Studies In Vitro, In Vivo, and by Electron Microscope of a Virus Recovered From a C3H Mouse Mammary Tumor: Relationship to Polyoma Virus23

Abstract

Previous studies indicated that a virus we recovered in tissue culture from a C3H mouse mammary tumor had some effects in mice and hamsters that were similar to and others dissimilar from those of the polyoma virus. To clarify the relationship between these two viruses, further studies in vitro, in vivo, and with the electron microscope were made and are reported here. An important finding from the studies in vitro was that the two viruses were indistinguishable by hemagglutination inhibition tests. The studies in vivo related chiefly to the effects of the virus in rats; this had not previously been determined. Our virus was found to be much more pathogenic for this species than the polyoma virus was. Finally, electron-microscope studies were made on hamster kidneys 5 to 7 days after infection; previous light-microscope studies had shown that the necrotizing effect of the virus was then at its peak. These studies revealed particles 28 mµ in diameter particularly in the nuclei and in phagocytosed material in the cytoplasm of medullary stromal cells. Similar particles were found in nuclei of cells in which the virus was being propagated, and a few were occasionally seen in the nuclei of cells of parotid tumors induced in mice by the virus. These particles probably represent the virus responsible for the tumors; their morphology is similar to that described by others for the polyoma virus. The significance of larger viruslike particles observed in some of the tumors induced in mice is discussed. The conclusion from all our studies is that the virus recovered from the C3H mammary carcinoma belongs to the polyoma family. However our virus preparations are less carcinogenic for mice and more carcinogenic for hamsters and rats than the polyoma virus recovered by Stewart, Eddy et al. These differences suggest that the virus recovered in our laboratory is a variant of the polyoma virus.