The immune system as seen through the eyes of a platelet

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Background and Objectives

The primary hemostatic nature of platelets closely links these cellular fragments with the immune system. Platelet aggregation and activation on damaged endothelium initiates secretion of their granule contents and expression of both pro- and anti-inflammatory molecules. This review will highlight some of the major non-hematologic functions of platelets.


For example, the platelet secretome affects many local innate immune responses by, for example, attracting neutrophils to sites of inflammation. On the other hand, secretion and expression of platelet molecules such as CD40/CD40L may directly regulate adaptive immune responses. Perhaps more striking is that platelets express molecules that have no obvious hemostatic function such as Toll-Like Receptors. This allows platelets to bind infectious agents causing both direct destruction via thrombocidins and enhanced presentation to neutrophils and other professional phagocytes for engulfment.


To date, there are many published reports of platelet-immune interactions suggesting that they significantly regulate immunity. It appears that platelets play a much more active role as non-hemostatic immune-regulators than was previously thought.

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