Histiocytic differentiation in acute monocytic leukemia

Myeloid histocytes of dendritic cells (DCs), Langerhans cells (LCs), and macrophages in varied tissues, as leukemic blasts in acute monoblastic and monocytic leukemia (AML-M5a and M5b), are derived from monocyte progenitors in bone marrow. Based on DC induction from hematopoietic stem cells, myeloid progenitors, and monocytes, and occasional expressions of histocyte-related antigens (HRAs) in M5, we presume some M5 cases share histiocytic phenotypes originally. To clarify the conception, 93 M5 cases were tested with antibodies for HRAs, CD1a, CD163, S100, fascin, and langerin by immunostaining, and their morphologic characteristics were studied by light and transmission electron microscopy. The study revealed that 23 M5 cases were positive for two or more kinds of HRAs and shared a serial of histocytic immunophenotype and morphologic features, which were closely associated with M5b subtype and expression of CD14 in M5.