Francisella tularensis, the etiological agent of tularemia, is intracellular Gram-negative cocci. F. tularensis can survive for weeks at low temperatures in water, moist soil, hay, straw, and decaying animal carcasses. Its hardy nature and potentially lethal effects following inhalation have made this organism attractive for weaponization. This bacterium is one of the most infectious pathogens identified when inhaled, and yet very little is known about how F. tularensis interacts with its human host. One reason for the lack of information about this highly virulent organism is the requirement for BSL 3 safety procedures that makes associated research labor intensive. Virtually nothing is known about the interaction between F. tularensis and resident lung cells, specifically alveolar epithelial cells (AEC) and human pulmonary microvascular endothelial cells (HPMEC). The respiratory epithelium is a dynamic interface between the outside environment and the host. AEC are vital for maintaining lung homeostasis and providing a physical barrier against inhaled pathogens. Two inducible defense mechanisms provided by AEC include the production of antimicrobial factors and secreting cytokines for the recruitment and activation of immune cells. Therefore, I propose to examine how pulmonary AEC and HPMEC respond to a virulent strain of F. tularensis (Schu 4) to promote immune cell migration and activation. The second goal of this proposal will be to examine the response of AEC to F. tularensis in an intranasal mouse model and correlate these results with the human cell studies in Aim 1. These studies will, for the first time, provide vital information for understanding the interaction of F. tularensis and AEC and the cell-cell communication between human lung epithelium/endothelium and immune cells in response to F. tularensis. This is essential for gaining insight into the pathogenicity of tularemia, and will allow us to identify novel avenues for targeted vaccine development. F. tularensis can be used as a bioweapon against the public. Therefore, this application proposes to better understand how this organism interacts with lung cells and responses of the lung cells to F. tularensis. This funding of this proposal will provide crucial insight into the effective and ineffective innate immune responses to help find future vaccines and therapeutic development.