Structural analysis of regulatory factors of complement on erythrocyte membranes

红细胞与异种补体溶血，但与同源补体不溶血；这种证据被称为补体的同源限制性。有人认为，一种未知的膜因子是造成这种限制的原因。我试图找出原因。DAF, C3， c5转换酶的衰变加速因子，在本项目开始阶段似乎是第一候选，因为DAF调节红细胞的补体活化。采用改进的方法从兔红细胞中分离DAF。家兔和人daf均表现出较弱的同源限制性。因此，我得出结论，DAF不是造成这种限制的主要因素。HRF是1986年报道的一种人红细胞膜攻击复合物（MAC）形成抑制剂，被选为第二个候选物。然而，由于检测方法不可靠，无法通过原论文中描述的方法分离HRF。我开发了一种新的检测mac形成抑制剂的可靠方法，并分离出一个分子量为18Kd的新因子，命名为MACIF。MACIF对人类补体表现出有效的抑制活性，但对豚鼠补体没有抑制活性，这表明可能是限制的候选物。我成功克隆了MACIF mRNA的cDNA，并确定了MACIF的完整氨基酸序列。

Erythrocytes are hemolyzed with hetrologous complement, but not with homologous one; this evidence is called homologous restriction of complement. It has been suggested that an unidentified membrane factor is responsible for the restriction.I tried to identify the factor. DAF, decay-accerelating factor of C3,C5-convertase, seemed to be the first candidate at the starting stage of this project, because DAF regulates the complement activation on erythrocytes. DAF was isolated from rabbit erythrocytes by an improved method applied. Both of rabbit and human DAFs showed only a weak homologous restriction. Thus, I concluded that DAF is not a major factor responsible for the restriction.HRF, an inhibitor of membrane attack complex(MAC)-formation on human erythrocytes reported in 1986, was chosen for the second candidate. HRF, however, could not be isolated by the method described in the original paper, because the assay method was unreliable. I developed a new reliable method for detecting the inhibitor of MAC-formation, and isolated a new factor of a molecular weight 18Kd, designated MACIF. MACIF showed a potent inhibitory activity to human complement, but not to guinea pig one indicating a likely candidate responsible for the restriction. I succeeded in cDNA cloning of MACIF mRNA and determined the complete amino acid sequence of MACIF.