Langone J J, Boyle M D, Borsos T
J Immunol. 1978 Jul;121(1):327-32.
Staphylococcal protein (A (PA) and IgG anti-Forssman immunoglobulin formed complexes that behaved functionally like IgM in their ability to lyse sheep erythrocytes (E) in the presence of whole guinea pig complement (GPC) and to fix purified guinea pig C1. Concanavalin A, a plant lectin that inhibited IgM but not IgG hemolytic activity, inhibited the hemolytic activity of IgG-protein A complexes that behaved like IgM but had no effect on complexes that behaved functionally like IgG. Since Con A is known to bind specifically to glucose and mannose residues, our results suggested that the interaction of protein A with the Fc region of IgG led to exposure of sugar moieties that may participate in complement (C) binding. The production of IgM-like complexes depended on the ratio of protein A to IgG and the empirical formula of these IgM-like complexes was found to be [(IgG)2PA]n. As the ratio of PA to IgG was increased, the resulting complexes tended to behave functionally like IgG but with reduced hemolytic activity and C1 fixing ability. Furthermore, the binding of C1 to EIgG was inhibited by PA and the binding of PA to EIgG was inhibited by C1 indicating that the binding sites for C1 and PA were located near each other or were identical. Our results offer a reasonable explanation for the reported effects of PA or mixtures of PA and IgG in vitro and in vivo.
葡萄球菌蛋白A（PA）与抗福斯曼免疫球蛋白IgG形成复合物，这些复合物在功能上类似于IgM，即在存在全豚鼠补体（GPC）的情况下能够溶解绵羊红细胞（E），并能结合纯化的豚鼠C1。伴刀豆球蛋白A是一种抑制IgM而非IgG溶血活性的植物凝集素，它抑制了表现得像IgM的IgG-蛋白A复合物的溶血活性，但对功能上像IgG的复合物没有影响。由于已知伴刀豆球蛋白A能特异性结合葡萄糖和甘露糖残基，我们的结果表明蛋白A与IgG的Fc区域相互作用导致糖基暴露，这些糖基可能参与补体（C）的结合。IgM样复合物的产生取决于蛋白A与IgG的比例，并且发现这些IgM样复合物的经验式为[(IgG)2PA]n。随着PA与IgG比例的增加，产生的复合物在功能上倾向于像IgG，但溶血活性和C1结合能力降低。此外，PA抑制C1与EIgG的结合，C1抑制PA与EIgG的结合，这表明C1和PA的结合位点彼此靠近或相同。我们的结果为报道的PA或PA与IgG混合物在体外和体内的作用提供了合理的解释。
