Cells are activated after exposure to endotoxin through a CD14-dependent pathway. This signaling pathway requires interactions of membrane or soluble CD14, lipopolysaccharide binding protein (LBP), and endotoxin. After cell activation, mediators are released from phagocytic cells that express membrane CD14 (neutrophils, macrophages) as well cells that lack membranous CD14 but respond to the soluble CD14-LPS complex (e.g., epithelial cells).We will study the role of CD14 in inflammatory responses of the lung by studying the time course of appearance of soluble and membrane-associated CD14 in the lung following direct endotoxin challenge to a pulmonary subsegment (under Protocol 92-CC-0141). Levels of CD14, LBP, and endotoxin will be measured in bronchoalveolar lavage at several time points after endotoxin challenge of a lung subsegment. To assess the contribution of these inflammatory mediators to airway responses, cell lines will be cocultured with bronchoalveolar lavage containing CD14, LBP, and endotoxin, and cell-derived mediators (e.g., IL-8) will be evaluated. The CD14 pathway is important in the initiation of inflammatory responses to gram-negative bacteria. Defining the time course and secondary responses that result from the CD14 signaling pathway will be important in understanding factors that result in the initiation, amplification, and resolution of, as well as tolerance to, the inflammatory response to endotoxin.