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.     

真菌细胞壁病原相关分子模式TLR/Dectin-1通路及相关细胞因子的免疫作用

侵袭性真菌感染(IFI)是致ICU患者死亡的重要原因之一。机体通过天然免疫重要的模式识别受体(PRR)Toll样受体(TLR)及C型凝集素受体(CLR)与病原相关分子模式(PAMP)识别后启动抗真菌免疫反应。目前明确磷脂甘露聚糖(PLM)的识别主要依赖TLR2和TLR4;β-葡聚糖经TLR2/树突状细胞相关性C型凝集素-1(Dectin-1)或只经Dectin-1识别。PLM和β-葡聚糖被识别后及经Dectin-1驱动获得性免疫后产生一系列下游细胞因子,一些下游细胞因子的免疫作用对不同组织有所不同、不确定或存在争议,一些免疫反应在细节上还没有详尽描述。因此,深入研究PAMP与PRR相互作用及其细胞因子对免疫调节影响,对IFI的预防治疗有重要意义。     

模式识别受体Dectin-1的免疫学研究进展

Dectin-1是C型凝集素家族中最重要的受体,它能诱导自身胞内信号传导触发一系列细胞反应,在抗真菌免疫中发挥着重要的作用。该文对Dectin-1的信号传导途径、在抗微生物免疫中的作用、与其他受体的相互作用、在自身免疫及疾病中的作用、在β 葡聚糖诱导的免疫调节中的作用、潜在的临床应用予以综述。     

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。     

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。     

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.     

C 型凝集素受体CLR 对树突状细胞功能的调控效应

树突状细胞(Dendritic cells,DC) 是专职性抗原提呈细胞, 其表面表达的C 型凝集素受体(C-type lectinreceptors,CLR ) 在DC 的摄取糖蛋白和识别微生物抗原,并将抗原信息提呈给T、B淋巴细胞的过程中发挥重要作用,从而在调节抗真菌寄生虫感染、过敏反应和肿瘤免疫中扮演重要角色。故通过研究C 型凝集素受体对DC功能的调控效应来深入了解疾病的发生发展并进一步调控其过程具有重要意义。本文将对近期相关研究成果作一综述。     

C-型凝集素家族在Th17细胞免疫反应中的作用

Th17细胞是近年来发现的一群新的细胞亚群,在感染、自身免疫性及肿瘤等疾病中发挥重要作用,是目前研究的热点之一.而C-型凝集素是一类重要的模式识别受体,能调节Th1细胞和Th17细胞间的免疫平衡,识别真菌等多种病原体,在抗感染免疫中具有重要作用.近年来有大量的研究发现,多种C-型凝集素受体参与Th17细胞的分化.因而对其深入研究可明确疾病的发病机制,为疾病的治疗提供了新的思路和靶点.     

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。     

活化性受体NKG2D及其配体的研究进展

NK细胞是肌体免疫系统至关重要的组成部分,其表达多种活化性和抑制性细胞表面受体。NKG2D是较为独特的活化性受体,属C型凝集素家族跨膜蛋白,分布较广,NK细胞、T细胞和其他免疫细胞都可以产生,其配体具有多样性,MHCⅠ类相关分子（MIC）是人类NKG2D识别的配体之一,应激性表达在一些肿瘤细胞或病原体感染细胞的表面。NKG2D既能直接活化NK细胞,又能以协同刺激的方式促进CD8^＋αβT细胞的活化,在抗肿瘤免疫和病毒感染等方面发挥重要作用。     

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.     

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.     

Dectin-2 is predominantly myeloid restricted and exhibits unique activation-dependent expression on maturing inflammatory monocytes elicited in vivo

Dectin-2 is a recently described dendritic-cell-associated receptor, suggested to be involved in the initiation and maintenance of UV-induced tolerance. To understand the physiological relevance of the proposed functions of this C-type lectin-like receptor, we have generated monoclonal antibodies against its extracellular domain and performed a detailed study of its expression. In naive mice, Dectin-2 has a novel distribution pattern compared with other myeloid markers, but is predominantly expressed by a wide variety of tissue macrophages. Its expression was limited on dendritic cells and notably absent from brain microglia and choroid plexus or meningeal macrophages. On peripheral blood monocytes, Dectin-2 expression was very low on the surface but was transiently and markedly up-regulated on induction of inflammation in vivo using a variety of stimuli. This change in Dectin-2 expression occurs on 'inflammatory' monocytes after arrival at the inflammatory lesion as demonstrated by adoptive cell-transfer studies, and is independent of whether the macrophages elicited by the stimuli ultimately expressed Dectin-2. These observations show Dectin-2 expression to be characteristic of monocyte activation/maturation at an inflammatory lesion and provide a new perspective on the interpretation of Dectin-2 function in vivo.     

Dectin-1 and Dectin-2 in innate immunity against fungi

Dectin-1 and Dectin-2 are type II transmembrane proteins of the C-type lectin family with single carbohydrate recognition domains (CRDs) in their extracellular region. They are expressed mainly in dendritic cells and macrophages. Dectin-1 recognizes β-glucans with its CRD and transduces signals through its immunoreceptor tyrosine-based activation motif (ITAM)-like motif in the cytoplasmic domain, whereas Dectin-2 recognizes α-mannans and transduces its signal through association with the ITAM-containing Fc receptor γ chain. Upon ligand binding, spleen tyrosine kinase is recruited to the ITAM and activates the caspase recruitment domain family member 9 (CARD9)-nuclear factor-κB axis, resulting in the activation of various genes including those encoding pro-inflammatory cytokines. Both β-glucans and α-mannans are major cell wall components of fungi including Candida albicans and Pneumocystis carinii. Recently, it was reported that Dectin-1 is important in protection against P. carinii by inducing reactive oxygen species, whereas both Dectin-1 and Dectin-2 play important roles in defense against C. albicans by preferentially inducing T(h)17 cell differentiation. In this review, we briefly revisit the structures, ligands, signal transduction and functional roles of Dectin-1 and Dectin-2 in host defense against fungal infection.     

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.     

Syk-coupled C-type lectins in immunity

The Syk-coupled C-type lectin receptor Dectin-1 was the first non-Toll like receptor described that could mediate its own intracellular signalling. It was initially identified as important for the innate recognition of and response to fungal pathogens but later studies revealed that it is also involved in triggering adaptive immune responses. It subsequently emerged that Dectin-1 is one of a number of spleen tyrosine kinase-coupled C-type lectin receptors that have been implicated not just in fungal immunity, but also in viral, mycobacterial and helminth infections. Here, we consider the ability of these receptors to trigger different aspects of immunity and highlight their emerging roles in a number of infection scenarios.     

CD4+ T-cell survival in the GI tract requires dectin-1 during fungal infection

Dectin-1 is an innate antifungal C-type lectin receptor necessary for protective antifungal immunity. We recently discovered that Dectin-1 is involved in controlling fungal infections of the gastrointestinal (GI) tract, but how this C-type lectin receptor mediates these activities is unknown. Here, we show that Dectin-1 is essential for driving fungal-specific CD4⁺ T-cell responses in the GI tract. Loss of Dectin-1 resulted in abrogated dendritic cell responses in the mesenteric lymph nodes (mLNs) and defective T-cell co-stimulation, causing substantial increases in CD4⁺ T-cell apoptosis and reductions in the cellularity of GI-associated lymphoid tissues. CD8⁺ T-cell responses were unaffected by Dectin-1 deficiency. These functions of Dectin-1 have significant implications for our understanding of intestinal immunity and susceptibility to fungal infections.