Suppression of specific antibody production by inescapable shock: stability under varying conditions

The impact of stress and anesthesia on animal models of infectious disease

Stress and general anesthesia have an impact on the functional response of the organism due to the detrimental effects on cardiovascular, immunological, and metabolic function, which could limit the organism's response to an infectious event. Animal studies have formed an essential step in understanding and mitigating infectious diseases, as the complexities of physiology and immunity cannot yet be replicated in vivo. Using animals in research continues to come under increasing societal scrutiny, and it is therefore crucial that the welfare of animals used in disease research is optimized to meet both societal expectations and improve scientific outcomes. Everyday management and procedures in animal studies are known to cause stress, which can not only cause poorer welfare outcomes, but also introduces variables in disease studies. Whilst general anesthesia is necessary at times to reduce stress and enhance animal welfare in disease research, evidence of physiological and immunological disruption caused by general anesthesia is increasing. To better understand and quantify the effects of stress and anesthesia on disease study and welfare outcomes, utilizing the most appropriate animal monitoring strategies is imperative. This article aims to analyze recent scientific evidence about the impact of stress and anesthesia as uncontrolled variables, as well as reviewing monitoring strategies and technologies in animal models during infectious diseases.

An evaluation of the rat intestinal monoamine biogeography days following exposure to acute stress

Stress-induced abnormalities in gut monoamine levels (e.g., serotonin, dopamine, norepinephrine) have been linked to gastrointestinal (GI) dysfunction, as well as the worsening of symptoms in GI disorders. However, the influence of stress on changes across the entire intestinal monoamine biogeography has not been well-characterized, especially in the days following stress exposure. Therefore, the aim of this study was to comprehensively assess changes to monoamine neurochemical signatures across the entire rat intestinal tract days after exposure to an acute stressor. To the end, adult male F344 rats were subjected to an episode of unpredictable tail shocks (acute stress) or left undisturbed. Forty-eight hours later rats were euthanized either following a 12 h period of fasting or 30 min of food access to evaluate neurochemical profiles during the peri- and early postprandial periods. Monoamine-related neurochemicals were measured via UHPLC in regions of the small intestine (duodenum, jejunum, ileum), large intestine (cecum, proximal colon, distal colon), cecal contents, fecal contents, and liver. The results suggest a relatively wide-spread increase in measures of serotonin activity across intestinal regions can be observed 48 h after exposure to acute stress, however some evidence was found supporting localized differences in serotonin metabolization. Moreover, acute stress exposure reduced catecholamine-related neurochemical concentrations most notably in the ileum, and to a lesser extent in the cecal contents. Next, stress-related fecal serotonin concentrations were consistent with intestinal profiles. However, fecal dopamine was elevated in association with stress, which did not parallel findings in any other intestinal area. Finally, stress exposure and the food access period together only had minor effects on intestinal monoamine profiles. Taken together, these data suggest nuanced differences in monoaminergic profiles exist across intestinal regions the days following exposure to an acute stressor, highlighting the importance of assessments that consider the entire intestinal tract biogeography when investigating stress-related biological outcomes that may be relevant to GI pathophysiology.

Post Mortem Study on the Effects of Routine Handling and Manipulation of Laboratory Mice

Routine handling and manipulation of laboratory mice are integral components of most preclinical studies. Any type of handling and manipulation may cause stress and result in physical harm to mice, potentially leading to unintended consequences of experimental outcomes. Nevertheless, the pathological effects of these interventions are poorly documented and assumed to have a negligible effect on experimental variables. In that context, we provide a comprehensive post mortem overview of the main pathological changes associated with routine interventions (i.e., restraint, blood drawing, and intraperitoneal injections) of laboratory mice with an emphasis on presumed traumatic osteoarticular lesions. A total of 1000 mice from various studies were included, with 864 animals being heavily manipulated and 136 being handled for routine husbandry procedures only. The most common lesions observed were associated with blood collection or intraperitoneal injections, as well as a series of traumatic osteoarticular lesions likely resulting from restraint. Osteoarticular lesions were found in 62 animals (61 heavily manipulated; 1 unmanipulated) with rib fractures and avulsion of the dens of the axis being over-represented. Histopathology and micro-CT confirmed the traumatic nature of the rib fractures. While these lesions might be unavoidable if mice are manipulated according to the current standards, intentional training of research personnel on appropriate mouse handling and restraint techniques could help reduce their frequency and the impact on animal wellbeing as well as study reproducibility.

A Review of the Effects of Pain and Analgesia on Immune System Function and Inflammation: Relevance for Preclinical Studies

One of the most significant challenges facing investigators, laboratory animal veterinarians, and IACUCs, is how to balance appropriate analgesic use, animal welfare, and analgesic impact on experimental results. This is particularly true for in vivo studies on immune system function and inflammatory disease. Often times the effects of analgesic drugs on a particular immune function or model are incomplete or don't exist. Further complicating the picture is evidence of the very tight integration and bidirectional functionality between the immune system and branches of the nervous system involved in nociception and pain. These relationships have advanced the concept of understanding pain as a protective neuroimmune function and recognizing pathologic pain as a neuroimmune disease. This review strives to summarize extant literature on the effects of pain and analgesia on immune system function and inflammation in the context of preclinical in vivo studies. The authors hope this work will help to guide selection of analgesics for preclinical studies of inflammatory disease and immune system function.

Psychoneuroimmunology: Then and Now

Psychoneuroimmunology (PNI) emerged in the neurosciences in the late 1970s to early 1980s and has extended to influence the fields of psychology, psychiatry, endocrinology, physiology, and the biomedical research community. This review documents the journey of PNI from the early 1980s to the present. Today, we recognize that the highly complex immune system interacts with an equally complex nervous system in a bidirectional manner. Evolutionarily old signals continue to play a role in these communications, as do mechanisms for protection of the host. The disparity between physical and psychological stressors is only an illusion. Host defense mechanisms respond in adaptive and meaningful ways to both. The present review will describe a new way of thinking about evolutionarily old molecules, heat shock proteins, adding to a body of evidence suggesting that activation of the acute stress response is a double-edged sword that can both benefit and derail optimal immunity.

Observed parent-child relationship quality predicts antibody response to vaccination in children

BACKGROUND

Quality of the parent-child relationship is a robust predictor of behavioral and emotional health for children and adolescents; the application to physical health is less clear.

METHODS

We investigated the links between observed parent-child relationship quality in an interaction task and antibody response to meningococcal conjugate vaccine in a longitudinal study of 164 ambulatory 10-11 year-old children; additional analyses examine associations with cortisol reactivity, BMI, and somatic illness.

RESULTS

Observed Negative/Conflict behavior in the interaction task predicted a less robust antibody response to meningococcal serotype C vaccine in the child over a 6 month-period, after controlling for socio-economic and other covariates. Observer rated interaction conflict also predicted increased cortisol reactivity following the interaction task and higher BMI, but these factors did not account for the link between relationship quality and antibody response.

CONCLUSIONS

The results begin to document the degree to which a major source of child stress exposure, parent-child relationship conflict, is associated with altered immune system development in children, and may constitute an important public health consideration.

"Anatomy of an Illness": control from a caregiver's perspective

Caregivers of loved ones with chronic illnesses experience an uncontrollable challenge with potentially negative behavioral and medical consequences. Extensive research has demonstrated immune and endocrine regulation can be significantly disrupted by negative behavioral factors based on both animal models and human studies. However, fewer studies have focused on how psychosocial interventions might reverse the negative consequences of stressors such as caregiving. The distress of caring for individuals with cancer has only recently begun to receive attention. These interventions addressing caregiver distress are rare overall and caregivers of patients receiving hematopoietic stem cell transplants (HSCT) have received even less attention. HSCT caregivers report feelings of loss of control. Animal studies suggest that control over aversive events can mitigate the negative consequences of stressors. Caregivers of allogeneic HSCT patients for blood cancers must be available 24/7 for three months or longer following stem cell infusion to closely monitor the recipients' health and well-being. Does establishing a greater sense of control have positive impacts on caregivers? A randomized control trial of a cognitive behavioral stress management intervention for allogeneic HSCT caregivers is briefly described. A model of caregiver mental health which may potentially impact the patient's quality of life is proposed. These relationships exist in a complex system that includes genetic influences, sex, social environment, and prior experience. This system fits well within recent formulations of a "complexity science" approach to health and well-being.

Stress-evoked sterile inflammation, danger associated molecular patterns (DAMPs), microbial associated molecular patterns (MAMPs) and the inflammasome

Since the inception of the field of psychoneuroimmunolology research, there has been an appreciation that the physiological response to stressors includes modulation of immune function. Investigators initially focused on the effect of stress on cellular migration and immunosuppression and the resultant decreases in tumor surveillance, anti-viral T cell immunity and antigen-specific antibody responses. More recently, it has become clear that exposure to stressors also potentiate innate immune processes. Stressor exposure, for example, can change the activation status of myeloid lineage cells such as monocytes, macrophages, neutrophils, and microglia, leading to a primed state. In addition, stressor exposure increases the synthesis and release of a vast cadre' of inflammatory proteins both in the blood and within tissues (i.e., spleen, liver, adipose, vasculature and brain). The mechanisms for stress-evoked innate immune 'arousal' remain unknown. The goals of this presidential address are the following: (1) offer a personalized, brief overview of stress and immunity with a focus on 'aroused' innate immunity; (2) describe sterile inflammatory processes and the role of the inflammasome; and (3) suggest that these same processes likely contribute to primed myeloid cells and inflammatory protein responses (systemic and tissue) produced by stress in the absence of pathogens.

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.

Acute Exercise as an Adjuvant to Influenza Vaccination

Acute exercise prior to vaccine administration can improve the immune response. Animal data are now supported by human trials, which have shown that immune responses are enhanced by a bout of acute exercise before innoculation; this effect is particularly prominent in vaccines that normally produce weak immune responses. Although there remain many aspects of this phenomenon to be investigated, including task characteristics such as duration and form of exercise, it appears that even a moderate bout of exercise of the muscles into which vaccine will be administered can enhance the antibody response. In this review, the authors will summarize the animal and human literature and discuss the investigation of potential mechanisms of acute exercise–induced immunoenhancement.

Effects of small increases in corticosterone levels on morphology, immune function, and feather development

Stressors encountered during avian development may affect an individual's phenotype, including immunocompetence, growth, and feather quality. We examined effects of simulated chronic low-level stress on American kestrel (Falco sparverius) nestlings. Continuous release of corticosterone, a hormone involved in the stress response, can model chronic stress in birds. We implanted 13-d-old males with either corticosterone-filled implants or shams and measured their growth, immune function, and feather coloration. We found no significant differences between groups at the end of the weeklong exposure period in morphometrics (mass, tarsus, wing length, and asymmetry), immunocompetence (cutaneous immunity, heterophil/lymphocyte ratio, and humoral immunity), or feather coloration. One week subsequent to implant removal, however, differences were detected. Sham-implanted birds had significantly longer wings and a reduced level of cutaneous immune function compared with those of birds given corticosterone-filled implants. Therefore, increases of only 2 ng/mL in basal corticosterone titer can have small but measurable effects on subsequent avian development.

Effects of corticosterone on innate and humoral immune functions and oxidative stress in barn owl nestlings

The costs of coping with stressful situations are traded-off against other functions such as immune responses. This trade-off may explain why corticosterone secretion reduces immune reactions. Corticosterone differentially affects various immunity components. However, which component is suppressed varies between studies. It remains unclear whether the trade-off in energy, nutrition, autoimmunity or oxidative stress accounts for differential immunosuppression. In this study, we investigated whether corticosterone differentially affects the constitutive innate and humoral acquired immunity. We used barn owl nestlings, implanting 50% with a corticosterone-releasing pellet and the other 50% with a placebo pellet. To measure the effect on humoral immunity we vaccinated 50% of the corticosterone-nestlings and 50% of the placebo-nestlings with the antigens 'Tetravac' and the other 50% were injected with PBS. To assess the costs of elevated corticosterone, we measured body mass and resistance to oxidative stress. Administration of corticosterone increased corticosterone levels whereas vaccination induced the production of antibodies. Corticosterone reduced the production of antibodies, but it did not significantly affect the constitutive innate immunity. Corticosterone reduced body growth and resistance to oxidative stress. Under stressful conditions barn owl nestlings seem to keep the constitutive innate immunity, whereas elevated corticosterone levels negatively affected inducible immune responses. We found evidence that mounting a humoral immune reaction is not costly in terms of growth, but reduces the resistance to oxidative stress independently of corticosterone administration. We suggest that humoral immunity is suppressed because the risk of immunopathologies may be disproportionately high when mounting an antibody response under stressful situations.

Psychosocial influences on immunity, including effects on immune maturation and senescence

Studies investigating the influence of psychosocial factors on immunity played a critical and formative role in the field of psychoneuroimmunology (PNI), and have been a major component of articles published in Brain, Behavior and Immunity (BBI). An analysis of papers during the first two decades of BBI from 1987-2006 revealed three behavior-related topics were most prominent: (1) stress-induced changes in immune responses, (2) immune correlates of psychopathology and personality, and (3) behavioral conditioning of immunity. Important subthemes included the effect of early rearing conditions on immune maturation in the developing infant and, subsequently, psychosocial influences affecting the decline of immunity in the senescent host. The responsiveness of cell functioning in the young and elderly helped to validate the view that our immune competence is malleable. Many technical advances in immune methods were also evident. Initially, there was a greater reliance on in vitro proliferative and cytolytic assays, while later studies were more likely to use cell subset enumerations, cytokine quantification, and indices of latent virus reactivation. The reach of PNI extended from the traditional clinical entities of infection, autoimmunity, and cancer to attain a broader relevance to inflammatory physiology, and thus to asthma, cardiovascular and gastrointestinal disease. There continue to be many theoretical and applied ramifications of these seminal findings. Fortunately, the initial controversies about whether psychological processes could really impinge upon and modify immune responses have now receded into the pages of history under the weight of the empirical evidence.

Effects of chronic stress on the immune response to oral human serum albumin-conjugated starch microparticles in rats

Uptake of antigens and bacteria over the follicle-associated epithelium (FAE) is increased after chronic psychological stress. We investigated whether stress affects the immune response to particle-conjugated antigens taken up via the FAE. Rats were submitted to two 10-day periods of water avoidance stress and orally immunized during these periods. Stressed immunized rats displayed altered cell populations and a Th1-skewed immune response within the lymphoid follicles, together with enhanced delayed-type hypersensitivity. We conclude that chronic stress affects the cell-mediated immune response after oral immunization, which may have implications for the understanding of allergic and autoimmune diseases and development of oral vaccines.

Acute restraint stress enhances calcium mobilization and proliferative response in splenic lymphocytes from mice

Calcium (Ca2+ ) plays an essential role in lymphocyte activation and maturation. Acute and chronic stress has been shown to modulate the lymphocyte immune response; but the relationship between cytosolic free Ca2+ concentration ([Ca2+ ]i) and the immune response in lymphocytes following exposure to stress has not been examined. In the present study, we investigated the effects of acute restraint stress on [Ca2+ ]i and the proliferation of splenic lymphocytes from mice. We observed that 2 h of restraint significantly increased plasma corticosterone levels in mice. On examining [Ca2+ ]i and the proliferation ex vivo of splenic lymphocytes isolated from restraint-stressed mice using fura-2 and 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide, respectively, we found that acute restraint stress caused a significant increase in resting [Ca2+ ]i and significantly enhanced the ability of concanavalin A (Con A; a T-cell-selective mitogen) to increase [Ca2+ ]i but not that of lipopolysaccharide (LPS; a B-cell-selective mitogen). In addition, acute restraint stress significantly enhanced Con A-stimulated but not LPS-stimulated lymphocyte proliferation. Overall, there was a positive correlation between [Ca2+ ]i and T-cell proliferation following acute restraint stress. The enhancements of [Ca2+ ]i and T-cell proliferation were completely suppressed by verapamil (a Ca2+ channel blocker). These results suggest that acute restraint stress enhances Con A-stimulated T-cell proliferation by increasing [Ca2+ ]i via stimulation of Ca2+ entry.

The Flinders Sensitive Line rat: a selectively bred putative animal model of depression

The Flinders Sensitive Line (FSL) rats were originally selectively bred for increased responses to an anticholinesterase agent. The FSL rat partially resembles depressed individuals because it exhibits reduced appetite and psychomotor function but exhibits normal hedonic responses and cognitive function. The FSL rat also exhibits sleep and immune abnormalities that are observed in depressed individuals. Neurochemical and/or pharmacological evidence suggests that the FSL rat exhibits changes consistent with the cholinergic, serotonergic, dopaminergic, NPY, and circadian rhythm models but not the noradrenergic, HPA axis or GABAergic models of depression. However, evidence for the genetic basis of these changes is lacking and it remains to be determined which, if any, of the neurochemical changes are primary to the behavioral alterations. The FSL rat model has been very useful as a screen for antidepressants because known antidepressants reduced swim test immobility when given chronically and psychomotor stimulants did not. Furthermore, rolipram and a melatonin agonist were shown to have anti-immobility effects in the FSL rats and later to have antidepressant effects in humans. Thus, the FSL rat model of depression exhibits some behavioral, neurochemical, and pharmacological features that have been reported in depressed individuals and has been very effective in detecting antidepressants.

Stress applied during primary immunization affects the secondary humoral immune response in the rat: involvement of opioid peptides

The effect of unpredictable, inescapable and uncontrollable electric tail shocks (ES) on the humoral immune response to bovine serum albumin (BSA) was investigated in the rat. Contributions of the procedures that accompany shock delivery, such as witnessing the ES procedure (stress witnessing, SW) and exposure to the apparatus for shock delivery (apparatus control, AC) to the changes in specific immunity induced by ES were also tested. All procedures were applied during primary and/or secondary immunization. It was demonstrated that exposure to ES during primary immunization with BSA significantly suppressed specific anti-BSA antibody production after secondary and tertiary immunization with the same antigen. Exposure to the SW procedure during primary immunization with BSA enhanced the specific antibody level after secondary immunization, while exposure to the apparatus alone did not influence the development of either the primary or secondary humoral immune response to BSA. Both ES-induced suppression and SW-induced potentiation of the humoral immune response were partially inhibited by prior treatment with the opioid receptor antagonist naloxone. Additionally, treatments with the opioid peptides methionine- and leucine-enkephalin decreased anti-BSA antibody level, mimicking to some extent the effects of ES. It is suggested that ES and endogenous opioid peptides had long-term effects on humoral immunity through mechanisms involving immunologic memory.

Stressor exposure produces long-term reductions in antigen-specific T and B cell responses

Exposure to an acute laboratory stressor at the time of keyhole limpet hemocyanin (KLH) immunization results in a long-term suppression in circulating anti-KLH antibody. The mechanism for the stress-induced reduction in anti-KLH immunoglobulin (Ig) remains unknown. Given that the generation of anti-KLH antibody requires T cell help, we hypothesize that stress reduces the proliferation of anti-KLH T cells, thus leading to a reduction in anti-KLH antibody. The present studies examined the effect of tail shock stress (100, 1.6 mA, 5-s, 60 s ITI) on the KLH specific T cell response. Fischer F344 rats were immunized either intraperitoneally (i.p.) or subcutaneously (s.c.) at the base of the tail with 200 microg KLH, and exposed to inescapable tail shock (IS) or remained in their home cages (HCC). T cell proliferation after KLH restimulation, but not ConA, was markedly suppressed in IS animals in both the spleen after i.p. immunization and the draining lymph nodes after s.c. immunization. Other secondary lymphoid cells did not differ in their proliferative capacity. Anti-KLH IgG, IgG1 and IgG2a, but not anti-KLH IgM serum levels were significantly suppressed. These data support the conclusion that stress suppresses the generation of antigen specific T cells. In addition, the methods employed in the current study allow the isolation of the site of the acquired T cell immune response, making it possible to further elucidate the cellular mechanisms that contribute to stress-induced modulation of the antigen-specific acquired immune response.

Voluntary freewheel running selectively modulates catecholamine content in peripheral tissue and c-Fos expression in the central sympathetic circuit following exposure to uncontrollable stress in rats

Modulation of sympathetic drive to the spleen is one potential mechanism whereby physical activity prevents stress-induced splenic immune suppression in rats. The current study tested the hypothesis that voluntary freewheel running reduces peripheral sympathetic drive by modulating stress-induced activity of brain regions synaptically linked to sympathetically innervated peripheral organs, including the adrenals and spleen. To this end, adrenal and splenic catecholamine content and activity of the central sympathetic circuit indexed by c-Fos protein induction, elicited by acute exposure to inescapable tail shock, were measured. Stressor exposure depleted adrenal and splenic norepinephrine content and elicited a robust increase in c-Fos in the brains of sedentary rats. Physical activity status had no effect on adrenal norepinephrine content. Indicative of attenuated sympathetic drive to the spleen, however, 6 weeks of voluntary freewheel running diminished stress-induced splenic norepinephrine depletion, and significantly attenuated stress-induced c-Fos in specific brain regions responsible for sympathetic regulation, including tyrosine hydroxylase-immunoreactive neurons of the locus coeruleus, A5 cell group and rostral ventrolateral medulla. Results suggest that voluntary activity attenuates sympathetic drive to the spleen during stressor exposure by selectively modulating stress-induced activity of the central sympathetic circuit. The attenuation of sympathetic responses observed in this study may be one important mechanism for the protective effect of physical activity against stress-related illness and immunosuppression.

The effect of hypnotic-guided imagery on psychological well-being and immune function in patients with prior breast cancer

OBJECTIVE

To determine the effect of hypnotic-guided imagery on immune function and psychological parameters in patients being treated for Stage I or II breast cancer.

METHODS

To determine the effects of hypnotic-guided imagery on immune function and psychological parameters, the following study was undertaken. Psychological profiles, natural killer (NK) cell number and activity were measured at baseline, after the 8-week imagery training program and at the 3-month follow-up.

RESULTS

There were significant increases in improvement in depression (P<.04) and increase in absolute number of NK cells, but these were not maintained at the 3-month follow-up. Hypnotic-guided imagery did cause some transient changes in psychological well-being and immune parameters. However, these changes were not retained after the treatment ended.

CONCLUSIONS

Many studies during the last 15 years have demonstrated interactions between the central nervous and the immune systems. While a negative effect of stress on immune responses has been demonstrated, there have also been published reports that psychological treatments can positively alter the immune system. However, given the complexities of immune system kinetics, the transient nature of any psychological effect and the insensitivity of immune assays, our study indicates that there is a role for hypnotic-guided imagery as an adjuvant therapy.

On learned helplessness

"Learned helplessness" and its Pavlovian analog, learned irrelevance, are phenomena thought integral to understanding depression, PTSD, psychosomatic vulnerability, and a variety of diseases and immune disorders. The origin and development of research on learned helplessness is briefly overviewed with attention to the reasons for the controversy that surrounds the study of learned helplessness and derived physiological, psychological, and behavioral phenomena. The need to remedy past focus on American research and English language journals in this area is noted. The heuristic value as well as the wide ranging empirical value of the research domain is lauded. The meretricious emerging social and legal barriers to this research are noted to be unrealistic and unfortunate.

Acute and chronic social defeat suppresses humoral immunity of male Syrian hamsters (Mesocricetus auratus)

Stressors, both physical and psychological, can activate the hypothalamic-pituitary-adrenal (HPA) axis, leading to a wide range of physiological responses including increased glucocorticoid release and suppression of immune function. The majority of studies published to date have focused on the effects of physical stressors (e.g., cold exposure, electric shock) on immunity. The present study examined the role of a stressor, social defeat, on humoral immune function of Syrian hamsters (Mesocricetus auratus). Specifically, adult male Syrian hamsters experienced social defeat (i.e., exposure to a dominant animal in that animal's home cage) that was either acute (i.e., a single exposure) or chronic (i.e., daily exposures across 5 days). A control group of animals was placed in a resident's home cage without the resident animal present and did not experience defeat. After the last encounter, blood samples were drawn and animals were subsequently injected with keyhole limpet hemocyanin (KLH). Blood samples were again taken 5 and 10 days postimmunization and serum was analyzed to determine serum cortisol and anti-KLH immunoglobulin G (IgG) concentrations. Cortisol concentrations were elevated in both acutely and chronically defeated hamsters compared with control animals. In contrast, serum IgG concentrations were significantly reduced in both groups of defeated hamsters compared with control animals. Collectively, these results demonstrate that both acute social defeat and chronic social defeat lead to activation of the HPA axis and suppression of humoral immune function. These data suggest that social defeat is an important, ecologically relevant model with which to examine stress-induced immune suppression in rodents.

Psychological stress and antibody response to immunization: a critical review of the human literature

OBJECTIVE

The objective of this review was to evaluate the evidence for the hypothesis that psychological stress influences antibody response to immunization in humans.

METHODS

A critical review of the literature was conducted.

RESULTS

The evidence supports an association between psychological stress and suppression of humoral immune (antibody) response to immunization. This association is convincing in the case of secondary immune response but weak for primary response. The lack of consistent evidence for a relation with primary response may be attributed to a failure to consider the critical points when stress needs to be elevated in the course of the production of antibody. Lower secondary antibody responses were found among patients with chronically high levels of stress (severe enduring problems or high levels of trait negative affect). These responses were found most consistently among older adults. Lower secondary responses were also found for those reporting acute stress or negative affect, but only in studies of secretory immunoglobulin A antibody in which psychological and antibody measures were linked very closely in time. Health practices did not mediate relations between stress and antibody responses; however, there were indications that elevated cortisol levels among stressed patients could play a role. Evidence also suggests the possible influences of dispositional stress-reactivity and low positive affect in the inhibition of antibody production.

CONCLUSIONS

The literature supports a relationship between psychological stress and antibody responses to immunizations. The data are convincing in the case of secondary response but weak for primary response. More attention to the kinetics of stress and antibody response and their interrelations is needed in future research.

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.

Effects of mild stress on the immune response against pseudorabies virus in mice

Stress is a recognised problem in intensive pig husbandry, which might lead to changes in immune reactivity. To study the effect of stress on the development of an anti-viral immune response, we used a murine model in which mice were immunized with an attenuated strain of pseudorabies virus (PRV). The effect of two stress treatments, both relevant to intensive pig husbandry, on the development of the specific immune response against PRV was investigated. The stress treatments consisted of restraint, social isolation, and transport and they differed in predictability. The specific immune response against PRV, which developed in the draining lymph nodes, was measured by a lymphocyte proliferation assay and cytokine production assays. Our results showed that the unpredictable stress treatment had no effect on the development of the immune response against PRV in mice, whereas the predictable stress treatment actually hastened the immune response.

Exposure to acute stress induces brain interleukin-1beta protein in the rat

Peripheral immune stimulation such as that provided by lipopolysaccharide (LPS) has been reported to increase brain levels of IL-1beta mRNA, immunoreactivity, and bioactivity. Stressors produce many of the same neural and endocrine responses as those that follow LPS, but the impact of stressors on brain interleukin-1beta (IL-1beta) has not been systematically explored. An ELISA designed to detect IL-1beta was used to measure levels of IL-1beta protein in rat brain. Brain IL-1beta was explored after exposure to inescapable shock (IS; 100 1.6 mA tail shocks for 5 sec each) and LPS (1 mg/kg) as a positive control. Rats were killed either immediately or 2, 7, 24, or 48 hr after IS. Brains were dissected into hypothalamus, hippocampus, cerebellum, posterior cortex, and nucleus tractus solitarius regions. LPS produced widespread increases in brain IL-1beta, but IS did not. Adrenal glucocorticoids are known to suppress IL-1beta production in both the periphery and brain. Thus, it was possible that the stressor did provide stimulus input to the brain IL-1beta system(s), but that the production of IL-1beta protein was suppressed by the rapid and prolonged high levels of glucocorticoids produced by IS. To test this possibility rats were adrenalectomized or given sham surgery, with half of the adrenalectomized rats receiving corticosterone replacement to maintain basal corticosterone levels. IS produced large increases in brain IL-1beta protein in the adrenalectomized subjects 2 hr after stress, whether basal corticosterone levels had been maintained. Thus elimination of the stress-induced rise in corticosterone unmasked a robust and widespread increase in brain IL-1beta.

The effect of depression in an animal model on 5'-ectonucleotidase, antibody production, and tissue ascorbate stores

The learned helplessness model of depression in rats was tested. It was hypothesized that 5'-ectonucleotidase (NT), ascorbate, and antibody to sheeps' red blood cells (SRBC) are significantly reduced in rats who experienced uncontrollable shock, compared with rats who did not receive shock or could control it. During a learned-helplessness manipulation, antibody response to SRBC and NT values were unaffected. However, tissue ascorbate stores fell significantly, by 20-30%. The lack of effects on antibody responses and NT are discussed n terms of the acute nature of the stressor used in this model, as opposed to the more chronic stressors that have occurred in the human model.

Conditioned immunomodulation: investigations of the role of endogenous activity at mu, kappa, and delta opioid receptor subtypes

The present investigations were designed to determine the role of activity at mu, kappa, and delta opioid receptor subtypes in conditioned immunomodulation by evaluating the effects of selective opioid receptor antagonists on conditioned stimulus-induced alterations in immune status. Lewis rats were exposed to an aversive conditioned stimulus that was developed through pairings with electric footshock. This aversive conditioned stimulus induces a reduction in splenic natural killer cell activity, splenocyte proliferation in response to mitogens, and diminished levels of interferon-gamma (IFN-gamma) production by splenocytes. Intracerebroventricular (i.c.v.) administration of the opioid antagonist naltrexone or the mu 1-selective antagonist naloxonazine blocked conditioned alterations of immune status, indicating that activity at mu-opioid receptors is involved in conditioned immunomodulation. Further support for the involvement of mu-opioid receptors within the central nervous system is provided by data showing that peripheral administration of naloxonazine, at doses shown to be effective when administered i.c.v., had no effect on conditioned alterations of immune status. Ventricular administration of the kappa receptor antagonist nor-binaltorphimine (nor-BNI) did not antagonize the immunomodulatory effects of the conditioned stimulus. Administration of the delta receptor antagonist naltrindole also did not antagonize the conditioned alterations of immune status. Collectively, the results of this study indicate that the alterations of immune status produced by an aversive conditioned stimulus require activity at mu-opioid receptors, possibly mu 1, within the central nervous system.

Stress affects corticosteroid and immunoglobulin concentrations in male house mice (Mus musculus) and prairie voles (Microtus ochrogaster)

Glucocorticoids, secreted in response to perceived stress, can suppress immunoglobulin (Ig) levels and compromise immune function in mice and rats. Prairie voles (Microtus ochrogaster) have been reported to exhibit basal corticosterone concentrations that would cause pathological changes in the immune function of most other rodents. The goals of the present study were to verify that serum corticosterone concentrations are high in prairie voles, as compared with house mice (Mus musculus), by measuring serum corticosterone with the same RIA; to examine the effects of mild stressors on corticosterone response in both species and to examine the effects of elevated corticosterone levels on IgM and IgG levels in prairie voles and house mice. After 2 weeks of randomly timed 15-min daily restraint or cold-water swim sessions, animals were injected with sheep red blood cells. The data confirmed that basal blood concentrations of corticosterone were higher in prairie voles than house mice, but these high levels doubled after the first swim session in prairie voles, indicating that the adrenals can respond to stressors by producing increased corticosterone. After stress, antibody production (both IgM and IgG) was reduced in house mice but not in prairie voles, despite higher blood concentrations of glucocorticoids in prairie voles. Although body mass was statistically equivalent between species, prairie voles and mice differed dramatically in adrenal and splenic masses. Average adrenal mass of prairie voles was approximately three times the average mass of these organs in house mice; in contrast, the average splenic mass of house mice was approximately three times that of prairie voles. These data may be relevant to seasonal changes in immune function and survival.

The influence of physical restraint or fasting on plaque-forming cell response in mice

This study was designed to investigate the effects of 1- and 3-day (16 h/day) physically restrained or fasting on immunological and endocrine responses in CBF1 mice. The influence of stressors on these responses was evaluated using anti-sheep red blood cell plaque-forming assay, and by examining T cell subsets, thymus weight and endocrine hormone levels. The results revealed that a significant elevation of the plaque-forming cells (PFC) was found in spleen cells in 1-day restrained mice, that the PFC were conversely suppressed following 3-day physically restrained stress, and that the PFC were not affected by 1- or 3-day fasting stress. Serum levels of norepinephrine were found to be significantly increased only in 1-day physically restrained mice. No change of T cell subsets and thymus weight was found in 1-day physically restrained mice. A significant increase in serum corticosterone levels was elicited in both 1- and 3-day physically restrained mice, and 3-day fasting mice, while increased Lyt2-positive T cell and thymic atrophy were found only in 3-day physically restrained mice. These findings suggest that immune function was differentially affected by the duration and types of stressors.

Corticotropin-releasing hormone is involved in conditioned stimulus-induced reduction of natural killer cell activity but not in conditioned alterations in cytokine production or proliferation responses

Research from our laboratory has demonstrated that the presentation of an aversive conditioned stimulus produces pronounced suppression of several in vitro measures of immune status. The present study was designed to evaluate the role of central corticotropin-releasing hormone (CRH) in the mechanisms mediating these conditioned effects. The aversive conditioned stimulus was a distinct environment that had previously been associated with electric footshock. Lewis rats received intraventricular administration of either buffered saline or a dose of the CRH-selective receptor antagonist alpha-helical CRH(9-41) (0, 0.5, 5, or 50 micrograms) prior to exposure to the aversive conditioned stimulus or home cage control treatment. The aversive conditioned stimulus produced decreases in splenic natural killer cell activity, splenocyte responsiveness to the mitogens concanavalin A (ConA), phytohemagglutinin (PHA), lipopolysaccharide (LPS), and the combination of ionomycin and phorbol myristate acetate (PMA), blood leukocyte responsiveness to ConA and PHA, and the production of interleukin-2 and interferon-gamma by activated splenocytes. The conditioned stimulus also produced an increase in plasma levels of corticosterone. Pretreatment with alpha-helical CRH(9-14) completely blocked the conditioned stimulus-induced suppression of natural killer cell activity. The CRH antagonist had no attenuative effect on the conditioned suppression of splenocyte or blood leukocyte proliferation in response to mitogens, or the production of interleukin-2 or interferon-gamma by activated splenocytes. There was also no effect of alpha-helical CRH(9-14) on the conditioned stimulus-induced increase in plasma corticosterone. These findings suggest that conditioned stimulus-induced suppression of natural killer cell activity is mediated by a mechanism that involves activity at central CRH receptors, and that this conditioned modulation is independent of HPA activation. Furthermore, these results indicate that the mechanisms involved in conditioned stimulus-induced suppression of proliferative or cytokine production responses are distinct from those involved in the modulation of natural killer cell activity.

Mechanisms of conditioned immunomodulation

This article presents some recent work from our laboratory indicating that multiple physiological systems play a role in conditioned immunomodulation. The first study shows that naltrexone, but not N-methylnaltrexone, blocks the suppressive effects of an aversive conditioned stimulus on Con-A-induced proliferation and natural killer cell activity of splenic lymphocytes. This finding indicates that central opioid activity is involved in the conditioned effects. The second study shows that the beta-adrenergic antagonists atenolol and ICI-118,551 block of the suppressive effects of an aversive conditioned stimulus on Con-A-induced proliferation, but have no effect on natural killer cell activity. This result indicates the involvement of the adrenergic system in a subset of the conditioned effects. Collectively, these experiments provide evidence that both the opioid system and the sympathetic nervous system are involved in conditioned immunomodulatory changes elicited by an aversive conditioned stimulus.

Effects of sleep on the production of cytokines in humans

The restorative functions of sleep may affect immunologic functioning. The present study examined the effects of sleep on stimulated cytokine release in 13 healthy men. The subjects spent 2 experimental nights in the sleep laboratory. In one condition, lights were turned off at 11:00 PM to enable sleep for 3.5 hours. Thereafter, they stayed awake till 7:00 AM. In the other condition, conversely, subjects stayed awake between 11:00 PM and 3:00 AM. Then, lights were turned off for a 3.5-hour phase of sleep. Blood was sampled every 30 minutes between 11:00 PM and 7:00 AM. Sleep was monitored by polysomnographic recordings. Release of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta) was determined after stimulation of mononuclear cells with lipopolysaccharide from Escherichia coli. The release of IL-2 was stimulated with phytohemagglutinin. Compared with wakefulness, after 3 hours of sleep, production of TNF-alpha and IL-1 beta was substantially diminished (p < .01). Production of IL-2 was enhanced during sleep (p < .05), with this effect being limited to the second nocturnal sleep phase after 3:00 AM. Sleep-dependent changes in stimulated cytokine release were independent of changes in plasma cortisol concentrations. These results indicate a specific reducing effect of sleep (vs. wakefulness) on cytokine production by monocytes (TNF-alpha and IL-1 beta). The rather slow development of the effects calls for further studies to establish the exact time course of the influence of sleep on cytokine production.

Suppression of lymphocyte mitogenesis in different rat strains exposed to footshock during early diurnal and nocturnal time periods

The present study examined stressor interactions with genotype and light/dark cycle. Male Brown Norway (BN), Fischer 344 (F344), Lewis (from two different vendors: Lew/CR and Lew/H) and Sprague Dawley (SD) rats were exposed to footshock either in the early light or early dark circadian phase. Immediately after footshock, the spleen and whole blood proliferation to PHA and Con A was assessed. To provide endocrine indices of stress, serum was measured for corticosterone and interleukin-6 (IL-6). All rats showed significant increases in serum corticosterone and IL-6 following footshock either in the light or the dark. Rat strain differences were noted in the IL-6 response, while the corticosterone response was strong for all strains. The criterion for 'suppression' of lymphocyte proliferation was p < .05 (as determined by ANOVA) compared to non-shocked controls. Spleen: with the exception of BN rats, the other strains showed suppressed spleen cell proliferation to PHA and Con A both in the light and the dark. BN rats failed to show suppression of mitogenic activity to PHA when footshock was given in the light. Peripheral blood lymphocytes: suppression in Lew rats from either vendor, and in F344 and BN rats, did not vary with time of day nor with the type of mitogen tested. SD rats did not show suppression to PHA if shocked in the light. These results highlight the generality of stressor-induced mitogenic lymphocyte proliferation during the early diurnal and nocturnal periods of the day.

A permissive role of corticosterone in an opioid form of stress-induced analgesia: blockade of opiate analgesia is not due to stress-induced hormone release

The 100 inescapable tail-shock paradigm produces three sequential analgesic states as the number of shocks increases: an early opioid analgesia (after 2 shocks) that is attenuated by systemic naltrexone, a middle analgesia (after 5-40 shocks) that is unaffected by systemic naltrexone, and a late opioid analgesia (after 80-100 shocks) that is attenuated by systemic naltrexone. In order to determine whether the absence of adrenal hormones would affect any of these analgesias, we tested adrenalectomized (ADX) versus sham-operated control rats 2 weeks post-surgery. Pain threshold was assessed using the tail-flick (TF) test. ADX attenuated both the early (2 shock) and late (80-100 shock) opiate analgesias and failed to reduce the naltrexone-insensitive analgesia after 5-40 shocks. We demonstrated that a loss of adrenomedullary catecholamines does not underlie the ADX-induced attenuation of opioid analgesia since sympathetic blockade using systemic chlorisondamine (6 mg/kg) failed to reduce analgesia at any point in the shock session. It was further shown that stress levels of adrenal hormones are not critical since (a) analgesia was unaffected when animals were tested 48 h after ADX, (b) 2 shocks do not produce a surge in corticosterone (CORT) over and above levels observed in animals restrained and TF tested in preparation for shock, and (c) basal CORT replacement in drinking water fully restored analgesia in ADX rats. These experiments demonstrate that basal CORT, rather than adrenomedullary substances, is critical to the expression of analgesia. The function of CORT here is not linked to a shock-induced surge of the steroid. CORT appears to play a permissive role in the expression of analgesia. Potential effects of the absence of corticosteroids on neurotransmitter biosynthesis important in analgesia production are discussed.

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.

Chronic restraint attenuates the immunosuppressive response induced by novel aversive stimuli

The exposure to a novel aversive event, such as foot shock, induced a decrease in the percentage of T lymphocytes and a clear reduction in the delayed-type hypersensitivity reaction (DTH). This immunosuppressive response to an acute stressor was absent in rats that were previously exposed to a chronic immobilization stress regime (2 h daily during 7 consecutive days), but was still present in animals with prior exposure to only one or three restraint sessions. No stress effect was observed in other immunologic parameters, such as the percentage of B lymphocytes or the hemagglutinin titer, in any of the experimental treatments. The possible involvement of central adaptive mechanisms in the attenuation of the immunosuppressive response induced by an acute stress is discussed.

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.

Modulation of the in vivo antibody response by a benzodiazepine inverse agonist (DMCM) administered centrally or peripherally

Exposure to stressors can result in changes in immune function. Although there is increasing information concerning the peripheral hormonal and neural mediators of stress-induced changes in immune function, there is little information concerning the central nervous system mechanisms that lead to the peripheral changes. The following experiments examined the possible involvement of the benzodiazepine-GABAA-chloride complex in modulation of the in vivo antibody response. Rats were given either peripheral or intracerebroventricular injections of methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM), a drug that has been shown to act at the benzodiazepine-GABAA complex and produces a behavioral state similar to anxiety. Rats were then immunized with keyhole limpet hemocyanin (KLH) and serum levels of KLH-specific antibody were measured for 2 weeks after immunization. Both peripheral and central administration of DMCM modulated the in vivo antibody response. The dose-response relationship of DMCM and changes in antibody levels was nonmonotonic, with high doses resulting in an increase in serum antibody levels and moderate doses resulting in a decrease in serum antibody levels. A possible role of the benzodiazepine-GABAA system in stress-induced immunomodulation is discussed.

Specific antibody levels in free-ranging rhesus monkeys: relationships to plasma hormones, cardiac parameters, and early behavior

Levels of tetanus-specific antibodies were assessed in free-ranging, yearling rhesus monkeys following prophylactic immunization with tetanus toxoid. Each subject's behavior had been observed between 11 and 25 weeks of age and approximately 2 months later during its mother's first concentrated mating period as a part of another study. Prior to immunization, at approximately 1 year of age, cardiovascular parameters, and several plasma parameters [cortisol, adrenocorticotrophic hormone (ACTH), growth hormone (GH), interleukin-2 (IL-2), and total plasma immunoglobulin G (IgG)] were measured during a brief period of captivity. Antibody titers noted approximately 2 weeks after immunization were related to cardiovascular parameters. Thus, yearlings with high heart rates and low heart rate variability during captivity had the highest tetanus-specific serum IgG. Levels of plasma cortisol, ACTH, total IgG, and IL-2 noted at the time of capture were unrelated to subsequent antibody levels. Antibody titers were, however, positively correlated with GH noted immediately following capture on the day prior to immunization. Antibody titers were also related to the infants' behavior observed during their mother's first concentrated mating period. Infants who were most distressed (high levels of distress vocalization) when their mother resumed mating (a time particularly stressful for free-ranging rhesus infants) showed lower antibody titers to tetanus immunization as a yearling. The present observations add support to the existence of a relationship between behavior during exposure to an early stressor and later immune regulation and that certain cardiovascular parameters may be related to certain indicators of immunoregulation.

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.

Effects of voluntary exercise on immune function in rats

We investigated effects of voluntary wheel running on specific antibody responses to Keyhole Limpet Hemocyanin (KLH) and on mitogen-stimulated lymphocyte proliferation in adult male rats. Each subject was placed in a running wheel for 12 h daily during the dark portion of the light cycle for a total of 8 weeks. For experimental animals the wheels rotated freely, enabling subjects to exercise at will, while for control animals the wheels were prevented from rotating. Subjects were immunized with KLH (25 micrograms) 5 weeks into the study, and blood samples were collected intermittently from the tail for 3 weeks and later assayed for anti-KLH antibody levels. At the end of the study, subjects were sacrificed and spleens were dissected and assayed for lymphocyte proliferative responses to the mitogen Concanavalin A. Exercised rats gained less weight and had higher splenic proliferative responses than control rats; however, there were no significant group differences in anti-KLH antibody levels.

Seven-day variable-stress regime alters cortical beta-adrenoceptor binding and immunologic responses: reversal by imipramine

Rats were submitted daily to a variable stressor for 1 week with or without concurrent imipramine (IMI) administration. One day after the last injection or stressful event, binding of cortical beta-adrenoceptors was determined in all experimental groups. Another group of chronically stressed animals with or without concurrent IMI administration were sacrificed 24 h following the last stress or injection treatment, and several immunologic parameters were evaluated. Chronically stressed rats showed an enhanced number of cortical beta-adrenergic sites without changes in their affinity. This effect was not present following concurrent administration with the antidepressant. In addition, a decreased percentage of T lymphocytes and a reduced delayed-type hypersensitivity reaction was also observed in stressed animals. Both responses were no longer evident when stressed rats were previously administered IMI. A possible link between behavioral, neurochemical, and immunologic alterations due to the stress regime is discussed.

Inescapable footshock exposure differentially alters antigen- and mitogen-stimulated spleen cell proliferation in rats

A variety of stressors have been shown to influence specific and non-specific measures of immune function in laboratory animals. One of the most common tools used to evaluate lymphocyte function is the non-specific mitogen proliferation assay. Assessment of this function in the rat spleen has revealed profound suppression following restraint, electric shock, and re-exposure of animals to a fearful context. However, there have been no studies that have compared the effects of stressor exposure on mitogen- and specific antigen-stimulated spleen cell proliferation. Therefore, the present study addressed this issue through experiments in which rats were immunized intraperitoneally with 1 microgram cholera toxin and exposed to acute (one session) or repeated (three consecutive daily sessions) footshock. The results showed that footshock exposure prior to immunization inhibited cholera toxin stimulated spleen cell proliferation 7 days after immunization. Acute or repeated footshock exposure 5-7 days after cholera toxin immunization depressed non-specific spleen cell proliferation, while augmenting the proliferative response to specific antigen. From these observations it can be hypothesized that footshock exposure either differentially regulates lymphocyte activation by clonal and polyclonal signals, and/or naive and memory cells react differently to stressor exposure.