Figure 6.

IBV replication is not affected by trypsin cleavage in CK cells. Three strains of IBV were passaged in the presence of TPCK-treated trypsin at three concentrations, 0.2, 0.5 and 1.0 µg/mL, alongside untreated (UT) samples of each strain. Cells were infected with each IBV diluted at a ratio of 1:1 in serum free BES media containing each concentration of TPCK-treated trypsin. Supernatant was harvested at 48 hpi and used for the subsequent passage following the same protocol. Supernatant from each passage was titrated on CK cells in triplicate and viral titres were calculated (pfu/mL). The average viral titre at each passage is shown for M41-CK (A), Beau-R (B) and 4/91 (C).