Fibroblast-derived PGE₂ is the critical PGE₂ for stimulation of IL-23 secretion from DC_act. (A) Fibroblasts or DCs were transfected with Cox-2 siRNA or scrambled siRNA. To induce PGE₂ expression, Cox-2– and scrambled-transfected fibroblasts were stimulated with TNF-α/IL-1β (Fb[Cox-2si]+TNFalpha/IL-1beta; Fb[scr] + TNFalpha/IL-1beta). Cox-2– and scrambled-transfected DCs (DC[Cox-2si] + LPS; DC[scr] + LPS) were activated with LPS. PGE₂ release was measured by ELISA. *P < .05 compared with scrambled-transfected cells (n = 3 independent experiments). (B) LPS-preactivated DCs (DCact) were cocultured with scrambled-siRNA-transfected fibroblasts (DCact + Fb[scr]) or with Cox-2-siRNA transfected fibroblasts (DCact + Fb[Cox-2si]). As control, DC_act were cultured alone. IL-23 production was measured by ELISA. *P < .001 (n = 5 independent experiments). (C) Cox-2– or scrambled siRNA–transfected DCs were preactivated with LPS and subsequently cocultured with fibroblasts (DCact[scr] + Fb; DCact[Cox-2si] + Fb). As control, transfected DC_act were cultured alone (DCact[scr]; DCact[Cox-2si]). *P < .001.