Sammendrag
The aim of the present study was to characterize the expression of some genes in the blood and spleen that are involved in the immune response of Atlantic cod following intraperitoneal vaccination with heat-killed V. anguillarum. The effects on the reduction in bacterial count when incubated with serum samples obtained from the vaccinated fish were also investigated. Total serum protein was not significantly different between the vaccinated and non-vaccinated groups. There were at least 2-log reductions in bacterial count in the sera of the vaccinated group relative to the non-vaccinated group at 3 dpv and it continued until 10 dpv. In the blood, the expression of antibacterial genes, bactericidal/permeability-increasing protein/ lipopolysaccharide-binding protein (BPI/LBP), g-type lysozyme and transferrin was significantly upregulated in the vaccinated fish, having maximum expression levels within 7 dpv. Apolipoprotein A-I and the non-specific cytotoxic cell receptor protein (NCCRP-1) had maximum expression at 3 and 7 dpv, respectively. Significant transcriptional upregulation of pro-inflammatory cytokines, IL-1beta and IL- 8 was also observed in the vaccinated fish. In the spleen, the transcript levels of selected genes such as the BPI/LBP, g-type lysozyme and transferrin, were upregulated throughout the duration of sampling. The expressions of interferon stimulated gene-15 (ISG-15) and interferon regulatory factor-1 (IRF-1) were enhanced after vaccination. Likewise, the transcript levels of the non-specific cytotoxic cell receptor protein-1 (NCCRP-1) and granzyme A/K were also upregulated. Among the antioxidants, the transcript levels of catalase and phospholipid hydroperoxide glutathione peroxidase (GSH-Px) significantly increased following vaccination, while glucose transporter-3 (GLUT-3) was enhanced among the genes involved in glucose transport. It is evident that the innate mechanisms of defense have crucial roles in preventing bacterial diseases in fish. The reduction of bacterial population upon incubation with sera from the vaccinated fish implies that some immune factors were upregulated, which were responsible in suppressing the growth of the pathogen. Since the reduction was observed during the early stages after vaccination, it is likely that these factors are involved in the innate immunity of Atlantic cod. In the blood, majority of the immune-related genes were immediately upregulated as early as 1 dpv and the levels were maintained for at least a week post-vaccination. This indicates that these genes are involved in the acute phase response in fish. The upregulation of several immune-related genes, particularly the antibacterial genes, in the spleen following vaccination, suggests that Atlantic cod are able to produce an immune reaction even if their antibody response against V. anguillarum is negligible. The increased transcription of catalase and GSH-Px after vaccination indicates that antioxidant defense is taking place in the cells and tissues of the host to combat any deleterious consequences of vaccination. Transcriptional upregulation of GLUT-3 following vaccination suggests its involvement in glucose transport between cells to meet the metabolic demands during antigenic stimulation.
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