IMMUNOGOLD LABELING FOR THE DIAGNOSIS OF LEUKEMIA BY TRANSMISSION ANDSCANNING ELECTRON-MICROSCOPY

For the cell type diagnosis of leukemia in adult patients, particularl y when the sampling of bone marrow is difficult, the study of peripher al blood leukocytes (PBLs) by immune-electron microscopy provides sign ificant information, as illustrated here in two cases of hairy cell le ukemia and seven cases tentatively identified as megakaryoblastic leuk emia (M7). Indirect immunogold labeling with the B-ly7 monoclonal anti body (CD103) proved valuable in confirming the diagnosis of hairy cell leukemia. Immunogold labeling for the GpIIIa platelet glycoprotein (C D61) was used in cases where the light microscopy of blood films revea led 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 cytoplasm ic differentiation markers such as alpha granules and demarcation memb ranes, further confirming the presence of circulating megakaryocythemi a, a phenomenon described many years ago in various myeloproliferative disorders. It is suggested, therefore, that many of these cases shoul d not be identified as true megakaryoblastic leukemias.