Type 1 Diabetes (T1D) is an autoimmune disease where the immune system destroys the insulin-producing beta cells within the pancreas. Due to the difficulty of obtaining relevant tissue samples from patients at risk of disease, many researchers have utilized the nonobese diabetic (NOD) mouse as a model of T1D due to their natural high susceptibility for this disease which shares many characteristics with human patients. This model has been critical for uncovering many mechanisms involved in the pathogenesis of T1D including the key roles played by autoreactive T cells in the destruction of beta cells. More recently, NOD mice have shown that self-reactive B cells act as important antigen presenting cells for activating and amplifying the T cell response against beta cells. In order to identify faulty self-tolerance mechanisms causing production and activation of B cells recognizing beta cell proteins, we have developed a transgenic mouse model whereby elevated numbers of B cells are made specific for a neo-self antigen whose expression is restricted to beta cells on the T1D-prone NOD genetic background and compared it to that of transgenic mice of the non-autoimmune prone C57BL/6 (B6) genetic background. These studies revealed that NOD and B6 B cells can both be effectively tolerized to the model beta cell-restricted antigen. However, provision of help from activated T cells readily overturned this tolerance on the NOD but not the B6 background. Prior evidence has associated Idd5 (chromosome 1) and Idd9/11 (chromosome 4) diabetes susceptibility loci in NOD mice with the development of self reactive B cells contributing to T1D. The gene encoding CTLA-4 has been identified as the major candidate susceptibility gene within Idd5, thus leading to our studies comparing B cell expression of this molecule in NOD and diabetes-resistant strains. Although almost always associated with down-modulating T cells responses, our studies and that of others confirm expression of CTLA-4 by activated B cells. We encountered B cell expression of CTLA-4 to vary from that of T cells, being expressed earlier and predominantly on the cell surface rather than within intracellular vesicles. Our studies also showed aberrant expression of different splice variants of CTLA-4 by NOD B cells compared to diabetes-resistant mice controlled by genes within and outside the Idd5 genetic locus. Hence, these studies raise the possibility that CTLA-4 may contribute to T1D through its actions on both T and B cells. Given the large nature of the Idd9/11 susceptibility locus in NOD mice and the absence of any strong candidate genes that may influence the diabetogenic capacity of B cells in this strain, we resorted to microarray technology to reveal putative genes within this genomic region with the potential to control the B cell phenotype. We focused our microarray studies on the first transitional (T1) B cell population in the spleen given that it is an important stage of tolerance to peripherally expressed self-antigens which have been found to possess various defects in NOD mice. Comparing gene expression profiles of NOD T1 B cells that expressed susceptibility or resistance alleles at the Idd9/11 locus identified 20 differentially expressed genes with the potential to contribute to development of diabetogenic B cells. Overall, data presented in this thesis provides a greater understanding of the molecular and cellular mechanisms underlying B cell contribution to T1D in NOD mice. These data are hoped to eventually lead to the development of selective strategies for removing or inhibiting only those B cells that contribute to development of T1D while ensuring that humoral immunity to foreign pathogens remains intact in human patients at risk of developing disease.
| Identifer | oai:union.ndltd.org:ADTP/258277 |
| Date | January 2009 |
| Creators | Cox, Selwyn Lewis, Garvan Institute of Medical Research, Faculty of Medicine, UNSW |
| Publisher | Publisher:University of New South Wales. Garvan Institute of Medical Research |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://unsworks.unsw.edu.au/copyright, http://unsworks.unsw.edu.au/copyright |
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