Comparative effects of beta-propiolactone on mice, mouse-derived cell cultures, and Venezuelan equine encephalomyelitis virus

Studies were made comparing the toxicity of beta-propiolactone (BPL) for mammalian (mouse) cells in vitro and for mice and for Venezuelan equine encephalomyelitis (VEE) virus which is highly cytopathogenic for each. The mammalian cells grown in tissue culture were found to be adversely affected by BPL in concentrations ranging from 0.001 to 0.1 mg/ml of supernatant fluid. The difference in response was influenced by the menstruum in which the BPL was suspended and the difference in cell types tested. Tenfold less BPL appeared to be required to destroy the cells when it was suspended in a balanced salt solution than when it was suspended in protein-containing solutions such as beef heart infusion broth or medium 199 plus 20% horse serum. Secondary embryonic mouse lung cells seemed slightly more adversely affected by BPL than the established embryonic lung or L cells. BPL given to mice by intranasal instillation and by intracerebral injection was lethal to half of the animals within 2 days at doses of 0.31 and 0.39 mg, respectively. Higher concentrations of BPL were required to rapidly inactivate the virus in vitro than were required to kill mice or to cause a toxic effect on cells in culture. It required 10 mg/ml of BPL to completely inactivate a high-titered VEE virus preparation in 5 min and 1 mg/ml to inactivate most, but not all, of the virus in 15 min. A concentration of 0.1 mg/ml of BPL had only a slight effect on the virus after a period as long as 60 min. Evidence is presented indicating that simultaneous inactivation of all of the properties of the VEE virus particles by BPL aerosols did not occur at the same time but that, after treatment, the virus possessed a limited ability to immunize mice despite a loss in infectivity.

Structure and development of viruses as observed in the electron microscope. V. Western equine encephalomyelitis virus

Stages in the development and release of Western equine encephalomyelitis virus are illustrated and described. It is suggested that precursor particles 22 mmicro in diameter differentiate at template sites close to membranes bordering cytoplasmic vacuoles and that these particles either pass into the lumen of the vacuole, acquiring in the process a coat and peripheral membrane, or are dispersed in the cytoplasm and extruded through the cellular wall, emerging as viral particles on the surface. Although necrosis and dissolution of the cell with release of contents, including virus, may intervene at any stage of infection, ejection of virus from the vacuoles presumably can occur without rupture of the cell. The virus consists of a 30 mmicro core separated by a zone of lesser density from a sharply defined peripheral membrane 45 to 48 mmicro in diameter. Precursor particles, as well as viral particles, occasionally crystallize, the former in the cytoplasm, the latter in vacuoles and probably on the cellular surface.

Nutritive requirements of a small plaque mutant of Western equine encephalitis virus

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