FIG. 4.

Characterization of plaque phenotypes of candidate LAIV-delNS1 and wild-type (Wt) viruses. Monolayers of primary CEK cells were infected with each virus and incubated at 37.5°C for 3 days, fixed with formalin, and stained with Giemsa. Plaque sizes or numbers did not change when 2-aminopurine, an inhibitor of IFN induction in chicken embryonic cells (24), was included in the overlay, indicating that any differences in plaque size were not attributable to the IFN system (24). The plaque plates have been arranged in the order of increasing diameter (mean ± standard deviation mm; n = 55).