C-type Lectin Receptor Dectin-1 Research Articles

Differential pathways regulating innate and adaptive antitumor immune responses by particulate and soluble yeast-derived β-glucans

Abstractβ-glucans have been reported to function as a potent adjuvant to stimulate innate and adaptive immune responses. However, β-glucans from different sources are differential in their structure, conformation, and thus biologic activity. Different preparations of β-glucans, soluble versus particulate, further complicate their mechanism of action. Here we show that yeast-derived particulate β-glucan activated dendritic cells (DCs) and macrophages via a C-type lectin receptor dectin-1 pathway. Activated DCs by particulate β-glucan promoted Th1 and cytotoxic T-lymphocyte priming and differentiation in vitro. Treatment of orally administered yeast-derived particulate β-glucan elicited potent antitumor immune responses and drastically down-regulated immunosuppressive cells, leading to the delayed tumor progression. Deficiency of the dectin-1 receptor completely abrogated particulate β-glucan–mediated antitumor effects. In contrast, yeast-derived soluble β-glucan bound to DCs and macrophages independent of the dectin-1 receptor and did not activate DCs. Soluble β-glucan alone had no therapeutic effect but significantly augmented antitumor monoclonal antibody-mediated therapeutic efficacy via a complement activation pathway but independent of dectin-1 receptor. These findings reveal the importance of different preparations of β-glucans in the adjuvant therapy and allow for the rational design of immunotherapeutic protocols usable in clinical trials.

Recognition of non-self-polysaccharides by C-type lectin receptors dectin-1 and dectin-2

Recognition of non-self-polysaccharides by C-type lectin receptors dectin-1 and dectin-2

Dectin-1 Y238X polymorphism associates with susceptibility to invasive aspergillosis in hematopoietic transplantation through impairment of both recipient- and donor-dependent mechanisms of antifungal immunity

AbstractThe C-type lectin receptor Dectin-1 plays a pivotal role in antifungal immunity. In this study, the recently characterized human DECTIN1 Y238X early stop codon polymorphism leading to diminished Dectin-1 receptor activity was studied in relation to invasive aspergillosis susceptibility and severity in patients receiving hematopoietic stem cell transplantation. We found that the presence of the DECTIN1 Y238X polymorphism in either donors or recipients of hematopoietic stem cell transplantation increased susceptibility to aspergillosis, with the risk being highest when the polymorphism was present simultaneously in both donors and recipients (adjusted hazard ratio = 3.9; P = .005). Functionally, the Y238X polymorphism impaired the production of interferon-γ and interleukin-10 (IL-10), in addition to IL-1β, IL-6, and IL-17A, by human peripheral mononuclear cells and Dectin-1 on human epithelial cells contributed to fungal recognition. Mechanistically, studies on preclinical models of infection in intact or bone marrow-transplanted Dectin-1 knockout mice revealed that protection from infection requires a distinct, yet complementary, role of both donor and recipient Dectin-1. This study discloses Dectin-1 deficiency as a novel susceptibility factor for aspergillosis in high-risk patients and identifies a previously unsuspected role for Dectin-1 in antifungal immunity that is the ability to control both resistance and tolerance to the fungus contingent on hematopoietic/nonhematopoietic compartmentalization.

Induction of reactive oxygen species in bovine neutrophils is CD11b, but not dectin-1-dependent

Neutrophils play a key role in initiating an innate immune response, being the first type of immune cell arriving at the site of injury or infection. These cells are able to mount a direct anti-bactericidal response by the production of reactive oxygen or reactive nitrogen species (ROS/RNS). An important component of the host innate immune response is recognition of pathogen-associated molecular patterns (PAMPs) by pattern recognition receptors (PRRs). Toll-like receptors (TLRs) are an important family of PRRs and, are a key component in activation of innate immune mechanisms. In the present study we described the presence of mRNA transcripts for TLR1, TLR2, TLR4, TLR6, TLR7 and TLR10 in bovine neutrophils. In contrast, the presence of mRNA transcripts for TLR3 varied between animals, whereas no transcripts were detected for TLR5, TLR8, TLR9 or the C-type lectin receptor dectin-1 in neutrophils isolated from bovine blood. Additionally, zymosan, a dectin-1/TLR2 ligand, induced ROS, but not RNS production in a CD11b-, but not dectin-1-dependent manner. This effect was dependent on Store Operated Calcium Entry (SOCE), and partially inhibited using monoclonal antibodies to CD11b. Taken together, our data describe the presence of specific PRRs transcripts in the mRNA isolated from bovine neutrophil and show a CD11b-/Ca 2+ dependent ROS production by these cells.

Cot/tpl2 (MAP3K8) Mediates Myeloperoxidase Activity and Hypernociception following Peripheral Inflammation*

Cot/tpl2 (also known as MAP3K8) has emerged as a new and potentially interesting therapeutic anti-inflammatory target. Here, we report the first study of Cot/tpl2 involvement in acute peripheral inflammation in vivo. Six hours after an intraplantar injection of zymosan, Cot/tpl2(-/-) mice showed a 47% reduction in myeloperoxidase activity, concomitant with a 46% lower neutrophil recruitment and a 40% decreased luminol-mediated bioluminescence imaging in vivo. Accordingly, Cot/tpl2 deficiency provoked a 25-30% reduction in luminol-mediated bioluminescence and neutrophil recruitment together with a 65% lower macrophage recruitment 4 h following zymosan-induced peritonitis. Significantly impaired levels of G-CSF and GM-CSF and of other cytokines such as TNFα, IL-1β, and IL-6, as well as some chemokines such as MCP-1, MIP-1β, and keratinocyte-derived chemokine, were detected during the acute zymosan-induced intraplantar inflammatory response in Cot/tpl2(-/-) mice. Moreover, Cot/tpl2 deficiency dramatically decreased the production of the hypernociceptive ligand NGF at the inflammatory site during the course of inflammation. Most importantly, Cot/tpl2 deficiency significantly reduced zymosan-induced inflammatory hypernociception in mice, with a most pronounced effect of a 50% decrease compared with wild type (WT) at 24 h following intraplantar injection of zymosan. At this time, Cot/tpl2(-/-) mice showed significantly reduced NGF, TNFα, and prostaglandin E(2) levels compared with WT littermates. In conclusion, our study demonstrates an important role of Cot/tpl2 in the NGF, G-CSF, and GM-CSF production and myeloperoxidase activity in the acute inflammatory response process and its implication in inflammatory hypernociception.

Curdlan-mediated regulation of human phagocyte-specific chitotriosidase

Human phagocyte-specific chitotriosidase is part of innate immunity and shows anti-fungal activity towards chitin-containing fungi. We investigated the effect of stimulation of the C-type lectin receptor dectin-1 by β-1,3-glucan (curdlan) on chitotriosidase expression and release by human phagocytes. We observed that curdlan triggers chitotriosidase release from human neutrophils. In addition, we show that curdlan impairs chitotriosidase induction in monocytes. Finally, curdlan temporarily induces chitotriosidase in enzyme-expressing monocyte-derived macrophages, followed by reduction of chitotriosidase expression after prolonged stimulation. These data on regulation of phagocyte-specific chitotriosidase following curdlan recognition support an important role of chitotriosidase in the elimination of chitin-containing pathogens.

Engagement of the Mannose Receptor by Tumoral Mucins Activates an Immune Suppressive Phenotype in Human Tumor‐Associated Macrophages

Tumor-Associated Macrophages (TAMs) are abundantly present in the stroma of solid tumors and modulate several important biological processes, such as neoangiogenesis, cancer cell proliferation and invasion, and suppression of adaptive immune responses. Myeloid C-type lectin receptors (CLRs) constitute a large family of transmembrane carbohydrate-binding receptors that recognize pathogens as well as endogenous glycoproteins. Several lines of evidence demonstrate that some CLRs can inhibit the immune response. In this study we investigated TAM-associated molecules potentially involved in their immune suppressive activity. We found that TAMs isolated from human ovarian carcinoma samples predominantly express the CLRs Dectin-1, MDL-1, MGL, DCIR, and most abundantly the Mannose Receptor (MR). Components of carcinomatous ascites and purified tumoral mucins (CA125 and TAG-72) bound the MR and induced its internalization. MR engagement by tumoral mucins and by an agonist anti-MR antibody modulated cytokine production by TAM toward an immune-suppressive profile: increase of IL-10, absence of IL-12, and decrease of the Th1-attracting chemokine CCL3. This study highlights that tumoral mucin-mediated ligation of the MR on infiltrating TAM may contribute to their immune suppressive phenotype.

Recognition of non-self-polysaccharides by C-type lectin receptors dectin-1 and dectin-2

The discovery of several transmembrane receptors expressed by antigen presenting cells, including those that detect and interact with specific sugar moieties on the surface of microbes, has improved our understanding of how immunity against infection is generated. This knowledge, in turn, prompted us to review such interactions with emphasis on C-type lectin receptors and a focus on the roles of dectin-1 and dectin-2 in anti-fungal immunity.

Adjuvanticity of a synthetic cord factor analogue for subunit Mycobacterium tuberculosis vaccination requires FcRγ–Syk–Card9–dependent innate immune activation

Novel vaccination strategies against Mycobacterium tuberculosis (MTB) are urgently needed. The use of recombinant MTB antigens as subunit vaccines is a promising approach, but requires adjuvants that activate antigen-presenting cells (APCs) for elicitation of protective immunity. The mycobacterial cord factor Trehalose-6,6-dimycolate (TDM) and its synthetic analogue Trehalose-6,6-dibehenate (TDB) are effective adjuvants in combination with MTB subunit vaccine candidates in mice. However, it is unknown which signaling pathways they engage in APCs and how these pathways are coupled to the adaptive immune response. Here, we demonstrate that these glycolipids activate macrophages and dendritic cells (DCs) via Syk–Card9–Bcl10–Malt1 signaling to induce a specific innate activation program distinct from the response to Toll-like receptor (TLR) ligands. APC activation by TDB and TDM was independent of the C-type lectin receptor Dectin-1, but required the immunoreceptor tyrosine-based activation motif–bearing adaptor protein Fc receptor γ chain (FcRγ). In vivo, TDB and TDM adjuvant activity induced robust combined T helper (Th)-1 and Th-17 T cell responses to a MTB subunit vaccine and partial protection against MTB challenge in a Card9-dependent manner. These data provide a molecular basis for the immunostimulatory activity of TDB and TDM and identify the Syk–Card9 pathway as a rational target for vaccine development against tuberculosis.

Chitin, Chitinases and Chitinase-like Proteins in Allergic Inflammation and Tissue Remodeling

Chitin, the second most abundant polysaccharide in nature after cellulose, consist exoskeleton of lower organisms such as fungi, crustaceans and insects except mammals. Recently, several studies evaluated immunologic effects of chitin in vivo and in vitro and revealed new aspects of chitin regulation of innate and adaptive immune responses. It has been shown that exogenous chitin activates macrophages and other innate immune cells and also modulates adaptive type 2 allergic inflammation. These studies further demonstrate that chitin stimulate macrophages by interacting with different cell surface receptors such as macrophage mannose receptor, toll-like receptor 2 (TLR-2), C-type lectin receptor Dectin-1, and leukotriene B4 recepptor (BLT1). On the other hand, a number of chitinase or chitinase-like proteins (C/CLP) are ubiquitously expressed in the airways and intestinal tracts from insects to mammals. In general, these chitinase family proteins confer protective functions to the host against exogenous chitin-containing pathogens. However, substantial body of recent studies also set light on new roles of C/CLP in the development and progression of allergic inflammation and tissue remodeling. In this review, recent findings on the role of chitin and C/CLP in allergic inflammation and tissue remodeling will be highlighted and controversial and unsolved issues in this field of studies will be discussed.

Stimulation of dendritic cells via the dectin-1/Syk pathway allows priming of cytotoxic T-cell responses

AbstractThe C-type lectin receptor dectin-1 functions as a pattern recognition receptor for β-glucans and signals via Syk kinase but independently of the Toll-like receptor (TLR) pathway to regulate expression of innate response genes. Dectin-1 signaling can promote activation of dendritic cells (DCs), rendering them competent to prime Th1 and Th17 responses. Here we show that dectin-1–activated DCs can also prime cytotoxic T-lymphocyte (CTL) responses. DCs exposed to a dectin-1 agonist induced antigen-specific expansion of TCR transgenic CD8+ T cells and their differentiation into CTLs in vitro. Dectin-1 agonist also acted as an adjuvant for CTL crosspriming in vivo, eliciting potent CTL responses that protected mice from tumor challenge. In vitro but not in vivo, CTL crosspriming was dependent on IL-12 p70, which was produced by dectin-1–activated DCs in response to IFN-γ secreted by newly activated CD8+ T cells. The dectin-1/Syk pathway is thus able to couple innate immune recognition of β-glucans to all branches of the adaptive immune system, including CD4+ T-helper cells, B cells, and CD8+ cytotoxic T cells. These data highlight the ability of non-TLR receptors to bridge innate and adaptive immunity and suggest that dectin-1 agonists may constitute useful adjuvants for immunotherapy and vaccination.

Costimulation of Dectin-1 and DC-SIGN Triggers the Arachidonic Acid Cascade in Human Monocyte-Derived Dendritic Cells

Inflammatory mediators derived from arachidonic acid (AA) alter the function of dendritic cells (DC), but data regarding their biosynthesis resulting from stimulation of opsonic and nonopsonic receptors are scarce. To address this issue, the production of eicosanoids by human monocyte-derived DC stimulated via receptors involved in Ag recognition was assessed. Activation of FcgammaR induced AA release, short-term, low-grade PG biosynthesis, and IL-10 production, whereas zymosan, which contains ligands of both the mannose receptor and the human beta-glucan receptor dectin-1, induced a wider set of responses including cyclooxygenase 2 induction and biosynthesis of leukotriene C(4) and IL-12p70. The cytosolic phospholipase A(2) inhibitor pyrrolidine 1 completely inhibited AA release stimulated via all receptors, whereas the spleen tyrosine kinase (Syk) inhibitors piceatannol and R406 fully blocked AA release in response to immune complexes, but only partially blocked the effect of zymosan. Furthermore, anti-dectin-1 mAb partially inhibited the response to zymosan, and this inhibition was enhanced by mAb against DC-specific ICAM-3-grabbing nonintegrin (SIGN). Immunoprecipitation of DC lysates showed coimmunoprecipitation of DC-SIGN and dectin-1, which was confirmed using Myc-dectin-1 and DC-SIGN constructs in HEK293 cells. These data reveal a robust metabolism of AA in human DC stimulated through both opsonic and nonopsonic receptors. The FcgammaR route depends on the ITAM/Syk/cytosolic phospholipase A(2) axis, whereas the response to zymosan involves the interaction with the C-type lectin receptors dectin-1 and DC-SIGN. These findings help explain the distinct functional properties of DC matured by immune complexes vs those matured by beta-glucans.

The C-type Lectin Receptors CLEC-2 and Dectin-1, but Not DC-SIGN, Signal via a Novel YXXL-dependent Signaling Cascade

The two lectin receptors, CLEC-2 and Dectin-1, have been shown to signal through a Syk-dependent pathway, despite the presence of only a single YXXL in their cytosolic tails. In this study, we show that stimulation of CLEC-2 in platelets and in two mutant cell lines is dependent on the YXXL motif and on proteins that participate in signaling by immunoreceptor tyrosine-based activation motif receptors, including Src, Syk, and Tec family kinases, and on phospholipase Cgamma. Strikingly, mutation of either Src homology (SH) 2 domain of Syk blocks signaling by CLEC-2 despite the fact that it has only a single YXXL motif. Furthermore, signaling by CLEC-2 is only partially dependent on the BLNK/SLP-76 family of adapter proteins in contrast to that of immunoreceptor tyrosine-based activation motif receptors. The C-type lectin receptor, Dectin-1, which contains a YXXL motif preceded by the same four amino acids as for CLEC-2 (DEDG), signals like CLEC-2 and also requires the two SH2 domains of Syk and is only partially dependent on the BLNK/SLP-76 family of adapters. In marked contrast, the C-type lectin receptor, DC-SIGN, which has a distinct series of amino acids preceding a single YXXL, signals independent of this motif. A mutational analysis of the DEDG sequence of CLEC-2 revealed that the glycine residue directly upstream of the YXXL tyrosine is important for CLEC-2 signaling. These results demonstrate that CLEC-2 and Dectin-1 signal through a single YXXL motif that requires the tandem SH2 domains of Syk but is only partially dependent on the SLP-76/BLNK family of adapters.

DEteCTINg fungal pathogens

Fungal infection is 'sensed' by host cell–expressed receptors. Two papers demonstrate that the C-type lectin receptor dectin-1 is required in vivo for cytokine production and killing of different fungal pathogens.