Association of maternal killer-cell immunoglobulin-like receptors and parental HLA-C genotypes with recurrent miscarriage

A genome-wide scan for candidate lethal variants in Thoroughbred horses

Domestic animal populations are often characterised by high rates of inbreeding and low effective population sizes due to selective breeding practices. These practices can result in otherwise rare recessive deleterious alleles drifting to high frequencies, resulting in reduced fertility rates. This study aimed to identify potential recessive lethal haplotypes in the Thoroughbred horse breed, a closed population that has been selectively bred for racing performance. In this study, we identified a haplotype in the LY49B gene that shows strong evidence of being homozygous lethal, despite having high frequencies of heterozygotes in Thoroughbreds and other domestic horse breeds. Variant analysis of whole-genome sequence data identified two SNPs in the 3'UTR of the LY49B gene that may result in loss of function. Analysis of transcriptomic data from equine embryonic tissue revealed that LY49B is expressed in the trophoblast during placentation stage of development. These findings suggest that LY49B may have an essential, but as yet unknown function in the implantation stage of equine development. Further investigation of this region may allow for the development of a genetic test to improve fertility rates in horse populations. Identification of other lethal variants could assist in improving natural levels of fertility in horse populations.

Parental human leukocyte antigen-C allotypes are predictive of live birth rate and risk of poor placentation in assisted reproductive treatment

OBJECTIVE

To study the pregnancy, miscarriages, and live birth rates (LBRs) according to maternal killer cell immunoglobulin-like receptor (KIR) genes expressed by uterine natural killer cells and paternal or oocyte donor human leukocyte antigen-C (HLA-C) genes expressed by trophoblast cells in patients with recurrent reproductive failure.

DESIGN

Prospective observational cohort study.

SETTING

Private infertility center.

PATIENT(S)

Participants included 204 women with recurrent miscarriage or recurrent implantation failure.

INTERVENTION(S)

The KIR and HLA-C genotypes of all women and HLA-C of their partners, gamete donors, miscarriage tissue, and babies were analyzed.

MAIN OUTCOME MEASURE(S)

All clinical variables (pregnancy, miscarriage, and LBRs) were analyzed and categorized based on KIR, oocyte origin, and single embryo transfer (SET)/double embryo transfer (DET).

RESULT(S)

A higher miscarriage rate was observed after DETs in KIR AA mothers (47.8% egg donation and 37.5% in vitro fertilization [IVF]) compared with KIR AB (10.5% egg donation and 12.5% IVF) or KIR BB (6.7% egg donation and 0% IVF). A significantly decreased LBR was observed after DETs with oocyte donation in KIR AA patients (4.3%) compared with KIR AB (26.3%) or BB (46.7%). The LBR decreased significantly as the fetal HLA-C2 load increased in KIR AA women.

CONCLUSION(S)

Elective SET improves the reproductive outcomes compared with DET. An increased embryo HLA-C2 load has a negative impact on the LBR in KIR AA patients. The selection of HLA-C1 over HLA-C2 donors could have a positive impact on the LBR in KIR AA patients.

CLINICAL TRIAL REGISTRATION NUMBER

NCT04052438.

Polymorphism in killer cell immunoglobulin-like receptors and human leukocyte antigen-c and predisposition to preeclampsia in Ethiopian pregnant women population

INTRODUCTION

Preeclampsia (PE) is a human specific pregnancy-related syndrome of unknown etiology that affects 2-8 % of pregnancies. Polymorphism in maternal Killer Cell Immunoglobulin-like Receptors (KIRs) and the ligand fetal Human Leukocyte Antigen-C (HLA-C) may predispose pregnant mothers for PE due to defective trophoblast invasion into the maternal decidua. Our study aimed to investigate the association between maternal KIR and fetal HLA-C polymorphism and PE in Ethiopian pregnant women.

METHODS

We included a total of 288 (157 controls and 131 PE cases) in a case-controls study at Adama Regional Referral Hospital, Ethiopia. The KIR and HLA-C genotyping was done using traditional polymerase chain reaction on genomic DNA extracted form maternal venous and cord blood followed by 2% agarose gel electrophoresis.

RESULTS

The statistical associations between variables were evaluated using Pearson's Chi-square test. P < 0.05, with 95 % confidence interval was considered statistically significant. A significant association was observed between the KIR2DS1 and PE, with a higher frequency (60.5 %) of the gene in the control group. Similarly, a significant association was observed between KIR AA genotype and PE, with a higher frequency (38.2 %) of this genotype in the PE group. Ethiopians share the same risk genotype for PE as seen in previous African and European studies, namely homozygosity of a maternal KIR AA genotype. However, Ethiopians differ from other East African populations by sharing the same protective KIR2DS1 gene as Europeans.

Recurrent Spontaneous Abortion (RSA) and Maternal KIR Genes: A Comprehensive Meta-Analysis

Natural killer cells (NKs) are the most important cells in the fetomaternal immune tolerance induced through interaction of maternal killer-cell immunoglobulin-like receptors (KIR) and fetal human leucocyte antigens (HLA). Hence, we intend to perform a meta-analysis on the role of maternal KIR genes diversity in recurrent spontaneous abortion (RSA). The present paper is a meta-analysis of previous genetic association studies and our previous original study. The results showed that KIR3DL1 was a significantly protecting factor for RSA (p=0.044; OR=0.833 [0.698-0.995]; fixed effect model). KIR2DS2 (p=0.034; OR=1.195 [1.013-1.408]; fixed effect model) and KIR2DS3 (p=0.013; OR=1.246 [1.047-1.483]; fixed effect model) were significantly risk factors for RSA. For KIR2DS1 there was a high heterogeneity and publication bias. Briefly, the inhibitory gene KIR3DL1 was a protecting factor, and the activating genes KIR2DS2 and KIR2DS3 were risk factors for RSA. However, the effect sizes were not suitable. We suggest further studies on different causes of pregnancy loss, to find the role of KIR2DS1.

Diversity of KIR/HLA Genotypes and Their Association with Psoriasis Vulgaris in the Western Mexican Population

NK and some T cell functions are regulated by the interaction between KIR and HLA molecules. Several studies have shown an association between activating KIR genes and the development of autoimmune diseases, including psoriasis vulgaris (PsV). Our objective was to determine the association between KIR/HLA genes and genotypes with PsV in the Western mestizo Mexican population. One hundred subjects diagnosed with PsV (SP) and 108 healthy subjects (HS) were genotyped for 14 KIR genes, HLA-Bw4, HLA-C1, and HLA-C2 by PCR-single specific primer (SSP). Positive associations of the KIR3DS1 gene (odds ratio (OR) 1.959, p = 0.021), G11 genotype (OR 19.940, p = 0.008), and KIR3DS1/HLA-ABw4 (OR 2.265, p = 0.009) were found with susceptibility to PsV. In contrast, the G1 genotype (OR 0.448, p = 0.031) and KIR3DL1/HLA-Bw4Ile80 (OR 0.522, p = 0.022) were negatively associated with susceptibility to this disease. These results suggest an implication of the KIR3DS1/HLA-ABw4 genotype in PsV pathology.

Regulatory mechanisms of endometrial decidualization and pregnancy-related diseases

Endometrial decidualization is one of the earliest changes by which the uterus adapts to pregnancy. During this period, the endometrium undergoes complex changes in its biochemistry, physiology, and function at various levels, providing a suitable microenvironment for embryo implantation and development. Favorable decidualization lays an essential foundation for subsequent gestation, without which pregnancy failure or pregnancy complications may occur. The interaction between pregnancy-related hormones and cytokines produced by embryonic and uterine cells is known to be essential for decidualization, in which some transcription factors also play pivotal roles. Increasing evidence has revealed the importance of metabolism in regulating decidualization. Here, we summarize and discuss these crucial elements in decidualization and the relationship between decidualization and pregnancy complications. A better comprehension of these issues should help to improve the prediction of pregnancy outcomes and the use of appropriate intervention.

Genomic Analysis of Spontaneous Abortion in Holstein Heifers and Primiparous Cows

Background: The objectives of this study were to identify loci, positional candidate genes, gene-sets, and pathways associated with spontaneous abortion (SA) in cattle and compare these results with previous human SA studies to determine if cattle are a good SA model for humans. Pregnancy was determined at gestation day 35 for Holstein heifers and cows. Genotypes from 43,984 SNPs of 499 pregnant heifers and 498 pregnant cows that calved at full term (FT) were compared to 62 heifers and 28 cows experiencing SA. A genome-wide association analysis, gene-set enrichment analysis–single nucleotide polymorphism, and ingenuity pathway analysis were used to identify regions, pathways, and master regulators associated with SA in heifers, cows, and a combined population. Results: Twenty-three loci and 21 positional candidate genes were associated (p < 1 × 10⁻⁵) with SA and one of these (KIR3DS1) has been associated with SA in humans. Eight gene-sets (NES > 3.0) were enriched in SA and one was previously reported as enriched in human SA. Four master regulators (p < 0.01) were associated with SA within two populations. Conclusions: One locus associated with SA was validated and 39 positional candidate and leading-edge genes and 2 gene-sets were enriched in SA in cattle and in humans.

Uterine natural killer cells: Time for a re-appraisal?

The presence of unusual natural killer cells in human endometrium has been recognized for 30 years, but despite considerable research effort, the in vivo role of uterine natural killer (uNK) cells in both normal and pathological pregnancy remains uncertain. uNK cells may differentiate from precursors present in endometrium, but migration from peripheral blood in response to chemokine stimuli with in situ modification to a uNK cell phenotype is also possible. uNK cells produce a wide range of secretory products with diverse effects on trophoblast and spiral arteries which may play an important role in implantation and early placentation. Interactions with other decidual cell populations are also becoming clear. Recent evidence has demonstrated subpopulations of uNK cells and the presence of other innate lymphoid cell populations in decidua which may refine future approaches to investigation of the role of uNK cells in human pregnancy.

Treatment with intravenous immunoglobulin in patients with recurrent pregnancy loss: An update

Intravenous immunoglobulin (IVIg) has a documented clinical effect in many autoimmune diseases and has so far been tested in >10 randomised controlled trials (RCTs) in women with recurrent pregnancy loss (RPL). The results of the RCTs have, however, been very divergent. In meta-analyses of all trials, no significant impact on live birth rate has been reported. In contrast, in sensitivity analyses, IVIg significantly increased live birth rates when initiated prior to conception and it had a borderline significant therapeutic effect in women with secondary RPL. Higher dosages of IVIg and serological signs of autoimmunity in the treated patients tended to increase the success rate after treatment. A follow-up study of patients from our recent RCT also supports a significant therapeutic effect in patients who had received IVIg before conception. The lessons learned from the published trials and meta-analyses should be incorporated in the design of future RCTs of IVIg in the treatment of RPL.

Activating Killer-cell Immunoglobulin-like Receptor genes confer risk for Crohn's disease in children and adults of the Western European descent: Findings based on case-control studies

Background

Killer-cell Immunoglobulin-like Receptor (KIR) genes encode receptors, which are mainly expressed on, and control functional activities of, Natural Killer (NK) cells. There exist six distinct activating KIR genes in humans, who differ from one another with respect to the repertoire of these genes. Because activated NK cells can potentially cause tissue destruction, we hypothesized that variation in the inherited activating KIR genes in humans is associated with their innate susceptibility/resistance to developing Crohn disease (CD).

Methods

We performed case control studies on three independent Canadian CD patient cohorts (all of the Western European descent): two comprising children (Montreal having 193 cases and 245 controls, and Ottawa having 93 cases and 120 controls) and the third one comprising predominantly adults (Winnipeg having 164 cases and 200 controls). We genotyped cases and controls for activating KIR genes by PCR with gene-specific primers and investigated associations between the genes and cases using unconditional logistic regression.

Results

We observed strong associations between all the six KIR genes and CD in Ottawa children, with the strongest risk observed for the KIR2DS1 (p = 1.7 x10^-10). Associations between all but the KIR2DS2 were replicated in the Montreal cohort with the strongest association evident for the KIR2DS5 (8.0 x 10⁻¹⁰). Similarly associations between five genes were observed in the adult Winnipeg cohort. In this cohort, strongest associations were evident with the KIR2DS5 (8.75 x 10⁻⁸). An overall analysis for all cohorts showed strong associations with four of the genes, with the strongest association evident for the KIR2DS5 (p = 1.35 x 10−¹⁷). In the combined analysis for four KIR genes, individuals carrying one or more of the KIR genes were at significantly higher risks for acquiring CD (p = 3.5 x 10⁻³⁴).

Conclusions

Activating KIR genes are associated with risk for developing CD in both children and adults.

Human Natural Killer Receptors, Co-Receptors, and Their Ligands

In the last 20 years, the study of human natural killer (NK) cells has moved from the first molecular characterizations of very few receptor molecules to the identification of a plethora of receptors displaying surprisingly divergent functions. We have contributed to the description of inhibitory receptors and their signaling pathways, important in fine regulation in many cell types, but unknown until their discovery in the NK cells. Inhibitory function is central to regulating NK-mediated cytolysis, with different molecular structures evolving during speciation to assure its persistence. More recently, it has become possible to characterize the NK triggering receptors mediating natural cytotoxicity, unveiling the existence of a network of cellular interactions between effectors of both natural and adaptive immunity. This unit reviews the contemporary history of molecular studies of receptors and ligands involved in NK cell function, characterizing the ligands of the triggering receptor and the mechanisms for finely regulating their expression in pathogen-infected or tumor cells. © 2018 by John Wiley & Sons, Inc.

Pregnancy Immunogenetics and Genomics: Implications for Pregnancy-Related Complications and Autoimmune Disease

Pregnancy presents a singular physiological scenario during which the maternal immune system must accommodate the semiallogeneic fetus. Fluctuations between pro- and anti-inflammatory states are required throughout gestation to facilitate uterine tissue remodeling, fetal growth and development, and finally birth. Tolerance for the fetus must be established and maintained without fundamentally compromising the maternal immune system function, so that both the mother and fetus are protected from foreign insults. Here, we review our current understanding of how genetic variation at both maternal and fetal loci affects implantation and placenta formation, thereby determining the likelihood of a successful pregnancy outcome or the development of pregnancy-related complications. We also consider the impact of pregnancy on both the maternal and fetal systemic immune systems and the related implications for modulating ongoing autoimmune diseases and triggering their development.

Understanding the role of killer cell immunoglobulin-like receptors in pregnancy complications

Pregnancy is a unique immunological situation in which a fetus-bearing paternal histocompatibility antigens can survive in a maternal environment without apparent rejection. To face this challenge, cells of the uterine immune system show characteristic changes in absolute number and composition during pregnancy. Particularly relevant to this process are uterine natural killer (uNK) cells and their cell surface receptors, killer immunoglobulin-like receptors (KIRs). The main purpose of this review is to outline the current body of knowledge on the involvement of KIRs in the complications of pregnancy. Implantation depends on the invasion of embryonic trophoblast cells into maternal uterine tissue and remodeling of the uterine spiral arterioles, which is essential for placental perfusion and successful pregnancy. The proper interaction between maternal KIRs and their ligands human leukocyte antigen (HLA) class I molecules, expressed by the extravillous trophoblast cells, is crucial in this process. KIRs are a complex family that includes both activator and inhibitory receptors. The activation profile is genetically determined in each individual and leads to diverse levels of functionality for NK and T cells on engagement with specific HLA class I molecules. An association between different KIR alleles and HLA molecules has been reported in pregnancy complications, supporting the idea of a relevant role of these receptors in successful pregnancy.

qKAT: Quantitative Semi-automated Typing of Killer-cell Immunoglobulin-like Receptor Genes

Killer cell immunoglobulin-like receptors (KIRs) are a set of inhibitory and activating immune receptors, on natural killer (NK) and T cells, encoded by a polymorphic cluster of genes on chromosome 19. Their best-characterized ligands are the human leukocyte antigen (HLA) molecules that are encoded within the major histocompatibility complex (MHC) locus on chromosome 6. There is substantial evidence that they play a significant role in immunity, reproduction, and transplantation, making it crucial to have techniques that can accurately genotype them. However, high-sequence homology, as well as allelic and copy number variation, make it difficult to design methods that can accurately and efficiently genotype all KIR genes. Traditional methods are usually limited in the resolution of data obtained, throughput, cost-effectiveness, and the time taken for setting up and running the experiments. We describe a method called quantitative KIR semi-automated typing (qKAT), which is a high-throughput multiplex real-time polymerase chain reaction method that can determine the gene copy numbers for all genes in the KIR locus. qKAT is a simple high-throughput method that can provide high-resolution KIR copy number data, which can be further used to infer the variations in the structurally polymorphic haplotypes that encompass them. This copy number and haplotype data can be beneficial for studies on large-scale disease associations, population genetics, as well as investigations on expression and functional interactions between KIR and HLA.

Two to Tango: Co-evolution of Hominid Natural Killer Cell Receptors and MHC

Natural killer (NK) cells have diverse roles in hominid immunity and reproduction. Modulating these functions are the interactions between major histocompatibility complex (MHC) class I molecules that are ligands for two NK cell surface receptor types. Diverse killer cell immunoglobulin-like receptors (KIR) bind specific motifs encoded within the polymorphic MHC class I cell surface glycoproteins, while, in more conserved interactions, CD94:NKG2A receptors recognize MHC-E with bound peptides derived from MHC class I leader sequences. The hominid lineage presents a choreographed co-evolution of KIR with their MHC class I ligands. MHC-A, -B, and -C are present in all great apes with species-specific haplotypic variation in gene content. The Bw4 epitope recognized by lineage II KIR is restricted to MHC-B but also present on some gorilla and human MHC-A. Common to great apes, but rare in humans, are MHC-B possessing a C1 epitope recognized by lineage III KIR. MHC-C arose from duplication of MHC-B and is fixed in all great apes except orangutan, where it exists on approximately 50% of haplotypes and all allotypes are C1-bearing. Recent study showed that gorillas possess yet another intermediate MHC organization compared to humans. Like orangutans, but unlike the Pan-Homo species, duplication of MHC-B occurred. However, MHC-C is fixed, and the MHC-C C2 epitope (absent in orangutans) emerges. The evolution of MHC-C drove expansion of its cognate lineage III KIR. Recently, position −21 of the MHC-B leader sequence has been shown to be critical in determining NK cell educational outcome. In humans, methionine (−21M) results in CD94:NKG2A-focused education whereas threonine (−21T) produces KIR-focused education. This is another dynamic position among hominids. Orangutans have exclusively −21M, consistent with their intermediate stage in lineage III KIR-focused evolution. Gorillas have both −21M and −21T, like humans, but they are unequally encoded by their duplicated B genes. Chimpanzees have near-fixed −21T, indicative of KIR-focused NK education. Harmonious with this observation, chimpanzee KIR exhibit strong binding and, compared to humans, smaller differences between binding levels of activating and inhibitory KIR. Consistent between these MHC-NK cell receptor systems over the course of hominid evolution is the evolution of polymorphism favoring the more novel and dynamic KIR system.

KIR/HLA Gene Profile Implication in Systemic Sclerosis Patients from Mexico

Introduction

Systemic Sclerosis (SSc) is an autoimmune, inflammatory, and multisystemic disease characterized by the presence of autoantibodies and fibrosis. The pathogenesis involves the interaction between immune system cells such as macrophages, NK cells, T cells, and B cells. Killer-cell Immunoglobulin-like Receptors (KIR) are expressed in NK cells and some T cell subsets that recognize HLA class I molecules as ligands and are involved in regulating the activation and inhibition of these cells. The KIR family consists of 14 genes and two pseudogenes; according to the gene content, the genotype could be AA and Bx. The aim of this study was to evaluate the association between KIR/HLA genes and genotypes with SSc and the clinical characteristics.

Methods

We included 50 SSc patients and 90 Control Subjects (CS). Genotyping of KIR, HLA-C, -Bw4, and -A^∗03/^∗11 was made by SSP-PCR.

Results

In SSc patients, a higher frequency of KIR2DL2 (p = 0.0007, p′ = 0.011), KIR2DS4del (p = 0.001, p′ = 0.021), and HLA-C2 (p = 0.02, p′ = 0.09) was found. This is the first study to evaluate the frequency of HLA-A^∗03/^∗11 in SSc patients, of which a low frequency was found in both groups. Compound genotypes KIR2DL2+/HLA-C1+ or KIR2DL2+/HLA-C2+ have a higher frequency in SSc patients. The Bx genotype was the most frequent and was associated with risk to SSc (p = 0.007, OR = 3.1, 95% CI = 1.4–7.9, p′ = 0.014). The genotypes with a higher iKIR number than aKIR (iKIR > aKIR) were found in all individuals; genotypes with 7-8 iKIR genes were increased in SSc patients. We do not find an association between the KIR genes with the clinical characteristics.

Conclusion

The results suggest that KIR2DL2 and 2DS4del could have a risk role in the development of SSc, but not with clinical manifestations.

Fetal human leukocyte antigen-C and maternal killer-cell immunoglobulin-like receptors in cases of severe preeclampsia

INTRODUCTION

The pathogenesis of preeclampsia may involve inadequate trophoblast invasion caused by excessive inhibition of uterine natural killer cells (uNK) by extravillous trophoblast cells (EVT). This may be the result of a combination of maternal killer-cell immunoglobin-like receptor (KIR) AA genotype and fetal human leukocyte antigen-C2 (HLA-C2) genotype. A few studies have reported a significantly increased frequency of the maternal KIR AA/fetal HLA-C2 combination in cases of preeclampsia compared to controls.

METHODS

Study subjects were 259 cases of severe preeclampsia/eclampsia and 259 matched pregnant women without preeclampsia or eclampsia. All pregnancies were singleton pregnancies, and mothers were preferentially primigravidae. Blood samples from women and their newborns were obtained from the Danish National Birth Cohort (DNBC) and the Danish Neonatal Screening Biobank. Significant differences in the frequencies of KIR AA and HLA-C2 between cases and controls were investigated.

RESULTS

No significant difference was observed between cases and controls in the frequency of maternal KIR AA (OR = 0.86, 95%CI = 0.60-1.23, P = 0.41), neither when the fetus carried an HLA-C2 allele (OR = 0.85, 95%CI = 0.52-1.38, P = 0.51), nor when the fetus carried an HLA-C2 allele more than its mother (OR = 0.75, 95%CI = 0.34-1.64, P = 0.47).

CONCLUSION

The Results show no influence of HLA-C/KIR genetic variation on the risk of severe preeclampsia, contrary to what some previous studies have observed. An explanation could be that severe preeclampsia represents a separate pathological entity compared to mild preeclampsia.

Regulation of Placental Extravillous Trophoblasts by the Maternal Uterine Environment

During placentation invasive extravillous trophoblasts (EVTs) migrate into the maternal uterus and modify its vessels. In particular, remodeling of the spiral arteries by EVTs is critical for adapting blood flow and nutrient transport to the developing fetus. Failures in this process have been noticed in different pregnancy complications such as preeclampsia, intrauterine growth restriction, stillbirth, or recurrent abortion. Upon invasion into the decidua, the endometrium of pregnancy, EVTs encounter different maternal cell types such as decidual macrophages, uterine NK (uNK) cells and stromal cells expressing a plethora of growth factors and cytokines. Here, we will summarize development of the EVT lineage, a process occurring independently of the uterine environment, and formation of its different subtypes. Further, we will discuss interactions of EVTs with arteries, veins and lymphatics and illustrate how the decidua and its different immune cells regulate EVT differentiation, invasion and survival. The present literature suggests that the decidual environment and its soluble factors critically modulate EVT function and reproductive success.

High-Resolution Genetic and Phenotypic Analysis of KIR2DL1 Alleles and Their Association with Pre-Eclampsia

Killer-cell Ig-like receptor (KIR) genes are inherited as haplotypes. They are expressed by NK cells and linked to outcomes of infectious diseases and pregnancy in humans. Understanding how genotype relates to phenotype is difficult because of the extensive diversity of the KIR family. Indeed, high-resolution KIR genotyping and phenotyping in single NK cells in the context of disease association is lacking. In this article, we describe a new method to separate NK cells expressing allotypes of the KIR2DL1 gene carried by the KIR A haplotype (KIR2DL1A) from those expressing KIR2DL1 alleles carried by the KIR B haplotype (KIR2DL1B). We find that in KIR AB heterozygous individuals, different KIR2DL1 allotypes can be detected in both peripheral blood and uterine NK cells. Using this new method, we demonstrate that both blood and uterine NK cells codominantly express KIR2DL1A and KIR2DL1B allotypes but with a predominance of KIR2DL1A variants, which associate with enhanced NK cell function. In a case-control study of pre-eclampsia, we show that KIR2DL1A, not KIR2DL1B, associates with increased disease risk. This method will facilitate our understanding of how individual KIR2DL1 allelic variants affect NK cell function and contribute to disease risk.

NK cell frequency and cytotoxicity in correlation to pregnancy outcome and response to IVIG therapy among women with recurrent pregnancy loss

BACKGROUND

Recurrent miscarriage (RM) has a multifactorial etiology mainly due to chromosomal abnormalities and immunological factors. Treating RM has remained to be a challenging issue and the role of intravenous immunoglobulin (IVIG) in treating RM is still controversial.

MATERIALS AND METHODS

This study aimed to evaluate the changes in natural killer (NK) cells' frequency and cytotoxicity in patients with RM who received the IVIG therapy. A total of 78 women with a history of three or more recurrent miscarriages were included and their peripheral blood was drawn in case of positive pregnancy test. On the same date, 400 mg/kg of IVIG was administrated intravenously in 38 women and it continued every four weeks through weeks 30-32 of gestation. The remaining 40 patients with RM were included to be the untreated control group. Then, the effects of IVIG on NK cell frequency, cytotoxic activity, and the expression of inhibitory and activating receptors in the patients with RM, pre and posttreatment were assessed.

RESULTS

NK cells percentage and cytotoxicity were significantly reduced in the IVIG-treated patients after 32 weeks of gestation (p < 0.0001). Expression levels of inhibitory receptors was increased, however, the expression levels of activating receptors were significantly decreased after the IVIG therapy. Pregnancy outcome after the treatment was significantly higher (86.8%) in the IVIG-treated patients than controls (45%; p = 0.0006).

CONCLUSION

Our results suggested that women with RM may benefit from IVIG as a therapeutic approach and the frequency and functional status of peripheral NK cells may serve as a valuable predictive factor of therapy response.

Decidual Vasculopathy in Preeclampsia and Spiral Artery Remodeling Revisited: Shallow Invasion versus Failure of Involution

Decidual vasculopathy is commonly associated with preeclampsia and develops in the late pregnancy in the uterine spiral arteries, which were previously remodeled by the extravillous trophoblasts. In normal early pregnancy, trophoblasts invade into the spiral artery, leading to vascular transformation, and this transformation is found to be associated with phenotypic switch of the endovascular trophoblasts to express CD56, a maternal protein likely from the natural killer (NK) cells. These endovascular trophoblasts are diminished at term. The decidual vessels are also returned to near normal at the delivery. Both the uterus and the uterine spiral arteries undergo involution after delivery. In preeclampsia, the endovascular trophoblasts are present within the vessel wall associated with the persistence of switched phenotype similar to those seen in the early implantation. The persistence of the endovascular trophoblasts in decidual vasculopathy indicates a failure to return to normal vessels in preeclampsia, thus suggesting a potential mechanism of pathogenesis. NK cells seem critical not only for early implantation and spiral artery remodeling but also for the development of decidual vasculopathy in preeclampsia. In this short review, some critical aspects of decidual vasculopathy in normal pregnancy and preeclampsia are reexamined and a new hypothesis is proposed.

Recommendations regarding the genetic and immunological study of reproductive dysfunction

In this article several members of diverse scientific associations and reproduction experts from Spain have updated different genetic and immunological procedure recommendations in couples affected by reproductive dysfunction with the goal of providing a set of useful guidelines for the clinic. The laboratory test has been considered as highly recommendable for making clinical decisions when the result of the diagnostic test is relevant, moderately recommendable when the results are of limited evidence because they are inconsistent, and low when the benefit of the test is uncertain. It is expected that these recommendations will provide some useful guidelines for the diagnosis, prognosis and treatment of couples presenting reproductive dysfunction.

Maternal obesity alters uterine NK activity through a functional KIR2DL1/S1 imbalance

In pregnancy, uterine natural killer cells (uNK) play essential roles in coordinating uterine angiogenesis, blood vessel remodeling and promoting maternal tolerance to fetal tissue. Deviances from a normal uterine microenvironment are thought to modify uNK function(s) by limiting their ability to establish a healthy pregnancy. While maternal obesity has become a major health concern due to associations with adverse effects on fetal and maternal health, our understanding into how obesity contributes to poor pregnancy disorders is unknown. Given the importance of uNK in pregnancy, this study examines the impact of obesity on uNK function in women in early pregnancy. We identify that uNK from obese women show a greater propensity for cellular activation, but this difference does not translate into increased effector killing potential. Instead, uNK from obese women express an altered repertoire of natural killer receptors, including an imbalance in inhibitory KIR2DL1 and activating KIR2DS1 receptors that favors HLA-C2-directed uNK activation. Notably, we show that obesity-related KIR2DS1 skewing potentiates TNFα production upon receptor crosslinking. Together, these findings suggest that maternal obesity modifies uNK activity by altering the response toward HLA-C2 antigen and KIR2DL1/2DS1-controlled TNFα release. Furthermore, this work identifies alterations in uNK function resulting from maternal obesity that may impact early developmental processes important in pregnancy health.

Natural killer cell education in human health and disease

Natural killer (NK) cells maintain immune homeostasis by detecting and eliminating damaged cells. Simultaneous activating and inhibitory input are integrated by NK cells, with the net signal prompting cytotoxicity and cytokine production, or inhibition. Chief among the inhibitory ligands for NK cells are 'self' human leukocyte antigen (HLA) molecules, which are sensed by killer immunoglobulin-like receptors (KIR). Through a process called 'education', the functional capabilities of each NK cell are counterbalanced by their sensitivity for inhibition by co-inherited 'self' HLA. HLA and their ligands, the killer immunoglobulin-like receptors (KIR), are encoded by polymorphic, polygenic gene loci that segregate independently, therefore, NK education and function differ even between related individuals. In this review, we describe how variation in NK education, reactivity and sensitivity for inhibition impacts reproductive success, infection, cancer, inflammatory and autoimmune diseases.

Congenital Cytomegalovirus Infection: Maternal-Child HLA-C, HLA-E, and HLA-G Affect Clinical Outcome

Congenital CMV infection (cCMV) is the most common congenital infection causing permanent long-term impairments (LTI). cCMV immunopathogenesis is largely unknown due to the complex interplay between viral, maternal, placental, and child factors. In this study, a large retrospective nationwide cohort of children with cCMV and their mothers was used. HLA-C, HLA-E, and HLA-G were assessed in 96 mother–child pairs in relation to symptoms at birth and LTI at 6 years of age. The mothers were additionally typed for killer cell immunoglobulin-like receptors. The maternal HLA-G 14 bp deletion/deletion polymorphism was associated with a worse outcome, as the immunomodulation effect of higher protein levels may induce less CMV control, with a direct impact on placenta and fetus. The absence of maternal HLA-C belonging to the C2 group was associated with symptoms at birth, as activating signals on decidual NK may override inhibitory signals, contributing to a placental pro-inflammatory environment. Here, the increased HLA-E*0101 and HLA-C mismatches, which were associated with symptoms at birth, may enhance maternal allo-reactivity to fetal Ags, and cause suboptimal viral clearance. Finally, HLA-C non-inherited maternal antigens (NIMAs) were associated with LTI. The tolerance induced in the fetus toward NIMAs may indirectly induce a suboptimal CMV antiviral response throughout childhood. In light of our findings, the potential role of maternal–child HLA in controlling CMV infection and cCMV-related disease, and the clinical value as predictor for long-term outcome certainly deserve further evaluation.

Maternal natural killer cell immunoglobulin receptor genes and human leukocyte antigen-C ligands influence recurrent spontaneous abortion in the Han Chinese population

The underlying mechanism of recurrent spontaneous abortion (RSA) has remained elusive for many years. Several previous studies have suggested that the killer cell immunoglobulin receptor (KIR) gene family is associated with RSA, however, it is not clear exactly how. The present study detected KIR and human leukocyte antigen-C (HLA-C) genes in 110 Han Chinese women with unexplained RSA and 105 Han Chinese healthy females. The aim of the present study was to determine if certain genotypes were more susceptible to the occurrence of miscarriage. The frequency of KIR genes and different KIR haplotypes in the 2 groups demonstrated no statistical differences. However, in women who had miscarried ≥3 times, the frequency of KIR3DL1 was significantly reduced and the BB haplotype frequency was significantly higher compared with the control group. HLA-C2C2 was significantly increased in the KIR AB and KIR BB groups in the RSA groups compared with the control group. The women in the RSA group who had a homozygous HLA-C2C2 had a significantly higher frequency of the 2DS1 gene compared with the control group. The reduction of inhibitory gene and increased activation combinations may induce the activation of uterine natural killer cells, which may reduce the probability of fetal survival. To the best of our knowledge, the present study is the first report demonstrating the association between maternal KIR and HLA-C genes and RSA in women of a Han Chinese ethnicity. The present study revealed that females who miscarry ≥3 times may be used as selection criteria for RSA and so may exhibit higher research value.

Immunologic Abnormalities, Treatments, and Recurrent Pregnancy Loss: What Is Real and What Is Not?

Recurrent pregnancy loss, depending on the definition, affects 1% to 3% of women aiming to have a child. Little is known about the direct causes of recurrent pregnancy loss, and the condition is considered to have a multifactorial and complex pathogenesis. The aim of this review was to summarize the evaluation and the management of the condition with specific emphasis on immunologic biomarkers identified as risk factors as well as current immunologic treatment options. The review also highlights and discusses areas in need of further research.

The regulation of ovary and conceptus on the uterine natural killer cells during early pregnancy

Uterine natural killer (uNK) cells are short-lived, terminally differentiated and the most abundant lymphocytes in the uterus which play a crucial role in the spiral arteriole modification and establishment of successful pregnancy. Dysregulation of uNK cells has been linked to gestational implications such as recurrent pregnancy loss, preeclampsia and fetal growth retardation. There is evidence showing that progesterone and estrogen can regulate the recruitment, proliferation, differentiation and function of uNK cells via direct action on intracellular nuclear receptors or through intermediary cells in the uterus during early pregnancy. As the deepening of related research in this field, the role of conceptus in such regulation has received extensive attention, it utilizes endocrine signaling (hCG), juxtacrine signaling (HLA-C, HLA-E, HLA-G) and paracrine signaling (cytokines) to facilitate the activities of uNK cells. In addition, under the influence of ovarian hormones, conceptus can increase expression of PIBF and HLA-G molecules to reduce cytotoxicity of uNK cells and promote angiogenesis. In this review, we aim to concentrate on the novel findings of ovarian hormones in the regulation of uNK cells, emphasize the regulatory role of conceptus on uNK cells and highlight the proposed issues for future research in the field.

Missing or altered self: human NK cell receptors that recognize HLA-C

Natural killer (NK) cells are fast-acting and versatile lymphocytes that are critical effectors of innate immunity, adaptive immunity, and placental development. Controlling NK cell function are the interactions between killer-cell immunoglobulin-like receptors (KIRs) and their HLA-A, HLA-B and HLA-C ligands. Due to the extensive polymorphism of both KIR and HLA class I, these interactions are highly diversified and specific combinations correlate with protection or susceptibility to a range of infectious, autoimmune, and reproductive disorders. Evolutionary, genetic, and functional studies are consistent with the interactions between KIR and HLA-C being the dominant control mechanism of human NK cells. In addition to their recognition of the C1 and C2 epitopes, increasing evidence points to KIR having a previously unrecognized selectivity for the peptide presented by HLA-C. This selectivity appears to be a conserved feature of activating KIR and may partly explain the slow progress made in identifying their HLA class I ligands. The peptide selectivity of KIR allows NK cells to respond, not only to changes in the surface expression of HLA-C, but also to the more subtle changes in the HLA-C peptidome, such as occur during viral infection and malignant transformation. Here, we review recent advances in understanding of human-specific KIR evolution and how the inhibitory and activating HLA-C receptors allow NK cells to respond to healthy cells, diseased cells, and the semi-allogeneic cells of the fetus.

The role of KIR and HLA interactions in pregnancy complications

Combinations of KIR and HLA genes associate with pregnancy complications as well as with many other clinical scenarios. Understanding how certain KIR and HLA genes influence the biology of a disease is, however, a formidable challenge. These are the two most variable gene families in the human genome. Moreover, the biology of a disease is best understood by studying the cells of the affected tissue. Natural Killer (NK) cells express KIR and are the most abundant leukocytes in the uterus. Most of our knowledge of NK cells is based on what we have learned from cells isolated from blood, but these are different from their tissue resident counterparts, including uterine NK (uNK) cells. Reproductive immunology faces an additional challenge: Two genotypes must be considered because both maternal and foetal HLA class I molecules may influence the outcome of pregnancy, most likely through interactions with maternal KIR expressed on uNK cells. Maternal uNK cells are not spontaneously cytotoxic and instead engage in interactions with trophoblast. We hypothesise that these interactions regulate allocation of resources between the foetus and the mother and may go wrong in diseases of pregnancy.

KIR, LILRB and their Ligands' Genes as Potential Biomarkers in Recurrent Implantation Failure

Reproductive failure in humans is a very important social and economic problem, because nowadays women decide to conceive later in life and delay motherhood. Unfortunately, with increasing age they have less chance for natural fertilization and maintenance of pregnancy. Many of them need assisted reproductive technology. Approximately 10% of women after in vitro fertilization-embryo transfers experience recurrent implantation failure (RIF). Multiple factors may contribute to RIF, including oocyte and sperm quality, parental chromosomal anomalies, genetic or metabolic abnormalities of the embryo, poor uterine receptivity, immunological disturbances in the implantation site, and some gynecologic pathologies such as endometriosis, uterine fibroids, hydrosalpinx and endometrial polyps. Moreover, the procedure of in vitro fertilization itself could adversely influence the implantation. Nowadays, many studies are focused on the role of natural killer (NK) cells in normal and pathologic pregnancy because NK cells constitute the dominant cell population in the endometrium and they come in close contact with the allogeneic extravillous trophoblast cells in early pregnancy decidua. The majority of these cells are of CD56^bright phenotype. These cells can express killer immunoglobulin-like receptors (KIRs), which, upon recognition of HLA class I molecules (HLA-C and HLA-G) on trophoblasts, may either stimulate or inhibit NK cells to produce soluble factors, and display low cytotoxicity necessary for maintenance of the allogeneic embryo and fetus in the next steps of pregnancy. Moreover, some members of the leukocyte immunoglobulin-like receptor (LILR) family, also named ILT (immunoglobulin-like transcript), are present in the human placenta. LILRB1 (ILT2) was described mainly on stromal cells, while LILRB2 (ILT4), in addition to stromal cells, was also found around vessels in the smooth muscle layer. In this review we focus on the possible role of polymorphism of KIR, LILRB and their ligands (HLA-C, HLA-G) in susceptibility to recurrent implantation failure, which could serve as diagnostic biomarkers of this disease.

Why natural killer cells are not enough: a further understanding of killer immunoglobulin-like receptor and human leukocyte antigen

The immune system's role in recurrent reproductive failure is a controversial issue in assisted reproduction. Most studies into immune system implication in reproduction have focused on finding markers of peripheral blood and less on the uterine environment. Peripheral blood natural killer cells have become an "immune study core" for women with recurrent miscarriage or recurrent implantation failure, based on the mistaken notion that they cause reproductive failure by killing or "rejecting" the embryo. Maternal-fetal tolerance begins at the uterine level, so successful adaptation to the fetus occurs after a complicated process. Insufficient uterine lining invasion by an invading extravillous trophoblast is the primary defect in pregnancy disorders such as recurrent miscarriage. This process is regulated by the interaction between maternal killer immunoglobulin-like receptors (KIRs), expressed by uterine natural killer cells (uNK), and their ligand human leukocyte antigen (HLA) C, expressed by the extravillous trophoblast. Pregnancies are an increased risk of disorders in mothers with KIR AA when the fetus has paternal HLA-C2. A recent report has indicated that the expression of more than one paternal HLA-C by the extravillous trophoblast in assisted reproduction may affect placentation in mothers with KIR AA. This review provides insight into the immune system's role in assisted reproductive treatments. These insights can have an impact on the selection of single-embryo transfer and/or oocyte/sperm donor according to HLA-C in patients with recurrent implantation failure and recurrent miscarriage depending on their KIR haplotype.

Uterine Natural Killer Cells: Functional Distinctions and Influence on Pregnancy in Humans and Mice

Our understanding of development and function of natural killer (NK) cells has progressed significantly in recent years. However, exactly how uterine NK (uNK) cells develop and function is still unclear. To help investigators that are beginning to study tissue NK cells, we summarize in this review our current knowledge of the development and function of uNK cells, and what is yet to be elucidated. We compare and contrast the biology of human and mouse uNK cells in the broader context of the biology of innate lymphoid cells and with reference to peripheral NK cells. We also review how uNK cells may regulate trophoblast invasion and uterine spiral arterial remodeling in human and murine pregnancy.

KIR2DL2 and KIR2DS2 as genetic markers to the methotrexate response in rheumatoid arthritis patients

CONTEXT

Disease Modifying Anti-Rheumatic Drugs (DMARDs) are aimed to interfere with rheumatoid arthritis (RA) progression and reduce the joint damage; however, not all patients respond alike. Killer-cell immunoglobulin-like receptors (KIR) and their ligands, human leucocyte antigen class I (HLA-I), have been associated with RA pathology; therefore, KIR and HLA genes may influence the treatment response.

MATERIALS AND METHODS

We evaluated the association of KIR genotype and their ligands HLA-C genes with the response to DMARDs in RA patients. We included 69 patients diagnosed with RA and 82 healthy individuals as the reference group. KIR and HLA-C genotyping was performed using SSP-PCR. RA patients were assessed at baseline and under treatment at 6 and 12 months; subsequently classified as responders and non-responders in each time period. We evaluated the association between DMARD response and genes using statistical analysis by using Fisher exact test with Bonferroni correction; results were regarded as statistically significant at p < 0.05.

RESULTS

Significant difference was observed in gene frequencies of patients and the reference group, KIR2DL2 was associated with RA (p = 0.031, OR = 2.119). We also observed an association between KIR2DS2 and the response to methotrexate (MTX), moreover, the combination KIR2DL2+/KIR2DS2+ was more frequent in responders to MTX (p = 0.043).

DISCUSSION AND CONCLUSIONS

In our results, responders and non-responders to DMARDs showed KIR2DS2 and KIR2DL2 different gene frequencies, therefore, these genes could be used as response predictors to DMARDs treatment. Thus, these genes were also associated with disease severity, as well as the treatment response possibly by the immunoregulatory function of NK cells.

Human Birth Weight and Reproductive Immunology: Testing for Interactions between Maternal and Offspring KIR and HLA-C Genes

BACKGROUND/AIMS

Maternal and offspring cell contact at the site of placentation presents a plausible setting for maternal-fetal genotype (MFG) interactions affecting fetal growth. We test hypotheses regarding killer cell immunoglobulin-like receptor (KIR) and HLA-C MFG effects on human birth weight by extending the quantitative MFG (QMFG) test.

METHODS

Until recently, association testing for MFG interactions had limited applications. To improve the ability to test for these interactions, we developed the extended QMFG test, a linear mixed-effect model that can use multi-locus genotype data from families.

RESULTS

We demonstrate the extended QMFG test's statistical properties. We also show that if an offspring-only model is fit when MFG effects exist, associations can be missed or misattributed. Furthermore, imprecisely modeling the effects of both KIR and HLA-C could result in a failure to replicate if these loci's allele frequencies differ among populations. To further illustrate the extended QMFG test's advantages, we apply the extended QMFG test to a UK cohort study and the Norwegian Mother and Child Cohort (MoBa) study.

CONCLUSION

We find a significant KIR-HLA-C interaction effect on birth weight. More generally, the QMFG test can detect genetic associations that may be missed by standard genome-wide association studies for quantitative traits.

Combination of uterine natural killer cell immunoglobulin receptor haplotype and trophoblastic HLA-C ligand influences the risk of pregnancy loss: a retrospective cohort analysis of direct embryo genotyping data from euploid transfers

OBJECTIVE

To compare maternal uterine natural killer cell immunoglobulin receptor (KIR) genotype and haplotype frequencies between patients whose euploid single-embryo transfer resulted in pregnancy loss and those that resulted in delivery and to determine if the risk of pregnancy loss was affected by the HLA-C genotype content in the embryo.

DESIGN

Retrospective cohort.

SETTING

Academic research center.

PATIENT(S)

Autologous fresh IVF cycles resulting in positive serum β-hCG during 2009-2014.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

1) Relative risk of pregnancy loss according to maternal KIR genotypes and haplotypes. 2) Comparison of pregnancy loss rates within each KIR haplotype according to HLA-C ligand present in trophectoderm biopsy samples.

RESULT(S)

A total of 668 euploid single-embryo transfers with stored maternal DNA and available preamplification DNA from prior trophectoderm biopsy samples were studied. KIR2DS1, KIR3DS1, and KIR2DS5 were more common in patients who experienced pregnancy loss. Carriers of KIR A haplotype exhibited a decreased risk of pregnancy loss compared with KIR B haplotype carriers. However, among KIR A haplotype carriers, the risk of loss was significantly influenced by whether the transferred embryo carried a C1 allele versus no C1 alleles.

CONCLUSION(S)

KIR A haplotype carriers experienced fewer pregnancy losses than KIR B haplotype carriers after euploid single-embryo transfer. However, this risk was modified by HLA-C alleles present in the embryo. High-risk combinations (KIR A/homozygous C2 and KIR B/homozygous C1) resulted in a 51% increased risk of loss over all other combinations.

BIRTH ORDER AND ANDROPHILIC MALE-TO-FEMALE TRANSSEXUALISM IN BRAZIL

Previous research has indicated that biological older brothers increase the odds of androphilia in males. This finding has been termed the fraternal birth order effect. The maternal immune hypothesis suggests that this effect reflects the progressive immunization of some mothers to male-specific antigens involved in fetal male brain masculinization. Exposure to these antigens, as a result of carrying earlier-born sons, is hypothesized to produce maternal immune responses towards later-born sons, thus leading to female-typical neural development of brain regions underlying sexual orientation. Because this hypothesis posits mechanisms that have the potential to be active in any situation where a mother gestates repeated male fetuses, a key prediction is that the fraternal birth order effect should be observable in diverse populations. The present study assessed the association between sexual orientation and birth order in androphilic male-to-female transsexuals in Brazil, a previously unexamined population. Male-to-female transsexuals who reported attraction to males were recruited from a specialty gender identity service in southern Brazil (n=118) and a comparison group of gynephilic non-transsexual men (n=143) was recruited at the same hospital. Logistic regression showed that the transsexual group had significantly more older brothers and other siblings. These effects were independent of one another and consistent with previous studies of birth order and male sexual orientation. The presence of the fraternal birth order effect in the present sample provides further evidence of the ubiquity of this effect and, therefore, lends support to the maternal immune hypothesis as an explanation of androphilic sexual orientation in some male-to-female transsexuals.

Activating KIR2DS4 Is Expressed by Uterine NK Cells and Contributes to Successful Pregnancy

Tissue-specific NK cells are abundant in the pregnant uterus and interact with invading placental trophoblast cells that transform the maternal arteries to increase the fetoplacental blood supply. Genetic case-control studies have implicated killer cell Ig-like receptor (KIR) genes and their HLA ligands in pregnancy disorders characterized by failure of trophoblast arterial transformation. Activating KIR2DS1 or KIR2DS5 (when located in the centromeric region as in Africans) lower the risk of disorders when there is a fetal HLA-C allele carrying a C2 epitope. In this study, we investigated another activating KIR, KIR2DS4, and provide genetic evidence for a similar effect when carried with KIR2DS1 KIR2DS4 is expressed by ∼45% of uterine NK (uNK) cells. Similarly to KIR2DS1, triggering of KIR2DS4 on uNK cells led to secretion of GM-CSF and other chemokines, known to promote placental trophoblast invasion. Additionally, XCL1 and CCL1, identified in a screen of 120 different cytokines, were consistently secreted upon activation of KIR2DS4 on uNK cells. Inhibitory KIR2DL5A, carried in linkage disequilibrium with KIR2DS1, is expressed by peripheral blood NK cells but not by uNK cells, highlighting the unique phenotype of uNK cells compared with peripheral blood NK cells. That KIR2DS4, KIR2DS1, and some alleles of KIR2DS5 contribute to successful pregnancy suggests that activation of uNK cells by KIR binding to HLA-C is a generic mechanism promoting trophoblast invasion into the decidua.

The role of decidual NK cells in pregnancies with impaired vascular remodelling

The pathologies of the dangerous pregnancy complications pre-eclampsia (PE) and fetal growth restriction (FGR) are established in the first trimester of human pregnancy yet we know little of how this happens. Finely tuned interactions between maternal and placental cells are essential for pregnancy to progress without complications; however, the precise nature of this cross-talk and how it can go wrong are crucial questions that remain to be answered. This review summarises recent studies examining the role played by natural killer cells in regulating normal placentation and remodelling. Their involvement when it is impaired in PE/FGR pregnancies will additionally be discussed.

Variation of maternal KIR and fetal HLA-C genes in reproductive failure: too early for clinical intervention

A distinctive type of (uterine) natural killer (NK) cell is present in the uterine decidua during the period of placental formation. Uterine NK cells express members of the killer immunoglobulin-like receptor (KIR) family that bind to parental HLA-C molecules on the invading placental trophoblast cells. The maternal KIR genes and their fetal ligands are highly variable, so different KIR/HLA-C genetic combinations occur in each pregnancy. Some women only possess inhibitory KIR genes, whereas other women also express activating KIR genes. The overall signal that NK cells receive from paternal HLA-C on trophoblast depends on the ratio of activating and inhibitory KIR genes expressed by them. Therefore, NK cells provide a balance during placentation to ensure maternal survival and an adequately nourished fetus. Because inhibitory KIRs are found more frequently in women with defective placentation, e.g. pre-eclampsia, fetal growth restriction or recurrent spontaneous abortion, some fertility clinics suggest that women should be 'tissue typed' for their KIR genotypes. We explain why, presently, it is premature to introduce KIR and HLA-C typing to predict pregnancy outcome. In future, however, selecting for certain combinations of KIR and HLA-C variants in surrogacy, egg or sperm donation may prove useful to reduce disorders of pregnancy.

Reproduction, infection and killer-cell immunoglobulin-like receptor haplotype evolution

Killer-cell immunoglobulin-like receptors (KIRs) are encoded by one of the most polymorphic families in the human genome. KIRs are expressed on natural killer (NK) cells, which have dual roles: (1) in fighting infection and (2) in reproduction, regulating hemochorial placentation. Uniquely among primates, human KIR genes are arranged into two haplotypic combinations: KIR A and KIR B. It has been proposed that KIR A is specialized to fight infection, whilst KIR B evolved to help ensure successful reproduction. Here we demonstrate that a combination of infectious disease selection and reproductive selection can drive the evolution of KIR B-like haplotypes from a KIR A-like founder haplotype. Continued selection to survive and to reproduce maintains a balance between KIR A and KIR B.

Killer-cell immunoglobulin-like receptors and cytomegalovirus reactivation during late pregnancy

Human cytomegalovirus (CMV) represents an important public health concern as it is associated with severe morbidity and mortality in transplant recipients, HIV-infected individuals and pregnant women given the risk of congenital infection. Congenital CMV is a leading cause of neurological sequelae, developmental delay and birth defects worldwide. Cytomegalovirus can be transmitted to the foetus following maternal infection or reactivation. NK cells expressing killer-cell immunoglobulin-like receptors (KIR) are part of the innate immune system and the first line of defence against viral incursions. Previous reports have shown that KIR genes are associated with CMV infections in the post-transplant setting. In this study, we set out to determine whether a protective effect of KIR genes over CMV infection is seen in Mexican pregnant women. Cytomegalovirus infection was assessed through nucleic acid testing in 200 pregnant women and 600 healthy blood donors comprising the Mexican mestizo reference population. Killer-cell immunoglobulin-like receptors and HLA-C genotypes were obtained from 200 pregnant women and 300 reference samples using a comprehensive PCR-SSP approach. We observed statistically lower carrier frequencies of cB03|tA01 gene-content haplotype, of cB03 haplotype motif, of the KIR2DL5 + 2DS3/2DS5 gene pair and of KIR2DL5 amongst CMV-positive pregnant women in comparison with those CMV negative. None of these were associated with CMV status in the reference population. Logistic regression analysis revealed that the most important factor determining CMV status during third-trimester pregnancies was the KIR2DL5 + 2DS3/2DS5 gene pair (OR 0.376 (95%CI 0.174, 0.811, P = 0.013). Our results indicate that CMV-protective KIR gene associations described in Caucasoid populations are also present in the genetically distinct Mexican mestizo population. Our results suggest that certain KIR gene combinations provide protection against CMV infections occurring during late-term pregnancies, a finding of utmost epidemiological importance given its implication with congenital CMV infections.