Immune adjuvant effects of interferon-gamma (IFN-γ) of flounder (Paralichthys olivaceus) against Edwardsiella tarda

IFN-gamma plays a key role in T-cell activation and the establishment of the adaptive immune response, which has a potential as a cytokine adjuvant in the context of vaccination. In this study, we evaluated the immune adjuvant effects of two forms of flounder (Paralichthys olivaceus) IFN-gamma, including pcDNA3.1-IFN-gamma (pcIFN-gamma) and recombinant IFN-gamma (rIFN-gamma), and comparatively analyzed the immune responses of flounder to E. tarda subunit vaccine rOmpV. The results showed that vaccination with rOmpV plus pcIFN-gamma or rIFN-gamma produced a relative percent survival of 57% and 71%, respectively, which were significantly higher than that of the control groups, rOmpV plus pcN3 (36%) or rHis (40%). Compared with the two control groups, vaccination with rOmpV plus pcIFN-gamma or rIFN-gamma could induce significantly higher levels of specific serum antibodies and sIg + lymphocytes in peripheral blood, spleen and head kidney, and significantly higher upregulated expressions of CD4-1, CD8 alpha, IgM, MHC I alpha, MHC II alpha, IL-1 beta and TNF-alpha were also detected in rOmpV plus pcIFN-gamma or rIFN-gamma vaccinated fish. In addition, compared with pcIFN-gamma, rOmpV co-vaccination with rIFN-gamma elicited higher levels of sIg + lymphocytes, specific serum antibodies and several immune-related genes expressions in vaccinated flounder. These results demonstrated that rOmpV co-vaccination with rIFN-gamma or pcIFN-gamma could both boost the immune responses and evoke highly protective effects against E. tarda, indicating that flounder IFN-gamma is a promising adjuvant candidate for fish vaccination via an injection administering route.