Induction of antiviral state in fish cells by Japanese flounder, Paralichthys olivaceus, interferon regulatory factor-1

Interferon regulatory factors inhibit TiLV replication by activating interferon-a3 in tilapia (Oreochromis niloticus)

Tilapia lake virus (TiLV) is an emerging virus that seriously threatens the tilapia industries worldwide. Interferon regulatory factors (IRFs), which are the crucial mediators regulating the response of interferon (IFN) to combat invading viruses, have not yet been reported in tilapia during TiLV infection. Here, six IRF (IRF1, IRF2, IRF4, IRF7, IRF8, and IRF9) homologs from tilapia were characterized and analyzed. These IRFs typically shared the conserved domains and phylogenetic relationship with IRF homologs of other species. Tissue distribution analysis showed that all six IRF genes were expressed in various tissues, with the highest expression in immune-related tissues. Furthermore, overexpression of IRFs in tilapia brain (TiB) cells significantly inhibited TiLV propagation, as evidenced by decreased viral segment 8 gene transcripts and copy numbers of viral segment 1. More importantly, all six IRF genes significantly enhanced the promoter activity of type I interferon-a3 (IFNa3) in TiB cells, suggesting that tilapia IRF genes serve as positive regulators in activating IFNa3. Surprisingly, the promoter activity of IFNa3 mediated by IRF genes was markedly inhibited post-TiLV infection, indicating that TiLV antagonized IRF-mediated IFN immune response. Taken together, six IRF genes of tilapia are highly conserved transcription factors that inhibit TiLV infection by activating the promoter of IFNa3, which is in turn restrained by TiLV. These findings broaden our knowledge about the functionality of IRF-mediated antiviral immunity in tilapia against TiLV infection and host-TiLV interaction, which lays a foundation for developing antiviral strategies in tilapia cultural industries.

Fundamentals of Fish Vaccination

Fish health management has become a critical component of disease control and is invaluable for improved harvests and sustainable aquaculture. Vaccination is generally accepted as the most effective prophylactic measure for fish disease prevention, on environmental, social, and economic grounds. Although the historical approach for developing fish vaccines was based on the principle of Louis Pasteur's "isolate, inactivate and inject," but their weak immunogenicity and low efficacies in many cases, have shifted the focus of fish vaccine development from traditional to next-generation technologies. However, before any fish vaccine can be successfully commercialized, several hurdles need to be overcome regarding the production cost, immunogenicity, effectiveness, mode of administration, environmental safety, and associated regulatory concerns. In this context, the chapter summarises the basic aspects of fish vaccination such as type of vaccine, modalities of vaccine delivery, the immunological basis of fish immunization as well as different challenges associated with the development process and future opportunities.

Functional domains and amino acid residues of Japanese eel IRF1, AjIRF1, regulate its nuclear import and IFN/Mx promoter activation

Interferon regulatory factors (IRFs) are a family of transcriptional factors capable of regulating the expression of distinct subsets of interferon (IFN)-stimulated genes by binding to their promoters. IRF1 was the first member identified for its ability to regulate the IFNβ gene and has now been revealed to exhibit remarkable functional diversity in the regulation of different cellular responses. In the present study, the IRF1 gene was identified and characterized in Japanese eel, Anguilla japonica (AjIRF1). The open reading frame of AjIRF1 was 804 bp in length, encoding a protein of 267 amino acids (aa) that encompasses a conserved N-terminal DNA binding domain (DBD). Sequence alignment shows the presence of six highly conserved tryptophan (W) residues in the DBD of IRF1, IRF2 and IRF11, while other IRF members have only five tryptophans. Expression analysis showed that AjIRF1 was significantly upregulated in all tested organs/tissues in response to Poly I:C stimulation or Edwardsiella tarda infection. Furthermore, the functional activity of AjIRF1 was confirmed in driving the transcription of AjIFN promoters, which depends on the highly conserved residues within DBD. Subcellular distribution analysis revealed that AjIRF1 was localized exclusively in the nucleus, which is cooperatively regulated by a bipartite NLS embedded within the DBD and a monopartite NLS located immediately downstream of the DBD. Taken together, this study presents the expression profile of AjIRF1 and defines the functional motifs required for its nuclear import and its role in activating IFN promoters, thus providing helpful information for further research on the regulatory mechanisms of teleost IRF1.

Molecular and functional characterization of interferon regulatory factor 1 (IRF1) in amphibian Xenopus tropicalis

Interferon regulatory factor 1 (IRF1) is an important regulator in controlling the transcription of type I interferon genes, and its functions have been well-characterized in mammals, birds and fish. However, little information is available regarding the function of amphibian IRF1. In this study, an IRF1 gene homolog named as Xt-IRF1 was identified in the Western clawed frog (Xenopus tropicalis), an amphibian model specie widely used for comparative immunology research. Xt-IRF1 and IRF1 in other vertebrates possess similar genomic structure and flanking genes, and were grouped together to form a separate clade in phylogenetic tree. In addition, Xt-IRF1 gene was constitutively expressed in all tissues examined, with the highest expression level observed in spleen, and was inducible after poly(I:C) stimulation. Importantly, the expression of Xt-IRF1 was markedly induced by recombinant type I interferon, and Xt-IRF1 induced a strong activation of both IFNβ and ISRE promoters. The present study opens the door to investigate the roles of IRF1 in amphibians, and thus contributes to a better understanding of the functional evolution of IRFs in lower tetrapods.

Optimization of the efficacy of a SWCNTs-based subunit vaccine against infectious spleen and kidney necrosis virus in mandarin fish

Infectious spleen and kidney necrosis virus (ISKNV) cause a high mortality disease which brings substantial economic losses to the mandarin fish culture industry in China. This study was aimed at optimizing the efficacy of a SWCNTs-based immersion subunit vaccine (SWCNTs-M-MCP) which as a promising vaccine against ISKNV. Mandarin fish were vaccinated by immersion, then we designed an orthogonal experiment to optimize different parameters affecting vaccination such as immune duration of bath immunization, immune dose, and fish density when immunized. Our results showed that the highest relative percent survival (86.7%) was found in the group 6 with 8 h of immune duration, 20 mg/L of immune dose, and 8 fish per liter of fish density. And other immune responses (serum antibody production, enzyme activities, and immune-related genes expression) also demonstrated similar results. In addition, the expression of IRF-I in group 6 (8 h, 20 mg/L, 8 fish per liter) was significant extents, and about 16-folds increases were obtained than the control group at 21 d post-vaccination. And the highest specific antibody response was significantly increased (more than 4-folds) than control group which was found in group 6. The optimum immune duration, immune dose, and fish density of SWCNTs-M-MCP were 8 h, 20 mg/L, 8 fish per liter, respectively. Importantly, our results also showed that immune duration had the greatest effect on the immune response of our vaccine, followed by immune dose. The study reported herein provides a helpful reference for the effective use of vaccine in fish farming industry.

A signal transducers and activators of transcription (STAT) gene from Scylla paramamosain is involved in resistance against mud crab reovirus

A STAT gene from Scylla paramamosain, named SpSTAT, was cloned and characterized. The full length of SpSTAT mRNA contains a 5'untranslated region (UTR) of 238 bp, an open reading frame (ORF) of 2388 bp and a 3' UTR of 326 bp. The SpSTAT protein contains four characteristic STAT domains and showed 84% identity (90% similarity) and 44% identity (64% similarity) to Litopenaeus vannamei STAT protein and Human STAT5a/b protein, respectively. The mRNA of SpSTAT was high expressed in the intestine and eyestalk and low expressed in the heart and muscle. Moreover, expression of SpSTAT was significantly responsive to challenge of mud crab reovirus (MCRV), Poly(I:C), LPS and Staphylococcus aureus. SpSTAT could be activated by Poly(I:C) and LPS to translocate to the nucleus of Drosophila Schneider 2 (S2) cells. SpSTAT could be phosphorylated by interaction with JAK of S. paramamosain (SpJAK) and activated to translocate to the nucleus of S2 cells. Furthermore, Silencing of SpSTAT in vivo resulted in higher mortality rate of MCRV infected mud crab and increased the viral load in tissues, suggesting that SpSTAT could play an important role in defense against MCRV in mud crab.

The crab Relish plays an important role in white spot syndrome virus and Vibrio alginolyticus infection

Relish is a transcription factor and forms an important part of the immune deficiency signaling pathway. In the current study, a Relish homolog was cloned from the hemolymph of Scylla paramamosain using RT-PCR and RACE. The full length cDNA of Relish consists of 4263 base pairs (bp), including a 3552 bp open reading frame encoding a 1184 amino acid protein. The data showed that Relish was highly expressed in the gonad and digestive organs of S. paramamosain. Furthermore, the expression of Relish was up-regulated by infection with white spot syndrome virus (WSSV) or Vibrio alginolyticus. When Relish was knocked down, immune genes such as Janus Kinase, signal transducer and activator of transcription, crustin antimicrobial peptide, prophenoloxidase, C-type-lectin and myosin-II-essential-light-chain-like-protein were significantly down-regulated (P < 0.01), and Toll-like receptor was significantly up-regulated (P < 0.01) in hemocytes. The mortality of WSSV-infected or V. alginolyticus-infected crabs was enhanced following Relish knockdown. Thus, Relish is very important in the progression of WSSV and V. alginolyticus infection. It was found that Relish knockdown caused the highest level of apoptosis in the disease-free group, and higher levels of apoptosis in the WSSV group and V. alginolyticus group compared with that in the control group. Knockdown of Relish influenced the activity of phenoloxidase (PO) and superoxide dismutase (SOD), and total hemocyte count (THC) following WSSV or V. alginolyticus infection, indicating that Relish plays a regulatory role in the immune response to WSSV or V. alginolyticus infection in crabs. Thus, we conclude that Relish may anticipate host defense mechanisms against pathogen infection by affecting apoptosis, THC, PO activity and SOD activity.

DNA vaccines for fish: Review and perspectives on correlates of protection

Recently in 2016, the European Medicines Agency (EMA) recommended granting a marketing authorization in the EU for "Clynav," a DNA vaccine against salmon pancreas disease (salmonid alphavirus-3). Generally, DNA vaccines induce both early and late immune responses in fish that may be protective against disease. Several transcriptomic approaches have been performed to map immunome profiles following DNA vaccination, but the precise immune mechanism(s) that is responsible for protection is not known, although reasonable suggestions have been made. The current review includes an overview on main transcriptomic findings from microarray experiments after DNA vaccination against VHSV, IHNV, HIRRV and IPNV-with considerations of what can be considered as correlates of protection (CoP) or merely a surrogate of protection. Identification and use of correlates of protection (COPs) may be a strategic tool for accelerated and targeted vaccine design, testing and licensure. General rules on what can be considered as CoPs can be extracted from past knowledge on protective immune responses following vaccination that induced protection. Lastly, there will be an overview on non-viral molecular adjuvants that have been exploited to obtain higher vaccine potencies and efficacies.

Expression profile of carp IFN correlate with the up-regulation of interferon regulatory factor-1 (IRF-1) in vivo and in vitro: the pivotal molecules in antiviral defense

Interferon regulatory factors (IRFs) are a family of transcription factors that mediate the transcriptional regulation of interferon (IFN) genes and IFN-inducible genes. In this study, IRF-1 gene is cloned from the common carp, Cyprinus carpio L., named CcIRF-1. The full-length cDNA of CcIRF-1 is 1427 bp, including an open reading frame of 861 bp encoding a protein of 286 amino acids. The putative CcIRF-1 is characterized by a conserved DNA-binding domain and includes a signature of six conserved tryptophan residues. The genomic sequence of CcIRF-1 is described, which consists of 9 exons and 8 introns. The sequence analysis shows that CcIRF-1 is clustered into IRF-1 subfamily, and has the closest relationship with the zebrafish IRF-1. CcIRF-1 is found constitutively expressed in different organs of healthy common carp. The main findings are that CcIRF-1 is up-regulated following stimulation with poly(I:C) in all tested tissues. Moreover, the downstream gene of IRF-1 - IFN is found to be correlated with the up-regulation of IRF-1 after injection with poly(I:C). Furthermore, we also isolate the peripheral blood leukocytes (PBLs) and find that there is a relevance between the expression profile of CcIRF-1 and IFN in poly(I:C) stimulated PBLs.

Innate Multigene Family Memories Are Implicated in the Viral-Survivor Zebrafish Phenotype

Since adaptive features such as memory were discovered in mammalian innate immunity, interest in the immunological status of primitive vertebrates after infections has grown. In this context, we used zebrafish (Danio rerio), a primitive vertebrate species suited to molecular and genetic studies to explore transcriptional memories of the immune system in long-term survivors of viral haemorrhagic septicemia virus infections. Immune-gene targeted microarrays designed in-house, multipath genes, gene set enrichment, and leading-edge analysis, reveal unexpected consistent correlations between the viral-survivor phenotype and several innate multigene families. Thus, here we describe in survivors of infections the upregulation of the multigene family of proteasome subunit macropains, zebrafish-specific novel gene sets, mitogen activated protein kinases, and epidermal growth factor. We also describe the downregulation of the multigene families of c-reactive proteins, myxovirus-induced proteins and novel immunoglobulin-type receptors. The strength of those immunological memories was reflected by the exceptional similarity of the transcriptional profiles of survivors before and after re-infection compared with primary infected fish. On the other hand, the high levels of neutralizing antibodies in the blood plasma of survivors contrasted with the depletion of transcripts specific for most cell types present in lymphoid organs. Therefore, long-term survivors maintained unexpected molecular/cellular memories of previous viral encounters by modulating the expression levels of innate multigene families as well as having specific adaptive antibodies. The implications of the so-called "trained immunity" for future research in this field are also discussed.

Function of shrimp STAT during WSSV infection

JAK/STAT signaling pathway plays key roles in the antiviral immunity of mammals, fish and insect. However, limited knowledge is known about the function of JAK/STAT signaling pathway in the antiviral immunity of shrimp although virus disease has caused severe mortality in shrimp aquaculture. In order to understand the function of JAK/STAT signaling pathway in the antiviral immunity of shrimp, dsRNA interfering technique was used to silence the expression of STAT gene in Litopenaeus vannamei, and the mortality of shrimp was detected after WSSV infection. Furthermore, the expressions of some potential target genes regulated by STAT or genes related to RNA interfering pathway were detected in STAT silenced shrimp during WSSV infection. The WSSV copy number in STAT silenced shrimp was 10(2)-10(3) copies/ng DNA which was much lower than that in the control. The mortality in STAT silenced shrimp caused by WSSV infection decreased very significantly compared to their controls. The function of STAT was verified in vitro cultured cells of hematopoietic tissue of crayfish Cherax quadricarinatus by adding specific inhibitor of STAT3(S3I-201), and the cultured cells treated with S3I-201 showed much less WSSV copy number than their controls, which further suggested that STAT might be helpful for the replication of WSSV. Expression analysis on the potential STAT target genes and genes in RNA interfering pathway provide important information for understanding the functional mechanism of STAT in antiviral immunity of shrimp.

A murrel interferon regulatory factor-1: molecular characterization, gene expression and cell protection activity

In this study, we have reported a first murrel interferon regulatory factor-1 (designated as Murrel IRF-1) which is identified from a constructed cDNA library of striped murrel Channa striatus. The identified sequence was obtained by internal sequencing method from the library. The Murrel IRF-1 varies in size of the polypeptide from the earlier reported fish IRF-1. It contains a DNA binding domain along with a tryptophan pentad repeats, a nuclear localization signal and a transactivation domain. The homologous analysis showed that the Murrel IRF-1 had a significant sequence similarity with other known fish IRF-1 groups. The phylogenetic analysis exhibited that the Murrel IRF-1 clustered together with IRF-1 members, but the other members including IRF-2, 3, 4, 5, 6, 7, 8, 9 and 10 were clustered individually. The secondary structure of Murrel IRF-1 contains 27% α-helices (85 aa residues), 5.7% β-sheets (19 aa residues) and 67.19% random coils (210 aa residues). Furthermore, we predicted a tertiary structure of Murrel IRF-1 using I-Tasser program and analyzed the structure on PyMol surface view. The RNA structure of the Murrel IRF-1 along with its minimum free energy (-284.43 kcal/mol) was also predicted. The highest gene expression was observed in spleen and its expression was inducted with pathogenic microbes which cause epizootic ulcerative syndrome in murrels such as fungus, Aphanomyces invadans and bacteria, Aeromonas hydrophila, and poly I:C, a viral RNA analog. The results of cell protection assay suggested that the Murrel IRF-1 regulates the early defense response in C. striatus. Moreover, it showed Murrel IRF-1 as a potential candidate which can be developed as a therapeutic agent to control microbial infections in striped murrel. Overall, these results indicate the immune importance of IRF-1, however, the interferon signaling mechanism in murrels upon infection is yet to be studied at proteomic level.

Adjuvants and immunostimulants in fish vaccines: current knowledge and future perspectives

Vaccination is the most adequate method to control infectious diseases that threaten the aquaculture industry worldwide. Unfortunately, vaccines are usually not able to confer protection on their own; especially those vaccines based on recombinant antigens or inactivated pathogens. Therefore, the use of adjuvants or immunostimulants is often necessary to increase the vaccine efficacy. Traditional adjuvants such as mineral oils are routinely used in different commercial bacterial vaccines available for fish; however, important side effects may occur with this type of adjuvants. A search for alternative molecules or certain combinations of them as adjuvants is desirable in order to increase animal welfare without reducing protection levels. Especially, combinations that may target specific cell responses and thus a specific pathogen, with no or minor side effects, should be explored. Despite this, the oil adjuvants currently used are quite friendlier with respect to side effects compared with the oil adjuvants previously used. The great lack of fish antiviral vaccines also evidences the importance of identifying optimal combinations of a vaccination strategy with the use of a targeting adjuvant, especially for the promising fish antiviral DNA vaccines. In this review, we summarise previous studies performed with both traditional adjuvants as well as the most promising new generation adjuvants such as ligands for Toll receptors or different cytokines, focussing mostly on their protective efficacies, and also on what is known concerning their effects on the fish immune system when delivered in vivo.

Association between SNPs in interferon regulatory factor 2 (IRF-2) gene and resistance to Aeromonas hydrophila in freshwater mussel Hyriopsis cumingii

Interferon regulatory factor 2 (IRF-2) is a multi-functional transcription factor in the IRF family exhibiting both transcriptional activating and repressing activities. In this study, an IRF-2 gene (HcIRF-2) from Hyriopsis cumingii was identified and characterized. The cDNA sequence consisted of 2688 bp, encoding a 329 amino acid-protein. The amino acid sequence had a highly conserved N-terminal DBD structure, containing characteristic repeats of six tryptophan residues. The 5'-flanking region contained several transcription regulation elements such as AP1, CdxA, HSF, NIT2 and HNF-3b. Nine SNPs were obtained through direct sequencing of HcIRF-2 from resistant and susceptible stock. Only +2365T/C SNP was significantly associated with resistance/susceptibility of H. cumingii to Aeromonas hydrophila both in genotype (P = 0.021) and allele (P = 0.006) analysis. The SNPs +2248T/C and +2365T/C were in high linkage disequilibrium, and haplotype analysis revealed that haplotype TT frequency in the resistant group was significantly higher than in the susceptible group. The mortality in +2248CC genotype individuals was significantly higher than in CT and TT genotype individuals. These results indicated that haplotype TT and genotype +2248CT and +2248GT individuals were resistant to A. hydrophila, which could make them potential markers in selective breeding of H. cumingii.

Establishing a cell line from Atlantic cod as a novel tool for in vitro studies

The present work describes the generation of a cell line from newly hatched Atlantic cod (Gadus morhua) larvae (ACL cells). Primary cultures were initiated by explant outgrowth from partially minced tissues and subcultured cells were exposed to UV radiation. After a substantial period of growth lag, cells started to proliferate and different growth conditions were tested to establish the cell line. At present, the ACL cell line has been subcultured for more than 100 passages. ACL cells had a polygonal shape and the morphology appeared homogenous with epithelial-like cells. Cell growth was dependent on the presence of foetal bovine serum and cells proliferated in a wide temperature range with optimal growth at 15 °C. By exposure to a viral dsRNA mimic (poly I:C) the cells expressed high levels of a repertoire of genes comprising both inflammatory mediators and interferon stimulated genes. Infection studies with two different viruses showed that infectious pancreatic necrosis virus (IPNV) propagated efficiently, and induced low level expression of genes of both pathways before the cells rapidly died. No productive infection was obtained with nervous necrosis virus (NNV), but a transient increase in the viral RNA level, followed by a high increase in expression of selected ISGs, suggests that the virus enters the cells but is unable to complete its replication cycle. To our knowledge, ACL cells are at the moment the only existing cell line from Atlantic cod. Our results demonstrate that ACL cells can be a useful research tool for further exploration of host-pathogen interactions and it is believed that this cell line will serve as a valuable tool also for studies within other research areas.

Inhibition of Hirame rhabdovirus growth by RNA aptamers

RNA aptamers are artificial nucleic acids that specifically bind to a wide variety of targets. They are an effective tool for pharmaceutical research and development of antiviral agents. Here, we describe four Hirame rhabdovirus (HIRRV)-RNA aptamers (H1, H2, H3 and H4) that we obtained from an in vitro process called the systematic evolution of ligands by exponential enrichment (SELEX). The HIRRV-RNA aptamers specifically bind to HIRRV. Hirame natural embryo (HINAE) cells treated with virus and the RNA aptamer showed a decrease in appearance of cytopathic effect when compared with control (treated only with virus). Rhodovulum sulfidophilum was transformed with genes for the RNA aptamers, and the aptamers were detected in the culture medium, indicating that they were secreted from the cells. Thus, the recombinant R. sulfidophilum might be a powerful tool for the prevention of HIRRV in aquaculture.

Teleost fish interferons and their role in immunity

Interferons (IFNs) are the hallmark of the vertebrate antiviral system. Two of the three IFN families identified in higher vertebrates are now known to be important for antiviral defence in teleost fish. Based on the cysteine patterns, the fish type I IFN family can be divided into two subfamilies, which possibly interact with distinct receptors for signalling. The fish type II IFN family consists of two members, IFN-γ with similar functions to mammalian IFN-γ and a teleost specific IFN-γ related (IFN-γrel) molecule whose functions are not fully elucidated. These two type II IFNs also appear to bind to distinct receptors to exert their functions. It has become clear that fish IFN responses are mediated by the host pattern recognition receptors and an array of transcription factors including the IFN regulatory factors, the Jak/Stat proteins and the suppressor of cytokine signalling (SOCS) molecules.

Influence of alginic acid and fucoidan on the immune responses of head kidney leukocytes in cod

The present study investigated the immunomodulatory activities of alginic acid and fucoidan, both derived from brown seaweeds, on selected cellular immune responses and antibacterial activity of head kidney (HK) leukocytes of cod, Gadus morhua. Primary cultures of HK leukocytes were incubated with either 10 or 100 μg ml⁻¹ of the substances and the effects on respiratory burst, cellular proliferation, acid and alkaline phosphatase activity and cellular myeloperoxidase were measured at 3- and 24-h post-incubation. The antibacterial activity of the supernatants collected from the cell cultures incubated with 100 μg ml⁻¹ of the substances were tested against Vibrio anguillarum and Aeromonas salmonicida. Respiratory burst was significantly elevated in cells incubated with either alginic acid or fucoidan in a dose-dependent manner. Incubation with a higher dose of alginic acid and fucoidan resulted in lower cellular proliferation at 3- and 24-h, respectively. Both acid and alkaline phosphatase activities of HK leukocytes were not significantly modulated, except for a slight elevation of acid phosphatase in cells incubated with 100 μg ml⁻¹ of alginic acid for 24-h. Fucoidan, but not alginic acid significantly increased cellular myeloperoxidase activity at a concentration of 100 μg ml⁻¹. The growth of the bacteria in both the treated and control supernatants was significantly lower than what was observed in the bacterial culture medium. However, the supernatants from the treated cells had significantly higher bacterial growth compared with supernatants of the control cells. Taken together, these results showed that at the tested concentrations, both alginic acid and fucoidan are able to differentially stimulate some cellular immune responses of cod HK leukocytes in vitro and the respiratory burst activity was significantly stimulated by these brown algal derivatives. These substances could be tested as potential immunostimulants in future in vivo studies.

Responses of Atlantic cod Gadus morhua head kidney leukocytes to phytase produced by gastrointestinal-derived bacteria

This study identified phytase-producing bacteria that were previously isolated from the gastrointestinal tract of Atlantic cod, Gadus morhua and determined its effect on head kidney leukocytes. Out of the 216 bacterial strains tested, the two phytase producers were identified as Pseudomonas sp. and Psychrobacter sp. based on their 16S rDNA sequence. Crude phytase from these two bacterial strains was produced employing the shake flask method. Even though the total protein of the crude phytase was not significantly different for the two bacteria, the phytase activity of the crude enzyme produced by Pseudomonas sp. (97.1±16.7 U) was significantly higher than that of the enzyme from Psychrobacter sp. (75.9±2.4 U). When cod head kidney leukocytes were incubated with the crude phytase (50 μg ml(-1)), it resulted in enhanced cell proliferation, higher myeloperoxidase, and acid phosphatase activities. Extracellular responses-respiratory burst activity and hydrogen peroxide production were not enhanced by the crude enzyme. As a consequence, the growth of two pathogenic bacteria Aeromonas salmonicida and Vibrio anguillarum was not suppressed by the supernatants obtained from head kidney leukocytes incubated with the crude bacterial phytase. Thus, the enzyme from phytase-producing intestinal bacteria of Atlantic cod can stimulate intracellular head kidney leukocyte activities but not the production of extracellular substances that are involved in antibacterial response. These have implications on the potential use of bacterial phytase as feed supplement to boost cellular immune response of the fish and could be employed as a health management strategy in culture systems.

Characterization of fish IRF3 as an IFN-inducible protein reveals evolving regulation of IFN response in vertebrates

In mammals, IFN regulatory factor (IRF) 3 is a critical player in modulating transcription of type I IFN and IFN-stimulated genes (ISGs). In this study, we describe the roles of crucian carp (Carassius auratus L.) IRF3 in activating fish IFN and ISGs. Fish IRF3 exhibits a large sequence divergence from mammalian orthologs. Whereas mammalian IRF3 is constitutively expressed, fish IRF3 protein is significantly upregulated by IFN, poly-IC, and other stimuli known as IFN inducers in mammals. The IFN-inducible property of fish IRF3 is consistent with the comparative analysis of 5' flanking regulatory region of vertebrate IRF3 genes, which reveals the presence of typical IFN-stimulated response elements in fish and amphibians, but an absence in tetrapods. Furthermore, either IFN or poly-IC induces phosphorylation and cytoplasmic-to-nuclear translocation of IRF3, which seems essential for its function in that phosphomimic active IRF3 exhibits stronger transactivation than wild type IRF3. Finally, overexpression of fish IRF3 activates production of IFN that in turn triggers ISG transcription through Stat1 pathway, whereas transfection of dominant negative mutant IRF3-DN abrogates poly-IC induction of ISGs, probably owing to blockade of IFN production. Therefore, regulation of IFN response by vertebrate IRF3 is another ancient trait. These data provide evidence of the evolving function of vertebrate IRF3 on regulating IFN response.

Molecular cloning and characterization of interferon regulatory factors 4 and 8 (IRF-4 and IRF-8) in rainbow trout, Oncorhynchus mykiss

Mammalian interferon regulatory factor (IRF)4 (PIP, LSIRF, and ICSAT) and IRF8 (ICSBP) are known to be critical in regulating a spectrum of functional and developmental processes in lymphomyeloid cell lineages either through direct binding to IRF-E motifs in target gene promoters or indirectly by binding to composite motifs recognized by Ets family members, PU.I and Sp.I. Here we report, for the first time in fish, the sequencing and characterization of full-length cDNA homologues of rainbow trout (rt) IRF4 and rtIRF8. The rtIRF4 molecule consists of 1848 bp with a 45 bp 5' UTR and a predicted 378 bp 3' UTR translating into a 474 aa protein. RtIRF8 consists of 1951 bp with a 52 bp 5' UTR and a 564 bp 3' UTR translating into a 444 aa protein. Each gene possesses a putative DNA binding domain (DBD) containing the tryptophan pentad-repeat domain found in all IRF family members. Both molecules also possess a well conserved IRF association domain (IAD). The presence of these domains along with phylogenetic analysis places the two genes in the IRF4 subfamily. Both genes were detected in a range of trout tissues where IRF8 was the overall predominant transcript. Consistent with mammalian studies, the highest expression levels of IRF4 and IRF8 were observed in the lymphomyeloid-rich fish tissues, spleen, head kidney and gills. IRF8 expression in stimulated trout splenocytes was significantly up-regulated by polyinosinic:polycytidylic acid (poly I:C), trout recombinant (r)IL-15, phorbol 12-myristate 13-acetate (PMA), and phytohaemagglutinin (PHA) treatment whilst remaining refractory towards lipopolysaccharide (LPS) treatment. IRF4 was significantly down-regulated by LPS stimulation and remained refractory towards poly I:C, trout rIL15, and PHA. PMA stimulation elicited a significant upregulation of IRF4 expression. Overall, these data support the premise that these IRFs are likely to play important roles in the functional and developmental processes occurring in fish lymphomyeloid tissues.

Molecular cloning and expression of IRF1 in large yellow croaker, Pseudosciaena crocea

The interferon regulatory factor (IRF) family is known to be crucial in mediating the host defense against pathogen infection by binding to characteristic elements in promoters within interferon (IFN) genes and IFN-inducible genes. In this report, the full-length cDNA of IRF1 was cloned from the large yellow croaker, Pseudosciaena crocea. It was of 1667 bp, including a 5'-terminal untranslated region (UTR) of 142 bp, a 3'-terminal UTR of 674 bp and an open reading frame (ORF) of 861 bp encoding a polypeptide of 286 amino acids. The putative amino acid sequence contained a typical IRF domain at the N-terminal. Quantitative real-time reverse transcription PCR analysis revealed a broad expression of IRF1 in most detected tissues, with the predominant expression in the gill and spleen and the weakest expression in the brain. The expression of IRF1 after challenged with LPS and poly I:C was tested in blood, spleen and liver, which showed that IRF1 changed obviously with the most significantly up-regulated expression was 37 times (at 6 h) after injection with poly I:C in the blood and 13 times (at 3 h) after injection with LPS in the liver compared with the control values (p < 0.01). These results indicated that as a crucial factor in regulating the IFN and IFN-inducible elements in mammals, IRF1 might play an important role in large yellow croaker defense against the pathogen infection.

Identification and characterization of interferon regulatory factor-1 from orange-spotted grouper (Epinephelus coioides)

Interferon-regulatory factor 1 (IRF-1) is the first member of IRF family, which is involved in many biological processes such as immune response, antiviral defense, cell growth regulation, and apoptosis. In this study, an IRF-1 gene, EcIRF-1, was isolated and characterized from orange-spotted grouper (Epinephelus coioides). The full-length cDNA of EcIRF-1 is 1,730 bp, including an open reading frame of 906 bp, a 5'-terminal untranslated region (5'-UTR) of 153 bp, and a 3'-UTR of 671 bp. The EcIRF-1 gene consists of 10 exons and 9 introns, spanning over approximate 4.3 kb of genomic sequence. The 5'-UTR sequence contains an exon and an intron, and the 3'-UTR sequence is included in the last exon. Expression analysis by real-time PCR reveals that the EcIRF-1 gene is ubiquitously expressed in various healthy fish tissues, whereas its expression is upregulated in vivo in response to polyinosinic-polycytidylic acid or lipopolysaccharide stimulation. Subcellular localization analysis shows the EcIRF-1 is an intranuclearly localized and immobile protein in the cultured fish cells. Data presented in this paper provide an important base to further understand EcIRF-1 gene function and its regulation associated with interferon immune system in orange-spotted grouper.

Molecular characterization of IRF3 and IRF7 in rainbow trout, Oncorhynchus mykiss: functional analysis and transcriptional modulation

Interferon regulatory factors (IRF) 3 and 7 in mammals are known to be crucial in regulating the type I interferon (IFN) response to viral infection as part of transcriptional complexes binding to IRF-binding elements (IRF-Es) and interferon stimulatory response elements (ISREs) within IFN and interferon-stimulated genes (ISGs). Here we report the sequencing and characterization of full-length cDNA homologues of rainbow trout (rt)IRF7 and, for the first time in fish, IRF3. RtIRF3 consists of 2127 bp with a 159 bp 5'-UTR-containing two upstream AUGs and a 573 bp 3'-UTR. RtIRF7 was found to be 2055 bp, with a 102 bp 5'-UTR and a 705 bp 3'-UTR. The open reading frames (ORFs) translate into 464 amino acid and 415 amino acid proteins, respectively, each possessing a putative DNA-binding domain (DBD) containing a tryptophan cluster, which is characteristic of all IRF family members. The presence of putative IRF association domain (IAD)s, serine-rich C terminal domains (poorly conserved in trout IRF3), and phylogenetic analysis places the two genes in the IRF3 subfamily. Both genes were found to be upregulated by poly I:C, type I recombinant rainbow trout (r) IFN (second isoform, type I rIFN), type II rIFN (rIFNgamma), LPS, and rIL-1beta in the trout macrophage cell line, RTS-11. Poly I:C and type I rIFN also induced IRF3 and IRF7 expression in a trout fibroblast cell line (RTG-2). Transient transfection of RTG-2 cells with each IRF fused to GFP revealed a predominant cytoplasmic distribution found most intensely around the nucleus and, to a lesser extent, within cell nuclei. Transient transfection of rtIRF3 in the Mx-1-luciferase reporter cell line, RTG-P1, revealed a modest increase in luciferase activity relative to the vehicle control, which was lost in cells over-expressing a DBD-truncated form of rtIRF3. Both full-length and DBD-truncated forms of rtIRF7 increased reporter activity relative to the control, although to a non-significant extent. Electromobility shift assays (EMSAs) did not reveal a specific interaction between each IRF and the ISRE element found in the Mx-1 promoter, although the Mx-1 ISRE bound specifically to endogenous transcriptional complexes. These data support the premise that rtIRF3 and rtIRF7 are important molecules in the regulation of antiviral responses in fish, with the impact of rIFNgamma on rtIRF3/7 expression implying a role for these IRFs in immune processes other than type I IFN-driven antiviral responses.

Molecular characterization and subcellular localization of Carassius auratus interferon regulatory factor-1

Interferon (IFN)-regulatory transcription factor-1 (IRF-1) has been studied in mammals and fish, but little is known about the relationship between its gene structure and nuclear localization of IRF-1 protein. In this study, a cDNA encoding Carassius auratus IRF-1 (CaIRF-1) was isolated from an interferon-producing cell line, C. auratus blastulae embryonic (CAB) cells, exposed to UV-inactivated grass carp hemorrhagic virus (GCHV). The CaIRF-1 genomic locus exhibits exon-intron arrangements similar to those of other vertebrate IRF-1 loci, with nine exons and eight introns, although together with pufferfish IRF-1, CaIRF-1 distinguishes itself from other vertebrate IRF-1 genes by a relatively compact genomic size. Similar to the known IRF-1 genes, CaIRF-1 is ubiquitously expressed, and is upregulated in vitro and in vivo in response to virus, Poly I:C, or CAB IFN-containing supernatant (ICS). Subcellular localization analysis confirms the nuclear distribution of CaIRF-1 protein, and reveals two nuclear localization signals (NLS), any one of which is sufficient for nuclear translocation of CaIRF-1. One NLS locates to amino acids 117-146, and appears to be the structural and functional equivalent of the NLS in mammalian IRF-1. The second NLS (amino acids 73-115) is found within the DNA-binding domain (DBD) of CaIRF-1, and contains two regions rich in basic amino acids ("95 KDKSINK 101" and "75 KTWKANFR 82"). In comparison with mammalian IRF-1, in which the corresponding amino acid stretch does not seem to drive nuclear translocation, five conserved basic amino acids (K75, K78, R82, K95, and K101) and one non-conserved basic amino acid (K97) are present in this NLS from CaIRF-1. This observation suggests that K97 of CaIRF-1 might be essential for the function of its second NLS, wherein the six basic amino acids might cooperate to drive CaIRF-1 to the nucleus. Therefore, the current study has revealed a new nuclear localization motif in the DBD of a vertebrate IRF-1.

Genetic vaccines protect red seabream, Pagrus major, upon challenge with red seabream iridovirus (RSIV)

We have investigated the protective effect of immunization of juvenile red seabream, Pagrus major, with DNA plasmids encoding the viral major capsid protein (MCP) and an open reading frame (ORF) containing a transmembrane domain against red seabream iridovirus (RSIV). The expression of the MHC class I transcript in the DNA-vaccinated fish was significantly upregulated at the 15th day post-vaccination and the relative level of expression was maintained until the 30th day post-vaccination. This pattern of expression was similar in fish vaccinated with a commercially prepared formalin-inactivated RSIV vaccine. In vaccine efficiency tests, the relative percentage survival (RPS) of fish receiving the DNA vaccines and their combination ranged from 42.8 to 71.4% in two experimental runs, and these were significantly different from the control groups. Our results clearly demonstrate that DNA vaccines are able to induce robust protection in fish against RSIV infection, and a cellular immune response as shown by the upregulation of the MHC class I transcript after vaccination, which may be associated with such protection.