The role of innate and adaptive pulmonary immune responses in shaping the spectrum of Latent Tuberculosis Infection
Lead Research Organisation:
Imperial College London
Department Name: National Heart and Lung Institute
Abstract
In 2008 tuberculosis (TB) killed 1.8 million people. However, most people who are infected with the bacteria causing tuberculosis never become unwell. Instead, their body‘s defence cells interact with the organism so that it becomes dormant within the human body. This is called LATENT INFECTION. In a proportion of these people the bacteria later wakes up and causes the person to become unwell. We don‘t yet understand how in most people the body is able to keep the infection dormant, especially in the lung where most illness occurs. Understanding this process will allow better treatments to be developed for those other people where the body is unable to control the bacteria and TB is a serious and often fatal disease.
We propose to do this by firstly demonstrating that latent infection not one condition, but a spectrum of illness; to do this, we plan to use specialist scans and new techniques of sampling the lung. We will then look at specific defence cells from the blood and lungs to see how the body controls TB in those with different types of latent infection, both early in the course of infection, and in established disease.
We propose to do this by firstly demonstrating that latent infection not one condition, but a spectrum of illness; to do this, we plan to use specialist scans and new techniques of sampling the lung. We will then look at specific defence cells from the blood and lungs to see how the body controls TB in those with different types of latent infection, both early in the course of infection, and in established disease.
Technical Summary
AIMS
We will for the first time in humans comprehensively and systematically evaluate the role of both innate and adaptive host responses in different stages of the spectrum of latent tuberculosis infection (LTBI), focussing on the primary anatomical site of infection and disease control: the lung.
OBJECTIVES
Our objectives are to test the following three hypotheses in these subgroups:
A) In patients with cleared and transient TB infection following exposure to infectious
cases, up-regulated innate gene expression (including but not limited to: genes
related to autophagy, key transcription factors e.g. MyD88, and cytokines e.g. IL-12)
in alveolar macrophages will explain why some patients are resistant to TB infection.
B) In those infected with the bacillus, successful containment of latent infection is associated with an expansion of the pulmonary population of mucosal-tropic T cells secreting IL-17, such as CD4+Th17 cells and CD161+CD8 cells.
C) As antigen load increases towards active disease, there is a change in the MTB-specific
CD4+T cell memory pool from an effector-memory to an effector phenotype.
DESIGN
A cross-sectional case-control study comparing patient groups reflecting a spectrum of TB infection and disease, as determined by detailed and advanced clinical phenotyping (including endobronchial-ultrasound guided transbronchial needle aspiration and positron emission computed tomography scanning). Each patient will have blood and bronchoalveolar fluid sampling with assays performed on these samples and their resultant cell populations to test our hypotheses.
METHODOLOGY
1) For Hypothesis A, Quantitative Real-Time PCR will be used to measure gene expression
of key innate effector mediators in alveolar macrophages and monocyte-derived-
macrophages, with and without stimulation with M.tuberculosis.
2) For Hypothesis B, Intracellular Cytokine Staining (ICS) of peripheral blood mononuclear
cells (PBMC) and BAL cells will be used to determine CD4/CD8/Th17/CD161 phenotypes.
3) For Hypothesis C, Fluorescence-linked-Immunospot assays will be used with PBMC and
BAL cells to define IFN-? only, IL-2 only, and dual-secreting cells and thus enumerate
functional T cell subsets for the CD4+T cell population.
SCIENTIFIC AND MEDICAL OPPORTUNITIES
This study will be the first to comprehensively explore the scientific basis of the spectrum of latent TB infection, using state-of-the-art phenotyping to determine TB disease stage. This will have significant bearing on the finding of local and systemic markers of clearance and containment of M.tuberculosis and thus contribute to two key translational outputs: the risk stratification of individuals following TB infection, and the correlates of protective sterilisation and non-sterilising immunity to TB infection.
We will for the first time in humans comprehensively and systematically evaluate the role of both innate and adaptive host responses in different stages of the spectrum of latent tuberculosis infection (LTBI), focussing on the primary anatomical site of infection and disease control: the lung.
OBJECTIVES
Our objectives are to test the following three hypotheses in these subgroups:
A) In patients with cleared and transient TB infection following exposure to infectious
cases, up-regulated innate gene expression (including but not limited to: genes
related to autophagy, key transcription factors e.g. MyD88, and cytokines e.g. IL-12)
in alveolar macrophages will explain why some patients are resistant to TB infection.
B) In those infected with the bacillus, successful containment of latent infection is associated with an expansion of the pulmonary population of mucosal-tropic T cells secreting IL-17, such as CD4+Th17 cells and CD161+CD8 cells.
C) As antigen load increases towards active disease, there is a change in the MTB-specific
CD4+T cell memory pool from an effector-memory to an effector phenotype.
DESIGN
A cross-sectional case-control study comparing patient groups reflecting a spectrum of TB infection and disease, as determined by detailed and advanced clinical phenotyping (including endobronchial-ultrasound guided transbronchial needle aspiration and positron emission computed tomography scanning). Each patient will have blood and bronchoalveolar fluid sampling with assays performed on these samples and their resultant cell populations to test our hypotheses.
METHODOLOGY
1) For Hypothesis A, Quantitative Real-Time PCR will be used to measure gene expression
of key innate effector mediators in alveolar macrophages and monocyte-derived-
macrophages, with and without stimulation with M.tuberculosis.
2) For Hypothesis B, Intracellular Cytokine Staining (ICS) of peripheral blood mononuclear
cells (PBMC) and BAL cells will be used to determine CD4/CD8/Th17/CD161 phenotypes.
3) For Hypothesis C, Fluorescence-linked-Immunospot assays will be used with PBMC and
BAL cells to define IFN-? only, IL-2 only, and dual-secreting cells and thus enumerate
functional T cell subsets for the CD4+T cell population.
SCIENTIFIC AND MEDICAL OPPORTUNITIES
This study will be the first to comprehensively explore the scientific basis of the spectrum of latent TB infection, using state-of-the-art phenotyping to determine TB disease stage. This will have significant bearing on the finding of local and systemic markers of clearance and containment of M.tuberculosis and thus contribute to two key translational outputs: the risk stratification of individuals following TB infection, and the correlates of protective sterilisation and non-sterilising immunity to TB infection.