Reduced Natural Killer Activity Research Articles

Natural cytotoxicity of murine cytomegalovirus-infected cells mediated by mouse lymphoid cells: role of interferon in the endogenous natural cytotoxicity reaction.

Lymphoid cells from unstimulated normal C57BL/6J mice were shown to lyse murine cytomegalovirus (MCMV)-infected syngeneic mouse embryo fibroblasts but not uninfected mouse embryo fibroblasts. This cytotoxicity by mouse effector cells was not restricted to MCMV-infected syngeneic cells since MCMV-infected xenogeneic rat heart fibroblasts were also lysed. Characterization of the effector cells mediating this cytotoxicity against MCMV-infected cells indicated that the effector cells are similar to described natural killer (NK) cells mediating lysis of tumor cells and virus-infected cells. Because of the described augmentation of NK activity by interferon, we examined the role of interferon in the NK reaction. Although low levels of virus-induced interferon were detectable in supernatants of MCMV-infected mouse embryo fibroblasts, no interferon was detectable in supernatants of MCMV-infected rat heart fibroblasts, a target significantly more sensitive to NK cytolysis than infected mouse embryo fibroblasts. We were able to augment the NK reaction against MCMV-infected cells by in vitro treatments with interferon. However, the amounts of interferon required for augmentation were significantly greater than the amounts generated by infected target cells. In vitro interferon-stimulated NK cells retained selective cytotoxic activity since they continued to remain incapable of lysing uninfected target cells. MCMV-infected rat heart fibroblasts induced more interferon and were also more susceptible to NK activity than MCMV-infected mouse embryo fibroblasts. In spite of this difference in interferon-inducing capacity, there was no augmentation of cytotoxicity of MCMV-infected mouse embryo fibroblasts when mouse splenocytes were cocultivated with both target cells. Finally, when production of interferon in the NK reaction was inhibited by the addition of actinomycin D, no reduction of NK activity was seen. Our findings suggest that native mouse NK cells can discriminate between MCMV-infected cells and uninfected cells, this ability leading to the selective lysis of the virus-infected cells. Furthermore, although we could demonstrate augmentation of NK activity by interferon, interferon activation of NK cells may not be a necessary precondition for the development of endogenous NK activity.

In vivo effects of anti-asialo GM1. I. Reduction of NK activity and enhancement of transplanted tumor growth in nude mice.

Intravenous injection of anti-asialo GM1, which has been shown to eliminate natural killer (NK) activity in vitro in the presence of complement, completely abolished NK activity against lymphoma cell line (YAC-1) in spleen cells from athymic nude mice as well as from conventional mice. An immunofluorescence study revealed a decreased number of asialo GM1 positive cells in the spleens of mice injected with anti-asialo GM1 than in those of mice injected with normal rabbit serum. In the nude mice with reduced NK activity, incidence of tumor take and the growth were enhanced when syngeneic (RL male-1), and allogeneic (YAC-1) tumors and human tumors were transplanted subcutaneously. These results strongly suggest that NK cells play an important role in transplanted-tumor growth in vivo.

Natural cytotoxicity in rheumatoid arthritis and systemic lupus erythematosus

Natural killer (NK) activity was investigated in 23 patients with rheumatoid arthritis (RA) and 7 patients with systemic lupus erythematosus (SLE). Killing of K-562 target cells by the peripheral blood lymphocytes of 7 patients with inactive RA did not differ from that observed in 18 controls. However, 16 patients with active RA and all patients with SLE exhibited impaired natural cytotoxicity. A strong correlation existed between reduced NK activity and elevated erythrocyte sedimentation rate but no correlations were observed with total peripheral blood lymphocyte counts, or total T, or Fcγ-receptor-positive lymphoid subpopulations. Impaired NK activity also correlated with elevated concentrations of circulating immune complexes in SLE, but not in RA. The contribution of circulating humoral factors to the observed decreases in natural cytotoxicity was analyzed by the addition of sera from different sources to normal lymphocytes either throughout the NK cell assay or by preincubation with the lymphocytes prior to the actual test. Little or no effect was observed with normal serum, with serum from patients with acquired hypogammaglobulinemia, or with serum from patients with RA. In contrast, SLE serum strongly inhibited NK activity at 37°C even when lymphocytes were simply pretreated and then throughly washed before the assay. The consequences of defective NK activity are largely unknown but may be associated with, although not necessarily a cause of, the enhanced rate of malignancy noted in SLE and RA.

Induction and characterization of splenic suppressor cells directed to natural killer cells in Japanese quails.

Intravenous inoculation of chicken amniotic fluid (ChAmF) markedly reduced natural killer (NK) cell activity of spleen cells from Japanese quails. The reduction of NK activity was mediated by non-adherent thymus-dependent lymphoid cells which were resistant to treatment with anti-immunoglobulin serum and sensitive to treatment with anti-thymocyte serum in the presence of complement. The suppressing activity was selectively directed to NK cells, since Rous sarcoma virus-specific cytotoxicity or hemagglutinating antibody production against sheep erythrocytes was not suppressed in ChAmF-treated quails. Spleen cells from normal 1-week-old quails had similar characteristics to those from ChAmF-treated 4-week-old quails, lacking NK activity and exhibiting suppressive effect on NK activity, and were also shown to be thymus-dependent. Biological significance of the presence of NK cells and their suppressor cells is discussed in relation to embryonic development and tumor-surveillance mechanism.

Natural cell mediated cytotoxicity in autoimmune diseases

The significantly reduced natural killer (NK) cell activity was demonstrated in the peripheral blood lymphocytes (PBL) from 20 female patients with systemic lupus erythematosus (SLE) when compared with NK activity in the age- and sex-matched controls. The reduced NK activity did not correlate with clinical parameters including daily prednisolone doses, serum CH50, antinuclear antibody titers, anti DNA activities, circulating immune complex levels and cytotoxic activities of antilymphocyte antibodies (ALA). The effects of prednisolone and aggre-gated human IgG on NK activity were only slightly suppessive in the in vitro studies. When normal PBL were pretreated with rabbit complement and SLE sera containing ALA, the NK activity of the surving cells was markedly decreased. The decrease was specific and did not seem to be due to physical hindrance of the dead cells. Other heterologous ALA of rabbit origin did not exert a suppressive effect on NK activity. These results suggest that the suppressed NK activity in SLE may possibly be ascribed to an anti NK cell specific antibody in lupus sera although the participation of circulating immune complexes was not completely excluded.

Natural cell mediated cytotoxicity in systemic lupus erythematosus: suppression by antilymphocyte antibody.

The significantly reduced natural killer (NK) cell activity was demonstrated in the peripheral blood lymphocytes (PBL) from 20 female patients with systemic lupus erythematosus (SLE) when compared with NK activity in the age- and sex-matched controls. The reduced NK activity did not correlate with clinical parameters including daily prednisolone doses, serum CH50, antinuclear antibody titers, and antiDNA activities, circulating immune complex levels, and cytotoxic activities of antilymphocyte antibodies (ALA). The effects of prednisolone and aggregated human IgG on NK activity were only slightly suppressive in the in vitro studies. When normal PBL were pretreated with rabbit complement and SLE sera containing ALA, the NK activity of the surviving cells was markedly decreased. The decrease was specific and did not seem to be due to the physical hindrance of the dead cells. Other heterologous ALA of rabbit origin did not exert a suppressive effect on NK activity. These results suggest that the suppressed NK activity in SLE can be ascribed to an antiNK cell specific antibody in lupus sera, although the participation of circulating immune complexes was not completely excluded.

Natural killer activity of human lymphocytes against colon cancer cells

A human colon cancer cell line, HCT-8, is shown to be an appropriate target cell for study of natural killer (NK) activity in man. In parallel experiments, effector cell characteristics for NK and antibody-dependent cellular cytotoxicity (ADCC) were found to be vested in a single lymphocyte subpopulation, which bore receptors for the Fc fragment of IgG, but lacked other surface receptors. The effector cell failed to adhere to glass and was inactivated by exposure to 3500 rod x-irradiation. Cells forming rosettes with SRBC and cells bearing receptors for complement were inactive in both systems. A wide distribution of NK activity was noted among individuals that correlated with the distribution of effector cell activity in ADCC (r = 0.8). Preincubation of NK effector cells with antibody-coated ADCC target cells markedly reduced NK activity. Neuraminidase treatment of effector cells led to increased NK and diminished ADCC, while trypsin treatment led to reduced NK activity and showed no effect on ADCC. Thus, NK and ADCC effector cells are highly overlapping if not identical populations, but different structures on the cell membrane may mediate the two activities.

Activation of mouse macrophages by pyran copolymer and role in augmentation of natural killer activity

Inoculation of mice with pyran copolymer resulted in activation of natural killer (NK) cells as well as macrophages. Conditions optimal for the boosting of NK activity seemed to differ from those optimal for macrophage activation as assessed by cytostasis of tumor target cells. Peak levels of macrophage cytostatic reactivity were found at about 7 days after drug injection and were only achieved by the highest doses of pyran tested. Macrophage activation was consistently higher in the peritoneal cavity than in the spleen, regardless of route of administration, in contrast to the failure of i.v. pyran to induce high NK reactivity in peritoneal exudate cells. At 2-3 days after pyran treatment of older mice, NK augmentation reached peak levels, but only minimal macrophage activation was found. Despite these differences, macrophages played a role in regulating NK activity in pyran-treated mice. Functional macrophages appeared to be required for augmentation of NK activity by pyran, since boosting was impaired by prior in vivo inoculation of silica. Macrophages also appeared able to inhibit NK activity. In younger mice that exhibited high spontaneous levels of NK activity, pyran treatment produced a substantial reduction in NK activity to levels below those of untreated mice. This depression coincided with the time of peak levels of macrophage cytostasis. Furthermore, removal of adherent cells from the spleen cells of these pyran-treated mice resulted in levels of NK activity almost as high as those of untreated mice. The possibility that the depression of NK activity in young mice by pyran copolymer is due to suppressor cells is discussed.

Correlation Between Natural and Antibody-Dependent Cell-Mediated Cytotoxicity Against Tumor Targets in the Mouse. II. Characterization of the Effector Cells

Direct comparison of the effector cells mediating natural killer (NK) activity against mouse tumor cells and antibody-dependent cell-mediated cytotoxicity (ADCC) against mouse tumor target cells coated with alloantisera indicated that NK cells and K-cells (effector cells mediating ADCC) may belong to the same subpopulation of lymphocytes, but they have a different mechanism of killing. Effector cells mediating NK activity and ADCC were nonadherent, nonphagocytic Fc receptor-bearing cells that sediment at 3.5-4.5 mm/hour. Treatment with anti-Thy 1.2 serum in the absence of complement resulted in an increase of NK activity, whereas this treatment caused a substantial loss in ADCC. Both NK activity and ADCC were equally sensitive to the in vivo or in vitro effects of X-irridiation. In vivo inoculations of high doses of hydrocortisone resulted in a reduction of NK activity, but ADCC was not affected. NK cells were trypsin-sensitive, with a profound decrease in the cytolytic activity being observed in a 4-hour 51Cr release assay. The activity, however, could be recovered after overnight incubation at 37 degrees C. Trypsin treatment did not inhibit ADCC as measured by the 18-hour assay.