An aliquot from a continuous fermenter culture of baby hamster kidney cells (BHK-21 Clone PD-4) (Wistar) maintained in Ca free Eagle's Basal Medium containing 2% Kaolin adsorbed fetal calf serum was planted in spinner flasks at 300,000 cells per ml, total volume 600 ml. After equilibration for one day at 35°C to insure that cells were in log phase, the culture was infected with the M-33-AGMK25 BHK-219 strain of rubella at an input multiplicity of about 6 TCID50 per cell. The virus was identified with specific rubella antiserum.Preliminary experiments had shown that such cultures would reach a peak or plateau HA titer of approximately 1:64, 24 hrs after inoculation and would continue to yield virus for 6 to 12 days. One hundred ml aliquot harvests were withdrawn daily and the culture was returned to volume with growth medium and incubation continued. The harvested cells were spun down rapidly at 2500 rpm per 15 mins., fixed in 3.7% gluteraldehyde in Ca free phosphate buffer saline, and post fixed in osmium tetraoxide. After dehydration, the cells were embedded in Epon 812 and cured approximately 20 hrs at 60°C.
