DP1 has been suggested to be expressed on murine mast cells having a role on murine mast cell maturation and Trichostatin A 58880-19-6 differentiation. In our experiments, we are dealing basically with mature human mast cell systems subject to a short term incubation with AH6809. No such maturation effect is expected under our circumstances/conditions. Regarding AH23848, there is very little information on the presence of TP receptors on the human mast cells surface. In fact, it has been reported that the TP agonits U-46619 has no effect on human mast cells. We found that when PGE2 triggers the EP3 receptor, it exerts a limited protective effect on mannitol-induced mast cell degranulation. In contrast, when PGE2 acts through EP2 and EP4 receptors, mannitol-induced mast cell degranulation and calcium influx are significantly nullified. Our data agree with other studies in which PGE2 has been shown to work through EP2 receptors to stabilize lung mast cells after IgE dependent activation and with studies reporting that the EP2 agonist butaprost exerts a protective effect in allergen-sensitized mice. Additionally, a recent study using human bronchial smooth muscle proposes that PGE2-induced relaxation is mediated via the EP4 receptor, which contrasts with reported role of the EP3 receptor in the induction of PGE2 airway irritability and cough. Gas, the EP2 and EP4 receptor stimulation protein, results in adenylate cyclase activation and intracellular cAMP production. Conversely, EP3 receptor signaling is predominantly coupled to protein Gai and produces reduced cAMP levels. The accumulation of cAMP promoted by EP2 and EP4 receptors is associated with inhibition of cell function, whereas intracellular calcium increases induced by the EP3 receptor are linked to cellular activation. The evidence from this study, along with other reports, supports the notion that PGE2 stabilizes mast cells through the EP2 and/or EP4 receptors, thereby providing control of the deleterious effects of mast cell degranulation in the airways. The presence of various EP3 isoforms could explain the differential release of mediators in degranulation assays at different PGE2 concentrations. It has been reported that, by interacting with the EP3 receptor, higher doses of PGE2 increase mediator release through IgE dependent mechanisms. In addition, the presence of several EP3 isoforms might explain the protective effects of EP3 in suppressing allergic inflammation in mice. Additionaly, it should be noted that the EP receptors expression pattern has been reported to be different in murine mast cells. EP1, EP3, and EP4 transcripts have been found in IL-3-dependent murine mast cell line, MC/9 and murine bone marrow derived mast cells. but not EP2. Our data in LAD2 cells is supported by the data obtained in CD34+ derived cells and HLMCs where the decrease in mannitol-induced degranulation was significant when the EP2 and EP4 receptors were free to interact with PGE2. The mannitol stimulus caused increased activation in both MAPK and PI3K signaling pathways in mast cells. PGE2 modulated the mannitol phosphorylation profile of these pathways differently according to the receptor that was triggered. Thus, when the EP3 receptor was involved, ERK1/2, p38, and JNK phosphorylation remained active, while their phosphorylation decreased with EP2 or EP4 receptor engagement. Our results suggest that PGE2 is not only able to modulate early mast cell events through degranulation, but that it can regulate downstream events that may perpetuate airway inflammation in diseases such as asthma. Experimental treatment with PGE2 prevents exercise–induced airway obstruction.