Background：CD5 is a 67 kD single chain type I glycoprotein also known as Leu-1, Ly-1 and T1. It is a member of the scavenger receptor superfamily found on T cells, thymocytes, B cell subsets, chronic B lymphocytic leukemia （B-Cells）, and peripheral blood dendritic cells. CD5 modulates T and B cell receptor signaling, thymocyte maturation, and T-B cell interactions upon binding to ligands such as CD72.
