ELECTRON MICROSCOPE OBSERVATIONS ON INTRACELLULAR VIRUS-LIKE PARTICLES ASSOCIATED WITH THE CELLS OF THE LUCKÉ RENAL ADENOCARCINOMA

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Abstract
The common renal adenocarcinoma of the leopard frog was studied in thin sections with the electron microscope. Approximately a third of the tumors examined contained spheroidal bodies of uniform size and distinctive morphology that are believed to be virus particles. These consist of hollow spheres (90-100 m[mu]) having a thick capsule and a dense inner body (35-40 m[mu]) that is eccentrically placed within the central cavity (70-80 m[mu]). Virus particles of this kind occur principally in the cytoplasm but occasionally they are also found in the nucleus and in the extracellular spaces of the tumor. The intranuclear inclusion bodies that are visible with the light microscope are largely comprised of hollow, spherical vesicles with thin limiting membranes. These are embedded in a finely granular matrix. A few of the thin walled vesicles contain a dense inner body like that of the cytoplasmic virus particles. This suggests that they may be immature virus particles. The inclusion bodies are believed to be formed in the course of virus multiplication but they usually contain very few mature virus particles. These findings are discussed in relation to previous work suggesting that the Lucke adenocarcinoma is caused by an organ-specific filtrable agent. The "virus particles" described here may be the postulated tumor agent but the possibility that they are not causally related to the tumors cannot be excluded.