Induction of transient murine T cell anergy by a low molecular weight compound obtained from supernatants of human placental cultures is linked to defective phosphorylation of TCR CD3 chain

Cooperative inflammation: The recruitment of inflammatory signaling in marsupial and eutherian pregnancy

The evolution of viviparity in therian mammals, i.e. marsupials and "placental" mammals, occurred by retention of the conceptus in the female reproductive tract and precocious "hatching" from the shell coat. Both eutherian embryo implantation and the opossum embryo attachment reaction are evolutionarily derived from and homologous to a defensive inflammatory process induced after shell coat hatching. However, both lineages, marsupials and placental mammals, have modified the inflammatory response substantially. We review the induction, maintenance, and effects of inflammation throughout pregnancy, with special attention to the role of prostaglandins and the mucosal inflammatory response, both of which likely had roles in early mammalian viviparity. We propose that the key step was not only suppression of the inflammatory response after implantation in placental mammals, but also the transfer of the inflammatory cell-cell communication network to a different set of cell types than in generic inflammation. To support this conclusion we discuss evidence that pro-inflammatory signal production in the opossum is not limited to maternal cells, as expected in bona fide defensive inflammation, but also includes fetal tissues, in a process we term cooperative inflammation. The ways in which the inflammatory reaction was independently modified in these two lineages helps explain major life history differences between extant marsupials and eutherians.

Regulatory T-cells in pregnancy: historical perspective, state of the art, and burning questions

In this review, we first revisit the original concept of "suppressor T-cells" in pregnancy, put it in a historical perspective, and then highlight the main data that licensed its resurrection and revision into the concept of "regulatory T-cells" (Tregs) in pregnancy. We review the evidence for a major role of Tregs in murine and human pregnancy and discuss Treg interactions with dendritic and uterine natural killer cells, other players of maternal-fetal tolerance. Finally, we highlight what we consider as the most important questions in the field.

T CD3+CD8+ lymphocytes are more susceptible for apoptosis in the first trimester of normal human pregnancy

Aims. Normal human pregnancy is a complex process of many immunoregulatory mechanisms which protect fetus from the activation of the maternal immune system. The aim of the study was to investigate the apoptosis of lymphocytes in peripheral blood of normal pregnant patients and healthy nonpregnant women. Methods. Sixty pregnant women and 17 nonpregnant women were included in the study. Lymphocytes were isolated and labeled with anti-CD3, anti-CD4, and anti-CD8 monoclonal antibodies. Apoptosis was detected by CMXRos staining and analyzed using the flow cytometric method. Results. We found significantly higher apoptosis of total lymphocytes in peripheral blood of pregnant patients when compared to healthy nonpregnant women. The percentage of apoptotic T CD3⁺CD8⁺ cells in the first trimester was significantly higher when compared to the third trimester of normal pregnancy. The ratio of T CD3⁺CD4⁺ : T CD3⁺CD8⁺ apoptotic lymphocytes was significantly lower in the first trimester when compared to other trimesters of pregnancy and to both of the phases of the menstrual cycle. Conclusions. The higher apoptosis of T CD3⁺CD8⁺ lymphocytes and the lower ratio of T CD3⁺CD4⁺ : T CD3⁺CD8⁺ apoptotic cells in the first trimester of normal pregnancy may suggest a higher susceptibility of T CD3⁺CD8⁺ cells for apoptosis as a protective mechanism at the early stage of pregnancy.

Tolerance to the foetal allograft?

In this review, we will detail the concept of tolerance and its history in reproductive immunology. We will then consider whether it applies to the foetal-maternal relationship and discuss the mechanisms involved in non-rejection of the foeto-placental unit.

The Th1/Th2 paradigm: still important in pregnancy?

The enunciation of the T helper 1/T helper 2 (Th1/Th2) paradigm in pregnancy has represented a major step forward in our understanding of physiological and pathologic materno-foetal relationship. However, recent developments in studies of the implantation process and in the emergence of the uterine vascular bed and its control by natural killer cells and cytokines suggest that one must go beyond this hitherto useful scheme. In this review, we replace the emergence of the paradigm in its historical context and then emphasises what it does explain and what it no longer account for. A final reappraisal of the paradigm is suggested.

Immune cells in uteroplacental tissues throughout pregnancy: a brief review

In a brief introduction, this review states why the presence of immune cells at the interface poses problems for an immunologist (Medawar paradigm). Different types of placentation are then discussed, and the various interactions with leukocytes, the extreme being with the equids where a certain degree of 'attack' is often seen. The limits of animal models when dealing with the human situation are emphasized. It is then stated why the various phases of pregnancy are different, and an analysis made of the cellular movements at the implantation, peri-implantation, immediate post-implantation and resorption windows in rodents. Details of the cellular components involved are given, as are hints for the human situation. The Th1/Th2 paradigm is described, with clinical examples, and its limits. Thus, the newly appraised dual role of natural killer (NK) cells is discussed, with examples in rodents and in humans (pre-eclampsia, implantation failure, abortion systems). Clinical data on the IL-12/IL-18/NK tripod and implantation failure in humans are detailed.

Specific Isolation of Placenta-Derived Exosomes from the Circulation of Pregnant Women and Their Immunoregulatory Consequences

PROBLEM

One immunoregulatory pathway receiving little attention is placental exosome release. In normal pregnancy, as factors linked with early immunomodulation decline, placental exosomes become critical in modulating T-cell activation, suppressing effector T cells by enhancing lymphocyte apoptosis and CD3-zeta loss.

METHOD OF STUDY

Placental exosomes were specifically isolated from the maternal peripheral circulation by a chromatographic/immunosorbent procedure. Exosomal suppression of T-cell signaling molecules on unfractionated T cells and T subsets was analyzed by Western immunoblot. The role of Fas ligand (FasL) was defined by use of Fas-blocking antibody.

RESULTS

While exosomes of lymphoid origin could be demonstrated in all women, placenta-derived exosomes were only identified in pregnant patients. Placental exosomes suppressed T-cell expression of CD3-zeta and JAK3, while inducing SOCS-2. This downregulation of CD3-zeta was partially reversed by pre-incubating T cells with ZB4 antibody. Using T subsets, the level of CD3-zeta on CD8+ cells was inhibited 1.43-fold more than in CD4+ cells. On CD4+ CD25+ cells, CD3-zeta was not significantly inhibited.

CONCLUSION

Placental exosomes suppressed T-cell signaling components; however, while exosomal FasL is an important contributor, it does not appear to be the sole mediator. The additional expression of PD-L1 may explain immunoregulatory consequences of exosomes with low or absent FasL.

Inhibition of lymphocyte proliferation and activation: a mechanism used by equine invasive trophoblast to escape the maternal immune response

At days 36-38 of gestation, the equine invasive trophoblast cells migrate into the endometrium of the pregnant mare to form the endometrial cups. During their migration, they become surrounded by maternal CD4+ and CD8+ T lymphocytes, and stimulate a cytotoxic antibody response to the paternal major histocompatibility complex class I antigens that they express. Nevertheless, endometrial cup cells remain viable at the site of uterine invasion up to days 80-100 of gestation, suggesting the participation of immunomodulatory mechanisms to the maternal cellular immune response. To determine the effects of the invasive trophoblast cells on lymphocyte proliferation, an in vitro co-culture system was developed using isolated equine invasive trophoblast cells and peripheral blood lymphocytes. Fetal fibroblast cells from the same conceptuses were used as controls. The presence of invasive trophoblast cells or their pre-conditioned medium inhibited 50% or more of lymphocyte proliferation, while fetal fibroblasts had no effect. The invasive trophoblast cell inhibitory factor needed to be present constantly to affect lymphocyte proliferation, and it was ineffective if lymphocytes had been previously stimulated to proliferate. The lymphoproliferative inhibitory mechanism affected lymphocyte subpopulations similarly. In addition, lymphocyte expression of cytokine mRNA including IFNgamma, IL-2, IL-4, and IL-10 was affected compared to controls. The implication of these observations in vivo may explain, in part, the apparent equine maternal immune acceptance of the presence and development of endometrial cup cells.

Dialogue materno-fœtal et implantation embryonnaire humaine : des concepts qui évoluent

Multiple immunogical mechanisms allow fetal allograft tolerance. In this review, we first describe the maternal and embryological side in order to expose the dangers for the embryo enabling the development of materno-fetal strategies that will allow fetal survival and growth.

Modulation of T-cell CD3-zeta chain expression during normal pregnancy

The objectives of this study were to assess the modulation of T-cell CD3-zeta expression by factor(s) present in sera of pregnant women, to correlate this activity with markers of T-cell function associated with pregnancy, and to identify the presence of a circulating pregnancy-associated factor responsible for the suppression of CD3-zeta chain. The suppression of TcR/CD3-zeta expression on cultured T-lymphocytes (Jurkat cells) by sera and amniotic fluids from pregnant women was examined by Western immunoblots and quantitated by densitometry. This suppression was correlated with the induction of T-cell apoptosis and reduced production of IL-2. The serum component suppressing zeta expression was characterized by ultrafiltration and protease sensitivity. Incubation of Jurkat cells with sera obtained from women in the first trimester produced a slight, but not statistically significant, suppression of zeta expression; however, sera from pregnant women in the second and third trimesters and amniotic fluids significantly suppressed zeta levels in a dose-dependent manner. The loss of zeta chain correlated with both reduced secretion of IL-2 and induction of lymphocyte apoptosis. Fractionation of sera by ultrafiltration demonstrated that the zeta chain suppressive factor was <5 kDa, and its trypsin-sensitivity suggests a proteinaceous moiety. Pregnancy is associated with a progressive suppression of cell-mediated immunity. These suppressed T-cell functions have been linked to Fas/Fas ligand-induced apoptosis and suppression of Th1 cytokines, including IL-2. We demonstrate that these pregnancy-associated events are mimicked by a factor(s) present in patient-derived fluids. Suppression of zeta expression appears to be due to a circulating low-molecular-weight protein that suppresses CD3-zeta in a concentration-dependent manner.

Effects of the chromatographic fractions of the pig placental trophoblast on graft-versus-host reaction

The trophoblast has a significant role in regulation of immune reactions at the materno-fetal interface by producing biologically active substances. In our previous studies five fractions with immunomodulatory activities were isolated by gel chromatography from trophoblast of pig placentas. To confirm the immunomodulatory effect of these trophoblast fractions on allogeneic in vivo systems and to obtain more evidence for the relevance of their activity on the maternofetal interface, their effect was studied on graft-versus-host reaction (GVHR). To assess the GVHR, the primary and secondary popliteal lymph nodes assay was used in mice. In the primary GVHR, 100 microg protein of Fraction 2-5, mixed with 5 x 10(6) allogeneic spleen cells (C57BL/6), were injected into one of the foot pads of recipient (BALB/c) mice. The secondary GVHR was induced in F1 (BALB/c x C57BL/6) mice by injection of spleen cells of BALB/c mice intraperitoneally preimmunized with allogeneic cells. The GVHR was measured by the weight of lymph nodes and by the lymphocyte proliferation. Flow cytometric analyses of the cells in the nodes with GVHR and under the influence of Fraction 4 or 5 were performed using monoclonal antibodies. In the primary GVHR, Fraction 4 or 5, injected simultaneously with allogeneic spleen cells, significantly suppressed the lymph nodes reactivity. Fractions 4 and 5 inhibited the ability of the spleen cells of mice intraperitoneally preimmunized with allogeneic cells to induce secondary GVHR in F1 mice. The Fraction 2 and 3 had no effect on GVHR. The results revealed that a group of proteins with Mr 37-7 kDa, isolated from trophoblast of pig placenta, strongly suppressed popliteal lymph node reactivity in the primary and secondary GVHR. The data provide convincing evidence for these fractions in vivo activity, for their effect across the species barrier and suggest the relevance of the same reactions on the materno-fetal interface.

Human decidualized endometrial T lymphocytes do not substantially down-regulate CD3zeta

PROBLEM

The T-cell antigen receptor (TCR) has been reported to be down-regulated on T-cells in the decidualized endometrium in early pregnancy.

METHOD OF STUDY

The expression of CD3zeta, a component of the TCR complex, has been investigated in human first-trimester decidual T-cells using flow cytometric analysis of permeabilized cells.

RESULTS

Levels of CD3zeta expression were significantly lower in decidual than in peripheral T-cells from non-pregnant women, as assessed by mean fluorescence intensity (4.2 vs. 5.5, logarithmic scale, P < 0.05). However, when decidual and peripheral T-cells from the same subjects were analyzed (n = 10), mean levels of CD3zeta were slightly, but not significantly, lower in decidual than in peripheral T-cells (P > 0.1). CD3zeta was not substantially down-regulated systemically as mean cytoplasmic CD3zeta levels did not differ significantly between peripheral blood T-cells from pregnant women and non-pregnant controls (P > 0.2). CD8+ cells outnumber CD4+ cells in decidua, but neither the proportions of these two T-cell subsets positive for cytoplasmic CD3zeta nor the mean levels of CD3zeta were significantly different.

CONCLUSIONS

These results indicate that human decidual T-cells do not greatly down-regulate CD3zeta, but it is unclear if a small decrease in mean levels may be sufficient to compromise their capacity for activation.

How might pregnancy immunize against breast cancer?

PROBLEM

This study investigated how pregnancy might protect against breast cancer.

METHOD OF STUDY

A critical review of the literature was done.

RESULTS/CONCLUSIONS

Support for an active role in pregnancy immunizing against breast cancer comes from case studies demonstrating a reciprocal correlation between pregnancy and breast cancer as well as recent experiments supporting the fetal antigen hypothesis that confirms the presence of a tumor-specific antigen, MUC1, on both fetal and breast cancer tissues. Multiparous women also generate anti-MUC1 major histocompatibility complex-restricted cytotoxic T cell cytolytic activity against MUC1-bearing tumor cell lines. Careful investigation of the fetal antigen hypothesis and tolerogenic mechanisms may lead to effective vaccination protocols against breast cancer and other cancers.