Elevated NK cell cytotoxicity, CD158a expression in NK cells and activated T lymphocytes in peripheral blood of women with IVF failures

Expression of NKp46 and other activating inhibitory receptors on uterine endometrial NK cells in females with various reproductive failures: A review

Background

Uterine endometrial natural killer (uNK) cells represent major leukocytes in the mid-secretory phase of the cell cycle, and their number is further increased during early pregnancy. The activating and inhibitory receptors expressed on their surface mediate various functions of uNK cells, such as cytotoxicity, cytokine production, spiral artery remodeling, and self-recognition.

Methods

This study reviewed the most recent information (PubMed database, 175 articles included) regarding the activating and inhibitory receptors on uNK cells in human females with healthy pregnancies and the evidence indicating their significance in various reproductive failures.

Main Findings

Numerous studies have indicated that the natural cytotoxic receptors, killer cell immunoglobulin-like receptors, and C-type lectin receptors, particularly those expressed on uNK cells, play crucial roles in successful pregnancy.

Conclusion

As studies on human uNK cells are limited owing to the low availability of fertile samples, and the extrapolation of animal models has certain limitations, the in vivo role of uNK cells has not yet been fully elucidated. However, immunotherapies focusing on modulating uNK cell function have been controversial in terms of pregnancy outcomes. Further research is required to elucidate the role of uNK cells in reproduction.

The impact of reproductive hormones on T cell immunity; normal and assisted reproductive cycles

During pregnancy, a unique immune milieu is established systemically and locally at the maternal-fetal interface. While preparing for embryonic implantation, endometrial effectors significantly change their proportions and function, which are synchronized with hormonal changes. During assisted reproductive technology cycles, various cytokines, chemokines, and immune factors dynamically change with the altered receptor expressions on the immune effectors. Thus, the hormonal regulation of immune effectors is critical to maintaining the immune milieu. In this review, hormonal effects on T cell subsets are reviewed. Sex hormones affect T cell ontogeny and development, consequently affecting their functions. Like other T cell subsets, CD4+ T helper (Th) cells are modulated by estrogen, where low estrogen concentration promotes Th1-driven cell-mediated immunity in the uterus and in vitro by enhancing IFN-γ production, while a high estrogen level decreases it. The abundance and differentiation of T regulatory (Treg) cells are controlled by estrogen, inducing Treg expansion. Conversely, progesterone maintains immune homeostasis by balancing Th1/Th2 and Th17/Treg immunity, leading to maternal-fetal tolerance. Therefore, the understanding of the hormonal impact on various T cell subsets during the reproductive cycles is critical to improving reproductive outcomes in women with recurrent pregnancy losses, repeated implantation failures, and undergoing assisted reproductive cycles.

Exploring Natural Killer Cell Testing in Embryo Implantation and Reproductive Failure: An Overview of Techniques and Controversies

The blastocyst nidation is the most crucial stage to a successful pregnancy, as the white cells work to promote a favorable endometrial microenvironment for this process. Intriguingly, this implantation window lasts, on average, 6 days in most regular women, and its quality is affected by many pathological conditions. Since the grounds of reproductive failure in healthy couples are still uncharted, studies have widely suggested a potential hostile role of the immune system in the equilibrium of the maternal-fetal interface. In recent years, natural killer cells have been the highlight as they represent the greatest lymphocyte in the uterus and have immune surveillance through cytotoxicity during the implantation window. This review explored the main techniques used for natural killer (NK) cell testing in the implantation window over the last 13 years on the PubMed® database. Of 2167 published articles potentially relevant for the review, only thirty-three were about cell evaluation in healthy women, met the inclusion criteria, and had their methodology critically analyzed. Here, we bring a summary from the study group and sample collection to evidence comments about their findings and correlations. Meanwhile, we also summarize the current relationship between NK cells and endometrial receptivity with reproductive failure to help enhance the possibilities for future research. In conclusion, our overview points out that restricted and unstandardized methods support the controversy between the NK population and unsuccessful embryo implantation, which is an obstacle to studying why healthy eggs do not thrive and finding a solution for one of the most controversial topics in human reproduction.

Accentuated Peripheral Blood NK Cytotoxicity Forms an Unfavorable Background for Embryo Implantation and Gestation

Problem Many studies have demonstrated the negative impact of high rates of NK cytotoxicity (NKc) on reproductive processes, but there is no agreement as to the appropriateness and feasibility of using the NKc for routine diagnostic in IVF patients. This study conducted a retrospective analysis of embryo transfer (ET) success rates and live birth rates (LBR) in patients with different NKc values. Method of study 1854 cycles of ET were selected and divided into three groups according to NKc levels, and randomized by anamnesis and age: normal (nNKc, n = 871), elevated (eNKc, n = 759), and reduced NKc (rNKc, n = 123). ET with donors’ embryos (n = 101) were analyzed separately. NKc-to-K562 was measured in PBMC (peripheral blood mononuclear cells) by flow cytometry before ET. The patients did not obtain any additional treatments. Results Patients with eNKc, in addition to having reduced clinical pregnancy rates (OR1.59, p < 0.0001), had increased levels of subsequent pregnancy failures (OR2.545, p < 0.0001) when compared to nNKc patients. As a result, patients with eNKc had almost half the LBR than patients with nNKc (OR2.2, p < 0.0001). In patients with rNKc, LBR was also lowered. eNKc was equally unfavorable for implantation and delivery in cryo- or fresh cycles. Markedly, eNKc was much more unfavorable for reproduction than slightly elevated NKc. The donor’s embryos were implanted irrespective of the recipient’s NKc levels, but the later stages of pregnancy were worse in patients with eNKc. Conclusions Our findings highlighted the negative impact of high levels of NK cytotoxicity on pregnancy outcomes.

Extracellular Vesicles: An Important Biomarker in Recurrent Pregnancy Loss?

Recurrent pregnancy loss (RPL) has an estimated incidence of 1–3% of all couples. The etiology is considered to be multifactorial. Extracellular vesicles (EVs) take part in numerous different physiological processes and their contents show the originating cell and pathophysiological states in different diseases. In pregnancy disorders, changes can be seen in the composition, bioactivity and concentration of placental and non-placental EVs. RPL patients have an increased risk of pregnancy complications. The aim of this prospective study was to examine whether measuring different specific EV markers in plasma before and during pregnancy could be used as predictors of pregnancy loss (PL) in women with RPL. Thirty-one RPL patients were included in this study; 25 had a live birth (LB group) and six had a new PL (PL group). Five blood samples were obtained, one before achieved pregnancy and the others in gestational week 6, 8, 10 and 16. Moreover, some of the patients received intravenous immunoglobulin (IVIG) infusions as part of treatment, and it was also examined whether this treatment influenced the EV levels. Seventeen EV markers specific for the immune system, coagulation, placenta and hypoxia were analyzed in the samples with EV Array, a method able to capture small EVs by using an antibody panel targeting membrane proteins. Comparing the LB and PL groups, one EV marker, CD9, showed a significant increase from before pregnancy to gestational week 6 in the PL group. The changes in the other 16 markers were nonsignificant. One case of late-onset PL showed steeply increasing levels, with sudden decrease after gestational week 10 in nine of 17 markers. Moreover, there was an overall increase of all 17 markers after IVIG treatment in the LB group, which was significant in 15 of the markers. Whether increases in EVs positive for CD9 characterize RPL patients who subsequently miscarry should be investigated in future larger studies.

Natural killer frequency determines natural killer cytotoxicity directly in accentuated zones and indirectly in "moderate-to-normal frequency" segment

Natural killer (NK) frequency and NK cytotoxicity (NKc) are key determining factors of a clinical outcome. In our previous study, we showed the prognostic clinical significance of immune parameters when they are beyond the optimal range (accentuated). In this study, we attempted to explain the disparity of accentuated but physiologically and immunologically normal NK parameters that might serve as negative clinical prognostics indications of failed pregnancies. We have analyzed NK%, NKc levels, and their reciprocal correlation in 2,804 patients with reproductive failures. In the entire clinical population, NK% correlates with NKc. Interestingly, we found this relationship to be strongly dependent on NK level's status. NK%-NKc correlation was the strongest (r = 0.2021, p < 0.0001) in a patient group with high NK% (> 17.5%). Patients with NK% between 15-17.5% manifested lower but still significant correlation NK%-NKc (r = 0.1213, p = 0.0155). Additionally, significant correlation (r = 0.2689, p < < 0.0001) between NK% and NKc was observed in a group of patients with NK levels < 7% (1.7-7%). While patients' groups with NK% (7-15%) did not reveal NK%-NKc association. This led us to hypothesize that the qualitative-quantitative status of NK population is responsible for their cytotoxic activity. Consistent with our hypothesis, the "balanced zone" NK% is tightly controlled, and thus does not correlate directly with NKc. In contrast, the "accentuated zones" of NK% escape this control and directly affecting NKc. Demonstrated phenomena supports our idea about the clinical significance of immune accentuation and explains its novel physiological role.

Association between microRNA machinery gene polymorphisms and recurrent implantation failure

The present study aimed to investigate the potential association of five miRNA machinery gene polymorphisms (DICER1 rs3742330A>G, DROSHA rs10719T>C, RAN rs14035C>T, XPO5 rs11077A>C and DGCR8 rs417309G>A) with recurrent implantation failure (RIF), a clinical condition in which good-quality embryos repeatedly fail to implant following two or more in vitro fertilization cycles, and its associated risk factors in Korean women. Therefore, the present study performed genotype analysis and assessed the frequency of these miRNA gene polymorphisms in patients diagnosed with RIF (n=119) and randomly selected controls (n=210) with at least one live birth and no history of pregnancy loss. The DROSHA rs10719T>C and RAN rs14035C>T polymorphisms were identified to be significantly associated with decreased prevalence of RIF. Additionally, the DROSHA rs10719 TC and the RAN rs14035 CT genotypes were present at significantly lower frequencies in the RIF group than in the control group (adjusted odds ratio=0.550; 95% CI, 0.339-0.893; P=0.016; and adjusted odds ratio=0.590; 95% CI, 0.363-0.958; P=0.033, respectively). Furthermore, the combined RAN rs14035 CT+TT genotype was observed to be associated with decreased RIF prevalence (adjusted odds ratio=0.616; 95% CI, 0.386-0.982; P=0.042). Genotype combination analysis for the various miRNA polymorphisms revealed that the DROSHA TC genotype exhibited a highly significant negative association with RIF prevalence when combined with the RAN CT genotype (adjusted odds ratio=0.314; 95% CI, 0.147-0.673; P=0.003; false discovery rate-adjusted P=0.023). The present study revealed an association between the DROSHA rs10719 and RAN rs14035 3'UTR polymorphisms and decreased risk of RIF in Korean women, which suggests that these gene polymorphisms could represent potential markers for predicting RIF risk.

Comparison of T and NK lymphocyte subsets between human endometrial tissue and peripheral blood

Immune profiles in endometrium may be changed in patients with IVF failure and its possible correlations with immune parameters in peripheral blood are important for the diagnostic approach. Such correlations in healthy women are unknown and have been studied in the present research. The expression of CD56, CD158a, HLA DR, CD69 in T lymphocytes, CD4 T lymphocytes, CD8+ T lymphocytes and NK cells were studied by flow-cytometry in endometrium and peripheral blood in healthy 24 donors of oocytes aged 25-32 years. Levels of T lymphocyte and T helper cells were lower in endometrium and no differences in CD8 T lymphocytes were registered between endometrium and peripheral blood. The expression of HLA DR and especially CD69 was higher in CD3, CD4, CD8 T cells in endometrium in comparison with peripheral blood. The endometrium lymphocyte population was enriched by NK cells that were generally CD56++ with a higher expression of HLA DR and almost in total were CD69 positive. Strong positive correlations of CD8 expression in NK cells (r = 0.6478, p < 0.001) and HLA DR expression in CD8 T cells (r = 0.6107, p < 0.01) between peripheral blood and endometrium were registered in fertile women. The endometrial CD56 expression in CD8+ T cells negatively correlated with endometrial CD8 expression in NK cells (r = -0.5252, p < 0.01) which possibly reflected a suppressive and regulating mechanism in the endometrium. CD8+ NK cells and HLA DR+ CD8 T cells in endometrium were related to the same subsets in peripheral blood.

shRNA-Induced Knockdown of a Bioinformatically Predicted Target IL10 Influences Functional Parameters in Spontaneously Hypertensive Rats with Asthma

One of the most common comorbid pathology is asthma and arterial hypertension. For experimental modeling of comorbidity we have used spontaneously hypertensive rats with ovalbumin (OVA)-induced asthma. Rats were randomly divided into three groups: control group, OVA-induced asthma group; OVA-induced asthma + IL10 shRNA interference group. Target gene (IL10) was predicted by ANDSystem. We have demonstrated that RNA-interference of IL10 affected cardiovascular (tested using Millar microcatheter system) as well as respiratory functions (tested using force-oscillation technique, Flexivent) in rats. We have shown that during RNA-interference of IL10 gene in vivo there were changes in both cardiac and lung function parameters. These changes in the cardiovascular parameters can be described as positive. But the more intensive heart workload can lead to exhaust and decompensation of the heart functions. Knockdown of IL10 gene in asthma modeling induces some positive changes in respiratory functions of asthmatic animals such as decreased elastance and increased compliance of the lungs, as well as less pronounced pathomorphological changes in the lung tissue. Thus, we provide the data about experimentally confirmed functionality changes of the target which was in silico predicted to be associated with both asthma and hypertension – in our new experimental model of comorbid pathology.

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.