The naturally occurring prostaglandin E2 (PGE2) is known in medicine as dinoprostone, and it is the most common and most biologically active of the mammalian prostaglandins. It has important effects during labour and also stimulates osteoblasts to release factors which stimulate bone resorption by osteoclasts (a type of bone cell that removes bone tissue by removing the bone's mineralized matrix). PGE2 is also the prostaglandin that ultimately induces fever. PGE2 has been shown to increase vasodilation and cAMP production, enhance the effects of bradykinin and histamine, and induce uterine contractions and platelet aggregation. PGE2 is also responsible for maintaining the open passageway of the fetal ductus arteriosus, decreasing T-cell proliferation and lymphocyte migration, and activating the secretion of IL-1 and IL-2. PGE2 exhibits both pro- and anti-inflammatory effects, particularly on dendritic cells (DC). Depending on the nature of maturation signals, PGE2 has different and sometimes opposite effects on DC biology. PGE2 exerts an inhibitory action, reducing the maturation of DC and their ability to present antigen. PGE2 has also been shown to stimulate DC and promote IL-12 production when given in combination with TNF-alpha. PGE2 is an environmentally bioactive substance. Its action is prolonged and sustained by other factors especially IL-10. It modulates the activities of professional DC by acting on their differentiation, maturation, and their ability to secrete cytokines. PGE2 is a potent inducer of IL-10 in bone marrow-derived DC (BM-DC). PGE2-induced IL-10 is a key regulator of the BM-DC pro-inflammatory phenotype. Prostaglandins are eicosanoids. The eicosanoids consist of the prostaglandins (PGs), thromboxanes (TXs), leukotrienes (LTs), and lipoxins (LXs). The PGs and TXs are collectively identified as prostanoids. Prostaglandins were originally shown to be synthesized in the prostate gland, thromboxanes from platelets (thrombocytes), and leukotrienes from leukocytes, hence the derivation of their names. All mammalian cells except erythrocytes synthesize eicosanoids. These molecules are extremely potent and are able to cause profound physiological effects at very dilute concentrations. All eicosanoids function locally at the site of synthesis through receptor-mediated G-protein linked signalling pathways.