Endothelium–platelet interactions in inflammatory lung disease

In addition to their established role in hemostasis, recent studies have identified platelets as key regulators of inflammatory reactions. Upon activation, platelets interact with both endothelial cells and circulating leukocytes. By receptor-mediated activation of interacting cell types and by release of mitogenic, pro-inflammatory and -coagulatory mediators, platelets contribute crucially to the initiation and propagation of pathological conditions and processes such as inflammatory bowel disease or atherosclerosis. In inflammatory lung disease, platelets play a critical role in the recruitment of neutrophils, eosinophils and lymphocytes as shown in experimental models of acute lung injury and allergic airway inflammation. Circulating platelet–leukocyte aggregates have been detected in patients with allergic asthma and cystic fibrosis, and in experimental lung injury. Here, we discuss the molecular mechanisms regulating the interaction of platelets with leukocytes, endothelial cells, and the subendothelial matrix with special regard to platelet kinetics in pulmonary microvessels and the putative role of platelets in inflammatory lung disorders. In light of the existing data from experimental and clinical studies it is conceivable that platelet adhesion molecules and platelet mediators provide promising targets for novel therapeutic strategies in inflammatory lung diseases.