Enhancement and suppression by actinomycin D of a Vero cell nontransmissible measles infection.

The effect of low doses of actinomycin D on Vero cell nontransmissible measles infection produced after cocultivation with a HeLa subline with persistent defective infection by Edmonston measles virus was examined by pretreatment of Vero cells with the drug and treatment at 1, 4, and 7 days after Vero cell infection. Pretreatment enhanced focal formation of viral immunofluorescent Vero cell syncytia but did not induce synthesis of detectable amounts od cocultures suppressed syncytial formation, and treatment of 4- and 7-day-old cocultures had little, if any, effect on syncytial formation. Pretreatment also eliminated a transient resistance to homologous superinfection. A possible relation of these findings to the presence of a cell-associated viral inhibitor in the persistently infected HeLa cells is discussed.