Myxovirus resistance (Mx) gene and its differential expression regulated by three type I and two type II IFNs in mandarin fish, Siniperca chuatsi

Transcription of NOD1 and NOD2 and their interaction with CARD9 and RIPK2 in IFN signaling in a perciform fish, the Chinese perch, Siniperca chuatsi

NOD1 and NOD2 as two representative members of nucleotide-binding oligomerization domain (NOD)-like receptor (NLR) family play important roles in antimicrobial immunity. However, transcription mechanism of nod1 and nod2 and their signal circle are less understood in teleost fish. In this study, with the cloning of card9 and ripk2 in Chinese perch, the interaction between NOD1, NOD2, and CARD9 and RIPK2 were revealed through coimmunoprecipitation and immunofluorescence assays. The overexpression of NOD1, NOD2, RIPK2 and CARD9 induced significantly the promoter activity of NF-κB, IFNh and IFNc. Furthermore, it was found that nod1 and nod2 were induced by poly(I:C), type I IFNs, RLR and even NOD1/NOD2 themselves through the ISRE site of their proximal promoters. It is thus indicated that nod1 and nod2 can be classified also as ISGs due to the presence of ISRE in their proximal promoter, and their expression can be mechanistically controlled through PRR pathway as well as through IFN signaling in antiviral immune response.

Type II interferons (IFN-γ and IFN-γrel) activate downstream genes through various potential receptor combinations to exert antiviral functions in spotted sea bass (Lateolabrax maculatus)

Type II interferons (IFNs) exert antiviral functions by binding to receptors and activating downstream signaling pathways. However, our understanding of the antiviral functions and the receptor complex model of type II IFNs in teleost fish remains limited. In this study, we determined the functions of type II IFNs (LmIFN-γ and LmIFN-γrel) in Lateolabrax maculatus and assessed their antiviral ability mediated by their combination with different cytokine receptor family B members (LmCRFB6, LmCRFB13, and LmCRFB17). After infection with largemouth bass ulcer syndrome virus (LBUSV), the expression levels of LmIFNs and LmCRFBs increased significantly in vitro and in vivo. Incubation or injection with LmIFNs-His activated the expressions of LmISG15, LmMx, and LmIRF1. LmIFN-γ and LmIFN-γrel both bound to the extracellular domains of the three CRFBs via Pull-down. Furthermore, LmIFN-γ combined with LmCRFB6, LmCRFB6+LmCRFB13, and LmCRFB6+LmCRFB13+LmCRFB17 and LmIFN-γrel combined with all combinations containing LmCRFB17 induced the transcription of downstream genes and reduced the number of LBUSV copies. Therefore, type II IFNs (LmIFN-γ and LmIFN-γrel) contribute to enhanced antiviral immunity in L. maculatus and that ligand-receptor combinations effectively suppress virus replication. These findings provide a reference for future studies of the signal transduction mechanism of type II IFNs in teleost fish.

Vitamin D3 can effectively and rapidly clear largemouth bass ranavirus by immunoregulation

Largemouth bass ranavirus (LMBV) is a highly destructive pathogen that causes significant mortality rates among largemouth bass populations. Unfortunately, there is a dearth of drug development efforts specifically aimed at treating LMBV. To address this, our study sought to investigate the potential effectiveness of incorporating varying doses of VD3 into the diet as a treatment for LMBV. Through qRT-PCR and semi-qPCR, we observed significant suppression and clearance of LMBV pathogens in largemouth bass fed with 15000 IU/Kg and 20000 IU/Kg of VD3 within 14 days. In addition, VD3 treatment significantly increased the expression levels of key immune-related genes such as IL-1β, IFN-γ, Mx, and IgM. Encouragingly, we observed that VD3 significantly increased antioxidant and immune activities such as TSOD, TAOC and C3 in serum and maintained total protein levels. Additionally, tissue pathology sections highlighted a dose-dependent relationship between VD3 supplementation and tissue damage, with the 15000 IU and 20000 IU groups exhibiting minimal damage. In conclusion, a reasonable concentration of VD3 effectively reduced LMBV replication and tissue damages, while improved immune-related genes expression and serum biochemical indices. These findings declare the considerable therapeutic potential of VD3 supplementation for combating LMBV disease and provide an alternative treatment option for fish farming.

CRFB5a, a Subtype of Japanese Eel (Anguilla japonica) Type I IFN Receptor, Regulates Host Antiviral and Antimicrobial Functions through Activation of IRF3/IRF7 and LEAP2

IFNAR1, one of the type I IFN receptors, is crucial to mammalian host defense against viral invasion. However, largely unknown is the immunological role of the fish teleost protein IFNAR1, also known as CRFB5. We have successfully cloned the whole cDNA of the Japanese eel's (Anguilla japonica) CRFB5a homolog, AjCRFB5a. The two fibronectin-3 domains and the transmembrane region (238-260 aa) of AjCRFB5a are normally present, and it shares a three-dimensional structure with zebrafish, Asian arowana, and humans. According to expression analyses, AjCRFB5a is highly expressed in all tissues found, particularly the liver and intestine. In vivo, Aeromonas hydrophila, LPS, and the viral mimic poly I:C all dramatically increased AjCRFB5a expression in the liver. Japanese eel liver cells were reported to express AjCRFB5a more strongly in vitro after being exposed to Aeromonas hydrophila or being stimulated with poly I: C. The membranes of Japanese eel liver cells contained EGFP-AjCRFB5a proteins, some of which were condensed, according to the results of fluorescence microscopy. Luciferase reporter assays showed that AjCRFB5a overexpression strongly increased the expression of immune-related genes in Japanese eel liver cells, such as IFN1, IFN2, IFN3, IFN4, IRF3, IRF5, and IRF7 of the type I IFN signaling pathway, as well as one of the essential antimicrobial peptides LEAP2, in addition to significantly inducing human IFN-promoter activities in HEK293 cells. Additionally, RNA interference (RNAi) data demonstrated that knocking down AjCRFB5a caused all eight of those genes to drastically lower their expression in Japanese eel liver cells, as well as to variable degrees in the kidney, spleen, liver, and intestine. Our findings together showed that AjCRFB5a participates in the host immune response to bacterial infection by inducing antimicrobial peptides mediated by LEAP2 and favorably modulates host antiviral immune responses by activating IRF3 and IRF7-driven type I IFN signaling pathways.

Molecular cloning and functional analysis of polymeric immunoglobulin receptor, pIgR, gene in mandarin fish Siniperca chuatsi

Polymeric immunoglobulin receptor (pIgR) can bind and transport immunoglobulins (Igs), thus playing a role in mucosal immunity. In this study, pIgR gene was cloned in mandarin fish, Siniperca chuatsi, with the open reading frame (ORF) of 1011 bp, encoding 336 amino acids. The pIgR protein consists of a signal peptide, an extracellular domain, a transmembrane domain and an intracellular region, with the presence of two Ig-like domains (ILDs) in the extracellular domain, as reported in other species of fish. The pIgR gene was expressed in all organs/tissues of healthy mandarin fish, with higher level observed in liver and spleen. Following the immersion infection of Flavobacterium columnare, pIgR transcripts were detected in immune related, especially mucosal tissues, with significantly increased transcription during the first two days of infection. Through transfection of plasmids expressing pIgR, IgT and IgM, pIgR was found to be interacted with IgT and IgM as revealed by co-immunoprecipitation and immunofluorescence.

Specificity of DNA Vaccines against the Genogroup J and U Infectious Hematopoietic Necrosis Virus Strains Prevalent in China

Infectious hematopoietic necrosis virus (IHNV) is the most important pathogen threatening the aquaculture of salmonid fish in China. In addition to the common genogroup J IHNV, genogroup U has been newly discovered in China. However, there is no effective DNA vaccine to fight against this emerging genogroup U IHNV in China. In this study, DNA vaccines encoding the IHNV viral glycoprotein (G) gene of the GS2014 (genogroup J) and BjLL (genogroup U) strains isolated from northern China were successfully developed, which were identified by restriction analysis and IFA. The expression of the Mx-1 gene and G gene in the spleens and muscles of the injection site as well as the titers of the serum antibodies were measured to evaluate the vaccine efficacy by RT-qPCR and ELISA. We found that DNA vaccine immunization could activate Mx1 gene expression and upregulate G gene expression, and the mRNA levels of the Mx1 gene in the muscles were significantly higher than those in the spleens. Notably, DNA vaccine immunization might not promote the serum antibody in fish at the early stage of immunization. Furthermore, the efficacy of the constructed vaccines was tested in intra- and cross-genogroup challenges by a viral challenge in vivo. It seemed that the DNA vaccines were able to provide great immune protection against IHNV infection. In addition, the genogroup J IHNV-G DNA vaccine showed better immune efficacy than the genogroup U IHNV-G or divalent vaccine, which could provide cross-immune protection against the genogroup U IHNV challenge. Therefore, this is the first study to construct an IHNV DNA vaccine using the G gene from an emerging genogroup U IHNV strain in China. The results provide great insight into the advances of new prophylactic strategies to fight both the genogroup J and U IHNV in China.

Development and characterization of a skin cell line from Chinese perch (Siniperca chuatsi) and its application in aquatic animal viruses

Chinese perch (Siniperca chuatsi), an important fish for the aquaculture industry of China, is often affected by viral diseases. A stable and sensitive cell line can play an important role in virus identification and isolation, functional gene identification, virus pathogenic mechanism and antiviral immunity study. In the present study, a new cell line (S. chuatsi skin cell, SCSC) derived from the skin of S. chuatsi was established. The SCSC mainly consisted of fibroblastic-like cells, which grew well in M199 medium supplemented with 10% foetal bovine serum at 25°C. Chromosome analysis revealed that the SCSC (44%) has a diploid chromosome number of 2n = 48. The SCSC can be transfected and expressed exogenous gene efficiently. It also showed high sensitivity to several aquatic animal viruses from different families including Rhabdoviridae, Iridoviridae and Reoviridae. In addition, RT-PCR showed that S. chuatsi rhabdovirus (SCRV) started genome replication as early as 3 h post infection in the cells, which also induced the up-regulation of a variety of immune-related genes including these related to interleukin family, pattern recognition receptors, JAK-STAT pathway and interferon regulatory factors. In summary, current study provided a new tool in research of fish viruses and its interaction with host.

Transcriptome analysis of pre-immune state induced by interferon gamma inhibiting the replication of H9N2 avian influenza viruses in chicken embryo fibroblasts

Interferon (IFN), a critical antiviral cytokine produced by pathogens-induced cells, plays an important role in host innate immune system. In this study, to investigate the inhibition effect of IFN on avian influenza virus (AIV), Chicken Embryo Fibroblasts (CEFs) was infected by H₉N₂ AIV. The pre-immune state and transcriptome analysis have been observed and performed. The result showed chicken interferon gamma (chIFN-γ) have the most inhibitory effect on H₉N₂ virus among three types of chicken interferons (chIFNs). Inhibition of chIFN-γ on H₉N₂ virus was verified by indirect immunofluorescence, RT-qPCR and western blot. The possible signaling pathways induced by chIFN-γ with or without virus were analyzed by transcriptome. The transcriptome data were compared among H₉N₂-infected, chIFN-γ-treated, chIFN-γ + H₉N₂-treated, and Control groups. In summary, RNA-sequencing (RNA-seq) data suggested that H₉N₂ virus infection resulted in corresponding response of certain defensive, inflammatory and metabolism pathways to the virus replication in CEFs. Furthermore, while CEFs were treated with chIFN-γ, many immune-related signaling pathways in cells are affected and altered. Antiviral genes involved in these immune pathways such as interferon regulatory factors, chemokines, interferon-stimulated genes (ISGs) and transcription factors were significantly up-regulated, and showed significant antiviral responses. Compared with virus infected CEFs alone, pretreatment with IFN induced the expression of antiviral genes and activated related antiviral pathways, inhibited the viral replication as result. Our study provided functional annotations for antiviral genes and the basis for studying the mechanism of chIFN-γ mediated response against H₉N₂ AIV.

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.

Molecular characterization and transcriptional conservation of N-myc-interactor, Nmi, by type I and type II IFNs in mandarin fish Siniperca chuatsi

N-myc-interactor (Nmi) belongs to interferon (IFN) stimulated genes (ISGs) and is involved in the regulation of physiological processes including viral infection, inflammatory response, apoptosis and tumorigenesis in mammals. However, the function of Nmi in teleost fish remains to be explored. In this study, an Nmi homologue was characterized from mandarin fish Siniperca chuatsi. The mandarin fish Nmi shares two conserved functional Nmi/IFP35 homology domains (NIDs) with mammalian Nmi protein in its C-terminal domain and a coiled coil region (CC) in its N-terminal domain, with its genomic DNA sequence consisting of nine exons and eight introns. Subcellular localization analysis shows that mandarin fish Nmi is a cytoplasmic protein and that its localization is dependent on the CC and NID1 regions. High and constitutive mRNA level of Nmi was observed in all examined tissues, with the highest level being observed in blood. In addition, the Nmi gene was significantly induced in various organs/tissues following the infection of infectious spleen and kidney necrosis virus (ISKNV), and its mRNA and protein level was also significantly induced in vitro after the treatment of IFNh, IFNc, as well as IFN-γ. The dual luciferase activity analysis indicated that the Nmi promoter was activated by the three type I IFNs through interferon-stimulated response element (ISRE) sites, and it can be also transcriptionally activated by IFN-γ via IRF1 which can activate the expression of Nmi through ISRE. Taken together, it is demonstrated in this study that the transcription of Nmi in mandarin fish can be regulated by type I and type II IFNs, thus confirming that Nmi in fish is also an ISG, and is involved in antiviral and IFN-induced innate immunity.

A myxovirus resistance like protein involved in CgIFNLP mediated immune response of oyster Crassostrea gigas

The myxovirus resistance (Mx) proteins belong to interferon (IFN)-induced dynamin GTPase and play a pivotal role in the inhibition of replication of numerous viruses. In the present study, an Mx homologue (designated as CgMx1) was identified from oyster Crassostrea gigas. The open reading frame (ORF) of CgMx1 cDNA was of 1689 bp encoding a peptide of 562 amino acid residues. There was an N-terminal dynamin GTPase domain in the predicted peptide, which consisted of a tripartite GTP-binding motif (GDXXSGKS, DLPG and T/NKXD). The deduced amino acid sequence of CgMx1 shared 30-39% similarity with other Mx family members. And CgMx1 was clustered with Mx from H. discus, and then assigned into the invertebrate branch of the phylogenetic tree. The mRNA transcripts of CgMx1 were constitutively distributed in all the tested tissues, with the highest level in haemocytes (1342.45-fold of labial palps, p < 0.05). The mRNA expression of CgMx1 in haemocytes was significantly up-regulated to the highest level at 6 h (13.14-fold, p < 0.001) after poly (I:C) treatment and at 24 h (66.28-fold, p < 0.001) after recombinant IFN-like protein (rCgIFNLP) stimulation, respectively. CgMx1 protein was found to distribute in both the cytoplasm and nucleus of haemocytes. In the oysters with CgIFNLP and signal transducer and activator of transcription (CgSTAT) silenced by RNAi, the mRNA expression of CgMx1 decreased significantly in the haemocytes at 12 h after poly (I:C) stimulation, which was 0.02-fold and 0.04-fold of that in EGFP-RNAi oysters (p < 0.001), respectively. Meanwhile, EMSA assay revealed that CgSTAT was able to transactivate CgMx1 promoter through directly binding to its interferon-stimulated response element (ISRE) and gamma interferon activation site (GAS). The above results indicated that CgMx1 participated in the immune response of C. gigas through the signal pathway mediated by CgIFNLP and CgSTAT.

Evidence for a Novel Antiviral Mechanism of Teleost Fish: Serum-Derived Exosomes Inhibit Virus Replication through Incorporating Mx1 Protein

Exosomes are associated with cancer progression, pregnancy, cardiovascular diseases, central nervous system-related diseases, immune responses and viral pathogenicity. However, study on the role of exosomes in the immune response of teleost fish, especially antiviral immunity, is limited. Herein, serum-derived exosomes from mandarin fish were used to investigate the antiviral effect on the exosomes of teleost fish. Exosomes isolated from mandarin fish serum by ultra-centrifugation were internalized by mandarin fish fry cells and were able to inhibit Infectious spleen and kidney necrosis virus (ISKNV) infection. To further investigate the underlying mechanisms of exosomes in inhibiting ISKNV infection, the protein composition of serum-derived exosomes was analyzed by mass spectrometry. It was found that myxovirus resistance 1 (Mx1) was incorporated by exosomes. Furthermore, the mandarin fish Mx1 protein was proven to be transferred into the recipient cells though exosomes. Our results showed that the serum-derived exosomes from mandarin fish could inhibit ISKNV replication, which suggested an underlying mechanism of the exosome antivirus in that it incorporates Mx1 protein and delivery into recipient cells. This study provided evidence for the important antiviral role of exosomes in the immune system of teleost fish.

Transcriptional and subcellular characterization of interferon induced protein-35 (IFP35) in mandarin fish, Siniperca chuatsi

Interferon (IFN)-stimulated genes (ISGs) exert multiple functions in immune system, and IFN-induced protein 35 (IFP35), which is a member of ISG, has been suggested to be involved in numerous cellular activities including the regulation of antiviral immunity in mammals. However, the role of IFP35 in fish innate immunity remains largely unknown. In the present study, we characterized the IFP35 gene in mandarin fish Siniperca chuatsi, which contains two conserved Nmi/IFP35 homology domains (NIDs) at C-terminus, but no leucine zipper motif, with its genomic DNA sequence consisting of eight exons and seven introns. High and constitutive mRNA level of IFP35 was observed in all examined tissues, with the highest level being observed in gills. Moreover, the IFP35 gene was significantly induced in vivo for 120 h following the infection of infectious spleen and kidney necrosis virus (ISKNV), and its mRNA and protein level was also significantly induced in vitro following the treatment of poly I:C, IFNh, IFNc, as well as IFN-γ. The subcellular localization results indicated that exogenous IFP35 protein was mainly located in cytoplasm, while endogenous IFP35 protein was transferred into, or aggregated around, the nucleus with the induction of poly I:C or IFNs. The dual luciferase activity analysis indicated that the IFP35 promoter was activated by type I and type II IFNs through ISRE site. It is considered that IFP35 in fish is involved in antiviral, as well as in IFN-induced innate immunity.

IRF11 regulates positively type I IFN transcription and antiviral response in mandarin fish, Siniperca chuatsi

In vertebrates, a total of eleven interferon (IFN) regulatory factors (IRFs), IRF1 to IRF11 are reported, with the conserved presence of IRF1 to IRF9 in all classes of vertebrates. However, IRF10 has been reported only in fish and birds, and IRF11 seems to be a fish specific IRF member. In this study, IRF11 in mandarin fish Siniperca chuatsi was found upregulated following virus infection, and IRF11 was localized constitutively in nucleus as revealed through immunofluorescence test. The overexpression and/or luciferase reporter assays showed that IRF11 can induce transcriptionally the ISRE activity, and the expression of type I IFNs, IFNc and IFNh, as well as the IFN-stimulated gene, Mx, thus inhibiting the Siniperca chuatsi rhabdovirus (SCRV) replication as indicated in the reduced expression of virus protein genes. It is thus suggested that IRF11 in mandarin fish and probably in other teleost fish can exert its antiviral effect through the upregulation of type I IFNs and ISGs.

Impact of Aeromonas hydrophila and infectious spleen and kidney necrosis virus infections on susceptibility and host immune response in Chinese perch (Siniperca chuatsi)

Co-infections with pathogenic microorganisms are common in aquaculture, resulting in more serious economic losses than single-pathogen infection. Infection of Aeromonas hydrophila (A. hydrophila) often occurs together with infectious spleen and kidney necrosis virus (ISKNV) in Chinese perch (Siniperca chuatsi) culture ponds. In this study, A. hydrophila and ISKNV were inoculated into Chinese perch to mimic individual infection, secondary infection, and mixed infection. The effects of concurrent infections on the susceptibility and the immune response of the host and changes in bacterial and viral load were studied. The results showed relatively complex interaction between ISKNV and A. hydrophila for different infection modes, acting in an antagonistic or synergistic manner. The experimental groups infected with a mixture of ISKNV and A. hydrophila showed higher mortality rate than groups infected with single-pathogen or secondary infection groups, suggesting a synergistic lethal effect of A. hydrophila and ISKNV co-infection. Serious clinical symptoms and obvious histopathological changes were observed in moribund fish under the mixed-infection condition. In addition, obviously higher mortalities were caused by secondary bacterial infections than the number caused by secondary viral infections. ISKNV-primary infection increased the mortality caused by secondary bacterial infections, but A. hydrophila-primary infection did not significantly increase the mortality caused by secondary viral infections. Co-infected fish showed high expression levels of IRF1, Mx, Viperin, Hepcidin, TNFα, and IL-1β mRNAs relative to the levels in healthy fish, which suggested that the co-infection of these two pathogens activated the host immune system and caused host inflammation. These results of infection with A. hydrophila and ISKNV provided the theoretical basis to analyze the pathogenic effects and interaction between pathogens, and could facilitate design of strategies for clinical prevention and control measures of outbreak of fulminant hemorrhagic disease and bacterial sepsis in Chinese perch.