Development of DNA vaccines encoding ribosomal proteins (RplL and RpsA) against Nocardia seriolae infection in fish

Nocardia seriolae, a Gram-positive pathogen, has been identified as the causative agent of fish nocardiosis. DNA vaccination has been proven to be effective in conferring protection against bacterial infection in fish. The 30S ribosomal protein S1 (RpsA) and 50S ribosomal protein L7/L12 (RplL) were identified to be the common immunodominant antigens of three fish pathogenic Nocardia (N. seriolae, N. salmonicida and N. asteroids) by immunoproteomics profiling in our previous study. In current study, the immunogenicity and protective efficacy of two DNA vaccines encoding RplL and RpsA were evaluated and compared in hybrid snakehead. The results showed vaccination of hybrid snakehead with the pcDNA-RplL and pcDNA-RpsA DNA vaccines provided protective efficacy with relative percentage survival (RPS) of 78.31% and 71.08%, respectively. Meanwhile, the immune response of hybrid snakehead induced by these two DNA vaccines were investigated, and it revealed that the non-specific immunity parameters (serum lysozyme (LYZ), peroxidase (POD), acid phosphatase (ACP), alkaline phosphatase (AKP) and superoxide dismutase (SOD) activities), specific antibody (IgM) production and immune-related genes expression (MHCIα, MHCIIα, CD4, CD8α, IL-1β and TNFα) were significantly increased compared with the corresponding control groups after immunization. Taken together, these results indicated that both pcDNA-RplL and pcDNA-RpsA DNA vaccines could boost the innate, humoral and cellular immune responses in hybrid snakehead and show highly protective efficacy against fish nocardiosis, suggesting that ribosomal proteins RplL and RpsA were promising candidates for DNA vaccines and it will promote the vaccine development against fish nocardiosis.