Natural Cytotoxic Cell Activity Research Articles

Changes in the organism of patients with chronic inflammatory diseases of the upper respiratory tract at different periods after administration of influenza vaccine. Message 1. Status of congenital immune parameters after a single anti-influenza vaccination

Introduction: Studies of the clinical status, production of antibodies to hemagglutinins of influenza A and B viruses and the content of immune complexes in patients with chronic inflammatory diseases (CID) of the upper respiratory tract (URT) before and within 36 weeks of vaccination after parenteral vaccination Vaxigrip leads to a short-term (~ 6 months) increase in anti-influenza hemagglutinin t itres. According to modern ideas about the mechanisms of antiviral protection, in addition to humoral, mainly due to antibodies, antiviral protection is largely due to the activation of innate immune factors, both systemic and local. Aim: to evaluate in the dynamics of observations the influence of a single parenteral influenza vaccination on the factors of innate immunity in patients with chronic inflammatory diseases of the upper respiratory tract. Material and methods: Among the factors of innate immunity a significant role is played by interferons, the activity of natural cytolytic cells (NK) of various histogenesis, phagocytic cells and non-specific proteins such as defensins, elafins. Therefore, quantitative and functional characteristics of NK-cells, phagocytic absorption activity of polymorphonuclear leukocytes (PMN), systemic content of γ-interferon (IFN-γ) were studied in patients at the systemic level. At the local level, the concentrations of defensin-β and α-interferon were studied in mucosa secretes (MS) according to modern ideas about the state of the mechanisms of innate antiviral immunity. From the autumn-winter period of 2019 to November 2020, 32 donors (control group) and 32 patients with CID of both sexes were examined, 11 of whom were diagnosed with chronic rhinosinusitis, 9 with chronic tonsillitis, and 12 with chronic pharyngitis. No vaccinations were given 1 year before the study. Samples of venous serum and oropharyngeal secretes of all clinically healthy patients, as well as persons with CID were obtained at the initial examination. After parenteral vaccination with Vaxigrip (SANOFI PASTEUR, S.A., France), blood and MS were tested twice more in vaccinated patients: 12 and 36 weeks after vaccination. The obtained samples of experimental material were stored at a temperature of -20 C◦ until the simultaneous determination of innate immune factors (interferons), in particular with the help of reagents from Cytokine, Hema Medica (RF), defensin-β (Hucalt-bio, the Netherlands). Measurements were performed on a microplate enzyme-linked immunosorbent assay "STAT FAX 2100 (USA). Statistical processing was performed using the non-parametric criterion "U" - Mann-Whitney or Fisher's exact method. Differences were considered statistically significant at p <0.05. The results were given in the form of arithmetic mean (M), median (Me) and percentiles (P25-P75). Results: In determining the role of innate immunity factors in vaccination with influenza vaccine, we conducted clinical and immunological examination of patients with chronic inflammatory diseases of the upper respiratory tract, which included systemic determination of γ-interferon, quantitative and functional activity of natural cytotoxic cells, phagocytosis activity at the stage of attraction and capture. Levels of α-interferon and defensin-β in oropharyngeal secretion (MS) were studied. It was found that before influenza vaccination in patients with chronic inflammatory diseases of the upper respiratory tract found an increased content of γ-interferon and decreased phagocytic activity of polymorphonuclear leukocytes. Decreased α-interferon and defensin-β concentrations were detected in MS patients before vaccination. After vaccination, there were positive changes in the direction of increasing the concentration of nonspecific local immunity factor – defensing 1β and partly in the observation period of 3 months after vaccination- α-interferon. Сonclusion: Among the factors of innate immunity in patients with CІD at the systemic level, decreased cytolytic activity of NK, increased levels of γ-interferon and decreased phagocytic function of neutrophils. Decreased concentration of α-interferon and defensin-1β is determined in the saliva of patients with CID. Vaccination of patients with chronic inflammatory diseases of the upper respiratory tract with influenza vaccine has a positive effect on the state of innate immune factors of local and systemic level: concentration of γ-interferon, phagocytic activity of neutrophils and enhancing the functional activity of natural killer cells, increase in saliva of defensin-1β.

레바미졸이 틸라피아(Oreochromis niloticus)의 자연살해세포 활성에 미치는 영향

The study examined the effect of levamisole on the natural cytotoxic cell (NCC) activity of Nile tilapia (Oreochromis niloticus) head kidney (HK) leukocytes. In vitro, HK leukocytes were incubated with to ng of levamisole/ml for 5, 20 or 40 h and then their NCC activity against target cells was assayed. The NCC activity appeared to increase after a 20 h of incubation. In vivo, tilapia were fed commercial diet containing 0, 50, 100 or 300 mg of levamisole/kg for 12 consecutive days. Then, the fish were fed a commercial normal diet and samples harvested weekly 0 to 8 weeks after levamisole administration. The NCC activity was augmented uniformly at all times examined until the end of the experiment. In conclusion, levamisole effectively enhanced and maintained tilapia NCC activity.

Reduced natural cytotoxic cell activity in patients receiving cisplatin-based chemotherapy and in mice treated with cisplatin

In mice natural cytotoxic (NC) cells are known to play a role in the rejection of tumours that are sensitive to NC-mediated lysis. We have recently shown that in vitro human and murine tumour cells become more sensitive to lysis mediated by NC cells in the presence of the anti-cancer drug cisplatin. If NC activity plays a role in tumour surveillance in humans, then the ability of NC cells to eliminate tumours in patients treated with cisplatin would not only be dependent on cisplatin increasing the sensitivity of tumours to NC mediated lysis, but would also depend on the maintenance of high levels of NC activity during chemotherapy. Here we report that patients receiving chemotherapy that included cisplatin showed a time-dependent reduction in NC activity. NC activity was normal 1 day after treatment; however, 15 days after treatment patients had an eight- to 16-fold reduction in NC activity that returned to normal levels by day 21. The reduction in NC activity of patients was coincident with a reduction in circulating monocytes. Mice treated with only cisplatin showed a similar reduction in NC activity. Mice treated with cisplatin had a reduced level of NC activity that was first apparent 8 days after treatment, reached a nadir on day 15, and returned to normal levels on day 22.

Levamisole enhances the natural cytotoxic cell activity of Japanese flounder (paralichthys olivaceus) head kidney leukocytes

Japanese flounder (Paralichthys olivaceus) head kidney (HK) leukocytes were incubated with 103 to 10‐3 ng levamisole/ml for 4, 24 or 48 h and then assayed for their natural cytotoxic activity against xenogeneic tumor cells. This activity was slightly increased after 24 h of incubation. In a second experiment, fish were fed 0, 75, 150 or 300 mg levamisole/kg diet for 10 consecutive days. The fish were then fed a commercial non‐supplemented diet and sampled 0,1,2,3,4 or 6 weeks post‐administration of levamisole. The cytotoxic activity was found to be increased with increasing levamisole dose and remained greatly enhanced until the end of the experiment. In conclusion, levamisole enhanced flounder natural cytotoxic cell activity both in vitro and in vivo and had a great lasting action when administered by feeding.

Effects of different stressor agents on gilthead seabream natural cytotoxic activity

Several common situations in gilthead seabream ( Sparus aurata L.) farming, such as air exposure, crowding and the use of anaesthetics, have been demonstrated to be stressful. In the present study, these conditions were simulated in the laboratory, after which head-kidney natural cytotoxic cell (NCC) activity was evaluated. For this, several specimens were air exposed for 2 min, returned to the aquarium and sampled from 0 to 4 days after exposure. NCC activity was significantly lower on the day following air–exposure compared with the control (rested fish) but not at any other time studied. Other fish were crowded (100 kg biomass m −3, 2 h), returned to an aquarium with the same density as the control group (9 kg m −3) and sampled from 0 to 4 days after treatment. Head-kidney NCC activity was statistically increased compared with the control (resting) fish, 1 day after crowding. Anaesthesis for 1 h with 60 or 200 μl 2-phenoxyethanol l −1had no significant effect on NCC activity, while the use of 50 mg MS222 l −1for 1 h reduced such activity (by about 40%) compared with the control. In other experiments, fish were consecutively treated with crowding and anaesthetics. When treated with the lowest 2-phenoxyethanol concentration after crowding, the NCC activity inhibition was abolished compared with the activity in fish treated either with crowding or anaesthetic alone, while the use of the highest concentration increased such inhibition. The use of MS222 after crowding did not produce any differential effect compared with the fish treated with only one of the factors. In conclusion, NCC activity is affected differently according to the stress factor applied (hypoxia, crowding and/or anaesthetics). Differences in the effects provoked by these stressors on other seabream innate immune parameters are discussed.

Levamisole is a potent enhancer of gilthead seabream natural cytotoxic activity

Gilthead seabream ( Sparus aurata L.) head–kidney (HK) leucocytes were incubated with 10 3 to 10 −4 ng levamisole/ml for 4, 24 or 48 h and then assayed for their natural cytotoxic activity against xenogeneic tumor cells. This activity was slightly increased after 24 h of incubation. In a second experiment, fish specimens were fed 0, 75, 150 or 300 mg levamisole/kg diet for 10 consecutive days. The fish were then fed a commercial non-supplemented diet and sampled 0, 1, 2, 3, 4 and 6 weeks post-administration of levamisole. The cytotoxic activity was found increased along the experiment and remained greatly enhanced at the end. In conclusion, levamisole enhanced seabream natural cytotoxic cell activity both in vitro and in vivo and had a great and lasting action when administered by feeding.

Vitamin E increases natural cytotoxic activity in seabream (Sparus aurata L.)

The natural cytotoxic activity of head-kidney leucocytes from gilthead seabream (Sparus aurata L.), after in vitro and in vivo vitamin E treatment, against tumor cells was studied by flow cytometry. Leucocytes were incubated in culture medium with different vitamin E supplementations (0·01–10μg ml−1) for 6, 24 or 48h and the results demonstrate that all the assayed vitamin E supplementations significantly enhanced the natural cytotoxic activity of leucocytes. To determine the effect of a high dietary level of vitamin E on this activity, fish were fed with 0 (control), 600, 1200 or 1800mg of vitamin E supplementation kg−1diet for 2, 4 or 6 weeks. After 2 and 4 weeks of treatment, the natural cytotoxic activity was significantly enhanced at the highest (1·8g kg−1diet) and lowest (600mg kg−1diet) vitamin E supplement dosage, respectively. No effect of the vitamin E supplemented diet on seabream leucocyte natural cytotoxic cell activity was observed after 6 weeks of treatment.

Innate cellular immune function of anterior kidney leucocytes in the gulf killifish,Fundulus grandis

Non-specific cell-mediated immune functions of the gulf killifish (Fundulus grandis) were characterised so that the potential of this fish as a model species in stress immunophysiology and pollution studies could be assessed. Leucocytes from the pronephros were separated over discontinuous Percoll gradients and identified based on differential staining characteristics. Two enriched fractions of cells were then examined for their ability to phagocytose zymosan orVibrio anguillarum, to produce the reactive oxygen intermediates (ROIs) superoxide and hydrogen peroxide, and their natural cytotoxic cell (NCC) activity against K562 and YAC-1 targets. The leucocyte population at the 1·040–1·060g ml−1interface was comprised of macrophages, lymphocytes and eosinophilic granulocytes (EGCs), while the 1·060/1·080g ml−1interface contained mostly EGCs. There were typically 10-fold fewer cells in the former fraction. Light and electron microscopy revealed that both macrophages and EGCs were able to ingest zymosan andV. anguillarum. Fractions containing these cells also produced ROIs in response to phagocytic stimuli, with the EGCs having activity levels several times greater than that of the macrophages. NCC activity was limited to the 1·040–1·060 fraction, and was evident only against YAC-1 targets, but not against K562 targets. These results indicate that this fish would be suitable as a biomedical model in studies of non-specific cellular immune function as it relates to immunophysiology and environmental quality.

Response of fish immune cells to in vitro organotin exposures

The presence of contaminants in aquatic environments may compromise the health and survival of fish. Many of these compounds are known immunotoxins in mammals; however, relatively little information is available on the immunotoxic responses of fish to these pollutants. Organotins are examples of widespread industrial and agricultural compounds which persist in aquatic environments. In this study, we investigate the effects of tributyltin (TBT) and its dealkylated metabolite dibutyltin (DBT) on fish immune responses. Immune cells were isolated from the spleen and head kidney of juvenile rainbow trout ( Oncorhynchus mykiss) and exposed to 0, 2.5, 50 and 500 ppb of either TBT or DBT. Mitogenesis was quantified by tritiated thymidine incorporation into cells cultured with the mitogens concanavalin A (Con A) or lipopolysaccharide (LPS). No changes in immune function occurred at the lowest organotin dose of 2.5 ppb. Con A-stimulated mitogenesis was significantly suppressed by 85% in spleen cells on exposure to 50 ppb DBT. LPS-stimulated mitogenesis was significantly suppressed by 96% in spleen cells and by 58% in head kidney cells with 50 ppb DBT. The highest concentration of 500 ppb of TBT and DBT inhibited both Con A- and LPS-stimulated mitogenesis by more than 95% in both head kidney and spleen cells. Flow cytometric analysis revealed dose-dependent changes in the cell population profile which correlated with the inhibition of mitogen-stimulated lymphoproliferation. In contrast, natural cytotoxic cell activity was not inhibited by in vitro exposure to either compound, as determined by the lysis of chromium-51-labelled K562 human erythroleukaemia cells and P815 mouse mastocytoma cells. These results show that organotins have both functional and tissue-specific effects on the fish immune system, i.e. spleen ⪢ head kidney tissue and, in general. LPS-responsive ⪢ Con A-responsive leukocytes. In aquatic systems, TBT is considered to be the most toxic organotin compound, and this toxicity decreases with progressive dealkylation to diand mono-organotins. However, our results indicate that DBT is a more potent immunotoxin than TBT, and suggest a need for the reassessment of the potential toxicity of DBT to aquatic organisms.

Some thoughts on the response to antigens that are effector T-helper independent ('thymus independence')

The Self-Non-Self discrimination is germline-selected for defence mechanisms ('innate immune systems') whereas it is somatically learned for immune systems ('adaptive immune systems'). It is proposed that immune system evolved from defence mechanisms by adding large recognitive repertoires that, by aggregating with antigens, were able to trigger the already existent effector functions of defence mechanisms. Thus today there are two pathways to triggering each class of effector function (macrophage opsonization, complement lysis or natural killer/-natural cytotoxic cell activity). The antigen-antibody complex and the T-cell antigen-receptor interaction trigger the immune pathway: the receptors of the defence mechanism trigger the 'alternate' or 'innate' pathway. The evolutionary selection pressure on defence mechanisms was to increase the size of the recognitive repertoire, which in turn, necessitated the emergence of a somatically learned Self-Non-Self discrimination. By contrast with defence mechanisms that are triggered effector T-helper (eTh) independently by polymers (Signal[3]), immune systems can be activated by monomers, a pathway that requires associative recognition of monomer and the reading of two Signals, Signal[1] resulting from the binding of an epitope to the antigen-receptor complex, Signal[2] delivered by an eTh cell. The evolving immune system hijacked part of this eTh-independent pathway (Signal[3]) into which Signal ([1] + [2]) merged. A model of these relationships is proposed.

Evidence of aberration of the natural cytotoxic cell activity in Fundulus heteroclitus (Pisces: Cyprinodontidae) from the Elizabeth River, Virginia

There is a general agreement that exposure to high concentrations of polynuclear aromatic hydrocarbons (PAH) in sediments is associated with high frequencies of neoplasms in feral fish species. Since PAH modulate the activity of murine and amphibian natural cytotoxic (killer) cells, a leukocyte subpopulation that is believed to play an important role in immunosurveillance, we wished to determine if fish exposed to PAH could have an altered natural cytotoxic cell (NCC) activity. In the present study, mummichog ( Fundulus heteroclitus L.) were collected from two sites in the Elizabeth River, VA that are heavily contaminated with PAH, and from a relatively unpolluted reference site in the York River, VA. The cytotoxic activity of anterior kidney and splenic leukocytes was tested against the tumor cell line K562. The leukocytes from Elizabeth River fish displayed a significant depression of the in vitro tumorilytic activity as compared with leukocytes from the York River fish. Analysis of leukocyte-tumor cell conjugates indicated that Elizabeth River fish leukocytes were unable to recognize and subsequently bind to the tumor target cells. This suggests an aberration in the early events of the cytotoxic mechanism. By keeping the fish in cleaner York River water for up to 28 weeks the suppressed NCC activity was reversed totally in one site, which is slightly contaminated, and partially in the other site, which is heavily polluted with creosote from an operating wood treatment plant. This indicates that the decreased NCC activity was related, at least in part, to exposure to the chemical pollutants in the Elizabeth River sediments.

Effects of trichloroethylene on hepatic and splenic lymphocytotoxic activities in rodents

The effects of trichloroethylene (TRI), a widely used industrial solvent, on various immunological and toxicological parameters have been examined in Sprague-Dawley rats and B6C3F1 mice. Rats were administered TRI in vivo at 0.05, 0.5 and 5.0 mmol/kg per day intraperitoneally (i.p.) for 3 days. Mice were similarly treated with TRI at 10.0 mmmol/kg. The highest TRI dose resulted in decreased splenocyte count and relative spleen weights, in rats and mice respectively and inhibition of hepatic natural killer cell (NK), natural cytotoxic cell (NC) and NPK cell (a new described immune cell killing) activities in both rats and mice. High dose TRI in vitro resulted in minor decreases (< 10 %) in splenocyte viability, inhibition of LPS-stimulated mitogenesis in rat cells and marked inhibitions of NK and NC activities in all groups of effector cells. At the lowest in vitro dose mouse hepatic NK activity was still inhibited. Overall the data show that TRI is able to inhibit the activity of lymphocytotoxic cells which are involved in the immune surveillance of cancerous cells. This inhibition is particularly evident in the liver after in vivo administration and both liver and spleen cells after in vitro exposure. This suggests the possibility that compromised immune function may play a role in the carcinogenic responses in experimental animals on exposure to TRI.

Natural cell-mediated immunity in the rabbit ∗

Susceptibility and resistance to tumors represent the interplay of many factors. One factor felt to govern the development of tumors is natural killer and natural cytotoxic cellular activity. The constitutional resistance of rabbits to spontaneous tumor development raises questions regarding the activity of natural cell-mediated immunity in this species. We therefore examined the ability of rabbit spleen, lymph node, and peripheral blood lymphocytes to mediate natural killer cell (NK) and natural cytotoxic cell (NC) activity in vitro. Using classical approaches to the study of NK and NC activity, we found no evidence of these activities in leporine spleen, lymph node, and peripheral blood lymphocytes. Preincubation of these cells with IL-2 did not induce such activity. Antibody-dependent cell-mediated cytotoxic reactivity (ADCC), which is believed to be mediated by NK cells, was also undetectable in rabbit lymphocytes. As controls, lymphocytes from other species were capable of mediating NK, NC, and ADCC functions normally in these experiments. Finally, we were unable to identify a population of large granular lymphocytes, the cells believed to mediate NK activity in other animals. Therefore, we could not demonstrate in the rabbit either natural cell-mediated immunity or the population of cells usually associated with natural cell-mediated immunity. If such activity exists in rabbits, it is different from that seen in other animals. More likely, the basis for the natural resistance of rabbits to tumor development must be sought elsewhere.

Effect of cerebral hemisphere decortication on the cytotoxic activity of natural killer and natural cytotoxic lymphocytes in the mouse

A comparison was made of the effects of left and right cerebral decortication on cytotoxic activity of natural killer and natural cytotoxic lymphocytes in the mouse. Natural killer cytotoxic activity was significantly reduced after right decortication, whereas left decortication led to a less pronounced, though still significant fall. The cytotoxic activity of natural cytotoxic cells, on the other hand, was significantly i increased, particularly 15 days after left decortication. These findings mirror the results of previously published personal findings following electrothermocoagulation of the hypothalamus. The suggestion is made that the cortex and the hypothalamus form an integrated system for the control of certain aspects of natural immunity.

Human Natural Cytotoxic Activity Mediated by Tumor Necrosis Factor: Regulation by Interleukin-2

Freshly obtained normal lymphoid cells kill certain tumor target cells in vitro. Using peripheral blood lymphocytes (PBLs) and the human tumor target cell line BT-20, we have defined a tumor necrosis factor (TNF)-dependent, cell-mediated cytotoxic mechanism that is homologous to the murine natural cytotoxic (NC) cell activity. Human NC cell activity was detected in freshly isolated PBLs and was augmented by short in vitro pulses with recombinant human interleukin-2 but not with recombinant human alfa interferon. Monoclonal anti-TNF antibodies inhibited the killing of the target cells. The independence of interferon and the mediation of killing by TNF distinguish human NC cell activity from natural killer and lymphokine-activated killer cell activities.

Suppression of natural cytotoxic cell activity by social aggressiveness in [formula omitted

Our earlier observations revealed that social stress causes drastic effects on different physiological mechanisms and degenerative changes in leucocytes. In this preliminary work, we analyzed the effect of social aggressiveness on functional activites of leucocytes emphasizing (NCC) activity in Tilapia . At 10 hr post stress induction, fish could be differentiated into three categories: 1) dominants; 2) subordinates; and 3) indeterminants. Results of NCC as indicated by 4 hr. 51 Cr-release assay, demonstrated a significant suppression in cytotoxic reactivity in the subordinates and indeterminants compared to dominants. This suppression appears to be due to a decrease in the binding capacity of effector cells to YAC-1 target cells as indicated by the decreased number of conjugate forming cells. This binding process is a key event in activating the fish equivalent of NK cells in mammals. Decreased NCC-activity in stressed fish suggests that aberrations in cell mediated immunity result from social aggressiveness.

Augmentation of human natural cytotoxic cell activity by leukotriene B4 mediated by enhanced effector-target cell binding and increased lytic efficiency.

The addition of leukotriene B4 (LTB4) to cytotoxicity assays measuring natural killer (NK) or natural cytotoxic (NC) cell activities resulted in significantly augmented killing of K562 or herpes simplex virus (HSV)-infected target cells, respectively. Since the mechanism of cytotoxicity implies several steps, including the binding of effectors to targets which is Mg2+-dependent and the programming of lysis of the target which is Ca2+-dependent, we undertook to define the step(s) at which LTB4 acted in augmenting cytotoxicity. Our results showed that LTB4 significantly increased the percentage of effector-target conjugates when K562- or HSV-infected targets were incubated with lymphocytes. Maximal binding occurred at a concentration of LTB4 of 1 X 10(-10) M. Preincubation of lymphocytes and not target cells with LTB4 was sufficient to observe the increased binding. PBML binding to and killing of the NK-resistant target clone I, derived from K562, was not enhanced by LTB4. In the absence of Ca2+, cytotoxicity was impaired and LTB4 could not restore it. Use of a single cell lytic assay demonstrated augmented efficiency of lysis of both K562 and HSV-infected targets in the presence of LTB4. These findings suggest that LTB4 may augment natural cytotoxicity by enhancing target cell recognition by cytotoxic effector cells and subsequently by augmenting their lytic efficiency.

Human natural cytotoxic cells: Activation by a measles virus-induced lymphocyte factor which increases the expression of the HNC-1A3 antigen

When human lymphocytes were exposed to measles virus antigen or to SSPE virus-infected cells, their cytotoxic activity against uninfected MA-160 cells was markedly enhanced. In contrast, mumps virus or herpes simplex virus-infected cells did not show such an enhancing effect and were rather inhibitory. SSPE cells and measles virus antigen, but not mumps-virus-infected cells or mumps virus antigen, also induced a two-fold increase in the number of lymphocytes bearing the HNC-1A3 membrane antigen, which we recently reported to be associated with a natural cytotoxic cell population. Pretreatment of SSPE cells or measles virus antigen with anti-measles antibody abolished the enhancing effect. Heat-treating the cells or the antigen at 56°C for 30 min similarly abolished the effect. Supernatants of lymphocyte-SSPE cell cocultures were also effective in enhancing natural cytotoxicity. The soluble factor was a low molecular weight dialyzable molecule which was unaffected by boiling or trypsinization. It was released within 4 hours of coculture even in the presence of cycloheximide or following irradiation. Neither interferon nor leukotriene B 4 appeared to be responsible for this enhancement. Virus-lymphocyte interaction may thus enhance natural cytotoxic cell activity through the rapid production or release of a virus-induced small molecular weight lymphocyte factor.

Humans express natural cytotoxic (NC) cell activity that is similar to murine NC cell activity.

The expression of natural cytotoxic (NC) activity is well defined in mice, but poorly defined in humans. In this paper we report that humans express naturally occurring cytotoxic cell activity that recognizes and lyses murine targets that are sensitive to lysis mediated by murine NC cells, but not murine targets that are resistant to lysis by murine NC cells. We present data showing that these naturally occurring human cytotoxic cells and murine NC cells have similar lytic mechanisms. Both the human cytotoxic cells described here, and murine NC cells, use tumor necrosis factor (TNF) to mediate the lysis of sensitive targets. Moreover, targets that resist murine NC-mediated lysis by a protein synthesis-dependent post-recognitive mechanism use a similar mechanism to prevent lysis mediated by naturally occurring human cytotoxic cells. In addition to the similarity of naturally occurring human cytotoxic cells and murine NC cells in their specificity and lytic mechanism, naturally occurring human cytotoxic cells and murine NC cells are also similar in that their activity is both associated with a monocyte lineage and age independent. Taken together, these data indicate that humans express NC activity.

Evidence for the involvement of the thromboxane synthase pathway in human natural cytotoxic cell activity.

We and other investigators have recently shown that inhibitors of lipoxygenase reversibly inhibit natural cytotoxic (NC) or natural killer (NK) cell activity, whereas some inhibitors of cyclooxygenase enhance these functions. In addition, exogenous LTB4 augments NC and NK activity, whereas PGE2 depresses it. In the present studies, we sought to investigate the possible role of the TxA2 synthase pathway in NC function. Inhibition of this pathway by OKY-1581 or dazoxiben significantly inhibited NC activity against HSV-infected cells as well as NK function against K562 target cells. The inhibition was dose dependent, reversible, and not due to direct toxicity. NC activity was also significantly inhibited by the addition of PGE2 or PGI2 to the 4-hr assay, whereas addition of 6-keto-PGF1 alpha had no effect. Addition of PGH2, which could be converted to TxA2 or other PG, had no significant effect, but concomitant use of OKY-1581 produced a greater inhibition of NC function than by using OKY-1581 alone. U44069, a TxA2 analog, was inhibitory by itself and could not alter the inhibition caused by OKY-1581 or dazoxiben. In contrast, the TxA2 receptor blocker 13-APA significantly enhanced NC activity and even reversed the inhibitory effect of U44069 at equimolar (10(-7)M) concentrations. Taken together, these data suggest that most of the inhibitory effect of the TxA2 synthase inhibitors on NC and NK cell function derives from their ability to reorient cyclic endoperoxide metabolism toward more inhibitory compounds. In addition, TxA2 itself could exert a negative feedback on NC function through its receptor, as evidenced by the use of a TxA2 analog and a TxA2 blocker.