FIG 1.

Serially egg-passaged viruses exhibit an in vitro phenotype similar to that of the virulent parent M41-CK. (A) Growth kinetics of serially egg passaged virus on CK cells. Confluent 6-well plates of CK cells were infected with virus at an MOI of 0.05. At 1, 24, 48, 72, and 96 h postinfection, cell medium was harvested for analysis of viral progeny by plaque titration assay on CK cells. Each value represents the mean of three replicates, with SEMs plotted as error bars. (B) Ciliary activity of viral growth in TOCs. TOCs were infected with 5 × 10⁴ PFU of IBV or mock infected with medium. Ciliary activity was assessed under a light microscope at days 4 to 8 postinfection and scored as follows: ≈100% activity = 4, ≈75% = 3, ≈50% = 2, ≈25% = 1, and ≈0% = 0. Each value plotted represents the mean score of 11 replicates, with SEMs plotted as error bars.