PAX5,also named B-cell specific activator protein (BSAP),is a member of the highly conserved paired box (PAX)-domain family of transcription factors. PAX5 is essential in normal B-cell lymphopoiesis. It is expressed in pro-B,pre-B and mature B lymphocytes but not in plasma cells. PAX5 is a common target in leukemogenesis of B-ALL ( B-lineage acute lymphoblastic leukemia) along with CDKN2A. Owing to its frequent deletion in B-ALL,PAX5 could be used as one of the molecular markers in diagnosis and monitoring of the disease. This antibody is specific to PAX5. It will not cross react with other PAX members.