CD5

A cell surface protein expressed on most thymocytes, immature peripheral T cells, and nearly all mature T cells, but not on NK cells. Also stains normal mantle zone B cells in lymph nodes and spleen, and B cells in pleural and peritoneal cavities. Aberrant expression occurs in certain B-cell neoplasms, including CLL/SLL, mantle cell lymphoma, and hairy cell leukemia, as well as in most T-cell malignancies and thymic carcinomas. Typically negative in spindle cell thymoma. In fetuses, most B cells in spleen and cord blood are CD5 positive.