Abstract
Platelets are anucleated cells that are fragments of megacaryocytes, and they play a unique role in primary haemostasis. As they also contain numerous secretory products, they can exert crucial roles in several aspects of haemostasis. Furthermore, they contain and secrete a variety of cytokines, chemokines and associated molecules, which behave as ligands for receptors/counterparts displayed by both endothelial cells lining the vessels and most leukocyte subsets. These latter observations have sparked debate whether platelets play an important role in innate as well as adaptative immunity, thus highlighting the potential for platelets to take part in immune regulation. Moreover, platelets display receptors for several types of cytokines/chemokines (and associated molecules) along with FcγRII receptors. Platelets not only express a large variety of Toll-like receptors with recently identified or as-yet unknown functions, but they have also been shown to express a key tandem pair of inflammatory and antigen presentation molecules (CD40 and CD40-ligand/CD154) making them the major purveyors of soluble CD40L in the plasma. It appears that platelets may be regarded as one of the neglected players in immune cell regulation, and so we propose that they contribute to bridging innate and adaptative immunity. This review will present experimentally-driven arguments in favour of a role of platelet TLRs in regulating certain immune activities.
Keywords: Platelets, TLRs, adaptative and innate immunity, CD40/CD40L
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