Highly pathogenic respiratory viruses, like the influenza virus and Severe Acute Respiratory Coronavirus (SARS-CoV), represent significant threats to the overall public health and to global economic stability. They cause an acute lung injury (ALI) that rapidly progresses to ARDS, the former most notably in the elderly. Moreover, after virus clearance many SARS and H5N1 patients developed an organizing phase diffuse alveolar damage (DAD) that oftentimes progresses to pulmonary fibrosis (PF), another devastating end stage lung disease effecting 5 million people globally, characterized by dysregulated cell proliferation during wound repair. We have developed a genetically tractable model of induced acute lung injury using the SARS-CoV. We will use this model to study the host factors and cell types that determine the progression from acute lung injury to pulmonary fibrosis. Our preliminary studies demonstrate that the Epithelial Growth Factor Receptor (EGFR) is a key mediator of acute lung injury after infection with the SARS Coronavirus and EGFR is a key intermediate in the regulation of both the innate and wound healing response to acute lung injury. In Aim 1 we will identify how EGFR over activation causes exacerbated disease. In Aim 2 we will examine whether inhibition of EGFR signaling can protect the host from disease progression and in Aim 2 we will identify the cell type where EGFR is necessary for disease progression. These studies will allow us to identify the cells that are responsible for the development of acute lung disease and ARDS. The current therapy for pulmonary fibrosis is blunt and treats the whole individual rather than targeting a specific cell population. These therapies work in only a fraction of the patients and can potentially produce more damage than they treat. These studies will identify the specific cell types that lead to acute lung disease induction and progression, allowing for cell directed therapies and targets interventions.