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Regulation of inflammation by platelets in tuberculosis

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Title: Regulation of inflammation by platelets in tuberculosis
Authors: Fox, Katharine
Item Type: Thesis or dissertation
Abstract: Introduction: Mycobacterium tuberculosis (M.tb) infection, causing tuberculosis (TB), kills more people than any other pathogen in the world. Innate immune cells are stimulated by M.tb antigens to result in an inflammatory and tissue-degrading phenotype associated with TB transmission, morbidity and mortality. Platelets are known to interact with the innate immune system and regulate matrix metalloproteinase (MMP)-driven tissue destruction but their role in the pathology of TB is not understood. My hypothesis is that platelets drive TB immunopathology through mechanisms that regulate key innate immune cell responses to M.tb infection. Methods: Multiplex analysis of bronchoalveolar lavage (BALF) and immunohistochemistry of a pulmonary TB mouse model detected platelets in the M.tb-infected lung. I developed a novel in vitro TB model using freshly isolated and thrombin-activated platelets in co-culture with primary human monocytes, neutrophils and airway epithelial cells. I assessed MMP and cytokine regulation at the gene, protein and functional level, with quantitative RT-PCR, Luminex bead array, ELISA, DQ matrix degradation, western blot and bacterial colony counts. Results: Investigation in the M.tb-infected lung revealed abundant platelets in a murine TB model, and activated platelet-derived factors in human BALF. Platelets upregulated specific MMPs, cytokines and chemokines in M.tb-infected monocytes, leading to type I collagen destruction and reduced intracellular bacterial killing. The platelet-secreted product CD40 ligand (CD40L) upregulated MMP-1 secretion, however, direct platelet-monocyte contact enhanced MMP regulation further. Platelets regulated monocytes through phosphorylated phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K), extracellular signal-regulated kinase (ERK)-1/2 and p38 pathways. Interestingly, platelets inhibited early neutrophil MMP secretion in TB. Platelet-secreted factors upregulated airway epithelial cell collagenase and gelatinase activity alone and in combination with TB networks. Conclusions: My data show that platelets are present at the site of pulmonary M.tb infection. Platelets regulate inflammation and tissue destruction driven by different leukocytes and respiratory epithelial cells through multiple signalling pathways.
Content Version: Open Access
Issue Date: Mar-2017
Date Awarded: Jul-2017
URI: http://hdl.handle.net/10044/1/72825
DOI: https://doi.org/10.25560/72825
Supervisor: Friedland, Jonathon
Sponsor/Funder: Wellcome Trust (London, England)
Department: Department of Medicine
Publisher: Imperial College London
Qualification Level: Doctoral
Qualification Name: Doctor of Philosophy (PhD)
Appears in Collections:Medicine PhD theses



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