to their offspring than IDDM fathers. Given the markedly lower frequency of autoantibodies in offspring of mothers, larger sample sizes will be required to determine whether islet autoantibodies are influenced by age of IDDM onset of mothers, maternal age of pregnancy, and presence of diabetes in these mothers prior to conception.

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.