Emerging roles for platelets as immune and inflammatory cells

Abstract

Despite their small size and anucleate status, platelets have diverse roles in vascular biology. Not only are platelets the cellular mediator of thrombosis, but platelets are also immune cells that initiate and accelerate many vascular inflammatory conditions. Platelets are linked to the pathogenesis of inflammatory diseases such as atherosclerosis, malaria infection, transplant rejection, and rheumatoid arthritis. In some contexts, platelet immune functions are protective, whereas in others platelets contribute to adverse inflammatory outcomes. In this review, we will discuss platelet and platelet-derived mediator interactions with the innate and acquired arms of the immune system and platelet-vessel wall interactions that drive inflammatory disease. There have been many recent publications indicating both important protective and adverse roles for platelets in infectious disease. Because of this new accumulating data, and the fact that infectious disease continues to be a leading cause of death globally, we will also focus on new and emerging concepts related to platelet immune and inflammatory functions in the context of infectious disease.

Figure 1

Schematic of platelet-derived immune mediators. 5-HT, serotonin; ADP, adenosine 5′-diphosphate; COX-1, cyclooxygenase 1; P-selectin glycoprotein ligand-1; TbxA, thromboxane; WBC, white blood cell; PSGL-1.

Figure 2

Platelet and liver sinusoid interactions in a Plasmodium berghei–infected mouse (* denotes platelets).