Enhanced Virus Production Research Articles

Induction of type C viruses in cultured guinea pig cells.

Particles morphologically resembling type C viruses were activated by bromodeoxyuridine (BUdR; 10(-4) M) treatment of cultured guinea pig cells. Virus particles were isolated from the cells of normal and leukemic strain 2 and random-bred guinea pigs (adult and embryonic). Immature virus particles with electron-lucent cores were found in the cytoplasmic matrix. The mature particles with electron-dense cores were found outside the cells and some appeared in the process of budding from the plasma membrane. The peak of virus production was observed within 4 days of BUdR treatment. When compared to the amount of virus produced in darkness, visible light enhanced virus production, whereas exposure of BUdR-treated cells to UV light either had no effect or inhibited virus production. Virus particles had a density of 1.16 gm/ml, possessed an oncornavirus-specific reverse transcriptase, and contained a large-molecular-weight RNA (65-70S) which dissociated into 36S subunits after heat denaturation. The BUdR-activated virus particles, therefore, possessed the morphological, biophysical, and biochemical characteristics of type C oncornaviruses.

The effect of proflavine on rubella virus replication in baby hamster kidney (BHK-21) cells.

When BHK-21 cells are pretreated with proflavine for 24 hours prior to rubella infection there is a significant delay in virus replication. This, however, is followed by improved yields of infectious virus, haemagglutinin and complement-fixing antigens. The enhanced virus production appears to be related to maintenance of the cell monolayer in a healthy condition for a longer period of time, secondary to depression of the metabolic rate of the cells by the proflavine.

Inhibition and stimulation of tobacco mosaic virus by purines

Fourteen compounds were tested for their effect on the multiplication of tobacco mosaic virus (TMV) in tobacco ( Nicotiana tabacum L.) tissue cultures. Three compounds, 6-chloropurine, purine, and 8-chloroxanthine, inhibited TMV about as well as 8-azaguanine and thiouracil. These compounds were effective as virus inhibitors at concentrations from 10 to 100 mg/l, but they also inhibited the host tissue at these levels. The compounds 2-aminopurine, 2,6,8-trichloropurine, caffeine, and isoguanine inhibited the host tissue at lower concentrations than they inhibited the virus; theophylline, 6-mercaptopurine, and 2,6-di(diethylamino)purine had a comparable effect. Caffeine, and most other compounds in this group, stimulated production of the virus at low concentrations; caffeine at 1 g/l enhanced virus production 80%. Thus caffeine may be useful for stimulation of at least this virus. The concentration of these compounds effective in inhibiting tissue growth was generally over 100 mg/l; however, 10 mg/l of 6-mercaptopurine or isoguanine was inhibitory. Hypoxanthine, 2-oxypurine, and 6-methyl-2-oxypurine were without apparent effect on the host or virus at the concentrations tested. 6-Methylpurine was the first compound observed to inhibit virus production without inhibiting growth of the host. Its antiviral activity was evident at as low as 0.01 mg/l, and 0.1 mg/l reduced the number of local lesions by 40%. Concentrations of 0.25 mg/l or greater were necessary to damage the host tissue. 6-Methylpurine had to be applied at a concentration of 10 mg/l to whole plants to delay the appearance of symptoms for about 7 days.