Maintaining immune tolerance requires the production of Foxp3-expressing regulatory T (T) cells in the thymus. Activation of NF-?B transcription factors is critically required for T cell development, partly via initiating Foxp3 expression. NF-?B activation is controlled by a negative feedback regulation through the ubiquitin editing enzyme A20, which reduces proinflammatory signaling in myeloid cells and B cells. In naive CD4 T cells, A20 prevents kinase RIPK3-dependent necroptosis. Using mice deficient for A20 in T lineage cells, we show that thymic and peripheral T cell compartments are quantitatively enlarged because of a cell-intrinsic developmental advantage of A20-deficient thymic T differentiation. A20-deficient thymic T cells exhibit reduced dependence on IL-2 but unchanged rates of proliferation and apoptosis. Activation of the NF-?B transcription factor RelA was enhanced, whereas nuclear translocation of c-Rel was decreased in A20-deficient thymic T cells. Furthermore, we found that the increase in T cells in T cell-specific A20-deficient mice was already observed in CD4 single-positive CD25 GITR Foxp3 thymic T cell progenitors. T cell precursors expressed high levels of the tumor necrosis factor receptor superfamily molecule GITR, whose stimulation is closely linked to thymic T cell development. A20-deficient T cells efficiently suppressed effector T cell-mediated graft-versus-host disease after allogeneic hematopoietic stem cell transplantation, suggesting normal suppressive function. Holding thymic production of natural T cells in check, A20 thus integrates T cell activity and increased effector T cell survival into an efficient CD4 T cell response.     «

Maintaining immune tolerance requires the production of Foxp3-expressing regulatory T (T) cells in the thymus. Activation of NF-?B transcription factors is critically required for T cell development, partly via initiating Foxp3 expression. NF-?B activation is controlled by a negative feedback regulation through the ubiquitin editing enzyme A20, which reduces proinflammatory signaling in myeloid cells and B cells. In naive CD4 T cells, A20 prevents kinase RIPK3-dependent necroptosis. Using mice d...     »