Extrathymic development of V alpha 11 T cells in placenta during pregnancy and their possible physiological role

Bi-directional cell trafficking between mother and fetus in mouse placenta

It is now well established that cells are exchanged between mother and fetus during gestation. It has been proposed that some of these exchanges take place in the placenta, but it has never been demonstrated. Here, we made use of EGFP (Enhanced Green Fluorescent Protein) transgenic mice to precisely visualize the juxtaposition of maternal and fetal tissues at the implantation site, as well as to describe the bi-directional cell trafficking between mother and fetus at different stages of gestation. The influence of genetic differences between mother and fetus on the cell migration was also addressed by studying various types of matings: syngeneic, allogeneic and outbred. The frequency of maternal-fetal cell exchanges within the placenta is much higher in syngeneic and allogeneic gestations than in outbred ones. Maternal cells were mainly localized in the labyrinth where they were scattered or sometimes grouped in or near blood spaces. Groups of maternal cells could also be observed in maternal blood sinuses of the spongiotrophoblast. Conversely, fetal cells were organized in rings surrounding maternal blood sinuses in the decidua at 10-12 days of gestation. After day 13, they invaded the decidua. Fetal cells could also be detected in maternal peripheral blood and organs by nested PCR and fluorescence microscopy on cryosections, respectively. This suggests a role in the establishment and maintenance of the maternal tolerance to the fetus.

The skewed TCR-BV repertoire displayed at the maternal-fetal interface of women with unexplained pregnancy loss

PROBLEM

The study was undertaken to investigate T-cell receptor (TCR) variable beta (BV)-chain usage at maternal-fetal interface and explore the relationship between the skewed TCR-BV usage and unexplained pregnancy losses.

METHOD OF STUDY

A total of 57 patients with unexplained pregnancy loss including 39 cases with unexplained spontaneous abortion and 18 cases with unexplained recurrent spontaneous abortion (RSA) were chosen in Renji Hospital, Shanghai Second Medical University matched with 41 women with normal pregnancies in first trimester between September 2002 and November 2003. A high-resolution spectratyping analysis of complementarity-determining region 3 (CDR3) was used to detect and compare the degree and pattern of TCR-BV repertoire usage at the maternal-fetal interface between patients with pregnancy loss and normal controls.

RESULTS

There were two comparisons of TCR usage performed between patients and controls, which included the degree (mean value of every TCR-BVn expression) and the pattern (skewed TCR-BVn frequency). The skewed TCR-BVn is defined as an absolute BVn usage of > 5% calculated from the formula or a double increased BVn usage compared with the mean value of normal BVn. According to the degree of TCR-BV usage, BV2 (P = 0.046), BV10 (P = 0.016), and BV11 (P = 0.030) in spontaneous abortion group and BV19 (P = 0.038) in RSA group showed higher usage, while BV5.2 (P = 0.006 and P = 0.046) in both abortion groups showed significantly lower usage when compared with normal controls. About the pattern of skewed TCR-BV distribution, we found that TCR-BV2, -3, -6, and -7 were the four most common BV families in deciduas of patients with both types of abortion and normal controls. Women with spontaneous abortion demonstrated higher frequency of BV10 (P = 0.035) and lower frequencies of BV4 (P = 0.002) and BV5.2 (P = 0.003) in comparison with controls. In RSA, higher frequencies of BV15 (P = 0.018), BV19 (P = 0.049), and BV20 (P = 0.018), in the mean time, lower frequencies of BV4 (P = 0.026) and BV7 (P = 0.018) distributions were verified.

CONCLUSIONS

Our results suggested that a significant skewed TCR-BV repertoire occurred at the maternal-fetal interface with patients undergoing abortion. The specific skewed usages of TCR-BV might be associated with the susceptibility to unexplained pregnancy loss.

Tolerance of the fetus by the maternal immune system: role of inflammatory mediators at the feto-maternal interface

The adaptive immune system of placental mammals has evolved to tolerate the fetus. Rejection of the fetus by adaptive immune responses is therefore a rare event, with abortion being caused more frequently by inflammation in the placenta. This review will cover recent aspects of immune privilege and the innate immune system at the feto-maternal interface, citing examples of the role played by microbial infections in fetal demise.

Syngeneic pregnancy induces overexpression of natural killer T cells in maternal liver

Conditions such as stress, infection, autoimmune disease, etc. elevate the number and function of extrathymic T cells that are generated mainly in the liver. As primitive, self-reactive clones of T cells that coexpress receptors of the natural killer (NK) lineage, they mediate cytotoxicity against altered self, malignant and infected cells and have the unique potential to rapidly secrete large amount of T helper 1 (Th1) or Th2 cytokines. To elucidate whether some of these changes occur even during the syngeneic pregnancy, we made phenotypic and functional characterization of mononuclear lymphatic cells (MNLCs) isolated from the liver and spleen of pregnant C57BL/6 mice, testing their cytotoxicity against syngeneic thymocytes as well as against NK- and lymphokine-activated killer (LAK)-sensitive targets. The data have shown that on the sixteenth day of syngeneic pregnancy TCRint, NK1.1+ and IL-2Rbeta+ cells were accumulated in the liver, while the quantities of CD4+ and CD8+ T cells and total number classical NK (NK1.1+CD3- or IL-2Rbeta+CD3-) cells were increased in the spleen. Pregnancy-activated hepatic and splenic MNLCs were more cytotoxic against syngeneic thymocytes, YAC-1 and P815 targets, suggesting that the maternal liver is a main producer of autoreactive NKT clones, which subsequently augment NK- and LAK cell-mediated cytotoxicity in the liver and spleen.

At the innate frontiers between mother and fetus: linking abortion with complement activation

The intricate mechanisms regulating fetomaternal interactions are still largely uncharacterized. Recent papers have revealed a major role for the innate immune system during abortion. Different experimental conditions-deletion of a complement regulator, injection of anti-phospholipid antibodies into mothers, or allo-recognition of fetuses in the presence of an IDO inhibitor-all lead to complement activation, inflammation, and fetal loss. These observations also raise new questions on the relationship between the adaptive and innate systems during pregnancy.

Removing the vertebrate-specific TBP N terminus disrupts placental beta2m-dependent interactions with the maternal immune system

Mammalian TBP consists of a 180 amino acid core that is common to all eukaryotes, fused to a vertebrate-specific N-terminal domain. We generated mice having a modified tbp allele, tbp(DeltaN), that produces a version of TBP lacking 111 of the 135 vertebrate-specific amino acids. Most tbp(DeltaN/DeltaN) fetuses (>90%) died in midgestation from an apparent defect in the placenta. tbp(DeltaN/DeltaN) fetuses could be rescued by supplying them with a wild-type tetraploid placenta. Mutants also could be rescued by rearing them in immunocompromised mothers. In immune-competent mothers, survival of tbp(DeltaN/DeltaN) fetuses increased when fetal/placental beta2m expression was genetically disrupted. These results suggest that the TBP N terminus functions in transcriptional regulation of a placental beta2m-dependent process that favors maternal immunotolerance of pregnancy.