Suppressive effects of interferon on syncytium formation by RD-114 virus in human transformed cells.

The RD-114 virus rapidly induced syncytia in the human transformed cell lines, RSa, RSb and IFr. Treatment of the virus with heat or ultrasonic vibration completely eliminated the syncytium-forming activity. Irradiation with u.v.-light or treatment with beta-propiolactone (BPL) reduced but did not completely destroy the activity. Pre-treatment of the cells for 16 h with 25 to 500 units/ml of human leucocyte interferon (Le-IF) or fibroblast interferon (F-IF) significantly reduced formation of syncytia by active virus or inactivated (u.v. or BPL) virus. This activity of interferon was inhibited by treatment of the cells with cycloheximide. Interferon did not increase the binding of 3H-uridine-labelled RD-114 virus to the cells. It is postulated that interferon treatment altered the plasma membrane of the cells and thus reduced their capacity to fuse.