Smith R I, Coloma M J, Morrison S L
Department of Microbiology and Molecular Genetics, University of California, Los Angeles 90024.
J Immunol. 1995 Mar 1;154(5):2226-36.
The 18-amino acid carboxyl-terminal tailpiece from IgM (mutp) has now been added to the carboxyl-termini of IgG1, IgG2, IgG3, and IgG4 constant regions to produce recombinant IgM-like IgGs. Polymeric IgGs obtained by this approach possess up to six Fcs and 12 antigen-combining sites, greatly increasing the avidity of their interactions with other molecules. Not surprisingly, the C activity of normally active IgG1 and IgG3 and somewhat less active IgG2 Abs is shown to be dramatically enhanced upon polymerization. The multiple Fcs present in a single molecule apparently allow for more efficient interactions with the multiple C1q heads present in C1, the first component of the classical C cascade. An unexpected result however, is that IgG4, normally devoid of C activity, when polymerized in the same fashion directs C-mediated lysis of target cells almost as effectively as the other polymers. Interestingly though, IgG4mutp does not deplete C activity in a standard consumption assay using soluble Ag. The other gamma mutp isotypes are capable of depleting 100% of the serum lytic ability even in the absence of Ag, whereas IgG4mutp shows no evidence of activity in this assay under any of the conditions tested. Additionally, we show that, in contrast to monomeric IgG, polymeric IgGs bind with very high affinity to Fc gamma receptor II (Fc gamma RII), a low affinity receptor for wild-type antibodies; however, binding to Fc gamma Rl, the high affinity receptor, appears to be unaltered. Finally, the in vivo t1/2 of the gamma mutp proteins is decreased relative to wild-type IgG, apparently because of rapid clearance of the polymeric fraction.
来自IgM的18个氨基酸的羧基末端尾段（mutp）现已添加到IgG1、IgG2、IgG3和IgG4恒定区的羧基末端，以产生重组IgM样IgG。通过这种方法获得的聚合IgG拥有多达6个Fc段和12个抗原结合位点，极大地增加了它们与其他分子相互作用的亲和力。不出所料，正常具有活性的IgG1和IgG3以及活性稍低的IgG2抗体的补体活性在聚合后显著增强。单个分子中存在的多个Fc段显然允许与经典补体级联反应的第一个成分C1中存在的多个C1q头部进行更有效的相互作用。然而，一个意外的结果是，通常缺乏补体活性的IgG4，以相同方式聚合时，几乎与其他聚合物一样有效地指导补体介导的靶细胞裂解。不过有趣的是，IgG4mutp在使用可溶性抗原的标准消耗试验中不会消耗补体活性。其他γmutp亚型即使在没有抗原的情况下也能够耗尽100%的血清溶解能力，而IgG4mutp在任何测试条件下在该试验中均未显示出活性证据。此外，我们表明，与单体IgG相比，聚合IgG以非常高的亲和力与Fcγ受体II（FcγRII）结合，FcγRII是野生型抗体的低亲和力受体；然而，与高亲和力受体FcγRI的结合似乎未改变。最后，γmutp蛋白在体内的半衰期相对于野生型IgG缩短，显然是因为聚合物部分的快速清除。
