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Cytochemical Markers of Differentiation in Acute Leukemia¹

MRC Leukaemia Unit, Royal Postgraduate Medical School, and Department of Haematology, Royal Free Hospital, London, United Kingdom

Material from 110 adult patients with acute myeloid leukemia, acute lymphoblastic leukemia, and chronic granulocytic leukemia (CGL) in blast crisis (BC) was studied by light microscopy (LM) and transmission electron microscopy cytochemistry in order to examine the sensitivity of the tests used to define myeloid differentiation.

Granulocytic differentiation was best visualized by the myeloperoxidase (MPO) reaction. By LM, the Hanker method using 3,3'-diaminobenzidine at pH 7.6 was the most sensitive in demonstrating MPO and the presence of bodies in most acute myeloid leukemias and some CGLs in "myeloid" BC. bodies were more numerous when the reaction was carried out at pH 9.7, suggesting that they originate from catalase-containing microperoxisomes. MPO at transmission electron microscope level (with 3,3'-diaminobenzidine) was more sensitive than the LM techniques because it demonstrated myeloblasts with few positive granules and reaction product in the endoplasmic reticulum. The platelet-peroxidase technique of Breton-Gorius, using a higher concentration of 3,3'-diaminobenzidine and unfixed material, was of even greater sensitivity for the study of myeloid precursors and allowed the identification of megakaryoblasts in CGL in BC.

Monocytic differentiation was best recognized by LM using an esterase method (naphthol AS-acetate or -naphthyl acetate) and the acid phosphatase reaction. By transmission electron microscopy, the acid phosphatase reaction was positive in small electron-dense granules which are MPO negative and appear to be characteristic of the early maturation stages of monoblasts.

The techniques described were of value in the classification of CGL in BC and demonstrating the myeloid component in 8 of 56 (14%) acute myeloid leukemia cases which were positive with the enzyme terminal transferase. Five of the latter were "pure" myeloid cell proliferations, and 3 others were "mixtures" of lymphoblasts and myeloblasts (or monoblasts), but with lymphoid cells predominating in 2 of them.

¹ Presented at the Conference on Cell Markers in Acute Leukemia, March 4 and 5, 1980, Bethesda, Md.

² To whom requests for reprints should be addressed, at MRC Leukaemia Unit, RPMS, Ducane Road, London. W12 0HS, United Kingdom.