Evaluation of a multi-epitope vaccine for Nocardia seriolae in Micropterus salmoides

Nocardia seriolae can cause chronic granulomatous bacterial disease in fish, resulting in tissue necrosis. Currently, there is no effective method to control N. seriolae infection, which has led to significant economic losses in the aquaculture industry. In this study, immunoinformatics tools were employed to predict antigenic epitopes of seven antigenic proteins of N. seriolae : DnaK, GroEL, RpsA, PspA, TerD, RplL, and Ag85L. A total of 21 B-cell epitopes and 21 T-cell epitopes were predicted and concatenated into a multi-epitope protein named NSEP. To evaluate its immunogenicity, NSEP was used to immunize Miropterus salmoides . Four weeks post-immunization, compared with the adjuvant group, significant increases were observed in the serum activities of lysozyme (LYZ), acid phosphatase (ACP), alkaline phosphatase (AKP), and superoxide dismutase (SOD). Moreover, the transcription levels of immune related genes IL-10 , IL-1 β , TNF-α , IFN-γ , IgM , and MHCI-α were significantly upregulated in both liver and spleen tissues. Following challenge with N. seriolae NS01, the NSEP-immunized group exhibited a relative percentage survival (RPS) of 61.29 %, along with significantly reduced bacterial loads. These results demonstrated that the multi-epitope protein NSEP holds promise as a candidate subunit vaccine against N. seriolae infection in M. salmoides .