Immune response of turbot (Scophthalmus maximus L.) to a broad spectrum vaccine candidate, recombinant glyceraldehyde-3-phosphate dehydrogenase of Edwardsiella tarda

Edwardsiella tarda is a Gram-negative pathogen which causes systemic infection in turbot. The increasing frequency of edwardsiellosis in turbot farming has stressed the need to understand the immune responses of fish, for the further development of prevention and control strategies. As a broad spectrum protective antigen, a recombinant glyceraldehyde-3-phosphate dehydrogenase (GAPDH) of E. tarda EIB202 has been proven to present remarkable protection against E. tarda, Aeromonas hydrophila, Vibrio anguillarum, Vibrio alginolyticus and Vibrio harvei in zebrafish. Here, the protection and immune responses of turbot vaccinated with this antigen were studied. Fish vaccinated with recombinant GAPDH via intraperitoneal injection exhibited a low cumulative mortality when challenged with E. tarda EIB202, while high levels of specific antibodies and enhanced bactericidal activities of the immunized sera were observed. In addition, significantly increased transcription levels of four immune-related genes including IL-1β, MHC Iα and IIα, and IgM in the liver, spleen and kidney tissues of vaccinated fish showed that both humoral and cellular immune responses were soundly aroused in the vaccinated fish. Moreover, the IgM antibodies induced by recombinant GAPDH exhibited obvious cross-reactions with the other four pathogens. These results suggested that recombinant GAPDH could present effective protective immunity not only against E. tarda but also other extracellular pathogens, and would be a potential vaccine candidate against polymicrobial infections in the aquaculture industry.