Soluble HLA-G molecules induce apoptosis in natural killer cells

Membrane-bound human leukocyte antigen-G (HLA-G) molecules are primarily expressed by cytotrophoblasts of the fetus. They are thought to protect the fetus from immunologic attack by the maternal immune system and have recently been associated with transplantation graft acceptance. In addition, soluble HLA-G molecules (sHLA-G) have been shown to play a role in the success of pregnancies, but are upregulated in certain cancers. However, the exact mechanism for this regulation has remained elusive. The aim of this study was to examine the mechanism by which sHLA-G interact with natural killer (NK) cells in vitro. sHLA-G effectively blocked NK lysis of target cells via fracticide killing of NK cells by apoptosis. These studies support the protective role of sHLA-G in immunologic reactions by interacting with NK cells, thus providing a regulatory function.     

Soluble HLA-G molecules impair natural killer/dendritic cell crosstalk via inhibition of dendritic cells

HLA-G molecules are known to exert immunosuppressive action on DC maturation and on NK cells, and can in consequence inhibit respectively T cell responses and NK cytolysis. In this study, we show that monocyte-derived DC, differentiated in the presence of GM-CSF and IL-4, are sensitive to soluble (s) HLA-G molecules during LPS/IFN-gamma maturation as demonstrated by the decrease of CD80 and HLA-DR expressions and IL-12 secretion. Moreover, DC pretreated with sHLA-G were found to activate NK/DC crosstalk less than non-treated DC. Early activation of NK cells co-cultured with autologous DC was diminished as assessed by CD69 expression. The IFN-gamma production was impaired whereas a slight inhibition of the NK cell cytotoxicity against Daudi cell line was observed. Since sHLA-G is expressed in grafts or sites of tumour proliferation, its indirect action on NK cells via DC could constitute a pathway of early inhibition for both innate and specific immune responses.     

Uterine natural killer cells and angiogenesis in recurrent reproductive failure

BACKGROUND: Increased numbers of phenotypically unusual CD56^bright CD16–uterine natural killer (uNK) cells have been associated withrecurrent reproductive failure. uNK cells produce angiogenicgrowth factors and are potential regulators of decidual angiogenesisin early pregnancy. The final common mechanism for early pregnancyloss is thought to be early onset of the maternal circulationand excessive placental oxidative stress. We tested the hypothesisthat increased uNK cells in preimplantation endometrium areassociated with altered angiogenesis. METHODS: Women with recurrent reproductive failure (n = 122) were investigatedwith uterine artery Doppler and endometrial biopsy. Immunohistochemistrywas used to identify uNK, endothelial and vascular smooth musclecells and image analysis was used to assess location, densityand differentiation. RESULTS: uNK cell density was positively correlated with the formationof blood (P = 0.005, r = 0.5) and lymphatic vessels (P = 0.0001,r = 0.6), spiral arteriole smooth muscle differentiation (P= 0.01, r = 0.5) and endometrial oedema (P = 0.004). The functionaleffect of this was a reduced uterine artery resistance to bloodflow. CONCLUSIONS: These data suggest that uNK cells may regulate angiogenesisin non-pregnant endometrium. The mechanisms of reproductivefailure associated with increased uNK cell density appear tobe increased angiogenesis and peri-implantation blood flow,which may lead to early maternal circulation and hence pregnancyfailure due to excessive oxidative stress.     

Membrane-bound HLA-G activates proliferation and interferon-gamma production by uterine natural killer cells

The expression of HLA-G by invading trophoblasts suggests a role for this molecule in embryo implantation. Putative targets for HLA-G are the uterine natural killer cells (uNK) that are abundantly present at the time of implantation. Since NK cells are potent producers of a variety of cytokines, interaction with HLA-G may result in the production of cytokines involved in trophoblast differentiation or tissue remodelling. In the present study we investigated the effect of membrane-bound HLA-G (mHLA-G) on the uterine mononuclear cell population (UMC) as a whole and on uNK cells in particular by measuring proliferation and cytokine production [interferon-gamma (IFN-gamma)/vascular endothelial growth factor (VEGF)/leukaemia inhibitory factor (LIF)/interleukin-3 (IL-3)]. Uterine cells were isolated from endometrium of non-pregnant women at the time that the endometrium is thought to be receptive to implantation, and then co-cultured with HLA-class I(-)/HLA-class II(+) 721.221 B-LCL cells transfected with mHLA-G. HLA-G suppressed the alloproliferative response of unfractionated UMC to 721.221 cells. Also, IFN-gamma and IL-3 production was strongly reduced. In contrast, purified uNK cells were stimulated by mHLA-G. Proliferation as well as IFN-gamma production was increased after co-culture with mHLA-G transfected 721.221 cells. HLA-G stimulated VEGF production by UMC as well as purified uNK cells. LIF-levels were below the detection level of our enzyme-linked immunosorbent assay. In conclusion, our data show that mHLA-G stimulates proliferation and cytokine production by NK cells, while down-modulating the response of unfractionated UMC.     

Prognostic value of the measurement of uterine natural killer cells in the endometrium of women with recurrent miscarriage

BACKGROUND: Studies in mice suggest that CD56 + uterine natural killer (uNK) cells play an important role in implantation. Studies in humans have described an increase in the number of uNK cells in the non-pregnant mid-secretory endometrium of women with unexplained recurrent miscarriage (RM). However, the predictive value of uNK cell number in the maintenance of pregnancy is controversial. METHODS: A blind retrospective study was undertaken. The percentage of stromal cells positive for CD56 was identified by immunocytochemistry in endometrial biopsies from 10 normal control women and 87 women with unexplained RM, of whom 51 became pregnant following biopsy. Biopsies were obtained on days LH + 7 to LH + 9. RESULTS: As in previous studies, the number of uNK cells in the 87 women with RM (mean 11.2% range 1.1-41.4%) was significantly higher (P = 0.013) than in the control women (mean 6.2% range 2.2-13.9%). No significance difference in uNK numbers was observed between 19 women who miscarried (mean 9.6% range 1.7-25.0%) and 32 women who had a live birth (mean 13.3% range 1.1-41.4%) in a subsequent pregnancy. CONCLUSIONS: In this study numbers of uNK cells in the peri-implantation endometrium of women with unexplained recurrent miscarriage did not predict subsequent pregnancy outcome.     

Interleukin 12 enhances deficient HCV-antigen-induced Th1-type immune response of peripheral blood mononuclear cells

The aim of this study was to examine the possible immunomodulating effects of rhIL-12 on the immune response induced by different hepatitis C virus (HCV) antigens. Freshly isolated peripheral blood mononuclear cells (PBMC) of 33 patients with chronic HCV infection were stimulated with optimal concentrations of antigens from the NS3, NS4, NS5, and core region of HCV in the absence or presence of interleukin12 (IL-12). Stimulation by α-CD3 + α-CD28, lipopolysaccharide (LPS), and pokeweed mitogen (PWM) were used as controls. Proliferation and cytokine production were determined by ³H-thymidine uptake and enzyme-linked immunosorbent assay (ELISA) after 72 hr. After stimulation with antigen or antigen + IL-12, increased proliferation and production of interferon-γ (IFNγ) and tumor necrosis factor-α (TNFα) were observed in 23 of the 33 patients. Thus, a separation of the patients into HCV-antigen/;IL-12 responders (group 1, n = 23) and HCV-antigen/;IL-12 nonresponders (group 2, n = 10) was possible. Lower baseline IL-12- and LPS-induced IFNγ, TNFα, and IL-12 production was observed in group 2 due to a possible dysfunction of accessory cells. Significant antigen-induced Th2-type cytokine (IL-4, IL-10, IL-13) production was not found. According to clinical and serological parameters, group 2 comprised mostly patients with advanced liver disease. These data suggest an HCV-related cellular immune defect in patients with hepatitis C that can be restored in most patients by IL-12. J. Med. Virol. 56:112–117, 1998. © 1998 Wiley-Liss, Inc.     

Expression and regulation of complement receptors by human natural killer cells

Integration of cellular and humoral arms of the innate immune response is fundamental to the development of powerful effector functions in host defence as well as aberrant immune responses. Here, we provide evidence in support of the relationship between complement activation and NK cell functional modulation. We demonstrate that human NK cells and both CD56^brightCD16⁻ and CD56^dimCD16⁺ populations express receptors known to detect the biologically active peptides C3a and C5a (i.e. C3aR, C5aR, C5L2) and the covalently-bound fragments C3b and metabolites iC3b and C3d which serve in immune adhesion (e.g. CR3, CR4). We also show that several pathogen- or tumour/inflammation-related stimuli differentially regulated those complement receptor expression. Furthermore, our results suggest that C3 fragments (C3a, iC3b) have a negative regulatory effect on IFN-γ production in NK cells. This work provides extensive information of human complement receptors relevant to the integrated actions of complement and NK cells which has been suggested by animal studies. The observations may act as a resource that allows further understanding and exploitation of role of complement in human health and immune mediated diseases.     

Dietary gluten increases natural killer cell cytotoxicity and cytokine secretion

Dietary gluten influences the development of type 1 diabetes in nonobese diabetic (NOD) mice and biobreeding rats, and has been shown to influence a wide range of immunological factors in the pancreas and gut. In the present study, the effects of gluten on NK cells were studied in vitro and in vivo. We demonstrated that gliadin increased direct cytotoxicity and IFN‐γ secretion from murine splenocytes and NK cells toward the pancreatic beta‐cell line MIN6 cells. Additionally, stimulation of MIN6 cells led to a significantly increased proportion of degranulating C57BL/6 CD107a⁺ NK cells. Stimulation of C57BL/6 pancreatic islets with gliadin significantly increased secretion of IL‐6 more than ninefold. In vivo, the gluten‐containing diet led to a higher expression of NKG2D and CD71 on NKp46⁺ cells in all lymphoid organs in BALB/c and NOD mice compared with the gluten‐free diet. Collectively, our data suggest that dietary gluten increases murine NK‐cell activity against pancreatic beta cells. This mechanism may contribute to development of type 1 diabetes and explain the higher disease incidence associated with gluten intake in NOD mice.     

Tissue-resident natural killer cells and their potential diversity

Conventional NK cells are well characterized in the mouse spleen and circulate in the blood. Less well described are NK cells found in organs such as the liver, thymus, and uterus. Recently we identified a tissue-resident NK (trNK) cell population in the liver, suggesting a potential diversity of trNK cells in other organs. In this review we compare and contrast the similarities and differences among the subpopulations of NK and innate lymphoid cells to the trNK cells in the liver.     

IL-18 time-dependently modulates Th1/Th2 cytokine production by ligand-activated NKT cells

While IL-18 synergizes with IL-12 to induce a Th1 immune response, it also promotes a Th2 response. Here we investigate the modulatory role of IL-18 on the Th1/Th2 cytokine response. The injection of alpha-galactosylceramide (alpha-GalCer), a ligand for NKT cells, elevated mouse serum levels of both IFN-gamma and IL-4. When the mice were treated 2 h before alpha-GalCer challenge with IL-18, IFN-gamma production but not IL-4 production was remarkably up-regulated. In contrast, pretreatment with IL-18 6 h before the challenge enhanced IL-4 production. However, this IL-18-enhanced IL-4 production was not elicited in mice injected with anti-CD3 Ab. Liver mononuclear cells (MNC) produced a similar cytokine production pattern when MNC from mice treated with IL-18 either 2 h or 6 h before challenge were stimulated with alpha-GalCer in vitro. Expression of SOCS1 and SOCS3 was notably up-regulated in the liver MNC from mice pretreated 6 h before with IL-18; in particular, SOCS3 expression was confined to the liver NKT cells. Inhibition of SOCS3 by RNA interference up-regulated the phosphorylation of STAT3 and suppressed in vitro IL-4 production by IL-18-primed liver MNC stimulated with alpha-GalCer, but it did not affect IFN-gamma production. These results suggest that IL-18 time-dependently modulates Th1/Th2 cytokine production in ligand-activated NKT cells by regulating/inducing SOCS3 expression.     

Endometrial CD56+ natural killer cells in women with recurrent miscarriage: a histomorphometric study.

Endometrial natural killer (NK) cells were compared in luteal-phase endometrial samples from women with recurrent miscarriage and from normal subjects. Cryostat sections were labelled using a monoclonal antibody to CD56 using an avidin-biotin complex method and a morphometric study performed. Increased mean numbers of CD56+ cells were documented in the endometrium of women with recurrent early miscarriage only. These findings suggest a possible role for NK cells in the pathogenesis of recurrent early pregnancy loss.     

Decidual natural killer cell tuning by autologous dendritic cells

PROBLEM: Dendritic cells (DC)/natural killer (NK) cells interactions in the deciduas of early human pregnancies were analyzed in vitro. METHOD OF STUDY: Phenotype, cytokine expression and/or cytolytic mediators' expression were measured by flow cytometry in NK and DC from the freshly isolated decidual mononuclear cells or after their purification and co-culture in vitro. Proliferation of 5(6)-Carboxyfluorescein diacetate N-succinimidyl ester (CFSE)-labeled CD56(+) cells was analyzed by flow cytometry after the co-culture with CD1a(+) or CD83(+) DC. RESULTS: Decidual CD1a(+) cells show less mature phenotype with no expression of CD197, lower expression of CD80 and CD86 and higher expression of CD206 and CD195 in comparison to CD83(+) cells. Interleukin (IL)-15, interferon-gamma and tumor necrosis factor-alpha productions were higher in immature than mature DC, whereas IL-10 and IL-18 were equally produced in both subpopulations. Immature DC increase perforin, FasL and TRAIL protein expression and proliferation of NK cells, but decrease their intracellular IL-15 production. Mature DC caused less efficient proliferation of NK cells, and did not affect cytokine and cytolytic mediator expression. CONCLUSION: These results suggest that decidual CD1a(+) cells regulate and shape NK cell function more profoundly than CD83(+) cells in decidua.     

Pit cells as liver-associated natural killer cells: morphology and function

Pit cells are one type of hepatic sinusoidal cells, defined morphologically as large granular lymphocytes (LGLs) and functionally as liver-associated natural killer (NK) cells. They are situated inside the sinusoidal lumen, adhering to the endothelial cells and Kupffer cells. They contain multivesicular body-related dense granules and rod-cored vesicles. The number and size of granules and vesicles differ between hepatic NK cells and peripheral blood cells, suggesting possible differentiation of the latter into the former in the microenvironment of the liver. In addition to NK cells, natural killer T (NKT) cells are also abundant in the liver. They share several morphological properties with NK cells, and at least some are probably observed as pit cells under an electron microscope. NK cells recognize target cells with their surface receptors such as inhibitory and activating receptors. They exert antitumor functions by exocytosis of perforin/granzyme-containing granules, induction of death receptor-mediated apoptosis in target cells, and production of various cytokines that augment the activities of other immune cells. NKT cells play important roles in initiating and assisting the function of NK cells by producing interferon-gamma.     

Uterine (CD56+) natural killer cells recruitment: association with decidual reaction rather than embryo implantation

PROBLEM: Whether decidual leukocyte recruitment and/or increase is primarily hormonally regulated or induced mainly by blastocyst implantation is a matter of debate. Thus, this study investigated the number and distribution of leukocyte populations, with emphasis on natural killer (NK) cells of uterine and peripheral type, within decidual tissue from women with decidualized endometrium both related and unrelated to pregnancy and those with ectopic decidua associated with intrauterine pregnancy, as well as in tubal implantation sites. METHOD OF STUDY: Immunohistochemical characterization of immune cells using antibodies to CD3, CD4, CD8, CD20, CD68, CD16, CD56, CD57, in formalin-fixed, paraffin-embedded tissue, and a quantitative analysis of these subpopulations was conducted in tissue blocks from four groups of patients: (i) 20 women with decidualized endometrium due to progestin therapy (i.e. not associated with gestation) (group Prog-D); (ii) 20 women with intrauterine pregnancy-associated ectopic decidua (seven in the Fallopian tube, five in the ovary, five in the uterine cervix, and three in the omentum) (group Ect-D); (iii) 20 women with spontaneous abortion who had an histologic sample of the decidua at the uterine implantation site (group Uter-D); and (iv) 20 consecutive patients who had had an ectopic tubal pregnancy (group Tub-Preg). Twenty gynecologic specimens with marked inflammatory reaction were used as controls (group Con). RESULTS: CD3+, CD4+, CD8+, CD68+ cells were detected in all tissue samples investigated. In contrast, CD20+ cells were detected in all samples in group Con, but only in 75%, 25%, 55% and 70% of groups Prog-D, Ect-D, Uter-D and Tub-Preg, respectively. In all tissue samples investigated, CD57+ and CD16+ cells were detected. Conversely, CD56+ cells were completely absent in 15 of 40 cases (37.5%) lacking decidual reaction (group Tub-Preg, 7/20; group Con, 8/20) but were present in all cases showing decidual reaction. In contrast with CD56+ cells, CD57+ NK cells were more abundant in group Con than in the four study groups. CONCLUSIONS: CD56+ NK cells are closely related to decidua irrespective of its eutopic or ectopic location rather than to the implantation site. This suggests that the recruitment and/or increase of uterine NK cells into the uterus is not dependent on the physical presence of an implanting embryo but instead is controlled hormonally.     

Effect of glutamine on Th1 and Th2 cytokine responses of human peripheral blood mononuclear cells

Decreased glutamine concentrations are found in patients with catabolic stress and are related to susceptibility to infections. In this study, we evaluated the role of glutamine in Th1/Th2 cytokine responses. Peripheral blood mononuclear cells were stimulated with phytohemagglutinin (PHA), live attenuated bacillus Calmette-Guérin (BCG), or measles virus in the presence of different glutamine concentrations. We found that glutamine at an optimal concentration (0.6 mM) significantly enhanced PHA-stimulated lymphocyte proliferation as well as Th1 [interferon-gamma (IFN-gamma) and interleukin-2 (IL-2)] and Th2 cytokine (IL-4 and IL-10) production. In the absence of glutamine, BCG and measles virus elicited minimal lymphocyte proliferation, whereas BCG enhanced Th1 cytokine response and measles virus promoted Th2 cytokine response. Interestingly, addition of glutamine promoted the BCG-elicited Th1 cytokine response (IFN-gamma), but suppressed the measles-induced Th2 cytokine response (IL-10). These results suggest that appropriate glutamine levels may influence host responses to different antigens and microorganisms. Furthermore, predominately Th1, but not Th2, cytokine responses required the presence of optimal concentrations of glutamine.     

Viral- and tumor-reactive natural killer cells

When we can understand what natural killer (NK) cells recognize during an encounter with an infectious pathogen or a tumor cell, and when we can understand how the NK cell responds to that encounter, we can then begin to understand the role of NK cells in human health and how to improve upon their role for the prevention and treatment of human disease. In the quest to understand how these cells function in antiviral and antitumoral immunity, there have been previously described mechanisms established for NK cells to participate in clearing viral infections and tumors, including classical NK cell antibody dependent cellular cytotoxicity (ADCC) as well as recognition and elimination of transformed malignant cells through direct ligand interactions. However, it is now clear that there are additional mechanisms by which NK cells can participate in these critical immune tasks. Here we review two recently described types of NK cell recognition and response: the first is to primary infection with herpes virus, recognized and responded to by non-specific Fc bridged cellular cytotoxicity (FcBCC), and the second describes a novel phenotypic and functional response when a subset of NK cells recognize myeloid leukemia.     

Human peripheral blood mononuclear cells enhance cell-cell interaction between human endometrial epithelial cells and BeWo-cell spheroids

BACKGROUND: Previously, it was reported that T-lymphocytes derived from non-pregnant mice promote murine embryo implantation. In order to examine the immunological regulation of endometrial receptivity in humans, the effects of peripheral blood mononuclear cells (PBMCs) on endometrial epithelial cell (EEC) function were monitored by a newly developed attachment assay using primary human EEC culture and BeWo cell-derived spheroids. METHODS AND RESULTS: EECs isolated from 25 women in the mid- and late proliferative and early, mid- and late secretory phases were subjected to monolayer culturing. Spheroids were constructed from BeWo cells, a human choriocarcinoma cell line, by incubation with continuous rolling, after which their interaction with cultured EECs was studied. The mean (+/- SEM) number of attached spheroids was significantly higher (P < 0.01) in the EEC culture derived from women in the mid-secretory phase (90 +/- 2.9%) than the other groups (ranging from 0 to 5.8 +/- 3.7%), which is in agreement with the existence of a so-called 'implantation window'. After 72 h co-culture of EECs with PBMCs, the number of attached spheroids significantly increased in the EEC cultures derived from the late proliferative and early secretory phases [65.0 +/- 21.7 versus 5.0 +/- 2.0% (P < 0.05) and 83.1 +/- 4.1 versus 4.4 +/- 1.9% (P < 0.01)]. CONCLUSIONS: This attachment assay appears to be a useful method with which to assess endometrial receptivity. Functional change of EECs induced by PBMCs suggests possible regulation of endometrial receptivity by immune cells.     

Evaluation of oestrogen and progesterone receptor expression in uterine mucosal lymphocytes

Expression of the oestrogen and progesterone receptors on uterinemueosal leukocytes has been examined by dual immunohistology.Neither the oestrogen receptor nor the progesterone receptorwas expressed by lymphocytes, macrophages or the distinctivepopulation of uterine natural killer (NK) cells. Although theaccumulation and survival of these NK cells appears to be hormonallydependent, the effects must therefore be indirect.