Acute myelomonocytic leukemia: an immunoelectron microscopic study.

Acute myelomonocytic leukemia (M4; French-American-British classification) is light microscopically defined as the leukemia constituting leukemic cells in both granulocytic and monocytic lineages. Therefore, the characteristics of M4 have not been fully elucidated. The author previously indicated that normal neutrophilic granulocytes could be ultrastructurally differentiated from normal monocytes by the double staining of lactoferrin and lysozyme. In this investigation, the ultrastructural localization of both proteins were observed in order to make the outline of M4 clear. The leukemic cells in acute myeloid leukemia (M2) were also examined in comparison with those in M4. The leukemic cells in M4 showed the double stainability of lactoferrin and lysozyme, and the positive reactions were localized in the cytoplasmic matrix and in the granules. The staining pattern was similar to that in M2. The coexistence of lactoferrin and lysozyme in the leukemic cells in M4, which has ultrastructurally the monocytic characteristics, implied that the leukemic cells also possess the characteristics of the cells in the granulocytic lineage. This suggests that the presence of the various leukemic cells in the granulocytic lineage. This suggests that the presence of the various leukemic cells signifies the diversely abnormal maturations in vivo of the monocytes/granulocytes precursor cell and that M4 consists of not two kinds of distinguishable cells of granulocytic and monocytic lineages but various consecutive cells based on a malignant transformation of the precursor cell.