Mycobacterium Tuberculosis Induced Transcription in Macrophages: the Role of TPL2/ERK Signalling in the Negative Regulation of T
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Mycobacterium tuberculosis induced transcription in macrophages: the role of TPL2/ERK signalling in the negative regulation of type I interferon production and implications for control of tuberculosis John Benson Ewbank August 2012 Division of Immunoregulation MRC National Institute for Medical Research The Ridgeway, Mill Hill London NW7 1AA Submitted to University College London for the Degree of Doctor of Philosophy I, John Benson Ewbank, confirm that the work presented in this thesis is my own. Where information has been derived from other sources, I confirm that this has been indicated in the thesis Abstract Abstract Mycobacterium tuberculosis is an important global cause of mortality and morbidity. The major host cell of Mycobacterium tuberculosis is the macrophage, and Mycobacterium tuberculosis is able to subvert the macrophage response in order to survive and replicate. The majority of infected individuals mount an immune response capable of controlling Mycobacterium tuberculosis infection. This requires the cytokines IL-12, TNFα, IL-1 and IFNγ, which promote eradication or control of infection. However, other immune factors, including IL-10 and type I IFN, can inhibit this protective response. In this study we have used microarray analysis to study the temporal response of macrophages to Mycobacterium tuberculosis infection, in an unbiased fashion. In response to Mycobacterium tuberculosis infection, macrophages produced cytokines and chemokines, upregulated genes involved with major histocompatability class I antigen presentation, activated both pro- and anti-apoptotic genes and downregulated many genes involved in cell-division and metabolism. We also observed the early induction of genes regulated by the extracellular-regulated kinase (ERK) MAP kinase pathway, and the upregulation of genes known to be induced by type I IFN, leading us to further investigate the role of these pathways in the macrophage response to Mycobacterium tuberculosis. Both pathways were found to regulate the production of protective and detrimental cytokines in macrophages in response to Mycobacterium tuberculosis infection. In addition, microarray analysis found that these pathways controlled the transcription of numerous genes in response to Mycobacterium tuberculosis infection. Finally, type I IFN was found to inhibit the macrophage response to IFNγ, including IFNγ-mediated killing of Mycobacterium tuberculosis in macrophages, a crucial step in the control of Mycobacterium 1 Abstract tuberculosis infection in vivo. We have therefore identified important regulatory mechanisms in macrophages, which are likely have an important role during Mycobacterium tuberculosis infection in vivo. 2 Acknowledgements Acknowledgements I would first like to thank my principal supervisor, Dr Anne O’Garra, for giving me the opportunity to take on this project in such a prestigious lab. This has allowed me to learn a huge amount about immunology and infection, and given me the opportunity to interact with prominent scientists from all over the world. Anne’s tireless enthusiasm, and her encyclopaedic knowledge of the literature, has helped make this project what it is. All members of the AOG lab have contributed to this project, but special thanks must go to Finlay McNab for a rewarding collaboration on TPL2-ERK signalling, and many helpful suggestions and comments for during the writing of this thesis; Vangelis Stavropoulos for initially training me to work in containment 3, and for providing common sense solutions to a wide range of problems; Paul Redford for constant support, advice and assistance for all things containment 3; Xuemei Wu, and more recently Damian Carragher, for breeding and looking after the various strains of mice required for this project; Christine Graham for assistance with carrying out microarray studies; Chloe Bloom for helpful discussion and suggestions about microarray analysis; Mary Holman for training in the early days; Ashleigh Howes for teaching me Western blotting; and Jon Pitt, Ashleigh Howes and Finlay McNab for last minute proofreading. I would like to thank others at the MRC NIMR, particularly my thesis committee, Douglas Young and Sebastien Gagneux, for helpful discussions and suggestions; Harsha Jani and Abdul Sesay for assistance in carrying out the microarray studies presented in Chapters 4-6; Anna Gibson for her efforts as lab manager, which were beyond the call of duty; and staff at the MRC NIMR animal 3 Acknowledgements facility for breeding and taking care of the mice. The microarray study presented in Chapter 3 was carried out at the Baylor Institute of Immunology Research, with the help and guidance of Damian Chaussabel and Quynh-Anh Nguyen. 4 Table of contents Table of Contents Abstract ................................................................................................................... 1 Acknowledgements ................................................................................................. 3 Table of Contents .................................................................................................... 5 Table of Figures ..................................................................................................... 11 Table of Tables ...................................................................................................... 14 List of Abbreviations ............................................................................................. 15 Chapter 1. Introduction ........................................................................................... 17 1.1. Tuberculosis and Mycobacterium tuberculosis .............................................. 18 1.1.1. Tuberculosis: a major global health problem ......................................... 18 1.1.2. The outcome of infection with Mtb ........................................................ 19 1.1.3. Different strains of Mtb show increased virulence and may affect disease outcome............................................................................................................. 20 1.2. Early events following Mtb infection ............................................................. 21 1.2.1. The innate immune system ..................................................................... 22 1.2.2. Mtb infects cells of the innate immune system in the lung..................... 23 1.2.3. The interactions between Mtb and macrophages .................................... 24 1.2.3.1. Mtb can avoid macrophage killing mechanisms ........................ 25 1.2.3.2. Recognition of Mtb through PRRs on innate immune cells ....... 26 1.2.3.2.1. Toll-like receptors .......................................................... 26 1.2.3.2.2. Dectin-1 ......................................................................... 28 1.2.3.2.3. DC-SIGN ....................................................................... 29 1.2.3.2.2. NOD2 ............................................................................. 29 1.2.4. Dendritic cells initiate the adaptive immune response to Mtb ................ 30 1.2.5. Apoptosis of innate immune cells promotes immunity to Mtb .............. 33 1.3. Factors involved in protection against Mtb infection ..................................... 34 1.3.1. CD4+ T cells ........................................................................................... 34 1.3.2. The different subsets of effector CD4+ T cells ....................................... 34 1.3.3. IFNγ and cell-mediated immunity is critical for protection against Mtb 35 1.3.3.1. IL-12 is required for control of Mtb infection in mice ............... 36 1.3.3.2. IFNγ activates macrophages to kill intracellular Mtb ................ 37 1.3.3.3. Requirement for the Th1 response in human disease ................. 39 1.3.4. The Th17 response in infection and vaccination .................................... 40 1.3.5. CD8+ T cells ........................................................................................... 41 1.3.6. IL-1α and IL-1β ...................................................................................... 42 5 Table of contents 1.3.7. TNFα in mouse and man ........................................................................ 43 1.3.8. The granuloma in Mtb infection ............................................................. 44 1.4. Factors that regulate the immune response to Mtb ......................................... 46 1.4.1. IL-10 and the suppression of the immune response to Mtb .................... 47 1.4.1.1. IL-10 background ....................................................................... 47 1.4.1.2. The regulation of IL-10 production in innate immune cells ...... 48 1.4.1.3. The role of IL-10 in infectious disease....................................... 49 1.4.1.4. The role of IL-10 in Mtb infection ............................................. 50 1.4.1.4.1. Results from the mouse model ...................................... 51 1.4.1.4.2. IL-10 in human TB ........................................................ 53 1.4.2. Suppression of the immune response to Mtb by Tregs ........................... 53 1.5. Tuberculosis and type I IFN ........................................................................... 54 1.5.1. Background ............................................................................................. 54 1.5.2. The Regulation of type I IFN production ............................................... 55 1.5.3. IFN signalling ........................................................................................