Gene expression analysis of common carp (Cyprinus carpio L.) lines during Cyprinid herpesvirus 3 infection yields insights into differential immune responses

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.

Molecular cytogenetic analysis of the olive flounder embryonic cell line FGBC8 and its applicability to biotechnology

We explored the biotechnological applicability of a previously established olive flounder (Paralichthys olivaceus) embryonic cell line (FGBC8). FGBC8 was transfected with pEGFP-c1 and pluripotency-related genes, then infected with viral hemorrhagic septicemia virus (VHSV), and the expression of immune-related genes was observed through quantitative real-time polymerase chain reaction. Transfected cells showed strong green fluorescence 48 h after transfection, and pluripotency-related genes were successfully transfected. In addition, FGBC8 cells were highly susceptible to VHSV and the expression of immune-related genes was induced during infection. Our results demonstrate that FGBC8 cells are valuable research tools for assessing host-pathogen interactions and biotechnological applications.

Immune responses in carp strains with different susceptibility to carp edema virus disease

Carp edema virus disease (CEVD), also known as koi sleepy disease (KSD), represents a serious threat to the carp industry. The expression of immune-related genes to CEV infections could lead to the selection of crucial biomarkers of the development of the disease. The expression of a total of eleven immune-related genes encoding cytokines (IL-1β, IL-10, IL-6a, and TNF-α2), antiviral response (Mx2), cellular receptors (CD4, CD8b1, and GzmA), immunoglobulin (IgM), and genes encoding-mucins was monitored in gills of four differently KSD-susceptible strains of carp (Amur wild carp, Amur Sasan, AS; Ropsha scaly carp, Rop; Prerov scaly carp, PS; and koi) on days 6 and 11 post-infection. Carp strains were infected through two cohabitation infection trials with CEV genogroups I or IIa. The results showed that during the infection with both CEV genogroups, KSD-susceptible koi induced an innate immune response with significant up-regulation (p < 0.05) of IL-1β, IL-10, IL-6a, and TNF-α2 genes on both 6 and 11 days post-infection (dpi) compared to the fish sampled on day 0. Compared to koi, AS and Rop strains showed up-regulation of IL-6a and TNF-α2 but no other cytokine genes. During the infection with CEV genogroup IIa, Mx2 was significantly up-regulated in all strains and peaked on 6 dpi in AS, PS, and Rop. In koi, it remained high until 11 dpi. With genogroup I infection, Mx2 was up-expressed in koi on 6 dpi and in PS on both 6 and 11 dpi. No significant differences were noticed in selected mucin genes expression measured in gills of any carp strains exposed to both CEV genogroups. During both CEV genogroups infections, the expression levels of most of the genes for T cell response, including CD4, CD8b1, and GzmA were down-regulated in AS and koi at all time points compared to day 0 control. The expression data for the above experimental trials suggest that both CEV genogroups infections in common carp strains lead to activation of the same expression pattern regardless of the fish's susceptibility towards the virus. The expression of the same genes in AS and koi responding to CEV genogroup IIa infection in mucosal tissues such as gill, gut, and skin showed the significant up-regulation of all the cytokine genes in gill and gut tissues from koi carp at 5 dpi. Significant down-regulation of CD4 and GzmA levels were only detected in koi gill on 5 dpi but not in other tissues. AS carp displayed significant up-expression of Mx2 gene in all mucosal tissues on 5 dpi, whereas in koi, it was up-regulated in gill and gut only. In both carp strains, gill harbored a higher virus load on 5 dpi compared to the other tissues. The results showed that resistance to CEV could not be linked with the selected immune responses measured. The up-regulation of mRNA expression of most of the selected immune-related genes in koi gill and gut suggests that CEV induces a more systemic mucosal immune response not restricted to the target tissue of gills.

Thyme essential oil inhibits intracellular replication of CyHV-3 and inactivates extracellular virus. An in vitro study

Cyprinid herpesvirus 3 (CyHV-3) can induce up to 100% mortality among carp populations. To date, there has been no safe method to prevent the consequences of the activity of CyHV-3. Thyme is widely used in cooking due to its flavour. Both thyme and thyme essential oil (TEO) are used in traditional herbal medicine, mainly to treat respiratory system disorders. In this study, TEO containing predominantly cymene and thymol was applied to explore its antiviral effect. The toxicity of TEO was examined in MTT and crystal violet assays. The anti-CyHV-3 activity of TEO in the intracellular and extracellular stages of the viral replication cycle was explored in a plaque assay and TaqMan qPCR. TEO interfered with the intracellular stages of the CyHV-3 replication cycle with selectivity indexes (SI) of around 5. It also displayed virucidal activity in a dose- and time-dependent manner. Two-hour preincubation of CyHV-3 with TEO generated SI, ranging from 13.37 to 18.47 depending on cell line and method of examination. Preincubation of cells with TEO at a safe concentration did not decrease the intracellular viral DNA copy number, which suggests that TEO does not disturb the attachment of the virus to the cells. Further research regarding the antiviral activity of compounds of TEO is required in order to indicate the most potent molecules that could be considered candidates for application in aquaculture.

Impact of Global Warming on the Severity of Viral Diseases: A Potentially Alarming Threat to Sustainable Aquaculture Worldwide

With an ever-increasing human population, food security remains a central issue for the coming years. The magnitude of the environmental impacts of food production has motivated the assessment of the environmental and health benefits of shifting diets, from meat to fish and seafood. One of the main concerns for the sustainable development of aquaculture is the emergence and spread of infectious animal diseases in a warming climate. We conducted a meta-analysis to investigate the influence of global warming on mortality due to viral infections in farmed aquatic animals. We found a positive trend between increasing temperature and increasing viral virulence, with an increase in water temperature of 1 °C resulting in an increase in mortality of 1.47-8.33% in OsHV-1 infected oysters, 2.55-6.98% in carps infected with CyHV-3 and 2.18-5.37% in fishes infected with NVVs. We suggest that global warming is going to pose a risk of viral disease outbreaks in aquaculture and could compromise global food security.

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.

Don't Let It Get Under Your Skin! - Vaccination Protects the Skin Barrier of Common Carp From Disruption Caused by Cyprinid Herpesvirus 3

Vaccination is the best form of protecting fish against viral diseases when the pathogen cannot be contained by biosecurity measures. Vaccines based on live attenuated viruses seem to be most effective for vaccination against challenging pathogens like Cyprinid herpesvirus 3. However, there are still knowledge gaps how these vaccines effectively protect fish from the deadly disease caused by the epitheliotropic CyHV-3, and which aspects of non-direct protection of skin or gill integrity and function are important in the aquatic environment. To elucidate some elements of protection, common carp were vaccinated against CyHV-3 using a double deletion vaccine virus KHV-T ΔDUT/TK in the absence or presence of a mix of common carp beta-defensins 1, 2 and 3 as adjuvants. Vaccination induced marginal clinical signs, low virus load and a minor upregulation of cd4, cd8 and igm gene expression in vaccinated fish, while neutralisation activity of blood serum rose from 14 days post vaccination (dpv). A challenge infection with CyHV-3 induced a severe disease with 80-100% mortality in non-vaccinated carp, while in vaccinated carp, no mortality was recorded and the virus load was >1,000-fold lower in the skin, gill and kidney. Histological analysis showed strongest pathological changes in the skin, with a complete destruction of the epidermis in non-vaccinated carp. In the skin of non-vaccinated fish, T and B cell responses were severely downregulated, inflammation and stress responses were increased upon challenge, whereas vaccinated fish had boosted neutrophil, T and B cell responses. A disruption of skin barrier elements (tight and adherence junction, desmosomes, mucins) led to an uncontrolled increase in skin bacteria load which most likely exacerbated the inflammation and the pathology. Using a live attenuated virus vaccine, we were able to show that increased neutrophil, T and B cell responses provide protection from CyHV-3 infection and lead to preservation of skin integrity, which supports successful protection against additional pathogens in the aquatic environment which foster disease development in non-vaccinated carp.

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.

Emodin resists to Cyprinid herpesvirus 3 replication via the pathways of Nrf2/Keap1-ARE and NF-κB in the ornamental koi carp (Cyprinus carpio haematopterus)

Cyprinid herpesvirus 3 (CyHV-3) causes high mortality in carp. Emodin has been shown of the effects of antioxidant, anti-inflammatory and antiviral. In present study, we investigated the preventive effects and mechanism of emodin on CyHV-3 infection. The ornamental koi carp (Cyprinus carpio haematopterus) were intraperitoneally injected with emodin (10 mg/kg, 20 mg/kg, or 40 mg/kg). 72 h later, an intraperitoneal injection of CyHV-3 was administered, and collected the samples one week later to detect the antioxidant parameters, antioxidant genes, inflammatory genes and to perform histopathology assays. The results showed that emodin significantly suppressed CyHV-3 replication (P < 0.05), improved the koi survival rate and slowed the damage caused by CyHV-3. Emodin treatment increased the antioxidant activity and decreased the lipid peroxidation level of the koi. Compared to the CyHV-3 group, emodin treatment resulted in the same antioxidant parameters after CyHV-3 infection. Emodin treatment activated the Nuclear factorery throid 2-related factor 2/Kelch-like ECH-associated protein 1-antioxidatant response element (Nrf2/Keap1-ARE) pathway and upregulated the expression of heme oxygenase 1 (HO-1), superoxide dismutase (SOD), and catalase (CAT) in the hepatopancreas after CyHV-3 infection. Emodin activated the nuclear factor kappa-B (NF-κB) pathway and decreased the expression of interleukin-6 (IL-6), interleukin-8 (IL-8), and tumour necrosis factor-α (TNF-α) in the koi induced by CyHV-3. In conclusion, emodin treatment can suppress CyHV-3 replication and reduce the mortality of koi caused by CyHV-3. Emodin improves antioxidant function, relieves oxidative stress and inflammation cytokines via Nrf2/Keap1-ARE and NF-κB pathways, and protects against the adverse effects induced by CyHV-3.

Integrative Transcriptomic Analysis Reveals the Immune Mechanism for a CyHV-3-Resistant Common Carp Strain

Anti-disease breeding is becoming the most promising solution to cyprinid herpesvirus-3 (CyHV-3) infection, the major threat to common carp aquaculture. Virus challenging studies suggested that a breeding strain of common carp developed resistance to CyHV-3 infection. This study illustrates the immune mechanisms involved in both sensitivity and anti-virus ability for CyHV3 infection in fish. An integrative analysis of the protein-coding genes and long non-coding RNAs (lncRNAs) using transcriptomic data was performed. Tissues from the head kidney of common carp were extracted at days 0 (the healthy control) and 7 after CyHV-3 infection (the survivors) and used to analyze the transcriptome through both Illumina and PacBio sequencing. Following analysis of the GO terms and KEGG pathways involved, the immune-related terms and pathways were merged. To dig out details on the immune aspect, the DEGs were filtered using the current common carp immune gene library. Immune gene categories and their corresponding genes in different comparison groups were revealed. Also, the immunological Gene Ontology terms for lncRNA modulation were retained. The weighted gene co-expression network analysis was used to reveal the regulation of immune genes by lncRNA. The results demonstrated that the breeding carp strain develops a marked resistance to CyHV-3 infection through a specific innate immune mechanism. The featured biological processes were autophagy, phagocytosis, cytotoxicity, and virus blockage by lectins and MUC3. Moreover, the immune-suppressive signals, such as suppression of IL21R on STAT3, PI3K mediated inhibition of inflammation by dopamine upon infection, as well as the inhibition of NLRC3 on STING during a steady state. Possible susceptible factors for CyHV-3, such as ITGB1, TLR18, and CCL4, were also revealed from the non-breeding strain. The results of this study also suggested that Nramp and PAI regulated by LncRNA could facilitate virus infection and proliferation for infected cells respectively, while T cell leukemia homeobox 3 (TLX3), as well as galectin 3 function by lncRNA, may play a role in the resistance mechanism. Therefore, immune factors that are immunogenetically insensitive or susceptible to CyHV-3 infection have been revealed.

Molecular communication between the monogenea and fish immune system

Monogeneans parasitise mainly the outer structures of fish, such as the gills, fins, and skin, that is, tissues covered with a mucous layer. While attached by sclerotised structures to host's surface, monogeneans feed on its blood or epidermal cells and mucus. Besides being a rich source of nutrients, these tissues also contain humoral immune factors and immune cells, which are ready to launch defence mechanisms against the tegument or gastrointestinal tract of these invaders. The exploitation of hosts' resources by the Monogenea must, therefore, be accompanied by suppressive and immunomodulatory mechanisms which protect the parasites against attacks by host immune system. Elimination of hosts' cytotoxic molecules and evasion of host immune response is often mediated by proteins secreted by the parasites. The aim of this review is to summarise existing knowledge on fish immune responses against monogeneans. Results gleaned from experimental infections illustrate the various interactions between parasites and the innate and adaptive immune system of the fish. The involvement of monogenean molecules (mainly inhibitors of peptidases) in molecular communication with host immune system is discussed.

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.

Seroconversion and Skin Mucosal Parameters during Koi Herpesvirus Shedding in Common Carp, Cyprinus carpio

Seroconversion and the mucosal lysozyme G (lysG), complement 3 (c3), and immunoglobulins M (IgMsec) and Z2 (IgZ2) were measured for up to 900 degree days (DD) in skin swabs from common carp exposed to koi herpesvirus (KHV or CyHV-3) at either a non-permissive temperature (12 °C) or permissive temperatures (17 and 22 °C), and in survivors subjected to temperature increase to 22 °C 500 DD after the initial exposure. The survival rate at 22 °C varied from 100% in fish initially exposed at 12 °C, to 20% at 17 °C and 0% at 22 °C. Viral shedding episodes lasted for up to 29 days (493 DD) for fish clinically infected at 17 °C, and up to 57 days (684 DD) for asymptomatic fish held at 12 °C. Up-regulation of lysG transcripts was measured at 17 and 22 °C. Down-regulation of c3 and IgMsec transcripts was measured independent of the water temperature, followed by up-regulation after the temperature increase coinciding with seroconversion and clearance of KHV from the skin mucus. IgZ2 mRNA showed a negative correlation with IgM transcripts. KHV subversion of the complement system at the mucosal site coupled with poor immunoglobulin secretion during the viral replication might contribute to the long window of viral shedding, thus facilitating viral transmission.

Mass mortality associated with koi herpesvirus in common carp in Iraq

Koi herpesvirus disease is a serious disease affecting both wild and common carp species in different continents throughout the world. Based on pathological and molecular findings, we document the presence of koi herpesvirus disease in Iraq as a cause of mass mortality among the common carp of the Tigris river. On a macroscopic level, the fish exhibited variably sized skin ulcerations throughout the entire trunk. The gills showed variable degrees of discoloration with an increased amount of slimy mucus. Microscopically, degeneration and necrosis with infiltration of a heterogenous population of inflammatory cells characterized different organs, primarily the skin and gills, with occasional intranuclear inclusion bodies that are consistent with koi herpesvirus disease. A semi-nested PCR assay coupled with sequencing confirmed the pathological diagnosis. Genotyping and sequence analysis of the TK gene, ORF 136 and markers I and II identified the isolated CyHV-3 as variant A1 of the Asian genotype TUSMT1 (J strain) displaying the I⁺⁺II⁺ allele.

Teleost cytotoxic T cells

Cell-mediated cytotoxicity is one of the major mechanisms by which vertebrates control intracellular pathogens. Two cell types are the main players in this immune response, natural killer (NK) cells and cytotoxic T lymphocytes (CTL). While NK cells recognize altered target cells in a relatively unspecific manner CTLs use their T cell receptor to identify pathogen-specific peptides that are presented by major histocompatibility (MHC) class I molecules on the surface of infected cells. However, several other signals are needed to regulate cell-mediated cytotoxicity involving a complex network of cytokine- and ligand-receptor interactions. Since the first description of MHC class I molecules in teleosts during the early 90s of the last century a remarkable amount of information on teleost immune responses has been published. The corresponding studies describe teleost cells and molecules that are involved in CTL responses of higher vertebrates. These studies are backed by functional investigations on the killing activity of CTLs in a few teleost species. The present knowledge on teleost CTLs still leaves considerable room for further investigations on the mechanisms by which CTLs act. Nevertheless the information on teleost CTLs and their regulation might already be useful for the control of fish diseases by designing efficient vaccines against such diseases where CTL responses are known to be decisive for the elimination of the corresponding pathogen. This review summarizes the present knowledge on CTL regulation and functions in teleosts. In a special chapter, the role of CTLs in vaccination is discussed.

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.

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.

Quantitative proteomic profiling of immune responses to Ichthyophthirius multifiliis in common carp skin mucus

Ichthyophthirius multifiliis, a ciliated protozoan parasite, causes ichthyophthiriasis and leads to considerable economic losses to the aquaculture industry. Understanding the fish immune response and host-parasite interactions could support developing novel strategies for better disease management and control. Fish skin mucus is the first line of defence against infections through the epidermis. Yet, the common carp, Cyprinus carpio, protein-based defence strategies against infection with I. multifiliis at this barrier remain elusive. The skin mucus proteome of common carp was investigated at 1 day and 9 days post-exposure with I. multifiliis. Using nano-LC ESI MS/MS and statistical analysis, the abundance of 19 immune related and signal transduction proteins was found to be differentially regulated in skin mucus of common carp in response to I. multifiliis. The analysis revealed increased abundance values of epithelial chloride channel protein, galactose-specific lectin nattection, high choriolytic enzyme 1 (nephrosin), lysozyme C, granulin and protein-glutamine gamma-glutamyltransferase 2 in I. multifiliis-exposed carp skin mucus. Multiple lectins and a diverse array of distinct serpins with protease inhibitor activity were identified likely implicated in lectin pathway activation and regulation of proteolysis, indicating that these proteins contribute to the carp innate immune system and the protective properties of skin mucus. The results obtained from this proteomic analysis enables a better understanding of fish host response to parasitic infection and gives insights into the key role skin mucus plays in protecting fish against deleterious effects of I. multifiliis.

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.

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.

Proteome analysis reveals a role of rainbow trout lymphoid organs during Yersinia ruckeri infection process

Yersinia ruckeri is the causative agent of enteric redmouth disease in salmonids. Head kidney and spleen are major lymphoid organs of the teleost fish where antigen presentation and immune defense against microbes take place. We investigated proteome alteration in head kidney and spleen of the rainbow trout following Y. ruckeri strains infection. Organs were analyzed after 3, 9 and 28 days post exposure with a shotgun proteomic approach. GO annotation and protein-protein interaction were predicted using bioinformatic tools. Thirty four proteins from head kidney and 85 proteins from spleen were found to be differentially expressed in rainbow trout during the Y. ruckeri infection process. These included lysosomal, antioxidant, metalloproteinase, cytoskeleton, tetraspanin, cathepsin B and c-type lectin receptor proteins. The findings of this study regarding the immune response at the protein level offer new insight into the systemic response to Y. ruckeri infection in rainbow trout. This proteomic data facilitate a better understanding of host-pathogen interactions and response of fish against Y. ruckeri biotype 1 and 2 strains. Protein-protein interaction analysis predicts carbon metabolism, ribosome and phagosome pathways in spleen of infected fish, which might be useful in understanding biological processes and further studies in the direction of pathways.

Immune Response to Koi Herpesvirus (KHV) of Koi and Koi × Red Common Carp (Cyprinus carpio)

Koi herpesvirus (KHV), also known as Cyprinid herpes virus 3 (Cyprinid 3) is lethal disease in common carp and koi (Cyprinus carpio). Two different groups (KK and RK) were infected KHV by intraperitoneal injection. Fish for gene expression analysis were sampled at 0 h, 12 h, 24 h, 48 h and 72 h post infection (p.i). The results showed that two immune related gene, Interferons (INFs) ɑβ and Interleukin (IL)-12 p35 induced a high response in RK. The IL-12 p35 cytokine and Toll-like receptor (TLR) 9 were significantly high expressed on 48 h post infection (p.i) in RK as compared to the KK. The histopatological examination reveals focal necrosis in liver and infiltrate of lymphocytes in spleen of KK as compared to the RK. In immunohistochemistry analysis, the KHV protein high expressed in the infected kidney cell and slenocyte of KK. Therefore, the expression of IL-12 p35, IFN ɑβ and TLR 9 may provide a potentially genes related with KHV resistance in Koi and red common carp × koi.

Viral infections in common carp lead to a disturbance of mucin expression in mucosal tissues

In response to the constant challenge by potential pathogens, external surfaces of fish, their skin, gills and intestinal tract, are coated with mucus, a gel like substance which largely prevents the entry of pathogens. This mucus gel consists mainly of water and mucins, large O-glycosylated proteins, which are responsible for forming a gel like mixture. A modulation of the mRNA expression of mucins, was described in viral diseases in mammals however there is a knowledge gap about the regulation of mucins during viral infection in fish. Therefore, novel sequences for common carp mucins were located in an early version of the common carp genome and their mRNA expression measured in carp under infection with three different viral pathogens: (i) the alloherpesvirus cyprinid herpesvirus 3, (ii) the rhabdovirus spring viremia of carp virus and (iii) the poxvirus carp edema virus. The results showed a downregulation of mucin mRNA expression in gills and gut of common carp under infection with these pathogenic viruses. This could be a sign of a severe distress to the mucosal tissues in carp which occurs under viral infection. The reduced expression of mucins could help explaining the increased susceptibility of virus-infected carp to secondary bacterial infection.

Conserved Fever Pathways across Vertebrates: A Herpesvirus Expressed Decoy TNF-α Receptor Delays Behavioral Fever in Fish

Both endotherms and ectotherms (e.g., fish) increase their body temperature to limit pathogen infection. Ectotherms do so by moving to warmer places, hence the term “behavioral fever.” We studied the manifestation of behavioral fever in the common carp infected by cyprinid herpesvirus 3, a native carp pathogen. Carp maintained at 24°C died from the infection, whereas those housed in multi-chamber tanks encompassing a 24°C–32°C gradient migrated transiently to the warmest compartment and survived as a consequence. Behavioral fever manifested only at advanced stages of infection. Consistent with this, expression of CyHV-3 ORF12, encoding a soluble decoy receptor for TNF-α, delayed the manifestation of behavioral fever and promoted CyHV-3 replication in the context of a temperature gradient. Injection of anti-TNF-α neutralizing antibodies suppressed behavioral fever, and decreased fish survival in response to infection. This study provides a unique example of how viruses have evolved to alter host behavior to increase fitness.

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Behavioral fever exhibited by carp in response to CyHV-3 infection is host beneficial

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CyHV-3 ORF12 delays behavioral fever expression, thereby promoting its own replication

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CyHV-3 ORF12 encodes a soluble decoy receptor for TNF-α

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TNF-α is a mediator of behavioral fever expressed by CyHV-3 infected carp

Label-free proteomic analysis of intestinal mucosa proteins in common carp (Cyprinus carpio) infected with Aeromonas hydrophila

Outbreaks of infectious diseases in common carp Cyprinus carpio, a major cultured fish in northern regions of China, constantly result in significant economic losses. Until now, information proteomic on immune defence remains limited. In the present study, a profile of intestinal mucosa immune response in Cyprinus carpio was investigated after 0, 12, 36 and 84 h after challenging tissues with Aeromonas hydrophila at a concentration of 1.4 × 10⁸ CFU/mL. Proteomic profiles in different samples were compared using label-free quantitative proteomic approach. Based on MASCOT database search, 1149 proteins were identified in samples after normalisation of proteins. Treated groups 1 (T1) and 2 (T2) were first clustered together and then clustered with control (C group). The distance between C and treated group 3 (T3) represented the maxima according to hierarchical cluster analysis. Therefore, comparative analysis between C and T3 was selected in the following analysis. A total of 115 proteins with differential abundance were detected to show conspicuous expressing variances. A total of 52 up-regulated proteins and 63 down-regulated proteins were detected in T3. Gene ontology analysis showed that identified up-regulated differentially expressed proteins in T3 were mainly localised in the hemoglobin complex, and down-regulated proteins in T3 were mainly localised in the major histocompatibility complex II protein complex. Forty-six proteins of differential abundance (40% of 115) were involved in immune response, with 17 up-regulated and 29 down-regulated proteins detected in T3. This study is the first to report proteome response of carp intestinal mucosa against A. hydrophila infection; information obtained contribute to understanding defence mechanisms of carp intestinal mucosa.

Transcriptomic analysis of common carp anterior kidney during Cyprinid herpesvirus 3 infection: Immunoglobulin repertoire and homologue functional divergence

Cyprinid herpesvirus 3 (CyHV-3) infects koi and common carp and causes widespread mortalities. While the virus is a significant concern for aquaculture operations in many countries, in Australia the virus may be a useful biocontrol agent for pest carp. However, carp immune responses to CyHV-3, and the molecular mechanisms underpinning resistance, are not well understood. Here we used RNA-Seq on carp during different phases of CyHV-3 infection to detect the gene expression dynamics of both host and virus simultaneously. During acute CyHV-3 infection, the carp host modified the expression of genes involved in various immune systems and detoxification pathways. Moreover, the activated pathways were skewed toward humoral immune responses, which may have been influenced by the virus itself. Many immune-related genes were duplicated in the carp genome, and often these were expressed differently across the infection phases. Of particular interest were two interleukin-10 homologues that were not expressed synchronously, suggesting neo- or sub-functionalization. The carp immunoglobulin repertoire significantly diversified during active CyHV-3 infection, which was followed by the selection of high-affinity B-cells. This is indicative of a developing adaptive immune response, and is the first attempt to use RNA-Seq to understand this process in fish during a viral infection.

Transcriptome analysis of grey mullet (Mugil cephalus) after challenge with Lactococcus garvieae

Grey mullet (Mugil cephalus) is an economically important fish species in Taiwan mariculture industry. Moreover, grey mullet are common hosts of a bacterial infection by Lactococcus garvieae. However, until now the information related to the immune system of grey mullet is unclear. Therefore, to understand the molecular basis underlying the host immune response to L. garvieae infection, Illumina HiSeq™ 2000 was used to analyse the head kidney and spleen transcriptome of infected grey mullet. De novo assembly of paired-end reads yielded 55,203 unigenes. Comparative analysis of the expression profiles between bacterial challenge fish and control fish identified a total of 7192 from head kidney and 7280 in spleen differentially expressed genes (P < 0.05), including 4211 upregulated genes and 2981 downregulated genes in head kidney, while in spleen 3598 genes were upregulated and 3682 downregulated. A significant enrichment analysis of these differentially expressed genes (DEG) in spleen and head kidney revealed major immune-related pathways, including complement and coagulation cascades, Toll-like receptor signalling, and antigen processing and presentation. Moreover, selected DEGs were validated using qPCR. Altogether, the results obtained on immune-related genes may allow for a better understanding of immunity in grey mullet to Lactococcus garvieae, carrying out detailed functional analysis of these genes and developing strategies for efficient immune protection against infections in grey mullet.

The amino-terminal domain of ORF149 of koi herpesvirus is preferentially targeted by IgM from carp populations surviving infection

Recombinantly expressed fragments of the protein encoded by ORF149 (pORF149), a structural protein from the common- and koi-carp-infecting cyprinid herpesvirus-3 (CyHV-3) that was previously shown to be antigenic, were used to obtain evidence that its amino-terminal part contains immunodominant epitopes in fish populations that survived the infection. To obtain such evidence, nonspecific binding of carp serum tetrameric IgM had to be overcome by a novel ELISA protocol (rec2-ELISA). Rec2-ELISA involved pre-adsorption of carp sera with a heterologous recombinant fragment before incubation with pORF149 fragments and detection with anti-carp IgM monoclonal antibodies. Only in this way was it possible to distinguish between sera from uninfected and survivor carp populations. Although IgM from survivors recognised pORF149 fragments to a lesser degree than whole virus, specificity was confirmed by correlation of rec2- and CyHV-3-ELISAs, inhibition of rec2-ELISA by an excess of frgIIORF149, ELISA using IgM-capture, Western blotting, and reduction of reactivity in CyHV-3-ELISA by pre-adsorption of sera with frgIIORF149. The similarity of IgM-binding profiles between frgIORF149 (amino acid residues 42-629) and frgIIORF149 (42-159) and their reactivities with previously described anti-CyHV-3 monoclonal antibodies confirmed that most pORF149 epitopes were localised in its amino-terminal part.

Transcriptomic analysis of koi (Cyprinus carpio) spleen tissue upon cyprinid herpesvirus 3 (CyHV3) infection using next generation sequencing

Cyprinid Herpesvirus 3 (CyHV-3) can infect and specifically cause a huge economic loss in both common carp (Cyprinus carpio) and its ornamental koi variety. The molecular mechanisms underlying CyHV-3 infection are not well understood. In this study, koi spleen tissues of both mock and CyHV-3 infection groups were collected, and high-throughput sequencing technology was used to analyze the differentially expressed genes (DEGs) at the transcriptome level. A total of 105,356,188 clean reads from two libraries were obtained. After the de novo assembly of the transcripts, 129,314 unigenes were generated. Of these unigenes, 70,655 unigenes were matched to the known proteins in the database, while 2190 unigenes were predicted by ESTScan software. Comparing the infection group to the mock group, a total of 23,029 significantly differentially expressed unigenes were identified, including 10,493 up-regulated DEGs and 12,536 down-regulated DEGs. GO (Gene Ontology) annotation and functional enrichment analysis indicated that all of the DEGs were annotated into GO terms in three main GO categories: biological process, cellular component and molecular function. KEGG (Kyoto Encyclopedia of Genes and Genomes) analysis of the DEGs showed that a total of 12,002 DEG unigenes were annotated into 256 pathways classified into 6 main categories. Additionally, 20 differentially expressed genes were validated by quantitative real-time PCR. As the first report of a transcriptome analysis of koi carp with CyHV-3 infection, the data presented here provide knowledge of the innate immune response against CyHV-3 in koi carp and useful data for further research of the molecular mechanism of CyHV-3 infection.

Stress-induced adaptation of neutrophilic granulocyte activity in K and R3 carp lines

Both in mammals and fish, stress induces remarkable changes in the immune response. We focused on stress-induced changes in the activity of neutrophilic granulocytes in the R3 and K lines of common carp, which showed differential stress responses. Our study clearly demonstrates that a prolonged restraint stress differentially affects the activity of K and R3 carp neutrophils. In the K line, stress decreased the respiratory burst, while in the R3 line it reduced the release of extracellular DNA. Surprisingly, the stress-induced changes in ROS production and NET formation did not correlate with changes in gene expression of the inflammatory mediators and GR receptors. In neutrophilic granulocytes from K carp, gene expression of the stress-sensitive cortisol GR1 receptor was significantly higher than in neutrophils from R3 fish, which will make these cells more sensitive to high levels of cortisol. Moreover, upon stress, neutrophilic granulocytes of K carp up-regulated gene expression of the anti-inflammatory cytokine IL-10 while this was not observed in neutrophilic granulocytes of R3 carp. Therefore, we can hypothesize that, in contrast to R3 neutrophils, the more cortisol sensitive neutrophils from K carp respond to stress with up-regulation of IL-10 and consequently reduction of ROS production. Most probably the ROS-independent NET formation in K carp is not regulated by this anti-inflammatory cytokine. These data may indicate a predominantly ROS-independent formation of NETs by carp neutrophilic granulocytes. Moreover, they underline the important role of IL-10 in stress-induced immunoregulation.

Activity of the hypothalamus-pituitary-interrenal axis (HPI axis) and immune response in carp lines with different susceptibility to disease

The stress response transmitted by the HPA axis is one of the best examples of neuroendocrine-immune interactions that are critical for survival. Analogous to the situation in mammals, the stress response in fish is characterized by the activation of the hypothalamo-pituitary-interrenal axis (HPI). Effects of cortisol on the fish immune system comply with findings in mammals and suggest that the differences in sensitivity to stress will influence the immune response and as a consequence of survival. Therefore, we studied the stress response and its immunity-related effects in four different carp lines (R3, R3xR8, K and R2) that display a differential pathogen susceptibility. Previous studies indicate that R3xR8 and R3 carp are susceptible to bacterial and parasite infection, while R2 and K are relatively resistant to infection. Interestingly, the most striking effect of stress on leukocyte composition and activity was observed in the pathogen-resistant K carp, even though no robust changes in gene expression of stress-involved factors were observed. In contrast, R3 carp showed no spectacular stress-induced changes in their immunological parameters with concurrent significant activation of the HPI axis. Upon stress, the R3 carp showed up-regulation of crf, pomc and gr2 gene expression in the hypothalamus. Furthermore in R3 carp, at all levels of the HPI axis, stress induced the highest up-regulation of il-1β gene expression. Although we are aware of the complexity of the interactions between stress and pathogen susceptibility and of the risk of interpretation based on correlations, it is noteworthy that the fish more susceptible to infection also exhibited the highest response to stress.

Cyprinid Herpesvirus 3: An Archetype of Fish Alloherpesviruses

The order Herpesvirales encompasses viruses that share structural, genetic, and biological properties. However, members of this order infect hosts ranging from molluscs to humans. It is currently divided into three phylogenetically related families. The Alloherpesviridae family contains viruses infecting fish and amphibians. There are 12 alloherpesviruses described to date, 10 of which infect fish. Over the last decade, cyprinid herpesvirus 3 (CyHV-3) infecting common and koi carp has emerged as the archetype of fish alloherpesviruses. Since its first description in the late 1990s, this virus has induced important economic losses in common and koi carp worldwide. It has also had negative environmental implications by affecting wild carp populations. These negative impacts and the importance of the host species have stimulated studies aimed at developing diagnostic and prophylactic tools. Unexpectedly, the data generated by these applied studies have stimulated interest in CyHV-3 as a model for fundamental research. This review intends to provide a complete overview of the knowledge currently available on CyHV-3.

Cyprinid herpesvirus-3 (CyHV-3) disturbs osmotic balance in carp (Cyprinus carpio L.)--A potential cause of mortality

Cyprinid herpesvirus-3 (CyHV-3) causes a fatal disease in carp (Cyprinus carpio) and its ornamental koi varieties which seriously affects production and trade of this fish species globally. Up to now, the pathophysiology of this disease remains unclear. Affected individuals develop most prominent lesions in gills, skin and kidney, in tissues which are involved in the osmotic regulation of freshwater teleosts. Therefore, here serum and urine electrolyte levels were examined during the course of an experimental infection of carp with CyHV-3. In infected carp an interstitial nephritis with a progressive deterioration of nephric tubules developed, which was paralleled by elevated electrolyte losses, mainly Na(+) in the urine. The urine/plasma ratio for Na(+) increased from 0.03 in uninfected carp to 0.43-0.83 in carp under CyHV-3 infection, while concentration of divalent ions were not significantly changed. These electrolyte losses could not be compensated since plasma osmolality and Na(+) concentration dropped significantly in CyHV-3 infected carp. This was most probably caused by the progressive deterioration of the branchial epithelium, which in teleosts plays a prominent role in osmoregulation, and which was seen concomitantly with decreasing electrolyte levels in the serum of carp under CyHV-3 infection. Immediately after infection with CyHV-3, by day 2 post exposure, affected carp showed severe anaemia and prominent leucocytosis indicating the development of an acute inflammation, which could intensify the observed hydro-mineral imbalances. The data presented here show that an infection with CyHV-3 induces an acute inflammation and a severe dysfunction of osmoregulation in affected carp or koi, which may lead to death in particular in the case of acute disease progression.

Expression of immune-related genes of common carp during cyprinid herpesvirus 3 infection

Fish herpesviruses and their hosts may have coevolved for 400 to 450 million yr. During this coexistence, the hosts have equipped themselves with an elaborate immune system to defend themselves from invading viruses, whereas the viruses have developed strategies to evade host immunity, including the expression of cytokine genes that have been captured from the host. Taking advantage of our experimental model for cyprinid herpesvirus 3 (CyHV-3) persistence in carp, we studied the gene expression of host and virus immune-related genes in each stage of infection: acute, persistent and reactivation phases. IFNγ-1, IFNγ-2, IL-12 and IL-10 host genes, and the CyHV-3 vIL-10 gene (khvIL-10) were highly significantly up-regulated in different phases of CyHV-3 infection. Similarly, host IL-1β was up-regulated in the acute phase of CyHV-3 infection. There was no significant difference in the expression of host TNFα-1 and MHC-II genes during all phases of CyHV-3 infection. Based on the expression profile of carp immune-related genes in each stage of CyHV-3 infection, we propose a possible interaction between carp IL-12, carp IL-10 and khvIL-10 during the course of viral infection. To our knowledge, this is the first report on the expression of cytokine genes during all phases (acute, persistent and reactivation) of CyHV-3 infection.

Sensitivity of seven PCRs for early detection of koi herpesvirus in experimentally infected carp, Cyprinus carpio L., by lethal and non-lethal sampling methods

Koi herpesvirus (KHV) causes an economically important, highly infectious disease in common carp and koi, Cyprinus carpio L. Since the occurrence of mass mortalities worldwide, highly specific and sensitive molecular diagnostic methods have been developed for KHV detection. The sensitivity and reliability of these assays have essentially focused at the detection of low viral DNA copy numbers during latent or persistent infections. However, the efficacy of these assays has not been investigated with regard to low-level viraemia during acute infection stages. This study was conducted to compare the sensitivity of seven different polymerase chain reaction (PCR) assays to detect KHV during the first hours and days post-infection (hpi; dpi), using lethal and non-lethal sampling methods. The results highlight the limitations of the assays for detecting virus during the first 4 dpi despite rapid mortality in experimentally infected carp. False-negative results were associated with time post-infection and the tissue sampled. Non-lethal sampling appears effective for KHV screening, with efficient detection in mucus samples obtained from external swabs during this early infection period (<5 dpi), while biopsies from gills and kidney were negative using the same PCR assays. Non-lethal sampling may improve the reliability of KHV detection in subclinical, acutely infected carp.

Differential effects of alloherpesvirus CyHV-3 and rhabdovirus SVCV on apoptosis in fish cells

Whilst Herpesviridae, which infect higher vertebrates, actively influence host immune responses to ensure viral replication, it is mostly unknown if Alloherpesviridae, which infect lower vertebrates, possess similar abilities. An important antiviral response is clearance of infected cells via apoptosis, which in mammals influences the outcome of infection. Here, we utilise common carp infected with CyHV-3 to determine the effect on the expression of genes encoding apoptosis-related proteins (p53, Caspase 9, Apaf-1, IAP, iNOS) in the pronephros, spleen and gills. The influence of CyHV-3 on CCB cells was also studied and compared to SVCV (a rhabdovirus) which induces apoptosis in carp cell lines. Although CyHV-3 induced iNOS expression in vivo, significant induction of the genetic apoptosis pathway was only seen in the pronephros. In vitro CyHV-3 did not induce apoptosis or apoptosis-related expression whilst SVCV did stimulate apoptosis. This suggests that CyHV-3 possesses mechanisms similar to herpesviruses of higher vertebrates to inhibit the antiviral apoptotic process.

Interaction between type I interferon and Cyprinid herpesvirus 3 in two genetic lines of common carp Cyprinus carpio

Cyprinid herpesvirus 3 (CyHV-3) infection in common carp Cyprinus carpio L. and its ornamental koi varieties can induce the severe systemic disease known as koi herpesvirus disease. This disease is characterised by a rapid replication and spreading of the virus through multiple organs and results in a fast onset of mortality (starting on Day 6 post infection) in up to 100% of infected fish. During the first phase of viral infections, type I interferons (IFNs) have generally been proven to be essential in inducing an innate immune response; however, very little is known about the type I IFN response to herpesviruses in fish. The aim of this work was to study the type I IFN responses during CyHV-3 infection in 2 genetically divergent lines of common carp which presented differing survival rates. Our results show that CyHV-3 induced a systemic type I IFN response in carp, and the magnitude of type I IFN expression is correlated with the virus load found in skin and head kidney. In this in vivo experimental setup, the level of type I IFN response cannot be linked with higher survival of carp during CyHV-3 infection.

Feeding common carp Cyprinus carpio with β-glucan supplemented diet stimulates C-reactive protein and complement immune acute phase responses following PAMPs injection

The effect of β-glucan as a feed additive on the serum and gene profile of C-reactive protein (CRP) and complement acute phase responses was ascertained in common carp Cyprinus carpio. In addition effects of subsequent intraperitoneal injections of pathogen-associated molecular patterns (PAMPs), i.e. LPS or poly(I:C), to mimic bacterial or viral infection respectively, were studied. Carp were first orally fed with β-glucan (MacroGard®) with a daily β-glucan intake of 6 mg per kg body weight or with control food for 25 days and then injected with PBS containing either LPS (4 mg/kg) or poly(I:C) (5 mg/kg) or PBS alone. Fish were sampled during the 25 days of the feeding period and up to 7 days post-PAMPs injections for serum and liver, head kidney and mid-gut tissues. Oral administration of β-glucan for 25 days significantly increased serum CRP levels and alternative complement activity (ACP). In addition, the subsequent LPS and poly(I:C) challenges significantly affected CRP and complement related gene expression profiles (crp1, crp2, c1r/s, bf/c2, c3 and masp2), with the greatest effects observed in the β-glucan fed fish. However, in fish fed β-glucan the PAMPs injections had less effects on CRP levels and complement activity in the serum than in control fed fish, suggesting that the 25 days of β-glucan immunostimulation was sufficient enough to reduce the effects of LPS and poly(I:C) injections. Results suggest that MacroGard® stimulated CRP and complement responses to PAMPs immunological challenges in common carp thus highlighting the beneficial β-glucan immunostimulant properties.

C-reactive protein and complement as acute phase reactants in common carp Cyprinus carpio during CyHV-3 infection

Cyprinid herpesvirus 3 (CyHV-3) is the aetiological agent of a highly virulent and lethal disease of common carp Cyprinus carpio and its ornamental koi varieties. However, specific knowledge about immune mechanisms behind the infection process is very limited. We aimed to evaluate the effect of the CyHV-3 infection on the profile of 2 major components of the common carp immune acute phase response: the C-reactive protein (CRP) and the complement system. Common carp were infected with CyHV-3 by bath immersion. Fish were sampled before the infection and at 6, 12, 24, 72, 120 and 336 h post-infection for serum and head kidney, liver, gill and spleen tissues. CRP levels and complement activity were determined from the serum, whereas CRP- and complement-related genes (crp1, crp2, c1rs, bf/c2, c3, masp2) expression profiles were analysed in the tissues by quantitative PCR. Both CRP levels and complement activity increased significantly up to 10- and 3-fold, respectively, in the serum of infected fish during the challenge. Analysis revealed distinct organ- and time-dependent expression profile patterns for all selected genes. These results suggest that CRP and complement behave as acute phase reactants to CyHV-3 infection in common carp with an organ- and time-dependent response.

In vitro inhibition of Cyprinid herpesvirus-3 replication by RNAi

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Cyprinid herpesvirus-3 causes high mortality rates in common and koi carp.

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siRNAs were designed to target thymidine kinase and DNA polymerase genes in vitro.

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siRNA targeting DNA polymerase gene was most effective at reducing viral release.

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The inhibition of viral replication by the siRNAs was quantitated by qPCR.

Cyprinid herpesvirus-3 (CyHV-3) is an etiological agent of a notifiable disease that causes high mortality rates affecting both the common and koi carp Cyprinus carpio L. There is no current treatment strategy to save CyHV-3 infected fish. RNA mediated interference (RNAi) is an emerging strategy used for understanding gene function and is a promising method in developing novel therapeutics and antiviral medications. For this study, the possibility of activating the RNAi pathway by the use of small interfering (si)RNAs was tested to inhibit in vitro viral replication of CyHV-3 in common carp brain (CCB) cells. The siRNAs were designed to target either thymidine kinase (TK) or DNA polymerase (DP) genes, which both code for transcripts involved in DNA replication. The inhibition of viral replication caused by the siRNAs was measured by a reporter gene, termed ORF81. Treatment with siRNA targeting either TK or DP genes reduced the release of viral particles from infected CCB cells. However, siRNA targeting DP was most effective at reducing viral release as measured by qPCR.

Antiviral functions of CD8(+) cytotoxic T cells in teleost fish

Cytotoxic T-cells (CTLs) play a pivotal role in eliminating viruses in mammalian adaptive immune system. Many recent studies on T-cell immunity of fish have suggested that teleost CTLs are also important for antiviral immunity. Cellular functional studies using clonal ginbuan crucian carp and rainbow trout have provided in vivo and in vitro evidence that in many respects, virus-specific CTLs of fish have functions similar to those of mammalian CTLs. In addition, mRNA expression profiles of CTL-related molecules, such as CD8, TCR and MHC class I, have shown that in a wide range of fish species, CTLs are involved in antiviral adaptive immunity. These findings are a basis to formulate possible vaccination strategies to trigger effective antiviral CTL responses in teleost fish. This review describes recent advances in our understanding of antiviral CTL functions in teleost fish and discusses vaccination strategies for efficiently inducing CTL activities.

Biology and host response to Cyprinid herpesvirus 3 infection in common carp

Viruses from the family Alloherpesviridae form an aquatic clade of herpesviruses infecting fish and amphibia. Diseases caused by these herpesviruses are of increasing importance because of the high morbidity and mortality associated with the infection, and the difficulties in diagnosing latently infected carriers. Cyprinid herpesvirus 3 (CyHV-3) induces a severe disease and mortality in common carp and thus greatly affects carp aquaculture and trade. This review summarises advancements in the understanding of the infection process and the current knowledge on immune responses of carp to CyHV-3. A focus is laid on host genetics and immunity responsible for resistance/survival from the disease and on the viral mechanisms accountable for evasion of carp immune responses. As current knowledge of immune responses to CyHV-3 is still limited, perspectives for future studies are outlined. Analysing CyHV-3 fish-host interactions will be useful and thought-provoking for a basic understanding of fish immune responses.

Expression of immune system-related genes during ontogeny in experimentally wounded common carp (Cyprinus carpio) larvae and juveniles

We investigated the effect of full-thickness incisional wounding on expression of genes related to the immune system in larvae and juveniles of common carp (Cyprinus carpio). The wounds were inflicted by needle puncture immediately below the anterior part of the dorsal fin on days 7, 14, 28 and 49 after fertilization. We followed the local gene expression 1, 3 and 7 days after wounding by removing head and viscera before extracting RNA from the remaining part of the fish, including the wound area. In addition, we visually followed wound healing. Overall the wounds had regenerated to a point where they were microscopically indistinguishable from normal tissue by day 3 post-wounding in all but the juvenile carp wounded on day 49 post-fertilization. In these juveniles the wounded area was still visible even 7 days post-wounding. On the transcriptional level a very limited response was observed in the investigated genes as a result of the wounding. HSP70 was downregulated 1 and 3 days post-wounding in the smallest larvae. However, HSP70 was differentially expressed at different time-points in a similar manner in wounded and mock-wounded groups, thus suggesting a stress effect of the handling, which may have overshadowed some transcriptional effects of the wounding. MMP-9, TGF-β1 and IgZ1 were slightly but significantly upregulated at few time-points, while no effect of wounding was detected on the expression of IgM, C3, IL-1β and IL-6 family member M17.

Cyprinid herpesvirus 3: an interesting virus for applied and fundamental research

Cyprinid herpesvirus 3 (CyHV-3), a member of the family Alloherpesviridae is the causative agent of a lethal, highly contagious and notifiable disease in common and koi carp. The economic importance of common and koi carp industries together with the rapid spread of CyHV-3 worldwide, explain why this virus became soon after its isolation in the 1990s a subject of applied research. In addition to its economic importance, an increasing number of fundamental studies demonstrated that CyHV-3 is an original and interesting subject for fundamental research. In this review, we summarized recent advances in CyHV-3 research with a special interest for studies related to host-virus interactions.

Antibody screening identifies 78 putative host proteins involved in Cyprinid herpesvirus 3 infection or propagation in common carp, Cyprinus carpio L

Cyprinid herpesvirus 3 (CyHV-3) is the aetiological agent of a serious and notifiable disease afflicting common and koi carp, Cyprinus carpio L., termed koi herpesvirus disease (KHVD). Significant progress has been achieved in the last 15 years, since the initial reports surfaced from Germany, USA and Israel of the CyHV-3 virus, in terms of pathology and detection. However, relatively few studies have been carried out in understanding viral replication and propagation. Antibody-based affinity has been used for detection of CyHV-3 in enzyme-linked immunosorbent assay and PCR-based techniques, and immunohistological assays have been used to describe a CyHV-3 membrane protein, termed ORF81. In this study, monoclonal antibodies linked to N-hydroxysuccinimide (NHS)-activated spin columns were used to purify CyHV-3 and host proteins from tissue samples originating in either CyHV-3 symptomatic or asymptomatic fish. The samples were next analysed either by polyacrylamide gel electrophoresis (PAGE) and subsequently by electrospray ionization coupled to mass spectrometry (ESI-MS) or by ESI-MS analysis directly after purification. A total of 78 host proteins and five CyHV-3 proteins were identified in the two analyses. These data can be used to develop novel control methods for CyHV-3, based on pathways or proteins identified in this study.

CyHV-3: the third cyprinid herpesvirus

Common carp (including ornamental koi carp) Cyprinus carpio L. are ecologically and economically important freshwater fish in Europe and Asia. C. carpio have recently been endangered by a third cyprinid herpesvirus, known as cyprinid herpesvirus-3 (CyHV-3), the etiological agent of koi herpesvirus disease (KHVD), which causes significant morbidity and mortality in koi and common carp. Clinical and pathological signs include epidermal abrasions, excess mucus production, necrosis of gill and internal organs, and lethargy. KHVD has decimated major carp populations in Israel, Indonesia, Taiwan, Japan, Germany, Canada, and the USA, and has been listed as a notifiable disease in Germany since 2005, and by the World Organisation for Animal Health since 2007. KHVD is exacerbated in aquaculture because of the relatively high host stocking density, and CyHV-3 may be concentrated by filter-feeding aquatic organisms. CyHV-3 is taxonomically grouped within the family Alloherpesviridae, can be propagated in a number of cell lines, and is active at a temperature range of 15 to 28°C. Three isolates originating from Japan (KHV-J), USA (KHV-U), and Israel (KHV-I) have been sequenced. CyHV-3 has a 295 kb genome with 156 unique open reading frames and replicates in the cell nucleus, and mature viral particles are 170 to 200 nm in diameter. CyHV-3 can be detected by multiple PCR-based methods and by enzyme-linked immunosorbent assay. Several modes of immunization have been developed for KHVD; however, fish immunized with either vaccine or wild-type virus may become carriers for CyHV-3. There is no current treatment for KHVD.