Functional diversity of Mx proteins: variations on a theme of host resistance to infection

In vitro analysis of the expression of inflammasome, antiviral, and immune genes in an Oreochromis niloticus liver cell line following stimulation with bacterial ligands and infection with tilapia lake virus

The inflammasome is a multimeric protein complex that plays a vital role in the defence against pathogens and is therefore considered an essential component of the innate immune system. In this study, the expression patterns of inflammasome genes (NLRC3, ASC, and CAS-1), antiviral genes (IFNγ and MX), and immune genes (IL-1β and IL-18) were analysed in Oreochromis niloticus liver (ONIL) cells following stimulation with the bacterial ligands peptidoglycan (PGN) and lipopolysaccharide (LPS) and infection with TiLV. The cells were stimulated with PGN and LPS at concentrations of 10, 25, and 50 µg/ml. For viral infection, 106 TCID50 of TiLV per ml was used. After LPS stimulation, all seven genes were found to be expressed at specific time points at each of the three doses tested. However, at even higher doses of LPS, NLRC3 levels decreased. Following TiLV infection, all of the genes showed significant upregulation, especially at early time points. However, the gene expression pattern was found to be unique in PGN-treated cells. For instance, NLRC3 and ASC did not show any response to PGN stimulation, and the expression of IFNγ was downregulated at 25 and 50 µg of PGN per ml. CAS-1 and IL-18 expression was downregulated at 25 µg of PGN per ml. At a higher dose (50 µg/ml), IL-1β showed downregulation. Overall, our results indicate that these genes are involved in the immune response to viral and bacterial infection and that the degree of response is ligand- and dose-dependent.

Structural insights of Labeo catla (catla) myxovirus resistance protein,GTP binding recognition and constitutive expression induced with Poly I:C

The Myxovirus resistance (Mx) proteins are critical effectors belonging to the super-family of guanidine triphosphatase, often stimulated by type I interferon (IFN) and mediates antiviral responses to restrict the replication of numerous viral genes in fishes. In teleosts, Mx proteins display diverse and complicated antiviral activity in different species. The present investigation seeks to characterize the Mx gene from Labeo catla upon induction by double-stranded (ds) RNA, polyinosinic-polycytidylic acid, (poly I: C). Molecular modeling and all-atoms molecular dynamics (MD) simulations were employed to understand the architecture of the GTPase domain and its plausible mode of GTP recognition in Mx protein. The full-length L. catla Mx (LcMx) gene sequence (1821 bp nucleotides) encodes an open reading frame of 606 amino acids. Domain search indicated conserved tripartite domain architecture of LcMx and forms a major cluster with the Mx from other teleosts. The positively charged Arginine and polar Glutamine residues from helix 3 and 4 of stalk region LcMx aid in homo-oligomerization. MD simulation portrayed the role of conserved critical residues aid in GTP recognition by the GTPase domain which perfectly corroborates with experimental findings and prior MD studies. After injection of poly I:C, the temporal mRNA profile showed that LcMx expression was significantly elevated in the spleen, brain, kidney, liver, muscle, heart, intestine, and gill tissues. Collectively, these results suggest that the elevated expression of the major innate immune defense gene Mx was able to inhibit the poly I: C mediated virulence in fish.Communicated by Ramaswamy H. Sarma.

Immunomodulatory Role of Interferons in Viral and Bacterial Infections

Interferons are a group of immunomodulatory substances produced by the human immune system in response to the presence of pathogens, especially during viral and bacterial infections. Their remarkably diverse mechanisms of action help the immune system fight infections by activating hundreds of genes involved in signal transduction pathways. In this review, we focus on discussing the interplay between the IFN system and seven medically important and challenging viruses (herpes simplex virus (HSV), influenza, hepatitis C virus (HCV), lymphocytic choriomeningitis virus (LCMV), human immunodeficiency virus (HIV), Epstein-Barr virus (EBV), and SARS-CoV coronavirus) to highlight the diversity of viral strategies. In addition, the available data also suggest that IFNs play an important role in the course of bacterial infections. Research is currently underway to identify and elucidate the exact role of specific genes and effector pathways in generating the antimicrobial response mediated by IFNs. Despite the numerous studies on the role of interferons in antimicrobial responses, many interdisciplinary studies are still needed to understand and optimize their use in personalized therapeutics.

Surface display of major capsid protein on Bacillus subtilis spores against largemouth bass virus (LMBV) for oral administration

Largemouth bass virus (LMBV) infections resulting in enormous loss are becoming an increasing problem in the largemouth bass industry. Oral vaccination is considered to be an effective and economical measure because of the advantages of non-invasion, no size limitation, lower cost and easily-operated. Based on Bacillus subtilis (B. subtilis) spores, this study successfully constructed the CotC-LMBV recombinant B. subtilis spores and its protective efficacy and immune responses were evaluated. After challenged, the survival rate of largemouth bass orally vaccinated with CotC-LMBV spores was 53.3% and the relative percent survival (RPS) was 45.0% compared to the PBS group. In addition, the specific IgM level in serum in the CotC-LMBV group was significantly higher than in the control groups. In the spleen, the immune-related genes expression detected by quantitative real-time PCR (qRT-PCR) exhibited an increasing trend in different degrees in the CotC-LMBV group, suggesting that innate and adaptive immune responses were activated. This study indicated that oral administration of CotC-LMBV recombinant spores could stimulate an effective immune response and enhance fish immunity against LMBV infection. Therefore, oral vaccination could be an effective approach for the prevention of largemouth bass virus disease.

HPAI-resistant Ri chickens exhibit elevated antiviral immune-related gene expression

BACKGROUND

Highly pathogenic avian influenza viruses (HPAIVs) is an extremely contagious and high mortality rates in chickens resulting in substantial economic impact on the poultry sector. Therefore, it is necessary to elucidate the pathogenic mechanism of HPAIV for infection control.

OBJECTIVE

Gene set enrichment analysis (GSEA) can effectively avoid the limitations of subjective screening for differential gene expression. Therefore, we performed GSEA to compare HPAI-infected resistant and susceptible Ri chicken lines.

METHODS

The Ri chickens Mx(A)/BF2(B21) were chosen as resistant, and the chickens Mx(G)/BF2(B13) were selected as susceptible by genotyping the Mx and BF2 genes. The tracheal tissues of HPAIV H5N1 infected chickens were collected for RNA sequencing followed by GSEA analysis to define gene subsets to elucidate the sequencing results.

RESULTS

We identified four differentially expressed pathways, which were immune-related pathways with a total of 78 genes. The expression levels of cytokines (IL-1β, IL-6, IL-12), chemokines (CCL4 and CCL5), type interferons and their receptors (IFN-β, IFNAR1, IFNAR2, and IFNGR1), Jak-STAT signaling pathway genes (STAT1, STAT2, and JAK1), MHC class I and II and their co-stimulatory molecules (CD80, CD86, CD40, DMB2, BLB2, and B2M), and interferon stimulated genes (EIF2AK2 and EIF2AK1) in resistant chickens were higher than those in susceptible chickens.

CONCLUSIONS

Resistant Ri chickens exhibit a stronger antiviral response to HPAIV H5N1 compared with susceptible chickens. Our findings provide insights into the immune responses of genetically disparate chickens against HPAIV.

Myxovirus resistance (Mx) Gene Diversity in Avian Influenza Virus Infections

Avian influenza viruses (AIVs) pose threats to animal and human health. Outbreaks from the highly pathogenic avian influenza virus (HPAIV) in indigenous chickens in Bangladesh are infrequent. This could be attributed to the Myxovirus resistance (Mx) gene. To determine the impact of Mx gene diversity on AIV infections in chicken, we assessed the Mx genes, AIVs, and anti-AIV antibodies. DNA from blood cells, serum, and cloacal swab samples was isolated from non-vaccinated indigenous chickens and vaccinated commercial chickens. Possible relationships were assessed using the general linear model (GLM) procedure. Three genotypes of the Mx gene were detected (the resistant AA type, the sensitive GG type, and the heterozygous AG type). The AA genotype (0.48) was more prevalent than the GG (0.19) and the AG (0.33) genotypes. The AA genotype was more prevalent in indigenous than in commercial chickens. A total of 17 hemagglutinating viruses were isolated from the 512 swab samples. AIVs were detected in two samples (2/512; 0.39%) and subtyped as H1N1, whereas Newcastle disease virus (NDV) was detected in the remaining samples. The viral infections did not lead to apparent symptoms. Anti-AIV antibodies were detected in 44.92% of the samples with levels ranging from 27.37% to 67.65% in indigenous chickens and from 26% to 87.5% in commercial chickens. The anti-AIV antibody was detected in 40.16%, 65.98%, and 39.77% of chickens with resistant, sensitive, and heterozygous genotypes, respectively. The genotypes showed significant association (p < 0.001) with the anti-AIV antibodies. The low AIV isolation rates and high antibody prevalence rates could indicate seroconversion resulting from exposure to the virus as it circulates. Results indicate that the resistant genotype of the Mx gene might not offer anti-AIV protection for chickens.

Four Mx Genes Identified in Andrias davidianus and Characterization of Their Response to Chinese Giant Salamander Iridovirus Infection

Amphibians, including Andrias davidianus, are declining worldwide partly due to infectious diseases. The Myxovirus resistance (Mx) gene is a typical interferon (IFN)-stimulated gene (ISG) involved in the antiviral immunity. Therefore, knowledge regarding the antiviral immunity of A. davidianus can be used for improved reproduction in captivity and protection in the wild. In this study, we amplified and characterized four different A. davidianus Mx genes (adMx) and generated temporal mRNA expression profiles in healthy and Chinese giant salamander iridovirus (GSIV) infected A. davidianus by qualitative real-time PCR (qPCR). The four adMx genes ranged in length from 2008 to 2840 bp. The sequences revealed conserved protein domains including the dynamin superfamily signature motif and the tripartite guanosine-5-triphosphate (GTP)-binding motif. Gene and deduced amino acid sequence alignment revealed relatively high sequence identity with the Mx genes and proteins of other vertebrates. In phylogenetic analysis, the adMx genes clustered together, but also clustered closely with those of fish species. The four adMx genes were broadly expressed in healthy A. davidianus, but were differentially expressed in the spleen during the GSIV infection. Our results show that the adMx genes share major structural features with their homologs, suggesting similar functions to those in other species.

Protective efficacy of four heat-shock proteins as recombinant vaccines against photobacteriosis in Asian seabass (Lates calcarifer)

Photobacterium damselae subsp. piscicida (Phdp) is the causative agent of photobacteriosis in marine fish and is responsible for huge losses to marine aquaculture worldwide. Efforts have been made to develop a vaccine against this disease. Heat-shock proteins (HSPs) are a family of proteins that are ubiquitous in cellular life. Bacteria produce elevated levels of HSPs as a survival strategy when exposed to stressful environments in a host during infection. This group of proteins are also important antigens that can induce both humoral and cellular immune responses. In this study, four HSPs of Phdp, HSP90, HSP33, HSP70, and DnaJ, were selected for cloning and recombinant expression. Western blotting with rabbit anti-Phdp helped identify rHSP70 and rHSP33 as immunogenic proteins. Asian seabass (Lates calcarifer) immunised with rHSP90, rHSP33, rHSP70, and rDnaJ showed 48.28%, 62.07%, 51.72%, and 31.03% relative percent survival, respectively, after being challenged with Phdp strain AOD105021. High expression levels of immune-related genes and high antibody titres were observed in the rHSP33 group, and the sera of this group also exhibited a high level of bactericidal activity against Phdp. Collectively, our results suggest that HSP33 is a potential candidate for vaccine development against Phdp infection.

Labeo rohita Mx1 exhibits the critical structural motifs of the family of large GTPases of mammals and is activated by rhabdovirus vaccination and bacterial RNA stimulations

Myxovirus resistance (Mx) proteins belonging to the dynamin superfamily of high molecular weight GTPases exist in various isoforms and play crucial role in innate immunity. In addition to the isoforms, Mx1 also plays important role in exerting its anti-viral actions against a broad range of animal RNA viruses. In rohu (Labeo rohita), mx1 full-length cDNA sequence consists of 2440 nucleotides (nt) encoding 628 amino acids (aa) polypeptide of 71.289 kDa. Structurally, it belongs to the family of large GTPases with one DYNc domain (13-257aa) comprising of dynamin family motifs (LPRGSGIVTR) and the tripartite GTP-binding motifs (GDQSSGKS, DLPG and TKPD) at the N-terminal and one GED domain (537-628aa) at C-terminus. Rohu Mx1 is closely related to zebrafish Mx1 and is widely expressed in gill, liver, kidney, spleen and blood. In response to rhabdovirus vaccinations, poly I:C stimulation and bacterial infections, mx1 gene expression in rohu was significantly (p < 0.05) induced in majority of the tested organs/tissues. Stimulation of rohu gill cell line with bacterial RNA also induced mx1 gene expression. Together these data suggest the important role of Mx1 in innate immunity in rohu against wide spectrum of fish pathogens.

Pro-515 of the dynamin-like GTPase MxB contributes to HIV-1 inhibition by regulating MxB oligomerization and binding to HIV-1 capsid

Interferon-regulated myxovirus resistance protein B (MxB) is an interferon-induced GTPase belonging to the dynamin superfamily. It inhibits infection with a wide range of different viruses, including HIV-1, by impairing viral DNA entry into the nucleus. Unlike the related antiviral GTPase MxA, MxB possesses an N-terminal region that contains a nuclear localization signal and is crucial for inhibiting HIV-1. Because MxB previously has been shown to reside in both the nuclear envelope and the cytoplasm, here we used bioinformatics and biochemical approaches to identify a nuclear export signal (NES) responsible for MxB's cytoplasmic location. Using the online computational tool LocNES (Locating Nuclear Export Signals or NESs), we identified five putative NES candidates in MxB and investigated whether their deletion caused nuclear localization of MxB. Our results revealed that none of the five deletion variants relocates to the nucleus, suggesting that these five predicted NES sequences do not confer NES activity. Interestingly, deletion of one sequence, encompassing amino acids 505-527, abrogated the anti-HIV-1 activity of MxB. Further mutation experiments disclosed that amino acids 515-519, and Pro-515 in particular, regulate MxB oligomerization and its binding to HIV-1 capsid, thereby playing an important role in MxB-mediated restriction of HIV-1 infection. In summary, our results indicate that none of the five predicted NES sequences in MxB appears to be required for its nuclear export. Our findings also reveal several residues in MxB, including Pro-515, critical for its oligomerization and anti-HIV-1 function.

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.

The R614E mutation of mouse Mx1 protein contributes to the novel antiviral activity against classical swine fever virus

Mx proteins are interferon-induced GTPases that have broad antiviral activity against a wide range of RNA and DNA viruses. We previously demonstrated that porcine Mx1 protein (poMx1) inhibited the replication of classical swine fever virus (CSFV), an economically important Pestivirus, and that mouse Mx1 did so as well. It is unknown why the nucleus-localizing mouse Mx1 inhibits CSFV replication which occurs in the cytoplasm. To the end, we assessed the anti-CSFV actions of wild type mouse Mx1 and seven previously reported mutants (K49A, G83R, A222V, A516V, G540E, R614E and ΔL4) and identified the molecular mechanism of R614E action against CSFV replication. A series of experiments revealed that mmMx1 (R614E) mutant reposted to the cytoplasm and interacted with the CSFV nucleocapsid protein (Core), thereby inhibiting viral replication. These findings broaden our understanding of the function of Mx protein family members against CSFV and suggest that the relative conservation of Mx1 among species is the basis of broad-spectrum antiviral properties.

An interferon-induced GTP-binding protein, Mx, from the redlip mullet, Liza haematocheila: Deciphering its structural features and immune function

The interferon-induced GTP-binding protein Mx is responsible for a specific antiviral state against a broad spectrum of viral infections that are induced by type-I interferons (IFN α/β) in different vertebrates. In this study, the Mx gene was isolated from the constructed mullet cDNA database. Structural features of mullet Mx (MuMx) were analyzed using different in-silico tools. The pairwise comparison revealed that the MuMx sequence was related to Stegastes partitus Mx with an 83.7% sequence identity, whereas MuMx was clustered into the teleost category in the phylogentic analysis. Sequence alignment showed that the dynamin-type guanine nucleotide-binding domain (G_DYNAMIN_2), central interactive domain (CID), and GTPase effector domain (GED) were conserved among Mx counterparts. The transcriptional expression of MuMx was the highest in blood cells from unchallenged fish. The temporal mRNA profile showed that MuMx expression was significantly elevated in all tissues, including blood, spleen, head kidney, liver, and gills after the injection of polyinosinic-polycytidylic acid (poly I:C) at many time points. Moreover, MuMx expression increased slightly, in the blood, spleen, and head kidney at a few time points after the injection of lipopolysaccharide (LPS) and Lactococcus garvieae (L. garvieae). Results of the subcellular localization analysis confirmed that the MuMx protein was highly expressed in the cytoplasm. The analysis of the gene expression of the viral hemorrhagic septicemia virus (VHSV) under conditions of MuMx overexpression confirmed the significant inhibition of viral transcripts. The cell viability (MTT) assay and VHSV titer quantification with the presence of MuMx indicated a significant reduction in virus replication. Collectively, these findings suggest that Mx is a specific immune-related gene that elicits crucial antiviral functions against viral antigens in the mullet fish.

Molecular characterization, constitutive expression and GTP binding mechanism of Cirrhinus mrigala (Hamilton, 1822) Myxovirus resistance (Mx) protein

Myxovirus resistance (Mx) proteins represents the subclass of the dynamin superfamily of large Guanosine triphosphates (GTPases), play esential role in intracellular vesicle trafficking, endocytosis, organelle homeostasis and mitochondria distribution. These proteins are key players of the vertebrate immune system, induced by type-I and type-III interferons (IFN) of infected host and inhibit viral replication by sequestering its nucleoprotein. In the present study, we report the sequencing and characterization of Cirrhinus mrigala Mx protein (CmMx) for the first time and observed its constitutive expression in different tissues for a period of fourteen days. The synthetic peptide, LSGVALPRGTGI, was dissolved in PBS and injected into a rabbit and the antibody raised against CmMx was used to study the level of its expression. The full length of the CmMx cDNA is 2244 bp with a molecular mass of 70.9 kDa and a predicted isoelectric point of 8.25. The 627 amino acids polypeptide formed of three main functional domains: N-terminal GTPase domain (GD), a middle domain (MD) and GTPase effector domain (GED) with carboxy terminal leucine zipper motif. The 3D models of CmMx protein was modeled based on available close structural homologs and further validated through molecular dynamics (MD) simulations. MD study revealed the importance of G-domain responsible for recognition of GTP, which perfectly corroborate with earlier studies. MM/PBSA binding free energy analysis displayed that van der Waals and electrostatic energy were the key driving force behind molecular recognition of GTP by CmMx protein. The results from this study will illuminate more lights into the ongoing research on myxovirus resistance protein and its role in inhibition of viral replication in other eukaryotic system as well.

The Discovery of the Antiviral Resistance Gene Mx: A Story of Great Ideas, Great Failures, and Some Success

The discovery of the Mx gene-dependent, innate resistance of mice against influenza virus was a matter of pure chance. Although the subsequent analysis of this antiviral resistance was guided by straightforward logic, it nevertheless led us into many blind alleys and was full of surprising turns and twists. Unexpectedly, this research resulted in the identification of one of the first interferon-stimulated genes and provided a new view of interferon action. It also showed that in many species, MX proteins have activities against a broad range of viruses. To this day, Mx research continues to flourish and to provide insights into the never-ending battle between viruses and their hosts.

Identification of Mx gene nucleotide dimorphism (G/A) as genetic marker for antiviral activity in Egyptian chickens

Egyptian chickens, representing 2 breeds and 7 strains, were genotyped using the PCR-RFLP and sequencing techniques for detection of a non-synonymous dimorphism (G/A) in exon 14 of chicken Myxovirus resistance (Mx) gene. This dimorphic position is responsible for altering Mx protein's antiviral activity. Polymerase Chain reactions were performed using Egyptian chickens DNA and specific primer set to amplify Mx DNA fragments of 299 or 301 bp, containing the dimorphic position. Amplicons were cut with restriction enzyme Hpy81. Genotype and allele frequencies for the resistant allele A and sensitive allele G were calculated in all the tested chickens. Results of PCR-RFLP were confirmed by sequencing. The three genotypes AA, AG, GG at the target nucleotide position in Mx gene were represented in all the studied Egyptian chicken breeds and strains except Baladi strain which showed only one genotype AA. The average allele frequency of the resistant A allele in the tested birds (0.67) was higher than the sensitive G allele average frequency in the same birds (0.33). Appling PCR-RFLP technique in the breeding program can be used to select chickens carrying the A allele with high frequencies. This will help in improving poultry breeding in Egypt by producing infectious disease-resistant chickens.

Interferon induced Mx protein from Indian snow trout Schizothorax richardsonii (Gray) lacks critical functional features unlike its mammalian homologues

Viral attack within host cells triggers the production of type I interferons and leads to the induction of interferon stimulated genes (ISGs). One of the ISG Mx, encodes type I interferon inducible GTPase that is responsible for the establishment of an anti-viral state within cells. Intriguingly, several isoforms of Mx have been reported in fish, but the structural analysis of fish Mx proteins remains unexplored. For the first time, we have identified and unraveled the molecular structure of Mx protein from Indian snow trout, Schizothorax richardsonii (Gray) a Coldwater fish that inhabits the water bodies in the sub-Himalayan region. The snow trout Mx coding region consists of 2518 nucleotides with an open reading frame (ORF) of 1854 nucleotides. It codes for a polypeptide of 617 amino acids with a predicted molecular weight of 70 kDa. In silico analysis of snow trout Mx protein revealed signature of dynamin family (LPRGTGIVTR) along with a tripartite GTP-binding domain (GDQSSGKS, DLPG, and TKPD). Homology modelling established that the Mx protein is an elongated structure with a G domain, bundle signaling element (BSE) and a GTPase effector domain (GED). Moreover, the GED of Mx contains two highly conserved leucine zippers at the COOH-terminal of the protein suggesting its structural similarity with human homologues. However, snow trout Mx lacks the essential features of its mammalian homologues questioning its functional characteristics. Further, a ligand binding site in the said protein has also been predicted adjacent to the GTPase switch within the G domain.

Polymorphisms in MX2 Gene Are Related with SCS in Chinese Dairy Cows

Viral infections can play direct or indirect roles in the etiology of the bovine mastitis. Mx dynamin-like GTPase 2 (MX2) gene is a main effector of the antiviral innate immune defense mediated by type I interferon (IFN I), which was demonstrated to confer positive antiviral responses to many viruses. Given the importance of the MX2 in modulating the host immune response, MX2 gene may be a suitable candidate gene for studying disease resistance in dairy cattle. Here, we scanned the sequence variation of the MX2 gene in Chinese indigenous cattle breeds. Twenty-three previously reported SNPs were identified. To further analyze the effects of SNPs detected on mastitis disease, analysis of two SNPs (g.787527 C > T and g.787610 T > C) from 297 Chinese Holstein cows revealed a significant association with somatic cell score (SCS). Although functional studies are necessary to ascertain whether these two SNPs are causal polymorphisms or merely in linkage with the true causal SNPs, implementation of these two SNPs as genetic markers in the dairy industry may be beneficial in selecting individuals with lower SCS.

Molecular cloning, polymorphism, and functional activity of the bovine and water buffalo Mx2 gene promoter region

Background

Bovine Mx2 gene sequences were already reported, but further information about the gene properties is not yet available. The objective of the current study was to elucidate the structural properties of the bovine Mx2 gene mainly the promoter region and its possible functional role. If available, such information would help in assessing the functional properties of the gene, which was reported to confer antiviral action against recombinant VSV.

Results

Examinations on the bovine genomic BAC clone—confirmed to contain the Mx2 gene—revealed 883-bp sequences. A computer scan unequivocally identified a 788-bp promoter region containing a typical TATA box, three ISREs and other promoter-specific motifs. Comparative analysis of nine bovine genomic DNA samples showed 19 nucleotide substitutions suggesting the existence of five different genotypes in the promoter region. The water buffalo Mx2 promoter region was determined by using primers based on the bovine Mx2 promoter region disclosing 893-bp, with 56 substitutions, two insertions, 9 and 1 nt at two different sites. A functional analysis of the putative ISRE indicated that ISRE played a synergetic role in the activation of bovine Mx2 gene transcription.

Conclusion

Bovine and water buffalo Mx2 promoter region was identified disclosing, the conserved ISRE, located in the proximal end of the promoter region like other members of the antiviral family, suggesting functional activity under interferon stimulation.

Microevolution of bank voles (Myodes glareolus) at neutral and immune-related genes during multiannual dynamic cycles: Consequences for Puumala hantavirus epidemiology

Understanding how host dynamics, including variations of population size and dispersal, may affect the epidemiology of infectious diseases through ecological and evolutionary processes is an active research area. Here we focus on a bank vole (Myodes glareolus) metapopulation surveyed in Finland between 2005 and 2009. Bank vole is the reservoir of Puumala hantavirus (PUUV), the agent of nephropathia epidemica (NE, a mild form of hemorrhagic fever with renal symptom) in humans. M. glareolus populations experience multiannual density fluctuations that may influence the level of genetic diversity maintained in bank voles, PUUV prevalence and NE occurrence. We examine bank vole metapopulation genetics at presumably neutral markers and immune-related genes involved in susceptibility to PUUV (Tnf-promoter, Tlr4, Tlr7 and Mx2 gene) to investigate the links between population dynamics, microevolutionary processes and PUUV epidemiology. We show that genetic drift slightly and transiently affects neutral and adaptive genetic variability within the metapopulation. Gene flow seems to counterbalance its effects during the multiannual density fluctuations. The low abundance phase may therefore be too short to impact genetic variation in the host, and consequently viral genetic diversity. Environmental heterogeneity does not seem to affect vole gene flow, which might explain the absence of spatial structure previously detected in PUUV in this area. Besides, our results suggest the role of vole dispersal on PUUV circulation through sex-specific and density-dependent movements. We find little evidence of selection acting on immune-related genes within this metapopulation. Footprint of positive selection is detected at Tlr-4 gene in 2008 only. We observe marginally significant associations between Mx2 genotype and PUUV genogroups. These results show that neutral processes seem to be the main factors affecting the evolution of these immune-related genes at a contemporary scale, although the relative effects of neutral and adaptive forces could vary temporally with density fluctuations. Immune related gene polymorphism may in turn partly influence PUUV epidemiology in this metapopulation.

Atlantic salmon populations reveal adaptive divergence of immune related genes - a duplicated genome under selection

Background

Populations of Atlantic salmon display highly significant genetic differences with unresolved molecular basis. These differences may result from separate postglacial colonization patterns, diversifying natural selection and adaptation, or a combination. Adaptation could be influenced or even facilitated by the recent whole genome duplication in the salmonid lineage which resulted in a partly tetraploid species with duplicated genes and regions.

Results

In order to elucidate the genes and genomic regions underlying the genetic differences, we conducted a genome wide association study using whole genome resequencing data from eight populations from Northern and Southern Norway. From a total of ~4.5 million sequencing-derived SNPs, more than 10 % showed significant differentiation between populations from these two regions and ten selective sweeps on chromosomes 5, 10, 11, 13–15, 21, 24 and 25 were identified. These comprised 59 genes, of which 15 had one or more differentiated missense mutation. Our analysis showed that most sweeps have paralogous regions in the partially tetraploid genome, each lacking the high number of significant SNPs found in the sweeps. The most significant sweep was found on Chr 25 and carried several missense mutations in the antiviral mx genes, suggesting that these populations have experienced differing viral pressures. Interestingly the second most significant sweep, found on Chr 5, contains two genes involved in the NF-KB pathway (nkap and nkrf), which is also a known pathogen target that controls a large number of processes in animals.

Conclusion

Our results show that natural selection acting on immune related genes has contributed to genetic divergence between salmon populations in Norway. The differences between populations may have been facilitated by the plasticity of the salmon genome. The observed signatures of selection in duplicated genomic regions suggest that the recently duplicated genome has provided raw material for evolutionary adaptation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2867-z) contains supplementary material, which is available to authorized users.

Expression of Mx Protein and Interferon-α in Pigs Experimentally Infected with Swine Influenza Virus

Expression of Mx protein and interferon-α (IFN-α) was examined by immunohistochemistry in pigs experimentally infected with swine influenza virus. In infected pigs euthanatized at 1 day postinoculation (dpi), the lumen of bronchioles were filled with large numbers of mononuclear cells, small numbers of neutrophils, sloughing epithelial cells, and proteinaceous fluid. Lesions at 3 and 5 dpi were similar but less severe. Alveolar spaces were filled with neutrophils. By 7 and 10 dpi, microscopic lesions were resolved. The immunohistochemical signals for Mx protein and IFN-α antigen were confined to cells in areas that had hybridization signal for swine influenza virus. In situ hybridization and immunohistochemistry of serial sections of lung indicated that areas containing numerous swine influenza virus RNA-positive cells also have numerous Mx and IFN-α antigen-positive cells. Mean immunohistochemical scores for Mx protein-positive cells were correlated with mean immunohistochemical scores for IFN-α antigen-positive cells ( rs = 0.8799, p < 0.05). These results indicated that Mx protein and IFN-α antigen were expressed in the lung from pigs experimentally infected with swine influenza virus, but their biological functions remain to be examined.

Pathogenicity of Genetically Similar, H5N1 Highly Pathogenic Avian Influenza Virus Strains in Chicken and the Differences in Sensitivity among Different Chicken Breeds

Differences in the pathogenicity of genetically closely related H5N1 highly pathogenic avian influenza viruses (HPAIVs) were evaluated in White Leghorn chickens. These viruses varied in the clinical symptoms they induced, including lethality, virus shedding, and replication in host tissues. A comparison of the host responses in the lung, brain, and spleen suggested that the differences in viral replication efficiency were related to the host cytokine response at the early phase of infection, especially variations in the proinflammatory cytokine IL-6. Based on these findings, we inoculated the virus that showed the mildest pathogenicity among the five tested, A/pigeon/Thailand/VSMU-7-NPT/2004, into four breeds of Thai indigenous chicken, Phadu-Hung-Dang (PHD), Chee, Dang, and Luang-Hung-Khao (LHK), to explore effects of genetic background on host response. Among these breeds, Chee, Dang, and LHK showed significantly longer survival times than White Leghorns. Virus shedding from dead Thai indigenous chickens was significantly lower than that from White Leghorns. Although polymorphisms were observed in the Mx and MHC class I genes, there was no significant association between the polymorphisms in these loci and resistance to HPAIV.

Genome-wide transcriptome analysis of hypothalamus in rats with inherited stress-induced arterial hypertension

Background

The hypothalamus has an important role in the onset and maintenance of hypertension and stress responses. Rats with inherited stress-induced arterial hypertension (ISIAH), reproducing the human stress-sensitive hypertensive state with predominant involvement of the neuroendocrine hypothalamic-pituitary-adrenal and sympathoadrenal axes, were used for analysis of the hypothalamus transcriptome.

Results

RNA-seq analysis revealed 139 genes differentially expressed in the hypothalami of hypertensive ISIAH and normotensive Wistar Albino Glaxo (WAG) rats. According to the annotation in databases, 18 of the differentially expressed genes (DEGs) were associated with arterial hypertension. The Gene Ontology (GO) functional annotation showed that these genes were related to different biological processes that may contribute to the hypertension development in the ISIAH rats. The most significantly affected processes were the following: regulation of hormone levels, immune system process, regulation of response to stimulus, blood circulation, response to stress, response to hormone stimulus, transport, metabolic processes, and endocrine system development. The most significantly affected metabolic pathways were those associated with the function of the immune system and cell adhesion molecules and the metabolism of retinol and arachidonic acid. Of the top 40 DEGs making the greatest contribution to the interstrain differences, there were 3 genes (Ephx2, Cst3 and Ltbp2) associated with hypertension that were considered to be suitable for further studies as potential targets for the stress-sensitive hypertension therapy. Seven DEGs were found to be common between hypothalamic transcriptomes of ISIAH rats and Schlager mice with established neurogenic hypertension.

Conclusions

The results of this study revealed multiple DEGs and possible mechanisms specifying the hypothalamic function in the hypertensive ISIAH rats. These results provide a basis for further investigation of the signalling mechanisms that affect hypothalamic output related to stress-sensitive hypertension development.

Electronic supplementary material

The online version of this article (doi:10.1186/s12863-015-0307-8) contains supplementary material, which is available to authorized users.

Apoptotic Epitope-Specific CD8+ T Cells and Interferon Signaling Intersect in Chronic Hepatitis C Virus Infection

CD8(+) T cells specific to caspase-cleaved antigens derived from apoptotic T cells represent a principal player in chronic immune activation. Here, we found that both apoptotic epitope-specific and hepatitis C virus (HCV)-specific CD8(+) T cells were mostly confined within the effector memory (EM) or terminally differentiated EM CD45RA(+) cell subsets expressing a dysfunctional T-helper 1-like signature program in chronic HCV infection. However, apoptotic epitope-specific CD8(+) T cells produced tumor necrosis factor α and interleukin 2 at the intrahepatic level significantly more than HCV-specific CD8(+) T cells, despite both populations expressing high levels of programmed death 1 receptor. Contextually, only apoptotic epitope-specific CD8(+) T cells correlated with both interferon-stimulated gene levels in T cells and hepatic fibrosis score. Together, these data suggest that, compared with HCV-specific CD8(+) T cells, apoptotic epitope-specific CD8(+) T cells can better sustain chronic immune activation, owing to their capacity to produce tumor necrosis factor α, and exhibit greater resistance to inhibitory signals during chronic HCV infection.

Association of Myxovirus Resistance Gene Promoter Polymorphism with Response to Combined Interferon Treatment and Progression of Liver Disease in Chronic HCV Egyptian Patients

To evaluate the frequency of single-nucleotide polymorphism at the -88 myxovirus resistance (MxA) gene promoter region in relation to the status of hepatitis C virus (HCV) progression and response to combined interferon (IFN) in chronic HCV Egyptian patients. One hundred ten subjects were enrolled in the study; 60 HCV genotype 4-infected patients who underwent combined IFN therapy and 50 healthy individuals. All subjects were genotyped for -88 MxA polymorphism by the restriction fragment length polymorphism technique. There was an increasing trend of response to combined IFN treatment as 34.9% of GG, 64.3% of GT, and 66.7% of TT genotypes were sustained responders (P=0.05). The T allele was significantly affecting the response rate more than G allele (P=0.032). Moreover, the hepatic fibrosis score and hepatitis activity were higher in GG genotypes compared with the GT and TT genotypes. The multivariate analysis showed that the MxA GG genotype was an independent factor increasing the no response to IFN therapy (P=0.04, odds ratio [OR] 3.822, 95% confidence interval [CI] 1.056-11.092), also MxA G allele (P=0.0372, OR 2.905, 95% CI 1.066-7.919). MxA -88 polymorphism might be a potential biomarker to predict response to IFN and disease progression in chronic HCV-infected patients.

Production of transgenic pigs over-expressing the antiviral gene Mx1

The myxovirus resistance gene (Mx1) has a broad spectrum of antiviral activities. It is therefore an interesting candidate gene to improve disease resistance in farm animals. In this study, we report the use of somatic cell nuclear transfer (SCNT) to produce transgenic pigs over-expressing the Mx1 gene. These transgenic pigs express approximately 15–25 times more Mx1 mRNA than non-transgenic pigs, and the protein level of Mx1 was also markedly enhanced. We challenged fibroblast cells isolated from the ear skin of transgenic and control pigs with influenza A virus and classical swine fever virus (CFSV). Indirect immunofluorescence assay (IFA) revealed a profound decrease of influenza A proliferation in Mx1 transgenic cells. Growth kinetics showed an approximately 10-fold reduction of viral copies in the transgenic cells compared to non-transgenic controls. Additionally, we found that the Mx1 transgenic cells were more resistant to CSFV infection in comparison to non-transgenic cells. These results demonstrate that the Mx1 transgene can protect against viral infection in cells of transgenic pigs and indicate that the Mx1 transgene can be harnessed to develop disease-resistant pigs.

Diversity of interferon inducible Mx gene in horses and association of variations with susceptibility vis-à-vis resistance against equine influenza infection

Equine influenza (EI) is primarily an infection of the upper respiratory tract and is one of the major infectious respiratory diseases of economic importance in equines. Re-emergence of the disease, species jumping by H3N8 virus in canines and possible threat of human pandemic due to the unpredictable nature of the virus have necessitated research on devising strategies for preventing the disease. The myxovirus resistance protein (Mx) has been reported to confer resistance to Orthomyxo virus infection by modifying cellular functions needed along the viral replication pathway. Polymorphisms and differential antiviral activities of Mx gene have been reported in pigs and chicken. Here we report the diversity of Mx gene, its expression in response to stimulation with interferon (IFN) α/β and their association with EI resistance and susceptibility in Marwari horses. Blood samples were collected from horses declared positive for equine influenza and in contact animals with a history of no clinical signs. Mx gene was amplified by reverse transcription from total RNA isolated from peripheral blood mononuclear cells (PBMCs) stimulated with IFN α/β using gene specific primers. The amplified gene products from representative samples were cloned and sequenced. Nucleotide sequences and deduced amino acid sequences were analyzed. Out of a total 24 amino acids substitutions sorting intolerant from tolerant (SIFT) analysis predicted 13 substitutions with functional consequences. Five substitutions (V67A, W123L, E346Y, N347Y, S689N) were observed only in resistant animals. Evolutionary distances based on nucleotide sequences with in equines ranged between 0.3-2.0% and 20-24% with other species. On phylogenetic analysis all equine sequences clustered together while other species formed separate clades.

Effects of cortisol on the intestinal mucosal immune response during cohabitant challenge with IPNV in Atlantic salmon (Salmo salar)

Infectious pancreatic necrosis virus (IPNV) causes high incidence of disease in salmonids during the first period after SW transfer. During this period as well as during periods of stress, cortisol levels increase and indications of a relationship between IPNV susceptibility and cortisol have been suggested. The intestine is an entry route and a target tissue for IPNV displaying severe enteritis and sloughing of the mucosa in infected fish. The mechanisms behind effects of the virus on the intestinal tissue and the impact of cortisol on the effect remain unclear. In the present study, Atlantic salmon post smolts treated with or without slow release cortisol implants were subjected to a cohabitant IPNV challenge. Analysis of genes and proteins related to the innate and acquired immune responses against virus was performed 6 days post-challenge using qPCR and immunohistochemistry. An increased mRNA expression of anti-viral cytokine interferon type I was observed in the proximal intestine and head kidney as a response to the viral challenge and this effect was suppressed by cortisol. No effect was seen in the distal intestine. T-cell marker CD3 as well as MHC-I in both intestinal regions and in the head kidney was down regulated at the mRNA level. Number of CD8α lymphocytes decreased in the proximal intestine in response to cortisol. On the other hand, mRNA expression of Mx and IL-1β increased in the proximal intestine and head kidney in IPNV challenged fish in the presence of cortisol suggesting that the immune activation shifts in timing and response pathway during simulated stress. The present study clearly demonstrates that IPNV infection results in a differentiated epithelial immune response in the different intestinal regions of the Atlantic salmon. It also reveals that the epithelial immune response differs from the systemic, but that both are modulated by the stress hormone cortisol.

Innate immune responses of salmonid fish to viral infections

Viruses are the most serious pathogenic threat to the production of the main aquacultured salmonid species the rainbow trout Oncorhynchus mykiss and the Atlantic salmon Salmo salar. The viral diseases Infectious Pancreatic Necrosis (IPN), Pancreatic Disease (PD), Infectious Haemorrhagic Necrosis (IHN), Viral Haemorrhagic Septicaemia (VHS), and Infectious Salmon Anaemia (ISA) cause massive economic losses to the global salmonid aquaculture industry every year. To date, no solution exists to treat livestock affected by a viral disease and only a small number of efficient vaccines are available to prevent infection. As a consequence, understanding the host immune response against viruses in these fish species is critical to develop prophylactic and preventive control measures. The innate immune response represents an important part of the host defence mechanism preventing viral replication after infection. It is a fast acting response designed to inhibit virus propagation immediately within the host, allowing for the adaptive specific immunity to develop. It has cellular and humoral components which act in synergy. This review will cover inflammation responses, the cell types involved, apoptosis, antimicrobial peptides. Particular attention will be given to the type I interferon system as the major player in the innate antiviral defence mechanism of salmonids. Viral evasion strategies will also be discussed.

Identification, expression profiling of a grass carp TLR8 and its inhibition leading to the resistance to reovirus in CIK cells

TLR8 (toll-like receptor 8), a homolog of TLR3, TLR7 and TLR9 as prototypical intracellular members of TLR family, is generally associated with sensing single stranded RNA and plays a pivotal role in antiviral immune response. In this study, a TLR8 gene from grass carp Ctenopharyngodon idella (designated as CiTLR8) was obtained and characterized. The full-length cDNA of CiTLR8 was of 3766 bp. The open reading frame was of 3072 bp and encoded a polypeptide of 1023 amino acids, including seventeen LRR (leucine-rich repeat) motifs, one transmembrane domain and one TIR (toll/interleukin-1 receptor) domain. A single intron with the size of 839 bp was found on the neck of start codon (ATG). CiTLR8 mRNA was ubiquitously expressed in the 15 tested tissues and the expression level in gas bladder, spleen, brain, hindgut and trunk kidney tissues was high. Besides, the CiTLR8 expression in spleen and head kidney was significantly up-regulated and reached peak at 24 h post-injection of grass carp reovirus (GCRV). CiTLR8 transcription reached peak at 8 h and then declined below the normal level post-GCRV infection in the C. idella kidney (CIK) cell line; and it was rapidly and significantly down-regulated by the stimulation of the synthetic double-stranded RNA polyriboinosinic-polyribocytidylic acid sodium salt (poly I:C) in CIK cells in a dose and time-dependent manner. The inhibitor expression vectors were constructed and transfected into CIK cell line to obtain stably expressing shRNA targeting TLR8. In CiTLR8-knockdown cells, CiTLR7 transcript weakly increased, CiIFN-I mRNA was significantly down-regulated, and the expression of CiMyD88, CiIRF7 and CiMx1 scarcely changed. Post poly I:C stimulation, CiTLR8, CiTLR7 and CiMyD88 transcripts significantly increased, CiIRF7 was down-regulated after an initial phase of increase, and CiIFN-I and CiMx1 transcripts were up-regulated. After GCRV infection, the transcripts of CiTLR8, CiTLR7, CiMyD88 and CiIRF7 were up-regulated, but CiIFN-I and CiMx1 transcripts were inhibited. Nevertheless, cells transfected with pshTLR8 vectors had strong resistance against GCRV injection, suggesting CiTLR8 might play a negative role in antiviral immune response. These results collectively suggested that CiTLR8 was a novel member of TLR gene family, engaging in antiviral innate immune defense in C. idella, which laid a foundation for the further mechanism research of TLR8 in fishes.

Characterization of four Mx isoforms in the European eel, Anguilla anguilla

Mx protein is known to play an important role in vertebrate immune response to viral infection. In this study, cDNA sequences of four Mx isoforms, designated as MxA, B, C and D were characterized in the European eel, Anguilla anguilla. These sequences contained an open reading frame of 1899, 1896, 1866, 1779 bp, flanked by 95, 53, 138, 69 bp of 5' untranslated region and 389, 241, 136, 124 bp of 3' untranslated region, respectively. A phylogenetic tree constructed with Mx peptide sequences from vertebrates revealed that MxA, C and D in the European eel formed into a clade containing zebrafish MxA and MxB and Mx proteins in other teleosts, whereas MxB in the eel was clustered together with zebrafish MxD, MxG and MxF. The transcription level of all Mx isoforms increased in a poly I:C dose-dependent manner in peripheral blood leukocytes of eels, as revealed by real-time PCR. A further experiment was conducted to reveal the temporal change in expression of these isoforms in various organs/tissues following poly I:C stimulation, and significant increase in expression was observed at various degrees in different organs or in different sampling occasions within the 12 h experimental period. In particular, MxA had the highest level of increase, while MxB had the lowest; and three isoforms, MxA, MxB and MxD had the highest increase in intestine, while the highest increase of MxC expression was observed in liver. These four isoforms of eel Mx are thus expressed differentially, and further work is certainly required to clarify the activity of promoter elements and antiviral activity of these Mx isoforms.

The major fimbrial subunit protein of Edwardsiella tarda: vaccine potential, adjuvant effect, and involvement in host infection

Edwardsiella tarda is a Gram-negative bacterium that is reckoned one of the most severe fish pathogens. In this study, we analyzed the biological properties of the E. tarda major fimbrial subunit protein, FimA. We found that mutation of fimA resulted in defective biofilm growth, attenuated infectivity against host cells, and impaired ability to disseminate into and colonize host tissues following experimental infection. When used as a subunit vaccine, recombinant FimA (rFimA) elicited a high level of protection in turbot (Scophthalmus maximus) against lethal E. tarda challenge. Immunological analysis showed that rFimA vaccination induced production of specific serum antibodies that bound to live E. tarda via interaction with the FimA on bacterial cells, and that antibody-E. tarda interaction blocked bacterial infection. Furthermore, passive immunization of turbot with anti-rFimA serum before E. tarda infection reduced bacterial loads in fish tissues to significant extents. To examine the adjuvant potential of FimA, turbot were vaccinated with rVhhP2, a protective Vibrio harveyi antigen, in the presence or absence of rFimA. Subsequent analysis showed that the presence of rFimA significantly augmented the protectivity of rVhhP2. ELISA and quantitative real time RT-PCR showed that rFimA significantly increased rVhhP2-specific serum antibody production and enhanced the expression of immune relevant genes. Taken together, these results indicate that FimA is a virulence-associated protein that possesses vaccine as well as adjuvant potentials, and that the immunoprotectivity of FimA is most likely due to its ability to induce specific immune response that inhibits E. tarda infection.

Pathogen-driven adaptive evolution of myxovirus resistance (Mx) genes in fishes

Myxovirus resistance (Mx) proteins, which belong to the dynamin super-family, are known to inhibit RNA viral replication in a wide range of taxonomic groups, including fishes. Given their crucial role in host immune defense, the key amino acid residues in the GTP effector domain (GED) near the C-terminus are expected to evolve adaptively in order to protect the host against invading viral pathogens. The present study reveals the role of recombination and positive selection in the evolution of Mx proteins in fishes. While the GTP-binding domain in the N-terminal domain has experienced purifying selection, several amino acid residues in GED have evolved under positive selection, thus indicating adaptive evolution. Given the antiviral activity of GED, the adaptive evolutionary changes that were observed in this region are therefore predicted to be pathogen-driven.

Antiviral specificity of the Solea senegalensis Mx protein constitutively expressed in CHSE-214 cells

Interferons play a key role in fish resistance to viral infections by inducing the expression of antiviral proteins, such as Mx. The aim of the present study was to test the antiviral activity of the Senegalese sole Mx protein (SsMx) against RNA and DNA viruses pathogenic to fish, i.e. the infectious pancreatic necrosis virus (IPNV, dsRNA), the viral haemorrhagic septicaemia virus (VHSV, ssRNA), and the European sheatfish virus (ESV, dsDNA), using a CHSE-214 cell clone expressing this antiviral protein. A strong inhibition of IPNV and VHSV replication was recorded in SsMx-expressing cells, as has been shown by the virus yield reduction and the decrease in the synthesis of the viral RNA encoding the polyprotein (for IPNV) and the nucleoprotein (for VHSV). The titres of these viruses replicating on SsMx-expressing cells were 100 times lower than those recorded on non-transfected cells. In contrast, SsMx did not inhibit ESV replication since no significant differences were observed regarding the virus yield or the major capsid protein gene transcription in transfected and non-transfected cells.

Protective roles of grass carp Ctenopharyngodon idella Mx isoforms against grass carp reovirus

Background

Myxovirus resistance (Mx) proteins are crucial effectors of the innate antiviral response against a wide range of viruses, mediated by the type I interferon (IFN-I) signaling pathway. However, the antiviral activity of Mx proteins is diverse and complicated in different species.

Methodology/Principal Findings

In the current study, two novel Mx genes (CiMx1 and CiMx3) were identified in grass carp (Ctenopharyngodon idella). CiMx1 and CiMx3 proteins exhibit high sequence identity (92.1%), and low identity with CiMx2 (49.2% and 49.5%, respectively) from the GenBank database. The predicted three-dimensional (3D) structures are distinct among the three isoforms. mRNA instability motifs also display significant differences in the three genes. The spatial and temporal expression profiles of three C. idella Mx genes and the IFN-I gene were investigated by real-time fluorescence quantitative RT-PCR (qRT-PCR) following infection with grass carp reovirus (GCRV) in vivo and in vitro. The results demonstrated that all the four genes were implicated in the anti-GCRV immune response, that mRNA expression of Mx genes might be independent of IFN-I, and that CIK cells are suitable for antiviral studies. By comparing expression patterns following GCRV challenge or poly(I:C) treatment, it was observed that GCRV blocks mRNA expression of the four genes. To determine the functions of Mx genes, three CiMx cDNAs were cloned into expression vectors and utilized for transfection of CIK cells. The protection conferred by each recombinant CiMx protein against GCRV infection was evaluated. Antiviral activity against GCRV was demonstrated by reduced cytopathic effect, lower virus titer and lower levels of expressed viral transcripts. The transcription of IFN-I gene was also monitored.

Conclusions/Significance

The results indicate all three Mx genes can suppress replication of grass carp reovirus and over-expression of Mx genes mediate feedback inhibition of the IFN-I gene.

Microfluidic high-throughput RT-qPCR measurements of the immune response of primary bovine mammary epithelial cells cultured from milk to mastitis pathogens

Bovine mastitis, the inflammation of the udder, is a major problem for the dairy industry and for the welfare of the animals. To better understand this disease, and to implement two special techniques for studying mammary gland immunity in vitro, we measured the innate immune response of primary bovine mammary epithelial cells (pbMEC) from six Brown Swiss cows after stimulation with the heat-inactivated mastitis pathogens, Escherichia coli 1303 and Staphylococcus aureus 1027. The cells were extracted and cultivated from milk instead of udder tissue, which is usually done. The advantages of this technique are non-invasiveness and less contamination by fibroblasts. For the first time, pbMEC gene expression (GE) was measured with a microfluidic high-throughput real-time reverse transcription-quantitative PCR platform, the BioMark HD™ system from Fluidigm. In addition to the physiological analysis, the precision and suitability of this method was evaluated in a large data set. The mean coefficient of variance (± s.e.) between repeated chips was 4.3 ± 0.4% for highly expressed and 3.3 ± 0.4% for lowly expressed genes. Quantitative PCR (qPCR) replicate deviations were smaller than the cell culture replicate deviations, indicating that biological and cell culture differences could be distinguished from the background noise. Twenty-two genes (complement system, chemokines, inflammatory cytokines, antimicrobial peptides, acute phase response and toll-like receptor signalling) were differentially expressed (P < 0.05) with E. coli. The most upregulated gene was the acute phase protein serum amyloid A3 with 618-time fold. S. aureus slightly induced CCL5, IL10, TLR4 and S100A12 expression and failed to elicit a distinct overall innate immune response. We showed that, with this milk-derived pbMEC culture and the high-throughput qPCR technique, it is possible to obtain similar results in pbMEC expression as with conventional PCR and with satisfactory precision so that it can be applied in future GE studies in pbMEC.

Interferon-inducible protein Mx1 inhibits influenza virus by interfering with functional viral ribonucleoprotein complex assembly

Mx1 is a GTPase that is part of the antiviral response induced by type I and type III interferons in the infected host. It inhibits influenza virus infection by blocking viral transcription and replication, but the molecular mechanism is not known. Polymerase basic protein 2 (PB2) and nucleoprotein (NP) were suggested to be the possible target of Mx1, but a direct interaction between Mx1 and any of the viral proteins has not been reported. We investigated the interplay between Mx1, NP, and PB2 to identify the mechanism of Mx1's antiviral activity. We found that Mx1 inhibits the PB2-NP interaction, and the strength of this inhibition correlated with a decrease in viral polymerase activity. Inhibition of the PB2-NP interaction is an active process requiring enzymatically active Mx1. We also demonstrate that Mx1 interacts with the viral proteins NP and PB2, which indicates that Mx1 protein has a direct effect on the viral ribonucleoprotein complex. In a minireplicon system, avian-like NP from swine virus isolates was more sensitive to inhibition by murine Mx1 than NP from human influenza A virus isolates. Likewise, murine Mx1 displaced avian NP from the viral ribonucleoprotein complex more easily than human NP. The stronger resistance of the A/H1N1 pandemic 2009 virus against Mx1 also correlated with reduced inhibition of the PB2-NP interaction. Our findings support a model in which Mx1 interacts with the influenza ribonucleoprotein complex and interferes with its assembly by disturbing the PB2-NP interaction.

Functional characterization of new allelic polymorphisms identified in the promoter region of the human MxA gene

The Mx proteins are high-molecular-weight dynamin-like proteins whose expression depends strictly on type-I and type-III interferons (IFN). Some isoforms are able to inhibit the life cycle of one or several viruses and are thus components of innate immune response. The human MxA protein displays the broadest antiviral spectrum which makes it appear as a key antiviral effector of innate immunity. Allelic polymorphisms located in the MxA gene promoter can be expected to affect the magnitude of MxA mRNA transcription in response to IFNs and therefore to alter the severity of viral diseases in humans. Here, three single nucleotide polymorphism sites (-309, -101 and +20) were examined for their ability to alter MxA gene promoter-driven reporter expression. We show that, besides the previously reported role of -123A and -88T, the presence of -101G is equally important. Moreover, when a promoter construct carries these three critical nucleotides, a first additional positive effect is conferred by a C at position -309 and, in this latter case, a second additional effect is produced by a A at position +20. This finding is clinically useful to improve prediction of IFN-responsiveness in patients not only with viral diseases for which type-I IFN therapy is used.

Detection of new biallelic polymorphisms in the human MxA gene

The interferon-inducible human MxA protein plays an important role in innate defense against an array of viruses. One might expect allelic diversity at the MxA locus to influence the timing and magnitude of its expression or even the range of viruses whose biological cycle is inhibited by the encoded product. Here we have collected 267 samples of genomic DNA from three distinct populations (European, Asian, and African) and have systematically sequenced the promoter of the MxA gene and its 17 exons in order to inventory its allelic variants. Eighteen single-nucleotide polymorphisms were detected, four of which had never been identified before. Two of these, located in the promoter (at positions -309 and -101 respectively), might affect the MxA expression pattern. The other two result in substitutions (Gly255Glu and Val268Met) in the protein's N-terminal region that might directly affect its antiviral function.

Human/bovine chimeric MxA-like GTPases reveal a contribution of N-terminal domains to the magnitude of anti-influenza A activity

Type I interferons (IFN-α/β) provide powerful and universal innate intracellular defense mechanisms against viruses. Among the antiviral effectors induced by IFN-α/β, Mx proteins of some species appear as key components of defense against influenza A viruses. The body of work published to date suggests that to exert anti-influenza activity, an Mx protein should possess a GTP-binding site, structural bases allowing multimerisation, and a specific C-terminal GTPase effector domain (GED). Both the human MxA and bovine Mx1 proteins meet these minimal requirements, but the bovine protein is more active against influenza viruses. Here, we measured the anti-influenza activity exerted by 2 human/bovine chimeric Mx proteins. We show that substituting the bovine GED for the human one in human MxA does not affect the magnitude of anti-influenza activity. Strikingly, however, substituting the human GED for the bovine one in bovine Mx1 yields a chimeric protein with a much higher anti-influenza activity than the human protein. We conclude, in contradiction to the hypothesis currently in vogue in the literature, that the GED is not the sole determinant controlling the magnitude of the anti-influenza activity exercised by an Mx protein that can bind GTP and multimerise. Our results suggest that 1 or several motifs that remain to be discovered, located N-terminally with regard to the GED, may interact with a viral component or a cellular factor so as to alter the viral cycle. Identifying, in the N-terminal portion of bovine Mx1, the motif(s) responsible for its higher anti-influenza activity could contribute to the development of new anti-influenza molecules.

Enterovirus 71 disrupts interferon signaling by reducing the level of interferon receptor 1

The recent outbreak of enterovirus 71 (EV71) infected millions of children and caused over 1,000 deaths. To date, neither an effective vaccine nor antiviral treatment is available for EV71 infection. Interferons (IFNs) have been successfully applied to treat patients with hepatitis B and C viral infections for decades but have failed to treat EV71 infections. Here, we provide the evidence that EV71 antagonizes type I IFN signaling by reducing the level of interferon receptor 1 (IFNAR1). We show that the host cells could sense EV71 infection and stimulate IFN-β production. However, the induction of downstream IFN-stimulated genes is inhibited by EV71. Also, only a slight interferon response and antiviral effects could be detected in cells treated with recombinant type I IFNs after EV71 infection. Further studies reveal that EV71 blocks the IFN-mediated phosphorylation of STAT1, STAT2, Jak1, and Tyk2 by reducing IFNAR1. Finally, we identified the 2A protease encoded by EV71 as an antagonist of IFNs and show that the protease activity is required for reducing IFNAR1 levels. Taken together, our study for the first time uncovers a mechanism used by EV71 to antagonize type I IFN signaling and provides new targets for future antiviral strategies.