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Date of Award
Doctor of Philosophy (PhD)
The mammalian innate immune system is uniquely poised to respond to microbial insults and act as our first line of defense. Proper control of viral infection depends on the induction of interferon (IFN) and a multitude of interferon stimulated genes (ISGs) that aid in preventing viral replication and spread. However, an aberrant innate immune response can lead to overt inflammation, tissue damage, and more severe disease outcomes. Pro-inflammatory cytokinemia is a hallmark of highly pathogenic H5N1 influenza virus (IAV) disease, yet little is known about the role of host ISGs in modulating a pathogenic innate immune response. The host ISG Ifi35 (Interferon induced protein 35) has been implicated in increased susceptibility to H5N1 infection. In this dissertation, I show that Ifi35 deficiency leads to reduced morbidity in mouse models of highly pathogenic H5N1 and pandemic H1N1 IAV infection; the first in vivo characterization of the role of Ifi35 in a viral infection. Reduced weight loss in Ifi35-/- mice following H5N1 challenge was associated with reduced cellular infiltration and decreased production of specific cytokines and chemokines including IL-12p40. In addition, Ifi35 deficient primary macrophages produced less IL-12p40 following TLR-3, TLR-4, and TLR-7 stimulation in vitro. Decreased levels of IL-12p40 and its homodimer, IL-12p80, were found in bronchoalveolar lavage fluid of H5N1 infected Ifi35-/- mice. Specific antibody blockade of IL-12p80 ameliorated weight loss and reduced cellular infiltration following H5N1 infection in wild-type mice; suggesting that increased levels of IL-12p80 alters the immune response to promote inflammation and IAV disease. These data established an important in vivo role for Ifi35 in modulating cytokine production and exacerbating inflammation during IAV infection.
This pathogenic role of Ifi35 is not restricted to influenza virus infection. I also show that Ifi35 promotes lethality following intranasal Vesicular stomatitis virus (VSV) infection in mice. Protection from lethality in Ifi35-/- mice following VSV challenge was associated with significantly reduced viral burden in various regions of the brain and reduced virus invasion into the brain stem. Despite dramatic differences in lethality, production of VSV-specific neutralizing antibodies was equivalent between WT and Ifi35-/- mice. Additionally, VSV infection of Ifi35-/- mouse embryonic fibroblasts (MEFs) in vitro led to significantly reduced viral replication and cytopathic effect (CPE) compared to WT MEFs. These data establish an in vivo role for Ifi35 in modulating viral spread and neuro-invasion during VSV infection. Thus, this dissertation demonstrates the pathogenic potential of the host gene Ifi35 in two distinct in vivo viral infection models. Moreover, the work in this dissertation has identified a unique role for the pro-inflammatory cytokine IL-12p40 homodimer (IL-12p80) in promoting disease progression following IAV infection and was demonstrated to be a potential target for the development of host-directed therapeutics. These studies have characterized a biologically relevant in vivo role for Ifi35 during viral infection and inflammatory disease states, thereby addressing a major gap in knowledge in a field that previously only contained in vitro descriptions.
Chair and Committee
Michael Diamond, Anthony French, Shabaana Khader, Haina Shin,
Gounder, Anshu Priyanthi, "Insights into the In Vivo Role of Ifi35 in Promoting H5N1 Influenza and Neurotropic Vesicular Stomatitis Virus Disease" (2018). Arts & Sciences Electronic Theses and Dissertations. 1624.
Available for download on Monday, August 15, 2118