Multi-epitope microsphere vaccine modified immunological efficacy against LMBV in largemouth bass (Micropterus salmoides).

The largemouth bass iridovirus disease, caused by the largemouth bass virus (LMBV), has a mortality rate of up to 60 %, and no commercial vaccine is available. This study focused on developing a vaccine against LMBV by engineering Escherichia coli to express highly immunogenic antigen epitopes (S11, S12, S3) from preliminary research. A stable recombinant dodecapeptide antigen gene with flexible linkers was constructed, yielding a 25 kDa fusion protein (X1-J) confirmed by SDS-PAGE. The resulting antigen proteins were purified and combined with PLGA (poly (lactic-co-glycolic acid)) to form nanospheres (P-P) with a diameter of 17.2 μm, spherical shape, porous surface, and a 34.13 % drug loading efficiency. By day 21 post-vaccination, both the P groups (X1-J groups) and the P-P groups exhibited significantly elevated immune-related enzyme activities (AKP, CAT, SOD, ACP) in comparison to the controls (P < 0.05). Furthermore, the P-P groups exhibited elevated levels of immune-related gene expression, including IgM, IL-8, TNF-α, IFN-γ, CD40, TGF-β, and IL-10. Finally, we tested the relative percent survival values of the vaccine (P-P) using LMBV, which can reach 15.79 %, 31.58 %, and 47.37 % (5, 10, and 20 μg/g) at 14 days after the injection of the virus. These values were significantly higher than those of the P group at the same concentrations. Our study introduces a new strategy for against LMBV and a reference for developing vaccines using multi-epitope technology.