The molecular makeup and function of regulatory and effector synapses

Summary:  Physical interactions between T cells and antigen-presenting cells (APCs) form the basis of any specific immune response. Upon cognate contacts, a multimolecular assembly of receptors and adhesion molecules on both cells is created, termed the immunological synapse (IS). Very diverse structures of ISs have been described, yet the functional importance for T-cell differentiation is largely unclear. Here we discuss the principal structure and function of ISs. We then focus on two characteristic T-cell–APC pairs, namely T cells contacting dendritic cells (DCs) or naive B cells, for which extremely different patterns of the IS have been observed as well as fundamentally different effects on the function of the activated T cells. We provide a model on how differences in signaling and the involvement of adhesion molecules might lead to diverse interaction kinetics and, eventually, diverse T-cell differentiation. We hypothesize that the preferred activation of the adhesion molecule leukocyte function-associated antigen-1 (LFA-1) and of the negative regulator for T-cell activation, cytotoxic T-lymphocyte antigen-4 (CTLA-4), through contact with naive B cells, lead to prolonged cell–cell contacts and the generation of T cells with regulatory capacity. In contrast, DCs might have evolved mechanisms to avoid LFA-1 overactivation and CTLA-4 triggering, thereby promoting more dynamic contacts that lead to the preferential generation of effector cells.     

Increase in Ksp37-positive peripheral blood lymphocytes in mild extrinsic asthma

Killer-specific secretory protein of 37 kDa (Ksp37), identified as a Th1/Tc1 specific secretory protein is expressed preferentially in cytotoxic T lymphocytes (CTL) and natural killer (NK) cells and might be involved in essential processes of CTL-mediated immunity. Although extrinsic asthma is linked currently to a Th2-dominated pathogenesis, there is increasing evidence for Th1/Tc1-mediated processes in the aetiopathology of asthma. CTL from patients with asthma have been shown to express cytokines and effector molecules which were different from healthy controls. We hypothesized that Ksp37 could indicate the involvement of CTL in the pathogenesis of extrinsic asthma. We therefore investigated Ksp37 expression in PBMC from patients with mild extrinsic asthma (n = 7) and healthy controls (n = 7). Flow cytometric analysis was used to quantify Ksp37+ cells and to investigate cellular Ksp37 expression as relative mean fluorescence intensities (MFI). We found a significantly (P = 0.016) higher percentage of Ksp37+ cells within the total lymphocyte population obtained from patients with mild extrinsic asthma compared with healthy controls. Subdifferentiation revealed a significant difference limited exclusively to the CD8+ subset (P = 0.010). In addition, Ksp37 secretion from cultured peripheral blood mononuclear cells (PBMC) and MFI of Ksp37+ lymphocytes were increased in patients with asthma compared with healthy controls. We conclude that mild extrinsic asthma appears to be associated with an increased expression of the Tc1 related protein Ksp37. The functional role of Ksp37 in the pathogenesis of asthma remains to be elucidated.     

弓形虫诱导的黏膜细胞免疫应答研究进展

弓形虫经口感染可引起肠道黏膜诱导及效应部位的免疫应答，黏膜免疫研究对于研制弓形虫口服黏膜疫苗具有重要的指导作用。本文从细胞水平对弓形虫感染后肠道黏膜各类细胞的功能及作用机制的研究进展作了综述。     

A Fc engineering approach to define functional humoral correlates of immunity against Ebola virus

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Baicalin extracted from Huang qin (Radix Scutellariae Baicalensis) induces apoptosis in gastric cancer cells by regulating B cell lymphoma (Bcl-2)/Bcl-2-associated X protein and activating caspase-3 and caspase-9

Objective

To evaluate the effects of baicalin in human gastric cancer cells, including apoptosis-inducing effects, and to investigate its underlying mechanisms of action.

Are rats more human than mice?

In contrast to rats, mouse models are nowadays generally used for the investigation of immune responses and immune-mediated diseases, there are many different strains and mouse-specific tools available, and it is easy to generate transgenic and constitutive or inducible knockout mice for any gene. Many immune markers and mechanisms have been detected in mice and have been introduced as gold standard in immunology, however, some turned out to be not unconditionally transferable to the human immune system.Rats have been used more frequently in former days but are mostly outstripped by mice due to the fact that fewer strains are available, they need more space than mice, are more expensive to maintain and breed, and it is extremely difficult to generate transgenic or ko-rats. Consequently, the choice of rat-specific diagnostic tools like antibodies is quite poor and most researchers have switched to mouse models for the investigation of immune mechanisms, while rats are still widely used for toxicology by the pharmaceutical industry. However, it should be taken into consideration that there are some immunological similarities between rats and humans that are not presented in mice. Some of them like MHC class II and Foxp3 expression by activated effector T cells we have detected during our research on the immune response of rat models of experimental autoimmune uveitis.     

多发性骨髓瘤细胞XG-7诱导CD8和TCRαβ阳性的T细胞增殖分化成为细胞毒效应细胞

采用经密度梯度离心获得的正常健康人外周血淋巴细胞 (PBL )与多发性骨髓瘤细胞XG 7进行混合肿瘤淋巴细胞培养。3 H TdR掺入实验证实XG 7细胞可刺激PBL增殖 ;间接免疫荧光检测显示增殖的PBL中 ,CD4+ /CD8+ 细胞比例偏移 ,CD8+ T细胞增加。激活的CD8+ T细胞在含IL 2的培养体系中得到迅速扩增 ,占细胞总数的 96 %以上。流式细胞仪检测显示 ,扩增的T细胞表达CD3,CD8和TCRαβ ,而不表达CD4,CD16和CD5 6。细胞毒实验结果表明 ,扩增的CD8+ T细胞不仅杀伤原刺激细胞XG 7,也可杀伤其它肿瘤细胞如RPMI82 2 6 ,U2 6 6和Daudi。上述结果说明了经XG 7细胞所刺激PBL中的CD8+ T细胞可增殖分化成为抗肿瘤细胞的细胞毒效应细胞 ,这使得它们有可能在临床上用于肿瘤病人的治疗。     

The small molecule Zaractin activates ZAR1-mediated immunity in Arabidopsis

Pathogenic effector proteins use a variety of enzymatic activities to manipulate host cellular proteins and favor the infection process. However, these perturbations can be sensed by nucleotide-binding leucine-rich-repeat (NLR) proteins to activate effector-triggered immunity (ETI). Here we have identified a small molecule (Zaractin) that mimics the immune eliciting activity of the Pseudomonas syringae type III secreted effector (T3SE) HopF1r and show that both HopF1r and Zaractin activate the same NLR-mediated immune pathway in Arabidopsis. Our results demonstrate that the ETI-inducing action of pathogenic effectors can be harnessed to identify synthetic activators of the eukaryotic immune system.

Gram-negative bacterial plant pathogens such as Pseudomonas syringae use the type III secretion system (T3SS) to inject type III secreted effectors (T3SEs) into plant cells (1). A major function of T3SEs is to suppress plant immunity by targeting host proteins involved in disease resistance (2). However, plant nucleotide-binding leucine-rich-repeat (NLR) proteins can directly or indirectly recognize T3SEs and activate a response known as effector-triggered immunity (ETI), which can be accompanied by a hypersensitive cell death response (2, 3). The Arabidopsis thaliana NLR ZAR1 recognizes T3SE-induced complexes of ZED1-related kinases (ZRKs; RLCK XII-2 family) and PBS1-like (PBL) kinases (RLCK VII family) to activate ETI (4–7). T3SEs modify either ZRK and/or PBL kinases and promote their interaction, which activates ZAR1-mediated ETI (5, 6). For example, the Xanthomonas campestris AvrAC, uridylates PBL2 kinase, promoting an interaction with ZRK1 (also known as RKS1) that then acts as a nucleotide exchange factor to activate the ZAR1 resistosome (8, 9).In addition to AvrAC, five P. syringae effector families have been shown to trigger ZAR1/ZRK-mediated immunity in Arabidopsis (4, 10–13). ZAR1-mediated immunity triggered by the acetyltransferase HopZ1a requires the ZRK kinase ZED1 and the functionally redundant PBL kinases SZE1 and SZE2 (4, 7). Interestingly, acetylation of ZED1 by HopZ1a can activate immunity, suggesting that modification of either ZRK or PBL kinases can activate the ZAR1 resistosome (4, 6). HopX1i-recognition also requires ZED1 and SZE1, but not SZE2 (13). HopO1c- and HopF1r-mediated immunity requires ZRK3, whereas HopBA1a recognition requires ZRK2, but no PBL kinase requirement has been identified (11, 13). Based on the genetic requirements of ZAR1-mediated ETI against P. syringae effectors and the model of AvrAC recognition, a general mechanism of ZAR1 activation likely involves T3SE perturbations of ZRK and/or PBL kinases that promote their interaction, which in turn activates the ZAR1 resistosome (8, 9).We hypothesized that small molecules that mimic ETI-promoting effector perturbations would represent a powerful, targeted approach to activate plant immunity. Given the model of ZAR1 activation described above, we developed a chemical screen to identify small molecules that enhance ETI-inducing ZRK/PBL interactions. First, we show that the P. syringae T3SE HopF1r can enhance the interaction between ZRK3 and PBL27 and that PBL27 is a required component of ZAR1-mediated recognition of HopF1r. We then used our chemical screen to identify a small molecule (Zaractin) that can enhance the ZRK3/PBL27 interaction and activate ZAR1-dependent immunity. Overall, our results demonstrate that chemical mimicry of type III effector function can activate an NLR-mediated immune response, providing an approach to identify chemical immunomodulators.     

An ancient antimicrobial protein co-opted by a fungal plant pathogen for in planta mycobiome manipulation

Microbes typically secrete a plethora of molecules to promote niche colonization. Soil-dwelling microbes are well-known producers of antimicrobials that are exploited to outcompete microbial coinhabitants. Also, plant pathogenic microbes secrete a diversity of molecules into their environment for niche establishment. Upon plant colonization, microbial pathogens secrete so-called effector proteins that promote disease development. While such effectors are typically considered to exclusively act through direct host manipulation, we recently reported that the soil-borne, fungal, xylem-colonizing vascular wilt pathogen Verticillium dahliae exploits effector proteins with antibacterial properties to promote host colonization through the manipulation of beneficial host microbiota. Since fungal evolution preceded land plant evolution, we now speculate that a subset of the pathogen effectors involved in host microbiota manipulation evolved from ancient antimicrobial proteins of terrestrial fungal ancestors that served in microbial competition prior to the evolution of plant pathogenicity. Here, we show that V. dahliae has co-opted an ancient antimicrobial protein as effector, named VdAMP3, for mycobiome manipulation in planta. We show that VdAMP3 is specifically expressed to ward off fungal niche competitors during resting structure formation in senescing mesophyll tissues. Our findings indicate that effector-mediated microbiome manipulation by plant pathogenic microbes extends beyond bacteria and also concerns eukaryotic members of the plant microbiome. Finally, we demonstrate that fungal pathogens can exploit plant microbiome-manipulating effectors in a life stage–specific manner and that a subset of these effectors has evolved from ancient antimicrobial proteins of fungal ancestors that likely originally functioned in manipulation of terrestrial biota.

Microbes are found in a wide diversity of niches on our planet. To facilitate establishment within microbial communities, microbes secrete a multitude of molecules to manipulate each other. Many of these molecules exert antimicrobial activities and are exploited to directly suppress microbial coinhabitants in order to outcompete them for the limitedly available nutrients and space of a niche. Microbially secreted antimicrobials encompass diverse molecules including peptides and lytic enzymes but also nonproteinaceous molecules such as secondary metabolites. Soils are among the most biologically diverse and microbially competitive environments on earth. Microbial proliferation in the soil environment is generally limited by the availability of organic carbon (1), for which soil microbes continuously compete. Consequently, numerous saprophytic soil-dwelling microbes secrete potent antimicrobials that promote niche protection or colonization. Notably, these microbes are the primary source of our clinically used antibiotics (2, 3).Like free-living microbes, microbial plant pathogens also secrete a multitude of molecules into their environment to mediate niche colonization (4, 5). The study of molecules secreted by microbial plant pathogens has been largely confined to the context of binary interactions between pathogens and hosts. To establish disease, plant pathogenic microbes secrete a plethora of so-called effectors, molecules of various kinds that promote host colonization and that are typically thought to mainly deregulate host immune responses (4, 6, 7). Upon host colonization, plant pathogens encounter a plethora of plant-associated microbes that collectively form the plant microbiota, which represent a key factor for plant health. Beneficial plant-associated microbes are found in and on all organs of the plant and help to mitigate (a)biotic stresses (8–13). Plants shape their microbiota and specifically attract beneficial microbes to suppress pathogens (14–16). Hence, the plant microbiome can be considered an inherent, exogenous layer that complements the plant’s endogenous innate immune system. We previously hypothesized that plant pathogens not only utilize effectors to target components of host immunity as well as other aspects of host physiology to support host colonization but also to target the host microbiota in order to establish niche colonization (4, 5). We recently provided experimental evidence for this hypothesis by showing that the ubiquitously expressed effector VdAve1 that is secreted by the soil-borne fungal plant pathogen Verticillium dahliae acts as a bactericidal protein that promotes host colonization through the selective manipulation of host microbiomes by suppressing microbial antagonists (17, 18). Additionally, we demonstrated that VdAve1 and a further antibacterial effector named VdAMP2 are exploited by V. dahliae for microbial competition in soil and promote virulence of V. dahliae in an indirect manner (18). Collectively, these observations demonstrate that V. dahliae dedicates part of its effector catalog toward microbiota manipulation. Likely, the V. dahliae genome encodes further effectors that act in microbiome manipulation.Evidently, bacterial and fungal evolution on land preceded land plant evolution. As a consequence, fungal pathogen effectors involved in the manipulation of (host-associated) microbial communities may have evolved from ancestors that served in microbial competition in terrestrial niches hundreds of millions of years ago prior to land plant evolution. However, evidence for this hypothesis is presently lacking.V. dahliae is an asexual xylem-dwelling fungus that causes vascular wilt disease on hundreds of plant species (19). The fungus survives in the soil in the form of multicellular melanized resting structures, called microsclerotia, that offer protection against (a)biotic stresses and can persist in the soil for many years (20). Microsclerotia represent the major inoculum source of V. dahliae in nature, and their germination is triggered by carbon- and nitrogen-rich exudates from plant roots (21). Following microsclerotia germination, fungal hyphae grow through the soil and rhizosphere toward the roots of host plants. Next, V. dahliae colonizes the root cortex and crosses the endodermis, from which it invades xylem vessels. Once the fungus enters those vessels, it forms conidiospores that are transported with the water flow until they get trapped, for instance, by vessel end walls. This triggers germination of the conidiospores followed by penetration of cell walls, hyphal growth, and renewed sporulation, leading to systematic colonization of the plant (22). Once tissue necrosis commences and plant senescence occurs, host immune responses fade and V. dahliae enters a saprophytic phase in which it emerges from the xylem vessels to invade adjacent host tissues, which is accompanied by the production of microsclerotia. Upon littering and decomposition of plant tissues, these microsclerotia are released into the soil (23).