"Tuberculosis is a major public health threat to the populations of Europe and the world. Mycobacterium tuberculosis, the etiological agent of the disease, can multiply and persist within phagocytic cells and this early event is of primary importance for the outcome of the infection. The main objectives of this proposal are to use highly innovative approaches in molecular and cell biology, biochemistry, immunology and imagery to elucidate the function and interplay of three families of immunogenic proteins of M. tuberculosis, the ESX, PE and PPE families. It was recently found that the ESX systems constitute novel secretion machineries that export major virulence factors and important diagnostic and protective antigens. While the ESX-1 system is responsible for the secretion of the prototypic ESX proteins, namely, the 6 kDa early secreted antigenic target (ESAT-6) and the 10 kDa culture filtrate protein (CFP-10), which are the most important proteins of M. tuberculosis involved in host-pathogen interaction, ESX-5 is implicated in the secretion of PE/PPE proteins. Restriction to pathogenic mycobacteria makes them highly interesting targets for host-pathogen interaction. The ESX-3 system appears to be essential. Thus, in this project we propose to --> analyse the global gene expression network of ESX-1, ESX-3 and ESX-5, --> determine the nature and diversity of the effector proteins they secrete, --> establish their mode of action and sub-cellular localisation, --> survey potential genetic variation in clinical isolates, --> assess their interaction with the immune system of the host, --> evaluate the suitability of ESX systems as drug targets, --> screen small molecules for their potential to inhibit ESX-mediated secretion. The proposed approach will generate major insights into the role of these proteins in pathogenicity that are of utmost importance for the development of new diagnostics, vaccines and therapeutic agents for tuberculosis prevention and control."