Transformation of Rat Mammary Cell Cultures by R-35 Virus Isolated From Spontaneous Rat Mammary Adenocarcinoma<xref ref-type="fn" rid="FN1">1</xref><xref ref-type="fn" rid="FN2">2</xref>

Abstract

R-35 virus can infect and transform cells in monolayer cultures derived from mammary tissue of hydrocortisone-treated, lactating, Sprague-Dawley rats. Observed in cultures, within 6 days after infection, were discrete foci of hyperrefractile spindle and rounded cells that were readily distinguishable from the background monolayer of normal cells. On further incubation, the number of transformed cells in the focus increased, and the rounded transformed cells piled on top of each other, indicating a loss of contact inhibition. There were budding C-type virus particles in the infected cultures. The foci, after being stained with azurepyronine dye, were clearly visible macroscopically. Virus concentration was linearly related to number of foci produced when twofold dilutions of virus stocks were added to the normal, lactating, rat mammary cells. The yield of virus particles (as quantitated by electron microscopy) from infected cultures incubated at 33 °C was twice as much as that from cultures incubated at 37 °C. However, no statistically significant difference in infectivity titers was noted when virus harvested at these 2 temperatures were assayed. The virus-induced transformation could be neutralized if the virus was incubated with specific antiserum. R-35 virus-specific antigen(s) was detected in the cytoplasm of transformed cells by an indirect immunofluorescent technique.