Do NK cells play a role in anti-tumor surveillance?

Does the Selenium (SE) Level and Se-Dependent Enzyme Activity in Blood Plasma Correlate with Human Lymphocyte Subpopulations and Function?

Recent literature data on the effects of Se on subpopulations of T lymphocytes, on autologous mixed lymphocyte reaction (AMLR) and on natural killer (NK) cell cytotoxicity are limited or poorly defined. In healthy volunteers we have estimated se levels, glutathione peroxidase (GSH-Px) activity and lipid peroxide levels in human plasma and simultaneously, the subpopulations of T lymphocytes, proliferation in AMLR, and activity of NK cells.

We found a significantly positive correlation between the selenium level and GSH-Px activity. The proliferative response in AMLR significantly correlated with plasma selenium levels but not with GSH-Px activity. NK cytotoxicity, subpopulations of T lymphocytes, and lipid peroxide levels did not correlate with both selenium concentration and GSH-Px activity. We suppose that the effect of Se on the proliferation of suppressor T lymphocytes (Ts) in AMLR is not mediated through GSH-Px activity and fluctuations of Se concentration within a physiological range in healthy persons do not affect NK cytotoxicity.

Eosinophilic globule cells in mouse MFH-like sarcomas: Lectin histochemistry

Lectin binding patterns in ten mouse malignant fibrous histiocytoma (MFH)-like sarcomas containing eosinophilic globule (EG) cells and in granular metrial gland (GMG) cells of mouse placenta were stained with nine lectins (Con A, LCA, WGA, DBA, SBA, e-PHA, PNA, RCA-I and UEA-I) by an avidin-biotin-peroxidase-complex method. EG cells stained strongly with DBA, SBA and PNA which are specific for N-acetyl-D-galactosamine and/or D-galactose. DBA and SBA bound throughout the cytoplasm including the globules; PNA reacted preferentially at the cell surface. There was no evidence that these three lectins were reactive for immature EG cells. WGA, RCA-I and e-PHA also gave a slightly to moderately positive reaction to globules of EG cells. The results indicate that the globules contain abundant O-linked sequences of sugars, but also a few N-linked residues. MFH tumor cells showed a variable degree of binding with Con A, RCA-I, and WGA, but did not react with DBA, SBA and PNA. On the other hand, GMG cells exhibited specific affinities for DBA, SBA and PNA with staining patterns similar to those of EG cells. These findings suggest that EG and GMG cells may be of the same cellular lineage.

Suppression of natural killer cell activity by sera from patients with endometriosis

OBJECTIVE

We determined the effect of sera from patients who have endometriosis on natural killer cell activity.

STUDY DESIGN

The natural killer cell activity of lymphocytes from healthy volunteers was examined after incubation with sera from patients who had endometriosis or from controls, with K562 cells used as targets.

RESULTS

Lymphocytes treated with sera from patients who had endometriosis expressed significantly lower levels of cytotoxicity compared with lymphocytes treated with control sera. This suppression of cytotoxicity was dose dependent, and the degree of suppression was proportional to the incubation time of the effector cells with the sera. Decreased cytotoxicity after serum treatment was also observed with sera from patients who had been treated with danazol.

CONCLUSIONS

These findings show that humoral factors that can inhibit natural killer cell activity in vitro are present in the peripheral blood of patients who have endometriosis; moreover, they suggest that the suppressed natural killer cell activity may allow the development of endometrial cells at ectopic sites.

Pidotimod stimulates natural killer cell activity and inhibits thymocyte cell death

Experiments were performed to analyze the possible effect of the immunomodulating agent Pidotimod (3-L-pyroglutamyl-L-thiazolidine-4-carboxylic acid) on mouse Natural Killer (NK) cell activity and glucocorticoid hormone(GCH)-induced thymocyte apoptosis. The results indicate that in vivo treatment with Pidotimod (200 mg/Kg ip for 5 days) causes a significant increase in NK activity and in vitro treatment produces a significant reduction of dexamethasone-induced thymocyte apoptosis. This inhibition appears to be dose-dependent and is also evident against TPA or Ca(++)ionophore-induced apoptosis.

The in vivo clearance of Ha-ras transformants by natural killer cells

The experiments in this study were designed to test the hypothesis that natural killer (NK) cells play a role in host surveillance against early neoplastic changes in the malignant process. C3H 10T1/2 mouse fibroblasts were transfected with a pSV2-neo plasmid vector which contains EJ, the mutated c-Ha-ras, regulated by its own promoter. Control cells were transfected with pSV2-neo alone and did not contain the ras gene. Oncogene-transfected cells were compared with control cells for lung colony formation following tail vein injection into C3H mice. Intravenous injection of ras-transfected 10T1/2 cells induced marked lung colony formation in vivo, whereas C3H 10T1/2 parental lines or 10T1/2 cells transfected with pSV2-neo alone induced no lung colonies in C3H mice. The colonising potential of ras transfectants could be decreased by augmentation of NK activity by injection of polyinosinic cytidylic acid and increased by depletion of NK effectors with anti-asialo GM1. Experiments with beige mice demonstrated that the mortality of syngeneic, NK-deficient C3H-bg/bg mice injected with ras tranfectants was significantly greater than similarly treated NK-normal C3H(-)+/bg littermate controls. The results support the view that NK cells are capable in vivo of recognizing early defined stages in the neoplastic process initiated by oncogenes.

Increased natural killer cell activity and numbers of Leu-7 and Leu-11b (CD 16)-positive cells in bone marrow of children in remission from acute lymphoblastic leukaemia

Natural killer (NK) cell activity and related markers were analysed in childhood acute lymphoblastic leukaemia (ALL). Children with untreated ALL, children with active disease, and children in remission for less than 1 month and undergoing induction therapy had significantly lower NK cell activity in peripheral blood than the control group (P less than 0.05, P = 0.0005, and P less than 0.0025). Patients in remission for 1-3 months and undergoing consolidation chemotherapy had normal NK activity (P greater than 0.05). Children in complete remission for more than 3 months and undergoing maintenance therapy also had a normal NK activity in their peripheral blood (P greater than 0.05). However, their bone marrow cells showed an increased NK cell activity (P less than 0.0005). Cells positive for the Leu-7 marker were reduced in the peripheral blood from untreated children (P less than 0.025) and children in remission for less than 1 month (P = 0.025). The percentage of cells from peripheral blood expressing the marker Leu-11b (CD 16) did not differ significantly from that of the controls (P greater than 0.05). However, children in complete remission for more than 3 months had a higher number of bone marrow cells expressing the Leu-7 (P = 0.005) and the Leu-11b (CD 16) markers (P = 0.05) than controls. Stimulation of mononuclear cell suspensions with recombinant alpha interferon and recombinant interleukin 2 were shown to cause a normalization of the NK cell activity in peripheral blood and bone marrow.

Altered natural killer cell activity in childhood acute non-lymphoid leukaemia. Augmented natural killer cell activity and cells expressing the Leu 7 and Leu 11b (CD 16) markers in the bone marrow of children in remission

Peripheral blood and bone marrow mononuclear cells from 25 children with acute non-lymphoid leukaemia were analysed for natural killer cell activity and for cells with the Leu-7 and Leu-11b (CD 16) markers. Significantly reduced spontaneous cytotoxicity was detected in peripheral blood from children with untreated and active acute non-lymphoid leukaemia compared with that of the controls (P = 0.01 and P less than 0.05). Patients in remission, however, had normal natural cytotoxicity and normal numbers of Leu-7 and Leu-11b (CD 16)-positive cells. The natural killer cell activity in bone marrow from patients with untreated acute non-lymphoid leukaemia was also significantly reduced (P = 0.025). On the other hand, patients in remission had both an increased percentage of Leu-7 and Leu-11b (CD 16)-positive cells (P less than 0.05) and an increased natural killer cell activity (P less than 0.0005) in their bone marrow cells in comparison with the control group. This augmented natural killer cell activity is most probably a result of anti-leukaemic treatment. Stimulation with recombinant alpha interferon and recombinant interleukin 2 caused an increase in natural killer cell activity that was both significant and normal in both peripheral blood and bone marrow from children with acute non-lymphoid leukaemia.

Studies on the mechanism of activation of human natural killer function by interferon and inhibitors of thymidylate synthesis

Previous publications from this laboratory have demonstrated that agents such as methotrexate (MTX), 5-fluorodeoxyuridine (FUdR), trimethoprim, and D-glucosamine (D-GlcN), which are known to inhibit thymidylate synthesis, can augment human NK activity in vitro. Furthermore, this augmentation was inhibited by exogenous thymidine (TdR) at concentrations of 10(-6) to 10(-7) M. In this report, underlying mechanisms of action of FUdR, D-GlcN, and IFN are compared. Each of these agents increased the lytic activity of effector cells bound to targets but did not increase the percentage of conjugates formed. The augmentation could be induced in a population highly enriched for NK cells (Leu-1 lb positive in phenotype). FUdR and D-GlcN could not induce any augmentation in a Leu-1 lb-negative subpopulation whereas IFN could induce significant lytic activity. alpha-Amanitin, an inhibitor of RNA polymerase II, blocked the activation of NK activity by all three reagents; hence gene expression was required. Comparison of [35S]methionine-labeled proteins by two-dimensional gel electrophoresis revealed that six new proteins were induced in IFN-treated cells. Three of these were similar in pI and molecular weight to the newly synthesized proteins in the D-GlcN-treated cells. One protein was synthesized in increased amounts in the FuDR-treated cells and it was not common to either of the other treatments. Evidence to date is consistent with the hypothesis that separate mechanisms underlie the activation of NK cells by IFN and thymidylate synthesis inhibitors, although the existence of a final common pathway for all NK response modulators cannot be excluded at the present time.

Modulation of natural killer cell activity by tamoxifen in stage I post-menopausal breast cancer

Tamoxifen, an antiestrogen which competes for the estrogen receptor, modulates natural killer cell activity in vivo. Seventeen post-menopausal stage I breast cancer patients received tamoxifen for 1 month and a statistically significant increase in NK activity was demonstrated (P = 0.0005). There was a small incremental shift in the number of Leu-11b positive cells. These data demonstrate that tamoxifen functions as a biological response modifier.

Modulation of natural killer cell activity in stage I postmenopausal breast cancer patients on low-dose aminoglutethimide

Natural killer (NK) cells are important in surveillance against malignant cells. The activity of NK cells can be modulated by naturally occurring mediators; interferon, interleukin-2, and hormones. Low-dose aminoglutethimide (Ag 250 mg/day) inhibits the peripheral aromatization of androstenedione hence decreasing circulating estrogens. Of ten patients treated, seven were evaluable. There was a statistically significant increase in NK activity (P = 0.0025) following the administration of Ag. There was no consistent shift in NK cell number (Leu-11b positive cells). In vitro Ag did not alter NK activity whereas 17-beta-estradiol did. These data are consistent with an indirect effect of Ag on NK activity. Hence in vivo Ag which causes a reduction in serum estrogens in postmenopausal patients, also induces an increase in NK activity.

Pathogenesis and characteristics of spontaneously metastasizing mammary carcinomas and the general principle of metastasis

Chemical mammary carcinogenesis in immunologically attennuated W/Fu female rats, subjected to specific and nonspecific immunostimulations, yielded many spontaneously metastasizing adenocarcinomas with varying degrees of glandular differentiation, and growth rates. The pathogenesis of these tumors suggested that while carcinogens transform target cells, the host immune system endows them with metastatic potential. The metastatic pathways were recognizable as hematogenous, lymphogenous, or hematogenous-lymphogenous combined, according to the capacity of the tumor cells to intravasate the lymphatic and/or vascular channel and traverse the pulmonary artery. The same metastatic pattern can be reproduced with cells from any of the organs involved, indicating that it is inherent in all cells within a given tumor, rather than being determined by the organs they colonize. The biological, biochemical and immunological characteristics of these tumors resemble human breast cancer thus becoming an effective tool in the formulation of the general principle of metastasis by malignant solid tumors.

T cell receptor gene rearrangements in cells with natural killer activity in the mouse

Cell-mediated recognition can operate at different levels of complexity and specificity based largely on the time of appearance of effector mechanisms during the course of evolution. Antigen-specific cytotoxic T lymphocytes require both T cell receptor genes and lectin-like cell adhesion molecules (LFA-1, LFA-2, lymphocyte function-associated) to initiate and maintain stable effector target cell conjugates. Natural killer (NK) cells, on the other hand, do not require expression of T cell receptor genes in the recognition and killing of tumor cells and virally infected cells. Adhesion is mediated by a family of glycoprotein molecules, of which the LFA-1 and LFA-2 molecules appear as the most likely candidates. NK-mediated cytolysis proceeds in the absence of MHC restriction, but nevertheless appears to be triggered by depressed levels of self MHC products on the cell surface of target cells. Finally, interleukin 2-dependent, cloned cell lines with NK-like cytotoxic activity should no longer be considered as bona-fide NK cells but rather reclassified as a subset of T cells which displays NK function.

The cytolytic and regulatory role of natural killer cells in experimental neoplasia

NK cells are defined here as cells, other than macrophages and polymorphonuclear leucocytes, from non-immunized animals (or humans) which are cytotoxic for neoplastic and non-neoplastic targets in the absence of specific antibody. Though not requiring antibody, they may function as K cells in ADCC. This definition includes cells activated nonspecifically by such agents as IFN and IL-2. Murine NK cells may be subdivided into two types by differences in the kinetics of target-cell lysis. Those we label Type 1 correspond roughly to what others have called NKA, NKL or simply NK cells; those of Type 2 to NKB, NKS and NC cells. Type 1 cells express various antigens, including NK-1, Thy-1 (50%), Ly-1 (25%), Qa-3, Qa-4, Qa-5, Ly-5, Ly-6, Ly-10, Ly-11 and asialo-GM1, not expressed by Type 2 cells, whereas Mac-1 may be expressed by both types. At least some NK cells appear to be pre-thymic cells which, in the presence of a thymus, can differentiate into T cells. The level of NK activity is influenced by the age and genetic background of the mouse, the organ from which the cells are obtained, and a variety of experimental manipulations. Type 1 activity is increased by IFN and IL-2; Type 2 activity by IL-3. IFN appears to be concerned in the development of spontaneous NK activity in young mice. Many experiments have shown that NK cells may inhibit the growth of tumours which are sensitive to NK cells of the same type in vitro. Inhibitory cells which suppress NK activity may play an important regulatory role in vivo. There is still uncertainty about how NK cells recognize their targets. Possibilities discussed are: (1) specific interacting molecules; (2) more diffuse properties of target cell membranes; (3) absence of MHC-coded self-recognition markers. Certainly, the presence of a Class 1 MHC molecule is not necessary. NK killing appears to be mediated by cytotoxins released by NK cells. In vivo, NK cells contribute to limiting the development of transplanted and primary tumours, and metastasis from established tumours. NK cells seem well qualified to act as a first-line defence against neoplasia, and may kill cells not killed by T cells. Transfer of NK cells may be of value in the treatment of cancer.

The influence of chemical carcinogens on natural killer cell function in rats. A comparison of 2-acetylaminofluorene with 4-acetylaminofluorene

The influence of the carcinogen 2-acetylaminofluorene (2AAF) administration on splenic natural killer (NK) cell function in two strains of rats has been examined and compared with that of the non-carcinogenic analogue 4-acetylaminofluorene (4AAF). In both strains it was observed that daily exposure to 25 mg kg-1 2AAF induced a significant depression of both native and interferon (IFN)-activated NK cell function which was first apparent between 7 and 13 days following initiation of treatment. In contrast 4AAF failed to influence NK cell activity. These data indicate that 2AAF in common with some other carcinogens has the capacity to influence natural cytotoxic function and lend support to the hypothesis that carcinogenic potential may in some cases be associated with immunosuppressive properties.

Human seminal plasma is a potent inhibitor of natural killer cell activity in vitro

The effect of human seminal plasma on the natural killer (NK) activity of human peripheral blood leukocytes in vitro has been investigated. Small concentrations (as low as 0.01% v/v) of seminal plasma were found to inhibit the ability of human peripheral blood leukocytes to lyse K562 target cells. These inhibitory effects were observed with seminal plasma donations from normal and infertile individuals, including those who had been vasectomised. The inhibition noted appeared to be independent of the presence of antisperm antibodies which could conceivably cross-react with NK cells. Furthermore, the factors responsible survived boiling for 15 min and could not be absorbed out with K562 target cells. These profound inhibitory effects might be relevant to malignancy of the urogenital tract and the defence against sexually transmitted disease.

Spontaneous and induced primary oncogenesis in natural killer (NK)-cell-deficient beige mutant mice

Spontaneous tumor development and primary oncogenesis were compared in a large number of NK4-deficient, homozygous C57Bl/6-bg/bg mice and their NK normal, heterozygous +/bg littermate controls. In a group of 167 retired breeders followed for spontaneous tumors, the probability of survival for mice eventually dying with a tumor was greater for the NK-competent, +/bg than for the NK-deficient, homozygous C57BL/6-bg/bg mice (p = 0.0019), although the higher overall incidence of tumors in the bg/bg group (48%) was not significantly different from that in the +/bg group (37%). In the bg/bg group the incidence of tumor death appeared to increase relatively sharply in the 25- to 29-month age bracket compared to the fairly regular increase in incidence observed in the +/bg group. All the spontaneous tumors except 2 (discovered in +/bg mice) were classified histologically as widely disseminated malignant lymphomas. The other two were one squamous-cell carcinoma and one sarcoma. A total of 73 bg/bg mice injected s.c. with benzo[alpha]pyrene (BP) had a higher overall incidence of tumors (81%) (rhabdomyosarcomas) than 138 +/bg mice (64%) and in the largest group (0.3 mg, n = 85) the bg/bg group developed tumors, at a higher incidence (p = 0.01) and with a shorter latency (p = 0.025) than the +/bg group. On the other hand, mice injected with dimethylbenzanthracene or given 4 weekly doses of 160 rads of gamma irradiation showed no difference in overall tumor incidence. In addition, mice injected with various doses of DMBA-induced murine leukemia virus (DMBA-LV) also showed no significant difference in tumor incidence. Others have reported that some of these treatments (DMBA, split-dose irradiation) cause profound NK suppression, thereby reducing NK differences between the two groups of mice. These results suggest that a partial NK impairment in beige mutant mice early in life may lead to significantly greater rates of death with spontaneous malignant tumors late in life. Some primary oncogenesis treatments (BP) but not others (DMBA, split-dose irradiation, leukemia viruses) cause tumors with a greater incidence and shorter latency in beige mice. The results suggest, but do not prove, that NK cells play a role in surveillance against spontaneously arising, and possibly some types of carcinogen-induced, tumors.

Natural killer cells

It is proposed that this article will encompass a review of primarily the human natural killer cell. The following parameters of the human natural killer (NK) cell will be reviewed: its ontogeny; surface membrane characteristics including monoclonal antibody reactivity, cell lineage, the natural killer sensitive targets, and the proposed mechanism of action of natural killer cells cytotoxicity against these NK sensitive targets; the status of natural killer cell in relationship to clinical disease; the alteration of natural killer cells both in vitro and in vivo; and finally postulate relevance of the natural killer cell in context of the evolution or pathophysiology of human disease. There will be an attempt through this review to encompass the more recent publications that pertain to the various sections.

Treatment of patients with transitional cell carcinoma of the urinary bladder with intravesical poly I: poly C effects on natural killer function

Considerable interest has been focused on the use of interferon (IFN) and IFN-inducers as antineoplastic agents in humans. The current report will focus on the effect of intravesical administration of Poly I: Poly C on NK activity in patients with TCC of the urinary bladder. NK cytotoxicity was measured in 14 patients with primary TCC, 8 patients received Poly I: Poly C and 5 other patients received intravesical thiotepa. Blood samples were obtained prior to and 48 h following each drug treatment. A variation in the initial NK level determined prior to treatment was observed in the different TCC patients: 5 patients treated with Poly I: Poly C and 5 patients treated with thiotepa exhibited low NK activity prior to treatment, whereas the other 3 patients who were treated with Poly I: Poly C had high initial NK levels. Following drug treatment it was shown that a significant elevation in the NK cytotoxicity was only observed in patients treated by intravesical Poly I: Poly C who had low NK activity prior to treatment. No such effect was observed in patients treated with thiotepa or in patients treated with Poly I: Poly C who exhibited a high NK activity prior to treatment.

Towards a psychobiological model of cancer: biological considerations

The control of tissue homeostasis is extremely complex and many factors contribute to the growth and development of tumours. Although the immune system has been regarded as an essential intermediary between putative psychological factors and the development or restraint of malignant tumours, this review indicates that many other possible mechanisms also exist. Current aspects of tumour biology, immunology and hormonal control systems are reviewed, and detailed psychobiological mediating mechanisms are considered at each stage of tumour development. An approach to the future investigation of this difficult field is proposed.

Toxicity of bis(tri-n-butyltin)oxide in the rat. II. Suppression of thymus-dependent immune responses and of parameters of nonspecific resistance after short-term exposure

To evaluate the functional significance of bis(tri-n-butyltin)oxide (TBTO)-induced thymus atrophy, lymphocyte depletion in spleen and lymph nodes, lymphopenia, and increased serum IgM and decreased IgG concentrations, in vivo and in vitro function studies were performed for specific and nonspecific resistance. Weaned male rats were fed diets containing 0, 20, or 80 mg TBTO/kg for at least 6 weeks. Regarding the thymus-dependent immunity, delayed-type hypersensitivity reactions to ovalbumin as well as tuberculin were significantly depressed at both dietary concentrations. Resistance to the nematode Trichinella spiralis was significantly suppressed as shown by a retarded expulsion of adult worms from the small intestine, increased counts of muscle larvae, reduced inflammatory reaction in parasitized musculature, and suppressed serum IgE titers. Also the secondary mercaptoethanol-resistant (presumably IgG) hemagglutinating antibody titer to sheep red blood cells was significantly reduced, while no significant alterations were found in IgM and IgG titers to T. spiralis, ovalbumin, and tetanus toxoid. TBTO exposure reduced the response of thymocytes in both treatment groups and of spleen cells in the 80-mg/kg group upon stimulation with T-cell mitogens and increased the response of spleen cells to B-cell mitogens. When calculated per whole spleen, the response to T-cell mitogens was strongly impaired but unaltered by B-cell mitogens. This difference can be explained by a relative increase of splenic B cells as a result of reduced numbers of T cells, as shown by cell surface marker analysis using monoclonal antibodies. Reduced splenic T-cell numbers appeared equally due to a decreased number of T helper and to T suppressor cells. From these data and from results of a time-sequence study in which effects of TBTO on cell count and cell viability of thymus, spleen, and bone marrow were investigated, it is concluded that TBTO-induced immunodeficiency was primarily due to its direct toxic action on thymocytes. When cultured in vitro in the presence of TBTO, viability of thymus and bone marrow cells was equally reduced, while after in vivo treatment viability of bone marrow cells was unaffected. Thus, the in vitro situation does not mimic the in vivo one. Concerning the nonspecific resistance, TBTO reduced macrophage function as shown by impaired splenic clearance of Listeria monocytogenes bacteria. From in vitro studies it is concluded that impaired in vivo splenic clearance was due to a reduction in both the number of adherent cells in the spleen and bacterial digestion on a cell for cell basis.(ABSTRACT TRUNCATED AT 400 WORDS)

Regulation of NK cell activity by prostaglandin E2: the role of T cells

The influence of T cells on the production of prostaglandins (PGE2) and on PGE2-mediated regulation of natural killer (NK) activity was studied. Supernatants from peripheral blood mononuclear cells (PBMC) and from PBMC depleted of T cells ((PBMC)-T), both of which had been incubated in plastic petri dishes overnight, contained similar amounts of PGE2, as detected by radioimmunoassay and by their potential to inhibit NK activity of peripheral blood mononuclear cells in a 51Cr release assay with K 562 cells as the target population. However, the NK activity of PBMC was inhibited significantly more strongly (P less than 0.005) by PGE2-containing supernatants than was the NK activity of (PBMC)-T. In further assays, in which synthetic PGE2 in concentrations of 10(-4) and 10(-5)M was added, a significant inhibition of NK activity was observed in PBMC populations (P less than 0.05), but not in (PBMC)-T. Thus, T cells did not seem to be involved in the control of PGE2 production, but their presence was necessary for PGE2-mediated inhibition of NK activity.

The cooperative effect of the satin and beige mutations in the suppression of NK and CTL activities in mice

The functional activity of natural killer (NK) cells has been found to be modulated by several point mutations associated with coat color. The most commonly studied gene, beige (Bg), has been found to block a postrecognition event in the lytic cycle. Four other coat color mutations in the mouse (satin, leaden, fuzzy, pale ears) were studied for their effect on NK cell function, and only one, satin (Sa), was found to be suppressive. When both the Sa and Bg mutations were present in the same animal, their effects were synergistic in the suppression of NK levels. Normal numbers of NK cells were present in these double mutants, as determined by the frequency of IgG2b binding cells and by antiasialo GM1 staining. The ability of Sa/Bg NK cells to recognize and bind targets suggests that the defect is localized in the postbinding cytolytic pathway. These genes were not specific for NK cells and also suppressed alloimmune cytolytic T lymphocyte function. Since Sa/Bg mice are much more suppressed in NK function than Bg mice, we suggest that this double mutant may be a better model for NK deficiency in vivo.

Immunological surveillance of tumors in the context of major histocompatibility complex restriction of T cell function

The immunological surveillance hypothesis was formulated prior to the realization of the fact that an individual's effector T cells generally only see neoantigen if it is appropriately presented in the context of self MHC glycoproteins. The biological consequence of this mechanism is that T lymphocytes are focused onto modified cell-surface rather than onto free antigen. The discovery of MHC-restricted T cell recognition, and the realization that T cell-mediated immunity is of prime importance in promoting recovery from infectious processes, has thus changed the whole emphasis of the surveillance argument. Though the immunological surveillance hypothesis generated considerable discussion and many good experiments, there is no point in continuing the debate in the intellectual context that seemed reasonable in 1970. It is now much more sensible to think of "natural surveillance" and "T cell surveillance," without excluding the probability that these two systems have elements in common. We can now see that T cell surveillance probably operates well in some situations, but is quite ineffective in many others. Part of the reason for this may be that the host response selects tumor clones that are modified so as to be no longer recognized by cytotoxic T cells. The possibility that this reflects changes in MHC phenotype has been investigated, and found to be the case, for some experimental tumors. In this regard, it is worth remembering that many "mutations" in MHC genes that completely change the spectrum of T cell recognition are serologically silent. The availability of molecular probes for investigating the status of MHC genes in tumor cells, together with the capacity to develop cloned T cell lines, monoclonal antibodies to putative tumor antigens, and cell lines transfected with genes coding for these molecules, indicates how T cell surveillance may profitably be explored further in both experimental and human situations.

Increase of natural killer (NK) activity of mouse lymphocytes following in vitro treatment with cytosine-arabinoside

The in vitro influence of cytosine-arabinoside (Ara-C) on mouse NK activity was studied treating effector cells, target cells or effector and target mixture with graded concentrations of the drug. Ara-C increased the NK efficiency of mouse splenocytes without enhancing the susceptibility of target cells or the cytolytic events when added to effector-target mixture. This phenomenon was confirmed with splenocytes collected from congenitally athymic (nude) or conventional donors of different ages, untreated or depressed or boosted for NK activity by various agents. In addition Ara-C increased the NK activity of spleen cells of nude mice deprived of nylon-adherent cells, and did not affect suppressor cells capable of inhibiting the lytic phase of NK process. The drug was able to significantly augment the binding ability of spleen cells to the NK-sensitive YAC-1 target. It was concluded that Ara-C would increase the efficiency of natural cytotoxicity presumably through a direct influence on effector lymphocytes.

The chemiluminescence response of human natural killer cells. II. Association of a decreased response with low natural killer activity

Low natural killer (NK) responders selected from a panel of 600 normal, healthy volunteers exhibited 5- to 10-fold less cytotoxicity against the human erythroleukemic cell line K562, compared with high NK responders. Antibody-dependent cellular cytotoxicity against tumor cells, which is mediated by similar or identical effectors, was also depressed in low NK donors whereas lectin-dependent T cell killing and monocyte-mediated cytolysis of tumor cells was normal. Low NK donors exhibited normal frequencies of cells expressing the HNK-1 marker of human NK cells and highly enriched NK fractions were not impaired in their ability to recognize and bind to NK-sensitive target cells. Interferon partially activated low responder NK cells but did not restore the response to normal levels. The burst of chemiluminescence that is generated by NK cells within seconds of target cell contact was markedly impaired in low NK responder donors. We have previously shown that chemiluminescence detects reactive oxygen intermediates which are necessary but not sufficient for the activation of the NK cytolytic pathway.

The biology of the human natural killer cell

Natural killer (NK) cells in the human are a population of large granular lymphocytes (LGL) with at least one unique surface antigen not expressed on cells of other lineages. NK-target-cell interaction appears to involve carbohydrate recognition and, following binding, the NK cells are induced to generate O2-, transmethylate membrane phospholipids, and activate phospholipase A2. Some or all of these activities trigger a cascade of events which ultimately leads to the secretion of a substance toxic to the target cell. A variety of genes controls various steps in this cytolytic pathway. There is a good deal of evidence in the mouse, and some in the human, that NK cells play a role in host surveillance against tumor development, resistance to viral infections, and, possibly, hematopoietic regulation.

Resistance to infections in mice with defects in the activities of mononuclear phagocytes and natural killer cells: effects of immunomodulators in beige mice and 89Sr-treated mice

Beige mice, which are a homolog of the Chediak-Higashi syndrome, and mice treated with 89Sr to destroy the bone marrow provide animal models of defects in mononuclear phagocyte and natural killer cell functions. The innate resistance of these mice to viruses such as herpes simplex and encephalomyocarditis viruses, however, is normal. Moreover, treatment of the mice with immunomodulators such as Propionibacterium acnes (formerly designated Corynebacterium parvum) and pyran produced a significant increase in resistance to encephalomyocarditis virus. The antiviral effect of P. acnes in 89Sr-treated mice was exhibited during marked monocytopenia and without evidence for an inflammatory influx of macrophages into the peritoneal cavity. Treatment with P. acnes was also effective in increasing the resistance of beige mice to infection with Listeria monocytogenes. Thus, immunomodulators can be effective in mice that exhibit impaired macrophage and natural killer cell functions.

A cloned cell with NK function resembles basophils by ultrastructure and expresses IgE receptors

Natural killer (NK) cells are defined by their ability to lyse certain tumour cells in vitro without previous exposure to them, and have been postulated as effectors of immune surveillance against spontaneous neoplasms. Because they kill some non-neoplastic lymphoid cells, they may also have a role in immunoregulation. NK cell activity resides in a small proportion of normal mouse spleen cells (less than 5%) that have been difficult to characterize completely. They may represent a heterogeneous group of effector cells whose precise relationship to other myelopoietic or immunological cells has remained obscure. We have previously described a cloned mouse cell line (Cl. Ly 1-2-NK-1+/11) with the functional characteristics of natural killer cells activated by interferon or other factors. We now find that this cloned line, like basophils and mast cells, expresses high-affinity plasma membrane receptors (Fc epsilon R) specific for IgE antibody. In addition, the clone contains cytoplasmic granules similar by ultrastructure to those of basophils of the mouse and other species. Our findings indicate that cells sharing morphological and biochemical features of basophilic granulocytes can mediate NK lysis.

Escape of tumours from immunological destruction

This paper reviews the mechanisms of tumour escape from immune destruction that have been delineated in the past 2 decades. Current evidence indicates that the principal escape mechanisms are (i) weak or absent immunogenicity (ii) immunosuppression by tumour antigens or antigen-antibody complexes (iii) induction of suppressor cells and (iv) production of immunosuppressive factors. A classification of tumour escape mechanisms is presented.

Human natural killer-like activity against mouse spleen cells

Unstimulated human peripheral lymphocytes were cytotoxic for normal mouse spleen cells and suppressed the in vitro antibody plaque-forming cell (PFC) response of these cells to sheep red blood cells and dinitrophenylated Ficoll. The cells in the lymphocyte population that were responsible for the immunosuppression had properties of natural killer (NK) or NK-like cells in that they were: (a) non-E-rosetting, (b) nonadherent, (c) unaffected by treatment with anti-human immunoglobulin plus complement, (d) cytotoxic against an established human NK target, K562 leukemic cells, and (e) partially inactivated by mitomycin C. Addition of the human NK-like cells to mouse spleen cell cultures at the time of antigen addition and at an effector cell to target cell ratio as low as 0.67:1 resulted in 85 to 96% suppression of the PFC response. Addition of NK-like cells to cultures 18 h before harvesting in 5-day cultures required higher concentrations and ratios (2.7:1) of effector to target cells to significantly suppress the PFC response. The data suggest that human NK-like activity in suppression of the mouse PFC response is due to killing of the targets. The mouse spleen cell PFC system represents a potential model for assessment of human NK activity that is quite dramatic in its effect and can be used in addition to the well known 51Cr-release assay. Also, since the mouse spleen cell is a normal cell, it provides a model in the PFC system for studying the mechanism of NK regulation of normal cellular function. An additional finding of this study was the observation that E-rosetting T cells significantly enhanced the mouse PFC response. Thus, human peripheral lymphocytes contain discrete cellular population that either enhance or suppress the mouse PFC response.