Activation of NF-κB via endosomal Toll-like receptor 7 (TLR7) or TLR9 suppresses murine herpesvirus 68 reactivation

Novel adjuvant nano-vaccine induced immune response against Acinetobacter baumannii

Developing adjuvant vaccines to combat rising multidrug-resistant (MDR) Acinetobacter baumannii (A. baumannii) infections is a promising and cost-effective approach. The aim of this analysis was to construct a pDNA-CPG C274-adjuvant nano-vaccine and investigate its immunogenicity and protection in BALB/c mice. The CPG ODN C274 adjuvant was chemically synthesized and cloned into pcDNA3.1( +), and the cloning was verified using PCR and BamHI/EcoRV restriction enzyme digestion. Then, utilizing a complex coacervation approach, pDNA-CPG C274 was encapsulated by chitosan (CS) nanoparticles (NPs). TEM and DLS are used to explore the properties of the pDNA/CSNP complex. TLR-9 pathway activation was investigated in human HEK-293 and RAW 264.7 mouse cells. The vaccine's immunogenicity and immune-protective effectiveness were investigated in BALB/c mice. The pDNA-CPG C274/CSNPs were small (mean size 79.21 ± 0.23 nm), positively charged (+ 38.87 mV), and appeared to be spherical. A continuous slow release pattern was achieved. TLR-9 activation was greatest in the mouse model with CpG ODN (C274) at concentrations of 5 and 10 μg/ml with 56% and 55%, respectively (**P < 0.01). However, in HEK-293 human cells, by increasing the concentration of CpG ODN (C274) from 1 to 50 μg/ml, the activation rate of TLR-9 also increased, so that the highest activation rate (81%) was obtained at the concentration of 50 μg/ml (***P < 0.001). pDNA-CPG C274/CSNPs immunized BALB/c mice produced increased amounts of total-IgG, as well as IFN-γ and IL-1B in serum samples, compared to non-encapsulated pDNA-CPG C274. Furthermore, liver and lung injuries, as well as bacterial loads in the liver, lung, and blood, were reduced, and BALB/c mice immunized with pDNA-CPG C274/CSNPs showed potent protection (50-75%) against acute fatal Intraperitoneal A. baumannii challenge. pDNA-CPG C274/CSNPs evoked total-IgG antibodies, Th1 cellular immunity, and the TLR-9 pathway, as well as protection against an acute fatal A. baumannii challenge. Our findings suggest that this nano-vaccine is a promising approach for avoiding A. baumannii infection when used as a powerful adjuvant.

Toll-like receptor 9 (TLR9) gene deletion-mediated fracture healing in type II diabetic osteoporosis associates with inhibition of the nuclear factor-kappa B (NF-κB) signaling pathway

Diabetes is characterized by increased fracture risk. Evidence from in vivo studies is lacking for anti-fracture strategies in diabetes. Our microarray analyses predicted association of Toll-like receptor 9 (TLR9) with both diabetes and osteoporosis, which was the focus of this work in a murine model of type II diabetic osteoporosis (T2DOP). A T2DOP model with fracture was established in TLR9 knockout (TLR9^−/−) mice, which were then treated with the NF-κB signaling pathway inhibitor (PDTC) and activator (TNF-α). The obtained data suggested that TLR9 knockout augmented regeneration of bone tissues and cartilage area in the callus, and diminished fibrous tissues in T2DOP mice. Moreover, TLR9 depletion significantly affected bone mineral density (BMD), bone volume/tissue volume (BV/TV), connectivity density, trabecular number, trabecular separation and trabecular thickness, thus promoting fracture recovery. Bone morphology and structure were also improved in response to TLR9 depletion in T2DOP mice. TLR9 depletion inactivated NF-κB signaling in T2DOP mice. PDTC was found to enhance fracture healing in T2DOP mice, while TNF-α negated this effect. Collectively, these data indicate that TLR9 depletion may hold anti-fracture properties, making it a potential therapeutic target for T2DOP.

Abbreviations: Diabetic osteoporosis (DOP); bone mineral density (BMD); Toll-like receptors (TLRs); type 2 diabetes (T2D); Toll-like receptor 9 (TLR9); nuclear factor-kappaB (NF-κB); streptozotocin (STZ); type 2 diabetic osteoporosis (T2DOP); Gene Expression Omnibus (GEO); Kyoto encyclopedia of genes and genomes (KEGG); pyrrolidine dithiocarbamate (PDTC); computed tomography (CT); Hematoxylin–eosin (HE); bone morphogenetic protein 7 (BMP7); analysis of variance (ANOVA);

Anti-viral and pro-inflammatory functions of Toll-like receptors during gamma-herpesvirus infections

Toll-like receptors (TLRs) control anti-viral responses both directly in infected cells and in responding cells of the immune systems. Therefore, they are crucial for responses against the oncogenic γ-herpesviruses Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus and the related murine virus MHV68, which directly infect immune system cells. However, since these viruses also cause lifelong persistent infections, TLRs may also be involved in modulation of inflammation during latent infection and contribute to virus-driven tumorigenesis. This review summarizes work on both of these aspects of TLR/γ-herpesvirus interactions, as well as results showing that TLR activity can drive these viruses' re-entry into the replicative lytic cycle.

Role of intestinal extracellular matrix-related signaling in porcine epidemic diarrhea virus infection

Porcine epidemic diarrhea virus (PEDV) is emerging as a major threat to the global swine industry. Clinical PEDV infection is associated with severe intestinal lesions, resulting in absorptive dysfunction and high mortality rates in suckling piglets. The extracellular matrix (ECM) is an important component of intestinal tissue, providing a structural framework and conveying tissue-specific signals to nearby enterocytes. In this study, we investigated the extensive ECM remodeling observed in intestinal epithelial cells infected with PEDV and elucidated the associated activated ECM receptor-related pathways. Protein-protein interaction network analysis revealed two significantly differentially expressed genes (cluster of differentiation 44 [CD44] and serpin family E member 1 [SERPINE1]) associated with the ECM. At the transcriptional level, both genes exhibited significant positive correlation with the extent of PEDV replication. Similarly, the expression of CD44 and PAI-1 (encoded by SERPINE1) was also increased in the intestines of piglets during viral infection. Furthermore, CD44 exhibited antiviral activity by enhancing the expression of antiviral cytokines (e.g., interleukin [IL]-6, IL-18, IL-11, and antimicrobial peptide beta-defensin 1) by activating nuclear factor-κB signaling. Conversely, PAI-1 was found to promote the release of progeny virions during PEDV infection, despite a decreased intracellular viral load. Nevertheless, the underlying mechanisms are still unclear. Taken together, our results highlighted the biological roles of specific ECM-regulated genes, i.e., CD44 and SERPINE1 in suppressing and promoting PEDV infection, thereby providing a theoretical foundation for the role of the ECM in intestinal infections and identifying potential therapeutic targets for PEDV.

TLR7 Activation of Macrophages by Imiquimod Inhibits HIV Infection through Modulation of Viral Entry Cellular Factors

The Toll-like receptor (TLR) 7 is a viral sensor for detecting single-stranded ribonucleic acid (ssRNA), the activation of which can induce intracellular innate immunity against viral infections. Imiquimod, a synthetic ligand for TLR7, has been successfully used for the topical treatment of genital/perianal warts in immunocompetent individuals. We studied the effect of imiquimod on the human immunodeficiency virus (HIV) infection of primary human macrophages and demonstrated that the treatment of cells with imiquimod effectively inhibited infection with multiple strains (Bal, YU2, and Jago) of HIV. This anti-HIV activity of imiquimod was the most potent when macrophages were treated prior to infection. Infection of macrophages with pseudotyped HIV NL4-3-ΔEnv-eGFP-Bal showed that imiquimod could block the viral entry. Further mechanistic studies revealed that while imiquimod had little effect on the interferons (IFNs) expression, its treatment of macrophages resulted in the increased production of the CC chemokines (human macrophage inflammatory protein-1 alpha (MIP-1α), MIP-1β, and upon activation regulated normal T cells expressed and secreted (RANTES)), the natural ligands of HIV entry co-receptor CCR5, and decreased the expression of CD4 and CCR5. The addition of the antibodies against the CC chemokines to macrophage cultures could block imiquimod-mediated HIV inhibition. These findings provide experimental evidence to support the notion that TLR7 participates in the intracellular immunity against HIV in macrophages, suggesting the further clinical evaluation of imiquimod for its additional benefit of treating genital/perianal warts in people infected with HIV.

In vitro evidence suggesting that the toll-like receptor 7 and 8 agonist resiquimod (R-848) unlikely affects drug levels of co-administered compounds

Resiquimod (R-848) is an immune response modifier activating toll-like receptor 7 and 8. Its potential to cause pharmacokinetic interactions with concurrently administered drugs is unknown. To study the time course of the effect of resiquimod in LS180 cells as a model for intestinal tissue, luciferase-based reporter gene assays and reverse transcription polymerase chain reaction were used to investigate whether resiquimod affects the activities of nuclear factor kappa B (NF-ĸB), pregnane x receptor (PXR) or the transcription of selected central genes for drug disposition (cytochrome P-450 isozyme 3A4 (CYP3A4), CYP1A1, UDP-glucuronosyltransferase 1A1 (UGT1A1), ATP-binding cassette transporters ABCC2, ABCB1). Its impact on the activities of organic anion transporting polypeptides 1 or 3 (OATP1B1/3), breast cancer resistance protein (BCRP), P-glycoprotein (P-gp) or CYP3A4 was evaluated using fluorescence- or luminescence-based activity assays. Resiquimod irrelevantly increased NF-ĸB activity after 2 h (1 µM: 1.07-fold, P = 0.0188; 10 µM: 1.09-fold, P = 0.0142), and diminished it after 24 h (1 µM: 0.64-fold, P < 0.0001; 10 µM: 0.68-fold, P < 0.0001) and 30 h (10 µM: 0.68-fold, P = 0.0003). Concurrently, PXR activity after 24 h was marginally increased by 10 µM (1.05-fold, P = 0.0019). Resiquimod did not alter mRNA expression levels, activities of uptake or efflux transporters, or CYP3A4 activity. Given the marginal effects on NF-ĸB, PXR, expression levels of selected PXR target genes, and activities of important drug transporters and CYP3A4 in vitro, resiquimod is not expected to cause major pharmacokinetic drug-drug interactions in vivo.

R848 Is Involved in the Antibacterial Immune Response of Golden Pompano (Trachinotus ovatus) Through TLR7/8-MyD88-NF-κB-Signaling Pathway

R848 is an imidazoquinoline compound that is a specific activator of toll-like receptor (TLR) 7/8 and is often used in immunological research in mammals and teleosts. However, the immune responses initiated by R848 through the TLR7/8 pathway in response to bacterial infection remain largely unexplored in teleosts. In the current study, we investigated the antibacterial response and the participating signaling pathway initiated by R848 in golden pompano (Trachinotus ovatus). We found that R848 could stimulate the proliferation of head kidney lymphocytes (HKLs) in a dose-dependent manner, enhance the survival rate of HKLs, and inhibit the replication of bacteria in vivo. However, these effects induced by R848 were significantly reduced when chloroquine (CQ) was used to blocked endosomal acidification. Additionally, an in vivo study showed that R848 strengthened the antibacterial immunity of fish through a TLR7/8 and Myd88-dependent signaling pathway. A cellular experiment showed that Pepinh-MYD (a Myd88 inhibitor) significantly reduced the R848-mediated proliferation and survival of HKLs. Luciferase activity analysis showed that R848 enhanced the nuclear factor kappa B (NF-κB) activity, whereas this activity was reduced when CQ and Pepinh-MYD were present. Additionally, when an NF-κB inhibitor was present, the R848-mediated pro-proliferative and pro-survival effects on HKLs were significantly diminished. An in vivo study showed that knockdown of TLR7, TLR8, and Myd88 expression in golden pompano via siRNA following injection of R848 resulted in increased bacterial dissemination and colonization in fish tissues compared to that of fish injection of R848 alone, suggesting that R848-induced antibacterial immunity was significantly reduced. In conclusion, these results indicate that R848 plays an essential role in the antibacterial immunity of golden pompano via the TLR7/8-Myd88-NF-κB- signaling pathway.

Frontline Science: Targeting the TLR7 signalosome assembly

TLRs sense a broad range of microbial molecules and initiate antimicrobial immune response. The members of the TLR family use cytoplasmic Toll/interleukin-1R homology (TIR) domain to initiate intracellular signaling. The activated TLRs dimerize their TIRs and recruit adapter proteins to the dimer, through multiple interactions of receptor and adapter TIR domains. Although TLRs play an essential role in innate immunity, the aberrant TLR signaling may cause pathogenic inflammation. This study has screened a library of cell-permeable decoy peptides (CPDPs) derived from the TLR7 TIR for interference with TLR7 signaling and identified new CPDPs that target the TLR7 signalosome assembly. Peptides 7R1, 7R6, 7R9, and 7R11 inhibited the TLR7-induced signaling in murine and human macrophages. The most potent inhibitory peptide of the four, 7R11, significantly reduced the systemic cytokine levels elicited by administration of a TLR7 agonist to mice. TLR7 TIR surface regions that correspond to inhibitory peptides generally corresponded to four TIR sites that mediate signalosome assembly for other TLRs. The cell-based Förster resonance energy transfer/fluorescence lifetime imaging confirmed that 7R9 and 7R11 interact with adapter TIRs. These findings clarify the molecular mechanisms that trigger the adapter recruitment to activated TLR7 and suggest that 7R9 and 7R11 have a significant translational potential as candidate or lead therapeutics for treatment of TLR7-related inflammatory diseases.

Endosomal Toll-Like Receptors 7 and 9 Cooperate in Detection of Murine Gammaherpesvirus 68 Infection

Murine gammaherpesvirus 68 (MHV68) is a small-animal model suitable for study of the human pathogens Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus. Here, we have characterized the roles of the endosomal Toll-like receptor (TLR) escort protein UNC93B, endosomal TLR7, -9, and -13, and cell surface TLR2 in MHV68 detection. We found that the alpha interferon (IFN-α) response of plasmacytoid dendritic cells (pDC) to MHV68 was reduced in Tlr9-/- cells compared to levels in wild type (WT) cells but not completely lost. Tlr7-/- pDC responded similarly to WT. However, we found that in Unc93b-/- pDC, as well as in Tlr7-/-Tlr9-/- double-knockout pDC, the IFN-α response to MHV68 was completely abolished. Thus, the only pattern recognition receptors contributing to the IFN-α response to MHV68 in pDC are TLR7 and TLR9, but the contribution of TLR7 is masked by the presence of TLR9. To address the role of UNC93B and TLR for MHV68 infection in vivo, we infected mice with MHV68. Lytic replication of MHV68 after intravenous infection was enhanced in the lungs, spleen, and liver of UNC93B-deficient mice, in the spleen of TLR9-deficient mice, and in the liver and spleen of Tlr7-/-Tlr9-/- mice. The absence of TLR2 or TLR13 did not affect lytic viral titers. We then compared reactivation of MHV68 from latently infected WT, Unc93b-/-, Tlr7-/-Tlr9-/-, Tlr7-/-, and Tlr9-/- splenocytes. We observed enhanced reactivation and latent viral loads, particularly from Tlr7-/-Tlr9-/- splenocytes compared to levels in the WT. Our data show that UNC93B-dependent TLR7 and TLR9 cooperate in and contribute to detection and control of MHV68 infection.IMPORTANCE The two human gammaherpesviruses, Epstein-Barr virus (EBV) and Kaposi's sarcoma-associated herpesvirus (KSHV), can cause aggressive forms of cancer. These herpesviruses are strictly host specific, and therefore the homolog murine gammaherpesvirus 68 (MHV68) is a widely used model to obtain in vivo insights into the interaction between these two gammaherpesviruses and their host. Like EBV and KSHV, MHV68 establishes lifelong latency in B cells. The innate immune system serves as one of the first lines of host defense, with pattern recognition receptors such as the Toll-like receptors playing a crucial role in mounting a potent antiviral immune response to various pathogens. Here, we shed light on a yet unanticipated role of Toll-like receptor 7 in the recognition of MHV68 in a subset of immune cells called plasmacytoid dendritic cells, as well as on the control of this virus in its host.

Modulation of Apoptosis by Cytotoxic Mediators and Cell-Survival Molecules in Sjögren's Syndrome

The pathogenesis of Sjögren’s syndrome (SS) involves multiple factors including genetic background, cell death, and exocrine dysfunction. We here discuss apoptotic control in exocrine glands in SS by showing various pro- and anti-apoptotic pathways. Although the membrane-bound and soluble form of the Fas/Fas ligand system is a leading player with activation of the death domain and caspase 8/3 cleavage, the role of soluble Fas/FasL (including its polymorphism) in apoptosis is controversial. The tumor necrosis factor related apoptosis-inducing ligand (TRAIL)-mediated apoptosis of salivary gland epithelial cells (SGECs) involves a mitochondrial pathway that includes caspase 9 cleavage. The involvement of innate immunity cells such as toll-like receptors (TLRs) has been investigated; TLR2-4 and TLR7-9 are associated with the induction of inflammation in exocrine glands of SS patients. TLR3 has the potential to induce the apoptosis of SS patients’ SGECs. Linkage of epidermal growth factor (EGF) was shown in exocrine glands in SS, and it inhibited the Fas/FasL system with the help of cell-survival factors. TLR3 has dual actions to cause inflammation as well as apoptosis, which are inhibited by EGF. In conclusion, apoptosis in exocrine glands of SS patients is tightly controlled by balance of pro-apoptotic signals and growth factor.

Inhibition of murine herpesvirus-68 replication by IFN-gamma in macrophages is counteracted by the induction of SOCS1 expression

Gamma interferon (IFN-γ) is known to negatively regulate murine gammaherpesvirus-68 (MHV-68 or γHV-68) replication. This process involves the suppression of the viral gene replication and transcription activator (RTA) promoter, as well as activation of signal transducers and activators of transcription (STAT1). Notably, this effect is gradually attenuated during MHV-68 infection of bone marrow-derived macrophages (BMMs), which raised the possibility that the virus may utilize a mechanism that counteracts the antiviral effect of IFN-γ. By identifying the cellular factors that negatively regulate JAK-STAT1 signaling, we revealed that the infection of BMMs by MHV-68 induces the expression of suppressor of cytokine signaling 1 (SOCS1) and that depletion of SOCS1 restores the inhibitory effect of IFN-γ on virus replication. Moreover, we demonstrated that the expression of SOCS1 was induced as a result of the Toll-like receptor 3 (TLR3) mediated activation of the NF-κB signaling cascade. In conclusion, we report that TLR3-TRAF-NF-κB signaling pathway play a role in the induction of SOCS1 that counteracts the antiviral effect of IFN-γ during MHV-68 infection. This process is cell type-specific: it is functional in macrophages, but not in epithelial cells or fibroblasts. Our study reveals a mechanism that balances the immune responses and the escape of a gamma-herpesvirus in some antigen-presenting cells.

In ovo administration of Toll-like receptor ligands encapsulated in PLGA nanoparticles impede tumor development in chickens infected with Marek's disease virus

One of the economically important diseases in the poultry industry is Marek's disease (MD) which is caused by Marek's disease virus (MDV). The use of current vaccines provides protection against clinical signs of MD in chickens. However, these vaccines do not prevent the transmission of MDV to susceptible hosts, hence they may promote the development of new virulent strains of MDV. This issue persuaded us to explore alternative approaches to control MD in chickens. Induction of innate responses at the early stage of life in the chicken may help to prevent or reduce MDV infection. Further, prophylactic use of Toll-like receptor ligands (TLR-Ls) has been shown to generate host immunity against infectious diseases. In this regard, encapsulation of TLR-Ls in Poly(d, l-lactic-co-glycolic acid) (PLGA) may further enhance host responses by controlled release of TLR-Ls for an extended period. Hence, in the current study, protective effects of encapsulated TLR4 and TLR21 ligands, LPS and CpG, respectively, were investigated against MD. Results indicated that administration of encapsulated CpG and LPS first at embryonic day (ED) 18, followed by post-hatch at 14 days-post infection (dpi) intramuscularly, diminished tumor incidence by 60% and 42.8%, respectively at 21dpi compared to the MDV only group. In addition, analysis of cytokine gene profiles of interferon (IFN)-α, IFN-β, IFN-γ, inducible nitric oxide synthase (iNOS), interleukin (IL)-1β, IL-18 and IL-10 in spleen and bursa of Fabricius at different time points suggests that TLR-Ls possibly triggered host responses through the expression of IL-1β and IL-18 to reduce tumor formation. However, further studies are needed to explore the role of these pro-inflammatory cytokines and other influencing elements like lymphocytes in the hindrance of tumor development by TLR-Ls treatment in chickens.

IRAK4 is essential for TLR9-induced suppression of Epstein-Barr virus BZLF1 transcription in Akata Burkitt's lymphoma cells

Burkitt’s lymphoma (BL) is the most common childhood cancer in equatorial Africa, and is endemic to areas where people are chronically co-infected with Epstein-Barr virus (EBV) and the malaria pathogen Plasmodium falciparum. The contribution of these pathogens in the oncogenic process remains poorly understood. We showed earlier that the activation of Toll-like receptor (TLR) 9 by hemozoin, a disposal product formed from the digestion of blood by P. falciparum, suppresses the lytic reactivation of EBV in BL cells. EBV lytic reactivation is regulated by the expression of transcription factor Zta (ZEBRA), encoded by the EBV gene BZLF1. Here, we explore in the BL cell line Akata, the mechanism involved in repression by TLR9 of expression of BZLF1. We show that BZLF1 repression is mediated upon TLR9 engagement by a mechanism that is largely independent of de novo protein synthesis. By CRISPR/Cas9-induced inactivation of TLR9, MyD88, IRAK4 and IRAK1 we confirm that BZLF1 repression is dependent on functional TLR9 and MyD88 signaling, and identify IRAK4 as an essential element for TLR9-induced repression of BZLF1 expression upon BCR cross-linking. Our results unprecedentedly show that TLR9-mediated inhibition of lytic EBV is largely independent of new protein synthesis and demonstrate the central roles of MyD88 and IRAK4 in this process contributing to EBV’s persistence in the host’s B-cell pool.

RTA Occupancy of the Origin of Lytic Replication during Murine Gammaherpesvirus 68 Reactivation from B Cell Latency

RTA, the viral Replication and Transcription Activator, is essential for rhadinovirus lytic gene expression upon de novo infection and reactivation from latency. Lipopolysaccharide (LPS)/toll-like receptor (TLR)4 engagement enhances rhadinovirus reactivation. We developed two new systems to examine the interaction of RTA with host NF-kappaB (NF-κB) signaling during murine gammaherpesvirus 68 (MHV68) infection: a latent B cell line (HE-RIT) inducible for RTA-Flag expression and virus reactivation; and a recombinant virus (MHV68-RTA-Bio) that enabled in vivo biotinylation of RTA in BirA transgenic mice. LPS acted as a second stimulus to drive virus reactivation from latency in the context of induced expression of RTA-Flag. ORF6, the gene encoding the single-stranded DNA binding protein, was one of many viral genes that were directly responsive to RTA induction; expression was further increased upon treatment with LPS. However, NF-κB sites in the promoter of ORF6 did not influence RTA transactivation in response to LPS in HE-RIT cells. We found no evidence for RTA occupancy of the minimal RTA-responsive region of the ORF6 promoter, yet RTA was found to complex with a portion of the right origin of lytic replication (oriLyt-R) that contains predicted RTA recognition elements. RTA occupancy of select regions of the MHV-68 genome was also evaluated in our novel in vivo RTA biotinylation system. Streptavidin isolation of RTA-Bio confirmed complex formation with oriLyt-R in LPS-treated primary splenocytes from BirA mice infected with MHV68 RTA-Bio. We demonstrate the utility of reactivation-inducible B cells coupled with in vivo RTA biotinylation for mechanistic investigations of the interplay of host signaling with RTA.

Interplay of Murine Gammaherpesvirus 68 with NF-kappaB Signaling of the Host

Herpesviruses establish a chronic infection in the host characterized by intervals of lytic replication, quiescent latency, and reactivation from latency. Murine gammaherpesvirus 68 (MHV68) naturally infects small rodents and has genetic and biologic parallels with the human gammaherpesviruses (gHVs), Kaposi's sarcoma-associated herpesvirus and Epstein-Barr virus. The murine gammaherpesvirus model pathogen system provides a platform to apply cutting-edge approaches to dissect the interplay of gammaherpesvirus and host determinants that enable colonization of the host, and that shape the latent or lytic fate of an infected cell. This knowledge is critical for the development of novel therapeutic interventions against the oncogenic gHVs. The nuclear factor kappa B (NF-κB) signaling pathway is well-known for its role in the promotion of inflammation and many aspects of B cell biology. Here, we review key aspects of the virus lifecycle in the host, with an emphasis on the route that the virus takes to gain access to the B cell latency reservoir. We highlight how the murine gammaherpesvirus requires components of the NF-κB signaling pathway to promote replication, latency establishment, and maintenance of latency. These studies emphasize the complexity of gammaherpesvirus interactions with NF-κB signaling components that direct innate and adaptive immune responses of the host. Importantly, multiple facets of NF-κB signaling have been identified that might be targeted to reduce the burden of gammaherpesvirus-associated diseases.

Rabies virus lipopeptide conjugated to a TLR7 agonist improves the magnitude and quality of the Th1-biased humoral immune response in mice

In this study, we conjugated the rabies-derived lipopeptide CE536 to a TLR7 agonist, imiquimod, and evaluated its adjuvanticity. The synthetic construct (Lipo-I) targeted to TLR7, induced dendritic cell phenotypic maturation and production of both type I interferon and pro-inflammatory cytokines more efficiently than unconjugated TLR7 ligands or lipopeptide alone. The immunostimulatory effects of the conjugate were apparently the result of IκBα degradation and sustained p38 and JNK phosphorylation. The analysis of IgG isotypes and T cell differentiation showed that IgG2a dominant Th1-biased humoral and CD8(+) IFN-γ T cell responses were induced by Lipo-I. Lipo-I could facilitate the rabies vaccine to induce the production of an earlier and more vigorous rabies virus neutralizing antibody. In the post-exposure test, the Lipo-I adjuvanted vaccine provided a 73.3% survival rate, while the traditional vaccine bestowed only a 26.7% survival. Therefore, Lipo-I is a promising adjuvant for the development of more effective rabies vaccines.

Synergy of TLR3 and 7 ligands significantly enhances function of DCs to present inactivated PRRSV antigen through TRIF/MyD88-NF-κB signaling pathway

PRRS is one of the most important diseases in swine industry. Current PRRS inactivated vaccine provides only a limited protection and cannot induce sufficient cell-mediated immune responses. In this study, we first found that the mRNA and protein levels of Th1-type cytokines (IFN-γ, IL-12) and Th2-type cytokines (IL-6, IL-10) were significantly increased through TRIF/MyD88-NF-κB signaling pathway when porcine peripheral blood monocyte-derived dendritic cells (MoDCs) were treated with poly (I: C) of TLR3 ligand and imiquimod of TLR7 ligand, along with inactivated PRRSV antigen. Meanwhile, the ability of catching PRRSV antigen was also significantly enhanced. In mice experiment, it was found that the PRRSV-specific T lymphocyte proliferation, the percentages of CD4⁺, CD8⁺ T lymphocytes and PRRSV-specific CD3⁺ T cells producing IFN-γ and IL-4, the levels of Th1- and Th2-type cytokines and the titers of neutralization antibody were significantly enhanced in poly (I: C), imiquimod along with inactivated PRRSV group. Taken together, results of our experiments described for the first time that synergy of TLR3 and 7 ligands could significantly enhance the function of DCs to present inactivated PRRSV antigen through TRIF/MyD88-NF-κB signaling pathway and be used as adjuvant candidate for the development of novel PRRS inactivated vaccine.

Recent advances on viral manipulation of NF-κB signaling pathway

NF-κB transcription factors regulate the expression of hundreds of genes primarily involved in immune responses. Signaling events leading to NF-κB activation constitute a major antiviral immune pathway. To replicate and persist within their hosts, viruses have evolved diverse strategies to evade and exploit cellular NF-κB immune signaling cascades for their benefit. We summarize recent studies concerning viral manipulation of the NF-κB signaling pathway downstream of pattern recognition receptors. Signal transduction mediated by pattern recognition receptors is a research frontier for both infectious disease and innate immunology.

Porcine epidemic diarrhea virus infection induces NF-κB activation through the TLR2, TLR3 and TLR9 pathways in porcine intestinal epithelial cells

Porcine epidemic diarrhea virus (PEDV) is a coronavirus that induces persistent diarrhoea in swine, resulting in severe economic losses in swine-producing countries. Insights into the interplay between PEDV infection and the innate immune system are necessary for understanding the associated mechanism of pathogenesis. The transcription factor NF-κB plays an important role in regulating host immune responses. Here, we elucidated for the first time to our knowledge the potential mechanism of PEDV-mediated NF-κB activation in porcine small intestinal epithelial cells (IECs). During PEDV infection, NF-κB p65 was found to translocate from the cytoplasm to the nucleus, and PEDV-dependent NF-κB activity was associated with viral dose and active replication. Using small interfering RNAs to screen different mRNA components of the Toll-like receptor (TLR) or RIG-I-like receptor signalling pathways, we demonstrated that TLR2, TLR3 and TLR9 contribute to NF-κB activation in response to PEDV infection, but not RIG-I. By screening PEDV structural proteins for their ability to induce NF-κB activities, we found that PEDV nucleocapsid protein (N) could activate NF-κB and that the central region of N was essential for NF-κB activation. Furthermore, TLR2 was involved in PEDV N-induced NF-κB activation in IECs. Collectively, these findings provide new avenues of investigation into the molecular mechanisms of NF-κB activation induced by PEDV infection.

Immune effects of R848: evidences that suggest an essential role of TLR7/8-induced, Myd88- and NF-κB-dependent signaling in the antiviral immunity of Japanese flounder (Paralichthys olivaceus)

The imidazoquinoline compound R848 is a specific agonist of toll-like receptor (TLR) 7/TLR8 that has been used as an immunostimulant in humans against viral diseases. Although R848-induced immune response has been reported in teleost fish, the relevant mechanism is not clear. In this study, we investigated the antiviral potential and the signaling pathway of R848 in a model of Japanese flounder (Paralichthys olivaceus). We found that R848 was able to inhibit the replication of megalocytivirus, stimulated the proliferation of peripheral blood leukocytes (PBL), enhanced the expression of immune genes, and reduced apoptosis of PBL. When endosomal acidification was blocked by chloroquine (CQ), R848-mediated antiviral activity and immune response were significantly reduced. Likewise, inhibition of Myd88 activation markedly impaired the pro-proliferation and anti-apoptosis effect of R848. Cellular study showed that cultured founder cells treated with R848 exhibited augmented NF-κB activity, which, however, was dramatically reduced in the presence of CQ and Myd88 inhibitor. Furthermore, when NF-κB was inactivated, the effect of R848 on cell proliferation and apoptosis was significantly decreased. Taken together, these results indicate that R848 is an immunostimulant with antiviral property in a teleost species, and that the immune response of R848 is mediated by, most likely, TLR7/TLR8 signaling pathway, in which Myd88 and NK-κB play an essential role.

Innate Immune Recognition of EBV

The ability of Epstein-Barr virus (EBV) to establish latency despite specific immune responses and to successfully persist lifelong in the human host shows that EBV has developed powerful strategies and mechanisms to exploit, evade, abolish, or downsize otherwise effective immune responses to ensure its own survival. This chapter focuses on current knowledge on innate immune responses against EBV and its evasion strategies for own benefit and summarizes the questions that remain to be tackled. Innate immune reactions against EBV originate both from the main target cells of EBV and from nontarget cells, which are elements of the innate immune system. Thus, we structured our review accordingly but with a particular focus on the innate recognition of EBV in its two stages in its life cycle, latent state and lytic replication. Specifically, we discuss (I) innate sensing and resulting innate immune responses against EBV by its main target cells, focusing on (i) EBV transmission between epithelial cells and B cells and their life cycle stages; and (ii) elements of innate immunity in EBV's target cells. Further, we debate (II) the innate recognition and resulting innate immune responses against EBV by cells other than the main target cells, focusing on (iii) myeloid cells: dendritic cells, monocytes, macrophages, and neutrophil granulocytes; and (iv) natural killer cells. Finally, we address (III) how EBV counteracts or exploits innate immunity in its latent and lytic life cycle stages, concentrating on (v) TLRs; (vi) EBERs; and (vii) microRNAs.