: Central to the disease process in tuberculosis are the interactions of the bacilli with host macrophages. The infection of macrophages by Mycobacterium tuberculosis can be divided into four steps: adherence, entry, intracellular survival, and multiplication. This proposal will concentrate on one of these steps, survival. The role virulence factors of M. tuberculosis play in these complex interactions is virtually unknown.
The aim of the proposed research is to identify, clone, and characterize genes and their protein products of M. tuberculosis which are required for intracellular survival within macrophages. Potential virulence factor genes of M. tuberculosis will be cloned by first constructing a recombinant library and incorporating it into the non-pathogenic Mycobacterium smegmatis. This rapidly growing mycobacterium is internalized and killed by macrophages. Clones with enhanced survival in macrophages will be identified and examined for the presence of M tuberculosis genes involved in survival. Using this system we have already isolated a M. tuberculosis gene, named eis (enhanced intracellular survival gene), which does enhance intracellular survival of M. smegmatis within macrophages. The primary focus of this grant application is the further characterization of the eis gene and its protein product Eis.
The specific aims are: 1.Effect of eis Gene Inactivation on Survival and Multiplication of M tuberculosis in Macrophages and Mice. Mutations will be constructed in eis and introduced into the chromosome of both avirulent and virulent M tuberculosis (H37Ra and H37Rv) by allelic exchange. The ability of the eis knockout mutants to survive and replicate in the U-937 macrophage survival assay and in human mononuclear phagocytes will be tested and compared to the parental strain. Additionally, the ability of the eis mutants to persist and replicate in vivo in a mouse intravenous infection model will also be evaluated. 2.Mechanism(s) Whereby eis Enhances Survival and Multiplication of M tuberculosis in Unactivated and Interferon-gamma-Activated Macrophages. To learn how eis may enhance intracellular survival of mycobacteria in macrophages, survival in interferon-gamma-activated U-937 cells and human monocytes will be evaluated. The ability of M. smegmatis with and without eis, as well as wild-type M. tuberculosis and eis knock-out mutants, constructed in Specific Aim No.1, to survive/multiply in both unactivated and interferon-gamma-activated U-937 cells and human monocytes will be determined. Studies will also be done to determine what role Eis may play in the ability of M. tuberculosis to resist known killing mechanisms operating in macrophages. 3.Properties of the Eis Protein and their Relationship to its Survival-Increasing Action. These studies will include: (I) intracellular localization of Eis in M. tuberculosis and M. smegmatis, (2) purification of the Eis protein, (3) screening of sera from tuberculosis patients for presence of antibody to Eis, and (4) measurement of eis gene expression in vitro and within macrophages using integrative reporter gene vectors. 4.Identification of Non-eis Survival Genes in a New M. tuberculosis DNA Library. In initial studies, eis-containing clones were the predominate clones isolated after the sixth passage in the U-937 macrophage survival assay. Such eis-containing clones are preferentially selected and appear to out-compete/dominate other M. tuberculosis genes which may also play a role in intracellular survival. Thus, in order to identify these other potential genes, a new M. tuberculosis plasmid library will be constructed with larger (10-12 kb) DNA inserts of genomic DNA from an H37Rv eis knockout mutant. This eis knockout library will then be screened for survival in the U-937 macrophage survival assay. Clones with enhanced survival will be isolated and further characterized.
