Morris J E, Egan M L, Todd C W
Cancer Res. 1975 Jul;35(7):1804-8.
In order to assess the potency of antigenic fragments of carcinoembryonic antigen (CEA) in the radioimmune assay; it is necessary to know whether the high affinity of goat anti-CEA antibody (which makes possible the detection of as little as 10--11M CEA) is due to bivalent binding of the CEA molecule. Immunoglobulin G and the F(ab')2 and Fab fragments derived from it were prepared from an anti-CEA serum and tested for their abioity to bind CEA. Equivalent concentrations of binding sites of the bivalent F(ab)2 and univalent Fab fragments of anti-CEA were identical to the immunoglobulin G fraction in the standard inhibition curve. Fragments of CEA obtained by trypsin digestion produced equivalent inhigition curves when tested with either immunoglobulin G, F(ab')2, or Fab". This, increased avidity due to bivalent binding to a single antigen molecule cannot be invoked to explain the sensitivity observed in the CEA assay. This high sensitivity implicates the protein rather than the carbohydrate as an important part of the antigenic determinant(s) of CEA.
为了评估癌胚抗原（CEA）抗原片段在放射免疫测定中的效价；有必要了解山羊抗CEA抗体的高亲和力（这使得检测低至10-11M的CEA成为可能）是否归因于CEA分子的二价结合。从抗CEA血清中制备免疫球蛋白G及其衍生的F(ab')2和Fab片段，并测试它们结合CEA的能力。在标准抑制曲线中，抗CEA的二价F(ab)2和单价Fab片段的等效结合位点浓度与免疫球蛋白G组分相同。用胰蛋白酶消化获得的CEA片段，在用免疫球蛋白G、F(ab')2或Fab"测试时产生等效的抑制曲线。因此，不能用与单个抗原分子的二价结合导致的亲和力增加来解释CEA测定中观察到的灵敏度。这种高灵敏度表明蛋白质而非碳水化合物是CEA抗原决定簇的重要组成部分。
