Syphilis Division of the Department of Medicine, Johns Hopkins Medical School, Baltimore.
J Exp Med. 1930 Oct 31;52(5):717-38. doi: 10.1084/jem.52.5.717.
A. The lipoid antigen used in the serum diagnosis of syphilis, when colloidally dispersed in water, forms a relatively stable amphoteric suspension with predominantly hydrophilic properties. Although the colloidal particles flocculate at their isoelectric point (pH 1.9), in more alkaline reaction the negative surface potential prevents their cohesion and must be depressed to 1 to 5 millivolts before visible flocculation is obtained, indicating a very slight affinity between the colloidal particles. The amount of electrolyte necessary to depress this surface charge below its critical value decreases somewhat with increasing concentration of the sol, but is uniformly large: in a suspension containing 0.04 per cent lipoid, 1 M univalent and 1/40 M bivalent cation are the coagulation values. B. In normal serum, hydrophilic protein is adsorbed, forming a protective film around the individual lipoid particles, with a corresponding change in the cataphoretic potential and the isoelectric point towards those of serum protein, the degree of shift depending upon the extent of the adsorbed film. The critical potential, however, is not affected, and the lipoid remains as stable away from its isoelectric point as in the absence of serum. The water-soluble film of unchanged protein is readily removed by washing, and does not prevent the subsequent combination of the underlying lipoid with the specific component of syphilitic serum. C. When the lipoid antigen is added to syphilitic serum, in addition to this loose adsorption of normal protein it combines more or less irreversibly with a specifically altered fraction of the serum globulin (reagin), demonstrable in the washed precipitate both chemically and by sensitization experiments. Like adsorbed normal serum, it depresses the surface potential and causes a shift in the isoelectric point; but there the similarity ends. The reagin-globulin is rendered water-insoluble by its firm combination with the lipoid, exactly as any antibody is denatured upon combination with its specific antigen (bacteria, red cells, or dissolved protein). The hydrophobic films of reagin have five times as great an affinity for each other as the original lipoid surfaces; accordingly, the critical potential is raised from its original value of 1 to 5 millivolts to 10 to 15 millivolts, that of particles of denatured globulin or of any antigen-antibody complex, and relatively small quantities of electrolytes (at serum pH, cations) suffice to depress the stabilizing potential below this critical level, with resultant aggregation and flocculation. In brief, a specific globulin combines with the colloidal particles of the antigen, conferring upon them the unstable properties of a suspension of denatured protein. Like the antibody film on bacteria, or red cells, and unlike normal adsorbed protein, the reagin globulin on the lipoid particle can adsorb ("fix") complement. When this protein film is destroyed by heat-coagulation, the complement-fixing property is lost; concomitantly, the specific groups of the lipoid having been freed from the closely adherent reagin, the antigen becomes again active, able to react with more syphilitic serum. These changes in the properties of reagin globulin upon its combination with the lipoid antigen (denaturation) are in every sense analogous to those effected in any antibody by its specific antigen, and are probably due to the same, as yet unknown, factors. It has been suggested for bacterial and red cell "agglutinins" and protein "precipitins," that the groups of the antibody determining its specificity are also those which endow it with its hydrophilic properties; when these combine with antigen, residual free hydrophobic groups determine the surface properties of the complex. The same tentative hypothesis may be offered for the denaturation of reagin globulin by the lipoid antigen. The complete analogy between the flocculation reactions for syphilis and the so-called specific reactions (bacterial and red cell agglutination; protein precipitation) suggests that like agglutinins, precipitins, etc., reagin globulin represents an antibody response to products of infection.
A. 梅毒血清诊断中使用的类脂抗原，在胶体分散于水中时，形成具有主要亲水性质的相对稳定的两性悬浮液。虽然胶体颗粒在等电点（pH1.9）时絮凝，但在更碱性的反应中，负表面电位阻止它们的凝聚，必须将其表面电荷压低到 1 至 5 毫伏以下，才能获得可见的絮凝，表明胶体颗粒之间存在非常微弱的亲和力。将这种表面电荷压低到其临界值以下所需的电解质的量随着溶胶浓度的增加而略有减少，但均匀地很大：在含有 0.04%类脂的悬浮液中，1M 单价阳离子和 1/40M 二价阳离子是凝聚值。
B. 在正常血清中，亲水蛋白被吸附，在各个类脂颗粒周围形成一层保护性薄膜，相应地改变了电泳电位和等电点，使其更接近血清蛋白的等电点，这种位移程度取决于吸附膜的程度。然而，临界电位不受影响，并且类脂在远离等电点的情况下与血清中的特异性成分保持稳定，就像在没有血清的情况下一样。未改变的蛋白质的水溶性薄膜很容易通过洗涤去除，并且不会阻止随后与梅毒血清的特异性成分结合的类脂。
C. 当类脂抗原添加到梅毒血清中时，除了这种正常蛋白的松散吸附外，它还或多或少地不可逆地与血清球蛋白（反应素）的特异性改变部分结合，这在洗涤后的沉淀物中无论是通过化学方法还是通过敏化实验都可以证明。像吸附的正常血清一样，它会降低表面电位并导致等电点发生偏移；但这就是相似之处的终点。反应素球蛋白通过与类脂的牢固结合而变得不溶于水，就像任何抗体与特异性抗原（细菌、红细胞或溶解蛋白）结合时一样会变性。反应素的疏水性薄膜彼此之间的亲和力是原始类脂表面的五倍；因此，临界电位从原始的 1 至 5 毫伏升高到 10 至 15 毫伏，即变性球蛋白或任何抗原抗体复合物的颗粒的电位，并且相对少量的电解质（在血清 pH 值下，阳离子）足以将稳定电位压低到这个临界水平以下，导致聚集和絮凝。简而言之，一种特异性球蛋白与抗原的胶体颗粒结合，赋予它们变性蛋白质悬浮液的不稳定性质。像细菌或红细胞上的抗体膜一样，并且与正常吸附的蛋白质不同，类脂颗粒上的反应素球蛋白可以吸附（“固定”）补体。当这种蛋白质膜被热凝聚破坏时，固定补体的性质就会丧失；同时，由于紧密附着的反应素从紧密附着的类脂中释放出来，抗原再次变得活跃，能够与更多的梅毒血清反应。反应素球蛋白与类脂抗原结合（变性）后其性质的这些变化在所有意义上都与特定抗原对任何抗体产生的变化相似，并且可能是由于相同的、尚未可知的因素。有人提出，对于细菌和红细胞“凝集素”和蛋白质“沉淀素”，决定抗体特异性的基团也是赋予其亲水性的基团；当这些基团与抗原结合时，残留的游离疏水性基团决定了复合物的表面性质。对于反应素球蛋白通过类脂抗原的变性，也可以提出同样的试探性假设。梅毒和所谓的特异性反应（细菌和红细胞凝集；蛋白质沉淀）的絮凝反应之间的完全相似性表明，像凝集素、沉淀素等一样，反应素球蛋白代表对感染产物的抗体反应。
