Increased sensitivity of gastric cancer cells to natural killer and lymphokine-activated killer cells by antisense suppression of N-acetylgalactosaminyltransferase

UDP-N-acetylgalactosamine:polypeptide N-acetylgalactosaminyltransferases (GalNAc transferases) catalyze the initial reaction in O-linked (mucin type) oligosaccharide biosynthesis. To attempt to inhibit the synthesis of O-glycan, we transfected antisense cDNA of GalNAc transferase type 1 (GalNAc-T1) into a human gastric cancer cell line, JRST. A decreased expression of GalNAc-T1 at the level of both mRNA and protein was observed in the resultant transfectants. They demonstrated a significantly increased sensitivity to NK and lymphokine-activated killer cells in vitro compared with parental cells and mock transfectants. Although there was no significant difference in in vitro cell proliferation among parental cells, mock transfectants, or antisense transfectants, the in vivo growth rate of antisense transfectants using SCID mice was clearly lower than that of parental cells and mock transfectants. Furthermore, the treatment of mice with anti-asialo-G(M1) Ab abolished this growth-inhibitory effect of antisense transfection. From these results, we conclude that antisense suppression of GalNAc-T1 could increase the sensitivity of tumor cells to NK and lymphokine-activated killer cells, suggesting that this strategy may be of use as a new immunogene therapy.     

Transforming growth factor-beta inhibits interferon-gamma secretion by lymphokine-activated killer cells stimulated with tumor cells

The effect of transforming growth factor-beta (TGF-beta) secreted by glioblastoma (T98G) cells on the secretion of interferon-gamma (IFN-gamma) by lymphokine-activated killer (LAK) cells stimulated with tumor cells was investigated in cocultures of LAK and Daudi cells supplemented with T98G culture supernatant, T98G culture supernatant preincubated with anti-TGF-beta 1 and anti-TGF-beta 2 neutralizing antibodies, anti-TGF-beta 1 and anti-TGF-beta 2 antibodies, or natural human TGF-beta 1 or recombinant human TGF-beta 2. LAK cells were incubated with anti-TGF-beta 1 and anti-TGF-beta 2 antibodies, and with T98G cells of which the supernatant contained both active and latent forms of TGF-beta 1 and TGF-beta 2, with or without neutralizing antibodies. Addition of the supernatant from T98G cells to LAK/Daudi culture caused inhibition of IFN-gamma secretion by LAK cells. The inhibition was abolished by pretreatment of the supernatants with anti-TGF-beta antibodies. Addition of TGF-beta 1 and TGF-beta 2 to the LAK/Daudi culture inhibited IFN-gamma secretion by LAK cells in a dose-dependent manner. Addition of anti-TGF-beta antibodies to the LAK culture resulted in increased IFN-gamma secretion. T98G cells failed to stimulate LAK cells to secrete more IFN-gamma. Addition of anti-TGF-beta antibodies to the LAK-T98G culture resulted in increased IFN-gamma secretion by LAK cells. These results suggest that most malignant glioma cells which secrete high levels of TGF-beta can inhibit IFN-gamma secretion by LAK cells even after tumor cell stimulation.     

Reinforced cytotoxicity of lymphokine-activated killer cells toward glioma cells by transfection with the tumor necrosis factor-alpha gene

Lymphokine-activated killer (LAK) cells generated from peripheral blood lymphocytes incubated with recombinant interleukin-2 were transfected with the human tumor necrosis factor (TNF)-alpha gene by means of novel liposomes with a positive change on their surface. The cells secreted significant amounts of TNF-alpha into the culture medium and exhibited reinforcement of cytotoxicity toward a human glioma cell line (U251-SP), being three times more cytotoxic than nontransfected LAK cells. The mechanism for the reinforcement of cytotoxicity is considered to involve not only an increase in TNF-alpha secretion from LAK cells but also its expression on their surface. Intratumoral or intrathecal injection of LAK cells transfected with the TNF-alpha gene may be useful for the treatment of patients with malignant gliomas.     

Cytokine regulation of cell-to-cell interactions in lymphokine-activated killer cell cytotoxicity in vitro

The permanent pancreas carcinoma cell line, PCI-24, was developed in order to analyse cytokine regulation on pancreas carcinoma and lymphokine-activated killer (LAK) cell interaction. PCI cells expressed ICAM-1 and HLA-ABC, but not HLA-DR antigens. PCI cells showed augmented ICAM-1 and HLA-ABC expression when incubated with interferon gamma (IFN gamma) and tumour necrosis factor alpha. A similar but weak augmentary effect on the HLA-ABC and ICAM-1 surface expression was seen with interleukin-1 beta treatment. Natural attachment of LAK to PCI cells was augmented by recombinant IFN gamma in close association with ICAM-1 up-regulation on PCI cells. In addition, natural attachment was significantly inhibited by anti-LFA-1 and anti-ICAM-1 antibody treatments. Cytotoxicity of the LAK cells against PCI cells was also significantly inhibited with the same treatment. Thus, the attachment of LAK cells to PCI cells through LFA-1/ICAM-1 molecules appeared to be essential for the cytotoxicity for PCI cells. Pretreatment of PCI cells, but not of LAK cells, with IFN gamma or other cytokines resulted in a decrease of susceptibility for LAK cell cytotoxicity. The decreased susceptibility inversely correlated with HLA-ABC expression on the PCI cells. The collective evidence indicates that, although LAK cell attachment to pancreas carcinoma cells through the LFA-1/ICAM-1 molecule is augmented by IFN gamma, IFN gamma treatment of pancreas carcinoma cells reduces LAK cell cytotoxicity possibly through an increase in HLA-ABC or a regulation of molecules closely associated to HLA-ABC expression.     

Interleukin-12 synergizes with interleukin-2 to generate lymphokine-activated killer activity in peripheral blood mononuclear cells cultured in ovarian cancer ascitic fluid

OBJECTIVES: The ascites-associated lymphocytes in ovarian cancer have altered immunologic function, and cell-free ascitic fluid has immunomodulating properties. We determined (1) whether interleukin (IL)-2 could induce lymphokine-activated killer (LAK) activity in normal peripheral blood mononuclear cells (PBMC) cultured in ovarian cancer ascitic fluid, and (2) whether IL-12 could synergize with IL-2 to generate LAK activity in normal PBMC cultured in ascitic fluid. METHODS: Normal PBMC were cultured in control medium and in media consisting of 50% ascitic fluid (ascitic medium), with and without IL-2 and IL-12. Cell activation to assess LAK activity (cell lysis) was determined in a 51Cr-release assay with the tumor cell lines FMEX and SKOV3 as target cells. To determine a possible mechanism for any synergistic effect, the expression of perforin, a pore-forming protein, was determined by Northern blot analysis. RESULTS: Interleukin-2 alone could not induce LAK activity in normal PBMC cultured in 50% ascitic fluid for up to 3 days. Interleukin-12 did mediate some or minimal LAK activity after 1, 2, or 3 days of incubation in control medium or in 50% ascitic fluid. When IL-2 and IL-12 were used in combination, PBMC cultured for 3 days in 50% ascitic fluid had remarkably high lytic activity against FMEX and SKOV3 tumor cells. In some experiments, this cytotoxicity was greater than that in PBMC cultured in control medium with IL-2 and IL-12. Lower concentrations of IL-12 (1 U/mL) with IL-2 (100 U/mL) were as effective as, and often more effective than, higher doses of IL-12 with IL-2. Very low-dose IL-12 (0.01-0.03 U/mL) in combination with IL-2 also induced a range of cytotoxicities. Only the combination of IL-2 and IL-12 up-regulated expression of perforin mRNA in ascitic medium. CONCLUSIONS: The cytotoxicity responses of PBMC cultured in ascitic fluid in the presence of IL-2 and IL-12 are complex. Low-dose IL-2 and IL-12 can overcome the inhibitory property of ascitic fluid on LAK generation and can restore and enhance cytotoxic activity, possibly by reconstituting the expression of perforin. These findings may have therapeutic potential.     

Phospholipase A2 activity and calpactin I levels in rat lymphokine-activated killer cells: correlation with the cytotoxic activity

The interaction of carnitine with human placental brush-border membrane vesicles was investigated. Carnitine was found to associate with the membrane vesicles in a Na(+)-dependent manner. The time course of this association did not exhibit an overshoot, which is typical of a Na+ gradient-driven transport process. The absolute requirement for Na+ was noticeable whether the association of carnitine with the vesicles was measured with a short time incubation or under equilibrium conditions, indicating Na(+)-dependent binding of carnitine to the human placental brush-border membranes. The binding was saturable and was of a high-affinity type with a dissociation constant of 1.37 +/- 0.03 microM. Anions had little or no influence on the binding process. The binding process was specific for carnitine and its acyl derivatives. Betaine also competed for the binding process, but other structurally related compounds did not. Kinetic analyses revealed that Na+ increased the affinity of the binding process for carnitine and the Na+/carnitine coupling ratio for the binding process was 1. The dissociation constant for the interaction of Na+ with the binding of carnitine was 24 +/- 4 mM. This constitutes the first report on the identification of Na(+)-dependent high-affinity carnitine binding in the plasma membrane of a mammalian cell. Studies with purified rat renal brush-border membrane vesicles demonstrated the presence of Na+ gradient-driven carnitine transport but no Na(+)-dependent carnitine binding in these membrane vesicles. In contrast, purified intestinal brush-border membrane vesicles posses neither Na+ gradient-driven carnitine transport nor Na(+)-dependent carnitine binding.     

The murine nonclassical class I major histocompatibility complex-like CD1.1 molecule protects target cells from lymphokine-activated killer cell cytolysis

Classical class I major histocompatibility complex (MHC) molecules, as well as the nonclassical class I histocompatibility leukocyte antigen (HLA)-E molecule, can negatively regulate natural killer (NK) cell cytotoxicity through engagement of NK inhibitory receptors. We show that expression of murine (m)CD1.1, a nonpolymorphic nonclassical MHC class I-like molecule encoded outside the MHC, protects NK-sensitive RMA/S target cells from adherent lymphokine-activated killer cell (A-LAK) cytotoxicity. Passage of effector cells in recombinant interleukin (rIL)-2 enhanced protection by mCD1.1, suggesting an expansion of relevant A-LAK population(s) or modulation of A-LAK receptor expression. Murine CD1. 1 conferred protection from lysis by rIL-2-activated spleen cells of recombination activating gene (Rag)-1(-/-) mice, which lack B and T cells, demonstrating that mCD1.1 can protect RMA/S cells from lysis by NK cells. An antibody specific for mCD1.1 partially restored A-LAK lysis of RMA/S.CD1.1 transfectants, indicating that cell surface mCD1.1 can confer protection from lysis; therefore, mCD1.1 possibly acts through interaction with an NK inhibitory receptor. CD1.1 is by far the most divergent class I molecule capable of regulating NK cell activity. Finally, mCD1.1 expression rendered RMA/S cells resistant to lysis by A-LAK of multiple mouse strains. The conserved structure of mCD1.1 and pattern of mCD1.1 resistance from A-LAK lysis suggest that mCD1.1 may be a ligand for a conserved NK inhibitory receptor.     

Signal transduction via phosphorylated adhesion molecule, LFA-1 beta (CD18), is increased by culture of natural killer cells with IL-2 in the generation of lymphokine-activated killer cells

Anti-human platelet myosin antibodies and two anti-peptide antibodies, anti-peptide IIA and anti-peptide IIB, which recognize macrophage-type (MIIA) and brain-type (MIIB) isoforms of nonmuscle myosin heavy chain, respectively, were used to study expression of nonmuscle myosin isoforms in various tissues of mice during development. Tissue-specific changes in the relative isoform concentrations were observed by performing immunoblots of crude myosin extracts from nonmuscle and muscle tissues. In fetal and neonatal mouse tissues, the anti-peptide IIB antibodies stained a single band, called MIIB2, while the anti-peptide IIA and anti-platelet myosin antibodies stained a band that migrated faster than MIIB2. In brain, a slower moving band, MIIB1, started to appear at 2 weeks after birth, and in the adult cerebellum it was at least as abundant as MIIB2. In thymus, MIIB2 decreased selectively shortly after birth, while in liver both MIIB2 and MIIA rapidly disappeared, but the isoform(s) detected by anti-platelet myosin antibodies (MIIApla) remained constant. The MIIB2 and MIIA as well as MIIApla found in striated muscles from fetal and neonatal mice decreased to levels that were below the limit of detection by 3 weeks of age. In cryosections of skeletal and cardiac muscles, MIIB2 was localized within the muscle cells, while MIIA and MIIApla were primarily in the blood vessels and capillaries.     

Natural killer and lymphokine-activated cytotoxicity following anaesthesia in patients with uveal malignant melanoma

OBJECTIVE: The aim of the study was to determine the pattern of health care utilization of people aged 55-74 years with arthritic pain in the knee or hip. DESIGN: People with current pain were identified in a population-based study. A filter model was used to describe the pattern of health care utilization of people who presented as patients at different levels (GPs or specialist) of the health care system in the Netherlands. SETTING: The study was carried out in the district of Ommoord in Rotterdam in an age- and gender-representative sample of 831 (response 83%; n = 691) people. STUDY PARTICIPANTS: A group of 186 people with current pain was identified. They completed a questionnaire and were interviewed. MAIN OUTCOME MEASURES: Background variables, illness-related variables (including radiological osteoarthritis), and self-reported diagnoses were described and compared for attenders and non-attenders of GPs and specialists. A reference group of patients of GPs was used to determine the validity and generalizability of the findings. RESULTS: Eighty-two per cent consulted a GP (passed filter 1). In 69% of the GP attenders, 'arthritis' was identified (passed filter 2), and 65% of them attended a specialist (passed filter 3). People who did not pass the various filters were different from those who did with respect to the body mass index (lower; OR 1.24), the chronicity of pain (less chronic pain; OR 4.9) and attendance of a physiotherapist (lower; OR 5.6). The chronicity of pain seems of more importance in determining the health care utilization pattern than the severity of pain, the level of disability or the presence of radiological osteoarthritis. We suggest that health promotion interventions could increase the self-management ability of patients and could lower costs.     

Isolation perfusion in extracorporeal circulation with interleukin-2 and lymphokine-activated killer cells in the treatment of in-transit metastases from limb cutaneous melanoma

BACKGROUND: Therapies of advanced melanoma patients with interleukin-2 (IL-2) and cytotoxic lymphocytes have produced interesting results, but a larger diffusion of these treatments is limited by the severe side effects due to IL-2 systemic infusion. A strictly regional administration of IL-2 and cells by an isolation perfusion (IP) in extracorporeal circulation (ECC) for the treatment of regional melanoma metastases could improve tolerability and efficacy of this specific modality of immunotherapy. METHODS: Ten patients were submitted to adoptive immunotherapy with IL-2 and lymphokine-activated killer (LAK) cells by IP in ECC. The schedule of treatment included the first course of a 5-day systemic administration of IL-2 (Proleukin, EuroCetus 9-12 x 10(6) IU/m2/day continuous infusion); autologous LAK cells were obtained via leukapheresis and after in vitro activation were given (range 8-28 x 10(9)) along with IL-2 (120-2,400 IU/ml of perfusion priming) to the affected limb by IP; IL-2 (9-12 x 10(6) IU/m2/day) was also administered by systemic continuous infusion for 5 days starting on the day after IP. RESULTS: All patients concluded the treatment without any major local or systemic toxicities. Clinical responses included one complete and six partial remissions; three patients had stable disease. All patients are alive. Follow-up after IP ranged from 12 to 35 months (median: 22). The analysis of circulating lymphocytes revealed the rapid disappearance of LAK cells, suggesting their extravasation and/or endothelial adhesion in perfused tissues. CONCLUSIONS: IP with IL-2 and LAK cells is a new approach for the treatment of in-transit metastases due to cutaneous melanoma. The treatment appears to be feasible and reliable. Further biological and immunological studies should permit amelioration of the present modality of treatment.     

Generation of lymphokine-activated killer activity in rodents but not in humans is nitric oxide dependent

The role of nitric oxide (NO) in the generation of lymphokine-activated killer (LAK) cells was investigated. Here we report that L-arginine analog NG-monomethyl-L-arginine (NMMA), a specific inhibitor of nitric oxide synthase, prevents LAK cell generation from cultured rat splenic cells. Accumulated NO endproduct nitrite (NO2-), as measured in the supernatants of rat splenic cells, correlated well with the generation of LAK cells. In contrast, cell proliferation induced by rIL-2 or by Con A was not affected by NMMA. Similarly, phenotypic expression of CD25 in rIL-2-stimulated cultures was unaffected. Furthermore, we could not observe differences in percentages of CD5-CD8+ cells (NK and LAK cell phenotype markers in rats) between rIL-2-stimulated cultures performed in the presence or absence of NMMA. LAK cell generation could no longer be blocked if NMMA was added to the rat cell cultures 24 hr after rIL-2 stimulation. To further confirm the role of NO in LAK cell generation, rat splenic cells were cultured in medium without L-arginine. Under such conditions rIL-2 could not induce LAK cell generation. Hemoglobin, which is a scavenger of NO, also inhibited LAK cell generation. Finally, addition of sodium nitroprusside (SNP) which releases NO in cultures was able to overcome blocking effects of NMMA. To attempt the identification of NO-producing cells, lysosomotropic agent, L-leucine methyl ester (LME), was used. Generation of LAK cell activity was virtually abolished in cell cultures treated with LME. Addition of SNP to cultures, however, sufficed to restore LAK cell generation. These results suggest that LAK cell precursors depend on a exogenous NO supply from other cell types in order to display their full cytotoxic potential. Similar results were also obtained by using mouse splenocytes as responder cells. In contrast, NMMA did not affect generation of LAK cells from human peripheral blood or spleen mononuclear cells.     

Migratory response of human natural killer cells to lymphotactin

Lymphotactin (Lptn) is a new protein belonging to the C or gamma subfamily of chemokines with only two of the four cysteine residues. Lptn was reported to act specifically on T lymphocytes and not on monocytes and neutrophils. To understand better the spectrum of action of Lptn we have examined its ability to induce natural killer (NK) cell migration. Freshly isolated human NK cells as well as long-term cultured NK cells propagated in interleukin-2 (IL-2)-containing medium migrated in response to Lptn. Optimal activity was observed at concentrations ranging from 50 to 200 ng/ml, and the efficacy was comparable to that of MCP-1, the prototype of C-C chemokines. Migration in response to Lptn was chemotaxis rather than chemokinesis as determined in a checkerboard analysis. Migration of NK cells was comparable to that observed with T lymphocytes from the same donor, under the same experimental conditions. Finally, in contrast to other cytokines (IL-2 and IL-12) which in addition to chemotaxis augment NK cell adhesion to endothelial cells in vitro, Lptn did not affect the adhesiveness of NK cells to vascular endothelium.     

Decreased interleukin-12 (IL-12) from activated cord versus adult peripheral blood mononuclear cells and upregulation of interferon-gamma, natural killer, and lymphokine-activated killer activity by IL-12 in cord blood mononuclear cells

Remnants of lipoproteins, intestinal chylomicrons, and very low density lipoprotein (VLDL), are rapidly cleared from plasma and enter hepatocytes. It has been suggested that remnant lipoproteins are initially captured in the space of Disse by heparan sulfate proteoglycans (HSPGs), and that their subsequent internalization into hepatocytes is mediated by members of the LDL-receptor gene family. Similarly to lipoprotein remnants, malaria sporozoites are removed from the blood circulation by the liver within minutes after injection by Anopheles mosquitoes. The sporozoite's surface is covered by the circumsporozoite protein (CS), and its region II-plus has been implicated in the binding of the parasites to glycosaminoglycan chains of hepatocyte HSPGs. Lactoferrin, a protein with antibacterial properties found in breast milk and neutrophil granules, is also rapidly cleared from the circulation by hepatocytes, and can inhibit the hepatic uptake of lipoprotein remnants. Here we provide evidence that sporozoites, lactoferrin, and remnant lipoproteins are cleared from the blood by similar mechanisms. CS, lactoferrin, and remnant lipoproteins compete in vitro and in vivo for binding sites on liver cells. The relevance of this binding event for sporozoite infectivity is highlighted by our demonstration that apoliprotein E-enriched beta-VLDI and lactoferrin inhibit sporozoite invasion of HepG2 cells. In addition, malaria sporozoites are less infective in LDL-receptor knockout (LDLR -/-) mice maintained on a high fat diet, as compared with littermates maintained on a normal diet. We conclude that the clearance of lipoprotein remnants and sporozoites from the blood is mediated by the same set of highly sulfated HSPGs on the hepatocyte plasma membrane.     

Human natural killer cells

Human natural killer (NK) cells comprise 10 to 15% of peripheral blood lymphocytes, characterized by their morphologic appearance of large granular lymphocytes (LGLs) and phenotype CD3- CD56+ CD16+ or CD16-. Functionally, these cells are defined by their ability to lyse target cells without prior sensitization and without restriction by major histocompatibility (MHC) antigens. These cells play an important role in immune defenses, especially after hematopoietic transplantation. They contribute to the defenses against virus-infected cells, graft rejection, and neoplasias; they also participate in the regulation of hematopoiesis through cytokine production and cell to cell interaction. In this mini-review we attempt to summarize the most relevant findings about these cells in terms of their origin and differentiation, their cell surface characteristics including activation and their cytolytic pathways. We have also provided a brief approach of their potential clinical use. Increased knowledge of NK cell differentiation, ontogeny and regulatory mechanisms may be of use for the planning of immunotherapeutic strategies.     

Autologous lymphokine-activated killer cell therapy of Epstein-Barr virus-positive and -negative lymphoproliferative disorders arising in organ transplant recipients

Lymphoreticular malignancies, collectively called posttransplant lymphoproliferative disorders (PTLD), eventually develop in 2-5% of organ transplant recipients. They frequently undergo regression when immunosuppression is reduced or stopped. This feature has been associated with a previous or de novo Epstein-Barr virus (EBV) infection. We herein describe immunotherapy with autologous lymphokine-activated killer (LAK) cells in seven patients with PTLD (four EBV-positive patients and three EBV-negative patients). Autologous peripheral blood mononuclear cells were obtained by leukapheresis, depleted of monocytes, and cultured in the presence of interleukin 2 for 10 to 11 days. A single dose of 5.2 x 10(9) to 5.6 x 10(10) LAK cells was given intravenously. Systemic interleukin 2 was not administered. The four patients with EBV+ PTLD had complete tumor regression; two of them developed controllable rejection. Three patients are well 13-16 months after treatment; the fourth patient died of pneumonia 41 days after infusion. Three patients with EBV- lymphomas had no response despite prior evidence that their tumors also were subject to immune surveillance. Two of these three patients died after being given other treatment, and the third patient has persistent tumor. In conclusion, autologous LAK cell infusion was effective for treatment of four EBV+ organ transplant recipients. LAK cell efficacy for three patients with EBV- PTLD was not evaluable under the management circumstances in which this treatment was utilized.     

Elevated prostaglandin E2 production by monocytes is responsible for the depressed levels of natural killer and lymphokine-activated killer cell function in patients with breast cancer

BACKGROUND: Human natural killer (NK) cells mediate spontaneous cytotoxicity against tumor cells and represent the main precursors of lymphokine-activated killer (LAK) cell activity. A comparison of some aspects of NK and LAK cell activity was undertaken in 85 preoperative patients with breast cancer and 75 healthy donors. METHODS: NK cell activity (tested in 18-hour cultures of effector peripheral blood mononuclear cells [PBMC] with K562 or MOLT-4 tumor target cells) was significantly diminished in these patients as it was the fully mature LAK cell activity (i.e., interleukin-2 (IL-2)-induced cytotoxicity in PBMC) against NK resistant target cells. Using immunoenzymatic methods we showed that the reduced NK cell activity was due to abnormally high levels of prostaglandin E2 (PGE2) produced by monocytes in culture. RESULTS: PGE2 was found to suppress the production of IL-2 in these cultures. Removal of monocytes from PBMC restored to almost normal levels the deficient NK and LAK cell activity in patients with breast cancer and was also associated with a normalization in the levels of PGE2 and IL-2. Indomethacin and gamma-interferon (IFN-gamma) increased the NK and LAK cell activity in these patients up to the levels of healthy donors. When highly purified CD56+ cells (obtained by an immunomagnetic isolation technique) were used as effector cells, no differences in LAK cell activity could be noticed between healthy donors and patients with cancer. FACS and northern blot analyses demonstrated a PGE2-mediated down-regulation of IL-2 receptor (IL-2R) expression on CD56+ cells that correlated with reduced LAK cell activity. This inhibitory effect of PGE2 was noticeable in long-term LAK cultures and was abrogated in the presence of IFN-gamma or indomethacin. CONCLUSION: This study may have important implications in the potentiation of NK and LAK cell activity for immunotherapeutic protocols in patients with breast cancer.     

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.     

Natural killer activating receptors trigger interferon gamma secretion from T cells and natural killer cells

Proliferation of human CD4+ alphabeta T cells expressing a natural killer cell activating receptor (NKAR) has been shown to be enhanced, particularly in response to low doses of antigen, if the target cells present appropriate human class I major histocompatibility complex (MHC) molecules. Here, we show that NKAR also enhance proliferation and killing of target cells by subsets of CD8+ alphabeta and CD8+ gammadelta T cells, as well as by NK cells. Strikingly, interferon gamma secretion from all of these types of lymphocytes was markedly increased by interaction of the NKAR with their MHC class I ligands, independently of enhancement of proliferation. Thus, the recognition of class I MHC molecules by NKAR on both T cells and NK cells may provide a regulatory mechanism that affects immune responses through the secretion of interferon gamma and possibly other cytokines. It represents a signal for cytokine secretion alternative and/or augmentative to that through the T cell receptor.