FIG. 5.

(A) CEC (1 × 10⁶) were infected with 100 PFU of the parental or mutant MDV and used for determination of plaque areas. Infected cells were stained with a MDV-specific serum by indirect immunofluorescence, examined with a fluorescence microscope (Zeiss Axiovert 25), photographed with a digital camera (Zeiss Axiocam), and measured with the ImageJ software. Means and standard deviations (error bars) of 100 plaques per virus are given. (B) Multistep growth kinetics of mutant MDV. Fresh CEC were coseeded in six-well plates with 100 PFU of infected cells per well. At the indicated time points p.i., cells were trypsinized and coseeded with fresh cells. Titers were determined by immunofluorescence staining of virus plaques with the MDV-specific serum and counting of the plaques at 3 days after coseeding of infected cells with uninfected cells. Means and standard deviations (error bars) of three independent experiments are given.