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Dissertation
Contrasting effects of triggering Toll-Like Receptors 2, 3, 4, and 7 in the macrophage susceptibility to murine coronavirus infections
Doctor of Philosophy (Ph.D.), Drexel University
Apr 2012
DOI:
https://doi.org/10.17918/00009740
Abstract
Infection of mice with neurotropic murine coronaviruses (CoVs) Mouse Hepatitis Virus (MHV)-A59 and MHV-JHM provide animal models of virus-induced chronic demyelination and viral encephalitis, respectively. Within the first days post-inoculation, a strong innate immune response is generated that protects from virus spread and replication but at the same time, contributes to the immunopathological disease. Macrophages are productively infected by murine CoVs and represent the largest group of the innate immune cells infiltrating the CNS after infection with neurotropic MHVs. Macrophages express Toll-Like Receptors (TLRs) that sense invading pathogens and activate an innate immune response and prime adaptive immunity to protect the host. The role of TLRs in CoV recognition and pathogenesis is poorly characterized and the use of TLR agonists during MHV infection of macrophages as a potential antiviral therapy has not been assessed. We have investigated the effect of ligand-mediated TLR2, 3, 4, and 7 triggering of macrophages on their susceptibility to MHV infection. Using J774A.1 murine macrophages, we observed a strong, type I IFN-dependent antiviral response upon TLR3 activation with a synthetic analog of dsRNA poly I:C. Stimulation of TLR2 (HKLM, Heat-Killed Listeria Monocytogenes), TLR4 (LPS, ultrapure lipopolysaccharide from E. Coli) or TLR7 (R837, imiquimod) had no effect on MHV production but triggered a profound increase in virus-induced cell-to-cell fusion in TLR2- and TLR7-activated macrophages. The TLR7 agonist imiquimod-driven increase in MHV-induced cytopathic effect was ubiquitously observed in primary BMDM, immortalized macrophages and microglia, and HEK293 cells stably expressing murine TLR7. Mechanistically, the imiquimod effect was mediated by the TLR7-MyD88 pathway and depended on the furin protease and the cleavability of MHV Spike glycoprotein. Importantly, stimulation with imiquimod upregulated total and cleaved Spike protein levels as well as furin protein expression that correlated with a time-dependent accumulation of Spike cleavage products. Using BMDM from TLR7-/- and WT C57BL/6J mice, we further observed that macrophage TLR7 recognized MHV-A59 and mediated IL-6 and TNF-[alpha] production strictly through TLR7. Collectively, our findings demonstrate an antiviral potential of TLR3 ligand poly I:C against MHV infection, and a novel role of TLR7 in: 1) sensing CoV infection and mediating a proinflammatory response; and 2) triggering an increase in MHV-induced cell-to-cell fusion through furin upregulation in TLR7 agonist-activated macrophages.
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Details
- Title
- Contrasting effects of triggering Toll-Like Receptors 2, 3, 4, and 7 in the macrophage susceptibility to murine coronavirus infections
- Creators
- Liudmila Mazaleuskaya
- Contributors
- Sonia Navas-Martin (Advisor) - Drexel University, Drexel University (1970-)
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Number of pages
- ix, 151 pages
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- College of Medicine; Pharmacology and Physiology; Drexel University
- Other Identifier
- 991021889075904721