Interferon type I responses to virus infections in carp cells: In vitro studies on Cyprinid herpesvirus 3 and Rhabdovirus carpio infections

Single-chain antibody gene therapy strategy based on high-throughput screening triggers sustained antiviral activity in the body

The occurrence of viral diseases poses a huge threat and impact on human public health safety and the development of the animal and fishery industry. Here, a strain of single-chain antibody fragment, scFv-1, was isolated from the phage antibody display library construct by immunizing New Zealand white rabbits with rhabdovirus. In vitro analysis showed that the single-chain antibody could inhibit the infection of the virus in multiple pathways, including adsorption, fusion, and release. In vivo analysis revealed scFv-1 had a preventive and protective effect against the infection of virus. In addition, we describe that transposon-based transport of neutralizing genes allows for long-term, continuous expression, avoiding the need for lifelong, repeated passive immunization for treatment. In sum, high-throughput screening of neutralization genes based on phage display technology and transposon vector-based gene transfer provides effective methods for treating and preventing diseases and avoiding repetitive passive immunotherapy. This study also provides a reference for the prevention and treatment of unknown pathogens.IMPORTANCELivestock and fisheries play an important role in economic development and food security. The frequent outbreaks of viral diseases have caused great losses to the livestock industry, while the increase in drug resistance caused by the use of antibiotics as well as the potential risks to human health have raised serious concerns. Here, we constructed a phage display antibody library by immunizing New Zealand white rabbits with purified rhabdovirus and selected a single-chain antibody, scFv-1, with good neutralizing activity, which was validated and found to be able to block multiple phases of the virus and thus play a neutralizing role. In addition, we describe that transposon-based transport of neutralizing genes allows for long-term, continuous expression, reducing the need for lifelong, repeated passive immunization for treatment. Our work not only provides methods for the prevention and treatment of viral diseases but also provides the body with long-lasting and even permanent protection against repeated passive immunization.

The intestinal microbiome and Cetobacterium somerae inhibit viral infection through TLR2-type I IFN signaling axis in zebrafish

BACKGROUND

Evidence has accumulated to demonstrate that intestinal microbiome can inhibit viral infection. However, our knowledge of the signaling pathways and identity of specific commensal microbes that mediate the antiviral response is limited. Zebrafish have emerged as a powerful animal model for study of vertebrate-microbiota interactions. Here, a rhabdoviral infection model in zebrafish allows us to investigate the modes of action of microbiome-mediated antiviral effect.

RESULTS

We observed that oral antibiotics-treated and germ-free zebrafish exhibited greater spring viremia of carp virus (SVCV) infection. Mechanistically, depletion of the intestinal microbiome alters TLR2-Myd88 signaling and blunts neutrophil response and type I interferon (IFN) antiviral innate immunity. Through 16S rRNA sequencing of the intestinal contents from control and antibiotic(s)-treated fish, we identified a single commensal bacterial species, Cetobacterium somerae, that can restore the TLR2- and neutrophil-dependent type I IFN response to restrict SVCV infection in gnotobiotic zebrafish. Furthermore, we found that C. somerae exopolysaccharides (CsEPS) was the effector molecule that engaged TLR2 to mediate the type I IFN-dependent antiviral function.

CONCLUSIONS

Together, our results suggest a conserved role of intestinal microbiome in regulating type I IFN antiviral response among vertebrates and reveal that the intestinal microbiome inhibits viral infection through a CsEPS-TLR2-type I IFN signaling axis in zebrafish. Video Abstract.

Drug delivery system based on metal-organic framework improved 5-Fluorouracil against spring viremia of carp virus

Spring viremia of carp virus (SVCV), as a high pathogenicity pathogen, has seriously restricts the healthy and sustainable development of cyprinid farming industry. In this study, we selected 5-Fluorouracil (5-Fu) as the drug model based on zeolitic imidazolate framework-8 (ZIF-8) to construct a drug delivery system (5-Fu@ZIF-8), and the anti-SVCV activity was detected in vitro and in vivo. The results showed 5-Fu@ZIF-8 was uniform cubic particle with truncated angle and smooth surface, and the particle size was 90 nm. The anti-SVCV activity in vitro results showed that the highest inhibition rate of 5-Fu was 77.93% at 40 mg/L and the inhibitory concentration at half-maximal activity (IC50) was 20.86 mg/L. For 5-Fu@ZIF-8, the highest inhibition rate was 91.36% at 16 mg/L, and the IC50 value was 5.85 mg/L. In addition, the cell viability was increased by 18.1% after 5-Fu treatment. Similarly, after 5-Fu@ZIF-8 treatment, the cell viability increased by 27.3%. Correspondingly, in vivo experimental results showed the viral loads reduced by 18.1% on the days 7 and the survival rate increased to 19.4% at 80 mg/L after 5-Fu treatment. For 5-Fu@ZIF-8, the viral loads reduced by 41.2% and the survival rate increased to 54.8%. Mechanistically, 5-Fu inhibits viral replication by regulating p53 expression and promoting early apoptosis in infected cells. All results indicated that 5-Fu@ZIF-8 improved the anti-SVCV activity; it may be a potential strategy to construct a drug-loaded system with ZIF-8 as a carrier for the prevention and treatment of aquatic diseases.

Transcriptomic Responses to Koi Herpesvirus in Isolated Blood Leukocytes from Infected Common Carp

Koi herpesvirus (KHV, CyHV-3) causes severe economic losses in carp farms. Its eradication is challenging due to the establishment of latency in blood leukocytes and other tissues. To understand the molecular mechanisms leading to KHV infection in leukocytes, common carp were bath-exposed to KHV at 17 °C. After confirming the presence of viral transcripts in blood leukocytes at ten days post infection, RNA-Seq was performed on peripheral blood leukocytes on the Illumina NovaSeq. KHV infection triggered a robust immune response mediated by pattern recognition receptors, mainly toll-like receptors (tlr2, tlr5, tlr7, and tlr13), urokinase plasminogen activator surface receptor-like, galectin proteins, and lipid mediators such as leukotriene B4 receptor 1. Enriched pathways showed increased mitochondria oxidative phosphorylation and the activation of signalling pathways such as mitogen-activated protein kinases (MAPKs) and vascular endothelial growth factor (VEGF). KHV-infected leukocytes showed low production of reactive oxygen species (ROS) and glutathione metabolism, high iron export and phagocytosis activity, and low autophagy. Macrophage polarization was deduced from the up-regulation of genes such as arginase non-hepatic 1-like, macrophage mannose receptor-1, crem, il-10, and il-13 receptors, while markers for cytotoxic T cells were observed to be down-regulated. Further work is required to characterise these leukocyte subsets and the molecular events leading to KHV latency in blood leukocytes.

IRF9 inhibits CyHV-3 replication by regulating the PI3K-AKT signalling pathway in common carp (Cyprinus carpio) epithelial cells

Interferon regulatory factor 9 (IRF9) is an important transcriptional regulator involved in innate and adaptive immunity. Cyprinid herpesvirus-3 (CyHV-3) is a virus causing widespread death and great economic loss in farmed common carp (Cyprinus carpio). However, the effect of IRF9 on CyHV-3 infection in common carp has not been reported. In this study, during CyHV-3 infection, IRF9 overexpression in common carp fin epithelial (CCF) cells significantly reduced the expression of viral factor thymidine kinase (TK) and open reading frame 72 (ORF72), and knockdown of IRF9 produced the opposite results (p < 0.05). In CCF cells. The IRF9 protein was expression in the nucleus and was rapidly induced in CCF cells by CyHV-3 infection. In addition, several genes associated with virus infection, including type I interferon (IFNI), IFN-stimulated gene 15 (ISG15), myxovirus resistance 1 (Mx1) and Viperin were induced in CCF cells overexpressing IRF9 upon CyHV-3 infection. IRF9 overexpression induced by CyHV-3 infection significantly increased the gene expression of Mx1 and phosphoinositide 3-kinase (PI3K) and the protein expression of protein kinase B (AKT) (p < 0.01). Interestingly, IRF9 did not significantly affect Mx1 gene expression when AKT protein levels remained unchanged during CyHV-3 infection of CCF cells. Furthermore, a significant resistance-related locus was found in the IRF9 sequence in "Longke-11" mirror carp (M11) and Yellow River carp (p < 0.05). These results indicated that IRF9 inhibited viral replication by upregulating the expression of Mx1 via the PI3K-AKT signalling pathway during CyHV-3 infection in CCF cells and provide some basis for the study of the antiviral molecular mechanisms of common carp.

Identification of a novel immune-related long noncoding RNA in carp primary macrophages associated with bisphenol A' s immunoregulatory effects

Increasing evidence suggests that long non-coding RNAs (lncRNAs) play pivotal roles in various biological processes. However, current studies on lncRNAs mostly focus on mammalian species, with little research on the functional roles of lncRNAs in teleost fish. Here, we identified a novel intergenic lncRNA (linc-93.2) in the head kidney primary macrophages of common carp (Cyprinus carpio) after exposure to a typical environmental endocrine disrupting chemical, bisphenol A (BPA). As a result, linc-93.2 was more than 3,619 bp in length and predominantly localized to the nucleus of primary macrophages other than cytoplasm, with the highest expression level in spleen followed by head kidney among different organs. Bioinformatic analysis predicted a cis-target gene, dennd1b, and 20 trans-target genes including hsp70, gna13 and rasgap, were potentially regulated by linc-93.2; NFκB and estrogen receptor (ERα) binding sites were located in the promoter region upstream of its transcription start site, which together suggested the involvement of linc-93.2 in immune and neurological functions in fish. Based on that, the expression level of linc-93.2 was determined in macrophages following acute lipopolysaccharide (LPS) and BPA treatments, both of which significantly induced linc-93.2 and IL-1β expression in cells. Moreover, a NF-κB inhibitor PDTC significantly reduced linc-93.2 expression in macrophages, but co-exposure of macrophages to PDTC with BPA or LPS could significantly rescue linc-93.2 expression, consistent with the observation on that LPS or BPA alone significantly induced both linc-93.2 and its target gene expression. Interestingly, linc-93.2 and its target gene expression was significantly suppressed by an ER antagonist ICI 182,780, however, the co-exposure of macrophages to ICI 182,780 with BPA failed to attenuate their declined expression. Overall, the current study demonstrated that linc-93.2, a novel immune-related lncRNA, may participate in the immune processes of common carp macrophages via the NF-κB and ER pathway. The results presented in this study enhance our understanding of the immunotoxin mechanisms of BPA in teleost fish.

DDX5 inhibits type I IFN production by promoting degradation of TBK1 and disrupting formation of TBK1 - TRAF3 complex

DExD/H-box helicase (DDX) 5 belongs to the DExD/H-box helicase family. DDX family members play differential roles in the regulation of innate antiviral immune response. However, whether DDX5 is involved in antiviral immunity remains unclear. In this study, we found that DDX5 serves as a negative regulator of type I interferon (IFN) response. Overexpression of DDX5 inhibited IFN production induced by Spring viremia of carp virus (SVCV) and poly(I:C) and enhanced virus replication by targeting key elements of the RLR signaling pathway (MAVS, MITA, TBK1, IRF3 and IRF7). Mechanistically, DDX5 directly interacted with TBK1 to promote its autophagy-mediated degradation. Moreover, DDX5 was shown to block the interaction between TRAF3 and TBK1, hence preventing nuclear translocation of IRF3. Together, these data shed light on the roles of DDX5 in regulating IFN response.

Herbal active small molecule as an immunomodulator for potential application on resistance of common carp against SVCV infection

Herbal immunomodulators are an important part of prevention and control on viral diseases in aquaculture because of their propensity to improve immunity in fish. The present study was conducted to evaluate the immunomodulatory effect and antiviral activity of a synthesized derivative (serial number: LML1022) against spring viremia of carp virus (SVCV) infection in vitro and in vivo. The antiviral data suggested that LML1022 at 100 μM significantly inhibited the virus replication in epithelioma papulosum cyprini (EPC) cells, and may completely inhibit the infectivity of SVCV virion particles to fish cells by affecting the viral internalization. The results in the related stability of water environments also demonstrated that LML1022 had an inhibitory half-life of 2.3 d at 15 °C, which would facilitate rapid degradation of LML1022 in aquaculture application. For in vivo study, the survival rate of SVCV-infected common carp was increased 30% at least under continuous oral injection of LML1022 at 2.0 mg/kg for 7 d treatment. Additionally, pretreatment of LML1022 on fish prior to SVCV infection also obviously reduced the viral loads in vivo as well as an improved survival rate, showing that LML1022 was potential as an immunomodulator. As an immune response, LML1022 significantly upregulated the immune-related gene expression including IFN-γ2b, IFN-I, ISG15 and Mx1, indicating that its dietary administration may improve the resistance of common carp against SVCV infection.

Susceptibility and Permissivity of Zebrafish (Danio rerio) Larvae to Cypriniviruses

The zebrafish (Danio rerio) represents an increasingly important model organism in virology. We evaluated its utility in the study of economically important viruses from the genus Cyprinivirus (anguillid herpesvirus 1, cyprinid herpesvirus 2 and cyprinid herpesvirus 3 (CyHV-3)). This revealed that zebrafish larvae were not susceptible to these viruses after immersion in contaminated water, but that infections could be established using artificial infection models in vitro (zebrafish cell lines) and in vivo (microinjection of larvae). However, infections were transient, with rapid viral clearance associated with apoptosis-like death of infected cells. Transcriptomic analysis of CyHV-3-infected larvae revealed upregulation of interferon-stimulated genes, in particular those encoding nucleic acid sensors, mediators of programmed cell death and related genes. It was notable that uncharacterized non-coding RNA genes and retrotransposons were also among those most upregulated. CRISPR/Cas9 knockout of the zebrafish gene encoding protein kinase R (PKR) and a related gene encoding a protein kinase containing Z-DNA binding domains (PKZ) had no impact on CyHV-3 clearance in larvae. Our study strongly supports the importance of innate immunity-virus interactions in the adaptation of cypriniviruses to their natural hosts. It also highlights the potential of the CyHV-3-zebrafish model, versus the CyHV-3-carp model, for study of these interactions.

Long-term exposure to azoxystrobin induces immunodeficiency in fish that are vulnerable to subsequent rhabdovirus infection

Azoxystrobin (AZ) is one of the most widely used strobilurin fungicides in the world, and its residue has seriously endangered aquatic ecological security. Our previous data showed that AZ exposure may reduce the resistance of fish to rhabdovirus infection in aquatic environment. Here, we further reported a potential long-term adverse effect of AZ exposure on the antiviral and immunosuppressive recovery in fish, and observed that mitochondrial dynamic balance was disturbed by AZ in which excessive mitochondrial fission occurred in response to decreased ATP levels. When a recovery operation was performed in AZ-exposed cells and fish, infectivity of our model virus, spring viraemia of carp virus (SVCV), was significantly decreased in vitro (using the epithelioma papulosum cyprini [EPC] fish cell line) and in vivo (using zebrafish) in a time-dependent manner. Also, the expression of eight innate antiviral immune genes (IFNs, ISG15, MX1, RIG-I, IRF3, Nrf2 and HO-1) showed a similar change to SVCV replication between the longer exposure period and the expression recovery. Additionally, AZ facilitated horizontal transmission of SVCV in a static cohabitation challenge model, predicting the increase of the potential for the viral outbreak. Therefore, our data suggest that long-term effect of AZ on irreparable impairment in fish made AZ residue potentially greater for ecological risks.

The influence of viral infection on cell line characteristics: Lessons learned from working with new cell lines from common carp

Several factors influence the susceptibility of cell lines to infection by different viruses. These can be related to tissue specificity of the viruses, physiological status of the cells, their differentiation level and their capacity to mount immune responses to combat viral infection. To study the influence of cell characteristics and immune responses on their susceptibility on virus infection, newly developed cell lines from common carp brain (CCAbre), fins (CCApin), gills (CCAgill), and heart (CCAcar) and the established common carp brain (CCB) cells were exposed to the carp infecting viruses cyprinid herpesvirus 3 (CyHV-3), carp oedema virus (CEV), and the yet not fully characterized common carp paramyxovirus (CCPV). The susceptibility of these cells to viral infection was measured by formation of a cytopathic effect (CPE), estimation of viral particles produced by the cells and presence of viral mRNA in the cells. Viral susceptibility of the cells was compared to cell characteristics, measured by mRNA expression of the epithelial cell markers cadherin 1, occludin, and cytokeratin 15 and the mesenchymal cell marker vimentin, as well as to the level of type I interferon (IFN) responses. All cell lines were susceptible to CyHV-3 and CCPV but not to CEV infection. The cell lines had different levels of type I IFN responses towards the viruses. Typically, CyHV-3 did not induce high type I IFN responses, while CCPV induced high responses in CCAbre, CCAcar, CCApin cells but no response in CCAgill cells. Consequently, the type I IFN response modulated cell susceptibility to CCPV but not to CyHV-3. Interestingly, when the three different passage levels of CCB cells were examined, the susceptibility of one passage was significantly lower for CyHV-3 and higher for CCPV infection. This coincided with a loss of epithelial markers and lower type I IFN responses. This study confirms an influence of cell characteristics and immune responses on the susceptibility of carp cell lines for virus infection. Depending on the vulnerability of the virus to type I IFN responses, cells with a lower IFN-response can be superior for replication of some viruses. Batches of CCB cells can differentiate and thus may have significantly different levels of susceptibility to certain viruses.

Fish immune responses to natural infection with carp edema virus (Koi sleepy disease): An emerging fish disease in India

Emerging pathogen, carp edema virus (CEV) causes koi sleepy disease (KSD) in Koi and common carp causing severe mortalities worldwide. In the present study, a total of 150 fish species belonging to eight different families were sampled from the ornamental fish retailers and farms, located in Karnataka, India. The OIE protocol viz., level-I, II and III diagnoses confirmed the infection of CEV in 10 koi fish. Interestingly, other fish species belonging to different fish family including cyprinidae family were negative to CEV. Further, CEV infection was confirmed by sequencing (partial 4a gene); it showed the similarity with that of CEV reported from India and Germany strains with similarity of 97.4-99.94% and belonged to genogroup IIa. TEM analysis of purified CEV, in vivo cohabitation and tissue infection experiments confirmed the CEV infection. In addition, viral load was significantly higher (10^6-7 copies) in koi collected from Dakshina Kannada than of Bengaluru (10^3-4 copies). To understand the host-pathogen interaction, different organs such as gill, kidney, liver and spleen from naturally (CEV) infected koi were used to study the immune gene responses by using eight innate and one adaptive immune response. Results indicated that TNF-α, RohTNF-α, iNOS, IFN-γ and IL-10, and catalyze β-2M of MHC class I pathway genes were upregulated in koi. Higher expression of immune genes during the CEV infection may have inhibited viral replication and mount an antigenic adaptive response. Similar to other viral infections, interferon-γ play an important role during poxvirus infections. Quantification of immune genes in infected fish will provide insights into the host responses and provide valuable information to devise intervention strategies to prevent and control disease due to CEV.

Development of an attenuated vaccine against Koi Herpesvirus Disease (KHVD) suitable for oral administration and immersion

Since the end of the1990ies, Cyprinid herpesvirus 3 (also known as koi herpesvirus, KHV) has caused mass mortality events of koi and common carp all over the globe. This induced a high economic impact, since the KHV disease cannot be cured up to now, but only prevented by vaccination. Unfortunately, there is only one commercial vaccine available which is not approved in most countries. Therefore, there is an urgent need for new, safe and available vaccines. In this study, a live attenuated vaccine virus was generated by cell culture passages of virulent KHV, and shown to protect carp or koi after immersion or oral application against wild type challenge. An advantage of boost immunization was demonstrated, especially after oral application. Vaccination induced no or mild clinical signs and protecting antibodies have been measured. Additionally, the vaccine virus allowed differentiation of infected from vaccinated animals (DIVA) by PCR. The attenuation of the newly generated vaccine was tracked down to a partial deletion of open reading frame 150. This was confirmed by the generation of engineered ORF150 deletion mutants of wild-type KHV which exhibited a similar attenuation in vivo.

Early immune response of two common carp breeds to koi herpesvirus infection

Economic importance of common carp (Cyprinus carpio L.) increases every year. Viral diseases are major threat for carp aquaculture and cause significant economic losses. Koi herpesvirus (KHV) is one of the most serious carp diseases. Current study is focused on confirmation of possible differences in early immune response to KHV depending on level of resistance. Class I interferon signalling, complement cascade and cell-mediated cytotoxicity are hypothesized as major mechanisms of early innate immune response against KHV. Different breeds of common carp show distinct level of resistance to KHV. Two breeds of common carp with completely different susceptibility to KHV were chosen for current research: amur wild carp (AS) as highly resistant and koi carp (KOI) as very susceptible breed. KHV infection caused no mortalities, but the viral load in selected tissues increased during infection. Levels of expressions of chosen genes was examined using qRT-PCR and overall change in protein expression profiles was analysed by mass spectrometry. Significant differences in immune response between AS and KOI were detected mostly at the level of protein expression. Although cell-mediated cytotoxicity showed minimal influence during KHV infection, many immune response parameters related to class I interferon signalling pathway and complement cascade were increased earlier during KHV infection in AS comparing to KOI.

Fish Innate Immune Response to Viral Infection-An Overview of Five Major Antiviral Genes

Fish viral diseases represent a constant threat to aquaculture production. Thus, a better understanding of the cellular mechanisms involved in establishing an antiviral state associated with protection against virus replication and pathogenesis is paramount for a sustainable aquaculture industry. This review summarizes the current state of knowledge on five selected host innate immune-related genes in response to the most relevant viral pathogens in fish farming. Viruses have been classified as ssRNA, dsRNA, and dsDNA according to their genomes, in order to shed light on what those viruses may share in common and what response may be virus-specific, both in vitro (cell culture) as well as in vivo. Special emphasis has been put on trying to identify markers of resistance to viral pathogenesis. That is, those genes more often associated with protection against viral disease, a key issue bearing in mind potential applications into the aquaculture industry.

MicroRNA miR-155 inhibits cyprinid herpesvirus 3 replication via regulating AMPK-MAVS-IFN axis

Since emerged in the late 1990s, cyprinid herpesvirus 3 (CyHV-3) has caused huge economic losses in common and koi carp culture worldwide. Accumulating evidences suggest that teleost fish microRNA (miRNA), a class of non-coding RNA of ∼22 nucleotides, can participate in many cellular processes, especially in host antiviral defenses. However, the roles of miRNAs in CyHV-3 infection are still unclear. Here, using high-throughput miRNA sequencing and quantitative real-time PCR (qRT-PCR) verification, we found that miR-155 was significantly upregulated in common carp brain (CCB) cells upon CyHV-3 infection. Overexpression of miR-155 effectively inhibited CyHV-3 replication in CCB cells and promoted type I interferon (IFN-I) expression. Further study revealed that miR-155 targeted the 3' untranslated region (UTR) of the mRNA of 5'AMP-activated protein kinase (AMPK), and that AMPK could interact with and degrade the mitochondrial antiviral signaling protein (MAVS), resulting in the reduction of interferon (IFN) expression. Collectively, our results show that miR-155, induced by CyHV-3 infection, exhibits anti-CyHV-3 activity via regulating AMPK-MAVS-IFN axis, which will help design anti-CyHV-3 drugs.

Cytokines Studied in Carp (Cyprinus carpio L.) in Response to Important Diseases

Cytokines belong to the most widely studied group of intracellular molecules involved in the function of the immune system. Their secretion is induced by various infectious stimuli. Cytokine release by host cells has been extensively used as a powerful tool for studying immune reactions in the early stages of viral and bacterial infections. Recently, research attention has shifted to the investigation of cytokine responses using mRNA expression, an essential mechanism related to pathogenic and nonpathogenic-immune stimulants in fish. This review represents the current knowledge of cytokine responses to infectious diseases in the common carp (Cyprinus carpio L.). Given the paucity of literature on cytokine responses to many infections in carp, only select viral diseases, such as koi herpesvirus disease (KHVD), spring viremia of carp (SVC), and carp edema virus disease (CEVD), are discussed. Aeromonas hydrophila is one of the most studied bacterial pathogens associated with cytokine responses in common carp. Therefore, the cytokine-based immunoreactivity raised by this specific bacterial pathogen is also highlighted in this review.

Optimization of immunization procedure for SWCNTs-based subunit vaccine with mannose modification against spring viraemia of carp virus in common carp

Immersion vaccination of single-walled carbon nanotubes loaded with mannose-modified glycoprotein (SWCNTs-MG) vaccine has been proved to be effective in preventing spring viraemia of carp virus (SVCV). Immunization procedure has immense consequence on the immune effect of the immersion vaccine. However, immunization procedure optimization for SWCNTs-MG vaccine against SVCV has not been reported. In this study, accordingly, a full-factor experiment was designed to optimize the immunization procedure of SWCNTs-MG vaccine by three aspects of vaccine dose (30 mg/L, 40 mg/L and 50 mg/L), immunization density (8 fish L^-1 , 24 fish L^-1 and 48 fish L^-1 ) and immunization time (6, 12 and 24 hr). Furthermore, we used the immunization group (A1B2C1, 30 mg/L, 24 fish L^-1 and 6 hr) in the previous study as a positive control (PC) to evaluate the immunization effect optimized conditions from the expression of immune-related genes and relative percentage survival (RPS). At 28 days post-vaccination (DPV), common carps were intraperitoneal injected SVCV challenged test indicated that the A1B2C2 group (30 mg/L, 24 fish L^-1 , 12 hr) displayed superiority of protective efficacy compare with other groups and the RPS with 77.9%, which was 15.6% higher than the PC group of RPS with 62.3%. Moreover, the expression of immune-related genes such as IL-10, CD4 and MHC-II was also significantly higher than PC group. The specific experimental flow chart is shown in Figure 1. Conclusively, these results demonstrated that vaccine dose, immunization density and immunization time are 30 mg/L, 24 fish L^-1 and 12 hr, which is the more appropriate immunization programme with juvenile carp for SWCNTs-MG vaccine. This study provides a profitable reference for improving the immune efficiency of aquatic immersion vaccine. [Figure: see text].

Azoxystrobin increases the infection of spring viraemia of carp virus in fish

Azoxystrobin (AZ) has entered aquatic ecosystems and produced serious damages to fish associated with potentially increasing the susceptibility to pathogens. This study characterized the defense abilities of fish by exposed to AZ on challenging with the infection of spring viraemia of carp virus (SVCV). The results showed that SVCV replication increased significantly in EPC cells and zebrafish that were exposed to up to 50 μg/L of AZ at 3, 5, 7, and 14 d. Intracellular biochemical assays indicated that AZ at 5 and 50 μg/L inhibited the activation of Nrf2-ARE pathway including a decrease in Nrf2 expression, Nrf2 phosphorylation, HO-1 content, and three antioxidant activities. While no significant difference in ERK1/2 and JNK MAPKs in zebrafish was observed, P38 phosphorylation was significantly decreased at 7 and 14 d, and the changes in MAPKs were more evident in EPC cells previously exposed to AZ at 7 d. These results revealed that AZ initially induced low phosphorylation of MAPKs, triggering the attenuation of Nrf2 phosphorylation to weaken Nrf2 translocation into the nucleus in a longer exposure period (more than 5 d). The data in the cells and fish also showed that antioxidant activities were decreased to some extent at 5-7 d for the cells and 7-14 d for the fish. Furthermore, interferon-related factors were decreased in AZ-exposed zebrafish, explaining the reason that fish can't resist the virus infection. Overall, the present study provided a new adverse threat of AZ by amplifying the viral outbreak to endanger ecological safety in aquatic environment.

2D-DIGE proteomic analysis of blood plasma reveals changes in immune- and stress-associated proteins following hormonal stimulation of carp males

In carp aquaculture, hormonal manipulation with an analog of GnRH (Ovopel) and carp pituitary extract (CPE), which act at different levels of the hypothalamic-pituitary-gonadal axis, is a routine practice to enhance sperm production. Our recent studies revealed that hormonal stimulation of male carp was associated with changes in the seminal plasma proteome, including blood origin proteins. Here, we explored whether Ovopel and CPE could affect the blood proteome of male carp. Both preparations induced increases in semen volume, total number of sperm, and testosterone level. However, hormonal stimulation did not affect the plasma cortisol and glucose levels. A comparative proteomic analysis of carp blood plasma between the control (PBS) and the hormonally treated males revealed significant changes (>1.2 <-1.2-fold change, P < 0.05) in the abundance of 30 spots (14 up- and 16 downregulated) and 44 spots (28 up- and 16 downregulated) upon CPE and Ovopel treatment, respectively. The most significantly affected pathways were acute phase response signaling, the coagulation system, LXR/RXR and FXR/RXR activation; however, there were different sets of proteins in Ovopel- and CPE-treated males. The majority of differentially abundant proteins were involved in the regulation of the immune defense response, the response to stress, and complement activation. Moreover hormonal stimulation with CPE markedly increased the bactericidal activity of blood and both preparations caused profound changes in gene expression in hematopoietic organs. This work is important in understanding the biological processes behind the protein-based response to hormonal stimulation of sperm production in fish.

Integrated analysis of mRNA and long non-coding RNA expression profiles reveals the potential roles of lncRNA-mRNA network in carp macrophage immune regulation

Long non-coding RNAs (lncRNAs) have emerged as a hot topic in research as mounting evidence has indicated their transcriptional or post-transcriptional regulatory potential in multiple biological processes. Previous studies have revealed the involvement of lncRNAs in the immunoregulation of mammalian macrophages by changing mRNA expression; however, studies on the lncRNAs in fish macrophages and their potential roles in the immune system remain unknown. Primary macrophages were isolated from the head kidney (HK) of red common carp (Cyprinus carpio) and high-throughput lncRNA-mRNA sequencing was performed using the Illumina HiSeq platform. The results revealed that the most highly expressed mRNAs in primary HK macrophages were mainly involved in immune-related signal pathways. Furthermore, the most enriched immune-related GO term and KEGG pathway of the mRNAs were "immune system development" and "chemokine signaling pathway," respectively. A total of 20,333 lncRNAs, composed of 10,512 known and 9821 novel lncRNAs, were identified, and functional enrichment analysis of the lncRNA-mRNA network indicated that the expressed lncRNAs in primary HK macrophages could be associated with the regulation of multiple immune-related signaling pathways. In addition, the expressions of several selected lncRNAs and their related mRNAs were determined in carp macrophages following a 6-h exposure to lipopolysaccharide (LPS) and Poly(I: C), the results of which confirmed the co-expression regulation of lncRNAs and target mRNAs in the immune response of carp macrophages. These results suggest the correlative of the lncRNA-mRNA network in fish macrophage immune response, which may further affect the cross-talk of various signaling pathways by interaction with other network genes. Here, we provided fundamental data about the transcriptome profiles of primary HK macrophages from red common carp by analysis of the lncRNA-mRNA network, and ultimately suggest the potential roles of lncRNA-mRNA networks in immune regulation in teleost fish.

Carp edema virus and immune response in carp (Cyprinus carpio): Current knowledge

The importance of world aquaculture production grows annually together with the increasing need to feed the global human population. Common carp (Cyprinus carpio) is one of the most important freshwater fish in global aquaculture. Unfortunately, carp production is affected by numerous diseases of which viral diseases are the most serious. Koi herpesvirus disease (KHVD), spring viraemia of carp (SVC), and during the last decades also koi sleepy disease (KSD) are currently the most harmful viral diseases of common carp. This review summarizes current knowledge about carp edema virus (CEV), aetiological agent causing KSD, and about the disease itself. Furthermore, the article is focused on summarizing the available information about the antiviral immune response of common carp, like production of class I interferons (IFNs), activation of cytotoxic cells, and production of antibodies by B cells focusing on anti-CEV immunity.

Characterization of a novel brain cell line from Jian carp (Cyprinus carpio var. Jian)

Jian carp (Cyprinus carpio var. Jian) is an economically important cultured fish in China. Currently, it is facing threats from infectious diseases including koi herpesvirus (KHV). Here, we established a new cell line, designated CCB-J, derived from the brain tissue of the Jian carp. CCB-J cells grew well in Leibovitz's L-15 medium containing 20% fetal bovine serum at 25 °C and have been subcultured for more than 60 passages. At the 30th passage, analysis showed that the number of chromosomes was 100, which is identical to that of other carp variants. Sequencing of the 18S ribosomal DNA confirmed that CCB-J originated from Jian carp. After transfection with the pEGFP-N1 plasmid, green fluorescence was observed in CCB-J. The replication of KHV in CCB-J cells was confirmed by RT-PCR and transmission electron microscopy. The viral titers of KHV in CCB-J cells and CCB cells, which have been widely used in the study of KHV, reached 10^3.9 and 10^1.8 median tissue culture infectious dose (TCID₅₀/mL), respectively, within 14 days. The result of TaqMan PCR revealed that CCB-J cells were more sensitive to KHV than CCB cells. Meanwhile, a cytopathic effect (CPE) was also observed in the CCB-J cells in a shorter time post-infection compared with CCB cells. In summary, the CCB-J cell line will be a useful tool in the study of viral pathogenesis and vaccine research.

Antiviral Actions of 25-Hydroxycholesterol in Fish Vary With the Virus-Host Combination

Cholesterol is essential for building and maintaining cell membranes and is critical for several steps in the replication cycle of viruses, especially for enveloped viruses. In mammalian cells virus infections lead to the accumulation of the oxysterol 25-hydroxycholesterol (25HC), an antiviral factor, which is produced from cholesterol by the cholesterol 25 hydroxylase (CH25H). Antiviral responses based on CH25H are not well studied in fish. Therefore, in the present study putative genes encoding for CH25H were identified and amplified in common carp and rainbow trout cells and an HPLC-MS method was applied for determination of oxysterol concentrations in these cells under virus infection. Our results give some evidence that the activation of CH25H could be a part of the antiviral response against a broad spectrum of viruses infecting fish, in both common carp and rainbow trout cells in vitro. Quantification of oxysterols showed that fibroblastic cells are capable of producing 25HC and its metabolite 7α,25diHC. The oxysterol 25HC showed an antiviral activity by blocking the entry of cyprinid herpesvirus 3 (CyHV-3) into KFC cells, but not spring viremia of carp virus (SVCV) or common carp paramyxovirus (Para) in the same cells, or viral haemorrhagic septicaemia virus (VHSV) and infectious pancreatic necrosis virus (IPNV) into RTG-2 cells. Despite the fact that the CH25H based antiviral response coincides with type I IFN responses, the stimulation of salmonid cells with recombinant type I IFN proteins from rainbow trout could not induce ch25h_b gene expression. This provided further evidence, that the CH25H-response is not type I IFN dependent. Interestingly, the susceptibility of CyHV-3 to 25HC is counteracted by a downregulation of the expression of the ch25h_b gene in carp fibroblasts during CyHV-3 infection. This shows a unique interplay between oxysterol based immune responses and immunomodulatory abilities of certain viruses.

G protein-coupled estrogen receptor 1 mediates estrogen effect in red common carp (Cyprinus carpio)

G protein-coupled estrogen receptor 1 (GPER1) plays a crucial role in the regulation of non-genomic estrogen effect. However, the research about fish GPER1 is still limited. The present study aims to obtain the full-length sequence of gper1 from red common carp (Cyprinus carpio) and characterize its expression pattern, and to further explore its potential role in regulating the environmental estrogen induced immunotoxicity. We first cloned the full-length mRNA and genomic sequences of gper1 in C. carpio by PCR, and obtained a 1908 bp sequence with a 1062 bp open reading frame encoding GPER1 protein with 353 amino acids. Additionally, qRT-PCR showed that gper1 was expressed across different tissues in C. carpio, with the highest expression in the brain, which is similar to that in zebrafish. Moreover, applying a luciferase reporter system, we found that the promotor sequence of gper1 has strong activity, and similar to GPER1 in other animals, carp GPER1 also has seven-transmembrane domains, indicating its potential functions. We confirmed the binding ability of GPER1 with G1 and G15 in primary macrophages of C. carpio by testing the related gene expression levels after 6 h exposure, and similar to G1, bisphenol A (BPA), a typical environmental estrogen, could interact with GPER1 to increase the Ca²⁺ concentration in macrophages treated for 30 min. Furthermore, inhibition of GPER1 with GPER1 antagonist G36 rescued the cellular immunotoxicity caused by BPA, which further suggested that carp GPER1 could mediate the estrogen effect. Our findings contribute to better understanding of the role of carp GPER1.

Red elemental selenium (Se0 ) improves the immunoactivities of EPC cells, crucian carp and zebrafish against spring viraemia of carp virus

Selenium, as an essential trace element, interferes through selenoproteins in many physiological processes of plants and mammals. Its antiviral activity has recently attracted much attention because selenium improves the antiviral capacity of animal cells against a few viruses relevant to human diseases. In this study, the red elemental selenium was purified from the fermentative culture of Herbaspirillum camelliae WT00C and then used to culture epithelioma papulosum cyprinid (EPC) cells or feed crucian carp and zebrafish. Finally, its antiviral effects were investigated at the cell level and living fishes after spring viraemia of carp virus infection. At the cell level, 5, 10 and 20 μg ml^-1 red elemental selenium significantly induced the expression of interferon (IFN) and ISG15 genes in EPC cells. The viral TCID₅₀ (50% tissue culture infective dose) values in the EPC cells incubated with 5, 10 and 20 μg ml^-1 red elemental selenium were significantly less than those of the control. More expression of IFN and ISG15 genes and less TCID₅₀ values indicate that red elemental selenium indeed improves the antiviral capability of EPC cells. In the crucian carp fed with the food containing 5 and 10 μg g^-1 red elemental selenium, IFN expressions showed 13- and 39-fold increases at the 16th day of post-injection, and its expression was dependent on selenium concentrations. Meanwhile, no fish death occurred in all the experimental groups. In the zebrafish fed with the red worm containing 5 μg g^-1 red elemental selenium, IFN and Mx expressions and survival rate were significantly higher than those of the control. The results of this study show that red elemental selenium indeed improves the antiviral activity of fish. The antiviral effects of selenium mainly come from its immune regulation through its incorporation into selenoproteins. The optimum level of selenium contributes to improving fish immunity, whereas excess selenium causes excessive immune and inflammatory responses.

Hydroxycoumarin efficiently inhibits spring viraemia of carp virus infection in vitro and in vivo

Spring viremia of carp virus (SVCV) causes devastating losses in aquaculture. Coumarin has an advantageous structure for the design of novel antiviral agents with high affinity and specificity. In this study, we evaluated a hydroxycoumarin medicine, i.e., 7-(6-benzimidazole) coumarin (C10), regarding its anti-SVCV effects in vitro and in vivo. Results showed that up to 12.5 mg/L C10 significantly inhibited SVCV replication in the epithelioma papulosum cyprini (EPC) cell line, with a maximum inhibitory rate of >97%. Furthermore, C10 significantly reduced cell death and relieved cellular morphological damage in SVCV-infected cells. Decreased mitochondrial membrane potential (ΔΨm) also suggested that C10 not only protected mitochondria, but also reduced apoptosis in SVCV-infected cells. For in vivo studies, intraperitoneal injection of C10 resulted in an anti-SVCV effect and substantially enhanced the survival rate of virus-infected zebrafish. Furthermore, C10 significantly enhanced antioxidant enzyme activities and decreased reactive oxygen species (ROS) to maintain antioxidant-oxidant balance within the host, thereby contributing to inhibition of SVCV replication. The up-regulation of six interferon (IFN)-related genes also demonstrated that C10 indirectly activated IFNs for the clearance of SVCV in zebrafish. This was beneficial for the continuous maintenance of antiviral effects because of the low viral loads in fish. Thus, C10 is suggested as a therapeutic agent with great potential against SVCV infection in aquaculture.

In vitro and in vivo evaluation of antiviral activity of a phenylpropanoid derivative against spring viraemia of carp virus

Phenylpropanoids, common natural compounds, possess many different biological activities such as antioxidant, anti-inflammatory and antiviral. Spring viraemia of carp virus (SVCV) can cause a high mortality in common carp (Cyprinus carpio). However, there are currently no licenced drugs that effectively cure this disease. In this study, we designed and synthesized a phenylpropanoid derivative 4-(4-methoxyphenyl)-3,4-dihydro-2H-chromeno[4,3-d]pyrimidine-2,5(1 H)-dione (E2), and explored the antiviral effect against SVCV in vitro and in vivo. Up to 25 mg/L of E2 significantly inhibited the expression levels of SVCV protein genes in the epithelioma papulosum cyprini (EPC) cell line by a maximum inhibitory rate of >90%. As expected, E2 remarkably declined the apoptotic of SVCV-infected cells and suppressed potential enhancement of the mitochondrial membrane potential (ΔΨm), these data implied that E2 could protect mitochondria from structural damage in response to SVCV. Meanwhile, E2 was added to EPC cells under four different conditions: time-of-addition, time-of-removal, pre-treatment of viruses and pre-treatment of cells indicated that E2 may block the post-entry transport process of the virus. Additionally, the up-regulation of six interferon (IFN)-related genes also demonstrated that E2 indirectly activated IFNs for the clearance of SVCV in common carp. Drug cure effect showed that treatment with E2 at 0.5 d post infection (dpi) is more effective than at 0, 1 or 2 dpi. Most importantly, intraperitoneal therapy of E2 markedly improved common carp survival rate and reduced virus copies in body. Therefore, the E2 has potential to be developed into a novel anti-SVCV agent.

Identification of novel long non-coding RNAs involved in bisphenol A induced immunotoxicity in fish primary macrophages

Bisphenol A (BPA), a well-known environmental endocrine-disrupting chemical (EDC), could pose a great toxicity risk to aquatic organisms. The present study aimed to evaluate the underlying role of long non-coding RNAs (lncRNAs) in BPA-induced immunotoxicity in head kidney (HK) macrophages of the red common carp (Cyprinus carpio), using lncRNA-RNA sequencing (RNA-Seq). In BPA-exposed HK macrophages group, 2,095 and 1,138 differentially expressed mRNAs (DEGs) and lncRNAs (DE-lncRNAs) were obtained, respectively, compared with controls. The qRT-PCR validation results of DEGs and DE-lncRNAs were similar to the RNA-Seq results. The KEGG analysis of DEGs and target genes of DE-lncRNAs have shown that some immune-related signaling pathways, including NF-kappa B, Toll-like receptor, B-cell receptor, Jak-STAT, and Hippo signaling pathways, were severely disrupted by BPA exposure. Moreover, we observed the synergic regulation of some mRNAs involved in immune response such as two hub genes traf6 and mapk1/3 and their upstream lncRNAs in HK macrophages upon the BPA exposure or its analogue bisphenol S (BPS) exposure. This suggested the dysregulation of lncRNAs by BPA or BPS may lead to a change in the expression of hub genes, which affects the cross-talk of various signaling pathways by interaction with other network genes. In conclusion, the present study demonstrates the potential role of lncRNAs in immunotoxicity of bisphenol compounds in red common carp HK macrophages, and our results provide evidence for further exploring lncRNA's role in EDC-induced toxicity in aquatic organisms.

Protective immunity against CyHV-3 infection via different prime-boost vaccination regimens using CyHV-3 ORF131-based DNA/protein subunit vaccines in carp Cyprinus carpio var. Jian

Cyprinid Herpesvirus 3 (CyHV-3), also known as Koi Herpesvirus (KHV), causes Koi Herpesvirus Disease (KHVD) which leads to serious economic losses worldwide. To exploit DNA/subunit vaccine candidates, CyHV-3 ORF131 gene and cDNA was cloned and analyzed in the present study. Major B cell epitopes of deduced CyHV-3 pORF131 was also predicted. Then the complete CDS of CyHV-3 ORF131 was inserted into pEGFP-N1 vector and a modified pYD1/EBY100 system to construct the DNA and subunit vaccine, respectively. Subsequently, carp were immunized with homologous and heterologous prime-boost regimens relying on the constructed DNA and oral subunit vaccines. Then the protective immunity generated from different vaccines and regimens as well as the capacity of yeast (Saccharomyces cerevisiae) as an oral vaccine vehicle was evaluated. Our study confirmed that CyHV-3 ORF131 gene consisted of 2 introns and 3 exons encoding a 428 amino acids peptide. Further analysis indicated that four fragments of CyHV-3 pORF131 contained the major B cell epitopes (Cys20~Val140, Ser169~Tyr245, Thr258~Pro390, Phe414~Gln428), which could be linked and expressed in E. coli (BL21) as a truncated pORF131. The expression of full-length CyHV-3 pORF131 by pEGFP-N1 and yeast surface display was verified by In vitro assays before vaccination. Immunization of carp with CyHV-3 ORF131 DNA and subunit vaccines could evoke the activation of immune-related genes such as CXCa, CXCR1, IL-1β, TNF-α, INF-a1, Mx-1, IgM, IgT1 and production of specific serum IgM measured by ELISA. RPS (relative percent of survival) ranging from 53.33% to 66.67% was acquired post challenge test. Moreover, flow cytometry analysis illustrated the delivery of surface-displayed CyHV-3 pORF131 to midgut after oral gavage. Thus, our findings suggest that CyHV-3 ORF131 can serve as DNA/subunit vaccines candidate and the yeast as an ideal oral vaccine vehicle.

Application of antigen presenting cell-targeted nanovaccine delivery system in rhabdovirus disease prophylactics using fish as a model organism

Background

Targeted delivery of virus-associated antigens to professional antigen-presenting cells (APCs) is considered as an efficient strategy to enhance the pyrophytic effect of vaccines against rhabdovirus disease.

Materials and methods

In this study, we constructed a targeted carbon nanotubes-based vaccine deliver system (SWCNTs-MG) which can recognize the signature receptor (mannose) of APCs. An environmentally and economically important disease called spring viremia of carp (SVC) was studied as a model to evaluate the feasibility of single-walled carbon nanotubes (SWCNTs) conjugated with mannosylated antigen for rhabdovirus prevention.

Results

Results showed that SWCNTs-MG could cross into fish body and present to internal immune-related tissues through gill, muscle and intestine within 6 h immersed vaccination. With further modification of mannose moiety, the obtained nanovaccine showed enhanced uptake by carp macrophages and immune-related tissues, which would then trigger strong immune responses against spring viremia of carp virus (SVCV) infection. Moreover, the survival rate of fish vaccinated with SWCNTs-MG (30 mg/L) was 63.5% after SVCV infection, whereas it was 0% for the control group.

Conclusion

This study not only provide a theoretical basis and research template for the application of targeted nanovaccine system in aquatic animals, but also play an important role in supporting development of healthy aquaculture and ensuring the safety of aquatic products and ecology.

Inhibition of a novel coumarin on an aquatic rhabdovirus by targeting the early stage of viral infection demonstrates potential application in aquaculture

Spring viremia of carp virus (SVCV) is one of the most serious pathogens in aquaculture, resulting in devastating damage in cyprinid. In this study, we designed and synthesized a novel coumarin derivative (C3007) for evaluating its in vitro and in vivo anti-SVCV effects. Here, we determined that up to 25 mg/L C3007 significantly decreased SVCV protein gene expression levels in EPC cells by a maximum inhibitory rate of >95%. When C3007 was preincubated with SVCV, infectivity was significantly inhibited in vitro in a time-dependent manner, with complete inhibition at 25 mg/L. For in vivo studies, C3007 exhibited an anti-SVCV effect by substantially enhancing the survival rate of virus-infected fish via intraperitoneal injection. Although the horizontal transmission of SVCV was hindered by C3007 in a static cohabitation challenge model, it was not completely blocked, showing that the viral loads in recipient fish were obviously reduced. Thus, C3007 could potentially be used as a therapeutic agent with great potential in aquatic systems and may also be suitable for applications in pond aquaculture settings against viral transmission. Additionally, the C3007-preincubated virus induced an antiviral immune response with high levels of IFN expression, suggesting that C3007 pre-treatment could be used in vaccine development.

Anti-CyHV-3 Effect of Fluorescent, Tricyclic Derivative of Acyclovir 6-(4-MeOPh)-TACV in vitro

Introduction

Cyprinid herpesvirus 3 (CyHV-3) is a virus infecting carp with disease symptoms of gill necrosis, fish discoloration, sunken eyes, and mortality reaching 90%. Several research groups have examined how to potentially abate the consequences of viral activity. Recently we showed that acyclovir inhibits CyHV-3 replication in vitro and in the present study we examined the anti-CyHV-3 activity of the tricyclic derivative of acyclovir 6-(4-MeOPh)-TACV (T-ACV), a fluorescent molecule known for higher lipophilicity than acyclovir, and therefore potentially better candidate for application in vivo.

Material and Methods

CCB and KF1 cell lines were incubated with T-ACV at concentrations of 0, 66.67, and 133.33 μM for three days and toxicity examined with MTT and CV assays. To investigate the antiviral activity of T-ACV, the lines were infected with CyHV-3 or mock infected and incubated for three days with the drug at concentrations of 0 or 66.67 μM. The activity of T-ACV was evaluated by plaque assay and TaqMan qPCR.

Results

T-ACV at a concentration of 66.67 μM displayed low toxicity and inhibited CyHV-3 activity by 13–29%, varying by cell line and method.

Conclusion

The low anti-CyHV-3 activity of T-ACV indicates that it would be reasonable to screen several tricyclic derivatives of acyclovir for such activity.

Identification, expression profiles and antiviral activities of a type I IFN from gibel carp Carassius auratus gibelio

Type I interferons, as a class of multipotent cytokines, play a key role in host antiviral immune responses. In this study, a type I IFN coding gene of gibel carp, Carassius auratus gibelio, CagIFNa was cloned and sequenced. The full-length cDNA sequence of CagIFNa consists of 724 nucleotides that encode a predicted protein of 183 amino acids. CagIFNa has two highly conserved cysteine residues in the deduced protein, which is mostly conserved in the fish group I type I IFNs. CagIFNa was identified as a member of the IFNa subgroup of group I type I IFNs by phylogenetic analysis. CagIFNa transcripts were detected in all investigated tissues with higher levels in the liver, intestine, spleen and head kidney of gibel carp. Following injection with Cyprinid herpesvirus 2 (CyHV-2), CagIFNa gene expression was significantly inhibited in the spleen but delayed and then increased in head kidneys. Similarly, while CagIFNa expression was rapidly induced in gibel carp brain (GiCB) cells by poly I:C stimulation and its high induction level was delayed following CyHV-2 infection. CagIFNa overexpression in GiCB cells drastically reduced virus CPE and titer. Furthermore, several genes associated with type I IFN signaling pathway including IRF3, IRF7, IRF9, STAT1, Mx1 and PKR were induced in GiCB cells overexpressing CagIFNa upon CyHV-2 infection. These results show that CagIFNa plays a role in antiviral immune system in gibel carp.

Evaluation of zebrafish (Danio rerio) as an animal model for the viral infections of fish

Zebrafish (Danio rerio) is a laboratory model organism used in different areas of biological research including studies of immune response and host-pathogen interactions. Thanks to many biological tools available, zebrafish becomes also an important model in aquaculture research since several fish viral infection models have been developed for zebrafish. Here, we have evaluated the possible use of zebrafish to study infections with fish viruses that have not yet been tested on this model organism. In vitro studies demonstrated that chum salmon reovirus (CSV; aquareovirus A) and two alloherpesviruses cyprinid herpesvirus 1 (CyHV-1) and cyprinid herpesvirus 3 (CyHV-3) are able to replicate in zebrafish cell lines ZF4 and SJD.1. Moreover, CSV induced a clear cytopathic effect and up-regulated the expression of antiviral genes vig-1 and mxa in both cell lines. In vivo studies demonstrated that both CSV and CyHV-3 induce up-regulation of vig-1 and mxa expression in kidney and spleen of adult zebrafish after infection by i.p. injection but not in larvae after infection by immersion. CyHV-3 is eliminated quickly from fish; therefore, virus clearing process could be evaluated, and in CSV-infected fish, a prolonged confrontation of the host with the pathogen could be studied.

Antiviral activity of anisomycin against spring viraemia of carp virus in epithelioma papulosum cyprini cells and zebrafish

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Anisomycin caused profound inhibition of SVCV replication in EPC cells.

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Anisomycin blocked morphological cell damage caused by SVCV replication.

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Anisomycin suppressed SVCV replication in vivo, resulting in a prolonged survival of infected zebrafish.

Spring viraemia of carp (SVC) caused by spring viraemia of carp virus (SVCV) is an acute and highly lethal viral disease of cyprinid fish. However, effective therapy for SVC is still scarce until now. Here we evaluated the inhibition of anisomycin (Ani), a metabolite produced by Streptomyces griseolus, on the replication of SVCV in vitro and in vivo. Our results demonstrated that Ani could suppress SVCV replication with the maximum inhibitory rate > 95% in epithelioma papulosum cyprini (EPC) cells. And the half maximal inhibitory concentrations (IC₅₀) of Ani on SVCV glycoprotein (G), nucleoprotein (N) and phosphoprotein mRNA expressions were 21.79, 13.13 and 12.24 nM, respectively. Besides, Ani decreased SVCV-induced cytopathic effects and nucleus damages. As expected, Ani also showed a strong anti-SVCV activity in vivo, as indicated by inhibiting viral gene expression and increasing the survival rate of zebrafish. Intraperitoneal injection of Ani increased the survival rate of zebrafish by 30% and markedly inhibited the expressions of G and N mRNA by > 60% in kidney and spleen at day 1 and day 4 post-infection. Results so far suggest that Ani as a powerful agent against SVCV can be applied to the control of SVC in aquaculture.

Antiviral efficiency of a coumarin derivative on spring viremia of carp virus in vivo

Spring viraemia of carp (SVC) in aquaculture is challenging because there are few preventative measures and/or treatments. The previous study demonstrated that an antiviral coumarin derivative, 7-(4-(4-methyl-imidazole))-coumarin (C2), inhibits spring viremia of carp virus (SVCV) infection by targeting Nrf2-ARE signaling pathway in fish cells. Thus, we hypothesized whether C2 may be used as a potential therapeutic agent for controlling SVCV infection in aquaculture. In this study, SVCV infectivity was significantly inhibited in vitro in a dose-dependent manner by preincubation with C2. C2 was verified against SVCV in zebrafish, in which the mortality and viral titer in fish body were decreased. Like other coumarins, C2 was stable with a prolonged inhibitory half-life (3.5 days) at 15 °C in the early stage of SVCV infection. The results show that horizontal transmission of SVCV was reduced by C2 in a static cohabitation challenge model, especially for recipient fish in injection treatment, which suggested that C2 may be suitable as a possible therapeutic agent for SVCV in aquaculture. Overall, this study provides the new insight that a small molecule antiviral drug can be used to control rhabdovirus infection in fish aquacultures.

Hormonal stimulation of carp is accompanied by changes in seminal plasma proteins associated with the immune and stress responses

Hormonal stimulation in common carp is a routine practice to enhance sperm production and control gamete maturation. This study aimed to compare the proteome of carp seminal plasma between control and Ovopel-induced males using two-dimensional differential in-gel electrophoresis. Ovopel induction increased sperm volume, total sperm count, seminal plasma osmolality, and pH and decreased seminal plasma protein concentration. In total, 36 spots were identified (23 up- and 13 downregulated), corresponding to 23 proteins differentially abundant in seminal plasma after Ovopel induction (p < .05; fold change 1.2). The majority of proteins were associated with the immune and stress responses including the transport protein (hephaestin), antiproteases (fetuin, α2-macroglobulin, TIMP2), complement components (C3, complement factor B/C2A), regulator of the coagulation cascade (plasminogen), modulators of the innate immune response, such as intelectin, ApoA and ApoE, and the cathepsin/cystatin system, and stress response (enolase1). In addition, hormonal stimulation seems to be related to the proteins involved in lipid metabolism, signal transduction, and tissue remodeling. Our results suggest that hormonal stimulation is not just concomitant with the hydration of testis but also induces the synthesis and secretion of seminal plasma proteins involved in sperm maturation and protection against stress induced by administration of the exogenous hormone. SIGNIFICANCE: It is well known that hormonal stimulation of male fish induces the final maturation of spermatozoa. However, molecular and biochemical basis underlying hormone-induced changes in semen is unknown at present. This study for the first time reveals, using proteomic approach, that hormonal stimulation in addition to hydration of testis is accompanied by significant changes in seminal plasma proteins related mainly to immune and stress response, lipid metabolism, signal transduction and tissue remodeling. These changes are associated with gene expression and synthesis and secretion of seminal plasma proteins by reproductive tissues. Overall, our results provide a framework for understanding the molecular mechanism responsible for hormonal stimulation in the reproductive tract of fish males.

Type I interferon responses of common carp strains with different levels of resistance to koi herpesvirus disease during infection with CyHV-3 or SVCV

Carp from breeding strains with different genetic background present diverse levels of resistance to viral pathogens. Carp strains of Asian origin, currently being treated as Cyprinus rubrofuscus L., especially Amur wild carp (AS), were proven to be more resistant to koi herpesvirus disease (KHVD; caused by cyprinid herpesvirus 3, CyHV-3) than strains originating from Europe and belonging to Cyprinus carpio L., like the Prerov scale carp (PS) or koi carp from a breed in the Czech Republic. We hypothesised that it can be associated with a higher magnitude of type I interferon (IFN) response as a first line of innate defence mechanisms against viral infections. To evaluate this hypothesis, four strains of common carp (AS, Rop, PS and koi) were challenged using two viral infection models: Rhabdovirus SVCV (spring viremia of carp virus) and alloherpesvirus CyHV-3. The infection with SVCV induced a low mortality rates and the most resistant was the Rop strain (no mortalities), whereas the PS strain was the most susceptible (survival rate of 78%). During CyHV-3 infection, Rop and AS strains performed better (survival rates of 78% and 53%, respectively) than PS and koi strains (survival rates of 35% and 10%, respectively). The evaluation of virus loads and virus replication showed significant differences between the carp strains, which correlated with the mortality rate. The evaluation of type I IFN responses showed that there were fundamental differences between the virus infection models. While responses to the SVCV were high, the CyHV-3 generally induced low responses. Furthermore, the results demonstrated that the magnitude of type I IFN responses did not correlate with a higher resistance in infected carp. In the case of a CyHV-3 infection, reduced type I IFN responses could be related to the potential ability of the virus to interfere with cellular sensing of foreign nucleic acids. Taken together, the results broaden our understanding of how common carp from different genetic strains interact with various viral pathogens.

Molecular ontogeny of larval immunity in European eel at increasing temperatures

Temperature is a major factor that modulates the development and reactivity of the immune system. Only limited knowledge exists regarding the immune system of the catadromous European eel, Anguilla anguilla, especially during the oceanic early life history stages. Thus, a new molecular toolbox was developed, involving tissue specific characterisation of 3 housekeeping genes, 9 genes from the innate and 3 genes from the adaptive immune system of this species. The spatial pattern of immune genes reflected their function, e.g. complement component c3 was mainly produced in liver and il10 in the head kidney. Subsequently, the ontogeny of the immune system was studied in larvae reared from hatch to first-feeding at four temperatures, spanning their thermal tolerance range (16, 18, 20, and 22 °C). Expression of some genes (c3 and igm) declined post hatch, whilst expression of most other genes (mhc2, tlr2, il1β, irf3, irf7) increased with larval age. At the optimal temperature, 18 °C, this pattern of immune-gene expression revealed an immunocompromised phase between hatch (0 dph) and teeth-development (8 dph). The expression of two of the studied genes (mhc2, lysc) was temperature dependent, leading to increased mRNA levels at 22 °C. Additionally, at the lower end of the thermal spectrum (16 °C) immune competency appeared reduced, whilst close to the upper thermal limit (22 °C) larvae showed signs of thermal stress. Thus, protection against pathogens is probably impaired at temperatures close to the critical thermal maximum (CT_max), impacting survival and productivity in hatcheries and natural recruitment.

Cyprinid viral diseases and vaccine development

In the past decades, global freshwater fish production has been rapidly growing, while cyprinid takes the largest portion. Along with the rapid rise of novel forms of intensive aquaculture, increased global aquatic animal movement and various anthropogenic stress to aquatic ecosystems during the past century, freshwater fish farming industry encounter the emergence and breakout of many diseases, especially viral diseases. Because of the ability to safely and effectively prevent aquaculture diseases, vaccines have become the mainstream technology for prevention and control of aquatic diseases in the world. In this review, authors summarized six major cyprinid viral diseases, including koi herpesvirus disease (KHVD), spring viraemia of carp (SVC), grass carp hemorrhagic disease (GCHD), koi sleepy disease (KSD), carp pox disease (CPD) and herpesviral haematopoietic necrosis (HPHN). The present review described the characteristics of these diseases from epidemiology, pathology, etiology and diagnostics. Furthermore, the development of specific vaccines respective to these diseases is stated according to preparation methods and immunization approaches. It is hoped that the review could contribute to aquaculture in prevention and controlling of cyprinid viral diseases, and serve the healthy and sustainable development of aquaculture industry.

Antiviral effect of 7-(4-benzimidazole-butoxy)-coumarin on rhabdoviral clearance via Nrf2 activation regulated by PKCα/β phosphorylation

Coumarin forms an elite class of naturally occurring compounds that possess promising antiviral therapeutic perspectives. In the previous study, we designed and synthesized a coumarin derivative, 7-(4-benzimidazole-butoxy)-coumarin (BBC), to evaluate its antiviral activity on spring viraemia of carp virus (SVCV). In this study, our results show that BBC does not affect viral adhesion and delivery from endosomes to the cytosol, indicating BBC has no inhibitory activity in the early stage of viral infection. Further data are determined that BBC significantly declines SVCV-infected apoptosis and recovers caspase-3/8/9 activity. To reveal the pathway that affects Nrf2 translocation by BBC, we examine changes in protein kinase C (PKC) in EPC cells treated with BBC. We observe that BBC results in a higher phosphorylation of PKCα/β that is involved in the activation of erythroid 2-related factor 2 (Nrf2) phosphorylation to favor Nrf2 translocation to nucleus at 24 and 48 h. In addition, the results show that BBC also up-regulates both antiviral responses, heme oxygenase-1 (HO-1) expression and cellular IFN response. Overall, this mechanism of action provides a new therapeutic target for the treatment of SVCV infection, and these results suggest that treatment with BBC is effective in reducing SVCV infection and differently regulates SVCV-induced undesirable conditions.

Chromatin immunoprecipitation and high throughput sequencing of SVCV-infected zebrafish reveals novel epigenetic histone methylation patterns involved in antiviral immune response

Chromatin immunoprecipitation (ChIP) and high throughput sequencing (ChIP-seq) have been used to assess histone methylation (epigenetic modification) dynamics within the internal organs of zebrafish after spring viremia of carp virus (SVCV) infection. Our results show H3K4me3 up-methylation in gene promoters associated with innate immune response during the first 5 days after SVCV infection. Gene Ontology (GO) enrichment analysis confirmed up-methylation in 218 genes in the "immune system process" category. In particular, the promoters of interferon (ifn), interferon stimulated genes (isg), Toll-like receptors (tlr) and c-reactive protein (crp) multi gene sets were marked with the permissive H3K4 methylation. Higher histone 3 methylation was associated with higher transcription levels of the corresponding genes. Therefore, the evidence presented here suggests that transcriptional regulation at the promoter level of key immune genes of the interferon signaling pathway and c-reactive proteins genes can be modulated by epigenetic modification of histones. This study emphasizes the importance of epigenetic control in the response of zebrafish to SVCV infection.

Acyclovir inhibits Cyprinid herpesvirus 3 multiplication in vitro

Cyprinid herpesvirus 3 (CyHV-3), also known as koi herpesvirus (KHV), is an aetiological agent of a virulent and lethal disease in common and koi carp. In this study, we examined in vitro the anti-CyHV-3 activity of acyclovir (ACV), nucleoside analogue commonly used against human herpesviruses, as well as acyclovir monophospate (ACV-MP). The cytotoxicity of the ACV and the ACV-MP for two common carp cell lines, CCB (Common carp brain) and KF1 (Koi carp fin 1), was determined by means of MTT and crystal violet assays. In subsequent studies, the concentration of 66.67 μM was applied. The ACV and the ACV-MP (66.67 μM) inhibited a cytopathic effect (CPE) induced by the CyHV-3 virus in the CCB (ACV by 66%, ACV-MP by 58%) and the KF1 (ACV by 25%, ACV-MP by 37%). The viral load measured by the means of TaqMan qPCR was reduced in a range of 67%-93% depending on the analogue, the cell line and the time of incubation. The expression of viral genes (ORF149, ORF3, ORF134 and ORF78) in CCB cells infected with the CyHV-3 was strongly downregulated within the range of 78%-91%. In summary, both the ACV and the ACV-MP can inhibit CyHV-3 replication in vitro.

Synthesis and antiviral activity of a new coumarin derivative against spring viraemia of carp virus

Coumarin as a lead structure have received a considerable attention in the last three decades for the discovery of antiviral agents. Our previous study indicated that imidazole coumarins possessed antiviral activities against SVCV. Based on the structure-activity relationship in that study, a new imidazole coumarin derivative, 7-(4-benzimidazole-butoxy)-coumarin (BBC), was designed, synthesized and its anti-SVCV activity was evaluated. By comparing inhibitory concentration at half-maximal activity (IC₅₀), we found that BBC (IC₅₀ = 0.56 mg/L) possessed a higher antiviral activity than those imidazole coumarins in our previous study. Besides, BBC can significantly inhibit cell death and reduce cellular morphological damage induced by SVCV. Our further data indicated that intraperitoneal injection of BBC increased the survival rate of zebrafish by 17.5%, decreased viral titer in fish body and inhibited SVCV glycoprotein expression in kidney and spleen. In uninfected zebrafish, the expression levels of ifnγ, ifnφ1, ifnφ2 and rig1 genes were up-regulated after BBC treatment, which indicated that BBC could activate interferon response. In addition, data of the antioxidant enzymes activities and results of the antioxidant enzymes-related genes expressions suggested BBC could reduce SVCV-induced oxidative damage in infected zebrafish. Altogether, BBC is expected to be a therapeutic agent against SVCV infection in the field of aquaculture.

A new coumarin derivative plays a role in rhabdoviral clearance by interfering glycoprotein function during the early stage of viral infection

Coumarin forms an elite class of naturally occurring compounds that possess promising antiviral therapeutic perspectives. In this study, a coumarin derivative 7-[6-(2-methylimidazole) hexyloxy] coumarin (D5) was designed and synthesized to evaluate antiviral activity on a rhabdovirus, spring viraemia of carp virus (SVCV). Our results demonstrated that D5 had a robust antiviral activity with >90% inhibitory rate of SVCV expression in the host cells. And D5 significantly reduced viral-induced apoptosis and recovered virus-activated caspase-3/8/9 activities. Further data determined that SVCV could alter the cytoskeletal structure of EPC cells, characterized by a circumferential ring of microtubules and a disrupted microfilament organization, whereas cytoskeleton structure in D5-treated cells kept the normal morphology. Mechanistically speaking, D5 could interfere with SVCV replication inside or outside of cells through two different approaches. Before the process of virus entry into EPC cells, D5 had an impact on SVCV glycoprotein structure so as to disrupt viral binding to the cell surface or translocation to the cytosol. Another strategy for D5 to against SVCV was that D5 significantly suppressed SVCV-activated autophagy, which was beneficial for the host cells to restrict SVCV viral replication, accompanied by a higher phosphorylation of Akt-mTOR. In summary, our results revealed that D5 was effective in weakening SVCV infection and regulating SVCV-induced undesirable conditions, and this compound provided new therapeutic implications for the treatment of rhabdoviruses.

Monitoring changing cellular characteristics during the development of a fin cell line from Cyprinus carpio

The establishment and in-depth characterization of a novel continuous cell line derived from fin tissue of common carp (Cyprinus carpio), CCApin, is reported. The cells of the cell line could be propagated in Leibovitz's L-15 medium containing 15% foetal calf serum and 0.5% carp serum for >150 passages during the last 24 months, with a stable fast growth. Furthermore, antibody staining indicated that cell types obtained in primary cultures, containing the epithelial stem-cell marker tumorprotein 63, were different from cells in long-term cell cultures, containing tight junction protein zona occludens 1 and cytokeratin 7. These observations suggest a switch of dominant cell types. Molecular analysis of gene expression profiles of caudal fin tissue and CCApin cells showed that genes relevant in epithelial cells but also in mesenchymal cells were expressed. However, during cultivation of CCApin a set of very steadily expressed, primarily mesenchymal genes like collagen 1 alpha 1, fibronectin or cadherin 2 was found. In summary, the long-term cell culture could be described as a stably growing epithelial population with some mesenchymal features. There are several application possibilities, especially for virus susceptibility studies, e.g. cyprinid herpesvirus-3 (CyHV-3). The study leads to a better understanding of molecular and physiological mechanisms of in vitro fish cell cultures.

Highly efficient inhibition of spring viraemia of carp virus replication in vitro mediated by bavachin, a major constituent of psoralea corlifonia Lynn

As one of nine piscine viruses recognized by the International Office of Epizootics, spring viraemia of carp virus (SVCV) is an important pathogen bringing high mortality to cyprinids. Up to now, there is no approved therapy on SVCV, making them strong public health threat in aquaculture. In this study, the anti-SVCV activities of 12 plant crude extracts were investigated by using epithelioma papulosum cyprini (EPC) cells. Among these plants, Psoralea corylifolia Linn. showed the highest inhibition on SVCV replication, with an inhibitory percentage of 67.98%. Further studies demonstrated that bavachin (BVN), one of the major constituents of Psoralea corylifolia Linn., was also highly effective to SVCV infection. The half maximal inhibitory concentrations (IC₅₀) of BVN on SVCV glycoprotein and nucleoprotein expression were 0.46 (0.29-0.73) and 0.31 (0.13-0.55) mg/L, respectively. In addition, SVCV-induced apoptosis which may be negative to SVCV replication was inhibited by BVN. The apoptotic cells were decreased 21.42% for BVN compared with SVCV group. These results indicated that the inhibition of BVN on SVCV replication was, in some extent, via blocking SVCV induced apoptosis. Furthermore, cellular morphological damage induced by SVCV was also blocked by BVN treatment. Mechanistically, BVN did not affect SVCV infectivity and cannot be used for prevention of SVCV infection. Time-of-addition and viral binding assays revealed that BVN mainly inhibited the early events of SVCV replication but did not interfere with SVCV adsorption. In conclusion, BVN was considered to develop as a promising agent to treat SVCV infection.