The tick borne flaviviruses (TBFV) includes Tick borne encephalitis virus (TBEV), Omsk hemorrhagic fever virus, Kyasanur forest disease virus, Powassan virus and Langat virus (LGTV). The TBFV are listed among the NIAID category B and C lists of priority for research on pathogenesis, to identify novel targets for therapeutic and vaccine development. As their name suggests, these viruses are transmitted by ticks, and following infection of humans, cause encephalitis, meningitis or hemorrhagic fevers resulting in approximately 10,000 to 13,000 hospitalizations annually with mortality rates as high as 40%. The TBFV belong to the Family Flaviviridae, genus Flavivirus, which comprise some of the most medically significant emerging and re-emerging pathogens. Other members include the mosquito-borne West Nile virus (WNV), Japanese encephalitis virus (JEV), dengue virus (DEN) and yellow fever virus (YFV). Hence, research into the pathogenesis of TBFV will reveal insight into the biology of this globally important group of viruses. The research in our laboratory aims to identify and understand interactions between the TBFV and their hosts (both the tick and the mammal) critical to virus replication and pathogenesis. We have been studying LGTV which is a naturally attenuated member of the TBFV that shares approximately 80% identity with TBEV at the amino acid level. This makes LGTV an excellent model to gain insight into the TBFV. The main studies ongoing in the laboratory are outlined below. 1. Study of virus interactions with the invertebrate host. Ticks represent the natural reservoir of TBFV and therefore are critical for virus persistence in nature and are the major source of infection for humans. We have investigated global transcriptional changes in Ixodes scapularis nymphs infected with LGTV using custom Agilent microarrays. The microarray was based on sequences from an mRNA library derived from salivary glands of Ixodes scapularis ticks.
The aim of this work is to identify tick host proteins important for the replication or transmission of TBFV. These proteins can be used for the development of novel anti-tick vaccines that prevent virus transmission to the immunized mammalian host. We first examined transcriptional changes in uninfected ticks during feeding on mice. This revealed clusters of genes that were differentially regulated, particularly on day 0, 1 or 3 post tick attachment. Preliminary results from experiments with LGTV-infected ticks have identified a subset of these genes that are affected by infection. We are currently working to confirm these results and will then determine the immunogenic potential of those gene products. 2. Interactions between TBFV and host innate responses to infection. Following the bite from an infected tick, dendritic cells (DCs) resident in the skin of the mammalian host are among the first cell types infected by TBFV. These cells have important roles in innate immunity through the production of interferon (IFN), cytokines and chemokines, as well as in orchestrating adaptive immunity. Thus, early interactions between these cells and TBFV are likely to have a major influence on the outcome of infection. We have initiated a project in the lab to investigate the effects of TBFV infection on primary DCs and the ability of TBFV to modulate the signal transduction pathways involved in detecting virus infection and producing IFN. Following infection with LGTV, flow cytometry was used to distinguish between infected and uninfected bystander DCs. Maturation profiles revealed that infected DC, but not bystander cells, increased cell surface expression of MHC class II. However, infected DC did not upregulate CD80 and CD86, costimulatory molecules involved in activating T cell responses. Moreover, infected DC did not respond appropriately to stimulation with toll-like receptor (TLR) 3 or TLR4 ligands. The failure of LGTV-infected DC to express key molecules involved in anti-viral immunity in vivo may contribute to viral evasion of immune responses. Hence, examining these interactions will lead to an understanding of the mechanisms that contribute to TBFV pathophysiology. Type I and type II IFNs are crucial elements of the innate immune response to flavivirus infection, restricting virus replication, dissemination and lethality in mouse models. Type I IFN is a potential therapeutic candidate for flavivirus infection. However, such treatment often fails. We have previously shown that LGTV utilizes its nonstructural protein NS5 to interfere with IFN signaling by directly inhibiting Janus kinase-signal transducer and activator of transcription (JAK-STAT) signal transduction. Over the past year, we have shown that NS5 from other flaviviruses including TBEV also suppress IFN responses. We also found that the virulent New York (NY99) strain of WNV suppressed IFN-dependent JAK-STAT signaling. In contrast, NS5 from Kunjin virus (KUN), a naturally attenuated subtype of WNV, was a poor suppressor of IFN responses. Importantly, mutation of a single residue in KUN NS5 to the analogous residue in WNV-NY99 NS5 (S653F) rendered this protein an efficient inhibitor signaling. Thus, a naturally occurring mutation is associated with reduced ability of NS5 to function as an IFN antagonist and hence may influence virulence of WNV field isolates. This work identifies NS5 as a potential virulence factor of WNV and has implications for live-attenuated vaccine design.
| Grabowski, Jeffrey M; Offerdahl, Danielle K; Bloom, Marshall E (2018) The Use of Ex Vivo Organ Cultures in Tick-Borne Virus Research. ACS Infect Dis 4:247-256 |
| Paules, Catharine I; Marston, Hilary D; Bloom, Marshall E et al. (2018) Tickborne Diseases - Confronting a Growing Threat. N Engl J Med 379:701-703 |
| Mlera, Luwanika; Meade-White, Kimberly; Dahlstrom, Eric et al. (2018) Peromyscus leucopus mouse brain transcriptome response to Powassan virus infection. J Neurovirol 24:75-87 |
| Kellman, Eliza M; Offerdahl, Danielle K; Melik, Wessam et al. (2018) Viral Determinants of Virulence in Tick-Borne Flaviviruses. Viruses 10: |
| Offerdahl, Danielle K; Dorward, David W; Hansen, Bryan T et al. (2017) Cytoarchitecture of Zika virus infection in human neuroblastoma and Aedes albopictus cell lines. Virology 501:54-62 |
| Lewy, Tyler G; Grabowski, Jeffrey M; Bloom, Marshall E (2017) BiP: Master Regulator of the Unfolded Protein Response and Crucial Factor in Flavivirus Biology?. Yale J Biol Med 90:291-300 |
| Grabowski, Jeffrey M; Tsetsarkin, Konstantin A; Long, Dan et al. (2017) Flavivirus Infection of Ixodes scapularis (Black-Legged Tick) Ex Vivo Organotypic Cultures and Applications for Disease Control. MBio 8: |
| Mlera, Luwanika; Meade-White, Kimberly; Saturday, Greg et al. (2017) Modeling Powassan virus infection in Peromyscus leucopus, a natural host. PLoS Negl Trop Dis 11:e0005346 |
| Mlera, Luwanika; Lam, Jennifer; Offerdahl, Danielle K et al. (2016) Transcriptome Analysis Reveals a Signature Profile for Tick-Borne Flavivirus Persistence in HEK 293T Cells. MBio 7: |
| Offerdahl, Danielle K; Clancy, Niall G; Bloom, Marshall E (2016) Stability of a Tick-Borne Flavivirus in Milk. Front Bioeng Biotechnol 4:40 |
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