Stressor-induced alterations of natural killer cell activity and central catecholamines in mice

Social isolation in mice: behavior, immunity, and tumor growth

The aim of this study was to investigate the behavioral, immunological, and neurological effects of long-term isolation in an animal model. Male C3H/eB mice wereraised in either social isolation or standard conditions for 6 weeks. At 10 weeks, each group was further divided into 3 sets. (A) Physical strength and behavior were evaluated with the grip strength, hot plate, staircase, and elevated plus-maze tests. Natural-killer cell activity and lymphocyte proliferation were measured. (B) Half the animals were subjected to electric shock with 3 reminders, and freezing time was evaluated at each reminder. Cortisone levels were evaluated after 16 weeks. (C)Mice were injected with 38 C-13 B lymphoma cells and followed for tumor size and survival. Strength evaluation yielded asignificantly lower body weight and grip strength in the socially isolated mice. Behavioral test results were similar in the two groups. The pattern of reactions to stress conditioning differed significantly, with the socially isolated mice showing an incline in freezing with each successive reminder, and the control mice showing a decline. The socially isolated mice had significantly attenuated tumor growth, with no significant difference in survival from control mice. There were no significant between-group differences in immunological parameters. In conclusion, social isolation serves as a model for chronic stress. It was associated with significant changes in stress conditioning reaction, resembling symptoms of post-traumatic stress disorder, and attenuated tumor development. No differences from controls were found in behavior tests, immune parameters, or survival after tumor cell inoculation.Lay summaryThis article explores biological and behavioral consequences of social isolation in a mice model. Our results show that social isolation leads to changes in the Hypothalamic-hypophyseal-adrenal axis, which in turn alter the response to stress. Additionally, social isolation was shown to impact tumor progression.

Stress conditioning in mice: alterations in immunity and tumor growth

The neuroendocrine and autonomic nervous systems are known regulators of brain-immune interaction. However, the functional significance of this interaction under stress is not fully understood. We investigated the effect of a stress paradigm by applying electric foot shock followed by three reminders, on behavior, immune parameters, and lymphoma tumor growth. Male C3H mice were divided into two groups: Group 1-exposed to electric foot shock followed by three reminders, and Group 2-untreated (controls). Sets of mice underwent the elevated plus maze, staircase, and hot plate tests. After foot shock, natural killer (NK) cell activity, and lymphocyte proliferation were measured. In addition, sets of mice were either vaccinated twice with B-cell lymphoma 38C-13 immunoglobulin for determination of anti-idiotype (Id) antibodies in sera, or inoculated with tumor cells and monitored for tumor development and survival time. Mice exposed to electric foot shock followed by the three reminders had higher NK cell activity, levels of anti-Id antibodies, and a higher proliferation rate of splenocytes in response to mitogens, than the control mice. The exposed mice also showed attenuated tumor growth. Thus, the stress paradigm inhibited tumor development and lead to some immune changes that were not accompanied by behavioral changes.

Environmental enrichment in mice decreases anxiety, attenuates stress responses and enhances natural killer cell activity

The importance of environment in the regulation of brain, behaviour and physiology has long been recognized in biological, social and medical sciences. Animals maintained under enriched conditions have clearly been shown to have better learning abilities than those maintained under standard conditions. However, the effects of environmental enrichment (EE) on immunity and emotionality have been less documented and remain questionable. Therefore, we investigated the effect of EE on natural killer (NK) cell activity, psychological stress responses and behavioural parameters. Male C3H mice were housed either in enriched or standard conditions for 6 weeks. Behaviour was then examined by the grip-strength test, staircase and elevated plus maze, and corticosterone levels and NK cell activity were measured. Furthermore, animals exposed to the stress paradigm, achieved by electric shock with reminders, were tested for freezing time in each reminder. Corticosterone levels were also measured. The EE mice showed decreased anxiety-like behaviour and higher activity compared to standard mice, as revealed by a greater percentage of time spent in the open arms of the elevated plus maze, and a higher rate of climbing the staircase. A shorter freezing time in the stress paradigm and no corticosterone level reactivity were measured in EE mice. In addition, NK cell activity in spleens of EE mice was higher than that demonstrated in those of standard mice. Thus, EE has a beneficial effect on anxiety-like behaviour, stress response and NK cell activity. The effect on NK cell activity is promising, due to the role of NK cells in host resistance.

Association of plasma free-3-methoxy-4-hydroxyphenyl (ethylene)glycol, natural killer cell activity and delirium in postoperative patients

We measured and compared levels of plasma free 3-methoxy-4-hydroxyphenyl (ethylene)glycol (pMHPG), a major metabolite of noradrenaline, and natural killer (NK) cell activity in 26 patients prior to their undergoing an operation for cardiovascular diseases; 11 of whom expressed delirium and 15 who did not. In conclusion, we found that pMHPG levels before an operation were higher in patients with postoperative delirium than in the patients without, while NK cell activity showed no difference between the two groups. It is possible that hyperactivity of noradrenargic neurons is connected with the development of postoperative delirium. Furthermore, we considered that measurement of pMHPG level before operation might be a useful tool to predict the occurrence of postoperative delirium.

Acute stress impairs NK cell adhesion and cytotoxicity through CD2, but not LFA-1

Using a nonhuman primate model, we examined the mechanisms by which acute social stress inhibits the ability of NK cells to form conjugates with, and lyse target cells. We examined the expression and role of the primary NK cell adhesion molecules, CD2 and LFA-1, in mediating conjugation to target cells. Acute stress induced a decrease in NK cell expression of CD2 (17+/-3%); and to a lesser degree induced a decrease in expression of LFA-1 (CD11a: 8+/-3%; CD18: 7+/-3%). Antibody blocking studies indicated that anti-LFA-1 significantly inhibited NK cell conjugate formation and cytotoxicity in both control (approximately 40% and approximately 50%, respectively) and stressed (approximately 20% and approximately 45%, respectively) conditions. However, anti-CD2 blocked conjugation and cytotoxicity in the control condition by approximately 50%, but had no capacity to further affect the inhibition of conjugation or cytotoxicity of NK cells induced by acute stress. These data indicate that there are differential effects of acute stress on the expression and function of LFA-1 and CD2, and that the stress-induced inhibition of NK cell adhesion and cytotoxicity is dependent upon modulation of adhesion and/or signalling through CD2.

Time-dependent effects of stressor application on metastasis of tumor cells in the lung and its regulation by an immunomodulator in mice

The effects of the timing of stressor application on transplanted tumor cells and its possible regulation by an immunomodulator was investigated. Male C57 BL/6N mice were subjected to rotational stressor for 7 days relative to tumor cell inoculation: stressor after inoculation of Lewis lung cancer cells, stressor during inoculation and stressor before inoculation. Stressor application and tumor cell inoculation induced transient decreases in body weight, particularly in mice stressed after inoculation. The mice exposed to the stressor during inoculation or before inoculation showed significant increases in the number of metastatic foci relative to control mice. Early administration of an immunomodulator, PSK, significantly attenuated the increase of metastatic foci in stressed mice. The weights of thymus gland and spleen at 14 days after inoculation were similar in the three stressor groups and the control group. Application of the stressor reduced NK cell activity of the normal mice as well as tumor bearing mice. The lowest pre-inoculation NK cell activity was observed in mice stressed for 7 days beginning on the day of inoculation. The NK cell activity decreased in the tumor bearing mice which were stressed at the time of tumor inoculation. Decreased NK cell activity was reversed at day 14 after tumor inoculation. The mice exposed to the stressor after inoculation showed lowest level of NK cell activity relative to mice exposed to the stressor before or during inoculation. The treatment of mice with PSK reduced these changes significantly. The present results suggest that the rotational stress reduces splenic NK cell activity, which may influence the magnitude of tumor metastasis, depending on the time of tumor cell injection. Further, administration of an immunomodulator may counteract the reduction of the NK cell activity.

Influence of psychosocial, psychogenic and neurogenic stressors on several aspects of immune functioning in mice

Analysis of stressor effects on immune functioning is complicated by the fact that the nature of the changes observed may be influenced by organismic factors (e.g., species, strain, age), the nature, severity and chronicity of the stressor, as well as the specific immune parameters being examined. It is demonstrated in the present investigation that in the highly reactive inbred BALB/cByJ mouse, the relatively hardy C57BL/6ByJ strain, as well as in the noninbred CD-1 strain, acute psychogenic (predator exposure) and neurogenic (footshock) stressors reduced splenic macrophage activity, and this effect was less marked after a chronic stressor. With protracted, but not transient, psychosocial disturbances (isolated housing) similar effects were seen, suggesting that the effect was not simply due to a change of the social mileau. The psychogenic and neurogenic stressors also enhanced LPS-stimulated lymphocyte proliferation in CD-1, but not in the inbred strains. However, isolated housing reduced both B and T cell proliferation, indicating that social isolation likely affects processes distinct from those of other stressors. Interestingly, when the aversiveness of the psychogenic stressor was increased (by decreasing the distance between the rat and the mouse) LPS-stimulated lymphocyte proliferation was reduced in the reactive BALB/cByJ strain, but increased in the hardy C57BL/6ByJ mice. This stressor, however, enhanced T cell proliferation in both strains of mice. It is suggested that analysis of stressor effects need to consider in greater detail the characteristics of the organism being stressed, as well as the characteristics of the stressor itself.

Natural killer (NK) cell activity and NK cell subsets in workers with a tendency of burnout

The involvement of cellular immunity in the burnout syndrome remains to be elucidated. We assessed three components of burnout of the Maslach Burnout Inventory: emotional exhaustion; depersonalization (DP); and personal accomplishment, as well as natural killer cell activity (NKCA) and NK cell subsets in 42 male workers. Workers with a higher DP score showed a lower NKCA and a lower proportionality of CD57+CD16+ to total lymphocytes. There were no differences in any of the health behaviors (e.g., smoking, alcohol, or obesity) between workers showing higher burnout and those showing lower burnout. A stepwise multiple regressions analysis demonstrated that NKCA was closely correlated with DP, independent of other variables, including a stress index. These results suggest that the relationship between reduced cellular immunity and DP is not due to traditional work stress or health behavioral problems. Further studies on DP as a psychosomatic disorder as well as an occupational health problem should be performed in the future.

Influence of a psychogenic and a neurogenic stressor on several indices of immune functioning in different strains of mice

It is demonstrated that cell proliferation in response to mitogens, natural killer cell (NK) activity, and macrophage functioning of mice may be influenced by either a neurogenic stressor (footshock) or a psychogenic stressor (exposing the mouse to a predator, namely a rat). The nature and magnitude of the immune changes, however, varied across three strains of mice (BALB/cByJ, C57BL/6ByJ, and CD-1), differing in reactivity to stressors and also as a function of the type of stressor employed. While footshock reduced mitogen-stimulated B-cell proliferation in BALB/cByJ mice, it had the opposite effect in the CD-1 strain. Exposure to the predator, however, had little effect in any of the strains. Macrophage activity and NK cytotoxicity were reduced in response to both stressors in a strain-dependent fashion. Plasma corticosterone in response to footshock was greater in BALB/cByJ than in C57BL/6ByJ mice; however, the strain difference was not evident in response to the psychogenic stressor. It is suggested that analyses of stressor effects on immune functioning need to consider the specific strain/species employed, the particular immune parameters being examined, and the nature of the stressor employed.

Inhibitory effect of pregnancy on stress-induced immunosuppression through corticotropin releasing hormone (CRH) and dopaminergic systems

To clarify the involvement of pregnancy in the response of the neuroendocrine-immune system to stress, we examined splenic natural killer-cell-activity-(NKCA) and its relevant central and blood parameters in female virgin and pregnant rats (10 to 11 days gestation) exposed to forced water-immersion stress with durations of 90 min and 180 min. Decreases in splenic NKCA, corticotropin releasing hormone (CRH) in the hypothalamus, and increases in progesterone (P), beta-endorphin (beta EP), and dopamine (DA) metabolic ratios in the frontal cortex and nucleus accumbens produced by stress were recognized in the virgin rats, but not in the pregnant rats. Pregnancy reduced splenic NKCA in rats without stress, but elevated it in the rats exposed to stress with a duration of 180 min. These findings suggest inhibitory effects of pregnancy on stress-induced immunosuppression and neuroendocrine changes, thereby promoting homeostasis in the neuroendocrine-immune system against stress. Such enhanced homeostasis associated with pregnancy seemed to be mediated by the activation of placental P and placental or pituitary beta EP in cooperation with mesocortical and mesolimbic DA systems and hypothalamic CRH.

Stressor-induced alterations of the splenic plaque-forming cell response: strain differences and modification by propranolol

The effects of stressor application on the splenic plaque-forming cell (PFC) response was assessed in two strains of mice: the BALB/cByJ strain, which is highly responsive to stressors; and the more hardy DBA/2J strain. Both strains exhibited a peak PFC response 120 h following administration of sheep red blood cells (SRBC; 5 x 106 cells). Stressor exposure reduced the immune response; however, the appearance of such an outcome was dependent upon the time at which the stressor was applied relative to SRBC inoculation. In DBA/2J mice, foot-shock applied either immediately after SRBC inoculation or at the time of the peak immune response (120 h) resulted in suppression of the PFC response. In BALB/cByJ mice, both stressor severities provoked an immunosuppression when applied 120 h after inoculation, but when applied 96 h after immunization only foot-shock reduced the PFC response. At other intervals, the stressors were without effect. Pretreatment with the beta-norepinephrine antagonist propranolol precluded the immunosuppression elicited by a stressor applied 96 h after inoculation, but did not affect the reduction of the PFC response elicited by a stressor applied 120 h after inoculation. It is suggested that several factors may contribute to stressor-provoked alterations of the immune response, and that the contribution of these factors vary over the course of an immune response being mounted.

A role for CRH and the sympathetic nervous system in stress-induced immunosuppression

Central CRH coordination of the behavioral and physiologic sequelae of stress has been well established, and so it is parsimonious to suggest that CRH might also coordinate the immunologic sequelae. The studies presented here lend support to this suggestion. CRH administration into the brain was shown to modulate aspects of both cellular and humoral immune function, and the inhibition of CRH release in the brain following stress inhibited stress-associated immunosuppression. The effects of CRH appear to be mediated by the sympathetic branch of the autonomic nervous system, as chemical sympathectomy and pharmacological blockade of beta-adrenergic receptors both reversed the effects of CRH on immune function. In contrast, removal of the adrenal glands did not alter the immunologic effects of CRH. These links among CRH in the brain, sympathetic activation, and immune function suggest the possibility that immune function may be altered in other conditions characterized by elevated sympathetic tone, such as depression and aging, and that these alterations may be attributed to CRH dysregulation in the brain. These studies shed light on the intricate relationship between the brain and the immune system, and also illuminate its complexity. The differential regulation of CRH in the brain and the periphery is one example of the latter. These findings also set the stage for potential clinical intervention with CRH antagonists, for example, to treat compromised immune function associated with chronic stress, depression, or aging.

Influence of change from grouped to individual housing on a T-cell-dependent immune response in mice: antagonism by diazepam

Transferring CD-1 mice from grouped to individual housing and then maintaining them individually resulted in a decline in the peak IgM plaque-forming cell (PFC) response to sheep red blood cells (SRBCs). However, the immunosuppression was dependent on the amount of time mice were maintained individually. In particular, individual housing for 5-10 days prior to SRBC inoculation and for 4 days following inoculation resulted in a suppression of the splenic PFC response and serum antibody titers. Shorter periods of individual housing (4 days following inoculation) did not provoke the immunosuppression. Likewise, following more protracted individual housing (15-30 days prior to inoculation) the immunosuppression was not evident. Inasmuch as daily treatment with an anxiolytic, diazepam (1.0 mg/kg), antagonized the suppression induced by 5 days of individual housing, it was suggested that the change from group to individual housing and then maintenance of animals individually acted much like a stressor to induce the immunosuppression.

Acute and chronic stressor effects on the antibody response to sheep red blood cells

Exposure to inescapable foot-shock 72 h following immunization with sheep red blood cells resulted in a marked suppression of the peak splenic immunoglobulin (Ig)M plaque-forming cell response and plasma antibody titers in CD-1 mice. However, the nature of this effect was influenced by the animal's stressor history. In particular, if mice were initially exposed to a single stressor session immediately or 24 h following antigen treatment subsequent reexposure to the stressor (72 h following inoculation) did not provoke the immunosuppression. Moreover, reexposure to the stressor-related cues elicited a marked immunoenhancement. In contrast, if animals were exposed to a single stressor session 48 h prior to inoculation then later reexposure to the stressor-related cues provoked an immunosuppression. Among mice that had been exposed to a repeated stressor regimen on successive days prior to inoculation, the immunosuppression ordinarily elicited by an acute stressor was absent. Indeed, chronic stressor exposure typically favored potentiation of the immune response. However, the immunofacilitation elicited by the chronic stressor treatment likely was unrelated to the immunoenhancing effects of pairing a stressor with antigenic challenge.

Consequences of restraint stress on natural killer cell activity, behavior, and hormone levels in rhesus macaques (Macaca mulatta)

Three experiments were performed to determine the effect of stress on the neuroendocrine-immune system in nonhuman primates. In Experiment 1 the diurnal variation in cell and hormone levels was determined. The percentages of neutrophils, monocytes, and eosinophils fluctuated throughout the 24-hr period, while white blood cell (WBC), neutrophil-to-lymphocyte ratio (N:L), hemoglobin (Hgb), natural killer cell cytotoxicity (NK activity) and beta-endorphin levels did not. Experiment 2 investigated the effects of ketamine and restraint on behavior. Scratching was increased in control monkeys and animals receiving ketamine, whereas passivity was increased in chair-restrained animals. In Experiment 3, eight adult male rhesus monkeys were restrained in primate chairs at 0600h. Behavior was filmed for 3 hr and blood samples were collected at 0700, 0800, and 0900. Whole blood was analyzed for total WBC and percentage of each leukocyte type. NK activity was also measured. Plasma levels of cortisol and beta-endorphin were determined and behavior was quantitated from video-records. WBC and the percentage of neutrophils increased during the restraint period, while the percent lymphocytes and monocytes decreased. NK activity also decreased over time after restraint whereas plasma cortisol and beta-endorphin levels increased significantly. Although after the 3 hr of restraint stress, changes were found in hormone levels, behavior, and NK activity, there were no significant correlations between the parameters measured. Thus, our results indicate that there is not a common neuroendocrine response or single neuroendocrine mediator that results in predictable behavioral changes and immune suppression following stress.