Murine Natural Killer Cells Research Articles

Rejection of bone marrow cell allografts by natural killer cell subsets: 5E6+ cell specificity for Hh‐1 determinant 2 shared by H‐2d and H‐2f

The 5E6 antigen, defined by anti-5E6 mAb, is expressed on one-half of murine natural killer (NK) cells, and we have previously demonstrated (C. L. Sentman et al., J. Exp. Med. 1989. 170: 1991) that 5E6+ NK cells are necessary for the rejection of BALB/c (Hh-1d) but not C567BL/6 (Hh-1b) bone marrow cells (BMC). In experiments described here, we have characterized the specificity of 5E6+ and 5E6- NK cell subsets for hemopoietic histocompatibility-1 (Hh-1) antigens. Prospective recipient mice were treated with anti-5E6 mAb and challenged with BMC from a variety of donors. In addition, H-2d/Hh-1d C.B-17 scid 5E6+ or 5E6- NK cells were adoptively transferred into irradiated, NK cell-depleted hosts and challenged with H-2b/Hh-1b BMC. The data indicate that the 5E6+ NK cells are necessary for the rejection of only those BMC that express the Hh-1 determinant 2 shared by H-2d and H-2f haplotypes of strains BALB/c (d), A.Ca (f), and B10.M (f). No reactivity to other Hh-1 antigens resides in the 5E6+ population. In contrast, the ability of NK cells to lyse H-2d or H-2b tumor cells was independent of 5E6 expression. These results suggest that the 5E6 molecule is likely to be important in the specific recognition and rejection of BMC that express Hh-1 determinant 2, and is probably not involved in recognition of "tumor target cell structures".

Inhibition of Murine Natural Killer Cell Differentiation by Dehydroepiandrosterone

Dehydroepiandrosterone (DHEA) is a naturally occurring steroid. We have previously shown that dietary DHEA (0.45% wt/wt) inhibits murine lymphopoiesis but not myelopoiesis. To assess the effect of DHEA on stages of natural killer (NK) cell differentiation, lethally irradiated mice fed DHEA or not were infused with 10(6) or 20 x 10(6) syngeneic bone marrow cells (BMC) as a source of transplantable NK cell progenitors. The differentiation of progenitor cells to lytic NK cells was assessed by the ability to clear radiolabeled YAC-1 tumor cells from the lungs. DHEA-fed recipients of 10(6) or 20 x 10(6) BMC failed to generate NK activity. Because NK progenitor cells are believed to differentiate into interleukin-2 (IL-2)-responsive precursor cells before maturation, BMC from recipient mice were cultured with IL-2 and the generation of NK cells was assessed. DHEA feeding prevented the generation of IL-2-responsive precursor cells in recipients of 10(6) BMC, but this inhibition was overcome in recipients of 20 x 10(6) BMC. To evaluate the capacity of stem cells to generate NK progenitor cells in DHEA-fed mice, the ability of marrow cells from primary recipients to generate NK activity in irradiated secondary recipients was determined. The production of NK progenitors was inhibited 20-fold. Thus, DHEA appears to inhibit the generation of NK progenitors from more primitive stem cells, the differentiation of progenitors into IL-2-responsive precursors cells and the maturation of IL-2-responsive precursor cells into mature NK cells.

Inhibition of murine natural killer cell differentiation by dehydroepiandrosterone

Dehydroepiandrosterone (DHEA) is a naturally occurring steroid. We have previously shown that dietary DHEA (0.45% wt/wt) inhibits murine lymphopoiesis but not myelopoiesis. To assess the effect of DHEA on stages of natural killer (NK) cell differentiation, lethally irradiated mice fed DHEA or not were infused with 10(6) or 20 x 10(6) syngeneic bone marrow cells (BMC) as a source of transplantable NK cell progenitors. The differentiation of progenitor cells to lytic NK cells was assessed by the ability to clear radiolabeled YAC-1 tumor cells from the lungs. DHEA-fed recipients of 10(6) or 20 x 10(6) BMC failed to generate NK activity. Because NK progenitor cells are believed to differentiate into interleukin-2 (IL-2)-responsive precursor cells before maturation, BMC from recipient mice were cultured with IL-2 and the generation of NK cells was assessed. DHEA feeding prevented the generation of IL-2-responsive precursor cells in recipients of 10(6) BMC, but this inhibition was overcome in recipients of 20 x 10(6) BMC. To evaluate the capacity of stem cells to generate NK progenitor cells in DHEA-fed mice, the ability of marrow cells from primary recipients to generate NK activity in irradiated secondary recipients was determined. The production of NK progenitors was inhibited 20-fold. Thus, DHEA appears to inhibit the generation of NK progenitors from more primitive stem cells, the differentiation of progenitors into IL-2- responsive precursors cells and the maturation of IL-2-responsive precursor cells into mature NK cells.

In vivo depletion of natural killer cell activity leads to enhanced multiplication of Mycobacterium avium complex in mice

Earlier investigations have shown that murine natural killer (NK) cells inhibit the growth of fungal and bacterial pathogens in vivo and in vitro. In order to define the role of NK cells in Mycobacterium avium complex infection, in vivo depletion of NK cells by using anti-NK1.1 monoclonal antibody and conventional anti-asialo-GM1 antibody has been attempted. Repeated injection of 200 micrograms of anti-NK1.1 or 50 micrograms of anti-asialo-GM1 antibody effectively depleted NK activity in the spleens of C57BL/6 mice. The growth kinetics of M. avium complex over a period of 4 weeks showed that the colony counts in the spleens of the antibody-treated group were significantly (P less than 0.01) higher than those of the control group and compared well with those of the genetically NK cell-deficient C57BL/6 bg/bg mutant. The alternate strategy of in vivo stimulation of NK activity by poly(I:C) administration did not show a similar reduction in CFU in the spleen compared with the untreated control. The in vivo antibody depletion of NK activity provides direct evidence on the role of NK cells in the control of intracellular mycobacterial pathogens such as M. avium complex.

Studies on murine natural killer (NK) cells: V. Genetic analysis of NK cell markers

This paper attempts to clarify the number and nomenclature of murine natural killer (NK) cell specific alloantigens by defining the genetic relationships between them, that is, are they coded by loci which are independent, allelic, or linked. Strain typing and F 2 analyses using five alloantisera (C3H X BALB/c)F 1 anti-CE, CE anti-CBA, NZB anti-BALB/c, C3H anti-ST, and BALB/c anti-DBA/2 revealed that (a) the alloantigens NK-1.1 and NK-3.1 are determined by distinct loci which are linked on the same chromosomes, (b) the alloantigen NK-2.1 is determined by an independently segregating locus to those coding for NK-1.1 and NK-3.1, (c) the alloantisera, CE anti-CBA and NZB anti-BALB/c, which have been designated anti-NK-2.1 alloantisera recognize different alloantigens coded by independent genetic loci. Thus, these five alloantisera detect four NK cell specific alloantigens which, based on the chronology of their discovery, have been designated NK-1.1-(C3H X BALB/c)F 1 anti-CE, NK-2.1-CE anti-CBA, NK-3.1-C3H anti-ST, and BALB/c anti-DBA/2 and NK-4.1-NZB anti-BALB/c.

Stimulation of murine natural killer (NK) cells by a monoclonal antibody specific for the NK1.1 antigen. IL-2-activated NK cells possess additional specific stimulation pathways.

NK cells lyse certain tumor cell targets but the effector cell surface molecules responsible for this reactivity remain uncertain. The allotypic NK1.1 Ag is the most specific serologic marker on murine cells that display non-MHC-restricted cytolysis of tumor cell targets, but no function has been previously ascribed to this Ag. In this report, we demonstrate that, in the presence of a mAb specific for the NK1.1 Ag (mAb PK136), freshly isolated and IL-2-activated NK cells from C57BL/6 mice can be induced to lyse an otherwise resistant target cell, Daudi. This phenomenon is effector and mAb specific because NK cells derived from BALB/c mice do not express the NK1.1 Ag and cannot be triggered by mAb PK136. We demonstrate that IL-2 activated but not freshly isolated NK cells express the Ly-6 and VEA Ag, originally described as T cell activation Ag. Moreover, mAb specific for Ly-6 and VEA induce target cell lysis by IL-2 activated but not freshly isolated NK cells. These mAb effects are specific, concentration dependent, and display kinetics that are similar to spontaneous cytolysis of NK-sensitive targets. The Fc portion of the activating antibodies and only FcR bearing target cells participate in mAb-induced activation, consistent with the mechanism of redirected lysis. Finally, analysis of Daudi cells transfected with beta 2-microglobulin gene demonstrate that the expression of MHC class I Ag by the target cell does not affect its sensitivity to mAb-induced lysis by NK cells. These data demonstrate that the NK1.1 Ag is functionally active on both freshly isolated and IL-2-activated NK cells and that IL-2-activated NK cells possess additional pathways of specific stimulation.

Murine natural killer cells are fungicidal to Cryptococcus neoformans

Murine natural killer (NK) cells have been shown to bind to and inhibit the growth of Cryptococcus neoformans in vitro and to contribute to clearance of the organism in vivo. However, it is unclear whether NK cells actually kill cryptococci or simply inhibit proliferation of the fungal target. Therefore, the studies presented here were designed to determine whether NK cells are fungicidal to C. neoformans targets. C. neoformans viability was determined on the basis of the metabolic function of two different enzyme systems, as measured by the two vital stains MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] and fluorescein diacetate. Cryptococcal viability, as determined by vital stains, was compared with cryptococcal proliferation, as measured by microcolony formation in agarose at the individual cell level and by CFU counts or extinction dilution analysis in the total cell suspension. Initial comparisons of the vital stains and proliferation assays indicated that these methods effectively distinguished between live and heat-killed cryptococci at the individual cell level and in the total cell suspensions. After cryptococci were incubated with murine NK cells for 18 h, vital stains demonstrated that at the single conjugate level and in the total cell suspension, NK cells kill bound C. neoformans target cells. In addition, the numbers of dead cryptococci in the NK cell-C. neoformans suspensions as determined by the vital stains were comparable to the numbers of cryptococci that were unable to proliferate. Kinetics of NK cell-mediated C. neoformans binding and killing at the single conjugate level and in the total cell suspension were assessed by MTT staining at 2-h intervals after mixing effector and target cells, and the data support the concept that NK cell-C. neoformans binding precedes cryptococcal death. Furthermore, unbound, dead fungal cells were observed in the NK cell-C. neoformans suspensions after 18 h, suggesting that NK cell-C. neoformans interactions may involve both effector cell recycling and killing of unbound cryptococci by soluble cytotoxic factors. In conclusion, the results of these studies firmly establish that NK cells kill C. neoformans.

Binding interactions of murine natural killer cells with the fungal target Cryptococcus neoformans

Murine natural killer (NK) cells have been shown to inhibit the growth of the yeastlike organism Cryptococcus neoformans both in vivo and in vitro. An essential first step in NK cell-mediated damage of cryptococcal cells is the binding of the NK cell to the cryptococcal cell. The studies presented here focused on the binding event. Electron photomicrographs and three-dimensional reconstructions of NK cell-C. neoformans conjugates show that NK cells bind to cryptococci through many microvilli. This is in contrast to the broad membrane-membrane interactions which form the binding site of NK cell-YAC-1 tumor cell conjugates. NK cell binding to cryptococci is much slower than NK cell binding to YAC-1 targets. Maximal conjugate formation with cryptococcal targets is reached after 2 h, whereas maximal conjugate formation with YAC-1 targets is obtained after 20 min. Once maximum NK cell-C, neoformans conjugate formation is obtained, another 4 h is required before damage to the cryptococcal cells can be detected with the CFU assay. These data indicate that the binding and action of NK cells on C. neoformans cells requires considerably more time than is necessary for similar events to occur in the NK cell-tumor cell model. NK cell membrane integrity is necessary for NK cells to bind to tumor targets, since some disruption of membrane integrity with 0.1 M dimethyl sulfoxide reduces conjugate formation and tumor cell lysis. In contrast, 0.1 M dimethyl sulfoxide did not diminish NK cell binding to cryptococcal targets; however, it significantly reduced cryptococcal growth inhibition. Although we have observed several differences in NK cell binding to the cryptococcal target compared with NK cell binding to tumor cell targets, there are some similarities in binding interactions of NK cells with the two different targets. Disulfide bonding appears to play a role in the binding of NK cells to both targets, since 5 mM 2-mercaptoethanol, a reagent that reduces disulfide bonds, prevented NK cells from binding to the tumor targets as well as the cryptococcal targets. Actin filaments, components of the cytoskeletal network, must be intact for NK cells to bind to YAC-1 cells or cryptococci. Taken together, our data confirm that binding of NK cells to the cryptococcal target is prerequisite to the stages that result in damage to the cryptococcal cell and that there are similarities and differences in NK cell-binding interactions with structurally different target cells.

Responses of murine natural killer cells to binding of the fungal target Cryptococcus neoformans

Natural killer (NK) cells bind to and inhibit the growth of the fungal target Cryptococcus neoformans. Since C. neoformans is structurally and chemically distinct from the standard tumor cell target used in the model of NK cell-mediated cytotoxicity, this study was designed to investigate the NK cell response after binding to cryptococci. Transmission electron micrographs and three-dimensional reconstructions of NK cell-cryptococci conjugates demonstrated focusing of the NK cell centrioles and Golgi apparatus toward the cryptococcal attachment site. NK cell cytoskeletal changes after cryptococcal binding were confirmed by immunofluorescence studies in which NK cells were allowed to bind to cryptococci in Mg2(+)-containing, Ca2(+)-free medium. One hour after the addition of Ca2+ to the preformed conjugates, the bound NK cells demonstrated a significant increase in the percentage of microtubule organizing centers focused toward the cryptococcal binding site. Colchicine, a drug that inhibits microtubule assembly, did not affect NK cell-cryptococci binding but abrogated NK cell-mediated cryptococcal growth inhibition, indicating that microtubule assembly, an important prerequisite for the secretory process, is not required for NK cell-cryptococci binding but is essential for inhibition of cryptococcal growth. In addition, the Ca2+ channel-blocking reagents, lidocaine and verapamil, did not affect NK cell-cryptococci binding but blocked the NK cell-mediated anticryptococcal activity, suggesting that a Ca2+ flux is essential for inhibition of cryptococcal growth. Considered together, these data indicate that NK cells respond to binding of a target cell that has a capsule and cell wall, in addition to a cell membrane, in a manner similar to that seen following binding to target cells that are surrounded by only a cell membrane; however, the response of the NK cells to the binding of C. neoformans is slower and possibly less efficient than the response after tumor cell binding.

Identification of murine natural killer cell subsets with monoclonal antibodies derived from 129 anti-C57BL/6 immune spleen cells

Two hybridomas producing monoclonal antibodies reactive with natural killer cells were selected after fusion of 129 anti-C57BL/6 immune spleen cells with P3X63-Ag8.653 myeloma cells. Treatment of normal or stimulated cells with the 4LO3311 or the 4LO439 mAb and rabbit complement inhibited natural killer and antibody-dependent cellular cytotoxicities, whereas cell lysis mediated by natural cytotoxic cells, cytotoxic T lymphocytes, or activated macrophages was unaffected. Lymphokine-activated killer activity was reduced after complement-mediated treatment of interleukin-2-stimulated spleen cells with the 4LO3311 mAb but not after treatment with the 4LO439 mAb. Similar treatment of spleen cells with either mAb had no effect on the mitogen-induced proliferation of T and B lymphocytes and did not alter the frequency of antibody plaque-forming cells in immune spleen cell suspensions. The 4LO3311 and 4LO439 mAbs thus appear to be specific for NK cells and their progeny. Flow cytometry analysis confirmed that 4LO3311 + and 4LO439 + cells are phenotypically identical to NK-1.1 + cells. The epitope recognized by the 4LO3311 mAb has the same strain distribution as the NK-2.1 alloantigen previously detected with NZB anti-BALB/c antiserum, whereas the 4LO439 mAb appears to identify a new NK cell marker exclusively expressed in mice of C57BL lineage. The relationship of the molecules detected with either the 4LO3311 or the 4LO439 mAb to polymorphic antigens of the Ly series is discussed.

Demonstration of YAC target cell lysis by murine granulated metrial gland cells

Granulated metrial gland (GMG) cells are a consistently observed but poorly understood feature of the murine uterus during successful pregnancy. From morphological studies and antibody phenotyping it has been suggested that GMG cells may be members of the natural killer (NK) cell lineage. However, lysis of murine NK cell targets by GMG cells has not been observed although lysis of freshly dissociated trophoblast cells by GMG cells has been recorded using time-lapse video. We failed to demonstrate significant interactions between migrating GMG cells, collected from explant cultures under previously reported culture conditions, and YAC target cells. However, YAC cell lysis did occur if hrIL-2 was present throughout the periods of explant culture and lysis assay. Furthermore, lysis was enhanced if the pregnant females were treated with the interferon inducer poly I.C. 24 hr before metrial gland collection. GMG cells expressed perforin and serine protease mRNA. Consistent with the lysis experiments, expression of these genes was enhanced when the cells were incubated with hrIL-2. Our data provide further support for a relationship between GMG cells and NK cells, but do not establish a relationship of identity since hrIL-2, a growth factor sufficient for the culture of NK cells, cannot support growth or prolong survival Of GMG Cells.

RIL-4 differentially regulates rIL-2-induced murine NK and LAK killing in CD8+ and CD8−precursor cell subsets

Interleukin 4 (IL-4) and IL-2 have complementary or synergistic roles in many aspects of lymphocyte development. IL-2 supports the induction of cytolytic activity in cytotoxic T lymphocyte (CTL), natural killer (NK), and lymphokine-activated killer (LAK) cells. IL-4 has also been shown to support CTL and LAK in primary murine spleen cell culture. This report demonstrates that IL-4 selectively down-regulates IL-2 inducible murine CD8- precursors of NK cells. For maximal regulatory effect it is necessary to add IL-4 to cultures before 40 h. Enrichment for NK1.1+ cells failed to recover precursor cells which are down-regulated in overnight cultures or can be cultivated in vitro to yield NK cytolytic activity. Furthermore, phenotypic analysis of effector cells demonstrated a marked inhibition of development of NK1.1+ cells in cultures containing IL-4 plus IL-2 versus IL-2 alone. Thus, it appears that IL-4 down-regulates the precursors of murine NK cells by inhibiting proliferation and/or development. In addition, we show that IL-2-induced murine LAK activity mediated by CD8- precursor cells is unaffected by IL-4, while CD8(+)-derived LAK cells are up-regulated by co-culture with IL-4 and IL-2. Analysis of these data relative to reports documenting down-regulation of human LAK by IL-4 suggests that in vitro cultured, IL-2-activated murine NK cells are the correlates to what are commonly described as human LAK cells. The discrepancy may stem from differences in the characteristics of target cells used in the murine versus the human systems. These results clarify the conflicting reports on the effect of IL-4 on killing activity.

Effects of marijuana on human natural killer cell activity.

Marijuana and its major psychoactive component delta-9-tetrahydrocannabinol (THC) were first reported to depress various immune functions in humans as early as the mid 1970’s. (Reviewed in 1). However, these studies yielded conflicting data necessitating further investigations. Recent studies by Friedman and co-workers confirmed the immune suppressive effects of THC in mice using in vivo and in vitro experimental models (2–5). Klein et al. (6) reported depression of murine natural killer (NK) cell function in mice following in vitro exposure to THC while Patel et al. (7) demonstrated inhibition of rat NK cell cytotoxicity. A re-examination of responses of human peripheral blood mononuclear cells (PBMC) following exposure to THC in vitro indicates that lymphocyte blastogenesis (8), monocyte/macrophage spreading on plastic surfaces and phagocytosis (1) and NK cell activity (9,10) all are diminished in the presence of the drug.

Growth of murine natural killer cells from bone marrow in vitro: Role of TNFα and IFNγ

It has been previously shown that natural killer (NK) cell growth can be induced by interleukin-2 (IL-2) in bone marrow (BM) cultures and that other cytokines (CKs), including IL-1α, act synergistically with IL-2. However, as the effect of IL-2 and IL-1α could be due to direct stimulation of NK progenitor cell growth, as well as to the induction of other factors, we analysed the role of the endogenous production of CKs in BM cultures. Results show that mRNAs specific for tumour necrosis factor-α (TNFα) and interferongamma (INFγ) are detectable within hours in BM cultures supplemented with IL-2 and IL-1α, and that the amount is higher when both IL-2 and IL-1α are present. Antibodies directed against TNFα and IFNγ abrogate the NK cell development, indicating that these CKs play an essential role. The antibodies, however, had no effect on mature NK cells. Furthermore, pretreatment of BM cells with TNFα or IFNγ before culturing with IL-2, enhances IL-2 responsiveness and NK cell growth. These results suggest that induction of cytokines production may be important for growth of NK cells from BM precursors and that the synergistic effect of IL-1α could be due, at least in part, to increased TNFα and IFNγ production.

Activated murine natural killer cells control growth of mycobacterium lepraemurium in mouse macrophages; In vitro and in vivo evidence

The role of natural killer cells (NK) in murine leprosy was investigated in vivo and in vitro. In a first set of experiments, it was found that IL-2 (interleukin-2) activated NK cells reduced Mycobacterium lepraemurium (MLM) growth in mouse C57BL6/J peritoneal macrophages which had phagocytosed low numbers (MOI of 10 : 1) of MLM ( P<0.0001 at day 20). There was no cytotoxicity exerted by the NK cells against the infected cells in these conditions. Conversely, macrophages heavily infected with MLM (multiplicity of infection of 1000 : 1) were found to be susceptible to lysis by activated NK cells in vitro. In vivo, progressing murine leprosy was associated with a sharp increase in splenic NK cell activity, which was abrogated by treatment with a monoclonal antibody against NK cells. Administration of this monoclonal antibody against NK cells enhanced C57BL6/J mouse susceptibility to mouse leprosy, as seen by a decrease in survival time of mice infected with 10 7 MLM i.v. (81 days vs 110 days, P<0.0005). Overall, these findings suggest that NK cells may play an important role in resistance to leprosy, either by reducing MLM growth in macrophages or by lysing heavily infected macrophages.

Imexon and biological response modifiers in murine models of aids

The Rauscher murine leukemia retrovirus system provides an in vivo model of the human acquired immune deficiency syndrome for testing the ability of antiviral agents and biological response modifiers (BRM) to suppress viremia and retroviral disease. In the present report we examined three agents in the Rauscher retrovirus model: imexon, Ampligen and poly[I,C]-LC. Imexon reduced splenomegaly, viremia, and serum reverse transcriptase levels even when treatment was not initiated until 7 days after virus infection. Imexon also significantly prolonged the survival of infected mice. Thus it proved to be an effective antiviral agent in this system, although imexon did not completely eliminate retroviral infection in treated mice. Poly[I,C]-LC and Ampligen had immunomodulatory effects. Both of these BRM augmented the cytolytic activity of splenic natural killer (NK) cells in infected animals when treatment was initiated 24 h after infection. Poly[I,C]-LC had antiretroviral activity when administered on this schedule. In order to examine the role of NK cell augmentation in the antiviral activity of poly[I,C]-LC, we attempted to deplete NK activity by treatment with rabbit antibody to asialo GM 1, a ganglioside on the surface of murine NK cells. Combined treatment of infected mice with poly[I,C]-LC and anti-asialo GM 1 decreased the antiviral activity of poly[I,C]-LC. This finding suggests that NK cells may be involved in the antiviral effect of this BRM.

Characterization of Macrophage Subsets Regulating Murine Natural Killer Cell Activity

We examined the relationship of I-A expression by normal murine macrophages to their immunoregulatory role on natural killer cell activity. Macrophages were isolated on the basis of plastic adherence; characterized on the basis of conventional markers such as phagocytic ability, cytoplasmic non-specific esterase activity, surface MAC-1 and F4/80 antigen expression; and then used for functional studies relative to their expression of surface I-A. Two functional macrophage subsets were identified: NK-stimulatory and NK-suppressive subsets. The former function was associated with splenic macrophages, which were predominantly I-A+ as identified with a radioautographic immunolabeling technique; the latter function with peritoneal macrophages which were predominantly I-A-. Loss of macrophage I-A expression in vitro was delayed in the presence of indomethacin and enhanced in the presence of PGE2, indicating that PGE2 down-regulates I-A expression on macrophages. The NK stimulatory function of I-A+ macrophages was attributable to a soluble mediator, identified as IFN-gamma, since the stimulatory ability was abrogated with an anti-IFN-gamma antibody. I-A expression appears to be important for the stimulatory function, since some interference with this function was noted in the presence of anti-I-A antibody. The NK-suppressor function of I-A- macrophages was attributable to the soluble mediator PGE2, since this function was abrogated with indomethacin or anti-PGE2 antibody. These results are relevant to the understanding of normal in vivo immunoregulation by macrophages.

Exercise Stress and Murine Natural Killer Cell Function

Male C3He mice were trained to run on a treadmill (final speed, slope, and duration of 30 m/min, 8 degrees, 30 min/day, 5 days/week, respectively) for 10 weeks or they remained sedentary. At the end of the training program, half of the mice were sacrificed and half were given a single bout of exercise to exhaustion (50% stepwise increases in final running speed for 2-min intervals). Splenic catecholamine concentrations, splenic natural killer cell cytolytic activity against YAC-1 tumor targets, and frequency of asialo GM1 (a murine natural killer cell surface glycolipid)-positive splenocytes were assessed. Exhaustive exercise in both trained and untrained mice reduced the in vitro killing of tumor targets by splenic natural killer cells relative to killing by splenocytes from mice which did not undergo the acute exercise bout (P less than 0.05). The frequency of asialo GM1-positive splenocytes was also reduced in the exhaustively exercised animals (P less than 0.05). Training alone, without the additional stress of exhaustive exercise, reduced the frequency of asialo GM1-positive splenocytes relative to a sedentary condition (P less than 0.05), but did not compromise natural killer cell cytolytic activity against the tumor targets. Splenic epinephrine concentrations in the exhaustively exercised animals were elevated 3- to 5-fold above the concentrations observed in trained and sedentary mice. These results suggest that a single, acute exercise bout reduces the capacity of splenic natural killer cells to kill tumor targets in vitro and that training enhances splenic natural killer cell cytolytic activity, on a per cell basis, against tumor targets.

Suppression of murine natural killer cell activity by tributyltin: In vivo and in vitro assessment

The effects of tributyltin chloride (TBTCl) and inorganic tin (IT) on murine natural killer (NK) cell activity were tested in vivo and in vitro. In vivo studies demonstrated that mice fed with TBT (10 and 100 ppm) daily for 1 week exhibited suppression in NK activity 38-46% at effector:target (E:T) ratio = 50:1 compared to control mice. On the other hand, animals treated with inorganic tin showed no change in activity of NK cells. In vitro studies showed leukocytes, preincubated with TBTCl (0.01-0.1 ppm) at room temperature for 1 h and then washed three times, demonstrated significant suppression in NK activity (41 and 85%) at concentrations 0.01 and 0.05 ppm, respectively. Increasing the dose to 0.1 ppm, resulted in complete inhibition of the activity of NK cells. In contrast, IT had no effect on NK activity in vitro at the same concentrations of TBTCl. The effect of TBTCl appears to be due to interference with the binding capacity of effector cells, a necessary prerequisite for target cell lysis. In conclusion, TBTCl proved to be a very potent inhibitor of NK activity; this inhibition may predispose animals to malignancy, which is a characteristic feature reported recently for some TBT compounds.

Corticotropin‐releasing Hormone Enhances Murine Natural Killer Cell Activity through an Opioid‐Mediated Pathway

Corticotropin‐releasing Hormone Enhances Murine Natural Killer Cell Activity through an Opioid‐Mediated Pathway