FETAL CMV INFECTION: ROLE OF THE HUMAN PLACENTA

胚胎/胎儿的人巨细胞病毒（CMV）感染是先天性病毒感染的主要原因。 它发生在1%的活产在美国。 其后果包括神经发育不良、视力受损和感觉神经性听力损失。 先天性巨细胞病毒（CMV）自然流产妇女（15%）的胎盘显示感染的证据，但不涉及胎儿，表明胎盘感染先于病毒传播给胎儿。 成功的怀孕取决于正常的胎盘发育，这是一个涉及器官上皮干细胞（称为细胞滋养层细胞（CTB））分化的逐步过程。 CTB通过两种途径分化成绒毛，绒毛将胎盘锚在子宫壁上或漂浮在母体血液中。 在第一种途径中，锚定绒毛中的CTB开启粘附受体和蛋白酶的表达，这些受体和蛋白酶是侵入母体动脉所需的，以及引发母体耐受的免疫分子。 我们的研究表明，CMV感染的早期妊娠分化/入侵CTBs在体外下调两个功能重要的阶段特异性抗原的表达，非经典的MHC Ib类HLA-G和整合素α 1 β 1。 此外，感染的CTB在体外的侵袭能力显着受损，这是从体内感染CMV的胎盘中分离的CTB的侵袭能力。 这种侵袭受损和α 1 β 1失调之间的相关性表明，母体动脉的错误侵袭可能是CMV感染胎盘的标志。在第二种途径中，CTB融合形成覆盖漂浮绒毛的合胞体滋养层（STB）。 当漂浮的绒毛在体外暴露于CMV时，STB未被感染，而下面的CTB干细胞被感染。 这个意想不到的结果表明，STB将病毒从母体血液中传播，沐浴它们的表面，到绒毛核心附近的CTB干细胞。原发感染中的非中和性抗病毒IgG可增强IgG包被的病毒粒子的转胞吞作用。 据推测，CMV是通过跨STB屏障的转胞吞作用后感染漂浮绒毛中的CTB干细胞以及感染子宫壁内的侵袭性CTB而从母体传播至胎盘和胚胎/胎儿的。 具体目标是：（1）在体外确定CMV感染对CTB侵袭性和免疫功能的影响，然后在体内建立相关性。 2)鉴定/映射参与CTB分化/侵袭和免疫功能失调的CMV基因。 (3)确定绒毛间质核心附近的潜在CTB干细胞的感染是否通过IgG包被的CMV病毒体在体外跨STB表面层的转胞吞作用发生，然后在体内建立相关性。 这些实验将推进我们对胎盘在CMV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。 该结果可以提供有关传播途径的第一个分子证据，并制定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.