Establishment andMaintenance ofPersistent Infection by Sindbis Virus inBHK Cells

We haveestablished a persistent infection ofBHK cellswitha preparation of Sindbis virus heavily enriched indefective interfering (DI)particles. Thesmall fraction ofcellsthatsurvived theinitial infection grew outtoforma stable population ofcells[BHK(Sin-1) cells], mostofwhichsynthesized viral RNA and viral antigens. ThepresenceofDIparticles inthisvirus stock was required to establish this persistent state. BHK(Sin-1) cellsreleased asmall-plaque, temperature-sensitive virus(Sin-i virus) as wellas DIparticles containing DIRNAs larger thanthose present intheoriginal stockusedtoestablish thepersistent state. A cloned stock ofSin-i virus, freeofdetectable DIparticles, was ableto initiate apersistent infection more quickly andwithgreater cellsurvival thanthe original stock ofSindbis virus containing DIparticles. About2weeksafter the Sin-1 virus-infected cellswere cultured, DIRNAs aroseandsoon becamethe dominant viral RNA species produced bythese cells. Manyhighly cytopathic RNA viruses arecapable oflong-term persistence andreplication in cultured mammalian cells. Inthemostextensively studied systeminvolving vesicular stomatitis virus (VSV), three majorfactors were implicated intheestablishment andmaintenanceofsuchpersistently infected cultures: (i) defective interfering (DI)particles, (ii) mutations inthestandard virus (particularly tsmutations), and(iii) interferon production. Huang