Emerging roles for platelets as immune and inflammatory cells.

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.

Platelet induction of the acute-phase response is protective in murine experimental cerebral malaria.

Platelets are most recognized as the cellular mediator of thrombosis, but they are increasingly appreciated for their immunomodulatory roles, including responses to Plasmodium infection. Platelet interactions with endothelial cells and leukocytes contribute significantly to the pathogenesis of experimental cerebral malaria (ECM). Recently, it has been suggested that platelets not only have an adverse role in cerebral malaria, but platelets may also be protective in animal models of uncomplicated malaria.

Platelets present antigen in the context of MHC class I.

Platelets are most recognized for their vital role as the cellular mediator of thrombosis, but platelets also have important immune functions. Platelets initiate and sustain vascular inflammation in many disease conditions, including arthritis, atherosclerosis, transplant rejection, and severe malaria. We now demonstrate that platelets express T cell costimulatory molecules, process and present Ag in MHC class I, and directly activate naive T cells in a platelet MHC class I-dependent manner.