Role of γδ T cells in turkey herpesvirus vaccine protection against Marek's disease virus.

γδ T cells are a highly abundant lymphocyte subset in chickens and play key roles in early immune responses to infection. It has been recently shown that γδ T cells restrict Marek's disease virus (MDV) pathogenesis; however, it remained elusive if they play a role in vaccine protection. In this study, we vaccinated γδ T-cell-knockout chickens with the commercial turkey herpesvirus (HVT) vaccine and challenged them with very virulent MDV. The disease incidence was significantly increased in vaccinated chickens in the absence of γδ T cells. This increase was comparable to a previous study in unvaccinated γδ T-cell-knockout chickens, suggesting that γδ T cells only play a minor role in vaccine protection. Furthermore, the viral load in the spleen was significantly increased in the absence of γδ T cells. Interestingly, viral load in the skin and in dust shed by the animals was drastically increased, suggesting that the absence of γδ T cells affects MDV shedding. In addition, we quantified various immune cell subsets to determine if these could be responsible for the observed phenotypes. Together, our data indicate that γδ T cells only play a minor role in HVT-mediated protection, but their absence drastically affects shedding of this deadly pathogen in vaccinated animals.