Distribution of cell surface glycoprotein CD9 (P24) antigen on megakaryocyte lineage leukemias and cell lines

We herein describe CD9 (p24) antigen as existing on the cell surface of megakaryocyte lineage leukemias as well as megakaryocytic leukemia cell lines, MEG‐01 and HEL, by means of fluorescence‐activated cell sorter (FACS IV) with a panel of monoclonal antibodies (Mabs). We found CD9 antigen expression on the cell surface of megakaryoblastic leukemias as well as MEG‐01 and HEL cells. Furthermore, CD9 antigen expression increased while culturing these cells with phorbol esters, and was also found in the cytoplasm by means of indirect immunofluorescence test. These findings clearly showed that CD9 antigen exists on the cell surface of megakaryocytic cells which are capable of synthesizing the CD9.