A novel non-lineage antigen on human leucocytes: characterization with two CD-48 monoclonal antibodies.

Two murine monoclonal antibodies have been produced which identify a novel surface antigen expressed on human leucocytes in a non-lineage-restricted distribution. Antibodies WM-63 and WM-68 were derived after immunization of mice with human T-CLL cells and the leukaemic cell line HSB-2. Both antibodies were shown to react with over 90 per cent of normal T and B lymphocytes from peripheral blood and tonsil, and also with monocytes from peripheral blood. A subset of bone marrow leucocytes, including granulocyte-macrophage progenitors, were also reactive. No activity with non-haemopoietic cells or tissues could be identified, however WM-63 and WM-68 showed binding to virtually all cases of chronic B cell malignancy, including chronic lymphatic leukaemia and non-Hodgkin's lymphoma, as well as a proportion of cases of acute leukaemia. Although the antigen recognized by these antibodies could not be immunoprecipitated from membrane extracts, it was removed from the surface of intact cells using the proteolytic enzymes protease and papain. Re-expression on cultured cells was inhibited by incubation with puromycin, cycloheximide, and tunicamycin, indicating that the epitopes detected by WM-63 and WM-68 are likely to be carbohydrate moieties on a protein backbone. Removal of the antigen from the cell surface by treatment with the enzyme phosphatidyl-inositol phospholipase C indicates that it is linked by a phosphatidyl-inositol bond. WM-63 and WM-68 were both recently clustered at the Fourth International Workshop on Human Leucocyte Differentiation Antigens into CD-48, together with four other monoclonal antibodies. Although no biological function has been ascribed to the molecule detected by these antibodies, its restriction to the haemopoietic lineage suggests a role in regulation of leucocyte function.