Suppressive effects of interferon on cell fusion by Sendai virus.

Suppressive effects of human IFN-alpha, IFN-beta and mouse-IFN on syncytium formation in human and mouse transformed cells have been studied using u.v.-irradiated Sendai virus (UV-Sendai virus). After treatment of human RSa cells with 500 units/ml human IFN-alpha for 16 h, the syncytium formation induced by UV-Sendai virus was reduced to less than 10% of controls. The suppressive effect was dependent on the amount of interferon added, and it was blocked by the addition of cycloheximide. Suppression of syncytium formation was also observed on human IFr cells, which are partially resistant to the anticellular effect of interferon but are sensitive to the antiviral effect of interferon. Human IFN-beta also had a suppressive effect on syncytium formation in human transformed cells, and human IFN-alpha, IFN-beta and mouse IFN showed species specificity in their effect on fusion. This anti-cell fusion activity was developed in IFr cells from about 5 h after addition, of IFN-alpha and when the cells were treated with IFN-alpha for 16 h, the resistant state of cell continued for over 20 h after removal of IFN-alpha.