PGE₂ acts via EP2 to stimulate IDO expression. (A) We monitored EP2 and EP4 mRNA expression in DCs exposed to TNFα, PGE₂, or a combination of both stimuli. TBP was used as a reference for our qPCR studies because its expression levels matched that of the EP-Rs. Of note, no message could be detected for EP1 and EP3 by qPCR (data not shown). (B) PGE₂ was replaced by different EP agonists during DC maturation, and IDO activity was assessed after 48 hours. L-335677, Butaprost, L-826266, and L-161982 were used to stimulate EP1 to EP4, respectively. All were used at a concentration of 50 μM. In similar experiments, sulprostone was used as an EP1>> EP3 agonist and 19R-hydroxy PGE₂ as an EP2 agonist, with similar results (data not shown).