Fig8-3 The classical illustration of the antigen-antibody reaction in vitro is the precipitin reaction. As increasing concentrations of antigen are added to a constant amount of antibody, the amount of immune complex precipitated rises and then falls. The precipitin curve generated in this way has three zones Antibody excess zone: the amount of antigen is insufficient to react with and precipitate all the antibody present; thus free antibody can be detected in the supernatant. Equivalence zone: the added antigen is sufficient to combine with and precipitate all the antibody present and neither free antigen nor antibody can be detected in the supernatant Antigen excess zone: the amount of antigen exceeds that required to bind all the antibody, and this leads to a reduction in the amount of antibody precipitated. This fall is due to the solubilization of the antigen-antibody complexes by the excess antigen. The extent to which this phenomenon occurs varies with different antibodies and with the species from hich the antibody is derived. 抗原与抗体的结合,在一定浓度范围内,只有当两者分子比例合适时,才出现可见反应 以沉淀反应为例,分子比例合适,沉淀物产生既快又多,体积大。分子比例不合适时,沉淀 物产生少,体积小,或不产生沉淀物。对参与沉淀反应的抗原一抗体系统可进行定量测定 即将抗体置于一系列的试管中,加入不同量的相应纯抗原,混合后,观察所发生的反应,对 沉淀物可作精确定量。若抗体量固定不变,抗原量逐渐增加,可观察沉淀反应中抗原、抗体 分子的比例关系。由图83可见有三个抗原抗体相互作用的区带,1)抗体过剩区( antibody excess zone):加入抗原量少,则沉淀物少,上清液中有游离的抗体( free antibody)。2)平 衡区( equivalence zone):抗原量逐渐增加,沉淀物也逐渐增多,直到抗原、抗体比例最佳 时,则出现连续而稳定的抗原一抗体晶格( lattice)沉淀,此时沉淀物中抗原抗体复合物量 最多,上清中测不到游离的抗原( free antigen)或抗体,此为平衡区或等价带。3)抗原过 剩区( antigen excess zone):抗原量继续增加,所有抗体均与抗原结合,此时上清液中可测 出游离的抗原,在此区带中,由于抗原过剩,则形成可溶性抗原抗体复合物,因而沉淀反应 部分或完全被抑制 抗体与抗原的结合是否出现可见反应,则与抗原抗体的胶体特性及极性基吸附作用有 关。抗体球蛋白和抗原(大多为蛋白质、也有为多糖、类脂或其它化合物)在溶液中均属于 胶体物质,带有电荷。胶体粒子又有许多强极性基(如蛋白质的羧基、氨基及肽链等),它 们与水有很强的亲和力,以致在粒子外周构成水层,称为亲水胶体。胶体粒子不带水层者, 称为疏水胶体。胶体粒子的稳定性即依赖于所带的水层及电荷,其中亲水胶体的稳定性较高。159 Fig8-3 The classical illustration of the antigen-antibody reaction in vitro is the precipitin reaction. As increasing concentrations of antigen are added to a constant amount of antibody, the amount of immune complex precipitated rises and then falls. The precipitin curve generated in this way has three zones: Antibody excess zone: the amount of antigen is insufficient to react with and precipitate all the antibody present; thus free antibody can be detected in the supernatant. Equivalence zone: the added antigen is sufficient to combine with and precipitate all the antibody present and neither free antigen nor antibody can be detected in the supernatant. Antigen excess zone: the amount of antigen exceeds that required to bind all the antibody, and this leads to a reduction in the amount of antibody precipitated. This fall is due to the solubilization of the antigen-antibody complexes by the excess antigen. The extent to which this phenomenon occurs varies with different antibodies and with the species from which the antibody is derived. 抗原与抗体的结合，在一定浓度范围内，只有当两者分子比例合适时，才出现可见反应。 以沉淀反应为例，分子比例合适，沉淀物产生既快又多，体积大。分子比例不合适时，沉淀 物产生少，体积小，或不产生沉淀物。对参与沉淀反应的抗原―抗体系统可进行定量测定， 即将抗体置于一系列的试管中，加入不同量的相应纯抗原，混合后，观察所发生的反应，对 沉淀物可作精确定量。若抗体量固定不变，抗原量逐渐增加，可观察沉淀反应中抗原、抗体 分子的比例关系。由图 8-3 可见有三个抗原抗体相互作用的区带，1）抗体过剩区（antibody excess zone）：加入抗原量少，则沉淀物少，上清液中有游离的抗体（free antibody）。2）平 衡区（equivalence zone）：抗原量逐渐增加，沉淀物也逐渐增多，直到抗原、抗体比例最佳 时，则出现连续而稳定的抗原―抗体晶格（lattice）沉淀，此时沉淀物中抗原抗体复合物量 最多，上清中测不到游离的抗原（free antigen）或抗体，此为平衡区或等价带。3）抗原过 剩区（antigen excess zone）：抗原量继续增加，所有抗体均与抗原结合，此时上清液中可测 出游离的抗原，在此区带中，由于抗原过剩，则形成可溶性抗原抗体复合物，因而沉淀反应 部分或完全被抑制。 抗体与抗原的结合是否出现可见反应，则与抗原抗体的胶体特性及极性基吸附作用有 关。抗体球蛋白和抗原（大多为蛋白质、也有为多糖、类脂或其它化合物）在溶液中均属于 胶体物质，带有电荷。胶体粒子又有许多强极性基（如蛋白质的羧基、氨基及肽链等），它 们与水有很强的亲和力，以致在粒子外周构成水层，称为亲水胶体。胶体粒子不带水层者， 称为疏水胶体。胶体粒子的稳定性即依赖于所带的水层及电荷，其中亲水胶体的稳定性较高