Innate antiviral responses by means of TLR7-mediated recognition of single-stranded RNA

Interferons (IFNs) are critical for protection from viral infection, but the pathways linking virus recognition to IFN induction remain poorly understood. Plasmacytoid dendritic cells produce vast amounts of IFN-alpha in response to the wild-type influenza virus. Here, we show that this requires endosomal recognition of influenza genomic RNA and signaling by means of Toll-like receptor 7 (TLR7) and MyD88. Single-stranded RNA (ssRNA) molecules of nonviral origin also induce TLR7-dependent production of inflammatory cytokines. These results identify ssRNA as a ligand for TLR7 and suggest that cells of the innate immune system sense endosomal ssRNA to detect infection by RNA viruses.     

Autophagy-dependent viral recognition by plasmacytoid dendritic cells

Plasmacytoid dendritic cells (pDCs) detect viruses in the acidified endosomes by means of Toll-like receptors (TLRs). Yet, pDC responses to certain single-stranded RNA (ssRNA) viruses occur only after live viral infection. We present evidence here that the recognition of such viruses by TLR7 requires transport of cytosolic viral replication intermediates into the lysosome by the process of autophagy. In addition, autophagy was found to be required for the production of interferon-alpha by pDCs. These results support a key role for autophagy in mediating ssRNA virus detection and interferon-alpha secretion by pDCs and suggest that cytosolic replication intermediates of viruses serve as pathogen signatures recognized by TLR7.     

Toll-like receptor 8-mediated reversal of CD4+ regulatory T cell function

CD4+ regulatory T (Treg) cells have a profound ability to suppress host immune responses, yet little is understood about how these cells are regulated. We describe a mechanism linking Toll-like receptor (TLR) 8 signaling to the control of Treg cell function, in which synthetic and natural ligands for human TLR8 can reverse Treg cell function. This effect was independent of dendritic cells but required functional TLR8-MyD88-IRAK4 signaling in Treg cells. Adoptive transfer of TLR8 ligand-stimulated Treg cells into tumor-bearing mice enhanced anti-tumor immunity. These results suggest that TLR8 signaling could play a critical role in controlling immune responses to cancer and other diseases.     

Autoreactive B cell responses to RNA-related antigens due to TLR7 gene duplication

Antibodies against nuclear self-antigens are characteristic of systemic autoimmunity, although mechanisms promoting their generation and selection are unclear. Here, we report that B cells containing the Y-linked autoimmune accelerator (Yaa) locus are intrinsically biased toward nucleolar antigens because of increased expression of TLR7, a single-stranded RNA-binding innate immune receptor. The TLR7 gene is duplicated in Yaa mice because of a 4-Megabase expansion of the pseudoautosomal region. These results reveal high divergence in mouse Y chromosomes and represent a good example of gene copy number qualitatively altering a polygenic disease manifestation.     

Identification of Toll-like Receptor (TLR) 4 Gene in Wild Boar

Toll-like receptor (TLR) 4 plays an important role in the innate immune system and has been involved in resistance/ susceptibility to a number of diseases as revealed by studies in human and other domestic animals.Wild boar survives in natural environment without artificial interference and may be different from domestic pig in innate immune system.Here,the complete coding sequence of TLR4 and TLR4A was cloned in wild boar,and two other alternative splicing variants,TLR4B and TLR4C,were obtained.Compared to the counterpart from domestic pig (GenBank No.AJ628065),there were five SNPs,c.510T＞C,c.960A＞G,c.962A＞G,c.1605T＞G and c.1824A＞G,in the coding sequence of wild boar TLR4A gene.TLR4 gene was expressed in all the tissues from wild boar studied with the most abundance in spleen tissue,and mRNA level was significantly lower in spleen from wild boar than that from Min pig.The allele distribution was significantly different at polymorphic loci c.962G＞A and c.1027C＞A (p＜0.01) between wild boar and Min pig.The results would contribute to understand the innate immune system in wild boar.     

The TLR Expression Pattern on Monocyte-Derived Macrophages for Lipopolysaccharid Stimulation of Calves

In this paper, toll-like receptor expression pattern in monocytes-derived macrophages by lipopolysaccharid （LPS） stimulation was examined. Jugular venous blood samples from 4 Japanese calves were obtained and the peripheral blood mononuclear cells （PBMC） were isolated. The PBMC were cultured for 7 d so as to collect monocytes-derived macrophages in Repcell. The PBMC were stimulated by LPS for 24 h and the mRNA expression pattern of TLR and cytokines in monocytes-derived macrophages （Mod-Mφ） was analyzed. Results showed that LPS stimulation of Mod-Mφ could increase the mRNA levels of the genes of TNF-α, IL-6, and IL-8. In addition, the mRNA levels of the genes of TNF-α and IL-6 in the group of LPS stimulation were most significantly （P 〈 0.01） higher than those in control group and the mRNA levels of TLR1, 3, 5, 8, and 10 were significantly （P 〈 0.05） decreased after LPS stimulation. There was no difference in the mRNA expressions of TLR2, 4, 6, and 7 between the groups of the control and LPS stimulation. Besides, expression of TLR9 was not found. It suggested that monocytes-derived macrophages could respond to LPS and they might take an important role in the innate immunity. The important function of the cells might contribute to better disease treatment.     

Induction of direct antimicrobial activity through mammalian toll-like receptors

The mammalian innate immune system retains from Drosophila a family of homologous Toll-like receptors (TLRs) that mediate responses to microbial ligands. Here, we show that TLR2 activation leads to killing of intracellular Mycobacterium tuberculosis in both mouse and human macrophages, through distinct mechanisms. In mouse macrophages, bacterial lipoprotein activation of TLR2 leads to a nitric oxide-dependent killing of intracellular tubercle bacilli, but in human monocytes and alveolar macrophages, this pathway was nitric oxide-independent. Thus, mammalian TLRs respond (as Drosophila Toll receptors do) to microbial ligands and also have the ability to activate antimicrobial effector pathways at the site of infection.     

Toll-like receptor triggering of a vitamin D-mediated human antimicrobial response

In innate immune responses, activation of Toll-like receptors (TLRs) triggers direct antimicrobial activity against intracellular bacteria, which in murine, but not human, monocytes and macrophages is mediated principally by nitric oxide. We report here that TLR activation of human macrophages up-regulated expression of the vitamin D receptor and the vitamin D-1-hydroxylase genes, leading to induction of the antimicrobial peptide cathelicidin and killing of intracellular Mycobacterium tuberculosis. We also observed that sera from African-American individuals, known to have increased susceptibility to tuberculosis, had low 25-hydroxyvitamin D and were inefficient in supporting cathelicidin messenger RNA induction. These data support a link between TLRs and vitamin D-mediated innate immunity and suggest that differences in ability of human populations to produce vitamin D may contribute to susceptibility to microbial infection.     

TLR13 recognizes bacterial 23S rRNA devoid of erythromycin resistance-forming modification

Host protection from infection relies on the recognition of pathogens by innate pattern-recognition receptors such as Toll-like receptors (TLRs). Here, we show that the orphan receptor TLR13 in mice recognizes a conserved 23S ribosomal RNA (rRNA) sequence that is the binding site of macrolide, lincosamide, and streptogramin group (MLS) antibiotics (including erythromycin) in bacteria. Notably, 23S rRNA from clinical isolates of erythromycin-resistant Staphylococcus aureus and synthetic oligoribonucleotides carrying methylated adenosine or a guanosine mimicking a MLS resistance-causing modification failed to stimulate TLR13. Thus, our results reveal both a natural TLR13 ligand and specific mechanisms of antibiotic resistance as potent bacterial immune evasion strategy, avoiding recognition via TLR13.     

髓样分化蛋白-2研究进展

髓样分化蛋白-2(Myeloid differentiation protein-2,MD-2)是一种分子量为20～30 kD的分泌蛋白,它结合在Toll样受体4(Tolllike receptor 4,TLR4)胞外区,能与TLR4组成复合体(MD-2/TLR4),在细菌脂多糖(lipopolysaccharide,LPS)的识别及其信号转导中发挥重要作用,MD-2也是目前炎症、感染、免疫等病理过程研究的热点之一。本文对MD-2基因结构、基因表达及MD-2与机体天然免疫等方面研究结果进行综述,以期阐释MD-2的基因与天然免疫的关系,为揭示MD-2基因的功能提供技术参考。     

猪TLR4基因单核苷酸多态性对转录的影响

TLR4能识别革兰氏阴性菌脂多糖,并将信号向下游传递,启动天然免疫反应并诱发获得性免疫反应,在机体的防御反应中发挥重要作用。研究利用PCR-RFLP方法对TLR4基因的3个SNPs位点(c.611 T>A、c.962 G>A和c.1027 C>A)进行基因型分析,同时利用荧光定量PCR法检测每个个体TLR4基因的表达量,统计学方法比较不同基因型个体间表达量的差别。发现SNPs c.611 T>A和c.962 G>A显著影响TLR4的转录(P<0.05)。结果表明,SNPs c.611 T>A和c.962 G>A引起的蛋白质合成量变化,影响机体免疫反应。     

Toll-like receptor signaling pathways

Members of the Toll-like receptor (TLR) family recognize conserved microbial structures, such as bacterial lipopolysaccharide and viral double-stranded RNA, and activate signaling pathways that result in immune responses against microbial infections. All TLRs activate MyD88-dependent pathways to induce a core set of stereotyped responses, such as inflammation. However, individual TLRs can also induce immune responses that are tailored to a given microbial infection. Thus, these receptors are involved in both innate and adaptive immune responses. The mechanisms and components of these varied responses are only partly understood. Given the importance of TLRs in host defense, dissection of the pathways they activate has become an important emerging research focus. TLRs and their pathways are numerous; Science's Signal Transduction Knowledge Environment's TLR Connections Map provides an immediate, clear overview of the known components and relations of this complex system.     

TLR11 activation of dendritic cells by a protozoan profilin-like protein

Mammalian Toll-like receptors (TLRs) play an important role in the innate recognition of pathogens by dendritic cells (DCs). Although TLRs are clearly involved in the detection of bacteria and viruses, relatively little is known about their function in the innate response to eukaryotic microorganisms. Here we identify a profilin-like molecule from the protozoan parasite Toxoplasma gondii that generates a potent interleukin-12 (IL-12) response in murine DCs that is dependent on myeloid differentiation factor 88. T. gondii profilin activates DCs through TLR11 and is the first chemically defined ligand for this TLR. Moreover, TLR11 is required in vivo for parasite-induced IL-12 production and optimal resistance to infection, thereby establishing a role for the receptor in host recognition of protozoan pathogens.     

高迁移率族核小体结合蛋白及其应用潜能

高迁移率族核小体结合蛋白(High-mobility group nucleosome-binding proteins,HMGN)几乎存在于所有哺乳动物和多数脊椎动物的细胞核中,属于HMG蛋白家族。HMGN是现在唯一已知的特异性结合在核小体上的非组蛋白,能够改变染色质的结构、增强染色质模板的转录/复制,参与DNA复制/表达、细胞分化、器官发育及基因表达调控等细胞的生命活动。目前,HMGN包括HMGN1、HMGN2、HMGN3、HMGN4和HMGN5。研究显示,HMGN1据其所在位置的不同,有着截然不同的功能。在细胞核内,HMGN1作为一种特殊定位的生物蛋白,与核小体直接结合而调节基因的转录和影响染色质的结构;在细胞外环境,HMGN1通过toll样受体4(Toll-like receptor 4,TLR4)促进抗原提呈细胞(Antigen-presenting cells,APCs)的活化和补充,从而促进特定抗原免疫应答。警报素(Alarmins)是一种内源性介质,当机体受到危险信号刺激时,它能快速的释放到细胞外,招募并激活APCs增强特异性免疫和非特异性免疫反应。认识HMGN及其作用对其在多方面的应用有重要意义。     

粗提牛白细胞抗菌肽对小鼠免疫功能的影响

将粗提牛白细胞抗菌肽分别以低、中、高剂量(1.5,7.5,15 g·L~(-1))灌胃小鼠,0.2 mL·只~(-1);对照组分别为灌施体积分数为0.01%醋酸溶液和10 g·L~(-1)的牛血清白蛋白各0.2 mL.测定小鼠的细胞吞噬功能和免疫器官指数;同时采用流式细胞术测定小鼠外同血中T淋巴细胞亚群的总数及各亚群的百分数.结果表明,7.5 g·L~(-1)的粗提牛白细胞抗菌肽能明显提高小鼠的免疫器官指数(P<0.05),增强小鼠的细胞吞噬功能(P<0.05)以及小鼠外周血CD3~+,CD4~+及CD8~+T淋巴细胞的百分数(P<0.01),而高剂量组比中剂量有所降低.7.5 g·L~(-1)的粗提牛白细胞抗菌肽能明显增强小鼠的免疫功能,提高机体的免疫水平.     

Promotion of tissue inflammation by the immune receptor Tim-3 expressed on innate immune cells

CD4+ T helper 1 (TH1) cells are important mediators of inflammation and are regulated by numerous pathways, including the negative immune receptor Tim-3. We found that Tim-3 is constitutively expressed on cells of the innate immune system in both mice and humans, and that it can synergize with Toll-like receptors. Moreover, an antibody agonist of Tim-3 acted as an adjuvant during induced immune responses, and Tim-3 ligation induced distinct signaling events in T cells and dendritic cells; the latter finding could explain the apparent divergent functions of Tim-3 in these cell types. Thus, by virtue of differential expression on innate versus adaptive immune cells, Tim-3 can either promote or terminate TH1 immunity and may be able to influence a range of inflammatory conditions.     

Enhanced dendritic cell antigen capture via toll-like receptor-induced actin remodeling

Microbial products are sensed through Toll-like receptors (TLRs) and trigger a program of dendritic cell (DC) maturation that enables DCs to activate T cells. Although an accepted hallmark of this response is eventual down-regulation of DC endocytic capacity, we show that TLR ligands first acutely stimulate antigen macropinocytosis, leading to enhanced presentation on class I and class II major histocompatibility complex molecules. Simultaneously, actin-rich podosomes disappear, which suggests a coordinated redeployment of actin to fuel endocytosis. These reciprocal changes are transient and require p38 and extracellular signal-regulated kinase activation. Thus, the DC actin cytoskeleton can be rapidly mobilized in response to innate immune stimuli to enhance antigen capture and presentation.