Neutrophils are the innate immune system's first line of defense in response to an infection. During an infection in the tissue, chemical cues called chemoattractants are released, which signal neutrophils to exit circulation and enter the tissue. Once in the tissue, neutrophils directionally migrate in response to the chemoattractant and toward the site of infection in a process called chemotaxis. At the site of infection, they initiate antimicrobial responses to clear the infection and resolve inflammation, restoring homeostasis. However, neutrophils are exposed to multiple chemoattractants and must prioritize these signals in order to correctly migrate to the appropriate site. The ability of neutrophils to properly undergo chemotaxis in the presence of infection and inflammation is crucial for resolution of inflammation and pathogen clearance. It has been recently shown that when pre-conditioned with bacterial endotoxin (LPS), innate immune function can become dysregulated. Neutrophils start to display altered antimicrobial response as well as dysfunctional migration patterns. This behavior has been seen in patients with sepsis, where a person's immune system overreacts to an infection, leading to systemic inflammation throughout the body, causing tissue damage, multiple organ failure, and in many cases, death.
We explore the effects of inflammation on neutrophil migratory patterns and decision-making within chemotaxis. Additionally, to understand how inflammation within disease impacts chemotaxis, we measure the difference between neutrophils from healthy individuals and those from septic patients. We approached this using a combination of experimental and computational techniques. We developed a microfluidic assay to measure neutrophil decision-making in a competitive chemoattractant environment between an end-target (fMLP) and intermediary (LTB4) chemoattractant. Additionally, we probed for the expression level of molecules related to neutrophil chemotaxis. We also built a system of ordinary differential equations to model the dynamics of the molecular interactions underlying neutrophil chemotaxis. Our results showed that when neutrophils were induced into a highly inflammatory state, they prioritized pro-inflammatory signals over pro-resolution signals and displayed dysfunctional migration patterns. Similarly, neutrophils from patients with sepsis also displayed dysregulated migration patterns. This aberrant neutrophil chemotaxis may be implicated in the pathogenesis of sepsis, where accumulation of neutrophils in off-target organs is often seen. These results shed light onto the directional migratory decision-making of neutrophils exposed to inflammatory signals. Understanding these mechanisms may lead to the development of pro-resolution therapies that correct the neutrophil compass and reduce off-target organ damage. / Doctor of Philosophy / Neutrophils are innate immune cells that act as the first line of defense toward an infection. During an infection, chemical signals are released, stimulating neutrophils to migrate toward that specific site of infection. Once the cells are in the tissue, they can clear the pathogen and resolve inflammation. However, when neutrophils are migrating in the tissue, they are overwhelmed with multiple signals, directing them toward different sites. These signals must be prioritized by the cell so they can properly migrate toward the correct location. It has been recently shown that neutrophils that have been preconditioned into inflammatory states will display dysfunctional migration patterns. They are unable to migrate to the site of infection and instead migrate to healthy tissue, where they can cause damage. This has been shown in patients with sepsis, which is a condition where a person's immune system overreacts to an infection, causing inflammation throughout the body, leading to tissue damage and multiple organ failure. Our work explores the impact of inflammation on neutrophil migration patterns and the ability of the cell to properly prioritize when stimulated by multiple chemical signals. Additionally, we look at how neutrophils from healthy individuals differ from neutrophils from patients with sepsis, to understand how inflammation within disease impacts cellular migration. We approach this both experimentally and computationally. We designed a microfluidic assay to measure neutrophil migration in the presence of two competing chemical signals. We also measured the expression levels of molecules relevant to cell migration. We also built a mathematical model to investigate the molecular interactions underlying these processes. These results shed light on how inflammation impacts neutrophil migration and its role in inflammatory diseases.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/107299 |
| Date | 08 July 2020 |
| Creators | Boribong, Brittany Phatana |
| Contributors | Genetics, Bioinformatics, and Computational Biology, Jones, Caroline N., Li, Liwu, Ciupe, Stanca M., Childs, Lauren M. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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