B-cell activating CpG ODN 1668 enhance the immune response of Pacific red snapper (Lutjanus peru) exposed to Vibrio parahaemolitycus

• CpG ODN 1668 increased humoral immune response in serum in fish exposed to Vibrio parahaemolyticus.
• TLR9 and IgM were up-regulate after CpG ODN 1668 stimulation.
• CpG ODN 1668 no provoke histopathological damage in intestine.

B-class CpG ODN 1668 is known to possess clear immunostimulatory properties. In this study, we investigated the potential ability of CpG ODN 1668 to enhance the immune response of Pacific red snapper exposed to Vibrio parahaemolyticus. Four different treatments were evaluated in Pacific red snapper: (1) stimulatory CpG ODN 1668, (2) stimulatory CpG ODN 1668 and V. parahaemolyticus, (3) exposure only to V. parahaemolyticus and (4) PBS. Samples were taken at 24, 72, 168 and 240 h of stimulation/infection. The results show that intraperitoneal injection of CpG-ODN 1668 enhanced the anti-protease, superoxide dismutase and catalase activities in serum. CpG ODN 1668 upregulated TLR9 and IgM gene expression in head-kidney, intestine and skin, with higher expression in head-kidney. A higher correlation was observed between TLR9 and IgM in head-kidney and intestine. Finally, no histopathological damages were observed in fish stimulated with CpG ODN 1668. In contrast, melanomacrophages-like structures were present in higher numbers in infected fish. Taken together, these results indicate that CpG ODN 1668 activates innate immune response and upregulate the TLR9 and IgM-mediated immune response. These results may be exploited for the control of Vibriosis in farmed Pacific red snapper.