Immunologic and genetic studies of diabetes in the BB rat

The spontaneous development of diabetes in the Bio-Breeding (BB) rat is an excellent model of human insulin-dependent diabetes mellitus (IDDM). Disease expression is dependent on several genetically determined abnormalities, including specific major histocompatibility complex (MHC) genes. At least one MHC class II locus of the U haplotype is a necessary, but not sufficient, condition for disease expression. The immune system of BB rats is markedly abnormal. There is a striking reduction in the number and function of mature cytotoxic/suppressor T cells, a poor proliferative response to mitogens and in mixed lymphocyte culture, poor interleukin-2 production, and a reduced ability to reject skin allografts. While these immune system abnormalities are closely related to the development of diabetes, the immune recognition and effector mechanisms resulting in islet cell destruction are still poorly understood. The hypothesis that MHC class II induction on pancreatic beta cells serves to target these lymphokines, natural killer (NK) cells, macrophages, etc.) have been implicated in islet cell killing. The incidence of IDDM is reduced by immunosuppressive therapy in both rats and humans, further supporting the role of immune mechanisms in this disease.