Abstract
The adjuvant effect of Quillaja saponaria saponin (QSS) on protection of turbot fry was investigated with immersion vaccination of formalin-killed Vibrio anguillarum O1 and various concentrations of QSS (5, 25, 45 and 65 mg/L). Fish were challenged at days 7, 14 and 28 post-vaccination. Significantly high relative percent of survival (RPS) ((59.1 ± 13.6)%, (81.7 ± 8.2)%, (77.8 ± 9.6)%) were recorded in the fish that received bacterins immersion with QSS at 45 mg/L, which is comparable to the positive control group vaccinated by intraperitoneal injection (IP). Moreover, a remarkably higher serum antibody titer was also demonstrated after 28 days in the vaccinated fish with QSS (45 mg/L) than those vaccinated fish without QSS (p < 0.05), but lower than the IP immunized fish (p < 0.05). Significant upregulation of IgM gene expression has also been identified in the tissues of skin, gill, spleen and kidney from the immunized fish in comparison to the control fish. Taken together, the present study indicated that QSS was able to dramatically evoke systemic and mucosal immune responses in immunized fish. Therefore, QSS might be a promising adjuvant candidate for fish vaccination via an immersion administering route.
Highlights
Fish aquaculture is expanding rapidly, and is the fastest growing protein-producing sector in the world
When the fish were challenged with V. anguillarum at the 14th and 28th day post-vaccination, the fish in the group IP + V showed the best protection with the highest relative percent of survival (RPS) values ((95.8 ̆ 7.2)% and (87.8 ̆ 13.0)%, respectively) among all immunizing groups
The present study clearly shows the significantly higher protections and specific antibody titers in the fish that received a pretreatment in subtoxic Quillaja saponaria saponin (QSS) solution and was followed by an immersion vaccination in inactivated V. anguillarum bacterins solution
Summary
Fish aquaculture is expanding rapidly, and is the fastest growing protein-producing sector in the world. Fish vaccination has become an established and cost-effective method of controlling certain infectious diseases in industrial fish aquaculture in recent decades [3,4]. Fish vaccines are environmentally friendly biological products, such that application of fish vaccines has successfully reduced the indiscriminate use of antibiotics or other veterinary drugs. This has led to the decrease of antibiotic resistant strains in the aquatic environment, as well as a reduction in the harmful chemical residues in the seafood products [4]. Lower protection of immunized fish in response to some pathogens especially those antigens with insufficient immunogenicity has limited its broad applications in practice of fish aquaculture [6]. Fewer adjuvants have been available for fish vaccination, especially via the immersion/bath route, so the development of novel and more effective adjuvants for fish vaccine delivered by immersion/bath is a worthy and urgent endeavor
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