Variation in the yak dectin-1 gene (CLEC7A)

C-type lectin domain family 7, member A (CLEC7A, dectin-1) plays an important role in antifungal immunity and belongs to the family of C-type lectin receptors. Variation in the extended exon 4-6 region of the yak dectin-1 gene (CLEC7A), which encodes the β-glucan recognition domain, was investigated using polymerase chain reaction-single strand conformational polymorphism (PCR-SSCP). Three and two variant sequences were identified in exons 4 and 5, respectively, and no variation was found in exon 6. The variation included two single-nucleotide substitutions in exon 4 and one single-nucleotide polymorphism in exon 5, and two of these substitutions would nominally cause amino acid substitutions (p.I158T and p.S197G) in yak dectin-1. This is the first report identifying the yak dectin-1 gene, revealing that it is polymorphic and this polymorphism might affect the structure and function of this gene in yak.     

CLEC4F Is an Inducible C-Type Lectin in F4/80-Positive Cells and Is Involved in Alpha-Galactosylceramide Presentation in Liver

CLEC4F, a member of C-type lectin, was first purified from rat liver extract with high binding affinity to fucose, galactose (Gal), N-acetylgalactosamine (GalNAc), and un-sialylated glucosphingolipids with GalNAc or Gal terminus. However, the biological functions of CLEC4F have not been elucidated. To address this question, we examined the expression and distribution of murine CLEC4F, determined its binding specificity by glycan array, and investigated its function using CLEC4F knockout (Clec4f−/−) mice. We found that CLEC4F is a heavily glycosylated membrane protein co-expressed with F4/80 on Kupffer cells. In contrast to F4/80, CLEC4F is detectable in fetal livers at embryonic day 11.5 (E11.5) but not in yolk sac, suggesting the expression of CLEC4F is induced as cells migrate from yolk cells to the liver. Even though CLEC4F is not detectable in tissues outside liver, both residential Kupffer cells and infiltrating mononuclear cells surrounding liver abscesses are CLEC4F-positive upon Listeria monocytogenes (L. monocytogenes) infection. While CLEC4F has strong binding to Gal and GalNAc, terminal fucosylation inhibits CLEC4F recognition to several glycans such as Fucosyl GM1, Globo H, Bb3∼4 and other fucosyl-glycans. Moreover, CLEC4F interacts with alpha-galactosylceramide (α-GalCer) in a calcium-dependent manner and participates in the presentation of α-GalCer to natural killer T (NKT) cells. This suggests that CLEC4F is a C-type lectin with diverse binding specificity expressed on residential Kupffer cells and infiltrating monocytes in the liver, and may play an important role to modulate glycolipids presentation on Kupffer cells.     

Involvement of CLEC16A in Activation of Astrocytes After LPS Treated

CLEC16A, C-type lectin domain family 16, member A was recently found to be associated with inflation process in the autoimmune diseases. In this study, we elucidated the dynamic expression changes and localization of CLEC16A in lipopolysaccharide (LPS)-induced neuroinflammatory processes in adult rats. CLEC16A expression was strongly induced in active astrocytes in inflamed cerebral cortex. In vitro studies indicated that the up-regulation of CLEC16A may be involved in the subsequent astrocyte activation following LPS challenge. And Knock-down of CLEC16A in cultured primary astrocytes by siRNA showed that CLEC16A was required for the activation of astrocytes induced by LPS. Collectively, these results suggested CLEC16A may be important in host defense in astrocyte-mediated immune response. Understanding the cell signal pathway may provide a novel strategy against inflammatory and immune reaction in neuroinflammtion in CNS.     

BACL Is a Novel Brain-Associated,Non-NKC-Encoded Mammalian C-Type Lectin-Like Receptor of the CLEC2 Family

Natural Killer Gene Complex (NKC)–encoded C-type lectin-like receptors (CTLRs) are expressed on various immune cells including T cells, NK cells and myeloid cells and thereby contribute to the orchestration of cellular immune responses. Some NKC-encoded CTLRs are grouped into the C-type lectin family 2 (CLEC2 family) and interact with genetically linked CTLRs of the NKRP1 family. While many CLEC2 family members are expressed by hematopoietic cells (e.g. CD69 (CLEC2C)), others such as the keratinocyte-associated KACL (CLEC2A) are specifically expressed by other tissues. Here we provide the first characterization of the orphan gene CLEC2L. In contrast to other CLEC2 family members, CLEC2L is conserved among mammals and located outside of the NKC. We show that CLEC2L-encoded CTLRs are expressed as non-glycosylated, disulfide-linked homodimers at the cell surface. CLEC2L expression is fairly tissue-restricted with a predominant expression in the brain. Thus CLEC2L-encoded CTLRs were designated BACL (brain-associated C-type lectin). Combining in situ hybridization and immunohistochemistry, we show that BACL is expressed by neurons in the CNS, with a pronounced expression by Purkinje cells. Notably, the CLEC2L locus is adjacent to another orphan CTLR gene (KLRG2), but reporter cell assays did neither indicate interaction of BACL with the KLRG2 ectodomain nor with human NK cell lines or lymphocytes. Along these lines, growth of BACL-expressing tumor cell lines in immunocompetent mice did not provide evidence for an immune-related function of BACL. Altogether, the CLEC2L gene encodes a homodimeric cell surface CTLR that stands out among CLEC2 family members by its conservation in mammals, its biochemical properties and the predominant expression in the brain. Future studies will have to reveal insights into the functional relevance of BACL in the context of its neuronal expression.     

CLEC5A Regulates Japanese Encephalitis Virus-Induced Neuroinflammation and Lethality

CLEC5A/MDL-1, a member of the myeloid C-type lectin family expressed on macrophages and neutrophils, is critical for dengue virus (DV)-induced hemorrhagic fever and shock syndrome in Stat1 ^−/− mice and ConA-treated wild type mice. However, whether CLEC5A is involved in the pathogenesis of viral encephalitis has not yet been investigated. To investigate the role of CLEC5A to regulate JEV-induced neuroinflammation, antagonistic anti-CLEC5A mAb and CLEC5A-deficient mice were generated. We find that Japanese encephalitis virus (JEV) directly interacts with CLEC5A and induces DAP12 phosphorylation in macrophages. In addition, JEV activates macrophages to secrete proinflammatory cytokines and chemokines, which are dramatically reduced in JEV-infected Clec5a^−/− macrophages. Although blockade of CLEC5A cannot inhibit JEV infection of neurons and astrocytes, anti-CLEC5A mAb inhibits JEV-induced proinflammatory cytokine release from microglia and prevents bystander damage to neuronal cells. Moreover, JEV causes blood-brain barrier (BBB) disintegrity and lethality in STAT1-deficient (Stat1 ^−/−) mice, whereas peripheral administration of anti-CLEC5A mAb reduces infiltration of virus-harboring leukocytes into the central nervous system (CNS), restores BBB integrity, attenuates neuroinflammation, and protects mice from JEV-induced lethality. Moreover, all surviving mice develop protective humoral and cellular immunity against JEV infection. These observations demonstrate the critical role of CLEC5A in the pathogenesis of Japanese encephalitis, and identify CLEC5A as a target for the development of new treatments to reduce virus-induced brain damage.     

Human C-type lectin domain family 4, member C (CLEC4C/BDCA-2/CD303) is a receptor for asialo-galactosyl-oligosaccharides

Plasmacytoid dendritic cells are specialized in the production of type I interferon (type I IFN), which promotes antiviral and antitumor responses, as well as autoimmune disorders. Activation of type I IFN secretion depends on the pattern recognition receptors TLR7 and TLR9, which sense microbial RNA and DNA, respectively. Type I IFN production is modulated by several receptors, including the type II C-type lectin domain family 4, member C (CLEC4C). The natural ligand of CLEC4C is unknown. To identify it, here we probed a glycan array with a soluble form of the CLEC4C ectodomain. We found that CLEC4C recognizes complex type sugars with terminal galactose. Importantly, soluble CLEC4C bound peripheral blood leukocytes and tumor cells that express glycans with galactose residues at the non-reducing ends. The positive and negative modulation of galactose residues on cell membranes was paralleled by the regulation of type I IFN secretion by plasmacytoid dendritic cells in co-culture experiments in vitro. These results suggest that the modulation in the expression of non-sialylated oligosaccharides by invading pathogens or transformed cells may affect type I IFN response and immune surveillance.     

Methylation of CLEC14A is associated with its expression and lung adenocarcinoma progression

Our main objective is probing the effect of methylation of CLEC14A on its expression and lung adenocarcinoma (LUAD) progression. Microarray analysis was utilized to screen out differentially downregulated genes with hypermethylation in LUAD tissues. The CLEC14A expression level was measured by western blot analysis and qRT-PCR. Methylation-specific-PCR was performed to evaluate methylation status of CLEC14A. The 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromid (MTT) assay was used to check the relation between CLEC14A expression and cell proliferation. Cell cycle, cell apoptosis, migration, and invasion were respectively detected by the flow cytometry assay, wound healing assay, and transwell assay. Tumor xenograft models were established for investigating the effect of CLEC14A on tumor formation. CLEC14A expression in LUAD tissues was impaired compared with that in adjacent tissues, and CLEC14A promoter was highly methylated in LUAD. Overexpressing CLEC14A or inhibiting the methylation level of CLEC14A in A549 and LTEP-a-2 cells impeded the duplication of LUAD cells, promoted apoptosis, attenuated cell migration, and invasion ability, and arrested cell cycle at the G0/G1 phase. Overexpression of CLEC14A inhibited tumorigenesis of LUAD cells in nude mice. The promoter of CLEC14A is methylated in LUAD, leading to downregulation of CLEC14A in LUAD. CLEC14A acts as an antitumor role in LUAD by suppressing cell proliferation, migration, invasion, promoting cell apoptosis, and reducing tumorigenicity in nude mice. Thus, the inhibition of CLEC14A methylation is a novel strategy for the clinic treatment of LUAD.     

Shear stress, tip cells and regulators of endothelial migration

We have in recent years described several endothelial-specific genes that mediate cell migration. These include Robo4 (roundabout 4), CLEC14A (C-type lectin 14A) and ECSCR (endothelial cell-specific chemotaxis regulator) [formerly known as ECSM2 (endothelial cell-specific molecule 2)]. Loss of laminar shear stress induces Robo4 and CLEC14A expression and an endothelial 'tip cell' phenotype. Low shear stress is found not only at sites of vascular occlusion such as thrombosis and embolism, but also in the poorly structured vessels that populate solid tumours. The latter probably accounts for strong expression of Robo4 and CLEC14A on tumour vessels. The function of Robo4 has, in the past, aroused controversy. However, the recent identification of Unc5B as a Robo4 ligand has increased our understanding and we hypothesize that Robo4 function is context-dependent. ECSCR is another endothelial-specific protein that promotes filopodia formation and migration, but, in this case, expression is independent of shear stress. We discuss recent papers describing ECSCR, including intracellular signalling pathways, and briefly contrast these with signalling by Robo4.     

Mapping the CLEC12A expression on myeloid progenitors in normal bone marrow; implications for understanding CLEC12A‐related cancer stem cell biology

The C‐type lectin domain family 12, member A (CLEC12A) receptor has emerged as a leukaemia‐associated and cancer stem cell marker in myeloid malignancies. However, a detailed delineation of its expression in normal haematopoiesis is lacking. Here, we have characterized the expression pattern of CLEC12A on the earliest stem‐ and myeloid progenitor subsets in normal bone marrow. We demonstrate distinct CLEC12A expression in the classically defined myeloid progenitors, where on average 39.1% (95% CI [32.5;45.7]) of the common myeloid progenitors (CMPs) expressed CLEC12A, while for granulocyte‐macrophage progenitors and megakaryocyte‐erythroid progenitors (MEPs), the average percentages were 81.0% (95% CI [76.0;85.9]) and 11.9% (95% CI [9.3;14.6]), respectively. In line with the reduced CLEC12A expression on MEPs, functional assessment of purified CLEC12A^+/? CMPs and MEPs in the colony‐forming unit assay demonstrated CLEC12A⁺ subsets to favour non‐erythroid colony growth. In conclusion, we provide evidence that the earliest CLEC12A⁺ cell in the haematopoietic tree is the classically defined CMP. Furthermore, we show that CLEC12A‐expressing CMPs and MEPs are functionally different than their negative counterparts. Importantly, these data can help determine which cells will be spared during CLEC12A‐targeted therapy, and we propose CLEC12A to be included in future studies of myeloid cancer stem cell biology.     

miR‐938 promotes cell proliferation by regulating RBM5 in lung adenocarcinoma cells

A growing body of research suggests that microRNAs (miRNAs) may play a key part in the progression of various cancers, including lung adenocarcinoma (LUAD). However, the expression and mechanism of miR‐938 (microRNA‐938) in LUAD have not been defined. Compared with adjacent tissues, the level of miR‐938 was up‐regulated in LUAD tissues. miR‐938 expression was significantly associated with tumor size. In vitro assays indicated that miR‐938 expression was also increased in the LUAD cell lines. Overexpression of miR‐938 promoted LUAD cell proliferation, whereas down‐regulation of miR‐938 had the opposite effect. We identified RNA‐binding protein 5 (RBM5) as a potential target gene of miR‐938 in LUAD. Expression of RBM5 was down‐regulated in LUAD tumor tissues and negatively correlated with expression of miR‐938. Up‐regulation of RBM5 reversed cell proliferation by inhibition of miR‐938 expression in LUAD cells. These results showed that miR‐938 may act as an oncogenic miRNA by targeting RBM5 in LUAD, indicating that miR‐938 could be used as a potential therapeutic target for LUAD patients.     

Identification and tissue expression analysis of C-type lectin and galectin in the Pacific oyster, Crassostrea gigas

As an initial step in the functional analysis of lectins in the Pacific oyster, Crassostrea gigas, we attempted to obtain the full coding sequences of C. gigas lectins and conduct tissue expression analyses. To obtain lectin genes quickly, we identified C. gigas expressed sequence tags that coded for lectins in GenBank, and selected three encoding partial sequences of C-type lectin 1 (CgCLec-1), galectin (CgGal) and fucolectin. We obtained full open reading frames of CgCLec-1 and CgGal cDNAs by RACE-PCR. CgCLec-1 is a typical C-type lectin with a signal peptide and C-type lectin domain. CgCLec-1 mRNA was expressed only in specialized basophilic cells involved with digestive enzyme secretion in the digestive gland, suggesting that CgCLec-1 is secreted into the lumen of the digestive diverticula. CgGal is a prototype galectin with a single galactose-binding domain that was expressed in all of the tissues examined. As suggested for vertebrate galectin-1 (prototype galectin), CgGal may function in general cell activities such as cell adhesion. Fucolectin in C. gigas was expressed specifically in the gonads, indicating a possible function in gonadal development. CgCLec-1 and CgGal expression in hemocytes was not upregulated after injecting Vibrio tubiashii into adductor muscle, suggesting that bacterial infection does not induce synthesis of these lectins. Of the three lectins examined, CgCLec-1 is an interesting target for future investigations of innate immunity in the digestive system of C. gigas.     

Human CLEC18 Gene Cluster Contains C-type Lectins with Differential Glycan-binding Specificity

The human C-type lectin 18 (clec18) gene cluster, which contains three clec18a, clec18b, and clec18c loci, is located in human chromosome 16q22. Although the amino acid sequences of CLEC18A, CLEC18B, and CLEC18C are almost identical, several amino acid residues located in the C-type lectin-like domain (CTLD) and the sperm-coating protein/Tpx-1/Ag5/PR-1/Sc7 (SCP/TAPS) domain, also known as the cysteine-rich secretory proteins/antigen 5/pathogenesis-related 1 proteins (CAP) domain, are distinct from each other. Genotyping by real-time PCR and sequencing further shows the presence of multiple alleles in clec18a/b/c loci. Flow cytometry analysis demonstrates that CLEC18 (CLEC18A, -B, and -C) are expressed abundantly in human peripheral blood cells. Moreover, CLEC18 expression is further up-regulated when monocytes differentiate into macrophages and dendritic cells. Immunofluorescence staining reveals that CLEC18 are localized in the endoplasmic reticulum, Golgi apparatus, and endosome. Interestingly, CLEC18 are also detectable in human sera and culture supernatants from primary cells and 293T cells overexpressing CLEC18. Moreover, CLEC18 bind polysaccharide in Ca²⁺-independent manner, and amino acid residues Ser/Arg³³⁹ and Asp/Asn⁴²¹ in CTLD domain contribute to their differential binding abilities to polysaccharides isolated from Ganoderma lucidum (GLPS-F3). The Ser³³⁹ (CLEC18A) → Arg³³⁹ (CLEC18A-1) mutation completely abolishes CLEC18A-1 binding to GLPS-F3, and a sugar competition assay shows that CLEC18 preferentially binds to fucoidan, β-glucans, and galactans. Because proteins with the SCP/TAPS/CAP domain are able to bind sterol and acidic glycolipid, and are involved in sterol transport and β-amyloid aggregation, it would be interesting to investigate whether CLEC18 modulates host immunity via binding to glycolipids, and are also involved in glycolipid transportation and protein aggregation in the future.     

Identification of natural killer cell receptor clusters in the platypus genome reveals an expansion of C-type lectin genes

Natural killer (NK) cell receptors belong to two unrelated, but functionally analogous gene families: the immunoglobulin superfamily, situated in the leukocyte receptor complex (LRC) and the C-type lectin superfamily, located in the natural killer complex (NKC). Here, we describe the largest NK receptor gene expansion seen to date. We identified 213 putative C-type lectin NK receptor homologs in the genome of the platypus. Many have arisen as the result of a lineage-specific expansion. Orthologs of OLR1, CD69, KLRE, CLEC12B, and CLEC16p genes were also identified. The NKC is split into at least two regions of the genome: 34 genes map to chromosome 7, two map to a small autosome, and the remainder are unanchored in the current genome assembly. No NK receptor genes from the LRC were identified. The massive C-type lectin expansion and lack of Ig-domain-containing NK receptors represents the most extreme polarization of NK receptors found to date. We have used this new data from platypus to trace the possible evolutionary history of the NK receptor clusters. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Mincle,an Innate Immune Receptor,Is Expressed in Urothelial Cancer Cells of Papillomavirus-Associated Urothelial Tumors of Cattle

Background

Mincle, macrophage-inducible C-type lectin, is a member of C-type lectin receptors. It plays an important role in anti-mycobacterial and anti-fungal immunity. Furthermore it senses dead cells through its primary ligand SAP130.

Materials and Findings

We examined ten urothelial tumors of the urinary bladder of cattle. Eight of them expressed E5 cDNA of bovine papillomaviruses type 2 (BPV-2) and type 13 (BPV-13) that belong to Deltapapillomavirus genus. Two of them were not examined for detection of E5 cDNA. Mincle expression appeared to occur in urothelial neoplastic cells only. No mincle expression was detected in urothelial cells from healthy cattle. Mincle expression was characterized by a membranous pattern in papillary urothelial cancers; isolated and/or clustered urothelial cells showing a strong cytoplasmic immunoreactivity were primarily seen in invasive urothelial cancers.

Conclusion

This is the first study about the expression of mincle in veterinary oncology and the first report which describes the expression of functional mincle receptor in neoplastic cells in medical literature. As it has been shown that urothelial cancer cells have the ability to function as antigen-presenting cells (APCs), it is conceivable that mincle expression is involved in the presentation of cancer cell antigens to cells of the immune system. Furthermore, since expression of mincle contributes to the control of Mycobacterium bovis BCG infection, this study has exciting clinical implications in comparative medicine keeping in mind that Bacillus Calmette-Guérin (BCG) immunotherapy is currently the most effective treatment of non-muscle invasive bladder cancer in man. Mincle expression in urothelial tumor cells warrants further study to better understand the role, if any, of this receptor in bladder cancer. Future studies will provide insights in the role of mincle receptor of urothelial cancer cells in antitumor immunotherapy.     

The diagnostic and prognostic value of pseudogene SIGLEC17P in lung adenocarcinoma and a preliminary functional study

Among malignant tumors, lung adenocarcinoma (LUAD) is the leading cause of death worldwide. This study explored the diagnostic, prognostic value, and preliminary functional verification of sialic acid binding Ig like lectin 17, pseudogene (SIGLEC17P) in LUAD. Prognostic lncRNAs for LUAD were identified by The Cancer Genome Atlas and quantitative real-time PCR (qRT-PCR) was used to detect the expression of SIGLEC17P in LUAD and paracarcinoma tissues. Subsequently, lentiviral vectors were used to overexpress SIGLEC17P in A549 and H1299 cells. The effects of SIGLEC17P overexpression on the proliferation, migration, and invasiveness of LUAD cells (A549 and H1299) were evaluated by Cell Counting Kit-8, wound healing, and transwell migration assays, respectively. Bioinformatics analyses were performed to reveal the potential pathways in which SIGLEC17P is involved in LUAD. qRT-PCR results revealed low SIGLEC17P expression in LUAD tissues and a significant association with the N stage, T stage, and tumor node metastasis stage. Furthermore, the receiver operating characteristic curve demonstrated a reliable diagnostic value. The proliferation, migration, and invasion of LUAD cells were inhibited by overexpression of SIGLEC17P. Bioinformatics analyses suggested that SIGLEC17P might exert antioncogenic effects in LUAD through the mir-20-3p/ADH1B or mir-4476-5p/DPYSL axis. In summary, our results revealed that SIGLEC17P acts as a prognostic biomarker, independent prognostic factor, and potential therapeutic target for patients with LUAD.     

Allergen-Specific Immunotherapy Alters the Frequency,as well as the FcR and CLR Expression Profiles of Human Dendritic Cell Subsets

Allergen-specific immunotherapy (AIT) induces tolerance and shifts the Th2 response towards a regulatory T-cell profile. The underlying mechanisms are not fully understood, but dendritic cells (DC) play a vital role as key regulators of T-cell responses. DCs interact with allergens via Fc receptors (FcRs) and via certain C-type lectin receptors (CLRs), including CD209/DC-SIGN, CD206/MR and Dectin-2/CLEC6A. In this study, the effect of AIT on the frequencies as well as the FcR and CLR expression profiles of human DC subsets was assessed. PBMC was isolated from peripheral blood from seven allergic donors before and after 8 weeks and 1 year of subcutaneous AIT, as well as from six non-allergic individuals. Cells were stained with antibodies against DC subset-specific markers and a panel of FcRs and CLRs and analyzed by flow cytometry. After 1 year of AIT, the frequency of CD123⁺ DCs was increased and a larger proportion expressed FcεRI. Furthermore, the expression of CD206 and Dectin-2 was reduced on CD141⁺ DCs after 1 year of treatment and CD206 as well as Dectin-1 was additionally down regulated in CD1c⁺ DCs. Interestingly, levels of DNGR1/CLEC9A on CD141⁺ DCs were increased by AIT, reaching levels similar to cells isolated from non-allergic controls. The modifications in phenotype and occurrence of specific DC subsets observed during AIT suggest an altered capacity of DC subsets to interact with allergens, which can be part of the mechanisms by which AIT induces allergen tolerance.     

BDCA-2 signaling inhibits TLR-9-agonist-induced plasmacytoid dendritic cell activation and antigen presentation

Plasmacytoid dendritic cells (PDCs) express Toll-like receptor (TLR) 9, which mediates recognition of microbial DNA during infection or self-DNA in autoimmune diseases. Triggering TLR-9 in PDC induces either maturation (lysosomal TLR-9 triggering) or type I interferon (IFN-I) production (endosomal TLR-9 triggering). PDCs also express BDCA-2 (CD303), a C-type lectin receptor (CLR) unique to these cells. CLRs appear to function in innate immunity and microbial recognition, and may cooperate with TLRs to fine-tune inflammatory responses.It has been shown that anti-BDCA-2 monoclonal antibody is internalized by PDC for antigen presentation and inhibits TLR-9 induced IFN-I expression. Here we investigated the cross-talk between BDCA-2 and TLR-9-signaling during PDC maturation and antigen presentation. We found that BDCA-2-induced signaling in PDCs inhibits up-regulation of CD86 and CD40 molecules in CpG-activated PDCs, but not in CD40L-activated PDCs. Furthermore, triggering of BDCA-2 diminished the ability of CpG- and CD40L-stimulated PDCs to process and present antigen to antigen-specific autologous memory T cells. This study demonstrates that BDCA-2 represents an attractive target for clinical immunotherapy of IFN-I dependent autoimmune diseases influencing both, IFN-I production and antigen-specific T-cell stimulation by PDC.     

Characterization of a novel C-type lectin-like gene, LSECtin: demonstration of carbohydrate binding and expression in sinusoidal endothelial cells of liver and lymph node

A new C-type lectin-like gene encodes 293 amino acids and maps to chromosome 19p13.3 adjacent to the previously described C-type lectin genes, CD23, dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin (DC-SIGN), and DC-SIGN-related protein (DC-SIGNR). The four genes form a tight cluster in an insert size of 105 kb and have analogous genomic structures. The new C-type lectin-like molecule, designated liver and lymph node sinusoidal endothelial cell C-type lectin (LSECtin), is a type II integral membrane protein of approximately 40 kDa in size with a single C-type lectin-like domain at the COOH terminus, closest in homology to DC-SIGNR, DC-SIGN, and CD23. LSECtin mRNA was only expressed in liver and lymph node among 15 human tissues tested, intriguingly neither expressed on hematopoietic cell lines nor on monocyte-derived dendritic cells (DCs). Moreover, LSECtin is expressed predominantly by sinusoidal endothelial cells of human liver and lymph node and co-expressed with DC-SIGNR. LSECtin binds to mannose, GlcNAc, and fucose in a Ca(2+)-dependent manner but not to galactose. Our results indicate that LSECtin is a novel member of a family of proteins comprising CD23, DC-SIGN, and DC-SIGNR and might function in vivo as a lectin receptor.