Transcription factors early growth response gene (Egr) 2 and 3 control inflammatory responses of tolerant T cells

Introduction

Impaired proliferation and production of IL2 are the hallmarks of experimental T cell tolerance. However, in most autoimmune diseases, auto‐reactive T cells do not display hyper proliferation, but inflammatory phenotypes.

Methods

We have now demonstrated that the transcription factors Egr2 and 3 are important for the control of inflammatory cytokine production by tolerant T cells, but not for tolerance induction.

Results

In the absence of Egr2 and 3, T cell tolerance, as measured by impaired proliferation and production of IL2, can still be induced, but tolerant T cells produced high levels of inflammatory cytokines. Egr2 and 3 regulate expression of differentiation repressors and directly inhibit T‐bet function in T cells. Indeed, decreased expression of differentiation repressors, such as Id3 and Tcf1, and increased expression of inflammatory transcription factors, such as RORγt and Bhlhe40 were found in Egr2/3 deficient T cells under tolerogenic conditions. In addition, T‐bet was co‐expressed with Egr2 in tolerant T cells and Egr2/3 defects leads to production of high levels of IFNγ in tolerant T cells.

Conclusions

Our findings demonstrated that despite impaired proliferation and IL2 production, tolerant T cells can display inflammatory responses in response to antigen stimulation and this is controlled at least partly by Egr2 and 3.

Egr2 and 3 control adaptive immune responses by temporally uncoupling expansion from T cell differentiation

Miao et al. report a checkpoint mediated by Egr2 and 3 that controls the transition between T cell clonal expansion and differentiation by regulating genes involved in proliferation and differentiation, which is essential for optimal immune responses with limited immunopathology.

Egr2 and 3 are important for maintaining immune homeostasis. Here we define a fundamental function of Egr2 and 3 operating as a checkpoint that controls the transition between clonal expansion and differentiation of effector T cells. Egr2 and 3 deficiency resulted in defective clonal expansion but hyperactivation and excessive differentiation of T cells in response to viral infection. Conversely, sustained Egr2 expression enhanced expansion but severely impaired effector differentiation. Egr2 bound to and controlled the expression of genes regulating proliferation (Myc and Myb) and differentiation repressors (Bcl6, Id3), while repressing transcription factors required for effector function (Zeb2, RORa, RORc, and Bhlhe40). Egr2 and 3 expression in T cells was regulated reciprocally by antigen and IFNγ, providing a mechanism for adjusting proliferation and differentiation of individual T cells. Thus, Egr2 and 3 are upstream regulators of effector CD4 and CD8 T cells that are essential for optimal responses with limited immunopathology.

Egr2 and 3 Inhibit T-bet-Mediated IFN-γ Production in T Cells

T-bet is important for differentiation of cytotoxic CD8 and Th1 CD4 T cells. We have discovered that Egr2 and 3 are potent inhibitors of T-bet function in CD4 and CD8 effector T cells. Egr2 and 3 were essential to suppress Th1 differentiation in Th2 and Th17 conditions in vitro and also to control IFN-γ–producing CD4 and CD8 T cells in response to virus infection. Together with Egr2 and 3, T-bet is induced in naive T cells by Ag stimulation, but Egr2 and 3 expression was inhibited by Th1–inducing cytokines. We found that Egr2 and 3 physically interact with the T-box domain of T-bet, blocking T-bet DNA binding and inhibiting T-bet–mediated production of IFN-γ. Thus, Egr2 and 3 are antagonists of T-bet function in effector T cells and are important for the control of inflammatory responses of T cells.

Early Growth Response Genes 2 and 3 Regulate the Expression of Bcl6 and Differentiation of T Follicular Helper Cells

T follicular helper (Tfh) cells support differentiation of B cells to plasma cells and high affinity antibody production in germinal centers (GCs), and Tfh differentiation requires the function of B cell lymphoma 6 (BCL6). We have now discovered that early growth response gene 2 (EGR2) and EGR3 directly regulate the expression of Bcl6 in Tfh cells, which is required for their function in regulation of GC formation. In the absence of EGR2 and -3, the expression of BCL6 in Tfh cells is defective, leading to impaired differentiation of Tfh cells, resulting in a failure to form GCs following virus infection and defects in production of antiviral antibodies. Enforced expression of BCL6 in EGR2/3-deficient CD4 T cells partially restored Tfh differentiation and GC formation in response to virus infection. Our findings demonstrate a novel function of EGR2/3 that is important for Tfh cell development and Tfh cell-mediated B cell immune responses.