Abstract: To understand the mechanisms of DPV infection and immunity,the IFN-γ mRNA expression was investigated after infection with virulent and attenuated duck plague virus. The mRNA levels of IFN-γ in liver and PBL were evaluated dynamically after inoculation with virulent and attenuated DPV respectively by real-time PCR. The virus loads were also assessed. Results:①After infection by virulent DPV, IFN-γ mRNA levels in liver didn't show regulatory changes while high level of IFN-γ mRNA levels in PBL and few virus DNA could be detected in the early stage of infection (1-12 h). IFN-γ mRNA expression decreased dramatically after 6 h post infection and persisted in a very low level until death (144 h).Virus load increased gradually and reached peak at 144 h. ②After vaccination with attenuated DPV strain, there were persist and high levels of IFN-γ mRNA expression in liver,reached peak at 12 h (8 times higher than control), while the level in PBL was lower and unstable. The attenuated DPV loads increased dramatically with a relative low copy number in liver. However, the virus DNA could not be detected in PBL. IFN-γ possibly plays an important role in protecting ducks against virulent virus infection. It is also suggested that high level expression of IFN-γ in liver induced by attenuated DPV could enhance immunity against DPV infection.

Key words: IFN-γ; duck plague virus; virulent strain; attenuated strain