CD4+ T-cell help controls CD8+ T-cell memory via TRAIL-mediated activation-induced cell death

The 'help' provided by CD4+ T lymphocytes during the priming of CD8+ T lymphocytes confers a key feature of immune memory: the capacity for autonomous secondary expansion following re-encounter with antigen. Once primed in the presence of CD4+ T cells, 'helped' CD8+ T cells acquire the ability to undergo a second round of clonal expansion upon restimulation in the absence of T-cell help. 'Helpless' CD8+ T cells that are primed in the absence of CD4+ T cells, in contrast, can mediate effector functions such as cytotoxicity and cytokine secretion upon restimulation, but do not undergo a second round of clonal expansion. These disparate responses have features of being 'programmed', that is, guided by signals that are transmitted to naive CD8+ T cells during priming, which encode specific fates for their clonal progeny. Here we explore the instructional programme that governs the secondary response of CD8+ T cells and find that helpless cells undergo death by activation-induced cell death upon secondary stimulation. This death is mediated by tumour-necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL). Regulation of Trail expression can therefore account for the role of CD4+ T cells in the generation of CD8+ T cell memory and represents a novel mechanism for controlling adaptive immune responses.     

Anti-TOSO antibody treatment promotes T cell activation-induced cell death （AICD） in vitro and in vivo

T cell activation-induced cell death （AICD）, that involves the induction of Fas-mediated apoptosis, is very important for the maintenance of immune homeosta- sis. TOSO was firstly described as an inhibitor of Fas- mediated apoptosis and overexpressed in chronic lymphocytic leukemia. Recently, TOSO was identified as IgM FcR. In this study, we produced anti-TOSO monoclonal antibody （mAb） that could block the binding of IgM to TOSO and found that T cell apoptosis is negatively cor- related with TOSO expression during T cell activation. Treatment of activated T cells with anti-TOSO blocking mAb promoted T cell AICD in in vitro AICD model, and treatment of xenogeneic-GVHD mice with the antibody also increased the sensitivity of activated T cells to Fas- induced apoptosis, which was accompanied by reduction of c-FLIPL expression and up-regulation of AP-1 complex. In summary, our data indicate the anti-apoptotic effect of TOSO in T cell AICD and open up new therapeutic prospects for the treatment of hematologic malignancies and immune disorders.     

T-cell receptor delta gene rearrangements in early thymocytes

The T-cell receptor delta-chain variable region can be assembled from as many as four distinct gene segments, V, D1, D2 and J, more than any other antigen-receptor gene. In fetal thymocytes V----D joinings are as common as D----J or VDJ rearrangements and one V gene segment predominates. Analysis of rearrangements at TCR gamma and delta loci during fetal ontogeny suggests abrupt changes and possible coordinate control in the rearrangement and expression of these loci.     

Engagement of the CD4 molecule influences cell surface expression of the T-cell receptor on thymocytes

The intrathymic differentiation process by which precursor cells derived from the bone marrow develop into immuno-competent T lymphocytes is poorly understood. Most thymocytes express both CD4 and CD8 accessory molecules, yet little is known about either the function of these molecules or the responsiveness of the CD4+8+ double positive thymocytes that bear them. Here, we address the possibility that CD4 engagement influences T-cell receptor (TCR) expression on developing thymocytes. We engaged CD4 molecules on murine thymocytes by in vivo injection of an anti-CD4 monoclonal antibody, which reduced the surface expression of CD4 on CD4+ thymocytes. More importantly, CD4 engagement also affected TCR expression on CD4+ thymocytes, but the effect on CD4+8+ double positive and CD4+8- single positive thymocytes was very different. CD4+8+ thymocytes responded to CD4 engagement by dramatically increasing surface expression of TCR, whereas CD4+8- thymocytes decreased surface expression of TCR. These results demonstrate that the effect of CD4 engagement on TCR expression is dependent upon the developmental state of the responding thymocyte, and, most interestingly, results in increased TCR expression by double positive thymocytes.     

Expression of genes of the T-cell antigen receptor complex in precursor thymocytes

The antigen receptor on T lymphocytes has recently been characterized as a heterodimeric, transmembrane glycoprotein consisting of disulphide-linked alpha (acidic) and beta (basic) subunits of relative molecular mass (Mr) 40,000-45,000 each. The genes encoding these proteins have been cloned and shown to resemble immunoglobulin genes in both overall structure and the requirement for DNA rearrangement before expression. In humans, three additional proteins, termed the T3 complex, are found associated with the clonotypic receptor, and a role for T3 in receptor expression has been proposed. Despite these recent advances in characterizing the antigen receptor complex, there is as yet little understanding of T-cell maturation, particularly the stage of T-cell ontogeny at which the genes encoding the antigen receptor and its associated structures are expressed and assembled. In the adult, stem cells destined to differentiate into T cells arise in the bone marrow and migrate to the thymus, where T-cell precursors proliferate, develop a preference for recognizing antigens in the context of self MHC molecules and are released to the periphery. Recently, cells that have the properties of immature murine thymocytes have been isolated and described. We have now analysed these cells with a series of molecular probes and we describe three distinct patterns of T-cell antigen receptor gene rearrangements in developing thymocytes.     

The adult T-cell receptor delta-chain is diverse and distinct from that of fetal thymocytes

T lymphocytes recognize foreign molecules using the T-cell receptor (TCR), a disulphide-linked heterodimer closely associated with the CD3 polypeptide complex on the cell surface. The TCR alpha beta heterodimers seem largely responsible for the recognition properties of both helper (TH) and cytotoxic (TC) T cells. Recently, a second CD3-associated T-cell receptor heterodimer, gamma delta, has been described. Cells bearing the gamma delta receptor appear before those bearing alpha beta during thymic ontogeny and persist as a minor component (1-10%) of mature peripheral T cells. Their function is unknown. As there are a limited number of functional TCR V gamma gene segments, the size and potential diversity of the V delta repertoire is important for the number of different antigens that may be recognized by gamma delta heterodimers. The delta-chain locus is located 75 kilobases (kb) 5' to the TCR C alpha coding region, raising the possibility that the alpha and delta V-region repertoires may overlap. Also, analysis of rearrangements at the delta-chain locus in developing thymocytes shows distinct fetal and adult patterns indicating that there may be differences between the fetal and adult V delta repertoires. To address these questions, we have characterized a large number of delta-containing complementary DNA clones from adult double-negative thymocytes (CD4-8-), an immature population that is enriched for gamma delta-bearing cells. We find that a limited number of V delta sequences are used, showing little overlap with known adult V alpha s and differing significantly from fetal V delta s. But as two D elements may participate simultaneously in V delta gene assembly, and random nucleotides may be added at any one of three junctional points, the potential number of different delta chains that can be made in the adult thymus is very large (approximately 10(13)).     

A novel population of T-cell receptor alpha beta-bearing thymocytes which predominantly expresses a single V beta gene family

Recent studies have demonstrated that CD3 is expressed on a subset of thymocytes with a CD4-CD8- (double negative) phenotype. At least some of these cells bear the CD3-associated gamma delta T-cell receptor (TCR gamma delta). Here we describe a second subset of double negative thymocytes which expresses CD3-associated alpha beta receptors (TCR alpha beta). Surprisingly, these cells express predominantly the products of a single V beta gene family (V beta 8). These CD4-CD8-, TCR alpha beta+ cells appear relatively late in ontogeny (between birth and day 5 of life) and thus are unlikely to be the precursors to the TCR alpha beta-bearing cells (CD4+CD8- and CD4-CD8+) already present at birth. They can be selectively expanded in vitro by stimulation with a monoclonal antibody to V beta 8 (F23.1) in the presence of interleukin I (IL-1). We propose that this cell type is a unique T-cell population distinguishable from typical TCR alpha beta+ T cells by its CD4-CD8- phenotype and a restricted TCR V beta repertoire. Analysis of the unique phenotype of these cells suggests that they may represent the normal counterpart of the defective CD4-CD8- T cells found in the lpr autoimmune mouse.     

A one-hit model of cell death in inherited neuronal degenerations

In genetic disorders associated with premature neuronal death, symptoms may not appear for years or decades. This delay in clinical onset is often assumed to reflect the occurrence of age-dependent cumulative damage. For example, it has been suggested that oxidative stress disrupts metabolism in neurological degenerative disorders by the cumulative damage of essential macromolecules. A prediction of the cumulative damage hypothesis is that the probability of cell death will increase over time. Here we show in contrast that the kinetics of neuronal death in 12 models of photoreceptor degeneration, hippocampal neurons undergoing excitotoxic cell death, a mouse model of cerebellar degeneration and Parkinson's and Huntington's diseases are all exponential and better explained by mathematical models in which the risk of cell death remains constant or decreases exponentially with age. These kinetics argue against the cumulative damage hypothesis; instead, the time of death of any neuron is random. Our findings are most simply accommodated by a 'one-hit' biochemical model in which mutation imposes a mutant steady state on the neuron and a single event randomly initiates cell death. This model appears to be common to many forms of neurodegeneration and has implications for therapeutic strategies.     

Hybrid hybridomas and their use in immunohistochemistry

A normal antibody-producing cell only expresses one antibody, resulting in the well-known phenomenon of allelic exclusion. When two myeloma cells are fused, the derived hybrids are capable of co-dominantly expressing the antibody genes of both parents. Although the respective variable (V) and constant (C) region genes remain expressed in the same cis configuration, heavy and light chains of both parents are scrambled, and hybrid molecules are formed. The same is true when a myeloma and an antibody-producing cell are fused to produce a hybrid myeloma (hybridoma). Fusion therefore allows the production of hybrid immunoglobulin molecules containing two different combining sites. Hybrid molecules of this type retain antigen-binding activity and specificity. Bispecific monoclonal antibodies secreted by hybridomas may have a variety of uses in biology and in medicine. Here we have focused on their application in histochemistry. As an example, we have prepared and tested an anti-somatostatin-anti-peroxidase bispecific antibody. This way of producing hybrid molecules is superior to the production of hybrid antibodies by chemical reconstitution methods because the drastic treatment required for chain separation in the latter is likely to lead to some protein denaturation and loss of antibody activity. Intracellularly synthesized and assembled hybrids do not suffer from this disadvantage. In addition, the recombination of heavy and light chains from different antibody molecules is likely to lead to considerable waste.     

A novel human lymphokine that inhibits haematopoietic progenitor cell proliferation

T lymphocytes in culture synthesize and secrete a variety of factors that activate and guide the differentiation, replication and maturation of haematopoietic cells in vitro. Malignant T-cell lines as well as T-cell hybridomas producing several of these factors have been established. We report here a factor produced by a human cell line that exerts a potent inhibitory effect on the growth of bone marrow progenitor cells. The properties of this factor, which we have termed colony-inhibiting lymphokine ( CIL ), differ from other inhibitors of haematopoietic progenitor cell proliferation, but resemble those of a T-cell-derived factor causally linked with some cases of severe aplastic anaemia in humans. Sensitivity of cells to this factor appears to correlate positively with expression of HLA-DR surface antigens.     

器官发育与程序化细胞死亡

介绍了2002年诺贝尔生理医学奖的获奖内容，讨论了程序化细胞死亡的分子作用机制，探讨了这一基础研究对于治疗癌症等分子性疾病的重要作用。     

Social controls on cell survival and cell death.

Programmed cell death occurs in most animal tissues at some stage of their development, but the molecular mechanism by which it is executed is unknown. For some mammalian cells, programmed death seems to occur by default unless suppressed by signals from other cells. Such dependence on specific survival signals provides a simple way to eliminate misplaced cells, for regulating cell numbers and, perhaps, for selecting the fittest cells. But how general is this dependence on survival signals?     

环孢菌素A产生菌的分子鉴定及其原生质体制备

环孢菌素A高产菌株No.421502经形态学特征和分子标记鉴定,确认为镰孢菌属,命名为Fusariumsp.No.421502.收集Fusarium sp.No.421502孢子刚萌发的幼嫩菌丝体,以0.7 mol/L KCl为渗透压稳定剂,用质量浓度为20 mg/mL的蜗牛酶,30℃80 r/min处理5 h制备原生质体.原生质体为7×105/mL,原生质体形成率为62.8%.制备的原生质体稀释后接入再生培养基,再生率为29.6%.     

A novel method forin situ detection of apoptotic cell death in plants

A simple novel protocol suitable forin situ detection of apoptotic plant cell death is presented. This protocol combines the chromosome spreading technique with an extendedin situ end labeling version for plants and makes it possible to detect apoptosis directly at chromosome, nuclear and DNA levels simultaneously with high-sensitivity. False positive and nonspecific signals can be efficiently avoided. Moreover, the changes of chromosomes, nuclei and DNA during the process of apoptosis can be characterizedin situ. To illustrate this method, salt stress-induced cell death has been investigated in maize root meristematic cells.     

HIV-1 Nef inhibits ASK1-dependent death signalling providing a potential mechanism for protecting the infected host cell

In vivo infection of lymphatic tissues by the human immunodeficiency virus type 1 (HIV-1) leads to enhanced apoptosis, which prominently involves uninfected bystander cells. Increased killing of such bystander cells is mediated in part through Nef induction of Fas ligand (FasL) expression on the surface of the virally infected T cells. The subsequent interaction of FasL with Fas (CD95) displayed on neighbouring cells, including HIV-1-specific cytotoxic T lymphocytes, may lead to bystander cell killing and thus forms an important mechanism of immune evasion. As HIV-1 also enhances Fas expression on virally infected cells, it is unclear how these hosts avoid rapid cell-autonomous apoptosis mediated through cis ligation of Fas by FasL. Here we show that HIV-1 Nef associates with and inhibits apoptosis signal-regulating kinase 1 (ASK1), a serine/threonine kinase that forms a common and key signalling intermediate in the Fas and tumour-necrosis factor-alpha (TNFalpha) death-signalling pathways. The interaction of Nef with ASK1 inhibits both Fas- and TNFalpha-mediated apoptosis, as well as the activation of the downstream c-Jun amino-terminal kinase. Our findings reveal a strategy by which HIV-1 Nef promotes the killing of bystander cells through the induction of FasL, while simultaneously protecting the HIV-1-infected host cell from these same pro-apoptotic signals through its interference with ASK1 function.     

细胞编程性死亡及其生物学意义

细胞编程性死亡(英文编写为PCD)是多细胞生物的自然属性,它按照一定的基因编码在时空上顺次表达使死亡细胞呈现一定的表观现象及生理生化特征。PCD受来自机体内其它细胞信号等内源性因素和药物、物理等外源性因素的调节。PCD是一种主动死亡方式且表现为单细胞性,与病理因素作用下的坏死不同,但又有一定联系。PCD在动、植物体的生长发育和成体新陈代谢中有重要的调节作用,PCD异常是某些疾病发病的重要原因     

Intrathymic signalling in immature CD4+CD8+ thymocytes results in tyrosine phosphorylation of the T-cell receptor zeta chain

Thymic selection of the developing T-cell repertoire occurs in immature CD4+CD8+ double-positive thymocytes and is thought to be mediated by signals transduced by T-cell antigen receptor (TCR) molecules and possibly by CD4 and CD8 accessory molecules as well. It is not known, however, which signal-transduction mechanisms function in immature CD4+CD8+ thymocytes on engagement of TCR, CD4 or CD8 molecules. In mature T cells, CD4 and CD8 molecules are each associated with the src-like protein tyrosine kinase p56 lck and signals transduced by TCR and CD4 activate tyrosine kinases that phosphorylate TCR-zeta chains and other intracellular substrates. Consequently, we examined whether tyrosine kinases could be similarly activated in immature CD4+CD8+ thymocytes. Unexpectedly, we found that TCR-zeta chains from CD4+CD8+ thymocytes were already phosphorylated in vivo, and that dephosphorylation of this TCR subunit occurred on removal of CD4+CD8+ cells from their intrathymic environment. Rephosphorylation of TCR-zeta in cultured CD4+CD8+ thymocytes occurred rapidly in vitro, either in response to cross-linking of TCR, CD4 or CD8 by specific monoclonal antibodies, or on cell-cell contact. These observations indicate that tyrosine kinases are activated in vivo in immature CD4+CD8+ thymocytes undergoing thymic differentiation and selection. They also indicate that TCR, CD4 and CD8 molecules can function in CD4+CD8+ thymocytes as signalling molecules to activate tyrosine kinases and that phosphorylated TCR-zeta serves as a marker of these signalling events.