ABSTRACT
Dendritic cells (DCs) are the most potent APCs of the immune system that seed the peripheral tissues and lymphoid organs. In an immature state, DCs sample their surroundings for incoming pathogens. Upon Ag encounter, DCs mature and migrate to the lymph node to induce adaptive immune responses. The C-type macrophage galactose-type lectin (MGL), expressed in immature DCs, mediates binding to glycoproteins carrying GalNAc moieties. In the present study, we demonstrate that MGL ligands are present on the sinusoidal and lymphatic endothelium of lymph node and thymus, respectively. MGL binding strongly correlated with the expression of the preferred MGL ligand, alpha-GalNAc-containing glycan structures, as visualized by staining with the alpha-GalNAc-specific snail lectin Helix pomatia agglutinin. MGL(+) cells were localized in close proximity of the endothelial structures that express the MGL ligand. Strikingly, instead of inducing migration, MGL mediated retention of human immature DCs, as blockade of MGL interactions enhanced DC trafficking and migration. Thus, MGL(+) DCs are hampered in their migratory responses and only upon maturation, when MGL expression is abolished; these DCs will be released from their MGL-mediated restraints.
Subject(s)
Antigen-Presenting Cells/physiology , Cell Movement , Lectins, C-Type/physiology , Endothelium, Lymphatic/chemistry , Humans , Lectins, C-Type/metabolism , Ligands , Macrophages , Polysaccharides/analysis , Polysaccharides/metabolismABSTRACT
The spleen plays a pivotal role in the immune defense against encapsulated bacteria such as Streptococcus pneumoniae. Murine splenic marginal zone macrophages express the C-type lectin SIGNR1, which is crucial for the capture of S. pneumoniae from blood. In this study, we demonstrate that SIGNR1 is able to interact in vitro with the juxtaposing marginal zone B cell population, which is responsible for the production of the early IgM response against the S. pneumoniae-epitope phosphorylcholine. Strikingly, SIGNR1-deficient mice display a reduction in the marginal zone B cell population. In addition, ex vivo B cell stimulation assays demonstrate a decrease in phosphorylcholine specificity in the splenic B cell population derived from SIGNR1-deficient mice, whereas the total IgM response is unaffected. Therefore, we hypothesize that antigens are presented by SIGNR1 expressed by marginal zone macrophages to the developing marginal zone B cell population thereby influencing the repertoire of this B cell population, which is pivotal for the early immune response against encapsulated bacteria such as S. pneumoniae.
Subject(s)
B-Lymphocytes/immunology , B-Lymphocytes/microbiology , Cell Adhesion Molecules/immunology , Immunoglobulin M/immunology , Lectins, C-Type/immunology , Macrophages/immunology , Macrophages/microbiology , Receptors, Cell Surface/immunology , Streptococcus pneumoniae/immunology , Animals , B-Lymphocytes/cytology , Blood-Borne Pathogens , CHO Cells , Cell Adhesion Molecules/deficiency , Cell Count , Cricetinae , Cricetulus , Lectins, C-Type/deficiency , Mice , Phosphatidylcholines/immunology , Polysaccharides, Bacterial/immunology , Protein Binding , Receptors, Cell Surface/deficiencyABSTRACT
Professional antigen-presenting cells are essential for the initiation of adaptive immune responses; however, they also play a vital role in the maintenance of tolerance towards self-antigens. C-type lectins can function as antigen receptors by capturing carbohydrate ligands for processing and presentation. Here, we focused on the dendritic cell (DC)-expressed macrophage galactose-type lectin (MGL), a C-type lectin with a unique specificity for terminal GalNAc residues, such as the tumor-associated Tn antigen. Soluble model antigens are efficiently internalized by MGL and subsequently presented to responder CD4+ T cells. The tyrosine-5 residue in the YENF motif, present in the MGL cytoplasmic domain, was essential for the MGL-mediated endocytosis in CHO cells. In conclusion, MGL contributes to the antigen processing and presentation capacities of DC and may provide a suitable target for the initiation of anti-tumor immune responses.
Subject(s)
Antigen Presentation/immunology , Dendritic Cells/immunology , Lectins, C-Type/immunology , Amino Acid Motifs/immunology , Amino Acid Sequence , Animals , CHO Cells , Cricetinae , Cricetulus , Endocytosis/immunology , Flow Cytometry , Humans , Lectins, C-Type/chemistry , Lectins, C-Type/genetics , Microscopy, Confocal , Molecular Sequence Data , TyrosineABSTRACT
The epithelial mucin MUC1 is a high molecular weight membrane glycoprotein frequently overexpressed and aberrantly glycosylated in adenocarcinoma. Mucins normally contain high amounts of O-linked carbohydrate structures that may influence immune reactions to this antigen. During malignant transformation, certain glyco-epitopes of MUC1, such as Tn-antigen, TF-antigen and their sialylated forms become exposed. The role of these glycan structures in tumor biology is unknown, but their presence is known to correlate with poor prognosis in several adenocarcinomas. We analyzed the potency of MUC1 containing Tn-antigens (MUC1-Tn) to target C-type lectins that function as carbohydrate recognition and uptake molecules on dendritic cells (DC). We identified the macrophage galactose type C-type lectin (MGL), expressed by both DC and macrophages, as the receptor for recognition and binding of MUC1-Tn. To validate the occurrence of MGL-MUC1 interactions in situ, we studied the binding of MGL to MUC1 in primary colon carcinoma tissue. Isolation of MUC1 out of colon carcinoma tissue showed strong binding activity to MGL. Interestingly, MGL binding to MUC1 was highly correlated to binding by the lectin Helix pomatia agglutinin (HPA), which is associated with poor prognosis in colorectal cancer. The detection of MGL positive cells in situ at the tumor site together with the modified glycosylation status of MUC1 to target MGL on DC suggests that MGL positive antigen presenting cells may play a role in tumor progression.
Subject(s)
Adenocarcinoma/metabolism , Antigens, Neoplasm/metabolism , Antigens, Tumor-Associated, Carbohydrate/metabolism , Colonic Neoplasms/metabolism , Dendritic Cells/metabolism , Lectins, C-Type/metabolism , Mucins/metabolism , Neoplasm Proteins/metabolism , Acetylgalactosamine/pharmacology , Adenocarcinoma/immunology , Animals , Antigens, Neoplasm/immunology , Antigens, Neoplasm/isolation & purification , Antigens, Tumor-Associated, Carbohydrate/immunology , CHO Cells , Cell Adhesion Molecules/immunology , Cell Adhesion Molecules/metabolism , Colon/chemistry , Colon/cytology , Colonic Neoplasms/immunology , Cricetinae , Cricetulus , Dendritic Cells/immunology , Endocytosis , Female , Glycosylation , Humans , Immunoglobulin G/immunology , Intestinal Mucosa/chemistry , Intestinal Mucosa/cytology , Lectins, C-Type/immunology , Mice , Mice, Inbred BALB C , Monocytes/cytology , Monosaccharides/pharmacology , Mucin-1 , Mucins/immunology , Mucins/isolation & purification , Neoplasm Proteins/immunology , Neoplasm Proteins/isolation & purification , Protein Binding/drug effects , Protein Processing, Post-Translational , Protein Structure, Tertiary , Receptors, Cell Surface/immunology , Receptors, Cell Surface/metabolism , Recombinant Fusion Proteins/chemistry , Recombinant Fusion Proteins/immunology , Tandem Repeat SequencesABSTRACT
The dendritic cell-specific ICAM-3-grabbing nonintegrin (DC-SIGN) homolog, SIGN-related 1 (SIGNR1) is a pathogen receptor expressed by splenic marginal zone and peritoneal macrophages, and is essential for clearance of Streptococcus pneumoniae by phagocytosis after intraperitoneal infection. Here, we identified an important in vivo function for SIGNR1 in S. pneumonia infection induced via its natural entrance route. Upon intranasal infection with S. pneumoniae, SIGNR1-deficient mice did not clear bacteria from lung and blood, and displayed severely enhanced inflammatory parameters compared to the wild-type mice. However, SIGNR1 is not expressed by alveolar macrophages, suggesting that another mechanism than a decrease in phagocytosis is responsible for this difference. Natural anti-phosphorylcholine IgM produced by marginal zone B cells is essential for protection against infection with S. pneumoniae. Strikingly, during infection, SIGNR1-deficient mice failed to produce a rapid anti-phosphorylcholine IgM response. Marginal zone macrophages have been suggested to capture antigens for presentation to marginal zone B cells. We demonstrate that marginal zone macrophages from SIGNR1-deficient mice in contrast to wild-type mice are not able to capture pneumococci from blood, suggesting that SIGNR1 on marginal zone macrophages captures S. pneumoniae for antigen presentation to and activation of marginal zone B cells, resulting in an anti-phosphorylcholine IgM response.
