模式识别受体在抗真菌免疫中的作用

真菌感染机体后,通过模式识别作用及细胞内信号传导,启动固有免疫和适应性免疫应答.模式识别作用足抗真菌免疫的始动环节,Toll样受体(TLRs)和树突状细胞相关性C型凝集素-1(Dectin-1)是参与抗真菌免疫的主要模式识别受体(RPP).两者活化后启动机体免疫应答,产生各种细胞因子和趋化因子,并直接诱导巨噬细胞、自然杀伤细胞吞噬和杀灭病原体.TLRs和Dectin-1的信号传导、抗真菌感染的免疫机制以及两者之间的相互作用等已成为目前研究的热点.     

树突状细胞相关凝集素受体1和2在真菌免疫领域的研究进展

树突状细胞相关凝集素受体1和2(Dectin1和2)是2C型凝集素受体家族(CLR)的重要成员,作为模式识别受体( PRRs),其有效地识别病原体相关分子模式(PAMPs);Dectin-1识别β-葡聚糖,通过自身免疫受体络氨酸激活基序( ITAM)向胞内转导信号;Dectin-2识别α-甘露聚糖,通过耦联FcRγ链上的ITAM结构转导信号.ITAM招募并激活非受体络氨酸蛋白激酶(Syk),后者激活MAPKs或介导CARD9-Malt1-Bcl10复合体组装,激活核因子-κB(NF-κB),诱导合成炎症因子等一系列细胞活动.其配体β-葡聚糖和甘露聚糖都是真菌细胞壁的主要成分.近年来研究表明,Dectin-1和Dectin-2受体在真菌免疫防御中具有重要作用.     

C型凝集素受体在肿瘤免疫作用中的研究进展

C型凝集素受体(CLRs)是一种高表达于树突状细胞(DCs)的模式识别受体(PRRs),它参与了由DCs介导的针对肿瘤的非特异性免疫和特异性免疫。激活表达于DCs上的CLRs可显著提升机体免疫系统对肿瘤细胞的杀伤作用。本文将以CLRs中的Dectin-1和Dectin-2受体为例,对其在肿瘤免疫中发挥的作用及参与此过程的相关信号通路进行综述,并据此初步探讨CLRs未来在肿瘤免疫治疗中可能的应用。     

热灭活白念珠菌通过Dectin-1诱导外周血单个核细胞表达IL-12和IFN-γ

为研究Dectin-1在热灭活白念珠菌刺激外周血单个核细胞(PBMC)免疫应答中的作用。我们用不同浓度昆布多糖(Dectin-1封闭剂)与PBMC共培养1 h后,再用热灭活白念珠菌刺激PBMC 4 d;同时用不同剂量的Dectin-1激活剂酵母聚糖(zymosan)刺激PBMC 4 d,收集培养液上清,经ELISA检测IL-12和IFN-γ水平。结果发现,昆布多糖可以部分抑制热灭活白念珠菌刺激PBMC合成IL-12和IFN-γ的能力,酵母聚糖可以诱导PBMC合成IL-12和IFN-γ。因此,Dectin-1是介导热灭活白念珠菌诱导PBMC产生IL-12和IFN-γ的受体之一。     

C型凝集素受体Dectin-2的生物学特性及功能

树突细胞相关凝集素2（Dectin-2）是一种新发现的C型凝集素受体,具有一个碳水化合物识别域CRD,可识别高甘露糖结构,广泛存在于树突状细胞等固有免疫细胞表面。由于其具有抗真菌病原体感染和紫外线诱导耐受等作用,因此在机体的免疫系统中发挥重要作用。对于Dectin-2等C型凝集素受体的深入研究将有利于我们对微生物感染、肿瘤免疫和自身免疫等方面有更深入的认识,从而对预防和治疗疾病起着指导作用。     

免疫抑制剂对巨噬细胞Dectin-1 和TLR2 表达的影响

目的:研究地塞米松、环磷酰胺、环孢素A 和霉酚酸酯对小鼠RAW264.7 巨噬细胞Dectin-1 和TLR2 受体表达的影响。方法:体外培养RAW264.7 巨噬细胞,分别给予不同浓度的地塞米松、环磷酰胺、环孢素A 和霉酚酸酯刺激细胞24 h,CCK-8 检测RAW264.7 细胞毒性作用,RT-PCR 检测细胞Dectin-1 和TLR2 mRNA 表达情况,流式细胞术检测Dectin-1 和TLR2 蛋白水平变化。结果:不同剂量的地塞米松、环磷酰胺、环孢素A 和霉酚酸酯作用细胞24 h 后均对细胞表现出一定的毒性作用(P<0.05),且随着药物浓度增加毒性作用越大。地塞米松降低Dectin-1 mRNA 和蛋白水平的表达,上调TLR2 受体转录和翻译(P<0.05);环磷酰胺对巨噬细胞Dectin-1 和TLR2 的转录翻译无明显影响(P>0.05);霉酚酸酯和环孢素A 能够同时下调Dectin-1、TLR2 mRNA 和蛋白水平表达(P<0.05)。结论:不同免疫抑制剂对模式识别受体表达的调节作用具有差异性,通过选择性调节各自靶点PRRs 的表达抑制机体对各种真菌病原体的免疫识别过程,同时也能够抑制巨噬细胞的生长增殖,共同介导免疫抑制功能。     

蛋白激酶C-δ在Dectin-1-Src-Syk介导的巨噬细胞杀灭白假丝酵母菌中的作用研究

目的:研究蛋白激酶C-δ在Dectin-1-Src-Syk介导的巨噬细胞杀灭白假丝酵母菌中的作用,探讨固有免疫抗真菌的分子机制。方法:用流式细胞术检测细胞表面受体;用蛋白酶抑制剂预处理体外培养的小鼠巨噬细胞,通过Western blot分析相关蛋白的表达及磷酸化水平,并利用luminol法、荧光标记法和培养法检测巨噬细胞在白假丝酵母菌的刺激下释放活性氧分子、吞噬并杀灭真菌细胞的能力。结果:Dectin-1封闭剂与Src或Syk抑制剂均能抑制白假丝酵母菌诱导的PKC-δ磷酸化;蛋白激酶C-δ抑制剂Rottlerin对巨噬细胞吞噬白假丝酵母菌无显著影响;Rottlerin抑制白假丝酵母菌诱导的巨噬细胞p40phox磷酸化、活性氧分子的产生和对白假丝酵母菌的杀灭作用。结论:蛋白激酶C-δ抑制剂Rottlerin通过抑制巨噬细胞NADPH氧化酶复合物的活化和活性氧分子的释放降低对真菌细胞的杀灭作用,提示PKC-δ在固有免疫抗真菌中发挥重要的作用。     

蝙蝠蛾被毛孢菌丝体通过激活TLR2、TLR4和Dectin-1诱导Th1型免疫反应

目的:研究蝙蝠蛾被毛孢菌丝体(MHCS)对抗原呈递细胞树突状细胞(Dendritic cells,DCs)成熟和功能的调节作用.方法:利用流式细胞术、实时荧光定量PCR、Western blot和混合淋巴细胞培养等实验方法,检测了MHCS对DCs成熟和功能相关表面分子、细胞因子表达以及Toll样受体(TLR)2、TLR4和Dectin-1相关信号转导通路蛋白活性的调节作用.结果:MHCS显著上调DCs表面分子CD11c、MHCⅠ和MHC Ⅱ、辅助刺激分子CD40、CD80和CD86以及模式识别受体TLR2、TLR4和Dectin-1的表达;促进Th1型细胞因子IL-12产生,抑制Th2型细胞因子IL-10、IL-13和TGF-β1产生;诱导TAK1和IRF3磷酸化活性增加.MHCS也显著刺激幼稚型Th1细胞增殖,诱导幼稚型Th细胞向Th1方向分化.利用中和性抗体,分别阻断DCs细胞TLR2、TLR4或Dectin-1活性,可部分抑制MHCS诱导的DCs成熟.结论:MHCS能促进DO成熟,诱导Th1型免疫反应.MHCS的这些作用与其激活模式识别受体TLR2、TLR4或Dectin-1有关.     

Dectin-1与非Toll样模式识别受体免疫识别的研究进展

Toll样受体（TLR）是一类天然免疫相关的模式识别受体（PRR），在机体抵御感染中发挥着极为重要的作用。除TLR外，目前还发现了很多其它种类PRR，这些非Toll样PRR在天然免疫中的作用也是不可缺少的，它们既可以与TLR协同作用，也可以单独发挥作用。Dectin-1是近年来颇受关注的一种非Toll样PRR，属于NK细胞受体样C型凝集素，是一种Ⅱ型跨膜受体，通过对真菌的识别参与免疫效应细胞的吞噬及杀伤过程，诱导机体产生一系列的细胞因子及趋化因子，从而参与机体防御真菌病原体的天然免疫反应，但在某些情况下也可能引起自身免疫性疾病的发生。     

肝脏中死亡受体的生物学和病理生物学作用

死亡受体通过细胞内信号传导途径可诱导细胞凋亡，与机体的生长、发育、病变和死亡有关，本文对新近研究发现的死亡受体的种类、结构特征及其诱导细胞凋亡的机理进行了综述，并讨论了这些死亡受体在肝脏中的生物学和病理生物学作用。     

The role of Dectin-1 in antifungal immunity

beta-Glucans are structural components of fungal cell walls, which have a stimulatory effect on the immune system. Although a number of receptors for these carbohydrates have been proposed, the recently identified C-type lectin-like receptor, Dectin-1, appears to play a central role. Dectin-1 is expressed on phagocytic cells, including macrophages and neutrophils, and mediates both the internalization and cellular responses to beta-glucan, through unique mechanisms. Dectin-1 can recognize and respond to live fungal pathogens and is being increasingly appreciated as having a key role in the innate responses to these pathogens. In addition to its exogenous ligands, Dectin-1 can recognize an unidentified endogenous ligand on T cells and may act as a co-stimulatory molecule, although its function in these responses is less clear. This review will highlight the current knowledge of Dectin-1 and its potential role in antifungal immunity, as well as deficiencies in our understanding.     

The role of the beta-glucan receptor Dectin-1 in control of fungal infection

During fungal infection, a variety of receptors initiates immune responses, including TLR and the beta-glucan receptor Dectin-1. TLR recognition of fungal ligands and subsequent signaling through the MyD88 pathway were thought to be the most important interactions required for the control of fungal infection. However, recent papers have challenged this view, highlighting the role of Dectin-1 in induction of cytokine responses and the respiratory burst. Two papers, using independently derived, Dectin-1-deficient mice, address the role of Dectin-1 in control of fungal infection. Saijo et al. [1] argue that Dectin-1 plays a minor role in control of Pneumocystis carinii by direct killing and that TLR-mediated cytokine production controls P. carinii and Candida albicans. By contrast, Taylor et al. [2] argue that Dectin-1-mediated cytokine and chemokine production, leading to efficient recruitment of inflammatory cells, is required for control of fungal infection. In this review, we argue that collaborative responses induced during infection may partially explain these apparently contradictory results. We propose that Dectin-1 is the first of many pattern recognition receptors that can mediate their own signaling, as well as synergize with TLR to initiate specific responses to infectious agents.     

C-Type Lectin-Like Receptors of the Dectin-1 Cluster: Ligands and Signaling Pathways

Innate immunity is constructed around genetically encoded receptors that survey the intracellular and extracellular environments for signs of invading microorganisms. These receptors recognise the invader and through complex intracellular networks of molecular signaling, they destroy the threat whilst instructing effective adaptive immune responses. Many of these receptors, like the Toll-like receptors in particular, are well-known for their ability to mediate downstream responses upon recognition of exogenous or endogenous ligands; however, the emerging family known as the C-type lectin-like receptors contains many members that have a huge impact on immune and homeostatic regulation. Of particular interest here are the C-type lectin-like receptors that make up the Dectin-1 cluster and their intracellular signaling motifs that mediate their functions. In this review, we aim to draw together current knowledge of ligands, motifs and signaling pathways, present downstream of Dectin-1 cluster receptors, and discuss how these dictate their role within biological systems.     

Syk-dependent cytokine induction by Dectin-1 reveals a novel pattern recognition pathway for C type lectins

Pattern-recognition receptors (PRRs) detect molecular signatures of microbes and initiate immune responses to infection. Prototypical PRRs such as Toll-like receptors (TLRs) signal via a conserved pathway to induce innate response genes. In contrast, the signaling pathways engaged by other classes of putative PRRs remain ill defined. Here, we demonstrate that the beta-glucan receptor Dectin-1, a yeast binding C type lectin known to synergize with TLR2 to induce TNF alpha and IL-12, can also promote synthesis of IL-2 and IL-10 through phosphorylation of the membrane proximal tyrosine in the cytoplasmic domain and recruitment of Syk kinase. syk-/- dendritic cells (DCs) do not make IL-10 or IL-2 upon yeast stimulation but produce IL-12, indicating that the Dectin-1/Syk and Dectin-1/TLR2 pathways can operate independently. These results identify a novel signaling pathway involved in pattern recognition by C type lectins and suggest a potential role for Syk kinase in regulation of innate immunity.     

Soluble β-glucan from Grifola frondosa induces proliferation and Dectin-1/Syk signaling in resident macrophages via the GM-CSF autocrine pathway

MD-Fraction, a highly purified, soluble β-(1,3) (1,6)-glucan obtained from Grifola frondosa (an oriental edible mushroom), has been reported to inhibit tumor growth by modulating host immunity. β-Glucan, a major component of the fungal cell wall, is generally recognized by PRRs expressed on macrophages and DCs, such as Dectin-1, and the ability of β-glucans to modulate host immunity is influenced by their structure and purity. Most cellular studies have used particulate β-glucans, such as yeast zymosan (crude β-glucan) and curdlan (purified β-glucan). However, little is known about the cellular mechanism of soluble β-glucans, including MD-Fraction, despite significant therapeutic implications. In this study, we investigated the cellular mechanism of MD-Fraction in murine resident macrophages and compared it with two well-known β-glucan particles. MD-Fraction induced GM-CSF production rapidly through Dectin-1-independent ERK and p38 MAPK activation. Subsequently, MD-Fraction-induced GM-CSF enhanced proliferation and Dectin-1 expression, which permitted Dectin-1-mediated TNF-α induction through the Syk pathway. Curdlan induced not only the proliferation and activation of Dectin-1/Syk signaling in a manner similar to MD-Fraction but also the uncontrolled, proinflammatory cytokine response. Contrastingly, zymosan reduced proliferation and Dectin-1 expression significantly, indicating that the mechanism of macrophage activation by MD-Fraction differs from that of zymosan. This is the first study to demonstrate that purified β-glucans, such as MD-Fraction and curdlan, induce GM-CSF production directly, resulting in Dectin-1/Syk activation in resident macrophages. In conclusion, we demonstrated that MD-Fraction induces cell proliferation and cytokine production without excessive inflammation in resident macrophages, supporting its immunotherapeutic potential.     

Protein kinase Cδ is a critical component of Dectin-1 signaling in primary human monocytes

Zymosan, a mimic of fungal pathogens, and its opsonized form (ZOP) are potent stimulators of monocyte NADPH oxidase, resulting in the production of O(2)(.-), which is critical for host defense against fungal and bacterial pathogens and efficient immune responses; however, uncontrolled O(2)(.-) production may contribute to chronic inflammation and tissue injury. Our laboratory has focused on characterizing the signal transduction pathways that regulate NADPH oxidase activity in primary human monocytes. In this study, we examined the involvement of various pattern recognition receptors and found that Dectin-1 is the primary receptor for zymosan stimulation of O(2)(.-) via NADPH oxidase in human monocytes, whereas Dectin-1 and CR3 mediate the activation by ZOP. Further studies identified Syk and Src as important signaling components downstream of Dectin-1 and additionally identified PKCδ as a novel downstream signaling component for zymosan-induced O(2)(.-) as well as phagocytosis. Our results show that Syk and Src association with Dectin-1 is dependent on PKCδ activity and expression and demonstrate direct binding between Dectin-1 and PKCδ. Finally, our data show that PKCδ and Syk but not Src are required for Dectin-1-mediated phagocytosis. Taken together, our data identify Dectin-1 as the major PRR for zymosan in primary human monocytes and identify PKCδ as a novel downstream signaling kinase for Dectin-1-mediated regulation of monocyte NADPH oxidase and zymosan phagocytosis.     

Dectin-1 is inducible and plays a crucial role in Aspergillus-induced innate immune responses in human bronchial epithelial cells

Airway epithelial cells are the first cells to be challenged upon contact with the conidia of Aspergillus. In response, they express pattern-recognition receptors that play fundamental roles as sentinels and mediators of pulmonary innate immunity. The C-type lectin Dectin-1 is expressed predominantly on the surface of myeloid lineage cells. We examined the induction, regulation, and functions of Dectin-1 in pulmonary epithelial cells by challenging human bronchial epithelial (HBE) cells with A. fumigatus. Inflammatory, antimicrobial peptide genes and reactive oxygen species (ROS) were quantified, with and without knockdown of Dectin-1. We found that A. fumigatus induced the expression of Dectin-1 mRNA and protein in HBE cells in a toll-like receptor (TLR) 2-dependent manner. In addition, A. fumigatus-mediated generation of ROS was dependent on the upregulation of Dectin-1. Moreover, A. fumigatus actively induced the expression of TNFα, GM-CSF, IL8, HBD2, and HBD9. Knockdown of Dectin-1 inhibited TNFα, IL8, HBD2, and HBD9 expression. Hence, Dectin-1 was required for the upregulation of pro-inflammatory cytokines and antimicrobial peptides. Finally, knockdown of TLR2 significantly inhibited Dectin-1 upregulation. Our results demonstrate the novel induction of Dectin-1 in human bronchial epithelial cells and its critical role in the innate immune response against A. fumigatus in non-phagocytic cells.