Browsing by Subject "RNA Viruses"
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Item Factors That Influence Mammalian Enteric Virus Infection(2018-11-16) Aguilera, Elizabeth Renata; Schoggins, John W.; Pfeiffer, Julie K.; Reese, Tiffany A.; Winter, Sebastian E.RNA viruses are a common cause of emerging diseases due to their vast genetic diversity. This diversity is largely attributed to mutations generated by the error-prone viral RNA-dependent RNA polymerase during replication. Despite the ability to acquire mutations beneficial to the virus, most mutations are deleterious and reduce viral fitness. This poses an obstacle for RNA viruses to successfully infect the host. In addition, a subset of RNA viruses are also enteric pathogens. In particular, these viruses must navigate several environments for transmission and subsequent infection through the fecal-oral route. In this work, I used poliovirus, an enteric RNA virus from the Picornaviridae family, as a model system to study mechanisms of RNA virus co-infection and how bacteria influence picornavirus infection. Recent studies determined several modes of RNA virus transmission exist outside of canonical pathways, including en bloc transmission of multiple viruses into a single cell via bacteria or host-derived membrane vesicles. Co-infection of RNA viruses is important since it can enhance viral fitness. I determined that multiple polioviruses are found within a single plaque even at low multiplicity of infection. I also showed that poliovirus stocks contain virion aggregates and that aggregates induce co-infection. Furthermore, I found that co-infection frequency was increased when polioviruses were heavily mutagenized. This work suggests that co-infection can contribute to plaque formation and that co-infection may assist plaque formation in situations with high genomic damage. This work contributes to mechanisms that influence co-infection of RNA viruses and potentially drive viral evolution. Infection by members of the Picornaviridae family can cause respiratory, cardiac, gastrointestinal, and neurological disease. These and other viruses encounter various bacteria within the host and in the environment. Despite these close encounters, the effects of bacteria on picornaviruses is not completely understood. Previous work determined that poliovirus has enhanced virion stability when exposed to bacteria or bacterial polysaccharides. Therefore, I investigated whether bacteria broadly enhance stability of picornaviruses from three different genera: Enterovirus (PV and coxsackievirus B3 (CVB3)), Kobuvirus (Aichi virus) and Cardiovirus (Mengo virus). I determined that specific bacterial strains enhance thermal stability of subset of viruses, while others were stable in the absence of bacteria. Additionally, I determined that bacteria can stabilize the entire picornavirus panel when individually exposed to bleach. These effects are likely mediated through direct interactions with bacteria since viruses bound to bacteria in vitro. Overall, this work reveals shared and distinct effects of bacteria on a panel of picornaviruses with implications on viral transmission.Item The Interferon Stimulated Gene Product Lymphocyte Antigen 6 Complex, Locus E Promotes Entry of a Subset of Diverse RNA Viruses and Inhibits Infection by Coronaviruses(2019-02-05) Mar, Katrina Bockying; Hooper, Lora V.; Alto, Neal; Schmid, Sandra; Schoggins, John W.Interferons (IFNs) contribute to cell-intrinsic antiviral immunity by inducing hundreds of IFN-stimulated genes (ISG). In a screen to identify novel antiviral factors, the Schoggins lab unexpectedly uncovered a subset of genes that enhanced viral infection. Here, I describe my personal efforts to study lymphocyte antigen 6, locus E (LY6E), a protein which was identified in the screen to enhance the infection of viruses from Flaviviridae, Orthomyxoviridae, Retroviridae, and Alphaviridae viral families. In my studies, I confirmed that LY6E promotes viral infection of viruses from the same families, as demonstrated by both ectopic overexpression and endogenous knockout approaches. Using influenza A virus (IAV) as a model, I narrowed the enhancing effect of LY6E specifically to the entry step of uncoating, which precedes release of the viral genome into the cytoplasm and is required for viral replication. I also observed that the viral enhancement phenotype is conserved across evolution, as orthologs from bat, rhesus macaque, and mouse exerted a similar effect. To understand the physiological relevance of viral enhancement at the cellular level, I generated Ly6e conditional knockout mice and crossed them to multiple Cre recombinase transgenic mouse strains. As a result, I obtained mice with specific ablation of Ly6e in distinct immune cell compartments. From both ex vivo and in vivo studies using the Ly6e knockout mice, I concluded that Ly6e in alveolar macrophages is important for optimal defense against IAV infection. Finally, in collaboration with the postdoctoral fellow Stephanie Pfaender, I have shown that LY6E also possesses potent antiviral activity against a distinct subset of enveloped RNA viruses. Cumulatively, my work has uncovered three unique ways by which the ISG LY6E may contribute to the antiviral immune response. This work also provides insight regarding the multi-faceted ways a single ISG can provide broad protection against infection by viruses from diverse viral families.Item Mechanisms Controlling Virulence Thresholds of Mixed Viral Populations and Identification of Novel Host Barriers to Poliovirus Neuropathogenesis(2012-07-20) Lancaster, Karen; Pfeiffer, Julie K.Neurotropic viruses comprise some of the worlds most widespread and deadly pathogens, including West Nile virus, rabies virus, and poliovirus. Poliovirus, as a model neurotropic virus, is also an RNA virus. RNA viruses have high mutation rates and a propensity to revert attenuating mutations, contributing to disease and complicating treatment and vaccine development. Despite worldwide epidemics in the early nineteenth century, paralysis from poliovirus is a rare event occurring in less than 1% of poliovirus infections. This suggests the presence of viral and host barriers limiting disease. Here we examined viral barriers by exploring the concept of virulence thresholds using mixtures of virulent and attenuated viruses in a transgenic mouse model of poliovirus infection. We determined that 1000-fold excess of an attenuated strain of poliovirus was protective against disease induced by the virulent strain. Protection was induced locally, was a poliovirus specific effect, and inactivated virus conferred protection. Treatment with a poliovirus receptor-blocking antibody phenocopied the protective effect of inactivated viruses in vitro and in vivo, suggesting virulence thresholds may be modulated by competition for viral receptor. Furthermore, we found the attenuated virus became virulent in immune-deficient mice due to enhanced replication and reversion of attenuating mutations. We also identified additional host barriers limiting pathogenesis using a novel hybridization-based viral diversity assay to quantify the efficiency of poliovirus transport from the periphery to the central nervous system. We found viral replication in peripheral axons is limited and the type I interferon response limits viral replication in peripheral tissues, protecting against disease. Significantly, we discovered that retrograde axonal transport of poliovirus in the sciatic nerve was inefficient and only 20% of viral pool members reaching the brain. The efficiency of viral transport increased upon muscle damage, leading to increased viral diversity and pathogenesis. In summary, we identified a viral induced mechanism controlling virulence of mixed viral populations, and characterized three host barriers that restrict poliovirus pathogenesis in the nervous system. The identification of these barriers restricting virulence may help explain the rare incidence of neurological complications following poliovirus infection and aid in our understanding of viral population dynamics and pathogenesis.Item The Tradeoffs for a Viral Mutant with Enhanced Replication Speed(2021-07-26) Lanahan, Matthew Robert; Gammon, Don B.; Orchard, Robert C.; Winter, Sebastian E.RNA viruses exist as genetically heterogeneous populations due to high mutation rates and many of these mutations reduce fitness and/or replication speed. However, it is unknown whether mutations can increase replication speed of a virus already well adapted to replication in cultured cells. By sequentially passaging coxsackievirus B3 in cultured cells and collecting the very earliest progeny, we selected for increased replication speed. We found that a single mutation in a viral capsid protein, VP1-F106L, was sufficient for the fast-replication phenotype. Characterization of this mutant revealed quicker genome release during entry compared to wild-type virus, highlighting a previously unappreciated infection barrier. However, this mutation also reduced capsid stability in vitro and reduced replication and pathogenesis in mice. These results reveal a tradeoff between overall replication speed and fitness. Importantly, this approach -- selecting for the earliest viral progeny -- could be applied to a variety of viral systems and has the potential to reveal unanticipated inefficiencies in viral replication cycles.