Czop J, Nussenzweig V
J Exp Med. 1976 Mar 1;143(3):615-30. doi: 10.1084/jem.143.3.615.
Antigen (Ag)-antibody (Ab) aggregates prepared with several different antigens are solubilized by fresh serum at 37 degrees C (complex-release activity of serum or CRA). The rate of solubilization varies in different systems and is strongly influenced by the affinity of Ab for the Ag in the immune precipitate. With a given Ag-Ab precipitate, the maximum amount of complex that can be solubilized by individual sera is independent of the initial concentration of complexes and cannot be increased by prolonged incubation. CRA occurs in the absence of C2 and C4, but not in the absence of C3 and factor B of the properdin pathway. Addition of C2 to C2-deficient serum or C4 to C4-deficient serum enhances CRA. Solubilization does not involve extensive degradation of the complexed antibody, as might be detected by acrylamide gel electrophoresis of released antibody after reduction and alkylation to separate H and L chains. Immune precipitates can also be solubilized by incubation with monovalent fragments (Fab or Fab') of antibodies against determinants of the Ab molecules in the immune precipitate. In contrast, F(ab')2 fragments decrease the solubility of the immune precipitates. In view of these findings, we propose that CRA is mediated by the binding of functionally monovalent C fragments (C3 and C4) onto Ab molecules in the precipitates.
用几种不同抗原制备的抗原（Ag）-抗体（Ab）聚集体在37℃下可被新鲜血清溶解（血清的复合物释放活性或CRA）。溶解速率在不同系统中有所不同，并且受到免疫沉淀物中抗体对抗原亲和力的强烈影响。对于给定的抗原-抗体沉淀物，个体血清可溶解的最大复合物量与复合物的初始浓度无关，且延长孵育时间也无法增加。CRA在缺乏C2和C4的情况下发生，但在缺乏补体旁路途径的C3和B因子时不发生。向C2缺陷血清中添加C2或向C4缺陷血清中添加C4可增强CRA。溶解过程并不涉及复合抗体的广泛降解，这可通过对还原和烷基化后释放的抗体进行丙烯酰胺凝胶电泳以分离重链和轻链来检测。免疫沉淀物也可通过与针对免疫沉淀物中抗体分子决定簇的抗体单价片段（Fab或Fab'）孵育来溶解。相比之下，F(ab')2片段会降低免疫沉淀物的溶解度。鉴于这些发现，我们提出CRA是由功能性单价C片段（C3和C4）与沉淀物中抗体分子结合介导的。
