As shown in Figure 4A, the recombinant viruses and the parental virus achieved the highest replication level at 120 h post-infection with the viral titers of 104.92, 104.87, 104.89, and 104.90 PFU/mL (p > 0.05), indicating that insertion of the σB and σC genes in the US2 site had no significant effects on the replication of the MDV vaccine strains in CEFs. Here, PPIB is linked to infection.