The inflammation-resolving lipid mediator lipoxin A4 (LXA4), which is derived from arachidonic acid in the context of inflammation, can be generated physiologically in vivo However, the mechanism of physiologic formation of LXA4 remains elusive In this report, we provide evidence that platelet-derived microparticles contain lipoxygenase 12 (12-LO) protein and act as a mediator in transferring 12-LO to mast cells, leading to the production of LXA4 by mast cells Absence of either leukotriene, the precursor for LXA4, in mast cells or 12-LO in microparticles abolished LXA4 production. Using a mouse model, we demonstrated that platelet-derived microparticles were taken up by peritoneal mast cells in vivo and triggered LXA4 production We also found that similar to LXA4, platelet-derived microparticles attenuated LPS- or dextran sulfate sodium-induced inflammation by regulating inflammatory cytokines Together, these data suggest a critical role of platetlet-derived microparticles as a signal mediator, at least in LXA4 production, resulting in significant immunoregulatory consequences (C) 2010 Elsevier Inc. All rights reserved