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Grass carp (Ctenopharyngodon idella) is subject to a hemorrhagic disease caused by grass carp reovirus (GCRV), which can lead to mass mortality in grass carp culture, causing significant economic loss. Vaccination is the most promising strategy for the prevention of infectious diseases. Immersion vaccination is considered the most effective disease prevention method for juvenile fish because it can be implemented on many fish at once and administered without causing stress. However, immune responses by immersion vaccination are markedly less robust due to the skin barrier and insufficient antigen uptake. The display of heterologous proteins on the cell surface has been explored as a delivery system for viral antigens in veterinary and human vaccine studies. To improve the efficacy of the immersion vaccine, the major capsid protein (VP7) of GCRV was co-displayed with Aeromonas hydrophila outer membrane protein a (OmpA) and major adhesion protein (Mah) on the outer membrane surface of nonpathogenic Escherichia coli BL21 using the anchoring motif of ice-nucleation protein (Inp). The immune responses and protection efficiency against GCRV infection via both the injection and immersion routes were evaluated. The results indicated that the activities of anti-oxidant enzymes (ACP, AKP, SOD and T-AOC), as well as the expression of immune-related genes (TNF-α , IL-1β , MHCI and IgM) and specific VP7 antibody levels, were strongly increased in the grass carp from 7 to 21 days post-injection inoculation in a dose dependent manner. The cumulative mortality rates of injection-vaccinated groups were much lower than those of the control group after the GCRV challenge, and the relative percent survival (RPS) was greater than 80 %. Vitally, the surface co-display of vp7-Mah protein conferred marked protection to grass carp against GCRV infection after immersion administration (RPS >50 %); this was consistent with the production of high level of specific serum antibodies, non-specific immune responses, and the expression of immune-related genes. Moreover, the invasion analysis further showed that surface co-display of the vp7-Mah protein indeed significantly improved the invasion of E. coli BL21 (DE3) in vitro. Altogether, this study demonstrated that surface display GCRV core antigen vaccine system accompanied by invasion component from aquatic pathogenic microorganism is an effective prophylactic against GCRV viral diseases via the immersion administration approach. • A recombinant surface display vaccine prevented grass carp hemorrhagic disease. • Grass carp immersed in a vaccine with surface display of vp7-Mah elicited robust immunity against GCRV. • Surface display of the vp7-Mah improved the invasion of immersed vaccine. • Surface display-based immersion vaccines have prospects for application in aquaculture. [ABSTRACT FROM AUTHOR]

To reduce the economic losses caused by diseases in aquaculture industry, more efficient and economic prophylactic measures should be urgently investigated. In this research, the effects of a novel functionalized single-walled carbon nanotubes (SWCNTs) applied as a delivery vehicle for DNA vaccine administration in juvenile grass carp against Aeromonas hydrophila were studied. Our results showed that SWCNTs loaded with DNA vaccine induced a better protection to juvenile grass carp against A. hydrophila . Moreover, SWCNTs conjugated with DNA vaccine provided significantly protective immunity compared with free DNA vaccine. Thereby, SWCNTs may be considered as a potential efficient DNA vaccine carrier to enhance the immunological activity. [ABSTRACT FROM AUTHOR]

Intestinal microbiota has become an integral component of the fish, and plays a key role in host metabolism, immunity and health maintenance. However, information on the immune responses after vaccine administration in relation to the intestinal microbiota is absent in fish. The present study focused on the effect of a new recombinant Aeromonas hydrophila vaccine (Aera) by using a novel functionalized, single-walled carbon nanotubes (SWCNTs) as a delivery vehicle on the intestinal microbiota of grass carp ( Ctenopharyngodon idella ) through the bath immunization, and further explored the immunological responses in intestine, kidney and spleen. By performing deep sequencing, a total of 81,979 valid reads and 609 OTUs obtained from 4 intestine samples were analyzed. We detected 141 genuses, most of which belonged to Firmicutes, Fusobacteria and Proteobacteria. Of note, the quantity of Aeromonas in library Aera (after 6 h Aera vaccine pretreatment, fish were transferred to tanks without SWCNTs-Aera for 28 d) and Aera-GD (6 h Aera vaccine pretreated prior to the group injected by A. hydrophila ) was declined 6.5% and 14.6% compared with the control, respectively. Moreover, the expression of seven immune-related genes (IFN-I, TNF-α, CRP, IL-8, IgM, MHC I and CD8α) in the intestine, kidney and spleen of Aera treated fish was significantly enhanced, which indicated that a better tissue immune response in grass carp was induced by the SWCNTs-Aera vaccine. Therefore, a new recombinant SWCNT-Aera vaccine may represent potentially efficient and immunological role in grass carp intestine to resist A. hydrophila infection. [ABSTRACT FROM AUTHOR]

To reduce the economic losses caused by diseases in aquaculture industry, more efficient and economic prophylactic measures should be urgently investigated. In this research, the effects of a novel functionalized single-walled carbon nanotubes (SWCNTs) applied as a delivery vehicle for recombinant Aeromonas hydrophila vaccine administration via bath or injection in juvenile grass carp were studied. The results showed that SWCNT as a vector for the recombinant protein aerA, augmented the production of specific antibodies, apparently stimulated the induction of immune-related genes, and induced higher level of survival rate compared with free aerA subunit vaccine. Furthermore, we compared the routes of bath and intramuscular injection immunization by SWCNTs-aerA vaccine, and found that similar antibody levels induced by SWCNTs-aerA were observed in both immunization routes. Meanwhile, a similar relative percentage survival (approximately 80%) was found in both a 40 mg/L bath immunization group, and a 20 μg injection group. The results indicate that functionalized SWCNTs could be a promising delivery vehicle to potentiate the immune response of recombinant vaccines, and might be used to vaccinate juvenile fish by bath administration method. [ABSTRACT FROM AUTHOR]