title: Crosstalk between Platelets and the Immune System: Old Systems with New Discoveries.
abstract: Platelets are small anucleate cells circulating in the blood. It has been recognized for more than 100 years that platelet adhesion and aggregation at the site of vascular injury are critical events in hemostasis and thrombosis; however, recent studies demonstrated that, in addition to these classic roles, platelets also have important functions in inflammation and the immune response. Platelets contain many proinflammatory molecules and cytokines (e.g., P-selectin, CD40L, IL-1β, etc.), which support leukocyte trafficking, modulate immunoglobulin class switch, and germinal center formation. Platelets express several functional Toll-like receptors (TLRs), such as TLR-2, TLR-4, and TLR-9, which may potentially link innate immunity with thrombosis. Interestingly, platelets also contain multiple anti-inflammatory molecules and cytokines (e.g., transforming growth factor-β and thrombospondin-1). Emerging evidence also suggests that platelets are involved in lymphatic vessel development by directly interacting with lymphatic endothelial cells through C-type lectin-like receptor 2. Besides the active contributions of platelets to the immune system, platelets are passively targeted in several immune-mediated diseases, such as autoimmune thrombocytopenia, infection-associated thrombocytopenia, and fetal and neonatal alloimmune thrombocytopenia. These data suggest that platelets are important immune cells and may contribute to innate and adaptive immunity under both physiological and pathological conditions.
authors.affiliation: Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON, Canada M5S 1A8 ; Department of Laboratory Medicine, Keenan Research Centre, Li Ka Shing Knowledge Institute, St. Michael's Hospital, and Toronto Platelet Immunobiology Group, University of Toronto, Toronto, ON, Canada M5S 1A8.
authors.forename: Conglei
authors.initials: C
authors.lastname: Li
authors.forename: June
authors.initials: J
authors.lastname: Li
authors.forename: Yan
authors.initials: Y
authors.lastname: Li
authors.forename: Sean
authors.initials: S
authors.lastname: Lang
authors.forename: Issaka
authors.initials: I
authors.lastname: Yougbare
authors.forename: Guangheng
authors.initials: G
authors.lastname: Zhu
authors.forename: Pingguo
authors.initials: P
authors.lastname: Chen
authors.forename: Heyu
authors.initials: H
authors.lastname: Ni