在采采蝇中肠中发现的前循环型布氏锥虫的扫瞄电子显微图片，图片来自维基共享资源。
布氏锥虫(Trypanosoma brucei)导致的昏睡病(sleeping sickness)可通过采采蝇(tsetse fly)的叮咬传染给人类(和动物)。根据2012年2月15日发表在生物医学中心(BioMed Central)旗下开放存取的Microbial Cell Factories期刊上的一篇新研究论文，研究人员利用一种自然条件下生活在采采蝇体内的一种细菌释放纳米抗体(nanobody，一类抗体片段)对抗这种锥虫。这就意味这种细菌在采采蝇体内发挥着一种类似特洛伊木马的作用。这些结合到这种寄生虫表面的纳米抗体是制造能够杀死或阻断锥虫发育的特定纳米抗体的第一步。
昏睡病威胁着生活在非洲撒哈拉沙漠以南地区上百万人的生命。在布氏锥虫感染第一阶段(血淋巴阶段)，它导致人发热、头痛、关节疼痛和发痒。当这种寄生虫跨越血脑屏障时便进入感染第二阶段(神经阶段)，它导致思绪混乱、较差的协调能力和睡眠紊乱。若不进行治疗，昏睡病是致命的。然而，诊断和治疗这种疾病比较困难，只有接受过特别培训的人员才能开展。锥虫感染牛后会导致牛贫血，而且还能够导致它们死于贫血症。综合在一起就是，这些已经对整个非洲大陆的公共健康和农业发展带来严重影响。
细菌(Sodalis glossinidius)是一种内共生菌，类似于定居于人肠道的“有益细菌”，存在于采采蝇的中肠、肌肉、脂肪和唾液腺之中。鉴于雌性采采蝇会把这些细菌传给它的后代，那么一旦将这种雌性蝇放到野外，基因修饰的细菌也应当能够在采采蝇之间代代相传。比利时研究人员对这种内共生菌进行基因改良，这样它分泌一种单结构域抗体结合到布氏锥虫的一种可变表面糖蛋白(variant surface glycoprotein, VSG)上。这种基因突变细菌的生长不受影响，因此一旦放到大自然中会增加它们自己的存活率。
比利时安特卫普市热带疾病研究所的Van Den Abbeele教授解释道，“当我们在模拟采采蝇肠道内部的条件下研究活着的锥虫时，这种基因改造菌表达的纳米抗体有生物活性，能够结合到这种寄生虫的整个表面上。鉴于我们知道这种技术有效，我们正在研究能够在采采蝇肠道中破坏或阻断这种寄生虫发育的纳米抗体。”
最近的流行性昏睡病发生于20世纪70年代。尽管人们在过去10年持续的努力和新增病例数量在下降，但是迄今为止这种疾病还没有得到根除。这种新技术为人们对抗这种破坏性的疾病提供希望。(生物谷：towersimper编译)
doi:10.1186/1475-2859-11-23
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Expression and extracellular release of a functional anti-trypanosome Nanobody(R) in Sodalis glossinidius, a bacterial symbiont of the tsetse fly
Linda De Vooght, Guy Caljon, Benoit Stijlemans, Patrick De Beatselier, Marc Coosemans and Jan Van Den Abbeele
Background
Sodalis glossinidius, a gram-negative bacterial endosymbiont of the tsetse fly, has been proposed as a potential in vivo drug delivery vehicle to control trypanosome parasite development in the fly, an approach known as paratransgenesis. Despite this interest of S. glossinidius as a paratransgenic platform organism in tsetse flies, few potential effector molecules have been identified so far and to date none of these molecules have been successfully expressed in this bacterium.
Results
In this study, S. glossinidius was transformed to express a single domain antibody, (Nanobody(R)) Nb_An33, that efficiently targets conserved cryptic epitopes of the variant surface glycoprotein (VSG) of the parasite Trypanosoma brucei. Next, we analyzed the capability of two predicted secretion signals to direct the extracellular delivery of significant levels of active Nb_An33. We show that the pelB leader peptide was successful in directing the export of fully functional Nb_An33 to the periplasm of S. glossinidius resulting in significant levels of extracellular release. Finally, S. glossinidius expressing pelBNb_An33 exhibited no significant reduction in terms of fitness, determined by in vitro growth kinetics, compared to the wild-type strain.
Conclusions
These data are the first demonstration of the expression and extracellular release of functional trypanosome-interfering Nanobodies(R) in S. glossinidius. Furthermore, Sodalis strains that efficiently released the effector protein were not affected in their growth, suggesting that they may be competitive with endogenous microbiota in the midgut environment of the tsetse fly. Collectively, these data reinforce the notion for the potential of S. glossinidius to be developed into a paratransgenic platform organism.
