Early growth response genes 2 and 3 are potent inhibitors of T-bet function for interferon gamma production in Tcells

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonEarly growth response (Egr) gene 2 and 3 are genes encoding transcription factors important for maintaining immune homeostasis. Here we define a fundamental role of Egr2 and 3 to control T cell proliferation and differentiation of effector T cells. Egr2 and Egr3 deficiency in T cells resulted in impaired T cell proliferation, but hyper-activation and excessive differentiation of T cells in response to viral infection, while, conversely, sustained Egr2 expression enhanced proliferation, but severely impaired effector differentiation in to T helper (Th) subsets, such as, Th1 and Th17 subtypes. T-bet is important for differentiation of effector T cells in response to pathogen and in particular it is a master regulator for modulating the T helper 1 lineage specific differentiation programme. Although T-bet has been extensively studied in T cells, the regulation of T-bet function is less well known. We have now discovered that Egr2 and 3 are potent inhibitors for Tbet function in CD4 and CD8 effector T cells. Together with Egr2 and 3, T-bet is induced in naïve T cells by antigen stimulation, but the expression was reciprocally regulated by IFNγ, which inhibited Egr2 and 3, but promoted Tbet expression. The expression of Egr2 and 3 in CD4 T cells under TH2 and TH17 condition was essential to suppress TH1 differentiation in vitro. In response to viral infection, sustained Egr2 expression in T cells profoundly inhibited differentiation of effector cells, while Egr2 and 3 deficient T cells produced excessive levels of IFNγ. We found that both Egr2 and 3 can directly interact with the Tbox domain of T-bet, block its DNA binding and inhibit T-bet mediated production of IFNγ. Thus, Egr2 and 3 are antagonists for T-bet function in effector T cells and essential for the control of T cell differentiation and immune pathology