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• A recombinant IHNV virus expressing VP2 gene of IPNV was successfully constructed. • The recombinant virus showed significant protection efficacy against IHNV and IPNV. • The recombinant virus induced upregulation of innate and adaptive immune responses. • The recombinant virus could be a vaccine candidate protecting rainbow trout against two or more diseases. Infectious pancreatic necrosis virus (IPNV) and infectious hematopoietic necrosis virus (IHNV) are two common viral pathogens that cause severe economic losses in all salmonid species in culture, but especially in rainbow trout. Although vaccines against both diseases have been commercialized in some countries, no such vaccines are available for them in China. In this study, a recombinant virus was constructed using the IHNV U genogroup Blk94 virus as a backbone vector to express the antigenic gene, VP2, from IPNV via the reverse genetics system. The resulting recombinant virus (rBlk94-VP2) showed stable biological characteristics as confirmed by virus growth kinetic analyses, pathogenicity analyses, indirect immunofluorescence assays and western blotting. Rainbow trout were immunized with rBlk94-VP2 and then challenged with the IPNV ChRtm213 strain and the IHNV Sn1203 strain on day 45 post-vaccination. A significantly higher survival rate against IHNV was obtained in the rBlk94-VP2 group on day 45 post-vaccination (86%) compared with the PBS mock immunized group (2%). Additionally, IPNV loads decreased significantly in the rBlk94-VP2 immunized group in the liver (28.6-fold to 36.5-fold), anterior kidney (21.7-fold to 44.2-fold), and spleen (14.9-fold to 22.7-fold), as compared with the PBS mock control group. The mRNA transcripts for several innate and adaptive immune-related proteins (IFN-γ, IFN-1, Mx-1, CD4, CD8, IgM, and IgT) were also significantly upregulated after rBlk94-VP2 vaccination, and neutralizing antibodies against both IHNV and IPNV were induced on day 45 post-vaccination. Collectively, our results suggest that this recombinant virus could be developed as a vaccine vector to protect rainbow trout against two or more diseases, and our approach lays the foundations for developing live vaccines for rainbow trout. [ABSTRACT FROM AUTHOR]

Infectious hematopoietic necrosis virus (IHNV) is a common pathogen that causes severe disease in the salmonid aquaculture industry. Recent work demonstrated that autophagy plays an important role in pathogen invasion by activating innate and adaptive immunity. This study investigated the relationship between IHNV and autophagy in epithelioma papulosum cyprini cells. The electron microscopy results show that IHNV infection can induce typical autophagosomes which are representative structures of autophagy activation. The punctate accumulation of green fluorescence-tagged microtubule-associate protein 1 light chain 3 (LC3) and the protein conversion from LC3-I to LC3-II were respectively confirmed by confocal fluorescence microscopy and western blotting. Furthermore, the effects of autophagy on IHNV replication were also clarified by altering the autophagy pathway. The results showed that rapamycin induced autophagy can inhibit both intracellular viral replication and extracellular viral yields, while autophagy inhibitor produced the opposite results. These findings demonstrated that autophagy plays an antiviral role during IHNV infection. [ABSTRACT FROM AUTHOR]

Infectious hematopoietic necrosis virus (IHNV) is a common pathogen that causes severe disease in the salmonid aquaculture industry. Because oral vaccines induce more efficient mucosal immunity than parenteral immunization, an oral vaccine was developed with an improved yeast cell surface display technology to induce an immune response to IHNV. The oral yeast vaccine, designated EBY100/pYD1-bi-G, was delivered orally to rainbow trout ( Oncorhynchus mykiss ) on days 1 and 32, and the nonspecific and specific immune responses were measured 50 days after the first vaccination. In the hindgut, spleen, and head kidney, the expression of IFN-1 and Mx-1 was significantly upregulated after oral vaccination with EBY100/pYD1-bi-G, and the highest expression of IFN-1 and Mx-1 was observed in the spleen (7.5-fold higher than the control group) and head kidney (3.9-fold higher than the control group), respectively. Several markers of the adaptive immune response (IgM, IgT, CD4, and CD8) were also significantly upregulated, and the highest expression of these markers was observed in the hindgut, suggesting that the mucosal immune response was successfully induced by oral vaccination with EBY100/pYD1-bi-G. Sera from the orally vaccinated rainbow trout showed higher anti-IHNV neutralizing antibody titers (antibody titer 81 ± 4) than the control sera (antibody titer 7 ± 3), and the relative percentage survival after IHNV challenge was 45.8% compared with 2% in the control group. Although the protection afforded by this orally delivered vaccine was lower than that of a DNA vaccine (83%–98%), it is a promising candidate vaccine with which to protect larval fish against IHNV, which are most susceptible to the virus and difficult to inject with a DNA vaccine. [ABSTRACT FROM AUTHOR]

Background The development of oral vaccines using yeast surface display technology is an area of intensive study in vaccine development, but the protein level displayed on yeast surfaces is not currently high enough to obtain a robust immune response. Methods To address this issue, we established an efficient and simple method of increasing the level of displayed protein on the yeast cell surface. We used the single chain variable fragment (scFv) of an antibody against the infectious hematopoietic necrosis virus isolate Sn1203 as a target display protein. The yeast-derived scFv was first displayed on the yeast surface by galactose induction, and then Escherichia coli -derived scFv was also displayed on the same yeast via an artificial anchoring condition to increase the total scFv level on the yeast surface. Results The levels of yeast- and E . coli -derived scFv displayed on the yeast cell surface were analyzed by flow cytometry, western blotting, and fluorescent microscopy. The flow cytometry results indicated that when the cells were suspended in phosphate-buffered saline with 1 mmol/L glutathione, 0.2 mmol/L oxidized glutathione, and 5% dimethyl sulfoxide at 4 °C for 6 h, the E . coli -derived scFv protein was stably anchored to the yeast cell surface. The mean fluorescence intensity in these experiments, which is an indirect quantitative representation of the surface scFv expression, was three times higher in the treated cells than that in control cells. The western blotting results show two specific protein bands, the smaller of which was identified as the E . coli -derived scFv that was displayed on the yeast cell surface. Cell immunofluorescence is a more direct way to detect differentially produced proteins that are displayed on the yeast cell surface. The fluorescence microscopy results show that both fluorescence corresponding to the yeast-derived scFv and fluorescence corresponding to the E . coli -derived scFv can exist on the cell surface of same yeast cell. This confirms that the E . coli -derived scFv protein was successfully displayed on the yeast cell surface. Conclusions This method provides a rapid, simple, and high-efficiency strategy to increase the level of displayed protein on the yeast cell surface. Application of this technique may allow the yeast surface display system to be used to generate potential oral vaccines. [ABSTRACT FROM AUTHOR]

DDX3, a member of the DEAD-box RNA helicase family and has highly conserved ATP-dependent RNA helicase activity, has important roles in RNA metabolism and innate anti-viral immune responses. In this study, five transcript variants of the DDX3 gene were cloned and characterized from rainbow trout (Oncorhynchus mykiss). These five transcript variants of DDX3 encoded proteins were 74.2 kDa (686 aa), 76.4 kDa (709 aa), 77.8 kDa (711 aa), 78.0 kDa (718 aa), and 78.8 kDa (729 aa) and the predicted isoelectric points were 6.91, 7.63, 7.63, 7.18, and 7.23, respectively. All rainbow trout DDX3 proteins contained two conserved RecA-like domains that were similar to the DDX3 protein reported in mammals. Phylogenetic analysis showed that the five cloned rainbow trout DDX3 were separate from mammals but clustered with fish, especially Northern pike (Esox lucius) and Nile tilapia (Oreochromis niloticus). RT-qPCR analysis showed that the DDX3 gene was broadly expressed in all tissues studied. The expression of DDX3 after infectious hematopoietic necrosis virus (IHNV) infection increased gradually after the early stage of IHNV infection, decreased gradually with the proliferation of IHNV in vivo (liver, spleen, and kidney), and was significantly decreased after the in vitro infection of epithelioma papulosum cyprini (EPC) and rainbow trout gonad cell line-2 (RTG-2) cell lines. We also found that rainbow trout DDX3 was significantly increased by a time-dependent mechanism after the poly I:C treatment of EPC and RTG cells; however no significant changes were observed with lipopolysaccharide (LPS) treatment. Knockdown of DDX3 by siRNA showed significantly increased IHNV replication in infected RTG cells. This study suggests that DDX3 has an important role in host defense against IHNV infection and these results may provide new insights into IHNV pathogenesis and antiviral drug research. • Five transcript variants of DDX3 gene were cloned and characterized from rainbow trout. • Rainbow trout DDX3 contains conserved RecA-like domains similar with mammals. • Rainbow trout DDX3 was increased at early stage and decreased at late stage during IHNV infection in vivo. • DDX3 was increased after poly I:C treatment but decreased after IHNV infection in vitro. • Knockdown of DDX3 by siRNA increased IHNV replication in RTG-2 cells. [ABSTRACT FROM AUTHOR]

Infectious hematopoietic necrosis virus (IHNV) is a significant rhabdoviral pathogen of salmonid fish. In this study, a single chain variable fragment (scFv) antibody library derived from rainbow trout ( Oncorhynchus mykiss ) and a glycoprotein fragment (named G4, 540 nt, 180 aa) of IHNV-Sn1203 isolate were co-expressed by a bacterial display technology. The library was subjected to three rounds of screening by flow cytometry (FCM) to select IHNV specific antibodies. Seven antibody clones with different mean fluorescence intensities (MFI) were obtained by picking colonies at random. The antibody clone with the highest MFI was expressed and purified. The purified IHNV-specific scFv antibody was used successfully in Western blotting, enzyme linked immunosorbent assay and an immunofluorescence antibody test. This method provides a high throughput means to screen an antibody library by flow cytometry and isolate an antibody that can be used as a potential universal reagent for the detection and confirmation IHNV strains that are prevalent throughout China. Statement of relevance Outbreaks of infectious hematopoietic necrosis caused severe economic losses to salmon and trout aquaculture in China every year. In this study, a panel of recombinant antibodies against Chinese IHNV isolates was obtained. The isolated antibody was proven can be used as a universal diagnosis regent for IHNV prevalent in China. The study provides a novel method for rapid development of antibodies to emerging diseases. [ABSTRACT FROM AUTHOR]

Infectious hematopoietic necrosis virus (IHNV) is the main pathogen threatening the aquaculture used by the salmonid industry worldwide. Our previous study showed that IHNV infection induced autophagy activation in epithelioma papulosum cyprinid (EPC) cells, but the relationship between IHNV infectivity and autophagy induction had not yet been addressed. To investigate this question, IHNV was inactivated by ultraviolet (UV) irradiation and the complete protein sequence of IHNV glycoprotein was segmented by pepscan into 43 peptides. The induction of autophagy was analyzed by transmission electron microscopy, confocal fluorescence microscopy, flow cytometry, and western blotting. The results show that UV-inactivated IHNV and viral glycoprotein can induce autophagosome formation, obvious punctate clusters of LC3-II and an elevated LC3-II to LC3-I ratio. All these results suggested that UV-inactivated IHNV and viral glycoprotein can induce autophagy independently of viral infectivity. The flow cytometry and western blotting results show that EPC cells treated with peptide p108 displayed an obvious induction of autophagy (LC3-II increased by approximately 2.5-fold). The cells pretreated with peptide p108 showed a significant inhibition of intracellular viral mRNA replication levels and extracellular viral yields of IHNV. These results suggest that peptide p108 could be a promising drug for use in IHNV prevention, and they lay a new foundation for anti-IHNV drug development. • IHNV can trigger autophagy in EPC cells regardless of its viral infectivity. • IHNV glycoprotein can induce autophagy formation in EPC cells. • IHNV glycoprotein was divided into 43 small peptides to identify the autophagy-inducing region. • Peptide p108 induced autophagy activation and clearly inhibited IHNV replication. [ABSTRACT FROM AUTHOR]