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Fish nocardiosis is a widespread chronic granulomatous disease in aquatic environment, which was particularly caused by Nocardia seriolae. The phage shock protein A (PspA) and tellurium resistance protein D (TerD) were identified to be the immunodominant antigens of the wild-type N. seriolae strain ZJ0503 in our previous study. In an attempt to develop effective DNA vaccines against this pathogen, PspA and TerD were used as candidates to ligate with pcDNA3.1-Flag plasmids, respectively. In addition, the abilities of these two DNA vaccines to elicit various immune responses in hybrid snakehead and supply protective efficacy against artificial challenge with N. seriolae were determined in the present study. The results showed that intramuscular injection with pcDNA-PspA and pcDNA-TerD did not exhibit cytotoxic activities in hybrid snakehead via histopathological examination. Besides, hybrid snakehead immunization with pcDNA-PspA and pcDNA-TerD could increase several non-specific immune paraments in serum, including LYZ, POD, ACP, AKP and SOD activities. Meanwhile, the pcDNA-TerD DNA vaccine could induce strongly specific antibody (IgM) titer in hybrid snakehead with a relative percent of survival (RPS) value of 83.14% against N. seriolae , while that of pcDNA-PspA DNA vaccine was displayed comparably low IgM titer with RPS value of 57.83%. Furthermore, quantitative real-time PCR assays presented that the expression of immune-related genes (MHCIα , MHCIIα , CD4 , CD8α , IL-1β and TNFα) were up-regulated to various degrees after vaccination with pcDNA-PspA or pcDNA-TerD, indicating that these two DNA vaccines were able to boost humoral and cell-mediated immune responses in hybrid snakehead. Taken together, both the pcDNA-PspA and pcDNA-TerD DNA vaccines were proved to be safe, immunogenic and effective in protecting hybrid snakehead against N. seriolae infection, which can promote the development and application of DNA vaccines to control fish nocardiosis in aquaculture. • Two DNA vaccines were prepared by utilizing the ribosomal proteins (PspA and TerD) as antigens for treatment of fish nocardiosis. • Both DNA vaccines not only did not exhibit cytotoxic activities but also could boost the innate, humoral and cellular immune response in hybrid snakehead. • Two DNA vaccines show highly protective efficacy against N. seriolae infection in hybrid snakehead with relative percentage survival (RPS) of 57.83% and 83.14%, respectively. [ABSTRACT FROM AUTHOR]

Fish nocardiosis is a chronic granulomatous bacterial disease and three pathogens have been reported so far, including Nocardia asteroids , N. seriolae and N. salmonicida. However, the absence of antigen markers is a bottleneck for developing effective vaccines against fish nocardiosis. In this study, the antigenicity of whole-cell protein of these three pathogenic Nocardia species were profiled by immunoproteomic analysis and 7 common immunogenic proteins were identified as follows: molecular chaperone DnaK (DnaK), molecular chaperone GroEL (GroEL), 30 S ribosomal protein S1 (RpsA), TerD family protein (TerD), FHA domain-containing protein (FHA), 50 S ribosomal protein L7/L12 (RplL) and PspA/IM30 family protein (PspA). Furthermore, the DNA vaccine encoding FHA gene against fish nocardiosis was developed and its efficacy was investigated in hybrid snakehead. The results suggested that it needed at least 7 d to transport pcDNA-FHA DNA vaccine from injected muscle to head kidney, spleen and liver and stimulate host's immune system for later protection. In addition, non-specific immunity paraments (serum lysozyme (LYZ), peroxidase (POD), acid phosphatase (ACP), alkaline phosphatase (AKP) and superoxide dismutase (SOD) activities), specific antibody (IgM) titers production and immune-related genes (MHCIα , MHCIIα , CD4 , CD8α , IL-1β and TNFα) were used to evaluate the immune response induced in pcDNA-FHA vaccinated hybrid snakehead, it proved that all these mentioned immune activities were significantly enhanced after immunization. The results also showed hybrid snakehead vaccinated with pcDNA-FHA had higher survival rate (79.33%) compared with the controls after challenge with N. seriolae , indicating that the pcDNA-FHA DNA vaccine can supply immune protection against N. seriolae infection. Taken together, this study may warrant further development of these common immunogenic proteins as the antigens for vaccine or diagnosis and facilitate the prevention and treatment of fish nocardiosis. Image 1 • The antigenicity of whole-cell protein of three pathogenic Nocardia species (Nocardia serioale , N. asteroids , N. salmonicida) were profiled by immunoproteomic analysis. • The 7 common immunogenic proteins of three pathogenic Nocardia species were identified. • A DNA vaccine was prepared by applying one of the common immunogenic proteins (FHA) as antigen. [ABSTRACT FROM AUTHOR]