Replication and plaque formation of parainfluenza viruses in an established line of monkey kidney cells.

All four types of parainfluenza virus produced distinct plaques in an established line of monkey kidney cells (LLCMK2) under agar overlay containing trypsin and DEAE dextran. Parallel titration of these viruses in LLCMK2 and primary cynomologous monkey kidney (MK) cells showed that LLCMK2 cells were about tenfold more sensitive than MK cells. When trypsin was added to the fluid medium, the virus yield in LLCMK2 cells was significantly higher than in MK cells.