Treadmill exercise training blunts suppression of splenic natural killer cell cytolysis after footshock.

This study extended to treadmill exercise training our prior report (Dishman RK, Warren JM, Youngstedt SD, Yoo H, Bunnell BN, Mougey EH, Meyerhoff JL, Jaso-Friedmann L, and Evans DL. J Appl Physiol 78: 1547-1554, 1995) that activity wheel running abolished the suppression of footshock-induced natural killer (NK) cell cytolysis. Twenty-four male Fischer 344 rats were assigned to one of three groups (n = 8, all groups): 1) a home-cage control group, 2) a sedentary treatment group, or 3) a treadmill-running group (0 degrees incline, 25 m/min, 35 min/day, 6 days/wk). After 6 wk, the treadmill and sedentary groups received 2 days of footshock. Splenic NK cytotoxicity was determined by standard 4-h (51)Cr release assay. Percentages of lymphocytes were determined by flow cytometry. Plasma levels of ACTH, corticosterone, and prolactin concentration were measured by radioimmunoassay. After footshock, percentage of lysis relative to home-cage controls was 40% and 80% for sedentary and treadmill-trained animals, respectively (P < 0.05). Our results indicate that the protective effect of chronic exercise on innate cellular immunity in the Fischer 344 male rat is not restricted to activity wheel running, nor is it explained by elevations in basal NK activity, increased percentages of splenic NK and cytotoxic T cells, or increased plasma levels of ACTH, corticosterone, and prolactin.     

Evaluation of natural killer cell activity

Natural killer (NK) cells are being appreciated not only for their ability to recognize and lyse tumor cells and virus-infected cells but also for their immunoregulatory properties. NK cells provide a first line of defense against invading pathogens with a two pronged attack, lysis of infected cells and secretion of cytokines and chemokines with potent antipathogen effects. This article describes the standard chromium release assay, which measures the ability of NK cells derived from the peripheral blood to lyse appropriate target cells.     

Down-regulation of natural killer cell activity in MoLV leukemogenesis: evidence for tumor-cell-mediated suppression

The role of natural killer (NK) cells in retrovirus-induced leukemogenesis was studied. These cells which do not require prior sensitization are considered as a part of the body's defense system against tumor development and spread. Neonate BALB/c mice infected with Moloney murine leukemia virus (MoLV) develop leukemia within 3-6 months. The MoLV-infected mice showed a progressive loss of endogenous and augmented NK activity, correlated with the development of the leukemic state. Mixing of spleen cells from tumor-bearing mice with NK-augmented splenocytes resulted in suppression of NK activity. In addition, mixing of T cell lines isolated from MoLV-induced tumors with augmented splenocytes also resulted in the down-regulation of NK cell activity. The present study demonstrates that tumor cells from leukemic organs and leukemic T cell lines can actively suppress NK cell function. It is postulated that after MoLV infection the progression of virus-transformed T cells to a fully developed tumor depends on the ability of these cells to down-regulate NK cell activity and thus escape immune surveillance.     

Renewal of natural killer cells in mice having elevated natural killer cell activity

The present study was designed to examined the dynamics of splenic natural killer (NK) cells under two conditions of enhanced NK cell activity: (1) CBA/J mice given polyinosinic-polycytidylic acid (poly-I:C), an NK-cell-enhancing agent, and 62) untreated athymic nude (nu/nu) mice. The 'total NK cell activity' of the spleen (percentage specific lysis corrected for changes in organ cellularity) increased 5-fold and 2.7-fold after poly-I:C treatment for 1 day and 4 days, respectively. An injection of hydroxyurea (HU), a cell-cycle-toxic drug, given together with either poly-I:C or saline to CBA/J mice resulted in both cases in a 25% reduction in total NK cell activity 1 day later. This suggests that the renewal rate of nondividing NK cells is similar in poly-I:C-treated and saline-injected mice, and that the NK-enhancing effect of poly-I:C is not due to a stimulation of proliferation among NK cell precursors. HU administered simultaneously with poly-I:C or saline for 4 days eliminated NK cell activity in both cases, indicating that spleen NK cell activity is mediated almost entirely by newly formed (less than or equal to 4 days) cells. In nude mice, NK cell activity was assayed at various intervals after an HU depletion period of 2 days. NK depletion was initially more rapid in nu/nu mice than in control (nu/+) mice, although equally profound, and the subsequent recovery of NK cell activity after cessation of HU was also more rapid than in control (nu/+) mice.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhibition of natural killer cell activity by IgA

The in vitro effect of IgA on natural killer (NK) activities of human peripheral blood mononuclear cells was investigated. Purified myeloma polymeric IgA2 (pIgA2) and secretory IgA (S-IgA) from human colostrum inhibited NK activity, while myeloma polymeric IgA1 (pIgA1), monomeric IgA1 (mIgA1), IgG, and IgM were ineffective. Inhibition was proportional to the concentration of pIgA2 (0.125-1 mg/ml) and was observed after as little as 1 hr of incubation at various effector to K562 target cell ratios. pIgA2 and S-IgA also inhibited NK activity of NK cell-enriched lymphoid cells and gamma-interferon-treated effector cells, but did not interfere with effector-target cell binding. The inhibitory effect was slightly diminished after 24 hr culture in pIgA2-free medium. Inhibition of cytotoxicity was not due to direct toxicity on lymphoid cells by IgA because PBL treated with pokeweed mitogen in the presence of pIgA2 or S-IgA differentiated into immunoglobulin-producing cells. Viability after 24 hr of preculture with pIgA2 and S-IgA was comparable to that of untreated control cells. Morphological examination of effector cells cultured with pIgA2 or S-IgA showed a decrease in the number of granules, and the formation of cytoplasmic vacuoles. These morphological changes appeared to coincide with the depressed cytotoxicity of NK cells. The results demonstrate that purified pIgA2 and S-IgA have significant immunomodulatory effects on human NK activity.     

Adherent cell requirement for PWM-stimulated factor suppression of natural killer cytotoxicity

Natural killer cytotoxicity is enhanced in a 5-day mixed-leukocyte culture (MLC). This augmentation of NK can be suppressed by factor released from pokeweed-mitogen (PWM)-activated peripheral blood cells. To maximize activity, the PWM-soluble factor must be present within the first 6 hr of the MLC, and is required to be in the culture for at least 4 hr. The affect of the PWM factor is not due to the destruction of either effector or stimulator cells. This factor does, however, require the presence of an adherent, non-T cell in the effector population. Directly incubating adherent cells with the PWM-induced soluble factor activates this population to mediate suppression. Thus the adherent cells are required for the PWM-induced suppression of NK cytotoxicity, indicating a possible regulatory mechanism for this cytotoxicity.     

Inhibition of natural killer cell lysis by natural killer-inhibitory substance: mechanism of suppression

The mechanism of suppression of NK-mediated lysis by a soluble product of peritoneal cells (NK-IS, natural killer-inhibitory substance) was investigated. Pretreatment of effector cells resulted in depressed NK lysis while pretreatment of targets had no effect, indicating suppression is due to alterations in effector cell function rather than changes in target cells. NK-IS had no effect on the formation of conjugates between effectors and NK-susceptible targets. When NK-IS was added to effector-target cell mixtures after the binding step had been successfully completed, ensuing lysis was significantly depressed, confirming that NK-IS inhibited a postbinding lytic event. The degree of suppression caused by NK-IS was directly related to the duration of exposure to the inhibitory molecule. In addition, a preliminary temperature-dependent step of binding to and/or intracellular entry of NK-IS into effectors is required before suppression can occur. NK-IS prevents the activation of NK cell lysis by interferon and Corynebacterium parvum and effectively inhibits lysis mediated by already activated effectors. The potent suppression of NK lysis and prevention of interferon and C. parvum-mediated activation of NK lysis by a soluble product of peritoneal cells may explain the extremely low level of NK effector cell function within the peritoneal cavity.     

Analysis of natural killer activity and natural killer cell subsets in patients with bladder cancer

Summary In order to analyze the state of the natural resistance system of bladder cancer patients in vivo, we measured natural killer (NK) activity and NK cell subsets of peripheral blood lymphocytes (PBL) from 46 patients with bladder cancer and 25 age- and sex-matched healthy volunteers. The mean NK activity in patients with lowstage bladder cancer was similar to that in the controls, while NK activity in patients with high-stage bladder cancer was significantly depressed. The mean proportions of Leu7⁺ cells in patients with both low-stage and highstage bladder cancer were significantly higher than that in the controls. The mean proportion of Leu11a⁺ cells in patients with low-stage bladder cancer was similar to that in the controls, while in patients with high-stage bladder cancer it was significantly higher. This study demonstrates the abnormal immunological state of bladder cancer patients; namely, abnormalities exist not only in NK activity but also in the proportions of circulating NK cell subsets.     

Glucocorticoid receptor mediated suppression of natural killer cell activity: identification of associated deacetylase and corepressor molecules

Physical and psychological stressors reduce natural killer cell function. This reduction in cellular function results from stress-induced release of glucocorticoids. Glucocorticoids act upon natural killer cells to deacetylate and transrepress immune response genes through epigenetic processes. However, other than the glucocorticoid receptor, the proteins that participate in this process are not well described in natural killer cells. The purpose of this study was to identify the proteins associated with the glucocorticoid receptor that are likely epigenetic participants in this process. Treatment of natural killer cells with the synthetic glucocorticoid, dexamethasone, produced a significant time dependent reduction in natural killer cell activity as early as 8h post treatment. This reduction in natural killer cell activity was preceded by nuclear localization of the glucocorticoid receptor with histone deacetylase 1 and the corepressor, SMRT. Other class I histone deacetylases were not associated with the glucocorticoid receptor nor was the corepressor NCoR. These results demonstrate histone deacetylase 1 and SMRT to associate with the ligand activated glucocorticoid receptor within the nuclei of natural killer cells and to be the likely participants in the histone deacetylation and transrepression that accompanies glucocorticoid mediated reductions in natural killer cell function.     

Mechanism of cell contact-mediated inhibition of natural killer activity

Natural killer cell activity is inhibited by primary cultures of monolayer cells. In this study, we analyzed the mechanism of the inhibition. Inhibited NK cells showed unaltered binding capacity to NK sensitive K562 cells. The orientation of the effector cells' actin-containing microfilaments, an event known to occur during the programming for the lysis stage in lytic conjugates, was unaffected by the inhibition. In single cell cytotoxicity experiments, the number of killer cells among conjugate-forming cells was reduced. The capacity of the inactivated NK cells to secrete cytotoxic factors upon stimulation with Con A was also impaired. Both NK-resistant inactivating target cells and NK-sensitive K562 cells were sensitive to the toxic factors secreted by NK cells. Thus, the results indicate that the target cell-mediated inactivation of NK cell is based on a block in the lethal hit stage, possibly due to reduced release of toxic factor(s) from the effector cells. The capacity of inactivated effector cells to mediate antibody-dependent cellular cytotoxicity was unimpaired, suggesting that the contact-mediated inhibition of cytotoxicity selectively affects NK cells.     

Pulmonary compartmentalization of interferon and natural killer cell activity

Studies were performed to determine if natural killer (NK) activity in the mononuclear cells harvested from infected lungs was dependent on local or systemic factors. Mice were inoculated by intratracheal (it), intraperitoneal (ip), or intravenous (iv) routes with (a LD50 dose of) influenza virus A PR/8/34. At various days postinoculation cells from lungs, spleens, and peripheral blood were assayed for NK activity, and lung wash, lung homogenates, and serum were assayed for interferon. After it inoculation there was three- to fourfold increase of NK activity in the lung with little or no increase in NK activity in spleens or peripheral blood. The local augmentation of NK activity in the lung correlated with an increase in interferon (IFN) titer in the lung wash and lung homogenate of PR8 inoculated mice. The virus failed to induce IFN or augment NK activity when it was inoculated systemically. The observed local augmentation of NK activity and local induction of interferon production following it inoculation suggests that the NK population in the lung is capable of responding to locally derived regulatory factors.     

Acquisition of enhanced natural killer cell activity under anesthesia

An increase in natural killer (NK) cell activity can be conditioned with a one trial learning paradigm to demonstrate the interaction between the central nervous system (CNS) and the immune system. In order to demonstrate learning possibilities during ‘non-conscious’ state, mice were anesthetized with a ketamin/rompun mixture and underwent one trial learning with odor cue as the conditioned stimulus (CS) preceding the unconditioned stimulus (US). The results indicated that mice that were exposed to camphor odor cue under the influence of anesthesia can associate the signal with the poly I:C unconditioned stimulus and were able to recall the conditioned response upon reexposure to the CS. Secondly, the conditioned association made in a conscious state can be recalled by exposure to the same olfactory odor cue in a ‘non-conscious’ state. The increase in the conditioned change in NK cell activity of both situations was significantly higher than the control group. The results demonstrate that learning can take place and the learned response can be recalled under the reduced awareness caused by anesthesia. The findings we report are unusual and novel in that they demonstrate that the CNS can learn new associations under conditions where the host is apparently unaware of the signals being linked. Anesthesia combined with the long interstimulus interval indicates that certain neuronal pathways in the CNS are receptive to second signals (elicited by the US) even when the second signal is separated by one day. This means the conditioned learning of a physiological response can take place unconsciously at a separate level and under situations where the host is totally unaware of the events which the brain is processing and linking as incoming information.     

Characterization of natural killer cell activity in Macaca nemestrina

Natural killer (NK) cell activity was evaluated in three groups of Macaca nemestrina that varied with respect to SAIDS D retrovirus serotype 2 (SRV-2/W) and viremic status. Target cells used were Raji and K562 cells. No significant differences (ANOVA) in mean NK activity were detected among the three groups of animals studied. Using Raji targets, mean LU₃₀/10⁶ ± SEM was 6.3 ± 1.6 for seronegative (V-Ab−) animals, 7.3 ± 1.5 for seropositive (V-Ab+) animals, and 10.2 ± 3.5 for persistently viremic (V + Ab−) animals. Using K562 targets, mean LU₃₀/10⁶ was 7.6 ± 1.7 for seronegative (V-Ab−) animals, 6.5 ± 2.5 for seropositive (V-Ab+) animals, and 5.1 ± 1.9 for persistently viremic (V+Ab−) animals. Percentage blood CD16⁺ and CD8⁺cells also were not different in the three groups of animals. NK activity did not always correlate with percentage of CD16⁺ or CD8⁺ cells in peripheral blood at the time the assays were done. In persistently viremic animals, there was a strong positive correlation between percent CD16⁺ and CD8⁺ cells and NK activity using K562 cells but not Raji cells. Depletion experiments indicated that lysis was mediated by both CD8⁺ and CD16⁺ cells with both Raji and K562 cells. However, Raji targets were a better indicator of killing mediated by CD16⁺ cells. Our studies indicate that M. nemestrina may be classified as high or low responders with regard to NK activity, and there was no correlation with SRV-2/W viral or antibody status. Additionally, our results suggested that group housing of M. nemestrina was usually associated with increased NK activity. In conclusion, studies of NK activity in M. nemestrina should consider target cells used, phenotype of effectors, endogenous (high or low) levels of NK activity in individual animals, and housing conditions. © 1996 Wiley-Liss, Inc.