Cloning of a novel C-type lectin expressed by murine macrophages

CLEC4D as a Novel Prognostic Marker Boosts the Proliferation and Migration of Gastric Cancer via the NF-κB/AKT Signaling Pathway

Purpose

The functions of C-type lectin domain family 4 member D (CLEC4D), one member of the C-type lectin/C-type lectin-like domain superfamily, in immunity have been well described, but its roles in cancer biology remain largely unknown.

Patients and Methods

This study aims to explore the role of CLEC4D in gastric cancer (GC). Bioinformatics preliminarily analyzed the expression of CLEC4D in gastric cancer. Immunohistochemical staining was used to detect the expression level and clinical pathological characteristics of CLEC4D in gastric cancer. The biological function of CLEC4D in gastric cancer cell lines was verified through in vitro and in vivo experiments.

Results

In this study, CLEC4D expression was found to be markedly increased in gastric cancer (GC) tissues compared with matched normal gastric tissues, and high CLEC4D expression independently predicted unfavorable overall survival in patients with GC. Knockdown of CLEC4D markedly inhibited GC cell proliferation and migration. Mechanistically, CLEC4D knockdown deactivated the Akt and NF-κB signaling pathways in GC cells.

Conclusion

Together, these results demonstrate that aberrantly increased CLEC4D expression promotes cancer phenotypes via the Akt and NF-κB signaling pathways in GC cells.

Impact of Asialoglycoprotein Receptor and Mannose Receptor Deficiency on Murine Plasma N-glycome Profiles

The asialoglycoprotein receptor (ASGPR) and the mannose receptor C-type 1 (MRC1) are well known for their selective recognition and clearance of circulating glycoproteins. Terminal galactose and N-Acetylgalactosamine are recognized by ASGPR, while terminal mannose, fucose, and N-Acetylglucosamine are recognized by MRC1. The effects of ASGPR and MRC1 deficiency on the N-glycosylation of individual circulating proteins have been studied. However, the impact on the homeostasis of the major plasma glycoproteins is debated and their glycosylation has not been mapped with high molecular resolution in this context. Therefore, we evaluated the total plasma N-glycome and plasma proteome of ASGR1 and MRC1 deficient mice. ASGPR deficiency resulted in an increase in O-acetylation of sialic acids accompanied by higher levels of apolipoprotein D, haptoglobin, and vitronectin. MRC1 deficiency decreased fucosylation without affecting the abundance of the major circulating glycoproteins. Our findings confirm that concentrations and N-glycosylation of the major plasma proteins are tightly controlled and further suggest that glycan-binding receptors have redundancy, allowing compensation for the loss of one major clearance receptor.

The Role of C-Type Lectin Receptor Signaling in the Intestinal Microbiota-Inflammation-Cancer Axis

As a subset of pattern recognition receptors (PRRs), C-type lectin-like receptors (CLRs) are mainly expressed by myeloid cells as both transmembrane and soluble forms. CLRs recognize not only pathogen associated molecular patterns (PAMPs), but also damage-associated molecular patterns (DAMPs) to promote innate immune responses and affect adaptive immune responses. Upon engagement by PAMPs or DAMPs, CLR signaling initiates various biological activities in vivo, such as cytokine secretion and immune cell recruitment. Recently, several CLRs have been implicated as contributory to the pathogenesis of intestinal inflammation, which represents a prominent risk factor for colorectal cancer (CRC). CLRs function as an interface among microbiota, intestinal epithelial barrier and immune system, so we firstly discussed the relationship between dysbiosis caused by microbiota alteration and inflammatory bowel disease (IBD), then focused on the role of CLRs signaling in pathogenesis of IBD (including Mincle, Dectin-3, Dectin-1, DCIR, DC-SIGN, LOX-1 and their downstream CARD9). Given that CLRs mediate intricate inflammatory signals and inflammation plays a significant role in tumorigenesis, we finally highlight the specific effects of CLRs on CRC, especially colitis-associated cancer (CAC), hoping to open new horizons on pathogenesis and therapeutics of IBD and CAC.

Fungal-induced glycolysis in macrophages promotes colon cancer by enhancing innate lymphoid cell secretion of IL-22

Incorporation of microbiome data has recently become important for prevention, diagnosis, and treatment of colorectal cancer, and several species of bacteria were shown to be associated with carcinogenesis. However, the role of commensal fungi in colon cancer remains poorly understood. Here, we report that mice lacking the c-type lectin Dectin-3 (Dectin-3-/- ) show increased tumorigenesis and Candida albicans burden upon chemical induction. Elevated C. albicans load triggered glycolysis in macrophages and interleukin-7 (IL-7) secretion. IL-7 induced IL-22 production in RORγt+ (group 3) innate lymphoid cells (ILC3s) via aryl hydrocarbon receptor and STAT3. Consistently, IL-22 frequency in tumor tissues of colon cancer patients positively correlated with fungal burden, indicating the relevance of this regulatory axis in human disease. These results establish a C. albicans-driven crosstalk between macrophages and innate lymphoid cells in the intestine and expand our understanding on how commensal mycobiota regulate host immunity and promote tumorigenesis.

Innate Immune Pattern Recognition Receptors of Mycobacterium tuberculosis: Nature and Consequences for Pathogenesis of Tuberculosis

Innate immunity against Mycobacterium tuberculosis is a critical early response to prevent the establishment of the infection. Despite recent advances in understanding the host-pathogen dialogue in the early stages of tuberculosis (TB), much has yet to be learnt. The nature and consequences of this dialogue ultimately determine the path of infection: namely, either early clearance of M. tuberculosis, or establishment of M. tuberculosis infection leading to active TB disease and/or latent TB infection. On the frontline in innate immunity are pattern recognition receptors (PRRs), with soluble factors (e.g. collectins and complement) and cell surface factors (e.g. Toll-like receptors and other C-type lectin receptors (Dectin 1/2, Nod-like receptors, DC-SIGN, Mincle, mannose receptor, and MCL) that play a central role in recognising M. tuberculosis and facilitating its clearance. However, in a 'double-edged sword' scenario, these factors can also be involved in enhancement of pathogenesis as well. Furthermore, innate immunity is also a critical bridge in establishing the subsequent adaptive immune response, which is also responsible for granuloma formation that cordons off M. tuberculosis infection, establishing latency and acting as a reservoir for bacterial persistence and dissemination of future disease. This chapter discusses the current understanding of pattern recognition of M. tuberculosis by innate immunity and the role this plays in the pathogenesis and protection against TB.

Mincle: 20 years of a versatile sensor of insults

Macrophage-inducible C-type lectin, better known as Mincle, is a member of the C-type lectin receptor family and is encoded by Clec4e. Mincle was an orphan receptor for a long time after having been discovered as a lipopolysaccharide-induced protein, yet later an adjuvant glycolipid in mycobacteria-trehalose dimycolate-was identified as a ligand. Ligands for Mincle were also found existing in bacteria, fungi and even mammals. When confronted with foreign elements, Mincle can recognize characteristic pathogen-associated molecular patterns, mostly glycolipids, from Mycobacterium tuberculosis and other pathogens, and thus induce immune responses against infection. To maintain self-homeostasis, Mincle can recognize lipid-based damage-associated molecular patterns, thereby monitoring the internal environment. The mechanism by which Mincle functions in the immune system is also becoming more clear along with the identification of its ligands. Being expressed widely on antigen-presenting cells, Mincle activation leads to the production of cytokines and chemokines, neutrophil infiltration and other inflammatory responses. Besides, Mincle can induce acquired immunity such as antigen-specific T-cell responses and antibody production as an adjuvant receptor. In this review, we will retrospectively sketch the discovery and study of Mincle, and outline some current work on this receptor.

Inherited CARD9 Deficiency: Invasive Disease Caused by Ascomycete Fungi in Previously Healthy Children and Adults

Autosomal recessive CARD9 deficiency underlies life-threatening, invasive fungal infections in otherwise healthy individuals normally resistant to other infectious agents. In less than 10 years, 58 patients from 39 kindreds have been reported in 14 countries from four continents. The patients are homozygous (n = 49; 31 kindreds) or compound heterozygous (n = 9; 8 kindreds) for 22 different CARD9 mutations. Six mutations are recurrent, probably due to founder effects. Paradoxically, none of the mutant alleles has been experimentally demonstrated to be loss-of-function. CARD9 is expressed principally in myeloid cells, downstream from C-type lectin receptors that can recognize fungal components. Patients with CARD9 deficiency present impaired cytokine and chemokine production by macrophages, dendritic cells, and peripheral blood mononuclear cells and defective killing of some fungi by neutrophils in vitro. Neutrophil recruitment to sites of infection is impaired in vivo. The proportion of Th17 cells is low in most, but not all, patients tested. Up to 52 patients suffering from invasive fungal diseases (IFD) have been reported, with ages at onset of 3.5 to 52 years. Twenty of these patients also displayed superficial fungal infections. Six patients had only mucocutaneous candidiasis or superficial dermatophytosis at their last follow-up visit, at the age of 19 to 50 years. Remarkably, for 50 of the 52 patients with IFD, a single fungus was involved; only two patients had IFDs due to two different fungi. IFD recurred in 44 of 45 patients who responded to treatment, and a different fungal infection occurred in the remaining patient. Ten patients died from IFD, between the ages of 12 and 39 years, whereas another patient died at the age of 91 years, from an unrelated cause. At the most recent scheduled follow-up visit, 81% of the patients were still alive and aged from 6.5 to 75 years. Strikingly, all the causal fungi belonged to the phylum Ascomycota: commensal Candida and saprophytic Trychophyton, Aspergillus, Phialophora, Exophiala, Corynesprora, Aureobasidium, and Ochroconis. Human CARD9 is essential for protective systemic immunity to a subset of fungi from this phylum but seems to be otherwise redundant. Previously healthy patients with unexplained invasive fungal infection, at any age, should be tested for inherited CARD9 deficiency.

KEY POINTS

• Inherited CARD9 deficiency (OMIM #212050) is an AR PID due to mutations that may be present in a homozygous or compound heterozygous state. • CARD9 is expressed principally in myeloid cells and transduces signals downstream from CLR activation by fungal ligands. • Endogenous mutant CARD9 levels differ between alleles (from full-length normal protein to an absence of normal protein). • The functional impacts of CARD9 mutations involve impaired cytokine production in response to fungal ligands, impaired neutrophil killing and/or recruitment to infection sites, and defects of Th17 immunity. • The key clinical manifestations in patients are fungal infections, including CMC, invasive (in the CNS in particular) Candida infections, extensive/deep dermatophytosis, subcutaneous and invasive phaeohyphomycosis, and extrapulmonary aspergillosis. • The clinical penetrance of CARD9 deficiency is complete, but penetrance is incomplete for each of the fungi concerned. • Age at onset is highly heterogeneous, ranging from childhood to adulthood for the same fungal disease. • All patients with unexplained IFD should be tested for CARD9 mutations. Familial screening and genetic counseling should be proposed. • The treatment of patients with CARD9 mutations is empirical and based on antifungal therapies and the surgical removal of fungal masses. Patients with persistent/relapsing Candida infections of the CNS could be considered for adjuvant GM-CSF/G-CSF therapy. The potential value of HSCT for CARD9-deficient patients remains unclear.

Innate Immunity against Cryptococcus, from Recognition to Elimination

Cryptococcus species, the etiological agents of cryptococcosis, are encapsulated fungal yeasts that predominantly cause disease in immunocompromised individuals, and are responsible for 15% of AIDS-related deaths worldwide. Exposure follows the inhalation of the yeast into the lung alveoli, making it incumbent upon the pattern recognition receptors (PRRs) of pulmonary phagocytes to recognize highly conserved pathogen-associated molecular patterns (PAMPS) of fungi. The main challenges impeding the ability of pulmonary phagocytes to effectively recognize Cryptococcus include the presence of the yeast's large polysaccharide capsule, as well as other cryptococcal virulence factors that mask fungal PAMPs and help Cryptococcus evade detection and subsequent activation of the immune system. This review will highlight key phagocyte cell populations and the arsenal of PRRs present on these cells, such as the Toll-like receptors (TLRs), C-type lectin receptors, NOD-like receptors (NLRs), and soluble receptors. Additionally, we will highlight critical cryptococcal PAMPs involved in the recognition of Cryptococcus. The question remains as to which PRR-ligand interaction is necessary for the recognition, phagocytosis, and subsequent killing of Cryptococcus.

C-type lectin receptors in anti-fungal immunity

Host immune systems are constantly engaged with fungal pathogens which are common in environments as well as in healthy human skin and mucosa. C-type lectin receptors (CLRs) are expressed in myeloid cells and play central roles in host defenses against fungal infections by coordinating innate and adaptive immune systems. Upon ligand binding, CLRs stimulate cellular responses by inducing the production of cytokines and reactive oxygen species via the Syk/CARD9 signaling pathway, leading to fungal elimination. Due to identification and characterization of the CLRs, the underlying mechanisms of the anti-fungal immunity are being unveiled in the present decade. In this review, we focus on the anti-fungal activities of CLRs and summarize of current knowledge of the related expression profiles, modes of ligand recognition, and signaling cascades.

Lectin Receptors Expressed on Myeloid Cells

Lectins recognize a diverse array of carbohydrate structures and perform numerous essential biological functions. Here we focus on only two families of lectins, the Siglecs and C-type lectins. Triggering of intracellular signaling cascades following ligand recognition by these receptors can have profound effects on the induction and modulation of immunity. In this chapter, we provide a brief overview of each family and then focus on selected examples that highlight how these lectins can influence myeloid cell functioning in health and disease. Receptors that are discussed include Sn (Siglec-1), CD33 (Siglec-3), and Siglec-5, -7, -8, -9, -10, -11, -14, -15, -E, -F, and -G as well as Dectin-1, MICL, Dectin-2, Mincle/MCL, and the macrophage mannose receptor.

Mechanism of pathogen recognition by human dectin-2

Dectin-2, a C-type lectin on macrophages and other cells of the innate immune system, functions in response to pathogens, particularly fungi. The carbohydrate-recognition domain (CRD) in dectin-2 is linked to a transmembrane sequence that interacts with the common Fc receptor γ subunit to initiate immune signaling. The molecular mechanism by which dectin-2 selectively binds to pathogens has been investigated by characterizing the CRD expressed in a bacterial system. Competition binding studies indicated that the CRD binds to monosaccharides with modest affinity and that affinity was greatly enhanced for mannose-linked α1–2 or α1–4 to a second mannose residue. Glycan array analysis confirmed selective binding of the CRD to glycans that contain Manα1–2Man epitopes. Crystals of the CRD in complex with a mammalian-type high-mannose Man₉GlcNAc₂ oligosaccharide exhibited interaction with Manα1–2Man on two different termini of the glycan, with the reducing-end mannose residue ligated to Ca²⁺ in a primary binding site and the nonreducing terminal mannose residue occupying an adjacent secondary site. Comparison of the binding sites in DC-SIGN and langerin, two other pathogen-binding receptors of the innate immune system, revealed why these two binding sites accommodate only terminal Manα1–2Man structures, whereas dectin-2 can bind Manα1–2Man in internal positions in mannans and other polysaccharides. The specificity and geometry of the dectin-2-binding site provide the molecular mechanism for binding of dectin-2 to fungal mannans and also to bacterial lipopolysaccharides, capsular polysaccharides, and lipoarabinomannans that contain the Manα1–2Man disaccharide unit.

Signalling through MyD88 drives surface expression of the mycobacterial receptors MCL (Clecsf8, Clec4d) and Mincle (Clec4e) following microbial stimulation

The heterodimeric mycobacterial receptors, macrophage C-type lectin (MCL) and macrophage inducible C-type lectin (Mincle), are upregulated at the cell surface following microbial challenge, but the mechanisms underlying this response are unclear. Here we report that microbial stimulation triggers Mincle expression through the myeloid differentiation primary response gene 88 (MyD88) pathway; a process that does not require MCL. Conversely, we show that MCL is constitutively expressed but retained intracellularly until Mincle is induced, whereupon the receptors form heterodimers which are translocated to the cell surface. Thus this "two-step" model for induction of these key receptors provides new insights into the underlying mechanisms of anti-mycobacterial immunity.

The C-Type Lectin Receptor MCL Mediates Vaccine-Induced Immunity against Infection with Blastomyces dermatitidis

C-type lectin receptors (CLRs) are essential in shaping the immune response to fungal pathogens. Vaccine-induced resistance requires Dectin-2 to promote differentiation of antifungal Th1 and Th17 cells. Since Dectin-2 and MCL heterodimerize and both CLRs use FcRγ as the signaling adaptor, we investigated the role of MCL in vaccine immunity to the fungal pathogen Blastomyces dermatitidis. MCL(-/-) mice showed impaired vaccine resistance against B. dermatitidis infection compared to that of wild-type animals. The lack of resistance correlated with the reduced recruitment of Th17 cells to the lung upon recall following experimental challenge and impaired interleukin-17 (IL-17) production by vaccine antigen-stimulated splenocytes in vitro. Soluble MCL fusion protein recognized and bound a water-soluble ligand from the cell wall of vaccine yeast, but the addition of soluble Dectin-2 fusion protein did not augment ligand recognition by MCL. Taken together, our data indicate that MCL regulates the development of vaccine-induced Th17 cells and protective immunity against lethal experimental infection with B. dermatitidis.

Mycobacterial receptor, Clec4d (CLECSF8, MCL), is coregulated with Mincle and upregulated on mouse myeloid cells following microbial challenge

The C‐type lectin receptor (CTLR), Clec4d (MCL, CLECSF8), is a member of the Dectin‐2 cluster of CTLRs, which also includes the related receptors Mincle and Dectin‐2. Like Mincle, Clec4d recognizes mycobacterial cord factor, trehalose dimycolate, and we recently demonstrated its key role in anti‐mycobacterial immunity in mouse and man. Here, we characterized receptor expression in naïve mice, under inflammatory conditions, and during Mycobacterium bovis BCG infection using newly generated monoclonal antibodies. In naïve mice, Clec4d was predominantly expressed on myeloid cells within the peritoneal cavity, blood, and bone marrow. Unexpectedly, basal expression of Clec4d was very low on leukocytes in the lung. However, receptor expression was significantly upregulated on pulmonary myeloid cells during M. bovis BCG infection. Moreover, Clec4d expression could be strongly induced in vitro and in vivo by various microbial stimuli, including TLR agonists, but not exogenous cytokines. Notably, we show that Clec4d requires association with the signaling adaptor FcRγ and Mincle, but not Dectin‐2, for surface expression. In addition, we provide evidence that Clec4d and Mincle, but not Dectin‐2, are interdependently coregulated during inflammation and infection. These data show that Clec4d is an inducible myeloid‐expressed CTLR in mice, whose expression is tightly linked to that of Mincle.

Systems Level Dissection of Candida Recognition by Dectins: A Matter of Fungal Morphology and Site of Infection

Candida albicans is an ubiquitous fungal commensal of human skin and mucosal surfaces, and at the same time a major life-threatening human fungal pathogen in immunocompromised individuals. Host defense mechanisms rely on the capacity of professional phagocytes to recognize Candida cell wall antigens. During the past decade, the host immune response to Candida was dissected in depth, highlighting the essential role of C-type lectin receptors, especially regarding the power of the Dectins’ family in discriminating between the tolerated yeast-like form of Candida and its invading counterpart, the hyphae. This review focuses on the immuno-modulatory properties of the Candida morphologies and their specific interactions with the host innate immune system in different body surfaces.

The Dectin-2 family of C-type lectin-like receptors: an update

New discoveries reveal crucial roles for the Dectin-2 family in many aspects of the immune response.

Myeloid and non-myeloid cells express members of the C-type lectin-like receptor (CTLR) family, which mediate crucial cellular functions during immunity and homeostasis. Of relevance here is the dendritic cell-associated C-type lectin-2 (Dectin-2) family of CTLRs, which includes blood dendritic cell antigen 2 (BDCA-2), dendritic cell immunoactivating receptor (DCAR), dendritic cell immunoreceptor (DCIR), Dectin-2, C-type lectin superfamily 8 (CLECSF8) and macrophage-inducible C-type lectin (Mincle). These CTLRs possess a single extracellular conserved C-type lectin-like domain and are capable of mediating intracellular signalling either directly, through integral signalling domains, or indirectly, by associating with signalling adaptor molecules. These receptors recognize a diverse range of endogenous and exogenous ligands, and can function as pattern recognition receptors for several classes of pathogens including fungi, bacteria and parasites, driving both innate and adaptive immunity. In this review, we summarize our knowledge of each of these receptors, highlighting the exciting discoveries that have been made in recent years.

Role of the C-type lectin receptors MCL and DCIR in experimental colitis

Inflammatory bowel disease (IBD) is a chronic inflammatory disorder of the gastrointestinal tract. Though its exact etiology is still unclear, it is proposed that an imbalance in the intestinal homeostasis leads to a disturbed interaction between commensal microbiota and the mucosal immune system. Previous studies have shown that both innate and adaptive immunity are involved in an overwhelming colon inflammation, and thus contribute to the pathogenesis of IBD. In innate immunity, several pattern recognition receptors such as Toll-like receptors, NOD-like receptors or C-type lectin receptors (CLRs) are involved in IBD pathogenesis. Myeloid CLRs are mainly expressed by antigen-presenting cells and bind to glycan structures present on self or foreign antigens. The Macrophage-restricted C-type lectin (MCL) and the Dendritic cell immunoreceptor (DCIR) are two poorly characterized members of the CLR family. In this study, we investigated the role of MCL and DCIR in the pathogenesis of murine colitis. Both CLRs bound to intestinal microbiota to a different extent. They modulated the production of pro-inflammatory cytokines by antigen-presenting cells upon stimulation with heat-killed microbiota and impacted subsequent T cell responses. To analyze whether MCL and DCIR contribute to the pathogenesis of IBD, the dextran sulfate sodium (DSS) murine colitis model was employed. MCL^−/− as well as DCIR^−/− mice exhibited only a slightly increased severity of disease compared to wild-type mice indicating a limited role for MCL and DCIR in the regulation of intestinal immunity.

MCL and Mincle: C-Type Lectin Receptors That Sense Damaged Self and Pathogen-Associated Molecular Patterns

Macrophage C-type lectin (MCL) and macrophage inducible C-type lectin (Mincle) comprise part of an extensive repertoire of pattern recognition receptors with the ability to sense damage-associated and pathogen-associated molecular patterns. In this review, we cover the discovery and molecular characterization of these C-type lectin receptors, and highlight recent advances in the understanding of their roles in orchestrating the response of the immune system to bacterial and fungal infection, and damaged self. We also discuss the identification and structure-activity relationships of activating ligands, particularly trehalose dimycolate and related mycobacterial glycolipids, which have significant potential in the development of TH1/TH17 vaccination strategies.

Signaling while eating: MCL is coupled with Mincle

Recently, C-type lectin receptors (CLRs) have been identified as a newly emerging family of pattern-recognition receptors for pathogen-associated molecular patterns. The ligand and function of many "individual" CLRs have been clarified in the past few years. A new report by Lobato-Pascual et al. in this issue of the European Journal of Immunology [Eur. J. Immunol. 2013. 43: 3167-3174] shows that a rat CLR, named macrophage C-type lectin (also called Clec4d), forms a heterodimer with another CLR, macrophage inducible C-type lectin (also called Clec4e). This finding sheds light on a possible synergistic regulation of different C-type lectin receptors by forming heterodimers: such heterodimers may amplify signaling, expand ligand specificity, or confer multiple functions.

Mincle, the receptor for mycobacterial cord factor, forms a functional receptor complex with MCL and FcεRI-γ

Upon receptor activation, the myeloid C-type lectin receptor Mincle signals via the Syk-CARD9-Bcl10-MALT1 pathway. It does so by recruiting the ITAM-bearing FcεRI-γ. The related receptor macrophage C-type Lectin (MCL) has also been shown to be associated with Syk and to be dependent upon this signaling axis. We have previously shown that MCL co-precipitates with FcεRI-γ, but were unable to show a direct association, suggesting that MCL associates with FcεRI-γ via another molecule. Here, we have used rat primary cells and cell lines to investigate this missing link. A combination of flow cytometric and biochemical analysis showed that Mincle and MCL form heteromers on the cell surface. Furthermore, association with MCL and FcεRI-γ increased Mincle expression and enhanced phagocytosis of Ab-coated beads. The results presented in this paper suggest that the Mincle/MCL/FcεRI-γ complex is the functionally optimal form for these C-type lectin receptors on the surface of myeloid cells.

Transcriptional and post-transcriptional regulation of IκB-ζ upon engagement of the BCR, TLRs and FcγR

IκB-ζ is a nuclear IκB protein robustly induced in macrophages and fibroblasts upon TLR or IL-1R stimulation. IκB-ζ associates with NF-κB in the cell nucleus and is essential for the induction of a subset of secondary response genes represented by IL-6. Here, we analyzed induction of IκB-ζ in mouse B cells and found that IκB-ζ is induced by BCR or TLR stimulation. Similar to TLR stimulation, BCR stimulation elicited NF-κB-mediated transcriptional activation and mRNA stabilization of IκB-ζ via a cis-element in IκB-ζ mRNA. Proteasome inhibitors inhibited transcriptional activation but not post-transcriptional activation, indicating independency of the two signals. Co-stimulation of the BCR and TLR9 or TLR7, but not TLR2/1, synergistically induced IκB-ζ. Co-engagement of inhibitory Fcγ receptor suppressed BCR-mediated IκB-ζ expression but not that induced by TLR stimulation alone or co-stimulation of TLR and the BCR. The PI3K inhibitor LY294002 inhibited BCR-mediated, but not TLR-mediated, induction of IκB-ζ, consistent with the role of PI3K in BCR signaling and its suppression by FcγR. Analysis of IκB-ζ-deficient B cells demonstrated that IκB-ζ was essential upon stimulation of BCR or TLR for the expression of several genes including IL-10 and CTLA4. IκB-ζ-deficient B cells exhibited impaired proliferation and enhanced up-regulation of CD86 following stimulation of TLR9, but not the BCR, indicating critical roles for IκB-ζ in TLR signaling in B cells. Strict regulatory mechanisms for the induction of IκB-ζ via multiple pathways and its essential function upon stimulation indicate that IκB-ζ plays an important role in B cells.

C-type lectin MCL is an FcRγ-coupled receptor that mediates the adjuvanticity of mycobacterial cord factor

Cord factor, also called trehalose-6,6'-dimycolate (TDM), is a potent mycobacterial adjuvant. We herein report that the C-type lectin MCL (also called Clec4d) is a TDM receptor that is likely to arise from gene duplication of Mincle (also called Clec4e). Mincle is known to be an inducible receptor recognizing TDM, whereas MCL was constitutively expressed in myeloid cells. To examine the contribution of MCL in response to TDM adjuvant, we generated MCL-deficient mice. TDM promoted innate immune responses, such as granuloma formation, which was severely impaired in MCL-deficient mice. TDM-induced acquired immune responses, such as experimental autoimmune encephalomyelitis (EAE), was almost completely dependent on MCL, but not Mincle. Furthermore, by generating Clec4e(gfp) reporter mice, we found that MCL was also crucial for driving Mincle induction upon TDM stimulation. These results suggest that MCL is an FcRγ-coupled activating receptor that mediates the adjuvanticity of TDM.

Rat macrophage C-type lectin is an activating receptor expressed by phagocytic cells

Macrophage C-type lectin (MCL) is a membrane surface receptor encoded by the Antigen Presenting Lectin-like gene Complex (APLEC). We generated a mouse monoclonal antibody for the study of this receptor in the rat. We demonstrate that rat MCL is expressed on blood monocytes and neutrophils, as well as on several tissue macrophage populations, including alveolar and peritoneal cavity macrophages. We also demonstrate MCL expression on a subset of resident spleen macrophages. Immunohistochemistry analysis of the spleen showed staining specifically in the marginal zone and red pulp. Exposure to pro-inflammatory mediators or to yeast cell wall extract (zymosan) increased surface MCL expression on peritoneal macrophages. We characterized a rat myeloid cell line, RMW, which expresses high levels of MCL. We found that MCL co-immunoprecipitated with the activating adaptor protein FcεRIγ in these cells. Moreover, beads coated with anti-MCL antibody increased phagocytosis in the RMW cells. Together, these observations indicate that rat MCL is a receptor that activates phagocytosis in myeloid cells under inflammatory conditions.

The C-type lectin receptor CLECSF8 (CLEC4D) is expressed by myeloid cells and triggers cellular activation through Syk kinase

CLECSF8 is a poorly characterized member of the "Dectin-2 cluster" of C-type lectin receptors and was originally thought to be expressed exclusively by macrophages. We show here that CLECSF8 is primarily expressed by peripheral blood neutrophils and monocytes and weakly by several subsets of peripheral blood dendritic cells. However, expression of this receptor is lost upon in vitro differentiation of monocytes into dendritic cells or macrophages. Like the other members of the Dectin-2 family, which require association of their transmembrane domains with signaling adaptors for surface expression, CLECSF8 is retained intracellularly when expressed in non-myeloid cells. However, we demonstrate that CLECSF8 does not associate with any known signaling adaptor molecule, including DAP10, DAP12, or the FcRγ chain, and we found that the C-type lectin domain of CLECSF8 was responsible for its intracellular retention. Although CLECSF8 does not contain a signaling motif in its cytoplasmic domain, we show that this receptor is capable of inducing signaling via Syk kinase in myeloid cells and that it can induce phagocytosis, proinflammatory cytokine production, and the respiratory burst. These data therefore indicate that CLECSF8 functions as an activation receptor on myeloid cells and associates with a novel adaptor molecule. Characterization of the CLECSF8-deficient mice and screening for ligands using oligosaccharide microarrays did not provide further insights into the physiological function of this receptor.

Effects of single genetic damage in carbohydrate-recognizing proteins in mouse serum N-glycan profile revealed by simple glycotyping analysis

Gene knock-out of C-type lectin receptors expressed in dendritic cells induced significant alteration of serum N-glycans compared with that of gender-matched controls. Glycotyping analysis suggested that putative-core fucosylation is strongly influenced by differences in the dominant mechanisms after carbohydrate recognition by pattern-recognition receptors, endocytosis of ligands, or induction of cytokines/chemokines. However, the loss of galectin-9, a ligand for T-helper type 1-specific cell-surface molecule, did not affect most N-glycan profiles. Interestingly, lack of the Chst3 gene (chondroitin 6-sulfotransferase) appeared to influence markedly the expression of most N-glycans, especially highly modified glycoforms bearing multiple Neu5Gc, Fuc, and LacNAc units. In contrast, genetic mutations in B4galnt1 and B4galnt2 (GalNAc transferase, responsible for the synthesis of many gangliosides) induced no discernable alteration. These results indicate that the biosynthesis of N-glycans of serum glycoproteins can be affected not only by direct genetic mutations in the glycosyltransferases but also by changes in metabolite availability in sugar nucleotide synthesis and Golgi N-glycosylation pathways caused concertedly in whole cells, tissues, and organs by milder deficiencies in immune cell-surface lectins. Many common chronic conditions, such as autoimmunity, metabolic syndrome, and aging/dementia result.

Signaling by myeloid C-type lectin receptors in immunity and homeostasis

Myeloid cells are key drivers of physiological responses to pathogen invasion or tissue damage. Members of the C-type lectin receptor (CLR) family stand out among the specialized receptors utilized by myeloid cells to orchestrate these responses. CLR ligands include carbohydrate, protein, and lipid components of both pathogens and self, which variably trigger endocytic, phagocytic, proinflammatory, or anti-inflammatory reactions. These varied outcomes rely on a versatile system for CLR signaling that includes tyrosine-based motifs that recruit kinases, phosphatases, or endocytic adaptors as well as nontyrosine-based signals that modulate the activation of other pathways or couple to the uptake machinery. Here, we review the signaling properties of myeloid CLRs and how they impact the role of myeloid cells in innate and adaptive immunity.

The Dectin-2 family of C-type lectins in immunity and homeostasis

C-type lectins are a diverse family of proteins which recognize a wide range of ligands. This review focuses on the Dectin-2 family of C-type lectins that includes Dectin-2, BDCA-2, DCIR, DCAR, Clecsf8 and Mincle whose genes are clustered in the telomeric region of the NK-gene cluster on mouse chromosome 6 and human chromosome 12. These type II receptors are expressed on myeloid and non-myeloid cells and contain a single extracellular carbohydrate recognition domain and have diverse functions in both immunity and homeostasis. DCIR is the only member of the family which contains a cytoplasmic signalling motif and has been shown to act as an inhibitory receptor, while BDCA-2, Dectin-2, DCAR and Mincle all associate with FcRγ chain to induce cellular activation, including phagocytosis and cytokine production. Dectin-2 and Mincle have been shown to act as pattern recognition receptors for fungi, while DCIR acts as an attachment factor for HIV. In addition to pathogen recognition, DCIR has been shown to be pivotal in preventing autoimmune disease by controlling dendritic cell proliferation, whereas Mincle recognizes a nuclear protein released by necrotic cells. Here we review each of these receptors in detail describing their expression, ligand recognition, signalling and known physiological functions.

GpnmbIs Induced in Macrophages by IFN-γ and Lipopolysaccharide and Acts as a Feedback Regulator of Proinflammatory Responses

The process of inflammation requires the selective expression of a suite of genes in cells of the macrophage lineage. To identify candidate regulators of inflammation, we used cDNA microarrays to compare the transcriptome of inflammatory macrophages (thioglycolate-elicited peritoneal macrophages), bone marrow-derived macrophages, nonadherent spleen cells, and fibroblasts. We identified genes that were macrophage restricted and further elevated in inflammatory macrophages, and characterized the function of one such gene, gpnmb. Gpnmb mRNA expression was enriched in myelomonocytic cell lines and macrophage-related tissues and strongly up-regulated during macrophage differentiation. Epitope-tagged GPNMB expressed in RAW264.7 cells exhibited a perinuclear distribution and colocalized with the Golgi marker coat protein beta. Upon activation of macrophages with IFN-gamma and LPS, GPNMB translocated from the Golgi apparatus to vesicular compartments scattered toward the periphery. Gpnmb overexpression in RAW264.7 cells caused a 2-fold reduction in the production of the cytokines IL-6 and IL-12p40 and the inflammatory mediator NO in response to LPS. DBA mice, which have an inactivating point mutation in the gpnmb gene, exhibited reduced numbers of myeloid cells, elevated numbers of thioglycolate-elicited peritoneal macrophages, and higher levels of proinflammatory cytokines in response to LPS. Thus, GPNMB acts as a negative regulator of macrophage inflammatory responses.

Friend of GATA-1-independent transcriptional repression: a novel mode of GATA-1 function

The GATA-1-interacting protein Friend Of GATA-1 (FOG-1) is essential for the proper transcriptional activation and repression of numerous GATA-1 target genes. Although FOG-1-independent activation by GATA-1 has been described, all known examples of GATA-1-mediated repression are FOG-1 dependent. In the GATA-1-null G1E cell line, estrogen receptor ligand binding domain (ER) chimeras of either wild-type GATA-1 or a FOG-1-binding defective mutant of GATA-1 repressed several genes similarly upon activation with beta-estradiol. Repression also occurred in a FOG-1-null cell line expressing ER-GATA-1 and during ex vivo erythropoiesis. At the Lyl1 and Rgs18 loci, we found highly restricted occupancy by GATA-1 and GATA-2, indicating that these genes are direct targets of GATA factor regulation. The identification of genes repressed by GATA-1 independent of FOG-1 defines a novel mode of GATA-1-mediated transcriptional regulation.

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.

Role of the aryl hydrocarbon receptor in thymocyte emigration in vivo

The aryl hydrocarbon receptor (AHR) is a ligand-dependent member of the PAS-bHLH-family of nuclear receptors. Anthropogenic ligands include environmental contaminants such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Over-activation of the AHR causes thymus atrophy and immunosuppression. Signaling via the AHR changes the thymocyte differentiation program at several checkpoints, in particular within the CD4-CD8- double-negative (DN) thymocyte subset. Here, we show that AHR over-activation led to the preferential emigration of DN thymocytes to the periphery and accumulation in the spleen. Some of these recent thymic emigrants (RTE) had a novel "activated immature" phenotype (CD3-TCRbeta-CD25+/intCD44-CD45RB+/intCD62L+CD69- cells). Gene expression profiling of DN RTE revealed 15 genes that were up-regulated more than threefold by TCDD, including the S100A9 gene. Exposure of S100A9 null mice to TCDD showed a role for this protein in AHR-mediated thymic egress.

Macrophage receptors and immune recognition

Macrophages express a broad range of plasma membrane receptors that mediate their interactions with natural and altered-self components of the host as well as a range of microorganisms. Recognition is followed by surface changes, uptake, signaling, and altered gene expression, contributing to homeostasis, host defense, innate effector mechanisms, and the induction of acquired immunity. This review covers recent studies of selected families of structurally defined molecules, studies that have improved understanding of ligand discrimination in the absence of opsonins and differential responses by macrophages and related myeloid cells.

Gene expression profiling in type 1 diabetes prone NOD mice immunized with a disease protective autoantigenic peptide

Immunization with autoantigenic peptides skews T cell responses in type 1 diabetes (T1D), yet the gene-expression signature characterizing this change is unclear. We used cDNA microarray technology to identify genes differentially regulated in splenocytes of T1D prone NOD mice after immunization with a disease protective glutamic acid decarboxylase 65 (GAD(65) P14) peptide. We identified 96 genes involved in cytokine secretion, humoral immune response, T cell activation, signal transduction, cell proliferation, complement activation and inflammatory responses. Up-regulation of seven chemokine and cytokine genes confirmed our previous findings of increased interferon-gamma (IFN-gamma) secretion, which may lead to a protective response in T1D. Hierarchical clustering was used to organize treated and control groups on the basis of their overall similarity in gene-expression patterns, suggesting association or co-regulation. Semi-quantitative RT-PCR was used to confirm the expression of selected genes in spleen and pancreatic draining lymph nodes. These findings can be used to compare other immunization strategies affecting the expression of these genes and explore their mechanisms of action. This microarray-based study, thus, unravels the molecular mechanism of beta-cell associated autoantigenic peptide immunization in T1D prone NOD mice, paving the way for identification of diagnostic markers and drug targets for modulating immune responses in T1D.

Identification of lectin-like receptors expressed by antigen presenting cells and neutrophils and their mapping to a novel gene complex

In an experimental rat model, we recently mapped an arthritis susceptibility locus to the distal part of Chromosome 4 containing genes predicted to encode C-type lectin superfamily (CLSF) receptors. Here we report the cDNA cloning and positional arrangement of these receptor genes, which represent rat orthologues to human Mincle and DCIR and to mouse MCL and Dectin-2, as well as four novel receptors DCIR2, DCIR3, DCIR4 and DCAR1, not previously reported in other species. We furthermore report the cDNA cloning of human Dectin-2 and MCL, and of the mouse orthologues to the novel rat receptors. Similar to the killer-cell lectin-like receptors (KLR) some of these receptors exhibit structural features suggesting that they regulate leukocyte reactivity; e.g., human DCIR and rodent DCIR1 and DCIR2 carry an immunoreceptor tyrosine-based inhibitory motif (ITIM), predicting inhibitory function, and conversely, in all three species Mincle has a positively charged amino acid in the transmembrane region, suggesting activating function. Sequence comparisons show that the receptors form a discrete family, more closely related to group II CLSF receptors than to the group V KLR. Their distance to the KLR is underscored by their preservation of evolutionary conserved calcium/saccharide binding residues, present in group II and lacking in group V CLSF and their cellular expression patterns, with most of the genes preferentially expressed by professional antigen-presenting cells (dendritic cells, macrophages and B cells) and neutrophils. In all three species, the genes map together, forming an evolutionary conserved gene complex, which we call the antigen presenting lectin-like receptor complex (APLEC).

Signaling and immune regulatory role of the dendritic cell immunoreceptor (DCIR) family lectins: DCIR, DCAR, dectin-2 and BDCA-2

This review focuses on a distinct family of dendritic cells (DC) expressing C-type lectins that include DC immunoreceptor (DCIR), DC immunoactivating receptor (DCAR), DC-associated C-type lectin (dectin)-2 and blood DC antigen (BDCA)-2. DCIR is a type II C-type lectin expressed on antigen presenting cells and granulocytes and acts as an inhibitory receptor via an intracellular immunoreceptor tyrosine-based inhibitory motif (ITIM). In contrast, DCAR has been identified as a molecule that forms a putative pair with DCIR. While both molecules share the highly homologous extracellular lectin domain, DCAR lacks the ITIM in its short cytoplasmic tail and acts as an activating receptor through association with the Fc receptor gamma chain. Two other lectins, dectin-2 and BDCA-2, are highly related to DCAR by similarities of their amino acid sequence, molecular structure and chromosomal localization. Although they also lack the ITIM, they are capable of transducing signal to regulate cellular functions positively or negatively. Here we propose to designate these four highly related molecules as the "DCIR family lectins" and discuss their signaling mechanisms, carbohydrate recognition, and other features that contribute to the function of DC to control immunity.

Transcript signatures in experimental asthma: identification of STAT6-dependent and -independent pathways

The analysis of polygenic diseases such as asthma poses a challenging problem. In an effort to provide unbiased insight into disease pathogenesis, we took an empirical approach involving transcript expression profiling of lung tissue from mice with experimental asthma. Asthmatic responses were found to involve sequential induction of 4.7% of the tested genome; notably, there was ectopic expression of a series of genes not previously implicated in allergic or pulmonary responses. Genes were widely distributed throughout all chromosomes, but preferentially included genes involved in immunity, development, and homeostasis. When asthma was induced by two independent experimental regimens, unique gene transcript profiles were found depending upon the mode of disease induction. However, the majority of genes were common to both models representing an asthma signature genome. Analysis of STAT6-deficient mice revealed that an unexpectedly large segment of the asthma genes were STAT6 independent; this correlated with sustained inflammatory events in these mice. Notably, induction of asthma in STAT6-deficient mice resulted in gene induction not seen in wild-type mice. These results raise concern that therapeutic blockade of STAT6 in the asthmatic setting may reprogram the genetic signature, resulting in alternative lung pathology, which we indeed observed in STAT6-deficient mice. These results provide unprecedented insight into the complex steps involved in the pathogenesis of allergic airway responses; as such, these results have significant therapeutic and clinical implications.

Dendritic cell immunoactivating receptor, a novel C-type lectin immunoreceptor, acts as an activating receptor through association with Fc receptor gamma chain

An increasing number of C-type lectin receptors are being discovered on dendritic cells, but their signaling abilities and underlying mechanisms require further definition. Among these, dendritic cell immunoreceptor (DCIR) induces negative signals through an inhibitory immunoreceptor tyrosine-based inhibitory motif (ITIM) in its cytoplasmic tail. Here we identify a novel C-type lectin receptor, dendritic cell immunoactivating receptor (DCAR), whose extracellular lectin domain is highly homologous to that of DCIR. DCAR is expressed similarly in tissues to DCIR, but its short cytoplasmic portion lacks signaling motifs like ITIM. However, a positively charged arginine residue is present in the transmembrane region of the DCAR, which may explain its association with Fc receptor gamma chain and its stable expression on the cell surface. Furthermore, cross-linking of DCAR in the presence of gamma chain activates calcium mobilization and tyrosine phosphorylation of cellular proteins. These signals are mediated by the immunoreceptor tyrosine-based activating motif (ITAM) of the gamma chain. Thus, DCAR is closely related to DCIR, but it introduces activating signals into antigen-presenting cells through its physical and functional association with ITAM-bearing gamma chain. The identification of this activating immunoreceptor provides an example of signaling via a dendritic cell-expressed C-type lectin receptor.

Human macrophage lectin specific for galactose/N-acetylgalactosamine is a marker for cells at an intermediate stage in their differentiation from monocytes into macrophages

We studied the expression of a human macrophage lectin specific for galactose/N-acetylgalactosamine (hMGL) during macrophage differentiation. The expression of hMGL during the in vitro differentiation induced by human serum was examined by immunostaining and Western blotting with a specific mAb, MLD-1, as well as with RT-PCR analysis. hMGL was detected on cells at an intermediate stage of differentiation. These cells were round, slightly larger in size (12.7 +/- 0.2 microm) than monocytes (9.8 +/- 0.1 microm) and expressed the macrophage marker CD14, but lacked the dendritic cell marker CD1a. The highest levels of expression occurred after 2-4 days of culture. At this time point, MLD-1 prominently stained 20-40% of the cells. Monocytes cultured for 16 h or fully differentiated monocyte-derived macrophages were negative or weak for hMGL expression. Similar transient expression was also observed during granulocyte macrophage colony stimulating factor- or macrophage colony stimulating factor-dependent macrophage differentiation. The lectin was characterized as a functional endocytic receptor for glycosylated macromolecules, since the uptake of carbohydrate polymers was partially inhibited by the addition of MLD-1. The distribution of hMGL(+) cells in normal human skin was found by immunostaining to be mainly in the upper dermis distant from vascular structures. More than 90% of the hMGL(+) cells were double stained with anti-CD68 mAb and constituted approximately 20% of the CD68(+) cells. We suggest that the dermal hMGL(+) cells are a subset of differentiated cells derived from monocytes and that hMGL is a unique marker for cells at an intermediate stage of macrophage differentiation.

New alternatively spliced form of galectin-3, a member of the beta-galactoside-binding animal lectin family, contains a predicted transmembrane-spanning domain and a leucine zipper motif

Osteoclasts or their precursors interact with the glycoprotein-enriched matrix of bone during extravasation from the vasculature, and upon attachment prior to resorption. Reverse transcriptase-PCR studies showed that two new alternatively spliced forms of chicken galectin-3, termed Gal-3TM1 and Gal-3TR1, were enriched and preferentially expressed in highly purified chicken osteoclast-like cells. Gal-3TM1 and Gal-3TR1 mRNA were also detected in chicken intestinal tissue, but not in kidney, liver, or lung. Gal-3TM1 and Gal-3TR1 messages both contain an open reading frame encoding a predicted 70-amino acid TM1 sequence inserted between the N-terminal Gly/Pro repeat domain and the carbohydrate recognition domain (exons 3 and 4). Gal-3TR1 mRNA contains an additional 241-bp sequence, which encodes a truncated open reading frame between the 4th and 5th exons, and, whose translation is expected to terminate within the carbohydrate recognition domain encompassing exons 4, 5, and 6. Immunoblotting and affinity chromatography showed that purified osteoclast preparations and intestinal homogenates contained a 36-kDa lactose-binding galectin. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometric analyses on chymotryptic peptides from the 36-kDa lectin confirmed its identity as Gal-3TM1. The TM1 insert contains a single transmembrane-spanning region and a leucine zipper-like stalk domain that is predicted to position the intact carbohydrate recognition domain of Gal-3TM1 on the exterior surface of the plasma membrane. Immunofluorescent staining of chicken osteoclasts confirmed the expression of Gal-3TM1 at the plasma membrane. Gal-3TM1 is the first example of a galectin superfamily member capable of being expressed as a soluble protein and as a transmembrane protein.

Organization of the mouse macrophage C-type lectin (Mcl) gene and identification of a subgroup of related lectin molecules

A number of genes encoding C-type lectin molecules have been mapped to the natural killer gene complex (NKC) at the distal region of mouse chromosome 6 and to a syntenic region on human chromosome 12p12-p13. In addition to those receptors which regulate NK cell function, related structures expressed on other cells types have also been localized to this chromosomal region. Among these are a number of recently characterized genes, including macrophage C-type lectin (MCL), macrophage-inducible C-type lectin (Mincle), dendritic cell immunoreceptor (DCIR) and dendritic cell-associated lectin-2 (Dectin-2). The amino acid sequences comprising the single C-type lectin domains of MCL, Mincle, DCIR and Dectin-2 are shown here to be closely related to each other. These molecules show overall similarity to two groups of animal C-type lectins, groups II and V, which demonstrate type II transmembrane topology. In this study, sequence analysis suggests that MCL, Mincle, DCIR and Dectin-2 represent a subset of group II-related C-type lectins which may participate in analogous recognition events on macrophages and dendritic cells. The genomic organization of the MCL gene and the sequence of the promoter region, with putative regulatory elements, were determined from a mouse MCL genomic DNA clone and are described here in detail.

DCIR acts as an inhibitory receptor depending on its immunoreceptor tyrosine-based inhibitory motif

Major histocompatibility complex class II positive cells, namely dendritic cells, monocytes/macrophages, and B cells, are categorized as antigen-presenting cells. Dendritic cells, so-called professional antigen-presenting cells, use distinct sets of surface receptors before and after maturation: those to capture antigens and those to interact with T cells, respectively. But there remain many surface molecules whose functions are still unknown. In this study, we isolated dendritic cell immunoreceptor from mouse bone-marrow-derived mature dendritic cells. Dendritic cell immunoreceptor is a recently reported C-type lectin receptor characteristic with cytoplasmic immunoreceptor tyrosine-based inhibitory motif. Expression of mouse dendritic cell immunoreceptor mRNA was observed specifically in spleen and lymph node, slightly increased with dendritic cell maturation during in vitro culture of bone marrow cells, and was not detected in cultured natural killer cells. Surface expression of mouse dendritic cell immunoreceptor protein was observed in splenic antigen-presenting cells including B cells, monocytes/macrophages, and dendritic cells, but not in T cells. To reveal the downregulating capacity of dendritic cell immunoreceptor in antigen-presenting cells, the change of B-cell-receptor-mediated signals after coligation with a chimeric Fcgamma receptor IIB containing the cytoplasmic portion of mouse dendritic cell immunoreceptor was examined. As a result, we detected two distinct inhibitory effects of cytoplasmic dendritic cell immunoreceptor minus sign inhibition of B-cell-receptor-mediated Ca2+ mobilization and protein tyrosine phosphorylation minus sign and both of these effects required the tyrosine residue inside the immunoreceptor tyrosine-based inhibitory motif. This report presents immunoreceptor tyrosine-based inhibitory motif-dependent negative regulatory function of dendritic cell immunoreceptors. In conclusion, mouse dendritic cell immunoreceptor expressed on antigen-presenting cells can exert two distinct inhibitory signals depending on its immunoreceptor tyrosine-based inhibitory motif tyrosine residue.

Molecular and genomic characterization of human DLEC, a novel member of the C-type lectin receptor gene family preferentially expressed on monocyte-derived dendritic cells

We have identified a novel gene encoding a protein designated DLEC (dendritic cell lectin), which is a type II membrane glycoprotein of 213 amino acids and belongs to the human calcium-dependent (C-type) lectin family. The cytoplasmic tail of DLEC lacks consensus signaling motifs and its extracellular region shows a single carbohydrate recognition domain (CRD), closest in homology to the dendritic cell immunoreceptor (DCIR) CRD. The DLEC gene has been localized linked to DCIR on the telomeric region of the NK gene complex. RT-PCR and Northern blot analyses show that DLEC mRNA is preferentially expressed in monocyte-derived dendritic cells.