An electron microscopic examination of murine plasma cell neoplasms with and without paraproteinemia.

We have examined seven generalized neoplasias which developed in BALB/c mice subsequent to inoculation of subcellular leukemic material from mice with plasma cell leukemias. Based on light microscopic criteria the malignancies were classified as immature plasma cell neoplasms. Four were associated with paraproteinemia of the gamma-globulin G type and 3 had normal electrophoretic patterns. An electron microscopic examination of malignant infiltrates from spleens and peripheral lymph nodes from both groups of animals showed the dominant malignant cell to be a rather primitive mesenchymal cell with some plasmacellular differentiation. Cells from leukemias with paraproteinemia usually exhibited more nucleoli, ergastoplasmic channels, and free ribosomes than cells from leukemias with normal serum electrophoresis. Amyloid fibrils were present both extraand intracellularly in leukemic infiltrates from both groups of leukemias.