The human placental bed: histology, immunohistochemistry and pathology

There has been much interest recently on local intra-uterine materno-fetal interactions particularly in the placental bed where cellular relationships between mother and fetus are at their most intimate. While few histopathologists are expected to interpret formal placental bed biopsy specimens, confrontation with tissue from this site is common following abortion, post-partum haemorrhage or molar gestation. This review gives an account of recent advances in our knowledge of the histology, immunohistochemistry and pathology of the placental bed. It focuses particularly on extravillous trophoblast populations and their relationship to maternal cells and emphasizes the importance of vascular changes.     

人早孕期蜕膜和绒毛外滋养层细胞的免疫组织化学研究

侵入蜕膜组织的绒毛外滋养层细胞在HE染色标本上不易辨认。我们用免疫组织化学,ABC法,过氧化物-抗过氧化物酶标记蜕膜组织中的hCG与hPL阳性细胞。结果证明,子宫内膜中只要有一个绒毛外滋养层细胞存在就能被显示出来。这对提高妊娠诊断,防止残留滋养层细胞的增生与恶性病变很有意义。我们在蜕膜组织中还发现3类胎盘激素阳性细胞:hCG阳性细胞,hPL阳性细胞及hCG与hPL均为阳性的细胞。这一发现,证明了蜕膜有内分泌功能。     

A unifying concept of trophoblastic differentiation and malignancy defined by biomarker expression

Several trophoblast phenotypes, including cytotrophoblast, syncytiotrophoblast, and extravillous trophoblast, emerge during gestation. To clarify the lineage relationship between these subtypes, we profiled p63 localization in developing and term placental tissue, as well as in trophoblastic tumors, using antibodies specific to full-length (TAp63) and one against all p63 isoforms (TAp63 and DeltaNp63). Localization of p63 was compared with that of biomarkers of proliferation and trophoblastic differentiation, including mib-1, inhibin, and MelCAM. In early gestation, p63 was localized principally to villous cytotrophoblast after contact with the villous mesenchyme, absent in the trophoblast columns, and early implantation trophoblast. In the maturing placenta, intraplacental perivillous fibrin correlated with the emergence of a p63-positive "transitional" (vacuolated) extravillous trophoblast from cytotrophoblast, which differentiated further into a "mature" p63-negative extravillous trophoblast. The same lineage pathway emerged from entrapped villi on the chorionic membrane. Virtually all p63 immunopositivity was attributed to dominant-negative p63. The immunophenotypic patterns seen in the immature and mature placenta permit the resolution of all trophoblastic phenotypes within 3 lineage pathways of cytotrophoblast differentiation, including cytotrophoblast-to-trophoblast column/implantation site, cytotrophoblast-to-syncytiotrophoblast, and cytotrophoblast-to-mature extravillous trophoblast. In the latter pathway, a transitional (vacuolated) p63-positive extravillous trophoblast emerges from and links cytotrophoblast to mature extravillous trophoblast in intraplacental fibrin, chorionic membrane, and basal plate. The placental trophoblast is thus resolved within this continuum of differentiation. Terms such as transitional and mature extravillous trophoblast are proposed to reflect the differentiation phases of this unique epithelium. p63 staining patterns in trophoblastic tumors reflect timing of neoplastic transformation during trophoblastic differentiation.     

The expression of major histocompatibility complex antigens by trophoblast in ectopic tubal pregnancy

The reactivity of the various trophoblast populations found in ectopic fallopian tube pregnancy with established trophoblast-reactive markers and monoclonal antibodies to MHC antigens has been studied. In ectopic tubal pregnancy fetal trophoblast shows an identical reaction pattern with these antibodies to that seen in intrauterine pregnancy, suggesting that ectopic implantation is not related to an inherent immunological abnormality of fetal trophoblast. However, from this and other studies, it appears that extravillous trophoblast displays an unusual class I MHC antigenic structure. This observation may explain the ability of class I MHC--bearing fetal trophoblast--to survive both in the uterus and at an abnormal implantation site.     

Oxygen as modulator of trophoblast invasion

At the time of blastocyst implantation the uterine spiral arteries have already undergone morphological changes in the absence of any extravillous trophoblast invasion. Only 2 weeks after implantation, extravillous trophoblast cells develop and come into first contact with decidual tissues. Invading through the decidual interstitium, extravillous trophoblasts potentially reach and transform spiral arteries into uteroplacental arteries. Spiral arterial erosion starts at about mid-first trimester, whereas flow of maternal blood into the intervillous space is continuously established only at the beginning of the second trimester. One key regulator of the number of extravillous trophoblasts is oxygen. The steep gradient in oxygen concentration within the first trimester placenta is diminished with the onset of maternal blood flow. This gradient is used by the trophoblast to generate a large number of invasive cells to adapt the arterial vasculature in the placental bed to the growing needs of the fetus. Changes in oxygen concentrations or other factors leading to alterations in the rates of proliferation and/or apoptosis of extravillous trophoblast clearly impact on the remodelling of the vessels. The respective consequences of a failure in trophoblast invasion are growth restrictions of the baby and perhaps other pregnancy complications.     

早孕胎盘滋养层细胞的免疫组化研究

目的：研究早孕胎盘绒毛和子宫蜕膜中合体滋养层细胞、细胞滋养层细胞和中间滋养层细胞的免疫组化特征。方法：对２０例妊娠头３个月的刮宫标本进行Ｋｅｒａｆｉｎ、ｈＣＧ、ＨＰＬ、ＰＬＡＰ、ＥＭＡ和Ｐｒｏｌｅｃｔｉｎ等免疫组化染色。结果：角蛋白是各种滋养层细胞最可靠和最敏感的标记物，但其特异性差。合体滋养层细胞的ｈＣＧ和ＰＬＡＰ染色强于中间滋养层细胞，而中间滋养层细胞的ＨＰＬ和ＥＭＡ染色强于合体滋养层细胞。除角蛋白外，细胞滋养层细胞免疫组化染色均阴性。结论；早孕时三种滋养层细胞在免疫组化方面有其共性，也有各自不同的特点。     

基质胶对绒毛外细胞滋养层细胞体外侵袭的介导作用

目的探讨基质胶(Matrigel)在绒毛外细胞滋养层细胞(EVCT)的体外侵袭中的作用。方法取健康早孕妇女(孕7～9周)人工流产绒毛组织,利用Percoll梯度离心法及差速贴壁法,将纯化的绒毛外细胞滋养层细胞,按所需浓度接种于涂有Matrigel培养板或24孔Transwell侵入系统中培养。用细胞免疫荧光法检测TGFβ2、cytokeration7、integrinα1β1。用CCK-8评价细胞生长状况。用Transwell细胞侵入系统检测EVCT的体外侵袭作用。结果①EVCT在Matrigel包被的Petri皿培养4h,用细胞免疫荧光法显示有95%以上的细胞表达TGFβ2、cytokeration7和integrinα1β1;②EVCT在Matrigel培养不同时间后,其生长指数未有明显变化,提示Matrigel对EVCT的生长未有明显影响;③EVCT在Transwell侵袭系统中培养不同时间后,侵袭细胞的OD值提示48h细胞侵袭作用达到平台期。结论 Matrigel在EVCT体外侵袭中并不影响其细胞纯度及其生长曲线,其介导的体外侵袭在48h达到侵入平台期。     

Effect of ephrin-A1/EphA2 on invasion of trophoblastic cells

The effect of axon guidance factors ephrin-A 1/EphA2 on the invasion of trophoblastic cells and the possible mechanism were investigated in this study.The expression of EphA2 in vascular endothelial ce...     

Decidual NK cells kill Zika virus–infected trophoblasts

Zika virus (ZIKV) during pregnancy infects fetal trophoblasts and causes placental damage and birth defects including microcephaly. Little is known about the anti-ZIKV cellular immune response at the maternal–fetal interface. Decidual natural killer cells (dNK), which directly contact fetal trophoblasts, are the dominant maternal immune cells in the first-trimester placenta, when ZIKV infection is most hazardous. Although dNK express all the cytolytic molecules needed to kill, they usually do not kill infected fetal cells but promote placentation. Here, we show that dNK degranulate and kill ZIKV-infected placental trophoblasts. ZIKV infection of trophoblasts causes endoplasmic reticulum (ER) stress, which makes them dNK targets by down-regulating HLA-C/G, natural killer (NK) inhibitory receptor ligands that help maintain tolerance of the semiallogeneic fetus. ER stress also activates the NK activating receptor NKp46. ZIKV infection of Ifnar1^−/− pregnant mice results in high viral titers and severe intrauterine growth restriction, which are exacerbated by depletion of NK or CD8 T cells, indicating that killer lymphocytes, on balance, protect the fetus from ZIKV by eliminating infected cells and reducing the spread of infection.

In the first trimester of human pregnancy, when Zika virus (ZIKV) infection is most damaging to the developing fetus (1–3), ∼70% of maternal immune cells at the maternal–fetal interface are decidual natural killer cells (dNK), which are in close contact with extravillous trophoblasts (EVT), placental cells of fetal origin which invade the decidua to orchestrate placentation. T lymphocytes and natural killer (NK) cells generally do not kill EVT, which do not express the main classical HLA molecules responsible for T cell activation (HLA-A and B) (4–7) but do express HLA-C and nonclassical HLA-E and -G, which help inhibit NK cell activation. HLA-G, whose expression is mostly restricted to the placenta, helps maintain dNK tolerance of fetal cells. There is important cross-talk between dNK and EVT—EVT regulate the maturation of dNK precursor cells into tolerant dNK (8) and dNK promote EVT migration and invasion of spiral arteries, processes essential for placentation (9–13). Invading fetal EVT are susceptible to infection by a variety of pathogens, including human cytomegalovirus (HCMV), Toxoplasma gondii, and ZIKV (1, 14–17). dNK in the placenta face a difficult problem—they must tolerate the semiforeign fetus but still protect against infection. Although dNK contain the machinery needed to recognize and kill, they have reduced cytolytic activity against classical NK target cells recognized by peripheral blood NK cells (pNK) and are not known to kill infected trophoblasts (18–23). However, dNK degranulate and secrete cytokines, including interferon (IFN)-γ, in response to HCMV-infected maternal decidual stromal cells in equal levels to pNK (19, 20). We recently demonstrated that dNK can eliminate intracellular Listeria infection in trophoblasts without degranulating or killing the host cells (24). Although ZIKV infects the placenta and fetus and can cause severe birth defects including microcephaly, brain atrophy, and subcortical and chorioretinal and optic nerve atrophy, little is known about the response of decidual immune cells to ZIKV and its effect on maternal–fetal transmission (25).     

Apoptosis and its role in the trophoblast

During early placentation the trophoblast of the human placenta differentiates to the villous and extravillous types of trophoblast. Villous trophoblast provides the epithelial cover of the placental villous trees in direct contact to maternal blood. Extravillous trophoblast invades maternal uterine tissues thus directly contacting maternal stromal and immune cells. A subset of extravillous trophoblast, endovascular trophoblast initially occludes the lumen of spiral arteries and comes into direct contact with maternal blood. In recent years apoptosis has been described in both types of trophoblast and the importance of this cascade for the normal function of the trophoblast has become obvious. One feature of serious conditions such as preeclampsia or intrauterine growth restriction is changes in apoptosis regulation in villous and/or extravillous trophoblast resulting in altered trophoblast invasion and/or shedding into the maternal circulation. This review summarizes recent findings on trophoblast apoptosis in normal and pathologic pregnancies.