Electron microscopy study of Mott and Russell bodies in myeloma cells.

Ultrastructural examination of the bone marrow of 3 patients with multiple myeloma--two presenting with Mott cells and one with cells containing numerous Russell bodies--showed that these two types of intracytoplasmic inclusions are different in size and location. The Mott bodies in one patient appeared as clusters of electron dense material with round or oval shape and poorly delineated membrane. In the second, they possessed an amorphous structure, and were not surrounded by membrane. In both cases, they were not located in the endoplasmic reticulum. The Russell bodies were round, with high electron density, surrounded by membrane and located in dilated portions of the endoplasmic reticulum. It is concluded that Mott and Russell bodies are different types of inclusions in myeloma cells, at least from the ultrastructural point of view.