Changes of the cell type of BHK-21 lines by persistent Sindbis virus

Persistent infection by Sindbis virus (SV) can be induced in cultures of BHK-21 cells. In a persistently infected cell line only 5% of the cells produced virus. Virus titers in the medium reached 10(5) PFU per ml. A persistent infection could be eliminated from cultures by seeding at most 100 cells per bottle. Compared with the original line decontaminated lines differed in several properties. After infection with SV ten times less virus was released into the medium, and an infection persisted without producing periodic cell destructions as observed in establishing a persistent infection in the original line. In decontaminated lines plaques formed by different viruses were either not visible or smaller than those in normal cells. Persistently infected as well as decontaminated lines had lost three chromosomes. The altered cell type of persistently infected lines apparently originated by selection of a cell mutant which was not destroyed by SV. Results suggested that a small number of cells susceptible to the virus continuously arises from the population of altered cells, and that virus infection is transmitted and maintained in the cultures by these sensitive cells.