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-1β, 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 proteoglycan), 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.

Tumor‐Associated Macrophages (TAMs) are abundantly present in the stroma of solid tumors and modulate several important biological processes, such as neoangiogenesis, cancer cell proliferation and invasion, and suppression of adaptive immune responses. Myeloid C‐type lectin receptors (CLRs) constitute a large family of transmembrane carbohydrate‐binding receptors that recognize pathogens as well as endogenous glycoproteins. Several lines of evidence demonstrate that some CLRs can inhibit the immune response. In this study we investigated TAM‐associated molecules potentially involved in their immune suppressive activity. We found that TAMs isolated from human ovarian carcinoma samples predominantly express the CLRs Dectin‐1, MDL‐1, MGL, DCIR, and most abundantly the Mannose Receptor (MR). Components of carcinomatous ascites and purified tumoral mucins (CA125 and TAG‐72) bound the MR and induced its internalization. MR engagement by tumoral mucins and by an agonist anti‐MR antibody modulated cytokine production by TAM toward an immune‐suppressive profile: increase of IL‐10, absence of IL‐12, and decrease of the Th1‐attracting chemokine CCL3. This study highlights that tumoral mucin‐mediated ligation of the MR on infiltrating TAM may contribute to their immune suppressive phenotype.

BACKGROUND: The mannose receptor (MR) is involved in the initiation of the immune response and regulation of homeostasis during inflammation and tissue remodeling. METHODS: Distribution, endocytosis and possible natural ligand tumor associated glycoprotein-72 (TAG-72) for the MR have been examined by immunohistology, immunocytochemistry and flow cytometry at the maternal–fetal interface, characterized by extensive tissue remodeling. RESULTS: Contrary to disseminated distribution of the MR positive (MR+) cells in term placenta, the MR+ cells of early pregnancy decidua intimately surrounded glands and followed tissue distribution of CD14 positive cells. The mannose receptor was present on freshly isolated first trimester decidual mononuclear cells and distributed mostly on macrophages (77.08 ± 10.55%, mean ± SD). The expression of the MR on CD14 positive cells decreased following 18 h culture (P<0.01) and was accompanied by the reduction of fluorescein isothiocyanate (FITC)–dextran uptake. PAM-1 anti-MR antibody, mannan and TAG-72 reduced FITC–dextran uptake by decidual macrophages. CONCLUSIONS: These data indicate that the MR+ macrophages, surrounding early decidual glands, are able to internalize ligands for carbohydrate recognition domain of the receptor, including decidual secretory phase mucin TAG-72.