Greenspan N S, Dacek D A, Cooper L J
Institute of Pathology, Case Western Reserve University, Cleveland, OH 44106.
J Immunol. 1988 Dec 15;141(12):4276-82.
Previous studies have demonstrated that IgG3 anti-streptococcal group A carbohydrate (GAC) mAb bind to the surfaces of heat-killed, pepsin-digested group A streptococcal cells in an Fc region-dependent cooperative manner. This form of positive cooperative binding of antibody to Ag was hypothesized to result from noncovalent association of Fc regions of antibodies bound close to one another on the Ag surface. Because IgG3 Fc regions are self-aggregating and IgG3 molecules are frequently cryoprecipitable, we have now investigated the effect of temperature on the binding, and cooperative binding, of IgG3 anti-GAC mAb to solid-phase (sp) Ag. The Ag used was a covalent conjugate of N-acetyl-D-glucosamine (GlcNAc; the epitopes on GAC) and BSA. The main findings were: 1) IgG3 anti-GAC mAb bind to sp GlcNAc-BSA to greater extents at lower temperatures, 2) IgM anti-GAC mAb and Fab and F(ab')2 fragments, derived from an IgG3 anti-GAC mAb, bind to sp GlcNAc-BSA to comparable extents at different temperatures, 3) idiotope-expressing IgG3 anti-GAC mAb bind to sp anti-idiotope to comparable extents at different temperatures, and 4) unlabeled IgG3 anti-GAC mAb enhance the binding of radiolabeled IgG3 anti-GAC mAb to sp GlcNAc-BSA, and the degree of this enhancement is greater at lower temperature. These, and additional results, support the conclusion that for some sp Ag the functional affinities of IgG3 antibodies, are influenced by the Fc region in a temperature-dependent manner.
先前的研究表明，IgG3抗A群链球菌碳水化合物（GAC）单克隆抗体以Fc区域依赖性协同方式结合于热灭活、经胃蛋白酶消化的A群链球菌细胞表面。抗体与抗原这种形式的阳性协同结合被推测是由于在抗原表面彼此靠近结合的抗体Fc区域的非共价缔合所致。由于IgG3 Fc区域会自我聚集且IgG3分子经常可冷沉淀，我们现在研究了温度对IgG3抗GAC单克隆抗体与固相（sp）抗原的结合及协同结合的影响。所用抗原是N - 乙酰 - D - 葡萄糖胺（GlcNAc；GAC上的表位）与牛血清白蛋白的共价缀合物。主要发现如下：1）IgG3抗GAC单克隆抗体在较低温度下与sp GlcNAc - BSA的结合程度更高；2）IgM抗GAC单克隆抗体以及源自IgG3抗GAC单克隆抗体的Fab和F(ab')2片段在不同温度下与sp GlcNAc - BSA的结合程度相当；3）表达独特型的IgG3抗GAC单克隆抗体在不同温度下与sp抗独特型的结合程度相当；4）未标记的IgG3抗GAC单克隆抗体增强了放射性标记的IgG3抗GAC单克隆抗体与sp GlcNAc - BSA的结合，且这种增强程度在较低温度下更大。这些以及其他结果支持了以下结论：对于某些sp抗原，IgG3抗体的功能亲和力以温度依赖性方式受Fc区域影响。
