Full metadata record
| DC Field | Value | Language |
|---|---|---|
| dc.contributor | Department of Health Technology and Informatics | en_US |
| dc.contributor.advisor | Leung, Polly (HTI) | en_US |
| dc.contributor.advisor | Chow, Franklin (HTI) | en_US |
| dc.creator | Ayesha | - |
| dc.identifier.uri | https://theses.lib.polyu.edu.hk/handle/200/14590 | - |
| dc.language | English | en_US |
| dc.publisher | Hong Kong Polytechnic University | en_US |
| dc.rights | All rights reserved | en_US |
| dc.title | Role of outer membrane vesicles in legionella pneumophila pathogenesis and host immune modulation | en_US |
| dcterms.abstract | Background: Legionella pneumophila is a gram-negative bacterium widely distributed in natural and artificial freshwater systems. Amoebas residing in aquatic environments are essential for the survival of L. pneumophila. Upon ingestion by an amoeba, L. pneumophila continues to grow and replicate inside without dying. Hence, the amoeba host enables the propagation of L. pneumophila in aquatic environments. Being an opportunistic pathogen, L. pneumophila infects humans when they inhale aerosols containing Legionella from artificial water systems, leading to community-acquired pneumonia known as Legionnaires' disease (LD). L. pneumophila persistence in the host depends on its effective evasion of the host's conserved phagocytic mechanisms. Within the infected cells, the organism communicates with host cells through various methods. One well-known method is a specialized T4SS secretion system that modifies host cell signaling and metabolic processes by delivering approximately 330 effector proteins. Multiple factors influence the mortality rate of LD, particularly the host immune response. In clinical patients, Legionnaires' disease severity is associated with hyperinflammation and immunoparalysis, as well as a high bacterial load in the patient's lungs. | en_US |
| dcterms.abstract | Over the last 50 years, researchers have identified bacterial outer membrane vesicles as a means of communication. It is now recognized that Gram-negative bacteria intentionally release outer membrane vesicles (OMVs) to facilitate bacterial communication with the environment and the host. Recent studies have also elucidated their function as immune modulators. However, the effects of OMV-host interaction on disease pathogenesis are poorly understood. Additionally, knowledge about the composition of components transferred by OMVs is limited. | en_US |
| dcterms.abstract | Aims: Based on the literature on the immunomodulatory properties of OMVs and the clinical symptoms of Legionnaires' disease, it is hypothesized that L. pneumophila OMVs contribute to disease severity by modulating host immune responses and enhancing bacterial survival and replication within the host. To evaluate this hypothesis, pure OMVs were first isolated and briefly characterized to determine their molecular cargo and their biological implications in bacterial pathogenesis. Subsequently, THP-1 derived macrophages were sorted following OMV internalization, and single-cell RNA sequencing was performed to characterize high-resolution transcriptional responses to L. pneumophila OMVs in comparison to untreated THP-1-derived macrophages. Finally, transcriptional responses were verified through functional assays. | en_US |
| dcterms.abstract | Key findings: L. pneumophila OMVs contain a diverse range of cell components, with proteins constituting the most considerable fraction, followed by DNA and RNA. Numerous virulence factors were identified among the OMV-associated proteins, and functional pathways were predicted. However, the direct roles of these components in bacterial pathogenesis require further investigation. | en_US |
| dcterms.abstract | Differentially expressed gene (DEG) analysis after single-cell RNA sequencing revealed that the majority of altered genes were associated with cytokines, chemokines, and inflammatory mediators. Notably, L. pneumophila OMVs were found to modulate THP-1 derived macrophages toward an M2b phenotype, characterized by an immunoregulatory state that facilitates bacterial persistence while minimizing host cell damage. Additionally, M1 bactericidal phenotype and anti-legionellae responses, including caspase-1 activation, reactive oxygen species (ROS), and interferon gamma production, were not observed. In addition to transcriptional profiling, functional production of cytokines and chemokines was validated using a cytokine array comprising 105 chemokines, cytokines, and growth factors. Among 105, 46 factors were upregulated in OMV-treated macrophages. Ingenuity Pathway Analysis (IPA) demonstrated enrichment of inflammatory pathways, such as NF-κB signaling, pathogen-induced cytokine storm signaling, and IL-17 signaling, as well as anti-inflammatory pathways including wound healing and IL-10 signaling, further confirming the M2b macrophage phenotype. | en_US |
| dcterms.abstract | Furthermore, the immune modulation by OMVs did not induce cell death in the host cells, as no cytotoxicity was observed. MTT assays showed that OMVs were not toxic and promoted macrophage proliferation. Finally, the impact of L. pneumophila OMV-mediated modulation on bacterial replication and survival within the host was assessed using a CFU assay. Pre-treatment of THP-1 derived macrophages with L. pneumophila OMVs for 24 hours resulted in increased bacterial replication within host cells. | en_US |
| dcterms.abstract | Conclusion: Together, these findings indicate that L. pneumophila OMVs contribute to disease severity by converting the host cell into an immunoregulatory, bacterium-permissive niche, thereby increasing bacterial survival and replication. | en_US |
| dcterms.extent | 1 volume (various pagings) : color illustrations | en_US |
| dcterms.isPartOf | PolyU Electronic Theses | en_US |
| dcterms.issued | 2026 | en_US |
| dcterms.educationalLevel | Ph.D. | en_US |
| dcterms.educationalLevel | All Doctorate | en_US |
| dcterms.accessRights | open access | en_US |
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