Lehto T, Morgan B P, Meri S
Department of Bacteriology and Immunology, Haartman Institute, University of Helsinki, Finland.
Immunology. 1997 Jan;90(1):121-8. doi: 10.1046/j.1365-2567.1997.00120.x.
CD59-antigen (protectin) is a widely distributed glycolipid-anchored inhibitor of complement lysis. CD59 interacts with complement components C8 and C9 during assembly of the membrane attack complex (MAC). To evaluate species specificity of these interactions we have in the present study examined cross-species binding of isolated human and rat CD59 to the terminal complement components C8 and C9. By using primarily soluble CD59 isolated from urine (CD59U) potentially non-specific binding interactions of the phospholipid portion of the membrane forms of CD59 could be avoided. Sucrose density gradient ultracentrifugation analysis showed that human CD59U bound to both human and rat C8 in the SC5b-8 complexes. Similar binding occurred when rat CD59U was used. The degree of binding did not significantly differ between the heterologous and homologous CD59-C8 combinations. C9 from both species inhibited the binding of CD59 to soluble SC5b-8. In ligand blotting analysis human and rat CD59U bound to human and rat C8 alpha gamma-subunit and C9. Binding of human and rat CD59U was stronger to human than rat C9. In plate binding assays the erythrocyte form of CD59 (CD59E) bound to both human and rat C8. Binding of CD59E to heterologous C9 was considerably weaker than to homologous C9. Our results imply that the reciprocal binding sites between C8 and CD59 and to a lesser degree between CD59 and C9 are conserved between human and rat. Interactions of CD59 with the terminal C components are thus species selective but not 'homologously restricted'.
CD59抗原（保护素）是一种广泛分布的糖脂锚定补体溶解抑制剂。在膜攻击复合物（MAC）组装过程中，CD59与补体成分C8和C9相互作用。为了评估这些相互作用的物种特异性，我们在本研究中检测了分离的人源和大鼠源CD59与补体终末成分C8和C9的跨物种结合情况。通过主要使用从尿液中分离的可溶性CD59（CD59U），可以避免CD59膜形式的磷脂部分可能存在的非特异性结合相互作用。蔗糖密度梯度超速离心分析表明，人源CD59U在SC5b-8复合物中与人源和大鼠源C8均有结合。使用大鼠源CD59U时也出现了类似的结合情况。异源和同源CD59-C8组合之间的结合程度没有显著差异。两种物种的C9均抑制CD59与可溶性SC5b-8的结合。在配体印迹分析中，人源和大鼠源CD59U与人源和大鼠源C8αγ亚基及C9均有结合。人源和大鼠源CD59U与人源C9的结合强于与大鼠源C9的结合。在平板结合试验中，红细胞形式的CD59（CD59E）与人源和大鼠源C8均有结合。CD59E与异源C9的结合明显弱于与同源C9的结合。我们的结果表明，C8与CD59之间以及CD59与C9之间程度稍低的相互结合位点在人和大鼠之间是保守的。因此，CD59与补体终末成分的相互作用具有物种选择性，但并非“同源限制”。
