| 1. |
- Kurhade, Chaitanya, 1989-
(författare)
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Interplay between tick-borne encephalitis virus and the host innate immunity
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Flaviviruses are important emerging and re-emerging arthropod-borne pathogens that cause significant morbidity and mortality in humans. It consists of globally distributed human pathogens such as tick-borne encephalitis virus (TBEV), West Nile virus (WNV), Japanese encephalitis virus (JEV), yellow fever virus (YFV), dengue virus (DENV), and Zika virus (ZIKV). Depending on type, flaviviruses can cause a variety of symptoms ranging from haemorrhage to neurological disorders.Virus infection is detected by host pattern recognition receptors (PRRs), and through downstream signalling it leads to the production of interferons (IFNs). These IFNs then act in an autocrine or paracrine manner on the cells to induce various IFN-stimulated genes (ISGs), which have antiviral roles. However, the amount of IFN produced depends on the nature of the PRRs used by host cells to detect a particular virus. Although there are many PRRs present in the host cells, their relative contribution in different cell types and against a specific virus may vary. In the first study, we determined the importance of IPS-1 signalling in immunity and pathogenicity of tick-borne flaviviruses. This is an adaptor protein for cytoplasmic RIG-I-like receptors. Using IPS-1-deficient mice, we showed its importance against TBEV and Langat virus (LGTV) infection (the LGTV model virus belongs to the TBEV serogroup). Absence of IPS-1 leads to uncontrolled virus replication in the central nervous system (CNS), but it has only a minor role in shaping the humoral immune response at the periphery. LGTV-infected IPS-1-deficient mice showed apoptosis, activation of microglia and astrocytes, an elevated proinflammatory response, and recruitment of immune cells to the CNS. Interestingly, we also found that IFN-b upregulation after viral infection was dependent on IPS-1 in the olfactory bulb of the brain. Thus, our results suggest that local immune microenvironment of distinct brain regions is critical for determination of virus permissiveness.Interferons can upregulate several ISGs. Viperin is one such ISG that has a broad-spectrum antiviral action against many viruses. However, the importance of cell type and the significance of viperin in controlling many flavivirus infections in vivo is not known. Using viperin-deficient mice, we found that viperin was necessary for restriction of LGTV replication in the olfactory bulb and cerebrum, but not in the cerebellum. This finding was also confirmed with primary neurons derived from these brain regions. Furthermore, we could also show the particular importance of viperin in cortical neurons against TBEV, WNV, and ZIKV infection. The results suggested that a single ISG can shape the susceptibility and immune response to a flavivirus in different regions of the brain.Although viperin is such an important ISG against flaviviruses, the exact molecular mechanism of action is not known. To understand the mechanism, we performed co-immunoprecipitation screening to identify TBEV proteins that could interact with viperin. While viperin interacted with the prM, E, NS2A, NS2B, and NS3 proteins of TBEV, its interaction with NS3 led to its degradation through the proteosomal pathway. Furthermore, viperin could reduce the stability of other viperin-binding TBEV proteins in an NS3-dependent manner. We screened for viperin activity regarding interaction with NS3 proteins of other flaviviruses. Viperin interacted with NS3 of JEV, ZIKV, and YFV, but selectively degraded NS3 proteins of TBEV and ZIKV, and this activity correlated with its antiviral activity against these viruses.The last study was based on in vivo characterization of the newly isolated MucAr HB 171/11 strain of TBEV which caused unusual gastrointestinal and constitutional symptoms. This strain was compared with another strain, Torö-2003, of the same European subtype of TBEV but isolated from the different focus. Here we found unique differences in their neuroinvasiveness and neurovirulence, and in the immune response to these two strains.In summary, my work shed some light on the interplay between tick-borne flavivirus and the innate immune system. I have shown two examples of CNS region-specific differences in innate immune response regarding both in IFN induction pathways and antiviral effectors. Furthermore, we have investigated the in vivo pathogenesis of a strain of TBEV that caused unusual gastrointestinal and constitutional symptoms.
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| 2. |
- Lindqvist, Richard, 1985-
(författare)
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The role of the type I interferons and viperin during neurotropic flavivirus infection
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Flaviviruses are globally distributed pathogens that cause millions of human infections annually. One of the most detrimental outcomes of flavivirus infection is encephalitis, which is caused by neurotropic flaviviruses such as West Nile virus (WNV), Japanese encephalitis virus (JEV), and Tick-borne encephalitis virus (TBEV). The type I interferons (IFNs) are powerful cytokines, and they are known as the first line of defense against viral infection. IFNs are expressed at low or undetectable levels at the basal state, but recognition of invading pathogens triggers a robust IFN response. After synthesis, IFN is secreted and acts in an autocrine or paracrine manner by binding to the interferon-α/β receptor (IFNAR) receptor, which is expressed on the surface of all nucleated cells. Binding to IFNAR mediates a downstream cascade that triggers expression of hundreds of interferon-stimulated genes (ISGs). Some ISGs express signaling molecules to amplify the response while others are potent antiviral proteins that can efficiently limit viral infection. The impact of the type I IFN response in tick-borne flavivirus infection was not previously known. We found that the type I IFN response was crucial for protection of mice against neurotropic infection with tick-borne flaviviruses such as TBEV and Langat virus (LGTV). The response was needed both in the periphery as well as in the central nervous system (CNS), as transgenic mice lacking either peripherally or CNS-located IFNAR both succumbed to LGTV infection. Although we found that the local IFN response within the CNS is essential for protection against lethal LGTV infection, the cells responsible for the local IFN production were not known.Astrocytes are one of the most abundant cell types within the CNS, but their role in neurotropic flavivirus infection was not fully characterized. In other viral infections, astrocytes are potent IFN producers, thus we were interested in characterizing the role of the type I IFN response in astrocytes during neurotropic flavivirus infection and its contribution to flavivirus pathogenesis. We found that upon flavivirus infection, astrocytes mount a strong type I IFN response that protects neighboring astrocytes from TBEV, JEV, WNV, and ZIKV infection. Furthermore, IFN signaling was found to protect astrocytes from TBEV-induced cytopathic effects. However, the ISGs that mediated these effects were not known.In vitro studies of viperin, which was discovered in 2001 as an ISG with broad antiviral activity, has shown strong antiviral activity against TBEV, but its role in vivo and mode of action in flavivirus infection was not known. Using mice deficient in viperin, we wanted to determine the role of viperin in flavivirus infection. We found that viperin plays a region-specific role in the brain by controlling LGTV replication in the olfactory bulb and cerebrum. Remarkably, viperin was able to inhibit TBEV replication in primary cortical neurons isolated from the cerebrum but not in granule cell neurons isolated from the cerebellum. Furthermore, IFN treatment failed to compensate for loss of viperin in cortical neurons, indicating that viperin might be the most important ISG against TBEV in cortical neurons. Interestingly, we also found that viperin is needed for the IFN-mediated antiviral response against WNV and ZIKV in cortical neurons. Thus, viperin showed broad but region-specific antiviral mechanisms against different flaviviruses.Although viperin has been shown to inhibit many viruses, the molecular antiviral mechanism is not clear and appears to differ between viruses. We performed a co-immunoprecipitation (CoIP) screen to identify TBEV proteins that could interact with viperin, and prM, E, NS2A, NS2B, and NS3 were identified. Interaction of viperin with NS3 resulted in degradation of the viral protein. We screened NS3 of JEV, yellow fever virus (YFV), ZIKV, and TBEV. Interestingly, although all NS3 proteins tested interacted with viperin, only those of ZIKV, and TBEV were significantly degraded by viperin. The degradation of NS3 correlated well with the antiviral activity of viperin, as only TBEV and ZIKV were inhibited.In summary, this work revealed the importance of the local type I IFN response in the brain during neurotropic infections by flaviviruses. We identified astrocytes to be an important IFN producer within the CNS during neurotropic flavivirus infection. Astrocytes release type I IFN quickly after viral infection, and this interferon protects neighboring neurons and astrocytes from infection. Furthermore, viperin, a very potent antiviral ISG, is highly expressed in astrocytes and it is essential for controlling viral replication and mediating viral clearance in both neurons and astrocytes of the cerebrum. We also found that viperin specifically targeted the NS3 proteins of TBEV and ZIKV for degradation.
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| 3. |
- Rosendal, Ebba, 1993-
(författare)
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Host-pathogen interactions during tick-borne flavivirus infection : pathogenesis, tropism and tools
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Tick-borne encephalitis virus (TBEV) is a neurotropic member of the genus Flavivirus. It may transmit to humans through the bite of an infected tick or consumption of unpasteurized dairyproducts, and causes tick-borne encephalitis (TBE). TBE constitutes a significant health burden in Eurasia, with more than 10,000 cases reported every year. In this thesis, I have investigated the role of the innate immune response in restricting infection in the central nervous system (CNS), identified virulence factors and developed a new model system to study the structural proteins of TBEV.Viral tropism is important for understanding underlying mechanisms of pathology. In the first part,we combined whole-brain imaging with single nuclei RNA-sequencing after infection of wildtype (WT) and interferon (IFN) α/β receptor knockout (Ifnar-/-) mice by Langat virus (LGTV), a low-virulent model for TBEV. We found that absence of type I IFN signaling changes viral tropism and leads to an impaired inflammatory response. For neurons, astrocytes, and microglia we also compared the response to LGTV infection in vivo with the response of primary monocultures infected in vitro. Primary cells are often used for mechanistic studies of neurotropic viruses, but we found limited overlap in altered pathways between in vivo and in vitro, which emphasizes the role of cellular crosstalk in shaping the transcriptional response to infection in the brain.The second part addresses viral determinants of pathogenicity. By comparing disease progression induced by different TBEV strains in a mouse model, we identified TBEV 93/783 as a highly virulentstrain belonging to the European subtype. We could show that two unusual amino acid substitutions in the envelope (E) protein of 93/783 enhanced neurovirulence and contributed to pathogenesis. To facilitate further studies of the structural proteins of TBEV, we generated and thoroughlycharacterized a chimeric virus with the pre-membrane (prM) and ecto-E protein of TBEV 93/783 in the genetic background of LGTV. The chimeric virus shows similar growth kinetics as the parental LGTV in vitro but is less pathogenic in our mouse model. Meanwhile, it remained neurovirulent and structurally similar to TBEV, making it a useful tool for studying the structural proteins of TBEV under lower biosafety conditions. Taken together, these findings deepen our understanding of what determines the outcome of tick-borne flavivirus infection and the utility of the available model systems for studying disease mechanisms.
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| 4. |
- Vonderstein, Kirstin, 1986-
(författare)
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Viperin vs. tick-borne encephalitis virus : mechanism of a potent antiviral protein
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Tick-borne encephalitis virus (TBEV) is a very important virus medically, causing mild or severe encephalitis often with long-lasting sequelae. Treatment of tick-borne encephalitis is limited to supportive care, and antiviral drugs are much needed.The type-I interferon (IFN) system is the first line of host defense against many viruses. Infected cells secrete type-I IFN to alert neighboring cells. These cells in turn upregulate the expression of antiviral proteins to protect themselves from the virus.In this work, we found that the interferon-induced host protein viperin (virus-inhibitory protein, endoplasmic reticulum-associated, interferon-inducible) has a pronounced antiviral effect against TBEV. Viperin is an evolutionarily conserved protein with three domains: the N-terminus, the radical S-adenosyl methionine (SAM) domain, and the C-terminus. Viperin shows antiviral activity against a broad spectrum of different viruses. However, its mode of action appears to be virus-specific.We therefore concentrated on determining the antiviral mechanism of viperin against TBEV. The specific questions addressed in this thesis are: (1) which steps of the TBEV infectious cycle are targeted by viperin?, (2) which domains of viperin are responsible for its antiviral activity?, and (3) which interaction partners does viperin need in order to have an antiviral effect against TBEV?First, we investigated which step(s) of the TBEV life cycle viperin targets by using several assays to examine the effects of viperin on virus binding, entry, genome replication, assembly, and release.We found that viperin inhibited the replication of positive-sense genomic RNA and also targeted particle release, selectively enhancing the release of membrane-associated capsid particles.For inhibition of genome replication, viperin was dependent on the host cellular protein CIAO1 (cytosolic iron-sulfur assembly component 1). CIAO1 interacted with the C-terminus of viperin and was necessary for the maturation and stability of viperin, and also for loading of an iron-sulfur cluster onto the SAM domain. The SAM domain required this iron-sulfur cluster to perform its function as a radical SAM enzyme, which was required for the inhibition of TBEV genome replication. In addition to the SAM domain and the C-terminus, viperin needed its N-terminus in order to be fully antivirally active during late replication, since the N-terminus directed viperin to the endoplasmic reticulum, where genome replication takes place.Furthermore, viperin targeted GBF1 (Golgi-specific brefeldin A-resistance guanine nucleotide exchange factor 1), a host protein known to be involved in the secretory pathway. Interaction between the N-terminus of viperin and GBF1 appeared to induce an enhance release of capsid particles independently of the later steps of the classical secretory pathway. The enhanced secretion of capsid particles by viperin occurred at the expense of whole, infectious virions and is therefore a completely novel antiviral mechanism. In summary, this work identified viperin as a very strong inhibitor of TBEV, and its antiviral mechanism was characterized in detail. Viperin was found to target multiple steps in the TBEV infectious cycle by both inhibiting viral RNA replication and inducing secretion of capsid particles. These findings provide new insights into the interplay between TBEV and viperin, and offer new approaches to our understanding of the molecular and cellular mechanisms of TBEV infection, which may contribute to the development of a treatment for TBEV.
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| 5. |
- Wallenhammar, Amélie, 1986-, et al.
(författare)
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Developing a novel strategy to determine new Tick-borne encephalitis foci
- 2018
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Ingår i: 15th Smögen Summer Symposium on Virology, Smögen, Sweden, August 23-25, 2018..
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Konferensbidrag (refereegranskat)abstract
- TBEV is the most important viral tick-borne zoonosis in Europe, and infection may lead to severeCNS disease, including encephalitis and myelitis. Climate changes have increased the tickdistribution in Sweden, increasing the risk areas of Tick-borne encephalitis (TBE) at severalregions including the Örebro county. The TBE virus (TBEV) is usually transmitted to humans viatick bites, however oral transmission through consumption of non-pasteurized dairy products havealso been described. Both TBEV and antibodies against the viral proteins have been detected inmilk of goats, sheep and cattle. Since the prevalence of TBEV in the tick population is low there is a need for new and robust surveillance techniques identifying novel risk areas of TBEV at earlystages.In this study we have developed a strategy for identifying new TBEV foci. We have collected raw milk and colostrum samples from sheep and goats in the Örebro region. The milk samples were analyzed for the presence of TBEV antibodies by ELISA. In addition, the ELISA results were further verified by an in-house Western Blot assay where milk samples were used asprimary antibody to detect the Envelope-protein of TBEV. This method has so far revealed two novel TBEV foci within the Örebro county. Questing ticks and ticks feeding on sheep have been collected at areas of TBEV positive milk. The ticks are currently being analyzed for TBEV by PCR. The specific Örebro strains will be isolated from TBEV positive ticks and the viral genomeswill be further characterized using established next-generation sequencing technique.
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| 6. |
- Wallenhammar, Amélie, 1986-, et al.
(författare)
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Revealing new tick-borne encephalitis foci by screening antibodies in sheep milk
- 2019
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Ingår i: 16th Smögen Symposium on Virology, August 22-24, 2019.
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Konferensbidrag (refereegranskat)abstract
- Climate changes have increased the tick-distribution in Sweden, and the prevalence of ticks has been predicted to increase towards the northern parts of the country, increasing the risk of tick-borne zoonosis in new regions. Tick-borne encephalitis (TBE) is the most important viral tick-borne zoonosis in Sweden as well as in Europe. TBE virus (TBEV) infection often leads to severe CNS disease, including encephalitis and severe myelitis, which may lead to paralysis and respiratory failure in humans. TBEV and antibodies against TBEV are excreted in milk of goats, sheep and cattle and the virus can be ingested orally by consumption of non-pasteurized dairy products. Since the prevalence of TBEV in the tick population is low there is a need for new and robust surveillance techniques identifying new risk areas of TBEV at early stages.In this study we have developed a novel strategy for identifying new TBEV foci. We have collected raw milk and colostrum samples from sheep and goats in Örebro County, Sweden. The milk samples were analyzed for the presence of TBEV antibodies by ELISA, and validated by an in-house Western Blot assay where milk samples were used as primary antibody to detect purified TBEV E-protein. By monitoring TBEV antibodies in milk we have found three novel foci in the Örebro County which also overlap with the plausible place of infection of registered human TBE cases reported during 2009-2018. Furthermore, the stability of TBEV in milk and raw milk was studied at different temperatures. Our data indicates that keeping unpasteurized milk at 4 ˚C will preserve the infectivity of TBEV for several days. Ticks have also been collected from areas with TBEV positive milk. We aim to extract total RNA from the sampled ticks, followed by TBEV detection by nested-PCR and next-generation sequencing.Here we present a novel technique to reveal risk areas of TBE in Sweden, which is robust, reliable, and non-invasive and can accordingly be used to map TBEV “hotspots”. In the TBE foci, more than 50 % of the tested animals were antibody positive, and TBEV infectivity in refrigerated milk was preserved, stressing the importance of pasteurization before consumption.
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| 7. |
- Överby Wernstedt, Anna, et al.
(författare)
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Hiding from intracellular pattern recognition receptors, a passive strategy of flavivirus immune evasion
- 2011
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Ingår i: Virulence. - : Informa UK Limited. - 2150-5594 .- 2150-5608. ; 2:3, s. 238-240
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Tidskriftsartikel (refereegranskat)abstract
- Tick-borne encephalitis virus (TBEV) is a medically important flavivirus in Europe and Asia, causing meningitis and encephalitis in thousands of people annually. Despite its relevance for public health, the interaction of TBEV with the type I interferon (IFN) system is poorly characterized. Induction of these antiviral cytokines is normally triggered by cytoplasmic recognition of viral signature molecules such as double-stranded (ds) RNA. In a recent paper, we showed that TBEV infection leads to formation of intracellular membrane vesicles which protect the viral dsRNA from cellular recognition. This delays the onset of antiviral IFN production sufficiently enough for an unhindered release of progeny viruses over 24 h. Thus, TBEV has evolved a stealth strategy to outrun the antiviral IFN response.
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| 8. |
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