Immunogold labeling for the diagnosis of leukemia by transmission and scanning electron microscopy

For the cell type diagnosis of leukemia in adult patients, particularly when the sampling of bone marrow is difficult, the study of peripheral blood leukocytes (PBLs) by immuno-electron microscopy provides significant information, as illustrated here in two cases of hairy cell leukemia and seven cases tentatively identified as megakaryoblastic leukemia (M7). Indirect immunogold labeling with the B-ly7 monoclonal antibody (CD103) proved valuable in confirming the diagnosis of hairy cell leukemia. Immunogold labeling for the GpIIIa platelet glycoprotein (CD61) was used in cases where the light microscopy of blood films revealed possible megakaryoblastic leukemia. Under the electron microscope, however, the CD61 positive cells showed, in almost all cases, a wide spectrum of megakaryopoietic differentiation which made the diagnosis of M7 questionable. Most of the CD61 positive cells featured cytoplasmic differentiation markers such as alpha granules and demarcation membranes, further confirming the presence of circulating megakaryocythemia, a phenomenon described many years ago in various myeloproliferative disorders. It is suggested, therefore, that many of these cases should not be identified as true megakaryoblastic leukemias.