PAX5, also known as Paired Box 5, is a transcription factor that plays a key role in B-cell development and differentiation. It belongs to the PAX family of transcription factors, which are defined by a conserved paired box domain involved in DNA binding and protein interactions. PAX5 is essential for specifying B-cell lineage commitment during hematopoiesis and is expressed in progenitor cells destined to become B cells, supporting their development from hematopoietic stem cells.