The major goal of this proposal is to determine the role of Duffy Antigen/ Receptor for Chemokines (DARC) in endothelial cells during lung inflammation. DARC binds multiple CXC and CC chemokines and is expressed on post-capillary venular endothelial cells, the site where leukocytes traverse the endothelium in response to inflammatory signals released from a site of tissue injury. Although endothelial DARC is upregulated during inflammation, its biological function remains unknown. It's focal location at the site of leukocyte emigration, its upregulation during inflammation, and preservation of expression on endothelial cells in all individuals suggest that it may participate in the regulation of inflammatory cell recruitment at the bloodtissue interface. The specific aims will explore the following : (1)endothelial DARC's role in chemokine transport, (2) its ability to modify neutrophil transendothelial migration, (3) its in vivo expression in the lung during suppurative pneumonia, (4) and DARC's contribution to neutrophil recruitment in a mouse model of pneumonia. A human endothelial cell line stably expressing DARC cDNA has been developed to study its ability to modify the biological activity of chemokines in vitro. Immunohistochemical analysis of human lungs will define the expression pattern of endothelial DARC during suppurative pneumonia. Finally, DARC's role will be examined in an animal model of bacterial pneumonia using DARC knockout mice. These studies are important, as they will determine endothelial DARC's contribution to the pulmonary recruitment of neutrophils during lung inflammation. Understanding endothelial DARC's function may provide novel strategies in modifying the inflammatory component of specific diseases such as bacterial pneumonia. These studies will further the candidate's research training in cell and molecular biology and provide the foundation for a career as a physicianscientist. The proposed studies will be conducted at the Pulmonary VA Research laboratories under the guidance of the sponsor and co-sponsor. Interactions with consultants throughout the University of Washington research community will enrich the candidate's training and ensure the success of the proposal.