Dissecting autoimmune disease susceptibility in Lyn-deficient mice

© 2011 Dr. Evelyn TsantikosThis thesis dissects the nature of autoimmune disease development in mice deficient in the tyrosine kinase Lyn. In particular, the role of cellular defects, genetics, inflammation and its consequences that influence the pathogenesis of autoimmune disease are studied. Lyn-deficient mice develop antibody-mediated autoimmune disease resembling systemic lupus erythematosus (SLE). In this disease hyperactive B cells are major contributors to pathology. It is believed that the primary defects in B cell development, including an expansion of antibody-producing plasma cells, are responsible for disease, as interference with molecules essential for B cell function and development renders the mice disease-free. This thesis dissects the role of other immune cell types and molecules that as well as B cells make important contributions to disease. In addition to B cell developmental defects, several immune cell populations are perturbed in diseased Lyn-/- mice, including the expansion of immunosuppressive regulatory T cells, activated pathogenic T cells, dendritic cells, myeloid cells and erythroid cells. Despite expansion of functional Tregs, Lyn-/- mice remain autoimmune-disease prone, suggesting that the inflammatory environment in these mice may alter the suppressive capacity of these cells. In Lyn-/- mice, B cells produce interleukin-6 (IL-6), which facilitates activation of B and T cells, enhanced myelopoiesis, splenomegaly, and ultimately, generation of pathogenic autoreactive antibodies. These pathogenic autoantibodies deposit in the kidneys causing kidney pathology. Genetic deletion of IL-6 on a Lyn-/- background ablates disease in these mice without altering B cell development or plasma cell accumulation, partitioning cellular changes that are intrinsic to loss of Lyn from induction of autoimmunity. Lyn is an important regulator of autoimmune susceptibility as genetic deletion of Lyn on multiple genetic backgrounds results in autoimmune disease. Lyn is also a haploinsufficient gene for autoimmune disease as Lyn+/- mice develop autoimmune disease of varying severity, albeit milder and delayed. Genetic interaction between heterozygote mutations of Lyn and the inhibitory phosphatase SHP-1 result in amplification of cellular activation and autoantibody levels, ultimately resulting in exacerbated kidney pathology. This synergistic interaction between loss of key inhibitory molecules is highly relevant to human autoimmune disease, which is extensively polygenic and relies on multiple genetic anomalies. This thesis also examines the role of lymphangiogenesis in the development and exacerbation of autoimmune disease. Lymphangiogenesis occurs during development and de novo, where lymphatic vessels form in response to a stimulus. The lymphatic vasculature in Lyn-/- and Mev mutants are severely perturbed. These perturbations occur in a setting of autoimmune disease, characterized by expansion and activation of several immune cell subsets. The role of immune cells in producing lymphatic growth factors in response to an inflammatory stimulus was examined, with stimulated immune cells showing rapid and robust expression of vascular endothelial growth factors. These findings highlight the putative contribution of immune cell-derived growth factors to the expansion of lymphatic vasculature involved in the establishment of pathology. Collectively, the studies presented in this thesis provide strong support for the study of autoimmune disease in Lyn-/- mice and together highlight the complexity of autoimmune disease and pathogenic mechanisms present in this model