Aberrant cytoplasmic structures in avian virus tumor cells

Cells of avian virus-induced tumors occasionally show cytoplasmic masses containing structures of characteristic morphology. These consist of essentially spherical bodies of a 30–40 mμ diameter consisting of an electron-dense material enclosed in a shell of higher density surrounded by an indefinite outer zone with associated ribosome-like electron-dense bodies. The spherical bodies resemble somewhat the immature avian virus particles budding at the cell surface. Structures of this appearance are unique to avian virus tumors and occur in different neoplastic cell types in growths induced by a wide variety of avian tumor virus strains. The structures were interpreted to be the result of abortive processes of cytoplasmic virus synthesis in the absence of components and conditions for elaboration of the complete virus particle. No evidence indicated that the spheres developed into typical virus particles or were a stage in or contributed to the usual processes of virus assembly by budding at the cell membrane. There was the appearance, however, of possible involvement of cytoplasmic ribosome-like bodies in virus-budding from chondrocytes in which budding was impeded by cartilage components elaborated at the cell surface.