The ultrastructural localization of iron in human bone marrow plasma cells.

Ferritin was demonstrated by electron microscopy in bone marrow plasma cells of four patients with multiple myeloma and in one patient with another malignant disease. The ferritin molecules were present in membrane bound vesicles and freely dispersed in the cytoplasm. The plasma cells were often localized around and in close contact with dendritic macrophages, which frequently were laden with ferritin. In some of these plasma cells ferritin was seen at specialized contact zones with macrophage extensions.