Prostaglandin E2 Inhibits IL-18-Induced ICAM-1 and B7.2 Expression Through EP2/EP4 Receptors in Human Peripheral Blood Mononuclear Cells

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Abstract
Costimulatory molecules play important roles in immune responses. In the present study we investigated the effects of PGE2 on the expression of ICAM-1, B7.1, and B7.2 on monocytes in IL-18-stimulated PBMC using FACS analysis. Addition of PGE2 to PBMC inhibited ICAM-1 and B7.2 expression elicited by IL-18 in a concentration-dependent manner. We examined the involvement of four subtypes of PGE2 receptors, EP1, EP2, EP3, and EP4, in the modulatory effect of PGE2 on ICAM-1 and B7.2 expression elicited by IL-18, using subtype-specific agonists. ONO-AE1–259-01 (EP2R agonist) inhibited IL-18-elicited ICAM-1 and B7.2 expression in a concentration-dependent manner with a potency slightly less than that of PGE2, while ONO-AE1-329 (EP4R agonist) was much less potent than PGE2. The EP2/EP4R agonist 11-deoxy-PGE1 mimicked the effect of PGE2 with the same potency. ONO-D1-004 (EP1R agonist) and ONO-AE-248 (EP3R agonist) showed no effect on IL-18-elicited ICAM-1 or B7.2 expression. These results indicated that EP2 and EP4Rs were involved in the action of PGE2. Dibutyryl cAMP and forskolin down-regulated ICAM-1 and B7.2 expression in IL-18-stimulated monocytes. As EP2 and EP4Rs are coupled to adenylate cyclase, we suggest that PGE2 down-regulates IL-18-induced ICAM-1 and B7.2 expression in monocytes via EP2 and EP4Rs by cAMP-dependent signaling pathways. The fact that anti-B7.2 as well as anti-ICAM-1 Ab inhibited IL-18-induced cytokine production implies that PGE2 may modulate the immune response through regulation of the expression of particular adhesion molecules on monocytes via EP2 and EP4Rs.