T helper cell
Prostanoids are prostaglandins (PG), thromboxanes (TX), and prostacyclins (PGI). Seven, structurally-related, prostanoid receptors fall into three categories based on the cell activation pathways and activities which they regulate. Relaxant prostanoid receptors (IP, DP1, EP2, and EP4) raise cellular cAMP levels; contractile prostanoid receptors (TP, FP, and EP1) mobilize intracellular calcium; and the inhibitory prostanoid receptor (EP3) lowers cAMP levels. A final prostanoid receptor, DP2, is structurally related to the chemotaxis class of receptors and unlike the other prostanoid receptors mediates eosinophil, basophil, and T helper cell (Th2 type) chemotactic responses. Prostanoids, particularly PGE2 and PGI2, are prominent regulators of inflammation and allergic responses as defined by studies primarily in animal models but also as suggested by studies with human tissues and, in certain cases, human subjects.