Release of Leukemia C Particles from Murine Cell Lines Infected with Bittner Virus-containing Inocula1

Multiple attempts to infect cell lines derived from normal mouse embryos or from normal mouse mammary glands with inocula currently used for experimental transmission of mammary tumor virus have resulted in the abundant produc tion of type C virus particles. Skimmed infectious milk, acellular mammary tumor extracts, and what appeared to be pure mammary tumor virus virions (B particles), which all induce up to 60% of mammary tumors in sensitive mice, initiated the production of C particles in tissue culture. The viral particles were seen budding from the cell membrane and accumulated in the intercellular spaces. The characteriza tion of the C particles as a virus belonging to the leukemia group and evidence of the absence of mammary tumor virus were obtained by complement fixation, immunofluorescence, and bioassays. B particles, indicative of the mammary tumor virus, were not seen except for two of them found independently in two cell lines inoculated with tumor extracts. Apparently, these particles were not proliferating because none were observed in subsequent subcultures. The finding of C particles in a nontreated C57BL line suggested that the viral genome for leukemia and/or sarcoma might be carried in cells of this genotype.