Construction and properties of a recombinant pseudorabies virus with tetracycline-regulated control of immediate-early gene expression

A study was carried out to determine whether altering the control of expression of the IE180 gene of pseudorabies virus (PRV), by replacing the IE180 promoter with the tetracycline-responsive promoter (Ptet), affects virus replication and virulence. This PRV-BT90 mutant virus was constructed by complementation and recombination in Hela Tet-Off cells. The virus yield produced by infection of Hela Tet-Off cells with PRV-BT90 was similar to that of the parental virus vBecker2. Viral replication of PRV-BT90 was reduced in Vero cells as reflected by a reduction of virus yield and plating efficiency compared to vBecker2. PRV-BT90 plaque formation in Hela Tet-Off cells was inhibited in the presence of doxycycline, whereas vBecker2 plaque formation was not affected. Subcutaneous infection of mice with the two viruses revealed a LD50 higher than 106 TCID50 for the PRV-BT90 mutant virus while the LD50 was 178 TCID50 for the vBecker2 parental virus.