Hepatotoxicity induced by acetaminophen (APAP) has become the leading cause of acute liver failure among the general and the VA populations. The APAP overdose or abuse causing severe liver injury remains a great threat to veterans. Currently, the standard of care implemented uses high doses of the L-cysteine precursor N-Acetylcysteine (NAC) making it the only treatment option for patients that suffer from APAP-induced liver injury (AILI). Unfortunately, the therapeutic window of NAC administration between overdose and treatment is narrow leaving many patients with no other recourses. The focus of research in understanding the pathologic mechanisms of AILI has been always on intracellular changes in hepatocytes. However, emerging evidence suggests a critical role of sterile inflammation for modifying the outcome of disease progression. Our preliminary studies showed that ablation of scavenger receptor A (SRA), an innate pattern recognition receptor primarily expressed on myeloid cells, e.g., Kupffer cells (KCs), exacerbated AILI indicated by sharply increased mortality and hepatic inflammation. This was associated with markedly reduced production of anti-inflammatory cytokine IL-10. SRA expression also positively correlates with IL-10 levels in human blood samples after APAP exposure. SRA-IL-10 pathway regulates a sophisticated inflammatory cascade including activation of unconventional γδ T cells that are known to aggravate tissue damage. Our central hypothesis is that SRA acts as a master regulator of hepatic immunity and promotes liver homeostasis in AILI. The objective of this project is to interrogate and mechanistically understand SRA as a key hepatic immune `checkpoint' that operates in highly integrated immune processes during AILI. These include KC response to damage-associated molecular patterns released from injured hepatocytes, modulation of hepatocyte-intrinsic stress signaling, and mobilization of pathogenic inflammatory cells. Analyses of clinical specimens from APAP overdose patients for immune alterations will also be performed to validate our findings in animal models. Furthermore, we will test the feasibility of targeting SRA- regulated immune network to improve NAC treatment of AILI. Successful completion of this research will advance our understanding of a novel hepatocyte-extrinsic immunologic mechanism of AILI. It is anticipated that a crucial role of SRA, as a previously unrecognized immune determinant of AILI, will be established for the first time. Given an increased risk of drug overdose or abuse among veterans, our research is highly significant and clinically relevant to the healthcare of veterans. Elucidating the key elements and molecular pathways that define the pathogenesis of AILI not only will help identify risk factors to decrease the incidence of AILI, but also provide new opportunities to develop novel immune-targeted therapies that benefit the large population of veterans.