BACH2 (BTB and CNC Homology 1, Basic Leucine Zipper Transcription Factor 2): BACH2 is a gene that encodes a transcription factor involved in regulating the immune system. It plays a key role in maintaining immune balance by controlling the development and function of important immune cells, such as B cells and T cells. Dysregulation of BACH2 has been linked to autoimmune diseases and increased vulnerability to infections.