Furlong S T, Caulfield J P
Department of Medicine, Harvard Medical School, Boston, Massachusetts 02115.
Exp Parasitol. 1989 Jul;69(1):65-77. doi: 10.1016/0014-4894(89)90172-0.
Lipids in the two surface membranes of Schistosoma mansoni may play an important role in the parasite's defense against host immunity. In particular, lysophosphatidylcholine lyses erythrocytes attached to the parasite and alters the lateral mobilities of their membrane proteins and lipids (Golan et al. 1986). Here, we have studied the incorporation of radiolabeled precursors into the major lipid classes of schistosomula as well as into lipids released by schistosomula into the medium. Radiolabeled polar head groups (choline and ethanolamine) and fatty acid precursors (palmitate and oleate) were linearly incorporated into parasite phospholipids. Fatty acids were differentially incorporated into the various phospholipid classes, principally into phosphatidylcholine and, to a lesser extent, into phosphatidylethanolamine, lysophosphatidylcholine, and phosphatidylserine. The major neutral lipid class labeled, triglycerides, had a decrease in specific activity with time after pulse labeling and the specific activity of the phospholipids increased with time. Thus, triglycerides may provide acyl chains for phospholipid synthesis. Choline was incorporated into phosphatidylcholine and lysophosphatidylcholine, and ethanolamine into phosphatidylethanolamine and lysophosphatidylethanolamine. No evidence was found for phospholipid methylation or demethylation in schistosomula. Labeled lipids were linearly and selectively released into the medium. Triglycerides were released at the highest rate with measurable quantities of phosphatidylcholine, lysophosphatidylcholine, and phosphatidylethanolamine also observed. Monopalmitoylphosphatidylcholine was the only lysophosphatidylcholine present in the medium as demonstrated by reverse-phase chromatography of released choline-labeled lysophosphatidylcholine. These studies demonstrate that schistosomula synthesize phospholipids and neutral lipids and release some of them into the culture medium. In particular, they release a single molecular species of a potent biologically active molecule, monopalmitoylphosphatidylcholine, that may play a role in the parasite's evasion of the immune response.
曼氏血吸虫两个表面膜中的脂质可能在寄生虫抵御宿主免疫方面发挥重要作用。特别是，溶血磷脂酰胆碱可裂解附着于寄生虫的红细胞，并改变其膜蛋白和脂质的侧向流动性（戈兰等人，1986年）。在此，我们研究了放射性标记前体掺入血吸虫幼虫主要脂质类别的情况，以及血吸虫幼虫释放到培养基中的脂质情况。放射性标记的极性头部基团（胆碱和乙醇胺）以及脂肪酸前体（棕榈酸和油酸）被线性掺入寄生虫磷脂中。脂肪酸以不同方式掺入各种磷脂类别，主要掺入磷脂酰胆碱，其次少量掺入磷脂酰乙醇胺、溶血磷脂酰胆碱和磷脂酰丝氨酸。标记的主要中性脂质类别甘油三酯在脉冲标记后随时间比活性降低，而磷脂的比活性随时间增加。因此，甘油三酯可能为磷脂合成提供酰基链。胆碱掺入磷脂酰胆碱和溶血磷脂酰胆碱，乙醇胺掺入磷脂酰乙醇胺和溶血磷脂酰乙醇胺。未发现血吸虫幼虫中有磷脂甲基化或去甲基化的证据。标记的脂质被线性且选择性地释放到培养基中。甘油三酯释放速率最高，同时也观察到有可测量量的磷脂酰胆碱、溶血磷脂酰胆碱和磷脂酰乙醇胺。通过对释放的胆碱标记的溶血磷脂酰胆碱进行反相色谱分析表明，单棕榈酰磷脂酰胆碱是培养基中唯一存在的溶血磷脂酰胆碱。这些研究表明，血吸虫幼虫合成磷脂和中性脂质，并将其中一些释放到培养基中。特别是，它们释放出一种具有强大生物活性分子的单一分子种类，即单棕榈酰磷脂酰胆碱，其可能在寄生虫逃避免疫反应中发挥作用。
