Engagement of the Mannose Receptor by Tumoral  Mucins Activates an Immune Suppressive Phenotype in  Human Tumor‐Associated Macrophages

Guidato

The Journal of Immunology

et al. 2016

Arabinogalactan (AG) isolated from dust of a traditional farm prevents disease in murine models of allergy. However, it is unclear whether this polysaccharide has immune regulatory properties in humans. The aim of this study was to test the influence of AG on the immune-stimulating properties of human dendritic cells (DCs). Moreover, we sought to identify the receptor to which AG binds. AG was produced from plant callus tissue under sterile conditions to avoid the influence of pathogen-associated molecular patterns in subsequent experiments. The influence of AG on the human immune system was investigated by analyzing its impact on monocyte-derived DCs. To analyze whether the T cell stimulatory capacity of AG-stimulated DCs is altered, an MLR with naive Th cells was performed. We revealed that AG reduced T cell proliferation in a human MLR. In the search for a molecular mechanism, we found that AG binds to the immune modulatory receptors DC-specific ICAM-3–grabbing non integrin (DC-SIGN) and macrophage mannose receptor 1 (MMR-1). Stimulation of these receptors with AG simultaneously with TLR4 stimulation with LPS increased the expression of the E3 ubiquitin-protein ligase tripartite motif–containing protein 21 and decreased the phosphorylation of NF-κB p65 in DCs. This led to a reduced activation profile with reduced costimulatory molecules and proinflammatory cytokine production. Blocking of MMR-1 or DC-SIGN with neutralizing Abs partially inhibits this effect. We conclude that AG dampens the activation of human DCs by LPS via binding to DC-SIGN and MMR-1, leading to attenuated TLR signaling. This results in a reduced T cell activation capacity of DCs.

Section: Discussionsupporting

confidence: 89%

Allergy-Protective Arabinogalactan Modulates Human Dendritic Cells via C-Type Lectins and Inhibition of NF-κB

Guidato

The Journal of Immunology

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

“…Such T-cell irresponsiveness has been shown to inhibit the development of experimental autoimmune encephalomyelitis after injection of mannosylated myelin peptide (4). Second, MR engagement on monocyte-derived DCs induces an immune-suppressive phenotype (32,33). Third, substantial evidence points out that MR expression is directly correlated with the immunogenicity of the cellular environment.…”

Section: Discussionmentioning

confidence: 99%

Mannose receptor induces T-cell tolerance via inhibition of CD45 and up-regulation of CTLA-4

Schuette

Embgenbroich

Ulas

et al. 2016

The mannose receptor (MR) is an endocytic receptor involved in serum homeostasis and antigen presentation. Here, we identify the MR as a direct regulator of CD8 + T-cell activity. We demonstrate that MR expression on dendritic cells (DCs) impaired T-cell cytotoxicity in vitro and in vivo. This regulatory effect of the MR was mediated by a direct interaction with CD45 on the T cell, inhibiting its phosphatase activity, which resulted in up-regulation of cytotoxic T-lymphocyte-associated Protein 4 (CTLA-4) and the induction of T-cell tolerance. Inhibition of CD45 prevented expression of B-cell lymphoma 6 (Bcl-6), a transcriptional inhibitor that directly bound the CTLA-4 promoter and regulated its activity. These data demonstrate that endocytic receptors expressed on DCs contribute to the regulation of T-cell functionality.T he mannose receptor (MR) is an endocytic receptor belonging to the C-type lectin family and is expressed by distinct populations of dendritic cells (DCs), macrophages, and endothelial cells (1). It consists of an N-terminal cysteine-rich domain (CR), a fibronectin type II (FN II) domain, eight C-type lectinlike domains (CTLDs), a transmembrane region, and a short intracellular region. The CTLDs of the MR can bind to glycoconjugates terminated in mannose, fucose, or glucose. Despite the presence of eight CTLDs, only CTLD4 is responsible for carbohydrate binding. Additionally, the MR can bind to sulfated carbohydrates via its CR and to collagen via its FN II domain (1).In a previous study, we demonstrated that antigens internalized by the MR are processed specifically for cross-presentation (2). The correlation between the MR and cross-presentation offered the possibility that antigens targeted toward the MR could induce potent cytotoxic T-cell responses. Because the induction of a strong cytotoxic T-cell response against tumor-specific antigens is a crucial process in many tumor vaccination strategies, antigen targeting toward the MR seemed to be a promising approach. However, in in vivo tumor models, antigen targeting toward the MR did not result in a strong cytotoxic T-cell response but, instead, led to the induction of antigen-specific T-cell tolerance (3, 4). Therefore, we analyzed whether the MR has a regulatory effect on the induction of immune responses by means distinct from antigen uptake and presentation, and we investigated a direct influence of the MR on T-cell activation. We could demonstrate that the presence of the MR on the antigen-presenting cell (APC) directly impairs the cytotoxic activity of T cells in vitro and in vivo. We showed that this effect was due to a direct interaction of the MR with CD45 on the T-cell surface. This interaction inhibited CD45 activity and resulted in the up-regulation of the inhibitory molecule cytotoxic T-lymphocyte-associated Protein 4 (CTLA-4), which was responsible for the impaired cytotoxic activity of the T cells. ResultsThe Presence of the MR on DCs Reduces Cytotoxic Activity of CD8 + T Cells. To investigate whether the MR influences T-cell ...

“…34,35 Both TNF-α and IκBα siRNA decrease mRNA for CD206 in macrophages ( Figure 8C). The combination of the two treatments also significantly decreases CD206 mRNA.…”

mentioning

confidence: 93%

“…33 We have functionalized the surface of these particles with mannose as a targeting ligand in order to facilitate uptake of the particles in TAMs, which have increased amounts of mannose receptor (CD206) on their surface. 34,35 The mannose receptor is an endosomal pattern-recognition receptor, which, when present at high levels, is associated with suppression of the classical Figure 1 Overview of the two arms of the NF-κB pathway. Notes: The classical pathway is broadly activated by immunostimulatory molecules: TNF-α, lPs, Il-1, IFNγ, and others.…”

Section: Introductionmentioning

confidence: 99%

Manipulating the NF-κB pathway in macrophages using mannosylated, siRNA-delivering nanoparticles can induce immunostimulatory and tumor cytotoxic functions

Ortega¹,

Barham

Sharman

et al. 2016

IJN

Tumor-associated macrophages (TAMs) are critically important in the context of solid tumor progression. Counterintuitively, these host immune cells can often support tumor cells along the path from primary tumor to metastatic colonization and growth. Thus, the ability to transform protumor TAMs into antitumor, immune-reactive macrophages would have significant therapeutic potential. However, in order to achieve these effects, two major hurdles would need to be overcome: development of a methodology to specifically target macrophages and increased knowledge of the optimal targets for cell-signaling modulation. This study addresses both of these obstacles and furthers the development of a therapeutic agent based on this strategy. Using ex vivo macrophages in culture, the efficacy of mannosylated nanoparticles to deliver small interfering RNA specifically to TAMs and modify signaling pathways is characterized. Then, selective small interfering RNA delivery is tested for the ability to inhibit gene targets within the canonical or alternative nuclear factor-kappaB pathways and result in antitumor phenotypes. Results confirm that the mannosylated nanoparticle approach can be used to modulate signaling within macrophages. We also identify appropriate gene targets in critical regulatory pathways. These findings represent an important advance toward the development of a novel cancer therapy that would minimize side effects because of the targeted nature of the intervention and that has rapid translational potential.