Mannosylated chitosan nanoparticles loaded with ABP antigen server as a novel nucleic acid vaccine against Nocardia Seriolae infection in Micropterus Salmoides

Abstract

Largemouth bass (Micropterus Salmoides) is an important cultured fish in south China with a large scale of cultivation. However, bacterial disease has badly damaged the healthy development of the breeding industry. Nocardia Seriolae (N. seriolae), a gram-positive bacterial widely existing in soil and water, mainly infects bass and snakehead. This bacterial has caused a large financial loss in China. However, efficient methods to control this pathogeny still remain largely unexplored. Previous study suggested that vaccine was efficient method to prevent fish from bacterial infection. In this study, based on reverse vaccinology, a new DNA vaccine named pcDNA-ABP was obtained by genetic engineering technology. Furthermore, to enhance the stability and target ability, mannosylated chitosan (Mcs) was used to package the nucleic acid vaccine. In order to evaluate the immunoprotection effect of this vaccine, a total of 300 fish (N = 5) were vaccinated with PBS (50 μL per fish), pET32a-ABP (10 μg per fish), pcDNA (10 μg per fish), pcDNA-ABP (20 μg per fish), Mcs-pcDNA-ABP (20 μg per fish). After 28 days' vaccination, experiment fish were challenged with live N. seriolae. Then, some immune-related indexes were measured to evaluate the variation of fish's immunity. Results showed the highest relative percentage survival (RPS) was 80.73% in Mcs-pcDNA-ABP group. What's more, the serum antibody titer, enzyme activity in vaccinated group were significantly increased compared to that of control group. Furthermore, some innate immune-related genes (IL-1β, CD4, TNF-α) and adaptive immune-related gene (IgM) were significantly up-regulated in kidney and spleen. In a word, in this study, a new DNA vaccine packaged with mannosylated chitosan was developed. Results suggested that this vaccine could significantly enhance the immunity of fish after vaccination, and increase the survival rate after live bacterial infection. This research might provide some basic information for the development of N. seriolae vaccine, and make a contribution to the control of bacterial diseases in aquaculture.