FETAL CMV INFECTION: ROLE OF THE HUMAN PLACENTA

人巨细胞病毒（CMV）感染胚胎/胎儿是先天性病毒感染的主要原因。在美国，1%的活产婴儿患有此病。其后果包括神经发育不良、视力损害和感音神经性听力丧失。先天性巨细胞病毒自发流产妇女的胎盘（15%）显示无胎儿感染的证据，表明胎盘感染先于病毒传播给胎儿。成功怀孕取决于正常的胎盘发育，这是一个循序渐进的过程，涉及器官上皮干细胞的分化，称为细胞滋养细胞（CTBs）。CTBs通过两种途径分化成绒毛，绒毛要么将胎盘固定在子宫壁上，要么漂浮在母体血液中。在第一种途径中，锚定绒毛中的CTBs开启了粘附受体和蛋白酶的表达，这些受体和蛋白酶是入侵母体动脉所需的，以及引发母体耐受的免疫分子。我们的研究表明，体外孕早期CMV感染分化/侵袭CTBs可下调两种功能重要的阶段特异性抗原（非经典MHC类b） HLA-G和整合素（integrin alpha1beta1）的表达。此外，感染的CTBs在体外的侵袭能力被显著削弱，从感染巨细胞病毒的胎盘中分离的CTBs在体内的侵袭能力也被显著削弱。侵袭受损与alpha1beta1失调之间的相关性表明，母体动脉的错误侵袭可能是cmv感染胎盘的一个标志。在第二种途径中，CTBs融合形成覆盖漂浮绒毛的合胞滋养细胞（STBs）。当漂浮绒毛暴露于CMV体外时，STBs未被感染，而底层的CTB干细胞被感染。这一意想不到的结果表明，STBs将病毒从母体血液中通过表面传播到靠近绒毛核心的CTB干细胞。原发感染的非中和性抗病毒IgG可增强IgG包被病毒粒子的胞吞作用。据推测，巨细胞病毒通过漂浮绒毛中的CTB干细胞感染、通过STB屏障的胞吞作用以及侵入性子宫壁的CTB感染，从母体传播到胎盘和胚胎/胎儿。具体目的是：(1)在体外确定CMV感染对CTB侵袭性和免疫功能的影响，并在体内建立相关性。2)鉴定/定位参与CTB分化/侵袭和免疫功能失调的CMV基因。(3)体外通过igg包被的巨细胞病毒粒子跨STBs表面层的转胞作用，确定是否会感染绒毛间质核心附近的CTB底层干细胞，并在体内建立相关性。这些实验将促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认识，这是产前发育的一个关键问题。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.