CD28/B7-1与儿童肾病综合征

CD28/B7-1是一对参与机体特异性免疫应答极其重要作用的分子.CD28主要存在于T淋巴细胞表面,而B7-1为CD28的配体之一,可表达于肾脏足突细胞.初步研究显示,B7-1分子参与了足突细胞病变的发生发展,而肾脏足突细胞参与了肾病综合征病理免疫反应过程,尤其在微小病变型肾病综合征中起主导作用.国内外学者已经着手相关动物实验及少量临床试验的研究,并取得一定成果.通过阻断CD28/B7-1信号而抑制肾病综合征的发生发展过程,将为儿童肾病综合征的临床治疗提供新的思路.     

Both CD28 ligands CD80 (B7-1) and CD86 (B7-2) activate phosphatidylinositol 3-kinase, and wortmannin reveals heterogeneity in the regulation of T cell IL-2 secretion

In this report, the co-stimulatory signals provided by CD80(B7-1) or CD86 (B7-2) were compared to CD28 ligation by mAb.We demonstrate that while both anti-CD3 and anti-CD28 antibodiesinduced activation of phospholnositide (PI) 3-kinase, the kineticsof activation differed. Anti-CD28 produced a sustained activationof PI 3-kinase while anti-CD3 induced activation was transient.Both B7-1 and B7-2 could induce prolonged activation of PI 3-kinase.The co-stimulatory effects of B7-1 and B7-2 were dependent onCD28 cross-linking, based on complete inhibition of PI 3-kinaseactivation by CD28 antibody Fab fragments. While Jurkat T cellsco-stimulated with anti-CD3 and B7-1 or B7-2 secreted high levelsof IL-2, there were distinct effects of anti-CD28 mAb and B7-1or B7-2 on IL-2 secretion in conjunction with protein kinaseC activation. To assess functional effects of CD28 ligation,pharmacologic inhibitors of PI 3-kinase were evaluated. In Jurkatcells, efficient inhibition of PI 3-kinase activation afterB7-2 stimulation was achieved using wortmannin; however, weobserved a surprising increase in IL-2 secretion after B7 oranti-CD28 stimulation. The effect of wortmannin was concentrationdependent. Moreover, the effect was specific for receptor-mediatedactivation as wortmannin did not enhance phorbol ester pluslonomycin-induced IL-2 secretion. Another inhibitor of PI 3-kinase,LY294002, also resulted in augmentation of anti-CD28-inducedIL-2 secretion by Jurkat cells. The effects of wortmannin onIL-2 secretion were also examined in primary T cells. In markedcontrast, wortmannin resulted in a potent inhibition of anti-CD3plus B7-1 or anti-CD28-induced IL-2 secretion while phorbolester plus lonomycin-induced IL-2 secretion was wortmannin resistant.Together these observations demonstrate that signal transductionby both B7-1 and B7-2 involves PI 3-kinase, and that PI 3-kinaseor other wortmannin-sensitive targets are important for IL-2secretion. Finally, treatment of Jurkat cells with PI 3-kinaseinhibitors alone was sufficient to induce low levels of IL-2secretion. This is consistent with the notion that a wortmannin-sensitivetarget such as PI 3-kinase may down-regulate IL-2 secretionin Jurkat cells.     

Prevention and amelioration of collagen-induced arthritis by blockade of the CD28 co-stimulatory pathway: requirement for both B7-1 and B7-2

Collagen type II-induced arthritis (CIA) is an experimental model of arthritis that has been successfully used to dissect the pathogenesis of human rheumatoid arthritis and to identify potential therapeutic targets. We have used this model to evaluate the role of T cell co-stimulation in both disease development and progression. T cell co-stimulation is provided by ligation of CD28 with either B7-1 or B7-2 present on antigen-presenting cells and can be prevented by a soluble form of CTLA-4 (CTLA-4Ig) which binds with high affinity to both B7-1 and B7-2. We found that administration of CTLA-4Ig at the time of immunization prevented the development of CIA and was associated with lack of lymphocyte expansion within the draining lymph node and failure to produce anti-collagen IgG1 or IgG2a antibodies. To determine which CD28 ligand plays a more dominant role in CIA, we treated mice with monoclonal antibodies (mAb) against either B7-1 or B7-2. Neither anti-B7-1 nor anti-B7-2 had any effect on the course of CIA when given alone, but resulted in reduced incidence and clinical scores when given together. Interestingly, when treatment was delayed until after the onset of clinical disease, both CTLA-4Ig or anti-B7-1 plus anti-B7-2 mAb still ameliorated disease. Effective treatment was associated with a reduction in interferon-γ production by lymph node cells following stimulation in vitro, suggesting that Th1 responses were diminished. This study points to a critical role of CD28 co-stimulation in the development and perpetuation of CIA in DBA/1 mice. Interestingly, it demonstrates an active role for T cells in the later stages of this disease and implicates both B7-1 and B7-2-mediated co-stimulation in the pathogenesis of CIA.     

共刺激对T细胞功能和细胞因子格局的作用

利用Ｂ７－１单抗和环孢素Ａ处理ＡＰＣ：Ｔ细胞反应系统,探讨了Ｂ７／ＣＤ２８芡刺激对Ｔ细胞增殖及细胞因子产生的影响,并用ＲＴ－ＰＣＲ方法分析了细胞因子基因格局的改变。结果表明Ｂ７－１单抗可抑制特异性抗原诱导的Ｔ细胞增殖和ＩＬ－２的产生,Ｂ７－１单抗瑟ＣｓＡ联用可阻断Ｔ细胞增殖和ＩＬ－２产生。Ｂ７－１单抗绎ＩＬ－４的产生未显示明显的影响,而Ｂ７－１单抗与ＣｓＡ联用ＩＬ－４仍可检测到。     

CD28/B7信号在再生障碍性贫血T淋巴细胞异常活化中的作用

目的 通过淋巴细胞输注诱导自身免疫性再生障碍性贫血动物模型,探讨CD28/B7信号在淋巴细胞异常活化中的作用及可能机制.方法 将来自父本的淋巴细胞悬液(40×106个几左右)通过尾静脉注入CBYB6 F1代受鼠体内,采用CFDA-SE标记法跟踪淋巴细胞在体内的分布,尾静脉注射CD80和CD86阻断性单克隆抗体(单抗),不同时段检测受体小鼠外周血象的变化,病理切片观察骨髓及主要脏器的变化.将骨髓造血细胞与淋巴结淋巴细胞进行共培养,通过计数造血细胞的集落形成数来观察不同数量淋巴结淋巴细胞对骨髓造血细胞的影响.体外测试不同浓度环孢菌素A(cyclosporine A,CsA)对骨髓造血细胞的影响.结果 输注淋巴细胞后可诱导受体小鼠在第5天出现骨髓衰竭的表现,主要是白细胞、血红蛋白、血小板下降,21 d左右受体鼠出现死亡.不同时间段受体小鼠主要脏器冰冻切片显示荧光标记的淋巴细胞主要分布在骨髓组织中;病理切片显示有骨髓组织的破坏.同时注射CD80及CD86阻断性单抗的受体鼠同样出现上述表现;体外集落形成试验证实B6淋巴结淋巴细胞数量和F1造血细胞为5:1时,红系集落形成单位(CFU-E)和粒细胞集落形成单位(CFU-G)集落形成数目与空白组比较差异无统计学意义(P>0.05);将比例提高至10:1,CFU-E集落形成数目明显减少(P<0.05);至50:1时,则可完全抑制CFU-E集落的形成,CFU-E和CFU-G集落形成数日的减少呈现淋巴细胞剂量依赖性,加入CsA可显著提高CFU-E和CFU-G形成率.结论 通过模型证实T细胞在再生障碍性贫血的发生过程中起重要作用,仅通过阻断CD28/B7信号并不能阻断T淋巴细胞的异常活化.     

Expression and function of B7-1 (CD80) and B7-2 (CD86) on human epidermal Langerhans cells

In addition to T cell receptor triggering, activation of T cells requires co-stimulatory signals that have been shown to be mainly initiated through CD28. We analyzed the expression and function of the two ligands for CD28, B7-1 (CD80) and B7-2 (CD86), on human Langerhans cells (LC), the antigen-presenting cells from epidermis. Human LC freshly isolated from epidermis (fLC) expressed significant level of B7-2, which was increased upon a short culture in vitro. In contrast, B7-1 was undetectable on fLC but appeared at the cell surface after a 3-day culture in vitro. Pre-incubation of 18-h cultured LC with anti-B7-2 monoclonal antibodies (mAb) was sufficient to abrogate the binding of CTLA4-Ig fusion protein, while a combination of both mAb against B7-1 and B7-2 was necessary to obtain a complete inhibition of CTLA4-Ig binding on 3-day cultured LC, showing the absence of a third CTLA4 ligand. The function of B7-1 and B7-2 on human LC has been analyzed by adding mAb at the beginning of mixed epidermal cell lymphocyte reactions. Anti-B7-2 mAb and CTLA4-Ig, but not anti-B7-1 mAb, strongly inhibited allogeneic, as well as recall antigen-induced T cell proliferation supported by fLC or 3-day cultured LC. Collectively, these results demonstrate that B7-2 is the major ligand for CD28/CTLA4 at the LC surface and that it plays a crucial role in human LC co-stimulatory function with little, if any, dependence on B7-1 expression.     

Costimulatory molecules in Wegener's granulomatosis (WG): lack of expression of CD28 and preferential up-regulation of its ligands B7-1 (CD80) and B7-2 (CD86) on T cells

T cells are most likely to play an important role in the pathogenesis of WG, and recently a predominant Th1 pattern of immune response has been demonstrated in granulomatous inflammation. Since the expression of costimulatory molecules has a significant impact on the cytokine profile and proliferation response of T cells, the goal of this study was to characterize the expression of costimulatory molecules (CD28, CTLA-4 (CD152), B7-1 (CD80), B7-2 (CD86)) on T cells, monocytes and B cells in WG, and to correlate the findings with clinical parameters such as disease activity, extent and therapy. WG patients (n = 24) and healthy controls (HC; n = 17) were examined for the expression of costimulatory molecules by fluorescence-activated cell sorter analysis, both in whole peripheral blood and after in vitro activation of T cells and antigen-presenting cells. Results were correlated with clinical data. The expression of CD28 on CD4⁺ and CD8⁺ cells was significantly lower in WG than in HC (CD28⁺ 81.4% in WG versus 97.9% of CD4⁺ cells (P < 0.0001); CD28⁺ 44.6% in WG versus 68.5% of CD8⁺ cells (P < 0.00001)), both in peripheral blood and after in vitro activation. A lower percentage of monocytes was B7-2⁺ in WG than in HC in peripheral blood, whereas no significant differences in the expression of B7-1 and B7-2 were observed after in vitro stimulation of monocytes and B cells. After in vitro activation a significantly higher percentage of B7-1⁺ and B7-2⁺ T cells was seen in WG. There was no significant difference in the CTLA-4 expression pattern between WG and HC. The percentage of CD28⁺ lymphocytes correlated negatively with the Disease Extent Index cumulated over the course of disease (r = ?0.46, P = 0.03), indicating a more severe manifestation in patients with lower CD28 expression. Correlations with other clinical parameters such as activity or therapy were not seen. WG patients show a lack of CD28 expression on T cells and an unusual up-regulation of its ligands B7-1 and B7-2 on T cells after in vitro activation as well as a lower expression of B7-2 on freshly isolated monocytes compared with HC. These features might promote the Th1 cytokine pattern and thereby contribute to persistently high levels of immune activation in WG.     

B7-1分子诱导体外抗肝癌免疫反应

目的：了解Ｂ７分子在体外抗肝癌免疫中的作用。方法：健康人外周血单个核细胞（ＰＢＭＣ）与ＨｅｐＧ２／ｈＢ７－１，ＨｅｐＧ２／ｎｅｏ及亲代ＨｅｐＧ２瘤苗混合培养（ＭＬＴＣ），检测淋巴细胞活化增殖能力，淋巴细胞ＨＬＡ－Ｉ类抗原的表达，培养上清ＩＦＮ－γ水平，ＴＮＦ活性及ＬＡＫ，ＣＴＬ细胞活性。结果：ＨｅｐＧ２／ｈＢ７－１瘤苗促淋巴细胞增殖最高达１４．６倍，明显高于ＨｅｐＧ２／ｎｅｏ和ＨｅｐＧ２瘤苗的作用     

B7/CD28和ICAM-1/LFA-1共刺激信号对T及B细胞功能影响的研究

目的　研究共刺激途径Ｂ７／ＣＤ２８ 和ＩＣＡＭ１／ＬＦＡ１ 对Ｔ 细胞活化以及Ｂ 细胞效应的作用。方法　在体外建立ＡＰＣＴＢ 细胞反应系统, 用Ｂ７１ 单抗和ＩＣＡＭ１ 单抗分别阻断Ｂ７／ＣＤ２８ 和ＩＣＡＭ１／ＬＦＡ１ 共刺激途径, 利用３ ＨＴｄＲ 法检测Ｔ 细胞增殖,ＥＬＩＳＡ 法测定Ｂ 细胞分泌的抗体, 用ＲＴＰＣＲ 法检测细胞因子基因的表达。结果　Ｂ７１ 单抗和ＩＣＡＭ１ 单抗均可抑制Ｔ 细胞增殖及ＩＬ２ 的产生。Ｂ７１ 单抗可下调Ｂ 细胞抗体的产生（ Ｐ＜ ０ ．０５） , 而ＩＣＡＭ１ 单抗未见明显的抑制（ Ｐ＞ ０ ．０５） 。Ｂ７１ 单抗和ＣｓＡ 联用能阻断Ｔ 细胞增殖活性及Ｂ 细胞的效应, 而ＩＣＡＭ１ 单抗和ＣｓＡ联用则无此作用。Ｂ７１ 单抗能下调ＩＬ２ 和ＩＦＮγｍ ＲＮＡ 表达,Ｂ７１ 单抗和ＣｓＡ 联用则阻断ＩＬ２ 和ＩＦＮγｍ ＲＮＡ 表达,ＩＬ４ 和ＩＬ１０ ｍ ＲＮＡ 仍可表达。结论　Ｂ７／ＣＤ２８ 和ＩＣＡＭ１／ＬＦＡ１ 共刺激途径在Ｔ 细胞活化中具有不同的作用,Ｂ７１ 单抗和ＣｓＡ 联用可导致Ｔ 细胞功能失活即无能。     

Expression and function of B7-1 and B7-2 in hapten-induced contact sensitivity

We analyzed the expression and function of the co-stimulatory molecules B7-1 (CD80) and B7-2 (CD86) during contact sensitivity reactions induced by the hapten 2,4-dinitrofluorobenzene (DNFB). In the normal skin, only a few epidermal Langerhans cells or dermal dendritic cells express B7-2. In contrast, following challenge with DNFB, expression of B7-2 is up-regulated in both epidermis and dermis. Importantly, B7-1 is induced later and at lower levels compared to B7-2. Intravenous injections of anti-B7-2 mAb, but not anti-B7-1 mAb partially inhibit the hapten-induced contact sensitivity reaction. Experiments in which mice are injected differentially with anti-B7-2 mAb, either before the afferent or before the efferent phase of the contact sensitivity response, suggest that B7-2 is important for successful antigen priming.     

CD28 ligands CD80 (B7-1) and CD86 (B7-2) induce long-term autocrine growth of CD4+ T cells and induce similar patterns of cytokine secretion in vitro

The interaction of CD28 and its ligands is critical for antigen-inducedT cell activation. Recent studies have demonstrated the existenceof at least two members of the B7 receptor family. In this report,the co-stimulatory signals provided by CD80 (B7-1) or CD86 (B7-2)were compared to CD28 ligation by mAb. We demonstrate that thekinetics of induction of T cell proliferation after anti-CD3stimulation was similar regardless of the form of co-stimulation.Similarly, B7-1 and B7-2 could both maintain long-term expansionof CD4 cells. The co-stimulatory effects of both B7-1 and B7-2were dependent on CD28 cross-linking, based on complete inhibitionof proliferation by CD28 antibody Fab fragments. Co-stimulationwith B7-1 and B7-2 induced high levels of cytokine secretionby resting T cells, and the effects of B7-1 and B7-2 could notbe distinguished. This conclusion is based on analysis of theinitial activation of CD28⁺ T cells. as well as T cell subpopulationsconsisting of CD4⁺ and CD8⁺ T cells. Both B7-1 and B7-2 couldelicit IL-4 secretion from CD4⁺ T cells while anti-CD28 antibodyinduced substantially less IL-4 secretion. Furthermore, bothB7-1 and B7-2 could stimulate high levels of IFN- and IL-4 fromCD4⁺CD45RO⁺ cells, while neither B7 receptor could co-stimulateIFN- and IL-4 secretion from CD4⁺CD45RA⁺ T cells. B7-1 and B7-2could, however, co-stimulate CD4⁺CD45RA⁺ T cells to secreteIL-2. By contrast, when previously activated T cells were tested,re-stimulation of CD4⁺ T cell blasts with B7-1 or B7-2 resultedin higher secretion of IL-4 and IL-5 than anti-CD28, while re-stimulationwith anti-CD28 antibody maintained a higher level of secretionof IL-2 and IFN- than B7-1 or B7-2. These observations may haveimportant implications because they suggest that the mannerof CD28 ligation can be a critical determinant in the developmentof cytokine secretion that corresponds to T_h1- and T_h2-likepatterns of differentiation. Together these observations suggestthat there are no Intrinsic differences between B7-1 and B7-2in their ability to co-stimulate the populations of cells thatwe have tested.     

CD28 costimulation and CD28 expression in T lymphocyte subsets in HIV-1 infection with and without progression to AIDS

In a prospective study of 152 HIV-1 patients (with and without progression to AIDS) we examined CD28 MoAb costimulation and CD3 MoAb response using whole blood culture at baseline and up to either the time of AIDS diagnosis or the end of the observation period. CD28 antigen expression on both CD4+ and CD8+ T lymphocytes was also studied in both groups of patients. In patients who progressed to AIDS, CD28 MoAb costimulation was found to be decreased. Univariate time-dependent analysis showed that decreases in (i) absolute numbers of either CD4+, CD4+CD28+, CD8+CD28+ T cells, (ii) CD28 MoAb costimulation, and (iii) CD3 MoAb response, and an increase in CD8+CD28- %, are significant predictors for progression to AIDS. In addition, multivariate time-dependent analysis demonstrated that a decrease in CD28 MoAb costimulation (but not a decrease in CD3 MoAb response) was predictive for progression to AIDS, as were decreases in the percentage of CD4+ T cells and the absolute number of CD4+CD28+ T cells. Thus, CD28 MoAb costimulation can be considered a useful assay for monitoring HIV-1 infection. Furthermore, apart from the early increase in the percentage of CD8+CD28- T cells and an increase in the percentage of CD28- on CD8+ T cells in both groups of patients at baseline compared with normal controls, a negative correlation was found to exist between the percentages of CD4+ or CD4+CD28+ T cells and the percentage of CD8+CD28- T cells; this suggests that these cells are probably mutually regulated.     

关节炎中B7:CD28/CTLA-4共刺激途径的实验研究

目的：探讨Ｂ＆：ＣＤ２８／ＣＴＬＡ－４共刺激信号大关节炎发病机制中的作用。方法：经牛Ⅱ型胶原诱导ＳＤ大鼠建立关节炎动物模型;采用ＣＴＬＡ－４Ｉｇ作为负性调节因子,分析其对关节炎大鼠中特异性体液反应和组织病理学表现的影响。结果：ＣＴＬＡ＿４Ｉｇ可阻止ＳＤ大鼠发生胶原诱发 关节炎,降低大导ＢＩＩＣ的体液免疫反应。结论：Ｂ７：ＣＤ２８／ＣＴＬＡ－４共刺激信号在诱发Ｔ细胞介导的自身免疫病中起作用,ＣＴＬＡ     

CD28 Function: A Balance of Costimulatory and Regulatory Signals

Both the recognition of MHC/antigen complex by the T-cell receptor and engagement of costimulatory molecules are necessary for efficient T-cell activation. CD28 has been widely recognized as the major costimulation pathway for naive T-cell activation, and the CD28/B7 pathway plays a central role in immune responses against pathogens, autoimmune diseases, and graft rejection. In this review, we will summarize evidence that CD28 is also prominent in the regulation of immune responses and the maintenance of peripheral tolerance. Indeed, CD28 engagement increases the expression of the down-modulatory molecule CTLA-4, induces the differentiation of Th2 cells that have a protective function in autoimmunity, and has an obligatory role in the homeostasis of regulatory T cells. Therefore, CD28/B7 interactions induce a balance of costimulatory and regulatory signals that have opposite outcomes on immune responses. This new perspective on CD28 function suggests that caution should be taken in the development of immunotherapies targeting costimulatory pathways.     

Human B7-1 is more efficient than B7-2 in providing co-stimulation for alloantigen-specific T cells

Besides a signal via the T cell receptor/CD3 complex, an additional co-stimulatory signal is required for optimal T cell activation. This signal can be delivered by interaction of either B7-1 or B7-2 expressed by antigen-presenting cells with CD28 on the T cells. Comparison of the function of B7-1 and B7-2 in different experimental animal systems generated conflicting data on the roles for the co-stimulatory molecules. We therefore investigated whether there are differences between B7-1 and B7-2-mediated co-stimulation in an alloantigen-specific primary T cell response induced by B7-transfected human cell lines of epithelial origin. Both transfected keratinocyte cell lines efficiently induce T cell proliferation and the ratios of stimulator versus responder cells are similar. The kinetics of proliferation and interleukin (IL)-2, IL-4 and interferon-γ production are also comparable between both transfectant lines. However, despite equal B7 expression levels, it is consistently found that the magnitude of the B7-1-induced T cell proliferation was higher than that of B7-2. Comparison of precursor frequencies of helper T lymphocytes responsive with either B7-1 or B7-2 revealed that the frequency of B7-1-responsive T cells was higher than that of B7-2, and that the frequency of cells activated by a combination of B7-1 and B7-2 did not differ significantly from that of B7-1 alone. We therefore conclude that the B7-2-responsive T cells are part of the B7-1-responsive population, and that B7-1 on keratinocytes is more efficient in providing co-stimulation for alloantigen-specific T cells.     

Reciprocal expression of co-stimulatory molecules,B7-1 and B7-2, on murine T cells following activation

The co-stimulatory B7 molecules (B7-1 and B7-2) are expressed on professional antigen-presenting cells in mice. In this study, we demonstrate that B7-1 (CD80) and B7-2 (CD86) are also expressed on murine T cells in the absence of major histocompatibility complex class II molecules. The temporal expression of these two molecules on T cells varies with the state of activation where resting T cells express B7-2 but show little or no expression of B7-1. Following activation, B7-2 expression is down-regulated and there is a concomitant increase in the expression of B7-1 on the cell surface which peaks at about 72 h. Thus these two co-stimulatory molecules are reciprocally expressed on the T cell surface. This pattern of expression of B7-1 and B7-2 on T cells suggests that these two molecules may have different roles in the generation and regulation of immune responses.     

系统性红斑狼疮外周血单个核细胞CD28/B7分子mRNA的表达

目的 :探讨CD2 8 B7分子在系统性红斑狼疮 (SLE)发病机制中的作用及其临床意义。方法 :应用逆转录 聚合酶链反应 (RT PCR)检测 35例活动期SLE患者和 30例正常人外周血单个核细胞 (PBMC)中CD2 8、B7 1和B7 2mRNA的表达水平。结果 :35例活动期SLE患者PBMC中CD2 8的阳性表达率 (2 2 86 % )明显低于正常人对照组 (70 0 0 % ) ,差异非常显著 (P <0 0 0 1) ;B7 2的阳性表达率 (82 86 % )明显高于正常对照组 (5 3 33% ) ,差异显著 (P <0 0 1) ;活动期SLE组CD2 8的平均表达水平 (0 194 5± 0 2 0 74 )明显低于正常对照组 (0 4 2 38± 0 10 5 3) ,差异显著 (P <0 0 5 ) ;B7 2的平均表达水平 (0 86 75± 0 2 5 75 )明显高于正常人对照组 (0 4 898± 0 30 72 ) ,差异非常显著 (P <0 0 1) ;35例活动期SLE患者中仅有 2例B7 1呈阳性表达。结论 :CD2 8 B7分子的异常表达可能与SLE患者淋巴细胞和抗原呈递细胞 (APC)的功能变化有关。B7 1低水平与B7 2的高水平表达表明 ,SLE患者T细胞的活化可能主要是通过CD2 8与B7 2的交联传递共刺激信号 ,介导以Th2型反应为主的免疫应答反应 ;B7 2的表达水平可能与SLE疾病的活动性有一定的相关性。CD2 8mRNA的低水平表达可能与外周血CD2 8 T细胞凋亡增加或迁移到炎症部     

Ligation of B7 with CD28/CTLA-4 on T cells results in CD40 ligand expression,interleukin-4 secretion and efficient help for antibody production by B cells

It has been extensively shown that when T cells are co-stimulated with B7-CD28 interaction, a strong proliferative as well as cytolytic T cell response can be induced. In contrast, there exists only indirect evidence that the B7-CD28 interaction is of importance for the induction of T cell helper functions in B cell responses. Here we have used mouse fibroblasts transfected with the human Fcγ receptor type II and human B7 to address this issue. We found that T cells, when activated through the T cell receptor (TcR)/CD3 complex with monoclonal antibodies and co-stimulated by B7-CD28 interaction, can provide efficient help for the induction of both IgM and IgG production by resting B cells. This helper activity is, at least in part, mediated by the interaction between the CD40 ligand on the T cells and CD40 on the B cells. We also demonstrate that more than one signal to the T cell is required for the induction of the CD40 ligand, one being delivered through the TcR/CD3 complex and the second by ligation of CD28 with the B7 molecule. In addition to the induction of cognate T helper function, we provide evidence that co-stimulation of T cells with B7-CD28 interaction can result in the secretion of both Th1- and Th2-type lymphokines.     

Ligation of CD28 receptor by B7 induces formation of D-3 phosphoinositides in T lymphocytes independently of T cell receptor/CD3 activation

The co-stimulatory role of B7/CD28 interactions is important in promoting T cell activation. Very little is known about the intracellular events that follow CD28 engagement although recent evidence has implicated coupling of CD28 to a protein tyrosine kinase signal transduction pathway. In this study we have investigated the putative role of D-3 phosphoinositides as mediators of CD28 receptor signaling, since phosphoinositide (PI) 3-kinase, the enzyme responsible for D-3 phosphoinositide formation, is a known substrate for protein tyrosine kinases associated with certain T cell surface receptors such as CD4 and interleukin-2 receptor. The lipid products of PI 3-kinase activity have been suggested to play a role in mitogenic signaling and growth regulation in other cells. Chinese hamster ovary cells (CHO) previously transfected with B7 cDNA, induced time-dependent elevation above basal levels of phosphatidylinositol(3,4)-bisphosphate (PtdIns(3,4)P₂) and PtdIns(3,4,5)P₃, while parental CHO cells that did not express B7 had no effect on these lipids. Moreover, the elevation of these same lipids by CD3 ligation was potentiated in an additive manner by CHO-B7+ but not by CHO-B7^? cells. CHO-B7⁺ and CHO-B7^? cells did not activate phospholipase C as evidenced by their inability to modulate basal or CD3-induced changes in the levels of phosphatidic acid or D-4 and D-5 phosphoinositides. These data imply that PI 3-kinase but not phospholipase C, may be an important signal transduction molecule with respect to CD28-mediated co-stimulation and T cell activation following ligation by B7.