CTLA-4与超抗原对SEA诱导T细胞无能的关联研究

在建立超抗原SEA诱导T细胞无能的体外模型基础上 ,观察了无能T细胞受SEA刺激时共刺激分子CD2 8和CTLA 4的表达。结果发现 ,与活化组相比 ,在SEA加入后的不同时相点无能T细胞上CD2 8的表达都是正常的 ,而CTLA 4分子在SEA加入的第 60小时细胞表面有高水平的表达。这些结果表明 ,超抗原SEA诱导的这种无能状态与CTLA 4所介导的抑制作用增强有关     

CTLA4Ig诱导细胞无能的作用机制探讨

IL 2受体α链 (又称CD2 5 )是T淋巴细胞活化的标志分子 ,CTLA4Ig所诱导的细胞无能CD2 5的表达下降。用FACS方法检测CTLA4Ig诱导的细胞无能的凋亡现象 ,结果发现未处理组与处理组间无差异 ;CTLA4Ig处理后的细胞无能Fas和FasL的表达 ,与未处理对照组无差异。用免疫印迹方法 ,检测发现CTLA4Ig诱导的细胞无能与未处理组相比P2 1Ras没有明显变化。用RT PCR方法检测一些细胞因子mRNA的表达水平 ,发现CTLA4Ig所诱导的细胞无能不能表达IL 2mRNA ,IFN γmR NA的表达下降 ,而IL 4mRNA、IL 10mRNA仍可表达 ,表明细胞无能的基因格局显示Th1基因受抑 ,有向Th2偏移倾向     

CTLA4及其单克隆抗体功能及应用研究进展

细胞毒性T淋巴细胞相关抗原-4（cytotoxic T lymphocyte associated antigen 4，CTLA4）与CD28分子在基因结构、染色体定位、序列的同源性及基因表达具有十分相近的关系，都是共刺激分子B7的受体，主要表达于被激活T细胞表面。但是作为淋巴细胞激活的共刺激信号（costimulatory signal），CTLA4与CD28分子的功能是相反的，CTLA4与B7结合后能抑制小鼠和人T细胞的激活，在T细胞活化中起负调节作用。     

重症肌无力患者外周血B7：CD28／CTLA4共刺激分子表达的动态变化

目的：研究重症肌无力（MG）患者B7：CD28／CTLA4共刺激通路相关分子表达动态变化及其与MG发病的关系。方法：用流式细胞仪检测18例MG患者和16例健康对照者外周血单个核细胞（PBMC）在经PMA（佛波酯）＋ionomycin(钙离子导入剂）刺激的0h,6h,24h,48h时B7－1、B7－2、CD28、CTLA4分子在CD4^ T细胞和CD8^ T细胞表面的表达。结果：（1）0h,MG患者B7－1、B7－2分子总体表达增加，CD4^ 、CD8^ T细胞表面B7－1、B7－2的表达未见明显增加，PMA＋ionomycin刺激后B7－1、B7－2在CD4^ 、CD8^ T细胞表面也无增加；（2）0h,CD28、CTLA4的表达增强，其中CD28^ 细胞的增多主要表现在CD4^ T细胞亚群，CTLA4的表达增强主要在CD8^ T细胞，在PMA＋ionomycin激活后，CD28表达明显增强，持续到48h都处于较高水平（与对照组相比P＜0．01），CTLA4表达出现短暂增强，6h即达高峰，以后下降，与对照组相比无显著增强（P＞0．05）。结论：MG患者外周血中B7：CD28／CTLA4通路共刺激相关分子表达增高，持续时间延长，检测共刺激分子的表达可反映机体的免疫激活状态，B7：CD28／CTLA4通路在MG发病中可能起重要作用。     

超抗原SEA诱导T细胞无能的作用机制探讨

目的 探讨超抗原诱导T细胞无能的分子机制。方法 采用ELISA的FACS，分别检测超抗原对诱导T细胞无能的过程中，IL－2，IL－10的产生和IL－2Rα链（CD25）的表达，并以^3H-TdR掺入法，测定无能T细胞对rhIL-2,PMA及ionomycin的应答能力，而L－10的产生则逐渐升高；CD25的表达与活化组相比较无显著差异。rhIL-2的加入可恢复T细胞增殖。PMA单独作用能诱导无能T细胞的部分增殖能力，但PMA＋ionomycin则能更大程度地恢复T细胞的增殖。结论 超抗原SEA对T细胞无能的诱导，可能与降低IL－2的水平和升高IL－10的水平有关。超抗原SEA的反复刺激对T细胞无能的诱导，可能是干扰了TCR信号途径的近端事件，导致Ras/MAPK途径和Ca/calcineurin途径受阻，而使IL－2基因不能转录所致。     

重症肌无力患者外周血B7∶CD28/CTLA4共刺激分子表达的动态变化

目的研究重症肌无力(MG)患者B7∶CD28/CTLA4共刺激通路相关分子表达动态变化及其与MG发病的关系. 方法用流式细胞仪检测18例MG患者和16例健康对照者外周血单个核细胞(PBMC)在经PMA(佛波酯)+ionomycin(钙离子导入剂)刺激的0 h、6 h、24 h、48 h时B7-1、B7-2、CD28、CTLA4分子在CD4+ T细胞和CD8+ T细胞表面的表达. 结果 (1) 0 h,MG患者B7-1、B7-2分子总体表达增加,CD4+、CD8+ T细胞表面B7-1、B7-2的表达未见明显增加,PMA+ionomycin刺激后B7-1、B7-2在CD4+、CD8+ T细胞表面也无增加;(2) 0 h,CD28、CTLA4的表达增强,其中CD28+细胞的增多主要表现在CD4+ T细胞亚群,CTLA4的表达增强主要在CD8+ T细胞,在PMA+ionomycin激活后,CD28表达明显增强,持续到48 h都处于较高水平(与对照组相比P＜0.01),CTLA4表达出现短暂增强,6 h即达高峰,以后下降,与对照组相比无显著增强(P＞0.05). 结论 MG患者外周血中B7∶CD28/CTLA4通路共刺激相关分子表达增高,持续时间延长,检测共刺激分子的表达可反映机体的免疫激活状态,B7∶CD28/CTLA4通路在MG发病中可能起重要作用.     

BTLA信号对T细胞活化的起始和早期阶段的调节作用

目的:观察BTLA分子在T细胞上的表达并探讨其在各个阶段不同时相对T细胞活化的抑制。方法:分离人外周血单个核细胞,经阴性选择磁珠分离纯化获得T淋巴细胞。检测T细胞上BTLA、CTLA-4和PD-1的表达;用CD3抗体刺激T细胞活化,比较BTLA、CTLA-4和PD-1在T细胞活化过程中的动态表达。CD3抗体联合CD28抗体活化T细胞,在不同的活化时间,MTT法检测BTLA单抗8H9对T细胞增殖的影响。GM-CSF和IL-4体外诱导单核细胞分化成未成熟DC,CD40抗体刺激DC成熟,流式检测HVEM在DC上的表达。用DC诱导T细胞活化,加入游离8H9或抗HVEM抗体,阻断HVEM和BTLA结合,MTT法检测T细胞增殖。结果:静止T细胞组成性高表达BTLA,不表达CTLA-4和PD-1分子。T细胞活化后,BTLA分子表达有所降低,然后迅速回升至高水平。CTLA-4、PD-1分子在活化后两天几乎不表达,第三天开始表达并逐渐上升。8H9可以抑制CD3和CD28抗体活化的T细胞增殖。CD3和CD28抗体预先活化T细胞24小时或48小时后,再加入8H9仍然具有抑制效应,但不如在T细胞活化之初加入8H9的抑制效应。单核细胞诱导的不成熟DC上高表达HVEM,当DC成熟后,HVEM表达降低。用游离8H9或HVEM抗体阻断DC表面HVEM与T细胞表面BTLA结合,48小时之内均明显增强了DC诱导的T细胞增殖。结论:BTLA信号可以提高T细胞的活化阈值,在T细胞活化的起始和早期阶段发挥重要的负性调控作用。     

CTLA—4的研究进展

CTLA－4作为一T细胞活化的负性调节分子，在自身免疫性疾病和异种移植排斥过程中起着重要的作用，因而受到广泛的注意，它不但与Th1/Th2的分化有关，还参与T细胞无能的诱导过程，其对T细胞活化的抑制作用与其结构功能有着密切的关系。     

重症肌无力外周血单个核细胞CD28-B7共刺激通路相关分子的表达

目的 :探讨重症肌无力 (MG)患者CD2 8 B7共刺激信号通路相关分子的表达及其与MG发病的关系。方法 :用流式细胞仪检测 18例MG患者和 16例健康对照者外周血CD2 8、CTLA4、B7 1、B7 2分子在CD4 T细胞和CD8 T细胞表面的表达。结果 :MG组外周血CD2 8、CTLA4、B7 1、B7 2分子的表达均增强 ,其中CD2 8 细胞的增多主要表现在CD4 T细胞亚群 ,CT LA4的表达增强主要在CD8 T细胞 ,B7 1和B7 2分子在CD4 或CD8 T细胞的表达 ,MG组与对照组无差别。结论 :MG的发病与CD2 8共刺激通路的活化密切相关 ,检测外周血CD2 8共刺激相关分子的表达可反映MG患者的免疫反应状态 ,有助于临床诊断和用药。     

CD28共刺激信号的传导途径

目前大量实验已证实CD28和CTLA－4与其配体B7家族分子结合后所产生的共刺激信号（costimulatorysignal）在T细胞活化过程中起重要作用。关于CD28和CTLA－4信号传导的分子机制的研究正受到重视。由于CTLA－4的功能尚待进一步确定，信号传导方面的资料又较少，本文仅就CD28信号的启动、信号传导中涉及的分子作一综述，并将CD28共刺激途径与TCR途径进行了简略比较     

Involvement of CTLA-4 in T-cell anergy induced by staphylococcal enterotoxin A in vitro

Superantigens, like staphylococcal enterotoxin A (SEA), induce a strong proliferative response followed by clonal deletion of a substantial portion of defined V(beta) T-cells. The remaining cells display in vitro anergy. Anergy is a major mechanism to ensure antigen-specific tolerance in T-lymphocyte in the adult. Co-stimulatory molecules B7-1 (CD80)/B7-2 (CD86) and their counter-receptors CD28/CTLA-4 play pivotal roles in T-cell activation and immune regulation. While increasing data further suggested a role for CTLA-4 in regulating T-cell tolerance in vivo, the mechanism by which CTLA-4 influences T-lymphocyte tolerance is unclear. In the present study, we established an in vitro anergy model using superantigen SEA as the anergizing agents and examined CD3, CD28 and CTLA-4 expression of anergic T-cells in response to SEA rechallenge. It is found that anergic T-cell fails to produce the autocrine growth factor interleukin-2 (IL-2) upon stimulation, and addition of exogenous IL-2 can reverse the anergic state. Both TCR/CD3 complex and CD28 expression is not reduced in anergic cells during whole immune response, but the expression of CTLA-4 on the cell surface is enhanced dramatically in the late stages of an immune response. Using CTLA-4/B7-blocking agent, we found T-cell anergy was aborted and anergic T-cells restored the ability to proliferate and produce IL-2, suggesting that CTLA-4 may play a critical role in the induction of T-cell anergy.     

Differential expression of CTLA-4 among T cell subsets

CTLA‐4 (CD152), the CD28 homologue, is a costimulatory molecule with negative effects on T cell activation. In addition to its role in the termination of activation, CTLA‐4 has been implicated in anergy induction and the function of regulatory cells. As an intracellular molecule, it must first relocate to the cell surface and be ligated, in order to inhibit activation. Although some studies have investigated CTLA‐4 expression on CD4⁺ T cells, evidence is lacking regarding the kinetics of expression, and expression on T cell subpopulations. We have investigated CTLA‐4 kinetics on human purified peripheral CD4⁺, naïve, memory, CD4⁺CD25^–, CD4⁺CD25⁺ regulatory T cells, and T cell clones. Intracellular stores of CTLA‐4 were shown to be very low in naïve T cells, whilst significant amounts were present in memory T cells and T cell clones. Cell surface CTLA‐4 expression was then investigated on CD4⁺CD45RA⁺ (naïve), CD4⁺CD45RO⁺ (memory), CD4⁺CD25^–, and CD4⁺CD25⁺ T cells. CD25 and CD45RO are both expressed by regulatory T cells. On naïve and CD4⁺CD25^– T cells, CTLA‐4 expression declined after four hours. In contrast, on memory and CD4⁺CD25⁺ T cells, high levels of expression were maintained until at least 48 hours. In addition, significant CTLA‐4 expression was observed on T cell clones following anergy induction, indicating the potential involvement of CTLA‐4 also in this form of tolerance.     

Immunosuppression through biockade of CD28:B7-mediated costimulatory signals

It is now well established that T cells require two signals for activation and effector function. The first signal is provided through the T cell receptor for antigen. The best-characterized pathway which provides the second, or costimulatory, signal is through the CD28 receptor on the surface of T cells. In vitro, ligation of the T cell receptor without a second signal induces a long-lived state of anergy in T cells. CD28 has two known ligands, B7-1 and B7-2, expressed on activated antigen-presenting cells. A soluble fusion protein called CTLA4Ig has been produced which binds B7-1 and B7-2 and acts as a competitive inhibitor of CD28. In vitro and in vivo studies with CTLA4Ig demonstrate that it is an extremely effective immunosuppressive agent in models of transplantation and autoimmunity. Mechanistic studies indicate that CTLA4Ig may work by partially inhibiting the expansion of antigen-reactive cells and inducing anergy in the residual population.     

Role of CD80, CD86, and CTLA4 on mouse CD4(+) T lymphocytes in enhancing cell-cycle progression and survival after activation with PMA and ionomycin

Cell surface interactions between the T cell costimulatory receptors, CD28 and cytotoxic T-lymphocyte antigen-4 (CTLA4), with their cognate ligands, CD80 and CD86, on antigen-presenting cells play an important role in T cell activation. Although CD80 and CD86 are induced on T cells after activation, not much is known about their role in modulating T cell function. We show that CD80, CD86, and CTLA4 are induced on purified CD4(+) T cells after in vitro activation with phorbol 12-myristate 13-acetate (PMA) and ionomycin, and they play an essential role for proliferation and survival. Blockade of CTLA4-CD80/CD86 interactions greatly reduces PMA and ionomycin-mediated mouse CD4(+) T cell activation. The three key features of this inhibition of activation are: First, late events in T cell activation (after 18 h) are affected; second, these cells do not undergo anergy; and third, CD4(+)CD25(+) regulatory T cells are not responsible. Activation of T cells with PMA and ionomycin together with CTLA4-CD80/CD86 blockade results in decreased induction of CD25 and Bcl-X(L), reduced interleukin (IL)-2, and enhanced transforming growth factor-beta (TGF-beta) production. Furthermore, extended CTLA4-CD80/CD86 blockade results in decreased cell-cycle progression and enhanced apoptosis in a large proportion of cells. This inhibition of T cell proliferation can be rescued completely with anti-CD28 or IL-2 and partially with TGF-beta antagonists. This study reveals a functional role for CD80, CD86, and CTLA4 on CD4(+) T lymphocytes and sheds light on the mechanisms by which these molecules enhance activation and survival with PMA and ionomycin.     

CTLA4-Ig

The process of allograft rejection is a T cell-dependent phenomenon that occurs as a result of binding of foreign antigen and major histocompatibility complex (MHC) expressed on antigen-presenting cells to the T cell receptor/CD3 complex. Evidence suggests that binding of the alloantigen-MHC complex to the T cell receptor is insufficient by itself to initiate allograft rejection and induction of T cell responses, and a second or ;costimulatory' signal is required. This costimulatory response occurs as a result of activation of a distinct T cell surface molecule, CD28, by antigen-presenting cells that express a specific surface antigen, B7, that functions as a natural ligand to CD28. A similar T cell surface molecule, encoded on human chromosome 2 adjacent to CD28 and sharing 32% homology with CD28, has been cloned and termed CTLA4. CTLA4 is a member of the immunoglobulin gene superfamily, and exists as a complex on the surface of activated T cells. A fusion protein, CTLA4-Ig, consisting of the extracellular domain of CTLA4 in combination with the constant region of the human immunoglobulin Cgamma chain, has been developed to investigate the effects of inhibition of the B7/CD28 costimulatory pathway on transplant rejection. CTLA4-Ig acts as a competitive inhibitor of CD28 by specifically binding B7 and preventing the binding of CD28 to B7. CTLA4-Ig, administered alone, has been shown to prolong graft survival in in vivo models of allo- and xeno-transplantation, as well as to potentiate the effects of other immunosuppressive agents.     

Costimulatory markers in muscle of patients with idiopathic inflammatory myopathies and in cultured muscle cells.

In an attempt to understand the mechanisms of cell injury in the inflammatory myopathies, we analyzed the expression of costimulatory molecules, CTLA4, CD28, CD86, CD40, and CD154 as well as HLA class I, HLA class II, and ICAM-I in normal muscle and in muscle biopsies from patients with polymyositis (PM) or dermatomyositis (DM). By immunohistochemical staining, DM and PM biopsies showed the presence of CTLA4, CD28, CD86, and CD40 on inflammatory cells. More strikingly, however, low levels of CTLA4 and CD28 were observed on muscle cells. The expression of CTLA4 and CD28 on nonlymphoid cells has not been previously reported. These unexpected findings were confirmed in cultured normal human myoblasts: various proinflammatory cytokines induced the expression of CTLA4 and CD28 on normal human muscle cells. The sequences of the cDNAs were found to be identical to the sequences for these molecules in T cells. The data suggest a novel complexity in the network of cellular interactions between the infiltrated immune cells and the muscle cells in which the normal relationship between infiltrating inflammatory cells and target tissue is under a previously unrecognized set of controls.     

Functionally divergent T lymphocyte responses induced by modification of a self-peptide from a tumor-associated antigen

The N- and C-terminal flanking domains of the invariant chain peptide, CLIP, have remarkable immunological properties. Addition of these flanking domains to a foreign peptide antigen increases its immunologic potency. The present studies evaluated whether altering a peptide ligand from the tumor-associated antigen c-neu with the flanking domains of CLIP could modify the systemic immune response. The results indicate that the immunogenicity of an MHC class II restricted peptide (NEU) derived from c-neu was significantly altered by addition of the flanking domains from CLIP. Interestingly, selective modification of the peptide with either the N- or the C-terminal flanking domains resulted in functionally divergent systemic immune responses. Immunization of normal F344 rats with the NEU peptide modified with the N-terminal domain of CLIP (N-NEU) resulted in an immune response primarily consisting of type 1 (IL-2, IFNgamma) cytokine producing T cells. On the other hand, type 2 (IL-4) cytokine responses were largely predominant following immunization with the self-peptide modified with the C-terminal flanking domain (NEU-C). The functionally divergent responses elicited by the modified self-peptides were accompanied by significant changes in the expression of the CD28/CTLA4/B7 family of co-stimulatory molecules. Immunization with the N-NEU peptide led to enhanced expression of CD28 in the antigen-specific, CD4+ T cell compartment while expression of B7.1 was dramatically reduced in antigen-specific CD8+ T cells. Comparatively, expression of CTLA4 was down-regulated in the antigen-specific CD4+ T cell compartment following immunization with NEU-C peptide. The N-NEU peptide also had a direct effect on dendritic cells leading to the up-regulation of B7.1 expression. Taken together, functionally divergent systemic immune responses can be elicited by strategically altering a self-peptide ligand with the N- and C-terminal flanking domains of CLIP. Moreover, changes in expression of co-stimulatory molecules that are required for T cell activation and T cell-T cell communication may account for the polarization of the immune response elicited by the chimeric peptides.     

Superantigens anergize cytokine production but not cytotoxicity in vivo.

We have investigated the effect of the superantigen staphylococcal enterotoxin A (SEA) on the balance between T-cell response and non-responsiveness in T-cell receptor (TcR) V beta 3 transgenic mice. One injection of SEA resulted in a substantial activation of TcR V beta 3+ cells, whereas T cells from mice injected with repeated doses of SEA displayed a diminished response to a subsequent in vitro challenge. The reduced responsiveness became apparent when SEA was injected multiple times with short intervals. Proliferation and cytokine production in anergized T cells were severely reduced when stimulated with SEA in vitro, whereas cytotoxic T lymphocyte (CTL) activity remained unaffected. The dichotomy between these functions was examined in vitro with respect to different T-cell subsets. The total number of CD4+ T cells was reduced in the hyporesponsive spleens, compatible with cell deletion. The remaining CD4+ TcR V beta 3+ T cells showed anergy of all tested functions and did not respond to exogenous interleukin-2 (IL-2). In contrast, there was an expansion of CD8+ TcR V beta 3+ T cells with an intact cytotoxic activity. The in vitro proliferation and production of cytokines in the CD8+ compartment was impaired, but could be partially restored in the presence of exogenously added IL-2. Analysis of the cytokine response to SEA in vivo showed that IL-2 and tumour necrosis factor (TNF) were mainly produced by CD4+ T cells, while interferon-gamma (IFN-gamma) was predominantly released by CD8+ T cells. Induction of anergy resulted in a reduction of IL-2 and TNF mRNA levels, frequencies of producing cells as well as serum protein content. In contrast, there was only a moderate influence on the IFN-gamma level in vivo. The results suggest that SEA-induced hyporesponsiveness involves CD4+ cell deletion and a failure to produce cytokines in the remaining CD4+ T-cell compartment, while IFN-gamma production and cytotoxicity in the CD8+ T-cell compartment stay relatively intact.