Platelets as immune mediators: Their role in host defense responses and sepsis

Platelets occupy a central role at the interface between thrombosis and inflammation. At sites of vascular damage, adherent platelets physically and functionally interact with circulating leukocytes. Activated platelets release soluble factors into circulation that may have local and systemic effects on blood and vascular cells. Platelets can also interact with a wide variety of microbial pathogens. Emerging evidence from animal models suggests that platelets may participate in a wide variety of processes involving tissue injury, immune responses and repair that underlie diverse diseases such as atherosclerosis, autoimmune disorders, inflammatory lung and bowel disorders, host-defense responses and sepsis. In this review, we summarize the general mechanisms by which platelets may contribute to immune function, and then discuss evidence for their role in host defense responses and sepsis from preclinical and clinical studies.