CD6 is a 100-130 kD single chain transmembrane glycoprotein also known as T12. It is a member of the scavenger receptor superfamily found on T and B cell subsets, thymocytes, and acute lymphocytic leukemia cells (ALL). CD6, interacting with its ligand CD166 (also known as ALCAM), is involved in T cell development and activation, as well as thymocyte adhesion.