Immune Adjuvant Screening For Edwardsiella Tarda And Vibrio Anguillarum Inactivated Vaccines

Edwardsiella tarda and Vibrio anguillarum are two important fish pathogens that cause extensive losses in farmed fish around the world. Various types of vaccines have been developed against E. tarda and V. anguillarum infection, such as inactivated vaccine, live attenuated vaccine, subunit vaccine and DNA vaccine. Inactivated vaccine is widely used in aquaculture industry owing to its safety and low cost. However, inactivated vaccine based on either killed pathogens or isolated non-replicating pathogen subunits, are in many cases, weakly immunogenic. The key to increase the efficacy of inactivated vaccine would lie in the combinational application of adjuvants or immunostimulants.In this study, we analyzed the immunoprotective potentials of formalin-inactivated V. anguillarum vaccine firstly. The formalin-inactivated V. anguillarum vaccine has good immunogenicity alone or in combination with adjuvants, not suitable for screening immune adjuvants. Then we chose inactivated E. tarda vaccine to screen immune adjuvants. Among 13 different kinds of adjuvants, we found that FlgD could be an efficient adjuvant to enhance the immunological effects of the formalin-killed E. tarda vaccine. The relative percent survival (RPS) of turbot vaccinated with formalin-inactivated E. tarda vaccine reached 70% in the presence of FlgD adjuvant. Moreover, specific serum antibodies reached the highest levels at 3 week post vaccination. Furthermore, the expression of some immune response-related genes, such as MHC-I, IgM, IL-1(3, TCR, and TNFa were significantly up-regulated in turbot after vaccination, indicating that both humoral and cellular immune responses were induced by this vaccine.In summary, flagellin can enhance immunoprotection of the formalin-inactivated E. tarda vaccine, which can be used as a potential adjuvant in fish vaccine.