Pearlstein E, Sorvillo J, Gigli I
J Immunol. 1982 May;128(5):2036-9.
Fibronectin is a normal plasma protein that enhances reticuloendothelial system functioning, and may participate in immune complex clearance. The interaction of 125I-fibronectin with human C1 and C1q in vitro was investigated by employing a highly reproducible solid-phase binding assay in microtiter wells. We demonstrated that although fibronectin does not bind to antigen-antibody complex (BSA-anti-BSA) or immune complexes containing C1, a 20-fold increase in binding was obtained when the complexes contained C1q alone. In the absence of antigen-antibody complexes, fibronectin binds to the C1q fixed to the wells in a dose-response fashion but not to intact C1. C1q in the fluid phase inhibits 85% of the fibronectin binding to immobilized C1q. The amount of fibronectin bound by immobilized C1q or gelatin is approximately equal. The binding of fibronectin to C1q could be inhibited by the restoration of C1r + C1s to the C1 macromolecular complex before the addition of fibronectin. The inhibition was dependent on the concentration of C1r + C1s and achieved a maximum of 70% at 100 micrograms/ml. This inhibition could be reversed by the removal of C1r and C1s subunits with EDTA or C1 inhibitor. Digestion of C1q with pepsin resulted in an 85% loss of fibronectin binding. It therefore appears that at least one site of fibronectin binding to C1q is in the globular portion of this complement component.
纤连蛋白是一种正常的血浆蛋白，可增强网状内皮系统的功能，并可能参与免疫复合物的清除。通过在微量滴定孔中采用高度可重复的固相结合试验，研究了¹²⁵I-纤连蛋白与人C1和C1q在体外的相互作用。我们证明，尽管纤连蛋白不与抗原-抗体复合物（牛血清白蛋白-抗牛血清白蛋白）或含有C1的免疫复合物结合，但当复合物仅含有C1q时，结合增加了20倍。在没有抗原-抗体复合物的情况下，纤连蛋白以剂量反应方式与固定在孔中的C1q结合，但不与完整的C1结合。液相中的C1q可抑制85%的纤连蛋白与固定化C1q的结合。固定化C1q或明胶结合的纤连蛋白量大致相等。在添加纤连蛋白之前，将C1r + C1s恢复到C1大分子复合物中可抑制纤连蛋白与C1q的结合。这种抑制作用取决于C1r + C1s的浓度，在100微克/毫升时达到最大抑制率70%。用乙二胺四乙酸（EDTA）或C1抑制剂去除C1r和C1s亚基可逆转这种抑制作用。用胃蛋白酶消化C1q导致纤连蛋白结合损失85%。因此，似乎纤连蛋白与C1q结合的至少一个位点位于该补体成分的球状部分。
