Molecular and cellular mechanisms in the development of IDDM in non-obese diabetic mice

Sammanfattning: Insulin dependent diabetes mellitus (IDDM) is a disease caused by autoimmune destruction of the insulin producing b cells in the pancreas. The leukocytic infiltration into the b cell islets preceding disease is called insulitis. The non-obese diabetic (NOD) mouse, a useful model to study IDDM, spontaneously develops diabetes similar to the human disease. IDDM is strongly associated with genes in the major histocompatibility complex (MHC) class II region. NOD mice lack expression of the MHC class II E complex due to a deletion in the Ea gene. Transgenic insertion of an Ea gene, restoring E complex expression, protects the mice from insulitis. In this study mechanisms behind protection against insulitis are investigated in Ea-transgenic NOD mice. Three different mutated Ea transgenic mouse strains, with restricted E complex expression, were bred together to investigate the correlation between E complex expression patterns and insulitis. The results indicate that minute quantitative disturbances on peripheral immune cells may affect the level of protection. A bone marrow transfer model shows that for an optimal protection from insulitis, which is correlated with optimal levels of interleukin (IL)-4, E complex expression is necessary on both thymic epithelium and bone marrow derived cells. However, Ea transgenic NOD mice lacking the IL-4 gene still display protection from insulitis indicating that in the absence of IL-4, other cytokines may compensate for the protective effect. Ea transgenic mice were also used to study the correlation between defects in the VH (immunoglobulin heavy variable) gene utilization repertoire and development of disease in NOD mice. Protected Ea transgenic NOD mice display a similarly biased VH utilization pattern, suggesting that the bias in VH gene usage in NOD mice is not directly correlated to development of disease. Analysis of VH gene expression in mice transgenic for the apoptosis inhibitor bcl-2 indicates that a biased VH gene utilization may be correlated to an increased expression of Bcl-2. NOD mice transgenic for Bcl-2 over-expressed in B and T cells showed protection from insulitis, whereas no effect could be seen in mice only expressing the bcl-2 transgene in B cells. Analysis of T cell subsets in the protected bcl-2 transgenic mice did not reveal expansion of any of the major subsets in spleen or thymus.