The influence of the maternal uterine immune response on placentation in human subjects

Mifepristone (Ru486) antagonizes monocyte chemotactic protein-3 down-regulation at early mouse pregnancy revealing immunomodulatory events in Ru486 induced abortion

PROBLEM

The survival of an embryo bearing the paternal antigens within the immunocompetent environment of the maternal uterus renders 'pregnancy' to be a state of immunological paradox. The ratio of Th1/Th2 responses is crucial for pregnancy maintenance. Monocyte Chemotactic Protein-3 (MCP3) is a pro-inflammatory, CC chemokine and a Th1 effector which is capable of eliciting significant anti-tumoral immune responses.

METHOD OF STUDY

MCP3 expression was investigated in the murine uterine tissue at different days of initial pregnancy and the effect of RU 486 in immature and delayed implantation model studied using Western blotting and Immunocytochemical techniques.

RESULTS AND CONCLUSION

Our results show very high uterine MCP3 expression during pre-implantation followed by a significant MCP3 down-regulation at peri-implantation and low levels of MCP3 during post-implantation period. At the peri-implantation stage, embryos exhibited lowered MCP3 expression when compared with the pre-implantation stage. Ru486, a progesterone antagonist when given in a competitive mode with progesterone resulted in a massive surge in MCP3 expression in both immature mice and delayed implantation models. We hypothesize that it is imperative for MCP3 expression to be down-regulated for the success of pregnancy. The cross-talk between Ru486 and amplified MCP3 expression may be one of the mechanisms by way of which RU486 performs its abortificient and anti tumor role.

Abortive potency of Chlamydophila abortus in pregnant mice is not directly correlated with placental and fetal colonization levels

Abortion, placental and fetal colonization, and levels of gamma interferon were analyzed for four Chlamydophila abortus strains presenting antigenic variations in a mouse model. Expression of virulence of these strains varied and indicated that abortion was not directly related to the number of bacteria in the placenta, and thus, other factors may have an important role in activating the abortion process.

Syncytiotrophoblast is a barrier to maternal-fetal transmission of herpes simplex virus

Herpes simplex virus (HSV)-1 has been discovered in placental tissue from spontaneous miscarriages, but reports of transplacental transmission and fetal infection are extremely rare. Previously, we demonstrated that the villous syncytiotrophoblast, which forms a continuous layer between the maternal and fetal circulation, is resistant to HSV entry. Here, we tested our hypothesis that the villous syncytiotrophoblast prevents transplacental transmission of HSV secondary to decreased expression of HSV entry mediators (HveA, HveB, and HveC). In addition, we investigated the ability of HSV to infect extravillous trophoblast cells, which mediate placental attachment to the uterine wall, and the expression of HSV receptors in these cells. We performed fluorescence-activated cell sorting (FACS) analyses and immunostaining to demonstrate that HveA, HveB, and HveC were not expressed in third-trimester villous trophoblast cells. Consequently, villous explants obtained from third-trimester placentas were resistant to infection by a recombinant HSV-1 vector, HSV-1 KOS, but approximately 20% of mesenchymal cells within the villous core were infected when villous explants were pretreated with trypsin to disrupt the villous trophoblast layer. Conversely, FACS analysis and immunostaining demonstrated that extravillous trophoblast cells expressed HveA, HveB, and HveC, and these cells were efficiently infected by HSV vectors. Infection of extravillous trophoblast cells by HSV-1 was not reduced when the cells were pretreated with an antibody against HveA but was partially reduced when the cells were pretreated with antibodies directed against HveB and HveC. Thus, the decreased expression of herpesvirus entry mediators in villous syncytiotrophoblast prevents placental villous infection, thereby limiting maternal-fetal transmission of HSV.

The mechanisms of placental viral infection

The placenta is a dynamic organ whose structure and function change throughout pregnancy. There is compelling evidence that the placenta plays an integral role in the vertical transmission of viruses, such as cytomegalovirus and human immunodeficiency virus, from the mother to the fetus. Although the sequelae of congenital viral infection (i.e., fetal anomalies, intrauterine fetal death, and persistent postnatal infection) may be devastating, very little is known about the passage of viruses across the placenta and the pathologic consequences of placental viral infection. We postulate that the syncytiotrophoblast, which forms a continuous barrier between the maternal and fetal circulation, is relatively resistant to viral infection. In support of this hypothesis, we observed that the susceptibility of trophoblast cells to infection by adenovirus and herpes simplex virus and the expression of viral receptors were reduced as trophoblast cells terminally differentiated into syncytiotrophoblast. Conversely, we observed that undifferentiated, extravillous trophoblast cells, which are susceptible to adenovirus infection, underwent pathologic changes (i.e., apoptosis) when infected by adenovirus in the presence of decidual lymphocytes (which were used to simulate the maternal immune response to viral infection). Based on these findings, we speculate that viral infection of extravillous trophoblast cells may negatively impact the process of placental invasion and predispose the mother and fetus to adverse reproductive outcomes that result from placental dysfunction.

Angiogenic growth factor messenger ribonucleic acids in uterine natural killer cells

Angiogenesis is essential for endometrial growth and repair, and disruption of this process may lead to common disorders of women, including menorrhagia and endometriosis. In pregnancy, failure of the endometrial spiral arterioles to undergo remodeling leads to preeclampsia. Here we report that in addition to vascular endothelial growth factor A (VEGF-A), human endometrium expresses messenger ribonucleic acids (mRNAs) encoding VEGF-C, placenta growth factor (PlGF), the angiopoietins, angiopoietin 1 (Ang1) and Ang2, and the receptors VEGFR-3 (Flt-4), Tie 1, and Tie 2. Levels of VEGF-C, PlGF, and Tie 2 changed during the menstrual cycle. Intense hybridization for VEGF-C and PlGF mRNAs was found in uterine nature killer cells in secretory phase endometrium and for Ang2 mRNA in the same cells in the late secretory phase. Interleukin-2 (IL-2) and IL-15 up-regulated VEGF-C, but not PlGF or Ang2, mRNA levels in isolated NK cells. Conditioned medium from decidual NK cells did not induce human umbilical vein endothelial cell apoptosis. These results indicate that human endometrium expresses a wide range of angiogenic growth factors and that uterine nature killer cells may play an important role in the abnormal endometrial angiogenesis that underlies a range of disorders affecting women.

Differential expression of the coxsackievirus and adenovirus receptor regulates adenovirus infection of the placenta

The molecular mechanisms and pathologic significance of placental viral infections are poorly understood. We investigated factors that regulate placental infection by adenovirus, which is the most common viral pathogen identified in fetal samples from abnormal pregnancies (i.e., fetal growth restriction, oligohydramnios, and nonimmune fetal hydrops). We also determined the pathologic significance of placental adenovirus infection. Northern hybridization, flow cytometry, and immunostaining revealed that placental expression of the coxsackievirus and adenovirus receptor (CAR) varied with gestational age and trophoblast phenotype. The CAR was continuously expressed in invasive or extravillous trophoblast cells but not in villous trophoblast cells. We postulate that the villous syncytiotrophoblast, which does not express CAR and is resistant to adenovirus infection, limits the transplacental transmission of viral pathogens, including adenovirus. Conversely, extravillous trophoblast cells underwent apoptosis when infected by adenovirus in the presence of decidual lymphocytes (which simulated the maternal immune response to viral infection). Thus, adenovirus infection and/or the maternal immune response to adenovirus infection induced the death of placental cell types that expressed CAR. Consequently, we speculate that adenovirus infection of extra-villous trophoblast cells may negatively impact the process of placental invasion and predispose the mother and fetus to adverse reproductive outcomes that result from placental dysfunction.

Immunology at the maternal-fetal interface: lessons for T cell tolerance and suppression

Mammalian reproduction poses an immunological paradox because fetal alloantigens encoded by genes inherited from the father should provoke responses by maternal T cells leading to fetal loss. Current understanding of T cell immunobiology and the critical role of inflammatory processes during pregnancy is reviewed and discussed. Lessons derived from studies on the regulation of T cell responsiveness during mammalian gestation are considered in the wider context of T cell tolerance toward some microbial infections and tumors, avoidance of autoimmunity, and tissue allograft rejection.