Decidual Natural Killer Cells Research Articles

Aberrant Uterine Natural Killer (NK)‐Cell Expression and Altered Placental and Serum Levels of the NK‐Cell Promoting Cytokine Interleukin‐12 in Pre‐Eclampsia

Natural killer (NK) cells are the most abundant lymphocyte population at the maternal-fetal interface. They are suggested to be important during placentation by controlling trophoblast invasion. If placentation is suboptimal, pre-eclampsia can occur. Decidual NK (dNK) cells were examined at delivery in 46 women, 22 pre-eclamptic women and 24 healthy controls, by staining for CD56 and CD94 with immunohistochemistry (IHC). Furthermore, we investigated the placental expression and the serum levels of the NK-cell activating cytokines interleukin(IL)-12, IL-15, IL-18 and the anti-inflammatory cytokine IL-10 by IHC and enzyme-linked immunosorbent assay (ELISA), respectively. Pre-eclamptic women had higher number of CD56+ and CD94+ cells in the decidua, indicating an altered receptor expression of dNK cells. We also demonstrate for the first time that the villous trophoblasts show strong immunostaining for IL-12 in placentae from healthy controls, while women suffering from pre-eclampsia have significantly less IL-12. However, pre-eclamptic women had significantly elevated IL-12 and IL-15 levels in serum. Results show increased numbers and altered phenotype of dNK cells in pre-eclampsia, supporting the importance of these cells for a healthy pregnancy. The altered receptor expression of dNK cells together with diminished placental IL-12 expression could implicate an altered NK cell-regulation in pre-eclampsia.

Early pregnancy decidual lymphocytes beside perforin use Fas ligand (FasL) mediated cytotoxicity

Decidual natural killer (NK) cells are the predominant lymphocytes at the maternal–fetal interface. They are involved in defense against virally infected, parasitized and transformed cells and may contribute to the control of trophoblast invasion. The presence of perforin and other possible cytolytic mediators suggests these functions. Cytolytic mechanisms of unstimulated and Th1 cytokine stimulated decidual lymphocytes (DL), as well as purified decidual CD56+ cells, were analyzed against NK sensitive and resistant targets. DL were isolated from decidual mononuclear cells (DMC) cultured in the medium only or in the presence of Th1 cytokines: IL-2, IL-12, IL-15, IL-18 and their combinations (IL-12/IL-18 or IL-15/IL-18). Fas ligand (FasL), perforin and granzyme B mRNAs expression and cytotoxicity were analyzed by flow cytometry and/or RT-PCR. DL (containing 72.19±7.53% of CD56+ cells), obtained from 18h-cultured DMC in the medium only, expressed perforin, FasL and granzyme B mRNAs and lysed the NK-sensitive K-562 cell line, and also the NK-resistant P815 and P815-Fas transfected cell lines. Concanamycin A, a blocker of granule exocytosis, decreased significantly K-562 lysis, but not P815 lysis. However, the addition of anti-FasL antibody diminished significantly P815 lysis as well. IL-2 and IL-15, known inducers of perforin and FasL mRNAs and protein expression, could not additionally increase P 815 cell lysis by DL cultured within DMC. These results suggest that DL cultured in DMC for 18h, have the characteristics of lymphokine-activated killer (LAK) cells and are able to use efficiently both the perforin and the FasL cytolytic pathways.

Effects of 25-Hydroxyvitamin D3 and 1,25-Dihydroxyvitamin D3 on Cytokine Production by Human Decidual Cells1

The active form of vitamin D, 1,25-dihydroxyvitamin D(3) (1,25[OH](2)D(3)) is a potent immunomodulatory seco-steroid. We have demonstrated that several components of vitamin D metabolism and signaling are strongly expressed in human uterine decidua from first trimester pregnancies, suggesting that locally produced 1,25(OH)(2)D(3) may exert immunosuppressive effects during early stages of gestation. To investigate this further, we used primary cultures of human decidual cells from first and third trimester pregnancies to demonstrate expression and activity of the enzyme that catalyzes synthesis of 1,25(OH)(2)D(3), 1alpha-hydroxylase (CYP27B1). Synthesis of 1,25(OH)(2)D(3) was higher in first trimester decidual cells (41 +/- 11.8 fmoles/h/mg protein) than in third trimester cells (8 +/- 4.4 fmoles/h/mg protein; P < 0.05). Purification of decidual cells followed by quantitative RT-PCR analysis showed that CYP27B1 was expressed by both CD10(+VE) stromal-enriched and CD10(-VE) stromal-depleted cells, with higher levels of mRNA in first trimester pregnancies. Expression of CYP27B1 correlated with TLR4 and IDO. Functional responses to 1,25(OH)(2)D(3) were studied using CD56(+VE) natural killer (NK) cells isolated from first trimester decidua. Decidual NK cells treated with 1,25(OH)(2)D(3) or precursor 25-hydroxyvitamin D(3) (25OHD(3)) for 28 h showed decreased synthesis of cytokines, such as granulocyte-macrophage colony stimulating factor 2 (CSF2), tumor necrosis factor, and interleukin 6, but increased expression of mRNA for the antimicrobial peptide cathelicidin antimicrobial peptide. These data indicate that human decidual cells are able to synthesize active 1,25(OH)(2)D(3), particularly in early gestation, and this may act in an autocrine/paracrine fashion to regulate both acquired and innate immune responses at the fetal-maternal interface.

Inhibition of term decidual NK cell cytotoxicity by soluble HLA‐G1

Soluble (s)HLA-G1 is produced by trophoblast cells. Aim was to analyze the capacities and mechanisms of sHLA-G1 to regulate interleukin (IL)-2-induced cytotoxicity of natural killer (NK) cells from human deciduas. Natural killer cells were isolated from decidual layers of term placentae, stimulated or not with IL-2 and supplemented with various concentrations of recombinant soluble HLA-G1 (sHLA-G1). For NK cell cytotoxicity assays, K562 cells were used as targets. Expression of signal transducer and activator of transcription 3 (STAT3) and perforin was analyzed by Western blotting. Apoptosis was examined by assessment of poly(ADP-ribose) polymerase cleavage. NK cells were analyzed by flow cytometry for IL-2receptor-alpha (IL-2R alpha; CD25) and transferrin receptor CD71 expression. Interleukin-2 increases CD71, STAT3, perforin expression and cytotoxic potential of NK cells. Expression of CD71, STAT3 and perforin decreased simultaneously with cytotoxicity and dose-dependently when sHLA-G1 (1.6 micro g/mL-1.6 ng/mL) was added to IL-2 stimulated cultures. sHLA-G1 did not induce apoptosis and CD25 expression was not affected. Interleukin-2R alpha expression is not controlled by sHLA-G1, but its signal transducer STAT3 as well as several downstream effects, such as perforin expression, proliferation and cytotoxicity. The control of STAT3 bioavailability through sHLA-G1 may be a key regulator of the mentioned effects.

1141180772 Activated NK cells in spontaneous abortion cases induce apoptosis on extravillous trophoblast in a granulysin dependent manner

Extravillous trophoblast (EVT) is well known to undergo apoptosis in spontaneous abortion cases although the apoptotic mechanism is still unclear. Granulysin (Gr) is a cytotoxic granule protein of natural killer (NK) cells and cytotoxic T lymphocytes (CTLs) with tumoricidal activities. We have reported that the expression of granulysin, which was mainly produced by decidual NK cells, is significantly higher in the deciduas of spontaneous abortion cases than early normal pregnancy. We then have attempted to investigate the molecular mechanism of apoptosis associated with Gr. We also assessed apoptosis in the HTR8/SV40 cell, extravillous trophoblast (EVT) cell line, which were transfected with GFP‐fused Gr. Anti‐cleaved cytokeratin 18 antibody and Annexin‐V were used for detecting apoptosis by IS and FC. We detected the apoptosis of the EVT in miscarriage cases. In those EVT, we detected nuclear staining of Gr. We next examined the effect of Gr with the target trophoblast cells by using GFP‐fused Gr vector. Exogenously expressed GFP‐fused Gr preferentially accumulated in nucleus from cytoplasm, resulting in apoptosis. Similar findings were obtained by native granulysin produced by IL‐2 stimulated decidual lymphocytes. Our findings suggest that the granulysin‐positive NK cells might attack EVT and they release granulysin into the intracellular space, resulting in apoptosis of EVT. So far, other groups have reported that Fas‐FasL pathway and and/or TNF‐α pathway is associated with apoptosis of EVT. In additiont, we propose granulysin‐positive NK cells‐induced apoptosis as a new mechanism for EVT cell death.

Expression patterns of lectin-like natural killer receptors, inhibitory CD94/NKG2A, and activating CD94/NKG2C on decidual CD56 bright natural killer cells differ from those on peripheral CD56 dim natural killer cells

The balance of inhibitory and activating natural killer (NK) receptors on maternal decidual NK cells, most of which are CD56 bright, is thought to be crucial for the proper growth of trophoblasts in placenta. A lectin-like NK receptor, CD94/NKG2, is the receptor for human leukocyte antigen (HLA)-E, which is expressed on trophoblasts. To clarify the mechanism regulating the activity of decidual NK cells during pregnancy, we investigated the expression patterns of inhibitory NK receptor, CD94/NKG2A, and activating receptor, CD94/NKG2C, on decidual NK cells in an early stage of normal pregnancy and compared them with those on peripheral NK cells, most of which are CD56 dim. The rate of NKG2A-positive cells was significantly higher for decidual CD56 bright NK cells than for peripheral CD56 dim NK cells, but the rates of NKG2C-positive cells were comparable between the two cell types. Interestingly, peripheral CD56 dim NK cells reciprocally expressed inhibitory NKG2A and activating NKG2C, but decidual CD56 bright NK cells that expressed activating NKG2C simultaneously expressed inhibitory NKG2A. The co-expression of inhibitory and activating NKG2 receptors may fine-tune the immunoregulatory functions of the decidual NK cells to control the trophoblast invasion in constructing placenta.

Molecular characterization of KIR3DL3

Killer-cell immunoglobulin-like receptors (KIRs) are a structurally and functionally diverse family of molecules expressed by natural killer (NK) cells and T-cell subsets. The most centromeric gene in the human KIR cluster is KIR3DL3, a framework gene that is present in all haplotypes. KIR3DL3 has only one immunoreceptor tyrosine-based inhibitory motif and lacks the exon encoding the stem between the Immunoglobulin domains and the transmembrane region. We have investigated expression of KIR3DL3 in blood and decidual NK cells by reverse transcriptase polymerase chain reaction (RT-PCR) and protein analysis using a KIR3DL3-specific monoclonal antibody, CH21. KIR3DL3 mRNA was only detected in the CD56(bright) subset in cells from peripheral blood and in CD56(bright) decidual NK cells. The CD56(bright) NK92 cell line was also positive. Quantitative RT-PCR indicated a trend for higher expression of KIR3DL3 in female peripheral blood mononuclear cells compared to that in male. Using a bisulphite conversion method, we found that the promoter of KIR3DL3 was strongly methylated. Surface protein expression was detectable after demethylation. Like other KIRs, KIR3DL3 is highly polymorphic, and we detected 14 variants in 25 unrelated individuals. Nucleotide substitutions were scattered throughout the sequence, with a cluster of alleles at the start of the transmembrane region at the site where the remnant of the linking stem present in other KIR is found. We conclude that the KIR3DL3 gene is not a pseudogene but encodes a protein that is not expressed in healthy individuals. Protein expression might be induced under certain developmental or pathological situations.

Immunoregulation in normal pregnancy and pre-eclampsia: an overview

Pre-eclampsia is a major disorder of human pregnancy, which may have an immunological basis. It is a disease of two stages. The first stage concerns the relative failure of early trophoblast invasion and remodelling of the spiral arteries, leading to a poor blood supply to the placenta, exposing it to oxidative stress. The inadequate trophoblast invasion may result from decreased expression of human leukocyte antigen-G (HLA-G) leading to an abnormal interaction with decidual natural killer (NK) cells, which are believed to play a major role in these processes through the production of immunoregulatory cytokines and angiogenic factors. Recent evidence suggests that the interaction between trophoblast human leukocyte antigen-C (HLA-C) olecules and decidual NK cell receptors may be the point at which the apparent partner specificity of the disease originates. The second stage is the maternal syndrome, which is characterized by a generalized systemic inflammatory response involving both leukocytes and endothelium. The inflammatory stimulus is believed to come from the placenta. In pre-eclampsia, placental oxidative stress may lead to increased shedding of apoptotic and/or necrotic syncytiotrophoblast debris into the maternal circulation. There is evidence that such trophoblast debris interacts with maternal leukocytes and endothelial cells to stimulate the release of proinflammatory cytokines, which could then trigger the maternal disease.

Human decidual natural killer cells as a source and target of macrophage migration inhibitory factor

The human uterine mucosa of early pregnancy is largely populated by CD56(bright) natural killer (NK) cells (uterine (u) NK cells). The specific functions of these cells are still unknown, but their interaction and response to foetal trophoblasts are thought to be important for the establishment of a successful pregnancy. The study reported herein shows that uNK cells respond to, and produce, macrophage migration inhibitory factor (MIF), a cytokine highly expressed in the human placenta and in the cyclic and pregnant endometrium. Recombinant human MIF reduced in a dose-dependent manner the cytolytic activity of purified uNK cells against K562 cells. RT-PCR, Western blot analysis and ELISA demonstrated the synthesis and secretion of the cytokine by uNK cells. Double immunofluorescence staining showed the presence of MIF in uterine CD56 + cells. Finally, neutralization of the endogenous cytokine by a polyclonal antibody resulted in a sharp increase in the cytolytic activity of uNK cells. These findings indicate the existence of a previously unrevealed paracrine and autocrine action of MIF on uNK cells and support its contribution to the immune privilege at the maternal-foetal interface.

Human decidual NK cells form immature activating synapses and are not cytotoxic.

In early pregnancy invading fetal trophoblasts encounter abundant maternal decidual natural killer cells (dNK). dNK express perforin, granzymes A and B and the activating receptors NKp30, NKp44, NKp46, NKG2D, and 2B4 as well as LFA-1. Even though they are granular and express the essential molecules required for lysis, fresh dNK displayed very reduced lytic activity on classical MHC I negative targets K562 and 721.221, approximately 15% of that of peripheral NK cells. dNK formed conjugates and activating immune synapses with 721.221 and K562 cells in which CD2, LFA-1 and actin were polarized toward the contact site. However, in contrast to peripheral NK cells, they failed to polarize their microtubule organizing centers and perforin-containing granules to the synapse, accounting for their lack of cytotoxicity.

Expression of Killer Immunoglobulin‐like Receptors on Peripheral Blood NK Cell Subsets of Women with Recurrent Spontaneous Abortions or Implantation Failures

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. 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. 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. 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.

Preeclampsia: A Couples Disease with Maternal and Fetal Manifestations

Preeclampsia still ranks as one of obstetrics major problems. Clinicians typically encounter preeclampsia as maternal disease with variable degrees of fetal involvement. More and more the unique immunogenetic maternal-paternal relationship is appreciated, and as such also the specific 'genetic conflict' that is characteristic of haemochorial placentation. From that perspective preeclampsia can also been seen as a disease of an individual couple with primarily maternal and fetal manifestations. Factors that are unique to a specific couple would include the length and type of sexual relationship, the maternal (decidual natural killer cells) acceptation of the invading cytotrophoblast (paternal HLA-C), and seminal levels of transforming growth factor-beta and probably other cytokines. The magnitude of the maternal response would be determined by factors including a maternal set of genes determining her characteristic inflammatory responsiveness, age, quality of her endothelium, obesity/insulin resistance and probably a whole series of susceptibility genes amongst which the thrombophilias received a lot of attention in recent years.

Menstrual Cycle Hormones Induce Changes in Functional Interactions between Lymphocytes and Decidual Vascular Endothelial Cells

During the secretory phase of the menstrual cycle, a natural killer (NK) cell subset expressing cluster of differentiation (CD)56bright appears in the decidualizing uterus and remains until onset of menses. If pregnancy occurs, decidual NK cells increase to become the predominant uterine lymphocytes of early pregnancy. To elucidate mechanisms of CD56bright cell recruitment to the uterus, an in vitro adhesion assay was used to assess the effect of the menstrual cycle, as well as cycle-associated hormones on adhesive properties of human lymphocytes. Adhesion of human peripheral blood lymphocytes to pregnant mouse lymph nodes and Peyer's Patches tissue sections was constant throughout the cycle. When uterine tissue was used as the substrate, adhesive CD56+ cells were found only in decidua basalis. Adhesion increased at the LH surge. Adhesion was mediated through both L-selectin and alpha4-integrin-dependent mechanisms. Furthermore, we observed increased adhesive function in CD56+ cells from male donors which had been cultured with estradiol or LH compared with cell aliquots cultured without additives. Lymphocytes adherent to mouse uterine tissue were predominantly CD56bright, suggesting that peripheral NK cells may be actively recruited to the uterus in an important, brief endocrine-regulated fashion at the time of ovulation to establish the decidual NK population of early pregnancy.

The emerging role of decidual NK cells for regulation of trophoblast IL-10 synthesis in early pregnancy

To analyze the role of Natural Killer (NK) decidual cells in regulation of trophoblast IL-10 production. This dialog between decidua and trophoblast can happen through direct binding or by soluble factors. Our purpose is to study this communication by soluble factors.

The expression of chemokine receptors in CD56(bright) CD16- natural killer cells and the mechanism of their recruitment in decidua

To investigate the transcriptions of 18 chemokine receptors in human decidual natural killer (NK) cells and explore the possible mechanisms of preferential accumulation of CD56(bright)CD16(-)NK cells in decidua during first-trimester pregnancy. Villi and decidual tissue were collected from normal pregnant women with 5 approximately 10 gestational weeks by artificial abortion. The decidual CD56(bright)CD16(-)NK cells were isolated by immune magnetic beads. The transcription levels of 18 chemokine receptors in the decidual CD56(bright)CD16(-)NK cells were assessed by reverse transcription-polymerase chain reaction (RT-PCR). After the high expression of CXCR4 and CXCR3 mRNA in these cells was found, the expression of stromal cell-derived factor-1 (SDF-1), the specific ligand of CXCR4, in first-trimester human placenta was detected by in situ hybridization and immunohistochemistry. The concentration of SDF-1alpha in the supernatant of culture of isolated trophoblast cells derived from the first-trimester human placentas was measured by ELISA. The chemotaxis of SDF-1 to decidual CD56(bright)CD16(-)NK cells was tested in Transwell, and the chemotactic activity was quantitatively examined. Among the 18 chemokine receptors, CXCR4 and CXCR3 were found highly transcribed in decidual CD56(bright)CD16(-)NK cells. The concentration of SDF-1alpha in the supernatant was 385 ng/L +/- 91 ng/L after trophoblast cells had been cultured for 60 hours. Both rhSDF-1alpha and supernatants in the culture of trophoblast cells exhibited chemotactic activity on decidual CD56(bright)CD16(-)NK cells. When the concentration of rhSDF-1alpha was 10 micro g/L the number of cells that entered the lower chamber of Transwell accounted for 22.9% +/- 4.3% of the total calls. First-trimester human trophoblast cells produce SDF-1, which in turn endows the trophoblast cells with the capacity to attract decidual CD56(bright)CD16(-)NK cells highly expressing CXCR4. This activity contributes to the recruitment of decidual lymphocytes and may be used at a local level to manipulate the microimmune environment at the materno-fetal interface.

Differential expression of KIR/NKAT2 and CD94 molecules on decidual and peripheral blood CD56 bright and CD56 dim natural killer cell subsets

Objective To investigate killer inhibitory receptor (KIR) expression by natural killer (NK) cells in early pregnancy. Design Case-control study of immunologic markers. Setting University hospital. Patient(s) Thirty pregnant women and 22 nonpregnant women. Intervention(s) Peripheral venous blood sampling and decidual tissue collection after elective abortion. Main outcome measure(s) Flow cytometry was used to assess expression of KIR by NK cells in the cell samples. Result(s) In contrast to CD56 bright peripheral blood NK cells, CD56 dim cells express killer cell Ig-like receptor KIR/NKAT2. However, KIR/NKAT2 and lectin-like CD94 are present on both subsets of decidual NK cells. We found no differences between peripheral blood NK cell subsets from pregnant and nonpregnant women. Conclusion(s) Our findings demonstrate that NK cell subsets, distributed in accordance with CD56 molecule density on cell surface, express killer inhibitory receptors CD94 and KIR/NKAT2 in a different way. Our data support the view that CD56 brightKIR/NKAT2 +CD94 + decidual NK cells are specialized NK cells that have an important role to play in early pregnancy.

Osteopontin is up-regulated in human decidual stromal cells

Objective To analyze expression and regulation of osteopontin in human stromal endometrial and decidual cells. Design Study by immunohistochemistry, RNase protection assay, and in vitro study. Setting Academic research unit. Patient(s) Twenty-five fertile women. Intervention(s) Expression of osteopontin mRNA and protein was analyzed by RNase protection assay (RPA) and immunohistochemistry in secretory endometrium and decidua. Regulation of osteopontin expression in endometrial epithelial cell and stromal cells was analyzed by incubation with 17β-estrogen, progesterone, IL-1β, IL-6, and LIF and by incubation with cell culture supernatants of decidual natural killer cells. Furthermore, osteopontin expression was studied in stromal cells, decidualized in vitro. Main outcome measure(s) mRNA and protein expression and regulation of endometrial stromal osteopontin. Result(s) Osteopontin mRNA and protein are expressed at increasing concentrations in human secretory endometrium and in decidua. High concentrations in total decidua were due to high osteopontin concentrations in decidualized stromal cells. Osteopontin mRNA and protein expression was not regulated by incubation of endometrial epithelial and stromal cells with steroids, cytokines, and natural killer cell supernatant for 6 and 24 hours. In contrast, decidualization of stromal cells for 7, 14, and 21 days resulted in significant up-regulation of osteopontin mRNA and protein. Conclusion(s) Osteopontin is expressed at high concentrations in secretory endometrium in epithelial cells and in decidua in stromal cells. Decidual stromal expression of osteopontin is up-regulated by decidualization.

Human Decidual Natural Killer Cells Are a Unique NK Cell Subset with Immunomodulatory Potential

Natural killer cells constitute 50–90% of lymphocytes in human uterine decidua in early pregnancy. Here, CD56bright uterine decidual NK (dNK) cells were compared with the CD56bright and CD56dim peripheral NK cell subsets by microarray analysis, with verification of results by flow cytometry and RT-PCR. Among the ∼10,000 genes studied, 278 genes showed at least a threefold change with P ≤ 0.001 when comparing the dNK and peripheral NK cell subsets, most displaying increased expression in dNK cells. The largest number of these encoded surface proteins, including the unusual lectinlike receptors NKG2E and Ly-49L, several killer cell Ig-like receptors, the integrin subunits αD, αX, β1, and β5, and multiple tetraspanins (CD9, CD151, CD53, CD63, and TSPAN-5). Additionally, two secreted proteins, galectin-1 and progestagen-associated protein 14, known to have immunomodulatory functions, were selectively expressed in dNK cells.

CXCL12 expression by invasive trophoblasts induces the specific migration of CD16– human natural killer cells

AbstractIn the maternal decidua, natural killer (NK) cells, characterized by lack of CD16, are found in direct contact with the fetal extravillous trophoblasts (EVTs). It is yet unknown which factors contribute to the specific homing of this unique NK subset to the decidua. In this study we analyze the chemokine receptor repertoire on various NK populations derived from the peripheral blood and decidua. We show that CXCR4 and CXCR3 receptors are preferentially expressed on CD16– NK subsets derived either from the peripheral blood or the decidua and that these receptors are involved in migration of all NK subsets to their ligands. We further demonstrate in vivo that invading EVTs that eventually perform endovascular invasion express CXCL12, the ligand for CXCR4, but not ligands for CXCR3. Indeed, specific accumulation of the CD16– NK cells at the expense of CD16+ cells was observed only when in vitro migration was performed with ligands for CXCR4. Finally, incubation of the peripheral blood CD16– NK cells with cytokines present in the decidua, especially interleukin 15 (IL-15), resulted in the expression of chemokine receptor repertoire similar to that observed on decidual NK cells, suggesting an additional important regulatory effect of local decidual cytokines.

Unique Appearance of Proliferating Antigen-Presenting Cells Expressing DC-SIGN (CD209) in the Decidua of Early Human Pregnancy

Intact human pregnancy can be regarded as an immunological paradox in that the maternal immune system accepts the allogeneic embryo without general immunosuppression. Because dendritic cell (DC) subsets could be involved in peripheral tolerance, the uterine mucosa (decidua) was investigated for DC populations. Here we describe the detailed immunohistochemical and functional characterization of HLA-DR-positive antigen-presenting cells (APCs) in early pregnancy decidua. In contrast to classical macrophages and CD83(+) DCs, which were found in comparable numbers in decidua and nonpregnant endometrium, only decidua harbored a significant population of HLA-DR(+)/DC-SIGN(+) APCs further phenotyped as CD14(+)/CD4(+)/CD68(+/-)/CD83(-)/CD25(-). These cells exhibited a remarkable proliferation rate (9.2 to 9.8% of all CD209(+) cells) by double staining with Ki67 and proliferating cell nuclear antigen. Unique within the DC-family, the majority of DC-SIGN(+) decidual APCs were observed in situ to have intimate contact with CD56(+)/CD16(-)/ICAM-3(+) decidual natural killer cells, another pregnancy-restricted cell population. In vitro, freshly isolated CD14(+)/DC-SIGN(+) decidual cells efficiently took up antigen, but could not stimulate naive allogeneic T cells at all. Treatment with an inflammatory cytokine cocktail resulted in down-regulation of antigen uptake capacity and evolving capacity to effectively stimulate resting T cells. Fluorescence-activated cell sorting analysis confirmed the maturation of CD14(+)/DC-SIGN(+) decidual cells into CD25(+)/CD83(+) mature DCs. In summary, this is the first identification of a uterine immature DC population expressing DC-SIGN, that appears only in pregnancy-associated tissue, has a high proliferation rate, and a conspicuous association with a natural killer subset.