FETAL CMV INFECTION: ROLE OF THE HUMAN PLACENTA

人巨细胞病毒(CMV)对胚胎/胎儿的感染是先天性病毒感染的主要原因。在美国，它发生在1%的活产婴儿中。其后果包括神经发育不良、视力受损和感觉神经性听力丧失。患有先天性巨细胞病毒的妇女自然流产(15%)的胎盘显示出感染的证据，而不涉及胎儿，这表明胎盘感染先于病毒传播到胎儿。成功的妊娠依赖于正常的胎盘发育，这是一个涉及器官上皮干细胞分化的逐步过程，称为细胞滋养层细胞(CTB)。CTB通过两条途径分化成绒毛，这些绒毛要么将胎盘固定在子宫壁上，要么漂浮在母体血液中。在第一个途径中，锚定绒毛中的CTB启动黏附受体和蛋白酶的表达，这是入侵母体动脉所需的，以及诱导母体耐受的免疫分子。我们的研究表明，CMV感染早期妊娠分化/侵袭的CTB在体外下调了两个重要的阶段特异性抗原的表达，非经典的MHC类Ib、HLA-G和整合素α1beta1。此外，从感染CMV的胎盘中分离的CTB的体外侵袭能力和体内分离的CTB的侵袭能力也显著受损。这种侵袭受损和α1beta1失调之间的相关性表明，母体动脉的错误侵袭可能是CMV感染胎盘的一个特征。在第二种途径中，CTB融合形成覆盖浮动绒毛的合体滋养层细胞(STB)。当漂浮绒毛在体外暴露于CMV时，STB未被感染，而潜在的CTB干细胞被感染。这一意想不到的结果表明，STB将病毒从母体血液中传播到靠近绒毛核心的CTB干细胞，使其表面沐浴。初次感染时非中和抗病毒免疫球蛋白可增强包被免疫球蛋白的病毒粒子的转胞作用。据推测，CMV是通过感染漂浮绒毛中的CTB干细胞、穿过STB屏障的细胞转运以及侵袭性CTB在子宫壁内的感染从母亲传播到胎盘和胚胎/胎儿的。其具体目的是：(1)体外检测CMV感染对CTB侵袭力和免疫功能的影响，并建立体内相关性。2)鉴定/定位参与CTB分化/侵袭和免疫功能紊乱的CMV基因。(3)体外通过将包被免疫球蛋白的CMV病毒粒子穿透STBS表层，确定绒毛间质核心附近的CTB干细胞是否发生了感染，并建立了体内相关性。这些实验将增进我们对胎盘在巨细胞病毒感染引起的妊娠并发症中的作用的了解，巨细胞病毒感染是产前发育的关键问题。这一结果可能提供关于传播途径的第一个分子证据，并导致预防胎儿感染的策略。

Human cytomegalovirus (CMV) infection of the embryo/fetus is the leading cause of congenital viral infection. It occurs in 1 percent of live births in the United States. The consequences include poor neurologic development, visual impairment, and sensorineural hearing loss. Placentas from women with congenital CMV who abort spontaneously (15 percent) show evidence of infection without fetal involvement, indicating that placental infection precedes virus transmission to the fetus. Successful pregnancy depends on normal placental development, a stepwise process that involves differentiation of the organ's epithelial stem cells, termed cytotrophoblasts (CTBs). CTBs differentiate via two pathways into villi that either anchor the placenta to the uterine wall or float in maternal blood. In the first pathway, CTBs in anchoring villi switch on expression of adhesion receptors and proteinases that are needed for invasion of maternal arteries, as well as immune molecules that elicit maternal tolerance. Our studies showed that CMV infection of first trimester differentiating/invading CTBs in vitro downregulates expression of two functionally important stage-specific antigens nonclassical MHC class Ib HLA-G and integrin alpha1beta1. Moreover, the invasion competence of infected CTBs in vitro was dramatically impaired as was the 2invasiveness of CTBs isolated from a placenta infected with CMV in vivo. This correlation between impaired invasion and disregulation of alpha1beta1 suggests that faulty invasion of maternal arteries may be a hallmark of CMV-infected placentas. In the second pathway, CTBs fuse to form syncytiotrophoblasts (STBs) that cover floating villi. When floating villi were exposed to CMV in vitro, STBs were uninfected and the underlying CTB stem cells were infected. This unexpected result suggested that STBs transmit virus from maternal blood, bathing their surface, to the CTB stem cells adjacent to the villus core. Non-neutralizing anti-viral IgG in primary infection may enhance transcytosis of IgG-coated virions. It is hypothesized that CMV is transmitted from the mother to the placenta and the embryo/fetus by infection of CTB stem cells in floating villi, following transcytosis across the STB barrier, and by infection of invasive CTBs within the uterine wall. The specific aims are: (1) Determine the effects of CMV infection on CTB invasiveness and immune function in vitro and then establish relevance in vivo. 2) Identify/map CMV genes involved in disregulating CTB differentiation/invasion and immune function. (3) Determine whether infection of underlying CTB stem cells near the villus stromal core occurs by transcytosis of IgG-coated CMV virions across the surface layer of STBs in vitro and then establish relevance in vivo. These experiments will advance our knowledge of the role of the placenta in pregnancy complications due to CMV infection, a critical issue in prenatal development. The results could offer the first molecular evidence regarding the route of transmission and lead to strategies to prevent infection of the fetus.