Freigang S, Hörkkö S, Miller E, Witztum J L, Palinski W
Department of Medicine, University of California San Diego, La Jolla, CA, USA.
Arterioscler Thromb Vasc Biol. 1998 Dec;18(12):1972-82. doi: 10.1161/01.atv.18.12.1972.
We and others previously showed that immunization of rabbits with different forms of oxidized low density lipoprotein (LDL) significantly reduced atherogenesis. We now investigated the effect of continued immunization on atherosclerosis in LDL receptor-deficient (LDLR-/-) mice to determine whether a similar reduction of atherosclerosis occurred in murine models and whether this was due to humoral immune responses, ie, formation of high titers of antibodies to oxidation-specific epitopes. Three groups of LDLR-/- mice were repeatedly immunized with homologous malondialdehyde-modified LDL (MDA-LDL), native LDL, or phosphate-buffered saline (PBS) for 7 weeks. Extensive hypercholesterolemia and accelerated atherogenesis were then induced by feeding a cholesterol-rich diet for 17 weeks, during which immunizations were continued. Binding of immunoglobulin (Ig) M and IgG antibodies, as well as IgG1 and IgG2a isotypes, to several epitopes of oxidized LDL were followed throughout the study. After 24 weeks of intervention, atherosclerosis in the aortic origin was significantly reduced by 46.3% and 36.9% in mice immunized with MDA-LDL and native LDL, respectively, compared with PBS (133 558 and 157 141 versus 248 867 microm2 per section, respectively). However, the humoral immune response to oxidative neoepitopes in the MDA-LDL group was very different from that of the LDL or PBS group. IgG antibody binding to MDA-LDL and other epitopes of oxidized LDL, such as oxidized phospholipid (cardiolipin), oxidized cholesterol, or oxidized cholesteryl linoleate, but not native LDL, increased markedly in mice immunized with MDA-LDL, but not in mice immunized with native LDL or PBS. In the MDA-LDL group, both T helper cell (Th)2-dependent IgG1 antibody and Th1-dependent IgG2a antibody binding to oxidative neoepitopes increased significantly over time. The fact that mice immunized with both MDA-LDL and native LDL had a significant reduction in atherosclerosis, whereas only the MDA-LDL group developed very high titers of antibodies to oxidation-specific epitopes, suggests that the antiatherogenic effect of immunization is not primarily dependent on very high titers of antibodies to oxidation-specific epitopes but is more likely to result from the activation of cellular immune responses.
我们和其他研究人员之前表明，用不同形式的氧化低密度脂蛋白（LDL）免疫兔子可显著减少动脉粥样硬化的发生。我们现在研究了持续免疫对低密度脂蛋白受体缺陷（LDLR-/-）小鼠动脉粥样硬化的影响，以确定在小鼠模型中是否会出现类似的动脉粥样硬化减少情况，以及这是否归因于体液免疫反应，即形成高滴度的针对氧化特异性表位的抗体。三组LDLR-/-小鼠分别用同源丙二醛修饰的LDL（MDA-LDL）、天然LDL或磷酸盐缓冲盐水（PBS）反复免疫7周。然后通过喂食富含胆固醇的饮食17周诱导广泛的高胆固醇血症和加速的动脉粥样硬化形成，在此期间继续进行免疫。在整个研究过程中，跟踪免疫球蛋白（Ig）M和IgG抗体以及IgG1和IgG2a亚型与氧化LDL的几个表位的结合情况。干预24周后，与PBS组相比，用MDA-LDL和天然LDL免疫的小鼠主动脉起始处的动脉粥样硬化分别显著减少了46.3%和36.9%（每切片分别为133 558和157 141平方微米，而PBS组为248 867平方微米）。然而，MDA-LDL组对氧化新表位的体液免疫反应与LDL或PBS组非常不同。在用MDA-LDL免疫的小鼠中，IgG抗体与MDA-LDL以及氧化LDL的其他表位如氧化磷脂（心磷脂）、氧化胆固醇或氧化亚油酸胆固醇酯（而非天然LDL）的结合显著增加，而在用天然LDL或PBS免疫的小鼠中则没有。在MDA-LDL组中，随着时间的推移，依赖辅助性T细胞（Th）2的IgG1抗体和依赖Th1的IgG2a抗体与氧化新表位的结合均显著增加。用MDA-LDL和天然LDL免疫的小鼠动脉粥样硬化均显著减少，而只有MDA-LDL组产生了非常高滴度的针对氧化特异性表位的抗体，这一事实表明免疫的抗动脉粥样硬化作用并非主要依赖于非常高滴度的针对氧化特异性表位的抗体，而更可能是由细胞免疫反应的激活所致。
