Virus resuspended from
individual plaques was amplified to 105-106 plaque-forming
units by infection of about 105 BHK-21 cells, incubated for 2
hr at 40C with a 1:1 dilution of the supernatant of the
hybridoma culture, and plated (4) with a 1:50 dilution of the
same supernatant included in the agar overlay