Platelet immunology from the inside out
John W. Semple, Rick Kapur
Abstract
Platelets are the critical cellular mediators of hemostasis; however, many studies have now suggested that these tiny offspring of megakaryocytes can also perform multiple immune‐like functions that significantly affect both innate and adaptive immunity. For example, like whole blood, platelets can mediate transfusion‐related immunomodulation ( TRIM ) and it appears that activated platelets are more immunoregulatory that their resting counterparts. In addition, platelets express and secrete a wide variety of critical immune molecules such as TGF ‐ β , CD 40/ CD 40L and MHC class I molecules. This allows platelets to directly influence adaptive immune mechanisms and a variety of immune disease processes. It has also been demonstrated that both platelets and megakaryocytes can process and present both foreign and self‐antigens to CD 8+ T cells. This manuscript will highlight several non‐haemostatic attributes of platelets that deservedly categorize them as integral players in immunity.