Type II interferons activate MHC-I pathway to enhance antigen presentation of grass carp reovirus VP35 DNA vaccine.

Hemorrhagic disease caused by grass carp reovirus (GCRV) poses a significant threat to the health and sustainability of grass carp (Ctenopharyngodon idella) farming. There are no effective measures to control the outbreaks of the disease. While DNA vaccines have proved to be promising to enhance the survival of vaccinated fish to GCRV infection, the protective efficacy is not maximized, and necessitates further improvement. This study explores the immunomodulatory potential of type II interferons (IFNs), including IFN-γ and IFN-γ related molecule (IFN-γrel), as adjuvants for GCRV-VP35 DNA vaccine. Expression plasmids, including pcDNA3.1-VP35, pcDNA3.1-IFN-γ, and/or pcDNA3.1-IFN-γrel, were intramuscularly administered in grass carp, and their effects on the expression of immune genes evaluated. Immunofluorescence microscopy confirmed the localized expression of GCRV-VP35, IFN-γ and IFN-γrel at the injection site, with the persistent expression detected for at least five weeks. Moreover, co-administration of IFN-γ and IFN-γrel plasmids synergistically enhanced the expression of Mx1, Isg15 and Viperin to a greater extent than either plasmid alone. The Igm and Cd8 genes were also upregulated in the spleen and muscle of fish injected with the IFN-γ/IFN-γrel plasmids. Furthermore, our findings reveal that IFN-γ and IFN-γrel robustly upregulated the expression of Mhc I but not Mhc II to promote antigen presentation of VP35 vaccine. The results indicate that type II IFNs have potential as adjuvants to enhance the immunogenicity and efficacy of DNA vaccines in protecting fish against viral infection.