An antigen expressed by cells of the myelo‐monocytic lineage

We describe an antigen(s) characterized by a heteroantiserum raised in rabbits against mature human granulocytes. This antigen was found on neutrophils, monocytes, platelets, acute and chronic myelocytic leukemia cells and on granulocyte‐macrophage progenitor cells grown in agar. It was not found on lymphocytes, eosinophils, erythrocytes, or erythroid progenitor cells. On the basis of tissue distribution and absorption studies, the antigen (tentatively designated the “myelo‐monocytic” antigen) is distinct from antigens previously identified on human neutrophils. Restriction of the “myelo‐monocytic” antigen to normal and malignant cells of the myelo‐monocytic series suggests that it may represent a normal differentiation antigen of the myelomonocytic lineage.