Student Theses and Dissertations

Author

Tyler Lewy

Date of Award

2025

Document Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Thesis Advisor

Charles M. Rice

Keywords

West Nile virus (WNV), blood-brain barrier, interferon signaling, CNS immunity, poly(I:C), brain endothelial cells

Abstract

Vertebrates have a unique organ called the brain, which along with the spinal cord forms the central nervous system (CNS). This organ takes in sensory data from the environment for analysis and coordinates appropriate responses, enabling individuals to quickly react to highly complex problems and tasks. However, the CNS is extremely delicate. Neurons, the functional units of the CNS, are non-renewing post-mitotic cells and therefore extremely susceptible to damage. The brain has several layers of protective tissue to prevent both physical and biological trauma for this reason. Yet, in the evolutionary arms race, some pathogens have developed methods to gain access to this privileged Tissue. Orthoflaviviridae are a family of RNA viruses carried by arthropods. While these viruses are typically maintained in enzootic cycles, they occasionally spill over into human hosts. Many flaviviruses, including West Nile virus (WNV), can bypass the blood brain barrier (BBB) and wreak havoc in the CNS. Neurovirulent WNV infection elicits hyperinflammation in the CNS, leading to deleterious clinical outcomes including weakness, memory loss, paralysis, and death. Fortunately, only 1% of individuals infected with WNV progress to the encephalitic stage, although the reasons for this discrepancy remain unclear. Previous research has identified interferons (IFNs), small antiviral cytokines, as critical to control WNV infection. However, most work examines the role of IFN in the periphery or in the CNS only post-neuroinvasion. We still do not fully understand how the CNS responds to viral infection prior to neuroinvasion. This research addresses this gap in three chapters. First, we employ a disease-relevant murine model of WNV infection to demonstrate that the CNS responds immunologically to infection well before neuroinvasion by mounting an antiviral response. We expand the study to examine how the brain responds to diverse pathogenic stimuli of both viral and bacterial origin and find the CNS tailors a unique response depending on the offending insult. Viral motifs like poly(I:C) elicit antiviral genes whereas bacterial components like lipopolysaccharide accurate antibacterial pathways. Lastly, we show that the brain does not respond unless a physiological barrier is breached by contrasting the lack of CNS immune activation observed following airway inflammation. Next, we explore the physiological relevance of these CNS responses and find that footpad administered poly(I:C), but not other toll like receptor (TLR) agonists, protects animals against lethal intracranial WNV challenge. We demonstrate that poly(I:C) must be given prior to neuroinvasion, suggesting the elicited ISGs play a prophylactic role. Comparing brain tissue from animals pretreated with poly(I:C) or vehicle controls we show that poly(I:C) reduces the levels of viral replication and associated host immune responses in the CNS which likely accounts for the reduced disease burden. Lastly, we uncover the mechanism of footpad poly(I:C)-mediated encephalitic protection. Through cytokine profiling we identified several signaling molecules expressed following poly(I:C), but not other TLR agonists. Antibody neutralization experiments revealed that peripheral IFN signaling was critical to confer poly(I:C)-mediated protection into the CNS. Surprisingly, we find that despite utilizing the same receptor, intravenous IFNα, but not IFNβ, can reconstitute encephalitic protection. Further, we find that brain microvascular endothelial cells (BMECs) act as a relay for the IFN message between the periphery and the CNS. AAV-mediated ablation of IFN signaling on BMECs completely ameliorated poly(I:C) induced protection. Our findings raise several interesting implications. First, the brain has a far more active role in early infection than originally appreciated, mounting an antiviral response days before neuroinvasion. We show that sufficient peripheral IFN activity can confer a protective benefit against direct encephalitic challenge, mechanically linking with other studies which have found increased encephalitic incidence in humans with IFN signaling defects. Lastly, we identify a new role for BMECs in flaviviral pathogenesis beyond merely forming a physical barrier between the brain and the circulation. This study may inform new therapeutic treatments, of which there are currently none for flaviviral encephalitis, which target initial peripheral inflammation to limit later neurological damage.

Comments

A thesis presented to the faculty of The Rockefeller University in partial fulfillment of the requirements for the degree of Doctor of Philosophy

License and Reuse Information

Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License
This work is licensed under a Creative Commons Attribution-NonCommercial-Share Alike 4.0 International License.

Available for download on Saturday, May 15, 2027

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