干扰素抗病毒效力影响因素的研究进展

干扰素（interferons,IFN）是一类重要的细胞因子,具有多种抗病毒和免疫调节等作用。根据其结构特点、受体、细胞来源和生物学活性,可分为Ⅰ型、Ⅱ型和Ⅲ型。IFN通过与其特异性受体结合,通过一个复杂且部分重叠的基因转录过程来发挥作用,其核苷酸多态性和基因突变可影响IFN反应及对病毒感染的敏感性。几乎所有的病毒都有抵抗IFN抗病毒活性的机制和效力,包括直接影响IFN产生和影响下游效应因子。不同型别IFN在行使抗病毒或免疫调节功能时具有拮抗或协同作用。本文就IFN基因变异、病毒抗IFN策略及IFN之间的协同/拮抗作用进行综述,以期能更好地理解IFN的抗病毒作用。     

干扰素的信号传导和抗病毒效应机制

干扰素是一种具有抗病毒、抗增殖和免疫调节功能的细胞因子,它在宿主天然免疫防御中起着重要的作用。干扰素诱导的信号通路除了最初的Jak-Stat途径以外,很多新发现的信号途径对于干扰素反应也是必需的。干扰素反应最终导致抗病毒的效应蛋白通路,包括2′,5′-寡聚腺苷酸合成酶、蛋白激酶、ISG15等途径。这些效应蛋白通过抑制病毒转录、降解病毒RNA、抑制翻译和修饰蛋白的功能来控制病毒复制的过程。     

综述:天然免疫限制因子Tetherin的抗病毒机理研究进展

天然免疫限制因子Tetherin(骨髓基质细胞抗原2)是Ⅰ型干扰素诱导产生的Ⅱ型跨膜蛋白．Tetherin通过其特殊的拓扑结构,在病毒出芽过程中将病毒粒子连接在细胞膜表面,限制病毒的有效释放,从而发挥广谱性的抗病毒活性,而病毒也可以通过多种策略拮抗Tetherin的抗病毒活性．病毒与宿主长期抗争进化的结果表现为病毒特定拮抗蛋白对抗不同种属细胞Tetherin的限制存在种属特异性．本文通过对Tetherin的分子结构、抗病毒活性及其拮抗蛋白的对抗机制等最新进展进行综述,为研究病毒与宿主相互作用的分子机制以及新型抗病毒药物的筛选提供借鉴．     

天然免疫限制因子Tetherin的抗病毒机理研究进展

天然免疫限制因子Tetherin(骨髓基质细胞抗原2)是Ⅰ型干扰素诱导产生的Ⅱ型跨膜蛋白.Tetherin通过其特殊的拓扑结构,在病毒出芽过程中将病毒粒子连接在细胞膜表面,限制病毒的有效释放,从而发挥广谱性的抗病毒活性,而病毒也可以通过多种策略拮抗Tetherin的抗病毒活性.病毒与宿主长期抗争进化的结果表现为病毒特定拮抗蛋白对抗不同种属细胞Tetherin的限制存在种属特异性.本文通过对Tetherin的分子结构、抗病毒活性及其拮抗蛋白的对抗机制等最新进展进行综述,为研究病毒与宿主相互作用的分子机制以及新型抗病毒药物的筛选提供借鉴.     

抗病毒天然免疫通路中IRF-3调控新机制

干扰素调节因子-3(interferon regulatory factor-3,IRF-3)是IRF家族中重要 转录因子之一,在调控干扰素(interferon, IFN)基因表达和抗病毒天然免疫反应中具有重要作 用. 最新发现的MITA (mediator of IRF-3 activation, 又称STING/ERIS)蛋白是宿主抗病 毒天然免疫反应中的一种重要调节分子. 病毒侵染时,MITA与IRF-3相互作用,特异性激活 IRF-3,并募集TANK结合激酶1（TANK binding kinase 1, TBK1）与IFN通路中的线粒体抗 病毒信号蛋白MAVS(mitochondrial anti-viral signaling protein)形成复合物,且MITA可 被TBK1磷酸化,诱导Ⅰ型IFN及IFN刺激基因(interferon stimulate genes, ISG)的表达 ,诱发抗病毒天然免疫反应. 同时还发现,泛素连接酶RNF5（ring finger protein 5）可对MITA 发生泛素化修饰从而抑制其对IRF-3活化,实现对宿主抗病毒天然免疫反应负调节作用. 本 室研究发现,严重性急性呼吸系统综合症冠状病毒(severe acute respiratory syndrome co ronavirus, SARS-CoV）和人类新型冠状病毒（human coronavirus NL63, HCoV-NL63）的 木瓜样蛋白酶（papain-like protease, PLP）利用其特有的去泛素化酶（deubiquitinase, DUB）活性,通过宿主细胞泛素-蛋白酶体信号系统对IRF-3的泛素化等翻译后修饰进行调节 ,从而成为该种病毒逃逸机体抗病毒防御系统主要手段之一.     

猪流行性腹泻病毒nsp1蛋白对Ⅰ型干扰素应答的影响

猪流行性腹泻病毒 (PEDV) 能抑制宿主Ⅰ型干扰素及其诱导的细胞抗病毒免疫应答,但是PEDV抑制Ⅰ型干扰素应答的分子机制尚不明了,尤其是PEDV非结构蛋白 (Nonstructural proteins,nsps) 在Ⅰ型干扰素应答中的调控作用研究不多。为研究PEDV非结构蛋白1 (nsp1) 对细胞Ⅰ型干扰素应答的影响,构建了真核表达载体pCAGGS-nsp1,采用Western blotting和间接免疫荧光试验确定nsp1在细胞中的表达。通过报告基因法、ELISA以及病毒复制抑制试验评估nsp1对Ⅰ型IFN的影响。结果显示,nsp1在转染细胞和病毒感染细胞中均高效表达;双荧光报告基因试验结果表明,nsp1能显著抑制IFN-β启动子活性,且具有剂量依赖性。ELISA结果显示,nsp1能显著抑制IFN-β蛋白的表达。水泡性口炎病毒 (VSV) 复制抑制试验结果显示,nsp1明显抑制poly(I:C)介导的Ⅰ型IFN的抗病毒作用。结果提示,nsp1作为PEDV的保守蛋白,具有拮抗Ⅰ型干扰素启动子活性和应答的功能,为揭示PEDV逃逸宿主天然免疫应答的机制和研发新型高效抗PEDV疫苗奠定基础。     

干扰素刺激基因的抗病毒机制

干扰素刺激基因(Interferon-stimulated genes,ISGs)作为由干扰素(Interferons,IFNs)诱导表达的基因,在宿主抵抗病毒感染的过程中发挥着至关重要的作用。越来越多的研究表明,ISGs能够靶向病毒复制的不同阶段进而抵抗病毒感染。由于ISGs成员众多,且各自的结构及其在细胞中的定位也各不相同,这决定了ISGs在宿主体内以不同机制来发挥抗病毒作用。本文将简要介绍IFNs如何通过JAK-STAT通路调控ISGs的表达,并归纳和讨论不同ISGs家族蛋白较为典型的抗病毒机制。     

病毒感染与干扰素系统

对于病毒感染,干扰素(IFN)的作用机制可分为2个步骤,首先是IFN的产生,第二步是已产生的IFN诱导抗病毒状态.在第一步,病毒由于阻碍IRF-3的活化而抑制初期IFN-β的产生,在第二步,病毒由于抑制IFN信号通路,进而抑制IFN的大量产生和抗病毒蛋白质的诱导产生.     

STING在宿主天然免疫信号通路中的调节作用

STING(stimulator of interferon genes)是天然免疫信号通路中一种新发现的蛋白质,在防御病毒及胞内细菌感染、介导Ⅰ型IFN产生过程中发挥重要功能.来自病原体的B型DNA与5′-3p dsRNA暴露在宿主细胞中后被相应的模式识别受体识别,通过不同的通路传递信号给STING.STING随后通过相似的机制招募TBK1激活IRF3,诱导干扰素表达.对细菌中的环二核苷酸c-di-GMP和c-di-AMP,STING则可以直接作为模式识别受体引发Ⅰ型干扰素反应.此外STING还能激活STAT6诱导特异趋化因子产生,吸引各种免疫细胞抵抗病毒感染.本文通过对STING的发现、结构、定位、功能、机理以及调节机制进行综述,以期为揭示病毒逃逸天然免疫调节机制和抗病毒新型免疫调节剂提供新的思路.     

干扰素刺激基因15在人类免疫缺陷病毒感染中作用的研究进展

随着有效的联合抗反转录病毒疗法(combination antiretroviral therapy,cART)的普及,人类免疫缺陷病毒(human immunodeficiency virus,HIV)感染者的生存期逐步延长。这一过程中,HIV感染者自身免疫反应对免疫系统功能的恢复也发挥了至关重要的作用。HIV感染激活干扰素信号通路,诱导干扰素刺激基因(interferon-stimulated gene,ISG)上调表达,从而发挥抗病毒作用。其中,类泛素蛋白ISG15在HIV感染者中显著上调,通过ISG化抑制HIV颗粒的出芽和释放;而HIV的非结构蛋白则通过干扰ISG化过程或结合干扰素信号通路关键分子,逆转ISG15对病毒的抑制作用。本文从ISG15的生物学特性、在不同细胞亚群中的表达、抗病毒功能及病毒逃逸机制等方面进行综述,为进一步解析ISG15在HIV感染中扮演的角色、探索如何获得以抗HIV感染宿主因子为契机的治疗策略提供了思路。     

Interferon, Mx, and viral countermeasures

The interferon system provides a powerful and universal intracellular defense mechanism against viruses. Knockout mice defective in IFN signaling quickly succumb to all kinds of viral infections. Likewise, humans with genetic defects in interferon signaling die of viral disease at an early age. Among the known interferon-induced antiviral mechanisms, the Mx pathway is one of the most powerful. Mx proteins belong to the dynamin superfamily of large GTPases and have direct antiviral activity. They inhibit a wide range of viruses by blocking an early stage of the viral replication cycle. Likewise, the protein kinase R (PKR), and the 2–5 OAS/RNaseL system represent major antiviral pathways and have been extensively studied. Viruses, in turn, have evolved multiple strategies to escape the IFN system. They try to go undetected, suppress IFN synthesis, bind and neutralize secreted IFN molecules, block IFN signaling, or inhibit the action of IFN-induced antiviral proteins. Here, we summarize recent findings about the astonishing interplay of viruses with the IFN response pathway.     

Viral suppression of the interferon system

Type I interferons (IFN-alpha/beta) were originally discovered by their strong and direct antiviral activity [A. Isaacs, J. Lindenmann, Virus interference. I. The interferon, Proc. R. Soc. Lond. B Biol. Sci. 147 (1957) 258-267]. (see review by J. Lindenmann on p. 719, in this issue). Nevertheless, only very recently it was entirely realized that viruses would not succeed without efficient tools to undermine this potent host defense system. Current investigations are revealing an astonishing variety of viral IFN antagonistic strategies targeting virtually all parts of the IFN system, often in a highly specific manner. Viruses were found to interfere with induction of IFN synthesis, IFN-induced signaling events, the antiviral effector proteins, or simply shut off the host cell macromolecule synthesis machinery to avoid booting of the antiviral host defense. Here, we will describe a few well-characterized examples to illustrate the sophisticated and often multi-layered anti-IFN mechanisms employed by viruses.     

The interferon system of teleost fish

Interferons (IFNs) are secreted proteins, which induce vertebrate cells into an antiviral state. In mammals, three families of IFNs (type I IFN, type II IFN and IFN-lambda) can be distinguished on the basis of gene structure, protein structure and functional properties. Type I IFNs, which include IFN-alpha and IFN-beta, are encoded by intron lacking genes and have a major role in the first line of defense against viruses. The human IFN-lambdas have similar biological properties as type I IFNs, but are encoded by intron containing genes. Type II IFN is identical to IFN-gamma, which is produced by T helper 1 cells in response to mitogens and antigens and has a key role in adaptive cell mediated immunity. IFNs, which show structural and functional properties similar to mammalian type I IFNs, have recently been cloned from Atlantic salmon, channel catfish, pufferfish, and zebrafish. Teleost fish appear to have at least two type I IFN genes. Phylogenetic sequence analysis shows that the fish type I IFNs form a group separated from the avian type I IFNs and the mammalian IFN-alpha, -beta and -lambda groups. Interestingly, the fish IFNs possess the same exon/intron structure as the IFN-lambdas, but show most sequence similarity to IFN-alpha. Recently, IFN-gamma genes have also been cloned from several fish species and shown to have the same exon/intron structure as mammalian IFN-gamma genes. The antiviral effect of mammalian type I IFN is exerted through binding to the IFN-alpha/beta-receptor, which triggers signal transduction through the JAK-STAT signal transduction pathway resulting in expression of Mx and other antiviral proteins. Putative IFN receptor genes have been identified in pufferfish. Several interferon regulatory factors and members of the JAK-STAT pathway have also been identified in various fish species. Moreover, Mx and several other interferon stimulated genes have been cloned and studied in fish. Furthermore, antiviral activity of Mx protein from Atlantic salmon and Japanese flounder has recently been demonstrated.     

The Antiviral Innate Immune Response in Fish: Evolution and Conservation of the IFN System

Innate immunity constitutes the first line of the host defense after pathogen invasion. Viruses trigger the expression of interferons (IFNs). These master antiviral cytokines induce in turn a large number of interferon-stimulated genes, which possess diverse effector and regulatory functions. The IFN system is conserved in all tetrapods as well as in fishes, but not in tunicates or in the lancelet, suggesting that it originated in early vertebrates. Viral diseases are an important concern of fish aquaculture, which is why fish viruses and antiviral responses have been studied mostly in species of commercial value, such as salmonids. More recently, there has been an interest in the use of more tractable model fish species, notably the zebrafish. Progress in genomics now makes it possible to get a relatively complete image of the genes involved in innate antiviral responses in fish. In this review, by comparing the IFN system between teleosts and mammals, we will focus on its evolution in vertebrates.     

Type III IFNs in pteropid bats: differential expression patterns provide evidence for distinct roles in antiviral immunity

Bats are known to harbor a number of emerging and re-emerging zoonotic viruses, many of which are highly pathogenic in other mammals but result in no clinical symptoms in bats. The ability of bats to coexist with viruses may be the result of rapid control of viral replication early in the immune response. IFNs provide the first line of defense against viral infection in vertebrates. Type III IFNs (IFN-λs) are a recently identified IFN family that share similar antiviral activities with type I IFNs. To our knowledge, we demonstrate the first functional analysis of type III IFNs from any species of bat, with the investigation of two IFN-λ genes from the pteropid bat, Pteropus alecto. Our results demonstrate that bat type III IFN has similar antiviral activity to type I and III IFNs from other mammals. In addition, the two bat type III IFNs are differentially induced relative to each other and to type I IFNs after treatment or transfection with synthetic dsRNA. Infection with the bat paramyxovirus, Tioman virus, resulted in no upregulation of type I IFN production in bat splenocytes but was capable of inducing a type III IFN response in three of the four bats tested. To our knowledge, this is the first report to describe the simultaneous suppression of type I IFN and induction of type III IFN after virus infection. These results may have important implications for the role of type III IFNs in the ability of bats to coexist with viruses.     

Poxviruses: Interfering with Interferon

Interferon (IFN) is an important innate defense against virus infection and many viruses have consequently evolved ways to interfere with the action of IFN. The poxviruses are an excellent example and devote at least four proteins to this task. Two function within the infected cell to block the action of IFN-induced antiviral proteins, and two are secreted to capture type I and type II IFNs before they can bind to cellular IFN receptors. The vaccinia virus IFN receptors have a surprisingly broad species specificity that may aid virus replication in several species and provide clues about the enigmatic origin of vaccinia virus.     

The pros and cons of interferons for oncolytic virotherapy

Interferons (IFN) are potent immune stimulators that play key roles in both innate and adaptive immune responses. They are considered the first line of defense against viral pathogens and can even be used as treatments to boost the immune system. While viruses are usually seen as a threat to the host, an emerging class of cancer therapeutics exploits the natural capacity of some viruses to directly infect and kill cancer cells. The cancer-specificity of these bio-therapeutics, called oncolytic viruses (OVs), often relies on defective IFN responses that are frequently observed in cancer cells, therefore increasing their vulnerability to viruses compared to healthy cells. To ensure the safety of the therapy, many OVs have been engineered to further activate the IFN response. As a consequence of this IFN over-stimulation, the virus is cleared faster by the immune system, which limits direct oncolysis. Importantly, the therapeutic activity of OVs also relies on their capacity to trigger anti-tumor immunity and IFNs are key players in this aspect. Here, we review the complex cancer–virus–anti-tumor immunity interplay and discuss the diverse functions of IFNs for each of these processes.     

The yin and yang of type I interferon activity in bacterial infection

Interferons (IFNs) are cytokines that are important for immune responses, particularly to intracellular pathogens. They are divided into two structurally and functionally distinct types that interact with different cell-surface receptors. Classically, type I IFNs are potent antiviral immunoregulators, whereas the type II IFN enhances antibacterial immunity. However, as outlined here, type I IFNs are also produced in response to infection with other pathogens, and an increasing body of work shows that type I IFNs have an important role in the host response to bacterial infection. Strikingly, their activity can be either favourable or detrimental, and can influence various immune effector mechanisms.     

Interaction of the innate immune system with positive-strand RNA virus replication organelles

The potential health risks associated with (re-)emerging positive-strand RNA (+RNA) viruses emphasizes the need for understanding host-pathogen interactions for these viruses. The innate immune system forms the first line of defense against pathogenic organisms like these and is responsible for detecting pathogen-associated molecular patterns (PAMPs). Viral RNA is a potent inducer of antiviral innate immune signaling, provoking an antiviral state by directing expression of interferons (IFNs) and pro-inflammatory cytokines. However, +RNA viruses developed various methods to avoid detection and downstream signaling, including isolation of viral RNA replication in membranous viral replication organelles (ROs). These structures therefore play a central role in infection, and consequently, loss of RO integrity might simultaneously result in impaired viral replication and enhanced antiviral signaling. This review summarizes the first indications that the innate immune system indeed has tools to disrupt viral ROs and other non- or aberrant-self membrane structures, and may do this by marking these membranes with proteins such as microtubule-associated protein 1A/1B-light chain 3 (LC3) and ubiquitin, resulting in the recruitment of IFN-inducible GTPases. Further studies should evaluate whether this process forms a general effector mechanism in +RNA virus infection, thereby creating the opportunity for development of novel antiviral therapies.