Some Factors Affecting the Interferon-Induced Antiviral State

The results of the present study indicate that several factors affect the interferon-induced resistance to viruses in tissue culture. Reaction of cells and interferon results in rapidly increasing antiviral activity over about 7 hours. Thereafter antiviral activity remains relatively stable in the presence of an unchanging amount of interferon in the extracellular fluid. Continued presence of the initial concentration of interferon was required to maintain the established level of resistance. Addition of more interferon resulted in a further rise of resistance. The level of cellular antiviral activity was determined mainly by the concentration of interferon rather than by the amount applied. Maintenance of resistance required continued cellular protein synthesis and also probably required continued cellular RNA synthesis. These findings support the previous proposal that development of antiviral activity by cells exposed to interferon is due to the induction of a cellular antiviral protein. The results also suggest that maintenance of stable antiviral activity in the presence of interferon could be the result of continued induction by interferon of enough antiviral protein to offset decay.