T cell-intrinsic and -extrinsic contributions of the IFNAR/STAT1-axis to thymocyte survival.

STAT1 is an essential part of interferon signaling, and STAT1-deficiency results in heightened susceptibility to infections or autoimmunity in both mice and humans. Here we report that mice lacking the IFNa/b-receptor (IFNAR1) or STAT1 display impaired deletion of autoreactive CD4 + CD8 + -T-cells. Strikingly, co-existence of WT T cells restored thymic elimination of selfreactive STAT1-deficient CD4 + CD8 + -T cells. Analysis of STAT1-deficient thymocytes further revealed reduced Bim expression, which was restored in the presence of WT T cells. These results indicate that type I interferons and STAT1 play an important role in the survival of MHC class I-restricted T cells in a T cell intrinsic and non-cell intrinsic manner that involves regulation of Bim expression through feedback provided by mature STAT1-competent T cells.