[Persistent infection in murine L cells infected with the parainfluenza virus SV5].

Persistent infection of mouse L cells was achieved by serial passages of undiluted parainfluenza SV5 virus. At the level of the 10--12th passage a stationary noncytocidal type of persistent infection was established. A low level of the infectious virus produced by the persistently infected cells was observed; the number of cells synthesizing the virus-specific antigen detectable by immunofluorescence was high. Persistently infected cells were resistant to the infection with the homologous virus and sensitive to superinfection with heterologous viruses. The persisting virus had marked interfering activity. The possibility of participation of defective interfering particles and endogenous oncornavirus in the maintenance of the persistent infection is discussed.