Murine mast cells secrete a unique profile of cytokines and prostaglandins in response to distinct TLR2 ligands Salima Mrabet-Dahbi*, Martin Metz*, Anne Dudeck, Torsten Zuberbier and Marcus Maurer Allergie-Centrum-Charite ´, Department of Dermatology and Allergy, Charite ´ – Universita ¨tsmedizin Berlin, Berlin, Germany Correspondence: Marcus Maurer, MD, Department of Dermatology and Allergy, Allergie-Centrum-Charite ´, Charite ´ – Universita ¨tsmedizin Berlin, Charite ´platz 1, 10117 Berlin, Germany, Tel.: +49 30 450 518 043, Fax: +49 30 450 518 972, e-mail: marcus.maurer@charite.de *Equally contributing authors. Accepted for publication 5 March 2009 Abstract: Mast cells (MCs) are important effector cells in host defense against bacteria. In the course of a bacterial infection, MCs can be activated by various mechanisms, i.e. bacterial toxins, endogenously produced infection-associated peptides or via complement receptors, fimbrial adhesion molecules and toll-like receptors (TLRs). While some of these mechanisms are well established, the effects of TLR2 ligand-driven MC activation are far less understood. Here, we show that murine mature connective tissue-type MCs, but not immature bone marrow-derived cultured mast cells, express significant amounts of full length TLR2 on their surface. Activation by various TLR2 ligands only induces the selective release of cytokines in peritoneum-derived cultured mast cells (PCMCs) with preferential secretion of pro-inflammatory cytokines (IL-6 > IL-17 > IFN-c TNF > IL-1 > GM-CSF) upon stimulation with lipoteichoic acid (LTA). This response is much lower in PCMCs stimulated with the TLR2 ⁄ 6 agonist macrophage-activating lipopeptide-2 (MALP-2), which most prominently triggers the release of the immunomodulatory cytokine IL-10. Furthermore, only LTA but not MALP-2 induces prostaglandin D2 secretion which is again restricted to the mature MC phenotype. These findings suggest that TLR2 ligand-mediated activation of mature MCs, i.e. tissue-residing cells, which most likely occurs during infection, can selectively raise a potent inflammatory or anti-inflammatory response, depending on TLRs which are engaged. Key words: cytokines – inflammation – mast cells – toll-like receptors – urticaria Please cite this paper as: Murine mast cells secrete a unique profile of cytokines and prostaglandins in response to distinct TLR2 ligands. Experimental Dermatology 2009; 18: 437–444. Introduction Mast cells (MCs) are known to initiate and control effective innate immune responses against invading pathogens and they may additionally act as initiators of optimal pathogen- specific acquired adaptive immunity (1–3). The huge amount of diverse preformed or newly synthesized prod- ucts which can be released from MCs upon appropriate activation puts them in the position to fulfil two important functions: (i) they can rapidly combat bacterial infections in innate immune responses, e.g. by releasing preformed TNF and ⁄ or leukotrienes (4,5) and (ii) they can induce the migration, maturation and ⁄ or function of dendritic cells and interact with T and B cells, thus facilitating the induc- tion and ⁄ or maintenance of adaptive immune responses (1,6–8). An important prerequisite for these functions is the activation of MCs at the site of bacterial infection. Recent findings in models of septic peritonitis have shown that activation of murine MCs by the complement system (9), by endogenous peptides which are produced during bacte- rial infections (e.g. endothelin-1) (10), and by toll-like receptor 4 (TLR4) (11) is critically involved in optimal host defense against bacteria. Furthermore, many studies could provide evidence for TLR expression (TLR1, 2, 3, 4, 6, 7, 8 and ⁄ or 9) (1,2,12) in various murine MC populations thus potentially allowing microbial interactions. Of particular interest in this context is TLR2, which is an important sensor of many bacteria and their cell wall products peptidoglycan, lipoteichoic acid (LTA) and lipo- peptides (13). Although immature bone marrow-derived cultured mast cells (BMCMCs) are known to express TLR2 mRNA, it is still controversially discussed whether TLR2 ligands can induce MC degranulation. While Supajatura et al. (14) described peptidoglycan-induced, TLR2-medi- ated degranulation of BMCMCs, others could not confirm this finding (15,16). Differential results were also obtained in vivo. In this regard, intradermal injection of peptidogly- can resulted in MC-mediated extravasation (14), while increased MCs numbers could be observed in the dermis of allergen-sensitized mice following intradermal injection of LTA (17). DOI:10.1111/j.1600-0625.2009.00878.x www.blackwellpublishing.com/EXD Original Article ª 2009 John Wiley & Sons A/S, Experimental Dermatology, 18, 437–444 437