Adjuvant effects on protection and immune response of Japanese flounder immunized by the formalin-killed cells of Edwardsiella tarda

We evaluated the effects of Freund's adjuvants (FCA/FIA) on protection and immune response of Japanese flounder Paralichthys olivaceus immunized by the formalin-killed cell (FKC) of Edwardsiella tarda. Combination of FKC and FCA/FIA did not confer protection against the challenge, while they significantly induced higher antibody titers than that of FKC only. The suppression of FKC-dependent induction of interferon γ (IFNγ) mRNA levels by FCA/FIA was observed by gene expression profiling. Similarly, interleukin (IL)-12 p35 mRNA levels were not detected after FKC+FCA or +FIA. These results suggest that the mineral oil in Freund's adjuvants might suppress the signaling pathway(s) that induce IFNγ and IL-12 gene expression. •Effects of adjuvants (FCA, FIA) on protection and immune response of Japanese flounder were evaluated.•Freund's adjuvants enhanced antibody responses but did not confer protection.•Freund's adjuvants suppressed the induction of IFNγ and IL12p35 mRNA expression after the FKC vaccination.