Abstract: Tularemia is a fatal human disease caused by the Gram-negative intracellular pathogen Francisella tularensis (Ft). Francisella species are prevalent in the northern hemisphere, and in the past decade, an increasing incidence of tularemia has been reported in the mid-western states of the USA. Due to its potential to cause severe illness and death, Ft has been used in the biological weapon programs of several countries and is now classified by the CDC as a Tier 1 category A select agent. However, the factors responsible for the extreme virulence of Francisella and the host immune responses required to combat Ft infection are not well understood. From the host’s perspective, toll-like receptors (TLRs) play a role in recognizing pathogen-associated molecular patterns (PAMPs) outside the host cell, while Nod-like receptors (NLRs) are essential for detecting bacterial and host products in the cytoplasm. The NLRs assemble into a multi-protein complex known as the inflammasome in response to the recognition of pathogen and host-derived ligands. The inflammasome-dependent host- defense mechanisms include the production of bioactive pro-inflammatory cytokines and induction of cell death. This proposal builds on our previous research to further investigate the mechanisms underlying repression of the Aim2 and Nlrp3 inflammasomes during Ft infection. One question that remained unanswered is why both Aim2 and Nlrp3 inflammasomes are repressed in Ft-infected macrophages. This indicates that a common mechanism may be linked to the repression of both Aim2 and Nlrp3 inflammasomes. Our hypothesis is that Ft- induced mitophagy, a process that removes stressed/dysfunctional mitochondria, may be involved in the repression of both Aim2 and Nlrp3 inflammasomes in Ft-infected macrophages. In specific aim 1, we will investigate the mechanism of induction of mitophagy in Ft-infected macrophages. In specific aim 2, we will Investigate how repression of Aim2 and Nlrp3 inflammasomes in response to Ft infection is linked to mitophagy. The results will continue to improve our understanding of the immunopathogenesis of tularemia. These studies will elucidate how repression of Aim2 and Nlrp3 inflammasomes are linked to a common pathway in Ft-infected macrophages. This continuation proposal will provide additional opportunities for training undergraduate and master’s students.