Adjuvants emerge as the better tool to enhance the efficacy of vaccination. Traditional adjuvants used in aquaculture cause adverse alterations in fish. Thus, it is necessary the development of new adjuvants able to stimulate the immune system and generate high protection against infectious pathogens with minimal undesirable effects. To this end, flagellin emerges as an attractive candidate due to its potency to stimulate the immune response of fish. In the current study, we have evaluated the ability of recombinant flagellin from Marinobacter algicola (MA) and Vibrio vulnificus (Vvul), a non-pathogenic and a pathogenic bacteria, respectively, to stimulate the innate immune system of gilthead seabream (Sparus aurata L.) in comparison with the classical flagellin from Salmonella enterica serovar Thyphimurium (Salmonella Thyphimurium, STF). Intraperitoneal injection of MA and Vvul resulted in a strong inflammatory response characterized by increased reactive oxygen species production and the infiltration of acidophilic granulocytes at the injection site. Interestingly, however, only flagellin from MA consistently induced the expression of the gene encoding pro-inflammatory interleukin-1. These effects were further confirmed in vitro, where a dose-dependent activation of macrophages and acidophilic granulocytes by MA and Vvul flagellins was observed. In contrast, STF flagellin was found to be less potent in either in vivo or in vitro experiments. Our results suggest the potential use of MA and Vvul flagellins as immunostimulants and adjuvants for fish vaccination.Postprin
