Pepe M G, Curtiss L K
J Immunol. 1986 May 15;136(10):3716-23.
A normal plasma lipoprotein, termed LDL-In, has been shown to be a potent inhibitor of mitogen-driven human lymphocyte proliferation in vitro and of primary antibody responses in the mouse. To determine whether the immunoregulatory activity of LDL-In resided with the protein rather than the lipid constituents of LDL-In, one of the apoproteins of LDL-In, apoprotein E, was isolated from plasma and was analyzed for its inhibitory activity. Apoprotein E, isolated after delipidization of lipoproteins with either methyl ethyl ketone or ethanol and ethyl ether, was immunosuppressive. Furthermore, the characteristics of inhibition of cellular [3H]thymidine uptake by isolated apoprotein E were identical to those characteristics obtained with suppression by LDL-In. Inhibition by apoprotein E and LDL-In required preincubation of the cells with either apoprotein or lipoprotein for 24 hr before exposure of the cells to mitogen for maximal expression of suppressive activity, and this inhibition could not be reversed by removal of non-cell-associated inhibitor before stimulation. Neither apoprotein E or LDL-In was inhibitory when they were added to the cells after mitogen stimulation. The only difference noted between suppression by apoprotein E and LDL-In was that of dose. Compared with quantitative estimates of the apoprotein E content of LDL-In, significantly more isolated apoprotein E was required than lipoprotein-associated E for comparable levels of suppression. The potency of apoprotein E could be increased by adding it to cells in the presence of dimyristoylphosphatidylcholine/cholesterol vesicles. The data suggesting that phospholipid increased the specific activity of apoprotein E by altering its molecular dispersion was obtained from analyses of the interaction of apo E with cells, as well as the plastic culture vessels. The results suggested that the molecular dispersion and perhaps organization of isolated apoprotein E in an aqueous system is critical to its interaction with lymphocytes and subsequently its biological activity.
一种正常的血浆脂蛋白，称为LDL-In，已被证明在体外是有丝分裂原驱动的人类淋巴细胞增殖以及小鼠初次抗体反应的有效抑制剂。为了确定LDL-In的免疫调节活性是存在于蛋白质部分而非脂质部分，从血浆中分离出LDL-In的一种载脂蛋白——载脂蛋白E，并分析其抑制活性。用甲乙酮或乙醇和乙醚对脂蛋白进行脱脂后分离得到的载脂蛋白E具有免疫抑制作用。此外，分离得到的载脂蛋白E对细胞[3H]胸腺嘧啶核苷摄取的抑制特性与LDL-In抑制所获得的特性相同。载脂蛋白E和LDL-In的抑制作用需要细胞在接触有丝分裂原之前，先与载脂蛋白或脂蛋白预孵育24小时，以实现抑制活性的最大表达，并且这种抑制作用在刺激前不能通过去除非细胞相关抑制剂来逆转。有丝分裂原刺激后将载脂蛋白E或LDL-In添加到细胞中时，两者均无抑制作用。载脂蛋白E和LDL-In抑制作用之间唯一的区别在于剂量。与LDL-In中载脂蛋白E含量的定量估计相比，要达到相当的抑制水平，所需的分离载脂蛋白E比脂蛋白相关的E要多得多。在二肉豆蔻酰磷脂酰胆碱/胆固醇囊泡存在的情况下，将载脂蛋白E添加到细胞中可增强其效力。从载脂蛋白E与细胞以及塑料培养容器相互作用的分析中获得的数据表明，磷脂通过改变载脂蛋白E的分子分散性来提高其比活性。结果表明，在水相系统中分离的载脂蛋白E的分子分散性以及可能的组织形式对于其与淋巴细胞的相互作用及其随后的生物学活性至关重要。
