Construction and expression of DNA vaccine against reddish body iridovirus and evaluation of immune efficacy in turbot (Scophthalmus maximus)

Turbot aquaculture is a very important industry in China. However, it is hampered because of viral reddish body syndrome (VRBS) and high mortality caused by piscine turbot reddish body iridovirus (TRBIV). TRBIV virus is an icosahedron‐like and cytoplasmic DNA virus, belonging to Iridoviridae, Megalocytivirus. In previous studies, we have identified two antigen mimotopes using bioinformatics and constructed prokaryotic expression vectors. In this study, a fragment of major capsid protein (MCP) gene with the two antigenic epitopes was cloned into eukaryotic expression vector pVAX1, to generate a recombinant plasmid pVAX1‐TRBIV‐MCP. The plasmid DNA was transferred into turbot cell line TK using liposome, and transient expression was detected using RT‐PCR. After injection into turbot (Scophthalmus maximus), the expression of the antigen gene was analysed using RT‐PCR and was shown to express in all tested tissues in vaccinated fish 2 and 7 days post‐vaccination. The cumulative mortalities in the vaccinated and unvaccinated control fish were 30% and 88% respectively. Immune responses and upregulation of the expression of chemokine receptor, tumour necrosis factor, interferon and interferon‐induced antiviral molecules were observed in the vaccinated fish 60 h post‐vaccination. These results demonstrate that the vaccinated turbots had higher survival rate and produced specific serum antibodies following the TRBIV challenge. More studies are needed to develop and apply the promising DNA vaccine for virus control in turbot.