On the Trail of Microparticles

Stimulation of a variety of cell types leads to the release ofsubmicron vesicles that bud off from the plasma mem-brane. These so-called microparticles (MPs) or microvesicles are defined by their small size (0.1 to 1 m) and the presence of surface antigens from the parental cells.1,2 MPs contribute to a variety of physiological and pathological processes. For instance, they appear to play a role in both hemostasis and thrombosis. MPs released into the bloodstream can act as messengers delivering a variety of cargos, such as cell surface receptors, proinflammatory cytokines, signaling molecules, and even mRNA, to distal cells.1,2 They may also contribute to disease by transporting viruses and prions.1,2 In addition, in vitro studies have shown that binding of MPs to endothelial cells and monocytes induces the expression of proinflamma-tory and procoagulant molecules (Figure 1). In this issue of Circulation Research, Simoncini et al explore the inflamma-