Short and long restraint differentially affect humoral and cellular immune functions

Bridging environment, physiology and life history: Stress hormones in a small hibernator

Our knowledge of the perception of stress and its implications for animals in the wild is limited, especially in regard to mammals. The aim of this study was therefore to identify sex specific effects of reproductive activity, body mass, food availability and hibernation on stress hormone levels in the edible dormouse (Glis glis), a small mammalian hibernator. Results of our study reveal that reproductive activity and pre-hibernation fattening were associated with high cortisol levels in both sexes. During the mating season, in particular individuals with low body masses had higher stress levels. Elevated levels of cortisol during pre-hibernation fattening were even higher in females that had formerly invested into reproduction compared to non-reproductive females. Previously observed impairments on health parameters and reduced survival rates associated with reproduction emphasize the functional relevance of high stress hormone levels for fitness. Prolonged food limitation, however, did not affect stress levels demonstrating the ability of dormice to predict and cope with food restriction.

It takes two to tango: Phagocyte and lymphocyte numbers in a small mammalian hibernator

Immunity is energetically costly and competes for resources with other physiological body functions, which may result in trade-offs that impair fitness during demanding situations. Endocrine mediators, particularly stress hormones, play a central role in these relationships and directly impact leukocyte differentials. To determine the effects of external stressors, energetic restraints and competing physiological functions on immune parameters and their relevance for fitness, we investigated leukocyte profiles during the active season of a small obligate hibernator, the edible dormouse (Glis glis), in five different study sites in south-western Germany. The highly synchronized yearly cycle of this species and the close adaptation of its life history to the irregular abundance of food resources provide a natural experiment to elucidate mechanisms underlying variations in fitness parameters. In contrast to previous studies on hibernators, that showed an immediate recovery of all leukocyte subtypes upon emergence, our study revealed that hibernation results in depleted phagocyte (neutrophils and monocytes) stores that recovered only slowly. As the phenomenon of low phagocyte counts was even more pronounced at the beginning of a low food year and primarily immature neutrophils were present in the blood upon emergence, preparatory mechanisms seem to determine the regeneration of phagocytes before hibernation is terminated. Surprisingly, the recovery of phagocytes thereafter took several weeks, presumably due to energetic restrictions. This impaired first line of defense coincides with lowest survival probabilities during the annual cycle of our study species. Reduced survival could furthermore be linked to drastic increases in the P/L ratio (phagocytes/lymphocytes), an indicator of physiological stress, during reproduction. On the other hand, moderate augmentations in the P/L ratio occurred during periods of low food availability and were associated with increased survival, but reproductive failure. In this case, the stress response probably represents an adaptive reaction that contributes to survival by activating energy resources. In contrast to our expectation, we could not detect an amplification of stress through high population densities. Summarized, results of our study clearly reveal that the leukocyte picture of active edible dormice responds sensitively to physiological conditions associated with hibernation, reproductive activity and food availability and can be linked to fitness parameters such as survival. Thus edible dormice represent an excellent model organism to investigate regulatory mechanisms of the immune system under natural conditions.

Restraint stress increases hemichannel activity in hippocampal glial cells and neurons

Stress affects brain areas involved in learning and emotional responses, which may contribute in the development of cognitive deficits associated with major depression. These effects have been linked to glial cell activation, glutamate release and changes in neuronal plasticity and survival including atrophy of hippocampal apical dendrites, loss of synapses and neuronal death. Under neuro-inflammatory conditions, we recently unveiled a sequential activation of glial cells that release ATP and glutamate via hemichannels inducing neuronal death due to activation of neuronal NMDA/P2X₇ receptors and pannexin1 hemichannels. In the present work, we studied if stress-induced glia activation is associated to changes in hemichannel activity. To this end, we compared hemichannel activity of brain cells after acute or chronic restraint stress in mice. Dye uptake experiments in hippocampal slices revealed that acute stress induces opening of both Cx43 and Panx1 hemichannels in astrocytes, which were further increased by chronic stress; whereas enhanced Panx1 hemichannel activity was detected in microglia and neurons after acute/chronic and chronic stress, respectively. Moreover, inhibition of NMDA/P2X₇ receptors reduced the chronic stress-induced hemichannel opening, whereas blockade of Cx43 and Panx1 hemichannels fully reduced ATP and glutamate release in hippocampal slices from stressed mice. Thus, we propose that gliotransmitter release through hemichannels may participate in the pathogenesis of stress-associated psychiatric disorders and possibly depression.

The effects of exercise on vaccination responses: a review of chronic and acute exercise interventions in humans

Vaccination programs, although feted for success in reducing infectious disease morbidity and mortality, are limited by vaccine efficacy, which is particularly problematic in populations with reduced immune function. Exercise has been identified as a behavioural factor that can improve immune function in some settings and cohorts, and therefore, in the setting of vaccination, it may serve as an adjuvant for immune responses. Here, we summarise the body of evidence that has investigated the effects of chronic or acute exercise interventions on vaccination responses. A systematic search of the literature was conducted including six major databases. Randomised control trials (RCTs), cross-sectional and observational studies that involved a variety of population samples and that employed any modality or intensity of acute exercise or chronic training prior to vaccine administration and measured any immune response were included. Twenty trials met the inclusion criteria for this review. Nine studies investigated the effect of acute exercise on the immune response to vaccination, whilst the remaining eleven studies investigated the effect of chronic exercise. Most of the current published literature suggests that exposure to either acute or chronic exercise significantly augments the immune response to vaccination. The clinical importance of this adjuvant action of exercise, if any, as well as variability in responsiveness across different cohorts, dose-response relationships and the optimal exercise modality to employ for this indication deserve further study.

Stress resilience and vulnerability: the association with rearing conditions, endocrine function, immunology, and anxious behavior

BACKGROUND

The current study explored the underlying behavioral, endocrine, and immune markers of vulnerability to stress-induced depression, and the impact of rearing environments on adult functioning.

METHOD

Adult Sprague-Dawley rats (n=195) were reared in either Maternal Separation (MS), Early Weaning and Isolation (EWI), or Non-Handled (NH) conditions. Anxiety behavior was assessed using the emergence test at mean postnatal day (PND) 60. Stress-induced depressive behavior was measured at mean PND 86 using an intermittent cold water swim stress and swim escape test (SET) paradigm. Immediately following the SET, and in a sample of naïve controls (N=31), trunk blood was collected to assay for serum corticosterone (CORT) and spleens were removed for determination of Concanavalin A (Con-A) stimulated T-cell proliferation.

RESULTS

Stress vulnerable rats (top tertile of SET swim time) were characterised by increased anxiety-like behavior, greater post-stress CORT concentrations, and a significantly higher Con-A induced T-cell proliferative response compared to stress resilient rats (bottom tertile of SET swim time). The EWI rearing condition was a contributing factor in predicting total swim escape time, however MS was not. MS offspring did have double the basal level of CORT than NH offspring, suggestive of a hyperfunctioning HPA axis.

CONCLUSION

The swim stress animal model enabled observation of stress vulnerability and resilience; results point towards the existence of distinct behavioral, endocrine, and immunological profiles of the vulnerable and resilient animal, which may have important implications for mental health and stress research.

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.

Immunomodulation property of hexane fraction of leaves of Cinnamomum tamala Linn. in rats

The leaves of Cinnamomum tamala Linn. (CT) (Lauraceae) clinically used in Ayurveda as antidiabetic and diuretic, but no reports are available towards immunomodulating property. Its hexane fraction (CTH) was orally given to rats for 10 days and delayed type of hypersensitivity (DTH), antibody production against sheep red blood cells (SRBCs), mitotic index in bone marrow cells and concanavalin A (Con A) mediated proliferation of lymphocytes were assessed. Further on 30 days treatment, change in body weight (BW), spleen weight, thymus weight, bone marrow cellularity and hematological changes were observed. It inhibited significantly the DTH response (IC(50) 1475 +/- 57.19 mg kg(-1) BW), antibody production, suppressed mitotic index in bone marrow cells along with the suppression of lymphocyte proliferation against Con A (IC(50) 63.33 +/- 1.95 microg mL(-1)). In all experiments, cyclophasphamide and dexamethasone had been used as reference drug for in vivo and in vitro studies, respectively. On 30 days treatment, the CTH (800 mg kg(-1) BW and above) significantly suppressed growth rate, increase of spleen and thymus weight and low bone marrow cellularity. In hematological examination, it inhibited total white blood cell and lymphocytes count and increased per cent of polymorphs. Thus, it could be suggested that the fraction possesses immunosuppressive property at doses, higher than 800 mg kg(-1) BW in rats.

The effects of vaccine timing on the efficacy of an acute eccentric exercise intervention on the immune response to an influenza vaccine in young adults

An acute bout of exercise prior to vaccination can improve the antibody and cell-mediated responses to influenza vaccination. The mechanisms underpinning this adjuvant effect remain unclear, and further investigation to determine the optimal exercise protocol is warranted. The aim of the current study was to determine whether exercise augmented the immune response to vaccination, and whether the timing of exercise relative to vaccination affected the efficacy of the intervention. One hundred and fifty-six (76 men) healthy participants were randomly assigned to a control group or one of three intervention groups who exercised immediately, 6h or 48 h prior to administration of a standard trivalent influenza vaccine. The exercise groups performed 50 repetitions of the eccentric portion of both the bicep curl and lateral raise movements at an intensity eliciting 85% of each participant's pre-determined concentric one repetition maxima. Antigen-specific serum antibody titres were measured at baseline and 28 days post-vaccination as indicators of the humoral response. All three viral strains elicited strong antibody responses; however, eccentric exercise did not further augment any antibody responses compared to the control group. Cell-mediated immunity at 28 days post-vaccination was determined by measuring the IFN-gamma response to in vitro stimulation of the blood with whole vaccine. There were no differences in cell-mediated immunity among the groups. Although these null findings were unexpected, they are consistent with previous research showing that exercise-induced immunoenhancement was only observed when the control group had relatively poor responses. In conclusion, it is likely that the robust immune responses to the vaccine observed in this study may have limited any further immune enhancement by exercise.

Suppression of T and B cell responses by Pterodon pubescens seeds ethanolic extract

The anti-arthritic property of hydro alcoholic extract of Pterodon pubescens seeds was previously demonstrated using the Collagen Induced Arthritis (CIA) in mice, the most similar arthritis experimental model to human rheumatoid arthritis. This disease is characterized by chronic inflamed joints resulting from exacerbated functions of macrophages and T and B lymphocytes. Anti-inflammatory and antinociceptive activities by ethanolic extract of Pterodon pubescens seeds (EEPp) have been also reported. This study describes the effects of EEPp on T and B lymphocytes functions from healthy mice. Delayed Type Hypersensitivity (DTH), in vivo antibody production, T and B lymphocyte proliferation and NO production were determined. Mice treated orally for 7 days with EEPp had inhibited 58% of B cell antibody production (10(-3) mg kg(-1) b.wt.) and 33% of the DTH response (10(-4) mg kg(-1) b.wt.), also reducing tissue leukocyte infiltration. EEPp (10(-2) mg mL(-1)) also inhibited in vitro T (89%) and B (68%) lymphocytes proliferation and NO production (53%) by macrophage cell line J774. The immunosuppression here described for EEPp supports its potential therapeutic use to control exacerbated humoral and/or cellular immune response as in autoimmune and chronic inflammatory diseases.

The Acute Stress-Induced Immunoenhancement Hypothesis

Acute stress, such as a bout of exercise, is accepted to cause an array of immunologic changes. Recently, it has been proposed that acute stress activation of the innate immune system might be harnessed as an adjuvant to enhance immune responses to antigen challenge. This review develops the acute stress-induced immunoenhancement hypothesis and its possible role as a vaccine adjuvant.

Immunosuppressive effects of Echinodorus macrophyllus aqueous extract

Echinodorus macrophyllus is a medicinal plant, popularly known in Brazil as "chapéu de couro", used to treat rheumatic diseases, which are usually characterized by exacerbated T and B lymphocyte response. We have evaluated the effects of the aqueous extract of Echinodorus macrophyllus (AEEm) on these cell functions, proliferation, and nitric oxide production. Mice treated orally for 7 days with AEEm had inhibited B cell antibody production (0.5mg/kg b.w.) and delayed type hypersensitivity (0.5 and 5mg/kg b.w.) mediated by T cells, reducing subcutaneous tissue leukocyte infiltration. AEEm inhibited, in vitro, NO production by stimulating J774 cells in a dose-dependent manner, with no cytotoxicity. We have demonstrated, for the first time, its immunosuppressive effect. This immunosuppressive effect supports a potential therapeutic use of AEEm to control exacerbated humoral and/or cellular immune response, as in autoimmune rheumatic diseases. However, it is important to be cautious about its indiscriminate popular use to avoid side effects, mainly in immunodeficiency diseases.

Eccentric exercise as an adjuvant to influenza vaccination in humans

The immune response to vaccination in animals can be enhanced by exposure to acute stress at the time of vaccination. The efficacy of this adjuvant strategy for vaccination in humans requires investigation. The current study employed a randomised controlled trial design to examine the effects of eccentric exercise prior to influenza vaccination on the antibody and cell-mediated responses. Sixty young healthy adults (29 men, 31 women) performed eccentric contractions of the deltoid and biceps brachii muscles of the non-dominant arm (exercise group) or rested quietly (control group), and were vaccinated 6h later in the non-dominant arm. Change in arm circumference and pain were measured to assess the physiological response to exercise. Antibody titres were measured pre-vaccination and at 6- and 20-week follow-ups. Interferon-gamma in response to in vitro stimulation by the whole vaccine, an index of the cell-mediated response, was measured 8 weeks post-vaccination. Interferon-gamma responses were enhanced by exercise in men, whereas antibody titres were enhanced by eccentric exercise in women but not in men. Men showed greater increase in arm circumference after eccentric exercise than women but there was no difference in reported pain. The interferon-gamma response was positively associated with the percentage increase in arm circumference among the exercise group. Eccentric exercise exerted differential effects on the response to vaccination in men and women, with enhancement of the antibody response in women, but enhancement of the cell-mediated response in men. Eccentric exercise of the muscle at the site of vaccine administration should be explored further as a possible behavioural adjuvant to vaccination.

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.

Acute stress exposure prior to influenza vaccination enhances antibody response in women

Animal studies have shown that an acute stressor in close temporal proximity to immune challenge can enhance the response to delayed-type hypersensitivity and antibody response to vaccination. The current study examined the effects of acute exercise or mental stress prior to influenza vaccination on the subsequent antibody response to each of the three viral strains. Sixty young healthy adults (31 men, 29 women) were randomly allocated to one of three task conditions: dynamic exercise, mental stress, or control. After an initial baseline, participants completed their allocated 45 min task and then received the influenza vaccine. Plasma cortisol and interleukin-6 were determined at the end of baseline, after the task, and after 60 min recovery. Antibody titres were measured pre-vaccination and at 4 weeks and 20 weeks post-vaccination follow-ups. For the A/Panama strain, women in both the exercise and mental stress conditions showed higher antibody titres at both 4 and 20 weeks than those in the control condition, while men responded similarly in all conditions. Interleukin-6 at +60 min recovery was found to be a significant predictor of subsequent A/Panama antibody response in women. In line with animal research, the current study provides preliminary evidence that acute stress can enhance the antibody response to vaccination in humans.

Effect of ACTH administration on biochemical and immune measures in boars

The effects of stress induced by adrenocorticotropic hormone (ACTH) on biochemical and immune changes in Swedish Landrace boars aged approximately 6-7 months were observed during ACTH administration and for 16 days after the cessation of treatment. Adrenocorticotropic hormone treated animals (n = 7) were given intravenously 10 microg/kg body mass of ACTH for 3 days. Control group of animals (n = 7) received intramuscularly 1 ml of sterile 0.9% saline. Total protein and globulin levels were significantly elevated during the induced stress period and for the next 16 days (P < 0.01 to P < 0.0001, respectively). Also, serum immunoglobulin IgG concentration was significantly elevated during and after ACTH injection (P < 0.001 to P < 0.0001). Adrenocorticotropic hormone treatment had no effect on serum albumin, IgA and IgM concentrations. Glucose concentration was significantly decreased on the second day of ACTH administration (P < 0.001) and on day 9 after treatment (P < 0.001). Calcium level was significantly decreased only for 24 h after the last ACTH dosage (P < 0.01). Also, serum phosphorus level was significantly decreased on the first (P < 0.05) and third (P < 0.001) days of ACTH challenge but remained unaffected after the cessation of ACTH treatment. It is concluded that the administration of ACTH to boars results in immune humoral and biochemical changes during stress and the post-stress period.

Endotoxin administration increases hypothalamic somatostatin mRNA through nitric oxide release

Acute inflammation induced by endotoxin (LPS) administration inhibits insulin-like growth factor (IGF-I) and growth hormone (GH) secretion. The aim of this study was to elucidate the role of glucocorticoids and nitric oxide (NO) in the effect of LPS on hypothalamic somatostatin gene expression. Adult male Wistar rats were injected with different doses of LPS (5, 10 and 100 microg/kg). Rats received two i.p. injections of LPS (at 17:30 and 8:30 h the following day) and were killed 4 h after the second injection. LPS administration at the dose of 100 microg/kg increased the hypothalamic somatostatin mRNA content, as well as the serum concentrations of corticosterone. Glucocorticoids do not seem to be involved in LPS-induced increase in hypothalamic somatostatin mRNA since adrenalectomy did not prevent this effect. In order to analyze the possible effect of NO, aminoguanidine, an inducible nitric oxide synthase inhibitor, was injected (100 mg/kg s.c.) simultaneously with LPS injection. Aminoguanidine administration did not modify somatostatin mRNA in saline injected rats, but it prevented LPS-induced increase in hypothalamic somatostatin mRNA. These data suggest that the stimulatory effect of endotoxin on hypothalamic somatostatin gene expression is not mediated by glucocorticoids, but instead by the increase in NO release.

Anti-inflammatory effect of the ghrelin agonist growth hormone-releasing peptide-2 (GHRP-2) in arthritic rats

Chronic arthritis induces hypermetabolism and cachexia. Ghrelin is a gastrointestinal hormone that has been proposed as a treatment to prevent cachexia. The aim of this work was to examine the effect of administration of the ghrelin agonist growth hormone-releasing peptide-2 (GHRP-2) to arthritic rats. Male Wistar rats were injected with Freund's adjuvant, and 15 days later arthritic and control rats were daily injected with GHRP-2 (100 microg/kg) or with saline for 8 days. Arthritis induced an increase in serum ghrelin (P < 0.01) and a decrease in serum concentrations of leptin (P < 0.01), whereas GHRP-2 administration increased serum concentrations of leptin. GHRP-2 increased food intake in control rats but not in arthritic rats. However, in arthritic rats GHRP-2 administration ameliorated the external symptoms of arthritis, as it decreased the arthritis score (10.4 +/- 0.8 vs. 13.42 +/- 0.47, P < 0.01) and the paw volume. In addition, circulating IL-6 and nitrites/nitrates were increased by arthritis, and GHRP-2 treatment decreased the serum IL-6 levels (P < 0.01). To elucidate whether GHRP-2 is able to modulate IL-6 release directly on immune cells, peritoneal macrophage cultures were incubated with GHRP-2 or ghrelin, the endogenous ligand of the growth hormone (GH) secretagogue receptor. Both GHRP-2 (10(-7) M) and ghrelin (10(-7) M) prevented endotoxin-induced IL-6 and decreased nitrite/nitrate release from peritoneal macrophages in vitro. These data suggest that GHRP-2 administration has an anti-inflammatory effect in arthritic rats that seems to be mediated by ghrelin receptors directly on immune cells.

Splenic norepinephrine and serum corticosterone level fluctuations associated with bacteria-induced stress

Corticosterone (CORT) and norepinephrine (NE), two effector molecules of the hypothalamic-pituitary-adrenal (HPA) and the sympathetic-lymphoid (SL) axes, respectively, differentially influence murine host resistance to Listeria monocytogenes (LM). Serum CORT and splenic NE levels early (< or =24 h) after infection correlated positively with host resistance, as long as the LM burden did not exceed approximately 10(6) cfu LM per spleen. As previously reported, mice with right-circling preference (R-mice) have significantly greater host resistance to LM than those with left-circling preference (L-mice) and early after infection, R-mice had significantly higher serum CORT levels than L-mice. However, rapid pathogenesis with a high bacterial burden induced high activation of the HPA and SL axes, which prevented observable differences in the defense against LM, especially later in infection. With the high bacterial inoculum (10(5) LM), the splenic NE levels significantly increased, but no differences among R- and L-mice were discernible. We suggest that endogenous asymmetry of neuroimmune circuits contributes to differential host resistance, but the level of stress (bacterial inoculum) is critical. With regard to the neuroendocrine factors assessed, CORT, but not NE, levels significantly correlated with the enhanced defenses of R-mice in comparison to L-mice. The differential host resistance based on brain laterality seems to be more a function of the HPA axis and possibly other CNS effects on peripheral immunity than neurotransmitter release by the sympathetic innervation of the spleen.

Stress-induced disruption of colonic epithelial barrier: role of interferon-gamma and myosin light chain kinase in mice

BACKGROUND & AIMS

Stressful life events are supposed to be involved in various diseases such as inflammatory bowel diseases and irritable bowel syndrome. Impairment of the intestinal epithelial barrier function is a suspected consequence of stress, but the underlying mechanisms remain unclear. This study aimed to determine the mechanisms through which stress modulates the colonic epithelial barrier.

METHODS

Cytokine messenger RNA (mRNA) expression was evaluated in murine colon, liver, and spleen by competitive reverse-transcription polymerase chain reaction after 1-4 days of daily 2-hour stress sessions. Colonic paracellular permeability was measured as the in vivo lumen-to-blood ratio of (51)Cr-ethylenediaminetetraacetic acid. The effect of a myosin light chain (MLC) kinase inhibitor (ML-7) was assessed on stress-induced interferon (IFN)-gamma mRNA expression and colonic epithelial barrier impairment, and MLC phosphorylation was determined by immunoblot. Finally, the incidence of repeated stress sessions on bacterial translocation was determined.

RESULTS

Repeated stress induced an overexpression of colonic IFN-gamma. In the liver, higher levels of IFN-gamma, interleukin (IL)-4, and IL-10 mRNAs were detected and were associated with bacterial translocation, inflammation, and apoptosis. Stress increased colonic permeability of control mice, but not of SCID and IFN-gamma-deficient mice. ML-7 inhibited the stress-induced increased permeability, bacterial translocation, and cytokine overexpression in the liver and restored a normal histology. Larger amounts of phosphorylated MLC were detected in stressed animals.

CONCLUSIONS

Repeated stress sessions drive organ-specific cytokine expression patterns and alter colonic mucosal barrier functions associated with bacterial translocation. This effect depends on the presence of CD4(+) T cells and requires IFN-gamma production and MLC phosphorylation.

Prolactin suppresses glucocorticoid-induced thymocyte apoptosis in vivo

The hypothesis that prolactin (PRL) functions as an immunomodulator was based on studies showing lymphocyte PRL receptors, and its effects on growth, differentiation, and apoptosis in lymphoid cells. However, studies of PRL (PRL-/-) and PRL receptor knockout mice indicated that PRL was not required for immune system development or function under basal conditions. Because PRL maintains survival in glucocorticoid (GC)-treated Nb2-T lymphocytes in vitro, and PRL and GCs are elevated during stress, we investigated whether PRL protected T cells in vivo from GC-induced apoptosis. Adrenalectomized mice [PRL -/-, undetectable PRL; pituitary grafted PRL-/- (PRL-/-Graft), elevated PRL; and PRL+/-, normal PRL] were treated with dexamethasone (DEX) or PBS. Thymocytes and splenocytes were isolated and annexin V labeling of phosphatidylserine, DNA fragmentation, and caspase-3 activation were assessed as indices of apoptosis. Total thymocytes and CD4+ and CD8+ T cells obtained from DEX-treated PRL-/- mice exhibited significantly increased annexin V binding. In contrast, binding was not altered by DEX in PRL-/-Graft thymocytes. In addition, DEX induced classic DNA fragmentation in PRL-/- thymocytes. Elevated serum PRL reduced this effect. Thymocytes from DEX-treated PRL-/- mice exhibited increased caspase-3 activation, which was inhibited in cells from PRL-/-Graft mice. Finally, elevated expression of X-linked inhibitor of apoptosis, XIAP, was observed in thymi from DEX-treated PRL -/-Graft mice. This is the first demonstration that elevated PRL antagonizes apoptosis in thymocytes exposed to GCs in vivo. These observations suggest that, under conditions of increased GCs, such as during stress, elevated PRL functions physiologically to maintain survival and function of T-lymphocytes.

Repeated, non-habituating stress suppresses inflammatory plasma extravasation by a novel, sympathoadrenal dependent mechanism

The mechanism by which chronic stress affects the course of inflammatory diseases is still not well understood. We have evaluated the effect of two types of nonhabituating stress on a major component of the inflammatory response, synovial plasma extravasation, induced by perfusion of the potent inflammatory mediator, bradykinin and evaluated the underlying neuroendocrine mechanism in the rat. Chronic intermittent noise or ether stress induced profound inhibition of bradykinin-induced plasma extravasation, which is associated with increased adjuvant-arthritis severity. This inhibition, however, took 24 h to fully develop after the last exposure to stress and persisted for at least 48 h. The inhibition could be reversed by an additional exposure to the stressor, just prior to measuring the inflammatory response, suggesting that the delay is due to stress-induced release of a factor that acutely masks the inhibition of the inflammatory response. This novel, unexpected feature of the effect of nonhabituating stress on inflammation may help explain variability in effects of stress in patients with inflammatory disease. The effect of nonhabituating stress on inflammation was dependent on the sympathoadrenal axis with no detectable contribution by the hypothalamic-pituitary-adrenal axis.

Stressor-induced modulation of immune function: a review of acute, chronic effects in animals

The present paper reviews recent studies on the effects of stress on immune function in laboratory animals. The emphasis is on those studies where a simultaneous comparison of acute and chronic stress regimens was determined, although additional relevant studies are also reviewed. The effects of stress on basic measurements of cellular and humoral immune measures are discussed, including the growing number of studies that have reported alterations in macrophage functions. The latter are key elements in the innate immune response, and like measurements of T cell function and antibody production, are inhibited and enhanced by stressor exposure. This review does not focus on the mechanisms by which stress alters immune function, there being little to add conceptually in terms of what was reported previously (see Kusnecov AW, Rabin BS, Int Arch Allergy Immunol 1994;105:107-121.). However, a question is raised in the conclusion as to how stressor effects on immune function should be interpreted, for it is clear that immunological processes in and of themselves elicit central nervous system responses that neurochemically and endocrinologically do not differ from those produced in response to psychological stressors. Therefore, at least in the short term stressor-induced immune changes may not necessarily reflect maladaptive adjustments, although, as demonstrated by some studies reviewed in this paper, they may pose a serious risk to health should stressor exposure be persistent and uncontrolled.

Acute and chronic stress differently affect visceral sensitivity to rectal distension in female rats

Stressful life events are frequently associated with outward signs of irritable bowel syndrome (IBS). Increasing evidence suggests that acute and chronic stress stimuli implicate different physiological mechanisms and neuroendocrine responses. Therefore, we investigated the influence of acute and chronic stress on visceral nociception in female rats and the involvement of colonic mast cells in this effect. The effect of acute and chronic partial restraint stress (PRS) on visceral sensitivity to rectal distension (RD) was assessed by abdominal muscle electromyography. Colonic mast cell activation was determined by measuring histamine release after in vitro stimulation with substance P (SP) in colonic samples from rats experiencing RD vs. controls. Acute PRS significantly enhanced abdominal response to RD compared with sham PRS for all volumes of distension. In contrast, chronic PRS induced a hyperalgesic response for the highest volumes of distension (0.8 and 1.2 mL), but did not affect the number of abdominal contractions for the lowest volume (0.4 mL) compared with controls. Both acute and chronic PRS increased in vitro SP-induced histamine release without affecting mast cell numbers. RD induced similar in vitro histamine release from colonic samples from both acute and chronic PRS rats; this release, however, was significantly higher than that measured in sham-PRS rats. Acute and chronic PRS differently influence visceral sensitivity in response to RD in female rats. This difference, however, cannot be attributed to a different effect of either stress paradigm on mast cell histamine release.

Neuroendocrine and other factors in the regulation of inflammation. Animal models

A variety of animal models have been used to study the role of neuroendocrine responses in various aspects of autoimmune/inflammatory disease. Complex models of autoimmune disease, such as inflammatory arthritis in rats and thyroiditis in chickens, indicate a role for blunted HPA axis and dysregulated sympathoneuronal responses in susceptibility to autoimmune disease. A variety of approaches including pharmacological, surgical (ablation, transplantation), genetic linkage and segregation studies have been used to identify factors contributing to the phenotypes of susceptibility or resistance to inflammatory/autoimmune disease. Innate inflammation, or the earliest nonspecific form of the inflammatory response, which is characterized by fluid exudation and migration of immune cells to inflammatory sites, is a subtrait of these forms of inflammatory disease. Genetic linkage and segregation studies in inflammatory susceptible and resistant rat strains indicate that this subtrait is multigenic and polygenic; that is, that multiple loci on multiple chromosomes, each with a weak effect, control this trait, and that there is a large environmental component to the variability of this trait. Such information derived from animal studies can be used to target candidate genes for further study and to inform the design of human studies.

Neurotropic, immunological and gastric effects of low doses of Atropa belladonna L., Gelsemium sempervirens L. and Poumon histamine in stressed mice

Previous studies realized in the laboratory have indicated that application of experimental stress (such as unavoidable footshock) induced significant behavioral, gastric and immunological alterations in mice. The aim of this study was to evaluate effects of low doses of Atropa belladonna L., Gelsemium sempervirens L. and Poumon histamine on stress-induced behavioral, immunological and gastric alterations. Locomotor, postural and exploratory activities have been evaluated by two behavioral tests: light/dark box and staircase tests. Immunological studies were investigated to count white blood cells subpopulations (lymphocytes, neutrophils, monocytes and basophils) by coulter counter. The severity of gastric erosions was evaluated by microscopic technique in mice after experimental stress. The results have demonstrated that low doses of G. sempervirens L. and A. belladonna L. had a significant neurotropic and protective effects on behavioral and gastric alterations induced by experimental stress. The immunological protective effects observed were probably induced via their neurotropic effects. The P. histamine showed a significant immunoprotective and gastroprotective effect in mice exposed to experimental stress.

Immunotoxic effects of inorganic lead on host resistance of mice with different circling behavior preferences

We have observed differential immune responses in mice with different circling preferences, which are posited to reflect interindividual immune response differences influenced by brain laterality effects on neuroimmune circuits. In this study, we have investigated the influence of inorganic lead (Pb) and/or Listeria monocytogenes (LM) infection on the cytokine and corticosterone (CORT) levels of mice grouped by lateralized behavior. Pb increased the LM susceptibility of mice with both left (LC)- and right-circling (RC) preferences; however, Pb did not inhibit the host resistance of mice with no circling preference (NP mice). The basal serum IFNgamma levels were lowered in all groups after Pb exposure, which coincided with a decrease in host resistance in LC and RC mice, but not NP mice. Pb also altered the basal serum CORT levels, and these changes appear to correlate better with changes in the host resistance of all groups. The basal CORT levels were significantly lowered by Pb in mice with a circling preference, and Pb significantly suppressed the host resistance of mice with a circling preference. However, Pb slightly increased the serum CORT level of NP mice, and their host resistance was slightly improved by Pb. After infection, the increase in CORT levels was associated with an increase in the serum IL-6 levels, which may reflect cytokine influences on the hypothalamic-pituitary-adrenal axis. At 3 days after infection, the serum IL-6 level seems to be a good indicator of the severity of the infection. We suggest that environmental stressors can reorder the observed differential susceptibility to LM in mice with different circling preferences, in that relatively resistant mice (RC mice) become more susceptible than NP mice after exposure to Pb. The results suggest that environmental stressors may have differential effects among individuals with endogenous differences in their neuroimmune circuits, since brain laterality is known to influence immune functions.

Augmented humoral immune function in metallothionein-null mice

Stress response proteins can play integral roles as modulators of cellular function and can be involved in mechanisms that are important to immune function. Metallothionein (MT), a cysteine-rich stress response protein, has been shown to play numerous roles in the cell: it serves as a reservoir of essential heavy metals, it scavenges free radicals, and it can sequester heavy metals. These various functions suggest that MT may also participate in modulating immune responses. In previous work, we have shown that exogenous metallothionein can suppress the developing humoral immune response when coinjected with antigen. The present study was designed to evaluate the effects of endogenous MT on the development of humoral immunity. We compared the humoral immune function of animals with a targeted disruption of Mt-1 and -2 genes (MTKO) and their wild-type counterparts. MTKO mice displayed a significantly higher humoral response to challenge with ovalbumin (OVA) compared to wild-type controls. The secondary anti-OVA response in MTKO mice is as much as 58% higher than the response in control mice injected at the same time. Overall circulatory immunoglobulin levels are also substantially higher in MTKO mice (0.039 mg/ml IgM and 0.42 mg/ml IgG) than wild-type controls. MTKO mice displayed increased B cell differentiation following OVA challenge and an enhanced lymphoproliferative response to mitogenic stimulation. These changes in immune functional capacity occur in the context of changes in the makeup of the lymphoid compartments of the blood and spleen. There are substantially fewer T and B cells in the circulation of MTKO mice, but more T cells in the spleen of these mice than in control animals. Finally, we have found that splenocytes from MTKO animals displayed significantly elevated levels of NF-kappaB activity compared to wild-type controls. In conclusion, we have provided evidence that endogenous metallothionein can modulate the immune response in vivo and that intracellular MT may modulate immune function by regulation of transcription factor 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.

The effect of cyclosporine administration on growth hormone release and serum concentrations of insulin-like growth factor-I in male rats

The aim of this work was to study the effect of cyclosporine on the somatotropic axis. Accordingly, growth hormone (GH) secretion, circulating insulin-like growth factor I (IGF-I) and IGF binding proteins (IGFBPs) in response to cyclosporin A (CsA) treatment were examined in adult male Wistar rats. Cyclosporine administration (5, 10 or 20 mg/Kg daily) over 8 days did not modify the body weight, but it did decrease serum concentration of corticosterone and increased serum IGF-I and GH levels. Rats treated with 5 and 10 mg/Kg of cyclosporine had similar levels of serum IGFBPs to control rats, but there was an increase in circulating IGFBP-3 and IGFPB-1,2 in the group treated with 20 mg/Kg of CsA. The increase in circulating GH correlates with a decrease in pituitary GH content in CsA treated rats, with no modification in hypothalamic somatostatin content, suggesting an increase in pituitary GH release. In order to test this hypothesis, anterior pituitary cell cultures were exposed to different CsA concentrations during a 4 h incubation period. Cyclosporine increased GH secretion in cultured pituitary cells (p<0.05). These data suggest that cyclosporine increases circulating IGF-I and GH by stimulating pituitary GH release.

Effects of acute and chronic social stress on blood cellular immunity in rats

The study compares the impact of acute and chronic social confrontation on aspects of blood cellular immunity in Long-Evans intruder rats. An adult male was introduced for either 2 h or 48 h into a male-female resident group, which resulted in fights for dominance. Thirty-eight of the 42 intruders became losers. For immunologic measurements, blood samples were taken from the intruders before confrontation (baseline) and 2 h or 48 h after the beginning of confrontation. Two h of confrontation resulted in increased granulocyte (+65%) and decreased lymphocyte numbers (-60%), as well as in differential reductions in CD4, CD8, and B cell numbers. CD4/CD8 and T/B ratios were elevated. T cell responsiveness to ConA was markedly suppressed in proliferation assays using either whole blood (-90%) or PBMC (-50%). The direction of changes in leukocyte and lymphocyte subsets after 48 h resembled in many aspects the 2 h changes, although with lower magnitude. In contrast to acute stress, a lowered T/B cells ratio and unaffected CD4/CD8 ratio was determined after 48 h. Proliferative response of T cells was lowered by about 25% in the whole blood assay; but unaffected in the PBMC assay. Significant correlations were found between the amount of submissive behavior displayed by the losers and several immunologic measures after 2 h of confrontation. The data suggest that acute and chronic stressful conditions may not necessarily result in similar effects on immune functioning. This should be considered when evaluating the biologic and evolutionary consequences of social stress-induced immune alterations.

Effects of social status after mixing on immune, metabolic, and endocrine responses in pigs

The effects of social rank on immune, metabolic, and endocrine responses were studied in 10 newly mixed groups of German Landrace pigs (9 individuals each) at an age of 12 weeks. Immediately after mixing, the agonistic interactions (AI) of all group members were continuously recorded over 3 days (10 h daily). An individual dominance value (DV) was calculated by the number of wins minus defeats in relation to all decisive fights (DV < or = 0, subordinate; DV > 0, dominant). Blood samples were taken 24 h before and 3 days after mixing. The data showed that the social status had a significant effect on lymphocyte proliferation in responses to different mitogens: socially dominant pigs had higher proliferative response than subordinate pigs. In addition, during the observation period the lymphocyte activation by mitogens increased in the dominant animals and decreased in the subordinate animals with increasing number of agonistic interactions. The rise in total serum IgG concentration 3 days after mixing was higher in dominant pigs compared with subordinates. The dominance status did not significantly affect plasma metabolic levels nor cortisol concentrations. However, mixing appeared to increase glucose and total protein values and to decrease alkaline phosphatase and cortisol levels in both, dominant and subordinate pigs. In conclusion, mitogen induced cell proliferation seems to be a valuable marker for acute social stress in pigs.

Acute 3,4-methylenedioxymethamphetamine(MDMA) administration produces a rapid and sustained suppression of immune function in the rat

(+)-3,4-Methylenedioxymethamphetamine (MDMA;'Ecstasy') is a ring substituted phenylisopropylamine that is structurally related to both amphetamines and hallucinogens. The unique behavioural activating properties of MDMA have led to its widespread abuse. MDMA induces many neurochemical, behavioural and endocrine alterations which closely resemble those elicited by exposure to acute stress, suggesting that MDMA could be regarded as a 'chemical stressor'. In addition to the neurochemical, behavioural and endocrine effects of stressor exposure, it has been reported that stress produces alterations in immune function. However, to date the effects of MDMA on immune function have been restricted to in vitro investigations. In this study we report, for the first time, that acute in vivo administration of MDMA (20 mg/kg, i.p.) produced a rapid (within 30 min) suppression of Con A-induced lymphocyte proliferation and a profound reduction in the total leucocyte count in rats that persisted for at least 6 h following injection. These alterations in immune function were accompanied by a significant increase in plasma corticosterone concentrations 30 min post MDMA administration which had returned to baseline values within 6 h of drug administration. In addition, there was a significant depletion in cortical 5-HT concentrations both 30 min and 6 h after MDMA administration. The results of this study provide evidence that in addition to the well established toxic effects of MDMA on the central serotonergic system, a single administration of this widely abused drug induces a rapid and sustained suppression of immune function.

Effects of Acute Stress or Centrally Injected Interleukin-1beta on Neuropeptide Expression in the Immune System

Acute stress stimulates the expression and release of corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) from the hypothalamus, and the pro-opiomelanocortin products beta-endorphin and ACTH from the anterior pituitary. These neuropeptides are also expressed in immune tissues, and it has been proposed that they may modulate immune responses to stress through paracrine mechanisms. We subjected rats to restraint stress or central injection of interleukin (IL)-1beta to determine whether these acute stimuli can alter the expression of neuropeptides in the spleen and thymus. Restraint stress significantly increased the contents of all these neuropeptides in thymic, but not splenic, extracts. A single icv injection of IL-1beta increased contents of CRH, AVP, ACTH and beta-endorphin in the spleens of both sham-operated and adrenalectomised (ADX) rats. IL-1beta increased thymic contents of CRH and ACTH in sham-operated rats but these increases were not observed in ADX rats. These results suggest that the effects of IL-1beta on neuropeptide expression in the spleen are independent of glucocorticoids, whereas IL-1beta stimulation of neuropeptide expression in the thymus is dependent on circulating glucocorticoids. There were significant correlations between increases in CRH, ACTH and beta-endorphin in the spleen, and between CRH and ACTH in the thymus, consistent with the suggestion that IL-1beta-induced increases in ACTH and beta-endorphin may be mediated through CRH. These results provide evidence that stressors can directly influence neuropeptide expression in immune tissues. Thus stress may influence immune functions through paracrine mechanisms involving locally synthesised neuropeptides as well as through activation of the hypothalamo-pituitary-adrenal axis.