DC-SIGN, DC-SIGNR and LSECtin: C-type lectins for infection

Reduced Expression of CLEC4G in Neurons Is Associated with Alzheimer's Disease

CLEC4G, a glycan-binding receptor, has previously been demonstrated to inhibit Aβ generation, yet its brain localization and functions in Alzheimer's disease (AD) are not clear. We explored the localization, function, and regulatory network of CLEC4G via experiments and analysis of RNA-seq databases. CLEC4G transcripts and proteins were identified in brain tissues, with the highest expression observed in neurons. Notably, AD was associated with reduced levels of CLEC4G transcripts. Bioinformatic analyses revealed interactions between CLEC4G and relevant genes such as BACE1, NPC1, PILRA, TYROBP, MGAT1, and MGAT3, all displaying a negative correlation trend. We further identified the upstream transcriptional regulators NR2F6 and XRCC4 for CLEC4G and confirmed a decrease in CLEC4G expression in APP/PS1 transgenic mice. This study highlights the role of CLEC4G in protecting against AD progression and the significance of CLEC4G for AD research and management.

The functional role of L-fucose on dendritic cell function and polarization

Despite significant advances in the development and refinement of immunotherapies administered to combat cancer over the past decades, a number of barriers continue to limit their efficacy. One significant clinical barrier is the inability to mount initial immune responses towards the tumor. As dendritic cells are central initiators of immune responses in the body, the elucidation of mechanisms that can be therapeutically leveraged to enhance their functions to drive anti-tumor immune responses is urgently needed. Here, we report that the dietary sugar L-fucose can be used to enhance the immunostimulatory activity of dendritic cells (DCs). L-fucose polarizes immature myeloid cells towards specific DC subsets, specifically cDC1 and moDC subsets. In vitro, L-fucose treatment enhances antigen uptake and processing of DCs. Furthermore, our data suggests that L-fucose-treated DCs increase stimulation of T cell populations. Consistent with our functional assays, single-cell RNA sequencing of intratumoral DCs from melanoma- and breast tumor-bearing mice confirmed transcriptional regulation and antigen processing as pathways that are significantly altered by dietary L-fucose. Together, this study provides the first evidence of the ability of L-fucose to bolster DC functionality and provides rational to further investigate how L-fucose can be used to leverage DC function in order to enhance current immunotherapy.

The research status and prospects of MUC1 in immunology

In immune processes, molecular - molecular interactions are complex. As MUC1 often appears to be an important molecule in inflammation and tumor immunity, it is necessary to summarize the leading countries, authors, journals, and the cooperation among these entities and, most importantly, to determine the main research directions related to MUC1 in this field and the associated research frontiers. A total of 3,397 related studies published from 2012-2021 were retrieved from the Web of Science core database. The search strategy is TS= (MUC1 OR Mucin-1) refined by WEB OF SCIENCE CATEGORY (IMMUNOLOGY) AND [excluding] PUBLICATION YEARS: (2022) AND DOCUMENT TYPES: (ARTICLE OR REVIEW) AND LANGUAGES: (ENGLISH) AND WEB OF SCIENCE INDEX: (Web of Science Core Collection. SCI), with a timespan of 2012 to 2021. Documented bibliometric visual analysis was performed by CiteSpace and VOSviewer. The number of studies has increased every year. There are 1,982 articles and 1,415 reviews from 89 countries and regions, 3,722 organizations, 1,042 journals, and 17,948 authors. The United States, China, and Germany are the major countries producing publications on this issue. The most published author is Finn OJ and the most influential author is June CH. The key words "chimeric antigen receptor" and "T-cell" highlight the current hot spots and future trends in this field. Research on MUC1 in the field of immunology is still evolving. Through the bibliometric analysis of the existing publications, the current research hotspots and future development trends in this field can be obtained.

Antigen cross-presentation in dendric cells: From bench to bedside

Cross-presentation (XPT) is an adaptation of the cellular process in which dendritic cells (DCs) present exogenous antigens on major histocompatibility complex (MHC) class I molecules for recognition of the cytotoxic T lymphocytes (CTL) and natural killer (NK) cells, resulting in immunity or tolerance. Recent advances in DCs have broadened our understanding of the underlying mechanisms of XPT and strengthened their application in tumor immunotherapy. In this review, we summarized the known mechanisms of XPT, including the receptor-mediated internalization of exogenous antigens, endosome escape, engagement of the other XPT-related proteins, and adjuvants, which significantly enhance the XPT capacity of DCs. Consequently, various strategies to enhance XPT can be adopted and optimized to improve outcomes of DC-based therapy.

Multivalent glycosystems for human lectins

Human lectins are involved in a wide variety of biological processes, both physiological and pathological, which have attracted the interest of the scientific community working in the glycoscience field. Multivalent glycosystems have been employed as useful tools to understand carbohydrate-lectin binding processes as well as for biomedical applications. The review shows the different scaffolds designed for a multivalent presentation of sugars and their corresponding binding studies to lectins and in some cases, their biological activities. We summarise this research by organizing based on lectin types to highlight the progression in this active field. The paper provides an overall picture of how these contributions have furnished relevant information on this topic to help in understanding and participate in these carbohydrate-lectin interactions.

The XPA Protein-Life under Precise Control

Nucleotide excision repair (NER) is a central DNA repair pathway responsible for removing a wide variety of DNA-distorting lesions from the genome. The highly choreographed cascade of core NER reactions requires more than 30 polypeptides. The xeroderma pigmentosum group A (XPA) protein plays an essential role in the NER process. XPA interacts with almost all NER participants and organizes the correct NER repair complex. In the absence of XPA's scaffolding function, no repair process occurs. In this review, we briefly summarize our current knowledge about the XPA protein structure and analyze the formation of contact with its protein partners during NER complex assembling. We focus on different ways of regulation of the XPA protein's activity and expression and pay special attention to the network of post-translational modifications. We also discuss the data that is not in line with the currently accepted hypothesis about the functioning of the XPA protein.

ACE2-Independent Alternative Receptors for SARS-CoV-2

Severe acute respiratory syndrome-related coronavirus (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19), is highly contagious and remains a major public health challenge despite the availability of effective vaccines. SARS-CoV-2 enters cells through the binding of its spike receptor-binding domain (RBD) to the human angiotensin-converting enzyme 2 (ACE2) receptor in concert with accessory receptors/molecules that facilitate viral attachment, internalization, and fusion. Although ACE2 plays a critical role in SARS-CoV-2 replication, its expression profiles are not completely associated with infection patterns, immune responses, and clinical manifestations. Additionally, SARS-CoV-2 infects cells that lack ACE2, and the infection is resistant to monoclonal antibodies against spike RBD in vitro, indicating that some human cells possess ACE2-independent alternative receptors, which can mediate SARS-CoV-2 entry. Here, we discuss these alternative receptors and their interactions with SARS-CoV-2 components for ACE2-independent viral entry. These receptors include CD147, AXL, CD209L/L-SIGN/CLEC4M, CD209/DC-SIGN/CLEC4L, CLEC4G/LSECtin, ASGR1/CLEC4H1, LDLRAD3, TMEM30A, and KREMEN1. Most of these receptors are known to be involved in the entry of other viruses and to modulate cellular functions and immune responses. The SARS-CoV-2 omicron variant exhibits altered cell tropism and an associated change in the cell entry pathway, indicating that emerging variants may use alternative receptors to escape the immune pressure against ACE2-dependent viral entry provided by vaccination against RBD. Understanding the role of ACE2-independent alternative receptors in SARS-CoV-2 viral entry and pathogenesis may provide avenues for the prevention of infection by SARS-CoV-2 variants and for the treatment of COVID-19.

Immobilization of Biantennary N-Glycans Leads to Branch Specific Epitope Recognition by LSECtin

The molecular recognition features of LSECtin toward asymmetric N-glycans have been scrutinized by NMR and compared to those occurring in glycan microarrays. A pair of positional glycan isomers (LDN3 and LDN6), a nonelongated GlcNAc4Man3 N-glycan (G0), and the minimum binding epitope (the GlcNAcβ1-2Man disaccharide) have been used to shed light on the preferred binding modes under both experimental conditions. Strikingly, both asymmetric LDN3 and LDN6 N-glycans are recognized by LSECtin with similar affinities in solution, in sharp contrast to the results obtained when those glycans are presented on microarrays, where only LDN6 was efficiently recognized by the lectin. Thus, different results can be obtained using different experimental approaches, pointing out the tremendous difficulty of translating in vitro results to the in vivo environment.

Macrophage infection, activation, and histopathological findings in ebolavirus infection

Macrophages contribute to Ebola virus disease through their susceptibility to direct infection, their multi-faceted response to ebolaviruses, and their association with pathological findings in tissues throughout the body. Viral attachment and entry factors, as well as the more recently described influence of cell polarization, shape macrophage susceptibility to direct infection. Moreover, the study of Toll-like receptor 4 and the RIG-I-like receptor pathway in the macrophage response to ebolaviruses highlight important immune signaling pathways contributing to the breadth of macrophage responses. Lastly, the deep histopathological catalogue of macrophage involvement across numerous tissues during infection has been enriched by descriptions of tissues involved in sequelae following acute infection, including: the eye, joints, and the nervous system. Building upon this knowledge base, future opportunities include characterization of macrophage phenotypes beneficial or deleterious to survival, delineation of the specific roles macrophages play in pathological lesion development in affected tissues, and the creation of macrophage-specific therapeutics enhancing the beneficial activities and reducing the deleterious contributions of macrophages to the outcome of Ebola virus disease.

Different Roles of Dendritic Cells for Chronic Rhinosinusitis Treatment According to Phenotype

Dendritic cells (DCs) are antigen-presenting cells derived from the bone marrow that play an important role in the association between the innate and adaptive immune responses. The onset and development of chronic rhinosinusitis (CRS) involve a serious imbalance in immune regulation and mechanical dysfunction caused by an abnormal remodeling process. Recent studies have shown that an increase in DCs in CRS and their function of shaping the nasal mucosal immune response may play an important role in the pathogenesis of CRS. In this review, we discuss DC subsets in mice and humans, as well as the function of DCs in the nasal sinus mucosa. In addition, the mechanism by which DCs can be used as targets for therapeutic intervention for CRS and potential future research directions are also discussed.

Novel roles of LSECtin in gastric cancer cell adhesion, migration, invasion, and lymphatic metastasis

Liver and lymph node sinusoidal endothelial cell C-type lectin (LSECtin) plays an important regulatory role in a variety of diseases, including tumors. However, the underlying mechanism of LSECtin in gastric cancer (GC) remains largely unknown. In our research, LSECtin promoted the adhesion and invasion of GC cells, and was involved in lymphatic metastasis of GC cells. Mechanistically, LSECtin promoted the adhesion, proliferation and migration of GC cells by downregulating STAT1 expression. The circular RNA circFBXL4, which is regulated by LSECtin, sponges the microRNA miR-146a-5p to regulate STAT1 expression. The promotion of GC cell proliferation, migration and invasion mediated by LSECtin was largely inhibited by circFBXL4 overexpression or miR-146a-5p silencing. Moreover, in its role as a transcription factor, STAT1 modulated the expression of FN1 and CHD4. In conclusion, LSECtin might be involved in the lymphatic metastasis of GC by upregulating the expression of FN1 and CHD4 via the circFBXL4/miR-146a-5p/STAT1 axis, possibly indicating a newly discovered pathogenic mechanism.

Identification, expression patterns, evolutionary characteristics and recombinant protein activities analysis of CD209 gene from Megalobrama amblycephala

CD209 is a type II transmembrane protein in the C-type lectin family, which is involved in the regulation of innate and adaptive immune system. Although it has been widely studied in mammals, but little has been reported about fish CD209 genes. In the present study, Megalobrama amblycephala CD209 (MaCD209) gene was cloned and characterized, its expression patterns, evolutionary characteristics, agglutinative and bacteriostatic activities were analyzed. These results showed that the open reading frame (ORF) of MaCD209 gene was 795 bp, encoding 264 aa, and the calculated molecular weight of the encoded protein was 29.7 kDa. MaCD209 was predicted to contain 2 N-glycosylation sites, 1 functional domain (C-LECT-DC-SIGN-like) and 1 transmembrane domain. Multiple sequence alignment showed that the amino acid sequence of MaCD209 was highly homologous with that of partial fishes, especially the highly conserved C-LECT-DC-SIGN-like domain and functional sites of CD209. Phylogenetic analysis showed that the CD209 genes from M. amblycephala and other cypriniformes fishes were clustered into one group, which was reliable and could be used for evolutionary analysis. Then, adaptive evolutionary analysis of teleost CD209 was conducted, and several positively selected sites were identified using site and branch-site models. Quantitative real-time PCR analysis showed that MaCD209 gene was highly expressed in the liver and heart. Moreover, the expression of MaCD209 was significantly induced upon Aeromonas hydrophila infection, with the peak levels at 4 h or 12 h post infection. The immunohistochemical analysis also revealed increased distribution of MaCD209 protein post bacterial infection. In addition, recombinant MaCD209 (rMaCD209) protein was prepared using a pET32a expression system, which showed excellent bacterial binding and agglutinative activities in a Ca²⁺-independent manner. However, rMaCD209 could only inhibit the proliferation of Escherichia coli rather than A. hydrophila. In conclusion, this study identified the MaCD209 gene, detected its expression and evolutionary characteristics, and evaluated the biological activities of rMaCD209 protein, which would provide a theoretical basis for understanding the evolution and functions of fish CD209 genes.

The Endless Wars: Severe Fever With Thrombocytopenia Syndrome Virus, Host Immune and Genetic Factors

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging arboviral infectious disease with a high rate of lethality in susceptible humans and caused by severe fever with thrombocytopenia syndrome bunyavirus (SFTSV). Currently, neither vaccine nor specific antiviral drugs are available. In recent years, given the fact that both the number of SFTS cases and epidemic regions are increasing year by year, SFTS has become a public health problem. SFTSV can be internalized into host cells through the interaction between SFTSV glycoproteins and cell receptors and can activate the host immune system to trigger antiviral immune response. However, SFTSV has evolved multiple strategies to manipulate host factors to create an optimal environment for itself. Not to be discounted, host genetic factors may be operative also in the never-ending winning or losing wars. Therefore, the identifications of SFTSV, host immune and genetic factors, and their interactions are critical for understanding the pathogenic mechanisms of SFTSV infection. This review summarizes the updated pathogenesis of SFTS with regard to virus, host immune response, and host genetic factors to provide some novel perspectives of the prevention, treatment, as well as drug and vaccine developments.

HIV-1 trans-Infection Mediated by DCs: The Tip of the Iceberg of Cell-to-Cell Viral Transmission

HIV-1 cell-to-cell transmission is key for an effective viral replication that evades immunity. This highly infectious mechanism is orchestrated by different cellular targets that utilize a wide variety of processes to efficiently transfer HIV-1 particles. Dendritic cells (DCs) are the most potent antigen presenting cells that initiate antiviral immune responses, but are also the cells with highest capacity to transfer HIV-1. This mechanism, known as trans-infection, relies on the capacity of DCs to capture HIV-1 particles via lectin receptors such as the sialic acid-binding I-type lectin Siglec-1/CD169. The discovery of the molecular interaction of Siglec-1 with sialylated lipids exposed on HIV-1 membranes has enlightened how this receptor can bind to several enveloped viruses. The outcome of these interactions can either mount effective immune responses, boost the productive infection of DCs and favour innate sensing, or fuel viral transmission via trans-infection. Here we review these scenarios focusing on HIV-1 and other enveloped viruses such as Ebola virus or SARS-CoV-2.

The key amino acids of E protein involved in early flavivirus infection: viral entry

Flaviviruses are enveloped viruses that infect multiple hosts. Envelope proteins are the outermost proteins in the structure of flaviviruses and mediate viral infection. Studies indicate that flaviviruses mainly use envelope proteins to bind to cell attachment receptors and endocytic receptors for the entry step. Here, we present current findings regarding key envelope protein amino acids that participate in the flavivirus early infection process. Among these sites, most are located in special positions of the protein structure, such as the α-helix in the stem region and the hinge region between domains I and II, motifs that potentially affect the interaction between different domains. Some of these sites are located in positions involved in conformational changes in envelope proteins. In summary, we summarize and discuss the key envelope protein residues that affect the entry process of flaviviruses, including the process of their discovery and the mechanisms that affect early infection.

Glycodendritic structures as DC-SIGN binders to inhibit viral infections

DC-SIGN, a lectin discovered two decades ago, plays a relevant role in innate immunity. Since its discovery, it has turned out to be a target for developing antiviral drugs based on carbohydrates due to its participation in the infection process of several pathogens. A plethora of carbohydrate multivalent systems using different scaffolds have been described to achieve this goal. Our group has made significant contributions to this field, which are revised herein.

Polymorphisms in the DC-SIGN gene and their association with the severity of hand, foot, and mouth disease caused by enterovirus 71

Severe hand, foot, and mouth disease (HFMD) caused by enterovirus 71 (EV71) infection is associated with high mortality and disability. DC-SIGN, a receptor for EV71, is widely distributed in dendritic cells and may influence the severity of HFMD caused by EV71 infection. This observational study attempts to explore whether single-nucleotide polymorphisms (SNPs) in DC-SIGN are related to the severity of EV71-associated HFMD. Based on linkage disequilibrium and functional predictions, two DC-SIGN SNPs were selected and tested to explore their potential association with the severity of HFMD caused by EV71 infection. Two hundred sixteen Han Chinese children with HFMD caused by EV71 were enrolled to obtain clinical data, including the severity of HFMD, serum DC-SIGN levels, and DC-SIGN SNPs. We found a significant association between the rs7248637 polymorphism (A vs. G: OR = 0.644, 95% CI = 0.515-0.806) and the severity of HFMD caused by EV71 infection, as well as the rs4804800 polymorphism (A vs. G: OR = 1.539, 95% CI =1.229-1.928). These two DC-SIGN SNPs may have an effect on the severity of HFMD caused by EV71 infection.

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.

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.

The emerging tick-borne Crimean-Congo haemorrhagic fever virus: A narrative review

Crimean-Congo Haemorrhagic Fever (CCHF) is an increasingly relevant viral zoonosis caused by the negative-sense single-stranded (ss) RNA Crimean-Congo Haemorrhagic Fever Orthonairovirus (CCHFV) (Nairoviridae family, Bunyavirales order). The viral genome is divided into three segments (L-M-S) of distinct size and functions. The infection is generally mediated by a tick vector, in particular belonging to the Hyalomma genus, and the transmission follows a tick-vertebrate-tick ecologic cycle, with asymptomatic infected animals functioning as reservoirs and amplifiers for CCHFV. Human hosts could be infected primarily through infected ticks or by contact with infected hosts or their body fluids and tissues, also in a nosocomial way and in occupational contexts. Infected symptomatic patients generally manifest a nonspecific illness, which progresses across four stages, with possibly lethal outcomes. Disease outbreaks show a widespread geographic diffusion and a highly variable mortality rate, dramatically peaking in untreated patients. The lack of an adequate animal model and the elevated virus biological risk (only manageable under biosafety level 4 conditions) represent strongly limiting factors for a better characterization of the disease and for the development of specific therapies and vaccines. The present review discusses updated information on CCHFV-related disease, including details about the virus (taxonomy, structure, life cycle, transmission modalities) and considering CCHF pathogenesis, epidemiology and current strategies (diagnostic, therapeutic and preventive).

Role of Liver-Mediated Tolerance in Nanoparticle-Based Tumor Therapy

In the last decades, the use of nanocarriers for immunotherapeutic purposes has gained a lot of attention, especially in the field of tumor therapy. However, most types of nanocarriers accumulate strongly in the liver after systemic application. Due to the default tolerance-promoting role of liver non-parenchymal cells (NPCs), Kupffer cells (KCs), liver sinusoidal endothelial cells (LSECs), and hepatic stellate cells (HSCs), their potential role on the immunological outcome of systemic nano-vaccination approaches for therapy of tumors in the liver and in other organs needs to be considered. Concerning immunological functions, KCs have been the focus until now, but recent studies have elucidated an important role of LSECs and HSCs as well. Therefore, this review aims to summarize current knowledge on the employment of nanocarriers for immunotherapeutic therapy of liver diseases and the overall role of liver NPCs in the context of nano-vaccination approaches. With regard to the latter, we discuss strategies on how to address liver NPCs, aiming to exploit and modulate their immunological properties, and alternatively how to avoid unwanted engagement of nano-vaccines by liver NPCs for tumor therapy.

TETRALEC, Artificial Tetrameric Lectins: A Tool to Screen Ligand and Pathogen Interactions

C-type lectin receptor (CLR)/carbohydrate recognition occurs through low affinity interactions. Nature compensates that weakness by multivalent display of the lectin carbohydrate recognition domain (CRD) at the cell surface. Mimicking these low affinity interactions in vitro is essential to better understand CLR/glycan interactions. Here, we present a strategy to create a generic construct with a tetrameric presentation of the CRD for any CLR, termed TETRALEC. We applied our strategy to a naturally occurring tetrameric CRD, DC-SIGNR, and compared the TETRALEC ligand binding capacity by synthetic N- and O-glycans microarray using three different DC-SIGNR constructs i) its natural tetrameric counterpart, ii) the monomeric CRD and iii) a dimeric Fc-CRD fusion. DC-SIGNR TETRALEC construct showed a similar binding profile to that of its natural tetrameric counterpart. However, differences observed in recognition of low affinity ligands underlined the importance of the CRD spatial arrangement. Moreover, we further extended the applications of DC-SIGNR TETRALEC to evaluate CLR/pathogens interactions. This construct was able to recognize heat-killed Candida albicans by flow cytometry and confocal microscopy, a so far unreported specificity of DC-SIGNR. In summary, the newly developed DC-SIGNR TETRALEC tool proved to be useful to unravel novel CLR/glycan interactions, an approach which could be applied to other CLRs.

DC-SIGN Expression in Intestinal Epithelial Cells Regulates Sepsis-Associated Acute Intestinal Injury Via Activating ERK1/2-NF-κB/P65 Signaling

OBJECTIVE

The aim of the study was to investigate the role of dendritic cell-specific intercellular adhesion molecule 3-grabbing nonintegrin (DC-SIGN) in intestinal epithelial cells (IECs) in regulating sepsis-induced acute intestinal injury and systemic inflammatory response.

METHODS

To induce sepsis condition, Male C57BL/6 mice were exposed to cecal ligation and puncture (CLP) in vivo, whereas a normal human IECs line (FHs74Int) was stimulated with lipopolysaccharide (LPS) in vitro. DC-SIGN siRNA pretreatment was used to knock down DC-SIGN expression both in vivo and in vitro. The expression of DC-SIGN was detected by western blot and immunohistochemistry. The expression of total and phosphorylation of ERK1/2 and NF-κB/p65 was examined by western blot. The levels of cytokines in serum and culture supernatant were measured by ELISA. The survival rate and organ injures of septic mice were also assessed.

RESULTS

In vivo, DC-SIGN expression in mouse IECs was time-dependently upregulated by CLP. CLP-induced phosphorylation of ERK1/2 and NF-κB/p65 was effectively inhibited by DC-SIGN siRNA pretreatment, leading to the decrease of systemic inflammatory cytokines (TNF-α, IL-1β, IL-6, IL-10, and IFN-γ), which alleviated multiple organ injuries and increased the survival rate of septic mice. In vitro, DC-SIGN expression in FHs74Int was significantly upregulated by LPS stimulation in a time- and dose-dependent manner. DC-SIGN knockdown abolished LPS-induced ERK1/2 and NF-κB/p65 phosphorylation, resulting in the decrease of cytokines release by FHs74Int.

CONCLUSIONS

Sepsis-induced DC-SIGN expression in IECs plays a significant role in regulating acute intestinal injury and systemic inflammatory response. The inhibition of DC-SIGN exhibited protective effects on sepsis-associated organ injury and systemic inflammation.

CLEC4M overexpression inhibits progression and is associated with a favorable prognosis in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) remains the most common malignant cancer worldwide. Numerous studies have indicated that C-type lectin domain family 4 member M (CLEC4M) is associated with tumor progression; however, the biological functions of CLEC4M in HCC have not been investigated. In the present study, CLEC4M overexpression was observed to be associated with a favorable patient overall, relapse-free, progression-free and disease-specific survival by using the KMplot™ database. The present study then concentrated specifically on the functions of CLEC4M by performing cell counting kit-8 proliferation, 5-Ethynyl-2′-deoxyuridine and flow cytometric assays. CLEC4M overexpression inhibited proliferation and enhanced apoptosis in Huh7 and PLC/PRF/5 cells. Furthermore, the results demonstrated by using western blotting that CLEC4M overexpression inhibited the Janus kinase 1/signal transducer and activator of transcription 3 pathway, which is involved in various types of tumors including HCC. In conclusion, the present study reported that CLEC4M may be considered as a novel indicator of HCC and may provide a theoretical basis for improving the survival of patients with HCC.

Advances in the Immunology and Genetics of Leprosy

Leprosy, a disease caused by the intracellular parasite Mycobacterium leprae or Mycobacterium lepromatosis, has affected humans for more than 4,000 years and is a stigmatized disease even now. Since clinical manifestations of leprosy patients present as an immune-related spectrum, leprosy is regarded as an ideal model for studying the interaction between host immune response and infection; in fact, the landscape of leprosy immune responses has been extensively investigated. Meanwhile, leprosy is to some extent a genetic disease because the genetic factors of hosts have long been considered major contributors to this disease. Many immune-related genes have been discovered to be associated with leprosy. However, immunological and genetic findings have rarely been studied and discussed together, and as a result, the effects of gene variants on leprosy immune responses and the molecular mechanisms of leprosy pathogenesis are largely unknown. In this context, we summarized advances in both the immunology and genetics of leprosy and discussed the perspective of the combination of immunological and genetic approaches in studying the molecular mechanism of leprosy pathogenesis. In our opinion, the integrating of immunological and genetic approaches in the future may be promising to elucidate the molecular mechanism of leprosy onset and how leprosy develops into different types of leprosy.

XPA: DNA Repair Protein of Significant Clinical Importance

The nucleotide excision repair (NER) pathway is activated in response to a broad spectrum of DNA lesions, including bulky lesions induced by platinum-based chemotherapeutic agents. Expression levels of NER factors and resistance to chemotherapy has been examined with some suggestion that NER plays a role in tumour resistance; however, there is a great degree of variability in these studies. Nevertheless, recent clinical studies have suggested Xeroderma Pigmentosum group A (XPA) protein, a key regulator of the NER pathway that is essential for the repair of DNA damage induced by platinum-based chemotherapeutics, as a potential prognostic and predictive biomarker for response to treatment. XPA functions in damage verification step in NER, as well as a molecular scaffold to assemble other NER core factors around the DNA damage site, mediated by protein–protein interactions. In this review, we focus on the interacting partners and mechanisms of regulation of the XPA protein. We summarize clinical oncology data related to this DNA repair factor, particularly its relationship with treatment outcome, and examine the potential of XPA as a target for small molecule inhibitors.

CLEC4M is associated with poor prognosis and promotes cisplatin resistance in NSCLC patients

Cisplatin-based chemotherapy is the foundation of treatment for major non-small cell lung cancer (NSCLC) patients. However, cisplatin resistance is still a challenging issue, and the molecular mechanisms underlying this resistance remain to be fully explored. CLEC4M, a Ca²⁺-dependent C-type lectin, has recently been found to correlate with tumourigenesis. This study mainly focused on whether CLEC4M impacts clinical prognosis and how CLEC4M contributes to cisplatin resistance in NSCLC. Our results found that CLEC4M was correlated with poor prognosis in patients with lung cancer. In addition, a positive association between CLEC4M expression and the IC50 values of cisplatin was found, which suggests that CLEC4M may impact cisplatin sensitivity. In vitro results from cultured A549 and H1299 cells confirmed that CLEC4M could enhance cisplatin resistance, while CLEC4M knockdown led to higher sensitivity to cisplatin in these cells. Further experiments showed that the underlying mechanisms included inhibition of cisplatin-induced cell apoptosis by CLEC4M and improved DNA repair capacity by upregulating XPA and ERCC1 expression. In addition, CLEC4M was able to promote cell migration with or without cisplatin treatment. Collectively, these findings suggest the potential clinical significance of CLEC4M inhibition in overcoming cisplatin resistance in NSCLC patients.

Different Associations between DC-SIGN Promoter-336G/A (rs4804803) Polymorphism with Severe Dengue in Asians and South-Central Americans: a Meta-Analysis

Objective: This study was conducted to identify the association between rs4804803 polymorphism in DC-SIGN with the susceptibility of severe dengue. Methods: A comprehensive search was conducted to identify all eligible papers in PubMed, Web of Science, China National Knowledge Infrastructure (CNKI), and Google Scholar. Odds ratios (ORs) and corresponding 95% confidence intervals (95% CIs) were used to assess the association. Subgroup analyses were performed by ethnicity. Sensitivity analyses were performed through employing different statistical models (fixed versus random effect model). Results: A total of nine papers and 12 studies, with 1520 severe dengue and 1496 clinical dengue infection were included. The overall meta-analysis revealed significant associations between rs4804803 and severe dengue under the recession (GG versus GA/AA: OR = 0.44, 95%CI, 0.23–0.82) and a codominant model (GG versus AA: OR = 0.43, 95%CI, 0.23–0.81), but sensitivity analysis indicated that the significant pooled ORs were not robust. The subgroup analysis suggested that the carrier of G in rs4804803 was a risk factor for severe dengue under dominant (GG/GA versus AA: OR = 1.86,95%CI, 1.01–3.45), superdominant (GA versus GG/AA: OR = 1.81,95%CI, 1.02–3.21) and a codominant (GA versus AA: OR=1.82,95%CI, 1.02–3.26) models in Asians, while it was a protective factor for severe dengue in South-central Americans under recessive (GG versus GA/AA: OR = 0.27,95%CI, 0.10–0.70) and codominant (GG versus AA: OR=0.24,95%CI, 0.09–0.64) models. The results from subgroup analysis were robust. Conclusions: Dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN) promoter-336G/A (rs4804803) polymorphism is association with severe dengue, and it acts in different directions for Asians and South-central Americans.

Surface (S) Layer Proteins of Lactobacillus acidophilus Block Virus Infection via DC-SIGN Interaction

Alphaviruses and flaviviruses are important human pathogens that include Chikungunya virus (CHIKV), Dengue virus (DENV), and Zika virus (ZIKV), which can cause diseases in humans ranging from arthralgia to hemorrhagic fevers and microcephaly. It was previously shown that treatment with surface layer (S-layer) protein, present on the bacterial cell-envelope of Lactobacillus acidophilus, is able to inhibit viral and bacterial infections by blocking the pathogen’s interaction with DC-specific intercellular adhesion molecule 3-grabbing non-integrin (DC-SIGN), a trans-membrane protein that is a C-type calcium-dependent lectin. DC-SIGN is known to act as an attachment factor for several viruses including alphaviruses and flaviviruses. In the present study, we used alphaviruses as a model system to dissect the mechanism of S-layer inhibition. We first evaluated the protective effect of S-layer using 3T3 cells, either wild type or stably expressing DC-SIGN, and infecting with the alphaviruses Semliki Forest virus (SFV) and CHIKV and the flaviviruses ZIKV and DENV. DC-SIGN expression significantly enhanced infection by all four viruses. Treatment of the cells with S-layer prior to infection decreased infectivity of all viruses only in cells expressing DC-SIGN. In vitro ELISA experiments showed a direct interaction between S-layer and DC-SIGN; however, confocal microscopy and flow cytometry demonstrated that S-layer binding to the cells was independent of DC-SIGN expression. S-layer protein prevented SFV binding and internalization in DC-SIGN-expressing cells but had no effect on virus binding to DC-SIGN-negative cells. Inhibition of virus binding occurred in a time-dependent manner, with a significant reduction of infection requiring at least a 30-min pre-incubation of S-layer with DC-SIGN-expressing cells. These results suggest that S-layer has a different mechanism of action compared to mannan, a common DC-SIGN-binding compound that has an immediate effect in blocking viral infection. This difference could reflect slower kinetics of S-layer binding to the DC-SIGN present at the plasma membrane (PM). Alternatively, the S-layer/DC-SIGN interaction may trigger the activation of signaling pathways that are required for the inhibition of viral infection. Together our results add important information relevant to the potential use of L. acidophilus S-layer protein as an antiviral therapy.

Microbe-focused glycan array screening platform

Interactions between glycans and glycan binding proteins are essential for numerous processes in all kingdoms of life. Glycan microarrays are an excellent tool to examine protein-glycan interactions. Here, we present a microbe-focused glycan microarray platform based on oligosaccharides obtained by chemical synthesis. Glycans were generated by combining different carbohydrate synthesis approaches including automated glycan assembly, solution-phase synthesis, and chemoenzymatic methods. The current library of more than 300 glycans is as diverse as the mammalian glycan array from the Consortium for Functional Glycomics and, due to its microbial focus, highly complementary. This glycan platform is essential for the characterization of various classes of glycan binding proteins. Applications of this glycan array platform are highlighted by the characterization of innate immune receptors and bacterial virulence factors as well as the analysis of human humoral immunity to pathogenic glycans.

Induction of Tolerogenic Dendritic Cells by Endogenous Biomolecules: An Update

The importance of microenvironment on dendritic cell (DC) function and development has been strongly established during the last two decades. Although DCs with general tolerogenic characteristics have been isolated and defined as a particular sub-population, it is predominantly their unequivocal biological plasticity, which allows for unparalleled responsiveness to environmental ques and shaping of their tolerogenic characteristics when interacting with tolerance-inducing biomolecules. Dendritic cells carry receptors for a great number of endogenous factors, which, after ligation, can importantly influence the development of their activation state. For this there is ample evidence merely by observation of DC characteristics isolated from various anatomical niches, e.g., the greater immunosuppressive potential of DCs isolated from intestine compared to conventional blood DCs. Endogenous biomolecules present in these environments most likely play a major role as a determinant of their phenotype and function. In this review, we will concisely summarize in what way various, tolerance-inducing endogenous factors influence DC biology, the development of their particular tolerogenic state and their subsequent actions in context of immune response inhibition and induction of regulatory T cells.

Correlation of variable repeat number in the neck regions of DC-SIGN and DC-SIGNR with susceptibility to nasopharyngeal carcinoma in a Chinese population

Objective

To evaluate the potential association of variations in the number of tandem repeats in the dendritic cell-specific intercellular adhesion molecule-3 grabbing nonintegrin (DC-SIGN) and dendritic cell-specific intercellular adhesion molecule-3 grabbing nonintegrin-related (DC-SIGNR) neck region with susceptibility to nasopharyngeal carcinoma (NPC).

Methods

Variations in the number of repeats in the genotypes and alleles in the neck region of DC-SIGN/DC-SIGNR were analyzed in 477 unrelated NPC patients and 561 cancer-free controls.

Results

Genotypes and alleles in the DC-SIGN neck region did not differ significantly between NPC patients and controls, but the 9-repeat genotype in the DC-SIGNR neck region was significantly more frequent among patients (OR 1.339, 95% CI 1.018–1.760, P=0.037). The association between this genotype and NPC remained significant after adjusting for sex, age, smoking history, and presence of immunoglobulin against Epstein–Barr virus viral capsid antigen (OR 1.625, 95% CI 1.134–2.329, P=0.0082).

Conclusion

These results suggest that genotypes/alleles in the DC-SIGN neck region are not associated with NPC susceptibility, whereas the 9-repeat variant in the neck region of DC-SIGNR may increase the risk of NPC.

On-Chip Screening of a Glycomimetic Library with C-Type Lectins Reveals Structural Features Responsible for Preferential Binding of Dectin-2 over DC-SIGN/R and Langerin

A library of mannose‐ and fucose‐based glycomimetics was synthesized and screened in a microarray format against a set of C‐type lectin receptors (CLRs) that included DC‐SIGN, DC‐SIGNR, langerin, and dectin‐2. Glycomimetic ligands able to interact with dectin‐2 were identified for the first time. Comparative analysis of binding profiles allowed their selectivity against other CLRs to be probed.

Early Events in Japanese Encephalitis Virus Infection: Viral Entry

Japanese encephalitis virus (JEV), a mosquito-borne zoonotic flavivirus, is an enveloped positive-strand RNA virus that can cause a spectrum of clinical manifestations, ranging from mild febrile illness to severe neuroinvasive disease. Today, several killed and live vaccines are available in different parts of the globe for use in humans to prevent JEV-induced diseases, yet no antivirals are available to treat JEV-associated diseases. Despite the progress made in vaccine research and development, JEV is still a major public health problem in southern, eastern, and southeastern Asia, as well as northern Oceania, with the potential to become an emerging global pathogen. In viral replication, the entry of JEV into the cell is the first step in a cascade of complex interactions between the virus and target cells that is required for the initiation, dissemination, and maintenance of infection. Because this step determines cell/tissue tropism and pathogenesis, it is a promising target for antiviral therapy. JEV entry is mediated by the viral glycoprotein E, which binds virions to the cell surface (attachment), delivers them to endosomes (endocytosis), and catalyzes the fusion between the viral and endosomal membranes (membrane fusion), followed by the release of the viral genome into the cytoplasm (uncoating). In this multistep process, a collection of host factors are involved. In this review, we summarize the current knowledge on the viral and cellular components involved in JEV entry into host cells, with an emphasis on the initial virus-host cell interactions on the cell surface.

DC-SIGN Binding Contributed by an Extra N-Linked Glycosylation on Japanese Encephalitis Virus Envelope Protein Reduces the Ability of Viral Brain Invasion

The major structural envelope (E) protein of Japanese encephalitis virus (JEV) facilitates cellular binding/entry and is the primary target of neutralizing antibodies. JEV E protein has one N-linked glycosylation site at N154 (G2 site), but the related dengue virus E protein has two glycosylation sites at N67 (G1 site) and N153 (G2 site). We generated three recombinant JEVs with different glycosylation patterns on the E protein. As compared with wild-type (WT) JEV with G2 glycosylation, viral growth in culture cells as well as neurovirulence and neuroinvasiveness in challenged mice were reduced when infected with the G1 mutant (E-D67N/N154A) with glycosylation shifted to G1 site, and the G0 mutant (E-N154A) with non-glycosylation. The G1G2 mutant (E-D67N), with E-glycosylation on both G1 and G2 sites, showed potent in vitro viral replication and in vivo neurovirulence, but reduced neuroinvasiveness. Furthermore, the JEV mutants with G1 glycosylation showed enhanced DC-SIGN binding, which may then lead to reduced brain invasion and explain the reason why WT JEV is devoid of this G1 site of glycosylation. Overall, the patterns of N-linked glycosylation on JEV E proteins may affect viral interaction with cellular lectins and contribute to viral replication and pathogenesis.

IL-7-induced phosphorylation of the adaptor Crk-like and other targets

IL-7 is required for T cell differentiation and mature T cell homeostasis and promotes pro-B cell proliferation and survival. Tyrosine phosphorylation plays a central role in IL-7 signaling. We identified by two-dimensional electrophoresis followed by anti-phosphotyrosine immunoblotting and mass spectrometry sixteen tyrosine phosphorylated proteins from the IL-7-dependent cell line D1. IL-7 stimulation induced the phosphorylation of the proteins STI1, ATIC and hnRNPH, involved in pathways related to survival, proliferation and gene expression, respectively, and increased the phosphorylation of CrkL, a member of a family of adaptors including the highly homologous Crk isoforms CrkII and CrkI, important in multiple signaling pathways. We observed an increased phosphorylation of CrkL in murine pro-B cells and in murine and human T cells. In addition, IL-7 increased the association of CrkL with the transcription factor Stat5, essential for IL-7 pro-survival activity. The selective tyrosine kinase inhibitor Imatinib. counteracted the IL-7 pro-survival effect in D1 cells and decreased CrkL phosphorylation. These data suggested that CrkL could play a pro-survival role in IL-7-mediated signaling. We observed that pro-B cells also expressed, in addition to CrkL, the Crk isoforms CrkII and CrkI and therefore utilized pro-B cells conditionally deficient in all three to evaluate the role of these proteins. The observation that the IL-7 pro-survival effect was reduced in Crk/CrkL conditionally-deficient pro-B cells further pointed to a pro-survival role of these adaptors. To further evaluate the role of these proteins, gene expression studies were performed in Crk/CrkL conditionally-deficient pro-B cells. IL-7 decreased the transcription of the receptor LAIR1, which inhibits B cell proliferation, in a Crk/CrkL-dependent manner, suggesting that the Crk family of proteins may promote pro-B cell proliferation. Our data contribute to the understanding of IL-7 signaling and suggest the involvement of Crk family proteins in pathways promoting survival and proliferation.

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.

Myeloid C-Type Lectin Receptors in Viral Recognition and Antiviral Immunity

Recognition of viral glycans by pattern recognition receptors (PRRs) in innate immunity contributes to antiviral immune responses. C-type lectin receptors (CLRs) are PRRs capable of sensing glycans present in viral pathogens to activate antiviral immune responses such as phagocytosis, antigen processing and presentation, and subsequent T cell activation. The ability of CLRs to elicit and shape adaptive immunity plays a critical role in the inhibition of viral spread within the host. However, certain viruses exploit CLRs for viral entry into host cells to avoid immune recognition. To block CLR interactions with viral glycoproteins, antiviral strategies may involve the use of multivalent glycan carrier systems. In this review, we describe the role of CLRs in antiviral immunity and we highlight their dual function in viral clearance and exploitation by viral pathogens.

C-type lectins facilitate tumor metastasis

Metastasis, a life-threatening complication of cancer, leads to the majority of cases of cancer-associated mortality. Unfortunately, the underlying molecular and cellular mechanisms of cancer metastasis remain to be fully elucidated. C-type lectins are a large group of proteins, which share structurally homologous carbohydrate-recognition domains (CRDs) and possess diverse physiological functions, including inflammation and antimicrobial immunity. Accumulating evidence has demonstrated the contribution of C-type lectins in different steps of the metastatic spread of cancer. Notably, a substantial proportion of C-type lectins, including selectins, mannose receptor (MR) and liver and lymph node sinusoidal endothelial cell C-type lectin, are important molecular targets for the formation of metastases in vitro and in vivo. The present review summarizes what has been found regarding C-type lectins in the lymphatic and hematogenous metastasis of cancer. An improved understanding the role of C-type lectins in cancer metastasis provides a comprehensive perspective for further clarifying the molecular mechanisms of cancer metastasis and supports the development of novel C-type lectins-based therapies the for prevention of metastasis in certain types of cancer.

Glycan-protein interactions in viral pathogenesis

The surfaces of host cells and viruses are decorated by complex glycans, which play multifaceted roles in the dynamic interplay between the virus and the host including viral entry into host cell, modulation of proteolytic cleavage of viral proteins, recognition and neutralization of virus by host immune system. These roles are mediated by specific multivalent interactions of glycans with their cognate proteins (generally termed as glycan-binding proteins or GBPs or lectins). The advances in tools and technologies to chemically synthesize and structurally characterize glycans and glycan-GBP interactions have offered several insights into the role of glycan-GBP interactions in viral pathogenesis and have presented opportunities to target these interactions for novel antiviral therapeutic or vaccine strategies. This review covers aspects of role of host cell surface glycan receptors and viral surface glycans in viral pathogenesis and offers perspectives on how to employ various analytical tools to target glycan-GBP interactions.

Functionally aberrant dendritic cell subsets and expression of DC-SIGN differentiate acute from chronic HBV infection

BACKGROUND

Dendritic cells (DCs) promote pathogen recognition, uptake and presentation of antigen through DC-specific intercellular adhesion molecule 3-grabbing non-integrin (DC-SIGN) and toll-like receptors (TLRs).

AIMS AND OBJECTIVES

We aimed to study temporal changes in DCs, TLRs and DC-SIGN during acute viral hepatitis B (AVHB) infection and compare them to chronic (CHB) and to investigate the earliest time point of activated pathogen recognition receptors in hepatitis B viral infection.

METHODS

We measured the frequencies of circulating myeloid (mDC) and plasmacytoid (pDC) dendritic cells and IFN-α production along with the expression of DC-SIGN and Toll Like Receptors (TLR's) in HBV patients at different time points. Also investigated in healthy volunteers, the dynamic changes in TLRs expression after receiving hepatitis B vaccine.

RESULTS

On follow-up of AVHB patients, we found the mDC population was significantly higher at week 4 and 6 (p < 0.02, 0.01), whereas the pDC population was unchanged at week 6 compared with week 0. Whereas frequencies of mDCs and pDCs were found to be elevated in AVHB and CHB patients than HC (p < 0.00 and 0.01, respectively) but was comparable among AVHB vs CHB. The DCs in CHB patients were functionally impaired with significantly low IFN-α production and low DCSIGN expression (p < 0.04 and 0.00, respectively). Even after stimulation by TLR agonists, no change was found in IFN-α production in CHB patients. MyD88 and IL-6, IFN-α mRNA levels were also found down-regulated. Interestingly, on follow-up after HBV vaccine, TLRs expression was found high at day 3 after vaccination.

DISCUSSION

The initial events of immune activation might be responsible for modulating immune response. These novel observations would pave the way for the development of antiviral strategies for chronic HBV infection.

Influence of Core β-1,2-Xylosylation on Glycoprotein Recognition by Murine C-type Lectin Receptors and Its Impact on Dendritic Cell Targeting

Targeting antigens to dendritic cell subsets is a promising strategy to enhance the efficacy of vaccines. C-type lectin receptors (CLRs) expressed by dendritic cells are particularly attractive candidates since CLR engagement may promote cell uptake and may further stimulate antigen presentation and subsequent T cell activation. While most previous approaches have involved antibody-mediated CLR-targeting, glycan-based CLR targeting has become more and more attractive in recent years. In the present study, we show that small structural glycan modifications may markedly influence CLR recognition, dendritic cell targeting, and subsequent T cell activation. A biantennary N-glycan (G0) and its analogous O-2 core xylosylated N-glycan (XG0) were synthesized, covalently conjugated to the model antigen ovalbumin, and analyzed for binding to a set of murine CLR-Fc fusion proteins using lectin microarray. To evaluate whether the differential binding of G0 and XG0 to CLRs impacted dendritic cell targeting, uptake studies using murine dendritic cells were performed. Finally, effects of the ovalbumin glycoconjugates on T cell activation were measured in a dendritic cell/T cell cocultivation assay. Our results highlight the utility of glycan-based dendritic cell targeting and demonstrate that small structural differences may have a major impact on dendritic cell targeting efficacy.

DC-SIGN and L-SIGN Are Attachment Factors That Promote Infection of Target Cells by Human Metapneumovirus in the Presence or Absence of Cellular Glycosaminoglycans

It is well established that glycosaminoglycans (GAGs) function as attachment factors for human metapneumovirus (HMPV), concentrating virions at the cell surface to promote interaction with other receptors for virus entry and infection. There is increasing evidence to suggest that multiple receptors may exhibit the capacity to promote infectious entry of HMPV into host cells; however, definitive identification of specific transmembrane receptors for HMPV attachment and entry is complicated by the widespread expression of cell surface GAGs. pgsA745 Chinese hamster ovary (CHO) cells are deficient in the expression of cell surface GAGs and resistant to HMPV infection. Here, we demonstrate that the expression of the Ca(2+)-dependent C-type lectin receptor (CLR) DC-SIGN (CD209L) or L-SIGN (CD209L) rendered pgsA745 cells permissive to HMPV infection. Unlike infection of parental CHO cells, HMPV infection of pgsA745 cells expressing DC-SIGN or L-SIGN was dynamin dependent and inhibited by mannan but not by pretreatment with bacterial heparinase. Parental CHO cells expressing DC-SIGN/L-SIGN also showed enhanced susceptibility to dynamin-dependent HMPV infection, confirming that CLRs can promote HMPV infection in the presence or absence of GAGs. Comparison of pgsA745 cells expressing wild-type and endocytosis-defective mutants of DC-SIGN/L-SIGN indicated that the endocytic function of CLRs was not essential but could contribute to HMPV infection of GAG-deficient cells. Together, these studies confirm a role for CLRs as attachment factors and entry receptors for HMPV infection. Moreover, they define an experimental system that can be exploited to identify transmembrane receptors and entry pathways where permissivity to HMPV infection can be rescued following the expression of a single cell surface receptor.

IMPORTANCE

On the surface of CHO cells, glycosaminoglycans (GAGs) function as the major attachment factor for human metapneumoviruses (HMPV), promoting dynamin-independent infection. Consistent with this, GAG-deficient pgaA745 CHO cells are resistant to HMPV. However, expression of DC-SIGN or L-SIGN rendered pgsA745 cells permissive to dynamin-dependent infection by HMPV, although the endocytic function of DC-SIGN/L-SIGN was not essential for, but could contribute to, enhanced infection. These studies provide direct evidence implicating DC-SIGN/L-SIGN as an alternate attachment factor for HMPV attachment, promoting dynamin-dependent infection via other unknown receptors in the absence of GAGs. Moreover, we describe a unique experimental system for the assessment of putative attachment and entry receptors for HMPV.

S-layer proteins from Lactobacillus sp. inhibit bacterial infection by blockage of DC-SIGN cell receptor

Many species of Lactobacillus sp. possess Surface(s) layer proteins in their envelope. Among other important characteristics S-layer from Lactobacillus acidophilus binds to the cellular receptor DC-SIGN (Dendritic Cell-Specific Intercellular adhesion molecule-3-Grabbing Non-integrin; CD209), which is involved in adhesion and infection of several families of bacteria. In this report we investigate the activity of new S-layer proteins from the Lactobacillus family (Lactobacillus acidophilus, Lactobacillus brevis, Lactobacillus helveticus and Lactobacillus kefiri) over the infection of representative microorganisms important to human health. After the treatment of DC-SIGN expressing cells with these proteins, we were able to diminish bacterial infection by up to 79% in both gram negative and mycobacterial models. We discovered that pre-treatment of the bacteria with S-layers from Lactobacillus acidophilus and Lactobacillus brevis reduced bacteria viability but also prevent infection by the pathogenic bacteria. We also proved the importance of the glycosylation of the S-layer from Lactobacillus kefiri in the binding to the receptor and thus inhibition of infection. This novel characteristic of the S-layers proteins may contribute to the already reported pathogen exclusion activity for these Lactobacillus probiotic strains; and might be also considered as a novel enzymatic antimicrobial agents to inhibit bacterial infection and entry to host cells.

Antibody recognition of HIV and dengue glycoproteins

The last 6 years have witnessed an explosion of discoveries at the interface of glycobiology and immunology. Binding of clustered oligosaccharides has turned out to be a very frequent mode by which human antibodies have developed broadly neutralizing activity against HIV. This mini-review will cover many recent developments in the HIV antibody field, as well as emerging data about Dengue broadly neutralizing antibodies.

Sweet complementarity: the functional pairing of glycans with lectins

Carbohydrates establish the third alphabet of life. As part of cellular glycoconjugates, the glycans generate a multitude of signals in a minimum of space. The presence of distinct glycotopes and the glycome diversity are mapped by sugar receptors (antibodies and lectins). Endogenous (tissue) lectins can read the sugar-encoded information and translate it into functional aspects of cell sociology. Illustrated by instructive examples, each glycan has its own ligand properties. Lectins with different folds can converge to target the same epitope, while intrafamily diversification enables functional cooperation and antagonism. The emerging evidence for the concept of a network calls for a detailed fingerprinting. Due to the high degree of plasticity and dynamics of the display of genes for lectins the validity of extrapolations between different organisms of the phylogenetic tree yet is inevitably limited.

Analysis of the entry mechanism of Crimean-Congo hemorrhagic fever virus, using a vesicular stomatitis virus pseudotyping system

Crimean-Congo hemorrhagic fever (CCHF) is a tick-borne disease causing severe hemorrhagic symptoms with a nearly 30 % case-fatality rate in humans. The experimental use of CCHF virus (CCHFV), which causes CCHF, requires high-biosafety-level (BSL) containment. In contrast, pseudotyping of various viral glycoproteins (GPs) onto vesicular stomatitis virus (VSV) can be used in facilities with lower BSL containment, and this has facilitated studies on the viral entry mechanism and the measurement of neutralizing activity, especially for highly pathogenic viruses. In the present study, we generated high titers of pseudotyped VSV bearing the CCHFV envelope GP and analyzed the mechanisms involved in CCHFV infection. A partial deletion of the CCHFV GP cytoplasmic domain increased the titer of the pseudotyped VSV, the entry mechanism of which was dependent on the CCHFV envelope GP. Using the pseudotype virus, DC-SIGN (a calcium-dependent [C-type] lectin cell-surface molecule) was revealed to enhance viral infection and act as an entry factor for CCHFV.