Mason D W, Williams A F
Biochem J. 1980 Apr 1;187(1):1-20. doi: 10.1042/bj1870001.
The reaction kinetics of 125I-labelled mouse monoclonal antibodies binding to three cell-surface antigens of rat thymocytes (Thy-1.1, W3/25) were studied. The differences between bivalent and univalent interactions were determined by using antibody in the F(ab')2 or Fab' form and by using antigen in polymeric or monomeric forms. Association rate constants (k+1), dissociation rate constants (k-1) and equilibrium constants were determined. Also, the dissociation kinetics of rabbit antibodies against rat Thy-1 antigen were studied. The major findings were as follows. (i) With F(ab')2 antibody there was no simple relationship between antigen density at the cell surface and extent of bivalent binding. Extensive univalent binding was observed unless the antibody had a high k-1 for the univalent interaction, in which case all binding was bivalent. (ii) k+1 values were similar for F(ab')2 or Fab' antibody, and for the different antibodies were in the range 0.8 x 10(5)--1.1 x 10(6) M-1.s-1. These differences were sufficient to affect the interpretation of serological assays with the different antibodies. (iii) Antibody bound bivalently dissociated much more slowly than that bound univalently. However, the k-1 values for the univalently bound antibody were sufficiently low in most cases that the lifetime of the univalent complex was similar to or greater than the time needed for the assay. Thus the results could be interpreted on the basis of irreversible reactions. The overall conclusion from the study is that for an understanding of the binding of antibody to cell-surface antigens the kinetics of the interaction are of major importance and theories based on equilibrium binding are inappropriate.
研究了125I标记的小鼠单克隆抗体与大鼠胸腺细胞的三种细胞表面抗原（Thy-1.1、W3/25）结合的反应动力学。通过使用F(ab')2或Fab'形式的抗体以及聚合或单体形式的抗原，确定了二价和单价相互作用之间的差异。测定了缔合速率常数（k+1）、解离速率常数（k-1）和平衡常数。此外，还研究了兔抗大鼠Thy-1抗原抗体的解离动力学。主要发现如下：（i）对于F(ab')2抗体，细胞表面抗原密度与二价结合程度之间没有简单的关系。除非抗体对单价相互作用具有高的k-1，否则会观察到广泛的单价结合，在这种情况下所有结合都是二价的。（ii）F(ab')2或Fab'抗体的k+1值相似，不同抗体的k+1值在0.8×10(5) - 1.1×10(6) M-1·s-1范围内。这些差异足以影响用不同抗体进行血清学检测的解释。（iii）二价结合的抗体解离比单价结合的抗体慢得多。然而，在大多数情况下，单价结合抗体的k-1值足够低，以至于单价复合物的寿命与检测所需时间相似或更长。因此，结果可以基于不可逆反应来解释。该研究的总体结论是，为了理解抗体与细胞表面抗原的结合，相互作用的动力学至关重要，基于平衡结合的理论是不合适的。
