Effect of Carcinogenic and Noncarcinogenic Hydrocarbons on Interferon Synthesis and Virus Plaque Development2

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Abstract
In cultures of rat embryo cells, interferon production was depressed by the carcinogen, benzo[a]pyrene (BaP), but not by its noncarcinogenic counterpart, benzo[a]pyrene (BeP). This suggests a correlation between carcinogenic power and inhibition of interferon synthesis. When rat embryo cells were preincubated with BaP and 7,12-dimethylbenz[a]anthracene (DMBA), Sindbis virus plaques were significantly larger than in control cultures. In contradistinction, no increase in Sindbis plaque size was observed after incubation of the rat embryo cultures with 4 noncarcinogenic hydrocarbons. In a continuous line of rat cells, in which interferon was not active, no enhancing effect on plaque size was obtained with either BaP or DMBA. This provides evidence that the increased plaque size, obtained with carcinogens in rat embryo cells, is related to the depression of interferon synthesis. The possibility of a direct stimulation of virus growth by carcinogens, either by shortening the eclipse phase or by increasing the virus yield per cell, was excluded by the superposable one-step growth curves obtained with Sindbis virus in control and BaP-treated rat embryo cells.