Characterization of the parental virus, MDV △UL28-Re, MDV △UL28 and UL28 co-transfection resulted recombinant viruses. A Growth kinetics of recombinant viruses was examined by inoculation with 100 PFUs of the indicated virus into CEF cells, respectively. The infected CEF cells were trypsinized and seeded on fresh cells on days 0, 1, 2, 3, 4, 5, and 6 post-inoculation. MDV-specific plaques were counted at 7 days post-inoculation on fresh CEF for virus titers calculation. The experiment was performed in duplicate, and virus titer is indicated as PFUs for each 35-mm dish. Results represent mean values with error bars showing the standard error of the mean; B CEF cells were infected with 100 PFU per 60 mm dishes of parental, revertant or co-transfected mutant viruses and used to determine the plaque areas. Seven days post-infection, the infected cells were stained with MDV specific anti-gB monoclonal antibody and examined under fluorescence microscope. The virus plaque areas were measured by ImageJ software. Results represent mean values with error bars showing the standard error of the mean.