Combined treatment of adenosine nucleoside inhibitor NITD008 and histone deacetylase inhibitor vorinostat represents an immunotherapy strategy to ameliorate West Nile virus infection

West Nile virus (WNV), a member of the Flaviviridae family, is the leading cause of viral encephalitis in the United States. Despite efforts to control the spread of WNV, there has been an increase in the number of outbreaks and clinical cases with neurological problems. There are no antiviral compounds currently in trials for WNV. NITD008 is an adenosine analogue inhibitor that interrupts the RNA-dependent RNA polymerase of flaviviruses. Previous studies demonstrated NITD008 as a potent antiviral for dengue virus, however this drug was associated with preclinical toxicity. The ability of NITD008 to block WNV replication is only shown in Vero cells. Neuroinflammation is also a major cause of the WNV-associated pathology, therefore we evaluated the effect of NITD008 and a newly characterized anti-inflammatory drug vorinostat (SAHA), a histone deacetylase inhibitor, on WNV replication and disease progression in a mouse model. When administered at 10 and 25mg/kg at days 1-6 after WNV infection in C57BL/6 mice, NITD008 conferred complete protection from clinical symptoms and death, which correlated with reduced viral load in the serum and restriction of virus-CNS entry. Delay of NITD008 treatment to days 3-6 and days 5-9 after infection, when WNV replication was high in the periphery and brain, resulted in the gradual loss of protection against WNV infection. However, co-treatment with SAHA and NITD008 during the CNS phase of disease improved disease outcome significantly by reducing inflammation and neuronal death. Our results support potential synergistic effect of combination therapy of NITD008 with SAHA for the treatment of WNV encephalitis.

Expression of triggering receptor expressed on myeloid cells-1 (TREM-1) is up-regulated following West Nile virus infection (WNV): implication for a role in innate immune responses (VIR1P.968)

Activation of TREM-1 signaling via adaptor protein DAP12 is important for inflammation and activation of antigen presenting cells, however little is known about its role in viral infections. Innate immune responses are essential for the control of Flaviviruses including WNV, which has emerged as a significant cause of viral encephalitis in humans. Here, we investigated the effect of Flavivirus infection on the expression of TREMs and its potential role in production of cytokines. We show that expression of TREM-1 was markedly increased in dengue virus-infected THP-1 cells, which correlated with peak viral titers. Similarly, WNV infection significantly increased the mRNA levels of TREM-1 in mouse embryonic fibroblasts (MEFs), BMDM and BMDC. In vivo characterization of TREMs in mice demonstrated significant up-regulation in the transcripts of TREM-1, -3 and -4 in the peritoneal cavity cells and brain at day 3 and 8 after WNV infection respectively. Interestingly, serum levels of soluble-TREM-1 also increased significantly at days 2-3 after infection. Further, activation of TREM-1 using an agonist antibody increased mRNA of WNV-induced cytokines such as IFN-α, TNF-α and IL-6 in MEFs, which decreased following blocking of TREM-1. Collectively, our results for the first time document response of TREMs to Flavivirus infection and indicate a novel role of TREM-1 in modulating inflammatory response to WNV. Further studies are ongoing to define role of TREM-1 in WNV disease outcome.

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.

Reduced immune cells infiltration and increased neuroinflammation in type 2 diabetic mice infected with West Nile virus (P6038)

Diabetes is a significant risk factor for developing West Nile virus (WNV)-associated encephalitis (WNVE) in humans. Using a diabetic mouse model, db/db, we recently demonstrated that diabetes enhanced WNV replication and susceptibility of mice to WNVE. Herein, we have examined immunological and pathological events in the brain of wild-type (WT) and db/db mice after WNV infection. C57BL/6 WT and db/db mice were infected with WNV and leukocyte infiltration, expression of cell adhesion molecules (CAM), neuroinflammatory responses and neuronal death were analyzed. 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 enhanced inflammatory response in the brain characterized by significantly high levels of multiple cytokines and chemokines. Elevated levels of cytokines correlated with increased astrocytes activation and neuronal damage in the brain of db/db mice. These data suggest that reduced leukocytes recruitment in the brain, in part, due to lower levels of CAM, results in failure to clear WNV infection leading to increased neuroinflammation, which mediates increased neuronal death and mortality in db/db mice. This is the first study to elucidate neuropathogenesis of WNV infection in a diabetic mouse model and can be used to develop therapies to manage WNVE in diabetics.

Inflammasome adaptor protein ASC is critical for the immune response and survival in West Nile virus encephalitis (P6110)

Innate immune responses are essential for WNV clearance, dissemination and neurovirulence. Pattern recognition receptors and other danger signals activate assembly of inflammasome complex, which modulates antiviral defense responses. ASC is an important adaptor molecule, which mediates downstream signaling pathways of NLRP3 inflammasomes. In this study we defined the role of ASC in WNV immunity. Infection of cultured BMDCs showed that ASC was essential for the activation of caspase-1, a key component of inflammasome assembly. ASC-/- mice were highly susceptible to WNV infection marked by increased mortality, enhanced viremia and virus replication in the CNS. As compared to wild type mice, key cytokines including IL-1β and IFN-γ were significantly reduced in the sera of ASC mice. Additionally, antiviral IFN-α levels were also decreased in the sera of ASC-/- mice. Increased virus titers in the brain of ASC-/- mice correlated with increased inflammation and neuronal apoptosis. However, intracranial inoculation of WNV did not result in significant differences in the virus titers in both groups suggesting that impaired immune response coupled with failure to clear virus in the periphery leads to increased neuropathology and mortality in ASC-/- mice. Collectively, our data provides new insights into the role of ASC as an essential modulator of inflammasome-dependent and -independent immune response to effectively control WNV infection.

Expression of TREM-1 is triggered by flaviviruses: possible role in virus-associated innate immune responses (P1381)

Activation of Triggering Receptor Expressed on Myeloid cells 1 (TREM-1), an immunoreceptor expressed mainly on immune cells results in a cascade of inflammatory effects including cytokine production. In addition, TREM-1 also modulates signaling cascades of other PRRs such as TLRs and NLRs. Engagement of the TREM-1 receptor via adaptor protein DAP12 leads to the activation of downstream kinases, mobilization of intracellular calcium and production of pro-inflammatory cytokines. Innate immune responses are essential for the clearance, dissemination and neurovirulence of West Nile virus (WNV), a neurotropic flavivirus, which has emerged in the U.S. as a significant cause of viral encephalitis in humans. However, the role of TREM-1 signaling pathway in immunity to flaviviruses is unclear. In this study we investigated the changes in the expression kinetics and activation of TREM-1 following WNV infection. Expression of TREM-1 was markedly increased in WNV-infected mouse immune cells and embryonic fibroblasts (MEFs) at 48 hrs after infection and in the mouse brain at day 8 after infection. Further, activation of TREM-1 using agonist antibody resulted in an increase in the levels of IFN-β and key cytokines in WNV-infected MEFs. Our results so far indicate a possible role of TREM-1 in the induction of inflammatory innate immune responses to WNV and further studies are ongoing to characterize unexplored mechanisms of TREM-1 associated with the pathogenesis of flaviviruses.

Impaired virus clearance, compromised immune response and increased mortality in type 2 diabetic mice infected with West Nile virus

Clinicoepidemiological data suggest that type 2 diabetes is associated with increased risk of West Nile virus encephalitis (WNVE). However, no experimental studies have elucidated the role of diabetes in WNV neuropathogenesis. Herein, we employed the db/db mouse model to understand WNV immunopathogenesis in diabetics. Nine-week old C57BL/6 WT and db/db mice were inoculated with WNV and mortality, virus burden in the periphery and brain, and antiviral defense responses were analyzed. db/db mice were highly susceptible to WNV disease, exhibited increased tissue tropism and mortality than the wild-type mice, and were unable to clear the infection. Increased and sustained WNV replication was observed in the serum, peripheral tissues and brain of db/db mice, and heightened virus replication in the periphery was correlated with enhanced neuroinvasion and replication of WNV in the brain. WNV infection in db/db mice was associated with enhanced inflammatory response and compromised antiviral immune response characterized by delayed induction of IFN-α, and significantly reduced concentrations of WNV-specific IgM and IgG antibodies. The compromised immune response in db/db mice correlated with increased viremia. These data suggest that delayed immune response coupled with failure to clear the virus leads to increased mortality in db/db mice. In conclusion, this study provides unique mechanistic insight into the immunopathogenesis of WNVE observed in diabetics and can be used to develop therapeutics for the management of WNVE among diabetic patients.

West Nile virus-induced disruption of the blood-brain barrier in mice is characterized by the degradation of the junctional complex proteins and increase in multiple matrix metalloproteinases

West Nile virus (WNV) encephalitis is characterized by neuroinflammation, neuronal loss and blood-brain barrier (BBB) disruption. However, the mechanisms associated with the BBB disruption are unclear. Complex interactions between the tight junction proteins (TJP) and the adherens junction proteins (AJP) of the brain microvascular endothelial cells are responsible for maintaining the BBB integrity. Herein, we characterized the relationship between the BBB disruption and expression kinetics of key TJP, AJP and matrix metalloproteinases (MMPs) in the mice brain. A dramatic increase in the BBB permeability and extravasation of IgG was observed at later time points of the central nervous system (CNS) infection and did not precede virus-CNS entry. WNV-infected mice exhibited significant reduction in the protein levels of the TJP ZO-1, claudin-1, occludin and JAM-A, and AJP β-catenin and vascular endothelial cadherin, which correlated with increased levels of MMP-1, -3 and -9 and infiltrated leukocytes in the brain. Further, intracranial inoculation of WNV also demonstrated increased extravasation of IgG in the brain, suggesting the role of virus replication in the CNS in BBB disruption. These data suggest that altered expression of junction proteins is a pathological event associated with WNV infection and may explain the molecular basis of BBB disruption. We propose that WNV initially enters CNS without altering the BBB integrity and later virus replication in the brain initiates BBB disruption, allowing enhanced infiltration of immune cells and contribute to virus neuroinvasion via the 'Trojan-horse' route. These data further implicate roles of multiple MMPs in the BBB disruption and strategies to interrupt this process may influence the WNV disease outcome.