INTRODUCTION: SARS-CoV-2 is a novel virus from the coronavirus family that emerged in the Hubei province of China in December 2019 and rapidly spread throughout the world. On March 11, 2020, the World Health Organization declared a global pandemic. Infection with SARS-CoV-2 causes coronavirus disease 19 (COVID19) which can be fatal. There is an obvious and pressing need for research surrounding SARS-CoV-2 that will aid in eradication of this pandemic.
OBJECTIVE: The goal of this study was to absolve the dire need for small animal models of human disease that demonstrate hallmark pathological features of infection. Due to ethical and financial obstacles, the use of animals that closely resemble human immunity, such as non-human primates, is often not a viable option. For this reason, there is a push to develop small animal models that can mimic human disease responses, particularly those in viral infections that have a narrow species tropism. To achieve this in the context of the novel coronavirus, SARS-CoV-2, we studied various mouse models and their capacity to become infected with and mount an immune response to SARS-CoV-2. Our goal was to identify a model that sufficiently mimics severe COVID19 seen in humans as well as provide molecular insight into pathways that prevent the development of severe disease.
METHODS: NRG-L and HIS-NRGF-L mice were subcutaneously implanted with human fetal lung xenografts and infected with SARS-CoV-2. Tissues were stained with H&E for histopathological scoring. NRG-L and HIS-NRGF-L tissues were fluorescently labeled using 2 different multiplex immunohistochemistry panels. Slides were digitized by a Vectra Polaris™ fluorescent whole slide scanner and digital analysis was completed using HALO™. Statistical analysis was conducted using GraphPad Prism™ 9.0.1.
RESULTS: Infected NRG-L mice present extensive histopathological manifestations when compared to uninfected controls. Cumulative histology scores at both 2 and 7DPI were increased when compared to uninoculated fLX. Neutrophil influx, intra-airspace necrosis, capillary fibrin thrombi, and presence of syncytial cells were the most significant independent observations that contributed to the increased cumulative score. Together these findings indicate that fLX inoculated with SARS-CoV-2 faithfully recapitulate several features of diffuse alveolar damage (DAD) described in severe COVID-19. HIS-NRGF-L mice displayed decreased influx of neutrophils, intra-airway necrosis, and syncytial cells when compared to NRG-L fLX. Hemorrhage was decreased at both 2 and 7 DPI for HIS-NRGF-L fLX compared to NRG-L fLX. Cumulative histology scores were decreased in HIS-NRGF-L fLX at 7 DPI when compared to NRG-L fLX. Taken together these findings support the hypothesis that human myeloid and lymphoid infiltrates suppress or prevent the disparate host response observed in NRGL-L fLX that manifested in pronounced diffuse alveolar damage.
CONCLUSION: Using digital image analysis of multiplex immunohistochemistry paired with semi-quantitative histopathological scoring, this study characterized important hallmark lesions observed in severe COVID19 as seen in small animal models. NRG-L and HIS-NRGF-L mice that are subcutaneously implanted with human fetal lung xenografts are susceptible to infection with SARS-CoV-2 and can produce severe and moderate disease phenotypes respectively. Co-engraftment with human fetal lung tissue and human immune system components in HIS-NRGF-L mice suppresses the divergent host response that is observed in NRG-L mice. For this reason, NRG-L mice engrafted with fLX are an ideal small animal model of severe COVID19, whereas HIS-NRGF-L mice severe as a valuable and informative model for deciphering molecular mechanisms driving severe COVID-19 that will serve as targets for therapeutic development.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/43470 |
| Date | 24 November 2021 |
| Creators | Montanaro, Paige |
| Contributors | Crossland, Nicholas, Duffy, Elizabeth |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
| Rights | Attribution 4.0 International, http://creativecommons.org/licenses/by/4.0/ |
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