Abstract: Interferon (IFN) response is the first line of host defense against virus infection The recent years have witnessed tremendous progress in understanding of fish IFN antiviral response Varied number of IFN genes has been identified in different fish species but obviously, they do not show a one-to-one orthologous relationship with mammalian IFN homologs These genes are divided into two groups with different abilities to induce downstream gene expression through binding to different receptor complexes Consistently, some fish IFN-stimulated genes such as Mx and PKR have been confirmed for their antiviral effects In this review, we focus on how fish cells respond to IFNs and how fish IFNs are triggered through TLR pathway and RLR pathway We highlight the roles of IRF3 and IRF7 in activation of fish IFN response In addition, the unique mechanisms underlying IRF3/7-dependent fish IFN response and auto-regulation of fish IFN gene expression are discussed

Abstract: Innate immunity is the first line of defense against viral infection, and in turn, viruses have evolved to evade host immune surveillance. As a result, viruses may persist in host and develop chronic infections. Type I interferons (IFN-α/β) are among the most potent antiviral cytokines triggered by viral infections. Porcine reproductive and respiratory syndrome (PRRS) is a disease of pigs that is characterized by negligible induction of type I IFNs and viral persistence for an extended period. For IFN production, RIG-I/MDA5 and JAK-STAT pathways are two major signaling pathways, and recent studies indicate that PRRS virus is armed to modulate type I IFN responses during infection. This review describes the viral strategies for modulation of type I IFN responses. At least three non-structural proteins (Nsp1, Nsp2, and Nsp11) and a structural protein (N nucleocapsid protein) have been identified and characterized to play roles in the IFN suppression and NF-κB pathways. Nsp's are early proteins while N is a late protein, suggesting that additional signaling pathways may be involved in addition to the IFN pathway. The understanding of molecular bases for virus-mediated modulation of host innate immune signaling will help us design new generation vaccines and control PRRS.

Abstract: Toll-like receptor 3 (TLR3) is a pattern-recognition receptor known to initiate an innate immune response when stimulated by double-stranded RNA (dsRNA). Components of TLR3 signaling, including TIR domain-containing adapter inducing IFN-α (TRIF), have been demonstrated to contribute to dsRNA-induced cell death through caspase-8 and receptor interacting protein (RIP)1 in various human cancer cells. We provide here a detailed analysis of the caspase-8 activating machinery triggered in response to Poly(I:C) dsRNA. Engagement of TLR3 by dsRNA in both type I and type II lung cancer cells induces the formation of an atypical caspase-8-containing complex that is devoid of classical death receptors of the TNFR superfamily, but instead is physically associated to TLR3. The recruitment of caspase-8 to TLR3 requires RIP1, and is negatively modulated by cellular inhibitor of apoptosis protein (cIAP)2–TNF receptor-associated factor (TRAF)2–TNFR-associated death domain (TRADD) ubiquitin ligase complex, which regulates RIP1 ubiquitination. Intriguingly, unlike Fas- or TRAILR-dependent death signaling, caspase-8 recruitment and activation within the TLR3 death-signaling complex appears not to be stringently dependent on Fas-associated with death domain (FADD). Our findings uncover a novel aspect of the molecular mechanisms involved during apoptosis induced by the innate immune receptor TLR3 in cancer cells.

Abstract: Filoviruses, marburgvirus (MARV) and ebolavirus (EBOV), are causative agents of highly lethal hemorrhagic fever in humans. MARV and EBOV share a common genome organization but show important differences in replication complex formation, cell entry, host tropism, transcriptional regulation, and immune evasion. Multifunctional filoviral viral protein (VP) 35 proteins inhibit innate immune responses. Recent studies suggest double-stranded (ds)RNA sequestration is a potential mechanism that allows EBOV VP35 to antagonize retinoic-acid inducible gene-I (RIG-I) like receptors (RLRs) that are activated by viral pathogen–associated molecular patterns (PAMPs), such as double-strandedness and dsRNA blunt ends. Here, we show that MARV VP35 can inhibit IFN production at multiple steps in the signaling pathways downstream of RLRs. The crystal structure of MARV VP35 IID in complex with 18-bp dsRNA reveals that despite the similar protein fold as EBOV VP35 IID, MARV VP35 IID interacts with the dsRNA backbone and not with blunt ends. Functional studies show that MARV VP35 can inhibit dsRNA-dependent RLR activation and interferon (IFN) regulatory factor 3 (IRF3) phosphorylation by IFN kinases TRAF family member-associated NFkb activator (TANK) binding kinase-1 (TBK-1) and IFN kB kinase e (IKKe) in cell-based studies. We also show that MARV VP35 can only inhibit RIG-I and melanoma differentiation associated gene 5 (MDA5) activation by double strandedness of RNA PAMPs (coating backbone) but is unable to inhibit activation of RLRs by dsRNA blunt ends (end capping). In contrast, EBOV VP35 can inhibit activation by both PAMPs. Insights on differential PAMP recognition and inhibition of IFN induction by a similar filoviral VP35 fold, as shown here, reveal the structural and functional plasticity of a highly conserved virulence factor.

Abstract: Type 1 diabetes (T1D) is an autoimmune disease targeting pancreatic beta cells. Genome-wide association studies and gene expression analysis identified interferon (IFN)-driven gene networks as crucial pathways in the pathogenesis of T1D. IFNs are linked to the response to viral infections and might contribute to the initiation of the autoimmune process in T1D. We presently analyzed the role of ubiquitin-specific peptidase 18 (USP18), an interferon-stimulated gene 15-specific protease, on IFN-induced pancreatic beta cell inflammation and apoptosis. Our findings indicate that USP18 inhibition induces inflammation by increasing the STAT signaling and exacerbates IFN-induced beta cell apoptosis by the mitochondrial pathway of cell death. USP18 regulates activation of three BH3-only proteins, namely, DP5, Bim and PUMA in pancreatic beta cells, suggesting a direct link between regulators of the type I IFN signaling pathway and members of the BCL-2 family. USP18 depletion increases the expression of the T1D candidate gene MDA5, leading to an upregulation of double-stranded RNA-induced chemokine production. These data suggest a cross talk between the type I IFN signaling pathway and a candidate gene for T1D to increase pro-inflammatory responses in beta cells. The present study shows that USP18 is a key regulator of IFN signaling in beta cells and underlines the importance of this pathway in beta cell inflammation and death.

Abstract: With over one million copies, Alu elements are the most abundant repetitive elements in the human genome. When transcribed, interaction between two Alus that are in opposite orientation gives rise to double-stranded RNA (dsRNA). Although the presence of dsRNA in the cell was previously thought to only occur during viral infection, it is now known that cells express many endogenous small dsRNAs, such as short interfering RNA (siRNAs) and microRNA (miRNAs), which regulate gene expression. It is possible that long dsRNA structures formed from Alu elements influence gene expression. Here, we report that human mRNAs containing inverted Alu elements are present in the mammalian cytoplasm. The presence of these long intramolecular dsRNA structures within 3 0 -UTRs decreases translational efficiency, and although the structures undergo extensive editing in vivo, the effects on translation are independent of the presence of inosine. As inverted Alus are predicted to reside in >5% of human protein-coding genes, these intramolecular dsRNA structures are important regulators of gene expression.

Abstract: Type I interferon (IFN) induces the antiviral response in innate immunity. The type I IFN gene cloned from Japanese flounder ( Paralichthys olivaceus ) has a length of 1189 bp and consisting of 5 exons and 4 introns. In a phylogenetic tree of type I IFNs, Japanese flounder grouped with other Acanthopterygii. To gain insight into the transcriptional regulation of IFN gene, the 1.36 kb 5′-upstream region including numerous canonical motifs to bind transcription factors [for example, IFN regulatory factor (IRF)] was analyzed. In HINAE cells using a luciferase reporter assay, poly I:C-responsive transcriptional activity was found in the region from −634 to −179 bp. This region includes several IRF motifs. In the presence of poly I:C, overexpression of IRF3 and RLR strongly enhanced transcriptional activity. These results suggest that the transcriptional regulation of Japanese flounder type I IFN is regulated by IRF3 after triggering with dsRNA sensors.

Abstract: Retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs), such as RIG-I, melanoma differentiation-associated gene 5 (MDA5), and virus-induced signaling adaptor (VISA), are intracellular molecules that sense diverse viral RNAs and trigger immune responses In this study, we demonstrate that the ankyrin repeat protein ankrd17 interacts with RIG-I, MDA5, and VISA and upregulates RLR-mediated immune signaling Overexpression of ankrd17 enhances RLR-mediated activation of IRF-3 and NF-κB and upregulates the transcription of IFN-β It also promotes RLR signaling in response to poly (I:C), influenza virus RNA, and Sendai virus Consistently, knockdown of ankrd17 impairs RLR signaling Furthermore, we demonstrate that ankrd17 enhances the interaction of RIG-I and MDA5 with VISA; the ankyrin repeat domain of ankrd17 is required for its interaction with RIG-I as well as for its function in regulating the RLR pathway Taken together, our results indicate that ankrd17 is a positive regulator of the RLR signaling pathway

Abstract: Mesangial cells play an important role in inflammatory reactions in kidney. Although viral infections often trigger the worsening of chronic inflammatory renal diseases, the mechanisms are largely unknown. Melanoma differentiation-associated gene 5 (MDA5) is a member of RNA helicase family with a conserved Asp-Glu-x-His (DExH) box. In the present study, we examined the effect of polyinosinic-polycytidylic acid (poly IC), an authentic double-stranded RNA (dsRNA) that mimics viral dsRNAs, on MDA5 expression using primary culture of human mesangial cells. The cells were simply treated or transfected with poly IC; the former procedure is a model of cells exposed to viral dsRNA released from dying cells, and the latter is a model of entry of RNA virus into the cytoplasm. Expression levels of MDA5 mRNA in mesangial cells were increased about 70-100 fold in response to either treatment or transfection with poly IC. MDA5 protein expression was significantly induced as well. RNA interference experiments revealed that poly IC treatment induced MDA5 expression via Toll-like receptor 3 (TLR3) and interferon (IFN)-β, and that poly IC trasnfection induced MDA5 expression via another DExH box RNA helicase, retinoic acid-inducible gene-I (RIG-I), and IFN-β. Moreover, MDA5 induced by poly IC, in turn, increased the expression of a chemokine CXCL10. In addition, immunohistochemical staining demonstrated a high level of MDA5 expression in glomeruli, mainly in mesangial cells, of patients with severe lupus nephritis or proteinuric IgA nephropathy. MDA5 may be involved not only in physiological antiviral reactions but also in chronic inflammation in glomerular mesangial cells.

Abstract: Ovarian cancer is the most lethal gynecological cancer. Here we show that innate immune agonist, dsRNA, directly induces ovarian cancer cell death and identify biomarkers associated with responsiveness to this targeted treatment. Nuclear staining and MTT assays following dsRNA stimulation revealed two subpopulations, sensitive (OVCAR-3, CAOV-3; patient samples malignant 1 and 2) and resistant (DOV-13, SKOV-3). Microarray analysis identified 75 genes with differential expression that further delineated these two subpopulations. qPCR and immunoblot analyses showed increased dsRNA receptor expression after stimulation as compared to resistant and immortalized ovarian surface epithelial cells (e.g., 70-fold with malignant 2, 43-fold with OVCAR-3). Using agonists, antagonists, and shRNA-mediated knockdown of dsRNA receptors, we show that TLR3, RIG-I, and mda5 coordinated a caspase 8/9- and interferon-dependent cell death. In resistant cells, dsRNA receptor overexpression restored dsRNA sensitivity. When dsRNA was combined with carboplatin or paclitaxel, cell viability significantly decreased over individual treatments (1.5- to 7.5-fold). Isobologram analyses showed synergism in dsRNA combinations (CI=0.4–0.82) vs. an additive effect in carboplatin/paclitaxel treatment (CI=1.5–2). Our data identify a predictive marker, dsRNA receptor expression, to target dsRNA responsive populations and show that, in dsRNA-sensitive cells, dsRNA induces apoptosis and enhances the potency of cytotoxic chemotherapeutics.—Van, D. N., Roberts, C. F., Marion, J. D., Lepine, S., Harikumar, K. B., Schreiter, J., Dumur, C. I., Fang, X., Spiegel, S., Bell, J. K. Innate immune agonist, dsRNA, induces apoptosis in ovarian cancer cells and enhances the potency of cytotoxic chemotherapeutics.

Abstract: dsRNA is a common pathogen-associated molecular pattern that is recognized by cellular TLR3 and used by virus-infected cells to activate specific transcription factors and trigger induction of antiviral genes. In this article, we report a new branch of TLR3 signaling that does not lead to gene induction but affects many cellular properties, such as cell migration, adhesion, and proliferation. We demonstrated that the migration of multiple cell lineages was affected by dsRNA treatment or influenza virus infection in a TLR3-dependent fashion. Surprisingly, for this effect of TLR3 signaling, the adaptor proteins, TRIF and MyD88, were not required. The effects of the new pathway were mediated by the proto-oncoprotein c-Src, which bound to TLR3 after dsRNA stimulation of cells. The response was biphasic: upon dsRNA treatment, we observed an immediate increase in cell motility followed by its strong inhibition. Our results indicate that the first phase was mediated by dsRNA-induced phosphorylation and activation of Src, whereas the second phase resulted from the sequestration of activated Src in lipid rafts, thus decreasing its active cytoplasmic pool. As expected, two other functions of Src, its effect on cell adhesion and cell proliferation, were also inhibited by dsRNA treatment. These results demonstrate that activated TLR3 can engage Src to trigger multiple cellular effects and reveal a possible link between innate immune response and cell growth regulation. This study also provides a rare example of TLR-mediated cellular effects that do not require gene induction and the first example, to our knowledge, of an adaptor-independent effect of any TLR.

Abstract: Background: Retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs) had been demonstrated to prime interferon (IFN) response against viral infection via the conserved RLR signaling in fish, and a novel fish-specific gene, the grass carp reovirus (GCRV)-induced gene 2 (Gig2), had been suggested to play important role in host antiviral response. Methodology/Principal Findings: In this study, we cloned and characterized zebrafish Gig2 homolog (named Danio rerio Gig2-I, DreI), and revealed its antiviral role and expressional regulation signaling pathway. RT-PCR, Western blot and promoter activity assay indicate that DreI can be induced by poly I: C, spring viremia of carp virus (SVCV) and recombinant IFN (rIFN), showing that DreI is a typical ISG. Using the pivotal signaling molecules of RLR pathway, including RIG-I, MDA5 and IRF3 from crucian carp, it is found that DreI expression is regulated by RLR cascade and IRF3 plays an important role in this regulation. Furthermore, promoter mutation assay confirms that the IFN-stimulated regulatory elements (ISRE) in the 59 flanking region of DreI is essential for its induction. Finally, overexpression of DreI leads to establish a strong antiviral state against SVCV and Rana grylio virus (RGV) infection in EPC (Epithelioma papulosum cyprinid) cells. Conclusions/Significance: These data indicate that DreI is an antiviral protein, which is regulated by RLR signaling pathway.

Abstract: Background CD55 (decay-accelerating factor) is a complement-regulatory protein highly expressed on fibroblast-like synoviocytes (FLS). CD55 is also a ligand for CD97, an adhesion-type G protein-coupled receptor abundantly present on leukocytes. Little is known regarding the regulation of CD55 expression in FLS.

Abstract: Dicer-2 is a ribonuclease involved in the insect RNAi pathway. On attempting to knockdown Dicer-2 expression in the insect Blattella germanica by RNAi, we found that treatment with Dicer-2 dsRNA upregulated the targeted mRNA. This unexpected result was also observed after treating with a nucleopolyhedrovirus dsRNA. Experiments with this alien dsRNA showed an all-or-none response with a threshold for inducing Dicer-2 upregulation between 0.4 and 0.04 μg in terms of dsRNA concentration and between 50 and 20 bp in terms of dsRNA length. The response seems specific of dsRNA given that equivalent experiments carried out with dsDNA did not affect Dicer-2 expression. In insects, Dicer-2 is postulated to be a sensor of viral infections and a key antiviral defense element. The upregulation of Dicer-2 expression after dsRNA administration fits well with this sensor role, and the occurrence of this mechanism in B. germanica, a phylogenetically basal insect, suggests that sensing alien RNAs might be an ancestral function of Dicer-2 proteins.

Abstract: Background. Serine protease inhibitor B9 (serpinB9) protects against granzyme B-mediated apoptosis and could help to reduce tubular damage under inflammatory conditions like interstitial nephritis. Previously, we found that tubular serpinB9 expression was increased during subclinical rejection. Here, we studied the regulation of serpinB9 expression in tubular epithelial cells (TECs) under inflammatory conditions. Methods. SerpinB9 expression was analysed on messenger RNA (mRNA), and protein levels in primary human TECs were stimulated with various cytokines and pattern recognition receptor ligands and in kidney transplant biopsies obtained during different types of viral infection. Results. Of the inflammatory stimuli tested, only the double-stranded RNA (dsRNA) analogue poly(I:C) promoted serpinB9 mRNA and protein expression. We found that TECs express the viral dsRNA receptors Toll-like receptor 3 (TLR3), melanoma differentiation-associated gene 5 (MDA5) and retinoic acid-inducible gene-I (RIGI). dsRNA receptor ligands enhanced serpinB9 expression, which involved nuclear factor-kappaB (NF-κB) activation, did not require Type I interferon production and was a direct result of dsRNA receptor-induced gene transcription. In kidney transplants, serpinB9 transcription was increased during infection with cytomegalovirus, Epstein– Barr virus or BK virus compared to stable grafts. Immunohistochemistry showed that tubuli and lymphocytes expressed the inhibitor. Conclusion. SerpinB9 expression in human TECs is induced by triggering of the viral dsRNA sensors TLR3, MDA5 and RIG-I. Viral dsRNA may increase the threshold for granzyme B-mediated apoptosis in TECs via serpinB9 upregulation and thus help to protect the kidney against cytotoxic insults during viral infection.

Abstract: Cancer researchers have been looking for ways to harness the immune system and to reinstate immune surveillance, to kill cancer cells without collateral damage. Here we scan current approaches to targeting the immune system against cancer, and emphasize our own approach. We are using chemical vectors attached to a specific ligand, to introduce synthetic dsRNA, polyinosine/cytosine (polyIC), into tumors. The ligand binds to a receptor protein that is overexpressed on the surface of the tumor cells. Upon ligand binding, the receptor complex is internalized, introducing the polyIC into the cell. In this fashion a large amount of synthetic dsRNA can be internalized, leading to the activation of dsRNA-binding proteins, such as dsRNA dependent protein kinase (PKR), Toll-like receptor 3 (TLR3), retinoic acid-inducible gene I (RIG-1), and melanoma differentiation-associated gene 5 (MDA5). The simultaneous activation of these signaling proteins leads to the rapid demise of the targeted cell and to cytokine secretion. The cytokines lead to a strong bystander effect and to the recruitment of immune cells that converge upon the targeted cells. The bystander effects lead to the destruction of neighboring tumor cells not targeted themselves by the vector. Normal cells, being more robust than tumor cells, survive. This strategy has several advantages: (1) recruitment of the immune system is localized to the tumor. (2) The response is rapid, leading to fast tumor eradication. (3) The bystander effects lead to the eradication of tumor cells not harboring the target. (4) The multiplicity of pro-death signaling pathways elicited by PolyIC minimizes the likelihood of the emergence of resistance. In this chapter we focus on EGFR as the targeted receptor, which is overexpressed in many tumors. In principle, the strategy can be extended to other tumors that overexpress a protein that can be internalized by a ligand, which can be a small molecule, a single chain antibody, or an affibody.

Abstract: Background Upon viral recognition, innate and adaptive antiviral immune responses are initiated by genital epithelial cells (ECs) to eradicate or contain viral infection. Such responses, however, are often accompanied by inflammation that contributes to acquisition and progression of sexually transmitted infections (STIs). Hence, interventions/factors enhancing antiviral protection while reducing inflammation may prove beneficial in controlling the spread of STIs. Serine antiprotease trappin-2 (Tr) and its cleaved form, elafin (E), are alarm antimicrobials secreted by multiple cells, including genital epithelia. Methodology and Principal Findings We investigated whether and how each Tr and E (Tr/E) contribute to antiviral defenses against a synthetic mimic of viral dsRNA, polyinosine-polycytidylic acid (polyI∶C) and vesicular stomatitis virus. We show that delivery of a replication-deficient adenovector expressing Tr gene (Ad/Tr) to human endometrial epithelial cells, HEC-1A, resulted in secretion of functional Tr, whereas both Tr/E were detected in response to polyI∶C. Moreover, Tr/E were found to significantly reduce viral replication by either acting directly on virus or through enhancing polyI∶C-driven antiviral protection. The latter was associated with reduced levels of pro-inflammatory factors IL-8, IL-6, TNFα, lowered expression of RIG-I, MDA5 and attenuated NF-κB activation. Interestingly, enhanced polyI∶C-driven antiviral protection of HEC-Ad/Tr cells was partially mediated through IRF3 activation, but not associated with higher induction of IFNβ, suggesting multiple antiviral mechanisms of Tr/E and the involvement of alternative factors or pathways. Conclusions and Significance This is the first evidence of both Tr/E altering viral binding/entry, innate recognition and mounting of antiviral and inflammatory responses in genital ECs that could have significant implications for homeostasis of the female genital tract.

Abstract: Viral infection activates the transcription factors NF-κB and interferon regulatory factor 3 (IRF3), which collaborate to induce type I interferons (IFNs) and initiate host innate antiviral response. IFN-stimulated gene 56 (ISG56) induced by type I IFNs is a negative regulator of cellular antiviral response. In this study, we identified ISG60 as an ISG56-associated protein by biochemical purification and mass spectrometry analysis. Overexpression of ISG60 inhibited Sendai virus-induced activation of NF-κB and IRF3. Coimmunoprecipitation assays indicated that ISG60 interacted with MDA5 and VISA, two important signaling proteins participating in virus-triggered production of type I IFNs. Furthermore, ISG60 disrupted the interaction of VISA with MDA5 or RIG-I. These results indicate that ISG60 is a negative regulator of virus-triggered type I IFNs induction.

Abstract: Coxsackievirus B5 (CBV5) is a positive sense, single-stranded RNA virus belonging to the Enterovirus genus of the Picornaviridae family. It can cause many serious diseases, including viral myocarditis (which can lead on to dilated cardiomyopathy), aseptic meningitis, and pancreatitis. The structure and cell cycle of CBV5 is typical of a picornavirus. Viral RNA is detected by Toll-like receptors (TLRs) and retinoic acid inducible gene-I (RIG-I)-like receptors (RLRs). The RLR family, consisting of RIG-I, MDA5 (melanoma differentiation-associated gene 5), and LGP2, are pattern recognition receptors that detect a range of different viruses. RIG-I and MDA5 are homologous cytoplasmic proteins containing an N-terminal region with two caspase activation and recruitment domains (CARDs), a central SF2 type DExD/H-box RNA helicase domain, and a C-terminal repressor domain (RD). Once a viral ligand has been detected and bound by RIG-I and MDA5, both signal downstream through their CARDs to activate IRF3/7 and NF-κB indirectly, via the protein intermediate IPS-1 (IFN-β promoter stimulator 1), and initiate an immune response. RIG-I and MDA5 contribute to antiviral signalling in different ways depending on the virus involved. MDA5 has been shown to be critical for Picornaviridae detection, whilst RIG-I can detect a wide variety of different viruses and pathogen associated molecular patterns. Results presented here show the expression levels of both are upregulated in response to CBV5 infection in human cardiac cells, with MDA5 expression levels being slightly greater than RIG-I. However, in Huh cells, RIG-I expression levels are greater than those of MDA5, indicating that it plays a role in CBV5 sensing. The presence of both phospho-IκB (corresponding to NF-κB activation) and IRF3 is detected in both cardiac cells and Huh cells in response to CBV5, and IFN-β production is also greatly upregulated. RIG-I and MDA5 colocalise with the adaptor protein IPS-1 in response to CBV5 infection, again indicating the synergistic response by the two RLRs, and both RLRs form homodimers in the cytoplasm. Overall, this suggest that both MDA5 and RIG-I act synergistically to detect CBV5 and initiate a downstream immune response, although MDA5 appears to be the marginally stronger sensor.

Abstract: Innate antiviral reactions are induced within hours of a viral infection. These reactions are critical to the activation of adaptive immunity. The major innate antiviral reaction is that mediated by type I and III interferons (IFNs), which activate antiviral genes through cell surface receptors, signal transducers, and transcription factors (Samuel. Clin Microbiol Rev 14:778–809, 2001; Theofilopoulos et al. Annu Rev Immunol 23:307–336, 2005; Uze and Monneron. Biochimie 89:729–734, 2007). Once the antiviral gene products establish an antiviral state, viral replication is selectively repressed. Efficient expression of IFN is observed in cells infected with viruses, suggesting that viral components produced during replication are detected by cellular sensors. A family of RNA helicases termed RIG-I-like receptors (RLRs), including retinoic acid-inducible gene-I (RIG-I), melanoma differentiation associated gene 5 (MDA5), and laboratory of genetics and physiology 2 (LGP2), senses viral double-stranded (ds) RNA and triggers an antiviral program including the production of IFN (Kawai and Akira. Ann N Y Acad Sci 1143:1–20, 2008; Yoneyama and Fujita. Immunol Rev 227:54–65, 2009). We review here the structure and function of RLRs.

Abstract: The innate immune system is a vital part of the body‟s defences against viral pathogens. RIG-I and MDA5 belong to the retinoic acid inducible gene-I (RIG-I)-like receptors (RLRs) family and function as cytoplasmic PRRs that are involved in the elimination of actively replicating RNA viruses. Their location and their differential responses to RNA viruses emphasises the complexity of the innate detection system. RIG-I and MDA5 contribute to antiviral signalling in different ways depending on the virus involved. Coxsackieviruses are positive sense, single-stranded RNA viruses belonging to the Enterovirus genus of the Picornaviridae family. They cause many serious diseases, including viral myocarditis (which can lead on to dilated cardiomyopathy), aseptic meningitis, and pancreatitis. In order to identify which RLR recognises these viruses and which RNA species triggers RLR activation during Coxsackievirus infection, viral ssRNA and replicative intermediates of Coxsackievirus RNA as well as synthetic dsRNA were used in this study. The results revealed that MDA5 recognises not the genomic ssRNA but the dsRNA generated by the replication of these viruses. Confocal microscopy provided unique evidence between the relationship of viral dsRNA and MDA5 while cytokine assays using HEK-MDA5 cells showed a strong immune response to Coxsackievirus and the dsRNA intermediates. This shows very strong evidence that MDA5 is a key sensor of the dsRNA intermediate of Coxsackieviruses. As RIG-Is role in Coxsackie recognition still needs to be verified Huh7 and Huh7.5.1 cells were used and showed no difference in immune response in the absence of RIG-I to Coxsackievirus infection, as well as the isolated ssRNA, suggesting that the VPg group present on the RNA blocks recognition. Furthermore immunoprecipitation experiments showed that in response to Coxsackievirus stimulation, RLRs homodimerise as well as heterodimerise with LGP2, potentially upregulating their activity as a possible mechanism for viral detection. The data presented here show a much clearer role for RLRs in Coxsackievirus infection, while opening new questions as to MDA5s role in the diseases caused by Coxsackieviruses, as well as the specifics behind dimerisation of the RLRs

Abstract: The baculovirus Autographa californica multiple nuclear polyhedrosis virus (AcMNPV) has been widely used not only to achieve a high level of foreign gene expression in insect cells but also for efficient gene transduction into mammalian cells without any replication. In addition to the efficient gene delivery, baculovirus has been shown to induce host innate immune responses in various mammalian cells and in mice. The baculovirus has abundant CpG motifs in the viral genome and is capable of inducing pro-inflammatory cytokines and interferons (IFNs) through Toll-like receptor (TLR)-dependent and -independent signaling pathways in a cell-type-specific manner. The cytoplasmic helicase proteins RIG-I (retinoic-acid-inducible protein I) and MDA5 (melanoma-differentiation-associated gene 5) have been identified as viral dsRNA detectors and the adaptor IPS-1 (IFN-beta promoter stimulator-1) interacts with RIG-I and MDA5 to facilitate type-I IFN production mediated interferon regulatory factor 3 (IRF3) and 7 (IRF7). These helicases and IPS-1, however, were not essential for the type-I IFN and inflammatory cytokine responses to baculovirus. The baculovirus also has a strong adjuvant activity, and recombinant baculoviruses encoding neutralization epitopes elicit protective immunity in mice. This review deals with the current status of our knowledge of the induction of host innate immune responses by baculovirus and discusses the future prospects for baculovirus vectors.