Recombinant outer membrane protein T (OmpT) of Vibrio ichthyoenteri, a potential vaccine candidate for flounder (Paralichthys olivaceus).

Vibrio ichthyoenteri is a marine pathogen that primarily causes bacterial enteritis of flatfish. In order to screen out the effective vaccine candidate proteins, five outer membrane proteins (OMPs) of V. ichthyoenteri, including OmpV, OmpU, OmpT, Omp1 and Omp2, were selected and recombinantly expressed in Escherichia coli. The result of western blotting showed that all of these recombinant proteins could be recognized by flounder anti-V. ichthyoenteri antibodies. The immune protective effect of the five rOMPs were also investigated, and the relative percent survival (RPS) of rOmpV, rOmpU, rOmpT, rOmp1 and rOmp2 was 69.2%, 46.2%, 76.9%, 65.4% and 30.8%, respectively. The RPS of rOmpT was significantly higher than inactivated V. ichthyoenteri (57.7%) and other rOMPs, so the immune responses of flounder induced by rOmpT were further investigated. The results showed that both the production of specific serum antibodies and the proliferation of sIg + lymphocytes could be significantly induced by rOmpT. Meanwhile, the MHCIIα, INF-γ, CD4-1, and IL-1β genes were significantly up-regulated after immunization with rOmpT. These results demonstrated that rOmpT could induce strong innate and humoral immune response in flounder and provided effective immune protection against V. ichthyoenteri challenge, which indicated that OmpT is a promising vaccine candidate against V. ichthyoenteri infection.