Abstract: Background Amyloid plaque is one of the pathological hallmarks of Alzheimer's disease (AD). Anti-beta-amyloid (Aβ) immunotherapy is effective in removing brain Aβ, but has shown to be associated with detrimental effects. To avoid severe adverse effects such as meningoencephalitis induced by amyloid beta vaccine with adjuvant, and take advantage of amyloid beta antibody's therapeutic effect on Alzheimer's disease sufficiently, our group has developed a new Alzheimer vaccine with mutated amyloid beta 1-42 peptide stimulating dendritic cells (DC). Our previous work has confirmed that DC vaccine can induce adequate anti-amyloid beta antibody in PDAPP Tg mice safely and efficiently. The DC vaccine can improve impaired learning and memory in the Alzheimer's animal model, and did not cause microvasculitis, microhemorrhage or meningoencephalitis in the animal model. However, the exact mechanism of immunotherapy which reduces Aβ deposition remains unknown. In this report, we studied the mechanism of the vaccine, thinking that this may have implications for better understanding of the pathogenesis of Alzheimer's disease. Methods A new Alzheimer vaccine with mutated amyloid beta 1-42 peptide stimulating DC which were obtained from C57/B6 mouse bone marrow was developed. Amyloid beta with Freund's adjuvant was inoculated at the same time to act as positive control. After the treatment was done, the samples of brains were collected, fixed, cut. Immunohistochemical staining was performed to observe the expression of the nuclear hormone liver X receptor (LXR), membrane-bound protein tyrosine phosphatase (CD45), the ATP-binding cassette family of active transporters (ABCA1), receptor for advanced glycation end products (RAGE), β-site APP-cleaving enzyme (BACE) and Aβ in mouse brain tissue. Semi-quantitative analysis was used to defect CA1, CA2, CA3, DG, Rad in hippocampus region and positive neuron in cortex region. Results Aβ was significantly reduced in the experimental group and the positive control group (P = 0.000), but no changes were seen in the negative control group. The levels of LXR, ABCA1, CD45, BACE expression were significantly higher in the PFDM group with DC vaccine treatment and the levels of RAGE were lower than those in the control group. Conclusion The reduction of Aβ via the DC vaccine occurs through multiple factors to achieve a new immune balance. The beneficial results of DC vaccine, which did not produce side effects, may be caused by the LXR/ABCA1 path. DC alone may play an important role in clearing the Aβ to prevent the occurrence of adverse reaction.

Key words: Alzheimer disease, Dendritic cells, Amyloid beta-protein, Peptides, Vaccination, Vaccines

摘要： 研究背景   β-淀粉样蛋白在脑组织中沉积是阿尔茨海默病的典型病理特征之一，免疫疗法虽可有效清除β-淀粉样蛋白，但在治疗的同时也伴随出现一些不良反应。为了避免疫苗治疗过程中产生的严重不良反应如脑膜脑炎等，尝试采用突变型β-淀粉样蛋白（Aβ1 ~ 42）致敏树突状细胞制备阿尔茨海默病疫苗，并在充分评价其安全性和有效性的基础上，进一步探讨其治疗阿尔茨海默病转基因鼠的作用机制。方法  提取C57/B6 小鼠胫骨和股骨树突状细胞，分别以突变型Aβ1 ~ 42 致敏树突状细胞（实验组）和经弗氏佐剂免疫的野生型Aβ1 ~ 42 多肽（佐剂阳性对照组）制备疫苗，然后接种于阿尔茨海默病转基因鼠。免疫组织化学染色观察小鼠脑组织中核激素肝X 受体（LXR）、三磷酸腺苷结合盒转运子1（ABCA1）、CD45、晚期糖基化终产物受体（RAGE）和β-分泌酶（BACE）表达水平，体视学法半定量检测海马区CA1、CA2、CA3、DG、Rad 和皮质区阳性神经元。结果   与阴性对照组相比，实验组和佐剂阳性对照组转基因鼠脑组织β?淀粉样蛋白表达水平显著降低（P = 0.000），阴性对照组治疗前后无变化；经突变型Aβ1 ~ 42 致敏的树突状细胞疫苗治疗后，转基因鼠脑组织中的LXR、ABCA1、CD45 和BACE 表达水平升高（P = 0.000），RAGE 表达水平降低（P = 0.000）。结论   经突变型Aβ1 ~ 42 致敏树突状细胞制备的疫苗可通过多种因素的相互作用使阿尔茨海默病转基因鼠大脑β-淀粉样蛋白代谢达到新的免疫平衡，从而减少其在脑组织中的沉积，且无脑膜脑炎等严重不良反应，此与LXR/ABCA1 通道作用有关。树突状细胞自身也在清除β-淀粉样蛋白的过程中扮演着预防不良反应发生的重要角色。

关键词: 阿尔茨海默病, 树突细胞, 淀粉样β蛋白, 肽类, 接种, 疫苗