Distinct mechanisms mediate na?ve and memory CD8 T-cell tolerance

Peripheral tolerance to developmentally regulated antigens is necessary to sustain tissue homeostasis. We have now devised an inducible and reversible system that allows interrogation of T-cell tolerance induction in endogenous naïve and memory CD8 T cells. Our data show that peripheral CD8 T-cell tolerance can be preserved through two distinct mechanisms, antigen addiction leading to anergy for naïve T cells and ignorance for memory T cells. Induction of antigen in dendritic cells resulted in substantial expansion and maintenance of endogenous antigen-specific CD8 T cells. The self-reactive cells initially exhibited effector activity but eventually became unresponsive. Upon antigen removal, the antigen-specific population waned, resulting in development of a self-specific memory subset that recalled to subsequent challenge. In striking contrast to naïve CD8 T cells, preexisting antigen-specific memory CD8 T cells failed to expand after antigen induction and essentially ignored the antigen despite widespread expression by dendritic cells. The inclusion of inflammatory signals partially overcame memory CD8 T-cell ignorance of self-antigen. Thus, peripheral CD8 T-cell tolerance for naïve CD8 T cells depended on the continuous presence of antigen, whereas memory CD8 T cells were prohibited from autoreactivity in the absence of inflammation.     

Altered calcium transient and development of hypertrophy in beta2-adrenoceptor overexpressing mice with and without pressure overload

Transgenic (TG) mice with cardiac specific 200-fold overexpression of beta(2)-adrenoceptors (beta(2)-AR) have a facilitated development of heart failure following thoracic aortic constriction (TAC). We have studied the alterations of intracellular Ca(2+) transients and myocyte size in wild-type (WT) and TG mice after TAC. Cardiomyocytes were isolated from mice 9 weeks after TAC or sham operation, and incubated with Fura 2/AM. The Ca(2+) transients were determined by Spex dual wavelength Spectrometer during electrical stimulation. The cell size was also determined planimetrically. Cells of sham operated TG mice displayed higher systolic Ca(2+) amplitude than respective WT group (DeltaF(340)/F(380) ratio: 1.05+/-0.08 vs. 0.63+/-0.05; P<0.01), a finding in keeping with enhanced ventricular contractility in the TG mice. However, hypertrophied and failing myocytes of TG animals showed a fall in Ca(2+) transients from sham-operated control levels and there was no difference between TG and WT groups following TAC. In sham-operated groups, the cell size of TG mice was significantly bigger than in WT animals (3212+/-139 vs. 2605+/-162 microm(2); P<0.05). The cell size increased to a similar extent in both groups after TAC (4715+/-216 vs. 5027+/-365 microm(2), P=n.s.). In summary, hypertrophy of cardiomyocytes was present in beta(2)-AR TG mice under baseline conditions. A further hypertrophy occurred during pressure overload to an extent similar to that in WT animals. However, the increased intracellular Ca(2+) transient, seen in sham-operated TG mice, was no longer detectable following development of severe hypertrophy and heart failure. These findings provide explanation on the lack of hemodynamic benefit in beta(2)-AR TG mice subjected to pressure overload.     

Chronic leptin treatment does not prevent the development of obesity in transgenic mice with brown fat deficiency

Summary With the exception of ob/ob mice, circulating plasma leptin is elevated in all other obese rodents as well as in obese humans, suggesting that leptin resistance rather than leptin deficiency is a characteristic feature of obesity. The exact molecular mechanisms leading to leptin resistance and the applicability of exogenous leptin to overcome resistance to the anorectic effect of the hormone, are insufficiently characterized. The aim of this study was to investigate whether chronic leptin administration could prevent the development of obesity and its associated disorders in transgenic mice with toxigene mediated ablation of brown adipose tissue (BAT). Daily injections of leptin were started at the age of 6 weeks, when body weight, food intake and plasma leptin levels of transgenics were not different from control mice. Over the next 6 weeks, leptin treated transgenics showed the same excessive body weight gain as transgenic mice injected with saline. Leptin treatment was furthermore not able to prevent the development of hyperphagia, hyperglycaemia, hyperinsulinaemia and hyperlipidaemia in transgenic mice. In contrast, control mice injected with leptin had significantly lower body weight, food intake and plasma triglycerides than those treated with saline. In summary, leptin treatment was not able to prevent the development of obesity and its associated abnormalities in transgenic mice with BAT deficiency. This data suggests that intact BAT function is of critical importance for leptin's effect on food intake and energy expenditure, and that primary dysfunction of BAT is associated with leptin resistance, even when hyperleptinaemia is not yet present. [Diabetologia (1997) 40: 810–815] Received: 11 November 1996 and in final revised form: 8 April 1997     

心肌特异性Hsp27对ISO诱导小鼠心肌肥厚的保护作用

目的探讨人热休克蛋白(Hsp27)基因产物对异丙肾上腺素(ISO)诱导的小鼠心肌肥厚的影响。方法以本研究室建立的心肌特异性表达Hsp27转基因(TG)小鼠为模型,腹腔注射ISO[30mg/(kg·d)]共7d。实验在规定时间结束后,测定心脏质量与胫骨长度的比值(HW/TL)、心脏二维超声(echo),Masson三色染色观察心肌纤维化改变,各组均以野生型鼠(WT)为对照组。结果(1)ISO处理使TG鼠和WT鼠的HW/TL与生理盐水处理对照组比较分别增加了7·46%和17·65%,WT组增加比率有统计学差异(P<0·01);(2)echo显示ISO使TG心脏收缩期后壁厚度增加(P<0·05),而WT组心脏前、后壁在收缩、舒张末期均有显著的增加(P<0·05~0·01)。(3)每搏输出量、短轴缩短率、心脏射血分数没有统计学差异。WT鼠心肌纤维化明显多于TG鼠。结论Hsp27可显著抑制ISO诱导的小鼠早期心肌重构。其机制有待进一步探讨。     

口蹄疫病毒P12A-3C免疫原基因在百脉根中的遗传转化与表达

目的利用植物反应器研究口蹄疫转基因植物疫苗是近些年来科学家研究的热点,本研究以豆科牧草百脉根为转化受体,将口蹄疫病毒P12A-3C基因通过根癌农杆菌介导法导入百脉根基因组。方法百脉根外植体经过浸菌,抗性培养基上愈伤、出芽和生根等阶段。结果最终获得了转基因抗性植株。结论对转基因植株进行PCR、RT-PCR检测,表明外源基因整合在植物染色体基因组,并且具有转录活性,ELISA检测表明,转基因植株表达出外源目的蛋白。     

Features of syndrome X develop in transgenic rats expressing a non-insulin responsive phosphoenolpyruvate carboxykinase gene

Aims/hypothesis. Obesity, glucose intolerance, dyslipidaemia and hypertension are a cluster of disorders (syndrome X) affecting many people. It has been hypothesised that these abnormalities are caused by insulin resistance, but definitive proof is lacking. We have developed transgenic rats in which the rate-limiting gluconeogenic enzyme, phosphoenolpyruvate carboxykinase, is non-insulin responsive. The aim of our study was to investigate whether syndrome X develops in these animals and if a high-fat diet interacts with this genetic defect. Methods. Chow-fed transgenic and control rats aged 1, 3, 6 and 17 months and a subgroup of transgenic and control rats fed chow plus cafeteria foods for 6 months were examined for features of syndrome X. Results. At 3 months, transgenic rats had fasting and postprandial hyperinsulinaemia, mild obesity (in abdominal and, to a lesser extent, peripheral regions) and fasting hypercholesterolaemia. Hypertriglyceridaemia was evident after 6 months while hyperglycaemia was apparent at 17 months. Hypertension had not developed by 17 months. The effect of a high-fat diet on insulin, glucose, body weight and body fat was more dramatic than the effect of the transgene alone while the effect of a high-fat diet on cholesterol and triglyceride was similar to the transgene. This illustrates that a high-fat diet is a potent catalyst for many abnormalities associated with syndrome X. There was no evidence of an additive effect of the high-fat diet plus transgene. Conclusion/interpretation. Therefore rats genetically-engineered with a non-insulin responsive gluconeogenic enzyme develop several aspects of syndrome X, supporting the hypothesis that insulin resistance initiates this cluster of disorders. [Diabetologia (1999) 42: 419–426] Received: 21 September 1998 and in final revised form: 23 November 1998     

B‐Cell Depletion Extends the Survival of GTKO.hCD46Tg Pig Heart Xenografts in Baboons for up to 8 Months

Xenotransplantation of genetically modified pig organs offers great potential to address the shortage of human organs for allotransplantation. Rejection in Gal knockout (GTKO) pigs due to elicited non‐Gal antibody response required further genetic modifications of donor pigs and better control of the B‐cell response to xenoantigens. We report significant prolongation of heterotopic alpha Galactosyl transferase “knock‐out” and human CD46 transgenic (GTKO.hCD46Tg) pig cardiac xenografts survival in specific pathogen free baboons. Peritransplant B‐cell depletion using 4 weekly doses of anti‐CD20 antibody in the context of an established ATG, anti‐CD154 and MMF‐based immunosuppressive regimen prolonged GTKO.hCD46Tg graft survival for up to 236 days (n = 9, median survival 71 days and mean survival 94 days). B‐cell depletion persisted for over 2 months, and elicited anti‐non‐Gal antibody production remained suppressed for the duration of graft follow‐up. This result identifies a critical role for B cells in the mechanisms of elicited anti‐non‐Gal antibody and delayed xenograft rejection. Model‐related morbidity due to variety of causes was seen in these experiments, suggesting that further therapeutic interventions, including candidate genetic modifications of donor pigs, may be necessary to reduce late morbidity in this model to a clinically manageable level.     

异种移植的研究进展

供体器官和细胞的匮乏限制了临床同种移植的发展.开展以猪为供体的异种移植研究是缓解供体短缺的重要方法.目前,猪的胰岛细胞、神经元细胞、肝细胞和角膜移植已初步应用于临床,但实体器官移植,如心脏、肝脏、肾脏等仍存在较大的免疫障碍和生理屏障,距离临床应用尚有不小的差距.随着表达一种或多种人的免疫和凝血调节基因猪的出现,异种移植研究取得显著进展,受体和移植器官的存活时间明显延长,而种间交叉感染的风险也较低,但免疫排斥和生理屏障仍是阻碍异种移植进入临床应用的最大障碍.本文就当前异种移植临床前研究的最新进展作一综述,希望能为相关研究者提供一些参考.