Kaplan A V, Quimby F W
Vet Immunol Immunopathol. 1983 Apr;4(3):307-17. doi: 10.1016/0165-2427(83)90042-9.
A cell wall protein from Staphylococcus aureus, Protein A, (SpA) has been shown to have the ability to bind the Fc region of most mammalian IgG molecules. This study uses this unusual property as the basis for a quantitative assay for erythrocyte (RBC) bound antibodies. Test serum is incubated in a suspension of normal RBC's. The cells are then washed and incubated with 125Iodine-labeled SpA (125I-SpA). After incubation cells are pelleted and bound radiolabeled SpA counted. This procedure has been performed using canine anti-goat RBC (DagRBC) serum and human anti-D serum (positive controls) to establish the kinetics of the SpA reaction in the above system. The results indicate that SpA binds to red blood cells as a function of membrane bound antibody. RBC's incubated with indirect Coombs positive sera bound 42.6% and 43.3% of the 125I-SpA, as compared to 19.2%, the upper limit of the 95% confidence interval (n = 9) for normal sera. Furthermore, significant binding was observed for certain indirect Coombs negative (direct Coombs positive) sera indicating that the SpA assay is more sensitive than the indirect Coombs test. The SpA system should provide the clinician with an inexpensive, sensitive, quantitative assay for the diagnosis of warm agglutinin autoimmune hemolytic anemia, as well as other autoimmune disorders involving membrane bound IgG.
金黄色葡萄球菌的一种细胞壁蛋白A蛋白（SpA）已被证明能够结合大多数哺乳动物IgG分子的Fc区域。本研究利用这一独特特性，建立了一种定量检测红细胞（RBC）结合抗体的方法。将待测血清与正常红细胞悬液孵育。然后洗涤细胞，并与125碘标记的SpA（125I-SpA）孵育。孵育后，将细胞离心沉淀，对结合的放射性标记SpA进行计数。使用犬抗山羊红细胞（DagRBC）血清和人抗-D血清（阳性对照）进行该操作，以确定上述系统中SpA反应的动力学。结果表明，SpA与红细胞的结合是膜结合抗体的函数。与正常血清95%置信区间上限（n = 9）的19.2%相比，用间接抗人球蛋白试验阳性血清孵育的红细胞结合了42.6%和43.3%的125I-SpA。此外，某些间接抗人球蛋白试验阴性（直接抗人球蛋白试验阳性）血清也观察到明显的结合，这表明SpA检测比间接抗人球蛋白试验更敏感。SpA系统应为临床医生提供一种廉价、敏感的定量检测方法，用于诊断温抗体型自身免疫性溶血性贫血以及其他涉及膜结合IgG的自身免疫性疾病。
