An Electron Microscopic Study of a Series of Murine Lymphoid Neoplasms

Particles associated with a group of primary lymphoid neoplasms of the mouse were examined with the same electron microscope in tissues fixed, dehydrated, embedded, and stained in the same manner. The neoplasms studied were those induced with the Moloney, Gross, Manaker C-60 (Schwartz), and Friend agents, the strain C57BL/Ka radiation-induced lymphoid leukemia, and the spontaneous lymphoid leukemia s of strain AKR and C3Hf/FgLw mice. No particles were associated with the radiation-induced leukemia of C57BL/Ka mice, but in all the other neoplasms, particles of characteristic size and fine structure were identified. Megakaryocytes of the spleen and bone marrow were the most satisfactory sources of particles, both from the point of view of frequency of occurrence and state of preservation. Particles were formed within megakaryocytes and retained in channels in the cytoplasm, apparently for relatively long intervals. Immature particles (with electron-lucent nucleoids) associated with 6 of the 7 leukemias studied had an average diameter of 100 mµ. Mature particles (with electron-dense nucleoids) associated with the Moloney and Manaker C-60 (Schwartz) leukemias also averaged 100 mµ in diameter, while mature particles associated with the Gross and Friend neoplasms and the spontaneous leukemias of strain AKR and C3Hf/FgLw mice were measurably smaller. Approximately 20 percent of the platelets of peripheral blood of Osborne-Mendel rats with lymphoid leukemia induced with the Moloney agent contained characteristic particles, and in the sections of platelet pellets numerous particles were identified lying free in the plasma between the platelets. The significance of these observations is discussed.