Some Ultrastructural Characteristics of a Series of Primary and Transplanted Plasma-Cell Tumors of the Mouse

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Abstract
Cells of 21 plasma-cell neoplasms were examined with the electron microscope. Of these, 17 were mouse tumors, 11 of which were tested in transplant and found to be associated with serum hyperglobulinemia. Six primary tumors were also examined, 3 of which were studied in transplant. In addition, 4 multiple myelomas in man were examined. For comparative purposes other neoplasms from the same strains of mice, including 3 tumors diagnosed as undifferentiated plasma-cell tumors and 6 as fibrosarcomas, as well as normal plasma cells from lymph nodes and lamina propia of the gut, were examined. The cells of the plasma-cell tumors presented ultrastructural features basically similar to those of their normal prototypes. These features included 1) a well-developed Golgi complex with associated bodies having the ultra-structural characteristics of secretory granules; 2) a highly developed ergastoplasm occupying the remainder of the cytoplasmic area beyond the Golgi zone. The neoplastic plasma cells differed from normal plasma cells at the ultra-structural level in 3 respects: 1) The neoplastic cells did not show the great variation in size of the cisternae of the ergastoplasm characteristic of a series of normal plasma cells. 2) The neoplastic cells contained many more ribosomes lying free in the cytoplasm than did normal plasma cells. 3) Cells of all the plasma-cell neoplasms contained particles with the ultra-structural morphology of viruses (type A of Bernhard). No particles were observed in normal plasma cells or in multiple myeloma cells from 4 humans. The particles were not considered oncogenic viruses responsible for the development of plasma-cell neoplasms. A full discussion of this point is given.