Growth of Rubella Virus in BHK21 Cells. I. Production, Assay, and Adaptation of Virus.

Abstract

Summary Two clones of BHK21 baby hamster kidney fibroblasts were studied in relation to the growth of rubella virus (RV). One clone (13S) could easily be adapted to suspension culture. RV in titers of 10^7.0-10^7.5 PFU/ml were found in supernatant fluids harvested between 50 and 70 hours. About 30 PFU per cell were produced in the first cycle of infection. Large quantities of virus could be produced in suspension culture, particularly when chronic infection was produced. RV was cytopathogenic for BHK21 cells, and a second clone (WI-2) proved most useful in detection of this property. End-point titrations and neutralization tests could be performed in this cell strain, although environmental conditions had to be maintained within narrow limits. A plaque assay was developed using the WI-2 clone and a semisolid carboxymethylcellulose overlay. Small but distinct plaques appeared at 5-6 days. During passage in BHK21/13S, the titer of RV measured by PFU in BHK21/WI-2 was constant, but the titer of RV measured by interference in African green monkey kidney cells gradually declined, indicating a considerable degree of deadaptation. Of the RV strains studied, those propagated in BHK21, WI-38 or RK₁₃ cells produced larger and more numerous plaques in WI-2 cells than the two RV strains derived from monkey kidney cells.