Microarray analysis of host immune responses to Marek's disease virus infection in vaccinated chickens

Marek's disease (MD) is a commercially important disease of chickens caused by MD virus (MDV). Although avirulent MDV strains have been used for vaccination to prevent MD outbreaks, the protective mechanism of the vaccine has not been elucidated. In this study, a comprehensive transcriptional analysis using microarray was conducted in MDV-infected chickens with and without vaccination at 7 and 21 days post-infection (dpi). The data suggested that the expression of T cell receptor (TCR) 1-related genes was up-regulated in vaccinated-challenged compared to unvaccinated-challenged chickens during the latent phase of infection. Consistently, this induction was confirmed by quantitative PCR. Flow cytometric analysis revealed that most of TCR1(+) cells expressed CD8alpha chain brightly. The number of this subpopulation was significantly and specifically increased in vaccinated-challenged chickens at 21 dpi compared to unvaccinated-challenged chickens, though it was not the major population in spleen of chickens. The number of CD8alpha(high) TCR2(+) cells, the major subpopulation of chicken CD8alpha(high) cells, was increased in vaccinated chickens with or without challenge compared to unvaccinated control chickens. These data suggested that both CD8alpha(high) TCR1(+) and CD8alpha(high) TCR2(+) cells could be induced by the vaccination. It is also possible that CD8alpha(high) TCR1(+) cells might be primed by the vaccination and specifically induced by the challenge with virulent strain of MDV during the latent phase of infection. Thus, CD8alpha(high) TCR1(+) cell population is probably one of the key factors involved in the protective mechanism induced by a vaccine strain, CVI988.