Persistence of Sindbis virus in BHK-21 cell cultures

Summary

If BHK-21 cell monolayer cultures are inoculated with Sindbis virus individual surviving cells can be observed, which are capable to multiply thereby forming small colonies in which the virus persists. The virus causes periodical cell destructions usually starting in the centers of the colonies. Increasing virus titers are observed during the phases of cell destruction and decreasing titers during the phases of cell growth. It takes several weeks for the slow growing colonies to form confluent cell sheets. Those cultures can be trypsinized and grown in continuous passages. The above mentioned periodical cell destructions then do no longer occur because a more stable equilibrium between BHK-21 cells and Sindbis virus has been established. About 6% of the cells are virus producers as evidenced by infective center tests. The supernatant contains approximately 10⁴ to 10⁵ PFU per 0,1 ml. The behaviour of the cells is changed concerning plaque formation by Sindbis virus if the persistent infection is eliminated by addition of immune serum. Cell morphology, however, remains unchanged. Virus from persistently infected cells differs also from the original virus: it produces smaller plaques in BHK-21 cell and chick embryo fibroblast cultures.