M. tuberculosis remains a pathogen of global importance, currently infecting 1.6 billion people, killing 1.7 million annually. Successful human responses to infection depend critically on T cells, which were previously thought to be activated solely by peptide antigens bound to MHC proteins. However, CD1 proteins represent a newly discovered pathway for activation of T cells by mycobacteria and other pathogens. CD1 proteins are expressed in a highly regulated fashion on dendritic cells, where they capture mycobacterial lipid antigens for presentation to T cells. CD1 proteins are present in all mammals, so likely have an indispensable function in immune response. Although the basic functions of CD1d and NK T cells are becoming well understood, the natural functions of human CD1a, CD1b and CD1c proteins are not yet known. After discovering lipid antigens presented by CD1a (dideoxymycobactin), CD1b (glucose monomycolate) and CD1c (mannosyl phoshomycoketide), this renewal proposal uses a well developed model system to determine for the first time the general molecular mechanisms by which these antigens contact T cell receptors and the functions of lipid reactive T cells in human patients. Specifically, we will use chromatography and mass spectrometry to discover new antigens that bind to each type of CD1 protein and determine the general chemical rules of their recognition. Further, biophysical measurements and protein crystallization will determine the strength and mechanisms of how lipid antigens contact T cell receptors. Using human cells, we will measure the influence of the inflammasome and cytokines in regulating expression of CD1 proteins in dendritic cells and tissues. Last, we will use newly developed cell surface staining reagents to determine the key cytokines and anti-bacterial effector functions of T cells in cohorts of human patients located in Boston and KwaZulu-Natal, South Africa. These studies are relevant to the mission of the NIH because they focus on human subjects with natural diseases so that results can be translated into the clinic. Identification of the molecules necessary to initiate CD1 antigen presentation and T cell activation would allow their development as adjuvants or vaccines. Because experiments measure the general functions of the CD1-antigen-T cell receptor interaction, results would also inform understanding of the pathogenesis of related T cell-mediated diseases like sepsis, Lyme disease, allergic asthma and atherosclerosis.
Here we propose to determine which lipid antigens from M. tuberculosis trigger strong responses by tuberculosis patients. Identifying the chemical structures of lipid antigens that function in natural human infection will support development of tests that could rapidly diagnose tuberculosis or vaccines that could protect against future infection. We designed experiments to measure the general functions of CD1 and lipid antigens, so that these studies of tuberculosis would also provide knowledge about related T cell-mediated diseases like sepsis, Lyme disease, allergic asthma and atherosclerosis.
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