The BB (BioBreeding) rat is one of the best models of spontaneous autoimmune diabetes and is used to study non-MHC loci contributing to Type 1 diabetes. Type 1 diabetes in the diabetes-prone BB (BBDP) rat is polygenic, dependent upon mutations at several loci.Iddm1, on chromosome 4, is responsible for a lymphopenia (lyp) phenotype and is essential to diabetes. In this study, we report the positional cloning of theIddm1/lyp locus. We show that lymphopenia is due to a frameshift deletion in a novel member (Ian5) of the Immune-Associated Nucleotide (IAN)-related gene family, resulting in truncation of a significant portion of the protein. This mutation was absent in 37 other inbred rat strains that are nonlymphopenic and nondiabetic. The IAN gene family, lying within a tight cluster on rat chromosome 4, mouse chromosome 6, and human chromosome 7, is poorly characterized. Some members of the family have been shown to be expressed in mature T cells and switched on during thymic T-cell development, suggesting thatIan5 may be a key factor in T-cell development. The lymphopenia mutation may thus be useful not only to elucidate Type 1 diabetes, but also in the function of the Ian gene family as a whole.[Sequence data reported in this paper has been deposited in GenBank and assigned the following accession nos:AF517674, AF517675, AF517676, and AF517677. Supplemental material is available online at http://depts.washington.edu/rhwlab/ and http:www.genome.org. ] The following individuals and institutions kindly provided reagents, samples, or unpublished information as indicated in the paper: K. Matsumoto and the Sir Frederick Banting Research Centre.

SummaryInsulin-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, 0-14year-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-methioninelabelled recombinant GAD. [Diabetologia (1994) Abbreviations: IDDM, insulin-dependent diabetes mellitus; GAD, glutamic acid decarboxylase; ROC, receiver-operating characteristic; ICA, islet cell antibodies; JDF, Juvenile Diabetes Foundation 10p11.3-p12 [7]. GAD65 shows 65 % amino acid identity with GAD67, the isoform coded for by the GAD1 gene on chromosome 2q31 [7][8][9]. The molecular cloning of full-length human islet GAD65 [7] and rat islet GAD67 [10] cDNA has made it possible to demonstrate autoreactivity in diabetes to the recombinant proteins in both eukaryotic [11,12] and bacterial [13] expression systems. GAD65 (but not GAD67) is expressed in human islets [11,14], however, variable reactivity of patient sera has been reported [12,13,[15][16][17][18][19]. GAD65 specificity of IDDM sera was first demonstrated in our immunoprecipitation assay with recombinant GAD expressed in transfected cells [12] and recently confirmed in other assays with recombinant antigens [18,20]. The use of different assay systems and species-specific GAD65 and GAD67 may explain the lower frequency of GAD67 antibodies in these compared to previous reports [13,16]. We now report the

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.

Wild bank voles (Clethrionomys glareolus) may develop diabetes in laboratory captivity. The aim of this study was to test whether bank voles develop type 1 diabetes in association with Ljungan virus. Two groups of bank voles were analyzed for diabetes, pancreas histology, autoantibodies to glutamic acid decarboxylase (GAD65), IA-2, and insulin by standardized radioligand-binding assays as well as antibodies to in vitro transcribed and translated Ljungan virus antigens. Group A represented 101 trapped bank voles, which were screened for diabetes when euthanized within 24 hours of capture. Group B represented 67 bank voles, which were trapped and kept in the laboratory for 1 month before being euthanized. Group A bank voles did not have diabetes. Bank voles in group B (22/67; 33%) developed diabetes due to specific lysis of pancreatic islet beta cells. Compared to nondiabetic group B bank voles, diabetic animals had increased levels of GAD65 (P < .0001), IA-2 (P < .0001), and insulin (P = .03) autoantibodies. Affected islets stained positive for Ljungan virus, a novel picorna virus isolated from bank voles. Ljungan virus inoculation of nondiabetic wild bank voles induced beta-cell lysis. Compared to group A bank voles, Ljungan virus antibodies were increased in both nondiabetic (P < .0001) and diabetic (P = .0015) group B bank voles. Levels of Ljungan virus antibodies were also increased in young age at onset of newly diagnosed type 1 diabetes in children (P < .01). These findings support the hypothesis that the development of type 1 diabetes in captured wild bank voles is associated with Ljungan virus. It is speculated that bank voles may have a possible zoonotic role as a reservoir and vector for virus that may contribute to the incidence of type 1 diabetes in humans.

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

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.

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