Abstract||Autoimmune disease is comprised of a wide variety of disorders characterised by a loss of self-tolerance towards a target organ or systemic region leading to its eventual destruction. Type 1 diabetes (T1D), autoimmune thyroid disease (AITD) and inflammatory bowel disease (IBD) are debilitating organ-specific disorders. These disorders arise from a combination of genetic factors and environmental triggers. A greater level of basic understanding of these disorders is required to delay and/or prevent their effects. Numerous autoimmune susceptibility loci have been implicated in the development of these disorders, but only a few causative genes have been identified. The aim of this project was to use comparative mapping between the human and mouse genomes to provide a greater understanding of the human autoimmune susceptibility locus, IDDM6, shown to be involved in a number of autoimmune disease conditions.
Hall et al., (2003) previously demonstrated that the mouse autoimmune diabetes locus, Idd21, on distal mouse chr18 contains orthology to human IDDM6, IDDM10, IDDM18 and rat Iddm3. As part of this project the Idd21 locus was fine mapped using the congenic mapping technique. Beginning with the consomic mouse strain, NOD.ABHChr18 (90Mb of Biozzi/ABH-derived diabetes-resistant chr18 introgressed onto a non-obese diabetic (NOD) genetic background), 13 NOD.ABHIdd21 congenic mouse strains were established. The diabetes incidences of these congenic mouse strains were statistically compared stepwise along mouse chr18 and Idd21 was fine mapped to at least four independent autoimmune diabetes loci. Idd21.1 and Idd21.2 were located on distal mouse chr18 in regions orthologous to human IDDM6 and rat Iddm3 and Idd21.3a/b and Idd21.4 were located on proximal mouse chr18 in regions orthologous to human IDDM18 and IDDM10 respectively. Candidate genes of notable interest include Map3k8, Spink5, Cd14, Dcc, Smad4 and 7, Miz1, Nfatc1 and Cd226.
Idd21.1 was further fine mapped. Beginning with the NOD.ABHD18Mit8-D18Mit214[(75-85.1Mb)] (Idd21.1) congenic strain (containing at least 10.1Mb of distal chr18 Biozzi/ABH diabetes-resistant DNA introgressed onto a NOD genetic background), seven subcongenic mouse strains were created. The diabetes incidence of these subcongenic mouse strains were statistically compared stepwise along mouse chr18 and Idd21.1 was fine mapped to at least three independent autoimmune diabetes loci; Idd21.11 (72.6-76.1Mb), Idd21.12a/b (75-76.1Mb and 80.6-81.4Mb) and Idd21.13 (84.8-85.1Mb). Candidate genes of interest in these regions include Dcc, Smad4 and 7, Miz1, Nfatc1, and Cd226.
Functional characterisation of the Idd21.1 locus was performed by adoptively transferring splenocytes from female NOD or NOD.ABHIdd21.1 mice into cohorts of severe combined immune deficient (scid) female mice, NOD/LtSz.Prkdc[scid] and NOD/LtSz.Prkdc[scid].ABHIdd21.1. There were two notable findings from this work. Firstly, NOD.ABHIdd21.1 splenocytes are not as effective as NOD at transferring diabetes to either NOD/LtSz.Prkdc[scid] (P = 0.0004) or NOD/LtSz.Prkdc[scid].ABHIdd21.1 (P = 0.0178), suggesting that Idd21.1 acquired immune cells are not as diabetogenic as NOD. Secondly, NOD/LtSz.Prkdc[scid].ABHIdd21.1 mice are more resistant to autoimmune attack than NOD/LtSz.Prkdc[scid] when injected with either NOD (P = 0.0015) or NOD.ABHIdd21.1 splenocytes (P = 0.0014), suggesting that Idd21.1 either acts by altering the intrinsic resistance of beta-cells to autoimmune attack or due to changes in the innate immune system.
Other NOD-based models of autoimmune disease, spontaneous and experimental autoimmune thyroiditis and spontaneous colitis, were also investigated to determine whether Idd21.1 is a common autoimmune disease locus. When bred onto the NOD.Cg-H2[h4] (thyroiditis model) genetic background Idd21.1 was demonstrated to increase the development of thyroiditis and reduce the incidence of insulitis in spontaneous (untreated) but not experimental (NaI-induced) NOD.Cg-H2[h4] mice. When bred onto the NOD.Cg-Il10[tm1Cgn] (colitis) genetic background Idd21.1 was demonstrated to inhibit the development of rectal prolapse in breeding female NOD.Cg-Il10[tm1Cgn] mice.
Data from this thesis demonstrate that the IDDM6 orthologous region in mouse, Idd21.1, contains several loci that influence autoimmune diabetes, thyroiditis and colitis in NOD-based mouse models. These findings are consistent with previous knowledge that IDDM6 is a common autoimmune susceptibility locus.