Is lack of peripheral tolerance induction a cause for diabetes in the non-obese diabetic mouse?

The non-obese diabetic (NOD) mouse is a spontaneous animal model for type 1 diabetes characterized by a selective destruction of the insulin producing beta cells in the pancreas. As in humans, the disease is controlled by several susceptibility genes, some of which map to the major histocompatibility complex on chromosome 17. However, environmental factors also contribute to the development of the disease in the NOD mouse, presumably through controlling the balance between the Th1 and Th2 response in the animal. Recent observations have shown that the NOD mouse has abnormalities in the development of bone marrow-derived antigen-presenting cells. These include the most potent activators of naive T cells, the dendritic cells, which exist in at least two different sub-populations; DC1 cells, responsible for activation of Th1 cells, and DC2 cells, which produce Th2 cells. In addition to activating naive T cells, the dendritic cells are also involved in generating central and peripheral tolerance to self molecules. In this process DC2 cells appear to be more important for the development of peripheral tolerance than DC1 cells. Besides abnormalities in the development of bone marrow-derived antigen-presenting cells, the NOD mouse also has a defect in the thymic selection of T cells, leading to a higher concentration of autoreactive T cells. We speculate that the NOD mouse may develop an imbalance in the two subsets of dendritic cells with a skewing towards DC cells, thus having a reduced ability to generate peripheral tolerance to a number of autoantigens.