Bennett W A, Allbert J R, Brackin M N, Morrison J C, Cowan B D
Department of Obstetrics and Gynecology, University of Mississippi Medical Center, Jackson 39216-4505, USA.
J Soc Gynecol Investig. 1999 Nov-Dec;6(6):311-7. doi: 10.1016/s1071-5576(99)00037-4.
Prostaglandins (PGs) are essential mediators of labor during human pregnancy. Phospholipase A2 (PLA2) provides the essential substrate for PG synthesis through the liberation of arachidonic acid from membrane phospholipid stores. Nonlaboring amniotic fluid (NL-AF) contains secretory component (SC)-like protein(s) that suppress in vitro PLA2 activity. This study characterizes the biologic activity, identity, and tissue distribution of these protein(s) in NL-AF and gestational tissues.
Third-trimester NL-AF was collected by amniocentesis, fractionated by ammonium sulfate precipitation, and submitted to an in vitro PLA2 assay. Identity of the PLA2 inhibitor in NL-AF was confirmed by Western blot and antibody neutralization studies. Secretory component-immunoreactive proteins were purified by immunoaffinity chromatography and visualized by sodium dodecyl sulfate-gel electrophoresis. Tissue distribution of SC in gestational tissues was determined by immunohistochemistry.
The 100% pellet and supernatant fractions of NL-AF suppressed PLA2 activity, and this activity was neutralized by a polyclonal antibody to SC. Western blot studies revealed an SC-reactive protein in the 70-80-kD range in the 100% pellet fraction of NL-AF. Two SC-reactive proteins were detected in the 60-80-kD range in the eluate from the SC immunoaffinity column, along with minor proteins of 30 and greater than 100 kD. Immunohistochemical studies revealed SC in placental trophoblast, amniotic membranes, and decidual epithelium.
These results demonstrate that proteins homologous to SC are present in human gestational tissues and possess anti-PLA2 activity. These proteins may contribute to the maintenance of pregnancy by suppressing local PG production.
前列腺素（PGs）是人类妊娠期间分娩的重要介质。磷脂酶A2（PLA2）通过从膜磷脂储存中释放花生四烯酸为PG合成提供必需的底物。未临产羊水（NL-AF）含有抑制体外PLA2活性的分泌成分（SC）样蛋白。本研究对这些蛋白在NL-AF和妊娠组织中的生物学活性、特性及组织分布进行了表征。
孕晚期NL-AF通过羊膜穿刺术收集，经硫酸铵沉淀分级分离，并进行体外PLA2活性测定。通过蛋白质免疫印迹法和抗体中和研究确认NL-AF中PLA2抑制剂的特性。分泌成分免疫反应性蛋白通过免疫亲和层析纯化，并用十二烷基硫酸钠-凝胶电泳进行可视化分析。通过免疫组织化学法测定SC在妊娠组织中的组织分布。
NL-AF的100%沉淀和上清组分均抑制PLA2活性，且该活性可被抗SC多克隆抗体中和。蛋白质免疫印迹研究显示，NL-AF的100%沉淀组分中存在70 - 80 kD范围内的SC反应性蛋白。在SC免疫亲和柱洗脱液中检测到60 - 80 kD范围内的两种SC反应性蛋白，以及30 kD和大于100 kD的次要蛋白。免疫组织化学研究显示，胎盘滋养层、羊膜和蜕膜上皮中有SC存在。
这些结果表明，与SC同源的蛋白存在于人类妊娠组织中，并具有抗PLA2活性。这些蛋白可能通过抑制局部PG产生来维持妊娠。
