The largest and worst Ebola virus (EBOV) disease (EVD) outbreak ever recorded occurred in West Africa from 2013-2016, and resulted in a devastatingly high death toll, economic damages, and global anxiety. EVD is one of the most severe viral diseases, and is characterized by systemic viral replication, immune dysregulation, coagulopathy, and multi-organ dysfunction. The synergistic effects of systemic viral replication and immune dysregulation that characterize EVD lead to the induction of a systemic inflammatory response syndrome (SIRS) that evokes severe systemic pathology. This complicated disease process most likely makes it difficult to effectively treat severe/fatal EVD with therapeutics that target only the EBOV life cycle. Therefore, understanding the mechanisms of EBOV-induced SIRS is crucial for the development of effective therapeutic interventions that can counteract the aberrant immune activation. We have found that EBOV VP40, the viral matrix protein that is essential for virus assembly and budding, activates host inflammatory responses and release of pro-inflammatory cytokines in the human cells. Remarkably, we have also found that VP40 from Reston virus and Bundibugyo virus, which belong to the same genus as EBOV but are thought to be apathogenic or less pathogenic than EBOV in humans, activated the inflammatory pathway less efficiently than EBOV VP40, suggesting that VP40 is a novel virulence determinant at least partially responsible for the differential pathogenesis of these highly related viruses. Taken together, we hypothesize that the EBOV matrix protein VP40 activates an inflammatory response through a novel mechanism, which correlates with EBOV pathogenesis in humans. To understand this newly emerging aspect of EBOV pathogenesis, the applicant's group and collaborators will pursue three interactive specific aims, as follows: (Aim 1) Define the significance of unfolded protein response/ER-nucleus signaling pathway in VP40-mediated inflammatory activation; (Aim 2) Determine the interaction of VP40 with host transcriptional machinery associated with VP40-mediated inflammatory activation; and (Aim 3) Determine the role of EBOV VP40 as a virulence factor in inflammatory gene activation and pathogenesis. The proposed research will provide an essential base for the development of post-exposure therapeutic interventions that target the molecular triggers of the uncontrolled inflammatory responses that characterize the late stages of severe EVD.