Different antigen ratio in bivalent vaccine can affect immunological activation and protection against Aeromonas salmonicida and Vibrio anguillarum in Atlantic salmon.

To effectively prevent the outbreak of furunculosis and vibriosis in Atlantic salmon culture in northern China, the immunological properties and efficacies of bivalent inactivated vaccines composed of two local pathogenic strains, Aeromonas salmonicida C4 and Vibrio anguillarum M3, was analyzed in salmon. The effect of formalin-inactivated A. salmonicida C4, V. anguillarum M3, and their combined vaccines with different antigen ratio of 1:1, 1:2 and 2:1 on relative percentage of survival (RPS), specific antibody production and expression of immune-related genes of fish were investigated. It was found that both C4 and M3 antigen had adjuvant effects on each other's vaccines. Furthermore, the proportion of antigens in the combined vaccines had significantly different effects on immune response and protection against A. salmonicida or V. anguillarum infection. Compared with other vaccinated groups, the C4:M3 = 1:2 vaccine group had the highest immunological activation ability and best immune protection against A. salmonicida and V. anguillarum. Our studies suggest that the development of new multivalent vaccines should carefully design the ratio of different antigens in according to their immunological properties to achieve efficient protection and avoid inhibitory effects of antigens on specific pathogen.