Tumor necrosis factor alpha protects against lethal West Nile virus infection by promoting trafficking of mononuclear leukocytes into the central nervous system. J Virol. 2008;82:8956-8964. [PMID: 18632856 DOI: 10.1128/jvi.01118-08]

Differential expression and significance of cytokines in cerebrospinal fluid of patients with viral encephalitis

To extensively identify cerebrospinal fluid (CSF) cytokine profiles related to the occurrence, development and prognosis of viral encephalitis (VE) patients by using a high-throughput proteomic approach. We measured 80 cytokines in the CSF of acute-phase VE patients (n = 11) using high-throughput protein chip technology, comparing them to controls (n = 6). ELISA validated these findings and assessed additional cytokines from prior literature in a larger cohort (15 VE patients, 15 controls). Correlations between biomarkers and clinical characteristics were also examined. In the initial stage, we identified two differentially expressed cytokines: cathepsin-L (CTSL), which was up-regulated, and Fractalkine, which was down-regulated. Functional enrichment analysis revealed that these proteins are linked to inflammation, apoptosis, autophagy, and blood-brain barrier disruption. In stage2, the elevations of cathepsin-L (CTSL), fractalkine, interleukin-6 (IL-6), IL-1β, macrophage migration inhibitory factor (MIF), tumor necrosis factor-α (TNF-α), insulin-like growth factor Ⅱ (IGF-2) and CXC chemokine ligand 10 (CXCL10) in VE were validated by ELISA. The results of linear regression indicated that these cytokines was positively correlated with CSF reactive lesions (p < 0.05). In this study, some biomarkers related with CSF level changes and prognosis were obtained. Although these cytokines are not specific, they may be related to the occurrence and development of VE. CTSL, MIF, IL-1β, TNF-α and CXCL10 can be used as VE potential biomarkers. These cytokines may participate in the pathogenesis of VE through inflammatory response, cell apoptosis, autophagy, blood-brain barrier disruption and cytokine-cytokine receptor interaction pathway.

West Nile virus triggers intestinal dysmotility via T cell-mediated enteric nervous system injury

Intestinal dysmotility syndromes have been epidemiologically associated with several antecedent bacterial and viral infections. To model this phenotype, we previously infected mice with the neurotropic flavivirus West Nile virus (WNV) and demonstrated intestinal transit defects. Here, we found that within 1 week of WNV infection, enteric neurons and glia became damaged, resulting in sustained reductions of neuronal cells and their networks of connecting fibers. Using cell-depleting antibodies, adoptive transfer experiments, and mice lacking specific immune cells or immune functions, we show that infiltrating WNV-specific CD4+ and CD8+ T cells damaged the enteric nervous system (ENS) and glia, which led to intestinal dysmotility; these T cells used multiple and redundant effector molecules including perforin and Fas ligand. In comparison, WNV-triggered ENS injury and intestinal dysmotility appeared to not require infiltrating monocytes, and damage may have been limited by resident muscularis macrophages. Overall, our experiments support a model in which antigen-specific T cell subsets and their effector molecules responding to WNV infection direct immune pathology against enteric neurons and supporting glia that results in intestinal dysmotility.

CD11b maintains West Nile virus replication through modulation of immune response in human neuroblastoma cells

BACKGROUND

West Nile virus (WNV) is a rapidly spreading mosquito-borne virus accounted for neuroinvasive diseases. An insight into WNV-host factors interaction is necessary for development of therapeutic approaches against WNV infection. CD11b has key biological functions and been identified as a therapeutic target for several human diseases. The purpose of this study was to determine whether CD11b was implicated in WNV infection.

METHODS

SH-SY5Y cells with and without MEK1/2 inhibitor U0126 or AKT inhibitor MK-2206 treatment were infected with WNV. CD11b mRNA levels were assessed by real-time PCR. WNV replication and expression of stress (ATF6 and CHOP), pro-inflammatory (TNF-α), and antiviral (IFN-α, IFN-β, and IFN-γ) factors were evaluated in WNV-infected SH-SY5Y cells with CD11b siRNA transfection. Cell viability was determined by MTS assay.

RESULTS

CD11b mRNA expression was remarkably up-regulated by WNV in a time-dependent manner. U0126 but not MK-2206 treatment reduced the CD11b induction by WNV. CD11b knockdown significantly decreased WNV replication and protected the infected cells. CD11b knockdown markedly increased TNF-α, IFN-α, IFN-β, and IFN-γ mRNA expression induced by WNV. ATF6 mRNA expression was reduced upon CD11b knockdown following WNV infection.

CONCLUSION

These results demonstrate that CD11b is involved in maintaining WNV replication and modulating inflammatory as well as antiviral immune response, highlighting the potential of CD11b as a target for therapeutics for WNV infection.

The critical role of interleukin-6 in protection against neurotropic flavivirus infection

West Nile virus (WNV) and Japanese encephalitis virus (JEV) are emerging mosquito-borne flaviviruses causing encephalitis globally. No specific drug or therapy exists to treat flavivirus-induced neurological diseases. The lack of specific therapeutics underscores an urgent need to determine the function of important host factors involved in flavivirus replication and disease progression. Interleukin-6 (IL-6) upregulation has been observed during viral infections in both mice and humans, implying that it may influence the disease outcome significantly. Herein, we investigated the function of IL-6 in the pathogenesis of neurotropic flavivirus infections. First, we examined the role of IL-6 in flavivirus-infected human neuroblastoma cells, SK-N-SH, and found that IL-6 neutralization increased the WNV or JEV replication and inhibited the expression of key cytokines. We further evaluated the role of IL-6 by infecting primary mouse cells derived from IL-6 knockout (IL-6-/-) mice and wild-type (WT) mice with WNV or JEV. The results exhibited increased virus yields in the cells lacking the IL-6 gene. Next, our in vivo approach revealed that IL-6-/- mice had significantly higher morbidity and mortality after subcutaneous infection with the pathogenic WNV NY99 or JEV Nakayama strain compared to WT mice. The non-pathogenic WNV Eg101 strain did not cause mortality in WT mice but resulted in 60% mortality in IL-6-/- mice, indicating that IL-6 is required for the survival of mice after the peripheral inoculation of WNV or JEV. We also observed significantly higher viremia and brain viral load in IL-6-/- mice than in WT mice. Subsequently, we explored innate immune responses in WT and IL-6-/- mice after WNV NY99 infection. Our data demonstrated that the IL-6-/- mice had reduced levels of key cytokines in the serum during early infection but elevated levels of proinflammatory cytokines in the brain later, along with suppressed anti-inflammatory cytokines. In addition, mRNA expression of IFN-α and IFN-β was significantly lower in the infected IL-6-/- mice. In conclusion, these data suggest that the lack of IL-6 exacerbates WNV or JEV infection in vitro and in vivo by causing an increase in virus replication and dysregulating host immune response.

ZIKV infection differentially affects the transcriptional profiles in HTR8 and U251 cells

The mechanism by which Zika virus (ZIKV) causes severe birth defects in pregnant women remains unclear. Cell tropisms in placenta and brain play a crucial role in ZIKV pathogenesis, leading to congenital Zika syndrome (CZS). To identify the host factors involved in ZIKV infection, we compared the transcriptional profiles of ZIKV-infected human first-trimester placental trophoblast cells HTR8/SVneo and a human glioblastoma astrocytoma cell line U251. Our results demonstrated that ZIKV exhibited lower rates of mRNA replication and protein expression in HTR8 than in U251 cells, while showing a higher release of infectious viral particles. However, a greater number of differentially expressed genes (DEGs) were found in ZIKV-infected U251 cells than in ZIKV-infected HTR8 cells. Several of these DEGs were enriched in distinct biological processes related to the characteristics of each cell type that may contribute to foetal damage. Both cell types exhibited activation of common interferons, inflammatory cytokines, and chemokine production upon ZIKV infection. Moreover, the neutralization of tumour necrosis factor-alpha (TNF-α) promoted ZIKV infection in both trophoblasts and glioblastoma astrocytoma cells. Overall, we identified multiple DEGs associated with ZIKV pathogenesis.

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.

Intrauterine Viral Infections: Impact of Inflammation on Fetal Neurodevelopment

Intrauterine viral infections during pregnancy by pathogens such as Zika virus, Cytomegalovirus, Rubella and Herpes Simplex virus can lead to prenatal as well as postnatal neurodevelopmental disorders. Although maternal viral infections are common during pregnancy, viruses rarely penetrate the trophoblast. When they do cross, viruses can cause adverse congenital health conditions for the fetus. In this context, maternal inflammatory responses to these neurotropic pathogens play a significant role in negatively affecting neurodevelopment. For instance, intrauterine inflammation poses an increased risk of neurodevelopmental disorders such as microcephaly, schizophrenia, autism spectrum disorder, cerebral palsy and epilepsy. Severe inflammatory responses have been linked to stillbirths, preterm births, abortions and microcephaly. In this review, we discuss the mechanistic basis of how immune system shapes the landscape of the brain and how different neurotropic viral pathogens evoke inflammatory responses. Finally, we list the consequences of neuroinflammation on fetal brain development and discuss directions for future research and intervention strategies.

Intrinsic Innate Immune Responses Control Viral Growth and Protect against Neuronal Death in an Ex Vivo Model of West Nile Virus-Induced Central Nervous System Disease

Recruitment of immune cells from the periphery is critical for controlling West Nile virus (WNV) growth in the central nervous system (CNS) and preventing subsequent WNV-induced CNS disease. Neuroinflammatory responses, including the release of proinflammatory cytokines and chemokines by CNS cells, influence the entry and function of peripheral immune cells that infiltrate the CNS. However, these same cytokines and chemokines contribute to tissue damage in other models of CNS injury. Rosiglitazone is a peroxisome proliferator-activated receptor gamma (PPARγ) agonist that inhibits neuroinflammation. We used rosiglitazone in WNV-infected ex vivo brain slice cultures (BSC) to investigate the role of neuroinflammation within the CNS in the absence of peripheral immune cells. Rosiglitazone treatment inhibited WNV-induced expression of proinflammatory chemokines and cytokines, interferon beta (IFN-β), and IFN-stimulated genes (ISG) and also decreased WNV-induced activation of microglia. These decreased neuroinflammatory responses were associated with activation of astrocytes, robust viral growth, increased activation of caspase 3, and increased neuronal loss. Rosiglitazone had a similar effect on in vivo WNV infection, causing increased viral growth, tissue damage, and disease severity in infected mice, even though the number of infiltrating peripheral immune cells was higher in rosiglitazone-treated, WNV-infected mice than in untreated, infected controls. These results indicate that local neuroinflammatory responses are capable of controlling viral growth within the CNS and limiting neuronal loss and may function to keep the virus in check prior to the infiltration of peripheral immune cells, limiting both virus- and immune-mediated neuronal damage. IMPORTANCE West Nile virus is the most common cause of epidemic encephalitis in the United States and can result in debilitating CNS disease. There are no effective vaccines or treatments for WNV-induced CNS disease in humans. The peripheral immune response is critical for protection against WNV CNS infections. We now demonstrate that intrinsic immune responses also control viral growth and limit neuronal loss. These findings have important implications for developing new therapies for WNV-induced CNS disease.

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.

T cell engagement of cross-presenting microglia protects the brain from a nasal virus infection

The neuroepithelium is a nasal barrier surface populated by olfactory sensory neurons that detect odorants in the airway and convey this information directly to the brain via axon fibers. This barrier surface is especially vulnerable to infection, yet respiratory infections rarely cause fatal encephalitis, suggesting a highly evolved immunological defense. Here, using a mouse model, we sought to understand the mechanism by which innate and adaptive immune cells thwart neuroinvasion by vesicular stomatitis virus (VSV), a potentially lethal virus that uses olfactory sensory neurons to enter the brain after nasal infection. Fate-mapping studies demonstrated that infected central nervous system (CNS) neurons were cleared noncytolytically, yet specific deletion of major histocompatibility complex class I (MHC I) from these neurons unexpectedly had no effect on viral control. Intravital imaging studies of calcium signaling in virus-specific CD8+ T cells revealed instead that brain-resident microglia were the relevant source of viral peptide-MHC I complexes. Microglia were not infected by the virus but were found to cross-present antigen after acquisition from adjacent neurons. Microglia depletion interfered with T cell calcium signaling and antiviral control in the brain after nasal infection. Collectively, these data demonstrate that microglia provide a front-line defense against a neuroinvasive nasal infection by cross-presenting antigen to antiviral T cells that noncytolytically cleanse neurons. Disruptions in this innate defense likely render the brain susceptible to neurotropic viruses like VSV that attempt to enter the CNS via the nose.

West Nile Virus Restriction in Mosquito and Human Cells: A Virus under Confinement

West Nile virus (WNV) is an emerging neurotropic flavivirus that naturally circulates between mosquitoes and birds. However, WNV has a broad host range and can be transmitted from mosquitoes to several mammalian species, including humans, through infected saliva during a blood meal. Although WNV infections are mostly asymptomatic, 20% to 30% of cases are symptomatic and can occasionally lead to severe symptoms, including fatal meningitis or encephalitis. Over the past decades, WNV-carrying mosquitoes have become increasingly widespread across new regions, including North America and Europe, which constitutes a public health concern. Nevertheless, mosquito and human innate immune defenses can detect WNV infection and induce the expression of antiviral effectors, so-called viral restriction factors, to control viral propagation. Conversely, WNV has developed countermeasures to escape these host defenses, thus establishing a constant arms race between the virus and its hosts. Our review intends to cover most of the current knowledge on viral restriction factors as well as WNV evasion strategies in mosquito and human cells in order to bring an updated overview on WNV-host interactions.

The Society for Immunotherapy of Cancer perspective on regulation of interleukin-6 signaling in COVID-19-related systemic inflammatory response

The pandemic caused by the novel coronavirus SARS-CoV-2 has placed an unprecedented burden on healthcare systems around the world. In patients who experience severe disease, acute respiratory distress is often accompanied by a pathological immune reaction, sometimes referred to as 'cytokine storm'. One hallmark feature of the profound inflammatory state seen in patients with COVID-19 who succumb to pneumonia and hypoxia is marked elevation of serum cytokines, especially interferon gamma, tumor necrosis factor alpha, interleukin 17 (IL-17), interleukin 8 (IL-8) and interleukin 6 (IL-6). Initial experience from the outbreaks in Italy, China and the USA has anecdotally demonstrated improved outcomes for critically ill patients with COVID-19 with the administration of cytokine-modulatory therapies, especially anti-IL-6 agents. Although ongoing trials are investigating anti-IL-6 therapies, access to these therapies is a concern, especially as the numbers of cases worldwide continue to climb. An immunology-informed approach may help identify alternative agents to modulate the pathological inflammation seen in patients with COVID-19. Drawing on extensive experience administering these and other immune-modulating therapies, the Society for Immunotherapy of Cancer offers this perspective on potential alternatives to anti-IL-6 that may also warrant consideration for management of the systemic inflammatory response and pulmonary compromise that can be seen in patients with severe COVID-19.

Tumor Necrosis Factor-Alpha Signaling May Contribute to Chronic West Nile Virus Post-infectious Proinflammatory State

Background: West Nile virus (WNV) causes a spectrum of human disease ranging from a febrile illness (WNV fever) to severe neuroinvasive disease (meningitis, encephalitis, acute flaccid paralysis). Since WNV gained entry into North America in 1999, clinicians caring for WNV survivors have observed persistent neurological symptoms occurring long-after the production of neutralizing antibodies and clearance of the virus. Accordingly, alternative pathogeneses other than direct viral invasion have been hypothesized to explain these post-infectious symptoms. The dominant hypothesis is that antiviral inflammatory responses triggered initially to clear WNV may persist to promote a post-infectious proinflammatory state.

Methods: In 4 serologically-confirmed WNV patients with persistent post-infectious symptoms (3 WNV fever, 1 neuroinvasive disease), we ordered a comprehensive cytokine panel at weeks 8, 10, 12, and 36 months post-onset of illness, respectively, to better understand the pathophysiology of the protracted symptoms.

Results: All patients had abnormally elevated tumor necrosis factor alpha (TNF-α), a major molecule triggering antiviral cytokines and chronic inflammation in many human autoimmune diseases, but heretofore not reported to be upregulated in human WNV infection. Three patients also had elevations of other proinflammatory proteins. Major symptoms included fatigue, arthralgias, myalgias, generalized or multifocal pain or weakness, imbalance, headaches, cognitive problems, and symptoms of dysautonomia.

Conclusion: The findings provide support for an extended post-infectious proinflammatory state that may contribute to chronic inflammation and long-term morbidity in some WNV survivors and further suggest that TNF-α may play a pathogenic role in initiating this inflammatory environment. Clinical trials may be warranted to determine if TNF-α inhibitors or other immunosuppressive agents can improve patient outcomes.

Single-Cell Analysis of Neuroinflammatory Responses Following Intracranial Injection of G-Deleted Rabies Viruses

Viral vectors are essential tools for the study of neural circuits, with glycoprotein-deleted rabies viruses being widely used for monosynaptic retrograde tracing to map connectivity between specific cell types in the nervous system. However, the use of rabies virus is limited by the cytotoxicity and the inflammatory responses these viruses trigger. While components of the rabies virus genome contribute to its cytotoxic effects, the function of other neuronal and non-neuronal cells within the vicinity of the infected host neurons in either effecting or mitigating virally-induced tissue damage are still being elucidated. Here, we analyzed 60,212 single-cell RNA profiles to assess both global and cell-type-specific transcriptional responses in the mouse dorsal raphe nucleus (DRN) following intracranial injection of glycoprotein-deleted rabies viruses and axonal infection of dorsal raphe serotonergic neurons. Gene pathway analyses revealed a down-regulation of genes involved in metabolic processes and neurotransmission following infection. We also identified several transcriptionally diverse leukocyte populations that infiltrate the brain and are distinct from resident immune cells. Cell type-specific patterns of cytokine expression showed that antiviral responses were likely orchestrated by Type I and Type II interferon signaling from microglia and infiltrating CD4+ T cells, respectively. Additionally, we uncovered transcriptionally distinct states of microglia along an activation trajectory that may serve different functions, which range from surveillance to antigen presentation and cytokine secretion. Intercellular interactions inferred from transcriptional data suggest that CD4+ T cells facilitate microglial state transitions during the inflammatory response. Our study uncovers the heterogeneity of immune cells mediating neuroinflammatory responses and provides a critical evaluation of the compatibility between rabies-mediated connectivity mapping and single-cell transcriptional profiling. These findings provide additional insights into the distinct contributions of various cell types in mediating different facets of antiviral responses in the brain and will facilitate the design of strategies to circumvent immune responses to improve the efficacy of viral gene delivery.

Inflammation During Virus Infection: Swings and Roundabouts

Inflammation constitutes a concerted series of cellular and molecular responses that follow disturbance of systemic homeostasis, by either toxins or infectious organisms. Leukocytes modulate inflammation through production of secretory mediators, like cytokines and chemokines, which work in an autocrine and/or paracrine manner. These mediators can either promote or attenuate the inflammatory response and depending on differential temporal and spatial expression play a crucial role in the outcome of infection. Even though the objective is clearance of the pathogen with minimum damage to host, the pathogenesis of multiple human pathogenic viruses has been suggested to emanate from a dysregulation of the inflammatory response, sometimes with fatal consequences. This review discusses the nature and the outcome of inflammatory response, which is triggered in the human host subsequent to infection by single-sense plus-strand RNA viruses. In view of such harmful effects of a dysregulated inflammatory response, an exogenous regulation of these reactions by either interference or supplementation of critical regulators has been suggested. Currently multiple such factors are being tested for their beneficial and adverse effects. A successful use of such an approach in diseases of viral etiology can potentially protect the affected individual without directly affecting the virus life cycle. Further, such approaches whenever applicable would be useful in mitigating death and/or debility that is caused by the infection of those viruses which have proven particularly difficult to control by either prophylactic vaccines and/or therapeutic strategies using specific antiviral drugs.

Oral Antibiotic Treatment of Mice Exacerbates the Disease Severity of Multiple Flavivirus Infections

Although the outcome of flavivirus infection can vary from asymptomatic to lethal, environmental factors modulating disease severity are poorly defined. Here, we observed increased susceptibility of mice to severe West Nile (WNV), Dengue, and Zika virus infections after treatment with oral antibiotics (Abx) that depleted the gut microbiota. Abx treatment impaired the development of optimal T cell responses, with decreased levels of WNV-specific CD8⁺ T cells associated with increased infection and immunopathology. Abx treatments that resulted in enhanced WNV susceptibility generated changes in the overall structure of the gut bacterial community and in the abundance of specific bacterial taxa. As little as 3 days of treatment with ampicillin was sufficient to alter host immunity and WNV outcome. Our results identify oral Abx therapy as a potential environmental determinant of systemic viral disease, and they raise the possibility that perturbation of the gut microbiota may have deleterious consequences for subsequent flavivirus infections.

Dendritic cell-associated MAVS is required to control West Nile virus replication and ensuing humoral immune responses

Mitochondrial antiviral signaling protein (MAVS) is a critical innate immune signaling protein that directs the actions of the RIG-I-like receptor (RLR) signaling pathway of RNA virus recognition and initiation of anti-viral immunity against West Nile virus (WNV). In the absence of MAVS, mice die more rapidly after infection with the pathogenic WNV-Texas (TX) strain, but also produce elevated WNV-specific IgG concomitant with increased viral burden. Here we investigated whether there was a B cell intrinsic role for MAVS during the development of protective humoral immunity following WNV infection. MAVS-/- mice survived infection from the non-pathogenic WNV-Madagascar (MAD) strain, with limited signs of disease. Compared to wildtype (WT) controls, WNV-MAD-infected MAVS-/- mice had elevated serum neutralizing antibodies, splenic germinal center B cells, plasma cells and effector T cells. We found that when rechallenged with the normally lethal WNV-TX, MAVS-/- mice previously infected with WNV-MAD were protected from disease. Thus, protective humoral and cellular immune responses can be generated in absence of MAVS. Mice with a conditional deletion of MAVS only in CD11c+ dendritic cells phenocopied MAVS whole body knockout mice in their humoral responses to WNV-MAD, displaying elevated virus titers and neutralizing antibodies. Conversely, a B cell-specific deletion of MAVS had no effect on immune responses to WNV-MAD compared to WT controls. Thus, MAVS in dendritic cells is required to control WNV replication and thereby regulate downstream humoral immune responses.

Deletion of Pregnancy Zone Protein and Murinoglobulin-1 Restricts the Pathogenesis of West Nile Virus Infection in Mice

West Nile virus (WNV) is an enveloped positive-stranded RNA virus that causes meningitis, encephalitis, and acute flaccid paralysis in humans. There are no therapeutic agents available for use against WNV infection. Alpha-2 macroglobulin (A2M) is a major plasma proteinase inhibitor that also has important role in immune modulation. In mice, pregnancy zone protein (PZP) and murinoglobulin-1 (MUG-1) are two close homologous of human A2M. In this study, we investigated the role of PZP and MUG-1 proteins in the pathogenesis of WNV infection in mice. Adult C57BL/6J wild-type and PZP/MUG-1 double knockout (DKO) mice were inoculated subcutaneously with WNV and mortality, virus burden, and immune responses were analyzed. Infection of wild-type (WT) mice with WNV resulted in significantly high morbidity and mortality. In comparison, no mortality was observed in DKO mice, suggesting that PZP and MUG-1 play a deleterious role in WNV infection. Increased survival in WNV-infected DKO mice was associated with significantly low viral burden in serum, spleen, kidney, and brain compared to WT mice. In addition, significantly reduced levels of type 1 interferon and WNV-specific antibodies were observed in the DKO mice compared to WT mice. We further demonstrated that protein levels of inflammatory cytokines and chemokines in the serum, spleen, and brain were significantly reduced in DKO mice compared to WT mice. Collectively our data demonstrate that lack of PZP and MUG-1 restricts the pathogenesis of WNV infection in mice.

Differential Expression of Genes Related to Innate Immune Responses in Ex Vivo Spinal Cord and Cerebellar Slice Cultures Infected with West Nile Virus

West Nile virus (WNV) infection results in a spectrum of neurological symptoms, ranging from a benign fever to severe WNV neuroinvasive disease with high mortality. Many who recover from WNV neuroinvasive infection present with long-term deficits, including weakness, fatigue, and cognitive problems. While neurons are a main target of WNV, other cell types, especially astrocytes, play an important role in promoting WNV-mediated central nervous system (CNS) damage. Conversely, it has been shown that cultured primary astrocytes secrete high levels of interferons (IFNs) immediately after WNV exposure to protect neighboring astrocytes, as well as neurons. However, how intrinsic responses to WNV in specific cell types and different regions of the brain modify immune protection is not fully understood. Here, we used a mouse ex vivo spinal cord slice culture (SCSC) and cerebellar slice culture (CSC) models to determine the innate immune responses specific to the CNS during WNV infection. Slices were prepared from the spinal cord and cerebellar tissue of 7–9-day-old mouse pups. Four-day-old SCSC or CSC were infected with 1 × 10³ or 1 × 10⁵ PFU of WNV, respectively. After 12 h exposure to WNV and 3 days post-infection in normal growth media, the pooled slice cultures were processed for total RNA extraction and for gene expression patterns using mouse Affymetrix arrays. The expression patterns of a number of genes were significantly altered between the mock- and WNV-treated groups, both in the CSCs and SCSCs. However, distinct differences were observed when CSC data were compared with SCSC. CSCs showed robust induction of interferons (IFNs), IFN-stimulated genes (ISGs), and regulatory factors. Some of the antiviral genes related to IFN were upregulated more than 25-fold in CSCs as compared to mock or SCSC. Though SCSCs had twice the number of dysregulated genes, as compared CSCs, they exhibited a much subdued IFN response. In addition, SCSCs showed astrogliosis and upregulation of astrocytic marker genes. In sum, our results suggest that early anti-inflammatory response to WNV infection in CSCs may be due to large population of distinct astrocytic cell types, and lack of those specialized astrocytes in SCSC may make spinal cord cells more susceptible to WNV damage. Further, the understanding of early intrinsic immune response events in WNV-infected ex vivo culture models could help develop potential therapies against WNV.

Innate Immune Response of Primary Human Keratinocytes to West Nile Virus Infection and Its Modulation by Mosquito Saliva

West Nile Virus (WNV) is a flavivirus involved in many human infections worldwide. This arthropod-borne virus is directly co-inoculated with mosquito saliva through the epidermis and the dermis during blood meal. WNV starts replicating in the skin before migrating to the draining lymph node, leading to widespread viremia and in some cases to neurological symptoms. Skin is a complex organ composed of different cell types that together perform essential functions such as pathogen sensing, barrier maintenance and immunity. Keratinocytes, which represent 90% of the cells of the epidermis, are the organism's first line of defense, initiating innate immune response by recognizing pathogens through their pattern recognition receptors. Although WNV was previously known to replicate in human primary keratinocytes, the induced inflammatory response remains unknown. The aim of this study was first to characterize the inflammatory response of human primary keratinocytes to WNV infection and then, to assess the potential role of co-inoculated mosquito saliva on the keratinocyte immune response and viral replication. A type I and III interferon inflammatory response associated with an increase of IRF7 but not IRF3 mRNA expression, and dependent on infectious dose, was observed during keratinocyte infection with WNV. Expression of several interferon-stimulated gene mRNA was also increased at 24 h post-infection (p.i.); they included CXCL10 and interferon-induced proteins with tetratricopeptide repeats (IFIT)-2 sustained up until 48 h p.i. Moreover, WNV infection of keratinocyte resulted in a significant increase of pro-inflammatory cytokines (TNFα, IL-6) and various chemokines (CXCL1, CXCL2, CXCL8 and CCL20) expression. The addition of Aedes aegypti or Culex quinquefasciatus mosquito saliva, two vectors of WNV infection, to infected keratinocytes led to a decrease of inflammatory response at 24 h p.i. However, only Ae. Aegypti saliva adjunction induced modulation of viral replication. In conclusion, this work describes for the first time the inflammatory response of human primary keratinocytes to WNV infection and its modulation in presence of vector mosquito saliva. The effects of mosquito saliva assessed in this work could be involved in the early steps of WNV replication in skin promoting viral spread through the body.

Positive modulation of mGluR5 attenuates seizures and reduces TNF-α+ macrophages and microglia in the brain in a murine model of virus-induced temporal lobe epilepsy

Viral encephalitis markedly increases the risk for the development of epilepsy. The Theiler's murine encephalomyelitis virus (TMEV)-induced model of seizures/epilepsy is a murine model of both viral-induced seizures/epilepsy and human Temporal Lobe Epilepsy. The inflammatory cytokines interleukin (IL)-6 and tumor necrosis factor (TNF)-α have been shown to play a role in seizure development in the TMEV-induced model of seizures/epilepsy, and infiltrating macrophages along with microglia have been shown to be major producers of these cytokines. The metabotropic glutamate receptor 5 (mGluR5) is a G-protein coupled receptor that has been shown to reduce IL-6 and TNF-α and to provide neuroprotection in other disease models. Therefore, we hypothesized that stimulation of mGluR5 would not only reduce seizures but attenuate IL-6 and TNF-α production in microglia and macrophages in the TMEV model. We found that pharmacological stimulation of mGluR5 with the selective positive allosteric modulator VU0360172 not only reduced acute seizure outcomes, but also reduced the percent of microglia and macrophages producing TNF-α 3 days post infection. Furthermore, treatment with VU0360172 did not alter the level of viral antigen, compared to controls, showing that this treatment does not compromise viral clearance. These results establish that mGluR5 may represent a therapeutic target in the TMEV-induced model of seizures/epilepsy.

Let-7e inhibits TNF-α expression by targeting the methyl transferase EZH2 in DENV2-infected THP-1 cells

Tumor necrosis factor α (TNFα), an important inflammatory cytokine, is associated with dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS), a severe pathological manifestation of dengue virus (DENV) infection. However, the regulatory mechanism of microRNA on TNFα is currently unknown. Our study showed that the TNFα expression increased immediately and then later decreased, while a marked increase for the miRNA let-7e was detected in dengue virus type 2 (DENV2)-infected peripheral blood mononuclear cells (PBMCs). From this study, we found that let-7e was able to inhibit TNFα expression, but bioinformatics analysis showed that the enhancer of zeste homolog 2 (EZH2) was the potential direct target of let-7e instead of TNFα. EZH2 methyl transferase can produce H3K27me3 and has a negative regulatory role. Using a dual-luciferase reporter assay and Western blotting, we confirmed that EZH2 was a direct target of let-7e and found that siEZH2 could inhibit TNFα expression. In the further study of the regulatory mechanism of EZH2 on TNFα expression, we showed that siEZH2 promoted EZH1 and H3K4me3 expression and inhibited H3K27me3 expression. More importantly, we revealed that siEZH2 down-regulated NF-κB p65 within the nucleus. These findings indicate that the let-7e/EZH2/H3K27me3/NF-κB p65 pathway is a novel regulatory axis of TNFα expression. In addition, we determined the protein differences between siEZH2 and siEZH2-NC by iTRAQ and found a number of proteins that might be associated with TNFα.

Interleukin-1β Signaling in Dendritic Cells Induces Antiviral Interferon Responses

Induction of interferon beta (IFN-β), IFN-stimulated genes (ISGs), and inflammatory responses is critical for control of viral infection. We recently identified an essential linkage of stimulation of the inflammatory cytokine interleukin-1β (IL-1β) and induction of ISGs that function as host restriction pathways against the emerging flavivirus West Nile virus (WNV) in vivo Here we utilized ex vivo global transcriptome analysis of primary dendritic cells, known targets of WNV replication, to define gene signatures required for this IL-1β-driven antiviral response. Dendritic cells that were deficient in IL-1 receptor signaling showed dysregulation of cell-intrinsic defense genes and loss of viral control during WNV infection. Surprisingly, we found that in wild-type cells, IL-1β treatment, in the absence of infection, drove the transcription of IFN-β and ISGs at late times following treatment. Expression of these antiviral innate immune genes was dependent on the transcription factor IFN regulatory factor 3 (IRF3) and appears to reflect a general shift in IL-1β signaling from an early inflammatory response to a late IFN-mediated response. These data demonstrate that inflammatory and antiviral signals integrate to control viral infection in myeloid cells through a process of IL-1β-to-IRF3 signaling crosstalk. Strategies to exploit these cytokines in the activation of host defense programs should be investigated as novel therapeutic approaches against individual pathogens.IMPORTANCE West Nile virus is an emerging mosquito-borne flavivirus that can result in serious illness, neuropathology, and death in infected individuals. Currently, there are no vaccines or therapies for human use against West Nile virus. Immune control of West Nile virus infection requires inflammatory and antiviral responses, though the effect that each arm of this response has on the other is unclear. The significance of our research is in defining how virus-induced inflammatory responses regulate critical antiviral immune programs for effective control of West Nile virus infection. These data identify essential mechanisms of immune control that can inform therapeutic efforts against West Nile virus, with potential efficacy against other neuroinvasive viruses.

Astrocytes decrease adult neurogenesis during virus-induced memory dysfunction via IL-1

Memory impairment following West Nile virus neuroinvasive disease (WNND) is associated with loss of hippocampal synapses with lack of recovery. Adult neurogenesis and synaptogenesis are fundamental features of hippocampal repair, suggesting viruses impact these processes. Here, using an established model of WNND-induced cognitive dysfunction, transcriptional profiling revealed alterations in gene expression that limit adult neurogenesis, including interleukin (IL)-1. WNND-recovered animals exhibit decreased neuroblasts and increased astrogenesis, without recovery of hippocampal neurogenesis at thirty days. Analysis of cytokine production in ex vivo isolated microglia and astrocytes revealed the latter to be the predominant source of IL-1. IL-1R1-deficient, WNND-recovered mice exhibit normal neurogenesis, recovery of presynaptic termini, and resistance to spatial learning defects, the latter of which likewise occurred after treatment with IL-1R1 antagonist. Thus, preferential generation of proinflammatory astrocytes impairs neuronal progenitor cell homeostasis via expression of IL-1, which may underlie long-term cognitive consequences of WNND, but provides a therapeutic target.

Osteopontin facilitates West Nile virus neuroinvasion via neutrophil "Trojan horse" transport

West Nile virus (WNV) can cause severe human neurological diseases including encephalitis and meningitis. The mechanisms by which WNV enters the central nervous system (CNS) and host-factors that are involved in WNV neuroinvasion are not completely understood. The proinflammatory chemokine osteopontin (OPN) is induced in multiple neuroinflammatory diseases and is responsible for leukocyte recruitment to sites of its expression. In this study, we found that WNV infection induced OPN expression in both human and mouse cells. Interestingly, WNV-infected OPN deficient (Opn ^-/-) mice exhibited a higher survival rate (70%) than wild type (WT) control mice (30%), suggesting OPN plays a deleterious role in WNV infection. Despite comparable levels of viral load in circulating blood cells and peripheral organs in the two groups, WNV-infected polymorphonuclear neutrophil (PMN) infiltration and viral burden in brain of Opn ^-/- mice were significantly lower than in WT mice. Importantly, intracerebral administration of recombinant OPN into the brains of Opn ^-/- mice resulted in increased WNV-infected PMN infiltration and viral burden in the brain, which was coupled to increased mortality. The overall results suggest that OPN facilitates WNV neuroinvasion by recruiting WNV-infected PMNs into the brain.

Tumor Necrosis Factor Alpha-Induced Recruitment of Inflammatory Mononuclear Cells Leads to Inflammation and Altered Brain Development in Murine Cytomegalovirus-Infected Newborn Mice

Congenital human cytomegalovirus (HCMV) infection is a significant cause of abnormal neurodevelopment and long-term neurological sequelae in infants and children. Resident cell populations of the developing brain have been suggested to be more susceptible to virus-induced cytopathology, a pathway thought to contribute to the clinical outcomes following intrauterine HCMV infection. However, recent findings in a newborn mouse model of the infection in the developing brain have indicated that elevated levels of proinflammatory mediators leading to mononuclear cell activation and recruitment could underlie the abnormal neurodevelopment. In this study, we demonstrate that treatment with tumor necrosis factor alpha (TNF-α)-neutralizing antibodies decreased the frequency of CD45⁺ Ly6C^hi CD11b⁺ CCR2⁺ activated myeloid mononuclear cells (MMCs) and the levels of proinflammatory cytokines in the blood and the brains of murine CMV-infected mice. This treatment also normalized neurodevelopment in infected mice without significantly impacting the level of virus replication. These results indicate that TNF-α is a major component of the inflammatory response associated with altered neurodevelopment that follows murine CMV infection of the developing brain and that a subset of peripheral blood myeloid mononuclear cells represent a key effector cell population in this model of virus-induced inflammatory disease of the developing brain.IMPORTANCE Congenital human cytomegalovirus (HCMV) infection is the most common viral infection of the developing human fetus and can result in neurodevelopmental sequelae. Mechanisms of disease leading to neurodevelopmental deficits in infected infants remain undefined, but postulated pathways include loss of neuronal progenitor cells, damage to the developing vascular system of the brain, and altered cellular positioning. Direct virus-mediated cytopathic effects cannot explain the phenotypes of brain damage in most infected infants. Using a mouse model that recapitulates characteristics of the brain infection described in human infants, we have shown that TNF-α plays a key role in brain inflammation, including recruitment of inflammatory mononuclear cells. Neutralization of TNF-α normalized neurodevelopmental abnormalities in infected mice, providing evidence that virus-induced inflammation is a major component of disease in the developing brain. These results suggest that interventions limiting inflammation associated with the infection could potentially improve the neurologic outcome of infants infected in utero with HCMV.

CD8 T cells protect adult naive mice from JEV-induced morbidity via lytic function

Following Japanese encephalitis virus (JEV) infection neutralizing antibodies are shown to provide protection in a significant proportion of cases, but not all, suggesting additional components of immune system might also contribute to elicit protective immune response. Here we have characterized the role of T cells in offering protection in adult mice infected with JEV. Mice lacking α/β–T cells (TCRβ–null) are highly susceptible and die over 10–18 day period as compared to the wild-type (WT) mice which are resistant. This is associated with high viral load, higher mRNA levels of proinflammatory cytokines and breach in the blood-brain-barrier (BBB). Infected WT mice do not show a breach in BBB; however, in contrast to TCRβ-null, they show the presence of T cells in the brain. Using adoptive transfer of cells with specific genetic deficiencies we see that neither the presence of CD4 T cells nor cytokines such as IL-4, IL-10 or interferon-gamma have any significant role in offering protection from primary infection. In contrast, we show that CD8 T cell deficiency is more critical as absence of CD8 T cells alone increases mortality in mice infected with JEV. Further, transfer of T cells from beige mice with defects in granular lytic function into TCRβ-null mice shows poor protection implicating granule-mediated target cell lysis as an essential component for survival. In addition, for the first time we report that γ/δ-T cells also make significant contribution to confer protection from JEV infection. Our data show that effector CD8 T cells play a protective role during primary infection possibly by preventing the breach in BBB and neuronal damage.

Japanese encephalitis virus (JEV) commonly infects human beings in developing countries including those in Southeast Asia. While the majority of the infected people suffer from mild illness, a minority suffers from encephalitis which may lead to death. The virus is transmitted by mosquito bites and elimination of mosquitoes is not a practical answer to prevent the disease, therefore, prevention by vaccination is a desired goal. While various vaccines are clinically tried and some are marketed further improvement in vaccines is still possible. In a complex disease like JE many components of the immune system contribute to variable extent in protection. We show here that one subset of T cells called CD8 cells which are capable of killing infected cells are very critical for providing protection against JEV infection in mice. In the absence of T cells we also observed that virus reaches the brain early, unlike in the presence of T cells, and this possibly results in high virus load in the brain leading to worsening of the condition and death. Thus, our data help in identifying the role of CD8 T cells in protection from lethal JEV infection and the information may be useful for modifying and/or developing vaccine for prevention of JEV-mediated disease.

Mapping and Role of the CD8+ T Cell Response During Primary Zika Virus Infection in Mice

CD8+ T cells may play a dual role in protection against and pathogenesis of flaviviruses, including Zika virus (ZIKV). We evaluated the CD8+ T cell response in ZIKV-infected LysMCre+IFNARfl/fl C57BL/6 (H-2b) mice lacking the type I interferon receptor in a subset of myeloid cells. In total, 26 and 15 CD8+ T cell-reactive peptides for ZIKV African (MR766) and Asian (FSS13025) lineage strains, respectively, were identified and validated. CD8+ T cells from infected mice were polyfunctional and mediated cytotoxicity. Adoptive transfer of ZIKV-immune CD8+ T cells reduced viral burdens, whereas their depletion led to higher tissue burdens, and CD8-/- mice displayed higher mortality with ZIKV infection. Collectively, these results demonstrate that CD8+ T cells protect against ZIKV infection. Further, this study provides a T cell competent mouse model for investigating ZIKV-specific T cell responses.

Interleukin-17A Promotes CD8+ T Cell Cytotoxicity To Facilitate West Nile Virus Clearance

CD8⁺ T cells are crucial components of immunity and play a vital role in recovery from West Nile virus (WNV) infection. Here, we identify a previously unrecognized function of interleukin-17A (IL-17A) in inducing cytotoxic-mediator gene expression and promoting CD8⁺ T cell cytotoxicity against WNV infection in mice. We find that IL-17A-deficient (Il17a^-/-) mice are more susceptible to WNV infection and develop a higher viral burden than wild-type (WT) mice. Interestingly, the CD8⁺ T cells isolated from Il17a^-/- mice are less cytotoxic and express lower levels of cytotoxic-mediator genes, which can be restored by supplying recombinant IL-17A in vitro and in vivo Importantly, treatment of WNV-infected mice with recombinant IL-17A, as late as day 6 postinfection, significantly reduces the viral burden and increases survival, suggesting a therapeutic potential for IL-17A. In conclusion, we report a novel function of IL-17A in promoting CD8⁺ T cell cytotoxicity, which may have broad implications in other microbial infections and cancers.

IMPORTANCE

Interleukin-17A (IL-17A) and CD8⁺ T cells regulate diverse immune functions in microbial infections, malignancies, and autoimmune diseases. IL-17A is a proinflammatory cytokine produced by diverse cell types, while CD8⁺ T cells (known as cytotoxic T cells) are major cells that provide immunity against intracellular pathogens. Previous studies have demonstrated a crucial role of CD8⁺ T cells in recovery from West Nile virus (WNV) infection. However, the role of IL-17A during WNV infection remains unclear. Here, we demonstrate that IL-17A protects mice from lethal WNV infection by promoting CD8⁺ T cell-mediated clearance of WNV. In addition, treatment of WNV-infected mice with recombinant IL-17A reduces the viral burden and increases survival of mice, suggesting a potential therapeutic. This novel IL-17A-CD8⁺ T cell axis may also have broad implications for immunity to other microbial infections and cancers, where CD8⁺ T cell functions are crucial.

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.

Ablation of CD11c(hi) dendritic cells exacerbates Japanese encephalitis by regulating blood-brain barrier permeability and altering tight junction/adhesion molecules

Japanese encephalitis (JE), characterized by extensive neuroinflammation following infection with neurotropic JE virus (JEV), is becoming a leading cause of viral encephalitis due to rapid changes in climate and demography. The blood-brain barrier (BBB) plays an important role in restricting neuroinvasion of peripheral leukocytes and virus, thereby regulating the progression of viral encephalitis. In this study, we explored the role of CD11c(hi) dendritic cells (DCs) in regulating BBB integrity and JE progression using a conditional depletion model of CD11c(hi) DCs. Transient ablation of CD11c(hi) DCs resulted in markedly increased susceptibility to JE progression along with highly increased neuro-invasion of JEV. In addition, exacerbated JE progression in CD11c(hi) DC-ablated hosts was closely associated with increased expression of proinflammatory cytokines (IFN-β, IL-6, and TNF-α) and CC chemokines (CCL2, CCL3, CXCL2) in the brain. Moreover, our results revealed that the exacerbation of JE progression in CD11c(hi) DC-ablated hosts was correlated with enhanced BBB permeability and reduced expression of tight junction and adhesion molecules (claudin-5, ZO-1, occluding, JAMs). Ultimately, our data conclude that the ablation of CD11c(hi) DCs provided a subsidiary impact on BBB integrity and the expression of tight junction/adhesion molecules, thereby leading to exacerbated JE progression. These findings provide insight into the secondary role of CD11c(hi) DCs in JE progression through regulation of BBB integrity and the expression of tight junction/adhesion molecules.

A complement-microglial axis drives synapse loss during virus-induced memory impairment

Over 50% of patients who survive neuroinvasive infection with West Nile virus (WNV) exhibit chronic cognitive sequelae. Although thousands of cases of WNV-mediated memory dysfunction accrue annually, the mechanisms responsible for these impairments are unknown. The classical complement cascade, a key component of innate immune pathogen defence, mediates synaptic pruning by microglia during early postnatal development. Here we show that viral infection of adult hippocampal neurons induces complement-mediated elimination of presynaptic terminals in a murine WNV neuroinvasive disease model. Inoculation of WNV-NS5-E218A, a WNV with a mutant NS5(E218A) protein leads to survival rates and cognitive dysfunction that mirror human WNV neuroinvasive disease. WNV-NS5-E218A-recovered mice (recovery defined as survival after acute infection) display impaired spatial learning and persistence of phagocytic microglia without loss of hippocampal neurons or volume. Hippocampi from WNV-NS5-E218A-recovered mice with poor spatial learning show increased expression of genes that drive synaptic remodelling by microglia via complement. C1QA was upregulated and localized to microglia, infected neurons and presynaptic terminals during WNV neuroinvasive disease. Murine and human WNV neuroinvasive disease post-mortem samples exhibit loss of hippocampal CA3 presynaptic terminals, and murine studies revealed microglial engulfment of presynaptic terminals during acute infection and after recovery. Mice with fewer microglia (Il34(-/-) mice with a deficiency in IL-34 production) or deficiency in complement C3 or C3a receptor were protected from WNV-induced synaptic terminal loss. Our study provides a new murine model of WNV-induced spatial memory impairment, and identifies a potential mechanism underlying neurocognitive impairment in patients recovering from WNV neuroinvasive disease.

Tissue-specific transcription profile of cytokine and chemokine genes associated with flavivirus control and non-lethal neuropathogenesis in rabbits

We previously showed that New Zealand White (NZWRs) and cottontail rabbits (CTRs) are a suitable model for studying immune mechanisms behind virus control and non-lethal neuropathogenesis associated with West Nile virus (WNV) and Murray Valley encephalitis virus (MVEV) infections. In the current study, we observed that MVEV infection induced high IFNα, TNFα, IL6, and CXCL10 transcript levels in the brains of weanling NZWRs, unlike infection with the less virulent WNVNSW2011. These transcript levels also correlated with encephalitis severity. Widespread STAT1 protein expression in brain with moderate neuropathology suggests that IFN-I signaling is crucial for limiting neural infection and mediating non-lethal neuropathogenesis. Unlike NZWRs, CTRs limit neuroinvasion without upregulation of many cytokine/chemokine transcripts, suggesting a species-dependent virus control mechanism. However, the common IFNγ, TNFα and IL6 transcript upregulation in specific lymphoid organs suggest some conserved elements in the response against flaviviruses, unique to all rabbits.

Role of Immune Aging in Susceptibility to West Nile Virus

West Nile virus (WNV) can cause severe neuroinvasive disease in humans and currently no vaccine or specific treatments are available. As aging is the most prominent risk factor for WNV, age-related immune dysregulation likely plays an essential role in host susceptibility to infection with WNV. In this review, we summarize recent findings in effects of aging on immune responses to WNV infection. In particular, we focus on the age-dependent dysregulation of innate immune cell types-neutrophils, macrophages, and dendritic cells-in response to WNV infection, as well as age-related alterations in NK cells and γδ T cells that may associate with increased WNV susceptibility in older people. We also highlight two advanced technologies, i.e., mass cytometry and microRNA profiling, which significantly contribute to systems-level study of immune dysregulation in aging and should facilitate new discoveries for therapeutic intervention against WNV.

Differential Roles of Chemokines CCL2 and CCL7 in Monocytosis and Leukocyte Migration during West Nile Virus Infection

West Nile virus (WNV) is a re-emerging pathogen and the leading cause of epidemic encephalitis in the United States. Inflammatory monocytes are a critical component of the cellular infiltrate found in the CNS during WNV encephalitis, although the molecular cues involved in their migration are not fully understood. In mice, we previously showed that WNV infection induces a CCR2-dependent monocytosis that precedes monocyte migration into the CNS. Currently, the relative contribution of the CCR2 ligands, chemokines CCL2 and CCL7, in directing monocyte mobilization and leukocyte migration into the CNS is unclear. In this study, we demonstrate that, although both CCL2 and CCL7 are required for efficient monocytosis and monocyte accumulation in the CNS, only CCL7 deficiency resulted in increased viral burden in the brain and enhanced mortality. The enhanced susceptibility in the absence of CCL7 was associated with the delayed migration of neutrophils and CD8(+) T cells into the CNS compared with WT or Ccl2(-/-) mice. To determine whether CCL7 reconstitution could therapeutically alter the survival outcome of WNV infection, we administered exogenous CCL7 i.v. to WNV-infected Ccl7(-/-) mice and observed a significant increase in monocytes and neutrophils, but not CD8(+) T cells, within the CNS, as well as an enhancement in survival compared with Ccl7(-/-) mice treated with a linear CCL7 control peptide. Our experiments suggest that CCL7 is an important protective signal involved in leukocyte trafficking during WNV infection, and it may have therapeutic potential for the treatment of acute viral infections of the CNS.

Induction of virus-specific effector immune cell response limits virus replication and severe disease in mice infected with non-lethal West Nile virus Eg101 strain

Background

West Nile virus (WNV) is a neurotropic flavivirus that has emerged globally as a significant cause of viral encephalitis in humans. Herein, we investigated the immunological responses induced by two phylogenetically related WNV strains of lineage 1, WNV NY99, and WNV Eg101.

Methods

Eight-week-old C57BL/6J mice were inoculated with WNV NY99 or WNV Eg101 and mortality, virus burden in the periphery and brain, type 1 interferon response, WNV-specific antibodies, leukocyte infiltration, and inflammatory responses were analyzed.

Results

As expected, WNV NY99 infected mice demonstrated high morbidity and mortality, whereas no morbidity and mortality was observed in WNV Eg101 infected mice. Virus titers were comparable in the serum of both WNV NY99 and WNV Eg101 infected mice at day 3 after inoculation; however, at day 6, the virus was cleared from WNV Eg101 infected mice but the virus titer remained high in the WNV NY99 infected mice. Virus was detected in the brains of both WNV NY99 and Eg101 infected mice, albeit significantly higher in the brains of WNV NY99 infected mice. Surprisingly, levels of type 1 interferon and WNV-specific antibodies were significantly higher in the serum and brains of WNV NY99 infected mice. Similarly, protein levels of multiple cytokines and chemokines were significantly higher in the serum and brains of WNV NY99 infected mice. In contrast, we observed significantly higher numbers of innate and adaptive immune cells in the spleens and brains of WNV Eg101 infected mice. Moreover, total number and percentage of IFN-γ and TNF-α producing WNV-specific CD8⁺ T cells were also significantly high in WNV Eg101 infected mice.

Conclusions

Our data demonstrate that induction of virus-specific effector immune cell response limits virus replication and severe WNV disease in Eg101 infected mice. Our data also demonstrate an inverse correlation between leukocyte accumulation and production of pro-inflammatory mediators in WNV-infected mice. Moreover, increased production of pro-inflammatory mediators was associated with high-virus titers and increased mortality in WNV NY99 infected mice.

Risk factors for West Nile virus infection and disease in populations and individuals

West Nile virus (WNV) is a mosquito-borne enveloped positive-strand RNA virus that emerged in North America in 1999 in New York City. Over the past 15 years, WNV has become established throughout the USA and has spread into Canada, Mexico and the Caribbean. CDC reports indicate >41,000 clinical cases, including more than 1700 fatalities. An estimated 3 million people in the USA may have been infected to date. Infection with WNV is dependent on many factors including climate, mosquito habitats and immunologically naïve bird populations. In addition, variations within individuals contribute to the risk of severe disease, in particular, advanced age, hypertension, immunosuppression and critical elements of the immune response. Recent advances in technology now allow detailed analysis of complex immune interactions relevant to disease susceptibility.

Of Mice and Men: Protective and Pathogenic Immune Responses to West Nile virus Infection

West Nile virus, a mosquito-borne flavivirus, first emerged in the Western Hemisphere in 1999. Although the majority of infections are asymptomatic, WNV causes significant morbidity and mortality in a minority of individuals who develop neuroinvasive disease, in particular the elderly and immunocompromised. Research in animal models has demonstrated interactions between WNV and the innate and adaptive immune system, some of which protect the host and others which are deleterious. Studies of disease pathogenesis in humans are less numerous, largely due to the complexities of WNV epidemiology. Human studies that have been done support the notion that innate and adaptive immune responses are delicately balanced and may help or harm the host. Further human investigations are needed to characterize beneficial responses to WNV with the goal of such research leading to therapeutics and effective vaccines in order to control this emerging viral disease.

High producing tumor necrosis factor alpha gene alleles in protection against severe manifestations of dengue

Dengue virus (DENV) infection usually presents with mild self-limiting dengue fever (DF). Few however, would present with the more severe form of the disease, dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). In the present study, the association between IL-12B, IL-10 and TNF-α gene polymorphisms and dengue severity was investigated.

METHODS

A case-control study was performed on a total of 120 unrelated controls, 86 DF patients and 196 DHF/DSS patients. The polymorphisms in IL-12B, IL-10 and TNF-α genes were genotyped using PCR-RFLP and PCR-sequencing methods.

RESULTS

A protective association of TNF-α -308A allele and -308GA genotype against DHF/DSS was observed, while TNF-α -238A allele and -238GA genotype were associated with DHF/DSS. A combination of TNF-α -308GA+AA genotype and IL-10 non-GCC haplotypes, IL-12B pro homozygotes (pro1/pro1, pro2/pro2) and IL-12B 3'UTR AC were significantly correlated with protective effects against DHF/DSS. An association between the cytokine gene polymorphisms and protection against the clinical features of severe dengue including thrombocytopenia and increased liver enzymes was observed in this study.

CONCLUSION

The overall findings of the study support the correlation of high-producer TNF-α genotypes combined with low-producer IL-10 haplotypes and IL-12B genotypes in reduced risk of DHF/DSS.

Chemokines Referee Inflammation within the Central Nervous System during Infection and Disease

The discovery that chemokines and their receptors are expressed by a variety of cell types within the normal adult central nervous system (CNS) has led to an expansion of their repertoire as molecular interfaces between the immune and nervous systems. Thus, CNS chemokines are now divided into those molecules that regulate inflammatory cell migration into the CNS and those that initiate CNS repair from inflammation-mediated tissue damage. Work in our laboratory throughout the past decade has sought to elucidate how chemokines coordinate leukocyte entry and interactions at CNS endothelial barriers, under both homeostatic and inflammatory conditions, and how they promote repair within the CNS parenchyma. These studies have identified several chemokines, including CXCL12 and CXCL10, as critical regulators of leukocyte migration from perivascular locations. CXCL12 additionally plays an essential role in promoting remyelination of injured white matter. In both scenarios we have shown that chemokines serve as molecular links between inflammatory mediators and other effector molecules involved in neuroprotective processes.

IL-1R1 signaling regulates CXCL12-mediated T cell localization and fate within the central nervous system during West Nile Virus encephalitis

Immune cell entry into the virally infected CNS is vital for promoting viral clearance yet may contribute to neuropathology if not rigorously regulated. We previously showed that signaling through IL-1R1 is critical for effector T cell reactivation and virologic control within the CNS during murine West Nile virus (WNV) encephalitis. WNV-infected IL-1R1(-/-) mice also display increased parenchymal penetration of CD8(+) T cells despite lack of CD4-mediated full activation, suggesting dysregulation of molecular components of CNS immune privilege. In this study, we show that IL-1 signaling regulates the CNS entry of virus-specific lymphocytes, promoting protective immune responses to CNS viral infections that limit immunopathology. Analysis of blood-brain barrier function in the WNV-infected IL-1R1(-/-) mice revealed no alterations in permeability. However, parenchymal proinflammatory chemokine expression, including CCL2, CCL5, and CXCL10, was significantly upregulated, whereas microvasculature CXCL12 expression was significantly decreased in the absence of IL-1 signaling. We show that during WNV infection, CD11b(+)CD45(hi) infiltrating cells (macrophages) are the primary producers of IL-1β within the CNS and, through the use of an in vitro blood-brain barrier model, that IL-1β promotes CXCR4-mediated T cell adhesion to brain microvasculature endothelial cells. Of interest, IFNγ(+) and CD69(+) WNV-primed T cells were able to overcome CXCL12-mediated adhesion via downregulation of CXCR4. These data indicate that infiltrating IL-1β-producing leukocytes contribute to cellular interactions at endothelial barriers that impart protective CNS inflammation by regulating the parenchymal entry of CXCR4(+) virus-specific T cells during WNV infection.

Activation of intrinsic immune responses and microglial phagocytosis in an ex vivo spinal cord slice culture model of West Nile virus infection

West Nile virus (WNV) is a neurotropic flavivirus that causes significant neuroinvasive disease involving the brain and/or spinal cord. Experimental mouse models of WNV infection have established the importance of innate and adaptive immune responses in controlling the extent and severity of central nervous system (CNS) disease. However, differentiating between immune responses that are intrinsic to the CNS and those that are dependent on infiltrating inflammatory cells has proven difficult. We used a murine ex vivo spinal cord slice culture (SCSC) model to determine the innate immune processes specific to the CNS during WNV infections. By 7 days after ex vivo infection of SCSCs, the majority of neurons and a substantial percentage of astrocytes were infected with WNV, resulting in apoptotic cell death and astrogliosis. Microglia, the resident immune cells of the CNS, were activated by WNV infection, as exemplified by their amoeboid morphology, the development of filopodia and lamellipodia, and phagocytosis of WNV-infected cells and debris. Microglial cell activation was concomitant with increased expression of proinflammatory cytokines and chemokines, including CXCL10, CXCL1, CCL5, CCL3, CCL2, tumor necrosis factor alpha (TNF-α), TNF-related apoptosis-inducing ligand (TRAIL), and interleukin-6 (IL-6). The application of minocycline, an inhibitor of neuroinflammation, altered the WNV-induced proinflammatory cytokine/chemokine expression profile, with inhibited production of CCL5, CCL2, and IL-6. Our findings establish that CNS-resident cells have the capacity to initiate a robust innate immune response against WNV infection in the absence of infiltrating inflammatory cells and systemic immune responses.

IMPORTANCE

There are no specific treatments of proven efficacy available for WNV neuroinvasive disease. A better understanding of the pathogenesis of WNV CNS infection is crucial for the rational development of novel therapies. Development of a spinal cord slice culture (SCSC) model facilitates the study of WNV pathogenesis and allows investigation of the intrinsic immune responses of the CNS. Our studies demonstrate that robust CNS innate immune responses, including microglial activation and proinflammatory cytokine/chemokine production, develop independently of contributions from the peripheral immune system and CNS-infiltrating inflammatory cells.

Viral pathogen-associated molecular patterns regulate blood-brain barrier integrity via competing innate cytokine signals

Pattern recognition receptor (PRR) detection of pathogen-associated molecular patterns (PAMPs), such as viral RNA, drives innate immune responses against West Nile virus (WNV), an emerging neurotropic pathogen. Here we demonstrate that WNV PAMPs orchestrate endothelial responses to WNV via competing innate immune cytokine signals at the blood-brain barrier (BBB), a multicellular interface with highly specialized brain endothelial cells that normally prevents pathogen entry. While Th1 cytokines increase the permeability of endothelial barriers, type I interferon (IFN) promoted and stabilized BBB function. Induction of innate cytokines by pattern recognition pathways directly regulated BBB permeability and tight junction formation via balanced activation of the small GTPases Rac1 and RhoA, which in turn regulated the transendothelial trafficking of WNV. In vivo, mice with attenuated type I IFN signaling or IFN induction (Ifnar^−/−Irf7^−/−) exhibited enhanced BBB permeability and tight junction dysregulation after WNV infection. Together, these data provide new insight into host-pathogen interactions at the BBB during neurotropic viral infection.

West Nile virus (WNV) is an emerging pathogen capable of infecting the central nervous system (CNS), causing fatal encephalitis. However, the mechanisms that control the ability of WNV to cross the blood-brain barrier (BBB) and access the CNS are unclear. In this study, we show that detection of WNV by host tissues induces innate immune cytokine expression at the BBB, regulating BBB structure and function and impacting transendothelial trafficking of WNV. This regulatory effect is shown to happen rapidly following exposure to virus, to occur independently of viral replication within BBB cells, and to require the signaling of cytoskeletal regulatory Rho GTPases. These results provide new understanding of host-pathogen interactions at the BBB during viral encephalitis.

West Nile virus-induced cell adhesion molecules on human brain microvascular endothelial cells regulate leukocyte adhesion and modulate permeability of the in vitro blood-brain barrier model

Characterizing the mechanisms by which West Nile virus (WNV) causes blood-brain barrier (BBB) disruption, leukocyte infiltration into the brain and neuroinflammation is important to understand the pathogenesis of WNV encephalitis. Here, we examined the role of endothelial cell adhesion molecules (CAMs) in mediating the adhesion and transendothelial migration of leukocytes across human brain microvascular endothelial cells (HBMVE). Infection with WNV (NY99 strain) significantly induced ICAM-1, VCAM-1, and E-selectin in human endothelial cells and infected mice brain, although the levels of their ligands on leukocytes (VLA-4, LFA-1and MAC-1) did not alter. The permeability of the in vitro BBB model increased dramatically following the transmigration of monocytes and lymphocytes across the models infected with WNV, which was reversed in the presence of a cocktail of blocking antibodies against ICAM-1, VCAM-1, and E-selectin. Further, WNV infection of HBMVE significantly increased leukocyte adhesion to the HBMVE monolayer and transmigration across the infected BBB model. The blockade of these CAMs reduced the adhesion and transmigration of leukocytes across the infected BBB model. Further, comparison of infection with highly neuroinvasive NY99 and non-lethal (Eg101) strain of WNV demonstrated similar level of virus replication and fold-increase of CAMs in HBMVE cells suggesting that the non-neuropathogenic response of Eg101 is not because of its inability to infect HBMVE cells. Collectively, these results suggest that increased expression of specific CAMs is a pathological event associated with WNV infection and may contribute to leukocyte infiltration and BBB disruption in vivo. Our data further implicate that strategies to block CAMs to reduce BBB disruption may limit neuroinflammation and virus-CNS entry via 'Trojan horse' route, and improve WNV disease outcome.

Mechanism of West Nile virus neuroinvasion: a critical appraisal

West Nile virus (WNV) is an important emerging neurotropic virus, responsible for increasingly severe encephalitis outbreaks in humans and horses worldwide. However, the mechanism by which the virus gains entry to the brain (neuroinvasion) remains poorly understood. Hypotheses of hematogenous and transneural entry have been proposed for WNV neuroinvasion, which revolve mainly around the concepts of blood-brain barrier (BBB) disruption and retrograde axonal transport, respectively. However, an over‑representation of in vitro studies without adequate in vivo validation continues to obscure our understanding of the mechanism(s). Furthermore, WNV infection in the current rodent models does not generate a similar viremia and character of CNS infection, as seen in the common target hosts, humans and horses. These differences ultimately question the applicability of rodent models for pathogenesis investigations. Finally, the role of several barriers against CNS insults, such as the blood-cerebrospinal fluid (CSF), the CSF-brain and the blood-spinal cord barriers, remain largely unexplored, highlighting the infancy of this field. In this review, a systematic and critical appraisal of the current evidence relevant to the possible mechanism(s) of WNV neuroinvasion is conducted.

In vitro and in vivo characterization of a West Nile virus MAD78 infectious clone

The viral determinants governing the varied neuropathogenicity of different West Nile virus (WNV) strains are poorly understood. Here, we generated an infectious clone (WNV-MAD^IC) of the non-pathogenic strain WNV-MAD78 and compared its replication to that of parental WNV-MAD78 and a WNV-MAD78 infectious clone (WNV-MAD^TX-UTRs) containing the 5′ and 3′ untranslated regions (UTRs) of the pathogenic strain WNV-TX. All three viruses replicated at similar rates and caused similar lethality in mice. Thus, the infectious clone is indistinguishable from parental virus in replication and neurovirulence, and the UTRs alone do not account for the increased virulence of WNV-TX compared to WNV-MAD78.

Protective role of TNF-α, IL-10 and IL-2 in mice infected with the Oshima strain of Tick-borne encephalitis virus

Tick-borne encephalitis virus (TBEV) causes acute central nervous system disease. Here, we investigated the roles of the TNF-α, IL-10 and other cytokines in appropriate KO mice following infection with Oshima and Sofjin strains of TBEV. Following infection with the Oshima strain, mortality rates were significantly increased in TNF-α KO and IL-10 KO mice compared with wild type (WT) mice. These results suggested that TNF-α and IL-10 play protective roles against fatal infection due to Oshima strain infection. However, viral loads and proinflammatory cytokine levels in the brain of TNF-α KO andIL-10 KO mice were not significantly different compared with those of WT mice. On the other hand, all WT, TNF-α KO and IL-10 KO mice died following infection with Sofjin strain. Interestingly, Sofjin-infected mice did not exhibit an up-regulated mRNA level of IL-2 in the spleen in all groups of mice, whereas Oshima-infected mice showed significantly increased level of IL-2 compared with mock-infected mice. From these results, we suggest that TNF-α, IL-10 and IL-2 are key factors for disease remission from fatal encephalitis due to infection with Oshima strain of TBEV.

CD8 T-cell-mediated protection against liver-stage malaria: lessons from a mouse model

Malaria is a major global health problem, with severe mortality in children living in sub-Saharan Africa, and there is currently no licensed, effective vaccine. However, vaccine-induced protection from Plasmodium infection, the causative agent of malaria, was established for humans in small clinical trials and for rodents in the 1960s. Soon after, a critical role for memory CD8 T cells in vaccine-induced protection against Plasmodium liver-stage infection was established in rodent models and is assumed to apply to humans. However, these seminal early studies have led to only modest advances over the ensuing years in our understanding the basic features of memory CD8 T cells required for protection against liver-stage Plasmodium infection, an issue which has likely impeded the development of effective vaccines for humans. Given the ethical and practical limitations in gaining mechanistic insight from human vaccine and challenge studies, animal models still have an important role in dissecting the basic parameters underlying memory CD8 T-cell immunity to Plasmodium. Here, we will highlight recent data from our own work in the mouse model of Plasmodium infection that identify quantitative and qualitative features of protective memory CD8 T-cell responses. Finally, these lessons will be discussed in the context of recent findings from clinical trials of vaccine-induced protection in controlled human challenge models.

Reduced immune cell infiltration and increased pro-inflammatory mediators in the brain of Type 2 diabetic mouse model infected with West Nile virus

Background

Diabetes is a significant risk factor for developing West Nile virus (WNV)-associated encephalitis (WNVE) in humans, the leading cause of arboviral encephalitis in the United States. Using a diabetic mouse model (db/db), we recently demonstrated that diabetes enhanced WNV replication and the susceptibility of mice to WNVE. Herein, we have examined immunological events in the brain of wild type (WT) and db/db mice after WNV infection. We hypothesized that WNV-induced migration of protective leukocytes into the brain is attenuated in the presence of diabetes, leading to a high viral load in the brain and severe disease in diabetic mice.

Methods

Nine-week old C57BL/6 WT and db/db mice were infected with WNV. Leukocyte infiltration, expression of cell adhesion molecules (CAM), neuroinflammatory responses, activation of astrocytes, and neuronal death were analyzed using immunohistochemistry, qRT-PCR, flow cytometry, and western blot.

Results

We demonstrate that infiltration of CD45⁺ leukocytes and CD8⁺T cells was significantly reduced in the brains of db/db mice, which was correlated with attenuated expression of CAM such as E-selectin and ICAM-1. WNV infection in db/db mice was associated with an enhanced inflammatory response in the brain. mRNA and protein levels of key chemokines such as CXCL10, CXCL1, CCL2, CCL5, CCL3, and G-CSF, and cytokines such as IL-1β, TNF, IL-6, IFNγ, and IL-1α were significantly elevated in the brains of db/db mice compared to WT mice. Elevated levels of cytokines also correlated with increased astrocytes activation and neuronal damage in the brains of db/db mice.

Conclusion

These data suggest that reduced leukocytes recruitment, in part, due to lower levels of CAM results in failure to clear WNV infection from the brain leading to increased production of inflammatory molecules, which mediates increased neuronal death and mortality in db/db mice. This is the first study to elucidate the expression of CAM and their correlation with the migration of leukocytes, specifically cytotoxic CD8⁺ T cells, in increasing disease severity in the diabetic mouse model.