Erickson P R, Herzberg M C
J Immunol. 1987 May 15;138(10):3360-6.
The basis of similarities in the mechanism of human platelet aggregation induced by soluble collagen and the dental plaque bacterium Streptococcus sanguis was analyzed. Structural and functional comparisons were made by using molecular probes, including rabbit antibody fractions reactive with components on S. sanguis and a synthetic, collagen-like octapeptide mimicking segments from cyanogen bromide fragments 6 and 4 of types I and III collagen, respectively. When platelets were pretreated with tryptic peptides or class II antigen of S. sanguis or with the synthetic, collagen-like octapeptide, the onset of aggregation in response to S. sanguis and collagen was prolonged. When compared to other peptides of similar size and charge, the collagen-like peptide's action towards platelets was shown to be selective. Indeed, absorption of antiserum to S. sanguis cells with particulate type I collagen removed specificities directed at a single S. sanguis antigen. These observations suggested that a common platelet-interactive immunodeterminant on soluble types I and III collagens, particulate type I collagen, and S. sanguis cells was present. Selective inhibition by antibody was used to show structural similarities between the S. sanguis surface proteins and collagen. When either agonist was pretreated with anti-S. sanguis IgG or Fab fragments, the lag time to onset of platelet aggregation was increased. Greater increases in the lag time to aggregation was seen when S. sanguis cells or collagen were pretreated with anti-S. sanguis IgG or Fab fragments made relatively specific for the class II antigen. Neutralization of the platelet-interactive action of the octapeptide by anti-S. sanguis antibody fractions showed that the immunodeterminant common to S. sanguis and collagen triggered platelets in plasma to aggregate. Although the anti-S. sanguis antibodies could inhibit fibrillogenesis, this action was apparently independent of interactions with platelets. In contrast, S. sanguis could bind or adhere to platelets by different determinants. Our data suggest that platelets have at least two distinct sites that bind collagen or S. sanguis. One of these may be a common site for collagen and S. sanguis agonists.
分析了可溶性胶原蛋白和牙菌斑细菌血链球菌诱导人血小板聚集机制的相似性基础。使用分子探针进行了结构和功能比较，包括与血链球菌成分反应的兔抗体片段，以及分别模拟I型和III型胶原蛋白溴化氰片段6和4的合成类胶原八肽。当血小板用胰蛋白酶肽或血链球菌的II类抗原或合成类胶原八肽预处理时，对血链球菌和胶原蛋白的聚集反应起始时间延长。与其他大小和电荷相似的肽相比，类胶原肽对血小板的作用具有选择性。实际上，用颗粒状I型胶原蛋白吸收抗血链球菌细胞的抗血清可去除针对单一血链球菌抗原的特异性。这些观察结果表明，可溶性I型和III型胶原蛋白、颗粒状I型胶原蛋白和血链球菌细胞上存在共同的血小板相互作用免疫决定簇。利用抗体的选择性抑制来显示血链球菌表面蛋白与胶原蛋白之间的结构相似性。当任何一种激动剂用抗血链球菌IgG或Fab片段预处理时，血小板聚集起始的延迟时间会增加。当血链球菌细胞或胶原蛋白用对II类抗原相对特异的抗血链球菌IgG或Fab片段预处理时，聚集延迟时间增加得更多。抗血链球菌抗体片段对八肽血小板相互作用作用的中和表明，血链球菌和胶原蛋白共有的免疫决定簇触发血浆中的血小板聚集。虽然抗血链球菌抗体可抑制纤维蛋白生成，但这种作用显然与与血小板的相互作用无关。相反，血链球菌可通过不同的决定簇与血小板结合或粘附。我们的数据表明，血小板至少有两个不同的位点可结合胶原蛋白或血链球菌。其中一个可能是胶原蛋白和血链球菌激动剂的共同位点。
