De Miranda-Santos I K, Campos-Neto A
J Exp Med. 1981 Dec 1;154(6):1732-42. doi: 10.1084/jem.154.6.1732.
Members of the Trypanosomatidae were studied for their ability to acquire host IgG through a possible Fc receptor. A simple rosette test was devised in which the different species and forms of protozoa were mixed with SRBC sensitized with subagglutinating does of IgG, IgM, and F (ab') 2 anti-SRBC, and the pelleted mixture was observed for the number of clumps (rosettes) formed between the parasites and SRBC. Rosettes were formed between parasites and SRBC sensitized with IgG but not with IgM or F(ab')2, indicating the presence of a receptor for IgG Fc. The specificity of this receptor for Fc was confirmed by inhibition experiments with normal rabbit aggregated gammaglobulins or with purified normal rabbit Fc. The receptor is sensitive to treatment with trypsin but regenerates after a short period of incubation (1 h), which indicates that it is synthesized by the parasite itself. Interesting was the observation that only pathogenic members of the Trypanosomatidae formed rosettes with sensitized SRBC. In none of the nonpathogenic forms studied could we demonstrate the Fc receptor. Also important was the finding that freshly isolated blood stream forms of Trypanosoma cruzi from infected mice did not form rosettes. However, after trypsinization, these forms clearly displayed the ability to do so, possibly indicating a previous acquisition of the host IgG by the parasites in the mouse blood stream. These findings point to a possible and important means of parasite evasion of the host immune response by masking their surface with host IgG.
对锥虫科成员通过可能的Fc受体获取宿主IgG的能力进行了研究。设计了一种简单的玫瑰花结试验，将不同种类和形态的原生动物与用亚凝集剂量的IgG、IgM和F(ab')2抗SRBC致敏的SRBC混合，观察沉淀混合物中寄生虫与SRBC之间形成的团块（玫瑰花结）数量。寄生虫与用IgG致敏的SRBC之间形成了玫瑰花结，但与IgM或F(ab')2致敏的SRBC之间未形成，这表明存在IgG Fc受体。用正常兔凝集丙种球蛋白或纯化的正常兔Fc进行抑制实验，证实了该受体对Fc的特异性。该受体对胰蛋白酶处理敏感，但在短时间孵育（1小时）后可再生，这表明它是由寄生虫自身合成的。有趣的是观察到只有锥虫科的致病成员与致敏的SRBC形成玫瑰花结。在我们研究的任何非致病形态中，都未能证明存在Fc受体。同样重要的是发现，从感染小鼠新鲜分离的克氏锥虫血流型不形成玫瑰花结。然而，胰蛋白酶处理后，这些形态明显表现出形成玫瑰花结的能力，这可能表明寄生虫在小鼠血流中先前已获取宿主IgG。这些发现指出了寄生虫通过用宿主IgG掩盖其表面来逃避宿主免疫反应的一种可能且重要的方式。
