Evaluation of immune response after LCDV-Sa infection in DNA-vaccinated gilthead seabream

Abstract

The immune-related gene expression in vaccinated gilthead seabream after Lymphocystis Disease Virus 3 (LCDV-Sa) infection was analysed by using an OpenArray based on TaqMan qPCR. The DNA vaccine used in this study encodes the viral major capsid protein and confers protection against LCDV-Sa infection in juvenile gilthead seabream. Gilthead seabream juveniles were distributed into four experimental groups and intramuscularly injected with the vaccine (vaccinated group), the empty-plasmid (mock-vaccinated group), or PBS (control groups). Thirty days after vaccination, vaccinated and mock-vaccinated fish, as well as one of the control groups, were injected intraperitoneally with LCDV-Sa (106 TCID50/fish). Samples of head-kidney (HK) from 6 fish were individually collected 1 and 3 days post-infection (dpi). The relative expression levels of 49 genes related to the immune response and 4 reference genes were analysed using an OpenArray. Samples from the non-infected control group were used as calibrator. The number of genes differentially expressed (DEG) in HK at 1 dpi was higher in vaccinated fish compared with both mock-vaccinated and non-vaccinated animals. At 3 dpi, most DEG were upregulated, and the differences in their number among groups were minimized. The recombination-activating gene 1 (rag1), a mediator of development of B and T lymphocytes, was the only gene upregulated in HK samples at 1 dpi. This gene was also upregulated in non-vaccinated animals but at 3 dpi. In contrast, early mx induction was observed in non-vaccinated animals (upregulation of mx2 at 1 dpi) in comparison to vaccinated seabreams (upregulation of mx1 and mx2 at 3 dpi). The results that will be discussed could evidence the role of the DNA vaccine as regulator of the primary lymphoid tissues (HK) in gilthead seabream against LCDV-Sa infection, through downregulation of inflammation related-genes, early upregulation of rag1, and a later expression of interferon stimulated genes.