Medof M E, Walter E I, Rutgers J L, Knowles D M, Nussenzweig V
J Exp Med. 1987 Mar 1;165(3):848-64. doi: 10.1084/jem.165.3.848.
Decay-accelerating factor (DAF) is a 70 kD membrane regulatory protein that prevents the activation of autologous complement on cell surfaces. Using immunohistochemical methods and a radioimmunometric assay based on mAbs to DAF, we found large amounts of membrane-associated DAF antigen on the epithelial surface of cornea, conjunctiva, oral and gastrointestinal mucosa, exocrine glands, renal tubules, ureter and bladder, cervical and uterine mucosa, and pleural, pericardial and synovial serosa. Additionally, we detected soluble DAF antigen in plasma, tears, saliva, and urine, as well as in synovial and cerebrospinal fluids. While plasma, tear, and saliva DAF are larger than erythrocyte (Ehu) membrane DAF by Western blot analysis, urine DAF is slightly smaller (67,000) in Mr. Unlike purified Ehu DAF, however, urine DAF is unable to incorporate into the membrane of red cells. Although its inhibitory activity on the complement enzyme C3-convertase is lower than that of Ehu DAF, it is comparable to that of serum C4 binding protein (C4bp). Biosynthetic studies using cultured foreskin epithelium and Hela cells disclosed DAF levels (approximately 2 X 10(5) molecules/cell) exceeding those on blood cells. In addition, these studies revealed the synthesis of two DAF species, one with apparent Mr corresponding to that of epithelial cell membrane DAF and the other to urine DAF, suggesting that the urine DAF variant arises from adjacent epithelium. The function of DAF in body fluids is unknown, but the observation that urine DAF has C4bp-(or factor H-)like activity shows that it could inhibit the fluid phase activation of the cascade.
衰变加速因子（DAF）是一种70kD的膜调节蛋白，可防止自身补体在细胞表面激活。我们使用免疫组化方法和基于抗DAF单克隆抗体的放射免疫测定法，发现角膜、结膜、口腔和胃肠道黏膜、外分泌腺、肾小管、输尿管和膀胱、宫颈和子宫黏膜以及胸膜、心包膜和滑膜浆膜的上皮表面存在大量与膜相关的DAF抗原。此外，我们在血浆、泪液、唾液和尿液以及滑膜液和脑脊液中检测到可溶性DAF抗原。通过蛋白质印迹分析，血浆、泪液和唾液中的DAF比红细胞（Ehu）膜上的DAF大，而尿液中的DAF在分子量上略小（67,000）。然而，与纯化的Ehu DAF不同，尿液DAF无法整合到红细胞膜中。尽管其对补体酶C3转化酶的抑制活性低于Ehu DAF，但其与血清C4结合蛋白（C4bp）的抑制活性相当。使用培养的包皮上皮细胞和Hela细胞进行的生物合成研究表明，DAF水平（约2×10⁵个分子/细胞）超过血细胞上的水平。此外，这些研究揭示了两种DAF的合成，一种的表观分子量与上皮细胞膜DAF相对应，另一种与尿液DAF相对应，这表明尿液DAF变体来自相邻的上皮细胞。DAF在体液中的功能尚不清楚，但尿液DAF具有C4bp（或因子H）样活性这一观察结果表明，它可能抑制补体级联反应的液相激活。
