Abstract
The objective of the present study was to assess the effect of alginate-encapsulated infectious pancreatic necrosis virus antigens in inducing the immune response of Atlantic salmon as booster vaccines. One year after intraperitoneal injection with an oil-adjuvanted vaccine, post-smolts were orally boosted either by 1) alginate-encapsulated IPNV antigens (ENCAP); 2) soluble antigens (UNENCAP) or 3) untreated feed (control). This was done twice, seven weeks apart. Sampling was done twice, firstly at 7 weeks post 1st oral boost and the 2nd, at 4 weeks after the 2nd oral boost. Samples included serum, head kidney, spleen and hindgut. Serum antibodies were analyzed by ELISA while tissues were used to assess the expression of IgM, IgT, CD4, GATA3, FOXP3, TGF-β and IL-10 genes by quantitative PCR. Compared to controls, fish fed with ENCAP had a significant increase (p<0.04) in serum antibodies following the 1st boost but not after the 2nd boost. This coincided with significant up-regulation of CD4 and GATA3 genes. In contrast, serum antibodies in the UNENCAP group decreased both after the 1st and 2nd oral boosts. This was associated with significant up-regulation of FOXP3, TGF-β and IL-10 genes. The expression of IgT was not induced in the hindgut after the 1st oral boost but was significantly up-regulated following the 2nd one. CD4 and GATA3 mRNA expressions exhibited a similar pattern to IgT in the hindgut. IgM mRNA expression on the other hand was not differentially regulated at any of the times examined. Our findings suggest that 1) Parenteral prime with oil-adjuvanted vaccines followed by oral boost with ENCAP results in augmentation of the systemic immune response; 2) Symmetrical prime and boost (mucosal) with ENCAP results in augmentation of mucosal immune response and 3) Symmetrical priming and boosting (mucosal) with soluble antigens results in the induction of systemic immune tolerance.
Highlights
Infectious pancreatic necrosis is an important disease of salmonids responsible for great economic losses in the aquaculture industry
The results show that more mRNA of infectious pancreatic necrosis virus (IPNV) were retained in the encapsulated (ENCAP) versus unencapsulated (UNENCAP) groups at both time points (Fig. 1)
In order to gain insight into the suppression of antibody production by B cells in the UNENCAP group, we examined the expression of forkhead box protein 3 (FOXP3), TGF-b and IL-10
Summary
Infectious pancreatic necrosis is an important disease of salmonids responsible for great economic losses in the aquaculture industry. It is characterized by loss of appetite, darkened skin pigmentation, distended abdomen and mortalities ranging from negligible to almost 100%. Control of IPN is by vaccination and oil-based vaccines have earned their place in the market mainly because of their contribution to the control of bacterial diseases in the late 80s and early 90s in Norway The efficacy of these vaccines against diseases caused by intracellular pathogens such as viruses remains equivocal, the need for the continued search for more effective vaccines
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