The large cell in the center of this slide is a phagocytic histiocyte or macrophage. The nuclear chromatin may resemble that of a reticulum cell or that of a monocyte. The cell is distinguished by its cytoplasm, which contains ingested material. These cells are the scavengers of the bone marrow and do the clean-up job after cell destruction. They often contain granules that give a positive test for iron. The ferritin and hemosiderin granules appear greenish black with Wright's stain, like the ones seen in the cytoplasm of this cell. The cytoplasm is usually spread out without a definable cytoplasmic membrane. Phagocytic histiocytes are increased in hemolytic anemia, infection, exposure to toxic chemicals, leukemia, and solid tumors. If histoplasmosis or kala-azar is suspected, one looks for the inclusions in the macrophages, cells that are generally increased in number in these diseases.
Course Section: 06. Microscopic Examination of the Bone Marrow
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