CD5 is a receptor that is expressed on the surface of T-lymphocytes, thymocytes, and subsets of B-lymphocytes (such as mantle zone B cells). It is positive in T-cell leukemias, most B-cell chronic lymphocytic leukemias, B-cell small lymphocytic lymphoma, B-cell mantle cell lymphomas, T-cell lymphomas and T-cell leukemias. It is negative in most B-cell lymphomas other than mantle cell or CLL, and in cutaneous T cell lymphomas. It is a useful T-cell marker although not as sensitive as CD3. References: Arch Path Lab Med 2008, 132:1346; Int J Clin Exp Path 2010, 3:430, Curr Opin Immunol 2011, 23:301, Am J Clin Path 2009, 132:733, Immunol Lett 1993, 38:159