PAX5 is a gene that plays a crucial role in the development of B cells, which are a type of white blood cell important for the immune system. It encodes a protein that acts as a transcription factor, helping to regulate the expression of other genes necessary for B cell differentiation and function. Mutations in the PAX5 gene can lead to various health issues, including certain types of blood cancers like B-cell acute lymphoblastic leukemia. Understanding PAX5 is essential for researchers studying immune system disorders and developing targeted therapies for related diseases.