Date of Award
Doctor of Philosophy (PhD)
ABSTRACT OF DISSERTATION
Flaviviruses: Innate Immune Restriction and Host Adaptation
Matthew Joseph Gorman
Doctor of Philosophy in Biology and Biomedical Sciences
Washington University in St. Louis, 2017
Professor Michael Diamond, Chair
Flaviviruses are a diverse family of positive-sense RNA viruses that can cause diseases ranging from asymptomatic to lethal encephalitis or shock in humans. Two encephalitic flaviviruses, West Nile virus (WNV) and Zika virus (ZIKV), have recently spread to the Americas and have no approved treatments or vaccines. In this dissertation, I analyzed the role of the antiviral protein, interferon induced transmembrane protein 3 (Ifitm3), in restricting WNV. I also generated a mouse adapted ZIKV virus and combined it with a human STAT2 knock in mouse to create a novel model of ZIKV infection in mice.
IFITMs are a family of antiviral proteins that inhibit the fusion of viruses on the plasma membrane and endosome. Several studies have focused on characterizing Ifitm3 in vitro, but few in vivo studies have evaluated the function of Ifitm3 in vivo. I challenged Ifitm3-/- mice with WNV to determine the role of Ifitm3 in controlling a systemic neurotropic viral infection. Mice were found to be more susceptible to lethal WNV infection and had greater peripheral organ and central nervous system viral burden. I also observed a reduced immune response, with a lower number of B cells, CD4+ T cells, and antigen specific CD8+ T cells, in infected Ifitm3-/- mice. Bone marrow chimeria experiments established that Ifitm3 functions in both radiosensitive and radioresistant cells, as higher viral burden in the CNS was only observed in Ifitm3-/- mice reconstituted with Ifitm3-/- bone marrow. This work demonstrated that Ifitm3 is an important antiviral protein in resisting WNV infection in vivo.
ZIKV causes an asymptomatic to self-limiting febrile illness in the majority of infections, but in severe cases ZIKV may cause Guillian-Barré syndrome or encephalitis in adults or congenital malformations, such as microcephaly, in children from mothers infected during pregnancy. Unfortunately, ZIKV replicates poorly in mice due to a failure to evade Stat2-dependent interferon (IFN) responses, which greatly restricts the ability to perform mechanistic studies of ZIKV infection in mice. To establish an improved ZIKV mouse model, I serially passaged ZIKV-Dakar (ZIKV-Dak) in Rag1-/- mice to generate a mouse adapted ZIKV-Dakar (ZIKV-Dak-MA). I identified a NS4B G18R mutation in ZIKV-Dak-MA that caused greater viral burden in the CNS of C57BL/6 mice treated with an anti-Ifnar blocking antibody. I combined ZIKV-Dak-MA with a human STAT2 knock-in Stat2-/- mouse (hSTAT2 KI) to generate an immunocompetent mouse model in which ZIKV could antagonize the Stat2-dependent IFN response. Infection of 3 week old hSTAT2 KI mice demonstrated that ZIKV-Dak-MA was able to replicate in peripheral organs and the CNS of mice. This work created a new mouse model of ZIKV infection that will be beneficial in evaluating new vaccines and treatments for ZIKV.
Chair and Committee
Michael S. Diamond
Herbert W. Virgin, Deborah J. Lenschow, Jonathan J. Miner, Sebla B. Kutluay,
Gorman, Matthew Joseph, "Flaviviruses: Innate Immune Restriction and Host Adaptation" (2017). Arts & Sciences Electronic Theses and Dissertations. 1183.
Available for download on Wednesday, December 15, 2117