FIG. 5.
Effect of day of cell culture maintenance on the capacity of viruses from the persistently infected MA104 cell cultures to grow without trypsin pretreatment. Monolayers of MA104 cells (105 cells) were infected with cell culture lysates (0.2 ml of lysate stock) obtained from the persistently infected MA104/SA11-B and MA104/SA11-D cultures. Prior to adsorption, each viral inoculum was not treated with trypsin. After 1 h of adsorption, the inoculum was removed, fresh trypsinfree medium was added, and cells were incubated at 37°C for 24 h. Virus in cell lysates was titrated by plaque assay using MA104 cells. The results are presented as the mean viral yields (titer at 24 h divided by titer at 0 h) for two independent experiments.