HLA-E is expressed on trophoblast and interacts with CD94/NKG2 receptors on decidual NK cells

Non-classical MHC class I molecule HLA-E is the ligand for CD94/NKG2 NK cell receptors. Surface expression of HLA-E requires binding of specific HLA class I leader sequences. The uterine mucosa in early pregnancy (decidua) is infiltrated by large numbers of NK cells, which are closely associated with placental trophoblast cells. In this study we demonstrate that trophoblast cells express HLA-E on their cell surface in addition to the previously reported expression of HLA-G and HLA-C. Furthermore, we show that the vast majority of decidual NK cells bind to HLA-E tetrameric complexes and this binding is inhibited by mAb to CD94. Thus, recognition of fetal HLA-E by decidual NK cells may play a key role in regulation of placentation. The functional consequences of decidual NK cell interaction were investigated in cytotoxicity assays using polyclonal decidual NK cells. The overall effect of CD94/NKG2 interaction with HLA-E is inhibition of cytotoxicity by decidual NK cells. However, since decidual NK cells are unable to kill trophoblast even in the presence of mAb to MHC class I molecules and NK cell receptors, HLA-E interaction with CD94/NKG2 receptors may regulate other functions besides cytolysis during implantation.     

Expression of killer cell inhibitory receptors on human uterine natural killer cells

The establishment of the human placenta in early pregnancy is characterized by the presence of large numbers of natural killer (NK) cells within the maternal decidua in close proximity to the fetally-derived invading extravillous trophoblast which expresses at least two HLA class I molecules, HLA-G and HLA-C. These NK cells have an unusual phenotype, CD56^bright CD16, distinguishing them from adult peripheral blood NK cells. They may control key events in trophoblast migration and therefore placentation. Human NK cells in peripheral blood express receptors for polymorphic HLA class I molecules. This family of receptors, known as killer cell inhibitory receptors (KIR), are expressed on overlapping subsets of NK cells to give an NK cell repertoire which differs between individuals. Using a panel of monoclonal antibodies to several members of the KIR family and analysis by flow cytometry, we have found that KIR are expressed by decidual NK cells. There is variation in both the percentage of cells expressing a particular receptor and the density of receptor expression between decidual NK cells from different individuals. Comparison of NK cells from decidua and peripheral blood of the same individual showed that NK cells from these two different locations express different repertoires of KIR. Receptors are present in individuals who do not possess the relevant class I ligand, raising the possibility that these NK receptors may be involved in recognition of the allogeneic fetus by the mother at the implantation site.     

不明原因自然流产与蜕膜NK细胞表面活化性受体表达的相关性研究

探讨不明原因自然流产患者蜕膜NK细胞杀伤活性与其细胞表面活化性受体NKp46、NKp44、NKp30和NKG2D表达的相关性。选取21例早孕不明原因自然流产患者为病例组,25例正常早孕人流妇女为对照组,收集两组的蜕膜组织,Ficoll密度梯度离心分离淋巴细胞,MACS磁珠分选CD3-CD56+NK细胞。以K562细胞为靶细胞,用细胞染色及流式细胞技术检测两组蜕膜NK细胞杀伤活性,用流式细胞技术检测两组蜕膜CD56brightCD16-NK和CD56dimCD16+NK细胞上活化性受体NKp46、NKp44、NKp30和NKG2D的表达,并与NK细胞杀伤活性进行相关性分析。结果:(1)早孕蜕膜NK细胞具有杀伤活性;(2)病例组蜕膜NK细胞的杀伤活性较正常对照组显著增强(P=0.014);(3)病例组蜕膜CD56brightCD16-NK细胞中NKp44的表达比正常对照组显著升高(P=0.021);病例组蜕膜CD56dimCD16+NK细胞中NKp46和NKp44的表达比正常对照组显著升高(分别P=0.026,P=0.041);其余活化性受体的表达两组未见明显差异;(4)蜕膜NK细胞杀伤功能与蜕膜CD56brightCD16-NK细胞中NKp44的表达呈显著正相关(r=0.677,P<0.05),和蜕膜CD56dimCD16+NK细胞中NKp46的表达呈显著正相关(r=0.634,P<0.05)。蜕膜NK细胞活化性受体NKp46和NKp44表达增加,从而使蜕膜NK细胞的杀伤功能增强可能在不明原因自然流产的发病中起重要作用。     

Co-stimulation of human decidual natural killer cells by interleukin-2 and stromal cells

At the late secretory phase of the menstrual cycle and in early pregnancy, the uterine mucosa is infiltrated by large numbers of natural killer (NK) cells with a distinctive phenotype (CD56bright CD16- CD3-) and large granular lymphocyte (LGL) morphology. Circulating CD56bright NK cells generally proliferate in the presence of interleukin-2 (IL-2), but it is clear that cofactors besides IL-2 are required for optimal response. In the bone marrow, this co-stimulating signal is provided by stromal cells. In the present study we observe that uterine CD56+ cells from early pregnancy decidua similarly proliferate vigorously when cultured with decidual stromal cells and a suboptimal dose of IL-2. This response is dependent on cell-cell contact, as no proliferation of decidual NK cells was observed when they were separated from stromal cells by a permeable cyclopore membrane. In addition, we have studied the expression of Bcl-2 by decidual CD56+ cells. Our results show that the microenvironment of the uterus is likely to have a significant influence on the proliferation and survival of uterine CD56+ cells.     

Uterine NK Cells and Trophoblast HLA Class I Molecules

PROBLEM: To investigate the proposal that NK cells in decidua may control trophoblast migration during implantation of the human placenta. METHOD: Use Mab specific for HLA-G and for HLA-C in association with flow cytometry and immunoprecipitation to determine the expression of these HLA molecules by trophoblast. Expression of Killer inhibitory/activatory receptors (KIR/KAR) and the CD94 receptor by decidual NK cells was also studied. RESULTS: Extravillous trophoblast expressed HLA-G and HLA-C in both β₂m-associated form and as free heavy chains. KIR and KAR are expressed by decidual NK cells. The repertoire of receptors varied between different women and also between blood and decidual NK cells from the same women. The expression of CD94 was also different between blood and decidual NK cells. CONCLUSION: The recognition of HLA-G/HLA-C by KIR/KAR and CD94 could provide a mechansm by which decidual NK cells control trophoblast migration.     

CD3- leukocytes present in the human uterus during early placentation: phenotypic and morphologic characterization of the CD56++ population.

In this study, the CD3- LGL/NK cells present in the pregnant human uterus have been characterized. Phenotypic and morphologic analyses of decidual LGL revealed many similarities to the minor CD56bright+, CD16- subset in peripheral blood, but there were some important differences. The relative surface density of CD56+ is greatly increased on decidual LGL to 22x that found on the majority of CD56+ peripheral blood NK cells. The CD56bright+ cells in decidua show LGL morphology, whereas in peripheral blood, they are mainly agranular. Proliferation of CD56+ cells occurs predominantly during the nonpregnant secretory (luteal) phase, indicating these CD56+ uterine LGL do not migrate as terminally differentiated cells. The appearance of CD56+ cells was examined at the ultrastructural level using immunoelectron microscopy. Cells with phenotypic characteristics of decidual LGL occur in a higher percentage (1.11%) in the peripheral blood of women of reproductive age than in men (0.66%). On the basis of these results, it is proposed that the CD56bright+ uterine leukocytes represent a distinctive, hormonally regulated subset possibly adapted to control human placentation.     

Induction of CD16+ CD56bright NK cells with antitumour cytotoxicity not only from CD16- CD56bright NK Cells but also from CD16- CD56dim NK cells

The aim of this study was to examine the effect of cytokines on different subsets of NK cells, while especially focusing on CD16(-) CD56(dim) cells and CD16(-) CD56(bright) cells. When human peripheral blood mononuclear cells (PBMC) were cultured with a combination of IL-2, IL-12 and IL-15 for several days, a minor population of CD56(bright) NK cells expanded up to 15%, and also showed potent cytotoxicities against various cancer cells. Sorting experiments revealed that unconventional CD16(-) CD56(+) NK cells (CD16(-) CD56(dim) NK cells and CD16(-) CD56(bright) NK cells, both of which are less than 1% in PBMC) much more vigorously proliferated after cytokine stimulation, whereas predominant CD16(+) CD56(dim) NK cells proliferated poorly. In addition, many of the resting CD16(-) CD56(bright) NK cells developed into CD16(+) CD56(bright) NK cells, and CD16(-) CD56(dim) NK cells developed into CD16(-) CD56(bright) NK cells and also further into CD16(+) CD56(bright) NK cells by the cytokines. CSFE label experiments further substantiated the proliferation capacity of each subset and the developmental process of CD16(+) CD56(bright) NK cells. Both CD16(-) CD56(dim) NK cells and CD16(-) CD56(bright) NK cells produced large amounts of IFN-gamma and Fas-ligands. The CD16(+) CD56(bright) NK cells showed strong cytotoxicities against not only MHC class I (-) but also MHC class I (+) tumours regardless of their expression of CD94/NKG2A presumably because they expressed NKG2D as well as natural cytotoxicity receptors. The proliferation of CD16(+) CD56(bright) NK cells was also induced when PBMC were stimulated with penicillin-treated Streptococcus pyogenes, thus suggesting their role in tumour immunity and bacterial infections.     

The expression of killer cell inhibitory receptors on natural killer cells and activation status of CD4+ and CD8+ T cells in the decidua of normal and abnormal early pregnancies.

The establishment of the human placenta in early pregnancy is characterized by the presence of large numbers of natural killer cells within the maternal decidua. These NK cells have an unusual phenotype, CD3- CD16- CD56(bright), distinguishing them from peripheral blood NK cells. They may control trophoblast migration and placentation. Using a panel of monoclonal antibodies to several members of the KIR family and flow cytometry, we found that KIRs are expressed on decidual NK cells. There is variation in both the percentage of cells expressing a particular receptor and the density of receptor expression between decidual NK cells from different individuals. In anembryonic pregnancy, the proportions of decidual NK cells with a particular KIRs (GL183 and EB6) decreased significantly when compared with normal pregnancy (p = 0.01 and 0.01, respectively), raising the possibility that these NK receptors may be involved in recognition of the allogeneic fetus by the mother at the implantation site. In the decidua, more CD4+ and CD8+ T cells expressed CD69 and HLA-DR than in blood, indicating that T cells are regionally activated during early pregnancy. When compared with normal pregnancy, decidual HLA-DR+CD4+CD3+, CD69+CD8+CD3+ and HLA-DR+CD8+CD3+ T lymphocytes are significantly increased in anembryonic pregnancy. The over-activation of decidual T cells during anembryonic pregnancy may thus contribute to the increased NK cytotoxicity activity.     

Expression of killer immunoglobulin-like receptors on peripheral blood NK cell subsets of women with recurrent spontaneous abortions or implantation failures

PROBLEM: Decidual natural killer (NK) cells express inhibitory receptors (killer immunoglobulin-like receptors, KIRs), which bind to ligands on trophoblast cells (human leucocyte antigen, HLA-C). This interaction appears to block NK cytotoxicity against trophoblast cells. In this study, we investigated the expression of inhibitory and activating receptors in peripheral blood NK cells of women with recurrent spontaneous abortion (RSA) or implantation failures. METHOD OF STUDY: CD56(dim)/CD16(+), CD56(bright)/CD16(-) NK cells and CD56(+)/CD3(+) NKT cells of women with RSA or in vitro fertilization (IVF) failures and normal controls were analyzed for the expression of CD158a, CD158b inhibitory KIRs or CD161-activating receptors, by flow cytometric analysis. RESULTS: CD158a and CD158b inhibitory receptor expression by CD56(dim)/CD16(+) and CD56(bright)/CD16(-) NK cells were significantly decreased, and CD161-activating receptor expression by CD56(+)/CD3(+) NKT cells was significantly increased in women with implantation failures when compared with normal controls. CONCLUSIONS: An imbalance between inhibitory and activating receptor expression was found in NK cells of women with implantation failures. This imbalance may explain the adverse reproductive outcome.     

CD3- Leukocytes Present in the Human Uterus During Early Placentation: Phenotypic and Morphologic Characterization of the CD56++ Population

In this study, the CD3- LGL/NK cells present in the pregnant human uterus have been characterized. Phenotypic and morphologic analyses of decidual LGL revealed many similarities to the minor CD56^bright+, CD16^- subset in peripheral blood, but there were some important differences. The relative surface density of CD56⁺ is greatly increased on decidual LGL to 22 x that found on the majority of CD56 peripheral blood NK cells. The CD56bright cells in decidua show LGL morphology, whereas in peripheral blood, they are .mainly agranular. Proliferation of CD56⁺ cells occurs predominantly during the nonpregnant secretory (luteal) phase, indicating these CD56⁺ uterine LGL do not migrate as terminally differentiated cells. The appearance of CD56 cells was examined at the ultrastructural level using immunoelectron microscopy. Cells with phenotypic characteristics of decidual LGL occur in a higher percentage (1.11%) in the peripheral blood of women of reproductive age than in men (0.66%). On the basis of these results, it is proposed that the CD56^bright+ uterine leukocytes represent a distinctive, hormonally regulated subset possibly adapted to control human placentation.     

Differential distribution of NK cells in decidua basalis compared with decidua parietalis after uncomplicated human term pregnancy

As pregnancy progresses, a characteristic decline in the percentage of CD56bright CD16- uterine natural killer (NK) cells occurs. Studies of term decidua, however, have focused only on leukocytes derived from decidua basalis, the site of implantation. The decidua parietalis, lining the remainder of the uterine cavity is another important region of the maternal-fetal interface that forms contact with fetal tissue at the end of the first trimester. The aim of this study was to evaluate possible differences in expression of CD16 and CD56 on leukocytes from normal term decidua basalis and decidua parietalis. Decidua basalis and parietalis samples were obtained from 30 placentas collected after elective cesarean section. Percentages of leukocyte subpopulations and NK cell subsets within the CD45+ cell fraction were determined by flow cytometry. In six decidual samples, concurrent immunohistochemical staining was performed. Higher percentages of CD56dim CD16+ NK cells and CD56- CD16+ cells were found in decidua basalis in comparison to decidua parietalis. In contrast, the percentage of CD56bright CD16- uterine NK cells was significantly higher in decidua parietalis. Immunohistochemical quantification supported flow cytometric results. We conclude that significant differences exist with respect to the distribution of NK cells in term decidua basalis and parietalis. Future functional studies may improve our understanding of their role at the maternal-fetal interface.     

Leukocyte function-associated antigen-1 expression on decidual natural killer cells in patients with early pregnancy loss.

A large number of CD56(bright) natural killer (NK) cells, which comprise a very small fraction of peripheral blood lymphocytes, appear in the endometrium during the late secretory phase and early pregnancy. These cells are thought to immunologically maintain or inhibit pregnancy. However, the details regarding their contribution to the immuno-elimination systems of embryonic cells or decidual stromal cells remain unclear. Recently, leukocyte function-associated antigen-1 (LFA-1) was shown to play a critical role in the regulation of NK cytolysis in peripheral blood lymphocytes. We speculated that LFA-1 on the decidual CD56(bright) NK may be involved in the regulation of pregnancy. The expression of LFA-1 on the decidual CD56(bright) NK cells was analysed using flow cytometry with fluorescent monoclonal antibodies; CD56 (NKH1), CD16 (Fcg-R3) and CD11a (LFA-1 alpha-chain). In comparison with non-pregnant endometrium during the late secretory phase, the subpopulation of CD56(bright)CD16(-) cells in decidual lymphocytes was significantly increased during normal pregnancy, but was less than that in early pregnancy loss (P < 0.05). Furthermore, the number of CD56(bright) NK cells expressing LFA-1 was significantly higher in early pregnancy loss, and the late secretory phase, than during normal pregnancy (P < 0.05). Our results indicate that up-regulation of LFA-1 on CD56(bright) NK cells is related to spontaneous abortion or the onset of menstruation.     

Decidual natural killer cells in recurrent spontaneous abortion with normal chromosomal content.

PROBLEM: The maternal local immune responses in unexplained recurrent spontaneous abortion (RSA) are not yet well known. Maternal peripheral and decidual natural killer (NK) cells were evaluated in RSA with normal chromosomal content. METHOD OF STUDY: Maternal peripheral blood, villous trophoblast, and decidua were taken from 15 normal pregnancies and 9 RSA patients with normal chromosomes. The NK cells in decidual lymphocytes were evaluated by flow cytometry using monoclonal antibodies for CD56, CD16, and CD3. RESULTS: The percentages of CD56+ CD16- CD3- cells in decidual lymphocytes in RSA were lower than in normal pregnancies (P < 0.002). The CD56+CD16+/CD56+CD16- cells ratio in RSA was higher than in normal pregnancies (P < 0.02). CONCLUSION: The lower percentages of CD56+CD16-CD3- cells in RSA cases may show an inappropriate accumulation of NK cells in the decidua, and this finding may be a factor involved in RSA.     

Immunoregulatory properties of decidua macrophages

It has been suggested that decidual NK cells play a regulatory role in pregnancy with their heterocladic (activating/inhibitory) receptor repertoire to control trophoblast infiltration. Most of the NK receptors (NKRs) have as ligands HLA molecules (HLA-C,-G,-E), which are expressed on invading trophoblast and they may interact with their NKR counterparts and provide self-signals to evade trophoblastic damage.
When we studied the NKR repertoire in couples with unexplained recurrent spontaneous abortions by genotyping partners for NKRs (KIR and CD94/NKG receptors, known to have as ligands HLA molecules present on trophoblast), we found that aborting women usually have a limited inhibitory KIR (inhKIR) repertoire.
Our hypothesis that a limited inhKIR repertoire predisposes to miscarriage, because it is ineffective to abort activating signals and protect trophoblast, is supported by studies in selected couples, known to posses HLA-Cw antigens interacting with inhKIRs and by studies on the placental material of spontaneously lost or electively terminated pregnancies. Most of the aborters did not have inhKIRs specific for the HLA-C antigens possibly expressed on trophoblast and this seems to be confirmed when KIRs and HLA-Cs are genotyped using DNA extracted from decidual and trophoblastic cells, respectively.
Increasing knowledge about KIR haplotypes is expected to be helpful in the study of the suggestedinhKIR – HLA-C allorecognition system in pregnancy.     

Immunological relationship between the mother and the fetus

The immunological relationship between the mother and the fetus is a bi-directional communication determined on the one hand by fetal antigen presentation and on the other hand by recognition of and reaction to these antigens by the maternal immune system. There is evidence now that immunological recognition of pregnancy is important for the maintenance of gestation, and that inadequate recognition of fetal antigens might result in failed pregnancy. In contrast to HLA-A and -B Class I genes that are downregulated in human trophoblast cells, nonpolymorphic Class I molecules, e.g., HLA-G Class Ib, are expressed in extravillous cytotrophoblast and also in endothelial cells of fetal vessels in the chorionic villi as well as in amnion cells and amniotic fluid. The trophoblast does not induce transplantation immunity and resists NK- and CTL-mediated lysis in vitro. According to our present knowledge, HLA-G presents antigens for gamma/delta T cells and at the same time defends the trophoblast from cytotoxic effector mechanisms. Since polymorphic MHC is absent from the trophoblast, presentation of fetally derived antigens is unlikely to be MHC restricted. gamma/delta T cells recognize a distinct group of ligands with a smaller receptor repertoire than alpha/beta T cells. Most gamma/delta T cells recognize unprocessed foreign antigens without MHC. In the decidua gamma/delta TCR-positive cells significantly increase in number and the majority of decidual gamma/delta T cells are in an activated form due to recognition of conserved mammalian molecules on the trophoblast. Following recognition of fetally derived antigens, the immune system reacts with the setting in of a wide range of protective mechanisms. Many observations suggest that pregnancy is associated with an altered TH1/TH2 balance. Maternal immune response is biased toward humoral immunity and away from cell-mediated immunity that could be harmful to the fetus. Cytokines of maternal origin act on placental development. On the other hand, antigen expression on the placenta determines maternal cytokine pattern. Normal human pregnancy is characterized by low peripheral NK activity, and increased NK activity seems to play a role in spontaneous abortions of unknown etiology. In early human pregnancy the majority of uterine lymphocytes are CD56(bright) granulated NK cells, which do not express CD16 or CD3. In rodents and humans, uterine NK cells are under hormonal control. In early pregnancy they are enriched at sites where fetal trophoblast infiltrates the decidua. The dynamics of the appearance of uterine NK cells suggest that one of the functions of these cells is control of placentation. Another protective mechanism operating in favor of pregnancy is progesterone-dependent immunomodulation. Due to stimulation by fetally derived antigens, pregnancy lymphocytes develop progesterone receptors and in the presence of progesterone produce a mediator (PIBF) that, through altering the cytokine balance, inhibits NK activity and exerts an antiabortive effect in mice.     

Aberrant positioning of trophoblast and lymphocytes in the feto-maternal interface with pre-eclampsia

Pregnancy represents the growth of an allograft where fetal trophoblast cells evade immune rejection and invade maternal tissue. There should be a balance between fetal trophoblast and maternal immune-responsive cells and alterations in the proportion of these cells may relate to pregnancy disorders. To test this, the decidual tissue of placental bed biopsies was examined and trophoblast cells and lymphocytes were quantified morphometrically; spiral arteries were classified as unchanged, transformed or affected by acute atherosis. Normal pregnancy (n=19) was characterized by the transformation of about one half of all spiral arteries within the placental bed. We found that 40% of all lymphocytes were CD56+ uterine NK cells and 60%, CD3+ T-lymphocytes; about 30% of these were CD8+ T cells. Intrauterine growth retardation in the context of preeclampsia (n=15) was accompanied by reduced trophoblast numbers within smaller and more tortuous arteries and an increase in the proportion of CD56+ uterine NK cells and CD8+ T lymphocytes in the decidua (70% of all CD3+ cells). In the case of pre-eclampsia without fetal growth retardation (n=14) no increase in CD56+ uterine NK cells was seen, while CD8+ T lymphocytes were significantly increased compared with the normal level (50% of all CD3+ cells). Fetal growth retardation is associated with poor transformation of spiral arteries and characterized by an increase of uterine NK cells. Symptoms of pre-eclampsia are independently associated with an increase in the cytotoxic T subset of decidual lymphocytes. Pre-eclampsia and related fetal growth retardation are seemingly caused by an enhancement of the maternal cytotoxic defence against the fetal allograft.     

IMMUNOLOGICAL RELATIONSHIP BETWEEN THE MOTHER AND THE FETUS

The immunological relationship between the mother and the fetus is a bi-directional communication determined on the one hand by fetal antigen presentation and on the other hand by recognition of and reaction to these antigens by the maternal immune system. There is evidence now that immunological recognition of pregnancy is important for the maintenance of gestation, and that inadequate recognition of fetal antigens might result in failed pregnancy. In contrast to HLA-A and -B Class I genes that are downregulated in human trophoblast cells, nonpolymorphic Class I molecules, e.g., HLA-G Class Ib, are expressed in extravillous cytotrophoblast and also in endothelial cells of fetal vessels in the chorionic villi as well as in amnion cells and amniotic fluid. The trophoblast does not induce transplantation immunity and resists NK- and CTL-mediated lysis in vitro. According to our present knowledge, HLA-G presents antigens for γ/δ T cells and at the same time defends the trophoblast from cytotoxic effector mechanisms. Since polymorphic MHC is absent from the trophoblast, presentation of fetally derived antigens is unlikely to be MHC restricted. γ/δ T cells recognize a distinct group of ligands with a smallerreceptorrepertoire than α/β T cells. Most γ/δ T cells recognize unprocessed foreign antigens without MHC. In the decidua γ/δ TCR-positive cells significantly increase in number and the majority of decidual γ/δ T cells are in an activated form due to recognition of conserved mammalian molecules on the trophoblast. Following recognition of fetally derived antigens, the immune system reacts with the setting in of a wide range of protective mechanisms. Many observations suggest that pregnancy is associated with an altered TH1/TH2 balance. Maternal immune response is biased toward humoral immunity and away from cell-mediated immunity that could be harmful to the fetus. Cytokines of maternal origin act on placental development. On the other hand, antigen expression on the placenta determines maternal cytokine pattern. Normal human pregnancy is characterized by low peripheral NK activity, and increased NK activity seems to play a role in spontaneous abortions of unknown etiology. In early human pregnancy the majority of uterine lymphocytes are CD56 bright granulated NK cells, which do not express CD16 or CD3. In rodents and humans, uterine NK cells are under hormonal control. In early pregnancy they are enriched at sites where fetal trophoblast infiltrates the decidua. The dynamics of the appearance of uterine NK cells suggest that one of the functions of these cells is control of placentation. Another protective mechanism operating in favor of pregnancy is progesterone-dependentimmunomodulation. Due to stimulation by fetally derived antigens, pregnancy lymphocytes develop progesterone receptors and in the presence of progesterone produce a mediator (PIBF) that, through altering the cytokine balance, inhibits NK activity and exerts an antiabortive effect in mice.     

Comparative Analysis of the Immunophenotypes of Decidual and Peripheral Blood Large Granular Lymphocytes and T Cells During Early Human Pregnancy

PROBLEM : The functional role of the leukocytes in the decidua is not clear. They may regulate the maternal immune response to the fetal allograft. However, the factors controlling maternal and fetal communication have not yet been identified. METHOD : A comparative analysis of the phenotypes of decidual and peripheral blood large granular lymphocytes (LGLs) and T lymphocytes in early human pregnancy was performed on decidual tissue and blood samples obtained from ten patients at therapeutic abortion. RESULTS : Whereas most of the decidual LGLs were found to have a CD56^bright++ phenotype, most of the peripheral blood NK cells (90%) showed the classical CD56^dim+ phenotype, and only a small proportion were CD56^bright+ cells. Another striking difference was found in the expression of very late antigen 1 (VLA-1, CD49a): Almost all the decidual CD56^bright++ LGLs, but virtually none of the peripheral blood CD56⁺ NK cells expressed this antigen. Further differences were found in the expression of CD16, CD44, CD45RA, CD54, and CD57. There were also differences in phenotype between T cells derived from decidual tissue and those derived from peripheral blood. Approximately 31% of the CD3⁺ decidual T cells expressed VLA-1, but this antigen was virtually absent on peripheral blood T cells. A further difference was seen in the expression of HLA-DR. This activation antigen was found on 32 ± 13% of the decidual T cells but only 8 ± 5% of the peripheral blood T cells. Additionally, the proportion of cells expressing CD38 was higher among decidual than peripheral blood T cells. CONCLUSION : The findings suggest that both decidual LGLs and a subset of decidual T cells are activated and possibly play a role in the control of trophoblast growth and placental development.     

A bird's eye view of NK cell receptor interactions with their MHC class I ligands

The surveillance of target cells by natural killer (NK) cells utilizes an ensemble of inhibitory and activating receptors, many of which interact with major histocompatibility complex (MHC) class I molecules. NK cell recognition of MHC class I proteins is important developmentally for the acquisition of full NK cell effector capacity and during target cell recognition, where the engagement of inhibitory receptors and MHC class I molecules attenuates NK cell activation. Human NK cells have evolved two broad strategies for recognition of human leukocyte antigen (HLA) class I molecules: (i) direct recognition of polymorphic classical HLA class I proteins by diverse receptor families such as the killer cell immunoglobulin-like receptors (KIRs), and (ii) indirect recognition of conserved sets of HLA class I-derived peptides displayed on the non-classical HLA-E for recognition by CD94-NKG2 receptors. In this review, we assess the structural basis for the interaction between these NK receptors and their HLA class I ligands and, using the suite of published KIR and CD94-NKG2 ternary complexes, highlight the features that allow NK cells to orchestrate the recognition of a range of different HLA class I proteins.     

Natural killer (NK) cell receptors' repertoire in couples with recurrent spontaneous abortions

PROBLEM: Natural killer (NK) cell receptors (NKRs) have been suggested to protect trophoblast, but their function at the fetomaternal interface remains unknown. To investigate if the outcome of pregnancy depends on women's NKRs, we studied the NKR repertoire in couples with recurrent spontaneous abortions (RSA). METHODS: Twenty-six childless couples with > or = 2 abortions, characterized by alloimmune abnormalities, and 26 control couples were genotyped for five killer immunoglobulin-like receptors (KIR) and two CD94/NKG receptors, known to have as ligands human leukocyte antigen (HLA) class I molecules with trophoblastic expression: inhibitory 2DL1,2,3 and activating 2DS1,4 KIRs, inhibitory NKG2A and activating NKG2C. Detected repertoires of women and partners were compared between the two groups. RESULTS: Less aborters than controls were found to have all three inhibitory KIRs (30.77% versus 69.23%, P = 0.01), some of them had only one inhibitory KIR (19.23% versus 3.85%, P = 0.08) and most of them were lacking inhibitory KIRs possessed by their husbands (57.69% versus 15.38%, P = 0.001). CONCLUSIONS: Women with alloimmune abortions have a limited inhibiting KIR repertoire and such miscarriages may occur because trophoblastic HLA class I molecules are recognized by decidual NK cells lacking the appropriate inhibitory KIRs.