摘要
动脉粥样硬化是动脉壁免疫系统介导的炎症性疾病。动脉壁特异性和非特异性免疫系统对许多内源性和外源性抗原都有免疫反应。已有研究表明免疫系统在动脉粥样硬化进程中一方面促进动脉粥样硬化,另一方面延缓动脉粥样硬化。因此,通过针对抗原的主动免疫调节可以改变动脉粥样硬化的进程。本文讨论了特异性和非特异性免疫系统在动脉粥样硬化进程中的双重作用,介绍了已经在实验室阶段制成的疫苗以及在实验模型中成功延缓动脉粥样硬化进程的抗原的研究,探讨了动脉粥样硬化疫苗临床应用的前景和挑战。
动脉粥样硬化是一种慢性炎症疾病,疾病特征是动脉壁上的脂肪条纹逐渐发展成动脉粥样硬化和特征性斑块,这些动脉粥样斑块的急性破裂会形成局部血栓,导致病灶动脉的部分或全部闭塞,主要临床表现包括缺血性心脏病、缺血性脑卒中和周围动脉疾病。动脉粥样硬化及其伴随的临床并发症如脑卒中和缺血性心脏病,是全球死亡事件的主要原因,2016年约有1 790万人(占全球死亡总数的31%)死于此类心血管疾病。2013年,中国缺血性心脏病和脑卒中的住院总费用为705亿元,给国家和患者带来巨大的经济负担。
临床数据表明,动脉粥样硬化与免疫介导的炎症有关,特异性及非特异性免疫细胞,例如巨噬细胞、T淋巴细胞、树突状细胞(dendritic cells,DCs)、肥大细胞、B淋巴细胞等,在动脉粥样硬化斑块中普遍存
生物体对病原微生物和病原体的非特异性即时反应称为非特异性免疫。非特异性免疫系统细胞(DCs和巨噬细胞)作为第一响应者,检测内环境中的疾病相关分子,即氧化低密度脂蛋白(oxygenized low density lipoprotein,oxLDL)的表达。非特异性免疫细胞接触这些疾病相关分子,并与Toll样受体(Toll-like receptors,TLR)相互作用。TLR识别疾病相关分子,引起急性炎症基因的激活和急性非特异性免疫炎症介质的释放。敲除非特异性免疫信号通路基因的小鼠无论血液中胆固醇水平高低,都呈现动脉粥样硬化症状减轻现象,表明非特异性免疫在动脉粥样硬化中起作
巨噬细胞集落刺激因子(macrophage colony stimulating factor,M-CSF)基因对巨噬细胞增殖起促进作用。高脂血症小鼠的M-CSF基因被敲除,显示动脉粥样硬化减少的现
自然杀伤细胞(natural killer cell,NK)是促进动脉粥样硬化的非特异性免疫细胞。用Ly49A转基因小鼠的骨髓细胞移植的低密度脂蛋白(low density lipoprotein,LDL)受体缺陷型(LDL
肥大细胞也会影响动脉粥样硬化进程。在缺乏肥大细胞的高脂血症小鼠中,炎症减少,病变进程减慢。有研究报道了肥大细胞缺陷小鼠的胆固醇水平较低,这表明先天性肥大细胞信号传导与胆固醇体内平衡之间存在联
DCs是特异性和非特异性免疫系统的桥梁,是免疫细胞活化过程中的上游成分,DCs独特的地位使它成为疫苗研发重要的靶点。高脂血症中,内膜上的DCs迅速摄取脂质,而注射CD11c特异性白喉毒素受体(diphtheria toxin receptor,DTR)的转基因小鼠DCs缺失,引起LDL
与非特异性免疫系统的迟缓、非特异性相比,特异性免疫反应目标更为明确。免疫母细胞的发育产生识别特定抗原的多种T细胞和B细胞。
非特异性免疫细胞例如DCs和巨噬细胞,呈递经T细胞识别的抗原,形成了主要组织相容性复合体(major histocompatibility complex,MHC)。呈递抗原后,激活T细胞并增殖。CD
研究表明B细胞能延缓高胆固醇血小鼠动脉粥样硬化进
动脉粥样硬化斑块含有DCs、充当抗原呈递细胞(antigen-presenting cells,APC)作用的巨噬细胞和T细胞。APC-T细胞相互作用表明了可通过斑块中的突触激活特异性免疫(

图1 APC和T细胞间的作用
CD
CD
综上所述,特异性免疫系统和非特异性免疫系统的许多组成部分均参与调节动脉粥样硬化,这些组分之间的复杂的相互作用可导致动脉粥样硬化的恶化或改善(
抗动脉粥样硬化的疫苗治疗方案是诱导机体产生特异性免疫应答。这种方法的难点在于确定与动脉粥样硬化形成相关的特异性抗原,使其可用于激活抗原特异性免疫应答。大多数寻找潜在抗原的研究仍处于临床前试验阶段(
探索抗原的合理方法是将重点放在病灶本身即动脉粥样硬化斑块。在动脉粥样硬化斑块中已发现许多外源抗原,包括肺炎支原体、肺炎衣原体和牙龈卟啉单胞菌等,肠道病毒、人类免疫缺陷病毒、巨细胞病毒和丙型肝炎病毒等病毒。至于这些病原体是否引致动脉粥样硬化,仍未能确定。
牙周病原体最近在研究中受到重视,许多人发现牙周病患者多伴随动脉粥样硬化疾
因为LDL和其他含有ApoB-100的脂蛋白是动脉粥样硬化血栓形成的主要原因,所以源自它们的抗原是疫苗开发的首选。使用不同辅助基团修饰疫苗制剂中的全天然或oxLDL,在实验动物身上已经证明了其免疫效果。然而,抗原的确切表位和机制尚未完全清楚。
由于LDL是多种甘油三酯、载脂蛋白、磷脂和胆固醇酯等组成的大分子物质,所以在临床可用的疫苗制剂中使用天然的LDL作为抗原是不实际的。LDL分子的复杂性使得分子内的免疫原性表位难以确定。鉴于使用LDL作为抗原免疫得到了良好的实验数据,确定LDL中的抗动脉粥样硬化抗原表位是重中之重。为此,Antoniak
与对照受试者相比,使用p210疫苗免疫的患者主动脉粥样硬化显著减
除了减少主动脉粥样硬化之外,p210疫苗还激活CD
p210可诱导CD
由p210引起不同的细胞免疫应答可能是由于以下原因:(1)p210载体形式,用CTB重组或游离态;(2)递送途径-皮下给药与黏膜给药的差异;(3)p210的剂量;(4)p210给药的持续时间。然而,无论以何种形式递送,p210免疫后动脉粥样硬化的减轻,表明p210是疫苗制剂的候选抗原。
使用疫苗调节动脉粥样硬化中的免疫应答的方法不仅限于LDL和ApoB-100相关的抗原。动脉粥样硬化血管疾病的复杂性为其他抗原研究提供了可能性。
胆固醇酯转运蛋白(cholesterol ester transfer protein,CETP)是抗体诱导型动脉粥样硬化疫苗的候选抗原。CETP是一种酶,可促进胆固醇酯从HDL转移到LDL,甘油三酸酯从LDL转移到HD
天然IgM抗体可识别凋亡细胞表面的oxLDL表位和磷酰胆碱(Phosphorylcholine,PC)头部基团,并阻止巨噬细胞抑制和oxLDL凋亡细胞的摄取。抗PC抗体可用于预防肺炎链球菌感染。LDL
HSP是一种高度保守的应激蛋白,它们在正常条件下存在于细胞中,当细胞暴露于压力条件下(例如pH变化或缺氧)时可以高水平表达。HSP同样影响动脉粥样硬化进
DCs是最有效的抗原呈递细胞,通过DCs进入宿主的抗原递送可引起有效的免疫反应。有研究者以oxLDL作为抗原,将细胞静脉注射到新生小鼠中,负载oxLDL的DCs的转移诱导产生Th1应答,增加oxLDL IgG滴度,减少动脉粥样硬
随着医药科技水平的发展,疫苗消除了许多传染病的感染与影响。同样,为慢性流行的动脉粥样硬化疾病开发疫苗也具有重要意义。本文讨论了特异性和非特异性免疫系统在动脉粥样硬化进程中的双重作用,总结了通过接种疫苗诱导动脉粥样硬化相关抗原特异性免疫反应以及在实验模型中延缓动脉粥样硬化进程的抗原种类。通过自身抗原诱导免疫反应能有效地了解特异性免疫和非特异性免疫对于免疫受体识别和抗体表达的关系,从而为治疗动脉粥样硬化提供指导,并为其他心血管疾病如缺血性心脏病、脑卒中等疾病治疗提供参考。
然而,动脉粥样硬化疫苗的开发仍面临不少挑战。包括:(1)疫苗安全和稳定性的问题,确保疫苗可适当复制天然抗原,并确保免疫反应有适当的强度和质量从而提供有效的机体保护;(2)免疫疗程和持久性;(3)临床研究中的疗效终点的确定和监测;(4)缩短候选疫苗的开发时间、生产和临床应用;(5)成本投入巨大。像所有疫苗一样,动脉粥样硬化疾病疫苗的免疫反应也很难预测,开发出最佳疫苗需要长期耗时的动物疫苗免疫实验,然后表征所得的免疫结果,从而判断疫苗优劣;此外,物种差异造成疫苗的临床使用更加困难,有些疫苗在动物实验中表现良好,但在人体使用却无效(
目前,有许多可应用于人体的抗原选择,很多很有希望的结果都是在临床前实验中得到的,将这一疫苗治疗手段运用到临床研究中显得至关重要与紧迫。但将上述临床前观察转化为临床领域仍处于起步阶段,例如,许多临床前试验已经确定LDL在动脉粥样硬化形成中的作用,这使LDL和ApoB-100成为免疫调节治疗的初始靶标,但到目前为止,还没有针对此类靶标的药物上市。
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