An ultrastructural study of binucleate plasma cells.

Fifty surgical specimens from 10 different diseases were examined for the presence of binucleate plasma cells. Thirty-three specimens showed binucleated plasma cells. Morphologically, they resembled mononuclear cells and contained abundant basophilic cytoplasm which ultra-structurally showed extensive rough endoplasmic reticulum. Their 2 nuclei exhibited the "cart-wheel" arrangement of heterochromatin characteristic of plasma cells. When serially examined the 2 nuclei remained separate. In addition, pairs of closely apposed plasma cells were observed. Some of these cells showed distinct apposing membranes separated by a gap of approximately 15 nm. While others, exhibited localised areas of indistinct membranes. There were also pairs of closely apposed plasma cells showing cytoplasmic bridges. These results suggest that the mode of formation of binucleate plasma cells is probably cell fusion. They also show that these binucleate cells are not confined to a single disease as they were found in 10 different diseases.