Naturally occurring autoantibodies as a biomarker for preclinical Alzheimer`s Disease

在阿尔茨海默病（AD）的临床前阶段，迫切需要一种血液测试来识别认知功能未受损的个体，但目前还没有这样的测试。在这里，我们提出了解决这一未满足需求的实验。具体来说，我们将测量与阿尔茨海默病病因有关的蛋白质（淀粉样蛋白- β和tau）的水平，以及针对这些蛋白质的自然产生的自身抗体（nab）。许多先前的研究已经调查了抗体对淀粉样蛋白- β和tau的诊断效用，但这些研究在方法上受到了损害，并产生了不同的结果。实验混杂因素包括患者和对照选择标准和/或用于检测nab的测定方法的问题。重要的是，所有针对淀粉样蛋白- β和tau蛋白的抗体研究仅在一个时间点评估了它们的水平，并且没有纵向研究。考虑到阿尔茨海默病临床前和临床阶段的持续时间很长，以及在这些漫长的时期内不同形式的nab可能发生的变化，到目前为止，横断面研究得出的结果是可变的和不确定的，这并不奇怪。考虑到这些缺陷，我们提出了以下相关的目标，以便在仔细表征的研究对象的血浆样品中测量淀粉样蛋白- β、tau和nabs。我们将建立并验证检测游离nab和与抗原（淀粉样蛋白- β和tau）结合的nab的方法。将非常小心地包括控制抗体和内部标准，以监测我们的测定的敏感性和可重复性。除了nab外，血浆中的游离和nab结合的淀粉样蛋白和tau蛋白也将被测量。由于血浆中淀粉样蛋白- β和tau蛋白的水平太低，无法用标准的免疫分析方法可靠地检测到，我们将使用最先进的内部开发的超敏感分析方法（单分子分析）。为了深入了解淀粉样蛋白- β、tau和抗这两种蛋白质的抗体在整个疾病过程中是如何变化的，我们将对来自3个不同研究队列的血浆样本应用我们的特征分析。这些样本将包括315个样本，这些样本是在至少4年的时间里，每12个月从老年人中前瞻性地收集一次，同时收集一套详细的临床和脑成像数据，以及100个样本，来自6-65岁的唐氏综合症（DS）受试者。退行性痴呆是早发性AD最常见的遗传原因，绝大多数退行性痴呆的成年人在70岁左右就会出现痴呆，因此研究不同年龄退行性痴呆受试者的样本为了解不同阶段的AD提供了一个窗口。淀粉样蛋白- β、tau和nab水平在不同轨迹（无认知障碍的研究对象和AD患者）和不同年龄的DS受试者中的动态变化将被调查，以评估其作为临床前AD生物标志物的实用性。

A blood test to identify cognitively unimpaired individuals in a preclinical stage of Alzheimer`s Disease (AD) is desperately needed, but no such test exists. Here we propose experiments to address this unmet need. Specifically, we will measure levels of proteins implicated in the etiology of AD (amyloid-beta and tau), and naturally occurring autoantibodies (nabs) against these proteins. A number of prior studies have investigated the diagnostic utility of nabs against amyloid-beta and tau but these were methodologically compromised and produced variable results. Experimental confounders included problems with patient and control selection criteria and/or the assays used to detect nabs. Importantly, all studies on nabs against amyloid-beta and tau evaluated their levels at only one time-point and there have been no longitudinal studies. Considering the long duration of both the pre-clinical and clinical phases of AD and how distinct forms of nabs may change during these protracted periods it is not surprising that cross-sectional studies have thus far yielded variable and inconclusive results. Mindful of these pitfalls we propose the following interrelated aims to enable measurement of amyloid-beta, tau, and nabs against both proteins in plasma samples from carefully characterized study subjects. We will establish and validate assays to detect both free nabs and such that are bound to their antigen (amyloid-beta and tau). Great care will be taken to include control antibodies and internal standards so as to monitor the sensitivity and reproducibility of our assays. In addition to nabs, free and nabs-bound amyloid-beta and tau proteins in plasma will also be measured. Since plasma levels of amyloid-beta and tau are too low to be reliably detected using standard immunoassays we will use state-of-the-art in-house developed ultra-sensitive assays (single molecule assays). To gain insight on how amyloid-beta, tau, and nabs against both proteins change throughout disease we will apply our well characterized assays to plasma samples from 3 distinct study cohorts. These will include 315 samples that have been collected prospectively every 12 months for at least 4 years from elderly individuals along with a detailed set of clinical and brain imaging data, and 100 samples from 6-65 years old Down Syndrome (DS) subjects. DS is the most common genetic cause of early-onset AD and the great majority of DS adults becomes demented by the end of their 7th decade of life, thus studying samples from different aged DS subjects provides a window on different stages of AD. Dynamic changes of amyloid-beta, tau, and nabs levels in different trajectories (study subjects with no cognitive impairment over time, and patients that develop AD) and different aged DS subjects will be investigated to evaluate their usefulness as a biomarker for preclinical AD.