Rat Natural Killer Cells Research Articles

Recognition of Listeria monocytogenes infection by natural killer cells: Towards a complete picture by experimental studies in rats.

The study of cellular immune responses in animal disease models demands detailed knowledge of development, function, and regulation of immune cells, including natural killer (NK) cells. Listeria monocytogenes (LM) bacterium has been explored in a large area of research fields, including the host pathogen interaction. Although the importance role of NK cells in controlling the first phase of LM burden has been investigated, the interaction between NK cells and infected cells in details are far from being comprehended. From in vivo and in vitro experiments, we can drive several important pieces of knowledge that hopefully contribute to illuminating the intercommunication between LM-infected cells and NK cells. Experimental studies performed in rats revealed that certain NK cell ligands are influenced in LM-infected cells. These ligands include both classical- and non-classical MHC class I molecules and C-type lectin related (Clr) molecules that are ligands for Ly49- and NKR-P1 receptors respectively. Interaction between these receptors:ligands during LM infection, demonstrated stimulation of rat NK cells. Hence, these studies provided additional knowledge to the mechanisms NK cells utilise to recognise and respond to LM infection outlined in the current review.

Effect of moxibustion with wheat-grain-sized moxa cones on uterine natural killer cells and deci-dualization in rats with thin endometrium

To observe the effect of moxibustion at "Shenshu"(BL23) and "Guanyuan" (CV4) on decidua-lization and uterine natural killer cells in rats with thin endometrium, so as to explore its mechanism underlying promotion of embryo implantation. Female SD rats were randomly divided into normal control, model and wheat-grain-sized moxa cone moxibustion (moxibustion) groups, with 14 rats in each group. The thin endometrium model was established by bilaterally intrauterine perfusion of 95% ethanol (first) and saline (later) during estrus. For rats of the moxibustion group, the ignited wheat-grain-sized moxa cones were applied to bilateral BL23 and CV4, with 7 moxa cones for each acupoint, once a day, continuously for 3 estrous cycles. Then the male and female rats were raised in the same cage. On the 5th day of pregnancy, the rats were killed under anesthesia and the uterus tissue was collected for measuring the endometrium thickness and the numbers of blood vessels and glands after H.E. staining, detecting the levels of the proportion of natural killer cells with flow cytometry. After the uterine natural killer cells were sorted by the immunomagnetic bead method, the expression levels of insulin-like growth factor binding protein (IGFBP-1), interferon(INF-γ), tumor necrosis factor(TNF-α), transforming growth factor(TGF-β), interleukin 4(IL-4) and IL-10 mRNAs were detected by using fluorescence quantitative real-time PCR. Compared with the normal control group, the endometrium thickness, number of glands and blood vessels, and the expression levels of IGFBP-1, TGF-β, IL-4 and IL-10 mRNAs were significantly decreased (P<0.01, P<0.05), while the expression levels of IFN-γ and TNF-α mRNAs were significantly increased (P<0.05，P<0.01) in the model group. In contrast to the model group, the endometrium thickness, number of glands and blood vessels, and the expression levels of IGFBP-1, TGF-β, IL-4 and IL-10 mRNAs were significantly increased (P<0.05, P<0.01), while the expression levels of IFN-γ and TNF-α mRNAs were considerably down-regulated (P<0.05, P<0.01) in the moxibustion group. No significant difference was found among the 3 groups in the proportion of natural killer cells in the endometrium (P>0.05). Moxibustion of BL23 and CV4 with wheat-grain-sized moxa cones can improve the degree of thin endometrial decidualization, which may be related with its functions in regulating the levels of cytokines secreted from natural killer cells in the uterus.

Characterization of natural killer cells in colorectal tumor tissue of rats fed a control diet or a high-fat diet

BackgroundObesity is a major public health problem with an increasing prevalence reaching pandemic levels. The incidence and mortality for colorectal cancer is augmented in overweight and obese individuals. Previous studies demonstrated an impaired number, phenotype and functionality of natural killer (NK) cells under obese conditions. So far, the influence of obesity on NK cells in colorectal cancer tissue remained unclear. Therefore, the aim of the study was to investigate the occurrence and localization of NK cells in colorectal tumors of normal weight and diet-induced obese rats. MethodsWistar rats were fed a normal-fat diet (control) or a high-fat diet (HFD) to induce obesity. In half of the experimental groups azoxymethane (AOM) was injected to induce colorectal cancer. Tumors in colon and rectum were histopathologically classified in adenomas and adenocarcinomas and immunohistologically stained with the rat NK cell marker CD161. Occurrence and localization of NK cells were analyzed and quantified in the tunica mucosa and tunica submucosa of colorectal adenomas and the tunica submucosa of colorectal adenocarcinomas. ResultsNK cells are localized in the tunica mucosa and the tunica submucosa of colorectal tumors with NK cell accumulations as follicle-like aggregates especially in regions of the lamina muscularis mucosae and the lamina propria mucosae of the tunica mucosa as well as in regions of the tunica submucosa adjacent to the lamina muscularis mucosae. Although not statistically significant, the CD161 staining was clearly reduced in the tunica mucosa of colorectal tumors of rats fed a HFD compared to rats fed a control diet. Moreover, the CD161 staining in the tunica mucosa was positively correlated with the final body weight of AOM-treated rats independent of the supplied diet. DiscussionFor the first time, these results provide information about the localization and quantity of NK cells in colorectal tumor tissue of rats fed a control diet or high-fat diet. The slight reduction of NK cell number in colorectal tissue of rats fed a high-fat diet may contribute to an impaired tumor defense and the increased colorectal tumor outcome in diet-induced obese rats.

Production of recombinant soluble dimeric C-type lectin-like receptors of rat natural killer cells

Working at the border between innate and adaptive immunity, natural killer (NK) cells play a key role in the immune system by protecting healthy cells and by eliminating malignantly transformed, stressed or virally infected cells. NK cell recognition of a target cell is mediated by a receptor “zipper” consisting of various activating and inhibitory receptors, including C-type lectin-like receptors. Among this major group of receptors, two of the largest rodent receptor families are the NKR-P1 and the Clr receptor families. Although these families have been shown to encode receptor-ligand pairs involved in MHC-independent self-nonself discrimination and are a target for immune evasion by tumour cells and viruses, structural mechanisms of their mutual recognition remain less well characterized. Therefore, we developed a non-viral eukaryotic expression system based on transient transfection of suspension-adapted human embryonic kidney 293 cells to produce soluble native disulphide dimers of NK cell C-type lectin-like receptor ectodomains. The expression system was optimized using green fluorescent protein and secreted alkaline phosphatase, easily quantifiable markers of recombinant protein production. We describe an application of this approach to the recombinant protein production and characterization of native rat NKR-P1B and Clr-11 proteins suitable for further structural and functional studies.

Mesenchymal stem cells suppress hepatic fibrosis accompanied by expanded intrahepatic natural killer cells in rat fibrosis model.

Natural killer (NK) cells have antifibrotic effects. We have evaluated the influence of rat bone marrow-mesenchymal stem cell (BM-MSC) treatment on liver histology, biochemical liver function tests, systemic immunoregulatory state and NK cell distribution in liver and peripheral blood in rat model of common bile duct (CBD) ligation and compared the results with the control group. Rats were divided into three groups: (1) CBD ligated (CBDL) rats received phosphate-buffered saline (CBDL + PBS group) or (2) MSC (CBDL + MSC group) and sham-operated rats received MSC (healthy + MSC group). We found significantly decreased fibrosis scores with BM-MSC treatment in CBDL rats compared to the control (CBDL + PBS) group while no fibrosis developed in sham operated (healthy + MSC) group. BM-MSC treatment has decreased the inflammation as reflected by the significantly decreased T cell proliferation and inflammatory cytokine concentrations from splenocyte culture and liver tissue itself compared to CBDL + PBS. NK cells both in parenchyme and portal areas decreased significantly in liver and blood in CBDL + PBS compared to healthy + MSC while they were found to be increased in CBDL + MSC compared to CBDL + PBS rats. In conclusion, BM-MSCs may suppress hepatic fibrosis accompanied by expanded intrahepatic NK cells in CBDL rats. Thus, our animal study shows that MSC treatment holds great promise for treatment of patients with end-stage liver diseases through a possible mechanism by adopting the NK cell population and new studies investigating the role of NK cells and clinical fibrosis are warranted.Trial registration number: Marmara University Animal Care and Use Committee approval code: 73.2013.mar.

The Role of Interleukin‐2 (IL‐2) in Natural Killer Cell (NK) Activation and Hypertension in a Preclinical Rat Model of Preeclampsia

Women with preeclampsia (PE) have hypertension, placental ischemia, increased pro‐inflammatory cells (natural killer (NK) and Th1 cells) and cytokines, and intrauterine growth restriction (IUGR). Interleukin‐2 (IL‐2) is a Th1 cytokine that stimulates NK cell activation. We hypothesize that IL‐2 is one mechanism whereby Th1 cells, which are activated in response to placental ischemia, mediate NK cell activation, hypertension, and IUGR during pregnancy. The objective of this study was 2 fold: 1.) to determine if elevated IL‐2 during pregnancy will increase blood pressure, NK cell activation, and cause IUGR. 2.) to determine if blockade of IL‐2 (basiliximab) will decrease blood pressure, NK cell activation, and improve pup weight in the reduce uterine perfusion pressure (RUPP) preclinical rat model of PE The RUPP rat is a model of placental ischemia during pregnancy which has increased IL‐2 levels and mimics many of the symptoms of PE.MethodsOn gestational day 14, normal pregnant (NP) rats received IL‐2 infusion (0.20 ng/ml) via mini‐osmotic pump; while RUPP rats receive basiliximab (0.07 mg/per rat) via IV infusion. On day 19, conscious blood pressure (MAP), pups, placentas, and blood were collected. Flow cytometry was used for quantification of NK cells.ResultsIL‐2 infusion did not increase MAP (106 ± 3 vs. 100 ± 2 mmHg) nor change pup weight (2.24 ± 0.06 vs. 2.33 ± 0.06 g). However, IL‐2 infusion decreased placental weight (0.60 ± 0.02 vs. 0.67 ± 0.02 g, p&lt;0.05 vs. NP) and increased circulating activated NK cells (10.4 ± 1.8 vs. 3.1 ± 1%, p&lt;0.05 vs. NP). RUPPs rats exhibit elevated MAP (123 ± 3 vs. 103 ± 3 mmHg, p&lt;0.05 vs. NP), placental (14.1 ± 2.9 vs. 7.8 ± 0.6%, p&lt;0.05 vs. NP), and circulating (16.6 ± 1.3 vs. 7.7 ± 0.9%, p&lt;0.05 vs. NP) activated NK cells. Basiliximab treatment had no effect to lower MAP (123 ± 2 vs. 123 ± 3 mmHg) or improve pup weight (2.08 ± 0.07 vs. 2.04 ± 0.07 g) and placental weight (0.59 ± 0.03 vs. 0.53 ±0.04 g) in RUPP rats. However, basiliximab decreased total placental NK cells in RUPP rats (4.6 ± 1.4 vs. 14.1 ± 2.9%, p&lt;0.05 RUPP + basiliximab vs. RUPP).ConclusionIL‐2 appears to play a major role in NK cell activation during PE that could possibly impact placental health without causing increases in blood pressure during pregnancy.Support or Funding InformationResearch Supported by T32HL105324 and HL130456This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Abstract 133: Depletion of Natural Killer Cell Activation in Response to Placental Ischemia Improves Hypertension and Intrauterine Growth Restriction During Pregnancy

Women with preeclampsia (PE), newly developed hypertension and renal dysfunction during pregnancy, have small-for-gestational-age babies and demonstrate an increase in the cytolytic natural killer (NK) cell activation. The specific role of cytolytic NK cells in the pathophysiology of PE has not been clearly defined. The reduced uterine perfusion pressure (RUPP) model of placental ischemia (PI) exhibits many of the characteristics of PE including hypertension, renal dysfunction, chronic inflammation and intrauterine growth restriction (IUGR). In this study, we tested the hypothesis that PI results in cytolytic activation of NK cells, and examined a role for a reduction in NK cells in RUPP to attenuate PE-like characteristics in response to PI. In this study NK cells were depleted in RUPP rats by intraperitoneal administration of the Anti-asialo GM1 antibody on gestation days 15 and 17. PBMCs and placental lymphocytes were examined via flow cytometry to quantify cytolytic NK cells and to verify NK cell depletion, blood pressure (MAP) and pup weight were measured. While total placental NK cells numbers did not change in response to PI (NP: 14±4.5%; RUPP: 14.3±3.8%), cytolytic activation of placental NK cells significantly increased in response to PI (NP: 3.4±1.1% vs RUPP 10.0±3.4%; p&lt;0.05). Moreover, depletion of NK cells in RUPP (total NK: RUPP: 14.3±3.8% vs RUPP+NKD: 3.5±0.9%) significantly improved blood pressure and intrauterine growth restriction (IUGR): MAP significantly increased in response to PI from 109.5±2.3 mmHg in NP (n=10) to 125.4±2.7 mmHg (n=9) in RUPP rats (p&lt;0.001). Depletion of NK cells with the cell specific depleting antibody significantly lowered blood pressure to 114.4.±1.9 mmHg in RUPP+NKD rats (n=11, p&lt;0.01). Additionally, NK cell depletion in RUPP significantly reduced IUGR in response to PI (1.85±0.06g in RUPP vs. 2.0±0.4g in RUPP+NKD; p&lt;0.05). Depletion of NK cells in RUPP rats was positively associated with lowering blood pressure and blunting IUGR in response to PI. These results suggest a role for cytolytic NK in contributing to hypertension and IUGR in response to PI, potentially identifying previously unknown mechanisms of PE pathophysiology and new therapeutic targets to improve maternal and fetal outcomes of PE.

Antitumor effect of novel anti-podoplanin antibody NZ-12 against malignant pleural mesothelioma in an orthotopic xenograft model.

Podoplanin (aggrus) is highly expressed in several types of cancers, including malignant pleural mesothelioma (MPM). Previously, we developed a rat anti‐human podoplanin mAb, NZ‐1, and a rat–human chimeric anti‐human podoplanin antibody, NZ‐8, derived from NZ‐1, which induced antibody‐dependent cellular cytotoxicity (ADCC) and complement‐dependent cytotoxicity against podoplanin‐positive MPM cell lines. In this study, we showed the antitumor effect of NZ‐1, NZ‐8, and NZ‐12, a novel rat–human chimeric anti‐human podoplanin antibody derived from NZ‐1, in an MPM orthotopic xenograft SCID mouse model. Treatment with NZ‐1 and rat NK (CD161a+) cells inhibited the growth of tumors and the production of pleural effusion in NCI‐H290/PDPN or NCI‐H226 orthotopic xenograft mouse models. NZ‐8 and human natural killer (NK) (CD56+) cells also inhibited tumor growth and pleural effusion in MPM orthotopic xenograft mice. Furthermore, NZ‐12 induced potent ADCC mediated by human MNC, compared with either NZ‐1 or NZ‐8. Antitumor effects were observed following treatment with NZ‐12 and human NK (CD56+) cells in MPM orthotopic xenograft mice. In addition, combined immunotherapy using the ADCC activity of NZ‐12 mediated by human NK (CD56+) cells with pemetrexed, led to enhanced antitumor effects in MPM orthotopic xenograft mice. These results strongly suggest that combination therapy with podoplanin‐targeting immunotherapy using both NZ‐12 and pemetrexed might provide an efficacious therapeutic strategy for the treatment of MPM.

Sea buckthorn (Hippophae rhamnoides L.) oil protects against chronic stress-induced inhibitory function of natural killer cells in rats.

Chronic stress can suppress natural killer (NK) cell activity; this may also be related to the effect of stress on the neuroendocrine-immune network. Sea buckthorn (SBT) (Hippophae rhamnoides L.) is a thorny nitrogen fixing deciduous shrub, native to both Europe and Asia. It has been used as a medicinal plant in Tibetan and Mongolian traditional medicines. SBT has multifarious medical properties, including anti-fatigue as well as immunoregulatory effects. This study reports the effects of SBT oil with regard to the cytotoxicity and quantity of NK cells in the blood of a chronic-stress rat model, in addition to its mechanisms on the neuroendocrine-immune network. These results show that SBT oil, given by gavage to rats with chronic stress, could increase the following: body weight, NK cell quantities, and cytotoxicity, as well as the expression of perforin and granzyme B. The results also show that SBT oil in rats with chronic stress could suppress cortisol, ACTH, IL-1β and TNF-α levels, in addition to increasing 5-HT and IFN-γ serum levels. This leads to suggest that SBT oil, in rats with chronic stress, can increase NK cell cytotoxicity by upregulating the expression of perforin and granzyme B, thus causing associated effects of SBT oil on the neuroendocrine-immune network.

Fluoroquinolone and Ovariectomy in the Bitch: Physiology of the Immune System as to CD56 and CD16 Expression.

Natural killer (NK) cells are innate lymphoid cells which act against a variety of pathogens and tumours. Phenotypically they are characterized by surface markers named cluster designation (CD) antigens. CD56 and CD16 are recognized as specific NK markers in the dogs as well as in humans. Surgical interventions suppress NK cells both in rats and humans. In this direction, it has been shown that an antibiotic regimen (amoxicillin, benzylpenicillin/dihydrostreptomycin, sulfametazine/sulfamerazine/ sulfathiazole, enrofloxacin, lincomycin/spectinomycin) administered only twice is effective in preventing infections after laparatomic ovariectomy, in the bitch. On these grounds, this research will show that the administration of a fluoroquinolone (5 mg/kg of enrofloxacin, Baytril®, Bayer, Milan, Italy) one hour before and at the end of ovariectomy is able to increase CD56 and CD16 expression levels. Moreover, the antibiotic administration modifies the relative expression levels of the two CD; thus suggesting that the fluoroquinolone employed enhances the activation of a specific subset of NK cells mainly involved in body recovering during the post operative period as already observed in humans.

Targeting glucosylceramide synthase synergizes with C6-ceramide nanoliposomes to induce apoptosis in natural killer cell leukemia

Natural killer (NK) cell leukemia is characterized by clonal expansion of CD3 − NK cells and comprises both chronic and aggressive forms. Currently no effective treatment exists, thus providing a need for identification of novel therapeutics. Lipidomic studies revealed a dysregulated sphingolipid metabolism as evidenced by decreased levels of overall ceramide species and increased levels of cerebrosides in leukemic NK cells, concomitant with increased glucosylceramide synthase (GCS) expression. GCS, a key enzyme of this pathway, neutralizes pro-apoptotic ceramide by transfer of a uridine diphosphate (UDP)-glucose. Thus, we treated both rat and human leukemic NK cells in combination with: (1) exogenous C6-ceramide nanoliposomes in order to target mitochondria and increase physiological pro-apoptotic levels of long chain ceramide, and (2) 1-phenyl-2-palmitoylamino-3-morpholino-1-propanol (PPMP), an inhibitor of GCS. Co-administration of C6-ceramide nanoliposomes and PPMP elicited an increase in endogenous long-chain ceramide species, which led to cellular apoptosis in a synergistic manner via the mitochondrial intrinsic cell death pathway in leukemic NK cells.

Opiate Antagonist Prevents μ- and δ-Opiate Receptor Dimerization to Facilitate Ability of Agonist to Control Ethanol-altered Natural Killer Cell Functions and Mammary Tumor Growth

In the natural killer (NK) cells, δ-opiate receptor (DOR) and μ-opioid receptor (MOR) interact in a feedback manner to regulate cytolytic function with an unknown mechanism. Using RNK16 cells, a rat NK cell line, we show that MOR and DOR monomer and dimer proteins existed in these cells and that chronic treatment with a receptor antagonist reduced protein levels of the targeted receptor but increased levels of opposing receptor monomer and homodimer. The opposing receptor-enhancing effects of MOR and DOR antagonists were abolished following receptor gene knockdown by siRNA. Ethanol treatment increased MOR and DOR heterodimers while it decreased the cellular levels of MOR and DOR monomers and homodimers. The opioid receptor homodimerization was associated with an increased receptor binding, and heterodimerization was associated with a decreased receptor binding and the production of cytotoxic factors. Similarly, in vivo, opioid receptor dimerization, ligand binding of receptors, and cell function in immune cells were promoted by chronic treatment with an opiate antagonist but suppressed by chronic ethanol feeding. Additionally, a combined treatment of an MOR antagonist and a DOR agonist was able to reverse the immune suppressive effect of ethanol and reduce the growth and progression of mammary tumors in rats. These data identify a role of receptor dimerization in the mechanism of DOR and MOR feedback interaction in NK cells, and they further elucidate the potential for the use of a combined opioid antagonist and agonist therapy for the treatment of immune incompetence and cancer and alcohol-related diseases.

Novel method for isolating untouched rat natural killer cells with higher purity compared with positive selection and fluorescence‐activated cell sorting

Natural killer (NK) cells are important effectors of both innate and adaptive immune responses. Although human and mouse NK cells are extensively characterized, much less is known about the rat cells, partly because of the current lack of reliable isolation techniques. We aimed to develop a method for isolating highly pure 'untouched' rat NK cells by negative selection from splenocytes. Thereafter, we characterized them phenotypically and functionally in comparison with those isolated by positive selection targeting the NKR-P1 receptor. Our novel method isolated highly pure untouched NK cells reproducibly with 97 ± 0.7% (n = 7), 96.6 ± 0.8% (n = 3) and 88.3 ± 1.5% (n = 9) in LEWIS, Fischer and athymic nude rats, respectively. The positively selected NK cells were less homogeneous and exhibited undesired method-related activation profiles. Resting negatively selected NK cells were less proliferative and less robust compared with positively selected NK cells. Although resting positively selected NK cells were more cytotoxic, interleukin-2 (IL-2) activation increased the cytotoxicity of negatively selected cells three-fold. The negatively selected NK cells responded to cross-linking of the NKR-P1 receptor by calcium mobilization from intracellular stores. However, combined IL-2 and IL-12 activation resulted in significantly more interferon-γ release from positively selected NK cells. This new NK-cell isolation method will allow a deeper insight into rat NK-cell phenotypes and the roles of their receptors in the biology of these cells.

The complete inventory of receptors encoded by the rat natural killer cell gene complex

The natural killer cell gene complex (NKC) encodes receptors belonging to the C-type lectin superfamily expressed primarily by NK cells and other leukocytes. In the rat, the chromosomal region that starts with the Nkrp1a locus and ends with the Ly49i8 locus is predicted to contain 67 group V C-type lectin superfamily genes, making it one of the largest congregation of paralogous genes in vertebrates. Based on physical proximity and phylogenetic relationships between these genes, the rat NKC can be divided into four major parts. We have previously reported the cDNA cloning of the majority of the genes belonging to the centromeric Nkrp1/Clr cluster and the two telomeric groups, the Klre1–Klri2 and the Ly49 clusters. Here, we close the gap between the Nkrp1/Clr and the Klre1–Klri2 clusters by presenting the cDNA cloning and transcription patterns of eight genes spanning from Cd69 to Dectin1, including the novel Clec2m gene. The definition, organization, and evolution of the rat NKC are discussed.Electronic supplementary materialThe online version of this article (doi:10.1007/s00251-010-0455-y) contains supplementary material, which is available to authorized users.

Cancer Immunoediting from Immunosurveillance to Tumor Escape in Microvillus-Formed Niche: A Study of Syngeneic Orthotopic Rat Bladder Cancer Model in Comparison with Human Bladder Cancer

Cancer cells can develop an attenuated immunogenicity and/or create an immunosuppressive microenvironment to prevent tumor eradication by host immune system, the so-called “cancer immunoediting” hypothesis. The aim of the present study was to find evidence for this hypothesis by using a rat orthotopic bladder cancer model. Fisher rats were inoculated with AY-27 cells (a Fisher rat bladder cancer cell line). Cultured cancer cells, rat and human bladder cancer tissues, and publicly available microarray data from human bladder cancer were analyzed by means of bioinformatics and morphology. Results showed that 12 of 24 differentially expressed pathways were concordant in connection to cell cycle and proliferation between rats and humans (both non-muscle-invasive and muscle-invasive tumors) and that 11 of the 24 pathways, including major histocompatibility complex, were related to host immunosurveillance with activations of T cells and natural killer cells in rats. The altered pathways and morphogenesis of this rat model corresponded more closely with those of human muscle-invasive rather than non-muscle-invasive tumors. A unique ultrastructure displaying microvillus-formed niches was found in small areas within the tumor of both rats and humans. These niches were interconnected with desmosomes between cancer cells and without infiltration of lymphocytes. The expression of E-cadherin, selectins, PGP9.5, vascular endothelial growth factor, caspase-3, CD133, Oct-4, nestin, CD3, and CD45RA was lower in the tumor than in the adjacent normal epithelium. We suggest that the microvillus-formed niche that harbors a few implanted cancer cells might be the compartment that prevents the tumor eradication by the host immune system.

Innate Immunity in the Therapeutic Actions of Endothelial Progenitor Cells in Pulmonary Hypertension

Direct injection of endothelial progenitor cells (EPCs) into the circulation has shown therapeutic benefit in both experimental models and clinical studies of pulmonary arterial hypertension (PAH). Using the monocrotaline (MCT)-induced rat model of PAH, we investigated the role of innate immunity in the therapeutic activity of two types of putative EPCs derived from human peripheral blood mononuclear cells: an early population of endothelial-like, culture-modified monocytes (E-CMMs) and late-outgrowth EPCs (L-EPCs), which exhibit a strong endothelial phenotype. In the athymic nude rat, E-CMMs prevented MCT-induced increases in right ventricular systolic pressure (P < 0.001) and right ventricular hypertrophy (P < 0.01) when administered 3 days after MCT challenge, whereas L-EPCs were ineffective. However, in both cases, there was a lack of cell persistence within the lungs at 24 hours after injection, likely due to residual natural killer (NK) cell activity in the model. Although ablation of NK and NK-T cells with anti-asialo-GM-1 antiserum enhanced the retention of both E-CMMs and L-EPCs, still no benefit was seen with L-EPCs, and the efficacy of E-CMMs was lost. In vitro characterization revealed that E-CMMs resemble a regulatory subtype of dendritic cells, producing IL-10, but not IL-12, in response to inflammatory stimuli. Coculture studies demonstrated the capacity of E-EPCs to stimulate autologous human and nude rat NK cells in vitro. These data support a novel mode of action for human E-CMMs in the prevention of PAH, whereby they act through an immune-dependent mechanism, potentially involving the stimulation of NK cells.

Immunomodulation of NK Cell Activity by Red Ginseng Acidic Polysaccharide (RGAP) in Ovariectomized Rats

The in-vitro immunomodulatory function of murine natural-killer (NK) cells induced by red-ginseng acidic polysaccharide (RGAP) in ovariectomized (OVX) rats was examined in this study. The IL-2-induced NK cell activity was significantly decreased in the OVX rats compared to the sham groups, but the normally induced NK cell activity was not. RGAP, however, increased the NK cell activity in both groups, and this effect involved iNOS expression. The inhibition of iNOS activity did not increase the NK cell cytotoxicity by RGAP in the OVX rats. The data that were obtained also demonstrated that the expression of iNOS was increased in the spleen of the OVX rats. These results indicate that RGAP increases the tumoricidal activity of the NK cell in the OVX rats, which is a primed or activated state of innate immune cells resulting from the changes in cytokine production induced by estrogen-deficient stress. Therefore, RGAP has a synergistic effect on the NK cell activities, which are regulated by the iNOS signals in OVX rats. This suggests that RGAP is useful for potential therapeutic strategies as a nutrient in regulating the NK cells in OVX rats.

The Tumorigenicity of Mouse Embryonic Stem Cells and In Vitro Differentiated Neuronal Cells Is Controlled by the Recipients' Immune Response

Embryonic stem (ES) cells have the potential to differentiate into all cell types and are considered as a valuable source of cells for transplantation therapies. A critical issue, however, is the risk of teratoma formation after transplantation. The effect of the immune response on the tumorigenicity of transplanted cells is poorly understood. We have systematically compared the tumorigenicity of mouse ES cells and in vitro differentiated neuronal cells in various recipients. Subcutaneous injection of 1×106 ES or differentiated cells into syngeneic or allogeneic immunodeficient mice resulted in teratomas in about 95% of the recipients. Both cell types did not give rise to tumors in immunocompetent allogeneic mice or xenogeneic rats. However, in 61% of cyclosporine A-treated rats teratomas developed after injection of differentiated cells. Undifferentiated ES cells did not give rise to tumors in these rats. ES cells turned out to be highly susceptible to killing by rat natural killer (NK) cells due to the expression of ligands of the activating NK receptor NKG2D on ES cells. These ligands were down-regulated on differentiated cells. The activity of NK cells which is not suppressed by cyclosporine A might contribute to the prevention of teratomas after injection of ES cells but not after inoculation of differentiated cells. These findings clearly point to the importance of the immune response in this process. Interestingly, the differentiated cells must contain a tumorigenic cell population that is not present among ES cells and which might be resistant to NK cell-mediated killing.

Protease-activated receptor 1 activation is necessary for monocyte chemoattractant protein 1–dependent leukocyte recruitment in vivo

Thrombin, acting through a family of protease-activated receptors (PARs), is known to amplify inflammatory responses, but the in vivo importance of PARs in inflammation is not fully appreciated. In a mouse heart-to-rat transplant model, where it is possible to distinguish graft (mouse) from systemic (rat) chemokines, we show that donor PAR-1 is required to generate the local monocyte chemoattractant protein (MCP)-1 needed to recruit rat natural killer cells and macrophages into the hearts. We have confirmed the importance of this mechanism in a second model of thioglycollate-induced peritonitis and also show that PAR-1 is important for the production of MCP-3 and MCP-5. Despite the presence of multiple other mediators capable of stimulating chemokine production in these models, these data provide the first evidence that thrombin and PAR activation are required in vivo to initiate inflammatory cell recruitment.

Rapamycin, But Not Cyclosporine or FK506, Alters Natural Killer Cell Function

Infiltration of natural killer (NK) cells into solid organ allografts is observed in clinical and experimental transplantation. Studies suggest a role for NK cells in acute and chronic rejection of solid organ allografts; however, the effects of immunosuppressive agents on NK cells are not clearly established. Rat NK cell lines were analyzed for proliferation and cytotoxicity in the presence of cyclosporine, FK506, or rapamycin. Lewis recipients of DA liver allografts received immunosuppressive agents after transplantation. NK cells demonstrated robust function both in the absence and presence of cyclosporine and FK506. In contrast, rapamycin significantly inhibited proliferation and cytotoxicity of NK cells. NK cell numbers remained stable in graft recipients treated with cyclosporine and FK506, whereas there was a significant decrease in NK cells in rapamycin-treated recipients. These data indicate that immunosuppressive drugs have differential effects on NK cell function that may impact the immune response of transplant recipients.