Macrophages play pivotal roles in the biology of infectious diseases as hosts to intracellular pathogens, mediators of inflammation, and orchestrators of acquired immunity. It is no surprise that among most of the NIAID priority pathogens, macrophages are critical to the outcome of infection. A central hypothesis of this Program Project is that intracellular pathogens manipulate the response of macrophages to promote disease. Furthermore, the transcriptional response of macrophages to infection serves as a fundamental read-out of the overall response. The purpose of this Program Project is to use a taxonomically and structurally distinct and clinically relevant panel of intracellular pathogens to establish the transcription profile of macrophages in response to microbial infection using a newly developed and novel microarray containing probes for all known mouse genes (Core B). This transcriptional profile will then serve as a benchmark to understand how the host response is manipulated by each pathogen. By profiling the transcriptional response of macrophages to microbial mutants that are defective in their pathogenic interactions with macrophages, we will learn how pathogens manipulate host cells to promote infection. By using macrophages derived from knockout mice in combination with microbial mutants, we will identify the pathways of innate immune recognition that determine the host response and how pathogens can manipulate these pathways for their benefit. These studies will illuminate essential and conserved pathways of macrophage control of innate immunity, thereby providing potential targets of therapeutic intervention as well as pathogenic signatures that will serve to uncover basic mechanisms of microbial pathogenesis and host response. The specific Aims are to (1) Identify microbial determinants of pathogenesis that affect macrophage innate immune responses in Listeria monocytogenes, Francisella tularensis, Mycobacterium tuberculosis and Histoplasma capsulatum; (2) Characterize the intracellular replication and trafficking of microbial mutants in bone marrow-derived macrophages. (3) Characterize host gene expression profiles using custom synthesized DNA microarrays in response to wild-type and mutant microbial pathogens in macrophages from wild-type and mutant mice.