Dissertation
Inoculum dose and sepsis comorbidity alter disease outcomes in an MHV-1 murine model of beta-coronavirus infections
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Spring 2024
DOI: 10.25820/etd.007719
Abstract
While the immune responses to viral infections is primarily streamlined to protect the host, these responses can overexaggerate in some instances. Patients infected with SARS-CoV-2 for example experience variable disease susceptibility, from asymptomatic infection all the way to severe infection requiring critical care and respiratory support. However, the extent to which initial infectious inoculum dose determines disease outcomes and whether this can be utilized for immunological priming in a genetically susceptible host has not been completely defined. Comorbidities contribute to the severe form of infection, and a less commonly discussed comorbidity to severe SARS-CoV-2 infection is sepsis. Sepsis includes immune dysfunction that stems from a systemic infection, leading to long term immune impairments in survivors. As patients with prior sepsis were more likely to become infected and have poor outcomes with SARS-CoV-2, I believe it is also worthwhile to characterize this comorbidity in mice.
I utilized a previously established SARS-like murine model to conduct these studies, where mice are provided primary and/or secondary intranasal challenges with Murine Hepatitis Virus type 1 (MHV-1). I compared the response to infection in genetically-susceptible C3H/HeJ mice, genetically resistant C57BL/6J mice and genetically diverse, variably susceptible outbred Swiss Webster mice. Despite being defined as genetically susceptible to MHV-1, C3H/HeJ mice displayed decreasing dose-dependent pathological changes in disease severity, lung infiltrate/edema, and ultimately survival. Interestingly, I also observed lymphopenia in peripheral blood and spleen, suggesting a viral sepsis-like discourse which was also dose dependent. Importantly, an asymptomatic dose (500 PFU) was identified that yielded no measurable morbidity/mortality after infection of C3H/HeJ mice. These mice had active viral titers from infection, generated activated immune populations, and were functionally responsive to MHV-1 vii epitopes. However, the C3H/HeJ mice survived at this dose and were able to generate long term memory.
In this work I also asked how betacoronavirus infection is impacted at two phases of early sepsis and in two levels of MHV disease severity. Polymicrobial sepsis induced via cecal ligation and puncture (CLP) has been the preferred mouse model of the dynamic sepsis dysfunction and is a key line of investigation for our lab. Sepsis converted asymptomatic infections in C3H/HeJ and C57BL/6J mice to more pronounced disease, modeling the impact of sepsis as a comorbidity to beta-coronavirus infection. Sepsis also worsened already pathogenic infection in C3H/HeJ mice at the medium inoculum dose. Specifically, it was the combination of sepsis and MHV, and not sepsis alone, that generated these poor outcomes in C3H/HEJ and C57BL/6 mice. Mice experienced worsened morbidity, altered cytokine production, and decreased viral control at the site of infection. This alteration of MHV infection occurred whether the host was infected 2 days or 5 days after sepsis.
I then utilized the low dose infection for immunological priming in C3H/HeJ mice which provided neutralizing antibody-dependent, but not circulating CD4/CD8 T cell-dependent, protection against a high dose MHV-1 early re-challenge. Mice showed improved cytokine responses, antigen experienced populations, and viral control early in infection. Importantly, despite the formation of apt MHV-specific responses by T cells, neutralizing Ab by itself caused survival in infection that otherwise causes mortality. Together, these data define how infectious dose, immunological status, and comorbidities modulate outcomes of primary and secondary beta coronavirus infections in hosts with variable susceptibility.
Details
- Title: Subtitle
- Inoculum dose and sepsis comorbidity alter disease outcomes in an MHV-1 murine model of beta-coronavirus infections
- Creators
- Elvia Silva
- Contributors
- Vladimir Badovinac (Advisor)Josalyn Cho (Committee Member)Kevin Legge (Committee Member)John Harty (Committee Member)Ryan Zander (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Immunology
- Date degree season
- Spring 2024
- Publisher
- University of Iowa
- DOI
- 10.25820/etd.007719
- Number of pages
- xvii, 133 pages
- Copyright
- Copyright 2024 Elvia Elizabeth Silva
- Comment
- This thesis has been optimized for improved web viewing. If you require the original version, contact the University Archives at the University of Iowa: https://www.lib.uiowa.edu/sc/contact/
- Language
- English
- Date submitted
- 04/12/2024
- Description illustrations
- illustrations, graphs, tables
- Description bibliographic
- Includes bibliographical references (pages 116-133).
- Public Abstract (ETD)
- Immune responses against respiratory viruses have been studied in mouse models for decades, providing insight into the players involved in protection. However, it is also known that patients in the clinic can come in with different comorbidities which make infection worse. Additionally, although exposure length has been studied in the SARS-CoV-2 context, whether the immune response differs when initially exposed to different amounts of coronavirus, has been understudied. In this work I address how sepsis, an immune disorder, and the initial infection amount determine the outcome in beta-coronavirus infection using the MHV-1 mouse model. I noted that in a host whose genetics already predisposes them to severe infection with beta coronavirus, there is a tipping point of asymptomatic to symptomatic and severe infection depending on how much initial virus they receive. This is a different assessment than what is tested in the lungs several days in, which can be much more similar between inoculum doses. A low dose infection was asymptomatic in coronavirus-susceptible mice. While mice had active virus in their lungs and their adaptive immune was responding, they did not experience any outward symptoms and all of them survived. This low dose infection also worked to protect these mice from severe infection later. Specifically, the antibodies generated from the asymptomatic infection protected these mice from a lethal infection. All mice survived and had no detectible virus early after infection. Finally, I addressed the clinically relevant model of prior sepsis as a beta coronavirus infection comorbidity. Hosts who were otherwise resistant to infection due to genetics or initial infection level were worse off if they experienced sepsis before, including poorer morbidity and higher viral load. This thesis covers the alterations in pathology and immune responses after these infection alterations and closes with future directions in immune memory after sepsis.
- Academic Unit
- Interdisciplinary Studies Program
- Record Identifier
- 9984647355702771
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