Molecular and cellular regulation of the immune system: A study of Ikaros in Th2 cell lineage decisions and of mast cells' contribution to disease progression in a murine model of type 1 diabetes

This dissertation describes studies that investigate aspects of both branches of the immune system; the immediate nonspecific innate response and the downstream targeted adaptive response. Chapter III of this thesis examines the molecular mechanisms that control differentiation of T helper cells, a critical member of the adaptive immune response. We demonstrate that Ikaros, a hematopoietic cell-specific transcription factor with well defined effects on early lymphocyte development in the bone marrow and thymus, is a positive regulator of Th2 cytokine gene expression in peripheral T cells. CD4+ T cells from naive Ikarosnull mice were found to have decreased ability to express Th2 cytokines corresponding with histone H3 hypoacetylation detected across the Th2 cytokine locus as well as decreased GATA-3 and c-maf expression and increased T-bet and STAT1 expression in Ikarosnull cells. These data support the idea that Ikaros directly activates Th2 gene expression by promoting local chromatin accessibility during CD4+ T cell differentiation and also acts indirectly to regulate expression of Th2- and Th1-specific transcription factors.;A breakdown in adaptive regulatory mechanisms can result in misdirected immune responses against self or innocuous substances leading to pathologic consequences such as chronic inflammation, allergy or autoimmunity. In Chapter IV we investigate whether mast cells, a cell type previously restricted to the realm of allergy, impact the development of type 1 diabetes (T1D), a CD4+- and CD8+- T cell mediated disease. Mutations in c-kit, the receptor for stem cell factor which is necessary for mast cell survival, were backcrossed onto a genetic background susceptible to T1D resulting in a novel mast-cell deficient mouse, NODW/Wv. Characterization of these mice by histology and blood glucose analysis revealed that, although c-kit signaling is not necessary for the initiation of insulitis, without c-kit activity pancreatic islets remain relatively free of profound leukocyte invasion and the mice never progress to overt diabetes. Our data provides the first in vivo evidence that mast cells can significantly influence T1D and suggests that mast cells are crucial for progressive beta cell destruction.