THE VALUE OF IMMUNOHISTOCHEMISTRY
IN THE ASSESSMENT OF BONE MARROW DISORDERS

Attilio Orazi, M.D., FRCPath. and Dennis P. O'Malley, M.D.

MYELOPEROXIDASE This antibody is made in rabbits by the production of an antibody against human granulocytes. It is highly specific and stains only granulocytes and their precursors, and to a less extent the granules of monocytes. It works well in tissue sections fixed in formalin and B5 and can be used in decalcified material. The heat-induced epitope retrieval technique may improves results. This is the antibody of choice in the detection of cells of granulocytic lineage. It is more sensitive than elastase and chloroacetate esterase (CAE). It is more specific than lysozyme and also more specific than CAE, because it does not also stain mast cells as the latter does. In addition, and contrary to CAE, it stains cells of eosinophilic lineage. The sensitivity of myeloperoxidase by immunohistochemistry has been shown by us and others to be greater than the cytochemical myeloperoxidase and is frequently positive in more primitive myeloid leukemias in which cytochemical myeloperoxidase is negative. Clinical cases in which the technique is useful include the following: The distinction between acute myeloid and acute lymphoid leukemias in tissue sections. Identification of myeloblastic transformation in chronic myeloid leukemia and myelodysplastic syndromes. Identification of granulopoiesis and its differentiation from erythropoiesis in clinical conditions in which the hematopoietic cells are all primitive. The distinction between myeloid precursors and megaloblastic erythroid cells in cases of megaloblastic anemia. The distinction between primitive myeloid infiltrates in bone marrow and non-hematologic metastatic infiltrates. References Kotylo P. et al: Flow cytometric immunophenotypic characterization of pediatric and adult minimally differentiated acute myeloid leukemia (AML-M0). Am J Clin Pathol. 2000; 113:193-200. Pileri et al: Acute leukaemia immunophenotyping in bone-marrow routine sections. Br J Haematol. 1999 May; 105:394-401. Pinkus GS, Pinkus JL: Myeloperoxidase: a specific marker for myeloid cells in paraffin sections. Mod Pathol 1991;4:733.