Human Milk Oligosaccharide 2'-Fucosyllactose Inhibits Ligand Binding to C-Type Lectin DC-SIGN but Not to Langerin.

Human milk oligosaccharides (HMOs) and their most abundant component, 2'-Fucosyllactose (2'-FL), are known to be immunomodulatory. Previously, it was shown that HMOs and 2'-FL bind to the C-type lectin receptor DC-SIGN. Here we show, using a ligand-receptor competition assay, that a whole mixture of HMOs from pooled human milk (HMOS) and 2'-FL inhibit the binding of the carbohydrate-binding receptor DC-SIGN to its prototypical ligands, fucose and the oligosaccharide Lewis-B, (Leb) in a dose-dependent way. Interestingly, such inhibition by HMOS and 2'-FL was not detected for another C-type lectin, langerin, which is evolutionarily similar to DC-SIGN. The cell-ligand competition assay using DC-SIGN expressing cells confirmed that 2'-FL inhibits the binding of DC-SIGN to Leb. Molecular dynamic (MD) simulations show that 2'-FL exists in a preorganized bioactive conformation before binding to DC-SIGN and this conformation is retained after binding to DC-SIGN. Leb has more flexible conformations and utilizes two binding modes, which operate one at a time via its two fucoses to bind to DC-SIGN. Our hypothesis is that 2'-FL may have a reduced entropic penalty due to its preorganized state, compared to Leb, and it has a lower binding enthalpy, suggesting a better binding to DC-SIGN. Thus, due to the better binding to DC-SIGN, 2'-FL may replace Leb from its binding pocket in DC-SIGN. The MD simulations also showed that 2'-FL does not bind to langerin. Our studies confirm 2'-FL as a specific ligand for DC-SIGN and suggest that 2'-FL can replace other DC-SIGN ligands from its binding pocket during the ligand-receptor interactions in possible immunomodulatory processes.

Dectin-1 directs T helper cell differentiation by controlling noncanonical NF-kappaB activation through Raf-1 and Syk.

The C-type lectin dectin-1 activates the transcription factor NF-kappaB through a Syk kinase-dependent signaling pathway to induce antifungal immunity. Here we show that dectin-1 expressed on human dendritic cells activates not only the Syk-dependent canonical NF-kappaB subunits p65 and c-Rel, but also the noncanonical NF-kappaB subunit RelB. Dectin-1, when stimulated by the beta-glucan curdlan or by Candida albicans, induced a second signaling pathway mediated by the serine-threonine kinase Raf-1, which integrated with the Syk pathway at the point of NF-kappaB activation. Raf-1 antagonized Syk-induced RelB activation by promoting sequestration of RelB into inactive p65-RelB dimers, thereby altering T helper cell differentiation. Thus, dectin-1 activates two independent signaling pathways, one through Syk and one through Raf-1, to induce immune responses.

Synthesis of Asparagine Derivatives Harboring a Lewis X Type DC-SIGN Ligand and Evaluation of their Impact on Immunomodulation in Multiple Sclerosis.

The protein myelin oligodendrocyte glycoprotein (MOG) is a key component of myelin and an autoantigen in the disease multiple sclerosis (MS). Post-translational N-glycosylation of Asn31 of MOG seems to play a key role in modulating the immune response towards myelin. This is mediated by the interaction of Lewis-type glycan structures in the N-glycan of MOG with the DC-SIGN receptor on dendritic cells (DCs). Here, we report the synthesis of an unnatural Lewis X (LeX )-containing Fmoc-SPPS-compatible asparagine building block (SPPS=solid-phase peptide synthesis), as well as asparagine building blocks containing two LeX -derived oligosaccharides: LacNAc and Fucα1-3GlcNAc. These building blocks were used for the glycosylation of the immunodominant portion of MOG (MOG31-55 ) and analyzed with respect to their ability to bind to DC-SIGN in different biological setups, as well as their ability to inhibit the citrullination-induced aggregation of MOG31-55 . Finally, a cytokine secretion assay was carried out on human monocyte-derived DCs, which showed the ability of the neoglycopeptide decorated with a single LeX to alter the balance of pro- and anti-inflammatory cytokines, inducing a tolerogenic response.

Antibody-opsonized bacteria evoke an inflammatory dendritic cell phenotype and polyfunctional Th cells by cross-talk between TLRs and FcRs.

During secondary immune responses, Ab-opsonized bacteria are efficiently taken up via FcRs by dendritic cells. We now demonstrate that this process induces cross-talk between FcRs and TLRs, which results in synergistic release of several inflammatory cytokines, as well as altered lipid metabolite profiles. This altered inflammatory profile redirects Th1 polarization toward Th17 cell responses. Interestingly, GM-CSF-producing Th cells were synergistically evoked as well, which suggests the onset of polyfunctional Th17 cells. Synergistic cytokine release was dependent on activation via MyD88 and ITAM signaling pathways through TLRs and FcRs, respectively. Cytokine regulation occurred via transcription-dependent mechanisms for TNF-α and IL-23 and posttranscriptional mechanisms for caspase-1-dependent release of IL-1ß. Furthermore, cross-talk between TLRs and FcRs was not restricted to dendritic cells. In conclusion, our results support that bacteria alone initiate fundamentally different immune responses compared with Ab-opsonized bacteria through the combined action of two classes of receptors and, ultimately, may refine new therapies for inflammatory diseases.

New roles for CD14 and IL-ß linking inflammatory dendritic cells to IL-17 production in memory CD4+ T cells.

Interleukin (IL)-1ß has proven to be crucial in the differentiation of human and mouse Th17 cells. Although it has become evident that IL-1ß has potent IL-17-inducing effects on CD4+ T cells directly, it has not yet been explored whether IL-1ß can also prime dendritic cells (DCs) for a Th17 instruction program. Here, we show that human immature DCs exposed to IL-1ß promote IL-17 production in human memory CD4+ T cells. IL-1ß-primed DCs express high levels of CD14 that mediate IL-17 production through direct interaction with T cells. Moreover, culturing human CD4+CD45RO+ memory T cells with soluble CD14 is sufficient for the upregulation of retinoic acid-related orphan receptor-γ thymus and IL-17 production. In addition, in a human in situ model using tissue-resident skin DCs, upregulation of CD14 expression induced by IL-1ß on skin residents DCs promotes IL-17 production in memory T cells; strongly suggesting the in vivo relevance of this mechanism. Our findings uncover new roles for IL-1ß and CD14, and may therefore have important consequences for the development of new therapies for Th17-mediated autoimmune diseases and bacterial and fungal pathogenic infections.

Topical rather than intradermal application of the TLR7 ligand imiquimod leads to human dermal dendritic cell maturation and CD8+ T-cell cross-priming.

Toll-like receptor (TLR) ligands are attractive candidate adjuvants for therapeutic cancer vaccines, since TLR signaling stimulates and tunes both humoral and cellular immune responses induced by dendritic cells (DCs). Given that human skin contains a dense network of DCs, which are easily accessible via (intra-)dermal delivery of vaccines, skin is actively explored as an antitumor vaccination site. Here we used a human skin explant model to explore the potential of TLR ligands as adjuvants for DC activation in their complex microenvironment. We show that topical application of Aldara skin cream, 5% of which comprises the TLR7 agonist imiquimod, significantly enhanced DC migration as compared with that resulting from intradermal injection of the TLR7/8 ligand R848 or the soluble form of imiquimod. Moreover, Aldara-treated DCs showed highest levels of the costimulatory molecules CD86, CD83, CD40, and CD70. Topical Aldara induced the highest production of pro-inflammatory cytokines in skin biopsies. When combined with intradermal peptide vaccination, Aldara-stimulated DCs showed enhanced cross-presentation of the melanoma antigen MART-1, which resulted in increased priming and activation of MART-1-specific CD8(+) T cells. These results point to advantageous effects of combining the topical application of Aldara with antitumor peptide vaccination.

Notch controls generation and function of human effector CD8+ T cells.

The generation of effector CD8(+) T cells with lytic capacity is crucial for tumor control. Dendritic cells (DCs) provide important signals to promote naive CD8(+) T cell priming and activation of effector T cells. Here, we report that the Notch pathway has an important role in both these processes in human CD8(+) T cells. Activated monocyte-derived DCs express Notch ligands Jagged1 and Delta-like4, whereas naive CD8(+) T cells express Notch2. The role for Notch signaling in CD8(+) T cell priming was determined using an ex-vivo model system in which tumor antigen-specific primary CD8(+) T cell responses were measured. Inhibition of Notch using γ-secretase inhibitors or soluble Delta-like4-Fc during activation reduced expansion of antigen-specific CD8(+) T cells, which was mirrored by decreased frequencies of interferon (IFN)γ-, tumor necrosis factor-α-, and granzymeB-producing CD8(+) T cells. Moreover, T cells primed when Notch signaling was prevented are functionally low-avidity T cells. In addition, Notch partially regulates established effector T cell function. Activation-induced Notch signaling is needed for IFNγ release but not for cytolytic activity. These data indicate that Notch signaling controls human CD8(+) T cell priming and also influences effector T cell functions. This may provide important information for designing new immunotherapies for treatment of cancer.

Intradermal delivery of TLR agonists in a human explant skin model: preferential activation of migratory dendritic cells by polyribosinic-polyribocytidylic acid and peptidoglycans.

TLR agonists are attractive candidate adjuvants for therapeutic cancer vaccines as they can induce a balanced humoral and T cell-mediated immune response. With a dense network of dendritic cells (DCs) and draining lymphatics, the skin provides an ideal portal for vaccine delivery. Beside direct DC activation, TLR agonists may also induce DC activation through triggering the release of inflammatory mediators by accessory cells in the skin microenvironment. Therefore, a human skin explant model was used to explore the in vivo potential of intradermally delivered TLR agonists to stimulate Langerhans cells and dermal DCs in their natural complex tissue environment. The skin-emigrated DCs were phenotyped and analyzed for T cell stimulatory capacity. We report that, of six tested TLR-agonists, the TLR2 and -3 agonists peptidoglycan (PGN) and polyribosinic-polyribocytidylic acid (Poly I:C) were uniquely able to enhance the T cell-priming ability of skin-emigrated DCs, which, in the case of PGN, was accompanied by Th1 polarization. The enhanced priming capacity of Poly I:C-stimulated DCs was associated with a strong upregulation of appropriate costimulatory molecules, including CD70, whereas that of PGN-stimulated DCs was associated with the release of a broad array of proinflammatory cytokines. Transcriptional profiling further supported the notion that the PGN- and Poly I:C-induced effects were mediated through binding to TLR2/nucleotide-binding oligomerization domain 2 and TLR3/MDA5, respectively. These data warrant further exploration of PGN and Poly I:C, alone or in combination, as DC-targeted adjuvants for intradermal cancer vaccines.

Analysis of the glyco-code in pancreatic ductal adenocarcinoma identifies glycan-mediated immune regulatory circuits.

Pancreatic ductal adenocarcinoma (PDAC) remains one of the most aggressive malignancies with a 5-year survival rate of only 9%. Despite the fact that changes in glycosylation patterns during tumour progression have been reported, no systematic approach has been conducted to evaluate its potential for patient stratification. By analysing publicly available transcriptomic data of patient samples and cell lines, we identified here two specific glycan profiles in PDAC that correlated with progression, clinical outcome and epithelial to mesenchymal transition (EMT) status. These different glycan profiles, confirmed by glycomics, can be distinguished by the expression of O-glycan fucosylated structures, present only in epithelial cells and regulated by the expression of GALNT3. Moreover, these fucosylated glycans can serve as ligands for DC-SIGN positive tumour-associated macrophages, modulating their activation and inducing the production of IL-10. Our results show mechanisms by which the glyco-code contributes to the tolerogenic microenvironment in PDAC.

Campylobacter jejuni lipooligosaccharides modulate dendritic cell-mediated T cell polarization in a sialic acid linkage-dependent manner.

Carbohydrate mimicry between Campylobacter jejuni lipooligosaccharides (LOS) and host neural gangliosides plays a crucial role in the pathogenesis of Guillain-Barré syndrome (GBS). Campylobacter jejuni LOS may mimic various gangliosides, which affects the immunogenicity and the type of neurological deficits in GBS patients. Previous studies have shown the interaction of LOS with sialic acid-specific siglec receptors, although the functional consequences remain unknown. Cells that express high levels of siglecs include dendritic cells (DCs), which are crucial for initiation and differentiation of immune responses. We confirm that α2,3-sialylated GD1a/GM1a mimic and α2,8-sialylated GD1c mimic LOS structures interact with recombinant Sn and siglec-7, respectively. Although the linkage of the terminal sialic acid of LOS did not regulate expression of DC maturation markers, it displayed clear opposite expression levels of interleukin-12 (IL-12) and OX40L, molecules involved in DC-mediated Th cell differentiation. Accordingly, targeting DC-expressed siglec-7 with α2,8-linked sialylated LOS resulted in Th1 responses, whereas Th2 responses were induced by targeting with LOS containing α2,3-linked sialic acid. Thus, our data demonstrate for the first time that depending on the sialylated composition of Campylobacter jejuni LOS, specific Th differentiation programs are initiated, possibly through targeting of distinct DC-expressed siglecs.

Variation of Neisseria gonorrhoeae lipooligosaccharide directs dendritic cell-induced T helper responses.

Gonorrhea is one of the most prevalent sexually transmitted diseases in the world. A naturally occurring variation of the terminal carbohydrates on the lipooligosaccharide (LOS) molecule correlates with altered disease states. Here, we investigated the interaction of different stable gonoccocal LOS phenotypes with human dendritic cells and demonstrate that each variant targets a different set of receptors on the dendritic cell, including the C-type lectins MGL and DC-SIGN. Neisseria gonorrhoeae LOS phenotype C constitutes the first bacterial ligand to be described for the human C-type lectin receptor MGL. Both MGL and DC-SIGN are locally expressed at the male and female genital area, the primary site of N. gonorrhoeae infection. We show that targeting of different C-type lectins with the N. gonorrhoeae LOS variants results in alterations in dendritic cell cytokine secretion profiles and the induction of distinct adaptive CD4(+) T helper responses. Whereas N. gonorrhoeae variant A with a terminal N-acetylglucosamine on its LOS was recognized by DC-SIGN and induced significantly more IL-10 production, phenotype C, carrying a terminal N-acetylgalactosamine, primarily interacted with MGL and skewed immunity towards the T helper 2 lineage. Together, our results indicate that N. gonorrhoeae LOS variation allows for selective manipulation of dendritic cell function, thereby shifting subsequent immune responses in favor of bacterial survival.

TLR triggering on tolerogenic dendritic cells results in TLR2 up-regulation and a reduced proinflammatory immune program.

Tolerogenic dendritic cells (TDC) offer a promising therapeutic potential to ameliorate autoimmune diseases. Reported to inhibit adaptive immune responses, little is known about their innate immunity receptor repertoire. In this study, we compared three types of human TDC (IL-10-DC, dexamethasone (DX)-DC, and 1,25(OH)(2)D(3)-DC) by their TLR expression and response to a set of TLR ligands. TDC are endowed with the same TLR set as standard monocyte-derived dendritic cells but respond differentially to the TLR stimuli Pam3CSK4, polyinosinic-polycytidylic acid, LPS, and flagellin. TDC expressed low or no IL-12-related cytokines and remarkably elevated IL-10 levels. Interestingly, only TDC up-regulated the expression of TLR2 upon stimulation. This boosted the tolerogenic potential of these cells, because IL-10 production was up-regulated in TLR2-stimulated, LPS-primed DX-DC, whereas IL-12 and TNF-alpha secretion remained low. When comparing the TDC subsets, DX-DC and 1,25(OH)(2)D(3)-DC up-regulated TLR2 irrespective of the TLR triggered, whereas in IL-10-DC this effect was only mediated by LPS. Likewise, DX-DC and 1,25(OH)(2)D(3)-DC exhibited impaired ability to mature, reduced allostimulatory properties, and hampered capacity to induce Th1 differentiation. Therefore, both DX-DC and 1,25(OH)(2)D(3)-DC display the strongest tolerogenic and anti-inflammatory features and might be most suitable tools for the treatment of autoimmune diseases.

S layer protein A of Lactobacillus acidophilus NCFM regulates immature dendritic cell and T cell functions.

Dendritic cells (DCs) are antigen-presenting cells that play an essential role in mucosal tolerance. They regularly encounter beneficial intestinal bacteria, but the nature of these cellular contacts and the immune responses elicited by the bacteria are not entirely elucidated. Here, we examined the interactions of Lactobacillus acidophilus NCFM and its cell surface compounds with DCs. L. acidophilus NCFM attached to DCs and induced a concentration-dependent production of IL-10, and low IL-12p70. We further demonstrated that the bacterium binds to DC-specific ICAM-3-grabbing nonintegrin (DC-SIGN), a DC- specific receptor. To identify the DC-SIGN ligand present on the bacterium, we took advantage of a generated array of L. acidophilus NCFM mutants. A knockout mutant of L. acidophilus NCFM lacking the surface (S) layer A protein (SlpA) was significantly reduced in binding to DC-SIGN. This mutant incurred a chromosomal inversion leading to dominant expression of a second S layer protein, SlpB. In the SlpB-dominant strain, the nature of the interaction of this bacterium with DCs changed dramatically. Higher concentrations of proinflammatory cytokines such as IL-12p70, TNFalpha, and IL-1beta were produced by DCs interacting with the SlpB-dominant strain compared with the parent NCFM strain. Unlike the SlpA-knockout mutant, T cells primed with L. acidophilus NCFM stimulated DCs produced more IL-4. The SlpA-DC-SIGN interaction was further confirmed as purified SlpA protein ligated directly to the DC-SIGN. In conclusion, the major S layer protein, SlpA, of L. acidophilus NCFM is the first probiotic bacterial DC-SIGN ligand identified that is functionally involved in the modulation of DCs and T cells functions.

PPE38-Secretion-Dependent Proteins of M. tuberculosis Alter NF-kB Signalling and Inflammatory Responses in Macrophages.

It was previously shown that secretion of PE-PGRS and PPE-MPTR proteins is abolished in clinical M. tuberculosis isolates with a deletion in the ppe38-71 operon, which is associated with increased virulence. Here we investigate the proteins dependent on PPE38 for their secretion and their role in the innate immune response using temporal proteomics and protein turnover analysis in a macrophage infection model. A decreased pro-inflammatory response was observed in macrophages infected with PPE38-deficient M. tuberculosis CDC1551 as compared to wild type bacteria. We could show that dampening of the pro-inflammatory response is associated with activation of a RelB/p50 pathway, while the canonical inflammatory pathway is active during infection with wild type M. tuberculosis CDC1551. These results indicate a molecular mechanism by which M. tuberculosis PE/PPE proteins controlled by PPE38 have an effect on modulating macrophage responses through NF-kB signalling.

α2-3 Sialic acid binding and uptake by human monocyte-derived dendritic cells alters metabolism and cytokine release and initiates tolerizing T cell programming.

Dendritic cells (DCs) are key in the initiation of the adaptive T cell responses to tailor adequate immunity that corresponds to the type of pathogen encountered. Oppositely, DCs control the resolution phase of inflammation and are able to induce tolerance after receiving anti-inflammatory cytokines or upon encounter of self-associated molecular patterns, such as α2-3 linked sialic acid (α2-3sia). OBJECTIVE: We here investigated whether α2-3sia, that bind immune inhibitory Siglec receptors, would alter signaling and reprogramming of LPS-stimulated human monocyte-derived DCs (moDCs). METHODS AND RESULTS: Transcriptomic analysis of moDCs stimulated with α2-3sia-conjugated dendrimers revealed differentially expressed genes related to metabolic pathways, cytokines, and T cell differentiation. An increase in genes involved in ATPase regulator activity, oxidoreductase activity, and glycogen metabolic processes was detected. Metabolic extracellular flux analysis confirmed a more energetic moDC phenotype upon α2-3sia binding as evidenced by an increase in both glycolysis and mitochondrial oxidative phosphorylation. TH1 differentiation promoting genes IFNL and IL27, were significantly downregulated in the presence of α2-3sia. Functional assays confirmed that α2-3sia binding to moDCs induced phosphorylation of Siglec-9, reduced production of inflammatory cytokines IL-12 and IL-6, and increased IL-10. Surprisingly, α2-3sia-differentiated moDCs promoted FoxP3+CD25+/-CD127- regulatory T cell differentiation and decreased FoxP3-CD25-CD127- effector T cell proliferation. CONCLUSIONS: In conclusion, we demonstrate that α2-3sia binding to moDCs, phosphorylates Siglec-9, alters metabolic pathways, cytokine signaling, and T cell differentiation processes in moDCs and promotes regulatory T cells. The sialic acid-Siglec axis on DCs is therefore, a novel target to induce tolerance and to explore for immunotherapeutic interventions aimed to restore inflammatory processes.

Erythrocyte haemotoxicity profiling of snake venom toxins after nanofractionation.

Snakebite is classified as a priority Neglected Tropical Disease by the World Health Organization. Understanding the pathology of individual snake venom toxins is of great importance when developing more effective snakebite therapies. Snake venoms may induce a range of pathologies, including haemolytic activity. Although snake venom-induced erythrocyte lysis is not the primary cause of mortality, haemolytic activity can greatly debilitate victims and contributes to systemic haemotoxicity. Current assays designed for studying haemolytic activity are not suitable for rapid screening of large numbers of toxic compounds. Consequently, in this study, a high-throughput haemolytic assay was developed that allows profiling of erythrocyte lysis, and was validated using venom from a number of medically important snake species (Calloselasma rhodostoma, Daboia russelii, Naja mossambica, Naja nigricollis and Naja pallida). The assay was developed in a format enabling direct integration into nanofractionation analytics, which involves liquid chromatographic separation of venom followed by high-resolution fractionation and subsequent bioassaying (and optional proteomics analysis), and parallel mass spectrometric detection. Analysis of the five snake venoms via this nanofractionation approach involving haemolytic assaying provided venom-cytotoxicity profiles and enabled identification of the toxins responsible for haemolytic activity. Our results show that the elapid snake venoms (Naja spp.) contained both direct and indirect lytic toxins, while the viperid venoms (C. rhodostoma and D. russelii) only showed indirect lytic activities, which required the addition of phospholipids to exert cytotoxicity on erythrocytes. The haemolytic venom toxins identified were mainly phospholipase A2s and cytotoxic three finger toxins. Finally, the applicability of this new analytical method was demonstrated using a conventional snakebite antivenom treatment and a small-molecule drug candidate to assess neutralisation of venom cytotoxins.

Sialic acids in pancreatic cancer cells drive tumour-associated macrophage differentiation via the Siglec receptors Siglec-7 and Siglec-9.

Changes in glycosylation during tumour progression are a key hallmark of cancer. One of the glycan moieties generally overexpressed in cancer are sialic acids, which can induce immunomodulatory properties via binding to Siglec receptors. We here show that Pancreatic Ductal Adenocarcinoma (PDAC) tumour cells present an increased sialylation that can be recognized by Siglec-7 and Siglec-9 on myeloid cells. We identified the expression of the α2,3 sialyltransferases ST3GAL1 and ST3GAL4 as main contributor to the synthesis of ligands for Siglec-7 and Siglec-9 in tumour cells. Analysing the myeloid composition in PDAC, using single cell and bulk transcriptomics data, we identified monocyte-derived macrophages as contributors to the poor clinical outcome. Tumour-derived sialic acids dictate monocyte to macrophage differentiation via signalling through Siglec-7 and Siglec-9. Moreover, triggering of Siglec-9 in macrophages reduce inflammatory programmes, while increasing PD-L1 and IL-10 expression, illustrating that sialic acids modulate different myeloid cells. This work highlights a critical role for sialylated glycans in controlling immune suppression and provides new potential targets for cancer immunotherapy in PDAC.

Activation of the C-Type Lectin MGL by Terminal GalNAc Ligands Reduces the Glycolytic Activity of Human Dendritic Cells.

Many tumors display alterations in the biosynthetic pathways of glycosylation, resulting in increased expression of specific tumor-associated glycan structures. Expression of these altered glycan structures is associated with metastasis and poor prognosis. Antigen presenting cells can recognize tumor-associated glycan structures, including the truncated O-glycan Tn antigen, via specific glycan receptors. Tn antigen-mediated activation of the C-type lectin MGL on dendritic cells induces regulatory T cells via the enhanced secretion of IL-10. Although these findings indicate that MGL engagement by glycan ligands can modulate immune responses, the impact of MGL ligation on dendritic cells is still not completely understood. Therefore, we employed RNA sequencing, GO term enrichment and pathway analysis on human monocyte-derived dendritic cells stimulated with two different MGL glycan ligands. Our analyses revealed a reduced expression of genes coding for key enzymes involved in the glycolysis pathway, TCA cycle, and oxidative phosphorylation. In concordance with this, extracellular flux analysis confirmed the decrease in glycolytic activity upon MGL triggering in human dendritic cells. To our knowledge, we are the first to report a diminished glycolytic activity of human dendritic cells upon C-type lectin stimulation. Overall, our findings highlight the impact of tumor-associated glycans on dendritic cell biology and metabolism and will increase our understanding on how glycans can shape immunity.

Pairing Bacteroides vulgatus LPS Structure with Its Immunomodulatory Effects on Human Cellular Models.

The gut microbiota guide the development of the host immune system by setting a systemic threshold for immune activation. Lipopolysaccharides (LPSs) from gut bacteria are able to trigger systemic and local proinflammatory and immunomodulatory responses, and this capability strongly relies on their fine structures. Up to now, only a few LPS structures from gut commensals have been elucidated; therefore, the molecular motifs that may be important for LPS-mammalian cell interactions at the gut level are still obscure. Here, we report on the full structure of the LPS isolated from one of the prominent species of the genus Bacteroides, Bacteroides vulgatus. The LPS turned out to consist of a particular chemical structure based on hypoacylated and mono-phosphorylated lipid A and with a galactofuranose-containing core oligosaccharide and an O-antigen built up of mannose and rhamnose. The evaluation of the immunological properties of this LPS on human in vitro models revealed a very interesting capability to produce anti-inflammatory cytokines and to induce a synergistic action of MD-2/TLR4- and TLR2-mediated signaling pathways.

Targeting of the C-Type Lectin Receptor Langerin Using Bifunctional Mannosylated Antigens.

Langerhans cells (LCs) are antigen-presenting cells that reside in the skin. They uniquely express high levels of the C-type lectin receptor Langerin (CD207), which is an attractive target for antigen delivery in immunotherapeutic vaccination strategies against cancer. We here assess a library of 20 synthetic, well-defined mannoside clusters, built up from one, two, and three of six monomannosides, dimannosides, or trimannosides, appended to an oligopeptide backbone, for binding with Langerin using surface plasmon resonance and flow cytometric quantification. It is found that Langerin binding affinity increases with increasing number of mannosides. Hexavalent presentation of the mannosides resulted in binding affinities ranging from 3 to 12 µM. Trivalent presentation of the dimannosides and trimannosides led to Langerin affinity in the same range. The model melanoma gp100 antigenic peptide was subsequently equipped with a hexavalent cluster of the dimannosides and trimannosides as targeting moieties. Surprisingly, although the bifunctional conjugates were taken up in LCs in a Langerin-dependent manner, limited antigen presentation to cytotoxic T cells was observed. These results indicate that targeting glycan moieties on immunotherapeutic vaccines should not only be validated for target binding, but also on the continued effects on biology, such as antigen presentation to both CD8+ and CD4+ T cells.