CD28 mRNA rapidly decays when activated T cells are functionally anergized with specific peptide

The induction of non-responsiveness in specific clones of Tcells In vivo might be expected to reverse immunologlcally mediateddisease processes. With this goal in mind, experiments in vitrowith cloned T cells have investigated the mechanisms of inductionof anergy. Resting T cells can be functionally inactivated invitro by high doses of appropriate peptide in either the presenceor absence of antigen presenting cells. During the inductionof anergy, the modulation of the surface phenotype of T cellsis similar to that of cells proliferating in response to animmunogenic stimulus. The amount of T cell receptor at the cellsurface is down regulated, whereas the CD2 and CD25 receptorsare increased in density. in contrast, CD28 has been identifiedas a membrane protein that is differentially regulated duringactivation and the induction of non-responsiveness. Ligatlonof CD28 provides an efficient costlmulatory signal for activationof T cells. In this report, we show that not only resting cells,but also fully activated T cells can be rendered non-responsiveand that this process is accompanied by profound downregulationof CD28, both at the level of cytoplaamic mRNA and surface expressionof the mature protein. This observation anticipates clinicalintervention in immunologically mediated disease, where thetarget T cells are more likely to be activated than in a restingstate.     

CD28 superagonists put a break on autoimmunity by preferentially activating CD4+CD25+ regulatory T cells

There is strong evidence that a quantitative and/or functional deficiency in CD4+CD25+ regulatory T cells (T(reg) cells) plays a key role in the pathogenesis of many human autoimmune diseases. Therefore, targeting regulatory T cells with novel forms of immunotherapy should provide a means for successfully battling autoimmunity in humans. We have recently shown that superagonistic monoclonal antibodies with specificity for CD28 (CD28 superagonists) are capable of activating and preferentially expanding T(reg) cells over conventional T cells in vitro and, importantly, also in vivo. Moreover, therapeutic application of CD28 superagonists elicited profound therapeutic effects in various animal models of autoimmunity, including experimental autoimmune encephalomyelitis (EAE) and adjuvant arthritis (AA) of the Lewis rat. Adoptive transfer experiments with T(reg) cells from CD28 superagonist-treated rats proved that protection from EAE is, indeed, mediated by CD28 superagonist-activated T(reg) cells. Therefore, effective targeting of CD4+CD25+ regulatory T cells makes CD28 superagonists a promising novel tool for the treatment of human autoimmune diseases.     

Positive and negative regulation of IL-12 receptor expression of naive CD4(+) T cells by CD28/CD152 co-stimulation

IL-12 is a critical cytokine for polarizing naive CD4(+) T cells toward Th1 subset. Therefore, it is important to elucidate the mechanism of IL-12R expression of naive CD4(+) T cells. In this report, we present evidence to show that expression of both IL-12Rbeta1 and beta2 mRNA is regulated by signals mediated through CD28 and CD152. Naive CD4(+) T cells stimulated with anti-CD3 alone neither expressed IL-12Rbeta2 mRNA nor bound detectable level of rIL-12, although they expressed a very low level of IL-12Rbeta1 mRNA when stimulated with a high dose of anti-CD3. Expression of IL-12Rbeta1 and beta2 mRNA was induced by the co-ligation of CD3 and CD28, and it was down-regulated by the ligation of CD152. CD28 ligation induced not only IL-12Rbeta1 and beta2 mRNA expression, but also enhanced IFN-gammaR to mediate up-regulation of IL-12R by IFN-gamma.     

DNA甲基化在急性冠脉综合征患者CD4+CD28-T细胞CD28表达缺失中的作用

目的 通过研究急性冠脉综合征(acute coronary syndrome,ACS)患者外周血CD4+T细胞CD28 mRNA水平和CD28基因启动子调节序列的甲基化状态,旨在探讨DNA甲基化在ACS患者CD4+CD28-T细胞CD28表达缺失中的作用.方法 免疫磁珠分离CD4+T细胞经逆转录后,实时定量PCR(real time-PCR)技术检测CD4+T细胞CD28mRNA的表达水平,亚硫酸氢钠测序检测CD28基因启动子调节序列的甲基化状态.结果 与正常对照组相比,ACS患者CD4+T细胞CD28mRNA表达水平显著减低,差异具有统计学意义[正常对照组比ACS组:(1.066±0.162)比(0.401±0.069),P<0.05].CD28基因启动子区域的甲基化水平显著增高,差异有统计学意义[正常对照组比ACS组:(24.47±3.17)%比(43.33±1.52)%,P<0.05].CD28基因启动子区域DNA甲基化水平与CD28mRNA表达水平呈显著负相关(P=0.01,r=-0.579).结论 ACS患者CD4+T细胞CD28基因启动子区域高甲基化调控了CD28基因转录抑制.DNA甲基化参与了CD4+CD28-T细胞的形成.     

Differential proliferative responses in subsets of human CD28+cells delineated by BB27 mAb

We report the Identification of a novel 140 kDa disulflde-llnkeddimer expressed by a subset of peripheral blood T lymphocytes.This molecule, which Is recognized by mAb BB27, is also detectedon cells of the myelomonocytlc lineage. In the T cell lineage,Its expression Is positively modulated after lymphocyte activation.A series of double-labeling experiments revealed that BB27 mAbIdentifies new CD4 and CDS cell subsets different from thosedefined by CD45RA, CD45RO, CD26, CD29, CD31, and CD38. Finally,BB27 mAb also subdivides the CD28 subset. Of the utmost interestIs the finding that a proliferative response to CD28 mAb andphorbol myrlstate acetate stimulation is exclusively obtainedin the CD28⁺BB27⁺ cell subset, whereas the CD28⁺BB27^–subset falls to proliferate.     

Generation of CD28- cells from long-term-stimulated CD8+CD28+ T cells: a possible mechanism accounting for the increased number of CD8+CD28- T cells in HIV-1-infected patients.

According to CD28 molecule expression, CD8+ T cells can be classed as CD28bright, CD28dim, and CD28-. The CD28dim T cells were found to derive from mitogenic stimulated CD28-T cells but also from CD28bright T cells through a mechanism of CD28 down-modulation. Moreover, after prolonged in vitro interleukin-2 stimulation, clonal CD28bright, cells showed a CD28dim expression before further evolution to a stable CD28-phenotype. This loss was concomitant with the disappearance of CD28 mRNA. A study of the cytokine production pattern revealed that CD28dim and CD28- T cell clones produced similar levels of type 1 and type 2 cytokines, which differed from those produced by the CD28bright T cell clones. A high percentage of CD28dim and CD28- cells, with similarities in their cytokine production pattern, were found in the blood samples of HIV-infected patients, as compared to healthy donors. The CD28 down-modulation may account for the increased number of CD8+CD28- T cells in HIV-infected patients.     

急性髓细胞性白血病患者外周血单个核细胞CD28 mRNA的表达

背景：大量研究显示,肿瘤患者外周血T细胞表面共刺激分子CD28蛋白表达存在差异,提示共刺激通路异常可能与恶性肿瘤的发生进展有关。 目的：观察急性髓细胞性白血病外周血单个核细胞共刺激信号分子CD28 mRNA在中的表达。 方法：急性髓细胞性白血病患者80例,其中M0型7例,M1型6例,M2型18例,M3型15例,M4型17例,M5型9例,M6型8例。并根据急性白血病疗效标准将80例患者分为完全治愈组、缓解组、未缓解组。采用Taqman探针实时荧光定量PCR检测80例患者及76名健康人群外周血单个核细胞CD28 mRNA的表达。 结果与结论：急性髓细胞性白血病外周血单个核细胞M1,M3和M4亚型中的CD28 mRNA表达量低于健康人群 (P< 0.05);急性髓细胞性白血病未缓解组中CD28 mRNA低于健康人群 (P < 0.05),完全治愈组和缓解组中CD28 mRNA表达与健康人群差异无显著性意义。说明急性髓细胞白血病患者外周血单个核细胞存在CD28 mRNA表达缺陷,并与临床分期、病情进展及预后有关。     

Comparison of CD28-B7.1 and B7.2 functional interaction in resting human T cells: Phosphatidylinositol 3-kinase association to CD28 and cytokine production

CD28 is a 44-kDa homodimer present on T cells providing an important costimulatory signal for T cell proliferation, cytokine production and cytokine receptor expression. CD28 activation is mediated by interaction with its counter-receptors, B7.1/CD80 and B7.2/B70/CD86. The biochemical basis of these costimulatory signals are still poorly understood, particularly in resting T cells. However, various biochemical pathways such as tyrosine phosphorylation, phospholipase C, sphingomyelinase and phosphatidylinositol 3-kinase (PI3-K) activation have been reported to play a role in CD28 signaling in tumor T cell lines and CD28-transfected cells or pre-activated T cells. In addition, recent reports propose that CD28-B7.1 and B7.2 interaction could be involved in the production of Th1 and Th2 cytokines, respectively, but the putative biochemical basis for these different functions is still unknown. We have analyzed the functional and molecular consequences of CD28 activation by B7.1 and B7.2 in human resting T cells. We demonstrate in this report that both CD28-B7.1 and CD28-B7.2 interactions induce the association of PI3-K to CD28 in the CD4 subpopulation, whereas it was barely detectable in CD8 cells. This association involves the binding of the src homology domain 2 (SH2) of p85 to tyrosine-phosphorylated CD28 and does not require pre-activation by CD3-T cell receptor. Worthmannin, a specific inhibitor of PI3-K enzymatic activity within the nanomolar range also inhibits the interleukin-2 production induced by costimulation mediated by either the B7.1- and B7.2-transfected cells or CD28 monoclonal antibodies. The only slight difference between B7.1 and B7.2 costimulation is the IC₅₀ of wortmannin being 25 and 110 nM, respectively, which could suggest differences in their activation of the T cell PI3-K.     

Peripheral human CD8(+)CD28(+)T lymphocytes give rise to CD28(-)progeny, but IL-4 prevents loss of CD28 expression.

At birth, virtually all peripheral CD8(+) T cells express the CD28 co-stimulatory molecule, but healthy human adults accumulate CD28(-)CD8(+) T cells that often express the CD57 marker. While these CD28(-) subpopulations are known to exert effector-type functions, the generation, maintenance and regulation of CD28(-) (CD57(+) or CD57(-)) subpopulations remain unresolved. Here, we compared the differentiation of CD8(+)CD28(bright)CD57(-) T cells purified from healthy adults or neonates and propagated in IL-2, alone or with IL-4. With IL-2 alone, CD8(+)CD28(bright)CD57(-) T cell cultures yielded a prevailing CD28(-) subpopulation. The few persisting CD28(dim) and the major CD28(-) cells were characterized by similar telomere shortening at the plateau phase of cell growth. Cultures from adults donors generated four final CD8(+) phenotypes: a major CD28(-)CD57(+), and three minor CD28(-)CD57(-), CD28(dim)CD57(-) and CD28(dim)CD57(dim). These four end-stage CD8(+) subpopulations displayed a fairly similar representation of TCR V(beta) genes. In cultures initiated with umbilical cord blood, virtually all the original CD8(+)CD28(bright) T cells lost expression of CD28, but none acquired CD57 with IL-2 alone. IL-4 impacted on the differentiation pathways of the CD8(+)CD28(bright)CD57(-) T cells: the addition of IL-4 led both the neonatal and the adult lymphocytes to keep their expression of CD28. Thus, CD8(+)CD28(bright)CD57(-) T cells can give rise to four end-stage subpopulations, the balance of which is controlled by both the cytokine environment, IL-4 in particular, and the proportions of naive and memory CD8(+)CD28(+) T cells.     

Immune reconstitution following autologous transfers of CD3/CD28 stimulated CD4(+) T cells to HIV-infected persons

We have previously shown that adoptive transfer of in vitro CD3/CD28 activated autologous CD4(+) T cells results in increased CD4 counts and CD4/CD8 ratios in HIV+ subjects. In this report, analysis of variable beta (Vbeta) chain T cell receptor (TCR) repertoire showed that CD3/CD28 stimulation was able to increase polyclonality within skewed spectra types in vitro. In vivo, two of eight subjects showed increase in TCR diversity and importantly, in no subject did a highly skewed in vivo repertoire emerge. Measurement of proliferative response to alloantigen showed increases following infusions. Response to pharmacological stimulus and lectin via Interferon-gamma ELISpot assay showed increases in a subset of subjects following infusions. However, interferon-gamma response to HIV antigens and peptides declined concurrent with stable or diminishing latent infectious viral load in CD4(+) T cells. These data provide further evidence that adoptive transfer of activated autologous CD4(+) T cells can augment the immune system.     

Impaired CD28-mediated co-stimulation in anergic T cells

We have investigated a CD28 co-stimulation in anergic T cellsin staphylococcal enterotoxin Binoculated mice by stimulatingthe cells with a plate-coated anti-TCR antibody in the presenceor absence of an anti-CD28 antibody. CD28 co-stimulation increasedthe levels of IL-2 and IL-4 mRNAs in nalve CD4⁺V_ß8⁺T cells. However, it did not increase the levels of IL-4 mRNAat all and only partially increased those of IL-2 mRNA in anergicT cells. It was demonstrated that CD28 co-stimulation was impairedso that it no longer stabilized cytoklne mRNAs in anergic cells.The levels of IL-4 mRNA in response to TCR stimulation werehigher in anergic T cells than those in nalve T cells in spiteof the defective CD28 co-stimulation in the former cells. Anergyinduction and generation of a T_h2-type immune response in vivoare discussed