a transcription factor that plays a role in the inducible expression of cytokine genes in T cells, especially in the induction of the IL-2 and IL-4. Also control gene expression in embryonic cardiac cells. Could regulate not only the activation and proliferation but also the differentiation and programmed death of lymphoid and nonlymphoid cells. Six splice variant isoforms have been identified. Expressed in thymus, peripheral leukocytes as T-cells and spleen. Isoforms A are preferentially expressed in effector T-cells (thymus and peripheral leukocytes) whereas isoforms B and isoforms C are preferentially expressed in naive T-cells (spleen). Isoforms B are expressed in naive T-cells after first antigen exposure and isoforms A are expressed in effector T-cells after second antigen exposure. Note: This description may include information from UniProtKB.