Direct evidence for the contribution of the unique I-ANOD to the development of insulitis in non-obese diabetic mice

Grafts of supplementary thymuses injected with allogeneic pancreatic islets protect nonobese diabetic mice against diabetes

In nonobese diabetic (NOD) mice, the autoimmune attack of the beta-cells in pancreatic islets is now believed to result from abnormal thymic selection. Accordingly, grafts of thymic epithelium from NOD donors to athymic recipients promote autoimmune islet inflammation in normal strains, and intrathymic islet grafts decrease the incidence of disease in NOD animals. Two competing hypotheses of abnormal thymic selection in diabetic mice have been proposed: deficient negative selection with poor elimination of aggressive organ-specific T cells vs. deficient positive selection of protective T regulatory cells. We have now addressed these alternatives by grafting, into young NOD mice whose own thymus was left intact, newborn NOD thymuses containing allogeneic pancreatic islets. If the NOD defect represented poor negative selection, these animals would develop disease at control rates, as the generation of autoreactive T cells proceeds undisturbed in the autologous thymus. In contrast, if NOD thymuses are defective in the production of T regulatory cells, lower disease incidence is expected in the chimeras, as more protective cells can be produced in the grafted thymus. The results show a reduced incidence of diabetes in the chimeras (24%) as compared with control (72%) NOD mice, throughout adult life. We conclude that amelioration of NOD mice by intrathymic islet grafts is not caused by enhanced negative selection and suggest that autoimmune diabetes in this system is the result of inefficient generation of T regulatory cells in the thymus.

Understanding autoimmune diabetes: insights from mouse models

Type 1 or insulin-dependent diabetes is an autoimmune disease that causes the selective destruction of insulin-secreting beta cells in the pancreatic islets. Although this is a polygenic disease, with at least 20 genes implicated, the dominant susceptibility locus maps to the major histocompatibility complex (MHC), both in humans and in rodent models. However, in spite of progress on several fronts, the molecular pathology of autoimmune diabetes remains incompletely defined. Major areas of research include environmental trigger factors, the identification and role of beta-cell antigens in inducing and maintaining the autoimmune response, and the nature of the pathogenic and protective lymphocytes involved. In this review, we will focus on these areas to highlight recent advances in understanding the pathogenesis of autoimmune diabetes, drawing extensively on insights gained by studying the non-obese diabetic (NOD) mouse.

Genetic control of T and B lymphocyte activation in nonobese diabetic mice

Type 1 diabetes in nonobese diabetic (NOD) mice is characterized by the infiltration of T and B cells into pancreatic islets. T cells bearing the TCR Vbeta3 chain are disproportionately represented in the earliest stages of islet infiltration (insulitis) despite clonal deletion of most Vbeta3(+) immature thymocytes by the mammary tumor virus-3 (Mtv-3) superantigen (SAg). In this report we showed that a high frequency of NOD Vbeta3(+) T cells that escape deletion are activated in vivo and that this phenotype is linked to the Mtv-3 locus. One potential mechanism of SAg presentation to peripheral T cells is by activated B cells. Consistent with this idea, we found that NOD mice harbor a significantly higher frequency of activated B cells than nondiabetes-prone strains. These activated NOD B cells expressed cell surface molecules consistent with APC function. At the molecular level, the IgH repertoire of activated B cells in NOD mice was equivalent to resting B cells, suggesting a polyclonal response in vivo. Genetic analysis of the activated B cell phenotype showed linkage to Idd1, the NOD MHC haplotype (H-2(g7)). Finally, Vbeta3(+) thymocyte deletion and peripheral T cell activation did not require B cells, suggesting that other APC populations are sufficient to generate both Mtv-3-linked phenotypes. These data provide insight into the genetic regulation of NOD autoreactive lymphocyte activation that may contribute to failure of peripheral tolerance and the pathogenesis of type I diabetes.

IL-12 administration reveals diabetogenic T cells in genetically resistant I-Ealpha-transgenic nonobese diabetic mice: resistance to autoimmune diabetes is associated with binding of Ealpha-derived peptides to the I-A(g7) molecule

Nonobese diabetic (NOD) and NOD-DRalpha transgenic (tg) mice, expressing Aalpha(d):Abeta(g7) and Aalpha(d):Abeta(g7) plus DRalpha:Ebeta(g7) class II molecules, respectively, both develop insulin-dependent diabetes mellitus (IDDM), whereas NOD-Ealpha tg mice expressing Aalpha(d):Abeta(g7) plus Ealpha:Ebeta(g7) are protected. We show that IL-12 administration induces rapid IDDM onset in NOD-DRalpha but fails to provoke insulitis and diabetes in NOD-Ealpha tg mice. Nevertheless, T cells from IL-12-treated NOD-Ealpha tg mice secrete IFN-gamma and transfer IDDM to NOD-SCID and NOD-Ealpha-SCID recipients, demonstrating the presence of peripheral diabetogenic Th1 cells in the protected mice. Surprisingly, regulatory cells were undetectable. Moreover, Ealpha:Ebeta(g7) could substitute for DRalpha:Ebeta(g7) in Ag presentation, arguing against mechanisms of protection involving capture of diabetogenic I-A(g7)-restricted epitopes by Ealpha:Ebeta(g7)molecules. Interestingly, the expression of naturally processed epitopes derived from DRalpha- and Ealpha-chains bound to I-A(g7) is different in the two strains of tg mice, and the difference is enhanced by IL-12 administration. I-A(g7) molecules from both NOD-DRalpha and NOD-Ealpha tg mice present the conserved DRalpha/Ealpha 52-68 sequence, at high and low levels, respectively. In addition, only IDDM-resistant NOD-Ealpha tg mice possess APCs bearing Ealpha65-77/I-A(g7) complexes, which tolerize the specific T cells. This is associated with the selective inhibition of the response to insulinoma-associated protein 2 (IA-2), an autoantigen in IDDM. Our results support protective mechanisms based on I-A(g7) blockade by peptides unique to the Ealpha-chain, such as Ealpha65-77 and/or tolerance of diabetogenic T cells cross-reactive with Ealpha-peptide/I-A(g7) complexes.

Inhibition of autoimmune diabetes in nonobese diabetic mice by transgenic restoration of H2-E MHC class II expression: additive, but unequal, involvement of multiple APC subtypes

Transgenic restoration of normally absent H2-E MHC class II molecules on APC dominantly inhibits T cell-mediated autoimmune diabetes (IDDM) in nonobese diabetic (NOD) mice. We analyzed the minimal requirements for transgenic H2-E expression on APC subtypes (B lymphocytes vs macrophages/dendritic cells (DC)) to inhibit IDDM. This issue was addressed through the use of NOD stocks transgenically expressing high levels of H2-E and/or made genetically deficient in B lymphocytes in a series of genetic intercross and bone marrow/lymphocyte chimera experiments. Standard (H2-E(null)) NOD B lymphocytes exert a pathogenic function(s) necessary for IDDM. However, IDDM was inhibited in mixed chimeras where H2-E was solely expressed on all B lymphocytes. Interestingly, this resistance was abrogated when even a minority of standard NOD H2-E(null) B lymphocytes were also present. In contrast, in NOD chimeras where H2-E expression was solely limited to approximately half the macrophages/DC, an active immunoregulatory process was induced that inhibited IDDM. Introduction of a disrupted IL-4 gene into the NOD-H2-E transgenic stock demonstrated that induction of this Th2 cytokine does not represent the IDDM protective immunoregulatory process mediated by H2-E expression. In conclusion, high numbers of multiple subtypes of APC must express H2-E MHC class II molecules to additively inhibit IDDM in NOD mice. This raises a high threshold for success in future intervention protocols designed to inhibit IDDM by introduction of putatively protective MHC molecules into hemopoietic precursors of APC.

Multiple sclerosis associated amino acids of polymorphic regions relevant for the HLA antigen binding are confined to HLA-DR2

Among the candidate genes for multiple sclerosis (MS), the strongest influence is conferred by human leucocyte antigen (HLA) class II genes, in particular the DR2, DQ6, Dw2 haplotype (DRB1*1501, DQA1*0102, DQB1*0602). Similar to other autoimmune diseases, it is not clear yet how the presence of a specific HLA-DR or -DQ molecule translates into an increased disease susceptibility. Previous observations by us and others imply a HLA-DR2 dependent propensity of antigen-specific T-cell lines to produce increased amounts of TNF-alpha/beta as one mechanism how DR2 could contribute to susceptibility. In this article, we investigated the distribution of polymorphic stretches of the DRB1, DQA1, and DQB1 chains known to be relevant for antigen binding, in 66 unrelated patients with relapsing remitting MS and 210 unrelated controls. We found a significant association with disease for the appearance of proline at position 11, arginine at position 13, and alanine at position 71 of HLA-DRbeta1. Surprisingly, we identified only residues preferentially expressed in the MS group that were related to HLA-DR2. Thus, the contribution of HLA class II to the pathogenesis of MS is not mediated by allele-overlapping antigen binding sites, but is confined to the disease associated HLA allele.

The I-Ag7 MHC class II molecule linked to murine diabetes is a promiscuous peptide binder

Susceptibility to insulin-dependent diabetes mellitus is linked to MHC class II genes. The only MHC class II molecule expressed by nonobese diabetic (NOD) mice, I-Ag7, shares a common alpha-chain with I-Ad but has a peculiar beta-chain. As with most beta-chain alleles linked to diabetes susceptibility, I-Ag7 contains a nonaspartic residue at position beta57. We have produced large amounts of empty I-Ag7 molecules using a fly expression system to characterize its biochemical properties and peptide binding by phage-displayed peptide libraries. The identification of a specific binding peptide derived from glutamic acid decarboxylase (GAD65) has allowed us to crystallize and obtain the three-dimensional structure of I-Ag7. Structural information was critical in evaluating the binding studies. I-Ag7, like I-Ad, appears to be very promiscuous in terms of peptide binding. Their binding motifs are degenerate and contain small and/or small hydrophobic residues at P4 and P6 of the peptide, a motif frequently found in most globular proteins. The degree of promiscuity is increased for I-Ag7 over I-Ad as a consequence of a larger P9 pocket that can specifically accommodate negatively charged residues, as well as possibly residues with bulky side chains. So, although I-Ad and I-Ag7 are structurally closely related, stable molecules and good peptide binders, they differ functionally in their ability to bind significantly different peptide repertoires that are heavily influenced by the presence or the absence of a negatively charged residue at position 57 of the beta-chain. These characteristics link I-Ag7 with autoimmune diseases, such as insulin-dependent diabetes mellitus.

A self MHC class II beta-chain peptide prevents diabetes in nonobese diabetic mice

We explored T cell responses to the self class II MHC (I-Ag7) beta-chain-derived peptides in diabetic and prediabetic nonobese diabetic (NOD) mice. We found that one of these immunodominant epitopes of the beta-chain of I-Ag7 molecule, peptide 54-76, could regulate autoimmunity leading to diabetes in NOD mice. T cells from prediabetic young NOD mice do not respond to the peptide 54-76, but T cells from diabetic NOD mice proliferated in response to this peptide. T cells from older nondiabetic mice or mice protected from diabetes do not respond to this peptide, suggesting a role for peptide 54-76-specific T cells in pathogenesis of diabetes. We show that this peptide is naturally processed and presented by the NOD APCs to self T cells. However, the peptide-specific T cells generated after immunization of young mice regulate autoimmunity in NOD mice by blocking the diabetogenic cells in adoptive transfer experiments. The NOD mice immunized with this peptide are protected from both spontaneous and cyclophosphamide-induced insulin-dependent diabetes mellitus. Immunization of young NOD mice with this peptide elicited T cell proliferation and production of Th2-type cytokines. In addition, immunization with this peptide induced peptide-specific Abs of IgG1 isotype that recognized native I-Ag7 molecule on the cell surface and inhibited the T cell proliferative responses. These results suggest that I-Abetag7(54-76) peptide-reactive T cells are involved in the pathogenesis of diabetes. However, immunization with this peptide at young age induces regulatory cells and the peptide-specific Abs that can modulate autoimmunity in NOD mice and prevent spontaneous and induced diabetes.

Identification of a CD8 T cell that can independently mediate autoimmune diabetes development in the complete absence of CD4 T cell helper functions

Previous work has indicated that an important component for the initiation of autoimmune insulin-dependent diabetes mellitus (IDDM) in the NOD mouse model entails MHC class I-restricted CD8 T cell responses against pancreatic beta cell Ags. However, unless previously activated in vitro, such CD8 T cells have previously been thought to require helper functions provided by MHC class II-restricted CD4 T cells to exert their full diabetogenic effects. In this study, we show that IDDM development is greatly accelerated in a stock of NOD mice expressing TCR transgenes derived from a MHC class I-restricted CD8 T cell clone (designated AI4) previously found to contribute to the earliest preclinical stages of pancreatic beta cell destruction. Importantly, these TCR transgenic NOD mice (designated NOD.AI4alphabeta Tg) continued to develop IDDM at a greatly accelerated rate when residual CD4 helper T cells were eliminated by introduction of the scid mutation or a functionally inactivated CD4 allele. In a previously described stock of NOD mice expressing TCR transgenes derived from another MHC class I-restricted beta cell autoreactive T cell clone, IDDM development was retarded by elimination of residual CD4 T cells. Hence, there is variability in the helper dependence of CD8 T cells contributing to the development of autoimmune IDDM. The AI4 clonotype represents the first CD8 T cell with a demonstrated ability to progress from a naive to functionally activated state and rapidly mediate autoimmune IDDM development in the complete absence of CD4 T cell helper functions.

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.

The role of MHC class II molecules in susceptibility to type I diabetes: identification of peptide epitopes and characterization of the T cell repertoire

Susceptibility to type I diabetes is linked to class II MHC alleles in both mouse and man. However, the molecular mechanisms by which MHC molecules mediate disease susceptibility are unknown. To analyze how I-A alleles predispose to, or prevent, the development of type I diabetes, we have chosen, as the first step, to investigate the immune response to an important islet cell protein in diabetes-susceptible and diabetes-resistant mice. MHC class II alleles conferring susceptibility and resistance to diabetes select completely different sets of immunogenic epitopes from the beta islet cell autoantigen glutamic acid decarboxylase 65. Peptide-binding studies, analysis of MHC restriction, and immunization with these peptide epitopes indicate that the two amino acid substitutions within the I-A(beta) chain that distinguish a diabetes-susceptibility from a diabetes-resistance allele are sufficient to alter peptide binding and MHC restriction and may also influence antigen presentation and the selection of the T cell repertoire. The data indicate that the molecular mechanisms for class II-mediated selection of immunodominant epitopes are complex and differ for each individual peptide epitope. Further study of the functional characteristics of the response to these epitopes should provide insight into mechanisms of MHC-mediated diabetes susceptibility.

A Peptide Binding Motif for I-Eg7, the MHC Class II Molecule That Protects Eα-Transgenic Nonobese Diabetic Mice from Autoimmune Diabetes

The nonobese diabetic (NOD) mouse, a model of spontaneous insulin-dependent diabetes mellitus (IDDM), fails to express surface MHC class II I-Eg7 molecules due a deletion in the Eα gene promoter. Eα-transgenic NOD mice express the EαEβg7 dimer and fail to develop either insulitis or IDDM. A number of hypotheses have been proposed to explain the mechanisms of protection, most of which require peptide binding to I-Eg7. To define the requirements for peptide binding to I-Eg7, we first identified an I-Eg7-restricted T cell epitope corresponding to the sequence 4–13 of Mycobacterium tuberculosis 65-kDa heat shock protein (hsp). Single amino acid substitutions at individual positions revealed a motif for peptide binding to I-Eg7 characterized by two primary anchors at relative position (p) 1 and 4, and two secondary anchors at p6 and p9. This motif is present in eight of nine hsp peptides that bind to I-Eg7 with high affinity. The I-Eg7 binding motif displays a unique p4 anchor compared with the other known I-E motifs, and major differences are found between I-Eg7 and I-Ag7 binding motifs. Analysis of peptide binding to I-Eg7 and I-Ag7 molecules as well as proliferative responses of draining lymph node cells from hsp-primed NOD and Eα-transgenic NOD mice to overlapping hsp peptides revealed that the two MHC molecules bind different peptides. Of 80 hsp peptides tested, none bind with high affinity to both MHC molecules, arguing against some of the mechanisms hypothesized to explain protection from IDDM in Eα-transgenic NOD mice.

Dissecting the role of CD4+ T cells in autoimmune diabetes through the use of TCR transgenic mice

Insulin-dependent diabetes mellitus (IDDM) is an immunological disorder wherein autoimmune-mediated destruction of islet cells in the pancreas results in persistent hyperglycemia. The non-obese diabetic mouse model of IDDM has revealed the importance of multiple factors that impact upon the disease process; however, understanding of primary immune mechanisms leading to IDDM remains elusive. The emergence of transgenic mouse models for IDDM has made important contributions towards clarifying many of these factors, including the cell types, the various effector molecules and the genetic elements involved in the pathogenesis of IDDM. In this review, we will focus on the primary mechanism and mediators of islet beta-cell death, the impact of T-helper lymphocytes on disease progression and the potential role of major histocompatibility complex class II molecules in conferring susceptibility to IDDM.

Analysis of MHC Class II Genes in the Susceptibility to Lupus in New Zealand Mice

Hybrids of New Zealand Black (NZB) and New Zealand White (NZW) mice spontaneously develop a disease similar to human systemic lupus erythematosus. MHC and non-MHC genes contribute to disease susceptibility in this murine model. Multiple studies have shown that the NZW H2z locus is strongly associated with the development of lupus-like disease in these mice. The susceptibility gene(s) within H2z is not known, but different lines of evidence have pointed to class II MHC genes, either H2-E or H2-A (Ez or Az in NZW). Recent studies from our laboratory showed that Ez does not supplant H2z in the contribution to lupus-like disease. In the present work we generated C57BL/10 (B10) mice transgenic for Aaz and Abz genes (designated B10.Az mice) and used a (B10.Az × NZB)F1 × NZB backcross to assess the contributions of Az genes to disease. A subset of backcross mice produced high levels of IgG autoantibodies and developed severe nephritis. However, no autoimmune phenotype was linked to the Az transgenes. Surprisingly, in the same backcross mice, inheritance of H2b from the nonautoimmune B10 strain was strongly linked with both autoantibody production and nephritis. Taken together with our previous Ez studies, the present work calls into question the importance of class II MHC genes for lupus susceptibility in this model and provides new insight into the role of MHC in lupus-like autoimmunity.

Inhibition of thymocyte positive selection by natural MHC: peptide ligands

The 3A9 transgenic mouse line carries the rearranged TCR genes from a T cell hybridoma that recognizes hen egg lysozyme peptide 46-61 in the context of MHC class II Ak molecules. As expected, positive selection of immature 3A9 thymocytes to become mature CD4+ 8- T cells was efficient on the "selecting" CBA (H-2k) genetic background but not on the "non-selecting" C57BL/6 (H-2b) background. Surprisingly, positive selection was also inefficient on the CBA x C57BL/6 F1 background (H-2kb). We present evidence that expression of A(beta)b molecules on thymus epithelium (in conjunction with A(alpha)b or A(alpha)k molecules) inhibits the positive selection of 3A9 thymocytes mediated by A(alpha)k:A(beta)k complexes, in a process evocative of peptide antagonism of mature T cells.

The role of MHC class II molecules in susceptibility and resistance to autoimmunity

The mechanism by which particular MHC class II alleles mediate susceptibility to a given autoimmune disease is unknown. During the past year, reports have indicated that the effects of MHC class II alleles which protect against type I diabetes in the nonobese diabetic mouse strain may, in some cases, be due to negative selection of diabetogenic T cell receptors and, in other cases, to positive selection of other T cells with a suppressive action on the diabetic process. Progress towards understanding the mechanisms of susceptibility continues to lag.

Induction of insulitis by glutamic acid decarboxylase peptide-specific and HLA-DQ8-restricted CD4(+) T cells from human DQ transgenic mice

Insulin-dependent diabetes mellitus in humans is linked with specific HLA class II genes, e.g., HLA-DQA1*0301/ DQB1*0302 (DQ8). To investigate the roles of HLA-DQ8 molecules and glutamic acid decarboxylase (GAD) in disease development, we generated DQ8(+)/I-Abo transgenic mice expressing functional HLA-DQ8 molecules and devoid of endogenous mouse class II. DQ8(+)/I-Abo mice produced antigen-specific antibodies and formed germinal centers after immunization with GAD65 peptides. Two GAD peptide-specific (247-266 and 509-528), DQ8 restricted Th1 CD4(+) T cell lines, were generated from immunized DQ8(+)/I-Abo mice. They induced severe insulitis after adoptive transfer into transgene positive (but not negative) mice who were treated with a very low dose of streptozotocin that alone caused no apparent islet pathology. In addition to CD4, islet mRNA from these mice also showed expression of CD8, IFNgamma, TNFalpha, Fas, and Fas ligand. Our data suggest that a mild islet insult in the presence of HLA-DQ8 bearing antigen-presenting cells promotes infiltration of GAD peptide reactive T cells into the islet.

Characterization of self-glutamic acid decarboxylase 65-reactive CD4+ T-cell clones established from Japanese patients with insulin-dependent diabetes mellitus

To investigate autoimmunity to glutamic acid decarboxylase (GAD) 65 in Japanese patients with insulin-dependent diabetes mellitus (IDDM, type I diabetes), we established seven CD4+ T-cell clones, by stimulating peripheral blood mononuclear cells (PBMC) of six IDDM patients, using a mixture of overlapping human GAD65 peptides. No GAD65 autoreactive T-cell clones were evidenced in four healthy controls. Specificities of T-cell clones were as follows: (a) two clones specific to GAD65 p111-131 (residue 111 to 131) + DR53 (DRB4*0103); (b) one clone specific to GAD65 p413-433 + DR1 (DRB1*0101); (c) two clones specific to GAD65 p200-217 + either DR9 (DRB1*0901) or DR8 (DRB1*0802); and (d) two clones specific to GAD65 p368-388 + DP2 (DPA1*01 or 0201-DPB1*0201). Two DR53-restricted and one DR1-restricted T-cell clones, responded to a recombinant human GAD65 protein, and showed cytotoxicity against B lymphoblastoid cell lines pre-pulsed with the peptides. Six T-cell clones exhibited the Th1-like phenotype. Interestingly, two DR53-restricted T-cell clones killed a Fas-deficient B lymphoblastoid cell line, thereby indicating that cytotoxicity was not completely dependent on a Fas-Fas ligand interaction. Thus, the T-cell epitopes were mapped in a limited portion of GAD65 protein, with a tendency to be restricted by disease-associated HLA-DR, but not DQ molecules.

Systemic delivery of interleukin 10 by intramuscular injection of expression plasmid DNA prevents autoimmune diabetes in nonobese diabetic mice

We previously demonstrated that intramuscular plasmid injection serves as a useful method of long-term systemic delivery of cytokines. In the present study, we assess intramuscular DNA injection as a means of systemically delivering interleukin 10 (IL-10), a cytokine with immunosuppressive properties, and preventing the progression of autoimmune diabetes in the nonobese diabetic (NOD) mouse, an excellent model for human insulin-dependent diabetes mellitus (IDDM). We injected IL-10 expression plasmid (pCAGGS-IL10) or a control pCAGGS plasmid into the muscles of NOD mice twice at 3 and 5 weeks of age. IL-10 was detectable by ELISA in the sera of mice injected with pCAGGS-IL10 for more than 2 weeks after the injection. Although the severity of insulitis at 13 weeks of age was not improved by the intramuscular injection of pCAGGS-IL10, the incidence of diabetes was markedly reduced in NOD mice injected with pCAGGS-IL10 as compared with those injected with pCAGGS or as compared with nontreated NOD mice. These results show that the progression of autoimmune diseases in mice can effectively be suppressed by intramuscular DNA injection, and suggest that this method is potentially applicable to the treatment of human autoimmune diseases.

alpha/beta-T cell receptor (TCR)+CD4-CD8- (NKT) thymocytes prevent insulin-dependent diabetes mellitus in nonobese diabetic (NOD)/Lt mice by the influence of interleukin (IL)-4 and/or IL-10

We have previously shown that nonobese diabetic (NOD) mice are selectively deficient in alpha/beta-T cell receptor (TCR)+CD4-CD8- NKT cells, a defect that may contribute to their susceptibility to the spontaneous development of insulin-dependent diabetes mellitus (IDDM). The role of NKT cells in protection from IDDM in NOD mice was studied by the infusion of thymocyte subsets into young female NOD mice. A single intravenous injection of 10(6) CD4-/lowCD8- or CD4-CD8- thymocytes from female (BALB/c x NOD)F1 donors protected intact NOD mice from the spontaneous onset of clinical IDDM. Insulitis was still present in some recipient mice, although the cell infiltrates were principally periductal and periislet, rather than the intraislet pattern characteristic of insulitis in unmanipulated NOD mice. Protection was not associated with the induction of "allogenic tolerance" or systemic autoimmunity. Accelerated IDDM occurs after injection of splenocytes from NOD donors into irradiated adult NOD recipients. When alpha/beta-TCR+ and alpha/beta-TCR- subsets of CD4-CD8- thymocytes were transferred with diabetogenic splenocytes and compared for their ability to prevent the development of IDDM in irradiated adult recipients, only the alpha/beta-TCR+ population was protective, confirming that NKT cells were responsible for this activity. The protective effect in the induced model of IDDM was neutralized by anti-IL-4 and anti-IL-10 monoclonal antibodies in vivo, indicating a role for at least one of these cytokines in NKT cell-mediated protection. These results have significant implications for the pathogenesis and potential prevention of IDDM in humans.

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.

Subcongenic Analysis of the Idd13 Locus in NOD/Lt Mice: Evidence for Several Susceptibility Genes Including a Possible Diabetogenic Role for β2-Microglobulin

Although they share ∼88% of their genome with NOD mice including the H2g7 haplotype, NOR mice remain free of T cell-mediated autoimmune diabetes (IDDM), due to non-MHC genes of C57BLKS/J (BKS) origin. NOR IDDM resistance was previously found to be largely controlled by the Idd13 locus within an ∼24 cM segment on Chromosome 2 encompassing BKS-derived alleles for H3a, B2m, Il1, and Pcna. NOD stocks carrying subcongenic intervals of NOR Chromosome 2 were utilized to more finely map and determine possible functions of Idd13. NOR- derived H3a-Il1 (∼6.0 cM) and Il1-Pcna (∼1.2 cM) intervals both contribute components of IDDM resistance. Hence, the Idd13 locus is more complex than originally thought, since it consists of at least two genes. B2m variants within the H3a-Il1 interval may represent one of these. Monoclonal Ab binding demonstrated that dimerizing with the β2ma (NOD type) vs β2mb isoform (NOR type) alters the structural conformation, but not total expression levels of H2g7 class I molecules (e.g. Kd, Db). β2m-induced alterations in H2g7 class I conformation may partially explain findings from bone marrow chimera analyses that Idd13 modulates IDDM development at the level of non-hematopoietically derived cell types controlling selection of diabetogenic T cells and/or pancreatic β cells targeted by these effectors. Since trans-interactions between relatively common and functionally normal allelic variants may contribute to IDDM in NOD mice, the search for Idd genes in humans should not be limited to functionally defective variants.

Development of an I-Ag7-expressing antigen-presenting cell line: intrinsic molecular defect in compact I-Ag7 dimer generation

Insulin-dependent diabetes mellitus (IDDM) results from chronic, T-cell dependent, autoimmune destruction of the insulin-producing beta-cells in the Langerhans' islets of the pancreas. Non-obese diabetic (NOD) mice spontaneously develop IDDM that resembles human type I diabetes. The susceptibility to diabetes in the NOD strain is a complex polygenic trait that determines a phenotype of immune alterations. The unique MHC class II molecule expressed by NOD mice (I-Ag7) plays a major role in the development of disease. Recently, it has been reported that I-Ag7 molecules generate a lower proportion of compact alphabeta heterodimers, compared to other haplotypes. However, it is not clear whether this reflects an intrinsic defect of this molecule to bind peptide stably or is the result of abnormal processing and/or peptide loading into the I-Ag7 molecule. Our aim was to develop and characterize a suitable antigen-presenting cell (APC) that expressed I-Ag7 in the context of a non-diabetes-prone antigen processing and presentation machinery. Here, we report the generation of a mouse DAP.3 fibroblast cell line (DAP.3Ag7) that constitutively expresses high levels of I-Ag7. Using DAP.3 cells transfected with I-Ag7 or I-Ak, we show that the expression of compact dimers in the same cell type is proportionally less for I-Ag7 molecules than for I-Ak molecules, implying an intrinsic defect of the I-Ag7 molecule as the cause for the low generation of compact dimers. However, DAP.3Ag7 cells are able to process and present antigen, as indicated by I-Ag7-dependent IL-2 production by a GAD67-specific NDO T-cell hybridoma after stimulation with GAD and live, but not fixed, DAP.3Ag7 cells. The IL-2 response to GAD when presented by DAP.3Ag7 was significantly higher than the response to GAD presented by NOD splenocytes. Based on these data, we conclude that the low generations of compact dimers is an intrinsic feature of I-Ag7 molecules and not affected by other genes in the NOD background. The DAP.3Ag7 cell line should be a valuable tool with which to dissect the role of the I-Ag7 molecule in antigen presentation and T-cell activation in NOD mice, which clearly contributes to the development of IDDM.

A mechanism for the major histocompatibility complex-linked resistance to autoimmunity

Certain major histocompatibility complex (MHC) class II haplotypes encode elements providing either susceptibility or dominant resistance to the development of spontaneous autoimmune diseases via mechanisms that remain undefined. Here we show that a pancreatic beta cell-reactive, I-Ag7-restricted, transgenic TCR that is highly diabetogenic in nonobese diabetic mice (H-2(g7)) undergoes thymocyte negative selection in diabetes-resistant H-2(g7/b), H-2(g7/k), H-2(g7/q), and H-2(g7/nb1) NOD mice by engaging antidiabetogenic MHC class II molecules on thymic bone marrow-derived cells, independently of endogenous superantigens. Thymocyte deletion is complete in the presence of I-Ab, I-Ak + I-Ek or I-Anb1 + I-Enb1 molecules, partial in the presence of I-Aq or I-Ak molecules alone, and absent in the presence of I-As molecules. Mice that delete the transgenic TCR develop variable degrees of insulitis that correlate with the extent of thymocyte deletion, but are invariably resistant to diabetes development. These results provide an explanation as to how protective MHC class II genes carried on one haplotype can override the genetic susceptibility to an autoimmune disease provided by allelic MHC class II genes carried on a second haplotype.

Alleviation of insulitis in NOD mice is associated with expression of transgenic MHC E molecules on primary antigen-presenting cells

Major histocompatibility complex (MHC) class II genes are important in the pathogenesis of insulin-dependent diabetes mellitus (IDDM) both in the mouse and in man. The non-obese diabetic (NOD) mouse, which is a good model for human IDDM, has a particular MHC class II with an A complex consisting of A alpha d and the unique A beta g7 chain, as well as an absent E molecule due to a deletion in the Ea promoter region. Transgenic insertion of a functional Ea gene protects against insulitis and diabetes, but when the transgene expression is restricted to certain compartments of the immune system by deleting parts of the promoter region, the protection against insulitis is disrupted. We have analysed three promoter-mutated lines where one lacks expression on B cells and has a reduced expression on approximately 1/3 of the dendritic cells and macrophages (Sma), one lacks thymic cortical expression and has a slightly reduced B-cell expression (delta X), and one lacks expression in the thymic medulla, on macrophages, dendritic cells and about half of the B cells (delta Y). None of these lines is protected against insulitis, but Sma and delta X display a reduced intensity of insulitis, with an average of 10-15% of the islets infiltrated in each mouse, while delta Y resembles non-transgenic mice with 30-35% infiltrated islets. Bone-marrow chimeras between Sma and delta Y mice demonstrate that peripheral cells of Sma origin reduce insulitis significantly when developed in the delta Y host, while insulitis is enhanced when delta Y bone marrow is given to Sma mice. This shows that E expression on the primary antigen-presenting macrophages and dendritic cells is of crucial importance to the alleviation of insulitis.

Analysis of pathogenesis of autoimmune insulitis in NOD mice: adoptive transfer experiments of insulitis in ILI and NOD nude mice

In an effort to study the pathophysiological events in the development of insulitis in NOD mice, we have developed ILI- and NOD-nu/nu mice. ILI mice are a nondiabetic inbred strain but are derived from the same JcI:ICR mouse as NOD mice and share the same H-2 allotype with NOD mice. Splenocytes and CD4+ cells from diabetic NOD mice appeared to transfer insulitis to ILI-nu/nu mice, suggesting that ILI mice already express autoantigen(s) responsible for insulitis. But reciprocal thymic grafts from NOD mice into ILI-nu/ nu mice and those from ILI mice into NOD-nu/nu mice failed to allow the development of insulitis, implying that ILI mice possess neither precursor T cells nor the thymic environment responsible for the development of insulitis. In addition, splenocytes from ILI mice appeared to contain regulatory cells which suppress the development of diabetes but not that of insulitis in NOD mice. The use of these nude mice should provide more information on the products of insulitis-susceptibility genes of NOD mice.

Influence of T lymphocytes and major histocompatibility complex class II genes on diabetes susceptibility in the NOD mouse

Central to the autoimmune pathogenesis of IDDM in NOD mice is the MHC class II region. In all models studied to date, expression of NOD MHC class II genes is essential for disease development suggesting a crucial role for I-ANOD-restricted presentation of autoantigen. Protection has been afforded by transgene incorporation of other non-NOD class II genes and many models have been proposed to account for this effect. It is now clear that protection is not achieved by deletion or permanent silencing of all autoreactive T cell clones. It also appears that expression of these genes is required both intra- and extrathymically. It still remains to be determined what role these genes may have in the various compartments and how the autoreactive cells are held in check in protected NOD transgenic mice. Currently, the most likely explanation is that intrathymic expression of non-NOD class II genes is required for the positive selection of class II-restricted immunoregulatory T cells, while peripheral expression is necessary to bring about the interaction of these cells in a tricellular complex with NOD autoantigen-specific T cells and APCs, so that the response can be deviated to a nonpathogenetic one. Whether this process is active or passive is not known.

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.

L cells expressing DQ molecules of the DR3 and DR4 haplotypes: reactivity patterns with mAbs

cDNAs coding for the HLA class II DR and DQ alpha and beta chains of the diabetogenic haplotypes DR3 and DR4 were introduced into a mammalian expression vector and transfected into L-cell mouse fibroblasts to produce cells expressing individual human class II molecules. Stable L transfectants were generated expressing each of the DR or DQ isotypes of the cis-encoded alpha and beta chains of the DR3 or DR4 haplotypes, as well as the trans-encoded alpha and beta chains of the DQ molecules of the two haplotypes. However, isotype mismatched combinations (DR alpha/DQ beta or DQ alpha/DR beta) did not result in any stable transfectants. The stable DQ L-cell transfectants obtained, along with homozygous B-cell lines expressing the DQ2 and DQ8 specificities, were tested against a large panel of twentyone anti-HLA class II monoclonal antibodies (mAbs). Their unusual reactivity patterns are described including the failure of most "pan-DQ" mAbs to react with all DQ expressing L-cell transfectants. Interestingly, some mAbs react with certain alpha beta heterodimers expressed on B-LCL but fail to recognize the same heterodimers expressed on the transfectants. This is suggestive of minor structural modifications that class II molecules undergo depending on the cells they are expressed on.

CD4+ beta islet cell-reactive T cell clones that suppress autoimmune diabetes in nonobese diabetic mice

We report the isolation of a panel of CD4+ T helper type 1 autoreactive T cell clones from the spleen of unprimed nonobese diabetic mice, a murine model of human insulin-dependent diabetes mellitus. The T cell clones express a diverse repertoire of T cell receptors, three of which recognize beta islet cell autoantigen(s). The islet cell-reactive T cell clones inhibit adoptive transfer of insulin-dependent diabetes mellitus and intraislet lymphocytic infiltration. The protective capacity of the T cell clones correlates with their ability to produce a novel immunoregulatory activity that potently inhibits in vitro allogeneic mixed lymphocyte reaction. The partially purified activity significantly inhibited the adoptive transfer of diabetes. Our work provides evidence in support of the existence of T helper type 1, CD4+ T cells reactive to beta islet cell autoantigens that have acquired a protective instead of a diabetogenic effector function. These T cells mediate their protective action in part by production of an immunoregulatory activity capable of down-regulating immune responses, and they are likely to represent a population of regulatory T cells that normally plays a role in maintaining peripheral tolerance.

No evidence for TCR V beta repertoire changes influencing disease protection in E-transgenic NOD mice

In order to study whether positive selection of T cells plays any role in the MHC-dependent protection from diabetes in the non-obese-diabetic (NOD) mouse, the T cell V beta repertoire has been studied in NOD mice and in NOD mice either transgenic for the wildtype MHC class II E alpha gene, or for delta Y, a promotor-mutagenized E alpha gene with a restricted tissue expression. The E alpha transgenic line is protected from both insulitis and diabetes. The delta Y transgenic line is neither protected from insulitis nor from diabetes, although it can perform both positive and negative E-mediated selection in the thymus. The V beta repertoire was studied in the pancreatic lymph nodes as these drain the area which is the target for the autoimmune attack. We see no evidence for E alpha TCR V beta repertoire differing from both nontransgenic NOD mice and delta Y mice despite its striking difference in susceptibility to autoimmunity. We conclude that none of the differences in the TCR V beta repertoire of E alpha-transgenic NOD mice hitherto observed are likely to explain the protective effect of E molecule expression in NOD mice.

Tolerance induction as a therapeutic strategy for the control of autoimmune endocrine disease in mouse models

This chapter aims to describe ways in which autoimmunity can be prevented or reversed and 'self-tolerance' re-established. To this end we have largely restricted our overview to the two main autoimmune disease models with which we are involved, i.e. IDDM in NOD mice and EAT in H-2k mice although, where appropriate and to demonstrate a particular point, other models are mentioned. The chapter has been divided into sections covering protection afforded by 1) transgenes, 2) autoantigen and 3) by reagents targetting T-cell surface molecules. Where established, the mechanism by which protection or tolerance is achieved is described but where, as in most cases, it is unknown the possibilities are discussed. Investigations using T-cell lines and clones and on islet regeneration which are currently being followed as part of a comprehensive approach to the study of autoimmunity are included as separate sections and their relevance discussed.

Animal models of autoimmune endocrine disease and their uses in developing new methods of intervention

This review provides basic information concerning the major animal models in use for the study of autoimmune endocrine diseases (AEDs). Although several other models exist which parallel human AEDs such as autoimmune orchitis, most research in this area has centred on animal models of insulin-dependent diabetes mellitus (IDDM) and thyroiditis. These models, between them, appear to exhibit most of the disease manifestations of their human counterparts and thereby permit the study of possible methods of intervention in the disease process. While no one model represents a perfect correlation with the human disease it represents, common characteristics are recognizable between them. For instance, the central role of activated T cells in controlling the disease process. The chapter continues by examining the various ways in which models of autoimmunity, specifically IDDM and experimental allergic thyroiditis (EAT), have been used to investigate the possibility of preventing or arresting autoimmune destruction. Several different approaches are described that illustrate the variety of techniques that have proven both potentially, or in reality, effective and those that have proven less efficacious than first hoped.

T-cell tolerance and autoimmunity in transgenic models of central and peripheral tolerance

Experiments with transgenic mice expressing genes encoding both antigens in defined tissues and T-cell receptor genes of known specificities have enhanced our understanding of the mechanisms involved in the pathogenesis of autoimmune states. They have also shed light on the means by which potentially autoreactive cells may be prevented from exerting their autoaggressive potential. The value of the transgenic approach is that it can overcome the low frequency of peptide-specific T cells occurring in normal animals, and also provide a tissue-specific, cognate antigen that is absent in controls. These factors allow reactive T cells to be isolated or quantified by flow cytometry and their responses to antigen in vitro and in vivo be defined.

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.

Genetic requirements for acceleration of diabetes in non-obese diabetic mice expressing interleukin-2 in islet beta-cells

Diabetes was dramatically accelerated in non-obese diabetic (NOD) transgenic mice that expressed interleukin-2 (IL-2) in their beta cells. A single cross to C57BL/6 completely prevented this effect and a further backcross to the NOD genetic background showed that at least two diabetes susceptibility loci (Idd1s and Idd3/10s) were required for the diabetes acceleration T cells activated to islet antigens were not circulating in the mice. The accelerating effect of IL-2 was present; but decreased, in NOD mice that lacked CD8+ T cells as well as in NOD SCID mice. The implications are that in the NOD genetic background, the production of cytokines, such as IL-2, by islet-specific CD4+ T cells can lead to beta cell damage and diabetes and that CD8+ T cells may have a role in accelerating diabetes onset.

Production of interleukin 10 by islet cells accelerates immune-mediated destruction of beta cells in nonobese diabetic mice

The T helper type 2 (Th2) cell product interleukin 10 (IL-10) inhibits the proliferation and function of Th1 lymphocytes and macrophages (M phi). The nonobese diabetic mouse strain (NOD/Shi) develops a M phi and T cell-dependent autoimmune diabetes that closely resembles human insulin-dependent diabetes mellitus (IDDM). The objective of the present study was to explore the consequences of localized production of IL-10 on diabetes development in NOD/Shi mice. Surprisingly, local production of IL-10 accelerated the onset and increased the prevalence of diabetes, since diabetes developed at 5-10 wk of age in 92% of IL-10 positive I-A beta g7/g7, I-E- mice in first (N2) and second (N3) generation backcrosses between IL-10 transgenic BALB/c mice and (NOD/Shi) mice. None of the IL-10 negative major histocompatibility complex-identical littermates were diabetic at this age. Furthermore, diabetes developed in 33% of I-A beta g7/d, I-E+ N3 mice in the presence of IL-10 before the mice were 10 wk old. Our findings support the notion that IL-10 should not simply be regarded as an immunoinhibitory cytokine, since it possesses powerful, immunostimulatory properties as well. Furthermore, our observations suggest that beta cell destruction in NOD mice may be a Th2-mediated event.

Resistance to cyclophosphamide-induced diabetes in transgenic NOD mice expressing I-Ak

Transgenic expression of the MHC (major histocompatibility complex) class II I-Ak molecule was previously shown to effectively reduce the incidence of insulitis in non-obese diabetic (NOD) mice at the age of 20 weeks. We have further characterized the expression and function of the I-Ak molecule and examined its effects on the incidence of diabetes in NOD mice. The newly expressed I-Ak molecule was recognized as an alloantigen by the T lymphocytes of normal NOD mice as shown by mixed lymphocyte reaction (MLR). The levels of endogenous I-Ag7 expression on peripheral blood lymphocytes were not affected by the transgene expression. Transgenic NOD mice were completely resistant to spontaneous diabetes, but the treatment by cyclophosphamide, which effectively induces diabetes in normal NOD mice, caused diabetes, although at a much lower incidence than that of normal NOD mice. On the basis of these findings, we discuss the role of I-Ak in the prevention of diabetes in NOD mice.

Insulin dependent diabetes mellitus in the non-obese diabetic mouse: a disease mediated by T cell anergy?

The non-obese diabetic (NOD) mouse spontaneously develops autoimmune type I insulin-dependent diabetes mellitus (IDDM) with a similar immunopathological profile to the human disease. Development of the disease in both the NOD mouse and in humans is under polygenic control and influenced by many environmental factors. Diabetes results from a specific T cell-mediated destruction of pancreatic insulin-producing islet beta cells. Both CD4 and CD8 T cells as well as macrophages are required for the development of diabetes in NOD mice. An intriguing similarity between murine and human diabetes is a T cell proliferative unresponsiveness (anergy) that may be a susceptibility factor to disease onset. Defective communication between antigen-presenting cells (APC) and T cells, and/or an aberrant production or activity of inflammatory cytokines (e.g. chemokines) in the thymus and periphery (e.g. pancreas) may account for the unresponsiveness of regulatory T cells leading to a loss of immunological tolerance to beta cell autoantigens in NOD mice and in diabetic humans.

Major histocompatibility complex class I molecules are required for the development of insulitis in non-obese diabetic mice

An early step in the development of autoimmune diabetes is lymphocyte infiltration into the islets of Langerhans of the pancreas, or insulitis. The infiltrate contains both CD4+ and CD8+ T cells and both are required for progression to diabetes in non-obese diabetic (NOD) mice. It has been thought that the CD4+ lymphocytes are the initiators of the disease, the islet invaders, while CD8+ cells are the effectors, the islet destroyers. We question this interpretation because NOD mice lacking MHC class I molecules, hence CD8+ T cells, do not display even insulitis when expected.

Failure of a protective major histocompatibility complex class II molecule to delete autoreactive T cells in autoimmune diabetes

The association of major histocompatibility complex genes with autoimmune diseases is firmly established, but the mechanisms by which these genes confer resistance or susceptibility remain controversial. The controversy extends to the nonobese diabetic (NOD) mouse that develops disease similar to human insulin-dependent diabetes mellitus. The transgenic incorporation of certain class II major histocompatibility complex genes protects NOD mice from diabetes, and clonal deletion or functional silencing of autoreactive T cells has been proposed as the mechanism by which these molecules provide protection. We show that neither thymic deletion nor anergy of autoreactive T cells occurs in NOD mice transgenic for I-Ak. Autoreactive T cells are present, functional, and can transfer diabetes to appropriate NOD-recipient mice.