Exogenous but not endogenous prostanoids regulate cytokine secretion from murine bone marrow dendritic cells: EP2, DP, and IP but not EP1, EP3, and FP prostanoid receptors are involved

Abstract

Murine bone marrow-derived dendritic cells (DC), stimulated with lipopolysaccharide (LPS) and/or LPS+interferon-gamma (IFN-gamma), secrete a variety of inflammatory mediators which may modulate their functions. We have examined the potential for exogenous prostanoids, acting in a paracrine fashion, and endogenous prostanoids, acting in an autocrine fashion, to regulate secretion of tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), IL-10, and IL-12 in DC. In order to identify receptors mediating these effects, DC were treated in vitro with receptor-selective prostanoids. Agonists of cyclic AMP-elevating receptors, namely, prostaglandin E(2) (PGE(2)), butaprost (EP(2) receptor), iloprost (IP receptor), and BW245C (DP receptor), dose-dependently inhibited the release of IL-6, TNF-alpha, and IL-12 and enhanced the release of IL-10 from LPS-stimulated DC, with TNF-alpha secretion being the most strongly affected. In contrast, 15-deoxy-Delta(12,14)-PGJ(2)-an activator of nuclear peroxisome proliferator-activated receptor-gamma (PPAR-gamma) receptors-inhibited release of all tested cytokines. Exogenous prostanoids, cyclic AMP-elevating analogs, lost their ability to modulate cytokine release in cells pre-incubated for 4 h with LPS, indicating that prostanoids may affect DC functions during initial phases of LPS stimulation only. Sulprostone and (+)-fluprostenol failed to modulate any of responses tested, suggesting lack of involvement/expression of EP(1), EP(3), and FP receptors in DC activation. In order to examine the role of endogenous prostanoids, DC were treated with inhibitors of cyclooxygenases (COX). At concentrations that completely blocked PGE(2) release, neither indomethacin (nonselective inhibitor) nor rofecoxib (COX-2-selective inhibitor) influenced cytokine release from LPS-stimulated DC. Thus, cytokine release from LPS-stimulated DC does not seem to be autoregulated by endogenous prostanoids, whereas in vivo regulatory function may be fulfilled in a paracrine manner by PGD(2), PGE(2), and PGI(2) released from neighboring cells.