It has been established that insulin-dependent diabetes mellitus (IDDM) in nonobese diabetic (NOD) mice results from a CD4+ and CD8+ T cell–dependent autoimmune process directed against the pancreatic beta cells. The precise roles that beta cell–reactive CD8+ and CD4+ T cells play in the disease process, however, remain ill defined. Here we have investigated whether naive beta cell–specific CD8+ and CD4+ T cells can spontaneously accumulate in pancreatic islets, differentiate into effector cells, and destroy beta cells in the absence of other T cell specificities. This was done by introducing Kd– or I-Ag7–restricted beta cell–specific T cell receptor (TCR) transgenes that are highly diabetogenic in NOD mice (8.3- and 4.1-TCR, respectively), into recombination-activating gene (RAG)-2–deficient NOD mice, which cannot rearrange endogenous TCR genes and thus bear monoclonal TCR repertoires. We show that while RAG-2−/− 4.1-NOD mice, which only bear beta cell–specific CD4+ T cells, develop diabetes as early and as frequently as RAG-2+ 4.1-NOD mice, RAG-2−/− 8.3-NOD mice, which only bear beta cell–specific CD8+ T cells, develop diabetes less frequently and significantly later than RAG-2+ 8.3-NOD mice. The monoclonal CD8+ T cells of RAG-2−/− 8.3-NOD mice mature properly, proliferate vigorously in response to antigenic stimulation in vitro, and can differentiate into beta cell–cytotoxic T cells in vivo, but do not efficiently accumulate in islets in the absence of a CD4+ T cell–derived signal, which can be provided by splenic CD4+ T cells from nontransgenic NOD mice. These results demonstrate that naive beta cell– specific CD8+ and CD4+ T cells can trigger diabetes in the absence of other T or B cell specificities, but suggest that efficient recruitment of naive diabetogenic beta cell–reactive CD8+ T cells to islets requires the assistance of beta cell–reactive CD4+ T cells.

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-2g7) undergoes thymocyte negative selection in diabetes-resistant H-2g7/b, H-2g7/k, H-2g7/q, and H-2g7/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.

NOD mouse-derived beta-cell-specific cytotoxic T-cell (beta-CTL) clones are diabetogenic in adult NOD mice, but only if co-injected with splenic CD4+ T-cells from diabetic animals. This investigation was initiated to determine whether infiltration of pancreatic islets by beta-CTL is a major histocompatibility complex (MHC) class I-restricted response, and whether beta-CTL has a direct cytopathic effect on beta-cells in vivo. Pancreatic islets from BALB/c (H-2d) or B6 (H-2b) mice were transplanted under the renal capsule of streptozotocin (STZ)-induced diabetic (NOD x BALB/c) F1 (H-2Kd, H-2Dd,b) or NOD x B6) F1 (H-2Kd,b, H-2Db) mice, respectively. H-2Kd-restricted beta-CTL clones from NOD mice were transfused into euglycemic mice within 3 days after transplantation. In all of the H-2d islet-grafted (NOD x BALB/c) F1 mice that received the beta-CTL clones, the beta-CTLs homed into the grafts, recruited host Mac-1+ cells and CD4+ and CD8+ T-cells, and caused diabetes within 7 days. In contrast, none of the H-2b islet-grafted (NOD x B6) F1 mice who received the beta-CTL clones and none of the H-2d islet-grafted (NOD x BALB/c) F1 mice who received a non-beta-cell cytotoxic CTL clone (N beta-CTL) developed graft inflammation or diabetes. Depletion of CD4+ T-cells in H-2d islet-grafted (NOD x BALB/c) F1 mice did not prevent beta-CTL clone-induced diabetes but reduced its severity. In contrast, when the beta-CTL clones were injected > 8 days after transplantation, none of the H-2d islet-grafted (NOD x BALB/c) F1 mice became diabetic or developed graft inflammation. We conclude that (1) islet-derived beta-CTLs can destroy beta-cells in vivo; (2) infiltration of grafted islets by beta-CTLs is an MHC class I-restricted response; (3) beta-CTLs can recruit naive CD4+ T-cells to the site, leading to further beta-cell damage; and (4) revascularized islet grafts are, like pancreatic islets of irradiated adult NOD mice, "sequestered" from circulating beta-CTLs.

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