IMMUNIZATION OF NONOBESE DIABETIC (NOD) MICE WITH GLUTAMIC-ACID DECARBOXYLASE-DERIVED PEPTIDE-524-543 REDUCES CYCLOPHOSPHAMIDE-ACCELERATED DIABETES

NOD mice constitute a model for studying the prevention of human autoi mmune type 1 diabetes. Glutamic acid decarboxylase (GAD) could be a ke y antigen involved in this disease, and GAD65 peptide 524-543 has been implicated in early T cell response in young NOD mice. We performed t wo i.p. injections of GAD peptide 524-543 (100 mu g at each injection) , together with Freund's incomplete adjuvant (FIA), into female NOD mi ce at 30 and 45 days old. Diabetes was accelerated 2 weeks later by a single injection of cyclophosphamide (CY), which acts against suppress ive mechanisms. Treatment with GAD 524-543 peptide delayed the onset o f diabetes and reduced its incidence (28% versus 60%; P < 0.001) compa red with control mice injected with FIA alone, or GAD peptide 534-553, or an irrelevant peptide. In the same group, the severity of lymphocy tic inflammation of pancreatic islets was reduced (P < 0.03). Up to 3 months after peptide injections, a strong splenocytic proliferative re sponse occurred in immunized NOD mice against the immunizing peptide a lone (but not against a panel of seven other GAD65-derived peptides). After peptide challenge of splenocytes in vitro, protection against CY -accelerated diabetes was associated with higher peptide-specific prod uction of T helper type 2 (Th2)-associated interleukins 4 and 10, wher eas Th1-associated interferon-gamma and IL-2 were proportionally less represented. During cotransfer, T splenocytes from GAD 524-543-immuniz ed mice were able to reduce the capacity of T cells from diabetic dono rs to transfer the disease adoptively (P < 0.01), demonstrating the ge neration of cellular mechanisms that actively suppress the disease. It is concluded that immunization of NOD mice with GAD65 peptide 524-543 can counteract CY-accelerated diabetes, possibly through active cellu lar suppression linked to a shift of Th1/Th2 balance toward the produc tion of Th2 cytokines such as IL-4 and IL-10. This study provides addi tional support for the notion that GAD, and more precisely its epitope 524-543, could be one of the key targets for the pathogenesis of type 1 diabetes in NOD mice, as well as for the efficacy of disease-specif ic peptide therapy in type 1 diabetes.