PROJECT SUMMARY Ebola virus (EBOV) is an emerging, highly pathogenic virus associated with increasingly more frequent outbreaks of hemorrhagic disease in human populations. Approved countermeasures to prevent or treat EBOV disease are currently limited. Macrophages are the initial cells targeted by EBOV, and yet, little is known about the exact nature of EBOV-macrophage surface interactions and subsequent uptake into the cell. Due to their migratory properties, macrophages are also believed to rapidly disseminate the virus to distant tissues and organs despite the lack of experimental evidence. We have preliminary data showing that EBOV depends on podosomes, mechanosensitive adhesive structures used by macrophages to migrate through tissues and sample antigens, to enter macrophages. The data also shows that EBOV replication increases macrophage locomotion through a fibrillar 3D matrix and reduces podosome number, suggesting that the virus actively transforms infiltration of tissues by these cells. This proposal aims to examine the interactions between EBOV and podosomes. In Aim 1, we will determine whether podosomes serve as ports for EBOV entry into human macrophages. In Aim 2, we will characterize migratory and invasive properties of macrophages challenged with EBOV. In Aim 3, we will assess host resistance to systemic infection with EBOV in a mouse model of EBOV disease devoid of functional macrophages. Our findings will establish a new model of interactions between EBOV and macrophages, laying the groundwork for further investigations into pathogenesis of filoviruses. Importantly, these discoveries may lead to new areas of development of novel countermeasures targeting EBOV and related viruses.