Maturation of the Anitbody Response to a Protein Antigen

9630412 Jemmerson实验动物（如小鼠）的免疫系统接触小化合物后，白细胞最初产生的抗体与化合物的结合较弱，大约一周后，产生的抗体开始更强地与化合物结合，直到达到最大结合能力。这种结合强度的增加，也被称为亲和力，是由编码抗体的基因的变化或突变引起的。虽然还没有明确的证明，但人们相信这个模型也适用于对更复杂分子的免疫反应，包括存在于免疫系统通常会消除的微生物上的蛋白质。在本研究中，该模型将扩展到对细胞色素c蛋白的免疫反应，该蛋白在结构和化学上都得到了很好的表征。在初步工作中，已经确定在用细胞色素c蛋白免疫小鼠后，编码细胞色素c特异性抗体的基因中确实发生了一些突变，这些突变一起导致更高亲和力的抗体结合。现在，每个抗体基因的突变对亲和性的影响将通过单独改变几个位点上的基因来测试。此外，将使用x射线晶体学技术确定与蛋白质结合的抗体复合物的结构，以查明突变是否引起直接接触靶分子（抗原）的抗体的变化，还是间接的影响。本研究中使用的细胞色素c是一种在小鼠中表达的蛋白质。先前的研究发现，用于对这种自身抗原的免疫反应的抗体基因也用于对一种相关蛋白质的反应，并且在反应过程中，抗体对这种蛋白质的亲和力比对自身抗原的亲和力更高。在这项研究中，将确定允许这种转换的抗体基因中的突变。长期以来，人们一直认为这可能是免疫识别外来抗原的一般机制，但目前还没有实验系统来研究它。总之，这项研究将扩展我们对抗体反应亲和成熟的理解，从以前已知的模型化合物研究到更复杂的蛋白质抗原。它也将提供进一步的见解如何免疫识别外来抗原可能启动抗体产生白细胞的反应，可能进化到识别自身抗原。＊＊＊

9630412 Jemmerson Following exposure of the immune system of experimental animals such as mice to small chemical compounds, the antibodies that are produced initially by the white cells bind the compounds weakly, then after about one week, the antibodies that are made begin to bind the compounds more strongly until a maximum binding ability is achieved. This increased strength in binding, also known as affinity, results from changes, or mutations, in the genes that code for the antibodies. Although not yet definitively shown, it is believed that this model also applies to the immune response to more complex molecules including proteins which are present on microorganisms that the immune system normally eliminates. In this study, this model will be extended to the immune response to a protein that has been well-characterized both structurally and chemically, cytochrome c. In preliminary work it has been determined that several mutations in the genes encoding antibodies specific for cytochrome c do occur after immunizing mice with the protein and that together these mutants result in higher affinity antibody binding. Now, the effect of each of the mutations in the antibody genes on the affinity will be tested by altering the genes at each of the several sites independently. In addition, the structure of a complex of an antibody bound to the protein will be determined using the technique of X-ray crystallography to find out whether the mutations cause changes in the antibodies that directly contact the target molecule (antigen) or whether the effects are indirect. The cytochrome c to be employed in this study is a protein expressed in mice. Previously it was found that the antibody genes used in the immune response to this self antigen are also used in response to a related protein and that during the response the antibodies acquire higher affinity for this protein than for the self antigen. In this study, the mutations in the antibody genes that allo w for this conversion will be determined. It has been suggested for a long time that this may be a general mechanism for immunological recognition of foreign antigens but an experimental system to study it has been available. In summary, this study will extend our understanding of affinity maturation in the antibody response from what was previously known in studies of model compounds to a more complex, protein antigen. It will also provide further insight into how immune recognition of foreign antigens may initiate with the response of antibody-producing white blood cells that possibly evolved to recognize self antigens. ***