T-bet, a Th1 transcription factor, is up-regulated in T cells from patients with aplastic anemia

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Abstract
In aplastic anemia, immune destruction of hematopoietic cells results in bone marrow failure. Type 1 cytokines, especially IFN-γ, have been implicated in the pathophysiology of T-cell–mediated, Fas-mediated stem cell apoptosis of hematopoietic cells. Here, we show that the transcription factor T-bet (T-box expressed in T cells) is increased in T cells from patients with aplastic anemia. Patients' T-bet bound directly to the proximal site of the IFN-γ promoter without any prior stimulation, in contrast to healthy controls. Increased levels of Itk kinase participated in T-bet up-regulation and active transcription of the IFN-γ gene observed in these patients. Blocking PKC-θ, a kinase that lies downstream of Itk kinase, decreased T-bet protein and IFN-γ intracellular levels. These data suggest that the increased IFN-γ levels observed in aplastic anemia patients are the result of active transcription of the IFN-γ gene by T-bet. Blocking the transcription of the IFN-γ gene with kinase inhibitors might lead to the development of novel therapeutic agents for patients with aplastic anemia and other autoimmune diseases.