Changes of NK Cells in Preeclampsia

Natural killer cells and T lymphocytes in pregnancy and pre-eclampsia

Although pre-eclampsia (PE), a hypertensive disorder of pregnancy, has significant maternal and fetal morbidity and mortality worldwide, the mechanisms contributing to this disease have not been fully elucidated. Studies in patients and experimental models have shown that changes in the number or function of immune cells of both the adaptive and innate immune systems contribute to the development and pathogenesis of PE. This commentary summarizes our current understanding of the role of the immune system in the pathogenesis of PE, specifically focussing on dysfunction of natural killer (NK) cells and T lymphocyte populations.

Natural killer cells mediate pathophysiology in response to reduced uterine perfusion pressure

Preeclampsia is associated with hypertension, small-for-gestational-age babies, and increased cytolytic natural killer (NK) cells. The specific role of cytolytic NK cells in the pathophysiology of preeclampsia has not been clearly defined. We hypothesized that Reduced Uterine Perfusion Pressure (RUPP) stimulates proliferation and cytolytic activation of NK cells, and that reducing NK cells in RUPP would prevent hypertension, intrauterine growth restriction, and inflammation in response to placental ischemia. RUPP was induced on gestation day (GD) 14 in pregnant rats. NK cells were depleted by i.p. administration of anti-asialo GM1 antibody on GDs 15 and 17. Placental and circulating NK cells were quantified via flow cytometry, mean arterial pressure (MAP), fetal weights, and cytokines were measured on GD 19. Total placental NK cells were 7.4 ± 2% of gated cells in normal pregnant (NP; n=10) and 16.5 ± 3% of gated cells in RUPP (n=10) rats. Furthermore, cytolytic placental NK cells also increased in RUPP. Depletion of NK cells in RUPP (RUPP + anti-ASGM1) significantly improved MAP and fetal weights. MAP was 108 ± 2 mmHg in NP, 125 ± 2 mmHg in RUPP, and 112 ± 2 mmHg in RUPP + anti-ASGM1 (n=12). Fetal weight was 2.32 ± 0.05 in NP, 1.8 ± 0.04g in RUPP, and increased to 2.0 ± 0.04g in RUPP + anti-ASGM1. Placental interferon-γ (IFN-γ) was 40.4 ± 5.2 pg/mg in NP, 72.17 ± 3.2 pg/mg in RUPP, and 44.0 ± 6.5 pg/mg in RUPP + anti-ASGM1 (P<0.05). Placental tumor necrosis factor-α (TNF-α) was 17.9 ± 1.7 pg/mg in NP, 23.9 ± 2.2 pg/mg in RUPP, and 12.9 ± 2.3 pg/mg in RUPP + anti-ASGM1 (P<0.05). Depletion of NK cells significantly lowered MAP, intrauterine growth restriction, and inflammation in RUPP rats indicating that cytolytic NK cells are important in preeclampsia pathophysiology.

Recent Advances in Immunity and Hypertension

Persistent immune system activation plays an important role in the development of various forms of hypertension. Activation of the innate immune system, inflammation, and subsequent adaptive immune system response causing end-organ injury and dysfunction ultimately leads to hypertension and its associated sequelae including coronary artery disease, heart failure, stroke, and chronic kidney disease. In this review, we will provide updates on the innate and adaptive immune cells involved in hypertension, the current understanding of how the immune system gets activated, and examine the recently discovered mechanisms involved in several forms of experimental hypertension.

Natural killer cells in placentation and cancer: Implications for hypertension during pregnancy

Hypertension during pregnancy is the most common medical condition encountered during gestation. Despite this, knowledge of the mechanisms that underlie the disease and the development of new therapies are limited. Hypertension during pregnancy and some forms of cancer confer an increased risk to the development of cardiovascular disease later in life; one mechanism which may link these conditions is the involvement of natural killer (NK) cells. Whilst immunology and immunotherapy are well-developed areas in oncology; the complex mechanisms of the immune system in health and disease at the maternal-fetal interface are less well-defined. Natural killer (NK) cells have emerged as key immune cells involved in physiology and pathology of pregnancy. These small lymphocytes are present in the decidua (the uterine-specific uNK cells) and are distinct from peripheral NK cells. The uNK cell population plays a vital role in mediating trophoblast invasion and affecting decidual vascular remodelling whereas the role of the peripheral NK cell population during pregnancy is less well-defined. This review will give an overview of NK cell biology followed by a discussion of the current evidence for the role of uterine and peripheral NK cells at the maternal-fetal interface in health and disease. Furthermore, examples of NK cell research from cancer biology will be employed to inform future directions of research. By combining this knowledge from oncology where the field of immunotherapy has now matured into clinical trials; it is hopeful that new mechanisms can be elucidated to generate targets for similar therapeutic strategies for women with hypertensive pregnancies where interventions are needed.

Decreased Endothelial Progenitor Cells (EPCs) and increased Natural Killer (NK) cells in peripheral blood as possible early markers of preeclampsia: a case-control analysis

PURPOSE

Endothelial Progenitor Cells (EPCs) and Natural Killer (NK) cells were recently advocates in the pathogenesis of preeclampsia (PE), since they can be mobilized into the bloodstream and may orchestrate vascular endothelium function. The aim of our study was to evaluate in early pregnancy circulating EPCs and NK cells in peripheral blood in women who later developed PE compared to uncomplicated pregnancies.

METHODS

We prospectively enrolled pregnant women at 9⁺⁰-11⁺⁶ weeks of gestation at the time of first-trimester integrated screening for trisomy 21, who underwent peripheral venous blood (20 mL) sample. We included only women who later developed PE (cases) and women with uncomplicated pregnancy (controls), matched for maternal age, parity, and Body Mass Index. In these groups, we evaluated the levels of CD16⁺CD45⁺CD56⁺ NK cells and CD34⁺CD133⁺VEGF-R2⁺ EPCs in peripheral blood samples previously stored.

RESULTS

EPCs were significantly lower (p < 0.001), whereas NK cells were significantly higher (p < 0.001) in PE group compared to uncomplicated pregnancies during the first trimester.

CONCLUSION

The evaluation of EPCs and NK cells in peripheral blood during the first trimester may be considered an effective screening for the early identification of women at risk of developing PE.

Expression of Natural Cytotoxicity Receptors on and Intracellular Cytokine Production by NK Cells in Women with Gestational Diabetes Mellitus

PROBLEM

To determine the role of peripheral blood NK (pNK) cells in putative etiology of gestational diabetes, the expression of surface markers on pNK cells and the percentage of cytokine-producing pNK cells in women at 12 weeks of pregnancy with gestational diabetes mellitus (GDM) were studied.

METHOD OF STUDY

Multicolor flow cytometry was used to analyze the expression of NK cell surface receptors (CD16, NKp46, and NKp30) and intracellular cytokines (IFN-γ, TNF-α, TGF-β, and VEGF) in pNK cells (CD56(dim) and CD56(bright) ) at 12 weeks of pregnancy with GDM (n = 7) and non-GDM (n = 28).

RESULTS

CD56(bright) /CD16(-) NK and CD56(bright) /NKp46(+) NK cell percentage were significantly lower in GDM women than that in non-GDM women. IFN-γ- and TNF-α-producing CD56(+) cells, respectively, were significantly high, while TGF-β- and VEGF-producing CD56(+) cells and CD56(bright) cells, respectively, were significantly low in GDM women.

CONCLUSIONS

Women with GDM possibly have abnormal NK cell function for the expression of surface receptors and cytokine production.

Immunological Adaptations to Pregnancy in Women with Type 1 Diabetes

Despite adequate glycemic control, pregnancy outcome of women with type 1 diabetes (T1D) is still unfavorable as compared to healthy women. In a rat-model of T1D under normoglycemic conditions, adverse pregnancy outcome was also observed, which was associated with aberrant immunological adaptations to pregnancy. Because similar processes may occur in women with T1D we studied the systemic immune response in non-pregnant and pregnant women with and without T1D. The systemic immune response was assessed by using flow cytometry to evaluate the number and activational status of subpopulations of lymphocytes, Natural Killer cells and monocytes in peripheral blood of non-pregnant and pregnant women with and without T1D. An increased white blood cell count, an increased Th1/Th2 ratio, increased Natural Killer cell expression of CD335 and enhanced activation of intermediate and non-classical monocytes was observed in pregnant women with T1D vs. healthy pregnant women. Also, the pregnancy outcome (i.e. incidence of preterm delivery and macrosomia) of women with T1D was unfavorable as compared to healthy women. This study showed that in T1D, the immunological adaptations to pregnancy are disturbed. In addition to hyperglycemia, these different immunological adaptations may be responsible for the greater frequency of complications in pregnant women with T1D.

Preeclampsia: long-term consequences for vascular health

Preeclampsia (PE) is a pregnancy-specific syndrome and one of the leading causes of preterm birth, neonatal and maternal morbidity and mortality. This disease is characterized by new onset hypertension usually in the third trimester of pregnancy and is sometimes associated with proteinuria, although proteinuria is not a requirement for the diagnosis of PE. In developing countries, women have a higher risk of death due to PE than more affluent countries and one of the most frequent causes of death is high blood pressure and stroke. Although PE only affects approximately 2%-8% of pregnancies worldwide it is associated with severe complications such as eclampsia, hemorrhagic stroke, hemolysis, elevated liver enzymes and low platelets (HELLP syndrome), renal failure and pulmonary edema. Importantly, there is no "cure" for the disease except for early delivery of the baby and placenta, leaving PE a health care risk for babies born from PE moms. In addition, PE is linked to the development of cardiovascular disease and stroke in women after reproductive age, leaving PE a risk factor for long-term health in women. This review will highlight factors implicated in the pathophysiology of PE that may contribute to long-term effects in women with preeclamptic pregnancies.

NK cell abnormality and its treatment in women with reproductive failures such as recurrent pregnancy loss, implantation failures, preeclampsia, and pelvic endometriosis

The regulation of uterine and peripheral blood natural killer (NK) cells has been associated with problems related to reproductive immunology such as recurrent pregnancy loss (RPL), implantation failure or preeclampsia. NKp46, one of the natural cytotoxicity receptors (NCRs), is a unique marker that functions in NK cell cytotoxicity and cytokine production. Expression of NKp46 on NK cells is lower in women with recurrent pregnancy loss and pregnancy-induced hypertension. Moreover, expression of NKp46 on peritoneal fluid NK cells is lower in women with pelvic endometriosis. Therefore, evaluation of NKp46 on peripheral blood NK cells may provide a means of screening for reproductive abnormalities. Recently, a new type of NK cell, the NK22 cell, has been reported. This cell may be a regulator not only of the mucosal barrier but also of reproduction. For women with RPL showing abnormal uterine and/or peripheral blood NK cells, both intravenous immunoglobulin treatment and intralipid treatment have been reported. The effects of these treatments are still controversial, and further studies are needed in order to clarify their true impact. The present review examines variations in the expression of NCRs on NK cells, the participation of NK22 cells in reproduction, and the possible use of intravenous immunoglobulin or intralipid treatment for women with recurrent pregnancy loss and NK cell abnormality.

Liaison between natural killer cells and dendritic cells in human gestation

A successful pregnancy relies on immunological adaptations that allow the fetus to grow and develop in the uterus, despite being recognized by maternal immune cells. Among several immunocompetent cell types present within the human maternal/fetal interface, DC-SIGN(+) dendritic cells (DCs) and CD56(+) natural killer (NK) cells are of major importance for early pregnancy maintenance, not only generating maternal immunological tolerance but also regulating stromal cell differentiation. Previous reports show the presence of NK-DC cell conjugates in first trimester human decidua, suggesting that these cells may play a role in the modulation of the local immune response within the uterus. While effective immunity is necessary to protect the mother from harmful pathogens, some form of tolerance must be activated to avoid an immune response against fetal antigens. This review article discusses current evidence concerning the functions of DC and NK cells in pregnancy and their liaison in human decidua.

Pathophysiology of hypertension in pre-eclampsia: a lesson in integrative physiology

Despite being one of the leading causes of maternal death and a major contributor of maternal and perinatal morbidity, the mechanisms responsible for the pathogenesis of pre-eclampsia have yet to be fully elucidated. However, it is evident that this is a complex disorder involving multiple organ systems, and by using integrative approaches, enormous progress has been made towards understanding the pathophysiology of pre-eclampsia. Growing evidence supports the concept that the placenta plays a central role in the pathogenesis of pre-eclampsia and that reduced uteroplacental perfusion, which develops as a result of abnormal cytotrophoblast invasion of spiral arterioles, triggers the cascade of events leading to the maternal disorder. Placental ischaemia leads to release of soluble placental factors, many of which are classified as anti-angiogenic or pro-inflammatory. Once these ischaemic placental factors reach the maternal circulation, they cause widespread activation and dysfunction of the maternal vascular endothelium that results in enhanced formation of endothelin-1 and superoxide, increased vascular sensitivity to angiotensin II and decreased formation of vasodilators such as nitric oxide. This review highlights these links between placental ischaemia, maternal endothelial activation and renal dysfunction in the pathogenesis of hypertension in pre-eclampsia.

Elucidating immune mechanisms causing hypertension during pregnancy

Preeclampsia is associated with hypertension and increased infant and maternal morbidity and mortality. The underlying cause of preeclampsia is largely unknown, but it is clear that an immunological component plays a key pathophysiological role. This review will highlight immunological key players in the pathology of preeclampsia and discuss their role in the pathophysiology observed in the reduced placental perfusion (RUPP) rat model of preeclampsia.

NK cells in immunotolerant organs

Organs such as the liver, uterus and lung possess hallmark immunotolerant features, making these organs important for sustaining self-homeostasis. These organs contain a relatively large amount of negative regulatory immune cells, which are believed to take part in the regulation of immune responses. Because natural killer cells constitute a large proportion of all lymphocytes in these organs, increasing attention has been given to the roles that these cells play in maintaining immunotolerance. Here, we review the distribution, differentiation, phenotypic features and functional features of natural killer cells in these immunotolerant organs, in addition to the influence of local microenvironments on these cells and how these factors contribute to organ-specific diseases.