CD5 (Lymphocyte antigen T1/Leu-1) is a transmembrane glycoprotein which has been implicated as a receptor in the regulation of T-cell proliferation (1). CD5 is part of the scavenger receptor cysteine-rich (SRCR) family group B and it is found on 95% of thymocytes and 72% of peripheral blood lymphocytes. In lymph nodes, the main reactivity is observed in T cell areas. CD5 is expressed by T cell leukemia, lymphomas, and activated T cells. Occasionally, CD5 antigen is also expressed on a subset of B cells. Mantle cell lymphomas (same as diffuse centrocytic lymphomas) are CD5+ while the follicle center cell lymphomas are CD5. A ligand for CD72/LYB-2, CD5 has been linked to negative regulation of T cell and B cell receptors signaling (2)