RNA viruses represent a third of all emerging and re-emerging infectious diseases and are of continual global health concern as major causes of local epidemic and global pandemic outbreaks linked with mild to severe disease. The immune response to RNA viruses is initiated upon the recognition of non-self, viral RNA by the RIG-I-like receptors (RLRs), including retinoic acid inducible gene-I (RIG-I), melanoma differentiation antigen 5 (MDA5), and laboratory of genetics and physiology (LGP2). LGP2 function is poorly understood. West Nile Virus (WNV), an RNA Flavivirus, is of particular interest as it represents a viral family with a large global health footprint. WNV is neurotropic and the most common arboviral disease in the United States. It causes severe neuroinvasive disease in a high frequency of infected patients. Importantly, treatment for WNV infection is limited to supportive care because vaccines or antivirals are not available. The proposed studies will use WNV-Texas, the currently US circulating strain, in vitro and in mouse models of infection to study the role of LGP2 in the immunity to infection. These studies aim to define the role and mechanism of LGP2 modulation of RIG-I and MDA5 following Pathogen Associated Molecular Pattern (PAMP) recognition, and functional outcomes of LGP2 modulation in viral control of the important human pathogen, WNV. My central hypothesis is that LGP2 modulates RIG-I and MDA-5 signaling through non-direct mechanisms that dictates the end result of antiviral versus pro- inflammatory signaling after PAMP detection. To test this hypothesis the following specific aims will be investigated: 1) Determine the role of LGP2 in regulating RLR signaling during RNA virus infection; and 2) determine the contributions of each RLR during WNV infection to the overall innate immune profile. In vitro signaling approaches along with ex vivo and in vivo studies will be used to examine LGP2 function and mechanism of action in regulating the other RLRs. Further, mouse knockout models of LGP2 alone or in conjunction with other RLR family members will be utilized to investigate the role of LGP2 in immunity against WNV. The overall innate immune contributions to WNV immunity from LGP2 within the context of the other RLRs will be determined and presented through a computational model synthesizing the data generated in this proposal. Successfully defining the modulation of RLRs by LGP2 during WNV infection will have major implications in the fields of immunology, and will provide insights on innate immune regulation for possible applications in diverse fields impacted by RLR function including therapeutics, vaccinology, cancer biology, toxicology, and wound repair.