This antibody reacts with the CD5-antigen (T1-antigen), which is expressed on human T lymphocytes. The nonoclonal antibody reacts with 90% of human peripheral T lymphocytes, medullary thymocytes as well as with lymphocytes of patients with chronic B-cell derived leukaemia. It is also expressed on a small subpopulation of normal B cells in a range of neoplastic B cells. The antibody does not react with, monocytes, granulocytes and platelets.