Pulmonary endothelium is a major component of the alveolar-capillary unit, and is susceptible to injury from noxious agents that are either inhaled or delivered to the lung through the pulmonary circulation (57) . In ALI, pulmonary endothelium plays a major role by (a) altering metabolic activity to affect pulmonary and systemic homeostasis, (b) mediating polymorphonuclear PMN adhesion to promote PMN infiltration, (c) changing PMN barrier permeability to cause pulmonary edema and (d) secreting cytokines and chemokines to induce lung inflammation (58) .