Influence of chicken genotype on protection against Marek's disease by a herpesvirus of turkeys recombinant expressing the glycoprotein B (gB) of Marek's disease virus

Two inbred lines of White Leghorn chickens which differ in B-haplotype were immunized at 2 days of age with a thymidine kinase negative (tk-ve) herpesvirus of turkeys (HVT) recombinant expressing the glycoprotein B (gB) gene of Marek's disease virus (MDV) and were challenged 6 days later with 1000 p.f.u. of the highly virulent RB1B strain of MDV. Mock-vaccinated chickens and chickens immunized with a spontaneous tk-ve HVT mutant served as controls. Genetically resistant B21 chickens were protected by immunization with the recombinant as well as by the tk-ve HVT, whereas highly susceptible B13 chickens were partially protected by the recombinant but were not protected by the tk-ve HVT. Rhode Island Red chickens (HPRS RIR), which differ from the White Leghorns at the B locus, were protected by both vaccines but the recombinant conferred a significantly higher level of protection than the tk-ve HVT. The results suggest that the gB gene of MDV serotype 1 has an important role in the induction of protective immunity against highly virulent MDV in genetically susceptible lines of chickens and that vaccinal immunity in White Leghorns might be influenced by the B haplotype.