Functional Dissection of Lupus Susceptibility Loci on the New Zealand Black Mouse Chromosome 1

Systemic lupus erythematosus (SLE) is a multisystem autoimmune disease with a strong and complex genetic basis. To dissect the function of the lupus susceptibility loci on New Zealand black (NZB) mouse chromosome 1, the lab had previously generated congenic mice with an introgressed homozygous NZB chromosome 1 intervals extending from ~35 or ~82 to 106 cM on the C57BL/6 background. Although both mouse strains made IgG anti-nuclear antibodies (ANAs), ANA titres and cellular activation were significantly higher in mice with the longer interval. These studies suggest the presence of two susceptibility genes. In this thesis I have sought to further characterize the cellular abnormalities and underlying genetic polymorphisms that produce them in these mice. Using mixed hematopoietic chimeric mice, with a mixture of tagged-B6 and congenic bone marrow I demonstrate that there are intrinsic B and T cell functional defects in chromosome 1 congenic mice. I further show that an intrinsic B cell defect is required for efficient recruitment of B cells into the spontaneous germinal centres and differentiation of autoantibody producing cells in these mice. To more precisely localize the susceptibility loci, I produced and characterized a number of additional subcongenic mouse strains. This revealed surprising genetic complexity with the presence of at least four lupus susceptibility loci and a suppressor locus on chromosome 1, several of which appeared to impact on T cell function. Finally, I generated bicongenic mice carrying both NZB chromosome 1 and 13 intervals, hypothesizing that since these were two of the major intervals associated with autoimmune disease in NZB mice they would fully recapitulate the autoimmune phenotypes. Although this hypothesis was incorrect, several novel phenotypes developed including marked expansion of the plasmacytoid and myeloid dendritic cell compartments and increased BAFF and IgA autoantibody production. Although this expansion was associated with TLR hyper-responsiveness, disease severity remained mild, possibly due to the lack of IFN- production, which appeared to be inhibited in these mice. Thus, lupus arises from immune defects affecting several cellular populations, which are the product of multiple genetic polymorphisms that interact in a complex fashion to produce the autoimmune phenotype.Ph