Cowan F M, Klein D L, Armstrong G R, Stylos W A, Pearson J W
Biomedicine. 1979 Dec;31(8):220-3.
Staphylococcus aureus protein A (SPA) acts as a mitogen stimulating DNA synthesis and is not antagonistic to the mitogenic activity of other mitogens. The mitogenicity of SPA is due to the protein's multivalent Fc antibody receptors. Partial trypsin digestion of SPA yields monovalent Fc antibody receptors which are not mitogenic. Using a thymidine incorporation assay, results indicated that tryptic digests of SPA added to mouse splenic leukocytes 12 hours after stimulation with either concanavalin A, lipopolysaccaride or SPA suppressed the DNA synthesis normally elicited by these mitogens. SPA was digested with 1% trypsin at pH 8 for varying periods of time. As the digestion time increased from 0 to 60 minutes the mitogenicity of the SPA-trypsin digests decreased indicating cleavage from multivalent to monovalent SPA Fc antibody receptors. The decrease in mitogenicity of the SPA digests was directly associated with increased ability to inhibit DNA synthesis in mitogen stimulated leukocytes. A proposed mechanism for the inhibition of DNA synthesis suggests that SPA-monovalent Fc antibody receptors mimic cellular Fc receptor function thereby influencing cellular gene expression.
金黄色葡萄球菌蛋白 A（SPA）作为一种有丝分裂原，可刺激 DNA 合成，且对其他有丝分裂原的促有丝分裂活性无拮抗作用。SPA 的促有丝分裂作用归因于该蛋白的多价 Fc 抗体受体。对 SPA 进行部分胰蛋白酶消化可产生无促有丝分裂活性的单价 Fc 抗体受体。使用胸苷掺入试验，结果表明，在用伴刀豆球蛋白 A、脂多糖或 SPA 刺激小鼠脾白细胞 12 小时后添加的 SPA 胰蛋白酶消化产物抑制了这些有丝分裂原正常引发的 DNA 合成。在 pH 8 条件下，用 1%胰蛋白酶对 SPA 进行不同时间的消化。随着消化时间从 0 分钟增加到 60 分钟，SPA - 胰蛋白酶消化产物的促有丝分裂活性降低，表明从多价 SPA Fc 抗体受体裂解为单价。SPA 消化产物促有丝分裂活性的降低与抑制有丝分裂原刺激的白细胞中 DNA 合成的能力增加直接相关。一种关于 DNA 合成抑制的机制表明，SPA - 单价 Fc 抗体受体模拟细胞 Fc 受体功能，从而影响细胞基因表达。
