Project Summary/Abstract The innate immune system is the first-line of defense against both endogenous and exogenous threats, serving dual roles as both effectors and activators. However, when the innate immune system responds too robustly to a stimulus, this can lead to the host’s demise, a phenomenon we frequently call “sepsis”. Sepsis is frequently associated with infection by a gram-negative bacterial agent such as E. coli or P. aeruginosa and has been hypothesized to be driven by their immunogenic substances, with lipo-polysaccharide (LPS) likely playing a critical role in this aberrant over-signaling. This proposal outlines a plan to study the intracellular receptor of LPS, a recently discovered phenomenon seemingly the cause of endotoxemia, although the mechanisms underlying the exact nature of this receptor are still unknown. By probing both the enzyme’s activation and characterizing its downstream proteolytic events, we plan to identify if this receptor is the root cause of LPS-induced shock in human cell systems, as knockout of its murine homolog is protective against endotoxin shock when directly injected into mice. In addition to further characterizing the basic nature of this intracellular LPS receptor, we will initiate a screening campaign to identify selective molecules with a preference for this enzyme, over its closely related family members. The data generated by this proposal should identify either a validated therapeutic target for the reversal of sepsis and septic shock, a biomarker for the proper diagnosis of sepsis, or a new, highly sensitive assay for the detection of endotoxin in serum.