Two monoclonal antiplatelet antibodies as markers of human megakaryocyte maturation: immunofluorescent staining and platelet peroxidase detection in megakaryocyte colonies and in in vivo cells from normal and leukemic patients

Abstract

Abstract Two monoclonal anti-human platelet antibodies have been used in an immunofluorescent assay to study megakaryocyte maturation. The two antibodies were specific for platelets and megakaryocytes. AN 51 recognizes an antigen on platelet glycoprotein lb; the antigen detected by J 15 is on the glycoprotein IIb/IIIa complex, since it does not bind to platelets from patients with Glanzmann's thrombasthenia. AN 51 did not stain small cells of normal bone marrow, but it labeled most of the megakaryocytes and all of the platelets. In megakaryocyte colonies, megakaryocytes that had reached full maturity (at day 12 of culture) were stained specifically. AN 51 also labeled micromegakaryocytes (small mature megakaryocytes) in fetal or neonatal cultures and in leukemias, but could not be applied to identification of most leukemic promegakaryoblasts. In contrast, J 15 labeled all megakaryocytes in bone marrow as well as some rare small cells. These cells appear to represent an early cell of the megakaryocyte lineage, since their number was increased in autoimmune thrombocytopenia and they were present as early as the sixth day of culture of megakaryocyte colonies. The size of these cells progressively increased as the culture aged, probably due to endoreplication. In the bone marrow of three patients with leukemias in which promegakaryoblasts were identified ultrastructurally by the presence of platelet peroxidase, J 15 labeled blast cells. Thus, glycoprotein lb is progressively expressed during megakaryocyte maturation, but its expression is independent of megakaryocyte ploidy, while the glycoprotein IIb/IIIa complex is an early antigenic marker of megakaryocyte maturation that may be useful in isolation of megakaryocyte precursors and diagnosis of megakaryoblastic leukemia.