Toll样受体4信号转导研究进展

Toll样受体（Toll-like-receptors,TLRs）是一个主要分布于炎症细胞的识别病源分子的受体超家族,其中TLR4主要识别革兰阴性细菌细胞壁成分脂多糖（lipopolysaccharide,LPS）。LPS与TLR4结合后活化髓样分化因子88 (myeloid differentiation factor 88, MyD88)依赖性和非依赖性两条信号途径;前者活化丝裂原激活的蛋白激酶（mitogen-activated protein kinase,MAPK）和核因子-κB（nuclear factor kappa B,NF-κB）信号通路,后者活化NF-κB和干扰素调节因子-3(IFN-regulated factor-3,IRF3)信号通路。通过这些信号途径TLR4诱导炎症细胞释放炎症因子介导炎症反应;同时TLR4通过活化树突状细胞促进抗原递呈,介导先天性免疫向获得性免疫的转化。此外,TLR4能诱导磷脂酰肌醇-3激酶-蛋白激酶B（PI3K-AKT）的信号转导,LPS介导的细胞存活和增殖与TLR4活化 PI3K-AKT途径有关。     

TLR7介导抗病毒免疫应答研究进展

Toll样受体（Toll-like receptors，TLRs）是天然免疫中重要的模式识别受体，在机体抗病原体感染中发挥重要的作用，同时也是连接天然免疫与获得性免疫的桥梁。研究表明，Toll样受体7（TLR7）能识别某些小分子的抗病毒化合物和病毒单链RNA（single-stranded RNA，ssRNA），活化的TLR7启动髓系分化因子88（myeloid differentiation factor88，MyD88）依赖的信号通路，介导抗病毒免疫应答。TLR7的活化需要内体，溶酶体的成熟，目前一些小分子的TLR7配体已用于临床治疗病毒性感染疾病和肿瘤。     

TLR7介导抗病毒免疫应答研究进展

Toll样受体(Toll-like receptors,TLRs)是天然免疫中重要的模式识别受体,在机体抗病原体感染中发挥重要的作用,同时也是连接天然免疫与获得性免疫的桥梁。研究表明,Toll样受体7(TLR7)能识别某些小分子的抗病毒化合物和病毒单链RNA(single-stranded RNA,ssRNA),活化的TLR7启动髓系分化因子88(myeloid differentiation factor 88,MyD88)依赖的信号通路,介导抗病毒免疫应答。TLR7的活化需要内体/溶酶体的成熟,目前一些小分子的TLR7配体已用于临床治疗病毒性感染疾病和肿瘤。     

Toll样受体介导的抗病毒感染效应及其机制

Toll样受体(Toll Like Receptors,TLRs)在天然免疫中发挥着重要的作用。近年,越来越多的证据表明TLRs也参与了天然免疫系统对病毒的识别,同时它在病毒感染及其转归中也扮演了重要的角色。TLR3、TLR4、TLR7、TLR8、TLR9等TLRs可识别特异性蛋白、DNA和RNA等病毒源性分子,启动胞内抗病毒信号传导机制,通过一系列转接蛋白和转录因子,介导了以干扰素反应为主要机制的固有免疫防御机制,同时也参与调控针对病毒的特异性免疫应答。此外,某些病毒具有针对TLRs的免疫逃逸机制。     

托样受体3( TLR-3) 信号通路介导的病毒免疫逃逸

<正>天然免疫是机体抵御病毒入侵的首道防线,对病原快速有效地识别是激发天然免疫的前提。动物的天然免疫依赖一类能够识别微生物特定组分的模式识别受体(Pattern recognition receptors,PRRs)。其中,托样受体3(Toll like receptor-3,TLR3)通过识别病毒感染时产生的dsRNA,启动下游的信号转导,上调Ⅰ型干扰素α和β(Interferonα/β,IFNα/β)的表达,Ⅰ型干扰素能够诱导细胞产生抗病毒蛋白(Antivirus protein,AVP),同时也有助于激发机体的适应性免疫~([1])。     

Toll样受体4介导的抗病毒固有免疫研究进展

Toll样受体(TLR)是一类模式识别受体(PRR),人TLR分布在细胞表面或细胞内。不同TLR识别病原体的不同结构成分后,启动固有免疫反应。其中,TLR4在TLR家族中占有重要地位。它除了识别细菌的脂多糖(LPS)外,还可识别一些病毒的蛋白如水泡性口炎病毒的G糖蛋白、呼吸道合胞病毒的F蛋白。病毒包膜糖蛋白也是TLR4识别的配体。TLR4通过髓样分化因子88(My D88)和β干扰素TIR结构域衔接蛋白(TRIF)途径活化下游核因子κB(NF-κB)、干扰素调节因子3(IRF3)转录因子,产生细胞因子/趋化因子和1型干扰素等,在抗病毒免疫反应、免疫细胞分化及调节、发病机制、药物及疫苗研制等方面具有重要意义。     

Nod样受体与Toll受体介导炎症的研究进展

固有免疫系统是抵御微生物入侵的第一道防线,它依赖模式识别受体识别外源病原微生物然后将其清除。Toll样受体（TLR）和Nod样受体（NLR）是介导免疫识别的重要受体,其通过识别病原体相关分子模式不仅启动了固有免疫应答,而且激活了适应性免疫应答,是连接固有免疫和适应性免疫的桥梁。中性粒细胞是机体早期炎症反应中最重要的炎症细胞,其粘附、活化及凋亡的整个过程可受TLR的调节,促成炎症反应的无损伤性收敛,使机体维持内环境的稳态。     

Toll样受体3信号通路在人类病毒性心肌炎心肌细胞凋亡及炎症反应中的作用

 目的：研究Toll样受体3（TLR3）信号转导通路与人类病毒性心肌炎（VMC）炎症反应及细胞凋亡的关系。方法：采用免疫组化 SP 法分别检测TLR3、干扰素β TIR结构域衔接蛋白（TRIF）、核因子 κB（NF-κB）及半胱氨酸天冬氨酸蛋白酶 3（caspase-3）在心肌组织中的变化, 原位末端标记法（TUNEL）检测心肌细胞凋亡情况,比较VMC组及正常对照组组间的差异。结果：与对照组比较,VMC组心肌组织中TLR3、TRIF、NF-κB及caspase-3蛋白表达及细胞凋亡水平明显增高,差异有统计学意义(P<0.05), 并且TLR3和TRIF、TLR3和NF-κB、TRIF和NF-κB、NF-κB和caspase-3之间的表达均呈正相关,细胞凋亡指数的变化趋势与caspase-3一致。结论：通过TLR3信号通路介导的炎症反应和细胞凋亡在VMC发生、发展过程中起着重要作用,抑制其活化有可能成为治疗VMC的一个潜在的、有价值的靶位。     

视黄酸诱导基因1样受体(RLR)识别和调控的研究进展

天然免疫系统通过模式识别受体(PRR)识别病毒、细菌等病原体的病原体相关分子模式(PAMP),进而启动天然免疫反应、帮助机体清除入侵病原体。视黄酸诱导基因1(RIG-1)样受体(RLR)是PRR中具有DEx D/H-box RNA解螺旋酶结构域的一类受体,目前发现的RLR包括视黄酸诱导基因1(RIG-1/DDX58)、黑素瘤分化相关分子5(MDA5/IFIH1)和遗传学和生理学实验室蛋白2(LGP2/DHX58)。它们参与多种机体生理和病理过程,如抗病毒反应、自身免疫性疾病、肿瘤,其主要功能是识别病毒的寡聚核糖核苷酸,激活线粒体抗病毒信号蛋白[MAVS(IPS-1/VISA/cardif)]等关键接头分子,最终导致转录因子干扰素诱导因子3(IRF3)和核因子κB(NF-κB)活化,诱导1型干扰素和炎性细胞因子,从而介导宿主抗病毒免疫。本文重点阐述RLR在抗病毒免疫反应中识别RNA机制的研究进展。     

Toll样受体信号介导细胞凋亡的研究进展

细胞凋亡在病毒、细菌等感染的过程中和肿瘤等疾病的发生发展中起至关重要的作用。Toll样受体(TLR)存在于巨噬细胞、肿瘤细胞等细胞表面,能直接识别并结合病原微生物和宿主细胞表面的病原相关分子模式,然后通过髓样分化因子88/Fas相关死亡结构域/caspase-8、TIR结构域接头蛋白/蛋白激酶/干扰素调节因子和核因子κB路径等信号途径对巨噬细胞、肿瘤细胞等细胞的凋亡起调节作用。随着对TLR介导的细胞凋亡中Fas相关死亡结构域、TIR结构域接头蛋白等多种信号分子的深入研究,有助于了解它们在细胞凋亡中的作用,并为感染和肿瘤等疾病的分子靶向治疗提供新的目标。     

Lipopolysaccharide signaling in endothelial cells

Sepsis is the systemic immune response to severe bacterial infection. The innate immune recognition of bacterial and viral products is mediated by a family of transmembrane receptors known as Toll-like receptors (TLRs). In endothelial cells, exposure to lipopolysaccharide (LPS), a major cell wall constituent of Gram-negative bacteria, results in endothelial activation through a receptor complex consisting of TLR4, CD14 and MD2. Recruitment of the adaptor protein myeloid differentiation factor (MyD88) initiates an MyD88-dependent pathway that culminates in the early activation of nuclear factor-kappaB (NF-kappaB) and the mitogen-activated protein kinases. In parallel, a MyD88-independent pathway results in a late-phase activation of NF-kappaB. The outcome is the production of various proinflammatory mediators and ultimately cellular injury, leading to the various vascular sequelae of sepsis. This review will focus on the signaling pathways initiated by LPS binding to the TLR4 receptor in endothelial cells and the coordinated regulation of this pathway.     

A novel negative regulator for IL-1 receptor and Toll-like receptor 4

The Toll-IL-1 receptor (TIR) superfamily, defined by the presence of an intracellular TIR domain, initiates innate immunity via NF-kappaB activation, leading to production of proinflammatory cytokines. ST2 is a member of the TIR family that does not activate NF-kappaB and has been suggested as an important effector molecule of type 2 T helper cell responses. We have recently demonstrated that the membrane bound form of ST2 (ST2L) negatively regulated IL-1RI and TLR4 but not TLR3 signaling by sequestrating the adaptors MyD88 and Mal. In contrast to wild-type mice, ST2 deficient mice failed to develop endotoxin tolerance. Thus, ST2 suppresses IL-1R and TLR4 signaling via MyD88- and Mal-dependent pathways and modulates innate immunity. The results provide a molecular explanation for the role of ST2 in T(H)2 responses since inhibition of TLRs will promote a T(H)2 response and also identify ST2 as a key regulator of endotoxin tolerance.     

Toll-like receptor 4 is a sensor for autophagy associated with innate immunity

Autophagy has recently been shown to be an important component of the innate immune response. The signaling pathways leading to activation of autophagy in innate immunity are not known. Here we showed that Toll-like receptor 4 (TLR4) served as a previously unrecognized environmental sensor for autophagy. Autophagy was induced by lipopolysaccharide (LPS) in primary human macrophages and in the murine macrophage RAW264.7 cell line. We defined a new molecular pathway in which LPS-induced autophagy was regulated through a Toll-interleukin-1 receptor domain-containing adaptor-inducing interferon-beta (TRIF)-dependent, myeloid differentiation factor 88 (MyD88)-independent TLR4 signaling pathway. Receptor-interacting protein (RIP1) and p38 mitogen-activated protein kinase were downstream components of this pathway. This signaling pathway did not affect cell viability, indicating that it is distinct from the autophagic death signaling pathway. We further showed that LPS-induced autophagy could enhance mycobacterial colocalization with the autophagosomes. This study links two ancient processes, autophagy and innate immunity, together through a shared signaling pathway.     

MicroRNA in TLR signaling and endotoxin tolerance

Toll-like receptors (TLRs) in innate immune cells are the prime cellular sensors for microbial components. TLR activation leads to the production of proinflammatory mediators and thus TLR signaling must be properly regulated by various mechanisms to maintain homeostasis. TLR4-ligand lipopolysaccharide (LPS)-induced tolerance or cross-tolerance is one such mechanism, and it plays an important role in innate immunity. Tolerance is established and sustained by the activity of the microRNA miR-146a, which is known to target key elements of the myeloid differentiation factor 88 (MyD88) signaling pathway, including IL-1 receptor-associated kinase (IRAK1), IRAK2 and tumor-necrosis factor (TNF) receptor-associated factor 6 (TRAF6). In this review, we comprehensively examine the TLR signaling involved in innate immunity, with special focus on LPS-induced tolerance. The function of TLR ligand-induced microRNAs, including miR-146a, miR-155 and miR-132, in regulating inflammatory mediators, and their impact on the immune system and human diseases, are discussed. Modulation of these microRNAs may affect TLR pathway activation and help to develop therapeutics against inflammatory diseases.     

Grancalcin (GCA) modulates Toll‐like receptor 9 (TLR9) mediated signaling through its direct interaction with TLR9

Toll‐like receptors (TLRs) are playing important roles in stimulating the innate immune response and intensifying adaptive immune response against invading pathogens. Appropriate regulation of TLR activation is important to maintain a balance between preventing tumor activation and inhibiting autoimmunity. Toll‐like receptor 9 (TLR9) senses microbial DNA in the endosomes of plasmacytoid dendritic cells and triggers myeloid differentiation primary response gene 88 (MyD88) dependent nuclear factor kappa B (NF‐κB) pathways and type I interferon (IFN) responses. However, mechanisms of how TLR9 signals are mediated and which molecules are involved in controlling TLR9 functions remain poorly understood. Here, we report that penta EF‐hand protein grancalcin (GCA) interacts and binds with TLR9 in a yeast two‐hybrid system and an overexpression system. Using siRNA‐mediated knockdown experiments, we also revealed that GCA positively regulates type I IFN production, cytokine/chemokine production through nuclear localization of interferon regulatory factor 7 (IRF7), NF‐κB activation, and mitogen‐activated protein kinase (MAPK) activation in plasmacytoid dendritic cells. Our results indicate that heterodimerization of GCA and TLR9 is important for TLR9‐mediated downstream signaling and might serve to fine tune processes against viral infection.     

Interferon-�� and interleukin-12 are induced, respectively, by double-stranded DNA and single-stranded RNA in human myeloid dendritic cells

Dendritic cells (DCs) are initiators of innate immunity and acquired immunity as cells linking these two bio‐defence systems through the production of cytokines such as interferon‐α (IFN‐α) and interleukin‐12 (IL‐12). Nucleic acids such as DNA from damaged cells or pathogens are important activators not only for anti‐microbial innate immune responses but also in the pathogenesis of IFN‐related autoimmune diseases. Plasmacytoid DCs are regarded as the main effectors for the DNA‐mediated innate immunity by possessing DNA‐sensing toll‐like receptor 9 (TLR9). We here found that double‐stranded DNA (dsDNA) complexed with lipotransfectants triggered activation of human monocyte‐derived DCs (moDCs), leading to the preferential production of IFN‐α but not IL‐12. This indicates that myeloid DCs also function as supportive effectors against the invasion of pathogenic microbes through the DNA‐mediated activation in innate immunity. The dsDNA with lipotransfectants can be taken up by moDCs without co‐localization of endosomal LAMP1 staining, and the dsDNA‐mediated IFN‐α production was not impaired by chloroquine. These findings indicate that moDC activation by dsDNA does not involve the endosomal TLR pathway. In contrast, single‐stranded RNA (ssRNA) stimulated moDCs to secrete IL‐12 but not IFN‐α. This process was inhibited by chloroquine, suggesting an involvement of the TLR pathway in ssRNA‐mediated moDC activation. As might be inferred from our findings, myeloid DCs may function as a traffic control between innate immunity via IFN‐α production and acquired immunity via IL‐12 production, depending on the type of nucleic acids. Our results provide a new insight into the biological action of myeloid DCs underlying the DNA‐mediated activation of protective or pathogenic immunity.     

Identification of a TLR4- and TRIF-dependent activation program of dendritic cells

Dendritic cell activation by Toll-like receptors (TLR) is crucial for the generation of protective immune responses. In addition to the common myeloid differentiation factor 88 (MyD88)-dependent signaling pathway, TLR4 engages the adaptor protein Toll/IL-1 receptor (TIR)-domain-containing adaptor inducing IFN-beta (TRIF), leading to interferon regulatory factor 3 (IRF-3) activation and type I interferon production. Using microarray expression profiling we now identify TRIF as a major regulator of the TLR4-triggered activation program of dendritic cells. We show that the expression of 47% of the genes that are responsive to TLR4 stimulation in wild-type dendritic cells is significantly altered in cells carrying a loss-of-function mutation of TRIF. Specifically, expression of IL-12, IL-18, and IL-23 was impaired in the absence of functional TRIF, suggesting that TLR4-promoted Th1 responses are TRIF-dependent. Furthermore, we provide evidence that TRIF regulates TLR4-mediated gene expression both by type I IFN-dependent and -independent mechanisms. Whereas dendritic cell production of CXCL10 and CCL12 was dependent on both TRIF and the type I interferon receptor, expression of IL-6 required TRIF but not type I interferon activity. Functional TRIF was also required for the normal induction of numerous genes considered important for host defense against diverse pathogens.Together, these data therefore identify TRIF as a crucial regulator of TLR4-dependent dendritic cell responses.     

The induction of innate and adaptive immunity by biodegradable poly(γ-glutamic acid) nanoparticles via a TLR4 and MyD88 signaling pathway

The induction of adaptive immunity through the activation of innate immunity is indispensable for vaccine development. Although strategies for particulate antigen delivery are widely investigated, their immunological mechanisms are unclear. We describe in this study that biodegradable nanoparticles (NPs) elaborated with poly(γ-glutamic acid) (γ-PGA) are able to induce potent innate and adaptive immune responses through Toll-like receptor 4 (TLR4) and MyD88 signaling pathways. The production of inflammatory cytokines from macrophages and the maturation of dendritic cells were impaired in MyD88-knockout and TLR4-deficient mice compared with their wild-types, when the cells were stimulated with γ-PGA NPs. The immunization of these mice with antigen-carrying γ-PGA NPs also resulted in diminished induction of antigen-specific cellular immune responses. These results suggest that γ-PGA NPs have not only an antigen-carrying capacity but also a potent adjuvant function of eliciting adaptive immune responses to the carrying antigen through recognition of the first-line host-sensor system.     

Porin of Shigella dysenteriae directly promotes Toll-like receptor 2-mediated CD4 T cell survival and effector function

Porin of Shigella dysenteriae type 1 up-regulated Toll-like receptor (TLR)2 on CD3-stimulated CD4⁺ T cells but could not induce the expression of other TLRs. TLR2 in association with myeloid differentiating factor 88 (MyD88) triggered the downstream signal transduction pathway leading to activation of mitogen-activated protein kinase (MAPK) and nuclear factor κB (NF-κB), and degradation of IκB, the NF-κB inhibitor. TLR2 co-stimulation by porin resulted in T cell expansion by inducing both proliferation and survival of the CD4⁺ T cells. Extracellular signal-regulated kinase (ERK)1/2 activation inhibitor U0126 and NF-κB translocation inhibitor SN-50 significantly inhibited proliferation of T cells, highlighting a direct role of ERK and NF-κB in the process. However, cell survival involving Bcl-X_L induction was found to be regulated essentially by ERK with no significant role of NF-κB. Porin-induced proliferation was supported by induction of IL-2 and CD25 that are known to play a pivotal role in T cell expansion. Apart from inducing T cell proliferation, porin triggered effector functions of the cells, evident from TLR2- and MyD88-dependent release of type 1 cytokines tumor necrosis factor (TNF) and interferon (IFN)-γ along with the induction of type 1 chemokines macrophage-inflammatory protein (MIP)-1α and MIP-1β and their receptor CCR5. The proliferation, survival and effector function of CD4⁺ T cells through TLR2 co-stimulation show the capability of porin to directly turn adaptive immunity into action.