Marker for T-cell antigen T1, Tp67. Monoclonal antibody CRIS-1 recognizes the human CD5 antigen. CD5 is expressed at low density early on thymocytes and at high density on all mature T lymphocytes. CD5 is expressed at low density on a small subset of mature B lymphocytes (B1a cells) which is expanded during fetal life and in several autoimmune disorders as well as in some B-cell-derived lymphoproliferative disorders (chronic lymphocytic leukemia, CLL). CD5 is a glycoprotein monomer of 67kD which belongs to the scavenger receptor cysteine-rich (SRCR) family of extracellular domain-like structures and possesses a large cytoplasmic domain suitable for signal transduction. Application: IHC (f), FACS