NK cell tolerance and the maternal-fetal interface

The maternal-fetal interface at single-cell resolution: uncovering the cellular anatomy of the placenta and decidua

The maternal-fetal interface represents a critical site of immunological interactions that can greatly influence pregnancy outcomes. The unique cellular composition and cell-cell interactions taking place within these tissues has spurred substantial research efforts focused on the maternal-fetal interface. With the recent advent of single-cell technologies, multiple investigators have applied such methods to gain an unprecedented level of insight into maternal-fetal communication. Here, we provide an overview of the dynamic cellular composition and cell-cell communications at the maternal-fetal interface as reported by single-cell investigations. By primarily focusing on data from pregnancies in the second and third trimesters, we aim to showcase how single-cell technologies have bolstered the foundational understanding of each cell's contribution to physiologic gestation. Indeed, single-cell technologies have enabled the examination of classical placental cells, such as the trophoblast, as well as uncovered new roles for structural cells now recognized as active participants in pregnancy and parturition, such as decidual and fetal stromal cells, which are reviewed herein. Furthermore, single-cell data investigating the ontogeny, function, differentiation, and interactions among immune cells present at the maternal-fetal interface, namely macrophages, T cells, dendritic cells, neutrophils, mast cells, innate lymphoid cells, natural killer cells, and B cells are discussed in this review. Moreover, a key output of single-cell investigations is the inference of cell-cell interactions, which has been leveraged to not only dissect the intercellular communications within specific tissues but also between compartments such as the decidua basalis and placental villi. Collectively, this review emphasizes the ways by which single-cell technologies have expanded the understanding of cell composition and cellular processes underlying pregnancy in mid-to-late gestation at the maternal-fetal interface, which can prompt their continued application to reveal new pathways and targets for the treatment of obstetrical disease.

Cross-Generational Impact of Innate Immune Memory Following Pregnancy Complications

Pregnancy complications can have long-term negative effects on the health of the affected mothers and their children. In this review, we highlight the underlying inflammatory etiologies of common pregnancy complications and discuss how aberrant inflammation may lead to the acquisition of innate immune memory. The latter can be described as a functional epigenetic reprogramming of innate immune cells following an initial exposure to an inflammatory stimulus, ultimately resulting in an altered response following re-exposure to a similar inflammatory stimulus. We propose that aberrant maternal inflammation associated with complications of pregnancy increases the cross-generational risk of developing noncommunicable diseases (i.e., pregnancy complications, cardiovascular disease, and metabolic disease) through a process mediated by innate immune memory. Elucidating a role for innate immune memory in the cross-generational health consequences of pregnancy complications may lead to the development of novel strategies aimed at reducing the long-term risk of disease.

Uterine natural killer cells and recurrent spontaneous abortion

Recurrent spontaneous abortion (RSA), termed as two or more consecutive pregnancy loss is a great problem for some women of childbearing age. A large number of evidence confirm that there may be an immune background of RSA. As a member of the innate immune system, uterine natural killer (uNK) cells account for about 70% of total lymphocytes during pregnancy and play a critical role in the establishment and maintenance of pregnancy. This review mainly introduces the phenotype, origin, receptor, and function of uNK cells to illuminate its relationship with RSA.

Epidemiology and pathogenesis of maternal-fetal transmission of Trypanosoma cruzi and a case for vaccine development against congenital Chagas disease

Trypanos o ma cruzi (T. cruzi or Tc) is the causative agent of Chagas disease (CD). It is common for patients to suffer from non-specific symptoms or be clinically asymptomatic with acute and chronic conditions acquired through various routes of transmission. The expecting women and their fetuses are vulnerable to congenital transmission of Tc. Pregnant women face formidable health challenges because the frontline antiparasitic drugs, benznidazole and nifurtimox, are contraindicated during pregnancy. However, it is worthwhile to highlight that newborns can be cured if they are diagnosed and given treatment in a timely manner. In this review, we discuss the pathogenesis of maternal-fetal transmission of Tc and provide a justification for the investment in the development of vaccines against congenital CD.

Morphology and physiology of rat placenta for toxicological evaluation

The placenta plays a pivotal role in fetal growth, and placental dysfunction and injury are associated with embryo/fetal toxicity. Histological examination of the rat placenta for safety evaluation provides valuable clues to the mechanisms of this toxicity. However, the placenta has specific and complex biological features unlike those of other organs, and placental structure dramatically changes depending on the time during the gestation period. Thus, time-dependent histopathological examination of the rat placenta should be performed based on the understanding of normal developmental changes in morphology and function. The placentas of rats and humans are both anatomically classified as discoid and hemochorial types. However, there are differences between rats and humans in terms of placental histological structure, the fetal-maternal interface, and the function of the yolk sac. Therefore, extrapolation of placental toxicity from rats to humans should be done cautiously in the evaluation of risk factors. This review describes the development, morphology, physiology, and toxicological features of the rat placenta and the differences between the rat and human placenta to enable accurate evaluation of reproductive and developmental toxicity in studies.

Diminished Frequency of Menstrual and Peripheral Blood NKT-Like Cells in Patients With Unexplained Recurrent Spontaneous Abortion and Infertile Women

Systemic monitoring of immune system may not precisely outline the local immune status in the uterus. This survey is a continuation of our previous studies on potential usefulness of menstrual blood (MB) immunophenotyping as a tool for investigation of immunological disturbances in pregnancy-related disorders. Peripheral blood (PB) and MB from healthy fertile (n = 15), unexplained recurrent spontaneous abortion (URSA; n = 15), and unexplained infertile women (n = 8) were collected simultaneously in the second day of their menstrual cycle and frequency of natural killer T (NKT)-like cell subpopulations were assessed by flow cytometry. Menstrual blood of all experimental groups contained higher percentage of TCRαβ⁺, CD45RO⁺, and CD16^- NKT-like cells compared to corresponding PB. Frequency of MB NKT-like cells in unexplained infertile participants was lower than fertile and URSA groups. Compared to normal participants, patients with URSA had lower frequency of PB TCRαβ⁺ and higher CD16⁺, while in infertile woman frequencies of PB CD45RO⁺, CD45RO^-, CD16^-, IL17⁺, and MB CD45RO⁺ NKT-like cells were lower. Although, PB and MB seemingly have the same histological nature, our results showed that MB contained different composition of NKT-like subsets with different cytokine profiles and could be viewed as one potential biological sample for evaluation of patients with infertility and URSA.

Acute Fetal Demise with First Trimester Maternal Infection Resulting from Listeria monocytogenes in a Nonhuman Primate Model

Infection with Listeria monocytogenes during pregnancy is associated with miscarriage, preterm birth, and neonatal complications, including sepsis and meningitis. While the risk of these conditions is thought to be greatest during the third trimester of pregnancy, the determinants of fetoplacental susceptibility to infection, the contribution of gestational age, and the in vivo progression of disease at the maternal-fetal interface are poorly understood. We developed a nonhuman primate model of listeriosis to better understand antecedents of adverse pregnancy outcomes in early pregnancy. Four pregnant cynomolgus macaques (Macaca fascicularis) received a single intragastric inoculation between days 36 and 46 of gestation with 10⁷ CFU of an L. monocytogenes strain isolated from a previous cluster of human listeriosis cases that resulted in adverse pregnancy outcomes. Fecal shedding, maternal bacteremia, and fetal demise were consistently noted within 7 to 13 days. Biopsy specimens of maternal liver, spleen, and lymph node displayed variable inflammation and relatively low bacterial burden. In comparison, we observed greater bacterial burden in the decidua and placenta and the highest burden in fetal tissues. Histopathology indicated vasculitis, fibrinoid necrosis, and thrombosis of the decidual spiral arteries, acute chorioamnionitis and villitis in the placenta, and hematogenous infection of the fetus. Vascular pathology suggests early impact of L. monocytogenes infection on spiral arteries in the decidua, which we hypothesize precipitates subsequent placentitis and fetal demise. These results demonstrate that L. monocytogenes tropism for the maternal reproductive tract results in infection of the decidua, placenta, and the fetus itself during the first trimester of pregnancy.

Although listeriosis is known to cause significant fetal morbidity and mortality, it is typically recognized in the third trimester of human pregnancy. Its impact on early pregnancy is poorly defined. Here we provide evidence that exposure to L. monocytogenes in the first trimester poses a greater risk of fetal loss than currently appreciated. Similarities in human and nonhuman primate placentation, physiology, and reproductive immunology make this work highly relevant to human pregnancy. We highlight the concept that the maternal immune response that protects the mother from serious disease is unable to protect the fetus, a concept relevant to classic TORCH (toxoplasmosis, other, rubella, cytomegalovirus, and herpes) infections and newly illuminated by current Zika virus outbreaks. Studies with this model, using the well-understood organism L. monocytogenes, will permit precise analysis of host-pathogen interactions at the maternal-fetal interface and have broad significance to both recognized and emerging infections in the setting of pregnancy.

Effect of Indoleamine 2,3-Dioxygenase Expressed in HTR-8/SVneo Cells on Decidual NK Cell Cytotoxicity

PROBLEM

To study the effect of indoleamine 2,3-dioxygenase (IDO) expressed in HTR-8/SVneo cells on NKG2D and NKp46 expression and cytotoxicity of decidual NK (dNK) and peripheral NK (pNK) cells.

METHOD OF STUDY

CD56(+) dNK and pNK cells purified were cultured with HTR-8/SVneo cell conditioned medium (CM), 1-MT+HTR-8/SVneo cell CM, and complete RPMI 1640 medium (negative control) in vitro. The mRNA and protein expression of NKG2D and NKp46 in NK cells were then assessed by qRT-PCR and flow cytometry, respectively. Their cytotoxicity was evaluated with LDH assays, and TNF-α secretion was analyzed by ELISA.

RESULTS

For dNK cells, the mRNA and protein expression of NKp46 as well as NKG2D did not differ significantly among the three groups (P > 0.05), whereas for pNK cells, the expression level was significantly decreased in HTR-8/SVneo cell CM group than the other two groups (P < 0.01). Peripheral NK cells cultured with HTR-8/SVneo cell CM showed reduced cytotoxicity and TNF-α secretion than the other two groups (P < 0.01), although there were no significant differences among three groups for dNK cells (P > 0.05).

CONCLUSION

IDO expressed by HTR-8/SVneo cells can down-regulate NKp46 and NKG2D expression and reduce cytotoxicity in pNK cells, and may contribute to keep dNK cytotoxicity at a low level, suggesting an important role for IDO in the maintenance of normal pregnancy.

Oxidative Stress: Placenta Function and Dysfunction

During pregnancy, the placenta is a site of active oxygen metabolism that continuously generates oxidative stress (OS). Overproduction of reactive oxygen species and reactive nitrogen species can destroy normal placental functions. Therefore, the feto-placental unit generates abundant antioxidants to keep OS under control. Properly controlled oxidative species have been proven to serve as indispensable cellular signal messengers by regulating gene expression and downstream cellular activities. OS also plays an important immunoregulatory role during pregnancy. Oxidative disorder and immune disturbances are associated with adverse pregnancy outcomes such as spontaneous abortion, preeclampsia and intrauterine growth restriction. In this review, we introduce recent studies revealing basal functions and regulatory roles of placental OS in metabolism and immunity. The relationships between OS- and pregnancy-related disorders are also discussed.

Insights into the paracrine effects of uterine natural killer cells

Uterine natural killer (uNK) cells are recruited into the uterus during establishment of the implantation and placentation of the embryo, and are hypothesized to regulate uterine spiral artery remodeling and angiogenesis during the initial stages of pregnancy. Failures in uNK cell activation are linked to diseases associated with pregnancy. However, the manner in which these cells interact with the endometrium remain unknown. Therefore, this study investigated the paracrine effects of uNK cells on the gene expression profile of an endometrial epithelial and stromal cell co‑culture system in vitro, using a microarray analysis. Results from reverse transcription‑quantitative polymerase chain reaction and enzyme‑linked immunosorbent assay experiments showed that soluble factors from uNK cells significantly alter endometrial gene expression. In conclusion, this study suggests that paracrine effects of uNK cells guide uNK cell proliferation, trophoblast migration, endometrial decidualization and angiogenesis, and maintain non‑cytotoxicity of uNK cells.

MicroRNAs, immune cells and pregnancy

MicroRNAs (miRNAs) are a recently discovered class of non-coding RNAs that are expressed in many cell types, where they regulate the expression of complementary RNAs, thus modulating the stability and translation of mRNAs. miRNAs are predicted to regulate the expression of ∼50% of all protein coding genes in mammals. Therefore, they participate in virtually all cellular processes investigated so far. Altered miRNAs expressions are associated with both physiological (pregnancy) and pathological processes (cancer). As the dynamic maternal-fetal interface plays a critical role in the maintenance of successful pregnancy, it is not surprising that the miRNAs that are unique to reproductive tissues are abundantly expressed. Research in this field has demonstrated the presence and dysregulation of a distinct set of pregnancy-associated miRNAs; however, most studies have centered on localizing various miRNAs in reproductive microdomains associated with normal or complicated pregnancies. Although several independent miRNA regulatory mechanisms associated with endometrial receptivity, immune cells, angiogenesis and placental development have been studied, miRNA-mediated regulation of pregnancy remains poorly understood. This review provides a summary of the current data on miRNA regulation as well as functional profiles of miRNAs that are found in the uterus, in immune cells associated with maternal tolerance to the fetus, and those involved in angiogenesis and placental development.

Optimized nonclinical safety assessment strategies supporting clinical development of therapeutic monoclonal antibodies targeting inflammatory diseases

An increasing number of immunomodulatory monoclonal antibodies (mAbs) and IgG Fc fusion proteins are either approved or in early-to-late stage clinical trials for the treatment of chronic inflammatory conditions, autoimmune diseases and organ transplant rejection. The exquisite specificity of mAbs, in combination with their multi-functional properties, high potency, long half-life (permitting intermittent dosing and prolonged pharamcological effects), and general lack of off-target toxicity makes them ideal therapeutics. Dosing with mAbs for these severe and debilitating but often non life-threatening diseases is usually prolonged, for several months or years, and not only affects adults, including sensitive populations such as woman of child-bearing potential (WoCBP) and the elderly, but also children. Immunosuppression is usually a therapeutic goal of these mAbs and when administered to patients whose treatment program often involves other immunosuppressive therapies, there is an inherent risk for frank immunosuppression and reduced host defence which when prolonged increases the risk of infection and cancer. In addition when mAbs interact with the immune system they can induce other adverse immune-mediated drug reactions such as infusion reactions, cytokine release syndrome, anaphylaxis, immune-complex-mediated pathology and autoimmunity. An overview of the nonclinical safety assessment and risk mitigation strategies utilized to characterize these immunomodulatory mAbs and Fc fusion proteins to support first-in human (FIH) studies and futher clinical development in inflammatory disease indications is provided. Specific emphasis is placed on the design of studies to qualify animal species for toxicology studies, early studies to investigate safety and define PK/PD relationships, FIH-enabling and chronic toxicology studies, immunotoxicity, developmental, reproductive and juvenile toxicity studies and studies to determine the potential for immunosuppression and reduced host defence against infection and cancer. Nonclinical strategies to facilitate clinical and market entry in the most efficient timeframe are presented.

Natural killer cells and regulatory T cells in early pregnancy loss

Survival of the allogeneic embryo in the uterus depends on the maintenance of immune tolerance at the maternal-fetal interface. The pregnant uterus is replete with activated maternal immune cells. How this immune tolerance is acquired and maintained has been a topic of intense investigation. The key immune cells that predominantly populate the pregnant uterus are natural killer (NK) cells. In normal pregnancy, these cells are not killers, but rather provide a microenvironment that is pregnancy compatible and supports healthy placentation. In placental mammals, an array of highly orchestrated immune elements to support successful pregnancy outcome has been incorporated. This includes active cooperation between maternal immune cells, particularly NK cells, and trophoblast cells. This intricate process is required for placentation, immune regulation and to remodel the blood supply to the fetus. During the past decade, various types of maternal immune cells have been thought to be involved in cross-talk with trophoblasts and in programming immune tolerance. Regulatory T cells (Tregs) have attracted a great deal of attention in promoting implantation and immune tolerance beyond implantation. However, what has not been fully addressed is how this immune-trophoblast axis breaks down during adverse pregnancy outcomes, particularly early pregnancy loss, and in response to unscheduled inflammation. Intense research efforts have begun to shed light on the roles of NK cells and Tregs in early pregnancy loss, although much remains to be unraveled in order to fully characterize the mechanisms underlying their detrimental activity. An increased understanding of host-environment interactions that lead to the cytotoxic phenotype of these otherwise pregnancy compatible maternal immune cells is important for prediction, prevention and treatment of pregnancy maladies, particularly recurrent pregnancy loss. In this review, we discuss relevant information from experimental and human models that may explain the pregnancy disrupting roles of these pivotal sentinel cells at the maternal-fetal interface.

Expression of the activating receptor, NKp46 (CD335), in human natural killer and T-cell neoplasia

OBJECTIVES

To evaluate the expression of CD335 (NKp46), an activation receptor that is selectively expressed on natural killer (NK) cells.

METHODS

We assessed CD335's potential utility as a diagnostic marker in 657 cases by flow cytometry and 410 cases by immunohistochemistry.

RESULTS

We observed that CD335 was highly specific for NK cells in nonneoplastic tissues. Moreover, 61 (90%) of 68 of NK cell neoplasms demonstrated CD335 expression, whereas B-cell, myelomonocytic, and plasma cell neoplasms lacked expression. Notably, 16 (20%) of 82 mature T-cell neoplasms, particularly T-cell large granular lymphocytic leukemia, mycosis fungoides, and ALK+ anaplastic large cell lymphoma, aberrantly expressed CD335.

CONCLUSIONS

Collectively, these data support the diagnostic utility of CD335 in evaluating hematopoietic malignancies and suggest that CD335 could be a useful target for selective immunotherapy in patients with mature NK and T-cell neoplasms.

Maternal floor infarction/massive perivillous fibrin deposition: a manifestation of maternal antifetal rejection?

OBJECTIVE

Massive perivillous fibrin deposition (MPFD) and maternal floor infarction (MFI) are related placental lesions often associated with fetal death and fetal growth restriction. A tendency to recur in subsequent pregnancies has been reported. This study was conducted to determine whether this complication of pregnancy could reflect maternal antifetal rejection.

METHODS

Pregnancies with MPFD were identified (n = 10). Controls consisted of women with uncomplicated pregnancies who delivered at term without MPFD (n = 175). Second-trimester maternal plasma was analyzed for panel-reactive anti-HLA class I and class II antibodies. The prevalence of chronic chorioamnionitis, villitis of unknown etiology, and plasma cell deciduitis was compared between cases and controls. Immunohistochemistry was performed on available umbilical vein segments from cases with MPFD (n = 4) to determine whether there was evidence of complement activation (C4d deposition). Specific maternal HLA-antibody and fetal HLA-antigen status were also determined in paired specimens (n = 6). Plasma CXCL-10 concentrations were measured in longitudinal samples of cases (n = 28 specimens) and controls (n = 749 specimens) by ELISA. Linear mixed-effects models were used to test for differences in plasma CXCL-10 concentration.

RESULTS

(i) The prevalence of plasma cell deciduitis in the placenta was significantly higher in cases with MPFD than in those with uncomplicated term deliveries (40% versus 8.6%, P = 0.01), (ii) patients with MPFD had a significantly higher frequency of maternal anti-HLA class I positivity during the second trimester than those with uncomplicated term deliveries (80% versus 36%, P = 0.01); (iii) strongly positive C4d deposition was observed on umbilical vein endothelium in cases of MPFD, (iv) a specific maternal antibody against fetal HLA antigen class I or II was identified in all cases of MPFD; and 5) the mean maternal plasma concentration of CXCL-10 was higher in patients with evidence of MPFD than in those without evidence of MFPD (P < 0.001).

CONCLUSION

A subset of patients with MPFD has evidence of maternal antifetal rejection.

MicroRNA regulation of natural killer cells

Natural killer (NK) cells are innate immune lymphocytes critical for host defense against viral infection and surveillance against malignant transformation. MicroRNAs (miRNAs) are a family of small, non-coding RNAs that regulate a wide variety of cellular processes. Recent advances have highlighted the importance of miRNA-mediated post-transcriptional regulation in NK cell development, maturation, and function. This review focuses on several facets of this regulatory mechanism in NK cells: (1) the expressed NK cell miRNA transcriptome; (2) the impact of total miRNA deficiency on NK cells; (3) the role of specific miRNAs regulating NK cell development, survival, and maturation; (4) the intrinsic role of miRNAs regulating NK cell function, including cytokine production, proliferation, and cytotoxicity; and (5) the role of NK cell miRNAs in disease. Currently our knowledge of how miRNAs regulate NK cell biology is limited, and thus we also explore key open questions in the field, as well as approaches and techniques to ascertain the role of individual miRNAs as important molecular regulators.

Immune privilege of stem cells

Immune privilege provides protection to vital tissues or cells of the body when foreign antigens are introduced into these sites. The modern concept of relative immune privilege applies to a variety of tissues and anatomical structures, including the hair follicles and mucosal surfaces. Even sites of chronic inflammation and developing tumors may acquire immune privilege by recruiting immunoregulatory effector cells. Adult stem cells are no exception. For their importance and vitality, many adult stem cell populations are believed to be immune privileged. A preimplantation-stage embryo that derives from a totipotent stem cell (i.e., a fertilized oocyte) must be protected from maternal allo-rejection for successful implantation and development to occur. Embryonic stem cells, laboratory-derived cell lines of preimplantation blastocyst-origin, may, therefore, retain some of the immunological properties of the developing embryo. However, embryonic stem cells and their differentiated tissue derivatives transplanted into a recipient do not necessarily have an ability to subvert immune responses to the extent required to exploit their pluripotency for regenerative medicine. In this review, an extended definition of immune privilege is developed and the capacity of adult and embryonic stem cells to display both relative and acquired immune privilege is discussed. Furthermore, we explore how these intrinsic properties of stem cells may one day be harnessed for therapeutic gain.

Barriers of the Human Organism and Their Achilles’ Heels

The human body is covered by barriers separating it from the external and internal surroundings. The “milieu enterieur” has to be stabilised in spite of the variable external and internal conditions of toxic, osmotic, microbial and climatic environmental circumstances. This first line of barriers is composed of skin and mucous membranes of complicated structures.

A second line of barrier system is present in our organisms. Certain organs have to be separated from the immune system and other parts of the body because of evolutionary reasons (eye-bulb and testicles) because of unique proteins “unknown” for the acquired immune system. The blood-brain barrier (BBB) is providing enhanced safety circumstances for the central nervous system. The second line of barriers is represented by the special properties of the capillary endothelial system.

The maternal-fetal barrier is the most complex. At the maternal fetal interface two individuals of two different haplotypes has to be live 9 months separated by a very complicated dynamic barrier.

The placenta is the organ, which is separating the maternal and fetal tissues. Similar to others the bidirectional transport of gasses, metabolites, cells, proteins, regulatory substances, are transported by active or passive transcellular and intercellular mechanisms.

The fetal immune system develops immunotolerance to all maternal cells and antigens transferred transplacentally. The problem is to mitigate the maternal immune system to tolerate the paternal haplotype of the fetus. In the case of normal pregnancy a complex series of physiological modifications can solve the problem without harmful consequences to the mother and fetus.

The outermost contact cells of trophoblasts express instead of HLA-class Ia and class II antigens non-variable HLA-C, HLA-E, HLA-F and HLA-G antigens. The first consequence of this is reduction of the activity of maternal natural killer cells and maternal dendritic cells;

Progesteron, micro-RNA and mediators influence the development of T effector-cells. The production of soluble HLA-G(5 and 6) and IL-10 supports the differentiation of Th-2 CD4⁺ helper cells, reducing the ability of maternal cells to kill fetal cells.

Series of receptors and costimulators are expressed by the different lines of semi-allogenic trophoblast cells to bind HLA-G and mitigate maternal immune response;

The maternal immunotolerance is further facilitated by the activation of CD4⁺CD25^brightFoxp3⁺ regulatory T (T_REG) cells.

Infections have to be prevented during pregnancy. The cells of placenta express 10 Toll-like receptors a group of pattern recognition receptors responsible for innate immunity. The interferon level is also higher in the placental tissues than in the somatic fetal or maternal cells.

The complement system is also adapted to the requirements of the pregnancy and fetal damage is inhibited by the production of “assymmetric IgG antibodies” under hormonal and placental-regulation. These modifications prevent the activation of complement, cytotoxic activity, opsonising ability, antigen clearance and precipitating activity of the molecules.

The Achilles’ heels of the different barriers are regularly found by virus infections. Lamina cribrosa of the blood-brain barrier, optical nerve of the eyes, etc. the risk factors of the maternal-fetal barrier has been summarised in Table 1.1.

Maternal HLA panel-reactive antibodies in early gestation positively correlate with chronic chorioamnionitis: evidence in support of the chronic nature of maternal anti-fetal rejection

PROBLEM

Maternal tolerance of the fetus is essential for viviparity, yet anti-fetal rejection occurs in several pregnancy complications. Chronic chorioamnionitis is a feature of anti-fetal cellular rejection. There is a robust association between chronic chorioamnionitis and maternal seropositivity for anti-human leukocyte antigen (HLA) panel-reactive antibodies (PRA) at the time of delivery. This longitudinal study was performed to assess maternal HLA PRA status in early gestation and the temporal evolution of maternal HLA PRA in the context of chronic chorioamnionitis and, thereby, to determine whether HLA PRA during the course of pregnancy is useful for the detection of anti-fetal rejection.

METHOD OF STUDY

Maternal sera obtained before 16 weeks of gestation and at delivery were analyzed for HLA PRA in cases with (N = 100) and without (N = 150) chronic chorioamnionitis.

RESULTS

IgG (but not IgM) HLA class I and II PRA positivity at delivery was higher in cases with chronic chorioamnionitis than in those without chronic chorioamnionitis. IgG HLA class I PRA positivity before 16 weeks of gestation was higher in cases with chronic chorioamnionitis than in those without (30.3 versus 13.3%; P = 0.001). Positive conversion (negative HLA PRA before 16 weeks of gestation but positive at delivery) of IgG HLA class I and II PRA was significantly associated with chronic chorioamnionitis. Fetal HLA class I antigen-specific antibodies were confirmed in 12 of 16 mothers tested who were sensitized to HLA class I antigens before 16 weeks of gestation.

CONCLUSION

Positive maternal HLA PRA before 16 weeks of gestation and the temporal evolution of maternal HLA PRA are associated with the presence of chronic chorioamnionitis at the time of delivery. Maternal IgG HLA PRA has the potential to be a monitoring tool of anti-fetal rejection. Furthermore, the findings herein indicate that subsets of fetuses are exposed to alloimmune HLA antibodies for months, especially in cases with chronic chorioamnionitis.

Immunopharmacology of ulipristal as an emergency contraceptive

A new progesterone antagonist, ulipristal has been made available as an emergency contraceptive. Ulipristal’s major mechanism of action as an emergency contraceptive has been ascribed to its ability to delay ovulation beyond the life span of the sperm. This paper analyzes the potential action of ulipristal (1) when unprotected intercourse and administration of ulipristal occur outside the fertility window and (2) when unprotected intercourse and administration of ulipristal occur at or within 24 hours of ovulation. When unprotected intercourse and the use of a single low dose of ulipristal occur outside of the fertility window, ulipristal behaves like a placebo. When unprotected intercourse and the use of a single low dose of ulipristal occur within the fertility window but before ovulation, ulipristal behaves like an emergency contraceptive by delaying ovulation and thereby preventing fertilization. When unprotected intercourse and the administration of ulipristal occur at or within 24 hours of ovulation, then ulipristal has an abortifacient action. It is proposed that the abortifacient mechanism of a low dose of ulipristal taken after fertilization but before implantation is due to the ability of ulipristal to block the maternal innate immune system to become immunotolerant to the paternal allogenic embryo. Progesterone’s critical immunotolerant actions involving early pregnancy factor, progesterone-induced blocking factor, and uterine natural killer cells are compromised by ulipristal.

Mechanisms of NK cell activation: CD4(+) T cells enter the scene

Natural killer (NK) cells are innate lymphocytes involved in immunosurveillance through their cytotoxic activity and their capacity to secrete inflammatory cytokines. NK cell activation is necessary to initiate effector functions and results from a complex series of molecular and cellular events. We review here the signals that trigger NK cells and discuss recent findings showing that, besides antigen-presenting cells, T cells can play a central role in the initiation of NK cell activation in lymph nodes.

Effect of cisplatin on rat placenta development

We examined the sequential histopathological changes in the placenta from rats exposed to cisplatin. Cisplatin was intraperitoneally administered at 2 mg/kg/day during GDs 11-12 (GD11,12-treated group), or GDs 13-14 (GD13,14-treated group), and the placentas were sampled on GDs 13, 15, 17 and 21. Fetal mortality rates were increased up to approximately 65% from GD 17 onward, and fetal weights were decreased on GD 21 in the GD11,12-treated group. A reduction in placental weights was detected from GD 15 onward, and the placentas on GD 21 were macroscopically small and thin in both treated groups. Histopathologically, in the GD13,14-treated group, an increase in apoptotic cells was detected on GDs 15 and 17 in the labyrinth zone, and on GD 21 in the basal zone, resulting in labyrinth zone hypoplasia. By contrast, in the GD11,12-treated group, an increase in apoptotic cells was detected on GDs 13, 15 and 17 in the labyrinth zone, and during the experimental period in the basal zone. A decrease in Phospho-Histone H3 positive cells was detected on GD 13 in the labyrinth zone and basal zone, resulting in hypoplasia of the labyrinth zone and basal zone. In addition, a marked decrease in glycogen cell-islands in the basal zone was also detected on GDs 15 and 17. There was a reduction in interstitial invasion of glycogen cell-like trophoblasts into the metrial gland on GD 15, resulting in metrial gland hypoplasia. Therefore, we consider that cisplatin administration in pregnant rats induces growth arrest of the labyrinth zone and basal zone, leading to small placenta. It is assumed that metrial gland hypoplasia is secondarily induced by the failure of glycogen cell island development associated with basal zone hypoplasia.

Measurement of NK activity in whole blood by the CD69 up-regulation after co-incubation with K562, comparison with NK cytotoxicity assays and CD107a degranulation assay

In present study human peripheral blood NK cell activation after co-incubation with K569 cell line was investigated by CD69 expression. NK lytic activity was studied by two different assays: TDA (2,2':6',2″-terpyridine-6,6″-dicarboxylate) release assay (TRA) and flow cytometry assay (FCA) that display two approach to cytotoxicity measurement. We also investigated NK cell degranulation activity by estimation of CD107a (LAMPa) expression. Comparison of specific lysis value measured by both cytotoxicity assays showed high correlation coefficient between two methods (r=0.94447). Specific lysis value correlated significantly with CD69+ NK frequency and NK degranulation activity. We show that lymphocyte incubation with K562 results to increase CD69 expression on NK and NKT but not on T lymphocytes. Only a part of peripheral blood NK cells became CD69 positive after incubation with excess of K562 cells. CD69+ NK cell frequencies did not increase after elevation of K562/NK ratio or incubation period that confirmed existence of subset of NK cells able to response to K562. CD69 elevation on NK significantly correlated with NK cytotoxicity (r=0.726). CD69 increases were similar when whole blood or isolated PBMC was used in assay. We also found different capacity to activation in NK subsets that express CD62L at various densities. The results demonstrated that K562 induced CD69 expression displays NK lymphocyte functional condition that associated with cytotoxic function.

Toxicological pathology in the rat placenta

The placenta grows rapidly for a short period with high blood flow during pregnancy and has multifaceted functions, such as its barrier function, nutritional transport, drug metabolizing activity and endocrine action. Consequently, the placenta is a highly susceptible target organ for drug- or chemical-induced adverse effects, and many placenta-toxic agents have been reported. However, histopathological examination of the placenta is not generally performed, and the placental toxicity index is only the placental weight change in rat reproductive toxicity studies. The placental cells originate from the trophectoderm of the embryo and the endometrium of the dam, proliferate and differentiate into a variety of tissues with interaction each other according to the development sequence, resulting in formation of a placenta. Therefore, drug- or chemical-induced placental lesions show various histopathological features depending on the toxicants and the exposure period, and the pathogenesis of placental toxicity is complicated. Placental weight assessment appears not to be enough to evaluate placental toxicity, and reproductive toxicity studies should pay more attention to histopathological evaluation of placental tissue. The detailed histopathological approaches to investigation of the pathogenesis of placental toxicity are considered to provide an important tool for understanding the mechanism of teratogenicity and developmental toxicity with embryo lethality, and could benefit reproductive toxicity studies.

NK cells, autoantibodies, and immunologic infertility: a complex interplay

Infertility and recurrent spontaneous abortion (RSA) are heterogeneous conditions that have been frequently explained with an immunological pathomechanism. A deeper insight into apparently unexplained infertility and RSA shows increasing evidences supporting both alloimmune and autoimmune mechanisms, in which natural killer (NK) cells and autoantibodies seem to play a relevant role. Successful pregnancy is considered as Th1-Th2 cooperation phenomenon, with a predominantly Th2-type lymphocytes response, together with the emerging role of interleukin (IL)-12, IL-15, and IL-18 and of other unidentified soluble factors dependent on NK cells. Uterine NK cells comprise the largest population at implantation site, and their activity, characteristics, and abundance suggest that they participate at the "decidualization" process that, vice versa, induces NK activation and recruitment in each menstrual cycle. However, NK cell alteration may be associated with impaired pregnancy, and the modulation in the number of circulating NK cells is most likely to be a primary event rather than an active inflammation/drug administration consequence during an inflammatory/autoimmune process, thus playing an important role in the pathogenesis of immunological infertility. Relationships within immunological infertility, recurrent spontaneous abortion, autoantibodies, and NK cells will be reviewed herein.

Role of HLA-G and NCR in protection of umbilical cord blood haematopoietic stem cells from NK cell mediated cytotoxicity

Allogeneic umbilical cord blood haematopoietic stem cells (UCB-HSCs) can be transplanted into a host with the intact innate immunity with limited immuno-reaction, although the mechanisms remain unclear. The present studies aimed at investigating potential mechanisms of allogeneic UCB-HSCs escape from the cytolysis of natural killer (NK) cells. We compared UCB-HSCs ability to protect from NK-mediated cytotoxicity with peripheral blood or bone marrow haematopoietic stem cells (PB-HSCs and BM-HSCs). HSCs expressed lower levels of natural cytotoxicity receptor ligands including NKp30L, NKp44L and NKp46L than monocytes. Blocking these ligands respectively or in combination could increase the resistance of HSCs against NK cell mediated cytotoxicity. High expression of HLA-G was noticed on UCB-HSCs, rather than PB-HSCs or BM-HSCs, whereas blockade of HLA-G significantly elevated NK cell mediated cytolysis to UCB-HSCs. Thus, we conclude that natural cytotoxicity receptors and HLA-G on HSCs may contribute to the escape from NK cells, and activate and inhibitory NK cell receptors and their ligands can be novel therapeutic targets in cell transplantation.

The impairment of metrial gland development in tamoxifen exposed rats

We examined the sequential histopathological changes in the placenta from rats exposed to tamoxifen. Tamoxifen was administered intraperitoneally at doses of 0 and 2 mg/kg/day on gestation days (GDs) 8, 9 and 10, and the placentas were sampled on GDs 11, 13, 15, 17, and 21. The fetal mortality rates in the tamoxifen group were increased up to 56%. However, there were no effects on the weights of live embryos/fetuses and their placentas. Histopathologically, the size of metrial gland in the tamoxifen group was reduced on all sampling times. The spiral arteries appeared less well developed in the hypoplastic metrial gland. A decrease in uterine natural killer (uNK) cells and mitotic uNK cells around the spiral arteries in the metrial gland was detected from GD 13 onward and on GDs 11 and 13, respectively. There were no obvious changes in the labyrinth zone or basal zone. We consider that the anti-estrogen effect of tamoxifen inhibits the proliferation of decidualized endometrial stromal cells in the metrial gland and leads to inhibition of the proliferative activity of uNK cells, followed by defective development of spiral arteries, and metrial gland hypoplasia. It is assumed that the metrial gland hypoplasia might be involved in the tamoxifen-induced embryo/fetus-toxicity.

Immune surveillance of the maternal/fetal interface: controversies and implications

How the fetal 'allograft' avoids rejection during pregnancy remains a major unresolved immunological paradox. Recent work has suggested that fetomaternal tolerance is in fact maintained by a number of redundant mechanisms, but their relative importance has remained poorly defined. In this paper, I discuss an emerging controversy regarding the ability of maternal T cells to mediate fetal rejection at a time when they appear to be ignorant of fetal and placental antigens. This paradox within a paradox highlights two major research directions in the field of reproductive immunology that, when ultimately reconciled, promise to give significant insight into mechanisms of impaired fertility and compromised fetal and maternal health.

Safety and immunotoxicity assessment of immunomodulatory monoclonal antibodies

Most therapeutic monoclonal antibodies (mAbs) licensed for human use or in clinical development are indicated for treatment of patients with cancer and inflammatory/autoimmune disease and as such, are designed to directly interact with the immune system. A major hurdle for the development and early clinical investigation of many of these immunomodulatory mAbs is their inherent risk for adverse immune-mediated drug reactions in humans such as infusion reactions, cytokine storms, immunosuppression and autoimmunity. A thorough understanding of the immunopharmacology of a mAb in humans and animals is required to both anticipate the clinical risk of adverse immunotoxicological events and to select a safe starting dose for first-in-human (FIH) clinical studies. This review summarizes the most common adverse immunotoxicological events occurring in humans with immunomodulatory mAbs and outlines non-clinical strategies to define their immunopharmacology and assess their immunotoxic potential, as well as reduce the risk of immunotoxicity through rational mAb design. Tests to assess the relative risk of mAb candidates for cytokine release syndrome, innate immune system (dendritic cell) activation and immunogenicity in humans are also described. The importance of selecting a relevant and sensitive toxicity species for human safety assessment in which the immunopharmacology of the mAb is similar to that expected in humans is highlighted, as is the importance of understanding the limitations of the species selected for human safety assessment and supplementation of in vivo safety assessment with appropriate in vitro human assays. A tiered approach to assess effects on immune status, immune function and risk of infection and cancer, governed by the mechanism of action and structural features of the mAb, is described. Finally, the use of immunopharmacology and immunotoxicity data in determining a minimum anticipated biologic effect Level (MABEL) and in the selection of safe human starting dose is discussed.

How might infant and paediatric immune responses influence malaria vaccine efficacy?

Naturally acquired immunity to malaria requires repeat infections yet does not engender sterile immunity or long-lasting protective immunologic memory. This renders infants and young children the most susceptible to malaria-induced morbidity and mortality, and the ultimate target for a malaria vaccine. The prevailing paradigm is that infants initially garner protection due to transplacentally transferred anti-malarial antibodies and other intrinsic factors such as foetal haemoglobin. As these wane infants have an insufficient immune repertoire to prevent genetically diverse Plasmodium infections and an inability to control malaria-induced immunopathology. This Review discusses humoral, cell-mediated and innate immune responses to malaria and how each contributes to protection – focusing on how deficiencies in infant and paediatric immune responses might influence malaria vaccine efficacy in this population. In addition, burgeoning evidence suggests a role for inhibitory receptors that limit immunopathology and guide the development of long-lived immunity. Precisely how age or malaria infections influence the function of these regulators is unknown. Therefore the possibility that infants may not have the immune-dexterity to balance effective parasite clearance with timely immune-regulation leading to protective immunologic memory is considered. And thus, malaria vaccines tested in adults and older children may not be predictive for trials conducted in infants.

Hidden talents of natural killers: NK cells in innate and adaptive immunity

Natural killer (NK) cells are innate immune lymphocytes capable of killing target cells and producing immunoregulatory cytokines. Herein, we discuss recent studies that indicate that NK cells span the conventional boundaries between innate and adaptive immunity. For example, it was recently discovered that NK cells have the capacity for memory-like responses, a property that was previously thought to be limited to adaptive immunity. NK cells have also been identified in multiple tissues, and a subset of cells that specialize in the production of the T(H)17 cytokine IL-22, NK-22s, was recently described in mucosal-associated lymphoid tissue. Finally, we review work that shows that NK cells develop at sites that were traditionally thought to be occupied only by adaptive immune cells, including the thymus and lymph nodes.

Innate immunity, coagulation and placenta-related adverse pregnancy outcomes

Maternal immunity undergoes subtle adjustment in order to tolerate the semi-allogeneic embryo and maintain the host defense against potential pathogens. Concomitantly, coagulation systems change from an anti-coagulant state to a pro-coagulant state to meet the hemostatic challenge of placentation and delivery. Innate immunity and blood coagulation systems are the first line of defense to protect a host against exogenous challenges, including alloantigens and mechanical insults, and preserve the integrity of an organism. The interactions between coagulation and immune systems have been extensively studied. Immune cells play a pivotal role in the initiation of the coagulation cascade, whereas coagulation proteases display substantial immuno-modulatory effects. Upon exogenous challenges, the immune and coagulation systems are capable of potentiating each other leading to a vicious cycle. Natural killer (NK) cells, macrophages (Mphis) and dendritic cells (DCs) are three major innate immune cells that have been demonstrated to play essential roles in early pregnancy. However, immune maladaptation and hemostatic imbalance have been suggested to be responsible for adverse pregnant outcomes, such as preeclampsia (PE), miscarriage, recurrent spontaneous abortion (RSA) and intrauterine growth restriction (IUGR). In this review, we will summarize the mutual regulation between blood coagulation and innate immune systems as well as their roles in the maintenance of normal pregnancy and in the pathogenesis of adverse pregnancy outcomes.

Isoforms of human leukocyte antigen-G and their inhibitory receptors in human kidney allograft acceptance

Novel therapeutic strategies such as the modulation of dendritic cell and T-cell function have exhibited great potential in clinical transplantation. Human leukocyte antigen (HLA)-G is a molecule that plays a significant role in establishing complex mechanisms to protect semiallogeneic fetuses from rejection by the maternal immune system. The unique characteristics of both cell-surface and soluble isoforms of HLA-G, the formation of disulfide-bonded dimers with the potential to augment inhibitory receptor signaling, and the function of HLA-G as a preferential ligand for the immunoglobulin-like transcript receptors make HLA-G very important in fundamental approaches for the modulation of immune responses to improve allogeneic graft survival in clinical transplantation. Experimental data from several groups as well as our data from experiments involving HLA-G-mediated human tolerogenic dendritic cells in vitro and receptor transgenic mice in vivo indicate that different isoforms of HLA-G have various immunomodulatory effects through the inhibitory receptors. This knowledge is crucial in understanding mechanisms of prolongation of allograft survival. The analyses of HLA-G isoforms and inhibitory receptors in patients with kidney allograft and the relationship among different isoforms of HLA-G, inhibitory receptors, their mediated immunoregulation, and graft acceptance or failure will be discussed here.

Effector functions of human decidual NK cells in healthy early pregnancy are dependent on the specific engagement of natural cytotoxicity receptors

Natural killer (NK) cells represent the major lymphocyte population in the decidua basalis of the human uterus during healthy early pregnancy. The activity of decidual NK (dNK) cells and their activation status are different from those of peripheral blood (PB)-NK cells; i.e. dNK cells exhibit a unique phenotype. Decidual NK cells have been defined as CD56(bright), CD16(neg), and more recently CD160(neg). They express a unique repertoire of NK cell receptors, identical among all donors tested. Decidual NK cells express in particular NKp46-, NKp30- and NKp44-activating receptors, contrasting with PB-NK cells which are devoid of NKp44-activating receptors. Specific engagement of each of these three so-called natural cytotoxicity receptors in dNK cells has important functional consequences in terms of cytokine, chemokine and angiogenic factor secretion as well as cytotoxic potential. Strikingly, and in contrast with PB-NK cells, engagement of NKp46- but not NKp30-activating receptor on freshly isolated dNK cells triggers cytotoxicity. Such cytotoxic potential of dNK cells is negatively controlled by NKG2A inhibitory receptor co-engagement. This suggests that in situ, dNK cells cannot kill trophoblast cells during normal pregnancy. Whether such NKG2A-mediated inhibition is abolished during pregnancies complicated by pathologies including viral infection is an interesting hypothesis that remains to be tested.

Immunoactivation in preeclampsia: Vdelta2+ and regulatory T cells during the inflammatory stage of disease

Recent data suggest a dominant role of the innate, rather than the adaptive immune system in pregnancy-related immunoregulation. gamma/delta T cells, that comprise a minor subpopulation of human peripheral blood lymphocytes, represent a link between the innate and the acquired immune systems. However little is known about how they function in preeclampsia, which is suggested to be associated with a Th1 predominant immune response. The aim of our study was to investigate the presence and phenotype of Vdelta2+ cells and of regulatory T cells in the pathogenesis of preeclampsia. Since Vdelta2+ T cell function has been shown to be altered in patients with preeclampsia we investigated the expression of perforin, Fas and TIM-3 by Vdelta2+ T cells and the possible role of activating and inhibitory NK cell receptors as well as of regulatory T cells. Vdelta2+ T cells of preeclamptic patients demonstrated an increased perforin and IFNgamma production, which could be explained by dysregulation of NK cell receptor expression. These Th1 polarized cells were less susceptible to apoptosis than Vdelta2+ T cells from healthy pregnant women. Our data suggest that activated Vdelta2+ T cells of preeclamptic women have an increased cytotoxic potential, which may be due to altered expression of NK cell inhibitory and activating receptors. In this study we report a series of observations, which taken together suggest the role of multiple pathways in generating an exaggerated systemic inflammatory response observed in the clinical stage of preeclampsia.

Vascular endothelial growth factor C facilitates immune tolerance and endovascular activity of human uterine NK cells at the maternal-fetal interface

Although replete with cytotoxic machinery, uterine NK (uNK) cells remain tolerant at the maternal-fetal interface. The mechanisms that facilitate the uNK cell tolerance are largely unknown. In this study, we demonstrate that vascular endothelial growth factor (VEGF) C, a proangiogenic factor produced by uNK cells, is responsible for their noncytotoxic activity. VEGF C-producing uNK cells support endovascular processes as demonstrated in a three-dimensional coculture model of capillary tube formation on Matrigel. Peripheral blood NK cells fail to produce VEGF C and remain cytotoxic. This response can be reversed by exogenous VEGF C. We show that cytoprotection by VEGF C can be related to induction of the TAP-1 expression and MHC class I assembly in target cells. Small interfering RNA-mediated silencing of TAP-1 expression abolished the VEGF C-imparted protection. Overall, these results demonstrate that empowerment of uNK cells with angiogenic factors keeps them noncytotoxic. This phenotype is critical to their pregnancy-compatible immunovascular role during placentation and fetal development.

Natural killer cell tolerance licensing and other mechanisms

Armed with potent cytotoxic and immunostimulatory effector functions, natural killer (NK) cells have the potential to cause significant damage to normal self cells unless controlled by self-tolerance mechanisms. NK cells identify and attack target cells based on integration of signals from activation and inhibitory receptors, whose ligands exhibit complex expression and/or binding patterns. Preservation of NK cell self-tolerance must therefore go beyond mere engagement of inhibitory receptors during effector functions. Herein, we review recent work that has uncovered a number of mechanisms to ensure self-tolerance of NK cells. For example, licensing of NK cells allows only NK cells that can engage self-MHC to become functionally competent, or licensed. The molecular mechanism of this phenomenon appears to require signaling by receptors that were originally identified in effector inhibition. However, the nature of the signaling event has not yet been defined, but new interpretations of several published experiments provide valuable clues. In addition, several other cell-intrinsic and -extrinsic mechanisms of NK cell tolerance are discussed, including activation receptor cooperation and synergy, cytokine stimulation, and the opposing roles of accessory and regulatory cells. Finally, NK cell tolerance is discussed as it relates to the clinic, such as KIR-HLA disease associations, tumor immunotherapy, and fetal tolerance.