PREVENTION OF AUTOIMMUNE DIABETES IN NONOBESE DIABETIC FEMALE MICE BYTREATMENT WITH RECOMBINANT GLUTAMIC-ACID DECARBOXYLASE (GAD-65)

The nonobese diabetic (NOD) mouse spontaneously develops insulin-depen dent diabetes (IDDM or type I diabetes), resulting from T-lymphocyte-m ediated destruction of pancreatic beta cells. This autoimmune phenomen on includes mononuclear cell infiltration of the islets of Langerhans (insulitis) and the presence of circulating autoantibodies. The specif icity of the autoantibodies and of the autoreactive T cells was invest igated and several autoantigens were proposed, in particular glutamic acid decarboxylase (GAD). This enzyme exists in two forms (GAD 65 and GAD 67) encoded by two independent genes. To explain the role of GAD i n type I diabetes, we prepared recombinant rat GAD 65 as fusion protei n, produced in an Escherichia coli expression system, and we treated N OD female mice from 4 to 7 weeks of age by repeated intraperitoneal in jections of 5 mu g fusion protein (3 injections per week); control gro ups received the fusion partner, maltose binding protein (MBP) or diss olving agent (NaCl 0.9%). We investigated two parameters, the degree o f insulitis 5 weeks after the last injection and the overall incidence of the disease. Histological examination of the pancreata from GAD-tr eated mice revealed a significant reduction in the severity of insulit is compared with the two control groups. Furthermore, we observed that the time of onset and the frequency of diabetes in NOD females inject ed with GAD fusion protein differed significantly from the control gro ups receiving MBP or NaCl (P < 0.0001). These results show that a 3-we ek treatment of NOD female mice starting at 4 weeks of age protects th em from diabetes, again emphasizing the crucial role of GAD as autoant igen in type I diabetes. (C) 1995 Academic Press, Inc.