Detection of cells of megakaryocyte lineage in haematological malignancies by immuno‐alkaline phosphatase labelling cell smears with a panel of monoclonal antibodies

Immuno‐alkaline phosphatase staining (by the APAAP technique) has been used to identify promegakaryo‐blasts in cell smears from 10 cases of leukaemia (three acute leukaemia, seven blast transformations). In all cases pro‐megakaryoblasts were labelled by at least two anti‐platelet glycoprotein (gp) antibodies, the highest percentages being obtained with anti‐gp IIIa (antibody C17). HLA‐DR was expressed by a variable percentage of neoplastic cells in all cases, the T11 (CD2) antigen (sheep red cell receptor) in four of seven cases tested and the p150,95 antigen in three of the six cases tested. In some cases of acute myeloid leukaemia APAAP staining of blood smears revealed circulating promegakaryoblasts and micromegakaryocytes (which superficially resemble small lymphoid cells). It is concluded that immuno‐alkaline phosphatase staining of cell smears offers a convenient means of diagnosing acute megakaryoblastic leukaemia in the routine laboratory.