Mohamed M M, Shalaby K A, LoVerde P T, Karim A M
Department of Biochemistry, Faculty of Science, Ain Shams University, Cairo, Egypt.
Mol Biochem Parasitol. 1998 Oct 30;96(1-2):15-25. doi: 10.1016/s0166-6851(98)00088-7.
Two cDNA clones each encoding a 20.8-kDa protein (Sm20.8) were identified from the human blood fluke Schistosoma mansoni sporocyst and adult worm cDNA expression libraries by antibodies derived from rabbits vaccinated with irradiated cercariae and purified over an NP-40 extract of 3h schistosomula. Each identified cDNA has an open reading frame encoding a protein of 181 amino acids and shows homology (29-30%) with Sm21.7, Sm22.6, and Sj22.6, previously identified as belonging to a family of soluble schistosome tegumental antigens. An EF-hand calcium-binding motif is found in Sm20.8 protein in two different positions. However, neither motif binds 45calcium (45Ca) Recombinant Sm20.8 showed immunoreactivity with sera from infected humans and rabbits vaccinated with irradiated cercariae. Polyclonal rabbit sera against the Sm20.8 recognized the native protein in an extract of infected snail (sporocyst), cercariae, 3 hour schistosomules (3 h NP-40) and an adult worm preparation but not in uninfected snail tissue or eggs. Further demonstration that Sm20.8 was expressed in the different developmental stages of the parasite was by RT-PCR. Confocal microscopy demonstrates that Sm20.8 localizes to the tegument of adult worms and 3 h np-40. The IgG fraction specific to Sm20.8 mediated complement killing of schistosomules in vitro by 34%. Vaccination of mice with naked DNA containing the Sm20.8 gene and subsequently challenged with cercariae showed 30% reduction in worm burden compared to controls.
从曼氏血吸虫尾蚴和成虫cDNA表达文库中，通过用经辐射的尾蚴免疫的兔产生的抗体，并在3小时童虫的NP - 40提取物上进行纯化，鉴定出两个分别编码20.8 kDa蛋白质（Sm20.8）的cDNA克隆。每个鉴定出的cDNA都有一个编码181个氨基酸的开放阅读框，并且与之前鉴定为属于可溶性血吸虫体表抗原家族的Sm21.7、Sm22.6和Sj22.6具有同源性（29 - 30%）。在Sm20.8蛋白的两个不同位置发现了一个EF - 手型钙结合基序。然而，这两个基序都不结合45钙（45Ca）。重组Sm20.8与感染人类和经辐射尾蚴免疫的兔的血清呈现免疫反应性。针对Sm20.8的兔多克隆血清在感染的蜗牛（孢蚴）、尾蚴、3小时童虫（3小时NP - 40）和成虫制剂的提取物中识别天然蛋白，但在未感染的蜗牛组织或虫卵中未识别。通过RT - PCR进一步证明Sm20.8在寄生虫的不同发育阶段表达。共聚焦显微镜显示Sm20.8定位于成虫和3小时NP - 40的体表。Sm20.8特异性的IgG组分在体外介导对童虫的补体杀伤作用达34%。用含Sm20.8基因的裸DNA对小鼠进行免疫接种，随后用尾蚴攻击，结果显示与对照组相比，虫体负荷降低了30%。
