Evaluation of Gilthead Seabream (Sparus aurata) Immune Response after LCDV-Sa DNA Vaccination

Simple Summary Lymphocystis disease is the main viral pathology in gilthead seabream aquaculture. Currently, there are no treatments or vaccines to control this disease, thus our main goal was to construct a DNA vaccine that can be used in the future to stop the spread of this pathology in sea farms. The vaccine consisted of a plasmid DNA that contains a known viral gene. Once it was established that the vaccine drives the expression of the antigenic viral protein in fish, vaccination experiments were conducted to determine if the vaccinated fish become protected against the viral infection. In addition, the immune response triggered by the vaccine was also evaluated in order to understand the mechanisms underlying such protection. The obtained results showed that in vaccinated fish an activation of several genes relating to both the inflammatory process and the mucosal immunity were produced, as well as specific anti-viral antibodies. Although limited, our results deserve further investigation to assess the efficacy of the vaccine in bigger fish populations and to confirm the mode of action of the vaccine. Lymphocystis disease is the main viral pathology reported in gilthead seabream. Its etiological agent is Lymphocystis disease virus 3 (LCDV-Sa), genus Lymphocystivirus, family Iridoviridae. There are no effective treatments or vaccines for LCDV control, thus the main aim of this study was to develop a DNA vaccine, and to evaluate both the protection conferred against LCDV-Sa infection and the immune response in vaccinated fish. The vaccine was constructed by cloning the mcp gene (ORF LCDVSa062R) into pcDNA3.1/NT-GFP-TOPO. Two independent vaccination trials were conducted. In the first one, 5-7 g fish were intramuscularly injected with the vaccine (pcDNA-MCP) or the empty-plasmid, and the distribution and expression of the vaccine was investigated. Furthermore, vaccinated fish were challenged with LCDV-Sa in order to access the protective capacity of the vaccine. In the second trial, 70-100 g fish were vaccinated as specified, and the immune response was evaluated analyzing the expression of 23 immune-related genes and the production of specific antibodies. The results showed that the vaccine triggers an immune response characterized by the overexpression of genes relating to the inflammatory process, but not the innate antiviral immunity relating to type I IFN (interferon), and also induces the production of specific neutralizing antibodies, which could explain the protection against LCDV-Sa in vaccinated fish.

Automated summary

The study aimed to develop a DNA vaccine for the lymphocystis disease in gilthead seabream. The results showed that the vaccine triggered an immune response and produced specific anti-viral antibodies, providing protection against the disease.