Cross-Linking of the Mannose Receptor on Monocyte-Derived Dendritic Cells Activates an Anti-Inflammatory Immunosuppressive Program 1 Marcello Chieppa,* Giancarlo Bianchi,* Andrea Doni,* Annalisa Del Prete,* Marina Sironi,* Gordana Laskarin, 2 * Paolo Monti, † Lorenzo Piemonti, † Andrea Biondi, ‡ Alberto Mantovani,* § Martino Introna,* and Paola Allavena 3 * Immature monocyte-derived dendritic cells (DC) strongly express the endocytic mannose receptor (MR). Addition of a specific anti-MR mAb (clone PAM-1) for 24 h to cultures of immature DC induced phenotypical and functional maturation of the cells, assessed as up-regulation of costimulatory molecules and CD83, and chemotactic response to CCL19. A different isotype-matched anti-MR mAb (clone 19.2) had no significant effect. Engagement of MR with mAb PAM-1 induced the production of the anti- inflammatory cytokines IL-10, IL-1R antagonist, and of the nonsignaling IL-1R type II. In contrast IL-1, TNF, and IL-12 were not produced. PAM-1-treated DC were unable to polarize Th1 effector cells and did not secrete the chemokines CXCL10 and CCL19; in turn, they produced large amounts of CCL22 and CCL17, thus favoring the amplification of Th2 circuits. T cells cocultured with PAM-1-matured DC initially proliferated but later became anergic and behaved as suppressor/regulatory cells. Natural ligands binding to MR had differential effects. MUC III (a partially purified mucin), biglycan (a purified complex pro- teoglycan), and mannosylated lipoarabinomannan from Mycobacterium tuberculosis affected cytokine production with high IL-10, IL-1R antagonist, IL-1R type II, and inhibition of IL-12. In contrast, mannan, dextran, and thyroglobulin had no significant effect. In conclusion, the appropriate engagement of the MR by mAb PAM-1 and selected natural ligands elicit a secretory program in mono-derived DC characterized by a distinct profile of cytokines/chemokines with the ability to dampen inflammation and to inhibit the generation of Th1-polarized immune responses. The Journal of Immunology, 2003, 171: 4552– 4560. T he mannose receptor (MR) 4 is an endocytic receptor for glycans belonging to the type I C-type lectin receptor su- perfamily, comprising also DEC205, phospholipase A 2 receptor, and Endo180/urokinase plasminogen-activated receptor- associated protein (1– 4). MR was first identified on tissue macro- phages, but it is also expressed on the surface of myeloid dendritic cells (DC), hepatic and lymphatic endothelial cells, and Kaposi sarcoma cells (3, 5–10). The MR recognizes surface polysaccha- rides of several pathogens such as Gram-negative and Gram-pos- itive bacteria, yeasts, parasites, and mycobacteria. In addition to its endocytic activity, it is the only member of the C-type lectin family to have phagocytic properties and it is considered a pattern recogni- tion receptor involved in host defense and innate immunity (1, 11). The primary structure of the MR predicts the presence of an N-terminal extracellular cysteine-rich domain, followed by a fi- bronectin type II-like repeat and eight C-type lectin carbohydrate recognition domains (CRDs) repeated in tandem, a single trans- membrane domain, and a short cytoplasmic tail with the C termi- nus of the molecule (1– 4). MR has two distinct extracellular lectin binding sites. The cysteine-rich domain has been shown to bind sulfated sugars present in hormones such as lutropin and chon- droitin sulfates A and B, which are present on proteoglycans in the extracellular matrix (12, 13). The second lectin-like activity is me- diated by several of its eight CRDs and shows preference for branched sugars with terminal mannose, fucose, or N-acetyl-glu- cosamine (14). The binding to mannose is accomplished predom- inantly through the fourth recognition domain and is calcium de- pendent (3). Besides innate immunity, MR has been reported to have a role in adaptive immunity. Ag uptake by immature DC localized at peripheral sites is largely mediated by C-type lectin receptors (5– 8). Indeed, the presence of membrane-bound C-type lectins greatly facilitates the capture, internalization, and presentation of manno- sylated Ags (15, 16). The ability of MR and DEC205 in Ag de- livery, however, is strikingly different, with DEC205 being 30 times more effective than MR (17). More recent studies have pointed out that the two receptors have distinct intracellular des- tinations, as DEC205 directly targets to late endosomes close to lysosomes, while MR discharges its ligand in early endosomes, *Department of Immunology, Istituto “Mario Negri,” Milan, Italy; † Laboratory of Experimental Surgery, S. Raffaele Scientific Institute, Milan, Italy; ‡ Centro M. Tet- tamanti, Pediatric Clinic, University of Milan Bicocca, Monza (MI), Italy; and § In- stitute of Pathology, University of Milan, Milan, Italy Received for publication April 9, 2003. Accepted for publication August 20, 2003. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. 1 This work was supported by the Italian Association for Cancer Research (Associa- zione Italiana per la Ricerca sul Cancro), the Ministry of University and Research (Ministero dell’Universita ` e della Ricerca Scientifica e Technologica, Cofinaziamento 2002), the Ministery of Health (Ricerca Finanziata 2002, Convenzione, No. 170), FP6 Muvapred from the European Community, and “Special Project AIDS” No. 30D.83. M.C. was awarded a fellowship from the Associazione Italiana per la Ricerca sul Cancro; G.L. was supported by the National Research Council (Consiglio Nazionale delle Ricerche) Italy. 2 On leave from the Department of Physiology and Immunology, Medical Faculty, University of Rijeka, Croatia. 3 Address correspondence and reprint requests to Dr. Paola Allavena, Department of Immunology, Istituto di Ricerche Farmacologiche “Mario Negri” Via Eritrea 62, 20157 Milan, Italy. E-mail address: allavena@marionegri.it 4 Abbreviations used in this paper: MR, mannose receptor; DC, dendritic cell; IL-1ra: IL-1R antagonist; IL-1RII: IL-1R type II; CRD, carbohydrate recognition domain; ManLAM, mannose-capped lipoarabinomannan; CHO, Chinese hamster ovary; MFI, mean fluorescence intensity. The Journal of Immunology Copyright © 2003 by The American Association of Immunologists, Inc. 0022-1767/03/$02.00