Improving Anti-HIV activity and pharmacokinetics of enfuvirtide (T20) by modification with oligomannose

Dendritic cells (DCs) play a pivotal role in controlling HIV-1 infections of CD4+ T cells. DC-SIGN, which is expressed on the surface of DCs, efficiently captures HIV-1 virions by binding to the highly mannosylated membrane protein, gp120, and then the DCs transport the virus to target T cells in lymphoid organs. This study explored the modification of T20, a peptide inhibitor of HIV-1 fusion, by conjugation of the N-terminus with varying sizes of oligomannose, which are DC-SIGN-specific carbohydrates, aiming to create dual-targeting HIV inhibitors. Mechanistic studies indicated the dual-target binding of the conjugates. Antiviral assays demonstrated that N-terminal mannosylation of T20 resulted in increased inhibition of the viral infection of TZM-b1 cells (EC50 = 0.3-0.8 vs. 1.4 nM). Pentamannosylated T20 (M5-T20) exhibited a stronger inhibitory effect on virus entry into DC-SIGN+ 293T cells compared with T20 (67% vs. 50% inhibition at 500 μM). M5-T20 displayed an extended half-life in rats relative to T20 (T1/2: 8.56 vs. 1.64 h, respectively). These conjugates represent a potential new treatment for HIV infections with improved antiviral activity and pharmacokinetics, and this strategy may prove useful in developing dual-target inhibitors for other pathogens that require DC-SIGN involvement for infection.

The S1 spike protein of SARS-CoV-2 upregulates the ERK/MAPK signaling pathway in DC-SIGN-expressing THP-1 cells

Dendritic cells, macrophages, neutrophils, and other antigen-presenting cells express various C-type lectin receptors that function to recognize the glycans associated with pathogens. The dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN) binds various pathogens such as HIV glycoprotein 120, the Ebola glycoprotein, hemagglutinin, and the dengue virus glycoprotein in addition to the SARS-CoV-2 spike protein, and also triggers antigen-presenting cell endocytosis and immune escape from systemic infections. Many studies on the binding of SARS-CoV-2 spike protein with glycans have been published, but the underlying mechanism by which intracellular signaling occurs remains unclear. In this study, we report that the S1 spike protein of SARS-CoV-2 induces the phosphorylation of extracellular signal-regulated kinases (ERKs) in THP-1 cells, a DC-SIGN-expressing human monocytic leukemic cell line. On the other hand, the phosphorylation level of NF-κB remained unchanged under the same conditions. These data suggest that the major cell signaling pathway regulated by the S1 spike protein is the ERK pathway, which is superior to the NF-κB pathway in these DC-SIGN-expressing THP-1 cells and may contribute to immune hyperactivation in SARS-CoV-2 infections. Additionally, several glycans such as mannans, mannosylated bovine serum albumin, the serum amyloid beta protein, and intracellular adhesion molecule 3 suppressed ERK phosphorylation, suggesting that these molecules are target molecules for SARS-CoV-2 infection by suppressing immune hyperactivation that occurs in the ERK signaling pathway.

Aberrant Mannosylated and Highly Fucosylated Glycoepitopes of Prostatic Acid Phosphatase as Potential Ligands for Dendritic-Cell Specific ICAM-Grabbing Nonintegrin (DC-SIGN) in Human Seminal Plasma-A Step towards Explaining Idiopathic Infertility

Semen prostatic acid phosphatase (PAP) has been proposed as an endogenous ligand for dendritic cell-specific ICAM-3-grabbing nonintegrin (DC-SIGN), which plays a critical immuno-modulating role in maintaining homeostasis in the female reproductive tracts. In the current study, we assumed that semen PAP bears a set of fucosylated and mannosylated glycans, which may mediate the efficient binding of PAP to DC-SIGN. To investigate this hypothesis, we developed ELISA assays using Galanthus nivalis and Lotus tetragonolobus lectins capable of binding mannose-containing glycans or LewisX and LewisY motifs, respectively. In our assay with Galanthus nivalis, we detected that the relative reactivity of PAP mannose-presenting glycans in the normozoospermic idiopathic group was significantly higher than in the asthenozoospermic, oligozoospermic and oligoasthenozoospermic groups. Simultaneously, we observed slight differences in the relative reactivities of PAP glycans with Lotus tetragonolobus lectin among groups of patients with abnormal semen parameters. Subsequently, we examined whether DC-SIGN interacts with seminal plasma PAP glycans, and we detected a significantly higher relative reactivity in the normozoospermic group compared to the oligozoospermic group. Finally, we concluded that the significantly aberrant abundance of mannosylated functional groups of PAP among patients with semen disorders can suggest that PAP may thereby be engaged in modulating the immune response and promoting a tolerogenic response to male antigens in the female reproductive system.

The Antiviral Activity of the Lectin Griffithsin against SARS-CoV-2 Is Enhanced by the Presence of Structural Proteins

Although COVID-19 transmission has been reduced by the advent of vaccinations and a variety of rapid monitoring techniques, the SARS-CoV-2 virus itself has shown a remarkable ability to mutate and persist. With this long track record of immune escape, researchers are still exploring prophylactic treatments to curtail future SARS-CoV-2 variants. Specifically, much focus has been placed on the antiviral lectin Griffithsin in preventing spike protein-mediated infection via the hACE2 receptor (direct infection). However, an oft-overlooked aspect of SARS-CoV-2 infection is viral capture by attachment receptors such as DC-SIGN, which is thought to facilitate the initial stages of COVID-19 infection in the lung tissue (called trans-infection). In addition, while immune escape is dictated by mutations in the spike protein, coronaviral virions also incorporate M, N, and E structural proteins within the particle. In this paper, we explored how several structural facets of both the SARS-CoV-2 virion and the antiviral lectin Griffithsin can affect and attenuate the infectivity of SARS-CoV-2 pseudovirus. We found that Griffithsin was a better inhibitor of hACE2-mediated direct infection when the coronaviral M protein is present compared to when it is absent (possibly providing an explanation regarding why Griffithsin shows better inhibition against authentic SARS-CoV-2 as opposed to pseudotyped viruses, which generally do not contain M) and that Griffithsin was not an effective inhibitor of DC-SIGN-mediated trans-infection. Furthermore, we found that DC-SIGN appeared to mediate trans-infection exclusively via binding to the SARS-CoV-2 spike protein, with no significant effect observed when other viral proteins (M, N, and/or E) were present. These results provide etiological data that may help to direct the development of novel antiviral treatments, either by leveraging Griffithsin binding to the M protein as a novel strategy to prevent SARS-CoV-2 infection or by narrowing efforts to inhibit trans-infection to focus on DC-SIGN binding to SARS-CoV-2 spike protein.

Identification of a new DC-SIGN binding pentamannoside epitope within the complex structure of Candida albicans mannan

The dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN) is an innate immune C-type lectin receptor that recognizes carbohydrate-based pathogen associated with molecular patterns of various bacteria, fungi, viruses and protozoa. Although a range of highly mannosylated glycoproteins have been shown to induce signaling via DC-SIGN, precise structure of the recognized oligosaccharide epitope is still unclear. Using the array of oligosaccharides related to selected fragments of main fungal antigenic polysaccharides we revealed a highly specific pentamannoside ligand of DC-SIGN, consisting of α-(1 → 2)-linked mannose chains with one inner α-(1 → 3)-linked unit. This structural motif is present in Candida albicans cell wall mannan and corresponds to its antigenic factors 4 and 13b. This epitope is not ubiquitous in other yeast species and may account for the species-specific nature of fungal recognition via DC-SIGN. The discovered highly specific oligosaccharide ligands of DC-SIGN are tractable tools for interdisciplinary investigations of mechanisms of fungal innate immunity and anti-Candida defense. Ligand- and receptor-based NMR data demonstrated the pentasaccharide-to-DC-SIGN interaction in solution and enabled the deciphering of the interaction topology.

Engineered Nanovesicles Expressing Bispecific Single Chain Variable Fragments to Protect against SARS-CoV-2 Infection

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has resulted in high morbidity and mortality rates worldwide. Although the epidemic has been controlled in many areas and numerous patients have been successfully treated, the risk of reinfection persists due to the low neutralizing antibody titers and weak immune response. To provide long-term immune protection for infected patients, novel bispecific CB6/dendritic cell (DC)-specific intercellular adhesion molecule 3-grabbing nonintegrin (SIGN) nanovesicles (NVs) were constructed to target both the SARS-CoV-2 spike protein (S) and the DC receptors for virus neutralization and immune activation. Herein, we designed NVs expressing both CB6 and DC-SIGN single chain variable fragments (scFvs) on the surface to block SARS-CoV-2 invasion and activate DC function. Monophosphoryl lipid A (MPLA) was loaded into the CB6/DC-SIGN NVs as an adjuvant to promote this process. The CB6/DC-SIGN NVs prevented a pseudovirus expressing the S protein from infecting the target cells expressing high levels of angiotensin-converting enzyme 2 in vitro. Additionally, CB6/DC-SIGN NVs admixed with S-expressing pseudoviruses activated the DCs, which was promoted by the adjuvant MPLA loaded in the NVs. Using a mouse model, we also confirmed that the CB6/DC-SIGN NVs effectively improved the neutralizing antibody titer and inhibited the growth of tumors expressing the S protein after 3 weeks of treatment. This potential NV-based treatment not only exerts a blocking effect by binding the S protein in the short term but may also provide patients with long-term protection against secondary infections.

Interactions between DC-SIGN and the envelope protein from Dengue and Zika viruses: a structural perspective based on molecular dynamics and MM/GBSA analyses

Zika virus (ZIKV) and dengue virus (DENV) share a lot of similarities being both phylogenetically closely related, share the same insect vector passage for reaching the host, affinity for the same carbohydrate receptor domains (CRDs), indicating feasible competition between them on the natural field. Here, we prospected interactions of both envelope proteins with a DC-SIGN, a transmembrane c-type lectine receptor with the most implicated CRD with the Flavivirus infection presents on dendritic cells involved in viruses replication processes into the host, and among rares CRD receptors susceptible to interacting with a broad of subtypes of DENV. Protein-protein docking procedures produced structures for molecular dynamics experiments, suggesting the most energetically favorable complex. The difference found in the deltaG results prompted the experimentation with molecular dynamics. To investigate further specific residues involved with such interactions we produced a decomposition analysis using molecular dynamics of the docked proteins evaluated afterward with the Generalized Born Surface Area method. Solvent-accessible surface area (SASA) analysis for both showed very similar but with a slight reduction for ZIKV_E, which agreed with residues SASA analysis highlighting regions more exposed in the ZIVK protein than in DENV. Despite residues PHE313 is reponsible for most of the interactions with the envelope of these arboviruses, ZIKV interacted with this residue in DC-SIGN with lower energies and using more interactions with not expexted residues GLU241 and ARG386. Taken together these results suggest better competitive interaction of ZIKV with the DC-SIGN receptor, particularly in the CRD portion.

Targeting Lewis X oligosaccharide-modified liposomes encapsulated with house dust mite allergen Der f 2 to dendritic cells inhibits Th2 immune response

Allergen-specific immunotherapy (AIT) is the only curative treatment for allergic diseases. However, the long desensitization phase and potentially dangerous allergic side effects limit its broad application. Therefore, safer and more effective vaccines are required. Targeting dendritic cells (DCs) with novel allergen conjugates is a promising strategy for AIT. In this study, a novel vaccine with a DC-targeting effect for AIT was constructed. Liposomes were used as vehicles, and a targeted nanovaccine (Lex-lip-Der f 2) was constructed by loading the recombinant group 2 allergen of Dermatophagoides farinae (Der f 2) and conjugating with the DC-SIGN ligand Lewis X. The effect of the vaccine on DCs and T cell responses and the safety of the vaccine were investigated in vitro. The results showed that the Lex-lip-Der f 2 vaccine was spherical, with size of approximately 128 nm. The protein-loading capacity of the vaccine was 0.106 ± 0.001 mg per mg liposome and protein was gradually released from the liposomes during the first 12 h. Lex-lip-Der f 2 was taken up more efficiently by DCs than non-targeted liposomes or free Der f 2. Besides, Lex-lip-Der f 2 significantly inhibited the release of IL-4, IL-6, and TNF-a from DCs. Accordingly, Der f 2-lip loaded DCs significantly decreased IL-4 levels in autologous naïve CD4+T cells. Moreover, Lex-lip-Der f 2-treated basophils showed lower activation levels. These results suggest that DC-SIGN targeting mediated by Lewis X could inhibit the Th2 cell response and improve vaccine safety, and may be a novel vaccination strategy.

Dendritic Cell Subpopulations Are Associated with Prognostic Characteristics of Breast Cancer after Neoadjuvant Chemotherapy-An Observational Study

Breast cancer (BC) is the most prevalent malignancy in women and researchers have strived to develop optimal strategies for its diagnosis and management. Neoadjuvant chemotherapy (NAC), which reduces tumor size, risk of metastasis and patient mortality, often also allows for a de-escalation of breast and axillary surgery. Nonetheless, complete pathological response (pCR) is achieved in no more than 40% of patients who underwent NAC. Dendritic cells (DCs) are professional antigen-presenting cells present in the tumor microenvironment. The multitude of their subtypes was shown to be associated with the pathological and clinical characteristics of BC, but it was not evaluated in BC tissue after NAC. We found that highe r densities of CD123+ plasmacytoid DCs (pDCs) were present in tumors that did not show pCR and had a higher residual cancer burden (RCB) score and class. They were of higher stage and grade and more frequently HER2-negative. The density of CD123+ pCDs was an independent predictor of pCR in the studied group. DC-LAMP+ mature DCs (mDCs) were also related to characteristics of clinical relevance (i.e., pCR, RCB, and nuclear grade), although no clear trends were identified. We conclude that CD123+ pDCs are candidates for a novel biomarker of BC response to NAC.

The role of DC-SIGN as a trans-receptor in infection by MERS-CoV

DC-SIGN is a C-type lectin expressed in myeloid cells such as immature dendritic cells and macrophages. Through glycan recognition in viral envelope glycoproteins, DC-SIGN has been shown to act as a receptor for a number of viral agents such as HIV, Ebola virus, SARS-CoV, and SARS-CoV-2. Using a system of Vesicular Stomatitis Virus pseudotyped with MERS-CoV spike protein, here, we show that DC-SIGN is partially responsible for MERS-CoV infection of dendritic cells and that DC-SIGN efficiently mediates trans-infection of MERS-CoV from dendritic cells to susceptible cells, indicating a potential role of DC-SIGN in MERS-CoV dissemination and pathogenesis.

The Effect of Select SARS-CoV-2 N-Linked Glycan and Variant of Concern Spike Protein Mutations on C-Type Lectin-Receptor-Mediated Infection

The SARS-CoV-2 virion has shown remarkable resilience, capable of mutating to escape immune detection and re-establishing infectious capabilities despite new vaccine rollouts. Therefore, there is a critical need to identify relatively immutable epitopes on the SARS-CoV-2 virion that are resistant to future mutations the virus may accumulate. While hACE2 has been identified as the receptor that mediates SARS-CoV-2 susceptibility, it is only modestly expressed in lung tissue. C-type lectin receptors like DC-SIGN can act as attachment sites to enhance SARS-CoV-2 infection of cells with moderate or low hACE2 expression. We developed an easy-to-implement assay system that allows for the testing of SARS-CoV-2 trans-infection. Using our assay, we assessed how SARS-CoV-2 Spike S1-domain glycans and spike proteins from different strains affected the ability of pseudotyped lentivirions to undergo DC-SIGN-mediated trans-infection. Through our experiments with seven glycan point mutants, two glycan cluster mutants and four strains of SARS-CoV-2 spike, we found that glycans N17 and N122 appear to have significant roles in maintaining COVID-19's infectious capabilities. We further found that the virus cannot retain infectivity upon the loss of multiple glycosylation sites, and that Omicron BA.2 pseudovirions may have an increased ability to bind to other non-lectin receptor proteins on the surface of cells. Taken together, our work opens the door to the development of new therapeutics that can target overlooked epitopes of the SARS-CoV-2 virion to prevent C-type lectin-receptor-mediated trans-infection in lung tissue.

Dendritic Cell Subpopulations Are Associated with Morphological Features of Breast Ductal Carcinoma In Situ

Ductal carcinoma in situ (DCIS) is the preinvasive form of breast cancer (BC). It is disputed whether all cases of DCIS require extensive treatment as the overall risk of progression to BC is estimated at 40%. Therefore, the crucial objective for researchers is to identify DCIS with significant risk of transformation into BC. Dendritic cells (DC) are professional antigen presenting cells and as such play a pivotal role in the formation of immune cells that infiltrate in breast tumors. The aim of this study was to investigate the relationship between the density of DCs with different superficial antigens (CD1a, CD123, DC-LAMP, DC-SIGN) and various histopathological characteristics of DCIS. Our evaluation indicated that CD123⁺ and DC-LAMP⁺ cells were strongly associated with maximal tumor size, grading and neoductgenesis. Together with CD1a⁺ cells, they were negatively correlated with hormonal receptors expression. Furthermore, the number of DC-LAMP⁺ cells was higher in DCIS with comedo necrosis, ductal spread, lobular cancerization as well as comedo-type tumors, while CD1a⁺ cells were abundant in cases with Paget disease. We concluded that different subpopulations of DCs relate to various characteristics of DCIS. Of the superficial DCs markers, DC-LAMP seems particularly promising as a target for further research in this area.

SARS CoV-2 spike protein variants exploit DC-SIGN/DC-SIGNR receptor for evolution and severity: an in-silico insight

The Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) is related with the COVID-19 pandemic. Recent spike protein variations have had an effect on the transmission of the virus. In addition to ACE-2, spike proteins can employ DC-SIGN and its analogous receptor, DC-SIGNR, for host evasion. Spike variations in the DC-SIGN interaction region and role of DC-SIGN in immune evasion have not been well defined. To understand the spike protein variations and their binding mode, phylogenetic analysis of the complete GISAID (Global Initiative for Sharing Avian Influenza Data) data of the SARS-CoV-2 spike protein was considered. In addition, an in silico knockout network evaluation of the SARS-CoV-2 single-cell transcriptome was conducted to determine the key role of DC-SIGN/R in immunological dysregulation. Within the DC-SIGN-interacting region of the SARS-CoV spike protein, the spike protein of SARS-CoV-2 displayed remarkable similarity to the SARS-CoV spike protein. Surprisingly, the phylogenetic analysis revealed that the SARS-CoV-2's spike exhibited significantly diverse variants in the DC-SIGN interaction domain, which altered the frequency of these variants. The variation within the DC-SIGN-interacting domain of spike proteins affected the binding of a limited number of variants with DC-SIGN and DC-SIGNR and affected their evolution. MMGBSA binding free energies evaluation differed for variants from those of the wild type, suggesting the influence of substitution mutations on the interaction pattern. In silico knockout network analysis of the single-cell transcriptome of Bronchoalveolar Lavage and peripheral blood mononuclear cells revealed that SARS-CoV-2 altered DC-SIGN/R signaling. Early surveillance of diverse SARS-CoV-2 strains could preclude a worsening of the pandemic and facilitate the development of an optimum vaccine against variations. The spike Receptor Binding Domain genetic variants are thought to boost SARS CoV-2 immune evasion, resulting in its higher longevity.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13337-023-00820-3.

The Autophagy Nucleation Factor ATG9 Forms Nanoclusters with the HIV-1 Receptor DC-SIGN and Regulates Early Antiviral Autophagy in Human Dendritic Cells

Dendritic cells (DC) are critical cellular mediators of host immunity, notably by expressing a broad panel of pattern recognition receptors. One of those receptors, the C-type lectin receptor DC-SIGN, was previously reported as a regulator of endo/lysosomal targeting through functional connections with the autophagy pathway. Here, we confirmed that DC-SIGN internalization intersects with LC3⁺ autophagy structures in primary human monocyte-derived dendritic cells (MoDC). DC-SIGN engagement promoted autophagy flux which coincided with the recruitment of ATG-related factors. As such, the autophagy initiation factor ATG9 was found to be associated with DC-SIGN very early upon receptor engagement and required for an optimal DC-SIGN-mediated autophagy flux. The autophagy flux activation upon DC-SIGN engagement was recapitulated using engineered DC-SIGN-expressing epithelial cells in which ATG9 association with the receptor was also confirmed. Finally, Stimulated emission depletion (STED) microscopy performed in primary human MoDC revealed DC-SIGN-dependent submembrane nanoclusters formed with ATG9, which was required to degrade incoming viruses and further limit DC-mediated transmission of HIV-1 infection to CD4⁺ T lymphocytes. Our study unveils a physical association between the Pattern Recognition Receptor DC-SIGN and essential components of the autophagy pathway contributing to early endocytic events and the host's antiviral immune response.

Single-Molecule Analysis of SARS-CoV-2 Binding to C-Type Lectin Receptors

Despite intense scrutiny throughout the pandemic, development of efficacious drugs against SARS-CoV-2 spread remains hindered. Understanding the underlying mechanisms of viral infection is fundamental for developing novel treatments. While angiotensin converting enzyme 2 (ACE2) is accepted as the key entry receptor of the virus, other infection mechanisms exist. Dendritic cell-specific intercellular adhesion molecule-3 grabbing non-integrin (DC-SIGN) and its counterpart DC-SIGN-related (DC-SIGNR, also known as L-SIGN) have been recognized as possessing functional roles in COVID-19 disease and binding to SARS-CoV-2 has been demonstrated previously with ensemble and qualitative techniques. Here we examine the thermodynamic and kinetic parameters of the ligand-receptor interaction between these C-type lectins and the SARS-CoV-2 S1 protein using force-distance curve-based AFM and biolayer interferometry. We evidence that the S1 receptor binding domain is likely involved in this bond formation. Further, we employed deglycosidases and examined a nonglycosylated S1 variant to confirm the significance of glycosylation in this interaction. We demonstrate that the high affinity interactions observed occur through a mechanism distinct from that of ACE2.

Feasibility of Brewer's Spent Yeast Microcapsules as Targeted Oral Carriers

Brewer's spent yeast (BSY) microcapsules have a complex network of cell-wall polysaccharides that are induced by brewing when compared to the baker's yeast (Saccharomyces cerevisiae) microcapsules. These are rich in (β1→3)-glucans and covalently linked to (α1→4)- and (β1→4)-glucans in addition to residual mannoproteins. S. cerevisiae is often used as a drug delivery system due to its immunostimulatory potential conferred by the presence of (β1→3)-glucans. Similarly, BSY microcapsules could also be used in the encapsulation of compounds or drug delivery systems with the advantage of resisting digestion conferred by (β1→4)-glucans and promoting a broader immunomodulatory response. This work aims to study the feasibility of BSY microcapsules that are the result of alkali and subcritical water extraction processes, as oral carriers for food and biomedical applications by (1) evaluating the resistance of BSY microcapsules to in vitro digestion (IVD), (2) their recognition by the human Dectin-1 immune receptor after IVD, and (3) the recognition of IVD-solubilized material by different mammalian immune receptors. IVD digested 44-63% of the material, depending on the extraction process. The non-digested material, despite some visible agglutination and deformation of the microcapsules, preserved their spherical shape and was enriched in (β1→3)-glucans. These microcapsules were all recognized by the human Dectin-1 immune receptor. The digested material was differentially recognized by a variety of lectins of the immune system related to (β1→3)-glucans, glycogen, and mannans. These results show the potential of BSY microcapsules to be used as oral carriers for food and biomedical applications.

Importance of NFκβ, IL-10 serum levels and DC-SIGN polymorphic haplotypes in determining dengue disease severity among eastern Indian patients

OBJECTIVES

Dengue viral (DENV) infection is most prevalent arboviral infection in India resulting in wide-range of symptomatic manifestation from simple (DF) to severe dengue (SD). DENV is internalized by dendritic cell receptor, DC-SIGN, which in turn activates inflammatory cytokines: NFκβ, IL-10 as adaptive immune response. Present study focused on role of DC-SIGN polymorphisms and these cytokines in SD development among eastern Indian patients.

METHOD

DC-SIGN polymorphisms (rs735239, rs4804803, rs2287886) and NFκβ, IL-10 concentrations were analysed among 179 dengue patients and 123 healthy individuals by PCR-RFLP and sandwich ELISA, respectively. DENV copies/ml and serotype in patient-sera were measured by quantitative and qualitative real time PCR, respectively. Statistical and haplotype analysis were performed by GraphPad-Prism and SNPStat, respectively.

RESULT

Prevalence of DENV serotypes among infected patients: DENV2>DENV4>DENV3>DENV1; those with DENV3 infection reported significantly increased IL-10 level. NFκβ and IL-10 concentrations were significantly elevated among SD patients. ROC curve analysis predicted cut-off values of NFκβ>13.46 ng/ml and IL-10 > 490.5 pg/ml to detect SD among infected patients with a good sensitivity and specificity. Patients with rs735239-GG, rs2287886-GG genotypes and GGG, GAG haplotypes were significantly associated with SD development, whereas, those with rs4804803-AG exhibited high DENVcopies/ml. Patients with these haplotypes also demonstrated increased NFκβ and IL-10.

CONCLUSION

This study emphasised importance of DC-SIGN GGG and GAG haplotypes, NFκβ and IL-10 concentrations in WHO-defined severe dengue development among infected patients.

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, (Le^b) 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 Le^b. 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. Le^b 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 Le^b, 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 Le^b 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.

Tinker, tailor, soldier, cell: the role of C-type lectins in the defense and promotion of disease

C-type lectins (CTLs) represent a large family of soluble and membrane-bound proteins which bind calcium dependently via carbohydrate recognition domains (CRDs) to glycan residues presented on the surface of a variety of pathogens. The deconvolution of a cell's glycan code by CTLs underpins several important physiological processes in mammals such as pathogen neutralization and opsonization, leukocyte trafficking, and the inflammatory response. However, as our knowledge of CTLs has developed it has become apparent that the role of this innate immune family of proteins can be double-edged, where some pathogens have developed approaches to subvert and exploit CTL interactions to promote infection and sustain the pathological state. Equally, CTL interactions with host glycoproteins can contribute to inflammatory diseases such as arthritis and cancer whereby, in certain contexts, they exacerbate inflammation and drive malignant progression. This review discusses the 'dual agent' roles of some of the major mammalian CTLs in both resolving and promoting infection, inflammation and inflammatory disease and highlights opportunities and emerging approaches for their therapeutic modulation.

A novel SARS-CoV-2 subunit vaccine engineered on an immune-activating platform technology

While there are several SARS-CoV-2 vaccines currently available, additional options must be provided that are safe, effective, and affordable for the entire global population. We have developed a novel immune activating platform technology that will fill this need. This recombinant platform protein is produced in insect cells using baculoviral expression technology similar to what is currently used for several other approved vaccines as well as employed by myriad GMP facilities globally. Thus, infrastructure exists for rapid scale up following initial optimizations. Here we report initial results for a SARS-CoV-2 vaccine (OMN008) based on our platform technology. Unadjuvanted OMN008 vaccination resulted in robust antigenicity and neutralization. Additionally, OMN008 vaccination induced a specific CD8 T-cell response. All of these results taken together indicate OMN008 may be an excellent candidate to fill gaps left by the currently available vaccines. Further testing is necessary to fully optimize production; however, overall cost of production should remain low given the simple formulation of this recombinant platform.

Interleukin-34 Permits Porphyromonas gingivalis Survival and NF-κB p65 Inhibition in Macrophages

Interleukin-34 (IL-34) is a cytokine that supports the viability and differentiation of macrophages. An important cytokine for the development of epidermal immunity, IL-34 is present and plays a role in the immunity of the oral environment. IL-34 has been linked to inflammatory periodontal diseases, which involve innate phagocytes, including macrophages. Whether IL-34 can alter the ability of macrophages to effectively interact with oral microbes is currently unclear. Using macrophages derived from human blood monocytes with either the canonical cytokine colony-stimulating factor (CSF)1 or IL-34, we compared the ability of the macrophages to phagocytose, kill, and respond through the production of cytokines to the periodontal keystone pathogen Porphyromonas gingivalis. While macrophages derived from both cytokines were able to engulf the bacterium equally, IL-34 derived macrophages were much less capable of killing internalized P. gingivalis. Of the macrophage cell surface receptors known to interact with P. gingivalis, DC-SIGN was found to have the largest variation between IL-34 and CSF1-derived macrophages. We also found that upon interaction with P. gingivalis, IL-34 derived macrophages produced significantly less of the neutrophil chemotactic factor IL-8 than macrophages derived in the presence of CSF1. Mechanistically, we identified that levels of IL-8 corresponded with P. gingivalis survival and dephosphorylation of the major transcription factor NF-κB p65. Overall, we found that macrophages differentiated in the presence of IL-34, a dominant cytokine in the oral gingiva, have a reduced ability to kill the keystone pathogen P. gingivalis and may be susceptible to specific bacteria-mediated cytokine modification. This article is protected by copyright. All rights reserved.

Topological and Multivalent Effects in Glycofullerene Oligomers as EBOLA Virus Inhibitors

The synthesis of new biocompatible antiviral materials to fight against the development of multidrug resistance is being widely explored. Due to their unique globular structure and excellent properties, [60]fullerene-based antivirals are very promising bioconjugates. In this work, fullerene derivatives with different topologies and number of glycofullerene units were synthesized by using a SPAAC copper free strategy. This procedure allowed the synthesis of compounds 1–3, containing from 20 to 40 mannose units, in a very efficient manner and in short reaction times under MW irradiation. The glycoderivatives were studied in an infection assay by a pseudotyped viral particle with Ebola virus GP1. The results obtained show that these glycofullerene oligomers are efficient inhibitors of EBOV infection with IC₅₀s in the nanomolar range. In particular, compound 3, with four glycofullerene moieties, presents an outstanding relative inhibitory potency (RIP). We propose that this high RIP value stems from the appropriate topological features that efficiently interact with DC-SIGN.

Association of single nucleotide polymorphisms in the CD209, MMP9, TNFA and IFNG genes with susceptibility to Japanese encephalitis in children from North India

Japanese encephalitis (JE), an acute encephalitis syndrome disease caused by infection with JE virus (JEV), is an important mosquito borne disease in developing countries. The clinical outcomes of JEV infection show inter individual differences. Only in a minor percent of the infected subjects, the disease progresses into acute encephalitis syndrome. Single nucleotide polymorphisms in the host immune response related genes are known to affect susceptibility to JE. In the present study, 238 JE cases and 405 healthy controls (HCs) without any known history of encephalitis were investigated for SNPs in the CD209 MX1, TLR3, MMP9, TNFA and IFNG genes which are important in the immune response against JEV by PCR based methods. The results revealed higher frequencies of heterozygous genotypes of CD209 rs4804803, MMP9 rs17576, TNFA rs1800629 and IFNG rs2430561 in JE cases compared to HCs. These SNPs were associated with JE in an over-dominant genetic model (Odds ratio with 95% CI 1.51 (1.09-2.10) for CD209 rs4804803, 1.52 (1.09-2.11) for MMP9 rs17576, and 1.55 (1.12-2.15) for IFNG rs2430561). The association of G/A genotype of TNFA rs1800629 with JE was confirmed in a larger sample size. The results suggest the association of CD209 rs4804803, MMP9 rs17576, IFNG rs2430561 and TNFA rs1800629 polymorphisms with susceptibility to JE.

DC-SIGN Mediates the Interaction Between Neutrophils and Leishmania amazonensis-Infected Dendritic Cells to Promote DC Maturation and Parasite Elimination

Background

Leishmaniasis is a neglected arthropod-borne disease that affects millions of people worldwide. Successful Leishmania infections require the mitigation of immune cell functions leading to parasite survival and proliferation. A large body of evidence highlights the involvement of neutrophils (PMNs) and dendritic cells (DCs) in the establishment of immunological responses against these parasites. However, few studies, contemplate to what extent these cells interact synergistically to constrain Leishmania infection.

Objective

We sought to investigate how PMNs and infected DCs interact in an in vitro model of Leishmania amazonensis infection.

Material and Methods

Briefly, human PMNs and DCs were purified from the peripheral blood of healthy donors. Next, PMNs were activated with fibronectin and subsequently co-cultured with L. amazonensis-infected DCs.

Results

We observed that L. amazonensis-infected DC exhibited lower rates of infection when co-cultivated with either resting or activated PMNs. Surprisingly, we found that the release of neutrophil enzymes was not involved in Leishmania killing. Next, we showed that the interaction between PMNs and infected-DCs was intermediated by DC-SIGN, further suggesting that parasite elimination occurs in a contact-dependent manner. Furthermore, we also observed that TNFα and ROS production was dependent on DC-SIGN-mediated contact, as well as parasite elimination is dependent on TNFα production in the co-culture. Finally, we observed that direct contact between PMNs and DCs are required to restore the expression of DC maturation molecules during L. amazonensis infection.

Conclusion

Our findings suggest that the engagement of direct contact between PMNs and L. amazonensis-infected DC via DC-SIGN is required for the production of inflammatory mediators with subsequent parasite elimination and DC maturation.

Wnt-β-Catenin Signaling in Human Dendritic Cells Mediates Regulatory T-Cell Responses to Fungi via the PD-L1 Pathway

The signaling pathways activated following interaction between dendritic cells (DCs) and a pathogen determine the polarization of effector T-cell and regulatory T-cell (Treg) responses to the infection. Several recent studies, mostly in the context of bacterial infections, have shown that the Wnt/β-catenin pathway plays a major role in imparting tolerogenic features in DCs and in promotion of Treg responses. However, the significance of the Wnt/β-catenin pathway’s involvement in regulating the immune response to the fungal species is not known. Using Aspergillus fumigatus, a ubiquitous airborne opportunistic fungal species, we show here that fungi activate the Wnt/β-catenin pathway in human DCs and are critical for mediating the immunosuppressive Treg responses. Pharmacological inhibition of this pathway in DCs led to inhibition of maturation-associated molecules and interleukin 10 (IL-10) secretion without affecting the majority of the inflammatory cytokines. Furthermore, blockade of Wnt signaling in DCs suppressed DC-mediated Treg responses in CD4⁺ T cells and downregulated both tumor necrosis factor alpha (TNF-α) and IL-10 responses in CD8⁺ T cells. Mechanistically, induction of β-catenin pathway by A. fumigatus required C-type lectin receptors and promoted Treg polarization via the induction of programmed death-ligand 1 on DCs. Further investigation on the identity of fungal molecular patterns has revealed that the cell wall polysaccharides β-(1, 3)-glucan and α-(1, 3)-glucan, but not chitin, possess the capacity to activate the β-catenin pathway. Our data suggest that the Wnt/β-catenin pathway is a potential therapeutic target to selectively suppress the Treg response and to sustain the protective Th1 response in the context of invasive aspergillosis caused by A. fumigatus.

Riclinoctaose Attenuates Renal Ischemia-Reperfusion Injury by the Regulation of Macrophage Polarization

Renal ischemia-reperfusion injury is a major trigger of acute kidney injury and leads to permanent renal impairment, and effective therapies remain unresolved. Riclinoctaose is an immunomodulatory octasaccharide composed of glucose and galactose monomers. Here we investigated whether riclinoctaose protects against renal ischemia-reperfusion injury. In mice, pretreatment with riclinoctaose significantly improved renal function, structure, and the inflammatory response after renal ischemia-reperfusion. Flow cytometry analysis revealed that riclinoctaose inhibited ischemia-reperfusion-induced M1 macrophage polarization and facilitated M2 macrophage recruitment into the kidneys. In isolated mouse bone marrow-derived macrophages, pretreatment with riclinoctaose promoted the macrophage polarization toward M2-like phenotype. The inhibitor of Nrf-2/HO-1 brusatol diminished the effects of riclinoctaose on macrophage polarization. In mice, intravenous injection with riclinoctaose-pretreated bone marrow-derived macrophages also protected against renal ischemia-reperfusion injury. Fluorescence-labeled riclinoctaose specifically bound to the membrane of macrophages. Interfering with mDC-SIGN blocked the riclinoctaose function on M2 polarization of macrophages, consequently impairing the renoprotective effect of riclinoctaose. Our results revealed that riclinoctaose is a potential therapeutic agent in preventing renal ischemia-reperfusion injury.

Glycan Epitopes and Potential Glycoside Antagonists of DC-SIGN Involved in COVID-19: In Silico Study

Glycosylation is an important post-translational modification that affects a wide variety of physiological functions. DC-SIGN (Dendritic Cell-Specific Intercellular adhesion molecule-3-Grabbing Non-integrin) is a protein expressed in antigen-presenting cells that recognizes a variety of glycan epitopes. Until now, the binding of DC-SIGN to SARS-CoV-2 Spike glycoprotein has been reported in various articles and is regarded to be a factor in systemic infection and cytokine storm. The mechanism of DC-SIGN recognition offers an alternative method for discovering new medication for COVID-19 treatment. Here, we discovered three potential pockets that hold different glycan epitopes by performing molecular dynamics simulations of previously reported oligosaccharides. The "EPN" motif, "NDD" motif, and Glu354 form the most critical pocket, which is known as the Core site. We proposed that the type of glycan epitopes, rather than the precise amino acid sequence, determines the recognition. Furthermore, we deduced that oligosaccharides could occupy an additional site, which adds to their higher affinity than monosaccharides. Based on our findings and previously described glycoforms on the SARS-CoV-2 Spike, we predicted the potential glycan epitopes for DC-SIGN. It suggested that glycan epitopes could be recognized at multiple sites, not just Asn234, Asn149 and Asn343. Subsequently, we found that Saikosaponin A and Liquiritin, two plant glycosides, were promising DC-SIGN antagonists in silico.

Kinetic Studies of Acetyl Group Migration between the Saccharide Units in an Oligomannoside Trisaccharide Model Compound and a Native Galactoglucomannan Polysaccharide

Acyl group migration is a fundamental phenomenon in carbohydrate chemistry, recently shown to take place also between two non-adjacent hydroxyl groups, across the glycosidic bond, in a β-(1→4)-linked mannan trisaccharide model compound. With the central mannoside unit containing acetyl groups at the O2 and O3 positions, the O2-acetyl was in the earlier study shown to migrate to O6 of the reducing end. Potential implications of the general acyl migration process on cell signaling events and plant growth in nature are intriguing open questions. In the present work, migration kinetics in this original trisaccharide model system were studied in more detail together with potential interactions of the model compound and the migration products with DC-SIGN lectin. Furthermore, we demonstrate here for the first time that similar migration may also take place in native polysaccharides, here represented by galactoglucomannan from Norway spruce.

Glycan-Lectin Interactions in Cancer and Viral Infections and How to Disrupt Them

Glycan-lectin interactions play an essential role in different cellular processes. One of their main functions is involvement in the immune response to pathogens or inflammation. However, cancer cells and viruses have adapted to avail themselves of these interactions. By displaying specific glycosylation structures, they are able to bind to lectins, thus promoting pathogenesis. While glycan-lectin interactions promote tumor progression, metastasis, and/or chemoresistance in cancer, in viral infections they are important for viral entry, release, and/or immune escape. For several years now, a growing number of investigations have been devoted to clarifying the role of glycan-lectin interactions in cancer and viral infections. Various overviews have already summarized and highlighted their findings. In this review, we consider the interactions of the lectins MGL, DC-SIGN, selectins, and galectins in both cancer and viral infections together. A possible transfer of ways to target and disrupt them might lead to new therapeutic approaches in different pathological backgrounds.

SARS-CoV-2 Impairs Dendritic Cells and Regulates DC-SIGN Gene Expression in Tissues

The current spreading coronavirus SARS-CoV-2 is highly infectious and pathogenic. In this study, we screened the gene expression of three host receptors (ACE2, DC-SIGN and L-SIGN) of SARS coronaviruses and dendritic cells (DCs) status in bulk and single cell transcriptomic datasets of upper airway, lung or blood of COVID-19 patients and healthy controls. In COVID-19 patients, DC-SIGN gene expression was interestingly decreased in lung DCs but increased in blood DCs. Within DCs, conventional DCs (cDCs) were depleted while plasmacytoid DCs (pDCs) were augmented in the lungs of mild COVID-19. In severe cases, we identified augmented types of immature DCs (CD22+ or ANXA1+ DCs) with MHCII downregulation. In this study, our observation indicates that DCs in severe cases stimulate innate immune responses but fail to specifically present SARS-CoV-2. It provides insights into the profound modulation of DC function in severe COVID-19.

Suppression of DC-SIGN and gH Reveals Complex, Subset-Specific Mechanisms for KSHV Entry in Primary B Lymphocytes

Kaposi sarcoma-associated herpesvirus (KSHV) is the causative agent of multiple cancers in immunocompromised patients including two lymphoproliferative disorders associated with KSHV infection of B lymphocytes. Despite many years of research into the pathogenesis of KSHV associated diseases, basic questions related to KSHV molecular virology remain unresolved. One such unresolved question is the cellular receptors and viral glycoproteins needed for KSHV entry into primary B lymphocytes. In this study, we assess the contributions of KSHV glycoprotein H (gH) and the cellular receptor DC-SIGN to KSHV infection in tonsil-derived B lymphocytes. Our results show that (1) neither KSHV-gH nor DC-SIGN are essential for entry into any B cell subset, (2) DC-SIGN does play a role in KSHV entry into tonsil-derived B cells, but in all B cell subtypes alternative entry mechanisms exist, (3) KSHV-gH can participate in KSHV entry into centrocytes via a DC-SIGN independent entry mechanism, and (4) in the absence of KSHV-gH, DC-SIGN is required for KSHV entry into centrocytes. Our results provide a first glimpse into the complexity of KSHV entry in the lymphocyte compartment and highlight that multiple subset-dependent entry mechanisms are employed by KSHV which depend upon multiple cellular receptors and multiple KSHV glycoproteins.

Immunomodulatory effect of vitamin D on immune response to dengue virus infection

Dengue, an acute febrile illness which in some cases requires hospitalization and occasionally a fatal disease, caused by dengue virus is a potential threat to the public health systems throughout the world. Approved antivirals are not available for treating dengue. Immunomodulators, that can reduce inflammation which if not treated properly results in vascular leakage, are being attempted as therapeutics against severe dengue. Vitamin D, an immunomodulatory hormone, with both antiviral and immunomodulatory effects, is an appropriate choice for investigation as a potential drug against dengue. Investigations of vitamin D levels by many studies have suggested vitamin D levels as a potential marker for predicting severe dengue. In-vitro studies have shown that 1, 25 dihydroxy vitamin D₃ (1,25(OH)₂D₃), active form of vitamin D, can reduce the expression of dengue virus entry receptors, restrict the viral replication and can modulate the expression of inflammatory cytokines in dengue virus infected cells. The results from in-vitro studies also have cautioned that insufficient levels of vitamin D supplementation might increase the virus replication. Available evidence suggests vitamin D based therapeutics against dengue and provides ray of light for treating dengue patients but, the available evidence needs to be supported by beneficial outcomes in clinical trials.

Transfection of Vitamin D3-Induced Tolerogenic Dendritic Cells for the Silencing of Potential Tolerogenic Genes. Identification of CSF1R-CSF1 Signaling as a Glycolytic Regulator

The use of autologous tolerogenic dendritic cells (tolDC) has become a promising strategy to re-establish immune tolerance in autoimmune diseases. Among the different strategies available, the use of vitamin D3 for the generation of tolDC (VitD3-tolDC) has been widely tested because of their immune regulatory properties. To identify molecules and pathways involved in the generation of VitD3-tolDC, we established an easy and fast gene silencing method based on the use of Viromer blue to introduce siRNA into monocytes on day 1 of culture differentiation. The analysis of the effect of CD209 (DC-SIGN) and CD115 (CSF1R) down-modulation on the phenotype and functionality of transfected VitD3-tolDC revealed a partial role of CD115 in their tolerogenicity. Further investigations showed that CSF1R-CSF1 signaling is involved in the induction of cell metabolic reprogramming, triggering glycolysis to produce high amounts of lactate, a novel suppressive mechanism of T cell proliferation, recently found in autologous tolerogenic dendritic cells (ATDCs).

SARS-CoV-2 exacerbates proinflammatory responses in myeloid cells through C-type lectin receptors and Tweety family member 2

Despite mounting evidence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) engagement with immune cells, most express little, if any, of the canonical receptor of SARS-CoV-2, angiotensin-converting enzyme 2 (ACE2). Here, using a myeloid cell receptor-focused ectopic expression screen, we identified several C-type lectins (DC-SIGN, L-SIGN, LSECtin, ASGR1, and CLEC10A) and Tweety family member 2 (TTYH2) as glycan-dependent binding partners of the SARS-CoV-2 spike. Except for TTYH2, these molecules primarily interacted with spike via regions outside of the receptor-binding domain. Single-cell RNA sequencing analysis of pulmonary cells from individuals with coronavirus disease 2019 (COVID-19) indicated predominant expression of these molecules on myeloid cells. Although these receptors do not support active replication of SARS-CoV-2, their engagement with the virus induced robust proinflammatory responses in myeloid cells that correlated with COVID-19 severity. We also generated a bispecific anti-spike nanobody that not only blocked ACE2-mediated infection but also the myeloid receptor-mediated proinflammatory responses. Our findings suggest that SARS-CoV-2-myeloid receptor interactions promote immune hyperactivation, which represents potential targets for COVID-19 therapy.

Expression of the human or porcine C-type lectins DC-SIGN/L-SIGN confers susceptibility to porcine epidemic diarrhea virus entry and infection in otherwise refractory cell lines

Porcine epidemic diarrhea virus (PEDV) is an alphacoronavirus that causes great economic losses in the porcine industry. Although the functional receptor for the virus has not been identified, multiple isolates are able to infect different cell lines. Recently, it has been shown that the human C-type lectin DC-SIGN/L-SIGN (hDC-SIGN/L-SIGN) can promote entry of several coronaviruses. Here we examined whether hDC-SIGN/L-SIGN and its porcine homolog (pDC-SIGN) are entry determinants for PEDV. Expression of hDC-SIGN/L-SIGN or pDC-SIGN in refractory cells dramatically increased infection by a recombinant PEDV expressing green fluorescent protein. In both cases, lectin-mediated infection was inhibited by mannan or anti-hDC-SIGN/L-SIGN or pDC-SIGN antibodies; however, d-galactose had no effect on the virus-infected cells. Our results demonstrate that hDC-SIGN/L-SIGN or pDC-SIGN can mediate the cellular entry and propagation of PEDV, which provides a new theoretical basis for further understanding the infection mechanism of PEDV, and will be helpful for the development of novel therapeutic agents.

C-type lectin receptors MR and DC-SIGN are involved in recognition of hemocyanins, shaping their immunostimulatory effects on human dendritic cells

Hemocyanins are used as immunomodulators in clinical applications because they induce a strong Th1-biased cell-mediated immunity, which has beneficial effects. They are multiligand glycosylated molecules with abundant and complex mannose-rich structures. It remains unclear whether these structures influence hemocyanin-induced immunostimulatory processes in human APCs. We have previously shown that hemocyanin glycans from Concholepas concholepas (CCH), Fissurella latimarginata (FLH), and Megathura crenulata (KLH), participate in their immune recognition and immunogenicity in mice, interacting with murine C-type lectin receptors (CLRs). Here, we studied the interactions of these hemocyanins with two major mannose-binding CLRs on monocyte-derived human DCs: MR (mannose receptor) and DC-SIGN (DC-specific ICAM-3-grabbing nonintegrin). Diverse analyses showed that hemocyanins are internalized by a mannose-sensitive mechanism. This process was calcium dependent. Moreover, hemocyanins colocalized with MR and DC-SIGN, and were partly internalized through clathrin-mediated endocytosis. The hemocyanin-mediated proinflammatory cytokine response was impaired when using deglycosylated FLH and KLH compared to CCH. We further showed that hemocyanins bind to human MR and DC-SIGN in a carbohydrate-dependent manner with affinity constants in the physiological concentration range. Overall, we showed that these three clinically valuable hemocyanins interact with human mannose-sensitive CLRs, initiating an immune response and promoting a Th1 cell-driving potential.

miR-181a Modulation of ERK-MAPK Signaling Sustains DC-SIGN Expression and Limits Activation of Monocyte-Derived Dendritic Cells

DC-SIGN⁺ monocyte-derived dendritic cells (mo-DCs) play important roles in bacterial infections and inflammatory diseases, but the factors regulating their differentiation and proinflammatory status remain poorly defined. Here, we identify a microRNA, miR-181a, and a molecular mechanism that simultaneously regulate the acquisition of DC-SIGN expression and the activation state of DC-SIGN⁺ mo-DCs. Specifically, we show that miR-181a promotes DC-SIGN expression during terminal mo-DC differentiation and limits its sensitivity and responsiveness to TLR triggering and CD40 ligation. Mechanistically, miR-181a sustains ERK-MAPK signaling in mo-DCs, thereby enabling the maintenance of high levels of DC-SIGN and a high activation threshold. Low miR-181a levels during mo-DC differentiation, induced by inflammatory signals, do not support the high phospho-ERK signal transduction required for DC-SIGN^hi mo-DCs and lead to development of proinflammatory DC-SIGN^lo/- mo-DCs. Collectively, our study demonstrates that high DC-SIGN expression levels and a high activation threshold in mo-DCs are linked and simultaneously maintained by miR-181a.

Combining cross-coupling reaction and Knoevenagel condensation in the synthesis of glyco-BODIPY probes for DC-SIGN super-resolution bioimaging

Lectins are involved in a wide range of carbohydrate mediated recognition processes. Therefore, the availability of highly performant fluorescent tools tailored for lectin targeting and able to efficiently track events related to such key targets is in high demand. We report here on the synthesis of the glyco-BODIPYs 1 and 2, based on the efficient combination of a Heck-like cross coupling and a Knoevenagel condensation, which revealed efficient in addressing lectins. In particular, glyco-BODIPY 1 has two glycosidase stable C-mannose residues, which act as DC-SIGN (dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin) targeting modules. By using live-cell fluorescence microscopy, we proved that BODIPY-mannose 1 was efficiently taken up by immune cells expressing DC-SIGN receptors. Super-resolution stimulated emission depletion (STED) microscopy further revealed that the internalized 1 localized in membranes of endosomes, proving that 1 is a reliable tool also in STED applications. Of note, glyco-BODIPY 1 contains an aryl-azido group, which allows further functionalization of the glycoprobe with bioactive molecules, thus paving the way for the use of 1 for tracking lectin-mediated cell internalization in diverse biological settings.

Generation of Liposomes to Study the Effect of Mycobacterium Tuberculosis Lipids on HIV-1 cis- and trans-Infections

Tuberculosis (TB) is the leading cause of death among HIV-1-infected individuals and Mycobacterium tuberculosis (Mtb) co-infection is an early precipitate to AIDS. We aimed to determine whether Mtb strains differentially modulate cellular susceptibility to HIV-1 infection (cis- and trans-infection), via surface receptor interaction by their cell envelope lipids. Total lipids from pathogenic (lineage 4 Mtb H37Rv, CDC1551 and lineage 2 Mtb HN878, EU127) and non-pathogenic (Mycobacterium bovis BCG and Mycobacterium smegmatis) Mycobacterium strains were integrated into liposomes mimicking the lipid distribution and antigen accessibility of the mycobacterial cell wall. The resulting liposomes were tested for modulating in vitro HIV-1 cis- and trans-infection of TZM-bl cells using single-cycle infectious virus particles. Mtb glycolipids did not affect HIV-1 direct infection however, trans-infection of both R5 and X4 tropic HIV-1 strains were impaired in the presence of glycolipids from M. bovis, Mtb H37Rv and Mtb EU127 strains when using Raji-DC-SIGN cells or immature and mature dendritic cells (DCs) to capture virus. SL1, PDIM and TDM lipids were identified to be involved in DC-SIGN recognition and impairment of HIV-1 trans-infection. These findings indicate that variant strains of Mtb have differential effect on HIV-1 trans-infection with the potential to influence HIV-1 disease course in co-infected individuals.

Dectin-1-Mediated DC-SIGN Recruitment to Candida albicans Contact Sites

At host-pathogen contact sites with Candida albicans, Dectin-1 activates pro-inflammatory signaling, while DC-SIGN promotes adhesion to the fungal surface. We observed that Dectin-1 and DC-SIGN collaborate to enhance capture/retention of C. albicans under fluid shear culture conditions. Therefore, we devised a cellular model system wherein we could investigate the interaction between these two receptors during the earliest stages of host-pathogen interaction. In cells expressing both receptors, DC-SIGN was quickly recruited to contact sites (103.15% increase) but Dectin-1 did not similarly accumulate. Once inside the contact site, FRAP studies revealed a strong reduction in lateral mobility of DC-SIGN (but not Dectin-1), consistent with DC-SIGN engaging in multivalent adhesive binding interactions with cell wall mannoprotein ligands. Interestingly, in the absence of Dectin-1 co-expression, DC-SIGN recruitment to the contact was much poorer-only 35.04%. These data suggested that Dectin-1 promotes the active recruitment of DC-SIGN to the contact site. We proposed that Dectin-1 signaling activates the RHOA pathway, leading to actomyosin contractility that promotes DC-SIGN recruitment, perhaps via the formation of a centripetal actomyosin flow (AMF) directed into the contact site. Indeed, RHOA pathway inhibitors significantly reduced Dectin-1-associated DC-SIGN recruitment to the contact site. We used agent-based modeling to predict DC-SIGN transport kinetics with ("Directed + Brownian") and without ("Brownian") the hypothesized actomyosin flow-mediated transport. The Directed + Brownian transport model predicted a DC-SIGN contact site recruitment (106.64%), similar to that we observed experimentally under receptor co-expression. Brownian diffusive transport alone predicted contact site DC-SIGN recruitment of only 55.60%. However, this value was similar to experimentally observed DC-SIGN recruitment in cells without Dectin-1 or expressing Dectin-1 but treated with RHOA inhibitor, suggesting that it accurately predicted DC-SIGN recruitment when a contact site AMF would not be generated. TIRF microscopy of nascent cell contacts on glucan-coated glass revealed Dectin-1-dependent DC-SIGN and F-actin (LifeAct) recruitment kinetics to early stage contact site membranes. DC-SIGN entry followed F-actin with a temporal lag of 8.35 ± 4.57 s, but this correlation was disrupted by treatment with RHOA inhibitor. Thus, computational and experimental evidence provides support for the existence of a Dectin-1/RHOA-dependent AMF that produces a force to drive DC-SIGN recruitment to pathogen contact sites, resulting in improved pathogen capture and retention by immunocytes. These data suggest that the rapid collaborative response of Dectin-1 and DC-SIGN in early contact sties might be important for the efficient acquisition of yeast under flow conditions, such as those that prevail in circulation or mucocutaneous sites of infection.

Glycan-Modified Virus-like Particles Evoke T Helper Type 1-like Immune Responses

Dendritic cells (DCs) are highly effective antigen-presenting cells that shape immune responses. Vaccines that deliver antigen to the DCs can harness their power. DC surface lectins recognize glycans not typically present on host tissue to facilitate antigen uptake and presentation. Vaccines that target these surface lectins should offer improved antigen delivery, but their efficacy will depend on how lectin targeting influences the T cell subtypes that result. We examined how antigen structure influences uptake and signaling from the C-type lectin DC-SIGN (dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin or CD209). Virus-like particles (VLPs) were engineered from bacteriophage Qβ to present an array of mannoside ligands. The VLPs were taken up by DCs and efficiently trafficked to endosomes. The signaling that ensued depended on the ligand displayed on the VLP: only those particles densely functionalized with an aryl mannoside, Qβ-Man₅₄₀, elicited DC maturation and induced the expression of the proinflammatory cytokines characteristic of a T helper type 1 (T_H1)-like immune response. This effect was traced to differential binding to DC-SIGN at the acidic pH of the endosome. Mice immunized with a VLP bearing the aryl mannoside, and a peptide antigen (Qβ-Ova-Man₅₄₀) had antigen-specific responses, including the production of CD4⁺ T cells producing the activating cytokines interferon-γ and tumor necrosis factor-α. A T_H1 response is critical for intracellular pathogens (e.g., viruses) and cancer; thus, our data highlight the value of targeting DC lectins for antigen delivery and validate the utility of DC-targeted VLPs as vaccine vehicles that induce cellular immunity.

Identification of Important N-Linked Glycosylation Sites in the Hemagglutinin Protein and Their Functional Impact on DC-SIGN Mediated Avian Influenza H5N1 Infection

DC-SIGN, a C-type lectin mainly expressed in dendritic cells (DCs), has been reported to mediate several viral infections. We previously reported that DC-SIGN mediated H5N1 influenza A virus (AIVs) infection, however, the important DC-SIGN interaction with N-glycosylation sites remain unknown. This study aims to identify the optimal DC-SIGN interacting N-glycosylation sites in HA proteins of H5N1-AIVs. Results from NetNGlyc program analyzed the H5 hemagglutinin sequences of isolates during 2004–2020, revealing that seven and two conserved N-glycosylation sites were detected in HA1 and HA2 domain, respectively. A lentivirus pseudotyped A/Vietnam/1203/04 H5N1 envelope (H5N1-PVs) was generated which displayed an abundance of HA5 proteins on the virions via immuno-electron microscope observation. Further, H5N1-PVs or reverse-genetics (H5N1-RG) strains carrying a serial N-glycosylated mutation was generated by site-directed mutagenesis assay. Human recombinant DC-SIGN (rDC-SIGN) coated ELISA showed that H5N1-PVs bound to DC-SIGN, however, mutation on the N27Q, N39Q, and N181Q significantly reduced this binding (p < 0.05). Infectivity and capture assay demonstrated that N27Q and N39Q mutations significantly ameliorated DC-SIGN mediated H5N1 infection. Furthermore, combined mutations (N27Q&N39Q) significantly waned the interaction on either H5N1-PVs or -RG infection in cis and in trans (p < 0.01). This study concludes that N27 and N39 are two essential N-glycosylation contributing to DC-SIGN mediating H5N1 infection.

Soluble DC-SIGN isoforms: Ligands with unknown functions - A mini-review

The present study aimed to perform a mini-review of the complete soluble isoforms of Dendritic Cell-Specific Intercellular adhesion molecule-3-Grabbing Non-integrin (sDC-SIGN), their functions, and their correlation with diseases. The present review reveals the lack of studies regarding these soluble isoforms and poor understanding of the importance of the topic, considering the concordant findings on the relevant influence of sDC-SIGN in the viral and bacterial infection process, in addition to its possible use as a cancer marker.

C-type Lectin CD209L/L-SIGN and CD209/DC-SIGN: Cell Adhesion Molecules Turned to Pathogen Recognition Receptors

C-type lectin CD209/DC-SIGN and CD209L/L-SIGN proteins are distinct cell adhesion and pathogen recognition receptors that mediate cellular interactions and recognize a wide range of pathogens, including viruses such as SARS, SARS-CoV-2, bacteria, fungi and parasites. Pathogens exploit CD209 family proteins to promote infection and evade the immune recognition system. CD209L and CD209 are widely expressed in SARS-CoV-2 target organs and can contribute to infection and pathogenesis. CD209 family receptors are highly susceptible to alternative splicing and genomic polymorphism, which may influence virus tropism and transmission in vivo. The carbohydrate recognition domain (CRD) and the neck/repeat region represent the key features of CD209 family proteins that are also central to facilitating cellular ligand interactions and pathogen recognition. While the neck/repeat region is involved in oligomeric dimerization, the CRD recognizes the mannose-containing structures present on specific glycoproteins such as those found on the SARS-CoV-2 spike protein. Considering the role of CD209L and related proteins in diverse pathogen recognition, this review article discusses the recent advances in the cellular and biochemical characterization of CD209 and CD209L and their roles in viral uptake, which has important implications in understanding the host-pathogen interaction, the viral pathobiology and driving vaccine development of SARS-CoV-2.

New lipophilic glycomimetic DC-SIGN ligands: Stereoselective synthesis and SPR-based binding inhibition assays

The design and synthesis of efficient ligands for DC-SIGN is a topic of high interest, because this C-type lectin has been implicated in the early stages of many infection processes. DC-SIGN membrane-protein presents four carbohydrate-binding domains (CRD) that specifically recognize mannose and fucose. Therefore, antagonists of minimal disaccharide epitope Manα(1,2)Man, represent potentially interesting antibacterial and antiviral agents. In the recent past, we were able to develop efficient antagonists, mimics of the natural moiety, characterized by the presence of a real d-carbamannose unit which confers greater stability to enzymatic breakdown than the corresponding natural disaccharide ligand. Herein, we present the challenging stereoselective synthesis of four new amino or azide glycomimetic DC-SIGN antagonists with attractive orthogonal lipophilic substituents in C(3), C(4) or C(6) positions of the real carba unit, which were expected to establish crucial interactions with lipophilic areas of DC-SIGN CRD. The activity of the new ligands was evaluated by SPR binding inhibition assays. The interesting results obtained, allow to acquire important information about the influence of the lipophilic substituents present in specific positions of the carba scaffold. Furthermore, C(6) benzyl C(4) tosylamide pseudodisaccharide displayed a good affinity for DC-SIGN with a more favorable IC₅₀ value than those of the previously described real carba-analogues. This study provides valuable knowledge for the implementation of further structural modifications towards improved inhibitors.

Expression of DC-SIGN-like C-Type Lectin Receptors in Salmo salar

C-Type Lectin Receptors (CTLR) are involved in the activation of innate and adaptative immune responses. Among these receptors, the Dendritic Cell-Specific ICAM-3-Grabbing nonintegrin (DC-SIGN/CD209) has become a hot topic due to its ability to bind and facilitate the infections processes of several pathogens. Although well characterized in mammals, little documentation exists about the receptor in salmonid fishes. Here, we report the sequence and expression analysis of eight DC-SIGN-like genes in Salmo salar. Each receptor displays structural similarities to DC-SIGN molecules described in mammals, including internalization motifs, a neck region with heptad repeats, and a Ca⁺²-dependent carbohydrate recognition domain. The receptors are expressed in multiple tissues of fish, and fish cell lines, with differential expression upon infection with viral and bacterial pathogens. The identification of DC-SIGN-like receptors in Salmo salar provides new information regarding the structure of the immune system of salmon, potential markers for cell subsets, as well as insights into DC-SIGN conservation across species.

Lipopolysaccharide-induced DC-SIGN/TLR4 crosstalk activates NLRP3 inflammasomes via MyD88-independent signaling in gastric epithelial cells

Abnormal pattern recognition receptor (PRR) signaling plays an important role in gastric mucosal damage caused by stomach microbiota; however, the underlying molecular mechanisms remain obscure. Here, we show that DC-SIGN, a surface phenotype marker of dendritic cells, is overexpressed in gastric epithelial cells facing LPS stimulation. NLRP3 expression in gastric epithelial cells are significantly increased and related to the degree of LPS stimulation. Furthermore, DC-SIGN could interact with TLR4, promote NLRP3 and related genes expression via MyD88-independent signaling pathway and regulate the secretion of IL-1β and IL-18 in gastric epithelial cells. The results of flow cytometry analysis show that DC-SIGN primarily mediates Th1 differentiation when co-cultured with gastric epithelial cells. These results reveal that LPS-induced DC-SIGN expression modulates NLRP3 inflammasomes formation via MyD88-independent TLR4 signaling in gastric epithelial cell, and induces a Th1-predominant host immune response,these findings may indicate a new function of DC-SIGN in non-immune cells, and elucidate the diversity role of gastric epithelial cells in mechanism of immune damage caused by microbial flora.

Engineering anti-cancer nanovaccine based on antigen cross-presentation

Dendritic cells (DCs) present exogenous antigens on major histocompatibility complex (MHC) class I molecules, thereby activating CD8⁺ T cells, contributing to tumor elimination through a mechanism known as antigen cross-presentation. A variety of factors such as maturation state of DCs, co-stimulatory signals, T-cell microenvironment, antigen internalization routes and adjuvants regulate the process of DC-mediated antigen cross-presentation. Recently, the development of successful cancer immunotherapies may be attributed to the ability of DCs to cross-present tumor antigens. In this review article, we focus on the underlying mechanism of antigen cross-presentation and ways to improve antigen cross-presentation in different DC subsets. We have critically summarized the recent developments in the generation of novel nanovaccines for robust CD8⁺ T-cell response in cancer. In this context, we have reviewed nanocarriers that have been used for cancer immunotherapeutics based on antigen cross-presentation mechanism. Additionally, we have also expressed our views on the future applications of this mechanism in curing cancer.

Dendritic Cells and SARS-CoV-2 Infection: Still an Unclarified Connection

The ongoing pandemic due to Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) has so far infected about 2.42 × 107 (as at 27 August 2020) subjects with more than 820,000 deaths. It is the third zoonotic coronavirus-dependent outbreak in the last twenty years and represents a major infective threat for public health worldwide. A main aspect of the infection, in analogy to other viral infections, is the so-called "cytokine storm", an inappropriate molecular response to virus spread which plays major roles in tissue and organ damage. Immunological therapies, including vaccines and humanized monoclonal antibodies, have been proposed as major strategies for prevention and treatment of the disease. Accordingly, a detailed mechanistic knowledge of the molecular events with which the virus infects cells and induces an immunological response appears necessary. In this review, we will report details of the initial process of SARS-CoV-2 cellular entry with major emphasis on the maturation of the spike protein. Then, a particular focus will be devoted to describe the possible mechanisms by which dendritic cells, a major cellular component of innate and adaptive immune responses, may play a role in the spread of the virus in the human body and in the clinical evolution of the disease.

Correlating Glycoforms of DC-SIGN with Stability Using a Combination of Enzymatic Digestion and Ion Mobility Mass Spectrometry

The immune scavenger protein DC-SIGN interacts with glycosylated proteins and has a putative role in facilitating viral infection. How these recognition events take place with different viruses is not clear and the effects of glycosylation on the folding and stability of DC-SIGN have not been reported. Herein, we report the development and application of a mass-spectrometry-based approach to both uncover and characterise the effects of O-glycans on the stability of DC-SIGN. We first quantify the Core 1 and 2 O-glycan structures on the carbohydrate recognition and extracellular domains of the protein using sequential exoglycosidase sequencing. Using ion mobility mass spectrometry, we show how specific O-glycans, and/or single monosaccharide substitutions, alter both the overall collision cross section and the gas-phase stability of the DC-SIGN isoforms. We find that rather than the mass or length of glycoprotein modifications, the stability of DC-SIGN is better correlated with the number of glycosylation sites.