Cytokine profiles in chickens infected with virulent and avirulent Marek's disease viruses: interferon-gamma is a key factor in the protection of Marek's disease by vaccination.

Marek's disease has been controlled byvaccination with avirulent strains of MDV. However, the protection mechanism following vaccination is not fully understood. In this study immune responses of PBMC and splenocytes derived from vaccinated chickens challenged with virulent MDV were examined using real-time PCR and ELISA. Higher levels of IFN-gamma induction were observed in chickens vaccinated during the latent phase of infection with virulent MDV than in similarly challenged, unvaccinated chickens. Furthermore, the mean expression of IFNGR2 and IFN regulatory factor-3 mRNAs was significantly higher in vaccinated than in unvaccinated chickens. These results show that IFN-gamma could be one of the important factors in prevention of MD by vaccination and is effective during the latent phase of the infection.