Multiple pathways are employed by TLR and NOD agonists to induce PGE2 production in primary human monocytes and macrophages (P4163)

Abstract

Abstract Innate immune activators that are potent inducers of fever also up-regulate plasma PGE2. To determine whether TLR and NOD agonists activate production of PGE2 directly or through IL-1β, human monocytes (Mo) and differentiated macrophages (MF) were cultured with TLR agonists with or without Caspase-1 inhibitor ZVAD, which inhibited LPS-induced IL-1β in both cell types. PGE2 production in MF was not affected by ZVAD, while in Mo, ZVAD reduced PGE2 and COX2 expression by 30-60%. Surprisingly, IL-1β alone did not up-regulate PGE2 in Mo. However, in Mo pretreated with low dose of LPS, PGE2 and COX2 mRNA were up-regulated by IL-1β. LPS (but not TLR2 agonist) induced phosphorylation of IRF3 (Ser 396) in Mo. Knock-down of IRF3 or of TRIF by siRNA abrogated IL-1β induced COX2 mRNA expression in LPS-pretreated U937-CD14 cells. MDP did not induce PGE2 in Mo alone. However, COX2 mRNA and PGE2 protein in MDP-activated Mo was significantly augmented by human CD3 bead-purified T cells or T cell supernatant. Treatment of Mo with inhibitors of autophagy including ATG5 or ATG7 siRNA, inhibited MDP-induced PGE2 production. T cells were also required for PGE2 produced in response to flagellin and IE-DAP but not Poly I:C. In summary, Mo employ multiple pathways to produce PGE2, depending on the type of innate receptors involved: IRF3/TRIF pathway is employed in response to TLR4, while autophagy/ROS and T cell-derived signals are involved in PGE2 production after triggering of NOD1/2 and IPAF.