The tularemia pathogen, Francisella tularensis, is a highly virulent human pathogen and is easily transmitted through aerosols, thus its potential for use as a weapon of bioterrorism is high. The bacterium is a facultative intracellular pathogen, suggesting a crucial role for T cells in protective immunity against the organism as has been confirmed by studies in animal models. T cells contribute to protection against microbial infection by recognizing peptides presented by major histocompatibility complex (MHC) molecules and lipids presented by the MHC-like CD1 proteins. T cells reactive with peptide antigens from F. tularensis have been studied in both animal models and humans. However, T cell responses to the lipid antigens of F. tularensis have not been investigated. Lipids within the cellular envelope of Francisella species contain unusual hydroxy and long chain fatty acids, two components characteristic of lipid antigens from Mycobacterium species presented by CD1. In addition to its lipid chemistry, F. tularensis displays a number of other similarities to Mycobacterium tuberculosis in its site of intracellular growth, formation of granulomas by the host, and requirement for T cell function and IFN-gamma, production for protective immunity. Our overall hypothesis is that Francisella tularensis contains lipid antigens for the CD1 antigen presentation pathway and that F. tularensis-reactive CDl-restricted T cells contribute to the control of tularemia infection. We first propose to establish human CDl-restricted T cells that recognize lipid antigens of F. tularensis and identify the structure of lipids that stimulate CDl-restricted T cells. Second, we will determine the function of F. tularensis-reactive human CDl-restricted T cells. Protective immunity against F. tularensis requires IFN-gamma, production and individuals vaccinated against F. tularensis infection generate antigen-specific cytotoxic T cells (CTLs). CDl-restricted T cells against microbial lipids produce IFN-gamma and function as CTLs against infected macrophages. We propose to determine the cytokine pattern of F. tularensis-reactive CD1- restricted T cells and whether F. tularensis-reactive CDl-restricted T cells lyse bacteria-infected macrophages to reduce the bacterial load. From these studies we hope to expand the diversity of lipid antigens known to activate CDl-restricted T cells with the future goal to design lipid-based vaccines against tularemia infection.
