[Roles of Bioactive Lysophospholipids as Immunomodulators]

In addition to direct activation by pathogens and antigens, immune cell functions are further modulated by G protein-coupled receptor (GPCR) signals that are evoked by environmental factors produced in response to immune responses. Recent studies have revealed that membrane-derived lysophospholipids are such environmental factors. When immune cells are activated, phospholipid metabolism becomes active, and under such conditions lysophospholipids are produced by the action of various phospholipases. As a result, the immune responses are regulated positively or negatively via GPCR-type receptors. These lysophospholipids include lysophosphatidic acid (LPA), lysophosphatidylserine (LysoPS), and lysophosphatidylinositol (LPI). Here, we summarize our current knowledge of the synthetic pathways, receptors signaling for these LPLs, and discuss updated findings on the immunomodulatory functions of lysophospholipids, with a particular focus on the recently identified bioactive lysophospholipid, LysoPS.