The microbiota and allograft rejection: novel investigations into the consequences of obesity

捐赠者和受赠者之间遗传差异的程度构成了决定 同种异体免疫的强度和随后的移植物排斥反应动力学。近年来，环境保护发挥了重要作用 各种因素已经浮现。我们的初步结果确定了两个相互关联的环境因素，它们可以 调节同种异体免疫反应的强度。第一个是微生物区系，以群落为代表 栖息在体内的微生物。在这里，我们报告了通过使用细菌来消除微生物区系- 游离(GF)小鼠，或广谱抗生素(ABX)引起的两种供体微生物多样性下降 而受体小鼠在移植前导致同种异体反应性降低，移植物存活时间延长。 从机制上讲，来自GF和ABX预处理的小鼠的抗原提呈细胞(APC)的能力降低 激活供体反应性T细胞。第二个环境因素是高脂肪饮食(HFD)。我们展示了那个肥胖的 小鼠的同种异体免疫力增强，排斥移植的速度比瘦小的小鼠快。从机械上讲， 肥胖小鼠的APC向T细胞递呈同种异体抗原的能力比瘦小鼠的APC更强 这是在GF和ABX处理的小鼠中观察到的表型的镜像。基于已建立的链接 在肥胖和肠道微生物区系之间，我们认为肥胖依赖的生态失调超级激活APC， 这反过来会诱导同种异体反应性T细胞更有效的启动，从而加速移植的动力学 拒绝。使用元基因组鸟枪测序，我们已经确定了菲米米特和菲米库特的比例增加 饮食诱导肥胖(DIO)小鼠体内类杆菌和蠕形杆菌比例降低。有趣的是， 在接受减重手术(袖状胃切除术，SGX)的小鼠和小鼠中，这些变化被逆转 用TDCA/valine处理后，我们发现肥胖小鼠血清中的共代谢物减少并恢复 由新交所提供。与临床相关的是，我们检测到了高水平的普通芽孢杆菌，一种可以代谢的共生物种 TDCA，在一名肥胖病人的大便中。基于这些初步数据，我们提出了微生物的形成 社区通过饮食调节同种免疫。具体地说，我们假设肥胖症通过其对 微生物区系，并通过宿主/微生物区系中共代谢物的变化，增强DC平衡，从而导致 同种异体反应性T细胞预置增加和移植物排斥反应加速；这些效应可被减肥药物逆转 手术或通过恢复代谢物水平。这一假设将在以下背景下进行检验 遵循特定的目标。 具体目的1.确定减肥手术前后HFD所形成的微生物区系 不同地调节同种异体免疫和移植排斥反应的动力学。具体目标2.调查 肥胖患者依赖微生物的代谢物TDCA和Valine减少的机制 并由SGX恢复，调节同种异体免疫和移植物排斥反应。具体目标3.确定 在一项先导性人体研究中，减肥手术对微生物区系、TDCA/valine血清水平和APC调节的影响。

The extent of genetic disparities between donor and recipients constitutes the main driver that determines the strength of alloimmunity and subsequent kinetics of graft rejection. In recent years, a role for environmental factors has emerged. Our preliminary results have identified 2 inter-related environmental factors that can modulate the strength of the alloimmune response. The first is the microbiota, represented by the communities of microbes that inhabit the body. Here, we reported that the elimination of microbiota through the use of germ- free (GF) mice, or a decrease of microbial diversity induced by broad-spectrum antibiotics (Abx) in both donor and recipient mice prior to transplantation resulted in a reduction of alloreactivity and prolonged graft survival. Mechanistically, antigen-presenting cells (APCs) from GF and Abx-pre-treated mice had a reduced capacity to prime donor-reactive T cells. The second environmental factor is high fat diet (HFD). We showed that obese mice mounted an augmented alloimmunity and rejected transplants faster than lean mice. Mechanistically, APCs from obese mice had a greater capacity to present alloantigen to T cells compared with APCs from lean mice, a mirror image of the phenotype observed in GF and Abx-treated mice. Based on established links between obesity and the gut microbiota, we propose that obesity-dependent dysbiosis super-activates APCs, which, in turn, induces a more potent priming of alloreactive T cells leading to accelerated kinetics of transplant rejection. Using metagenomic shotgun sequencing, we have identified increased proportions of Firmicutes and decreased proportions of Bacteroidetes and Verrucomicrobia in diet-induced obese (DIO) mice. Interestingly, these changes were reversed in mice treated with bariatric surgery (sleeve gastrectomies, SGx), and in mice treated with TDCA/valine, co-metabolites that we found to be reduced in the serum of obese mice and restored by SGx. Of clinical relevance, we detected high levels of B. vulgatus, a commensal species that can metabolize TDCA, in the stool of an obese patient. Based on these preliminary data, we propose that shaping of microbial communities by diet modulates alloimmunity. Specifically, we hypothesize that obesity, via its alteration of the microbiota and through changes of co-metabolites in host/microbiota, enhances DC poising that results in increased priming of alloreactive T cells and accelerated graft rejection; those effects are reverted by bariatric surgery or through the restoration of metabolite levels. This hypothesis will be tested in the context of the following Specific Aims. Specific Aim 1. To determine if the microbiota shaped by HFD before and after bariatric surgery differentially modulates alloimmunity and the kinetics of graft rejection. Specific Aim 2. To investigate the mechanisms by which the microbiota-dependent metabolites TDCA and valine that are decreased in obesity and restored by SGx, modulate alloimmunity and graft rejection. Specific Aim 3. To determine the effects of bariatric surgery on the microbiota, TDCA/valine serum levels, and APC tuning in a pilot human study.