FlaC supplemented with VAA,OmpK or OmpR as bivalent subunit vaccine candidates induce immune responses against Vibrio anguillarum in flounder (Paralichthys olivaceus)

In our previous study, ten candidate proteins have been identified with immunogenicity and protection against Vibrio anguillarum in flounder (Paralichthys olivaceus). Among them, FlaC is the important outer protein in the flagellum with immunogenicity; VAA, OmpK and OmpR are protection proteins against V. anguillarum. In this paper, FlaC supplemented with VAA, OmpK or OmpR as bivalent subunit vaccine candidates, and their immune response of flounder and protective effects were evaluated, respectively. Recombinant(r) proteins of FlaC were mixed with rVAA, rOmpK and rOmpR, respectively, rVAA + rFlaC (AF), rOmpK + rFlaC (KF) and rOmpR + rFlaC (RF); formalin-killed cells (FKC) or PBS were injected to flounder, respectively. After immunization, the percentages of CD3⁺ T lymphocytes and surface membrane immunoglobulin-positive (sIg⁺) B lymphocytes in peripheral blood lymphocytes (PBLs), total antibodies (TA), specific antibodies against V. anguillarum (VA), specific antibodies against bivalent recombinant proteins (PA), the expression of immune-related genes and relative percent survivals (RPS) were measured, respectively. The results showed that three bivalent vaccines candidates and FKC could induce the proliferation of sIg⁺ B lymphocytes and CD3⁺ T lymphocytes in PBLs. The TA, VA and PA induced in bivalent vaccines candidates and FKC groups were significantly higher than that of the control group. CD3, IgM, CD4-1, CD4-2, CD8α and CD8β genes were up-regulated. After challenge with V. anguillarum, RPS in AF, KF, RF and FKC groups exhibited 62.6 ± 2.33%, 78.95 ± 3.01%, 75.45 ± 0.97%, and 56.71 ± 2.15% respectively. The results revealed that three bivalent vaccines candidates and FKC could induce the immune response in flounder, and have good protection against V. anguillarum, and KF can be an efficient bivalent subunit vaccine candidate.