Novel member of the CD209 (DC-SIGN) gene family in primates

Depletion and Dysfunction of Dendritic Cells: Understanding SARS-CoV-2 Infection

Uncontrolled severe acute respiratory syndrome-coronavirus (SARS-CoV)-2 infection is closely related to disorders of the innate immune and delayed adaptive immune systems. Dendritic cells (DCs) “bridge” innate immunity and adaptive immunity. DCs have important roles in defending against SARS-CoV-2 infection. In this review, we summarize the latest research concerning the role of DCs in SARS-CoV-2 infection. We focus on the complex interplay between DCs and SARS-CoV-2: pyroptosis-induced activation; activation of the renin–angiotensin–aldosterone system; and activation of dendritic cell-specific intercellular adhesion molecule 3-grabbing non-integrin. We also discuss the decline in DC number, the impaired antigen-presentation capability, and the reduced production of type-I interferon of DCs in severe SARS-CoV-2 infection. In addition, we discuss the potential mechanisms for pathological activation of DCs to understand the pattern of SARS-CoV-2 infection. Lastly, we provide a brief overview of novel vaccination and immunotherapy strategies based on DC targeting to overcome SARS-CoV-2 infection.

Human gene polymorphisms and their possible impact on the clinical outcome of SARS-CoV-2 infection

The SARS-CoV-2 pandemic has become one of the most serious health concerns globally. Although multiple vaccines have recently been approved for the prevention of coronavirus disease 2019 (COVID-19), an effective treatment is still lacking. Our knowledge of the pathogenicity of this virus is still incomplete. Studies have revealed that viral factors such as the viral load, duration of exposure to the virus, and viral mutations are important variables in COVID-19 outcome. Furthermore, host factors, including age, health condition, co-morbidities, and genetic background, might also be involved in clinical manifestations and infection outcome. This review focuses on the importance of variations in the host genetic background and pathogenesis of SARS-CoV-2. We will discuss the significance of polymorphisms in the ACE-2, TMPRSS2, vitamin D receptor, vitamin D binding protein, CD147, glucose-regulated protein 78 kDa, dipeptidyl peptidase-4 (DPP4), neuropilin-1, heme oxygenase, apolipoprotein L1, vitamin K epoxide reductase complex 1 (VKORC1), and immune system genes for the clinical outcome of COVID-19.

M2 Macrophage Co-Expression Factors Correlate With Immune Phenotype and Predict Prognosis of Bladder Cancer

Purpose

Therapeutic targets of tumor-associated macrophages have been discovered and used clinically as immunotherapy. M2 macrophages are tumor-associated macrophages that promote cancer progression. This article explores the related factors and the effects of type M2 macrophages.

Method

We obtained bladder cancer (BC) sequencing data from TCGA and GSE31189. We used the CIBERSORT algorithm calculate M2 macrophage proportions among 22 type immune cells. The Estimate package was used to measure BC purity. M2 macrophage-related genes were selected using WGCNA. Receiver operating characteristic curves and Kaplan–Meier analyses were performed to determine the risk score, conducted for M2 macrophage-related factors. The Pearson test was used to determine the correlation among M2 macrophage-related genes, clinical phenotype, immune phenotype and tumor mutation burden (TMB). The TIMER database was used to calculate correlations among M2 macrophages and other cancers.

Results

Expression of four M2 macrophages co-expressed genes (CD163, CD209, CSF1, MMD) positively correlated with infiltration of M2 macrophages, which were enriched in the negative regulation of immune system process and the positive regulation of tumor necrosis factor production. M2 macrophage-related factors are robust biomarkers for predicting the BC and immune phenotypes. The Cox regression model built on these four co-expression factors showed a close correlation with outcome (AUC = 0.64). The four co-expression factors negatively correlated outcome and TMB.

Conclusion

Four co-expressed genes promote high levels of infiltration of type M2 macrophages in the negative regulation of immune system processes and the positive regulation of tumor necrosis factor production processes. These co-expressed genes and the biological process they involve might suggest new strategies for regulation of chemotaxis in M2 macrophages.

Common Molecular Alterations in Canine Oligodendroglioma and Human Malignant Gliomas and Potential Novel Therapeutic Targets

Spontaneous canine (Canis lupus) oligodendroglioma (ODG) holds tremendous potential as an immunocompetent large animal model of human malignant gliomas (MG). However, the feasibility of utilizing this model in pre-clinical studies depends on a thorough understanding of the similarities and differences of the molecular pathways associated with gliomas between the two species. We have previously shown that canine ODG has an immune landscape and expression pattern of commonly described oncogenes similar to that of human MG. In the current study, we performed a comprehensive analysis of canine ODG RNAseq data from 4 dogs with ODG and 2 normal controls to identify highly dysregulated genes in canine tumors. We then evaluated the expression of these genes in human MG using Xena Browser, a publicly available database. STRING-database inquiry was used in order to determine the suggested protein associations of these differentially expressed genes as well as the dysregulated pathways commonly enriched by the protein products of these genes in both canine ODG and human MG. Our results revealed that 3,712 (23%) of the 15,895 differentially expressed genes demonstrated significant up- or downregulation (log2-fold change > 2.0). Of the 3,712 altered genes, ~50% were upregulated (n = 1858) and ~50% were downregulated (n = 1854). Most of these genes were also found to have altered expression in human MG. Protein association and pathway analysis revealed common pathways enriched by members of the up- and downregulated gene categories in both species. In summary, we demonstrate that a similar pattern of gene dysregulation characterizes both human MG and canine ODG and provide additional support for the use of the canine model in order to therapeutically target these common genes. The results of such therapeutic targeting in the canine model can serve to more accurately predict the efficacy of anti-glioma therapies in human patients.

Expression and Immunogenicity of Two Recombinant Fusion Proteins Comprising Foot-and-Mouth Disease Virus Structural Protein VP1 and DC-SIGN-Binding Glycoproteins

Improving vaccine immunogenicity by targeting antigens to dendritic cells has recently emerged as a new design strategy in vaccine development. In this study, the VP1 gene of foot-and-mouth disease virus (FMDV) serotype A was fused with the gene encoding human immunodeficiency virus (HIV) membrane glycoprotein gp120 or C2-V3 domain of hepatitis C virus (HCV) envelope glycoprotein E2, both of which are DC-SIGN-binding glycoproteins. After codon optimization, the VP1 protein and the two recombinant VP1-gp120 and VP1-E2 fusion proteins were expressed in Sf9 insect cells using the insect cell-baculovirus expression system. Western blotting showed that the VP1 protein and two recombinant VP1-gp120 and VP1-E2 fusion proteins were correctly expressed in the Sf9 insect cells and had good reactogenicity. Guinea pigs were then immunized with the purified proteins, and the resulting humoral and cellular immune responses were analyzed. The VP1-gp120 and VP1-E2 fusion proteins induced significantly higher specific anti-FMDV antibody levels than the VP1 protein and stronger cell-mediated immune responses. This study provides a new perspective for the development of novel FMDV subunit vaccines.

Cross-Linking of a CD4-Mimetic Miniprotein with HIV-1 Env gp140 Alters Kinetics and Specificities of Antibody Responses against HIV-1 Env in Macaques

Evaluation of the epitope specificities, locations (systemic or mucosal), and effector functions of antibodies elicited by novel HIV-1 immunogens engineered to improve exposure of specific epitopes is critical for HIV-1 vaccine development. Utilizing an array of humoral assays, we evaluated the magnitudes, epitope specificities, avidities, and functions of systemic and mucosal immune responses elicited by a vaccine regimen containing Env cross-linked to a CD4-mimetic miniprotein (gp140-M64U1) in rhesus macaques. Cross-linking of gp140 Env to M64U1 resulted in earlier increases of both the magnitude and avidity of the IgG binding response than those with Env protein alone. Notably, IgG binding responses at an early time point correlated with antibody-dependent cellular cytotoxicity (ADCC) function at the peak immunity time point, which was higher for the cross-linked Env group than for the Env group. In addition, the cross-linked Env group developed higher IgG responses against a linear epitope in the gp120 C1 region of the HIV-1 envelope glycoprotein. These data demonstrate that structural modification of the HIV-1 envelope immunogen by cross-linking of gp140 with the CD4-mimetic M64U1 elicited an earlier increase of binding antibody responses and altered the specificity of the IgG responses, correlating with the rise of subsequent antibody-mediated antiviral functions.IMPORTANCE The development of an efficacious HIV-1 vaccine remains a global priority to prevent new cases of HIV-1 infection. Of the six HIV-1 efficacy trials to date, only one has demonstrated partial efficacy, and immune correlate analysis of that trial revealed a role for binding antibodies and antibody Fc-mediated effector functions. New HIV-1 envelope immunogens are being engineered to selectively expose the most vulnerable and conserved sites on the HIV-1 envelope, with the goal of eliciting antiviral antibodies. Evaluation of the humoral responses elicited by these novel immunogen designs in nonhuman primates is critical for understanding how to improve upon immunogen design to inform further testing in human clinical trials. Our results demonstrate that structural modifications of Env that aim to mimic the CD4-bound conformation can result in earlier antibody elicitation, altered epitope specificity, and increased antiviral function postimmunization.

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.

Dendritic cell expression of the C-type lectin receptor CD209a: A novel innate parasite-sensing mechanism inducing Th17 cells that drive severe immunopathology in murine schistosome infection

Following infection with the trematode helminth Schistosoma mansoni, CBA mice develop severe parasite egg-induced hepatic granulomatous inflammation as well as prominent CD4(+) T helper 17 (Th17) cell responses driven by dendritic cell (DC)-derived IL-1β and IL-23. By comparison, C57BL/6 mice develop mild hepatic immunopathology, egg stimulation of DCs does not result in IL-1β and IL-23 production, and Th17 cells fail to develop. To investigate the reasons for strain-specific differences in antigen presenting cell (APC) reactivity to eggs, we performed a comparative gene profiling analysis of normal bone marrow-derived DCs (BMDCs) and found that CBA DCs display markedly elevated expression of C-type lectin receptors (CLRs). In particular, expression of CD209a, a murine homologue of human DC-specific ICAM-3-grabbing non-integrin (DC-SIGN, CD209), was strikingly higher in CBA than BL/6 DCs. High CD209a surface expression was observed in various CBA splenic and granuloma APC subpopulations; however, only DCs, and not macrophages, B cells or neutrophils, were able to induce Th17 cell differentiation in response to schistosome eggs. Lentiviral gene silencing in CBA DCs, and over-expression in BL/6 DCs, demonstrated CD209a to be critical for egg-induced DC IL-1β and IL-23 production necessary for Th17 cell differentiation and expansion. These findings reveal a novel innate parasite-sensing mechanism promoting CD4(+) Th17 cells that mediate severe immunopathology in schistosomiasis.

Expression of dendritic cell lysosome-associated membrane protein and dendritic cell-specific intercellular adhesion molecule-3 grabbing nonintegrin in condyloma acuminatum lesions

OBJECTIVE

Retrospective, observational study to explore the role of dendritic cells (DCs) in condyloma acuminatum lesions (genital warts) and their relationship with duration of the disease.

METHODS

Condyloma acuminatum lesion samples were collected from male patients with the condition and compared with normal foreskin samples from male volunteers. Cellular locations of dendritic cell lysosome-associated membrane protein (DC-LAMP) and dendritic cell-specific intercellular adhesion molecule-3 grabbing nonintegrin (DC-SIGN) were detected using immunohistochemistry. Levels of both proteins were determined using Western blot analysis; levels of their corresponding mRNAs were measured using reverse transcription-polymerase chain reaction.

RESULTS

The mRNA and protein levels of DC-LAMP and DC-SIGN were both significantly higher in condyloma acuminatum lesions (n = 30 samples) compared with normal skin samples (n = 13). Levels of DC-LAMP and DC-SIGN protein and duration of disease were inversely correlated.

CONCLUSIONS

DC-LAMP and DC-SIGN may be involved in the pathogenesis of condyloma acuminatum. Their levels were inversely correlated with the duration of disease, suggesting that DCs might be involved in human papillomavirus clearance.

Co-evolution of primate SAMHD1 and lentivirus Vpx leads to the loss of the vpx gene in HIV-1 ancestor

Cross-species transmission and adaptation of simian immunodeficiency viruses (SIVs) to humans have given rise to human immunodeficiency viruses (HIVs). HIV type 1 (HIV-1) and type 2 (HIV-2) were derived from SIVs that infected chimpanzee (SIVcpz) and sooty mangabey (SIVsm), respectively. The HIV-1 restriction factor SAMHD1 inhibits HIV-1 infection in human myeloid cells and can be counteracted by the Vpx protein of HIV-2 and the SIVsm lineage. However, HIV-1 and its ancestor SIVcpz do not encode a Vpx protein and HIV-1 has not evolved a mechanism to overcome SAMHD1-mediated restriction. Here we show that the co-evolution of primate SAMHD1 and lentivirus Vpx leads to the loss of the vpx gene in SIVcpz and HIV-1. We found evidence for positive selection of SAMHD1 in orangutan, gibbon, rhesus macaque, and marmoset, but not in human, chimpanzee and gorilla that are natural hosts of Vpx-negative HIV-1, SIVcpz and SIVgor, respectively, indicating that vpx drives the evolution of primate SAMHD1. Ancestral host state reconstruction and temporal dynamic analyses suggest that the most recent common ancestor of SIVrcm, SIVmnd, SIVcpz, SIVgor and HIV-1 was a SIV that had a vpx gene; however, the vpx gene of SIVcpz was lost approximately 3643 to 2969 years ago during the infection of chimpanzees. Thus, HIV-1 could not inherit the lost vpx gene from its ancestor SIVcpz. The lack of Vpx in HIV-1 results in restricted infection in myeloid cells that are important for antiviral immunity, which could contribute to the AIDS pandemic by escaping the immune responses.

The origin and evolution of variable number tandem repeat of CLEC4M gene in the global human population

CLEC4M is a C-type lectin gene serving as cell adhesion receptor and pathogen recognition receptor. It recognizes several pathogens of important public health concern. In particular, a highly polymorphic variable number tandem repeat (VNTR) at the neck-region of CLEC4M had been associated with genetic predisposition to some infectious diseases. To gain insight into the origin and evolution of this VNTR in CLEC4M, we studied 21 Africans, 20 Middle Easterns, 35 Europeans, 38 Asians, 13 Oceania, and 18 Americans (a total of 290 chromosomes) from the (Human Genome Diversity Panel) HGDP-CEPH panel; these samples covered most of alleles of this VNTR locus present in human populations. We identified a limited number of haplotypes among the basic repeat subunits that is 69 base pairs in length. Only 8 haplotypes were found. Their sequence identities were determined in the 290 chromosomes. VNTR alleles of different repeat length (from 4 to 9 repeats) were analyzed for composition and orientation of these subunits. Our results showed that the subunit configuration of the same repeat number of VNTR locus from different populations were, in fact, virtually identical. It implies that most of the VNTR alleles existed before dispersion of modern humans outside Africa. Further analyses indicate that the present diversity profile of this locus in worldwide populations is generated from the effect of migration of different tribes and neutral evolution. Our findings do not support the hypothesis that the origin of the VNTR alleles were arisen by independent (separate) mutation events and caused by differential allele advantage and natural selection as suggested by previous report based on SNP data.

DC-SIGN Family of Receptors

In the immune system, C-type lectins and CTLDs have been shown to act both as adhesion and as pathogen recognition receptors. The Dendritic cell-specific ICAM-3 grabbing non-integrin (DC-SIGN) and its homologs in human and mouse represent an important C-type lectin family. DC-SIGN contains a lectin domain that recognizes in a Ca²⁺-dependent manner carbohydrates such as mannose-containing structures present on glycoproteins such as ICAM-2 and ICAM-3. DC-SIGN is a prototype C-type lectin organized in microdomains, which have their role as pathogen recognition receptors in sensing microbes. Although the integrin LFA-1 is a counter-receptor for both ICAM-2 and ICAM-3 on DC, DC-SIGN is the high affinity adhesion receptor for ICAM-2/-3. While cell–cell contact is a primary function of selectins, collectins are specialized in recognition of pathogens. Interestingly, DC-SIGN is a cell adhesion receptor as well as a pathogen recognition receptor. As adhesion receptor, DC-SIGN mediates the contact between dendritic cells (DCs) and T lymphocytes, by binding to ICAM-3, and mediates rolling of DCs on endothelium, by interacting with ICAM-2. As pathogen receptor, DC-SIGN recognizes a variety of microorganisms, including viruses, bacteria, fungi and several parasites (Cambi et al. 2005). The natural ligands of DC-SIGN consist of mannose oligosaccharides or fucose-containing Lewis-type determinants. In this chapter, we shall focus on the structure and functions of DC-SIGN and related CTLDs in the recognition of pathogens, the molecular and structural determinants that regulate the interaction with pathogen-associated molecular patterns. The heterogeneity of carbohydrate residues exposed on cellular proteins and pathogens regulates specific binding of DC-expressed C-type lectins that contribute to the diversity of immune responses created by DCs (van Kooyk et al. 2003a; Cambi et al. 2005).

Incorporation of podoplanin into HIV released from HEK-293T cells, but not PBMC, is required for efficient binding to the attachment factor CLEC-2

BACKGROUND

Platelets are associated with HIV in the blood of infected individuals and might modulate viral dissemination, particularly if the virus is directly transmitted into the bloodstream. The C-type lectin DC-SIGN and the novel HIV attachment factor CLEC-2 are expressed by platelets and facilitate HIV transmission from platelets to T-cells. Here, we studied the molecular mechanisms behind CLEC-2-mediated HIV-1 transmission.

RESULTS

Binding studies with soluble proteins indicated that CLEC-2, in contrast to DC-SIGN, does not recognize the viral envelope protein, but a cellular factor expressed on kidney-derived 293T cells. Subsequent analyses revealed that the cellular mucin-like membranous glycoprotein podoplanin, a CLEC-2 ligand, was expressed on 293T cells and incorporated into virions released from these cells. Knock-down of podoplanin in 293T cells by shRNA showed that virion incorporation of podoplanin was required for efficient CLEC-2-dependent HIV-1 interactions with cell lines and platelets. Flow cytometry revealed no evidence for podoplanin expression on viable T-cells and peripheral blood mononuclear cells (PBMC). Podoplanin was also not detected on HIV-1 infected T-cells. However, apoptotic bystander cells in HIV-1 infected cultures reacted with anti-podoplanin antibodies, and similar results were obtained upon induction of apoptosis in a cell line and in PBMCs suggesting an unexpected link between apoptosis and podoplanin expression. Despite the absence of detectable podoplanin expression, HIV-1 produced in PBMC was transmitted to T-cells in a CLEC-2-dependent manner, indicating that T-cells might express an as yet unidentified CLEC-2 ligand.

CONCLUSIONS

Virion incorporation of podoplanin mediates CLEC-2 interactions of HIV-1 derived from 293T cells, while incorporation of a different cellular factor seems to be responsible for CLEC-2-dependent capture of PBMC-derived viruses. Furthermore, evidence was obtained that podoplanin expression is connected to apoptosis, a finding that deserves further investigation.

The DC-SIGN of zebrafish: insights into the existence of a CD209 homologue in a lower vertebrate and its involvement in adaptive immunity

Dendritic cell-specific ICAM-3-grabbing nonintegrin (DC-SIGN/CD209) has become hot topic in recent studies because of its important roles in immune responses and immune escape. CD209 has been well characterized in humans and several other mammals, but little documentation exists about it in lower vertebrates. This is the first report on the identification and functional characterization of a fish DC-SIGN/CD209 molecule. The zebrafish DC-SIGN/CD209 cDNA translates into 343 aa organized into three domains structurally conserved among vertebrates. An EPN motif essential for interacting with Ca(2+) and for recognizing mannose-containing motifs has been identified. Several conserved motifs crucial for internalization and signal transduction are also present within the cytoplasmic tail. Phylogenetic analysis supports the hypothesis that CD209 family members diverged from a common ancestor. The expression of DC-SIGN/CD209 in immune-related tissues can be significantly up-regulated by exogenous Ags and IL-4. This molecule associates with various APCs, including macrophages, B lymphocytes, and a possible dendritic cell-like (CD83(+)/CD80(+)CD209(+)) population. Functionally, T cell activation, Ab (IgM) production, and bacterial vaccination-elicited immunoprotection can be dramatically inhibited by a CD209 blockade after stimulation with keyhole limpet hemocyanin (KLH) in vivo or challenged with Aeromonas hydrophila, suggesting that DC-SIGN/CD209 in zebrafish is crucial for the initiation and development of adaptive immunity. Phagocytosis analysis showed that DC-SIGN/CD209 does not participate in the uptake of KLH Ag, suggesting that other mechanisms might exist that underlie DC-SIGN/CD209 involvement. We hope that the present study will contribute to a better cross-species understanding of the evolutionary history of the DC-SIGN/CD209 family.

A murine DC-SIGN homologue contributes to early host defense against Mycobacterium tuberculosis

The C-type lectin dendritic cell-specific intercellular adhesion molecule-3 grabbing nonintegrin (DC-SIGN) mediates the innate immune recognition of microbial carbohydrates. We investigated the function of this molecule in the host response to pathogens in vivo, by generating mouse lines lacking the DC-SIGN homologues SIGNR1, SIGNR3, and SIGNR5. Resistance to Mycobacterium tuberculosis was impaired only in SIGNR3-deficient animals. SIGNR3 was expressed in lung phagocytes during infection, and interacted with M. tuberculosis bacilli and mycobacterial surface glycoconjugates to induce secretion of critical host defense inflammatory cytokines, including tumor necrosis factor (TNF). SIGNR3 signaling was dependent on an intracellular tyrosine-based motif and the tyrosine kinase Syk. Thus, the mouse DC-SIGN homologue SIGNR3 makes a unique contribution to protection of the host against a pulmonary bacterial pathogen.

Evolutionary trajectories of primate genes involved in HIV pathogenesis

The current availability of five complete genomes of different primate species allows the analysis of genetic divergence over the last 40 million years of evolution. We hypothesized that the interspecies differences observed in susceptibility to HIV-1 would be influenced by the long-range selective pressures on host genes associated with HIV-1 pathogenesis. We established a list of human genes (n = 140) proposed to be involved in HIV-1 biology and pathogenesis and a control set of 100 random genes. We retrieved the orthologous genes from the genome of humans and of four nonhuman primates (Pan troglodytes, Pongo pygmaeus abeli, Macaca mulatta, and Callithrix jacchus) and analyzed the nucleotide substitution patterns of this data set using codon-based maximum likelihood procedures. In addition, we evaluated whether the candidate genes have been targets of recent positive selection in humans by analyzing HapMap Phase 2 single-nucleotide polymorphisms genotyped in a region centered on each candidate gene. A total of 1,064 sequences were used for the analyses. Similar median K(A)/K(S) values were estimated for the set of genes involved in HIV-1 pathogenesis and for control genes, 0.19 and 0.15, respectively. However, genes of the innate immunity had median values of 0.37 (P value = 0.0001, compared with control genes), and genes of intrinsic cellular defense had K(A)/K(S) values around or greater than 1.0 (P value = 0.0002). Detailed assessment allowed the identification of residues under positive selection in 13 proteins: AKT1, APOBEC3G, APOBEC3H, CD4, DEFB1, GML, IL4, IL8RA, L-SIGN/CLEC4M, PTPRC/CD45, Tetherin/BST2, TLR7, and TRIM5alpha. A number of those residues are relevant for HIV-1 biology. The set of 140 genes involved in HIV-1 pathogenesis did not show a significant enrichment in signals of recent positive selection in humans (intraspecies selection). However, we identified within or near these genes 24 polymorphisms showing strong signatures of recent positive selection. Interestingly, the DEFB1 gene presented signatures of both interspecies positive selection in primates and intraspecies recent positive selection in humans. The systematic assessment of long-acting selective pressures on primate genomes is a useful tool to extend our understanding of genetic variation influencing contemporary susceptibility to HIV-1.

Identification of a porcine DC-SIGN-related C-type lectin, porcine CLEC4G (LSECtin), and its order of intron removal during splicing: comparative genomic analyses of the cluster of genes CD23/CLEC4G/DC-SIGN among mammalian species

Human CLEC4G (previously named LSECtin), DC-SIGN, and L-SIGN are three important C-type lectins capable of mediating viral and bacterial pathogen recognitions. These three genes, together with CD23, form a lectin gene cluster at chromosome 19p13.3. In this study, we have experimentally identified the cDNA and the gene encoding porcine CLEC4G (pCLEC4G). Full-length pCLEC4G cDNA encodes a type II transmembrane protein of 290 amino acids. pCLEC4G gene has the same gene structure as the human and the predicted bovine, canis, mouse and rat CLEC4G genes with nine exons. A multi-species-conserved site at the extreme 3'-untranslated region of CLEC4G mRNAs was predicted to be targeted by microRNA miR-350 in domesticated animals and by miR-145 in primates, respectively. We detected pCLEC4G mRNA expression in liver, lymph node and spleen tissues. We also identified a series of sequential intermediate products of pCLEC4G pre-mRNA during splicing from pig liver. The previously unidentified porcine CD23 cDNA containing the complete coding region was subsequently cloned and found to express in spleen, thymus and lymph node. Furthermore, we compared the chromosomal regions syntenic to the human cluster of genes CD23/CLEC4G/DC-SIGN/L-SIGN in representative mammalian species including primates, domesticated animal, rodents and opossum. The L-SIGN homologues do not exist in non-primates mammals. The evolutionary processes of the gene cluster, from marsupials to primates, were proposed based upon their genomic structures and phylogenetic relationships.

Porcine DC-SIGN: molecular cloning, gene structure, tissue distribution and binding characteristics

DC-SIGN, a human C-type lectin, is involved in the transmission of many enveloped viruses. Here we report the cloning and characterization of the cDNA and gene encoding porcine DC-SIGN (pDC-SIGN). The full-length pDC-SIGN cDNA encodes a type II transmembrane protein of 240 amino acids. Phylogenetic analysis revealed that pDC-SIGN, together with bovine, canis and equine DC-SIGN, are more closely related to mouse SIGNR7 and SIGNR8 than to human DC-SIGN. pDC-SIGN has the same gene structure as bovine, canis DC-SIGN and mouse SIGNR8 with eight exons. pDC-SIGN mRNA expression was detected in pig spleen, thymus, lymph node, lung, bone marrow and muscles. pDC-SIGN protein was found to express on the surface of monocyte-derived macrophages and dendritic cells, alveolar macrophages, lymph node sinusoidal macrophage-like, dendritic-like and endothelial cells but not of monocytes, peripheral blood lymphocytes or lymph node lymphocytes. A BHK cell line stably expressing pDC-SIGN binds to human ICAM-3 and ICAM-2 immunoadhesins in a calcium-dependent manner, and enhances the transmission of porcine reproductive and respiratory syndrome virus (PRRSV) to target cells in trans. The results will help better understand the biological role(s) of DC-SIGN family in innate immunity during the evolutionary process.

DC-SIGN and L-SIGN: the SIGNs for infection

Two closely related trans-membrane C-type lectins dendritic cell-specific intracellular adhesion molecules (ICAM)-3 grabbing non-integrin (DC-SIGN or CD209) and liver/lymph node-specific ICAM-3 grabbing non-integrin (L-SIGN also known as DC-SIGNR, CD209L or CLEC4M) directly recognize a wide range of micro-organisms of major impact on public health. Both genes have long been considered to share similar overall structure and ligand-binding characteristics. This review presents more recent biochemical and structural studies, which show that they have distinct ligand-binding properties and different physiological functions. Of importance in both these genes is the presence of an extra-cellular domain consisting of an extended neck region encoded by tandem repeats that support the carbohydrate-recognition domain, which plays a crucial role in influencing the pathogen-binding properties of these receptors. The notable difference between these two genes is in this extra-cellular domain. Whilst the tandem-neck-repeat region remains relatively constant size for DC-SIGN, there is considerable polymorphism for L-SIGN. Homo-oligomerization of the neck region of L-SIGN has been shown to be important for high-affinity ligand binding, and heterozygous expression of the polymorphic variants of L-SIGN in which neck lengths differ could thus affect ligand-binding affinity. Functional studies on the effect of this tandem-neck-repeat region on pathogen-binding, as well as genetic association studies for various infectious diseases and among different populations, are discussed. Worldwide demographic data of the tandem-neck-repeat region showing distinct differences in the neck-region allele and genotype distribution among different ethnic groups are presented. These findings support the neck region as an excellent candidate acting as a functional target for selective pressures exerted by pathogens.

The evolutionary history of the CD209 (DC-SIGN) family in humans and non-human primates

The CD209 gene family that encodes C-type lectins in primates includes CD209 (DC-SIGN), CD209L (L-SIGN) and CD209L2. Understanding the evolution of these genes can help understand the duplication events generating this family, the process leading to the repeated neck region and identify protein domains under selective pressure. We compiled sequences from 14 primates representing 40 million years of evolution and from three non-primate mammal species. Phylogenetic analyses used Bayesian inference, and nucleotide substitutional patterns were assessed by codon-based maximum likelihood. Analyses suggest that CD209 genes emerged from a first duplication event in the common ancestor of anthropoids, yielding CD209L2 and an ancestral CD209 gene, which, in turn, duplicated in the common Old World primate ancestor, giving rise to CD209L and CD209. K(A)/K(S) values averaged over the entire tree were 0.43 (CD209), 0.52 (CD209L) and 0.35 (CD209L2), consistent with overall signatures of purifying selection. We also assessed the Toll-like receptor (TLR) gene family, which shares with CD209 genes a common profile of evolutionary constraint. The general feature of purifying selection of CD209 genes, despite an apparent redundancy (gene absence and gene loss), may reflect the need to faithfully recognize a multiplicity of pathogen motifs, commensals and a number of self-antigens.

In vivo targeting of DC-SIGN-positive antigen-presenting cells in a nonhuman primate model

In vivo targeting of antigen-presenting cells (APCs) with antigens coupled to antibodies directed against APC-specific endocytic receptors is a simple and a promising approach to induce or modulate immune responses against those antigens. In a recent in vitro study, we have shown that targeting of APCs with an antigen coupled to an antibody directed against the endocytic receptor DC-SIGN effectively induces a specific immune response against that antigen. The aim of the present study was to determine the ability of the murine antihuman DC-SIGN antibody AZN-D1 to target APCs in a cynomolgus macaque model after its administration in vivo. Immunohistochemical analysis demonstrated that macaques injected intravenously with AZN-D1 have AZN-D1-targeted APCs in all lymph nodes (LNs) tested and in the liver. DC-SIGN-positive cells were mainly located in the medullary sinuses of the LNs and in the hepatic sinusoids in the liver. No unlabeled DC-SIGN molecules were found in the LN of AZN-D1-injected macaques. Morphologic criteria and staining of sequential LN sections with a panel of antibodies indicated that the DC-SIGN-targeted cells belong to the myeloid lineage of APCs. In conclusion, this is the first study that shows specific targeting of APCs in vivo by using antibodies directed against DC-SIGN.

Innate immunogenetics: a tool for exploring new frontiers of host defence

The discovery of innate immune genes, such as those encoding Toll-like receptors (TLRs), nucleotide-binding oligomerisation domain-like receptors (NLRs), and related signal-transducing molecules, has led to a substantial improvement of our understanding of innate immunity. Recent immunogenetic studies have associated polymorphisms of the genes encoding TLRs, NLRs, and key signal-transducing molecules, such as interleukin-1 receptor-associated kinase 4 (IRAK4), with increased susceptibility to, or outcome of, infectious diseases. With the availability of high-throughput genotyping techniques, it is becoming increasingly evident that analyses of genetic polymorphisms of innate immune genes will further improve our knowledge of the host antimicrobial defence response and help in identifying individuals who are at increased risk of life-threatening infections. This is likely to open new perspectives for the development of diagnostic, predictive, and preventive management strategies to combat infectious diseases.

Modulation of HIV and SIV neutralization sensitivity by DC-SIGN and mannose-binding lectin

The C-type lectin DC-SIGN binds to oligosaccharides on the human and simian immunodeficiency virus (HIV, SIV) envelope glycoproteins and promotes infection of susceptible cells. Here, we show that DC-SIGN recognizes glycans involved in SIV sensitivity to neutralizing antibodies and that binding to DC-SIGN confers neutralization resistance to an otherwise sensitive SIV variant. Moreover, we provide evidence that mannose-binding lectin (MBL) can interfere with HIV-1 neutralization by the carbohydrate-specific antibody 2G12.

Length variation of DC-SIGN and L-SIGN neck-region has no impact on tuberculosis susceptibility

The C-type lectins DC-SIGN and L-SIGN are important pathogen-recognition receptors of the human innate immune system. Both lectins have been shown to interact with a vast range of infectious agents, including Mycobacterium tuberculosis, the etiologic agent of tuberculosis in humans. In addition, DC-SIGN and L-SIGN possess a neck region, made up of a variable number of 23 amino acid tandem repeats, which plays a crucial role in the tetramerization of these proteins and support of the carbohydrate recognition domain. The length of the neck region, which shows variable levels of polymorphism, can critically influence the pathogen binding properties of these two receptors. We therefore investigated the impact of the DC-SIGN and L-SIGN neck-region length variation on the outcome of tuberculosis by screening this polymorphism in a large cohort of Coloured South African origin. The analyses of 711 individuals, including 351 tuberculosis patients and 360 healthy controls, revealed that none of the DC-SIGN and L-SIGN neck-region variants or genotypes seems to influence the individual susceptibility to develop tuberculosis.

Genomics meets HIV-1

Genomics is now a core element in the effort to develop a vaccine against HIV-1. Thanks to unprecedented progress in high-throughput genotyping and sequencing, in knowledge about genetic variation in humans, and in evolutionary genomics, it is finally possible to systematically search the genome for common genetic variants that influence the human response to HIV-1. The identification of such variants would help to determine which aspects of the response to the virus are the most promising targets for intervention. However, a key obstacle to progress remains the scarcity of appropriate human cohorts available for genomic research.

The location of asparagine-linked glycans on West Nile virions controls their interactions with CD209 (dendritic cell-specific ICAM-3 grabbing nonintegrin)

Mammalian cell-derived West Nile virus preferentially infects cells expressing the C-type lectin CD209L (dendritic cellspecific ICAM-3 grabbing nonintegrin-related protein; liver- and lymph node-specific ICAM-3 grabbing nonintegrin) but not cells expressing CD209 (dendritic cell-specific ICAM-3 grabbing nonintegrin). In contrast, Dengue virus infection is enhanced in cells expressing either attachment factor. The West Nile virus envelope (E) protein contains a single N-linked glycosylation site at residue 154, whereas Dengue virus E contains sites at residues 153 and 67. We introduced a glycosylation site at position 67 into West Nile virus E. Reporter virus particles pseudotyped with this E protein infected cells using either CD209 or CD209L. We also introduced glycosylation sites at several novel positions. All sites allowed CD209L-mediated infection, but only a subset promoted CD209 use. As seen for other viruses, mannose-rich glycans on West Nile virus were required for its interactions with CD209. Surprisingly, however, mannose-rich glycans were not required for CD209L-mediated infection. Complex glycans, particularly N-acetylglucosamine-terminated structures, were able to mediate reporter virus particle interactions with CD209L. We propose that CD209L recognizes glycosylated flaviviruses with broad specificity, whereas CD209 is selective for flaviviruses bearing mannose-rich glycans. The location of the N-linked glycosylation sites on a virion determines the types of glycans incorporated, thus controlling viral tropism for CD209-expressing cells.

Intrahepatic gene expression in human alcoholic hepatitis

BACKGROUND/AIMS

Alcoholic hepatitis remains an important cause of morbidity and mortality. Treatment remains unsatisfactory, in part, due to limited understanding of the pathogenesis. The aim of this study is to define the global intrahepatic expression profile of human alcoholic hepatitis.

METHODS

Gene expression was analysed by DNA microarray on RNA isolated from liver of patients with alcoholic hepatitis (AH, n = 8), alcoholic steatosis (AS, n = 9) and explants from non-diseased donor liver controls (ND, n = 7). Differential expression of selected genes was confirmed by real-time RT-PCR and immunohistochemistry.

RESULTS

Cluster analysis allowed differentiation of alcoholic hepatitis from alcoholic steatosis. The gene expression profile of AH revealed 586 genes differentially expressed from AS and 211 genes differentially expressed from that of ND liver. In comparison, only 98 genes were differentially expressed in AS from ND. Novel differentially expressed genes in AH in comparison to ND and AS included claudins, osteopontin, CD209, selenoprotein and genes related to bile duct proliferation. Real-time RT-PCR confirmed up-regulation of IL-8, osteopontin, and TNFRSF14 and down-regulation of SAMeS and CD209.

CONCLUSIONS

This study has defined the intrahepatic gene expression profile of human alcoholic hepatitis and revealed a number of novel differentially expressed genes.

Methamphetamine modulates DC-SIGN expression by mature dendritic cells

We report that methamphetamine (meth) may act as cofactor in human immunodeficiency virus (HIV)-1 pathogenesis by increasing dendritic cell (DC)-specific intercellular adhesion molecule-3 (ICAM-3) grabbing non-integrin (DC-SIGN) expression on DCs. Mature DCs (MDCs), obtained from normal subjects, cultured with meth show an up-regulation of DC-SIGN gene and protein expression as analyzed by real-time quantitative polymerase chain reaction and fluorescence-activated cell-sorting analyses, respectively. Furthermore, these meth-induced effects were reversed by a dopamine D1 receptor antagonist (SCH 23390) and small interfering RNA specific to the D1 receptor (D1R) demonstrating that meth-induced effects are mediated through these receptors. Furthermore, meth in synergy with the HIV-1 peptide gp120 up-regulates DC-SIGN gene expression by MDCs. These data are the first evidence that meth up-regulates the expression of DC-SIGN on MDCs. A better understanding of the role of DC-SIGN in HIV-1 infection may help to design novel therapeutic strategies against the progression of HIV-1 disease in the drug-using population.

The C-type lectin-like domain superfamily

The superfamily of proteins containing C-type lectin-like domains (CTLDs) is a large group of extracellular Metazoan proteins with diverse functions. The CTLD structure has a characteristic double-loop ('loop-in-a-loop') stabilized by two highly conserved disulfide bridges located at the bases of the loops, as well as a set of conserved hydrophobic and polar interactions. The second loop, called the long loop region, is structurally and evolutionarily flexible, and is involved in Ca2+-dependent carbohydrate binding and interaction with other ligands. This loop is completely absent in a subset of CTLDs, which we refer to as compact CTLDs; these include the Link/PTR domain and bacterial CTLDs. CTLD-containing proteins (CTLDcps) were originally classified into seven groups based on their overall domain structure. Analyses of the superfamily representation in several completely sequenced genomes have added 10 new groups to the classification, and shown that it is applicable only to vertebrate CTLDcps; despite the abundance of CTLDcps in the invertebrate genomes studied, the domain architectures of these proteins do not match those of the vertebrate groups. Ca2+-dependent carbohydrate binding is the most common CTLD function in vertebrates, and apparently the ancestral one, as suggested by the many humoral defense CTLDcps characterized in insects and other invertebrates. However, many CTLDs have evolved to specifically recognize protein, lipid and inorganic ligands, including the vertebrate clade-specific snake venoms, and fish antifreeze and bird egg-shell proteins. Recent studies highlight the functional versatility of this protein superfamily and the CTLD scaffold, and suggest further interesting discoveries have yet to be made.

Consistent across-tissue signatures of differential gene expression in Crohn's disease

An approach based on analysis of variance was applied to raw expression data on 44,760 transcripts in order to identify those with significant differential expression across ileum and colon in Crohn's disease (CD) and ulcerative colitis (UC). The design treated tissue as a block effect, thereby removing this effect statistically and increasing the power to test for effects of disease states (control, CD, and UC). A significant F-statistic for the disease effect was not correlated with the ratios CD/control or UC/control, evidently because many transcripts with high-expression ratios to the control showed inconsistent patterns across tissues. Of 1,053 transcripts showing a significant effect of disease state at the 1% level by the bootstrap test, 508 showed significant difference at the 1% level in a post hoc test for difference between the mean scores for CD and control. These included a number of genes relevant to the mechanism of pathogenesis of CD and a number of genes mapping to genomic regions that have previously shown linkage to CD in association studies.

The heritage of pathogen pressures and ancient demography in the human innate-immunity CD209/CD209L region

The innate immunity system constitutes the first line of host defense against pathogens. Two closely related innate immunity genes, CD209 and CD209L, are particularly interesting because they directly recognize a plethora of pathogens, including bacteria, viruses, and parasites. Both genes, which result from an ancient duplication, possess a neck region, made up of seven repeats of 23 amino acids each, known to play a major role in the pathogen-binding properties of these proteins. To explore the extent to which pathogens have exerted selective pressures on these innate immunity genes, we resequenced them in a group of samples from sub-Saharan Africa, Europe, and East Asia. Moreover, variation in the number of repeats of the neck region was defined in the entire Human Genome Diversity Panel for both genes. Our results, which are based on diversity levels, neutrality tests, population genetic distances, and neck-region length variation, provide genetic evidence that CD209 has been under a strong selective constraint that prevents accumulation of any amino acid changes, whereas CD209L variability has most likely been shaped by the action of balancing selection in non-African populations. In addition, our data point to the neck region as the functional target of such selective pressures: CD209 presents a constant size in the neck region populationwide, whereas CD209L presents an excess of length variation, particularly in non-African populations. An additional interesting observation came from the coalescent-based CD209 gene tree, whose binary topology and time depth (approximately 2.8 million years ago) are compatible with an ancestral population structure in Africa. Altogether, our study has revealed that even a short segment of the human genome can uncover an extraordinarily complex evolutionary history, including different pathogen pressures on host genes as well as traces of admixture among archaic hominid populations.

RNAi-directed inhibition of DC-SIGN by dendritic cells: prospects for HIV-1 therapy

Drug-resistant human immunodeficiency virus (HIV) infections are increasing globally, especially in North America. Therefore, it is logical to develop new therapies directed against HIV binding molecules on susceptible host cells in addition to current treatment modalities against virus functions. Inhibition of the viral genome can be achieved by degrading or silencing posttranslational genes using small interfering (si) ribonucleic acids (RNAs) consisting of double-stranded forms of RNA. These siRNAs usually contain 21-23 base pairs (bp) and are highly specific for the nucleotide sequence of the target messenger RNA (mRNA). These siRNAs form a complex with helicase and nuclease enzymes known as "RNA-induced silencing complex" (RISC) that leads to target RNA degradation. Thus, siRNA has become a method of selective destruction of HIV now used by various investigators around the globe. However, given the sequence diversity of the HIV genomes of infected subjects, it is difficult to target a specific HIV sequence. Therefore, targeting nonvariable HIV binding receptors on susceptible cells or other molecules of host cells that are directly or indirectly involved in HIV infections may be an interesting alternative to targeting the virus itself. Thus, the simultaneous use of siRNAs specific for HIV and host cells may be a unique, new approach to the therapy of HIV infections. In this article, we present evidence that siRNA directed at the CD4 independent attachment receptor (DC-SIGN) significantly inhibits HIV infection of dendritic cells (DCs). This effect may be mediated by modulation of p38 mitogen activated protein kinase (MAPK).

Chimpanzee DC-SIGN alleles predict the existence of A and B isoforms, but do not support a role for resistance to HIV infection

We report here the gene sequence for DC-SIGN (CD209) from chimpanzees. DC-SIGN is a C-type lectin expressed by dendritic cells. It is involved in DC-T cell interactions as well as in HIV-1 and SIV transmission. We have cloned two new alleles for chimpanzee DC-SIGN. The coding sequences are highly homologous to the two previously described chimpanzee alleles. We confirm the existence of a polymorphism within the repeat region of DC-SIGN. In humans polymorphisms in the repeat region have been associated with resistance to HIV infection. However, we have not been able to correlate the number of repeats with susceptibility of chimpanzees to HIV infection. The actual impact of DC-SIGN variability in HIV infection therefore remains to be determined.

Cocaine modulates dendritic cell-specific C type intercellular adhesion molecule-3-grabbing nonintegrin expression by dendritic cells in HIV-1 patients

We report that cocaine may act as cofactor in HIV pathogenesis by increasing dendritic cell-specific C type ICAM-3-grabbing nonintegrin (DC-SIGN) expression on dendritic cells (DC). Our results show that cocaine-using, long-term nonprogressors and normal progressors of HIV infection manifest significantly higher levels of DC-SIGN compared with cocaine-nonusing long-term nonprogressors and normal progressors, respectively. Furthermore, in vitro HIV infection of MDC from normal subjects cultured with cocaine and/or HIV peptides up-regulated DC-SIGN, confirming our in vivo finding. Cocaine, in synergy with HIV peptides, also up-regulates DC-SIGN gene expression by MDC. Furthermore, the cocaine-induced effects were reversed by a D1 receptor antagonist demonstrating the specificity of the reaction. Our results indicate that cocaine exacerbates HIV infection by up-regulating DC-SIGN on DC and these effects are mediated via dysregulation of MAPKs. These data are the first evidence that cocaine up-regulates the expression of DC-SIGN on DC. A better understanding of the role of DC-SIGN in HIV infection may help to design novel therapeutic strategies against the progression of HIV disease in the drug-using population.

Characterization of DC-SIGN/R interaction with human immunodeficiency virus type 1 gp120 and ICAM molecules favors the receptor's role as an antigen-capturing rather than an adhesion receptor

The dendritic cell (DC)-specific intercellular adhesion molecule 3 (ICAM-3)-grabbing nonintegrin binding receptor (DC-SIGN) was shown to bind human immunodeficiency virus type 1 (HIV-1) viral envelope protein gp120 and proposed to function as a Trojan horse to enhance trans-virus infection to host T cells. To better understand the mechanism by which DC-SIGN and DC-SIGNR selectively bind HIV-1 gp120, we constructed a series of deletion mutations in the repeat regions of both receptors. Different truncated receptors exist in different oligomeric forms. The carbohydrate binding domain without any repeats was monomeric, whereas the full extracellular receptors existed as tetramers. All reconstituted receptors retained their ability to bind gp120. The dissociation constant, however, differed drastically from micromolar values for the monomeric receptors to nanomolar values for the tetrameric receptors, suggesting that the repeat region of these receptors contributes to the avidity of gp120 binding. Such oligomerization may provide a mechanism for the receptor to selectively recognize pathogens containing multiple high-mannose-concentration carbohydrates. In contrast, the receptors bound to ICAMs with submicromolar affinities that are similar to those of two nonspecific cell surface glycoproteins, FcgammaRIIb and FcgammaRIII, and the oligomerization of DC-SIGNR resulted in no increase in binding affinity to ICAM-3. These findings suggest that DC-SIGN may not discriminate other cell surface glycoproteins from ICAM-3 binding. The pH dependence in DC-SIGN binding to gp120 showed that the receptor retained high-affinity gp120 binding at neutral pH but lost gp120 binding at pH 5, suggesting a release mechanism of HIV in the acidic endosomal compartment by DC-SIGN. Our work contradicts the function of DC-SIGN as a Trojan horse to facilitate HIV-1 infection; rather, it supports the function of DC-SIGN/R (a designation referring to both DC-SIGN and DC-SIGNR) as an antigen-capturing receptor.

The structure of DC-SIGNR with a portion of its repeat domain lends insights to modeling of the receptor tetramer

The dendritic cell-specific ICAM-3 non-integrin (DC-SIGN) and its close relative DC-SIGNR recognize various glycoproteins, both pathogenic and cellular, through the receptor lectin domain-mediated carbohydrate recognition. While the carbohydrate-recognition domains (CRD) exist as monomers and bind individual carbohydrates with low affinity and are permissive in nature, the full-length receptors form tetramers through their repeat domain and recognize specific ligands with high affinity. To understand the tetramer-based ligand binding avidity, we determined the crystal structure of DC-SIGNR with its last repeat region. Compared to the carbohydrate-bound CRD structure, the structure revealed conformational changes in the calcium and carbohydrate coordination loops of CRD, an additional disulfide bond between the N and the C termini of the CRD, and a helical conformation for the last repeat. On the basis of the current crystal structure and other published structures with sequence homology to the repeat domain, we generated a tetramer model for DC-SIGN/R using homology modeling and propose a ligand-recognition index to identify potential receptor ligands.

Drug abuse and neuropathogenesis of HIV infection: role of DC-SIGN and IDO

Dendritic cells are the critical mediators of various immune responses and are the first line of defense against any infection including HIV. They play a major role in harboring HIV and the subsequent infection of T cells and passage of virus through the blood-brain barrier (BBB). The recently discovered DC-specific, CD4-independent HIV attachment receptor, DC-SIGN, and T-cell suppressing factor, indolamine 2,3-dioxygenase (IDO), are known to play a critical role in the immuno-neuropathogenesis of HIV infection. Since brain microvascular cells (BMVEC) express dendritic cell (DC)-specific C type ICAM-3 grabbing nonintegrin (DC-SIGN), it is possible that DC-SIGN may play a critical role in human immunodeficiency virus-type 1 (HIV-1) infection and migration of infected DC across BBB. Matrix metalloproteinases (MMPs) are proteolytic enzymes known to be responsible for maintenance, turnover and integrity of extracellular matrix. Our results show that cocaine upregulates IDO and DC-SIGN expression by DC. Further, cocaine upregulates DC-SIGN and MMPs in BMVEC supporting the hypothesis that cocaine causes membrane permeability facilitating endothelial transmigration of infected DC in to the CNS. Targeting DC-SIGN and IDO with specific monoclonal antibodies, inexpensive synthetic antagonists, antisense oligonucleotides and siRNA may lead to develop novel treatment strategies particularly in high-risk populations such as cocaine users.

Sequence and expression of C-type lectin receptors in Atlantic salmon (Salmo salar)

The diverse receptors of the C-type lectin superfamily play key roles in innate immunity. In mammals, cell surface receptors with C-type lectin domains are involved in pathogen recognition and in immune response, and in some cases are exploited by pathogens to gain entry into cells. This study reports on sequence and expression analysis of three paralogous group II C-type lectins from the teleost fish Atlantic salmon (Salmo salar). Each of the receptors showed similarity to immune-relevant mammalian receptors in terms of amino acid sequence and overall organization within the C-type lectin-like domain (CTLD). Two of the three have cytoplasmic motifs consistent with the immunoreceptor tyrosine-based activation motifs (ITAM), which are known to modulate downstream functions in leukocytes. All three C-type lectin receptors were expressed in multiple tissues of healthy fish, including peripheral blood leukocytes and salmon head kidney cells (SHK-1). Each receptor was up-regulated in salmon liver in response to infection by Aeromonas salmonicida and one receptor was substantially up-regulated in cultured SHK-1 cells in response to lipopolysaccharide (LPS). Putative binding sites for the CAAT-enhancer-binding protein (C/EBP) family of transcription factors in the regulatory regions of these C-type lectin genes may mediate their response to bacteria and LPS in salmon leukocytes. The identification of these types of receptors in distinct populations of cells within the immune system will provide important markers for identifying and categorizing the state of differentiation or activation of these cells and lead to further understanding of the interaction between the salmon host and multiple pathogens.

Domains of macaque DC-SIGN essential for capture and transfer of simian immunodeficiency virus

The C-type lectin DC-SIGN mediates the capture and transfer of simian immunodeficiency virus (SIV) from macaque dendritic cells (DCs) to permissive T-cells. To further identify the determinants in macaque DC-SIGN required for capture and transfer of virus, we created mutants containing deletions or point mutations in the extracellular domains, and tested their ability to capture and transmit SIV. We found that SIV bound to the carbohydrate recognition domain (CRD) of macaque DC-SIGN via the envelope protein. In addition, deleting the C-terminal half of the CRD, or mutating amino acids within this region that contact Ca(2+) or mannose, disrupted virion capture activity. However, an N-terminal CRD deletion mutant was capable of binding SIV, indicating that this region was not necessary for binding. Finally, deletion of the neck domain also reduced the capacity for macaque DC-SIGN to capture SIV. Interestingly, ICAM-3, the cellular ligand for DC-SIGN, did not bind to any of the DC-SIGN mutants, including mutants with amino acid changes in the N-terminal region of the CRD. These data suggest that the binding sites for SIV and ICAM-3 may be distinct but overlapping. Together, the data demonstrate the importance of both the neck and the CRD of macaque DC-SIGN for efficient capture of SIV and binding to ICAM-3.

Raji B cells, misidentified as THP-1 cells, stimulate DC-SIGN-mediated HIV transmission

A number of studies examining interactions of dendritic cell (DC)-specific ICAM-3 grabbing nonintegrin (DC-SIGN) with viral pathogens have relied on monocytic transfectants as models for primary DCs. Here we show that the presumed "THP-1" monocytic cells used in these studies are instead Raji B cells. Moreover, we demonstrate that true THP-1 cells do not support DC-SIGN-mediated HIV-1 transmission, whereas human B cell lines efficiently enhance this process. These data indicate that there are features common to B cells and DCs that facilitate transmission of HIV-1 and provide new insights toward the mechanism of DC-SIGN-mediated HIV-1 transmission.

DC-SIGN: Binding receptor for HCV?

DC-SIGN, a dendritic Cell-specific adhesion receptor and a type II transmembrane mannose-binding C-type lectin, is very important in the function of DC, both in mediating naive T cell interactions through ICAM-3 and as a rolling receptor that mediates the DC-specific ICAM-2-dependent migration processes. It can be used by viral and bacterial pathogens including Human Immunodeficiency Virus (HIV), HCV, Ebola Virus, CMV and Mycobacterium tuberculosis to facilitate infection. Both DC-SIGN and DC-SIGNR can act either in cis, by concentrating virus on target cells, or in trans, by transmission of bound virus to a target cell expressing appropropriate entry receptors. Recent work showed that DC-SIGN are high-affinity binding receptors for HCV. Besides playing a role in entry into DC, HCV E2 interaction with DC-SIGN might also be detrimental for the interaction of DC with T cells during antigen presentation. The clinical strategies that target DC-SIGN may be successful in restricting HCV dissemination and pathogenesis as well as directing the migration of DCs to manipulate appropriate immune responses in autoimmunity and tumorigenic situations.

DC-SIGN from African green monkeys is expressed in lymph nodes and mediates infection in trans of simian immunodeficiency virus SIVagm

African green monkeys (AGMs) infected by simian immunodeficiency virus (SIV) SIVagm are resistant to AIDS. SIVagm-infected AGMs exhibit levels of viremia similar to those described during pathogenic human immunodeficiency virus type 1 (HIV-1) and SIVmac infections in humans and macaques, respectively, but contain lower viral loads in their lymph nodes. We addressed the potential role of dendritic cell-specific intercellular adhesion molecule 3-grabbing nonintegrin (DC-SIGN; CD209) in viral dissemination. In previous studies, it has been shown that human DC-SIGN and macaque DC-SIGN allow transmission of HIV and SIVmac to T cells. Here, we looked at the ability of DC-SIGN derived from AGM lymph nodes to interact with SIVagm. We show that DC-SIGN-expressing cells are present mainly in the medulla and often within the cortex and/or paracortex of AGM lymph nodes. We describe the isolation and characterization of at least three isoforms of dc-sign mRNA in lymph nodes of AGMs. The predicted amino acid sequence from the predominant mRNA isoform, DC-SIGNagm1, is 92 and 99% identical to the corresponding human and rhesus macaque DC-SIGN amino acid sequences, respectively. DC-SIGNagm1 is characterized by the lack of the fourth motif in the repeat domain. This deletion was also detected in the dc-sign gene derived from thirteen animals belonging to five other African monkey species and from four macaques (Macaca fascicularis and M. mulatta). Despite three- to seven-amino-acid modifications compared to DC-SIGNmac, DC-SIGNagm1 allows transmission of SIVagm to T cells. Furthermore, AGM monocyte-derived dendritic cells (MDDC) expressed at least 100,000 DC-SIGN molecules and were able to transmit SIVagm to T cells. At a low multiplicity of infection (10(-5) 50% tissue culture infective doses/cell), viral transmission by AGM MDDC was mainly DC-SIGN dependent. The present study reveals that DC-SIGN from a natural host species of SIV has the ability to act as an efficient attachment and transmission factor for SIVagm and suggests the absence of a direct link between this ability and viral load levels in lymph nodes.