[Regulation of immune responses by prostaglandin]

Prostaglandin (PG), an arachidonic acid metabolite produced by various cell types, regulates a broad range of physiological activities, and maintains the local homeostasis. PGE2, one of the PGs, is produced by the action of the enzyme PGE synthase and cyclooxigenase (COX) on arachidonic acid liberated from the membrane phospholipid by phospholipase A2 (PLA2). In the immune system, PGE2 is mainly produced by antigen presenting cells such as macrophages and dendritic cells. PGE2 regulates immune responses, for example, the production of cytokines and chemokines and the expression of cytokine receptors and cell surface molecules, and the main action is mediated by intracellular accumulation of cyclic AMP via the activation of adenylate cyclase. The main function of PGE2 in the immune system is the suppression of Th1 activation and the enhancement of Th2 activation. Therefore, in this paper, PGE2, a pivotal factor in the pathogenesis of Th1/Th2-related diseases, is highlighted.