Human Pegivirus Infection of the Central Nervous System: Neural Cell Tropism and Neuroimmune Responses

• Author / Creator

  Doan, Matthew Anthony Lynn

• Human pegivirus (HPgV) is a positive sense, single-stranded RNA virus of the Flaviviridae family that is best characterized in the context of peripheral lymphocyte infection. Our group recently reported HPgV infection in the central nervous system (CNS) of two patients with fatal leukoencephalitis wherein HPgV NS5A antigen was detected chiefly in glial cells in cerebral white matter. Brain derived viral sequences from these patients revealed an 87-nucleotide deletion in the HPgV NS2 gene that had not been previously characterized. Other related members of the Flaviviridae family, including Zika virus (ZIKV) and West Nile virus (WNV), are known to cause encephalitis, establishing a precedent that prompted further investigation into HPgV as a putative causative agent of encephalitis. To date, HPgV has not been shown to be an etiological agent in any disease and HPgV neurotropism has yet to be investigated.

  In this thesis, HPgV was shown to infect, replicate, and spread in human fetal astrocytes in vitro. As HPgV has been described as a lymphotropic virus, this finding expands our understanding of HPgV tropism and provides new evidence that HPgV can infect CNS cells. Human microglia, the resident macrophages of the brain, were also identified as being permissive to HPgV infection. Using a HPgV viral clone containing the 87-nucleotide deletion in the NS2 gene, HPgV WT and ΔNS2 were tested in parallel and HPgV ΔNS2 showed greater infectivity, replication and spread in human astrocytes.
  Antiviral and proinflammatory responses to HPgV infection were also examined in human astrocytes and microglia. Similar transcriptional profiles in HPgV WT and ΔNS2-infected astrocytes were observed following infection of human astrocytes. In contrast, human microglia showed differential induction of proinflammatory genes such as interferon, following HPgV ΔNS2 infection compared to HPgV WT. Further, cell death mechanisms were not activated in either microglia nor astrocytes following infection with either HPgV WT or ΔNS2, unless infection was combined with a second stimulus in the form of an inflammatory cytokine. Within the human CNS, analysis of frontal cortical samples showed that HPgV infection was associated with the suppression of several antiviral and proinflammatory genes compared to uninfected patient samples. RNA deep sequencing analysis of patients in this cohort recapitulated the suppression of various antiviral pathways in the CNS of HPgV-infected patients and revealed the induction of specific neuroinflammatory pathways. NOS2, which can either exert proinflammatory or immunomodulatory effects, was identified by RNA sequencing as markedly induced in the CNS of HPgV-infected patients.

  This thesis provides previously unrecognized evidence that HPgV infects, replicates and spreads in primary human astrocyte and microglia cultures, and an 87-nucleotide deletion in the HPgV NS2 gene modulates these viral properties in vitro. In addition, the differential immune responses observed following HPgV WT and ΔNS2 infection suggested that the NS2 gene might also modulate host immune responses. Lastly, the identification and analysis of seven new HPgV-infected patients offered an opportunity to investigate the host responses in the CNS, which had not previously been possible. These findings represent a substantial advance in the understanding of HPgV biology within the context of the CNS.

• Subjects / Keywords

  • Viral encephalitis
  • GB Virus C
  • Encephalitis
  • Human Pegivirus
  • Hepatitis G
  • HPgV

• Graduation date

  Fall 2020

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-h3kf-6w22

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.