Biochemical characteristics of rat C-type virus WF-1.

The non-oncogenic rat C-type virus WF-1, isolated from a Wistar-Furth rat embryo cell line, was characterized biochemically. The purified virus has a buoyant density of 1.15 to 1.

Virus-induced peliosis hepatitis in rats.

Inoculation of newborn Fischer, W/Fu, or Lewis rats with the 9H virus recently isolated from leukemic rat tissues resulted in the development of peliosis hepatis. The virus was recoverable from the peliotic livers. The cystic lesions were of the parenchymal peliosis type and appeared to be the result of focal hepatic necrosis followed by hemorrhage.

Low malignancy of Rous sarcoma cells as evidenced by poor transplantability in turkeys.

Homologous and isologous transfers of Rous sarcoma cells in turkeys indicate that growth of the implanted cells contributes little, if at all, to the formation of these neoplasms. Infection of normal host cells by virus appears to be, at least in this species, the major factor in the induction and progressive growth of Rous sarcomas.

Critical Factors in Successful Recovery of Rous Sarcoma Virus from Turkey Tumors.

Studies of tumor cell cultures with antiviral antibody showed that most of the cell-associated virus and viral antigen were found at the cell membrane and were thus accessible to the effect of neutralizing antibody. Humoral antibody present in tumor tissue neutralized cell-associated virus in vivo and thus rendered the tumor cells temporarily noninfectious. When these cells were grown in vitro in the absence of antibody, virus eventually reappeared.

Studies on persistent infections of tissue cultures. IV. Evidence for the production of an interferon in MCN cells by myxoviruses.

In previous reports of this series, it was shown that persistent infection of MCN cultures with certain myxoviruses rendered the cells insusceptible to superinfection by several cytopathogenic viruses. It was thought that production of an interferon might be the cause of this resistance and efforts to confirm this suggestion have been presented. Addition of ultraviolet-inactivated myxoviruses (mumps, Newcastle disease, influenza A, and Sendai) to MCN cultures for periods of 2 to 3 hours, followed by washing and refeeding of the cells, led to the subsequent release into the media of a substance which induced in fresh MCN cells a transitory resistance to infection by vesicular stomatitis virus, and prevented incomplete reproductive cycles of influenza A and Sendai viruses.

Studies on persistent infections of tissue cultures. III. Some quantitative aspects of host cell-virus interactions.

Efforts were made to obtain information on some of the quantitative aspects of host cell-virus interactions in MCN cultures persistently infected with Newcastle disease, mumps, and 6-6 viruses, and to elicit the mechanism which permits simultaneous maintenance of virus and cells for indefinite periods of time. It was shown by 4 different technics that only between 10 and less than 1 per cent of the cells yield infectious virus, depending upon the agent employed and, possibly, variations in the conditions of the cultures. No evidence was found to indicate production of non-infectious virus materials.

Studies on persistent infections of tissue cultures. II. Nature of the resistance to vesicular stomatitis virus.

Efforts were made to elucidate the nature of the resistance to vesicular stomatitis virus (VSV) observed in MCN cultures persistently infected with Newcastle disease, mumps, or 6-6 viruses (MCN(NDV), MCN(Mps) and MCN(6-6), respectively). Cells derived from persistently infected cultures adsorbed VSV to the same extent as their uninfected counterparts. Only a fraction of the adsorbed virus could be recovered from the cells indicating that it enters into an eclipse in all of the cell types.

Studies on persistent infections of tissue cultures. I. General aspects of the system.

Inoculation of the MCN and Lung-To lines of human cells in continuous culture with Newcastle disease (NDV), mumps, or 6-6 viruses led to slight cytopathic effects (CPE) if the multiplicity of infection exceeded one. On second passage or with smaller initial inocula no CPE became apparent. The viruses multiplied, however, as determined by titrations in HeLa cultures or chick embryos.