Effects of environmental stimuli on immunoreactivity: further studies on passive avoidance behavior

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.

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.

Behavioral and immunological events induced by electrical stimulation of the rat midbrain periaqueductal gray region

We report here on the immunological and behavioral alterations induced by stimulation of the mesencephalic periaqueductal gray matter (PAG), a component of the brain aversive system. Male Wistar rats were implanted with stimulating electrodes in the caudal dorsolateral part of the PAG. After recovery, animals were screened for aversive behavior, characterized by running, jumping, vocalization or freezing reaction. Then, rats were subdivided to those which could control aversive stimulation (AS) by switch-off response (cAS group) and those which could not interrupt AS (uAS group). After sensitization with bovine serum albumin (BSA) in complete Freund's adjuvant, rats were stimulated 3 times/week for 40 days, each session lasting 30 min/rat. Immunological assessment included antibody production and hypersensitivity skin reactions to BSA 14 and 21 days after immunization. A behavioral profile of aversively stimulated animals was determined by a poststartle response, open field (OF) activity and two-way shuttle-box avoidance task. The results revealed elevated antibody production to BSA in cAS and lowered in uAS rats, compared to sham-stimulated and intact controls. Arthus and delayed hypersensitivity skin reactions increased in PAG-stimulated animals on day 14 but not on day 21 after immunization. Poststartle response was enhanced both in cAS and uAS rats. Along with immunopotentiation, administration of cAS produced hyperactivity in OF test and facilitation of the active avoidance learning, whereas uAS caused only moderate suppression of rearing in a novel OF environment. Physiological implications and possible mechanisms that may account for PAG-mediated immunobehavioral changes are outlined.

Differential effects of corticosteroids on rat peripheral blood T-lymphocyte mitogenesis in vivo and in vitro

The effects of corticosteroids were studied on the concanavalin A (Con A)-induced mitogenesis of peripheral blood T-lymphocytes obtained from intact and adrenalectomized (ADX) Wistar rats. One week of adrenalectomy reduced the proliferative response of T-cells by 65% compared with sham-operated controls. Substitution of ADX rats with subcutaneously implanted 12.5-mg corticosterone (Cort) pellets, which resulted in low circulating Cort levels (17 +/- 3 nM), restored the reduced proliferative capacity to that of sham-ADX animals. In contrast, T-lymphocyte proliferation was nearly absent in ADX rats substituted with high circulating Cort levels (173 +/- 15 nM; 100-mg Cort pellet). In vitro, Cort suppressed the mitogenic response of T-lymphocytes from ADX and sham-ADX animals. The glucocorticoid antagonist RU-486 (500 nM) completely blocked this suppressive effect. However, a 10 times lower concentration of RU-486 reversed the effects of a low (10 nM) Cort concentration from suppression to stimulation. It is concluded that high Cort concentrations in vivo and in vitro suppressed T-lymphocyte mitogenesis but that low concentrations in vivo were stimulatory, whereas this stimulation in vitro occurred only in the presence of antiglucocorticoids. These opposing effects of Cort emphasize a bimodal regulatory role of this hormone in immune regulation that may be mediated by different corticosteroid receptors.

Influence of perceived psychological stress and distress on antibody response to low dose rDNA hepatitis B vaccine

The present study focused on the relationship between psychological stress and immune reaction to a novel antigen. Participants completed questionnaires on daily hassles, psychoneurotic complaints, coping style, and loneliness, 2 and 6 months after the first of a series injections with a low dose recombinant DNA hepatitis B vaccine. Antibody response was determined 7 months after the first vaccination. Based on the psychological questionnaires two different stress measures were calculated: a Stress Index score-month-2 and a Stress Index score-month-6 indicating stress levels experienced at the beginning and at the end of the study respectively. Antibody levels were found to be negatively related with the Stress Index score-month-2. Although the influence of psychological stress reported on month 6 tended to be in the same direction, this effect was not significant. Coping styles and loneliness were not associated with antibody formation. These results suggest that antibody formation to rDNA hepatitis B vaccine is negatively influenced by psychological stress.

The impact of stressors on immune and central neurotransmitter activity: bidirectional communication

Antigenic challenge may have broad ranging effects which include not only immunological changes, but also endocrine and central neurotransmitter repercussions, and may thus elicit profound behavioral sequelae. Commensurate with the notion that bidirectional communication exists between the immune and central nervous systems it has been demonstrated that manipulations which influence central neurotransmitter or endocrine activity provoke alterations of immune functioning, and conversely immunological alterations will affect central neurotransmitter and endocrine activity. It seems, as well, that environmental stressors may provoke marked alterations of the activity of each of these systems. Indeed, in several respects the variables that influence vulnerability to stressor-provoked neurotransmitter changes, likewise affect the immunological alterations engendered by stressors. Moreover, immunological challenges will affect central neurotransmitter functioning in much the same way as stressors provoke such effects. It is thought that immune derived products (including cytokines as well as peptide hormones) may act directly or indirectly to moderate neurotransmitter functioning, and centrally derived neurotransmitters and hormones may affect receptors present on lymphocytes. In accordance with earlier suggestions, it is maintained that the immune system may be acting as a sensory organ informing the brain of the presence of antigenic challenges, and the brain may interpret such challenge as a stressor, hence leading to behavioral alterations.

Differential effects of controllable and uncontrollable acute stress on lymphocyte proliferation and leukocyte percentages in humans

This study examined the effects of a 30-min laboratory stressor on aspects of immune function in 24 men and whether behavioral control over the stressor moderates stress effects. The stressor consisted of mild (2.5 mA) electric shock and loud (100 dB) white noise administered in an unpredictable, intermittent fashion. During stress sessions, only half of the subjects were able to control the stressor. Subjects with control were yoked to subjects who could not control the stressor so that both groups were exposed to identical intensity and duration of noise and shock. Immunologic function was assessed across stress and nonstress conditions by measuring changes in lymphocyte proliferation to concanavalin A (Con A) and phytohemagglutinin (PHA) and by measuring changes in percentages of lymphocytes and their subpopulations, granulocytes, and monocytes. Results revealed that exposure to the uncontrollable stressor altered mood but did not affect immune function. In contrast, exposure to controllable stress did not alter mood but did result in lowered lymphocyte proliferation to Con A. Poststress percentages of monocytes were also lower in subjects exposed to the controllable stressor. Results suggest that acute stress can alter aspects of immune function in humans and underscore the importance of stressor controllability in moderating stress effects on human immunity.

Differential effects of beta-endorphin on cAMP levels in human peripheral blood mononuclear cells

In the present paper we demonstrate that one of the early effects of the opioid peptide beta-endorphin on human peripheral blood mononuclear cells is the induction of a change in the intracellular cAMP level. However, the effect of beta-endorphin on cAMP levels is not uniform; increases as well as decreases in cAMP level are observed. It appears that beta-endorphin is a true modulator of intracellular cAMP level: the peptide will increase cAMP levels in cells with a low baseline level. In contrast, beta-endorphin tends to decrease cAMP levels is cells with a high cAMP concentration. Moreover, beta-endorphin modulates the rise in cAMP induced by beta-adrenergic activation. The effect of beta-endorphin on cAMP level correlates negatively with the magnitude of the change in cAMP level induced by beta-adrenergic activation.