Evaluating the adjuvant potential of NK-lysin and HMGB1-derived peptides in enhancing immune responses in Salmo salar.

The development of effective vaccines for aquaculture is crucial to prevent infectious diseases and improve fish health. Inactivated and subunit vaccines are commonly used in salmon farming; however, their immunogenicity is often limited, requiring adjuvants to enhance their efficacy. In this study, we evaluated the adjuvant potential of immunomodulatory peptides derived from HMGB1 (11W) and NK-lysin (NK1 and NK4) in formulations containing the VP2 antigen of infectious pancreatic necrosis virus (IPNv) in Salmo salar. The peptides were co-administered with the recombinant VP2 protein by intraperitoneal injection in different experimental groups, and serum samples were subsequently analyzed to determine IgM levels. Furthermore, the induction of the cytokines IFN-γ, IL-17, and IL-4/13A in tissues and leukocytes from head kidneys re-stimulated with the antigen was evaluated by RT-qPCR. The results indicated that the formulations containing NK1, NK4, and 11W progressively stimulated IgM production from day 35 post-vaccination. Furthermore, these adjuvant peptides significantly induced the expression of the evaluated cytokines in the head kidney and spleen of immunized animals and in the primary culture model, suggesting the activation of Th1, Th2, and Th17 responses. These findings suggest that peptide adjuvants can enhance the immune response in salmonid vaccination, offering a promising alternative to conventional adjuvants.