Precise regulation of the immune system is required for protection from foreign invaders and tolerance of self. Dysfunctional immune regulation can lead to impaired immune responses to infections as well as development of autoimmune diseases. The role of the transcription factor Bach1 in regulating immune processes has been indirectly implicated but has not been directly explored; thus, the broad and long-term objective of this project is to determine the function of Bach1 and the mechanism by which it mediates protective immunity and autoimmune diseases at a cellular and molecular level. The following research design and methods will be employed to achieve this goal. 1) First, the mechanism by which Bach1 regulates transcription will be elucidated. Specifically, chromatin immunoprecipitation followed by microarray (ChIP-chip) will be used to determine whether Bach1 binds promoter proximal and/or distal regulatory elements to directly elicit transcriptional activation and repression. Computational motif analyses and luciferase reporter assays will be used to define those functional domains of Bach1 important for transcriptional regulation. 2) Second, the role of Bach1 during viral and bacterial infections will be determined. Bach1 will be ablated in macrophages and in mice during infection in order to characterize the molecular pathways by which Bach1 regulates protective immune responses. 3) Third, the role of Bach1 in autoimmunity will be investigated. Preliminary data demonstrated that Bach1 promotes the development of murine experimental autoimmune encephalomyelitis (EAE), which mimics human multiple sclerosis. Accordingly, bone marrow reconstitution and adoptive transfer experiments will be used to identify those immune cell(s) in which the intrinsic function of Bach1 modulates EAE. Microarray experiments will be performed in those cells to identify potential targets and downstream signaling pathways regulated by Bach1. 4) Fourth, Bach1 targets responsible for mediating its role in the development of EAE will be identified and characterized. The effect of Bach1-mediated EAE upon ablating these targets will be examined by generating double knockout animals of Bach1 and the target(s) of interest. Furthermore, functional domains of Bach1 necessary for its regulatory function in vivo will be identified. Overall, this project will identify a new regulator of the immune system (Bach1) and reveal those signaling cascades by which it modulates protective immunity during infection and autoimmunity during dysfunction. The successful completion of this project will therefore benefit public health by identifying new targets for therapy against immune-related and autoimmune diseases.