INTRODUCTION

During inflammation and thrombosis, signaling cascades result in activation of platelets, endothelial cells (ECs), and leukocytes. The complex interaction between these vascular cells is influenced by cell adhesion and by production of soluble stimulatory or inhibitory molecules that alter cell function. The net effect of this tridirectional “cellular cross talk” on thrombosis and inflammation depends on the balance between inputs and can lead to resolution and repair or perpetuation of inflammation and thrombosis. The specific aim of this chapter is to highlight the important role that platelets play in inflammation. Emphasis is placed on recent advances delineating molecular pathways that allow platelets, leukocytes, and ECs to “cross talk” in a coordinated fashion in the normal state and in inflammatory and thrombotic conditions. Major topics include the inflammatory mediators produced by platelets, the molecular interactions between platelets and ECs and platelets and leukocytes, and the role of platelets in facilitating leukocyte adhesion and transmigration through the blood vessel wall. Clinical implications of basic science research are outlined in each section.

At first glance, platelets are critical components of hemostatic pathways that prevent blood loss at sites of vascular injury. More careful examination, however, reveals that platelets are also inflammatory cells that regulate the initiation and progression of inflammatory processes and thereby link inflammation and thrombosis.