Natural killer (NK) cell cytotoxicity in athymic (nude) rats

The in vitro and in vivo natural killer (NK) cell activity of congenitally athymic, nude (ATH) rats and of normal, euthymic (EUTH) rats was compared. We found: a) a higher level of in vitro NK cell activity in blood, spleen and lymph nodes of ATH rats compared with their heterozygous littermates, b) in the spleen the number of NK lytic units per organ was not higher in ATH compared with EUTH whereas it was significantly higher in lymph nodes, c) a lack of age-dependence of in vitro NK cell activity tested in culture with heat inactivated fetal calf serum, d) a higher rate of in vivo elimination of target tumor cells in 4-week ATH rats compared with EUTH rats, e) an age-dependent decrease in the rate of in vivo target cell elimination in both groups, and finally, f) an age-dependent increase in the inhibitory effect of autologous serum on NK cell activity in vitro in both groups. These findings show that the blood and lymphoid organs of athymic rats contain a substantially higher proportion of NK cells, active both in vitro and in vivo against K562 tumor cells, than their euthymic littermates. In the spleen this increased proportion can be attributed to the lack of T cells, whereas in the ATH rat lymph nodes there is an absolute increase in NK cell activity, and that the decrease of cytotoxicity in vivo with age reflects the increasing inhibitory properties of autologous serum both in nude and in normal rats.     

Natural killer cell activity in the rat. VI. Characterization of rat large granular lymphocytes as effector cells in natural killer and antibody-dependent cellular cytotoxic activities

The present study examined rat natural killer (NK) cells, which mediate not only NK activity but also antibody-dependent cellular cytotoxicity (ADCC). NK and ADCC activities were compared with regard to organ distribution, strain distribution, Percoll fractionation of the effector cells, effects of aging, and potential to be augmented by biological response modifiers (BRM). Like NK activity, appreciable ADCC activity was observed in peripheral blood leukocytes (PBL), splenic leukocytes (SPL), and peritoneal exudate cells (PEC), but not in cell preparations from the peripheral lymph nodes (PLN), mesenteric lymph nodes (MLN), bone marrow (BM), and thymus (THY). ADCC activity, when compared with NK activity, was significantly higher in PBL but the same or lower in SPL and PEC. In terms of strain distribution, a high NK/ADCC strain (rnu/rnu), four intermediate NK and high ADCC strains (PVG/RTLRL, Lewis, PVG/OLA, and F344), an intermediate NK/ADCC strain (WF/N), and a low NK/ADCC strain (Buffalo) were observed. Fractionation of effector cells on discontinuous Percoll gradients revealed that both NK and ADCC activities were associated with relatively high-density large granular lymphocytes (LGL). In contrast, ADCC but little or no NK activity was associated with lower density LGL. However, the NK activity of this lower-density LGL population could be elicited following the in vitro incubation with a number of BRM, including rat interferon (IFN) and OK-432, but not rat interleukin-2 (IL-2). In general, the ADCC activity of both higher and lower density LGL-enriched cell populations correlated with both the frequency of FC gamma R+ LGL and the percentage of LGL binders to antibody-coated P815 target cells. The present study also has shown that in contrast to NK activity, which remained relatively stable with age, ADCC activity from F344 but not WF/N rats increased until 30-50 wk of age. This increase of ADCC activity in older F344 rats was accompanied by an increase in the percentage and absolute number of lower density FC gamma R+ LGL. This study demonstrates a number of similarities and differences between NK and ADCC activities in the rat. These findings should be useful for further examining and comparing the in vivo development and biological role of these two effector arms of the immune system.     

Natural cytotoxicity in the guinea-pig: the natural killer (NK) cell activity of the Kurloff cell.

Natural killer (NK) cell activity was found in the various lymphoid compartments of the normal guinea-pig, prominent in the spleen and absent in the thymus. Oestrogen treatment, which increased the Kurloff cell population in blood, spleen and thymus, did not alter NK cell activity in blood and spleen but markedly augmented the lytic capacity of the thymus. Rosetting reactions and selective depletion studies in normal and oestrogen-treated animals revealed the NK cells to belong to a small population of E+ Kurloff cells, some of which were Fc+ and others apparently Fc-. Some of these natural killer cells in the spleen also had receptors for C3 and carried Ig (probably cytophilic). In the lymph nodes, however, the NK cells were found to be E+ lymphocytes, again some of which were Fc+ and others Fc-.     

Regulation of natural killer cell activity and interferon production in the rat lung following aerosol challenge

High levels of natural cytotoxicity were detected in vitro in cells from the lung interstitium of the rat following collagenase digestion of lung tissue. In contrast, alveolar cells exhibited negligible levels of natural cytotoxicity and furthermore suppressed the natural cytotoxicity of interstitial lung leukocytes. This suppression was alleviated following in vivo administration of indomethacin. The natural cytotoxicity of cells from both the lung and spleen was transiently suppressed following exposure of normal rats to aerosols of Escherichia coli lipopolysaccharide or of ovalbumin-sensitized rats to an ovalbumin aerosol. Parenchymal lung leukocytes, like those from the spleen and peripheral blood, showed enhanced cytotoxicity when treated with interferon in vitro. In addition interstitial leukocytes were capable of producing interferon when cocultured with P815 cells and, as was the case with the spleen, low density cells produced the most interferon. However, alveolar cells did not produce interferon in this system. These studies suggest that the lung is capable of self-regulation of the high levels of natural cytotoxicity present in interstitial tissue; alveolar cells or their products may suppress interstitial natural killer cells whilst interstitial leukocytes have the capacity to stimulate natural killer cells by producing interferon.     

Natural killer cell function and interferon generation in patients with primary immunodeficiencies

Patients with primary immunodeficiency disorders were evaluated for three aspects of natural defense: natural killer (NK) cells which lyse HSV-infected fibroblasts [NK(HSV-FS)], NK cells which lyse K562 tumor targets [NK(K562)], and interferon-alpha generation. In addition, capacity to make interferon upon challenge with other commonly used inducers was also evaluated. Most patients with severe combined immunodeficiency disease (SCID) and deficits of both T- and B-cell function demonstrated normal NK function with one or both targets. Six of eight SCID patients generated interferon-alpha at or below the lower limit of normal while only two made clearly normal levels. Six of 10 patients with Wiskott-Aldrich syndrome (WAS) had normal NK(K562) and five of 10 generated normal levels of interferon-alpha but all had severely deficient NK(HSV-FS). Patients with Bruton's agammaglobulinemia demonstrated normal NK and interferon generation, as did patients with common variable immunodeficiency, even when subdivided into patients with T-cell proliferative deficiencies and those with only hypogammaglobulinemia. Natural defense parameters may help categorize patients with SCID and WAS and help define these heterogeneous diseases.     

Natural killer cell activity in chickens: target cell analysis and effect of antithymocyte serum on effector cells.

A battery of lymphoid and nonlymphoid cells was examined for susceptibility to lysis by natural killer cells of chickens. Several susceptible targets were recognized, and most susceptible among these were cells of line LSCC-RP9, derived from a lymphoid tumor induced by Rous-associated virus 2. The natural killer reactivity against LSCC-RP9 target cells did not appear to be directed against an antigen(s) induced by Rous-associated virus 2 because other lymphoid and nonlymphoid cells infected with this were resistant to lysis in vitro by natural killer cells. The effector cells of natural killer reactivity in chickens were refractory to treatment with potent anti-T-cell and anti-B-cell sera. Inoculation of Marek's disease virus in line 15 X 7 chickens resulted in enhanced natural killer cell activity, and the effector cells of this enhanced activity, and the effector cells of this enhanced activity were also resistant to anti-T-cell serum.     

Natural killer cell activity in asthma.

Peripheral blood natural killer (NK) activity was analysed from 32 asthma patients and 13 control donors. Male patients and female patients with atopic asthma had significantly stronger NK activity against the leukaemic cell line K-562. Fractionation of patient mononuclear cells by discontinuous density gradient centrifugation suggested that large granular lymphocytes (LGL) were the main mediators of the NK activity in asthmatics. Based on the lytic unit calculations, the strong NK activity in asthmatics is mainly due to increased frequency of LGL in peripheral blood rather than activity of individual NK cells.     

Regulation of human natural killer cell activity by an interferon inhibitor

Laboratory of Immunochemistry and Department of Interferons, N. F. Gamaleya Research Institute of Epidemiology and Microbiology, Academy of Medical Sciences of the USSR, Moscow. Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 112, No. 10, pp. 395–397, October, 1991.     

Conditioned increase of natural killer cell activity (NKCA) in humans.

Cumulating evidence suggests that immune parameters can be modified by behavioral conditioning processes in animals. The present results suggest that this also holds true for a human immune parameter. Healthy subjects were exposed to a conditioning procedure in which a neutral sherbet sweet (conditioned stimulus) was repeatedly paired with a subcutaneous injection of 0.2 mg epinephrine (unconditioned stimulus). After epinephrine administration an increase of natural killer (NK) cell activity could be observed (unconditioned response). On the conditioning test day the conditioned group showed increased NK cell activity after reexposure of the sherbet sweet combined with saline injection. No increase was found in control groups that previously received the sherbet sweet in combination with saline (saline control) or with epinephrine in an unpaired manner (unpaired control). This study supports previous findings of conditioned modulation of immune responses and represents a model to investigate conditioning processes of a human immune function.     

Natural killer cell activity in patients with multiple sclerosis: interferon and plasmapheresis

Peripheral blood lymphocytes from patients with multiple sclerosis (MS) were studied for natural killer (NK) cell activity and reactivity to interferon. NK activity determined at the same time in a 4-hr chromium-51 release assay using K562 target cells was significantly lower in MS patients than in controls. In-vitro treatment of MS lymphocytes with interferon resulted in only a slight increase in NK activity, while NK activity of normal individuals was markedly augmented by interferon. Leukopheresis of MS patients gave a rapid decrease in cytotoxic activity, which returned to pretreatment levels by 24 hrs. These results are consistent with the hypothesis of an immune deficit in multiple sclerosis.     

Natural killer cell function in trisomy-21 (Down''s syndrome)

Natural killer (NK) activity and antibody-dependent cell mediated cytotoxicity (ADCC) against a human myeloid target cell line (K 562) was measured in adult patients with trisomy-21 (Down's syndrome) and in chromosomally normal age and sex matched control subjects. The effect of human leucocyte interferon (IFN-alpha) on the NK activity was also estimated. Spontaneous NK activity was stronger in the adult patients with trisomy-21 than in the healthy controls, but the difference did not reach statistical significance. The augmentation of NK activity by IFN-alpha, measured using lymphocytes not depleted of monocytes as effector cells, was statistically significant in both the trisomic patients (P less than 0.004) and the healthy controls (P less than 0.0005). Using monocyte and macrophage depleted lymphocytes in the patients with trisomy-21 the NK activity proved stronger than in the healthy controls, but not significantly and IFN-alpha did not augment it as it did in the healthy controls (P = n.s., P less than 0.05), for augmentations respectively). These results support the view that monocytes and macrophages are connected with the NK cell system. ADCC correlated with NK activity in both groups. Since NK cells are important components of many immune processes, including tumour and virus and/or bacteria-infected cell elimination, and have regulatory functions in immune reactions, the deficient augmentation of trisomic NK cells shown in vitro with extrinsic human leucocyte interferon may, paradoxically be an explanation for the greater susceptibility of trisomic individuals to lymphatic leukaemia and virus and bacterial infections. In vivo, this could be explained by the more potent secondary suppression by the 'immune' interferon produced by the virus, bacteria and malignant cells. In other words, the potential of the 'fighting couple' of the immune system, NK cell/interferon, is perhaps disturbed genetically due to the chromosome 21.     

Herpetic keratitis in athymic (nude) mice.

The inflammatory response to herpes simplex virus infection of the cornea was studied in athymic nude (nu/nu) and heterozygote (nu/+) BALB/c mice. Although athymic mice were highly susceptible to HSV infection and died 13 to 17 days after corneal inoculation, they failed to develop necrotizing keratitis of the cornea. Heterozygote mice survived the initial virual infection, but many of these mice developed necrotizing keratitis and permanent corneal scarring. Light and electron microscopy showed numerous inflammatory cells (polymorphonuclear leukocytes and lymphocytes) in the corneas of heterozygote mice, but not in the athymic mice. These studies suggest that the immune system plays a dual role in herpes simplex virus infection of the cornea: protection against dissemination of the virus and immunopathogenesis of necrotizing keratitis in the cornea.     

Interleukin 2 enhances natural killer cell activity through induction of gamma interferon

Highly purified interleukin 2 (IL 2), free of interferon activity, enhanced natural killer (NK) cell activity against tumor cells in mouse spleen cell cultures and in human peripheral lymphocyte cultures in a manner similar to that of interferon (IFN). We determined that IL 2 enhanced NK activity indirectly in a cascade manner by the induction of gamma IFN (IFN-gamma) in the cultures, which actually mediated the enhanced killing. Accordingly, lymphocyte cultures treated with IL 2 alone produced 10 to 100 U of IFN per ml in 6 to 24 h of culture. The IFN was typed as IFN-gamma by specific antibodies. Specific antibodies either to natural IFN-gamma or to a synthetic peptide corresponding to the human IFN-gamma N-terminal amino acids, when added to cultures treated with IL 2, completely blocked IL 2 enhancement of NK cell activity for both the mouse and human systems. IL 2-induced proliferation was not affected by the antibodies. Thus, the enhancement of NK cell activity by IL 2 is completely mediated by IL 2-induced IFN-gamma. The findings clearly indicate a cascade effect whereby one lymphokine (IL 2) induces the production of another. The latter lymphokine (IFN-gamma) then mediates an important biological effect (natural killing).     

Decreased natural killer cell activity after prolonged administration of interferon in cancer patients

Two patients with metastatic neoplastic disease received 2-3 X 10(6) IU alpha recombinant interferon (IFN) 3 times/wk, every other week, for 3-6 mth. The natural killer (NK) activity of their peripheral blood leukocytes, was followed during the course of the treatment. A significant decrease was observed in the NK activity, which returned to normal values at the end of IFN administration. The treatment did not modify the evolution of metastasis.     

Enhancement of natural killer cell activity and interferon production by manganese in young mice

The effect that MnCl2 has on murine splenic natural killer (NK) cell activity was investigated in infant (10 days old), pre-weanling (18 days old) and weanling (24 days old) C57BL/6J mice. A single intraperitoneal injection of 10, 20 or 40 micrograms MnCl2/g body weight caused a significant enhancement in NK activity, as determined by the in vitro 51Cr release assay. Comparable enhancement of NK activity was observed for age-matched mice injected intraperitoneally with polyinosinic polycytidylic acid (Poly I:C). Both MnCl2 and Poly I:C caused elevations in serum interferon levels. Time-course studies revealed that interferon levels returned to normal within 48 hours following injection with either MnCl2 or Poly I:C; however enhanced NK activity persisted for up to 48 hours in Poly I:C-injected mice and 72 hours in MnCl2-injected mice. The administration of rabbit anti-asialo GMl to MnCl2-injected mice completely abrogated the enhanced NK activity. In addition, the injection of rabbit anti-mouse interferon alpha, beta but not gamma completely abrogated the enhanced NK activity. In addition, the injection of rabbit anti-mouse interferon alpha, beta but not gamma completely abrogated the enhancement of NK activity by MnCl2 and to a lesser extent the enhancement of NK activity by Poly I:C. These results indicate that despite low levels of NK activity in pre-weanling mice, MnCl2 is capable of enhancing this activity by 8-9 fold. Furthermore, Mn-enhanced NK activity in these young mice appears to be mediated by the production of interferon alpha, beta.     

Modulation of natural killer cell activity in mice after interferon induction: depression of activity and depression of in vitro enhancement by interferon.

Splenic natural killer (NK) cell activity of BALB/c and C3H mice was assayed after administration of the interferon inducers Escherichia coli endotoxin or Newcastle disease virus (NDV). As expected, the NK cell activity rose early in response to the interferon inducers. At 1 to 3 days after an injection of endotoxin, NK activity was hyperesponsive to interferon stimulation. At 5 to 9 days after injection of either endotoxin or NDV, splenic NK activity was depressed, and the spleen cells showed a relative refractoriness to in vitro interferon stimulation. It is postulated that this phenomenon may be related to hyporeactivity, the inability to reinduce interferon after an initial period of interferon production.