Pax-5

Identifies a B-cell–specific activator protein (BSAP) present throughout B-cell maturation until the plasma cell stage. PAX5 shows strong expression in most immature and mature B-cell neoplasms, as well as in nodular lymphocyte–predominant Hodgkin lymphoma. In classical Hodgkin lymphoma, staining is typically weaker, and plasma cell neoplasms are largely negative. This marker is highly specific for the B-cell lineage and does not label T cells.