Dysregulation of Toll-Like Receptor 7 Compromises Innate and Adaptive T Cell Responses and Host Resistance to an Attenuated West Nile Virus Infection in Old Mice

Pellino-1, a therapeutic target for control of SARS-CoV-2 infection and disease severity

Enhanced expression of Pellino-1 (Peli1), a ubiquitin ligase is known to be associated with COVID-19 susceptibility. The underlying mechanisms are not known. Here, we report that mice deficient in Peli1 (Peli1-/-) had reduced viral load and attenuated inflammatory immune responses and tissue damage in the lung following SARS-CoV-2 infection. Overexpressing Peli1 in 293 T cells increased SARS-CoV-2 infection via promoting virus replication and transcription, without affecting virus attachment and entry into the cells. Smaducin-6 treatment which is known to disrupt Peli1-mediated NF-KB activation, attenuated inflammatory immune responses in human lung epithelial cells as well as in the lung of K18-hACE2 mice following SARS-CoV-2 infection, though it had minimal effects on SARS-CoV-2 infection in human nasal epithelial cells. Overall, our findings suggest that Peli1 contributes to SARS-CoV-2 pathogenesis by promoting virus replication and positively regulating virus-induced inflammatory responses in lung epithelial cells. Peli1 is a therapeutic target to control SARS-CoV-2 -induced disease severity.

Recent insights on pattern recognition receptors and the interplay of innate immune responses against West Nile Virus infection

The recent outbreaks of neurotropic West Nile Virus (WNV) in humans are of grave public health concern, requiring a thorough understanding of the host immune response to develop effective therapeutic interventions. Innate immunity contributes to the primary immune response against WNV infection aimed at controlling and eliminating the virus from the body. As soon as WNV infects the body, pattern recognition receptors (PRRs) recognize viral pathogen-associated molecular patterns, particularly viral RNA, and initiate innate immune responses. This review explores the diverse PRRs in sensing WNV infection and orchestrating immune defenses. Specifically, this paper reviews the role of PRRs in WNV infection, encompassing both findings from mouse models and current clinical studies. Activation of PRRs triggers signaling pathways that induce the expression of antiviral proteins to inhibit viral replication. Understanding the intricacies of the immune response is crucial for developing effective vaccines and therapeutic interventions against WNV infection.

A murine model of post-acute neurological sequelae following SARS-CoV-2 variant infection

Viral variant is one known risk factor associated with post-acute sequelae of COVID-19 (PASC), yet the pathogenesis is largely unknown. Here, we studied SARS-CoV-2 Delta variant-induced PASC in K18-hACE2 mice. The virus replicated productively, induced robust inflammatory responses in lung and brain tissues, and caused weight loss and mortality during the acute infection. Longitudinal behavior studies in surviving mice up to 4 months post-acute infection revealed persistent abnormalities in neuropsychiatric state and motor behaviors, while reflex and sensory functions recovered over time. In the brain, no detectable viral RNA and minimal residential immune cell activation was observed in the surviving mice post-acute infection. Transcriptome analysis revealed persistent activation of immune pathways, including humoral responses, complement, and phagocytosis, and gene expression levels associated with ataxia telangiectasia, impaired cognitive function and memory recall, and neuronal dysfunction and degeneration. Furthermore, surviving mice maintained potent systemic T helper 1 prone cellular immune responses and strong sera neutralizing antibodies against Delta and Omicron variants months post-acute infection. Overall, our findings suggest that infection in K18-hACE2 mice recapitulates the persistent clinical symptoms reported in long-COVID patients and provides new insights into the role of systemic and brain residential immune factors in PASC pathogenesis.

Inflammatory Response Associated with West Nile Neuroinvasive Disease: A Systematic Review

BACKGROUND

West Nile virus (WNV) infection is a seasonal arbovirosis with the potential to cause severe neurological disease. Outcomes of the infection from WNV depend on viral factors (e.g., lineage) and host-intrinsic factors (e.g., age, sex, immunocompromising conditions). Immunity is essential to control the infection but may also prove detrimental to the host. Indeed, the persistence of high levels of pro-inflammatory cytokines and chemokines is associated with the development of blood-brain barrier (BBB) damage. Due to the importance of the inflammatory processes in the development of West Nile neuroinvasive disease (WNND), we reviewed the available literature on the subject.

METHODS

According to the 2020 updated PRISMA guidelines, all peer-reviewed articles regarding the inflammatory response associated with WNND were included.

RESULTS

One hundred and thirty-six articles were included in the data analysis and sorted into three groups (in vitro on-cell cultures, in vivo in animals, and in humans). The main cytokines found to be increased during WNND were IL-6 and TNF-α. We highlighted the generally small quantity and heterogeneity of information about the inflammatory patterns associated with WNND.

CONCLUSIONS

Further studies are needed to understand the pathogenesis of WNND and to investigate the extent and the way the host inflammatory response either helps in controlling the infection or in worsening the outcomes. This might prove useful both for the development of target therapies and for the development of molecular markers allowing early identification of patients displaying an inflammatory response that puts them at a higher risk of developing neuroinvasive disease and who might thus benefit from early antiviral therapies.

A Murine Model of Post-acute Neurological Sequelae Following SARS-CoV-2 Variant Infection

Viral variant is one known risk factor associated with post-acute sequelae of COVID-19 (PASC), yet the pathogenesis is largely unknown. Here, we studied SARS-CoV-2 Delta variant-induced PASC in K18-hACE2 mice. The virus replicated productively, induced robust inflammatory responses in lung and brain tissues, and caused weight loss and mortality during the acute infection. Longitudinal behavior studies in surviving mice up to 4 months post-acute infection revealed persistent abnormalities in neuropsychiatric state and motor behaviors, while reflex and sensory functions recovered over time. Surviving mice showed no detectable viral RNA in the brain and minimal neuroinflammation post-acute infection. Transcriptome analysis revealed persistent activation of immune pathways, including humoral responses, complement, and phagocytosis, and reduced levels of genes associated with ataxia telangiectasia, impaired cognitive function and memory recall, and neuronal dysfunction and degeneration. Furthermore, surviving mice maintained potent T helper 1 prone cellular immune responses and high neutralizing antibodies against Delta and Omicron variants in the periphery for months post-acute infection. Overall, infection in K18-hACE2 mice recapitulates the persistent clinical symptoms reported in long COVID patients and may be useful for future assessment of the efficacy of vaccines and therapeutics against SARS-CoV-2 variants.

Oral Supplementation with AHCC®, a Standardized Extract of Cultured Lentinula edodes Mycelia, Enhances Host Resistance against SARS-CoV-2 Infection

The coronavirus disease 2019 (COVID-19) pandemic has significantly impacted global public health safety and the economy. Multiple antiviral drugs have been developed, and some have received regulatory approval and/or authorization. The use of nutraceuticals can be beneficial for preventing and treating COVID-19 complications. AHCC is a standardized, cultured extract of an edible mushroom Lentinula edodes of the Basidiomycete family of fungi that is enriched in acylated α-1,4-glucans. Here, we evaluated the effects of the oral administration of AHCC on the host response to SARS-CoV-2 infection in two murine models, K18-hACE2 transgenic mice and immunocompetent BALB/c mice. Oral administration of AHCC every other day for one week before and one day post SARS-CoV-2 infection in both strains of mice decreased the viral load and attenuated inflammation in the lungs. AHCC treatment also significantly reduced SARS-CoV-2-induced lethality in the K18-hACE2 mice. AHCC administration enhanced the expansion of γδ T cells in the spleen and lungs before and after viral infection and promoted T helper 1-prone mucosal and systemic T cell responses in both models. In AHCC-fed BALB/c mice, SARS-CoV-2 specific IgG responses were also enhanced. In summary, AHCC supplementation enhances host resistance against mild and severe COVID-19 infection primarily via the promotion of innate and adaptive T cell immune responses in mice.

Interleukins, Chemokines, and Tumor Necrosis Factor Superfamily Ligands in the Pathogenesis of West Nile Virus Infection

West Nile virus (WNV) is a mosquito-borne pathogen that can lead to encephalitis and death in susceptible hosts. Cytokines play a critical role in inflammation and immunity in response to WNV infection. Murine models provide evidence that some cytokines offer protection against acute WNV infection and assist with viral clearance, while others play a multifaceted role WNV neuropathogenesis and immune-mediated tissue damage. This article aims to provide an up-to-date review of cytokine expression patterns in human and experimental animal models of WNV infections. Here, we outline the interleukins, chemokines, and tumor necrosis factor superfamily ligands associated with WNV infection and pathogenesis and describe the complex roles they play in mediating both protection and pathology of the central nervous system during or after virus clearance. By understanding of the role of these cytokines during WNV neuroinvasive infection, we can develop treatment options aimed at modulating these immune molecules in order to reduce neuroinflammation and improve patient outcomes.

A modified porous silicon microparticle potentiates protective systemic and mucosal immunity for SARS-CoV-2 subunit vaccine

Development of optimal SARS-CoV-2 vaccines to induce potent, long-lasting immunity and provide cross-reactive protection against emerging variants remains a high priority. Here, we report that a modified porous silicon microparticle (mPSM) adjuvant to SARS-CoV-2 receptor-binding domain (RBD) vaccine activated dendritic cells and generated more potent and durable systemic humoral and type 1 helper T (Th) cell- mediated immune responses than alum-formulated RBD following parenteral vaccination, and protected mice from SARS-CoV-2 and Beta variant challenge. Notably, mPSM facilitated the uptake of SARS-CoV-2 RBD antigens by nasal and airway epithelial cells. Parenteral and intranasal prime and boost vaccinations with mPSM-RBD elicited stronger lung resident T and B cells and IgA responses compared to parenteral vaccination alone, which led to markedly diminished viral loads and inflammation in the lung following SARS-CoV-2 Delta variant challenge. Overall, our results suggest that mPSM is effective adjuvant for SARS-CoV-2 subunit vaccine in both systemic and mucosal vaccinations.

Optimized production and immunogenicity of an insect virus-based chikungunya virus candidate vaccine in cell culture and animal models

A chimeric Eilat/ Chikungunya virus (EILV/CHIKV) was previously reported to replicate only in mosquito cells but capable of inducing robust adaptive immunity in animals. Here, we initially selected C7/10 cells to optimize the production of the chimeric virus. A two-step procedure produced highly purified virus stocks, which was shown to not cause hypersensitive reactions in a mouse sensitization study. We further optimized the dose and characterized the kinetics of EILV/CHIKV-induced immunity. A single dose of 10⁸ PFU was sufficient for induction of high levels of CHIKV-specific IgM and IgG antibodies, memory B cell and CD8⁺ T cell responses. Compared to the live-attenuated CHIKV vaccine 181/25, EILV/CHIKV induced similar levels of CHIKV-specific memory B cells, but higher CD8⁺ T cell responses at day 28. It also induced stronger CD8⁺, but lower CD4⁺ T cell responses than another live-attenuated CHIKV strain (CHIKV/IRES) at day 55 post-vaccination. Lastly, the purified EILV/CHIKV triggered antiviral cytokine responses and activation of antigen presenting cell (APC)s in vivo, but did not induce APCs alone upon in vitro exposure. Overall, our results demonstrate that the EILV/CHIKV vaccine candidate is safe, inexpensive to produce and a potent inducer of both innate and adaptive immunity in mice.

TLR7 Is Critical for Anti-Viral Humoral Immunity to EV71 Infection in the Spinal Cord

Enterovirus 71 (EV71) is a positive single-stranded RNA (ssRNA) virus from the enterovirus genus of Picornaviridae family and causes diseases ranged from the mild disease of hand, foot and mouth disease (HFMD) to the severe disease of neurological involvement in young children. TLR7 is an intracellular pattern recognition receptor (PRR) recognizing viral ssRNA. In this study, we investigated the role of TLR7 in EV71 infection in mouse pups (10-12 days old) and found that wild-type (WT) and TLR7 knock-out (TLR7KO) mice infected with EV71 showed similar limb paralysis at the onset and peak of the disease, comparable loss of motor neurons, and similar levels of antiviral molecules in the spinal cord. These results suggest that TLR7 is not the absolute PRR for EV71 in the spinal cord. Interestingly, TLR7KO mice infected with EV71 exhibited significantly delayed recovery from limb paralysis compared with WT mice. TLR7KO mice infected with EV71 showed significantly decreased levels of IgM and IgG2, important antibodies for antiviral humoral immunity. Furthermore, TLR7KO mice infected with EV71 showed a decrease of germinal center B cells in the spleen compared with WT mice. Altogether, our study suggests that TLR7 plays a critical role in anti-viral humoral immunity rather than in being a PRR in the spinal cord during EV71 infection in young mice.

Skin Viral Infections: Host Antiviral Innate Immunity and Viral Immune Evasion

The skin is an active immune organ that functions as the first and largest site of defense to the outside environment. Serving as the primary interface between host and pathogen, the skin’s early immune responses to viral invaders often determine the course and severity of infection. We review the current literature pertaining to the mechanisms of cutaneous viral invasion for classical skin-tropic, oncogenic, and vector-borne skin viruses. We discuss the skin’s evolved mechanisms for innate immune viral defense against these invading pathogens, as well as unique strategies utilized by the viruses to escape immune detection. We additionally explore the roles that demographic and environmental factors, such as age, biological sex, and the cutaneous microbiome, play in altering the host immune response to viral threats.

Immunity to acute virus infections with advanced age

New infections in general, and new viral infections amongst them, represent a serious challenge to an older organism. This review discusses the age-related alterations in responsiveness to infection from the standpoint of virus:host relationship and the host physiological whole-organism and specific immune response to the virus. Changes with age in the innate and adaptive immune system homeostasis and function are reviewed briefly. This is followed by a review of specific alterations and defects in the response of older organisms (chiefly mice and humans) to acute (particularly emerging and re-emerging) viral infections, with a very brief summary of the response to latent persistent infections. Finally, we provide a brief summary of the perspectives for possible interventions to enhance antiviral immunity.

The Role of Gamma-Delta T Cells in Diseases of the Central Nervous System

Gamma-delta (γδ) T cells are a subset of T cells that promote the inflammatory responses of lymphoid and myeloid lineages, and are especially vital to the initial inflammatory and immune responses. Given the capability to connect crux inflammations of adaptive and innate immunity, γδ T cells are responsive to multiple molecular cues and can acquire the capacity to induce various cytokines, such as GM-CSF, IL-4, IL-17, IL-21, IL-22, and IFN-γ. Nevertheless, the exact mechanisms responsible for γδ T cell proinflammatory functions remain poorly understood, particularly in the context of the central nervous system (CNS) diseases. CNS disease, usually leading to irreversible cognitive and physical disability, is becoming a worldwide public health problem. Here, we offer a review of the neuro-inflammatory and immune functions of γδ T cells, intending to understand their roles in CNS diseases, which may be crucial for the development of novel clinical applications.

Long-term, West Nile virus-induced neurological changes: A comparison of patients and rodent models

West Nile virus (WNV) is a mosquito-borne virus that can cause severe neurological disease in those infected. Those surviving infection often present with long-lasting neurological changes that can severely impede their lives. The most common reported symptoms are depression, memory loss, and motor dysfunction. These sequelae can persist for the rest of the patients’ lives. The pathogenesis behind these changes is still being determined. Here, we summarize current findings in human cases and rodent models, and discuss how these findings indicate that WNV induces a state in the brain similar neurodegenerative diseases. Rodent models have shown that infection leads to persistent virus and inflammation. Initial infection in the hippocampus leads to neuronal dysfunction, synapse elimination, and astrocytosis, all of which contribute to memory loss, mimicking findings in neurodegenerative diseases such as Alzheimer’s disease (AD) and Parkinson’s disease (PD). WNV infection acts on pathways, such as ubiquitin-signaled protein degradation, and induces the production of molecules, including IL-1β, IFN-γ, and α-synuclein, that are associated with neurodegenerative diseases. These findings indicate that WNV induces neurological damage through similar mechanisms as neurodegenerative diseases, and that pursuing research into the similarities will help advance our understanding of the pathogenesis of WNV-induced neurological sequelae.

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In patients with and without diagnosed WNND, there are long-lasting neurological sequelae that can mimic neurodegenerative diseases.

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Some rodent models of WNV reproduce some of these changes with mechanisms similar to neurodegenerative diseases.

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There is significant overlap between WNV and ND pathogenesis and this has been understudied.

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Further research needs to be done to determine accuracy of animal models compared to human patients.

An attenuated Zika virus NS4B protein mutant is a potent inducer of antiviral immune responses

Live attenuated vaccines (LAVs) are one of the most important strategies to control flavivirus diseases. The flavivirus nonstructural (NS) 4B proteins are a critical component of both the virus replication complex and evasion of host innate immunity. Here we have used site-directed mutagenesis of residues in the highly conserved N-terminal and central hydrophobic regions of Zika virus (ZIKV) NS4B protein to identify candidate attenuating mutations. Three single-site mutants were generated, of which the NS4B-C100S mutant was more attenuated than the other two mutants (NS4B-C100A and NS4B-P36A) in two immunocompromised mouse models of fatal ZIKV disease. The ZIKV NS4B-C100S mutant triggered stronger type 1 interferons and interleukin-6 production, and higher ZIKV-specific CD4+ and CD8+ T-cell responses, but induced similar titers of neutralization antibodies compared with the parent wild-type ZIKV strain and a previously reported candidate ZIKV LAV with a 10-nucleotide deletion in 3'-UTR (ZIKV-3'UTR-Δ10). Vaccination with ZIKV NS4B-C100S protected mice from subsequent WT ZIKV challenge. Furthermore, either passive immunization with ZIKV NS4B-C100S immune sera or active immunization with ZIKV NS4B-C100S followed by the depletion of T cells affords full protection from lethal WT ZIKV challenge. In summary, our results suggest that the ZIKV NS4B-C100S mutant may serve as a candidate ZIKV LAV due to its attenuated phenotype and high immunogenicity.

Current Understanding of West Nile Virus Clinical Manifestations, Immune Responses, Neuroinvasion, and Immunotherapeutic Implications

West Nile virus (WNV) is the most common mosquito-borne virus in North America. WNV-associated neuroinvasive disease affects all ages, although elderly and immunocompromised individuals are particularly at risk. WNV neuroinvasive disease has killed over 2300 Americans since WNV entered into the United States in the New York City outbreak of 1999. Despite 20 years of intensive laboratory and clinical research, there are still no approved vaccines or antivirals available for human use. However, rapid progress has been made in both understanding the pathogenesis of WNV and treatment in clinical practices. This review summarizes our current understanding of WNV infection in terms of human clinical manifestations, host immune responses, neuroinvasion, and therapeutic interventions.

Differential Expression Levels of Inflammatory Chemokines and TLRs in Patients Suffering from Mild and Severe Japanese Encephalitis

Japanese encephalitis (JE) is a vector-borne viral disease with clinical manifestations ranging from asymptomatic to severe neurological symptoms and even leading to death. The exact pathophysiology for diverse clinical spectrum of the disease is complex and has not yet been defined. Studies have postulated that during JE infection, inflammatory cytokines and chemokines are produced after the initial recognition of viral antigens through the engagement of toll-like receptors (TLR) pathways. However, there is paucity of knowledge on the expression levels of chemokines and TLRs among mild and severely affected JE patients. Hence, to better understand disease pathogenesis, we examined the mRNA expression of chemokines, CCL2 and CCL5, and their respective receptors CCR2 and CCR5 along with TLRs viz. TLR3, TLR7, TLR8, and TLR9 in context of mild and severely Japanese encephalitis virus (JEV)-infected (n = 19) and healthy (n = 19) individuals. Our study showed significant downregulation of CCL2, CCL5, CCR2, CCR5, and TLR3 by log 0.87, 1.02, 0.82, 0.68, and 0.37-fold respectively, among mild cases compared with controls. Significant difference of gene expression among mild and severe JE cases for CCL2 (p < 0.001), CCL5 (p < 0.01), and TLR7 (p < 0.05) was observed. In conclusion, our results proposes that chemokines viz. CCL2 and CCL5 along with TLR7 may be associated with degree of pathogenesis of JE and could be putative therapeutic targets for preventing severe inflammation during viral encephalitis.

Toll-Like Receptors and RIG-I-Like Receptors Play Important Roles in Resisting Flavivirus

Flaviviridae family is a class of single-stranded RNA virus, which is fatal to human and animals and mainly prevalent in subtropic and tropic countries. Even though people and animals are barraged with flavivirus infection every year, we have not invented either vaccines or antiviral for most flavivirus infections yet. Innate immunity is the first line of defense in resisting pathogen invasion, serving an important role in a resisting virus. Toll-like receptors (TLRs) and retinoic acid-inducible gene I- (RIG-I-) like receptors (RLRs) are crucial pattern recognition receptors (PRRs) that play essential roles in recognizing and clearing pathogens, including resisting flavivirus. In the present review, we provide a significant reference for further research on the function of innate immunity in resisting flavivirus.

Recent advances in understanding West Nile virus host immunity and viral pathogenesis

West Nile virus (WNV), a mosquito-borne flavivirus, has been a significant public health concern in the United States for nearly two decades. The virus has been linked to acute viral encephalitis, neurological sequelae, and chronic kidney diseases. Neither antiviral drugs nor vaccines are currently available for humans. In vitro cell culture and experimental animal models have been used to study WNV infection in humans. In this review, we will focus on recent findings and provide new insights into WNV host immunity and viral pathogenesis.

Reduced dynamic range of antiviral innate immune responses in aging

The worldwide population aged ≥ 65 years is increasing and the average life span is expected to increase another 10 years by 2050. This extended lifespan is associated with a progressive decline in immune function and a paradoxical state of low-grade, chronic inflammation that may contribute to susceptibility to viral infection, and reduced responses to vaccination. Here we review the effects of aging on innate immune responses to viral pathogens including elements of recognition, signaling, and production of inflammatory mediators. We specifically focus on age-related changes in key pattern recognition receptor signaling pathways, converging on altered cytokine responses, including a notable impairment of antiviral interferon responses. We highlight an emergent change in innate immunity that arises during aging – the dampening of the dynamic range of responses to multiple sources of stimulation – which may underlie reduced efficiency of immune responses in aging.

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We review the effects of aging on innate antiviral immunity, including recognition, signaling, and cytokine responses.

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Lower Toll-like receptor expression leads to impaired signaling and responses upon activation of these sensors.

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Effects of aging on cytosolic nucleic acid sensing receptors and inflammasomes remains incompletely characterized.

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In aging the dynamic range of innate immunity is compressed, with increased basal activation of many signaling pathways.

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Interferon production is impaired with age, which may lead to the increased viral susceptibility of older persons.

Alcohol, aging, and innate immunity

The global population is aging: in 2010, 8% of the population was older than 65 y, and that is expected to double to 16% by 2050. With advanced age comes a heightened prevalence of chronic diseases. Moreover, elderly humans fair worse after acute diseases, namely infection, leading to higher rates of infection-mediated mortality. Advanced age alters many aspects of both the innate and adaptive immune systems, leading to impaired responses to primary infection and poor development of immunologic memory. An often overlooked, yet increasingly common, behavior in older individuals is alcohol consumption. In fact, it has been estimated that >40% of older adults consume alcohol, and evidence reveals that >10% of this group is drinking more than the recommended limit by the National Institute on Alcohol Abuse and Alcoholism. Alcohol consumption, at any level, alters host immune responses, including changes in the number, phenotype, and function of innate and adaptive immune cells. Thus, understanding the effect of alcohol ingestion on the immune system of older individuals, who are already less capable of combating infection, merits further study. However, there is currently almost nothing known about how drinking alters innate immunity in older subjects, despite innate immune cells being critical for host defense, resolution of inflammation, and maintenance of immune homeostasis. Here, we review the effects of aging and alcohol consumption on innate immune cells independently and highlight the few studies that have examined the effects of alcohol ingestion in aged individuals.

MAVS Is Essential for Primary CD4+ T Cell Immunity but Not for Recall T Cell Responses following an Attenuated West Nile Virus Infection

The use of pathogen recognition receptor (PRR) agonists and the molecular mechanisms involved have been the major focus of research in individual vaccine development. West Nile virus (WNV) nonstructural (NS) 4B-P38G mutant has several features for an ideal vaccine candidate, including significantly reduced neuroinvasiveness, induction of strong adaptive immunity, and protection of mice from wild-type (WT) WNV infection. Here, we determined the role of mitochondrial antiviral signaling protein (MAVS), the adaptor protein for RIG-I-like receptor in regulating host immunity against the NS4B-P38G vaccine. We found that Mavs-/- mice were more susceptible to NS4B-P38G priming than WT mice. Mavs-/- mice had a transiently reduced production of antiviral cytokines and an impaired CD4+ T cell response in peripheral organs. However, antibody and CD8+ T cell responses were minimally affected. NS4B-P38G induced lower type I interferon (IFN), IFN-stimulating gene, and proinflammatory cytokine responses in Mavs-/- dendritic cells and subsequently compromised the antigen-presenting capacity for CD4+ T cells. Interestingly, Mavs-/- mice surviving NS4B-P38G priming were all protected from a lethal WT WNV challenge. NS4B-P38G-primed Mavs-/- mice exhibited equivalent levels of protective CD4+ T cell recall response, a modestly reduced WNV-specific IgM production, but more robust CD8+ T cell recall response. Taken together, our results suggest that MAVS is essential for boosting optimal primary CD4+ T cell responses upon NS4B-P38G vaccination and yet is dispensable for host protection and recall T cell responses during secondary WT WNV infection.IMPORTANCE The production of innate cytokines induced by the recognition of pathogen recognition receptors (PRRs) via their cognate ligands are critical for enhancing antigen-presenting cell functions and influencing T cell responses during microbial infection. The use of PRR agonists and the underlying molecular mechanisms have been the major focus in individual vaccine development. Here, we determined the role of mitochondrial antiviral-signaling protein (MAVS), the adaptor protein for RIG-I like receptor in regulating host immunity against the live attenuated West Nile virus (WNV) vaccine strain, the nonstructural (NS) 4B-P38G mutant. We found that MAVS is important for boosting optimal primary CD4+ T cell response during NS4B-P38G vaccination. However, MAVS is dispensable for memory T cell development and host protection during secondary wild-type WNV infection. Overall, these results may be utilized as a paradigm to aid in the rational development of other efficacious live attenuated flavivirus vaccines.

The natural killer cell response to West Nile virus in young and old individuals with or without a prior history of infection

West Nile virus (WNV) typically leads to asymptomatic infection but can cause severe neuroinvasive disease or death, particularly in the elderly. Innate NK cells play a critical role in antiviral defenses, yet their role in human WNV infection is poorly defined. Here we demonstrate that NK cells mount a robust, polyfunctional response to WNV characterized by cytolytic activity, cytokine and chemokine secretion. This is associated with downregulation of activating NK cell receptors and upregulation of NK cell activating ligands for NKG2D. The NK cell response did not differ between young and old WNV-naïve subjects, but a history of symptomatic infection is associated with more IFN-γ producing NK cell subsets and a significant decline in a specific NK cell subset. This NK repertoire skewing could either contribute to or follow heightened immune pathogenesis from WNV infection, and suggests that NK cells could play an important role in WNV infection in humans.

MicroRNA expression profiling of primary sheep testicular cells in response to bluetongue virus infection

Bluetongue virus (BTV) is a member of the genus Orbivirus within the family Reoviridae and causes a non-contagious, insect-transmitted disease in domestic and wild ruminants, mainly in sheep and occasionally in cattle and some species of deer. Virus infection can trigger the changes of the cellular microRNA (miRNA) expression profile, which play important post-transcriptional regulatory roles in gene expression and can greatly influence viral replication and pathogenesis. Here, we employed deep sequencing technology to determine which cellular miRNAs were differentially expressed in primary sheep testicular (ST) cells infected with BTV. A total of 25 known miRNAs and 240 novel miRNA candidates that were differentially expressed in BTV-infected and uninfected ST cells were identified, and 251 and 8428 predicted target genes were annotated, respectively. Nine differentially expressed miRNAs and their mRNA targets were validated by quantitative reverse transcription-polymerase chain reaction. Targets prediction and functional analysis of these regulated miRNAs revealed significant enrichment for several signaling pathways including MAPK, PI3K-Akt, endocytosis, Hippo, NF-kB, viral carcinogenesis, FoxO, and JAK-STAT signaling pathways. This study provides a valuable basis for further investigation on the roles of miRNAs in BTV replication and pathogenesis.

TLR8 Couples SOCS-1 and Restrains TLR7-Mediated Antiviral Immunity, Exacerbating West Nile Virus Infection in Mice

West Nile virus (WNV) is a neurotropic ssRNA flavivirus that can cause encephalitis, meningitis, and death in humans and mice. Human TLR7 and TLR8 and mouse TLR7 recognize viral ssRNA motifs and induce antiviral immunity. However, the role of mouse TLR8 in antiviral immunity is poorly understood. In this article, we report that TLR8-deficient (Tlr8^-/-) mice were resistant to WNV infection compared with wild-type controls. Efficient WNV clearance and moderate susceptibility to WNV-mediated neuronal death in Tlr8^-/- mice were attributed to overexpression of Tlr7 and IFN-stimulated gene-56 expression, whereas reduced expression of the proapoptotic gene coding Bcl2-associated X protein was observed. Interestingly, suppressor of cytokine signaling (SOCS)-1 directly associated with TLR8, but not with TLR7, indicating a novel role for TLR8 regulation of SOCS-1 function, whereas selective small interfering RNA knockdown of Socs-1 resulted in induced IFN-stimulated gene-56 and Tlr7 expression following WNV infection. Collectively, we report that TLR8 coupling with SOCS-1 inhibits TLR7-mediated antiviral immunity during WNV infection in mice.

Age-related alterations in immune responses to West Nile virus infection

West Nile virus (WNV) is the most important causative agent of viral encephalitis worldwide and an important public health concern in the United States due to its high prevalence, severe disease, and the absence of effective treatments. Infection with WNV is mainly asymptomatic, but some individuals develop severe, possibly fatal, neurological disease. Individual host factors play a role in susceptibility to WNV infection, including genetic polymorphisms in key anti-viral immune genes, but age is the most well-defined risk factor for susceptibility to severe disease. Ageing is associated with distinct changes in immune cells and a decline in immune function leading to increased susceptibility to infection and reduced responses to vaccination. WNV is detected by pathogen recognition receptors including Toll-like receptors (TLRs), which show reduced expression and function in ageing. Neutrophils, monocyte/macrophages and dendritic cells, which first recognize and respond to infection, show age-related impairment of many functions relevant to anti-viral responses. Natural killer cells control many viral infections and show age-related changes in phenotype and functional responses. A role for the regulatory receptors Mertk and Axl in blood-brain barrier permeability and in facilitating viral uptake through phospholipid binding may be relevant for susceptibility to WNV, and age-related up-regulation of Axl has been noted previously in human dendritic cells. Understanding the specific immune parameters and mechanisms that influence susceptibility to symptomatic WNV may lead to a better understanding of increased susceptibility in elderly individuals and identify potential avenues for therapeutic approaches: an especially relevant goal, as the world's populating is ageing.

Encephalitic Arboviruses: Emergence, Clinical Presentation, and Neuropathogenesis

Arboviruses are arthropod-borne viruses that exhibit worldwide distribution, contributing to systemic and neurologic infections in a variety of geographical locations. Arboviruses are transmitted to vertebral hosts during blood feedings by mosquitoes, ticks, biting flies, mites, and nits. While the majority of arboviral infections do not lead to neuroinvasive forms of disease, they are among the most severe infectious risks to the health of the human central nervous system. The neurologic diseases caused by arboviruses include meningitis, encephalitis, myelitis, encephalomyelitis, neuritis, and myositis in which virus- and immune-mediated injury may lead to severe, persisting neurologic deficits or death. Here we will review the major families of emerging arboviruses that cause neurologic infections, their neuropathogenesis and host neuroimmunologic responses, and current strategies for treatment and prevention of neurologic infections they cause.

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.