Andrews N W, Hong K S, Robbins E S, Nussenzweig V
Department of Pathology, New York University Medical Center, New York 10016.
Exp Parasitol. 1987 Dec;64(3):474-84. doi: 10.1016/0014-4894(87)90062-2.
The origin of Trypanosoma cruzi slender and broad forms found in the circulation of the mammalian host has remained obscure and, unlike what has been proposed for African trypanosomes, no precise form-function relationship has been ascribed to them. We show here that parasites circulating in the blood of infected animals display a high degree of polymorphism. Around 10% of the forms found circulating in mice during the acute phase of infection were amastigotes, and the other 90% included slender and broad trypomastigotes and intermediate forms between amastigotes and trypomastigotes. Slender trypomastigotes, from blood or cell culture, undergo extracellularly morphological rearrangements in which the parasites become gradually broader and transform into amastigotes. By scanning electron microscopy a progressive internalization of the flagellum and reorganization of the cell shape in a helical fashion were observed in parasites undergoing transformation. After 48 hr of extracellular incubation the parasite population consisted exclusively of amastigotes with a short protruding flagellum. The morphological changes were associated with the expression of different surface antigens defined by monoclonal antibodies: the trypomastigote-specific antigens Ssp-1 (a 100-120-150-Mr glycoprotein), Ssp-2 (a 70-Mr glycoprotein), Ssp-3 (undefined), and Ssp-4, an amastigote-specific surface antigen. Ssp-4 was also detected on intracellular amastigotes (in vitro and in vivo). We conclude that trypomastigotes are programmed to develop into amastigotes whether or not they enter cells, and that the differentiation can occur in the blood of the vertebrate host. These findings raise some questions regarding conventional views on the life cycle of T. cruzi.
在哺乳动物宿主体循环中发现的克氏锥虫细长型和宽阔型的起源一直不明，而且与非洲锥虫不同，尚未明确它们的形态与功能之间存在何种精确关系。我们在此表明，感染动物血液中循环的寄生虫呈现出高度的多态性。在感染急性期的小鼠血液中发现的约10%的形态为无鞭毛体，另外90%包括细长型和宽阔型的锥鞭毛体以及无鞭毛体与锥鞭毛体之间的中间形态。来自血液或细胞培养的细长型锥鞭毛体在细胞外会发生形态重排，寄生虫会逐渐变宽并转变为无鞭毛体。通过扫描电子显微镜观察到，正在转变的寄生虫中鞭毛逐渐内化，细胞形状呈螺旋状重新排列。在细胞外孵育48小时后，寄生虫群体完全由带有短突出鞭毛的无鞭毛体组成。这些形态变化与单克隆抗体所定义的不同表面抗原的表达相关：锥鞭毛体特异性抗原Ssp-1（一种分子量为100 - 120 - 150的糖蛋白）、Ssp-2（一种分子量为70的糖蛋白）、Ssp-3（未明确）以及无鞭毛体特异性表面抗原Ssp-4。在细胞内的无鞭毛体（体外和体内）也检测到了Ssp-4。我们得出结论，锥鞭毛体无论是否进入细胞都被编程发育为无鞭毛体，并且这种分化可以在脊椎动物宿主的血液中发生。这些发现对克氏锥虫生命周期的传统观点提出了一些疑问。
