Insulin dependent diabetes mellitus, an autoimmune disorder?

During the last 25 years the concept of a chronic autoimmune process leading to the development of insulin dependent diabetes (IDD) has emerged. The presence of two animal models for IDD, the BB rat and the NOD mouse, has improved our ability to understand the process leading to beta cell destruction. The hallmark of an autoimmune disease is the characteristic pathologic lesion of mononuclear infiltration of the pancreatic islets. Further histologic studies of the diabetic pancreas have identified the type of cells infiltrating the islets and led to the concept of pancreatic beta cells capable of presenting antigen. The initial description of linkage disequilibrium of HLA DR3 and DR4 alleles with IDD has now progressed to the molecular level with the identification of residue 57 of the HLA DQ beta chain as crucial to the genetic predisposition to IDD. Autoantibodies to cytoplasmic antigens (ICA), surface antigens, or a membrane protein of 64 kDa identified by immunoprecipitation, autoantibodies to secreted products such as insulin and proinsulin, and autoantibodies that are cytotoxic to cultured beta cells are islet specific autoantibodies that have been described. Some are probably only markers of immunologic activity; others might participate in the destruction itself. The use of ICA as a screening tool has been successful in identifying individuals prior to the onset of IDD. Widespread cellular immunological defects have been identified both in animal models and in man. In the BB rat, a seeming paradox of severe immunodeficiency occurs in an animal with autoaggressive destruction of beta cells. More subtle defects in immunoregulation have been described in the NOD mouse and in human IDD. The response of IDD in both animal models and in man to immunomodulation and to immunosuppression offers further evidence of an immunologically mediated disease. However, some therapies in the animal models, not typically considered immunologic, such as protein restriction and insulin therapy, have prevented IDD. The possibility of intervening prior to the onset of clinical disease at the level either of the initial process of recognition of the pancreatic beta cell as a target organ or of the effector mechanism is approaching a reality in human IDD.