Cellular immune responses to HIV

The cellular immune response to the human immunodeficiency virus, mediated by T lymphocytes, seems strong but fails to control the infection completely. In most virus infections, T cells either eliminate the virus or suppress it indefinitely as a harmless, persisting infection. But the human immunodeficiency virus undermines this control by infecting key immune cells, thereby impairing the response of both the infected CD4+ T cells and the uninfected CD8+ T cells. The failure of the latter to function efficiently facilitates the escape of virus from immune control and the collapse of the whole immune system.     

NK细胞免疫识别及其调节机制与免疫相关性疾病

自然杀伤受体(NKR)和Toll样受体(TLR)是天然免疫系统最重要的二群天然免疫识别受体家族,位于机体抵抗外来侵袭的第一道防线.二者各自具有独特的识别外来或内源性的危险信号、区分自我和非我的识别机制,是启动固有免疫和适应性免疫应答的关键链接分子.NK细胞是天然免疫系统的核心成员,具有早期识别和清除病毒感染和肿瘤细胞等功能,同时也是连接天然免疫和获得性免疫的桥梁.以NK细胞为载体将TLRs/NKRs连接起来,可以较好地反映机体内外环境变化或刺激时固有免疫对适应性免疫的调节作用,为有效控制感染、炎症、肿瘤及自身免疫性疾病提供崭新的治疗策略.     

Innate immune recognition of bacterial ligands by NAIPs determines inflammasome specificity

Inflammasomes are a family of cytosolic multiprotein complexes that initiate innate immune responses to pathogenic microbes by activating the caspase 1 protease. Although genetic data support a critical role for inflammasomes in immune defence and inflammatory diseases, the molecular basis by which individual inflammasomes respond to specific stimuli remains poorly understood. The inflammasome that contains the NLRC4 (NLR family, CARD domain containing 4) protein was previously shown to be activated in response to two distinct bacterial proteins, flagellin and PrgJ, a conserved component of pathogen-associated type III secretion systems. However, direct binding between NLRC4 and flagellin or PrgJ has never been demonstrated. A homologue of NLRC4, NAIP5 (NLR family, apoptosis inhibitory protein 5), has been implicated in activation of NLRC4 (refs 7-11), but is widely assumed to have only an auxiliary role, as NAIP5 is often dispensable for NLRC4 activation. However, Naip5 is a member of a small multigene family, raising the possibility of redundancy and functional specialization among Naip genes. Here we show in mice that different NAIP paralogues determine the specificity of the NLRC4 inflammasome for distinct bacterial ligands. In particular, we found that activation of endogenous NLRC4 by bacterial PrgJ requires NAIP2, a previously uncharacterized member of the NAIP gene family, whereas NAIP5 and NAIP6 activate NLRC4 specifically in response to bacterial flagellin. We dissected the biochemical mechanism underlying the requirement for NAIP proteins by use of a reconstituted NLRC4 inflammasome system. We found that NAIP proteins control ligand-dependent oligomerization of NLRC4 and that the NAIP2-NLRC4 complex physically associates with PrgJ but not flagellin, whereas NAIP5-NLRC4 associates with flagellin but not PrgJ. Our results identify NAIPs as immune sensor proteins and provide biochemical evidence for a simple receptor-ligand model for activation of the NAIP-NLRC4 inflammasomes.     

Humoral and cell-mediated immune responses to live recombinant BCG-HIV vaccines

Several viral and bacterial live recombinant vaccine vehicles are being developed to produce a new generation of vaccines against a broad spectrum of infectious diseases. The human tuberculosis vaccine Mycobacterium bovis bacillus Calmette-Guerin (BCG) has features that make it a particularly attractive live recombinant vaccine vehicle. BCG and other mycobacteria are highly effective adjuvants, and the immune response to mycobacteria has been studied extensively. With nearly two billion immunizations, BCG has a long record of safe use in man. It is one of the few vaccines that can be given at birth, it engenders long-lived immune responses with only a single dose, and there is a worldwide distribution network with experience in BCG vaccination. Recently developed molecular genetic tools and methods for mycobacteria have provided the means to introduce foreign genes into BCG. Here we report that a variety of human immunodeficiency virus type 1 polypeptides can be expressed in BCG recombinants under the control of the mycobacterial hsp70 promoter and that the foreign polypeptides produced in BCG can induce antibody and T-cell responses. These results demonstrate that BCG can be used as a live recombinant vaccine vehicle to induce immune responses to pathogen proteins produced by the bacillus.     

Transient cross-reactive immune responses can orchestrate antigenic variation in malaria

The malaria parasite Plasmodium falciparum has evolved to prolong its duration of infection by antigenic variation of a major immune target on the surface of the infected red blood cell. This immune evasion strategy depends on the sequential, rather than simultaneous, appearance of immunologically distinct variants. Although the molecular mechanisms by which a single organism switches between variants are known in part, it remains unclear how an entire population of parasites within the host can synchronize expression to avoid rapidly exhausting the variant repertoire. Here we show that short-lived, partially cross-reactive immune responses to parasite-infected erythrocyte surface antigens can produce a cascade of sequentially dominant antigenic variants, each of which is the most immunologically distinct from its preceding types. This model reconciles several previously unexplained and apparently conflicting epidemiological observations by demonstrating that individuals with stronger cross-reactive immune responses can, paradoxically, be more likely to sustain chronic infections. Antigenic variation has always been seen as an adaptation of the parasite to evade host defence: we show that the coordination necessary for the success of this strategy might be provided by the host.     

应用Adomian分解法求解免疫反应的数学模型

为加强对免疫反应动态机理的了解,用Adomian分解法求解一类免疫反应的数学模型,由此可同时得到模型的解析解和数值解.与Runga-Kuta法相比,Adomian分解法的数值结果具有更高的精确性和收敛速度.除免疫反应外,该方法还可推广到其他用微分方程描述的生命系统模型的求解.     

Timing of plant immune responses by a central circadian regulator

The principal immune mechanism against biotrophic pathogens in plants is the resistance (R)-gene-mediated defence. It was proposed to share components with the broad-spectrum basal defence machinery. However, the underlying molecular mechanism is largely unknown. Here we report the identification of novel genes involved in R-gene-mediated resistance against downy mildew in Arabidopsis and their regulatory control by the circadian regulator, CIRCADIAN CLOCK-ASSOCIATED 1 (CCA1). Numerical clustering based on phenotypes of these gene mutants revealed that programmed cell death (PCD) is the major contributor to resistance. Mutants compromised in the R-gene-mediated PCD were also defective in basal resistance, establishing an interconnection between these two distinct defence mechanisms. Surprisingly, we found that these new defence genes are under circadian control by CCA1, allowing plants to 'anticipate' infection at dawn when the pathogen normally disperses the spores and time immune responses according to the perception of different pathogenic signals upon infection. Temporal control of the defence genes by CCA1 differentiates their involvement in basal and R-gene-mediated defence. Our study has revealed a key functional link between the circadian clock and plant immunity.     

Co-option of a default secretory pathway for plant immune responses

Cell-autonomous immunity is widespread in plant-fungus interactions and terminates fungal pathogenesis either at the cell surface or after pathogen entry. Although post-invasive resistance responses typically coincide with a self-contained cell death of plant cells undergoing attack by parasites, these cells survive pre-invasive defence. Mutational analysis in Arabidopsis identified PEN1 syntaxin as one component of two pre-invasive resistance pathways against ascomycete powdery mildew fungi. Here we show that plasma-membrane-resident PEN1 promiscuously forms SDS-resistant soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) complexes together with the SNAP33 adaptor and a subset of vesicle-associated membrane proteins (VAMPs). PEN1-dependent disease resistance acts in vivo mainly through two functionally redundant VAMP72 subfamily members, VAMP721 and VAMP722. Unexpectedly, the same two VAMP proteins also operate redundantly in a default secretory pathway, suggesting dual functions in separate biological processes owing to evolutionary co-option of the default pathway for plant immunity. The disease resistance function of the secretory PEN1-SNAP33-VAMP721/722 complex and the pathogen-induced subcellular dynamics of its components are mechanistically reminiscent of immunological synapse formation in vertebrates, enabling execution of immune responses through focal secretion.     

Structural basis of RNA recognition and activation by innate immune receptor RIG-I

Retinoic-acid-inducible gene-I (RIG-I; also known as DDX58) is a cytoplasmic pathogen recognition receptor that recognizes pathogen-associated molecular pattern (PAMP) motifs to differentiate between viral and cellular RNAs. RIG-I is activated by blunt-ended double-stranded (ds)RNA with or without a 5'-triphosphate (ppp), by single-stranded RNA marked by a 5'-ppp and by polyuridine sequences. Upon binding to such PAMP motifs, RIG-I initiates a signalling cascade that induces innate immune defences and inflammatory cytokines to establish an antiviral state. The RIG-I pathway is highly regulated and aberrant signalling leads to apoptosis, altered cell differentiation, inflammation, autoimmune diseases and cancer. The helicase and repressor domains (RD) of RIG-I recognize dsRNA and 5'-ppp RNA to activate the two amino-terminal caspase recruitment domains (CARDs) for signalling. Here, to understand the synergy between the helicase and the RD for RNA binding, and the contribution of ATP hydrolysis to RIG-I activation, we determined the structure of human RIG-I helicase-RD in complex with dsRNA and an ATP analogue. The helicase-RD organizes into a ring around dsRNA, capping one end, while contacting both strands using previously uncharacterized motifs to recognize dsRNA. Small-angle X-ray scattering, limited proteolysis and differential scanning fluorimetry indicate that RIG-I is in an extended and flexible conformation that compacts upon binding RNA. These results provide a detailed view of the role of helicase in dsRNA recognition, the synergy between the RD and the helicase for RNA binding and the organization of full-length RIG-I bound to dsRNA, and provide evidence of a conformational change upon RNA binding. The RIG-I helicase-RD structure is consistent with dsRNA translocation without unwinding and cooperative binding to RNA. The structure yields unprecedented insight into innate immunity and has a broader impact on other areas of biology, including RNA interference and DNA repair, which utilize homologous helicase domains within DICER and FANCM.     

Adaptive immune responses in acute and chronic hepatitis C virus infection

The hepatitis C virus (HCV) persists in the majority of infected individuals and is a significant cause of human illness and death globally. Recent studies have yielded important insights into immunity to HCV, in particular revealing the central role of T cells in viral control and clearance. Other key features of adaptive immune responses remain obscure, including mechanisms by which T cells control HCV replication, the role of antibodies in conferring protection and how cellular and humoral immunity are subverted in persistent infection.     

Involvement of receptor-interacting protein 2 in innate and adaptive immune responses

Host defences to microorganisms rely on a coordinated interplay between the innate and adaptive responses of immunity. Infection with intracellular bacteria triggers an immediate innate response requiring macrophages, neutrophils and natural killer cells, whereas subsequent activation of an adaptive response through development of T-helper subtype 1 cells (TH1) proceeds during persistent infection. To understand the physiological role of receptor-interacting protein 2 (Rip2), also known as RICK and CARDIAK, we generated mice with a targeted disruption of the gene coding for Rip2. Here we show that Rip2-deficient mice exhibit a profoundly decreased ability to defend against infection by the intracellular pathogen Listeria monocytogenes. Rip2-deficient macrophages infected with L. monocytogenes or treated with lipopolysaccharide (LPS) have decreased activation of NF-kappaB, whereas dominant negative Rip2 inhibited NF-kappaB activation mediated by Toll-like receptor 4 and Nod1. In vivo, Rip2-deficient mice were resistant to the lethal effects of LPS-induced endotoxic shock. Furthermore, Rip2 deficiency results in impaired interferon-gamma production in both TH1 and natural killer cells, attributed in part to defective interleukin-12-induced Stat4 activation. Our data reflect requirements for Rip2 in multiple pathways regulating immune and inflammatory responses.     

TANK-binding kinase-1 delineates innate and adaptive immune responses to DNA vaccines

Successful vaccines contain not only protective antigen(s) but also an adjuvant component that triggers innate immune activation and is necessary for their optimal immunogenicity. In the case of DNA vaccines, this consists of plasmid DNA; however, the adjuvant element(s) as well as its intra- and inter-cellular innate immune signalling pathway(s) leading to the encoded antigen-specific T- and B-cell responses remain unclear. Here we demonstrate in vivo that TANK-binding kinase 1 (TBK1), a non-canonical IkappaB kinase, mediates the adjuvant effect of DNA vaccines and is essential for its immunogenicity in mice. Plasmid-DNA-activated, TBK1-dependent signalling and the resultant type-I interferon receptor-mediated signalling was required for induction of antigen-specific B and T cells, which occurred even in the absence of innate immune signalling through a well known CpG DNA sensor-Toll-like receptor 9 (TLR9) or Z-DNA binding protein 1 (ZBP1, also known as DAI, which was recently reported as a potential B-form DNA sensor). Moreover, bone-marrow-transfer experiments revealed that TBK1-mediated signalling in haematopoietic cells was critical for the induction of antigen-specific B and CD4(+) T cells, whereas in non-haematopoietic cells TBK1 was required for CD8(+) T-cell induction. These data suggest that TBK1 is a key signalling molecule for DNA-vaccine-induced immunogenicity, by differentially controlling DNA-activated innate immune signalling through haematopoietic and non-haematopoietic cells.