Effect of lipopolysaccharides from Vibrio alginolyticus on the Mx gene expression and virus recovery from gilthead sea bream (Sparus aurata L.) experimentally infected with Nodavirus

Nanomaterial inactivates environmental virus and enhances plant immunity for controlling tobacco mosaic virus disease

Tobacco mosaic virus (TMV) is extremely pathogenic and resistant to stress There are great needs to develop methods to reduce the virus in the environment and induce plant immunity simultaneously. Here, we report a multifunctional nano-protectant to reduce the virus in the environment and induce plant immunity simultaneously. The star polycation (SPc) nanocarrier can act as an active ingredient to interact with virus coat protein via electrostatic interaction, which reduces the proportion of TMV particles to 2.9% and leads to a reduction of the amount of virus in the environment by half. SPc can act as an adjuvant to spontaneously assemble with an immune inducer lentinan (LNT) through hydrogen bonding into nanoscale (142 nm diameter) LNT/SPc complex, which improves the physicochemical property of LNT for better wetting performance on leaves and cellular uptake, and further activates plant immune responses. Finally, the LNT/SPc complex displays preventive and curative effects on TMV disease, reducing TMV-GFP relative expression by 26% in the laboratory and achieving 82% control efficacy in the field We hope the strategy reported here would be useful for control of crop virus disease.

Characterization, Expression Pattern and Antiviral Activities of Mx Gene in Chinese Giant Salamander, Andrias davidianus

Mx, Myxovirus resistance is an important interferon-stimulated protein that mediates antiviral responses. In this study, the expression and activities of Chinese giant salamander, Andrias davidianus Mx gene, AdMx, were investigated. The AdMx cDNA sequence contains an open reading frame (ORF) of 2112 nucleotides, encoding a putative protein of 703 aa. Meanwhile, AdMx possesses the conserved tripartite GTP binding motif and a dynamin family signature. qRT-PCR analysis revealed a broad expression of AdMx in vivo, with the highest expression levels in brain, kidney and spleen. The AdMx expression level in kidney, spleen and muscle significantly increased at 6 h after Chinese giant salamander iridovirus (GSIV) infection and peaked at 48 h, while that in muscle cell line (GSM) was not noticeably up-regulated until 72 h post infection. Additionally, a plasmid expressing AdMx was constructed and transfected into the Chinese giant salamander GSM cells. The virus load and gene copies in AdMx over-expressed cells were significantly reduced compared with those in the control cells. Moreover, compared to the control cells, a lower level of virus major capsid protein (MCP) synthesis in AdMx over-expressed cells was confirmed by Western blot. These results collectively suggest that Mx plays an important antiviral role in the immune responses against GSIV in Chinese giant salamander.

Advances in the study of nodavirus

Nodaviruses are small bipartite RNA viruses which belong to the family of Nodaviridae. They are categorized into alpha-nodavirus, which infects insects, and beta-nodavirus, which infects fishes. Another distinct group of nodavirus infects shrimps and prawns, which has been proposed to be categorized as gamma-nodavirus. Our current review focuses mainly on recent studies performed on nodaviruses. Nodavirus can be transmitted vertically and horizontally. Recent outbreaks have been reported in China, Indonesia, Singapore and India, affecting the aquaculture industry. It also decreased mullet stock in the Caspian Sea. Histopathology and transmission electron microscopy (TEM) are used to examine the presence of nodaviruses in infected fishes and prawns. For classification, virus isolation followed by nucleotide sequencing are required. In contrast to partial sequence identification, profiling the whole transcriptome using next generation sequencing (NGS) offers a more comprehensive comparison and characterization of the virus. For rapid diagnosis of nodavirus, assays targeting the viral RNA based on reverse-transcription PCR (RT-PCR) such as microfluidic chips, reverse-transcription loop-mediated isothermal amplification (RT-LAMP) and RT-LAMP coupled with lateral flow dipstick (RT-LAMP-LFD) have been developed. Besides viral RNA detections, diagnosis based on immunological assays such as enzyme-linked immunosorbent assay (ELISA), immunodot and Western blotting have also been reported. In addition, immune responses of fish and prawn are also discussed. Overall, in fish, innate immunity, cellular type I interferon immunity and humoral immunity cooperatively prevent nodavirus infections, whereas prawns and shrimps adopt different immune mechanisms against nodavirus infections, through upregulation of superoxide anion, prophenoloxidase, superoxide dismutase (SOD), crustin, peroxinectin, anti-lipopolysaccharides and heat shock proteins (HSP). Potential vaccines for fishes and prawns based on inactivated viruses, recombinant proteins or DNA, either delivered through injection, oral feeding or immersion, are also discussed in detail. Lastly, a comprehensive review on nodavirus virus-like particles (VLPs) is presented. In recent years, studies on prawn nodavirus are mainly focused on Macrobrachium rosenbergii nodavirus (MrNV). Recombinant MrNV VLPs have been produced in prokaryotic and eukaryotic expression systems. Their roles as a nucleic acid delivery vehicle, a platform for vaccine development, a molecular tool for mechanism study and in solving the structures of MrNV are intensively discussed.

IRF9-Stat2 Fusion Protein as an Innate Immune Inducer to Activate Mx and Interferon-Stimulated Gene Expression in Zebrafish Larvae

Virus infection often causes large amounts of mortality during teleost larvae stage. Strong induction of innate immunity to increase survival rates of teleost larvae has been less reported. In this study, we present a zebrafish IRF9-Stat2 fusion protein (zIRF9-S2C) as a strong innate immunity inducer and characterized induction of interferon-stimulated genes (ISGs) in zebrafish larvae. zIRF9-S2C could mimic IFN-stimulated gene factor 3 (ISGF3) complex to constitutively activate transcription of Mx promoter through IFN-stimulatory element (ISRE) sites. Mutation of two ISRE sites on Mx promoter reduced transactivation activities of Mx promoter induced by zIRF9-S2C. An electrophoretic mobility shift assay experiment shows that zIRF9-S2C could directly bind to two ISRE sites of Mx promoter. Induction of transactivation of Mx promoter by zIRF9-S2C shows significantly higher activity than by zebrafish IFN1 (zIFN1), IFNγ (zIFNγ), and Tetraodon IRF9-S2C (TnIRF9-S2C). zIRF9-S2C raises transcription of Mxa, Mxb, Mxc, Ifnφ1, Ifnφ2, and Ifnφ3 in zebrafish liver ((ZFL) cell line) cells and zebrafish larvae. Collectively, we suggest that IRF9-S2C could activate transcription of ISGs with species-specific recognition and could be an innate immunity inducer in teleost larvae.

Expression of Mx Gene in Cirrhinus mrigala (Hamilton, 1822) to OmpC Protein of Aeromonas hydrophila and Bacterial Infection

The aims of this study were to identify alternative myxovirus (Mx) stimulatory compounds in Cirrhinus mrigala and to characterize the kinetics and intensity of their stimulated responses by semi-quantitative RT-PCR. Mx transcripts were measured in C. mrigala injected with Aeromonas OmpC (outer membrane protein) at a dose 0.4 mg/fish. At day 1, day 2, day 3, day 5, day 10, day 20 and day 30, samples were collected from kidney, spleen, liver, heart brain, gill, intestine and muscle for the study of Mx transcript and housekeeping gene β-actin. Similarly, Mx gene expression was also studied in Aeromonas hydrophila-infected fish for a period of 10 days. Mx/β-actin ratio was constitutively expressed from all the organs of OmpC-vaccinated fish. The expression was significantly highest (P ≤ 0.05) in spleen, followed by liver, kidney, intestine, gill, heart, muscle and brain. The expression was highest in day 2 except spleen (on day 3) and subsequently reduced up to day 30. Control fish also showed Mx expression. Similarly, A. hydrophila-infected fish showed Mx/β-actin ratio upregulated significantly in the spleen and kidney on day 5, liver on day 2 and intestine on day 3. This study revealed that OmpC of A. hydrophila and its infection could stimulate the antiviral Mx gene of C. mrigala.

Influence of temperature on Mx gene expression profiles and the protection of sevenband grouper, Epinephelus septemfasciatus, against red-spotted grouper nervous necrosis virus (RGNNV) infection after poly (I:C) injection

Influence of temperature on the susceptibility of fish against virus infection has been studied for a decade. Recent reports have been shown the effects of rearing temperatures on the fish immune system against virus infection. However, the roles of temperature in regulation of type I interferon (IFN) system has not yet been investigated. Thus, the effects of temperature on type I IFN response were investigated in this study using poly (I:C) injection in sevenband grouper and Mx gene was used as a marker for type I IFN expression. Quantitative real-time PCR (qPCR) result showed that Mx expression profiles were moderately different between temperatures. The highly up-regulated Mx transcripts at 3 h post injection (hpi) were observed in high temperatures (25 °C and 30 °C) but not in low temperatures (15 °C and 20 °C). Meanwhile, low temperatures (15 °C and 20 °C) could detect the highly up-regulated Mx transcripts at 24 hpi. Expression of Mx transcripts was also observed at 72 hpi at 15 °C. Poly (I:C)-injected fish were challenged with RGNNV after 72 and 168 hpi. At 72 hpi, 100% of fish survived at all temperatures, whereas 95% survival rate was observed at 168 hpi at 25 °C during 14 days of observation. To further verify the duration period of an antiviral state at different temperatures, qPCR and endpoint dilution assay were used to quantify the number of virus in fish challenged with RGNNV. The reduction of viral copy numbers and viral titers could be observed at 72 and 168 hpi. However, high viral copy numbers and viral titers could be detected at 168 hpi at 30 °C. These results demonstrate that temperatures influenced on the Mx expression profiles and the duration period of an antiviral state efficiently interfered with virus replication at different temperatures.

Immunity to betanodavirus infections of marine fish

Betanodaviruses cause viral nervous necrosis in numerous fish species, but some species are resistant to infection by these viruses. It is essential to fully characterize the immune responses that underlie this protective response. Complete characterization of the immune responses against nodaviruses may allow the development of methods that stimulate fish immunity and of an effective betanodavirus vaccine. Such strategies could include stimulation of specific immune system responses or blockage of factors that decrease the immune response. The innate immune system clearly provides a front-line defense, and this includes the production of interferons and other cytokines. Interferons that are released inside infected cells and that suppress viral replication may be the most ancient form of innate immunity. This review focuses on the immune responses of fish to betanodavirus infection.

Identification of the STAT1 gene and the characterisation of its immune response to immunostimulants, including nervous necrosis virus (NNV) infection, in Malabar grouper (Epinephelus malabaricus)

Signal Transducer and Activator of Transcription (STAT)-1 is an indispensable signal transduction protein that is involved in the interferon pathway. STAT-1 plays an important role in the innate immune response. The full-length cDNA of Malabar grouper (Epinephelus malabaricus) STAT-1, MgSTAT1, was cloned. Phylogenetic analysis was performed based on the amino acid sequence. Our results indicate that STAT1 is highly conserved with other vertebrates. We also report the expression of MgSTAT1 in different tissues treated with immune stimulants, including LPS, CpG ODN, and poly (I:C), in vivo. The expression of MgSTAT1 was significantly induced in the head kidney upon treatment with poly (I:C) compared to the control. Moreover, the results indicate that MgSTAT1 is up-regulated during nervous necrosis virus (NNV) infection. This study reveals that similar to the mammalian antiviral response, MgSTAT1 mediates the immune response in Malabar grouper.