This project, “Role of receptor-interacting serine/threonine-protein kinase 3 (RIPK3) in Herpes Simplex Virus (HSV) Encephalitis”, aims to define the precise contribution of RIPK3 to Herpes Simplex Virus (HSV)-1 pathogenesis by using the experimental Herpes Simplex Encephalitis (HSE) model. We have found that RIPK3 kinase-dependent necroptosis restricts HSV-1 replication in human cells as well as mouse cells. The attenuation of HSV-1 propagation in mice was attributed to RIPK3-mediated necroptosis in current literature. Little information is available about the precise contribution of RIPK3 toward onset and development of the life- threatening virus-induced encephalitis. Using a well-accepted mouse model of HSE and unique knock-in/out mice, we have now obtained new evidence suggesting that RIPK3 restricts HSV-1-induced encephalitis via a RIPK3-necroptosis independent scaffolding function in the central nervous system (CNS), which requires caspase 8 function. The mechanism through which RIPK3 collaborates with caspase 8 to restrict HSE will be determined over the course of the project. Two complementary and interrelated research directions will be pursued. Specific Aim 1 will test the hypothesis that HSV1 infection drives RIPK3 activation of caspase 8- mediated apoptosis in microglia to restrict pathogenesis of HSV1-induced encephalitis. Specific Aim 2 will test the hypothesis that RIPK3 scaffolding function coordinates protective neuroinflammation and dictates antiviral immune response to restrict pathogenesis of HSV1-induced encephalitis. Ultimately, we expect to (1) establish that RIPK3 scaffolding function, by collaborating with caspase 8, is important for HSE restriction rather than the kinase activity, and (2) show that RIPK3 regulates brain inflammation via stimulation of key proinflammatory cytokines/chemokines. The studies proposed herein are intended to fill a major existing knowledge gap in our understanding of the RIPK3 and the pathogenesis of HSE. The impact on the field of HSE will include establishing fundamental mechanisms of targeting RIPK3 signaling therapeutically towards diagnosing, preventing, and/or treating this life-threatening virus-induced encephalitis in human settings.