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Abstract

Introduction: Platelets are increasingly recognized for their roles in infection. Tuberculosis (TB) is characterized by excessive inflammation leading to disease and long-term sequelae. Platelets may be key drivers of immunopathology in TB, but the mechanisms involved are poorly understood. My hypothesis is that platelets regulate innate immune responses to TB.

Methods: An in vitro model of M.tb-infected monocytes co-cultured with autologous platelets was interrogated using specific inhibitors and recombinant proteins. Gene expression of matrix metalloproteinases (MMPs) was assessed using quantitative PCR, and secretion using ELISA.

Pulmonary TB patients, healthy controls, and patients undergoing diagnostic bronchoscopy were prospectively recruited. Agonist-induced platelet aggregation was quantified using light transmission aggregometry, and platelet activation and platelet-leukocyte binding measured using flow cytometry. Concentrations of cytokines, MMPs, and platelet-associated factors were assessed in bronchoalveolar lavage fluid (BALF) and plasma using Luminex multiplex analysis. Inflammatory responses were compared with those identified in a separate cohort of SARS-CoV-2-infected patients using multiplex analysis.

Results: Platelets respond to M.tb-secreted antigens. Co-culture with platelets increases MMP gene expression and secretion by M.tb-stimulated monocytes. Platelets enhance M.tb-induced upregulation of monocyte phosphorylated phosphatidylinositol 3-kinase (PI3K) and mitogen activated protein kinase (MAPK) pathways through a combination of direct receptor-mediated and indirect secretory stimulation.

Platelets from TB patients display a pro-inflammatory phenotype with decreased agonist-induced aggregation. Platelet-monocyte aggregation is increased in patients with TB and non-TB lung disease compared to healthy controls, but platelet-granulocyte aggregation was increased in TB patients only. Increased levels of inflammatory mediators including IP-10, platelet markers including von Willebrand factor (vWF), and MMPs were seen in both TB and SARS-CoV-2 infection; others including IL-8 showed divergent responses.

Conclusions: This study presents cellular and clinical evidence that platelets adopt a TB-specific pro-inflammatory phenotype in pulmonary TB. This will inform the development of therapeutic agents aiming to limit harmful platelet-driven inflammation in TB.

Publication Type:	Thesis (Doctoral)
Additional Information:	The copyright of this thesis rests with the author and is made available under a Creative Commons Attribution Non-Commercial No Derivatives licence. Researchers are free to copy, distribute or transmit the thesis on the condition that they attribute it, that they do not use it for commercial purposes and that they do not alter, transform or build upon it. For any reuse or redistribution, researchers must make clear to others the licence terms of this work.
Subjects:	R Medicine > R Medicine (General) R Medicine > RB Pathology R Medicine > RC Internal medicine
Departments:	School of Health & Medical Sciences > Infection and Immunity Research Institute School of Health & Medical Sciences > School of Health & Medical Sciences Doctoral Theses Doctoral Theses

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