Genetic control of diabetes and insulitis in the nonobese diabetic (NOD) mouse

Defective CD8+ T cell peripheral tolerance in nonobese diabetic mice

Nonobese diabetic (NOD) mice develop spontaneous autoimmune diabetes that involves participation of both CD4+ and CD8+ T cells. Previous studies have demonstrated spontaneous reactivity to self-Ags within the CD4+ T cell compartment in this strain. Whether CD8+ T cells in NOD mice achieve and maintain tolerance to self-Ags has not previously been evaluated. To investigate this issue, we have assessed the extent of tolerance to a model pancreatic Ag, the hemagglutinin (HA) molecule of influenza virus, that is transgenically expressed by pancreatic islet beta cells in InsHA mice. Previous studies have demonstrated that BALB/c and B10.D2 mice that express this transgene exhibit tolerance of HA and retain only low-avidity CD8+ T cells specific for the dominant peptide epitope of HA. In this study, we present data that demonstrate a deficiency in peripheral tolerance within the CD8+ T cell repertoire of NOD-InsHA mice. CD8+ T cells can be obtained from NOD-InsHA mice that exhibit high avidity for HA, as measured by tetramer (K(d)HA) binding and dose titration analysis. Significantly, these autoreactive CD8+ T cells can cause diabetes very rapidly upon adoptive transfer into NOD-InsHA recipient mice. The data presented demonstrate a retention in the repertoire of CD8+ T cells with high avidity for islet Ags that could contribute to autoimmune diabetes in NOD mice.

Increased expression of GPI-specific phospholipase D in mouse models of type 1 diabetes

Glycosylphosphatidylinositol-specific phospholipase D (GPI-PLD) is a high-density lipoprotein-associated protein. However, the tissue source(s) for circulating GPI-PLD and whether serum levels are regulated are unknown. Because the diabetic state alters lipoprotein metabolism, and liver and pancreatic islets are possible sources of GPI-PLD, we hypothesized that GPI-PLD levels would be altered in diabetes. GPI-PLD serum activity and liver mRNA were examined in two mouse models of type 1 diabetes, a nonobese diabetic (NOD) mouse model and low-dose streptozotocin-induced diabetes in CD-1 mice. With the onset of hyperglycemia (2- to 5-fold increase over nondiabetic levels), GPI-PLD serum activity and liver mRNA increased 2- to 4-fold in both models. Conversely, islet expression of GPI-PLD was absent as determined by immunofluorescence. Insulin may regulate GPI-PLD expression, because insulin treatment of diabetic NOD mice corrected the hyperglycemia along with reducing serum GPI-PLD activity and liver mRNA. Our data demonstrate that serum GPI-PLD levels are altered in the diabetic state and are consistent with liver as a contributor to circulating GPI-PLD.

Derivation of diabetes-resistant congenic lines from the nonobese diabetic mouse

Autoimmune diabetes is a polygenic disease process in man and rodents. To identify and characterize genes involved in the pathogenesis of diabetes in nonobese diabetic (NOD) mice, we initiated a repetitive backcross of diabetes-resistant C57L/J mice onto the NOD strain. This breeding scheme was based on the premise that selection for the trait of disease resistance among genetically mixed mice could be used to maintain transmission of nonpermissive alleles from the diabetes-resistant strain at critical diabetes susceptibility loci. Each of the three recombinant congenic mouse lines derived by this strategy retains a unique constellation of C57L/J-derived DNA segments. Consistent with the involvement of different genetic loci, the pancreatic histology of disease-resistant mice differs from that in NOD mice in a line-specific manner. Functional studies using these lines demonstrate that pathogenesis of autoimmune diabetes is a multistep process which can be blocked at a minimum of three critical, genetically determined points.

Two genetic loci regulate T cell-dependent islet inflammation and drive autoimmune diabetes pathogenesis

Insulin-dependent diabetes mellitus (IDDM) is a polygenic disease caused by progressive autoimmune infiltration (insulitis) of the pancreatic islets of Langerhan, culminating in the destruction of insulin-producing beta cells. Genome scans of families with diabetes suggest that multiple loci make incremental contributions to disease susceptibility. However, only the IDDM1 locus is well characterized, at a molecular and functional level, as alleleic variants of the major histocompatibility complex (MHC) class II HLA-DQB1, DRB1, and DPB1 genes that mediate antigen presentation to T cells. In the nonobese diabetic (NOD) mouse model, the Idd1 locus was shown to be the orthologous MHC gene I-Ab. Inheritance of susceptibility alleles at IDDM1/Idd1 is insufficient for disease development in humans and NOD mice. However, the identities and functions of the remaining diabetes loci (Idd2-Idd19 in NOD mice) are largely undefined. A crucial limitation in previous genetic linkage studies of this disease has been reliance on a single complex phenotype-diabetes that displays low penetrance and is of limited utility for high-resolution genetic mapping. Using the NOD model, we have identified an early step in diabetes pathogenesis that behaves as a highly penetrant trait. We report that NOD-derived alleles at both the Idd5 and Idd13 loci regulate a T lymphocyte-dependent progression from a benign to a destructive stage of insulitis. Human chromosomal regions orthologous to the Idd5 and -13 intervals are also linked to diabetes risk, suggesting that conserved genes encoded at these loci are central regulators of disease pathogenesis. These data are the first to reveal a role for individual non-MHC Idd loci in a specific, critical step in diabetes pathogenesis-T cell recruitment to islet lesions driving destructive inflammation. Importantly, identification of intermediate phenotypes in complex disease pathogenesis provides the tools required to progress toward gene identification at these loci.

MHC structure and autoimmune T cell repertoire development

Recent work has continued to clarify the relationship between MHC structure and thymic selection that leads to peripheral T cell repertoire development in the pathogenesis of autoimmune diseases. Particular attention has been focused on the nonobese diabetic model of autoimmune diabetes, in which a unique MHC class II molecule (I-Ag7) plays a central role. In the past year, reports on the biochemistry of I-Ag7-combined with analysis of the role of I-Ag7 in T cell repertoire selection--support a model of defective thymic selection as the basis of the association between particular MHC molecules and autoimmune diseases. Analogous work has been done on the structure of the human MHC disease-susceptible and -resistant alleles, DQA1*0301 DQB1*0302 and DQA1*0102 DQB1*0602, and their effect on autoimmune repertoire selection. Comparison of these results (in naturally occurring, spontaneous autoimmune human and murine diabetes), with results in a variety of transgenic and knockout models, has produced an integrated view of how avidity considerations in repertoire selection in the thymus could affect predisposition towards autoimmunity.

Minute defects in the expression of MHC E molecules lead to impaired protection from autoimmunity in NOD mice

The E complex of the major histocompatibility complex (MHC) can prevent the spontaneous development of diabetes in nonobese diabetic (NOD) mice transgenic for the Ea gene. None of three promoter-mutated Ea constructs with Ea expression directed to different subsets of immunocompetent cells exerts full protection in NOD mice. The promoter-mutated constructs are all capable of mediating intrathymic elimination of I-E-restricted T cells. Thus, thymic negative selection is not responsible for the protective effect but a more complex effect is likely. Here we show that combinations of two or three different mutated Ea constructs do not protect against intra-islet insulitis either. We also show that spleen cells from protected animals are sufficient to protect NOD mice in adoptive transfer experiments. The only detectable expression defects in splenic cells or cells influencing the repertoire of splenic cells are in the B-cell compartment. Furthermore, in three construct combinations, the differences to wild-type expression are extremely small. Thus, we conclude that even minute disturbances of the E expression pattern might reduce the protection of NOD mice from insulitis.

Cutting Edge: Homologous Recombination of the MHC Class I K Region Defines New MHC-Linked Diabetogenic Susceptibility Gene(s) in Nonobese Diabetic Mice

To localize the MHC-linked diabetogenic genes in the nonobese diabetic (NOD) mouse, a recombinational hotspot from the B10.A(R209) mouse was introduced to the region between the MHC class I K and class II A of the NOD mouse with the recombinational site centromeric to the Lmp2/Tap1 complex by breeding the two strains. Replacement of the NOD region centromeric to the recombinational site with the same region in R209 mice prevented the development of diabetes (from 71 to 3%) and insulitis (from 61 to 15%) in the N7 intra-MHC recombinant NOD mice. Similarly, the replacement of the NOD class II A, E and class I D region with the same region in R209 mice prevented the diseases (diabetes, from 71 to 0%; insulitis, from 61 to 3%). In addition to the MHC class II genes, there are at least two MHC-linked diabetogenic genes in the region centromeric to Lmp2.

I-Ag7-Mediated Antigen Presentation by B Lymphocytes Is Critical in Overcoming a Checkpoint in T Cell Tolerance to Islet β Cells of Nonobese Diabetic Mice

B cell-deficient nonobese diabetic (NOD) mice are protected from the development of spontaneous autoimmune diabetes, suggesting a requisite role for Ag presentation by B lymphocytes for the activation of a diabetogenic T cell repertoire. This study specifically examines the importance of B cell-mediated MHC class II Ag presentation as a regulator of peripheral T cell tolerance to islet β cells. We describe the construction of NOD mice with an I-Ag7 deficiency confined to the B cell compartment. Analysis of these mice, termed NOD BCIID, revealed the presence of functionally competent non-B cell APCs (macrophages/dendritic cells) with normal I-Ag7 expression and capable of activating Ag-reactive T cells. In addition, the secondary lymphoid organs of these mice harbored phenotypically normal CD4+ and CD8+ T cell compartments. Interestingly, whereas control NOD mice harboring I-Ag7-sufficient B cells developed diabetes spontaneously, NOD BCIID mice were resistant to the development of autoimmune diabetes. Despite their diabetes resistance, histologic examination of pancreata from NOD BCIID mice revealed foci of noninvasive peri-insulitis that could be intentionally converted into a destructive process upon treatment with cyclophosphamide. We conclude that I-Ag7-mediated Ag presentation by B cells serves to overcome a checkpoint in T cell tolerance to islet β cells after their initial targeting has occurred. Overall, this work indicates that the full expression of the autoimmune potential of anti-islet T cells in NOD mice is intimately regulated by B cell-mediated MHC class II Ag presentation.

Transfer of dendritic cells (DC) ex vivo stimulated with interferon-gamma (IFN-gamma) down-modulates autoimmune diabetes in non-obese diabetic (NOD) mice

The NOD mouse has been used to explore the many features of insulin-dependent diabetes mellitus (IDDM) that is caused by the destruction of insulin-producing beta cells in the islets of Langerhans of the pancreas. Self-reactive T cells have been considered to mediate IDDM in the NOD mouse, and antigen-presenting cells like DC and macrophages are expected to be involved in the processes from their role in generating regulatory or effector T cells. The present study shows that transfer of IFN-gamma-stimulated DC of the NOD or ICR mouse into the NOD mouse did not accelerate IDDM onset but afforded long-lasting protection against clinical and histological signs of IDDM in the recipient mice. The anti-diabetogenic ability was unique to IFN-gamma-stimulated DC when compared with unstimulated DC. A considerable proportion of the injected IFN-gamma-stimulated DC was demonstrated to migrate into the pancreas and its associated lymphoid tissues, suggesting the DC exert their anti-diabetogenic effects there. These findings suggest that development of autoimmune diabetes in the NOD mouse is under the control of DC, and that IDDM onset could be controlled by appropriately manipulating DC systems in vivo, which may open the gate for the therapeutic application of ex vivo-conditioned DC to human IDDM.

Both CD4(+) T cells and CD8(+) T cells are required for iodine accelerated thyroiditis in NOD mice

The nonobese diabetic (NOD) mouse, a spontaneous animal model for insulin-dependent diabetes mellitus, displays a tendency in common with human diabetic populations to develop autoimmune thyroiditis although incidence and severity of thyroid lesions vary widely among different colonies around the world. A congenic strain of NOD mice bearing I-Ak on a NOD background (NOD-H2(h4)) has recently been derived and displays a much greater tendency to develop thyroiditis and autoantibodies to mouse thyroglobulin (MTg) although it is free of diabetes. Both thyroid infiltrates and autoantibody formation are accelerated and enhanced in NOD-H2(h4) mice by increased iodine intake. The effect of increased iodine intake on NOD mice themselves has not been directly investigated although a recent study of these animals given high or low doses of iodine showed no follicular destruction unless the mice were first rendered goitrous by iodine deprivation. We found that dietary iodine increased both the incidence and the severity of thyroid lesions in our NOD mice although autoantibodies to MTg were absent. NOD background genes appear to be essential for the development of these lesions, which were maximal after 4 weeks of iodine administration and showed no significant regression when the iodine was stopped. Furthermore, our studies show for the first time that both CD4(+) and CD8(+) T cells are necessary for the development of this accelerated but essentially spontaneous murine thyroid disease.

Analysis of the role of variation of major histocompatibility complex class II expression on nonobese diabetic (NOD) peripheral T cell response

The current paradigm of major histocompatibility complex (MHC) and disease association suggests that efficient binding of autoantigens by disease-associated MHC molecules leads to a T cell-mediated immune response and resultant autoimmune sequelae. The data presented below offer a different model for this association of MHC with autoimmune diabetes. We used several mouse lines expressing different levels of I-Ag7 and I-Ak on the nonobese diabetic (NOD) background to evaluate the role of MHC class II in the previously described NOD T cell autoproliferation. The ratio of I-Ag7 to I-Ak expression correlated with the peripheral T cell autoproliferative phenotype in the mice studied. T cells from the NOD, [NOD x NOD. I-Anull]F1, and NOD I-Ak transgenic mice demonstrated autoproliferative responses (after priming with self-peptides), whereas the NOD.H2(h4) (containing I-Ak) congenic and [NOD x NOD. H2(h4) congenic]F1 mice did not. Analysis of CD4(+) NOD I-Ak transgenic primed lymph node cells showed that autoreactive CD4(+) T cells in the NOD I-Ak transgenic mice were restricted exclusively by I-Ag7. Considered in the context of the avidity theory of T cell activation and selection, the reported poor peptide binding capacity of NOD I-Ag7 suggested a new hypothesis to explain the effects of MHC class II expression on the peripheral autoimmune repertoire in NOD mice. This new explanation suggests that the association of MHC with diabetes results from "altered" thymic selection in which high affinity self-reactive (potentially autoreactive) T cells escape negative selection. This model offers an explanation for the requirement of homozygous MHC class II expression in NOD mice (and in humans) in susceptibility to insulin-dependent diabetes mellitus.

Evidence for the presence of insulin-dependent diabetes-associated alleles on the distal part of mouse chromosome 6

Type 1 diabetes (IDDM) is a complex disorder with multifactorial and polygenic etiology. A genome-wide screen performed in a BC1 cohort of a cross between the nonobese diabetic (NOD) mouse with the diabetes-resistant feral strain PWK detected a major locus contributing to diabetes development on the distal part of chromosome 6. Unlike the majority of other Idd loci identified in intraspecific crosses, susceptibility is associated with the presence of the PWK allele. Genetic linkage analysis of congenic lines segregating PWK chromosome 6 segments in a NOD background confirmed the presence of the Idd locus within this region. The genetic interval defined by analysis of congenic animals showed a peak of significant linkage (P = 0.0005) centered on an approximately 9-cM region lying between D6Mit11 and D6Mit25 genetic markers within distal mouse chromosome 6. [Genetic markers polymorphic between the NOD and PWK strains are available as a supplement at http://www.genome.org]

Major histocompatibility complex class II molecules can protect from diabetes by positively selecting T cells with additional specificities

Insulin-dependent diabetes is heavily influenced by genes encoded within the major histocompatibility complex (MHC), positively by some class II alleles and negatively by others. We have explored the mechanism of MHC class II-mediated protection from diabetes using a mouse model carrying the rearranged T cell receptor (TCR) transgenes from a diabetogenic T cell clone derived from a nonobese diabetic mouse. BDC2.5 TCR transgenics with C57Bl/6 background genes and two doses of the H-2(g7) allele exhibited strong insulitis at approximately 3 wk of age and most developed diabetes a few weeks later. When one of the H-2(g7) alleles was replaced by H-2(b), insulitis was still severe and only slightly delayed, but diabetes was markedly inhibited in both its penetrance and time of onset. The protective effect was mediated by the Abetab gene, and did not merely reflect haplozygosity of the Abetag7 gene. The only differences we observed in the T cell compartments of g7/g7 and g7/b mice were a decrease in CD4(+) cells displaying the transgene-encoded TCR and an increase in cells expressing endogenously encoded TCR alpha-chains. When the synthesis of endogenously encoded alpha-chains was prevented, the g7/b animals were no longer protected from diabetes. g7/b mice did not have a general defect in the production of Ag7-restricted T cells, and antigen-presenting cells from g7/b animals were as effective as those from g7/g7 mice in stimulating Ag7-restricted T cell hybridomas. These results argue against mechanisms of protection involving clonal deletion or anergization of diabetogenic T cells, or one depending on capture of potentially pathogenic Ag7-restricted epitopes by Ab molecules. Rather, they support a mechanism based on MHC class II-mediated positive selection of T cells expressing additional specificities.

Complex traits and polygenic inheritance in the mouse

Polygenic inheritance has recently become an increasingly active field of research due to the availability of techniques allowing in-depth screening of genetic markers across the entire genome. The mouse is being used both in its own right and as a model system for certain human traits. The advantages and disadvantages of the mouse for such studies are outlined and in this context, the adequacy of the mouse as a model for polygenic traits in humans is discussed. A detailed overview of the approaches and methods used in the analysis of polygenic inheritance in the mouse is presented.

The association of MHC with autoimmune diseases: understanding the pathogenesis of autoimmune diabetes

The current paradigm of MHC and disease association is efficient binding of autoantigens by disease-associated MHC molecules leading to a T cell-mediated immune response and resultant autoimmune sequelae. Data presented here offer a different model for this association of MHC with autoimmune diabetes. This new explanation suggests that the association of MHC with autoimmunity results from "altered" thymic selection in which high-affinity self-reactive (potentially autoreactive) T cells escape negative selection. This model offers an explanation for the requirement of homozygous MHC class II expression in NOD mice (and in man) in susceptibility to IDDM.

Abnormal T cell selection on nod thymic epithelium is sufficient to induce autoimmune manifestations in C57BL/6 athymic nude mice

To investigate the role of primary T cell repertoire selection in the immunopathogenesis of autoimmune diseases, pure thymic epithelium (TE) from nonobese diabetic (NOD) embryos was grafted into non autoimmune prone newborn C57BL/6 athymic mice. The results show that NOD TE selects host T cell repertoires that establish autoimmunity in otherwise nondiabetic animals. Thus, such chimeras regularly show CD4 and CD8 T cell-mediated insulitis and sialitis, in contrast with syngeneic or allogeneic chimeras produced with TE from nonautoimmune strains. This is the first demonstration that autoimmunity to pancreatic beta cells and salivary glands can be established by the sole alteration of the thymic environment involved in T cell selection, regardless of the nature and presentation of both major histocompatibility complex and tissue-specific antigens on the target organ. These data indicate that T cell repertoire selection by the NOD thymic epithelium is sufficient to induce specific autoimmune characteristics in the context of an otherwise normal host.

Immunogenetics and the cause of autoimmune disease

Autoimmune disease results from the action of environmental factors on a predisposed genotype. In this review, the role of genetic susceptibility in the aetiology of autoimmune disease is examined. As the genetics of autoimmune diabetes has been studied more intensively than that of other autoimmune diseases, supporting evidence is drawn principally from that example. Autoimmune diseases are not inherited as entities but as constitutions which confer an increased probability of developing disease. It is proposed that there are two components to autoimmune disease susceptibility. One confers susceptibility to autoimmunity per se, while the other determines tissue specificity. In this review, the concept of liability is introduced as a tool used in quantitative genetics and is applied to the analysis of autoimmune diabetes by considering a threshold model. In this example, empirically derived incidence figures are used to calculate heritability which is a relative measure of the influence of genetics and environmental factors. The validity of applying the concept of liability to diabetes is confirmed by examining the values of heritability calculated from empirical data obtained from different kindred relationships, and by confirming that the assumptions on which liability is based are supported by recent gene mapping data. Finally, the physiological significance of liability is considered and its significance to the cause of autoimmunity discussed.

Temporal discontinuities in progression of NOD autoimmune diabetes

Consideration of the pathophysiology of insulin-dependent diabetes mellitus in the nonobese diabetic (NOD) mouse can be viewed from a temporal perspective. We argue that there are discontinuous phases and each phase may reflect a phenotype educed by a particular set of genetic and epigenetic events. Therefore, temporal dissection may be a useful platform for causal dissection and we have set out this article as follows: 1. Introduction. 2. "Pre-time." a. Genetics. b. Parental effects. 3. Development of insulitis. a. Development of autoimmunity vs waning of or failure to establish tolerance. b. Importance of beta cell mass. c. Homing. 4. Onset of beta cell destruction. 5. Further Discussion.

Local expression of transgene encoded TNF alpha in islets prevents autoimmune diabetes in nonobese diabetic (NOD) mice by preventing the development of auto-reactive islet-specific T cells

Lately, TNF alpha has been the focus of studies of autoimmunity; its role in the progression of autoimmune diabetes is, however, still unclear. To analyze the effects of TNF alpha in insulin-dependent diabetes mellitus (IDDM), we have generated nonobese diabetic (NOD) transgenic mice expressing TNF alpha under the control of the rat insulin II promoter (RIP). In transgenic mice, TNF alpha expression on the islets resulted in massive insulitis, composed of CD4+ T cells, CD8+ T cells, and B cells. Despite infiltration of considerable number of lymphoid cells in islets, expression of TNF alpha protected NOD mice from IDDM. To determine the mechanism of TNF alpha action, splenic cells from control NOD and RIP-TNF alpha mice were adoptively transferred to NOD-SCID recipients. In contrast to the induction of diabetes by splenic cells from control NOD mice, splenic cells from RIP-TNF alpha transgenic mice did not induce diabetes in NOD-SCID recipients. Diabetes was induced however, in the RIP-TNF alpha transgenic mice when CD8+ diabetogenic cloned T cells or splenic cells from diabetic NOD mice were adoptively transferred to these mice. Furthermore, expression of TNF alpha in islets also downregulated splenic cell responses to autoantigens. These data establish a mechanism of TNF alpha action and provide evidence that local expression of TNF alpha protects NOD mice from autoimmune diabetes by preventing the development of autoreactive islet-specific T cells.

Non-obese diabetic mice hemizygous at the T cell receptor alpha locus are susceptible to diabetes and sialitis

To test the hypothesis that T cells carrying two T cell receptor (TCR) alpha chains play a role in autoimmunity, we backcrossed the non-obese diabetic (NOD) strain with one carrying a TCR alpha gene disrupted by homologous recombination. Mice carrying one copy of the disrupted gene are incapable of generating T cells carrying two cell surface TCR alpha chains. Our early results suggested that either dual TCR alpha T cells play a role in insulin-dependent diabetes mellitus (IDDM) induction in NOD mice or that a locus co-segregating with the disrupted TCR alpha locus protected mice from diabetes induction. From the analysis both of mice in which the region co-segregating with the disrupted TCR alpha locus is minimized and of the F1 offspring of NOD mice with the 129 strain (TCR alpha hemizygous mice), the apparent protective effect of the absence of dual TCR alpha T cells is lost; thus, such cells do not appear to play a critical role in autoimmune disease in NOD mice.

The contribution of insulitis to diabetes development in tumor necrosis factor transgenic mice

The inflammatory response mediated by cytokines such as TNF can promote recruitment of lymphocytes to a tissue. Moreover, if other conditions are met, this can provide a predisposing role to autoimmune disease. TNFs induce the appearance of adhesion molecules (and presumably, therefore, extravasation of lymphocytes into tissue from the vasculature) and increase the levels of MHC class I on tissue. However, it is not clear which of these effects plays the key role in induction of disease. This should be the subject of further study. The data substantiate the hypothesis that chronic inflammation might play a precipitating role in autoimmunity and could be one of the environmental factors of importance in the development of so many autoimmune diseases.

Development of insulin-dependent diabetes mellitus in [(NOD + BALB/c) --> NOD] mixed allogeneic bone marrow chimeras

To examine the possibility that the bone marrow cells of BALB/c genotype interfere with the development of insulitis and diabetes in NOD mice, we transplanted BALB/c bone marrow cells mixed with NOD bone marrow cells into NOD mice. The [(NOD + BALB/c) --> NOD] chimeras developed insulitis and diabetes, indicating that BALB/c bone marrow cells do not interfere with the development of the disease in NOD mice. Surprisingly, these mice have been reconstituted with only NOD hematolymphoid cells. When the pancreatic tissues from newborn NOD and BALB/c mice were grafted into [(NOD + BALB/c) --> NOD] chimeras, the BALB/c pancreatic tissues were rejected, whereas the NOD graft showed insulitis. Furthermore, the spleen cells of the chimeras showed responsiveness to BALB/c spleen cells in mixed lymphocyte reaction and generated cytotoxic T lymphocytes specific for the H-2d and third party targets. These findings indicate that the hematolymphoid cells (including hemopoietic stem cells) of NOD mice are more resilient than those of normal BALB/c mice, and that insulin-dependent diabetes mellitus will recur after bone marrow transplantation unless the hematolymphoid cells of NOD mice are completely destroyed by irradiation.

Exacerbated autoimmunity associated with a T helper-1 cytokine profile shift in H-2E-transgenic mice

Major histocompatibility complex (MHC) class II genes are the strongest susceptibility markers for many human autoimmune diseases. A perplexing aspect of this is that HLA alleles can confer either susceptibility or dominant protection. In nonobese diabetic (NOD) mice, the strongest known diabetes susceptibility locus is within the MHC and is presumed to be the H-2Ag7 product. When NOD mice carry a transgenic E alpha d molecule allowing expression of an H-2E heterodimer, diabetes is prevented. We investigated whether, as in human autoimmunity, a single class II heterodimer might protect from some autoimmune diseases while predisposing to others. NOD mice are susceptible to experimental autoimmune encephalomyelitis (EAE) induced by the proteolipoprotein (PLP) epitope 56-70. Susceptibility to EAE was analyzed in NOD mice which either have or lack transgenic H-2E expression. We found that H-2E expression in NOD mice has converse effects on diabetes and EAE: while diabetes is prevented, EAE is greatly exacerbated and leads to demyelination. Although PLP 56-70 could be presented both in the context of H-2A and H-2E, increased disease severity in H-2E transgenic mice could not be attributed either to an enhanced T cell proliferative response to PLP or to differences in determinant spread. However, cytokine analysis of the response revealed important differences between NOD mice and their H-2E transgenic counterparts: H-2E expression was associated with reduced interleukin-4 secretion and enhanced interferon-gamma (IFN-gamma) secretion by lymph node cells, while the response of central nervous system infiltrating T cells displayed a markedly enhanced IFN-gamma response. Thus, whether a particular class II molecule confers resistance or susceptibility to an autoimmune disease may depend on differential cytokine profiles elicited by particular class II/autoantigen complexes.

Genetic polymorphism of the human tumor necrosis factor region in insulin-dependent diabetes mellitus. Linkage disequilibrium of TNFab microsatellite alleles with HLA haplotypes

The TNF region within the MHC includes a number of immunologically important genes. Microsatellites TNFa and TNFb adjacent to TNF exhibit extensive polymorphism. Employing a PCR-based technique, we identified TNFab haplotypes and defined their distribution in 97 controls and 48 diabetics of Caucasoid origin in a search for other genes within the MHC potentially associated with IDDM. Twenty-five different TNFab haplotypes were identified. A significant difference (p < 0.0005) in frequency between patients and controls was found for TNFa1b5 (relative risk 53). However, no other TNFab microsatellites demonstrated significantly different frequencies. Among diabetics TNFa1b5 was found to be in linkage disequilibrium with HLA-DR3-B18, a haplotype known to be associated with IDDM. Thus the increased frequency of TNFa1b5 among diabetics could reflect a linkage disequilibrium with a gene within the TNF region or with other genes, including the HLAs, which characterize this haplotype. In both controls and diabetics TNFa2b3 and TNFa7b4 were in linkage disequilibrium with DR3-B8 and DR7, respectively. Among diabetics, TNFa2b1 and TNFa6b5 were in linkage disequilibrium with DR4-B62 and DR4-B44, respectively. It is intriguing that TNFab haplotypes, represented by a short piece of about 200 nucleotides in the untranslated region upstream of TNF beta gene, maintain strong linkage disequilibria with different HLA haplotypes extending over 1 million base pairs. The identification of TNFab microsatellites exhibiting a high polymorphic index in a region lacking known polymorphic markers may provide potentially important information regarding the association of HLA haplotypes with autoimmune diseases, as they are in close proximity to other genes of immunologic importance.

Identification of a new susceptibility locus for insulin-dependent diabetes mellitus by ancestral haplotype congenic mapping

The number and exact locations of the major histocompatibility complex (MHC)-linked diabetogenic genes (Idd-1) are unknown because of strong linkage disequilibrium within the MHC. By using a congenic NOD mouse strain that possesses a recombinant MHC from a diabetes-resistant sister strain, we have now shown that Idd-1 consists of at least two components, one in and one outside the class II A and E regions. A new susceptibility gene (Idd-16) was mapped to the < 11-centiMorgan segment of chromosome 17 adjacent to, but distinct from, previously known Idd-1 candidates, class II A, E, and Tap genes. The coding sequences and splicing donor and acceptor sequences of the Tnfa gene, a candidate gene for Idd-16, were identical in the NOD, CTS, and BALB/c alleles, ruling out amino acid changes in the TNF molecule as a determinant of insulin-dependent diabetes mellitus susceptibility. Our results not only map a new MHC-linked diabetogenic gene(s) but also suggest a new way to fine map disease susceptibility genes within a region where strong linkage disequilibrium exists.

Molecular genetics of diabetes mellitus

As a result of advances in technology, genome searches have been carried out for susceptibility genes for type 1 diabetes in humans and in the NOD mouse. These have shown that, in the NOD mouse, diabetes susceptibility is under the control of at least ten separate chromosomal loci. In the human, in addition to HLA and INS, two new susceptibility genes have been localized, IDDM4 on chromosome 11q and IDDM5 on 6q, demonstrating the polygenic nature of type 1 diabetes and the role of HLA as the major locus. Candidate genes at these loci are the subject of current investigation. Genetic and immunological markers of disease may be of value in screening the general population for individuals at risk of developing type 1 diabetes. The predictive power of different screening strategies should be tested in order to work out the potential value to the general population of preventive therapies that are now undergoing clinical trials in high risk 'pre-diabetics'. Type 2 diabetes is genetically heterogeneous, and, since 1992, two distinct genetic subtypes have been identified. The first is defined by mutations in the GCK gene, which cause up to 60% of cases of MODY. The second, designated MIDD (maternally inherited diabetes and deafness), is defined by mutation in the mitochondrial gene for tRNA(Leu(UUR)). MIDD patients are less obese than is usual for typical type 2 diabetes, may present in early adult life or occasionally in childhood and may have been diagnosed as having autoimmune type 1 diabetes, type 2 diabetes or MODY. Typically, patients with MIDD require insulin earlier than do type 2 diabetics without mitochondrial mutations. Genetically complex diseases, such as diabetes, hypertension, cancer and coronary heart disease, are common in most populations. The approaches to the genetic analysis of diabetes outlined in this review are likely to be useful to the genetic analysis of many of these disorders. Progress in this area will have important implications for public health strategies in the next decade and beyond.

A diabetes-associated T-cell autoantigen maps to a telomeric locus on mouse chromosome 6

Identification of diabetes-associated T-cell autoantigens is important for understanding the immunopathology of diabetes and developing improved therapeutic strategies. We have used a genetic approach to move toward identifying the autoantigen recognized by a diabetogenic islet-specific T-cell clone from a nonobese diabetic (NOD) mouse. The unique antigen recognition pattern of this clone was utilized to map the gene encoding the antigen (or its expression) by genetic linkage analysis. In vitro analysis of T-cell proliferation by this clone showed that the capacity of the islets to stimulate T cells segregates as a single codominant gene in BALB/cByJ x (BALB/cByJ x NOD/Bdc) backcross mice. This phenotype was tightly linked to two microsatellites in the telomeric region of mouse chromosome 6.

Autoimmune diabetes-prone NOD mice express the Lyt2 alpha (Lyt2.1) and Lyt3 alpha (Lyt3.1) alleles of CD8

Predisposition to Type I insulin-dependent diabetes (IDD) has a strong underlying genetic basis involving class II major histocompatibility complex (MHC) genes as well as several non-MHC genetic systems. In the non-obese diabetic (NOD) mouse, a model for human IDD, genes associated with the appearance of immune cell infiltrates in the pancreatic islets (insulitis) and/or overt IDD have been mapped to chromosomes 1, 3, 6, 11, and 17. A recent report has suggested that CD8+ lymphocytes of the NOD mouse might be deficient in the expression of the CD8 beta molecule, a protein encoded by a gene on chromosome 6. The CD8 beta molecule is a T-cell surface marker, the lack of which could affect selection in the thymus, possibly permitting auto-reactive T-cell clones to populate the peripheral lymphoid tissues. For this reason, we examined the expression of the CD8 molecule by lymphocytes in the NOD mouse. Results indicate that the NOD mouse is not deficient in its transcription of detectable mRNA encoding either the CD8 alpha or beta subunits. However, the NOD mouse expresses the Lyt2 alpha and Lyt3 alpha alleles, suggesting that a portion of chromosome 6 centromeric to the diabetes-susceptibility genetic region is derived from an ancestry common to AKR and, like AKR, the CD8 alpha and CD8 beta 3.1 (but not CD8 beta 3.2) subunits are detected on the cell surface of T lymphocytes of the NOD mouse. Interestingly, though, the CD8 beta 3.1 molecule may not be expressed in the NOD mouse to the same extent as it is expressed in the AKR/J mouse, suggesting the possibility that the NOD mouse possesses a defect somewhere between transcription and cell surface expression of the CD8 beta molecule.

Resistance alleles at two non-major histocompatibility complex-linked insulin-dependent diabetes loci on chromosome 3, Idd3 and Idd10, protect nonobese diabetic mice from diabetes

Development of diabetes in NOD mice is polygenic and dependent on both major histocompatibility complex (MHC)-linked and non-MHC-linked insulin-dependent diabetes (Idd) genes. In (F1 x NOD) backcross analyses using the B10.H-2g7 or B6.PL-Thy1a strains as the outcross partner, we previously identified several non-MHC Idd loci, including two located on chromosome 3 (Idd3 and Idd10). In the current study, we report that protection from diabetes is observed in NOD congenic strains having B6.PL-Thy1a- or B10-derived alleles at Idd3 or Idd10. It is important to note that only partial protection is provided by two doses of the resistance allele at either Idd3 or Idd10. However, nearly complete protection from diabetes is achieved when resistance alleles are expressed at both loci. Development of these congenic strains has allowed Idd3 to be localized between Glut2 and D3Mit6, close to the Il2 locus.

The role of genetic factors in multiple sclerosis susceptibility

There has been increasing evidence that genetic factors have a role in determining susceptibility to MS. Re-examination of results from prevalence and migration surveys reveals that there remains considerable ambiguity in interpretation. Some patterns previously thought to decisively support environmental determination may still be explained, at least in part, on a genetic basis. It seems inescapable that MS is probably due to an interaction of genetic and environmental factors. It remains undetermined whether or not genes exist which are truly necessary for the development of the disease. Existing data are consistent with the notion that the study of MS susceptibility will parallel the findings in experimental models of spontaneous autoimmunity and that at very least, two genes and almost certainly several genes will be found to influence susceptibility and interact in as yet unknown ways. One of these loci appears to be the Class II MHC, although its role may be minor at the germ line level. Roles for the T-cell receptor alpha and beta loci appear to be minor and may even be non-existent in contributing to heritable susceptibility. We predict that additional loci will be identified which influence both susceptibility and outcome and will be more important. Furthermore, it is clear that the understanding of the contribution of individual susceptibility loci will continue to be difficult because of the constraints of human pedigree data. It is likely that further resolution of the questions posed above related to genetic susceptibility in MS will require multicenter collaboration.

A role for non-MHC genetic polymorphism in susceptibility to spontaneous autoimmunity

Peripheral immunological tolerance is traditionally explained by mechanisms for deletion or inactivation of autoreactive T cell clones. Using an autoimmune disease model combining transgenic mice expressing a well-defined antigen, influenza hemagglutinin (HA), on islet beta cells (Ins-HA), and a T cell receptor transgene (TCR-HNT) specific for a class II-restricted HA peptide, we demonstrate that the conventional assumptions do not apply to this in vivo situation. Double transgenic mice displayed either resistance or susceptibility to spontaneous autoimmune disease, depending on genetic contributions from either of two common inbred mouse strains, BALB/c or B10.D2. Functional studies on autoreactive CD4+ T cells from resistant mice showed that, contrary to expectations, neither clonal anergy, clonal deletion, nor receptor desensitization was induced; rather, there was a non-MHC-encoded predisposition toward differentiation to a nonpathogenic effector (Th2 versus Th1) phenotype. T cells from resistant double transgenic mice showed evidence for prior activation by antigen, suggesting that disease may be actively suppressed by autoreactive Th2 cells. These findings shed light on functional aspects of genetically determined susceptibility to autoimmunity, and should lead to new therapeutic approaches aimed at controlling the differentiation of autoreactive CD4+ effector T cells in vivo.

Genetic analysis of immune dysfunction in non-obese diabetic (NOD) mice: mapping of a susceptibility locus close to the Bcl-2 gene correlates with increased resistance of NOD T cells to apoptosis induction

The non-obese diabetic (NOD) mouse strain provides a remarkable model for investigating the mechanisms of autoimmunity. Independent genetic analyses of this model have previously shown that chromosome 1-linked loci were involved in the control of periinsulitis and sialitis on the one hand and of insulitis and diabetes on the other hand. In the present work, analysis of a [NOD x (NOD x C57BL/6)F1] backcross progeny allowed us to clearly dissociate two genetic regions: one was associated with periinsulitis and mapped to the middle region of chromosome 1, in the vicinity of the Bcl-2 gene; the other was associated with insulitis and mapped to the proximal part of the chromosome. Three intermediate markers D1Mit18, D1Mit5 and D1Mit19 covering at least 25 centiMorgans between these two regions, were associated with neither periinsulitis nor insulitis. The role of the Bcl-2-linked region in the immune anomalies of NOD mice was further investigated in a (NOD x C57BL/6)F2 cross where the Bcl-2nod haplotype was linked to elevated serum levels of IgG (p < 0.0005). The middle region of chromosome 1 is, therefore, involved in the control of three phenotypes, including periinsulitis, sialitis and hyperIgG, pointing to Bcl-2 as a good candidate for a cause of the NOD mouse disease. Consistent with the anti-apoptotic function of the Bcl-2 gene product, activated T lymphocytes from NOD mice showed a markedly increased resistance to induction of apoptosis following deprivation of interleukin-2 when compared to those from non-autoimmune strains. After the recent observation of the Fas gene alterations in the lpr and lprcg mutations, these findings indicate that deregulation of lymphoid cell apoptosis may be a general pathogenetic mechanism in autoimmune diseases.

Determinant capture as a possible mechanism of protection afforded by major histocompatibility complex class II molecules in autoimmune disease

How peptide-major histocompatibility complex (MHC) class II complexes are naturally generated is still unknown, but accumulating evidence suggests that unfolding proteins or long peptides can become bound to class II molecules at the dominant determinant before proteolytic cleavage. We have compared the immunogenicity of hen egg-white lysozyme (HEL) in nonobese diabetic (NOD), (NOD x BALB/c)F1, and E(d) alpha transgenic NOD mice. We find that a response to the subdominant ANOD-restricted determinant disappears upon introduction of an E(d) molecule, and is restored when scission of HEL separates this determinant from its adjoining, competitively dominant, E(d)-restricted determinant. This suggests that the E(d) molecule binds and protects its dominant determinant on a long peptide while captured neighboring determinants are lost during proteolysis. These results provide clear evidence for "determinant capture" as a mechanism of determinant selection during antigen processing and a possible explanation for MHC-protective effects in insulin-dependent diabetes mellitus.

An Abd transgene prevents diabetes in nonobese diabetic mice by inducing regulatory T cells

Susceptibility to the human autoimmune disease insulin-dependent diabetes mellitus is strongly associated with particular haplotypes of the major histocompatibility complex (MHC). Similarly, in a spontaneous animal model of this disease, the nonobese diabetic (NOD) mouse, the genes of the MHC play an important role in the development of diabetes. We have produced transgenic NOD mice that express the class II MHC molecule I-Ad in addition to the endogenous I-Ag7 molecules in order to study the role of these molecules in the disease process. Although the inflammatory lesions within the islets of Langerhans in the pancreas appear similar in transgenic and nontransgenic animals, transgenic mice develop diabetes with greatly diminished frequency compared to their nontransgenic littermates (10% of transgenic females by 30 weeks of age compared to 45% of nontransgenic females). Furthermore, adoptive transfer experiments show that T cells present in the transgenic mice are able to interfere with the diabetogenic process caused by T cells from nontransgenic mice. Thus, the mechanism by which I-Ad molecules protect mice from diabetes includes selecting in the thymus and/or inducing in the periphery T cells capable of inhibiting diabetes development.

Characterizations of candidate genes for IDD susceptibility from the diabetes-prone NOD mouse strain

The nucleotide sequences of the NOD and C57BL/6J alleles of Glut-2, Sod-2, and Il-2 were determined by RT-PCR sequencing. Each of these loci is located in intervals that strongly correlated with susceptibility to diabetes in an (NOD/Uf x C57BL/6J)F1 x NOD/Uf backcross. No significant variations in the alleles of Glut-2 at 16 cM on Chromosome (Chr) 3 or Sod-2 at 8 cM on Chr 17 were detected. However, the Il-2 allele in NOD at 20 cM on Chr 3 was found to differ from that in C57BL/6J by a complex mutation involving the contraction of a simple sequence repeat (SSR). Il-2 in NOD differs from the allele in C57BL/6J via a complex mutation involving a deletion of four CAG codons from the SSR together with a length-compensatory four-codon duplication of a segment 5' from the SSR. Two nonsynonymous mutations in the coding region 5' to the SSR were also detected. Only these two allelic forms of Il-2 were detected in a survey of 13 standard inbred lines and 4 wild mouse strains. We propose to designate these alleles as Il-2a (for alleles such as C57BL/6J that contain 12 CAG repeats) and Il-2b (for alleles such as NOD), which occurred in a variety of standard inbred strains and in all four wild Mus musculus domesticus tested. The distribution of these Il-2 alleles among inbred strains correlated with the detection of Chr 3 as an interval effecting diabetes susceptibility in three separate genetic crosses.(ABSTRACT TRUNCATED AT 250 WORDS)

I-E+ nonobese diabetic mice develop insulitis and diabetes

The development of type I diabetes in the nonobese diabetic (NOD) mouse is under the control of multiple genes, one or more of which is linked to the major histocompatibility complex (MHC). The MHC class II region has been implicated in disease development, with expression of an I-E transgene in NOD mice shown to provide protection from insulitis and diabetes. To examine the effect of expressing an I-E+ or I-E- non-NOD MHC on the NOD background, three I-E+ and three I-E- NOD MHC congenic strains (NOD.H-2i5, NOD.H-2k, and NOD.H-2h2, and NOD.H-2h4, NOD.H-2i7, and NOD.H-2b, respectively) were developed. Of these strains, both I-E+ NOD.H-2h2 and I-E- NOD.H-2h4 mice developed insulitis, but not diabetes. The remaining four congenic strains were free of insulitis and diabetes. These results indicate that in the absence of the NOD MHC, diabetes fails to develop. Each NOD MHC congenic strain was crossed with the NOD strain to produce I-E+ and I-E- F1 mice; these mice thus expressed one dose of the NOD MHC and one dose of a non-NOD MHC on the NOD background. While a single dose of a non-NOD MHC provided a large degree of disease protection to all of the F1 strains, a proportion of I-E+ and I-E- F1 mice aged 5-12 mo developed insulitis and cyclophosphamide-induced diabetes. When I-E+ F1 mice were aged 9-17 mo, spontaneous diabetes developed as well. These data are the first to demonstrate that I-E+ NOD mice develop diabetes, indicating that expression of I-E in NOD mice is not in itself sufficient to prevent insulitis or diabetes. In fact, I-E- F1 strains were no more protected from diabetes than I-E+ F1 strains, suggesting that other non-NOD MHC-linked genes are important in protection from disease. Finally, transfer of NOD bone marrow into irradiated I-E+ F1 recipients resulted in high incidences of diabetes, indicating that expression of non-NOD MHC products in the thymus, in the absence of expression in bone marrow-derived cells, is not sufficient to provide protection from diabetes.

Linkage on chromosome 3 of autoimmune diabetes and defective Fc receptor for IgG in NOD mice

A congenic, non-obese diabetic (NOD) mouse strain that contains a segment of chromosome 3 from the diabetes-resistant mouse strain B6.PL-Thy-1a was less susceptible to diabetes than NOD mice. A fully penetrant immunological defect also mapped to this segment, which encodes the high-affinity Fc receptor for immunoglobulin G (IgG), Fc gamma RI. The NOD Fcgr1 allele, which results in a deletion of the cytoplasmic tail, caused a 73 percent reduction in the turnover of cell surface receptor-antibody complexes. The development of congenic strains and the characterization of Mendelian traits that are specific to the disease phenotype demonstrate the feasibility of dissecting the pathophysiology of complex, non-Mendelian diseases.

Genetic analysis of diabetes and insulitis in an interspecific cross of the nonobese diabetic mouse with Mus spretus

The nonobese diabetic (NOD) mouse is a widely used model for genetic studies of insulin-dependent diabetes mellitus due to the similarities between the murine and human diseases. To aid in the localization and identification of diabetes-related susceptibility genes, we have constructed an interspecific backcross between NOD and Mus spretus (SEG/Pas) mice. Although no diabetic animals were observed in the first backcross generation of (SEG/Pas x NOD) x NOD (BC1), the incidence of insulitis (lymphocyte infiltration of the islets of Langerhans) exceeded 20% after injections of cyclophosphamide, a treatment that provokes an acute form of diabetes in NOD mice. Insulitis, a prediabetic condition, is a useful phenotype in studies of diabetes susceptibility. In the second backcross (BC2) generation, 8% of the animals became diabetic and 76% were found to have insulitis. Genetic mapping studies in the BC2 families confirmed the importance of the major histocompatibility complex region on the severity of insulitis and suggested that additional susceptibility loci were linked to markers on mouse chromosomes 3, 6, and 15. Mus spretus crosses have been an important tool in recent advances in murine genetics, and our results extend their usefulness to the study of a multifactorial disease.

Short-term administration of anti-L3T4 MoAb prevents diabetes in NOD mice

We treated 2-week-old and 8-week-old non-obese diabetic (NOD) mice with 1 mg of anti-L3T4 MoAb weekly for 4 weeks. This short-term treatment of anti-L3T4 MoAb prevented the development of overt diabetes in NOD mice, in both groups, even after cessation of the therapy. However, there were overt mononuclear cell infiltrations in the majority of islets, and no appreciable differences in the degree of insulitis between treated and control mice. There were also no significant differences in the percentage of L3T4+ T cells expressing V beta 5, V beta 8 and V beta 11 antigens between the treated and the control group. In contrast, most of the male NOD mice injected with 200 mg/kg of cyclophosphamide did not become diabetic when the spleen cells from the MoAb-treated female NOD mice were transferred to these animals 48 h before the cyclophosphamide injection. Thus, the tolerance induced by the short-term administration of anti-L3T4 MoAb to NOD mice may not be due to clonal deletion, but rather to newly generated suppressor cells in the animals.

Insulin-dependent diabetes in the NOD mouse model. I. Detection and characterization of autoantibody bound to the surface of pancreatic beta cells prior to development of the insulitis lesion in prediabetic NOD mice

Type I, insulin-dependent diabetes (IDD) results from an autoimmune response against the insulin producing pancreatic beta cells. This autoimmune reaction involves both humoral and cell-mediated factors; nevertheless, the relative role of each remains unresolved. Furthermore, while adoptive transfer experiments have provided evidence for the role of T cells in beta cell destruction, the specific events which initiate leukocyte migration into the islets (insulitis) are unknown. Earlier studies indicated that NOD pancreatic beta cells may bind small amounts of autoantibody. Because of the possible importance of an early humoral response to the initiation of insulitis and subsequent disease, we have investigated a number of aspects of this phenomenon to determine the nature and specificity of the early autoantibodies as well as the time at which autoantibody binds to beta cells. Results of this study demonstrate that NOD/Uf mice are sensitized to islet-cell associated antigens, including GAD, prior to the first appearance of insulitis; that a small percentage of the beta cells of NOD/Uf mice have autoantibody bound to their surface prior to insulitis; that sera collected from preinsulitis NOD/Uf mice contain autoantibodies which will bind to beta cells of both IDD-prone and IDD-resistant mice; and that the autoantibodies which bind pancreatic beta cells are predominantly IgM with lesser amounts of IgG and IgA. These findings suggest that, in the natural course of IDD, insulitis may develop in response to an initial autoantibody-mediated injury of beta cells.

The effect of cyclophosphamide treatment on lymphocyte subsets in the nonobese diabetic mouse: a comparison of various lymphoid organs

The nonobese diabetic (NOD) mouse is a model for human Type 1 diabetes mellitus. Pancreatic beta-cell destruction in NOD mice is mediated by an autoimmune process which can be accelerated by cyclophosphamide (CP). We studied the phenotype of lymphocytes from central, peripheral and regional lymphoid tissues in prediabetic NOD and C3H mice before and after a single large dose of CP. All lymphoid organs showed a greatly diminished cell number and most alterations appeared early after CP and were transient, but an aggressive insulitis was not seen in NOD mice until 14 d after injection. The pancreatic islets in C3H mice remained intact and were not infiltrated. NOD female mice, which are most prone to spontaneous and CP-induced diabetes, exhibited the most unusual lymphoid kinetics after treatment with CP. Their thymus and spleen showed the least relative drop in total cell number and the most rapid rate of recovery. The thymus of these mice was also found to have an increased proportion of CD3+ thymocytes while CD4/CD8 double positive thymocytes decreased 7 d after CP. At 14 d after CP the number of IL-2R+ thymocytes had surpassed that of normal levels. The most dramatic observation was the rapid recovery and overshoot in the number of pancreatic lymph node cells of female NOD mice which coincided with aggressive insulitis.

Analysis of VH gene utilisation in the non-obese diabetic mouse

The immunoglobulin (Ig) heavy chain variable (VH) gene complexity and the VH gene utilisation pattern of the non-obese diabetic (NOD) mouse were investigated. We found that the NOD mouse displays a VH gene complexity which appears to be identical to that of the C57BL/6 mouse. Thus, Southern hybridisation using probes specific for 9 of the murine VH gene families revealed identical restriction fragment length polymorphism (RFLP) patterns in both mouse strains. As indicated by immunofluorescence analysis using allotype specific monoclonal antibodies the NOD mice were also found to carry the IgCH-1b allele. Collectively, these data suggest that the NOD mice carry an IgVH locus identical to that carried by C57BL/6. In contrast to the apparent identity at the level of germline VH gene repertoires, the pattern of VH gene utilisation differed considerably between these two mouse strains. Thus, in NOD mice the neonatal preference of D-proximal VH genes was found to be more pronounced than in C57BL/6 mice. Moreover, in contrast to adult C57BL/6 mice a D-proximal bias was evident also in adult NOD mice. On the basis of these findings we discuss the possibility that the distorted development of B cell repertoires in the NOD mouse could be directly or indirectly related to the T cell mediated, autoimmune process in the NOD mouse.

Type 1 diabetes mellitus: an imbalance between effector and regulatory T cells?

Abundant evidence now exists that autoimmunity plays a critical role in the pathogenesis of type 1 (insulin-dependent) diabetes mellitus. The non-obese diabetic (NOD) mouse is an extensively studied animal model of this T-cell-mediated autoimmune disease. Our laboratory has focused on isolating diabetogenic T cell clones from NOD mice as a means of elucidating the pathogenesis of type 1 diabetes. This experimental approach presupposes that type 1 diabetes in NOD mice results from the action of islet-reactive T cells that are not present in other mouse strains; the diabetogenic T cells would therefore represent "forbidden clones" which exist in NOD mice as a result of a failure of clonal deletion. While the inappropriate presence of diabetogenic T cells probably plays a central role in murine diabetes, it cannot explain all aspects of the disease. Type 1 diabetes is a chronic disorder with a lengthy preclinical stage; if the diabetogenic T cells acted in an unopposed fashion, one might expect to see a much more fulminant clinical course. This observation suggests that regulatory influences are likely to exist in this disease--a possibility supported by recent experimental data. If these regulatory influences could be identified and enhanced, specific immunotherapy for type 1 diabetes could be achieved.

T-cell subsets in autoimmunity

The demonstration that functionally different T-cell subsets can be defined by the isoforms of the leukocyte-common antigen, CD45, that they express, has prompted studies on the roles of these subsets in autoimmunity. The results have led to the identification of a particular subset of CD4+ T cells that have the ability to inhibit autoimmune disease. Further, it has been shown that diabetes in the B-B rat can be transferred by in vitro activation of T cells by Staphylococcal enterotoxin suggesting that superantigens may play a role in the pathogenesis of this disease. However, in this system too, it appears that a subset of T cells can inhibit the induction of autoaggressive cells. In other experimental autoimmune diseases there is evidence that CD8+ T cells can be protective and that these cells may mediate this protection by the synthesis of transforming growth factor-beta.