Mapping non-class II H2-linked loci for type 1 diabetes in nonobese diabetic mice

Differentiation of human induced pluripotent stem cells into insulin-like cell clusters with miR-186 and miR-375 by using chemical transfection

Diabetes mellitus is characterized by either the inability to produce insulin or insensitivity to insulin secreted by the body. Islet cell replacement is an effective approach for diabetes treatment; however, it is not sufficient for all the diabetic patients. MicroRNAs (miRNAs) are a class of small noncoding RNAs that play an important role in mediating a broad and expanding range of biological activities, such as pancreas development. The present study aimed to develop a protocol to efficiently differentiate human induced pluripotent stem (iPS) cells into islet-like cell clusters (ILCs) in vitro by using miR-186 and miR-375. The human iPS colonies were transfected with hsa-miR-186 and hsa-miR-375 by using siPORT™ NeoFX™ Transfection Agent, and the differentiation was compared to controls. Total RNA was extracted 24 and 48 h after transfection. The gene expressions of insulin, NGN3, GLUT2, PAX4, PAX6, KIR6.2, NKX6.1, PDX1, Glucagon, and OCT4 were then evaluated through real-time qPCR. On the third day, the potency of the clusters was assessed in response to high glucose levels. Dithizone (DTZ) was used to identify the existence of the β-cells. Besides, the presence of insulin and NGN3 proteins was investigated by immunocytochemistry. Morphological changes were observed on the first day after the chemical transfection, and cell clusters were formed on the third day. The expression of pancreatic specific transcription factors was increased on the first day and significantly increased on the second day. The ILCs were positive for insulin and NGN3 proteins in the immunocytochemistry. Besides, the clusters were stained with DTZ and secreted insulin in glucose challenge test. Overexpression of miR-186 and miR-375 can be an alternative strategy for producing ILCs from the iPS cells in a short time. This work provides a new approach by using patient-specific iPSCs for β-cell replacement therapy in diabetic patients.

Diubiquitin (Ubd) is a susceptibility gene for virus-triggered autoimmune diabetes in rats

Genetic studies of type 1 diabetes (T1D) have been advanced by comparative analysis of multiple susceptible and resistant rat strains with a permissive class II MHC haplotype, RT1(u). LEW.1WR1 (but not resistant LEW.1W or WF) rats are susceptible to T1D induced by a TLR3 agonist polyinosinic:polycytidylic acid followed by infection with parvovirus. We have mapped genetic loci for virus-induced T1D susceptibility, identifying a major susceptibility locus (Iddm37) near the MHC. The Iddm37 homologs on mouse and human chromosomes are also diabetes linked. We report that a major effect gene within Iddm37 is diubiquitin (Ubd). Gene expression profiling of pancreatic lymph nodes in susceptible and resistant rats during disease induction showed differences in Ubd transcript abundance. The LEW.1WR1 Ubd promoter allele leads to higher inducible levels of UBD than that of LEW.1W or WF. Using zinc-finger nucleases , we deleted a segment of the LEW.1WR1 Ubd gene and eliminated its expression. UBD-deficient rats show substantially reduced diabetes after viral infection. Complementary studies show that there may be another diabetes gene in addition to Ubd in the Iddm37 interval. These data prove that Ubd is a diabetes susceptibility gene, providing insight into the interplay of multiple genes and environmental factors in T1D susceptibility.

Comparative genetics: synergizing human and NOD mouse studies for identifying genetic causation of type 1 diabetes

Although once widely anticipated to unlock how human type 1 diabetes (T1D) develops, extensive study of the nonobese diabetic (NOD) mouse has failed to yield effective treatments for patients with the disease. This has led many to question the usefulness of this animal model. While criticism about the differences between NOD and human T1D is legitimate, in many cases disease in both species results from perturbations modulated by the same genes or different genes that function within the same biological pathways. Like in humans, unusual polymorphisms within an MHC class II molecule contributes the most T1D risk in NOD mice. This insight supports the validity of this model and suggests the NOD has been improperly utilized to study how to cure or prevent disease in patients. Indeed, clinical trials are far from administering T1D therapeutics to humans at the same concentration ranges and pathological states that inhibit disease in NOD mice. Until these obstacles are overcome it is premature to label the NOD mouse a poor surrogate to test agents that cure or prevent T1D. An additional criticism of the NOD mouse is the past difficulty in identifying genes underlying T1D using conventional mapping studies. However, most of the few diabetogenic alleles identified to date appear relevant to the human disorder. This suggests that rather than abandoning genetic studies in NOD mice, future efforts should focus on improving the efficiency with which diabetes susceptibility genes are detected. The current review highlights why the NOD mouse remains a relevant and valuable tool to understand the genes and their interactions that promote autoimmune diabetes and therapeutics that inhibit this disease. It also describes a new range of technologies that will likely transform how the NOD mouse is used to uncover the genetic causes of T1D for years to come.

Differentiation and transplantation of functional pancreatic beta cells generated from induced pluripotent stem cells derived from a type 1 diabetes mouse model

The nonobese diabetic (NOD) mouse is a classical animal model for autoimmune type 1 diabetes (T1D), closely mimicking features of human T1D. Thus, the NOD mouse presents an opportunity to test the effectiveness of induced pluripotent stem cells (iPSCs) as a therapeutic modality for T1D. Here, we demonstrate a proof of concept for cellular therapy using NOD mouse-derived iPSCs (NOD-iPSCs). We generated iPSCs from NOD mouse embryonic fibroblasts or NOD mouse pancreas-derived epithelial cells (NPEs), and applied directed differentiation protocols to differentiate the NOD-iPSCs toward functional pancreatic beta cells. Finally, we investigated whether the NPE-iPSC-derived insulin-producing cells could normalize hyperglycemia in transplanted diabetic mice. The NOD-iPSCs showed typical embryonic stem cell-like characteristics such as expression of markers for pluripotency, in vitro differentiation, teratoma formation, and generation of chimeric mice. We developed a method for stepwise differentiation of NOD-iPSCs into insulin-producing cells, and found that NPE-iPSCs differentiate more readily into insulin-producing cells. The differentiated NPE-iPSCs expressed diverse pancreatic beta cell markers and released insulin in response to glucose and KCl stimulation. Transplantation of the differentiated NPE-iPSCs into diabetic mice resulted in kidney engraftment. The engrafted cells responded to glucose by secreting insulin, thereby normalizing blood glucose levels. We propose that NOD-iPSCs will provide a useful tool for investigating genetic susceptibility to autoimmune diseases and generating a cellular interaction model of T1D, paving the way for the potential application of patient-derived iPSCs in autologous beta cell transplantation for treating diabetes.

Downregulation of the circadian rhythm related gene Arntl2 suppresses diabetes protection in Idd6 NOD.C3H congenic mice

1. Our previous studies of the murine genetic locus Idd6 revealed the aryl hydrocarbon receptor nuclear translocator-like protein 2 (Arntl2) as a candidate gene for type 1 diabetes; and in Idd6 NOD.C3H congenic mice, Arntl2 upregulation is linked to decreased diabetes development. 2. In the present study, shRNA plasmids capable of suppressing Arntl2 expression were developed and given to diabetes resistant NOD.C3H congenic mice by hydrodynamic tail vein injection. The effects of Arntl2 suppression on diabetes incidence and immune cell numbers were investigated. 3. Diabetes incidence was increased by Arntl2 mRNA interference in the congenic strain and this was associated with an increase in CD4(+) T cells and a decrease in regulatory T cells in the peripheral immune system. 4. These results provide additional support for the protective role of the Arntl2 gene located in locus Idd6 in diabetes progression in NOD.C3H congenic mice.

Novel Nonmajor Histocompatibility Complex–Linked Loci From Mouse Chromosome 17 Confer Susceptibility to Viral-Mediated Chronic Autoimmune Myocarditis

Background—

Development of viral-induced chronic myocarditis is thought to involve both environmental and genetic factors. However, to date, no susceptibility genes have been identified.

Methods and Results—

We sought to identify loci that confer susceptibility to viral-induced chronic myocarditis with the use of chromosome substitution strain mice that are composed of 1 chromosome from the disease susceptible A/J strain on an otherwise resistant C57BL/6 background. By this method, we identified chromosome 17 to confer susceptibility. To further isolate the region of susceptibility, 8 strains of mice congenic for different portions of chromosome 17 were generated. Characterization of these strains identified at least 4 susceptibility loci on the chromosome. Three of these loci are located in the proximal 22.8 cM, whereas the fourth locus is located in the portion of the chromosome distal to 34.3 cM.

Conclusions—

We have identified 4 loci that confer susceptibility of viral-induced chronic myocarditis. Of these loci, 3 were distinct from the major histocompatibility complex locus and thus represent novel susceptibility loci. The close proximately of the 2 novel loci with susceptibility loci for other autoimmune diseases such as type 1 diabetes and chronic experimental autoimmune thyroiditis suggests the presence of global autoimmune susceptibility genes.

Use of nonobese diabetic mice to understand human type 1 diabetes

In 1922, Leonard Thompson received the first injections of insulin prepared from the pancreas of canine test subjects. From pancreatectomized dogs to the more recent development of animal models that spontaneously develop autoimmune syndromes, animal models have played a meaningful role in furthering diabetes research. Of these animals, the nonobese diabetic (NOD) mouse is the most widely used for research in type 1 diabetes (T1D) because the NOD shares several genetic and immunologic traits with the human form of the disease. In this article, the authors discuss the similarities and differences in NOD and human T1D and the potential role of NOD mice in future preclinical studies, aiming to provide a better understanding of the genetic and immune defects that lead to T1D.

Virus-induced autoimmune diabetes in the LEW.1WR1 rat requires Iddm14 and a genetic locus proximal to the major histocompatibility complex

OBJECTIVE

To identify genes that confer susceptibility to autoimmune diabetes following viral infection in the LEW.1WR1 rat.

RESEARCH DESIGN AND METHODS

About 2% of LEW.1WR1 rats develop spontaneous autoimmune diabetes. Immunological perturbants including viral infection increase both the frequency and tempo of diabetes onset. To identify diabetes susceptibility genes (LEW.1WR1 x WF), F2 rats were infected with Kilham rat virus following brief pretreatment with polyinosinic:polycytidylic acid. This treatment induces diabetes in 100% of parental LEW.1WR1 rats and 0% of parental WF rats. Linkage to diabetes was analyzed by genome-wide scanning.

RESULTS

Among 182 F2 rats, 57 (31%) developed autoimmune diabetes after a mean latency of 16 days. All diabetic animals and approximately 20% of nondiabetic animals exhibited pancreatic insulitis. Genome-wide scanning revealed a requirement for the Iddm14 locus, long known to be required for diabetes in the BB rat. In addition, a new locus near the RT1 major histocompatibility complex (MHC) was found to be a major determinant of disease susceptibility. Interestingly, one gene linked to autoimmune diabetes in mouse and human, UBD, lies within this region.

CONCLUSIONS

The Iddm14 diabetes locus in the rat is a powerful determinant of disease penetrance in the LEW.1WR1 rat following viral infection. In addition, a locus near the MHC (Iddm37) conditions diabetes susceptibility in these animals. Other, as-yet-unidentified genes are required to convert latent susceptibility to overt diabetes. These data provide insight into the polygenic nature of autoimmune diabetes in the rat and the interplay of genetic and environmental factors underlying disease expression.

Gene-gene interactions in the NOD mouse model of type 1 diabetes

Human genome wide association studies (GWAS) have recently identified at least four new, non-MHC-linked candidate genes or gene regions causing type one diabetes (T1D), highlighting the need for functional models to investigate how susceptibility alleles at multiple common genes interact to mediate disease. Progress in localizing genes in congenic strains of the nonobese diabetic (NOD) mouse has allowed the reproducible testing of gene functions and gene-gene interactions that can be reflected biologically as intrapathway interactions, for example, IL-2 and its receptor CD25, pathway-pathway interactions such as two signaling pathways within a cell, or cell-cell interactions. Recent studies have identified likely causal genes in two congenic intervals associated with T1D, Idd3, and Idd5, and have documented the occurrence of gene-gene interactions, including "genetic masking", involving the genes encoding the critical immune molecules IL-2 and CTLA-4. The demonstration of gene-gene interactions in congenic mouse models of T1D has major implications for the understanding of human T1D since such biological interactions are highly likely to exist for human T1D genes. Although it is difficult to detect most gene-gene interactions in a population in which susceptibility and protective alleles at many loci are randomly segregating, their existence as revealed in congenic mice reinforces the hypothesis that T1D alleles can have strong biological effects and that such genes highlight pathways to consider as targets for immune intervention.

FGD2, a CDC42-specific exchange factor expressed by antigen-presenting cells, localizes to early endosomes and active membrane ruffles

Members of the Fgd (faciogenital dysplasia) gene family encode a group of critical guanine nucleotide exchange factors (GEFs), which, by specifically activating Cdc42, control cytoskeleton-dependent membrane rearrangements. In its first characterization, we find that FGD2 is expressed in antigen-presenting cells, including B lymphocytes, macrophages, and dendritic cells. In the B lymphocyte lineage, FGD2 levels change with developmental stage. In both mature splenic B cells and immature bone marrow B cells, FGD2 expression is suppressed upon activation through the B cell antigen receptor. FGD2 has a complex intracellular localization, with concentrations found in membrane ruffles and early endosomes. Although endosomal localization of FGD2 is dependent on a conserved FYVE domain, its C-terminal pleckstrin homology domain mediates recruitment to membrane ruffles. FGD2 overexpression promotes the activation of Cdc42 and leads to elevated JNK1 activity in a Cdc42- but not Rac1-dependent fashion. These findings are consistent with a role of FGD2 in leukocyte signaling and vesicle trafficking in cells specialized to present antigen in the immune system.

Advances in type I diabetes associated tolerance mechanisms

Type 1 diabetes (T1D) is an autoimmune disease resulting from the destruction of insulin-producing pancreatic beta cells by autoreactive T cells. The polygenic trait for T1D risk implicates many genes that have an impact on fundamental immunological processes such as central and peripheral tolerance. Several pieces of evidence have suggested that many of the genetic loci that are directly linked to type 1 diabetes susceptibility modulate the generation and/or the activation of autoreactive T-lymphocytes. We and others have proposed a critical role for medullary thymic epithelial cells (mTEC) forming the Hassall's corpuscles in T-cell tolerance. Indeed, mTEC have been found to express promiscuous self-antigens, used directly or through thymic dendritic cells to drive either negative selection of insulin-reacting precursors or their differentiation into naturally occurring regulatory Foxp3+ CD4+ CD25+ T cells. In the periphery, naturally occurring Foxp3+ CD4+ CD25+regulatory T (Treg) cells represent the master cells in dominant peripheral T-cell tolerance. The development and function of Treg cells are ultimately linked to IL-2 and Foxp3 expression. This review addresses recent literature and emerging concepts of central and peripheral T-cell tolerance with regards to T1D.

Candidate genes for plasma triglyceride, FFA, and glucose revealed from an intercross between inbred mouse strains NZB/B1NJ and NZW/LacJ

To identify the genes controlling plasma concentrations of triglycerides (TGs), FFAs, and glucose, we carried out a quantitative trait loci (QTL) analysis of the closely related mouse strains New Zealand Black (NZB/B1NJ) and New Zealand White (NZW/LacJ), which share 63% of their genomes. The NZB x NZW F(2) progeny were genotyped and phenotyped to detect QTL, and then comparative genomics, bioinformatics, and sequencing were used to narrow the QTL and reduce the number of candidate genes. Triglyceride concentrations were linked to loci on chromosomes (Chr) 4, 7, 8, 10, and 18. FFA concentrations were affected by a significant locus on Chr 4, a suggestive locus on Chr 16, and two interacting loci on Chr 2 and 15. Plasma glucose concentrations were affected by QTL on Chr 2, 4, 7, 8, 10, 15, 17, and 18. Comparative genomics narrowed the QTL by 31% to 86%; haplotype analysis was usually able to further narrow it by 80%. We suggest several candidate genes: Gba2 on Chr 4, Irs2 on Chr 8, and Ppargc1b on Chr 18 for TG; A2bp1 on Chr 16 for FFA; and G6pc2 on Chr 2 and Timp3 on Chr 10 for glucose.

Diabetic modifier QTLs in F(2) intercrosses carrying homozygous transgene of TGF-beta

When the homozygous active form of porcine TGF-beta1 transgene (Tgf/Tgf) (under control of the rat glucagon promoter) is introduced into the nonobese diabetic mouse (NOD) genetic background, the mice develop endocrine and exocrine pancreatic hypoplasia, low serum insulin concentrations, and impaired glucose tolerance. To identify genetic modifiers of the diabetic phenotypes, we crossed hemizygous NOD-Tgf with DBA/2J mice (D2) or C3H/HeJ mice (C3H) and used the "transgenic mice" for quantitative trait loci (QTL) analysis. Genome-wide scans of F(2)-D Tgf/Tgf (D2 x NOD) and F(2)-C Tgf/Tgf (C3H x NOD), homozygous for the TGF-beta1 transgene, identified six statistically significant modifier QTLs: one QTL (Tdn1) in F(2)-D Tgf/Tgf, and five QTLs (Tcn1 to Tcn5) in F(2)-C Tgf/Tgf. Tdn1 (Chr 13, LOD = 4.39), and Tcn3 (Chr 2, LOD = 4.94) showed linkage to body weight at 8 weeks of age. Tcn2 (Chr 7, LOD = 4.38) and Tcn4 (Chr 14, LOD = 3.99 and 3.78) showed linkage to blood glucose (BG) concentrations in ipGTT at 30, 0, and 120 min, respectively. Tcn1 (Chr 1, LOD = 4.41) and Tcn5 (Chr 18, LOD = 4.99) showed linkage to serum insulin concentrations in ipGTT at 30 min. Tcn2 includes the candidate gene, uncoupling protein 2 (Ucp2), and shows linkage to Ucp2 mRNA levels in the soleus muscle (LOD = 4.90). Identification of six QTLs for diabetes-related traits in F(2)-D Tgf/Tgf and F(2)-C Tgf/Tgf raises the possibility of identifying candidate susceptibility genes and new targets for drug development for human type 2 diabetes.

Activating Fc gamma receptors participate in the development of autoimmune diabetes in NOD mice

Type 1 diabetes mellitus (T1D) in humans is an organ-specific autoimmune disease in which pancreatic islet beta cells are ruptured by autoreactive T cells. NOD mice, the most commonly used animal model of T1D, show early infiltration of leukocytes in the islets (insulitis), resulting in islet destruction and diabetes later. NOD mice produce various islet beta cell-specific autoantibodies, although it remains a subject of debate regarding whether these autoantibodies contribute to the development of T1D. Fc gammaRs are multipotent molecules that play important roles in Ab-mediated regulatory as well as effector functions in autoimmune diseases. To investigate the possible role of Fc gammaRs in NOD mice, we generated several Fc gammaR-less NOD lines, namely FcR common gamma-chain (Fc Rgamma)-deficient (NOD.gamma(-/-)), Fc gammaRIII-deficient (NOD.III(-/-)), Fc gammaRIIB-deficient (NOD.IIB(-/-)), and both Fc Rgamma and Fc gammaRIIB-deficient NOD (NOD.null) mice. In this study, we show significant protection from diabetes in NOD.gamma(-/-), NOD.III(-/-), and NOD.null, but not in NOD.IIB(-/-) mice even with grossly comparable production of autoantibodies among them. Insulitis in NOD.gamma(-/-) mice was also alleviated. Adoptive transfer of bone marrow-derived dendritic cells or NK cells from NOD mice rendered NOD.gamma(-/-) animals more susceptible to diabetes, suggesting a possible scenario in which activating Fc gammaRs on dendritic cells enhance autoantigen presentation leading to the activation of autoreactive T cells, and Fc gammaRIII on NK cells trigger Ab-dependent effector functions and inflammation. These findings highlight the critical roles of activating Fc gammaRs in the development of T1D, and indicate that Fc gammaRs are novel targets for therapies for T1D.

Genetic mapping at 3-kilobase resolution reveals inositol 1,4,5-triphosphate receptor 3 as a risk factor for type 1 diabetes in Sweden

We mapped the genetic influences for type 1 diabetes (T1D), using 2,360 single-nucleotide polymorphism (SNP) markers in the 4.4-Mb human major histocompatibility complex (MHC) locus and the adjacent 493 kb centromeric to the MHC, initially in a survey of 363 Swedish T1D cases and controls. We confirmed prior studies showing association with T1D in the MHC, most significantly near HLA-DR/DQ. In the region centromeric to the MHC, we identified a peak of association within the inositol 1,4,5-triphosphate receptor 3 gene (ITPR3; formerly IP3R3). The most significant single SNP in this region was at the center of the ITPR3 peak of association (P=1.7 x 10(-4) for the survey study). For validation, we typed an additional 761 Swedish individuals. The P value for association computed from all 1,124 individuals was 1.30 x 10(-6) (recessive odds ratio 2.5; 95% confidence interval [CI] 1.7-3.9). The estimated population-attributable risk of 21.6% (95% CI 10.0%-31.0%) suggests that variation within ITPR3 reflects an important contribution to T1D in Sweden. Two-locus regression analysis supports an influence of ITPR3 variation on T1D that is distinct from that of any MHC class II gene.

Identification of the transcription factor ARNTL2 as a candidate gene for the type 1 diabetes locus Idd6

The Idd6 murine type 1 diabetes locus has been shown to control diabetes by regulating the protective activity of the peripheral immune system, as demonstrated by diabetes transfer assays using splenocytes. The analysis of three novel subcongenic (NOD.C3H nonobese. C3H) diabetes strains has confirmed the presence of at least two diabetes-related genes within the 5.8 Mb Idd6 interval with the disease protection conferred by splenocyte co-transfer being located to the 700 kb Idd6.3 subregion. This subinterval contains the circadian rhythm-related transcription factor Arntl2 (Bmal2), a homologue of the type 2 diabetes-associated ARNT (HIF1beta) gene. Arntl2 exhibited a six-fold upregulation in spleens of the NOD.C3H 6.VIII congenic strain compared with the NOD control strain, strain-specific splice variants and a large number of polymorphisms in both coding and non-coding regions. Arntl2 upregulation was not associated with changes in the expression levels of other circadian genes in the spleen, but did correlate with the upregulation of the ARNT-binding motif containing Pla2g4a gene, which has recently been described as being protective for the progression of insulitis and autoimmune diabetes in the NOD mouse via regulation of the tumour necrosis factor-alpha pathway. Our studies strongly suggest that the HIFbeta-homologous Arntl2 gene is involved in the control of type 1 diabetes.

Genetic susceptibility to type 1 diabetes

The recent discovery of PTPN22 as a novel susceptibility gene in human type 1 diabetes and continued progress in defining genes in animal models of the disease mark a fruitful period in the field of type 1 diabetes genetics. In addition, the similarities of the genetic and functional aspects across species have been substantiated. Future genome-wide association studies will reveal more loci, each providing a piece to the genetic puzzle of autoimmune disease.

Type 1 diabetes genes and pathways shared by humans and NOD mice

The identification of causative genes for the autoimmune disease type 1 diabetes (T1D) in humans and candidate genes in the NOD mouse has made significant progress in recent years. In addition to sharing structural aspects of the MHC class II molecules that confer susceptibility or resistance to T1D, genes and pathways contributing to autoimmune pathogenesis are held in common by the two species. There are data demonstrating a similar need to establish central tolerance to insulin. Gene variants for the interacting molecules IL2 and CD25, members of a pathway that is essential for immune homeostasis, are present in mice and humans, respectively. Variation of two molecules that negatively regulate T cells, CTLA-4 and the tyrosine phosphatase LYP/PEP, are associated with susceptibility to human and NOD T1D. These observations underscore the value of the NOD mouse model for mechanistic studies on human T1D-associated molecular and cellular pathways.

Establishment of NOD-Pdcd1-/- mice as an efficient animal model of type I diabetes

Mice deficient in programmed cell death 1 (PD-1, Pdcd1), an immunoinhibitory receptor belonging to the CD28/cytotoxic T lymphocyte-associated antigen-4 family, spontaneously develop lupus-like autoimmune disease and autoimmune dilated cardiomyopathy on C57BL/6 and BALB/c backgrounds, respectively. However, how PD-1 deficiency induces different forms of autoimmune diseases on these two strains was unknown. Here, we report that PD-1 deficiency specifically accelerates the onset and frequency of type I diabetes in NOD (nonobese diabetic) mice, with strong T helper 1 polarization of T cells infiltrating into islets. These results suggest that PD-1 deficiency accelerates autoimmune predisposition of the background strain, leading to the induction of different forms of autoimmune diseases depending on the genetic background of the strain. Using NOD-Pdcd1-/- mice as an efficient animal model of type I diabetes, we screened diabetes-susceptible loci by genetic linkage analysis. The diabetic incidence of NOD-Pdcd1-/- mice was controlled by five genetic loci, including three known recessive loci [Idd (insulin-dependent diabetes) 1, Idd17, and Idd20] and two previously unidentified dominant loci [Iddp (Idd under PD-1 deficiency) 1 and Iddp2].

Major histocompatibility complex-linked diabetes susceptibility in NOD/Lt mice: subcongenic analysis localizes a component of Idd16 at the H2-D end of the diabetogenic H2(g7) complex

The diabetogenic major histocompatibility complex (MHC) (H2(g7)) of NOD mice comprises contributions from several class II loci collectively designated as Idd1. Introduction of the H2(gx) haplotype from the related but diabetes-resistant cataract Shionogi (CTS) strain demonstrated an additional MHC-linked locus designated Idd16. The NOD-related alloxan resistant (ALR)/Lt strain is also characterized by the H2(gx) haplotype, which does not differ from H2(g7) from the class I H2-K(d) gene distally through the class II and into the class III region. Polymorphisms distal to the heat shock protein 70 locus (Hspa1b) include a rare H2-D(dx) rather than the H2(g7) encoded D(b) allele. Two differential-length NOD.ALR-H2(gx) congenic stocks (D.R1 and D.R2), both containing H2-D(dx), significantly suppressed diabetogenesis. This protection was lost when ALR alleles between the class III region and H2-D were removed in a shorter interval congenic (D.R3). Because no differences were observed in the ALR-derived interval extending 0.41 mB proximal to H2-K in any of these congenic stocks, a component of what was originally designated "Idd16" was sited to an interval shorter than 7.33 mB, distinguishing D.R2 from D.R3. Evidence supporting the candidacy of the ALR/CTS-shared H2-D(dx) MHC class I variant present in both diabetes-resistant stocks, but not the susceptible stock, is discussed.