Nonobese diabetic (NOD) mice spontaneously develop insulitis and destruction of pancreatic islet β cells similar to type 1 diabetes mellitis in humans. Insulitis also occurs in the BDC2.5 TCR transgenic line of NOD mice that express the rearranged TCR α- and β-chain genes of a diabetogenic NOD CD4 T cell clone. When activated with syngeneic islet cells in culture, BDC2.5 T cells adoptively transfer disease to NOD recipients, but the identity of the islet cell Ag responsible for pathogenicity is not known. To characterize the autoantigen(s) involved, BDC2.5 T cells were used to screen a combinatorial peptide library arranged in a positional scanning format. We identified more than 100 decapeptides that stimulate these T cells at nanomolar concentrations; they are then capable of transferring disease to NOD-scid mice. Surprisingly, some of the peptides include sequences similar (8 of 10 residues) to those found within the 528–539 fragment of glutamic acid decarboxylase 65. Although this 12-mer glutamic acid decarboxylase 65 fragment is only slightly stimulatory for BDC2.5 T cells (EC50 > 100 μM), a larger 16-mer fragment, 526–541, shows activity in the low micromolar range (EC50 = 2.3 μM). Finally, T cells from prediabetic NOD mice respond spontaneously to these peptide analogs in culture; this finding validates them as being related to a critical autoantigen involved in the etiology of spontaneous diabetes and indicates that their further characterization is important for a better understanding of underlying disease mechanisms.

The function of natural killer T (NKT) cells in the immune system has yet to be determined. There is some evidence that their defect is associated with autoimmunity, but it is still unclear how they play a role in regulating the pathogenesis of T cell–mediated autoimmune diseases. It was originally proposed that NKT cells could control autoimmunity by shifting the cytokine profile of autoimmune T cells toward a protective T helper 2 cell (Th2) type. However, it is now clear that the major function of NKT cells in the immune system is not related to their interleukin (IL)-4 secretion. In fact, NKT cells mainly secrete interferon (IFN)-γ and, activated in the presence of IL-12, acquire a strong inflammatory phenotype and cytotoxic function.

Neonatal islet-specific expression of IL-10 in nonobese diabetic (NOD) mice accelerates the onset of diabetes, whereas systemic treatment of young NOD mice with IL-10 prevents diabetes. The mechanism for acceleration of diabetes in IL-10-NOD mice is not known. Here we show, by adoptive transfers, that prediabetic or diabetic NOD splenocytes upon encountering IL-10 in the pancreatic islets readily promoted diabetes. This outcome suggests that the compartment of exposure, not the timing, confers proinflammatory effects on this molecule. Moreover, injection of IL-10-deficient NOD splenocytes into transgenic IL-10-NOD.scid/scid mice elicited accelerated disease, demonstrating that pancreatic IL-10 but not endogenous IL-10 is sufficient for the acceleration of diabetes. Immunohistochemical analysis revealed hyperexpression of ICAM-1 on the vascular endothelium of IL-10-NOD mice. The finding suggests that IL-10 may promote diabetes via an ICAM-1-dependent pathway. We found that introduction of ICAM-1 deficiency into IL-10-NOD mice as well as into NOD mice prevented accelerated insulitis and diabetes. Failure to develop insulitis and diabetes was preceded by the absence of GAD65-specific T cell responses. The data suggest that ICAM-1 plays a role in the formation of the “immunological synapse”, thereby affecting the generation and/or expansion of islet-specific T cells. In addition, ICAM-1 also played a role in the effector phase of autoimmune diabetes because adoptive transfer of diabetogenic BDC2.5 T cells failed to elicit clinical disease in ICAM-1-deficient IL-10-NOD and NOD mice. These findings provide evidence that pancreatic IL-10 is sufficient to drive pathogenic autoimmune responses and accelerates diabetes via an ICAM-1-dependent pathway.

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