One third of the world's population is currently infected with Mycobacterium tuberculosis (Mtb) and every second, another person is newly infected with Mtb around the world. Each year an estimated 8 million people develop clinical disease and 1.87 million people die of TB. The primary host cell of Mtb is the macrophage and the Mtb-macrophage interaction is critical to every phase of Mtb's infectious cycle. Gene expression analysis (GEA) is the most effective technology currently available to record a quantitative picture of a cell's functional state, and therefore to compare cell states and types. The critical need for such a comparison in TB research is heightened when one takes into account the heterogeneity of macrophages by organ, species of origin and donor history. The goals of this study are to extend our understanding of macrophage biology relevant to tuberculosis (TB), and in so doing, to define the extent to which mouse macrophages can serve as surrogates for human macrophages. The latter question is key if functional genomics is used as a tool in TB research to test the course of infection by wild type and genetically modified Mtb in wild type and genetically modified mice. Specifically, we will extend our current use of high-density oligonucleotide microarrays, quantitative PCR and in situ hybridization (ISH) to analyze and compare the gene expression profiles of three distinct populations of primary cells: mouse bone marrow macrophages (BMM), mouse pulmonary alveolar macrophages (PAM), and human PAM. These relatively pure macrophage populations will be compared with the heterogeneous mixture of all cells in mouse lung. Both human and mouse cells will come both from normal donors and individuals with active TB. Each cell population will be studied without further treatment, after infection in vitro with virulent Mtb, and/or after exposure to interferon gamma (IFNgamma), a cytokine critical for control of mycobacterial infection in both humans and mice. These comparisons will allow us to validate or qualify the use of mouse PAM, mouse BMM and human PAM as model systems for studying macrophage-Mtb interactions. The identification of genes regulated by Mtb in macrophages will generate hypotheses with respect to the role of these genes in pathogenesis. We will test at least one such hypothesis, that secretory leukocyte protease inhibitor (SLPI) plays a role in the pathogenesis of TB. Finally, we will share our GEA with others via the internet so that as many of the resulting hypotheses as possible can be rapidly and independently explored.