Rodman T C, Pruslin F H, Chauhan Y, To S E, Winston R
Department of Cell Biology and Anatomy, Cornell University Medical College, New York, New York 10021.
J Exp Med. 1988 Mar 1;167(3):1228-46. doi: 10.1084/jem.167.3.1228.
We have identified a set of natural IgM antibodies in human serum that are reactive with protamines, a class of low molecular weight basic nucleoproteins that are synthesized de novo in the postpubertal testis and are unique to sperm. Those antibodies were detected by ELISA in significant titer in all of 100 sera of normal adult males and females and in 26 of 28 sera of normal pediatrics aged 7 d to 2 yr. Commonality between the protamine-reactive IgM antibodies of pediatric and adult sera was established by the demonstration of similarity in antigen recognition and reaction kinetics. Therefore, the role of protamines as either immunogenic stimulus or antigenic target of that set of natural antibodies is not likely. The antigenic site recognized by the protein-reactive serum IgM antibodies was characterized by comparison with the pattern of antigen recognition by a monoclonal antibody to human sperm protamines (HPmAb). By the use of synthetic peptides simulating the amino acid sequences of various segments of human protamine 2 and of polyarginine, polylysine, and histones as test antigens, the principle characteristic of the antigenic site recognized by both HPmAb and the serum IgM antibodies was inferred to be that of clustered arginyl residues with an apparent minimum requirement of four arginyl residues, including a triplet, within a six residue piece; for both, the reaction was shown to be not dependent upon charge attraction. A series of immunoabsorption procedures indicated that the protamine-reactive serum IgM antibodies are a discrete set with a high order of specificity. A search of protein data bases revealed that the putative minimum epitope is present in four or five human autogenous proteins, all moieties of the immune system, and in a number of viral proteins. The possible implications of those findings are discussed in the light of early hypotheses concerning the origin and function of natural antibodies and the many recent reports of identification of natural antibodies in normal human sera. The set of natural antibodies identified in this study may be unique or may represent a class of antibodies present in the repertoire that, by virtue of the obscurity of their origin or function, have not been previously or extensively recognized.
我们在人血清中鉴定出一组天然IgM抗体，它们可与鱼精蛋白发生反应。鱼精蛋白是一类低分子量碱性核蛋白，在青春期后的睾丸中从头合成，且是精子所特有的。通过酶联免疫吸附测定法（ELISA），在100名正常成年男性和女性的所有血清以及28名年龄在7天至2岁的正常儿科患者的26份血清中均检测到了具有显著滴度的这些抗体。通过证明儿科和成人血清中与鱼精蛋白反应的IgM抗体在抗原识别和反应动力学方面的相似性，确立了它们之间的共性。因此，鱼精蛋白作为该组天然抗体的免疫原性刺激物或抗原靶点的作用不太可能。通过与抗人精子鱼精蛋白单克隆抗体（HPmAb）的抗原识别模式进行比较，对蛋白质反应性血清IgM抗体识别的抗原位点进行了表征。通过使用模拟人鱼精蛋白2各个片段氨基酸序列的合成肽以及聚精氨酸、聚赖氨酸和组蛋白作为测试抗原，推断出HPmAb和血清IgM抗体识别的抗原位点的主要特征是聚集的精氨酰残基，在六个残基片段中明显至少需要四个精氨酰残基，包括一个三联体；对于两者而言，反应均显示不依赖于电荷吸引。一系列免疫吸附程序表明，与鱼精蛋白反应的血清IgM抗体是一组具有高度特异性的离散抗体。对蛋白质数据库的搜索显示，推定的最小表位存在于四种或五种人类自身蛋白中，所有这些都是免疫系统的组成部分，并且还存在于许多病毒蛋白中。根据关于天然抗体起源和功能的早期假说以及最近许多关于在正常人血清中鉴定天然抗体的报道，讨论了这些发现的可能影响。在本研究中鉴定出的这组天然抗体可能是独特的，或者可能代表了抗体库中存在的一类抗体，由于其起源或功能不明确，以前未被广泛认识。
