Morphologic and Functional Characteristics of Bone Marrow Macrophages

The iron storage macrophage has been Isolated from the marrow of Imforontreated mice and studied in vitro by morphologic, histochemical, and functional tests and isotope labeling techniques. Those macrophages on stained preparations are large, many times binucleate cells (up to 150 ii), and show Prussian blue reactivity. In Epon-embeddod, stained thick sections they contain elongated narrow basophilic inclusions. These macrophages are actively phagocytic and plnocytic; histochemical studies show that these cells are rich in acid phosphatase, nonspecific osterase, and PAS diastaseresistant activity. Iron storage macrophages do not incorporate the 3H-thymidine. The electron microscopic appearance of this macrophage shows that the cell has ferntin free in the cytoplasm and several types of cytoplasmic granules: those with large quantities of electron-dense ferritin and/or hemosiderin (type A), elongated granules (type B) with moderately electron dense homogeneous matrix and some ferritin at the periphery, and granules with heterogeneous content (type C). The above findings demonstrate that the iron storage cell is a mature macrophago which contains hydrolases, ferritin, and a unique pepulation of cytoplasmic granules which are lysosomal in nature. There is some evidence to suggest that the unusual lysosome (type B granule) occurs after macrophages have ingested erythrocytes.