PROJECT SUMMARY/ABSTRACT Most humans are resistant to Mycobacterium tuberculosis (Mtb) and form granulomas that limit inflammatory tissue damage. Nevertheless, tuberculosis (TB) remains a leading infectious cause of death globally because a fraction of infected individuals develops massive necrotic granulomas and transmit Mtb via aerosols. This outcome of Mtb infection is relatively uncommon among immunocompetent humans, and its mechanisms are poorly characterized. We will study both host vulnerability (predisposition to necrotization of TB granulomas) and Mtb virulence determinants (the necrosis-inducing factor) to determine how their interactions lead to necrosis in susceptible but otherwise immunocompetent hosts. We will address this major knowledge gap using a well-characterized mouse model developed in our laboratory that recapitulates the formation of organized human-like necrotic pulmonary TB granulomas (mice with the susceptibility allele of the sst1(super-susceptibility to tuberculosis, sst1) locus) Our recent studies reveal that inadequate antioxidant defense (AOD) drives an aberrant response of the sst1 mutant macrophages to TNF and induce hyperactivity of type I interferon pathway (IFN-I). This mouse model also provides a unique opportunity to study the role of a recently discovered Tuberculosis Necrotizing Toxin (TNT). The major premise of this application is that impaired stress resilience of macrophages due to inadequate antioxidant defense (AOD) is exploited by Mtb to subvert local immunity within pulmonary TB granulomas of immunocompetent hosts and induce necrosis. We will investigate: (i) Crosstalk of Myc and IFN-I pathways in the deregulation of antioxidant response in activated macrophages. (ii) Host regulators of the anti-oxidant response and necrosis in vivo. This aim will address our hypothesis about the hierarchy of the antioxidant defense and IFN-I pathways in vivo and test whether boosting the antioxidant defense prevents the granuloma necrotization and reduce the IFN-I hyperactivity. (iii) Role of the Mtb Tuberculosis Necrotizing Toxin (TNT) in driving necrosis in TB granulomas of the susceptible but immunocompetent hosts. The ultimate goal of our studies is to develop mechanistic interventions to target necrosis in TB granulomas in order to overcome a major obstacle to the sterilization of TB lesions with antibiotics. This will improve the outcomes of TB chemotherapy and prevent the evolution and spread of drug resistant TB.

PROJECT NARRATIVE Only a minor fraction of immunocompetent humans develop tuberculosis with massive necrotic granulomas and cavitation in their lungs, but the host mechanisms causing this vulnerability are poorly characterized. We will use a well characterized mouse model that recapitulates the formation of organized necrotic pulmonary tuberculosis (TB) granulomas to examine the interplay of host mechanisms of susceptibility with the necrosis-inducing factor of virulent Mycobacterium tuberculosis (Mtb). Because necrosis of TB granulomas is a major obstacle to the sterilization of TB lesions with antibiotics, this study will lead to host-directed therapies that will synergize with antibiotics to shorten and improve TB chemotherapy.