Abdel-Wahab N, Kuo Y M, Wu Y, Tuan R S, Bianco A E
Imperial College of Science, Technology and Medicine, London, UK.
Mol Biochem Parasitol. 1996 Feb-Mar;76(1-2):187-99. doi: 10.1016/0166-6851(95)02558-8.
A cDNA of Onchocerca volvulus has been isolated by differential immunoscreening of an adult worm expression library using sera raised in cattle against the related species, O. lienalis. It was selected because of its recognition by antibodies from cattle immunized with irradiated third-stage (L3) larvae and not by antibodies from animals infected with non-irradiated larvae. The original 311-bp clone was used to isolate a 1478-bp cDNA. Designated OvB20, this codes for 460 amino acid residues, hybridizes with a approximately 1.6 kBp transcript and appears to be transcribed from a filarial-specific, single copy gene. It is expressed in developing stages from embryo to L4 larva, but not in the adult. The product of OvB20 appears to undergo co- or post-translational processing: in vitro transcription and translation give rise to a polypeptide consistent with the deduced amino acid sequence (approximately 52 kDa), whilst products of 52 and 65 kDa are detected in larvae by immunoblotting and following in vitro translations to which exogenous microsomes have been added. A 42-kDa protein was also detected in all in vitro translations. No homologous genes were found in the computer databases, although there are regions of weak sequence similarity with C-reactive proteins. The functional role of OvB20 may warrant further attention, as it has recently been shown that the recombinant protein confers host protection against a related rodent filaria following active immunization (Taylor, M.J., Abdel-Wahab, N., Wu, Y., Jenkins, R.E. and Bianco, A.E. (1995) Onchocerca volvulus larval antigen, OvB20 induces partial protection in a rodent model of onchocerciasis. Infect. Immun. 63, 4417-4422).
通过使用针对相关物种牛盘尾丝虫（O. lienalis）免疫牛所产生的血清，对盘尾丝虫成虫表达文库进行差异免疫筛选，分离出了盘尾丝虫的一个cDNA。之所以选择它，是因为它能被用辐照第三期（L3）幼虫免疫的牛产生的抗体识别，而不能被感染未辐照幼虫的动物产生的抗体识别。最初的311 bp克隆被用于分离一个1478 bp的cDNA。这个被命名为OvB20的cDNA编码460个氨基酸残基，与一个约1.6 kBp的转录本杂交，并且似乎是从一个丝虫特异性的单拷贝基因转录而来。它在从胚胎到L4幼虫的发育阶段表达，但在成虫中不表达。OvB20的产物似乎经历了共翻译或翻译后加工：体外转录和翻译产生了一个与推导的氨基酸序列一致的多肽（约52 kDa），而在幼虫中通过免疫印迹以及在添加了外源微粒体的体外翻译产物中检测到了52 kDa和65 kDa的产物。在所有体外翻译中还检测到了一个42 kDa的蛋白质。在计算机数据库中未发现同源基因，尽管与C反应蛋白有弱序列相似区域。OvB20的功能作用可能值得进一步关注，因为最近已经表明，重组蛋白在主动免疫后能赋予宿主对相关啮齿动物丝虫的保护作用（泰勒，M.J.，阿卜杜勒 - 瓦哈卜，N.，吴，Y.，詹金斯，R.E.和比安科，A.E.（1995年）盘尾丝虫幼虫抗原，OvB20在盘尾丝虫病的啮齿动物模型中诱导部分保护作用。感染与免疫。63，4417 - 4422）。
