Platelet - leukocyte interactions: multiple links between inflammation, blood coagulation and vascular risk

The aim of this review is to summarize the contribution of platelets and leukocytes and their interactions in inflammation and blood coagulation and its possible relevance in the pathogenesis of thrombosis. There is some evidence of an association between infection/inflammation and thrombosis. This is likely a bidirectional relationship. The presence of a thrombus may serve as a nidus of infection. Vascular injury indeed promotes platelet and leukocyte activation and thrombus formation and the thrombus and its components facilitate adherence of bacteria to the vessel wall. Alternatively, an infection and the associated inflammation can trigger platelet and leukocyte activation and thrombus formation. In either case platelets and leukocytes co-localize and interact in the area of vascular injury, at sites of inflammation and/or at sites of thrombosis. Following vascular injury, the subendothelial tissue, a thrombogenic surface, becomes available for interaction with these blood cells. Tissue factor, found not only in media and adventitia of the vascular wall, but also on activated platelets and leukocytes, triggers blood coagulation. Vascular-blood cell interactions, mediated by the release of preformed components of the endothelium, is modulated by both cell adhesion and production of soluble stimulatory or inhibitory molecules that alter cell function: adhesion molecules regulate cell-cell contact and facilitate the modulation of biochemical pathways relevant to inflammatory and/or thrombotic processes.