Social stress affects migration of blood T cells into lymphoid organs

Fasting-activated ventrolateral medulla neurons regulate T cell homing and suppress autoimmune disease in mice

Dietary fasting markedly influences the distribution and function of immune cells and exerts potent immunosuppressive effects. However, the mechanisms through which fasting regulates immunity remain obscure. Here we report that catecholaminergic (CA) neurons in the ventrolateral medulla (VLM) are activated during fasting in mice, and we demonstrate that the activity of these CA neurons impacts the distribution of T cells and the development of autoimmune disease in an experimental autoimmune encephalomyelitis (EAE) model. Ablation of VLM CA neurons largely reversed fasting-mediated T cell redistribution. Activation of these neurons drove T cell homing to bone marrow in a CXCR4/CXCL12 axis-dependent manner, which may be mediated by a neural circuit that stimulates corticosterone secretion. Similar to fasting, the continuous activation of VLM CA neurons suppressed T cell activation, proliferation, differentiation and cytokine production in autoimmune mouse models and substantially alleviated disease symptoms. Collectively, our study demonstrates neuronal control of inflammation and T cell distribution, suggesting a neural mechanism underlying fasting-mediated immune regulation.

Short- and long-term consequences of stocking density during rearing on the immune system and welfare of laying hens

Already during early life, chickens need to cope with chronic stressors that can impair their health and welfare, with stocking density being one of the most influential factors. Nevertheless, there is a gap in research on the influence of stocking density on laying hens during rearing and in the subsequent laying period. This study therefore investigated how stocking density during rearing affects the immune system and welfare of pullets, and whether effects are persistent later in life. Pullets were reared at either low (13 birds/m²) or high (23 birds/m²) stocking densities but in identical group sizes from wk 7 to 17. Afterward, hens were kept at the same stocking density (2.4 birds/m²) until wk 28. Blood and tissue samples (spleen and cecal tonsils) were collected at the end of the rearing period and in the laying period. The parameters evaluated encompassed number and distribution of leukocytes and lymphocyte subsets in blood and lymphatic tissue, lymphocyte functionality, plasma corticosterone concentrations as well as behavior and physical appearance of hens. At the end of rearing, pullets kept under high stocking density had lower numbers of T lymphocytes, especially γδ T cells in blood, spleen, and cecal tonsils and displayed a higher heterophil to lymphocyte ratio. These effects are mostly persistent during the laying period, although stocking density was identical at this time. Furthermore, birds from the high stocking density group showed less active behavior, more pecking behavior and worse physical appearance throughout both examination periods. In conclusion, stocking density during rearing affects pullets' immune system and behavior not only in the rearing, but also subsequently in the laying period, indicating a strong correlation between health and welfare during rearing and the laying period.

Determination of Psychological Stress, Serum Immune Parameters, and Cortisol Levels in Patients With Human Papilloma Virus

PURPOSE

Because the results of studies investigating the relation between human papilloma virus (HPV) infection and the effects of psychological stress are inconsistent, this study was conducted to expand on previous research by analyzing patient stress levels, serum immune parameters, and cortisol levels in patients with clinical HPV manifestations. It also looked for differences in clinical manifestations of HPV depending on patient level of experienced stress.

METHODS

This cross-sectional study included 213 subjects (94 women and 119 men aged ≥18 years; average age, 41 years) with clinical manifestations of HPV infection (165 subjects with extragenital manifestations and 48 with genital manifestations) who were treated at the Department of Dermatovenerology, Karlovac General Hospital, from January 1, 2012, to December 31, 2015. Psychological, neurohormonal and immune parameters (serum values of leukocytes, alpha₂-globulins, beta-globulins, albumins, and proteins), and serum cortisol levels were analyzed. Questionnaires were used to determine patients' perception of stress: the Recent Life Changes Questionnaire, the Perceived Stress Scale, and the Brief Cope Test. One group of subjects had confirmed stressful experiences, defined by the Recent Life Changes Questionnaire as a period of 1 year with at least 500 life change units; the control group included patients with no significant stressful experiences.

FINDINGS

Patients with confirmed significant stress experience had a statistically significant higher degree of perception of stress. There were no statistically significant differences in terms of the impact of stress on clinical HPV manifestations (genital and extragenital), sex, lesional duration, or recurrence. In patients with significant stress experience, significantly higher values of leukocytes (6.68 × 10⁹/L), alpha₂-globulins (6.85 g/L), and beta-globulins (7.33 g/L) were observed. Adaptive coping and a lower perception of stress significantly reduced the chances of having extragenital manifestations by 2.63 times. A higher perception of stress significantly increased the likelihood of genital manifestations.

IMPLICATIONS

Although this study found that stress increased the values of leukocytes, alpha₂-globulins, and beta-globulins, no evidence was found that it affected clinical manifestations of HPV infection. The redundancy of the immune system could account for this finding. This study is among the first to investigate the correlation between psychological, neurohormonal, and immune indicators of stress.

The Role of the Intestinal Microbiome in Chronic Psychosocial Stress-Induced Pathologies in Male Mice

Chronic psychosocial stress is a risk factor for the development of physical and mental disorders accompanied or driven by an activated immune system. Given that chronic stress-induced systemic immune activation is lacking in germ-free and antibiotics-treated mice, a causal role of the gut microbiome in the development of stress-related disorders is likely. To address this hypothesis in the current study we employed the chronic subordinate colony housing (CSC, 19 days) paradigm, a pre-clinically validated mouse model for chronic psychosocial stress, known to alter the gut microbial signature and to induce systemic low-grade inflammation, as well as physical and mental abnormalities. In detail, we investigated if (i) CSC-induced alterations can be prevented by repeated transplantation of feces (FT) from non-stressed single-housed control (SHC) mice during CSC exposure, and (ii) if the transplantation of a “stressed” CSC microbiome is able to induce CSC effects in SHC mice. Therefore, we repeatedly infused SHC and CSC recipient mice rectally with SHC donor feces at days 4 and 11 of the CSC paradigm and assessed anxiety-related behavior on day 19 as well as physiological, immunological, and bone parameters on day 20. Furthermore, SHC and CSC recipient mice were infused with CSC donor feces at respective days. To exclude effects of rectal infusions per se, another set of SHC and CSC mice was infused with saline, respectively. Our results showed that transplantation of SHC feces had mild stress-protective effects, indicated by an amelioration of CSC-induced thymus atrophy, anxiety, systemic low-grade inflammation, and alterations in bone homeostasis. Moreover, transplantation of CSC feces slightly aggravated CSC-induced systemic low-grade inflammation and alterations in bone homeostasis in SHC and/or CSC animals. In conclusion, our data provide evidence for a role of the host’s microbiome in many, but not all, adverse consequences of chronic psychosocial stress. Moreover, our data are consistent with the hypothesis that transplantation of healthy feces might be a useful tool to prevent/treat different adverse outcomes of chronic stress. Finally, our data suggests that stress effects can be transferred to a certain extend via FT, proposing therapeutic approaches using FT to carefully screen fecal donors for their stress/trauma history.

Duration dependent effect of chronic stress on primary and secondary lymphoid organs and their reversibility in rats

The present study was undertaken to investigate whether or not chronic stress effect and its reversibility on lymphoid organs is duration dependent. Male rats were exposed to restraint (1 h) followed by a gap of 4 h to forced swimming exercise (15 min) daily for 2, 4 and 8 weeks. After each exposure period, rats were allowed to recover for 6 weeks. Stress exposure resulted in duration dependent decreases in weight of thymus and axillary lymph nodes, lymphocyte counts of spleen, thymus and axillary lymph nodes and number of islets of white pulp of spleen and increases in apoptotic index of splenocytes, thymocytes and lymphocytes of axillary lymph nodes. All the parameters of lymphoid organs studied showed significant alterations in 2 weeks of stress exposure indicated their sensitivity to stress effects in short term exposure and thymus was the most sensitive organ among all. The alterations in all the parameters of spleen and majority of parameters of thymus and axillary lymph nodes returned to control level in recovery group rats of 2 and 4 weeks exposure but not in that of 8 weeks exposure. The present study for the first time reveal that severity of stress effects on lymphoid organs increases with increasing duration of exposure and shorter the exposure period faster the recovery. In addition, an in vitro study showed that corticosterone caused apoptosis of thymocytes, splenocytes and lymphocytes of axillary lymph nodes in dose dependent manner. Thus corticosterone induced death of cells of lymphoid organs under stress is the major cause of involution of lymphoid organs.

Biomarkers for classification and class prediction of stress in a murine model of chronic subordination stress

Selye defined stress as the nonspecific response of the body to any demand and thus an inherent element of all diseases. He reported that rats show adrenal hypertrophy, thymicolymphatic atrophy, and gastrointestinal ulceration, referred to as the stress triad, upon repeated exposure to nocuous agents. However, Selye's stress triad as well as its extended version including reduced body weight gain, increased plasma glucocorticoid (GC) concentrations, and GC resistance of target cells do not represent reliable discriminatory biomarkers for chronic stress. To address this, we collected multivariate biological data from male mice exposed either to the preclinically validated chronic subordinate colony housing (CSC) paradigm or to single-housed control (SHC) condition. We then used principal component analysis (PCA), top scoring pairs (tsp) and support vector machines (SVM) analyses to identify markers that discriminate between chronically stressed and non-stressed mice. PCA segregated stressed and non-stressed mice, with high loading for some of Selye's stress triad parameters. The tsp analysis, a simple and highly interpretable statistical approach, identified left adrenal weight and relative thymus weight as the pair with the highest discrimination score and prediction accuracy validated by a blinded dataset (92% p-value < 0.0001; SVM model = 83% accuracy and p-value < 0.0001). This finding clearly shows that simultaneous consideration of these two parameters can be used as a reliable biomarker of chronic stress status. Furthermore, our analysis highlights that the tsp approach is a very powerful method whose application extends beyond what has previously been reported.

Diurnal rhythms in peripheral blood immune cell numbers of domestic pigs

Diurnal rhythms within the immune system are considered important for immune competence. Until now, they were mostly studied in humans and rodents. However, as the domestic pig is regarded as suitable animal model and due to its importance in agriculture, this study aimed to characterize diurnal rhythmicity in porcine circulating leukocyte numbers. Eighteen pigs were studied over periods of up to 50 h. Cosinor analyses revealed diurnal rhythms in cell numbers of most investigated immune cell populations in blood. Whereas T cell, dendritic cell, and eosinophil counts peaked during nighttime, NK cell and neutrophil counts peaked during daytime. Relative amplitudes of cell numbers in blood differed in T helper cell subtypes with distinctive differentiation states. Mixed model analyses revealed that plasma cortisol concentration was negatively associated with cell numbers of most leukocyte types, except for NK cells and neutrophils. The observed rhythms mainly resemble those found in humans and rodents.

Laboratory environment and bio-medical experience: the impact of administration technique on the quality of immune-behavior data results in stress experience

Introduction: Often in an experiment, the control group and the intact group are not identified because most scientists neglect the fact that the sets of manipulation as technical administrations may be considered as an undesirable stress on the clarity of the data obtained from a scientific research specifically if it focuses on studying the effects of stress.

Methods: This study was conducted in two parts using 40 male Wistar rats. The first part aimed to treat a group of rats by repeated injections i.p route (1 mL/kg) of placebo or NaCl (0.9%) and the other by direct oral administration of NaCl (0.9%). Both groups spent 1 h of jet air stress with stressed group. Our objective was to consider the effects that these manipulations would have on the validity of behavioral results (the elevated plus maze test, the open field, the light/dark box test) and immune data (immune cell count) during this stress experience. The second part was devoted to the measurement of ACTH, IL6, and CRP in these experimental groups.

Results: Unlike oral administration, repeated intra-peritoneal injections cause a significant increase of plasma obtained levels of the adrenocorticotropin hormone (ACTH), interleukin-6 (IL-6) and the C-reactive protein (CRP) using injections of placebo: NaCl 0.9% (1 mL/kg) and it may have side effect on significant immune and behavioral alterations data quality induced by 1 h of air jet in the animal’s cage identified by the leukocyte formula and behavioral tests.

Conclusion: In an experimental protocol conducted on animal models, it is essential to opt for painless techniques such as oral administration instead of painful injections to avoid confusion at the behavioral and immunological results from biomedical experiments specifically one that focuses on the stress study.

Immune reactivity in rats selected for the enhancement or elimination of aggressiveness towards humans

This study analyzes immune reactivity in two lines of rats selected for the enhancement or elimination of aggressiveness toward humans. Compared to nonaggressive line, aggressive rats showed increased blood ratio of CD4(+) and CD8(+)T lymphocytes, monocyte chemoattractant protein (MCP)-1 level both before and after immunization with sheep red blood cells (SRBC), enhanced IgM-immune response, as well as decreased level of interleukin (IL)-1α before immunization. However, antigen administration produced IL-1α increase in aggressive rats and its decrease in nonaggressive rats compared to non-immunized rats of the same lines. In addition, line-dependent alterations of T lymphocyte distribution in response to immune activation have been found only in the spleen. It is suggested that genetic differences in aggressive behavior may contribute to differences in immune function.

Chronic subordinate colony housing paradigm: a mouse model to characterize the consequences of insufficient glucocorticoid signaling

Chronic, in particular chronic psychosocial, stress is a burden of modern societies and known to be a risk factor for numerous somatic and affective disorders (in detail referenced below). However, based on the limited existence of appropriate, and clinically relevant, animal models for studying the effects of chronic stress, the detailed behavioral, physiological, neuronal, and immunological mechanisms linking stress and such disorders are insufficiently understood. To date, most chronic stress studies in animals employ intermittent exposure to the same (homotypic) or to different (heterotypic) stressors of varying duration and intensity. Such models are only of limited value, since they do not adequately reflect the chronic and continuous situation that humans typically experience. Furthermore, application of different physical or psychological stimuli renders comparisons to the mainly psychosocial stressors faced by humans, as well as between the different stress studies almost impossible. In contrast, rodent models of chronic psychosocial stress represent situations more akin to those faced by humans and consequently seem to hold more clinical relevance. Our laboratory has developed a model in which mice are exposed to social stress for 19 continuous days, namely the chronic subordinate colony housing (CSC) paradigm, to help bridge this gap. The main aim of the current review article is to provide a detailed summary of the behavioral, physiological, neuronal, and immunological consequences of the CSC paradigm, and wherever possible relate the findings to other stress models and to the human situation.

High natural killer cell number might identify stroke patients at risk of developing infections

OBJECTIVE

To investigate early changes in leukocyte subsets and autonomic function as predictors of the development of poststroke infections.

METHODS

We assessed the time course of leukocyte subsets in the blood of 59 patients with acute ischemic stroke. We divided the patients into 2 groups: those who developed infections during the first 7 days after stroke onset and those who did not. We measured urinary norepinephrine and epinephrine concentrations and pulse rate variability indices within 24 hours of admission.

RESULTS

We found that the number of circulating natural killer (NK) cells within the first hours after stroke was higher in stroke patients who developed infections (mean 435 cells/mL; 95% confidence interval [CI] 321-588) than in stroke patients who did not develop infections (mean 236 cells/mL; 95% CI 186-300; p = 0.001). This was followed by a decrease in all lymphocyte subsets from admission to day 1, varying between 22% and 40%, which was not seen in patients without poststroke infection (mean increase varied between 2% and 23%; all p < 0.005). In the group that developed infections, pulse rate variability revealed a decreased high frequency component. These findings all remained significant after adjustment for age and stroke volume.

CONCLUSIONS

High circulating NK cell count within the first hours after ischemic stroke onset followed by a drop in all lymphocyte subsets identified patients who developed infections and may be caused by a sympathovagal imbalance with sympathetic overweight. These findings need to be validated in larger studies.

Cortisol increases CXCR4 expression but does not affect CD62L and CCR7 levels on specific T cell subsets in humans

Glucocorticoids are well known to affect T cell migration, leading to a redistribution of the cells from blood to the bone marrow, accompanied by a concurrent suppression of lymph node homing. Despite numerous studies in this context, with most of them employing synthetic glucocorticoids in nonphysiological doses, the mechanisms of this redistribution are not well understood. Here, we investigated in healthy men the impact of cortisol at physiological concentrations on the expression of different migration molecules on eight T cell subpopulations in vivo and in vitro. Hydrocortisone (cortisol, 22 mg) infused during nocturnal rest when endogenous cortisol levels are low, compared with placebo, differentially reduced numbers of T cell subsets, with naive CD4(+) and CD8(+) subsets exhibiting the strongest reduction. Hydrocortisone in vivo and in vitro increased CXCR4 expression, which presumably mediates the recruitment of T cells to the bone marrow. Expression of the lymph node homing receptor CD62L on total CD3(+) and CD8(+) T cells appeared reduced following hydrocortisone infusion. However, this was due to a selective extravasation of CD62L(+) T cell subsets, as hydrocortisone affected neither CD62L expression on a subpopulation level nor CD62L expression in vitro. Corresponding results in the opposite direction were observed after blocking of endogenous cortisol synthesis by metyrapone. CCR7, another lymph node homing receptor, was also unaffected by hydrocortisone in vitro. Thus, cortisol seems to redirect T cells to the bone marrow by upregulating their CXCR4 expression, whereas its inhibiting effect on T cell homing to lymph nodes is apparently regulated independently of the expression of classical homing receptors.

Influence of Different Housing Systems on Distribution, Function and Mitogen-Response of Leukocytes in Pregnant Sows

Simple Summary

The European Union imposes housing of pregnant sows in social groups since 2013 for animal welfare reasons. Nevertheless, the consequences of different housing conditions for the immune system of pregnant sows remain poorly investigated. We therefore analyzed important aspects of blood cellular immunity and cortisol concentrations of sows either housed in individual crates or in a group during gestation. The results show that individually housed sows had lower T cell numbers, but higher cortisol concentrations. Obviously, common housing conditions can differentially affect key elements of the adaptive immune system and hormonal indicators of stress in pregnant sows.

Abstract

In pig production, pregnant sows are either housed in individual crates or in groups, the latter being mandatory in the EU since 2013. The consequences of different housing conditions on the immune system are however poorly investigated, although immunological alterations may have severe consequences for the animal’s health, performance, and welfare. This study assessed measures of blood celluar immunity with special emphasis on T cells in pregnant German Landrace sows either housed in individual crates or in a social group. Blood samples were taken at four samplings pre partum to evaluate numbers of lymphocyte subpopulations, mitogen-induced lymphocyte proliferation and cytokine-producing T cells. Plasma cortisol concentrations were evaluated as an indicator of stress. We found lower blood lymphocyte numbers (p < 0.01) in individually housed as opposed to group-housed sows, an effect due to lower numbers of cytotoxic T cells, naive TH cells, and CD8⁺ γδ-T cells. Individually housed sows showed higher cortisol concentrations (p < 0.01), whereas lymphocyte functionality did not differ between sows of both housing systems. Possible implications and underlying mechanisms for the endocrine and immunological differences are discussed. We favor the hypothesis that differences in the stressfulness of the environment contributed to the effects, with crate-housing being a more stressful environment—at least under conditions of this study.

Emotional change-associated T cell mobilization at the early stage of a mouse model of multiple sclerosis

Autoimmune diseases like multiple sclerosis (MS) are known to be associated with debilitating emotional disorders that manifest long before the flaring of motor dysfunctions. Given the emerging role of T cells in controlling both emotions and autoimmunity, in this study we explored possible correlation between T cell activation and changes in emotional behavior in a mouse model of MS. Our results showed a significant increase in blood circulating T cells as soon as at day 4 post immunization. This lymphocytosis remained stable with time and preceded the infiltration of T cell in the CNS. The kinetic of T cell entry in the blood matched the kinetic of changes in behavior measured using the open field test. Treatment with glatiramer acetate, a well-known immunomodulatory drug for MS, suppressed behavioral changes while retaining the T cells in the draining lymph nodes. Together these results provide evidence of a positive correlation between the emigration of T cells in circulation and changes in emotions during chronic inflammatory diseases. The validation of these findings in the clinic might help to better understand the cause of the emotional and psychological burden of patients suffering MS or other autoimmune diseases. Most importantly our study suggests novel therapeutic venues for the treatment of the emotional changes associated with autoimmunity.

Endogenous glucocorticoid receptor signaling drives rhythmic changes in human T-cell subset numbers and the expression of the chemokine receptor CXCR4

In humans, numbers of circulating naive T cells strongly decline in the morning, which was suggested to be mediated by cortisol, inducing a CXCR4 up-regulation with a subsequent extravasation of the cells. As a systematic evaluation of this assumption is lacking, we investigated in two human placebo-controlled studies the effects of the glucocorticoid receptor (GR) antagonist mifepristone (200 mg orally at 23:00) and of suppressing endogenous cortisol with metyrapone (1 g orally at 04:00) on temporal changes in CXCR4 expression and numbers of different T-cell subsets using flow cytometry. Mifepristone attenuated, and metyrapone completely blocked, the morning increase in CXCR4 expression on naive T cells. In parallel, both substances also hindered the decline in naive T-cell numbers with this effect, however, being less apparent after mifepristone. We identified, and confirmed in additional in vitro studies, a partial agonistic GR effect of mifepristone at night (i.e., between 02:00 and 03:30) that could explain the lower antagonistic efficacy of the substance on CXCR4 expression and naive T-cell counts. CXCR4 expression emerged to be a most sensitive marker of GR signaling. Our studies jointly show that endogenous cortisol, specifically via GR activation, causes the morning increase in CXCR4 expression and the subsequent extravasation of naive T cells, thus revealing an important immunological function of the morning cortisol rise.

Differential effect of severe and moderate social stress on blood immune and endocrine measures and susceptibility to collagen type II arthritis in male rats

The effects of social stress on several blood immune measures and collagen-induced arthritis (CIA) were investigated in Wistar rats using the resident-intruder confrontation paradigm to induce stress of different intensity. Male intruders were exposed for one week to a dominant opponent either repeatedly for 4h daily (moderate stress) or continuously (severe stress). Arthritis was induced by intradermal injection of collagen type II (CII) into the tail skin at the end of day 3 of confrontation. Only severe stress was associated with decreased CD4 and CD8 T cells, and the increase in granulocyte numbers and body mass loss was more pronounced under these conditions. Only severe stress reduced the susceptibility to arthritis by about 50%. Severity scores did not differ in the first five days after disease onset between all groups. Subsequent experiments focused on severely stressed rats indicated that disease progressed until day 10 only in control animals, but not in severely stressed males. Stressor exposure resulted in increased blood monocyte numbers, but these males failed to accumulate macrophages into the skin at the site of CII injection. High numbers of attacks experienced by intruders correlated with delayed disease onset in severely stressed rats. We hypothesize that severe stress persisting after disease induction exhibits beneficial effects on the susceptibility of CIA and propose that the specific endocrine and immunological profile associated with severe stress is an important factor for disease outcome--a factor which probably explains many of the conflicting data of previous stress studies on CIA.

Chronic subordinate colony housing (CSC) as a model of chronic psychosocial stress in male rats

Chronic subordinate colony housing (CSC) is an adequate and reliable mouse model of chronic psychosocial stress, resulting in reduced body weight gain, reduced thymus and increased adrenal weight, long-lasting anxiety-like behaviour, and spontaneous colitis. Furthermore, CSC mice show increased corticotrophin (ACTH) responsiveness to acute heterotypic stressors, suggesting a general mechanism which allows a chronically-stressed organism to adequately respond to a novel threat. Therefore, the aim of the present study was to extend the CSC model to another rodent species, namely male Wistar rats, and to characterize relevant physiological, immunological, and behavioural consequences; placing particular emphasis on changes in hypothalamo-pituitary-adrenal (HPA) axis responsiveness to an acute heterotypic stressor. In line with previous mouse data, exposure of Wistar rats to 19 days of CSC resulted in a decrease in body weight gain and absolute thymus mass, mild colonic barrier defects and intestinal immune activation. Moreover, no changes in stress-coping behaviour or social preference were seen; again in agreement with the mouse paradigm. Most importantly, CSC rats showed an increased plasma corticosterone response to an acute heterotypic stressor (open arm, 5 min) despite displaying similar basal levels and similar basal and stressor-induced plasma ACTH levels. In contrast to CSC mice, anxiety-related behaviour and absolute, as well as relative adrenal weights remained unchanged in CSC rats. In summary, the CSC paradigm could be established as an adequate model of chronic psychosocial stress in male rats. Our data further support the initial hypothesis that adrenal hyper-responsiveness to ACTH during acute heterotypic stressors represents a general adaptation, which enables a chronically-stressed organism to adequately respond to novel challenges.

Chronic social stress impairs virus specific adaptive immunity during acute Theiler's virus infection

Prior exposure to social disruption (SDR) stress exacerbates Theiler's murine encephalomyelitis virus (TMEV) infection, a model of multiple sclerosis. Here we examined the impact of SDR on T cell responses to TMEV infection in SJL mice. SDR impaired viral clearance and exacerbated acute disease. Moreover, TMEV infection alone increased CD4 and CD8 mRNA expression in brain and spleen while SDR impaired this response. SDR decreased both CD4(+) and CD8(+) virus-specific T cells in CNS, but not spleen. These findings suggest that SDR-induced suppression of virus-specific T cell responses contributes to impairments in viral clearance and exacerbation of acute disease.

Stress-induced redistribution of immune cells--from barracks to boulevards to battlefields: a tale of three hormones--Curt Richter Award winner

BACKGROUND

The surveillance and effector functions of the immune system are critically dependent on the appropriate distribution of immune cells in the body. An acute or short-term stress response induces a rapid and significant redistribution of immune cells among different body compartments. Stress-induced leukocyte redistribution may be a fundamental survival response that directs leukocyte subpopulations to specific target organs during stress, and significantly enhances the speed, efficacy and regulation of an immune response. Immune responses are generally enhanced in compartments (e.g., skin) that are enriched with leukocytes, and suppressed in compartments that are depleted of leukocytes during/following stress. The experiments described here were designed to elucidate the: (1) Time-course, trajectory, and subpopulation-specificity of stress-induced mobilization and trafficking of blood leukocytes. (2) Individual and combined actions of the principal stress hormones, norepinephrine (NE), epinephrine (EPI), and corticosterone (CORT), in mediating mobilization or trafficking of specific leukocyte subpopulations. (3) Effects of stress/stress hormones on adhesion molecule, L-selectin (CD62L), expression by each subpopulation to assess its adhesion/functional/maturation status.

METHODS

Male Sprague Dawley rats were stressed (short-term restraint, 2-120 min), or adrenalectomized and injected with vehicle (VEH), NE, EPI, CORT, or their combinations, and blood was collected for measurement of hormones and flow cytometric quantification of leukocyte subpopulations.

RESULTS

Acute stress induced an early increase/mobilization of neutrophils, lymphocytes, helper T cells (Th), cytolytic T cells (CTL), and B cells into the blood, followed by a decrease/trafficking of all cell types out of the blood, except neutrophil numbers that continued to increase. CD62L expression was increased on neutrophils, decreased on Th, CTL, and natural killer (NK) cells, and showed a biphasic decrease on monocytes & B cells, suggesting that CD62L is involved in mediating the redistribution effects of stress. Additionally, we observed significant differences in the direction, magnitude, and subpopulation specificity of the effects of each hormone: NE increased leukocyte numbers, most notably CD62L⁻/⁺ neutrophils and CD62L⁻ B cells. EPI increased monocyte and neutrophil numbers, most notably CD62L⁻/⁺ neutrophils and CD62L⁻ monocytes, but decreased lymphocyte numbers with CD62L⁻/⁺ CTL and CD62L⁺ B cells being especially sensitive. CORT decreased monocyte, lymphocyte, Th, CTL, and B cell numbers with CD62L⁻ and CD62L⁺ cells being equally affected. Thus, naïve (CD62L⁺) vs. memory (CD62L⁻) T cells, classical (CD62L⁺) vs. non-classical (CD62L⁻) monocytes, and similarly distinct functional subsets of other leukocyte populations are differentially mobilized into the blood and trafficked to tissues by stress hormones.

CONCLUSION

Stress hormones orchestrate a large-scale redistribution of immune cells in the body. NE and EPI mobilize immune cells into the bloodstream, and EPI and CORT induce traffic out of the blood possibly to tissue surveillance pathways, lymphoid tissues, and sites of ongoing or de novo immune activation. Immune cell subpopulations appear to show differential sensitivities and redistribution responses to each hormone depending on the type of leukocyte (neutrophil, monocyte or lymphocyte) and its maturation/functional characteristics (e.g., non-classical/resident or classical/inflammatory monocyte, naïve or central/effector memory T cell). Thus, stress hormones could be administered simultaneously or sequentially to induce specific leukocyte subpopulations to be mobilized into the blood, or to traffic from blood to tissues. Stress- or stress hormone-mediated changes in immune cell distribution could be clinically harnessed to: (1) Direct leukocytes to sites of vaccination, wound healing, infection, or cancer and thereby enhance protective immunity. (2) Reduce leukocyte traffic to sites of inflammatory/autoimmune reactions. (3) Sequester immune cells in relatively protected compartments to minimize exposure to cytotoxic treatments like radiation or localized chemotherapy. (4) Measure biological resistance/sensitivity to stress hormones in vivo. In keeping with the guidelines for Richter Award manuscripts, in addition to original data we also present a model and synthesis of findings in the context of the literature on the effects of short-term stress on immune cell distribution and function.

In vivo suppression of plasma IL-12 levels by acute and chronic stress paradigms: potential mediating mechanisms and sex differences

Interleukin-12 (IL-12) is a major pro-inflammatory cytokine, which promotes cell-mediated immunity and T(H)1 differentiation. In vitro studies indicated suppression of IL-12 production by several stress-related factors, but no effects of behavioral stress were shown on plasma IL-12 levels. Therefore, in the current study we (i) examined the in vivo effects of various behavioral and pharmacological stress paradigms on baseline plasma IL-12 levels; (ii) compared these in vivo findings to those obtained following in vitro stimulation of leukocytes from the same rats; and (iii) assessed potential sexual dimorphism in these outcomes. The findings indicated that plasma IL-12 levels were significantly reduced by social confrontation, wet-cage exposure, surgery, and the administration of corticosterone, epinephrine, or prostaglandin-E(2). Notably, most in vivo impacts on plasma levels were not evident when assessed in vitro. The IL-12-reducing effects of wet-cage exposure, and of corticosterone and epinephrine administration, were significantly greater in males than in females, although females exhibited greater total corticosterone levels following stress. The duration of acute stressors predicted the degree of IL-12 reduction, but more prolonged stressors did not. Furthermore, seven days of alternating behavioral stressors reduced plasma IL-12 levels more than 14 days. These findings suggest animals' behavioral habituation to stress conditions, or a specific immune mechanism restricting the duration of IL-12 reduction. Overall, our findings indicate a generic and robust stress-induced reduction in plasma IL-12 levels, and suggest epinephrine, corticosterone, and prostaglandin-E(2), as potential mediators that should be scrutinized in vivo in the context of natural physiological stress responses.

Behavioural consequences of two chronic psychosocial stress paradigms: anxiety without depression

Chronic stress, in particular chronic psychosocial stress, is a risk factor in the aetiology of various psychopathologies including anxiety- and depression-related disorders. Therefore, recent studies have focussed on the development of social-stress paradigms, which are believed to be more relevant to the human situation than non-social-stress paradigms. The majority of these paradigms have been reported to increase both anxiety- and depression-related behaviour in rats or mice. However, in order to dissect the mechanisms underlying anxiety or depression, animal models are needed, which specifically induce one, or the other, phenotype. Here, we study both short- (1d after stressor termination) and long-term (4d or 7d after stressor termination) behavioural and physiological consequences of two well-validated chronic psychosocial stress models: social-defeat/overcrowding (SD/OC) and chronic subordinate colony housing (CSC). We demonstrate that SD/OC and CSC result in different physiological alterations: SD/OC more strongly affecting body-weight development, whereas CSC more strongly affects adrenal and pituitary morphology. Both stressors were shown to flatten circadian locomotor activity immediately after stress termination, which normalized 7d later in SD/OC group but reversed to hyperactivity during the dark phase in the CSC group. Importantly, neither stress paradigm resulted in an increase in depression-related behaviour as assessed using the forced swim test, tail suspension test and saccharin preference test at any time-point. However, both stress paradigms lead to an anxiogenic phenotype; albeit with different temporal profiles and not towards a novel con-specific (social anxiety). CSC exposure elevates anxiety-related behaviour immediately after stressor termination, which lasts for at least 1 wk. In contrast, the anxiogenic phenotype only develops 1 wk after SD/OC termination. In conclusion, both models are unique for uncovering the molecular underpinnings of anxiety-related behaviour without conflicting depression-based alterations.

Family matters: maternal and litter-size effects on immune parameters in young laboratory rats

A functional immune system is important for the survival of mammalian young, particularly at weaning when they lose the immunological support provided by the mother's colostrum and milk. In altricial mammals, litter size and maternal characteristics are important components of an animal's early environment, which affect postnatal growth and development. In a study of unculled litters of Long-Evans laboratory rats (Rattus norvegicus), we asked whether such parameters are also associated with the immune status of the young shortly before weaning. On postnatal day 17, we assessed numbers of several leukocyte and lymphocyte subsets, the activity of the complement system, and immunoglobulin G (IgG) concentrations in the serum. Averaging the values of all pups per litter, we found negative correlations between litter size and lymphocyte counts, complement system activity and IgG concentration. Maternal effects were seen in the positive correlation between maternal postpartum body mass and granulocyte and monocyte counts. In addition, lymphocyte and monocyte counts as well as complement activity were lower for the young of multiparous than of primiparous mothers. This suggests a trend towards a better developed immune system in such offspring, which may be relevant for their immediate and long-term survival. The effects described here have potential implications for the design and interpretation of biomedical studies of immune parameters in laboratory rats.

Chronological assessment of mast cell-mediated gut dysfunction and mucosal inflammation in a rat model of chronic psychosocial stress

Life stress and mucosal inflammation may influence symptom onset and severity in certain gastrointestinal disorders, particularly irritable bowel syndrome (IBS), in connection with dysregulated intestinal barrier. However, the mechanism responsible remains unknown. Crowding is a validated animal model reproducing naturalistic psychosocial stress, whose consequences on gut physiology remain unexplored. Our aims were to prove that crowding stress induces mucosal inflammation and intestinal dysfunction, to characterize dynamics in time, and to evaluate the implication of stress-induced mast cell activation on intestinal dysfunction. Wistar-Kyoto rats were submitted to 15 days of crowding stress (8 rats/cage) or sham-crowding (2 rats/cage). We measured spontaneous and corticotropin-releasing factor-mediated release of plasma corticosterone. Stress-induced intestinal chrono-pathobiology was determined by measuring intestinal inflammation, epithelial damage, mast cell activation and infiltration, and intestinal barrier function. Corticosterone release was higher in crowded rats throughout day 15. Stress-induced mild inflammation, manifested earlier in the ileum and the colon than in the jejunum. While mast cell counts remained mostly unchanged, piecemeal degranulation increased along time, as the mucosal content and luminal release of rat mast cell protease-II. Stress-induced mitochondrial injury and increased jejunal permeability, both events strongly correlated with mast cell activation at day 15. Taken together, we have provided evidences that long-term exposure to psychosocial stress promotes mucosal inflammation and mast cell-mediated barrier dysfunction in the rat bowel. The notable resemblance of these findings with those in some IBS patients, support the potential interest and translational validity of this experimental model for the research of stress-sensitive intestinal disorders, particularly IBS.

Plasma testosterone levels decrease after activation of skin immune system in a free-ranging mammal

The immunocompetence handicap hypothesis (ICHH) postulates a trade-off between the display of androgen-related, sexually selected traits and investment in immune functions, often summarized as immunosuppression by testosterone (TE). We investigated the relationship between delayed type hypersensitivity (DTH) skin responses and the endocrine system in a free-ranging mammal and asked: (i) are high plasma TE levels related to a weak DTH response or (ii) does an activation of the cellular immune system cause a decrease in plasma TE secretion? and (iii) does baseline cortisol (CORT) and the capacity to release CORT in response to stress influence the DTH response? We studied these questions in the bat Carollia perspicillata and conducted an immune challenge (IC), a DTH skin test with the antigen 1,4-dinitrofluorobenzene (DNFB), as a measure for antigen-specific cell-mediated immunity. We found a high individual variance in DTH response irrespective of sex. In addition, pre-IC plasma TE did not affect the extent of DTH responses, but instead the IC lowered post-IC TE titres in both sexes. Also, pre-IC baseline CORT titres did not influence the DTH responses significantly, but the extent of an induced CORT response was negatively related to the DTH reaction. Our study does not support the presumption of an immunosuppressive effect of TE, but suggests that an activation of the immune system reduces plasma TE. This is still in line with the ICHH as originally formulated, because only immunocompetent animals are able to cope with pathogens effectively and maintain high TE levels at the same time.

Mobilization of gammadelta T lymphocytes in response to psychological stress, exercise, and beta-agonist infusion

The mobilization of cytotoxic lymphocytes, such Natural Killer (NK) cells and CD8(+) T cells, during stress and exercise is well documented in humans. However, humans have another cytotoxic lymphocyte subset that has not been studied in this context: the Gamma Delta (gammadelta) T lymphocyte. These cells play key roles in immune processes including the elimination of bacterial infection, wound repair and delayed-type hypersensitivity reactions. The current study investigated the effects of stress, exercise, and beta-agonist infusion on the mobilization of gammadelta T lymphocytes. Three separate studies compared lymphocytosis in response to an acute speech stress task (n=29), high (85%W(max)) and low (35%W(max)) intensity concentric exercise (n=11), and isoproterenol infusion at 20 and 40 ng/kg/min (n=12). Flow cytometric analysis was used to examine lymphocyte subsets. gammadelta T lymphocytes were mobilized in response to all three tasks in a dose-dependent manner; the extent of mobilization during the speech task correlated with concomitant cardiac activation, and was greater during higher intensity exercise and increased dose of beta-agonist infusion. The mobilization of gammadelta T lymphocytes was greater (in terms of % change from baseline) than that of CD8(+) T lymphocytes and less than NK cells. This study is the first to demonstrate that gammadelta T cells are stress-responsive lymphocytes which are mobilized during psychological stress, exercise, and beta-agonist infusion. The mobilization of these versatile cytotoxic cells may provide protection in the context of situations in which antigen exposure is more likely to occur.

T-lymphocyte interaction with stromal, bone and hematopoietic cells in the bone marrow

Mature T cells in the bone marrow (BM) are in constant exchange with the blood pool. Within the BM, T-cell recognition of antigen presented by dendritic cell (DC) can occur, nevertheless it is thought that BM T cells mostly receive non-antigenic signals by either stimulatory, for example, interleukin (IL)-7, IL-15, tumor necrosis factor family members, or inhibitory molecules, for example, transforming growth factor-beta. The net balance is in favor of T-cell proliferation. Indeed, the percentage of proliferating T cells is higher in the BM than in spleen and lymph nodes, both within CD4 and CD8 T cells. High numbers of memory T cells proliferate in the BM, as they preferentially home to the BM and have an increased turnover as compared with naive T cells. I propose here that the BM plays an essential role in maintaining normal peripheral T-lymphocyte numbers and antigen-specific memory for both CD4 and CD8 T cells. I also discuss BM T-cell contribution to the homeostasis of bone metabolism as well as of hematopoiesis. It emerges that BM T cells play unexpected roles in several diseases, for example AIDS and osteoporosis. A better knowledge on BM T cells has implications for currently used clinical interventions, for example, vaccination, BM transplantation, mesenchymal stem cell-based therapies.

Exercise-induced redistribution of T lymphocytes is regulated by adrenergic mechanisms

Acute exercise is known for causing considerable changes in leukocyte counts and function. In this paper we report that differentiated changes in T-lymphocyte distribution occur in lymphoid and non-lymphoid organs depending on the type and the intensity of exercise. Using fluorescent cell tracking we observed a release of T-cells from the spleen while lung, bone marrow and Peyer's patches served as target organs. The number of T-cells in the blood rose after intensive running while lymphopenia occurred after swimming exercise. Changes in number of labelled T-cells were neither found in the lymph nodes nor in the thymus regardless of exercise protocol. Following an alpha- or beta-blockade, the exercise-induced release of T-cells from the spleen and the accumulation of T-cells in the lung were inhibited while the enhancement of T-cells in the Peyer's patches was not affected. The administration of epinephrine partially mimicked the effects of exercise and resulted in a release of T-cells from both, the spleen and the liver, as well as in an increase of circulating blood T-cells. In conclusion, exercise induces a substantial re-distribution of T-cells within lymphoid and non-lymphoid organs. The migrating properties of T-cells could be partially explained by adrenergic mechanisms associated with exercise while the involvement of certain homing receptors remains to be shown. Our results suggest that the accumulation of T-cells in both, lung and Peyer's patches, may enhance the immune vigilance in these compartments which serve as the body's major defence barriers.

Positive psychosocial factors and NKT cells in ovarian cancer patients

Psychosocial factors are known to be associated with properties of both NK cells and T cells in cancer patients. Less is known about the relationship between psychosocial factors and NKT cells, a rare group of lymphocytes that have known relevance for tumor control. We examined four psychosocial factors and percentage and number of CD3+CD56+ NKT cells, CD3-CD56+ NK cells, and CD3+CD56- T cells in peripheral blood lymphocytes (PBL), ascites, and tumor of 35 ovarian cancer patients and 28 patients with benign pelvic masses. Patients awaiting surgery for a suspected cancerous mass completed questionnaires and gave a pre-surgical blood sample. Ascites and tumor were taken during surgery. After lymphocyte isolation, subpopulations were analyzed by flow cytometry. Benign and cancer patients did not differ on PBL subpopulations. Among cancer patients, NKT cell percentage was significantly higher in tumor and ascites than in PBL; T cell percentage was significantly higher in PBL than tumor. NKT, NK, and T cell number were significantly higher in peripheral blood than in ascites. Positive reframing was related to significantly higher NKT cell percentage and number in PBL. Social support was related to significantly higher NKT cell percentage in tumor. Vigor was related to significantly higher NKT cell percentage in PBL. Total mood disturbance was not related to NKT cell percentage or number. No significant relationships were found between psychosocial factors and NK cell percentage and number and T cell percentage and number. Given the anti-tumor activity of CD3+CD56+ cells, these relationships may have relevance for cancer control.

Social stress, immune functions and disease in rodents

The link between social factors, stress and health has been the focus of many interdisciplinary studies mostly because: (i) animals, including humans, often live in societies; (ii) positive and negative social relationships affect disease and well being; (iii) physiological alterations, which parallel social interactions also modulate immune and neuroendocrine functions. This review will focus on studies conducted on laboratory and wild rodents where social factors such as dyadic interactions, individual housing and differential group housing were investigated. The results obtained allow one to conclude that social factors in rodents are causally linked with immune disorders/disease susceptibility. In particular, lower lymphocyte proliferation and antigen-specific-IgG, granulocytosis and lymphopenia, as well as higher tumor induction and progression, are reliably associated with negative social events. Finally, due to the increasing utilization of social stress-based animal models the reliability of the concept of "social stress" and its evolutionary context are re-evaluated.

Lymphocyte numbers and subsets in the human blood. Do they mirror the situation in all organs?

Lymphocyte numbers in the blood are used to evaluate the immune status on a daily basis in medicine. Several studies have documented the normal ranges of lymphocytes and lymphocyte subsets in the peripheral blood. A variety of techniques and criteria have revealed clear differences between the lymphocyte subsets in childhood and adolescence. Race and gender are also variables for blood lymphocytes, and even environmental factors seem to influence the numbers of some lymphocyte populations. However, do all these variations in lymphocyte subsets in the peripheral blood mirror changes in the lymphocyte populations of the whole body, or is it just a result of different migratory habits of cells? The factors influencing the distribution of lymphocytes in the peripheral blood with regard to the different abilities of T and B cells to migrate to distinct lymphoid or non-lymphoid tissue are summarized. In addition it will be described how the removal of organs (e.g. thymus, spleen, liver) influences the distribution of lymphocytes in the blood. All these parameters should be considered not only in the clinical situation when the immune status of a patient is extrapolated from the lymphocyte numbers in the blood, but also when interpreting treatment effects in patients.

Adrenergic inhibition of innate anti-viral response: PKA blockade of Type I interferon gene transcription mediates catecholamine support for HIV-1 replication

Type I interferons (IFN-alpha and -beta) play a key role in anti-viral immunity, and we sought to define the molecular mechanisms by which the sympathetic nervous system (SNS) inhibits their effects. In peripheral blood leukocytes and plasmacytoid dendritic cells (pDC2), induction of interferon anti-viral activity by double-stranded RNA (poly-I:C) or CpG DNA was substantially inhibited by norepinephrine and by pharmacologic activation of the cAMP/PKA signaling pathway. This effect was specific to Type I interferons and driven by PKA-mediated repression of IFNA and IFNB gene transcription. Luciferase reporter analyses identified tandem interferon response factor-binding sites in positive regulatory domains I and III of the IFNB promoter as a key target of PKA inhibition. PKA suppression of Type I interferons was associated with impaired transcription of interferon response genes supporting the "anti-viral state", and was sufficient to account for norepinephrine-induced enhancement of HIV-1 replication. Given the ubiquitous role of Type I interferons in containing viral replication, PKA-mediated inhibition of IFN transcription could explain the stimulatory effects of catecholamines on a broad range of viral pathogens.

Restraint stress decreases virus-induced pro-inflammatory cytokine mRNA expression during acute Theiler's virus infection

Stressful life events have been associated with the onset and/or exacerbation of multiple sclerosis (MS). Our previous studies have indicated that restraint stress (RS) reduces inflammation and virus-induced chemokine expression in the Theiler's virus-induced demyelination (TVID) model of MS. Here we report that RS significantly reduced the virus-induced interferon-gamma mRNA levels in the brain. Additionally, mRNA levels of lymphotoxin-beta, tumor necrosis factor-alpha, and interferon-gamma in the brain were negatively correlated with viral titers in the brain. These results indicated an immunosuppressive effect of stress during early TVID causing impaired viral clearance, which may be a potential exacerbating factor for later demyelination.

Gender difference in basal and stress levels of peripheral blood leukocytes in laboratory rats

The aim of the present study was to investigate gender differences in numbers and function of blood immune cells in stressed and non-stressed laboratory rats. Psychosocial stress in adult male or female rats was induced by social confrontation of an intruder rat with a resident opponent for 2 h. Behavioral analysis indicated that intruders of both sexes were clearly defeated and had markedly higher plasma corticosterone concentrations than unstressed home cage controls at the end of the confrontation. Lower numbers of CD4, CD8, and B cells as well as a reduced proliferative response of lymphocytes to ConA were observed in stressed groups of either sex. However, some important gender differences were also observed. Stressed males had higher granulocyte numbers than controls, while granulocyte numbers remained unchanged in stressed females. Similarly, stressed males had higher phagocytic activity than stressed females. Second, there was a gender difference in some basal values. Female controls had lower NK cell numbers than control males. Interestingly, NK numbers in stressed males decreased considerably, reaching the same low levels as in (stressed and control) females. In addition, females exhibited higher basal corticosterone concentrations than males. To summarise, these data do not indicate a superior blood cellular immune function in female rats, neither for the control nor the stress condition. However, the data clearly suggest that male and female rats should not be considered as a uniform group with respect to their immunological response to stress.

Three weekly courses of betamethasone administered to pregnant baboons at 0.6, 0.65, and 0.7 of gestation alter fetal and maternal lymphocyte populations at 0.95 of gestation

The hypothalamic-pituitary-adrenal (HPA) axis plays a major role in the communication between the immune and neuroendocrine systems. Glucocorticoids are potent immunomodulatory hormones. In the present study, we evaluated the effect of three weekly courses of betamethasone, administered to pregnant baboons at 0.6, 0.65, and 0.7 of gestation, on maternal hematological parameters during treatment, maternal and fetal hematological parameters and lymphocyte populations at 0.95 of gestation, and fetal lymphoid organs and placental structure. Each weekly betamethasone course resulted in decreased granulocytes and increased lymphocytes and monocytes in maternal circulation (by percentage, p < 0.05). The percentage and absolute number of CD8+ T-cells in the maternal circulation were lower and CD4+ T-cells higher (p < 0.05) in treated pregnant animals at 0.95 gestation. The percentage of proliferating CD3- CD8+ cells was lower in blood obtained from the fetal heart of betamethasone-treated animals. In the betamethasone group, the number of CD8+ T-cells and NK cells were elevated and the number of T and CD4+ T-cells were reduced in fetal heart blood compared with the umbilical vein blood. The number of placental macrophages (CD68+ cells) per visual field in betamethasone-treated and control animals were not different. Taken together, our data show that betamethasone treatment of pregnant females with no indication of preterm labor affects some components of the fetal and maternal immune system, altering the maternal CD4+/CD8+ ratio and absolute number of fetal NK cell and maternal CD8+ T-cell.

The long-term effects of perinatal glucocorticoid exposure on the host defence system of the respiratory tract

Glucocorticoids are used to mature the fetal lung at times of threatened premature delivery. These drugs modify leukocyte profiles when administered in adulthood, but their effects on the mature host defence system following administration during the perinatal period are incompletely understood. In this study, the long-term effects of perinatal dexamethasone exposure on rodent host defence cells in the pulmonary airspaces, the perivascular compartment of the lung, and the blood were investigated. Rats were treated prenatally (gestational days 16-19) or neonatally (postnatal days 1-7) by inclusion of dexamethasone in the mothers' drinking water (1 microg/ml). The pups were then allowed to develop to adulthood (P60-80), at which time respiratory tissues were collected for light and electron microscopy and bronchoalveolar lavage (BAL), and blood for cell count and fluorescent activated cell-sorting (FACS) analysis. Prenatal treatment had no effect on any parameter examined. Following neonatal dexamethasone exposure, light microscopy of the lung tissue revealed a significant reduction in the number of cells in the perivascular space in both the central and the peripheral regions of the adult lung, but no differences in the number of cells in the airspaces. Neonatal dexamethasone exposure was also characterized by a significant reduction in the total number of white cells in the peripheral blood in adulthood and in particular, the number of lymphocytes relative to neutrophils was significantly reduced at maturity in these animals. The results show that neonatal, but not prenatal, dexamethasone exposure significantly alters the distribution of host defence cells in the blood and lung at maturity compared with control animals. The early neonatal period is characterized by the stress hyporesponsive period in the rat, when endogenous glucocorticoid levels are very low. Therefore, exogenous glucocorticoids administered during this time are likely to have marked "programming" effects on glucocorticoid-sensitive tissues.

Pregnancy and social stress in female rats: Influences on blood leukocytes and corticosterone concentrations

The consequences of pregnancy and social stress on blood immune cells and on plasma corticosterone concentrations were assessed in Long Evans rats. Normal pregnancy in control females was characterized by a progressive increase in corticosterone concentration and increasing numbers of granulocytes. In contrast, CD4 T, CD8 T, and B cell numbers as well as the proliferative response of lymphocytes decreased as pregnancy progressed. Stress was induced in pregnant females by social confrontation for 2 h daily with a female resident opponent over a period of 2 months. Corticosterone concentrations were substantially higher in pregnant stressed than in pregnant control rats. Furthermore, the numbers of monocytes, NK and B cells were lower in stressed females, and there was a strong trend towards suppressed lymphocyte proliferation. Interestingly, pregnant females did not show granulocytosis in response to the stressor. In sum, the social stress paradigm in females appears to be a good model for the investigation of the interactions between stress, pregnancy and the immune system. It also provides an excellent platform for studies on prenatal stress under relatively naturalistic conditions.

Effects of social stress on blood leukocyte distribution: the role of α- and β-adrenergic mechanisms

Social stress in mammals has repeatedly been shown to cause substantial alterations in the distribution pattern of immune cells in the peripheral blood. The studies described here investigated the role of adrenergic mechanisms in mediating stressor-induced changes in blood leukocyte numbers using a social confrontation procedure in the rat. Experimental manipulations were carried out to eliminate the stress-associated release of adrenal hormones or to block the binding of endogenous catecholamines to alpha- and beta-adrenergic receptors. Adrenalectomy completely abolished the stressor-induced decreases in circulating numbers of T helper cells (CD4+), cytotoxic T cells (CD8+) and B cells but was ineffective in preventing neutrophil granulocytosis, monocytosis and an increase in natural killer (NK) cells. Treatment with the alpha-adrenergic antagonist phentolamine (PHE) was highly effective in preventing granulocytosis and partially blocked lymphopenia, but failed to abolish monocytosis and an increase in NK cells. Treatment with the beta-adrenergic antagonists propranolol (PROP) or nadolol (NAD) entirely blocked the increases in monocytes and NK cells. In addition, beta-adrenergic blockade also significantly reduced neutrophilia, with PROP being more effective than NAD. The results presented here provide evidence that catecholamines play an important role in the redistribution of blood leukocytes during social stress. In particular, the mobilization of cells of the innate immune response seems to be regulated by adrenergic mechanisms.

Alterations in chemokine expression following Theiler's virus infection and restraint stress

Restraint stress (RS) applied to mice during acute infection with Theiler's virus causes corticosterone-induced immunosuppression. This effect was further investigated by measuring chemokine changes in the spleen and central nervous system (CNS) using an RNase Protection Assay. mRNAs for lymphotactin (Ltn), interferon-induced protein-10 (IP-10), MIP-1 beta, monocyte chemoattractant protein-1 (MCP-1) and TCA-3 were detected in the spleen at day 2 pi, but not in the brain of CBA mice infected with Theiler's virus. Ltn, IP-10 and RANTES were elevated in both the spleen and the brain at day 7 pi, and were significantly decreased by RS in the brain. RS also resulted in decreased inflammation within the CNS.

Effects of repeated social stress on leukocyte distribution in bone marrow, peripheral blood and spleen

Leukocyte trafficking between the various body compartments has an important surveillance function that ensures the detection of antigen and enables the immune system to initiate a rapid and effective response. Repeated social defeat of group-housed male mice induced by daily, acute encounters with an aggressive conspecific substantially altered leukocyte trafficking and led to a gradual redistribution of immune cells in bone marrow, peripheral blood and spleen. Recurrent exposure to the stressor over a period of 2, 4 or 6 consecutive days was associated with cell mobilization and increased myelopoiesis in the bone marrow that was paralleled by an accumulation of neutrophils and monocytes in circulation and spleen. Substantial depletion of B cells in bone marrow and blood was associated with an increase in splenic B cells indicating a redirection of this cell type to the spleen. In contrast, T cells were markedly reduced in these immune compartments. The recruitment of CD11b+ leukocytes (i.e., monocytes/macrophages and neutrophils) from the bone marrow to the spleen might play a critical role in the development of functional glucocorticoid resistance in the murine spleen that was reported in context with repeated social defeat.

Cytokine production by spleen cells after social defeat in mice: activation of T cells and reduced inhibition by glucocorticoids

Social disruption (SDR) is an effective model of social stress associated with an enhanced inflammatory reactivity of the immune system. The aim of the present study was to further describe SDR effects on cytokine production by spleen cells, testing selectively monocyte and T cell functions as a result of this stressor. For this purpose, splenocytes from control mice (C) and mice socially stressed for 7 days (SDR) were cultured in the presence of lipopolysaccharide (LPS) or concanavalin A (Con A). Splenocyte proliferation, cytokine production and sensitivity of spleen cells to corticosterone were assessed in vitro. The humoral response to keyhole limpet hemocyanin (KLH) immunization was assessed. SDR induced splenomegaly and enhanced splenocyte basal proliferation. The pro-inflammatory influence of SDR was confirmed by an increased release of interleukin-6 (IL-6) by LPS-stimulated cultures and by a reduced sensitivity of spleen cells to the anti-inflammatory effect of corticosterone. The mechanism increasing cytokine production in response to LPS was cytokine specific, since among inflammatory cytokines, IL-6 but not interferon-gamma (IFN-gamma) was enhanced by stress. In stressed mice, the increase in IL-6 and IFN-gamma and the decrease in IL-10 release in Con A-stimulated cultures indicate that SDR did not modify the Th1/Th2 cytokine balance but globally activated T cells. Plasma anti-KLH antibody levels were similar in both groups. Wounded and non-wounded mice presented similar responses to stress. This study shows that social disruption stress enhances the reactivity of cells from both the acquired and innate immune systems.