The Chemerin/ChemR23 System Does Not Affect the Pro- Inflammatory Response of Mouse and Human Macrophages Ex Vivo Benjamin Bondue1,3., Olivier De Henau1., Souphalone Luangsay1,2, Thalie Devosse1, Patricia de Nadaı¨1, Jean-Yves Springael1, Marc Parmentier1*, Olivier Vosters1 1 Institut de Recherche Interdisciplinaire en Biologie Humaine et Mol e´culaire (I.R.I.B.H.M.), Faculte´ de Me´decine, Universite´ Libre de Bruxelles, Brussels, Belgium, 2 Euroscreen SA, Brussels, Belgium, 3 Service de Pneumologie, H oˆpital Erasme, Universite´ Libre de Bruxelles, Brussels, Belgium Abstract Macrophages constitute a major component of innate immunity and play an essential role in defense mechanisms against external aggressions and in inflammatory responses. Chemerin, a chemoattractant protein, is generated in inflammatory conditions, and recruits cells expressing the G protein-coupled receptor ChemR23, including macrophages. Chemerin was initially expected to behave as a pro-inflammatory agent. However, recent data described more complex activities that are either pro- or anti-inflammatory, according to the disease model investigated. In the present study, peritoneal macrophages were generated from WT or ChemR232/2 mice, stimulated with lipopolyssaccharide in combination or not with IFN-c and the production of pro- (TNF-a, IL-1b and IL-6) and anti-inflammatory (IL-10) cytokines was evaluated using qRT-PCR and ELISA. Human macrophages generated from peripheral blood monocytes were also tested in parallel. Peritoneal macrophages from WT mice, recruited by thioglycolate or polyacrylamide beads, functionally expressed ChemR23, as assessed by flow cytometry, binding and chemotaxis assays. However, chemerin had no effect on the strong upregulation of cytokine release by these cells upon stimulation by LPS or LPS/IFN-c, whatever the concentration tested. Similar data were obtained with human macrophages. In conclusion, our results rule out the direct anti-inflammatory effect of chemerin on macrophages ex vivo, described previously in the literature, despite the expression of a functional ChemR23 receptor in these cells. Citation: Bondue B, De Henau O, Luangsay S, Devosse T, de Nada¨ı P, et al. (2012) The Chemerin/ChemR23 System Does Not Affect the Pro-Inflammatory Response of Mouse and Human Macrophages Ex Vivo. PLoS ONE 7(6): e40043. doi:10.1371/journal.pone.0040043 Editor: Rachel Louise Allen, University of London, St George’s, United Kindom Received February 9, 2012; Accepted May 31, 2012; Published June 29, 2012 Copyright: 2012 Bondue et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was supported by the Interuniversity Attraction Poles Programme (P6/14) – Belgian State – Belgian Science Policy, the Actions de Recherche Concerte´es of the Communaute´ Franc¸aise de Belgique, the European Union (LSHB-CT-2005-518167/INNOCHEM), the Fonds de la Recherche Scientifique Me´dicale of Belgium, the Walloon Region (Programme d’excellence ‘‘CIBLES’’), the Fonds Ithier, the Fonds Alice and David Van Buuren, Te´le´vie and the Fondation Me´dicale Reine Elisabeth. B.B. and O.D.H. were aspirant of the Belgian National Fund for Scientific Research (FNRS). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: mparment@ulb.ac.be . These authors contributed equally to this work. Introduction As humans are continuously exposed to miscellaneous injuries, inflammation occurs frequently as a result of the activation of protective systems. Higher vertebrates have developed two highly interconnected systems of protection: the innate and adaptive immune systems, for the purpose of eliminating pathogenic insults, removing damaged tissues, and restoring tissue homeostasis [1]. Macrophages constitute a major component of innate immunity and play an essential role in defense mechanisms against external aggressions such as infectious diseases. These properties are mediated in part by their ability to synthesize cytokines and chemokines, which in turn modulate and recruit other leukocyte subsets, linking innate and adaptive immune responses [2]. Moreover, macrophages are also important players in the resolution phase of inflammation, a process considered as passive till recently. Indeed, as a result of their phagocytic properties, macrophages mediate the uptake and clearance of apoptotic cells, necrotic cell debris and wounded tissue components [3]. Chemoattractant agents play a crucial role in the initiation of immune responses, by regulating the traffic and function of leukocyte populations. Their receptors are therefore considered as potential targets for the development of new therapeutic agents, particularly in the fields of cancer and chronic inflammatory diseases. Chemerin is a small protein of 16 kDa isolated and identified from human inflammatory fluids as the natural ligand of the previously orphan G protein-coupled receptor ChemR23 (also termed CMKLR-1), and acting as a chemoattractant agent for leukocytes expressing this receptor [4]. ChemR23 is expressed by myeloid (mDC) and plasmacytoid dendritic cells (pDC), macro- phages and NK cells [4–9]. Two additional receptors have been reported to bind chemerin with high affinity, GPR1 [10] and CCLR2 [11,12], but the biological significance of these receptors in the activities of chemerin is still not known. In contrast, chemerin exerts, through ChemR23, potent chemoattractant properties on leukocyte populations at subnanomolar concentra- tions [7,13,14]. Chemerin is synthesized as an inactive precursor, called prochemerin, present at high concentration in plasma. PLoS ONE | www.plosone.org 1 June 2012 | Volume 7 | Issue 6 | e40043