Clark D A, Ding J W, Chaouat G, Coulam C B, August C, Levy G A
Department of Medicine, McMaster University Hamilton, Ontario, Canada.
Am J Reprod Immunol. 1999 Jul;42(1):37-43. doi: 10.1111/j.1600-0897.1999.tb00463.x.
Abortion of chromosomally normal embryos in the CBA X DBA/2 mating combination is triggered by release of Th1 cytokines (tumor necrosis factor [TNF]-alpha, interferon [IFN]-gamma, and interleukin [IL]-1), which cause abortion via a novel prothrombinase, Fgl2, and polymorphonuclear leukocytes. The site of activation may be maternal vascular endothelium on arteries and veins nourishing the placenta. Activation of coagulation is also prominent in spontaneous abortion of chromosomally normal human embryos. We asked where is Fgl2 up-regulated in the uterus in murine abortions, and if similar Fgl2 expression occurs in human pregnancy failure.
Control CBA X DBA/2 pregnant mice, or from mice injected with TNF-alpha + IFN-gamma on day 7.5 of gestation, were removed on day 8.5, fixed, sectioned, and subject to in situ hybridization for Fgl2. Sections were also stained for fibrin. Elective first trimester termination samples or biopsies taken early in the course of a recurrent miscarriage were similarly fixed, sectioned, and analyzed by in situ hybridization. Control and cytokine-treated mice were anticoagulated with heparin, an activator of antithrombin III, and/or the direct anti-thrombin inhibitor hirudin.
Low level Fgl2 expression localized to basal decidua remote from the embryo was noted in control mice; cytokine treatment, which causes greater than 80% of abortions, produced a striking up-regulation in this area as well as in a band at the junction of decidua and myometrium. Trophoblast also became strikingly positive. Fgl2 expression was associated with increased fibrin staining. Anticoagulation significantly protected against abortions, but doses were limited by the complication of retroplacental hemorrhage. In tissue from normal first trimester pregnancy, minimal Fgl2 positivity was seen in some villous syncytiotrophoblast, in villous stroma, cytotrophoblast, and in some cells in decidua. In spontaneous abortion of normal embryo, striking Fgl2 positivity was seen in syncytiotrophoblast and extravillous cytotrophoblast, in association with areas of thrombus formation.
Fgl2 appears to be physiologically expressed and may protect against the internal danger of maternal and/or fetal bleeding during pregnancy and at parturition; a role in inhibiting transplacental traffic is also possible. External dangers in the form of stress, endotoxin, and antigens eliciting Th1 cytokine responses upregulate Fgl2 prothrombinase in trophoblast as well as in decidua, which results in spontaneous abortion of immunogenetically "weaker" embryos.
CBA×DBA/2交配组合中染色体正常胚胎的流产是由Th1细胞因子（肿瘤坏死因子[TNF]-α、干扰素[IFN]-γ和白细胞介素[IL]-1）的释放引发的，这些细胞因子通过一种新型凝血酶原酶Fgl2和多形核白细胞导致流产。激活部位可能是滋养胎盘的动脉和静脉上的母体血管内皮。在染色体正常的人类胚胎自然流产中，凝血激活也很突出。我们想知道在小鼠流产中子宫内Fgl2在哪里上调，以及在人类妊娠失败中是否发生类似的Fgl2表达。
在妊娠第8.5天取出对照CBA×DBA/2怀孕小鼠，或在妊娠第7.5天注射TNF-α+IFN-γ的小鼠，固定、切片，并进行Fgl2原位杂交。切片也用纤维蛋白染色。选择性早期妊娠终止样本或复发性流产早期采集的活检组织同样固定、切片，并通过原位杂交进行分析。对照和细胞因子处理的小鼠用肝素（抗凝血酶III的激活剂）和/或直接抗凝血酶抑制剂水蛭素进行抗凝。
在对照小鼠中，低水平的Fgl2表达定位于远离胚胎的基底蜕膜；导致超过80%流产的细胞因子处理在该区域以及蜕膜与子宫肌层交界处的一条带中产生了显著的上调。滋养层也变得明显呈阳性。Fgl2表达与纤维蛋白染色增加有关。抗凝显著预防了流产，但剂量受到胎盘后出血并发症的限制。在正常早期妊娠组织中，在一些绒毛合体滋养层、绒毛间质、细胞滋养层以及蜕膜中的一些细胞中可见最小的Fgl2阳性。在正常胚胎自然流产中，在合体滋养层和绒毛外细胞滋养层中可见显著的Fgl2阳性，与血栓形成区域相关。
Fgl2似乎在生理上表达，可能在妊娠期间和分娩时预防母体和/或胎儿出血的内部危险；也可能在抑制胎盘转运中起作用。应激、内毒素和引发Th1细胞因子反应的抗原等外部危险会上调滋养层和蜕膜中的Fgl2凝血酶原酶水平，从而导致免疫遗传上“较弱”胚胎的自然流产。
