Lymphocystis disease is one of the main viral pathologies affecting cultured gilthead seabream in the Mediterranean area. Recently, we have developed a DNA-vaccine based on the major capsid protein of the Lymphocystis disease virus 3 (LCDV-Sa). The immune response triggered by LCDV-Sa or the vaccine in gilthead seabream has been previously study. In the present study, a comprehensive evaluation of immune-related gene expression in vaccinated fish after viral infection has been carried out to identify immune genes involved in the vaccine-induced protection.
Gilthead seabream specimens (5 g mean weight) were distributed into 3 experimental groups; two of them were inoculated with the vaccine and the empty plasmid at 0.1 µg/g fish dose, respectively, whereas fish in the control group were inoculated with PBS. Thirty days post-vaccination, fish were intramuscularly injected with the virus at 106 TCID50/fish. Samples of head-kidney, spleen, intestine and caudal fin from 6 fish per group were individually collected at 24, 48 and 72 h post-challenge. The expression and quantification of viral DNA in fins of fish challenged with LCDV-Sa were carried out by a qPCR assay targeting a viral structural gene (putative myristoylated membrane protein, MMP). Immune response was studied by an OpenArray® platform of 56 gene targets.
The global effect of vaccination was a significant decrease of viral replication in vaccinated fish compared to fish in the control group, and the differential expression of immune genes related to viral recognition (tlr9), humoral and cellular response (rag1 and cd48), inflammation (csf1r, elam, il1β, and il6), antiviral response (isg15, mx1, mx2, and mx3), cell-mediated cytotoxicity (nccrp1), and apoptosis (prf1).
The exclusive modulation of the immune response provoked by the vaccination seems to control the progression of the infection in the LCDV-Sa challenged gilthead seabream.
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