This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Regulatory cascades involving one of the several different s factors allows Mycobacterium tuberculosis (Mtb) to efficiently adapt to environmental changes during infection. SigmaH is induced in response to heat, thiol-oxidative stress and phagocytosis. The "reduced immunopathology in spite of comparable tissue persistence" phenotype associated with the Mtb-sigH mutant was studied in rhesus macaques. Animals infected with Mtb developed active TB, characterized by extensive lung granulomatous histopathology, while animals infected with the mutant exhibited reduced pathology, in the wake of discernible bacillary growth. We seek to understand the molecular mechanisms by which SigmaH causes immunopathology during Mtb infection. Recently, we have shown that SigmaH controls the expression of a much larger than anticipated number of genes and regulons, including the ATP-dependent Clp proteolysis complex, the mce1 virulence regulon, the anti-apoptotic nuoA-G operon, etc. A systemic reduction in lipid metabolism including biosynthesis of mycolic acids, mycobactin siderophores and polyketides coincides with the SigmaH driven induction of Clp proteolysis. We hypothesize that key, rate-limiting enzymes from lipid biosynthetic pathways are the selective targets of Clp proteolytic degradation. We are currently testing this hypothesis. We are looking at FoxP3 marked T regulatory cells and Granzyme B expressing cytolytic T cells as mediators of immunopathology. Studying host-Mtb interactions in the context of the mutant offer a chance to dissect the signaling cascades that lead to immunopathology. Such knowledge may open new avenues towards the future control and therapeutics of TB. This project has been funded for three more years. In the coming months, we plan to repeat the phenotype analysis of the mutant relative to Mtb using a low dose of infection.