Mariante Rafael Meyer, Lopes Letícia Coutinho, Benchimol Marlene
Programa de Ciências Morfológicas, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.
Parasitol Res. 2004 Mar;92(4):303-12. doi: 10.1007/s00436-003-1026-z. Epub 2004 Jan 14.
Tritrichomonas foetus is a parasitic protist of the urogenital tract of cattle. It presents the trophozoite stage, a motile elongated form that constitutes most of the cells in a normal population, and a pseudocyst stage, an immotile rounded form that appears under unfavourable environmental conditions. In the present report pseudocysts were studied in natural conditions and after induction by chemicals or cycles of cooling and warming of cultures. The capacity of T. foetus to adhere to vaginal epithelial cells (VECs) was compared for both trophozoite and pseudocyst forms. By the use of video-enhanced-contrast microscopy, scanning and transmission electron microscopy, and immunofluorescence microscopy techniques, we present evidence that: (1) T. foetus easily internalizes the flagella and forms pseudocysts under several unfavourable conditions; (2) T. foetus in both pseudocyst and trophozoite forms is able to adhere to VECs; (3) the adhesion rate is higher for pseudocysts than for trophozoites; (4) the adhesin Tf190 is expressed in both forms during interaction; (5) the adhesion process of pseudocysts seems to occur in a contact-dependent manner. Thus, we propose that the pseudocyst stage is not a degenerative form, but a functional life form that is able to interact with and firmly adhere to VECs.
胎儿三毛滴虫是牛泌尿生殖道的一种寄生原生生物。它具有滋养体阶段，即一种运动性的细长形态，在正常群体中构成大多数细胞，以及假包囊阶段，即一种在不利环境条件下出现的不运动的圆形形态。在本报告中，对自然条件下以及通过化学诱导或培养物冷却和升温循环诱导后的假包囊进行了研究。比较了滋养体和假包囊形式的胎儿三毛滴虫黏附阴道上皮细胞（VECs）的能力。通过使用视频增强对比显微镜、扫描和透射电子显微镜以及免疫荧光显微镜技术，我们提供了以下证据：（1）胎儿三毛滴虫在几种不利条件下容易内化鞭毛并形成假包囊；（2）假包囊和滋养体形式的胎儿三毛滴虫都能够黏附VECs；（3）假包囊的黏附率高于滋养体；（4）黏附素Tf190在相互作用期间的两种形式中均有表达；（5）假包囊的黏附过程似乎以接触依赖的方式发生。因此，我们提出假包囊阶段不是一种退化形式，而是一种能够与VECs相互作用并牢固黏附的功能性生命形式。
