Dendritic Cell-specific Intercellular Adhesion Molecule-3-grabbing Non-integrin Research Articles

DC-SIGN and Toll-like receptor 4 mediate oxidized low-density lipoprotein-induced inflammatory responses in macrophages

The regulation of inflammatory responses by innate immune receptors is recognized as a crucial step in the development of atherosclerosis, although the precise molecular mechanisms remain to be elucidated. This study focused on illustrating the roles of dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN)- and Toll-like receptor 4 (TLR4)-regulated inflammatory responses in macrophages. We found that DC-SIGN expression levels were increased in macrophages of atherosclerotic plaques. Oxidized low-density lipoprotein (oxLDL) significantly enhanced DC-SIGN protein expression levels after a short-term exposure. Knockdown of DC-SIGN decreased expression and secretion of interleukin 1-β (IL1-β), monocyte chemo-attractant protein 1 (MCP-1), tumor necrosis factor-α (TNFα) and matrix metalloproteinase-9 (MMP-9). Immunofluorescence studies demonstrated that DC-SIGN and TLR4 co-localized in regions of the plaques. Moreover, DC-SIGN was co-expressed with TLR4 on the plasma membrane after oxLDL stimulation. The presence of an endogenous interaction and the results of the in vitro pull-down assays revealed that DC-SIGN binds directly with TLR4. We also present evidence that DC-SIGN mediates TLR4-regulated NFκB activation but not activation of p38 and JNK. Our results suggest an essential role of DC-SIGN/TLR4 signaling in macrophages in the pathogenesis of atherosclerosis.

High doses of recombinant mannan-binding lectin inhibit the binding of influenza A(H1N1)pdm09 virus with cells expressing DC-SIGN.

The pandemic influenza A (H1N1)pdm09 virus continues to be a threat to human health. Low doses of mannan-binding lectin (MBL) (<1 μg/mL) were shown not to protect against influenza A(H1N1)pdm09 infection. However, the effect of high doses of MBL has not been investigated. Dendritic cell-specific intercellular adhesion molecule-3 grabbing non-integrin (DC-SIGN) has been proposed as an alternative receptor for influenza A(H1N1)pdm09 virus. In this study, we examined the expression of DC-SIGN on DCs as well as on acute monocytic leukemia cell line, THP-1. High doses of recombinant or human MBL inhibited binding of influenza A(H1N1)pdm09 to both these cell types in the presence of complement derived from bovine serum. Further, anti-DC-SIGN monoclonal antibody inhibited binding of influenza A(H1N1)pdm09 to both DC-SIGN-expressing DCs and THP-1 cells. This study demonstrates that high doses of MBL can inhibit binding of influenza A(H1N1)pdm09 virus to DC-SIGN-expressing cells in the presence of complement. Our results suggest that DC-SIGN may be an alternative receptor for influenza A(H1N1)pdm09 virus.

Pathogenesis and Inhibition of Flaviviruses from a Carbohydrate Perspective.

Flaviviruses are enveloped, positive single stranded ribonucleic acid (RNA) viruses with various routes of transmission. While the type and severity of symptoms caused by pathogenic flaviviruses vary from hemorrhagic fever to fetal abnormalities, their general mechanism of host cell entry is similar. All pathogenic flaviviruses, such as dengue virus, yellow fever virus, West Nile virus, Japanese encephalitis virus, and Zika virus, bind to glycosaminglycans (GAGs) through the putative GAG binding sites within their envelope proteins to gain access to the surface of host cells. GAGs are long, linear, anionic polysaccharides with a repeating disaccharide unit and are involved in many biological processes, such as cellular signaling, cell adhesion, and pathogenesis. Flavivirus envelope proteins are N-glycosylated surface proteins, which interact with C-type lectins, dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN) through their glycans. In this review, we discuss both host and viral surface receptors that have the carbohydrate components, focusing on the surface interactions in the early stage of flavivirus entry. GAG-flavivirus envelope protein interactions as well as interactions between flavivirus envelope proteins and DC-SIGN are discussed in detail. This review also examines natural and synthetic inhibitors of flaviviruses that are carbohydrate-based or carbohydrate-targeting. Both advantages and drawbacks of these inhibitors are explored, as are potential strategies to improve their efficacy to ultimately help eradicate flavivirus infections.

Fasciola hepatica glycoconjugates immuneregulate dendritic cells through the Dendritic Cell-Specific Intercellular adhesion molecule-3-Grabbing Non-integrin inducing T cell anergy

Dendritic cell-specific ICAM-3 grabbing non-integrin (DC-SIGN) expressed on a variety of DCs, is a C-type lectin receptor that recognizes glycans on a diverse range of pathogens, including parasites. The interaction of DC-SIGN with pathogens triggers specific signaling events that modulate DC-maturation and activity and regulate T-cell activation by DCs. In this work we evaluate whether F. hepatica glycans can immune modulate DCs via DC-SIGN. We demonstrate that DC-SIGN interacts with F. hepatica glycoconjugates through mannose and fucose residues. We also show that mannose is present in high-mannose structures, hybrid and trimannosyl N-glycans with terminal GlcNAc. Furthermore, we demonstrate that F. hepatica glycans induce DC-SIGN triggering leading to a strong production of TLR-induced IL-10 and IL-27p28. In addition, parasite glycans induced regulatory DCs via DC-SIGN that decrease allogeneic T cell proliferation, via the induction of anergic/regulatory T cells, highlighting the role of DC-SIGN in the regulation of innate and adaptive immune responses by F. hepatica. Our data confirm the immunomodulatory properties of DC-SIGN triggered by pathogen-derived glycans and contribute to the identification of immunomodulatory glyans of helminths that might eventually be useful for the design of vaccines against fasciolosis.

Lactobacillus reuteri Surface Mucus Adhesins Upregulate Inflammatory Responses Through Interactions With Innate C-Type Lectin Receptors.

The vertebrate gut symbiont Lactobacillus reuteri exhibits strain-specific adhesion and health-promoting properties. Here, we investigated the role of the mucus adhesins, CmbA and MUB, upon interaction of L. reuteri ATCC PTA 6475 and ATCC 53608 strains with human monocyte-derived dendritic cells (moDCs). We showed that mucus adhesins increased the capacity of L. reuteri strains to interact with moDCs and promoted phagocytosis. Our data also indicated that mucus adhesins mediate anti- and pro-inflammatory effects by the induction of interleukin-10 (IL-10), tumor necrosis factor alpha (TNF-α), IL-1β, IL-6, and IL-12 cytokines. L. reuteri ATCC PTA 6475 and ATCC 53608 were exclusively able to induce moDC-mediated Th1 and Th17 immune responses. We further showed that purified MUB activates moDCs and induces Th1 polarized immune responses associated with increased IFNγ production. MUB appeared to mediate these effects via binding to C-type lectin receptors (CLRs), as shown using cell reporter assays. Blocking moDCs with antibodies against DC-specific intercellular adhesion molecule 3-grabbing non-integrin (DC-SIGN) or Dectin-2 did not affect the uptake of the MUB-expressing strain, but reduced the production of TNF-α and IL-6 by moDCs significantly, in line with the Th1 polarizing capacity of moDCs. The direct interaction between MUB and CLRs was further confirmed by atomic force spectroscopy. Taken together these data suggest that mucus adhesins expressed at the cell surface of L. reuteri strains may exert immunoregulatory effects in the gut through modulating the Th1-promoting capacity of DCs upon interaction with C-type lectins.

Beyond attachment: Roles of DC-SIGN in dengue virus infection.

Dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN), a C-type lectin expressed on the plasma membrane by human immature dendritic cells, is a receptor for numerous viruses including Ebola, SARS and dengue. A controversial question has been whether DC-SIGN functions as a complete receptor for both binding and internalization of dengue virus (DENV) or whether it is solely a cell surface attachment factor, requiring either hand-off to another receptor or a co-receptor for internalization. To examine this question, we used 4 cell types: human immature dendritic cells and NIH3T3 cells expressing either wild-type DC-SIGN or 2 internalization-deficient DC-SIGN mutants, in which either the 3 cytoplasmic internalization motifs are silenced by alanine substitutions or the cytoplasmic region is truncated. Using confocal and super-resolution imaging and high content single particle tracking, we investigated DENV binding, DC-SIGN surface transport, endocytosis, as well as cell infectivity. DC-SIGN was found colocalized with DENV inside cells suggesting hand-off at the plasma membrane to another receptor did not occur. Moreover, all 3 DC-SIGN molecules on NIH3T3 cells supported cell infection. These results imply the involvement of a co-receptor because cells expressing the internalization-deficient mutants could still be infected.

Polymeric mannosides prevent DC-SIGN-mediated cell-infection by cytomegalovirus.

Human cytomegalovirus (HCMV) is a beta-herpesvirus with a high prevalence in the population. HCMV is asymptomatic for immunocompetent adults but is a leading cause of morbidity for new born and immunocompromised patients. It was recently shown that the envelope glycoprotein B (gB) of HCMV interacts with the Dendritic Cell-Specific ICAM-3 Grabbing Non integrin (DC-SIGN) to infect the host. In this work we developed a set of DC-SIGN blockers based on mono-, di-, tetra and polyvalent mannosides. The multivalent mannosides were designed to interact with the carbohydrate recognition domains of DC-SIGN in a chelate or bind and recapture process, and represent the first chemical antiadhesives of HCMV reported so far. Polymeric dextrans coated with triazolylheptylmannoside (THM) ligands were highly potent, blocking the gB and DC-SIGN interaction at nanomolar concentrations. The compounds were further assessed for their ability to prevent the DC-SIGN mediated HCMV infection of dendritic cells. A dextran polymer coated with an average of 902 THM ligands showed an outstanding effect in blocking the HCMV trans-infection with IC50 values down to the picomolar range (nanomolar when expressed in THM concentration). Each THM moiety on the polymer surpassed the antiadhesive effect of the methylmannoside reference by more than four orders of magnitude. The compound proved non-cytotoxic at the high concentration of 2 mM and therefore represents an interesting antiadhesive candidate against HCMV and potentially against other virus hijacking dendritic cells to infect the host.

Association of Single-Nucleotide Polymorphisms in DC-SIGN with Nasopharyngeal Carcinoma Susceptibility.

The aim of this study was to explore potential relationships of four single-nucleotide polymorphisms (SNPs) in the gene encoding dendritic cell-specific intercellular adhesion molecule 3-grabbing nonintegrin (DC-SIGN) with risk of nasopharyngeal carcinoma (NPC). The DC-SIGN SNPs rs7252229, rs4804803, rs2287886, and rs735240 were genotyped in 477 unrelated NPC patients and 561 cancer-free controls. At rs7252229, risk of NPC was significantly lower in individuals with GC (odds ratio [OR] 0.076, 95% confidence interval [CI] 0.008–0.690), GG (OR 0.056, 95%CI 0.006–0.487), or GC + GG (OR 0.059, 95%CI 0.007–0.515) than in individuals with the CC genotype, after adjusting for age, gender, smoking history, and EBV-VCA-IgA status. At rs4804803, risk of NPC was significantly higher in individuals with the genotype GG than in those with the genotype AA (adjusted OR 9.038, 95%CI 1.708–47.822). At rs735240, risk of NPC did not change significantly with genotypes AG, GG, or AG + GG after adjusting for age, gender, and smoking history. However, when data were also adjusted for EBV-VCA-IgA status, three genotypes emerged as associated with significantly higher risk of NPC than the AA genotype: AG (OR 2.976, 95%CI 1.123–7.888), GG (OR 3.314, 95%CI 1.274–8.622), or GG + AG (OR 3.191, 95%CI 1.237–8.230). Our results suggest that DC-SIGN SNPs rs7252229, rs4804803, and rs735240 may influence NPC risk in the Chinese population. The mechanisms mediating this risk require a further study.

PPAR-γ agonist pioglitazone regulates dendritic cells immunogenicity mediated by DC-SIGN via the MAPK and NF-κB pathways

Dendritic cell-specific ICAM-3 grabbing non-integrin (DC-SIGN) is a dendritic cell-specific lectin which participates in dendritic cell (DC) trafficking, antigen uptake and DC–T cell interactions at the initiation of immune responses. This study investigated whether peroxisome proliferator-activated receptor-gamma (PPAR-γ) activation in human DCs regulates the immunogenicity of DCs mediated by DC-SIGN and exploited the possible molecular mechanisms, especially focused on the signaling pathways of mitogen-activated protein kinases (MAPK) and nuclear factor-κB (NF-κB). Here, we show that the PPAR-γ agonist pioglitazone decreased DC adhesion and transmigration, and DC stimulation of T cell proliferation mediated by DC-SIGN dependent on activation of PPAR-γ, although it increased DC endocytosis independent of PPAR-γ activation. Furthermore, PPAR-γ activation by pioglitazone in DCs down-regulated the expression of DC-SIGN, which was mediated by modulating the balance of the signaling pathways of extracellular signal-regulated kinase, c-Jun N-terminal kinase and NF-κB, but not p38 MAPK. Therefore, we conclude that PPAR-γ activation in human DCs regulates the immunogenicity of DCs mediated by DC-SIGN via the pathways of MAPK and NF-κB. These findings may support the important role of these mediators in the regulation of DC-mediated inflammatory and immunologic processes.

HIV-1 gp120 Glycoprotein Interacting with Dendritic Cell-specific Intercellular Adhesion Molecule 3-grabbing Non-integrin (DC-SIGN) Down-Regulates Tight Junction Proteins to Disrupt the Blood Retinal Barrier and Increase Its Permeability

Approximately 70% of HIV-1 infected patients acquire ocular opportunistic infections and manifest eye disorders during the course of their illness. The mechanisms by which pathogens invade the ocular site, however, are unclear. Under normal circumstances, vascular endothelium and retinal pigment epithelium (RPE), which possess a well developed tight junction complex, form the blood-retinal barrier (BRB) to prevent pathogen invasion. We hypothesize that disruption of the BRB allows pathogen entry into ocular sites. The hypothesis was tested using in vitro models. We discovered that human RPE cells could bind to either HIV-1 gp120 glycoproteins or HIV-1 viral particles. Furthermore, the binding was mediated by dendritic cell-specific intercellular adhesion molecule 3-grabbing non-integrin (DC-SIGN) expressed on RPE cells. Upon gp120 binding to DC-SIGN, cellular NF-κB signaling was triggered, leading to the induction of matrix metalloproteinases, which subsequently degraded tight junction proteins and disrupted the BRB integrity. DC-SIGN knockdown or prior blocking with a specific antibody abolished gp120-induced matrix metalloproteinase expression and reduced the degradation of tight junction proteins. This study elucidates a novel mechanism by which HIV, type 1 invades ocular tissues and provides additional insights into the translocation or invasion process of ocular complication-associated pathogens.

Expression of C-type lectin receptors and Toll-like receptors in decidua of patients with unexplained recurrent spontaneous abortion.

In the present study, the mechanisms underlying the pathogenesis of unexplained recurrent spontaneous abortion (URSA) were explored. The protein and mRNA expression of two C-type lectin-like receptors (CLRs), namely dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN) and mannose receptor (MR), and two Toll-like receptors (TLRs), namely TLR2 and TLR4, in the decidua and dendritic cells (DCs) was compared between URSA patients and normal controls. URSA patients had significantly lower protein and mRNA expression of DC-SIGN and significantly higher expression of TLR2 and TLR4 in decidual tissues compared with normal controls. In addition, URSA patients had significantly higher levels of the T helper (Th) 1 cytokines interleukin (IL)-2 and interferon-γ, and significantly lower levels of the Th2 cytokines IL-10 and transforming growth factor β1 in decidual tissues compared with the control group. The TLR2 agonist synthetic triacylated lipoprotein (Pam3CSK4) and the TLR4 agonist lipopolysaccharide were used to demonstrate that TLR2 and TLR4 modulate Th1/Th2 cytokine imbalance in DC-T cell cocultures. The results suggest that the balance between CLRs and TLRs was tilted towards a TLR-dominant response in URSA patients, which may disrupt maternal-fetal immune tolerance, resulting in spontaneous abortion.

Vitamin C Attenuates Hemorrhagic Shock-induced Dendritic Cell-specific Intercellular Adhesion Molecule 3-grabbing Nonintegrin Expression in Tubular Epithelial Cells and Renal Injury in Rats.

Background:The expression of dendritic cell-specific intercellular adhesion molecule 3-grabbing nonintegrin (DC-SIGN) in renal tubular epithelial cells has been thought to be highly correlated with the occurrence of several kidney diseases, but whether it takes place in renal tissues during hemorrhagic shock (HS) is unknown. The present study aimed to investigate this phenomenon and the inhibitory effect of Vitamin C (VitC).Methods:A Sprague–Dawley rat HS model was established in vivo in this study. The expression level and location of DC-SIGN were observed in kidneys. Also, the degree of histological damage, the concentrations of tumor necrosis factor-α and interleukin-6 in the renal tissues, and the serum concentration of blood urea nitrogen and creatinine at different times (2–24 h) after HS (six rats in each group), with or without VitC treatment before resuscitation, were evaluated.Results:HS induced DC-SIGN expression in rat tubular epithelial cells. The proinflammatory cytokine concentration, histological damage scores, and functional injury of kidneys had increased. All these phenomena induced by HS were relieved when the rats were treated with VitC before resuscitation.Conclusions:The results of the present study illustrated that HS could induce tubular epithelial cells expressing DC-SIGN, and the levels of proinflammatory cytokines in the kidney tissues improved correspondingly. The results also indicated that VitC could suppress the DC-SIGN expression in the tubular epithelial cells induced by HS and alleviate the inflammation and functional injury in the kidney.

The effect of Dermatophagoides pteronyssinus group 7 allergen (Der p 7) on dendritic cells and its role in T cell polarization

The innate signaling pathway for Th2 immunity activated by inhaled allergens has not been well defined. Dendritic cells (DCs) can use their innate pattern-recognition Toll-like receptors and C-type lectin receptors to generate innate immunity and influence adaptive responses. The aim of this study was to investigate the glycoform of Dermatophagoides pteronyssinus group 7 allergen (Der p 7) and its functional interaction with dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN). Both bone marrow-derived dendritic cells (BMDCs) derived from mice and monocyte-derived DCs (MDDCs) derived from human peripheral blood mononuclear cells (PBMCs) were used to investigate the function of Der p 7. Dendritic cells derived from THP1 were used to investigate the glycol form of Der p 7. Der p 7 interacted with DC-SIGN as recognized by immunoprecipitation and glycoprotein staining, and its function was partially inhibited by deglycosylation. When BMDCs were cultured with Der p 7, the secretion of IL-6 and gene expressions of IL-6, OX40L and Jagged-1 were increased. IL4+/CD4+ T cells could be induced by Der p 7, however IFN-γ+/CD4+ T cells were down-regulated. The effects of Der p 7 on DCs were down-regulated in the presence of DC-SIGN or TLR4 antibodies and deglycosylation. rDer p 7 enhanced the DC differentiation of CD80 and CD86. The effects of Der p 7 pulsed-MDDCs on IL4+/CD4+ and IFN-γ+/CD4+ T-cell differentiation of human PBMCs were significantly increased after Der p 7 stimulation and decreased by DC-SIGN antibody inhibition. In conclusion, the Der p 7 is a glycoprotein and its function was partially through glycan binding. BMDCs could be activated by Der p 7 through TLR4 and DC-SIGN, and followed by the expression of OX40 ligand (OX40L) and Jagged-1, the expressions of IL4+/CD4+ cells were enhanced. These findings identify a previously unrecognized function of Der p 7 and establish a link between innate TLR4/C-type lectin receptors and adaptive Th2 immunity.

Human DC-SIGN binds specific human milk glycans.

Human milk glycans (HMGs) are prebiotics, pathogen receptor decoys and regulators of host physiology and immune responses. Mechanistically, human lectins (glycan-binding proteins, hGBP) expressed by dendritic cells (DCs) are of major interest, as these cells directly contact HMGs. To explore such interactions, we screened many C-type lectins and sialic acid-binding immunoglobulin-like lectins (Siglecs) expressed by DCs for glycan binding on microarrays presenting over 200 HMGs. Unexpectedly, DC-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN) showed robust binding to many HMGs, whereas other C-type lectins failed to bind, and Siglec-5 and Siglec-9 showed weak binding to a few glycans. By contrast, most hGBP bound to multiple glycans on other microarrays lacking HMGs. An α-linked fucose residue was characteristic of HMGs bound by DC-SIGN. Binding of DC-SIGN to the simple HMGs 2'-fucosyl-lactose (2'-FL) and 3-fucosyl-lactose (3-FL) was confirmed by flow cytometry to beads conjugated with 2'-FL or 3-FL, as well as the ability of the free glycans to inhibit DC-SIGN binding. 2'-FL had an IC50 of ∼1mM for DC-SIGN, which is within the physiological concentration of 2'-FL in human milk. These results demonstrate that DC-SIGN among the many hGBP expressed by DCs binds to α-fucosylated HMGs, and suggest that such interactions may be important in influencing immune responses in the developing infant.

Identification and characterization of DC-SIGN-binding glycoproteins in allergenic foods.

DC-SIGN (dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin) is a C-type lectin receptor expressed on macrophages and dendritic cells. DC-SIGN has high affinity for fucosylated glycans in several plant glycoproteins and pathogens. DC-SIGN is thought to be crucial for the development of allergic sensitization. However, the precise role of DC-SIGN in food allergy pathogenesis is not yet understood. We sought to characterize DC-SIGN-binding glycoproteins in a panel of allergenic and non-allergenic foods. Fluorescent-labeled peanut and soy extracts were used to test protein binding to human monocyte-derived dendritic cells (DCs) by flow cytometry. DC-SIGN-blocking assays were performed by incubating DCs with food extracts followed by staining with anti-DC-SIGN antibody. Using a DC-SIGN-Fc chimera, food extracts were tested for binding by ELISA and autoradiography. IgE immunoblotting was performed with pooled sera from food-allergic subjects. DC activation and maturation were assessed by flow cytometry. We demonstrate that peanut agglutinin, a minor peanut allergen, is a novel ligand for DC-SIGN. Peanut agglutinin activates DCs to induce the expression of costimulatory molecules in vitro. We present a comprehensive report on the characterization of DC-SIGN-binding proteins in common allergenic foods such as peanut, soy, tree nuts, egg, and milk. Foods that rarely induce allergy, such as pine nuts, chickpea, and corn, showed no binding to DC-SIGN. Several DC-SIGN-binding proteins show reactivity in serum IgE immunoblots. We have also identified novel non-IgE-binding proteins that interact with DC-SIGN; these proteins may be important for regulating immune responses to these foods.

Characterization of Glycoprotein-Mediated Entry of Severe Fever with Thrombocytopenia Syndrome Virus.

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging hemorrhagic fever with a high case fatality rate caused by SFTS virus (SFTSV). Effective vaccines and specific therapies for SFTS are urgently sought, and investigation into virus-host cell interactions is expected to contribute to the development of antiviral strategies. In this study, we have developed a pseudotype vesicular stomatitis virus (VSV) bearing the unmodified Gn/Gc glycoproteins (GPs) of SFTSV (SFTSVpv). We have analyzed the host cell entry of this pseudotype virus and native SFTSV. Both SFTSVpv and SFTSV exhibited high infectivity in various mammalian cell lines. The use of lysosomotropic agents indicated that virus entry occurred via pH-dependent endocytosis. SFTSVpv and SFTSV infectivity was neutralized by serial dilutions of convalescent-phase patient sera. Entry of SFTSVpv and growth of SFTSV were increased in Raji cells expressing not only the C-type lectin dendritic cell-specific intercellular adhesion molecule 3-grabbing nonintegrin (DC-SIGN) but also DC-SIGN-related (DC-SIGNR) and liver and lymph node sinusoidal endothelial cell C-type lectin (LSECtin). 25-Hydroxycholesterol (25HC), a soluble oxysterol metabolite, inhibited the cell entry of SFTSVpv and the membrane fusion of SFTSV. These results indicate that pH-dependent endocytosis of SFTSVpv and SFTSV is enhanced by attachment to certain C-type lectins. SFTSVpv is an appropriate model for the investigation of SFTSV-GP-mediated cell entry and virus neutralization at lower biosafety levels. Furthermore, 25HC may represent a potential antiviral agent against SFTS. SFTSV is a recently discovered bunyavirus associated with SFTS, a viral hemorrhagic fever with a high case fatality rate endemic to China, South Korea, and Japan. Because little is known about the characteristics of the envelope protein and entry mechanisms of SFTSV, further studies will be required for the development of a vaccine or effective therapies. In this study, we investigated the mechanism of SFTSV cell entry using SFTSVpv and the native virus. SFTSV can grow in nonsusceptible cell lines in the presence of certain C-type lectins. Moreover, 25HC, an oxysterol metabolite, may represent a potential therapeutic inhibitor of SFTSV infection.

Gp120 binding with DC-SIGN induces reactivation of HIV-1 provirus via the NF-κB signaling pathway.

The reactivation mechanism of latent human immunodeficiency virus type 1 (HIV-1) infection is unclear, especially in dendritic cells (DC). DC-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN) binds with HIV-1 and other pathogens to activate the extracellular regulated protein kinase (ERK) and nuclear factor-kappa B (NF-κB) pathways and regulate cytokine expression. We hypothesized that DC-SIGN-induced signaling pathways may activate HIV-1 provirus. To investigate this hypothesis, we generated a model by transfecting 293T cells with a DC-SIGN expression plasmid and an HIV-1 5' long terminal repeat (LTR) reporter plasmid, and then stimulated the 293T cells with HIV-1 gp120 protein, wild-type HIV-1 or VSV-G-pNL4.3 pseudotype virus (without gp120 protein). It was found that the HIV-1 5'LTR was reactivated by HIV-1 gp120 in DC-SIGN-expressing 293T cells. Then the HIV-1 chronically infected CEM-Bru cells were transfected with DC-SIGN expression plasmid and stimulated by HIV-1 gp120 protein. It was found that early and late HIV-1 provirus replication was reactivated by the HIV-1 gp120/DC-SIGN stimulation. We then investigated the involvement of the ERK, p38 mitogen-activated protein kinases and NF-κB signaling pathways in HIV-1 gp120/DC-SIGN-induced activation of HIV-1 provirus by inhibiting the pathways specifically. Our results indicated that HIV-1 gp120/DC-SIGN stimulation reactivates latent HIV-1 provirus via the NF-κB signal pathway.

Specific Neuropilins Expression in Alveolar Macrophages among Tissue-Specific Macrophages.

In the immune system, neuropilins (NRPs), including NRP-1 and NRP-2, are expressed in thymocytes, dendritic cells, regulatory T cells and macrophages. Their functions on immune cells around the neoplastic cells vary into pro-angiogenesis, tumor progression and anti-angiogenesis according to their ligands. Even though NRPs expression on malignant tumors and immune system has studied, a PubMed-based literature query did not yield any articles describing NRPs expression on tissue-specific macrophages. The aims of this study were (i) to detect NRPs expression on tissue-specific macrophages in the brain, liver, spleen, lymph node and lung; (ii) to observe NRPs expression in classes of macrophages, including alveolar macrophages (AMs), bronchial macrophages (BMs), interstitial macrophages (IMs), intravascular macrophages (IVMs) and macrophage subsets (M1, M2 and Mox) in lung; and (iii) to detect the co-expression of NRPs and dendritic cell-specific ICAM-3-grabbing nonintegrin (DC-SIGN) in AMs. Both NRPs were specifically detected in AMs among tissue-specific macrophages by immunohistochemistry (IHC). NRPs mRNA expression levels were characterized in normal lung by reverse transcriptase polymerase chain reaction (RT-PCR) and in situ-polymerase chain reaction (in situ-PCR). The expression of both NRPs was detected in AMs, BMs and IVMs by IHC. The frequency of NRPs+ AMs in lung tissue adjacent to the cancer margin was significantly higher than the frequencies in inflamed and normal lung tissue. Double and triple IHC demonstrated that NRPs are expressed on all macrophage subsets in lung. Double IHC showed co-expression of DC-SIGN and NRPs in AMs. This study demonstrated for the first time the specific expression of both NRPs in AMs among tissue-specific macrophages and their expression on M1, M2 and Mox macrophages. Furthermore, the possible origin of AMs from blood monocytes could be suggested from a co-expression of NRPs and DC-SIGN.

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

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

Reactive oxygen species production by human dendritic cells involves TLR2 and dectin-1 and is essential for efficient immune response against Mycobacteria.

Tuberculosis remains the single largest infectious disease with 10 million new cases and two million deaths that are estimated to occur yearly, more than any time in history. The intracellular replication of Mycobacterium tuberculosis (Mtb) and its spread from the lungs to other sites occur before the development of adaptive immune responses. Dendritic cells (DC) are professional antigen-presenting cells whose maturation is critical for the onset of the protective immune response against tuberculosis disease and may vary depending on the nature of the cell wall of Mtb strain. Here, we describe the role of the endogenous production of reactive oxygen species (ROS) on DC maturation and expansion of Mtb-specific lymphocytes. Here, we show that Mtb induces DC maturation through TLR2/dectin-1 by generating of ROS and through Dendritic Cell-Specific Intercellular adhesion molecule-3-Grabbing Non-integrin (DC-SIGN) in a ROS independently manner. Based on the differences observed in the ability to induce DC maturation, ROS production and lymphocyte proliferation by those Mtb families widespread in South America, i.e., Haarlem and Latin American Mediterranean and the reference strain H37Rv, we propose that variance in ROS production might contribute to immune evasion affecting DC maturation and antigen presentation.