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

Enriched environment housing improved the laying hen's resistance to transport stress via modulating the heat shock protective response and inflammation

An enriched environment can promote adaptability of animals to cope with complex environments. A total of 18-week-old 216 laying hens were randomly divided into 2 groups; of which, one group was housed in conventional battery cages (CC, n = 36), and the others were housed in furnished cages (FC, n = 180). At the end of 64 wk of age, 24 chickens of each group were selected for 4-hour transport treatment. The spleen tissues of laying hens were collected before transportation (BT), immediately after transportation, and at 48 h after transportation to detect the expression of the heat shock protective response signaling pathway and inflammatory factors. Serum samples were collected to detect the content of immune cytokines. Transport stress decreased heat shock proteins (HSP; including Small HSP, HSP27, HSP40, HSP60, HS70, HSP90, HSP110) in the CC group (P < 0.05), whereas there was no significant difference in the expression of HSP (except for Small HSP and HSP40) in the FC group (P > 0.05) immediately after transportation. At 48 h after transportation, mRNA levels of HSP (except for Small HSP and HSP40) in the FC group were upregulated, which were higher than those at BT (P < 0.05). The changes in HSP60, HSP70, and HSP90 protein levels had similar tendencies. The results showed that housing in furnished cages alleviated the inhibition of expression of HSP in the hens' spleen induced by transport stress. In addition, the hens housed in the FC group had lower expression levels of proinflammatory factors (nuclear transcription factor-kappa B, inducible nitric oxide synthase, cyclooxygenase-2, prostaglandin E synthase, inflammatory cytokines [IL-1β and IL-6], and tumor necrosis factor alpha) (P < 0.05). We suggest that the enriched environment can reduce transport stress damage in laying hens and improve resistance to transport stress by regulating expression of heat shock response proteins and inflammatory cytokines.

Psychoneuroimmunology: Then and Now

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

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.

Short-term stress enhances cellular immunity and increases early resistance to squamous cell carcinoma

In contrast to chronic/long-term stress that suppresses/dysregulates immune function, an acute/short-term fight-or-flight stress response experienced during immune activation can enhance innate and adaptive immunity. Moderate ultraviolet-B (UV) exposure provides a non-invasive system for studying the naturalistic emergence, progression and regression of squamous cell carcinoma (SCC). Because SCC is an immunoresponsive cancer, we hypothesized that short-term stress experienced before UV exposure would enhance protective immunity and increase resistance to SCC. Control and short-term stress groups were treated identically except that the short-term stress group was restrained (2.5h) before each of nine UV-exposure sessions (minimum erythemal dose, 3-times/week) during weeks 4-6 of the 10-week UV exposure protocol. Tumors were measured weekly, and tissue collected at weeks 7, 20, and 32. Chemokine and cytokine gene expression was quantified by real-time PCR, and CD4+ and CD8+ T cells by flow cytometry and immunohistochemistry. Compared to controls, the short-term stress group showed greater cutaneous T-cell attracting chemokine (CTACK)/CCL27, RANTES, IL-12, and IFN-gamma gene expression at weeks 7, 20, and 32, higher skin infiltrating T cell numbers (weeks 7 and 20), lower tumor incidence (weeks 11-20) and fewer tumors (weeks 11-26). These results suggest that activation of short-term stress physiology increased chemokine expression and T cell trafficking and/or function during/following UV exposure, and enhanced Type 1 cytokine-driven cell-mediated immunity that is crucial for resistance to SCC. Therefore, the physiological fight-or-flight stress response and its adjuvant-like immuno-enhancing effects, may provide a novel and important mechanism for enhancing immune system mediated tumor-detection/elimination that merits further investigation.

A hassle a day may keep the pathogens away: The fight-or-flight stress response and the augmentation of immune function

Stress is known to suppress or dysregulate immune function and increase susceptibility to disease. Paradoxically, the short-term fight-or-flight stress response is one of nature's fundamental defense mechanisms that galvanizes the neuroendocrine, cardiovascular, and musculoskeletal systems into action to enable survival. Therefore, it is unlikely that short-term stress would suppress immune function at a time when it may be critically required for survival (e.g., in response to wounding and infection by a predator or aggressor). In fact, studies have shown that stress can enhance immune function under certain conditions. Several factors influence the direction (enhancing versus suppressive) of the effects of stress on immune function: (1) DURATION: acute or short-term stress experienced at the time of activation of an immune response enhances innate and adaptive immune responses. Chronic or long-term stress can suppress or dysregulate immune function. (2) Leukocyte distribution: compartments (e.g., skin), that are enriched with immune cells during acute stress show immuno-enhancement, while those that are depleted of leukocytes (e.g., blood), show immuno-suppression. (3) The differential effects of physiologic versus pharmacologic stress hormones: Endogenous hormones in physiological concentrations can have immuno-enhancing effects. Endogenous hormones at pharmacologic concentrations, and synthetic hormones, are immuno-suppressive. (4) Timing: immuno-enhancement is observed when acute stress is experienced during the early stages of an immune response while immuno-suppression may be observed at late stages. The type of immune response (protective, regulatory/inhibitory, or pathological) that is affected determines whether the effects of stress are ultimately beneficial or harmful for the organism. Arguments based on conservation of energy have been invoked to explain potential adaptive benefits of stress-induced immuno-suppression, but generally do not hold true because most mechanisms for immuno-suppression expend, rather than conserve, energy. We propose that it is important to study, and if possible, to clinically harness, the immuno-enhancing effects of the acute stress response that evolution has finely sculpted as a survival mechanism, just as we study its maladaptive ramifications (chronic stress) that evolution has yet to resolve.

Enhancing versus suppressive effects of stress on immune function: implications for immunoprotection and immunopathology

Stress is known to suppress immune function and increase susceptibility to infections and cancer. Paradoxically, stress is also known to exacerbate asthma, and allergic, autoimmune and inflammatory diseases, although such diseases should be ameliorated by immunosuppression. Moreover, the short-term fight-or-flight stress response is one of nature's fundamental defense mechanisms that enables the cardiovascular and musculoskeletal systems to promote survival, and it is unlikely that this response would suppress immune function at a time when it is most required for survival (e.g. in response to wounding and infection by a predator or aggressor). These observations suggest that stress may suppress immune function under some conditions while enhancing it under others. The effects of stress are likely to be beneficial or harmful depending on the type (immunoprotective, immunoregulatory/inhibitory, or immunopathological) of immune response that is affected. Studies have shown that several critical factors influence the direction (enhancing vs. suppressive) of the effects of stress or stress hormones on immune function: (1) Duration (acute vs. chronic) of stress: Acute or short-term stress experienced at the time of immune activation can enhance innate and adaptive immune responses. Chronic or long-term stress can suppress immunity by decreasing immune cell numbers and function and/or increasing active immunosuppressive mechanisms (e.g. regulatory T cells). Chronic stress can also dysregulate immune function by promoting proinflammatory and type-2 cytokine-driven responses. (2) Effects of stress on leukocyte distribution: Compartments that are enriched with immune cells during acute stress show immunoenhancement, while those that are depleted of leukocytes, show immunosuppression. (3) The differential effects of physiologic versus pharmacologic concentrations of glucocorticoids, and the differential effects of endogenous versus synthetic glucocorticoids: Endogenous hormones in physiological concentrations can have immunoenhancing effects. Endogenous hormones at pharmacologic concentrations, and synthetic hormones, are immunosuppressive. (4) The timing of stressor or stress hormone exposure relative to the time of activation and time course of the immune response: Immunoenhancement is observed when acute stress is experienced at early stages of immune activation, while immunosuppression may be observed at late stages of the immune response. We propose that it is important to study and, if possible, to clinically harness the immunoenhancing effects of the acute stress response, that evolution has finely sculpted as a survival mechanism, just as we study its maladaptive ramifications (chronic stress) that evolution has yet to resolve. In view of the ubiquitous nature of stress and its significant effects on immunoprotection as well as immunopathology, it is important to further elucidate the mechanisms mediating stress-immune interactions and to meaningfully translate findings from bench to bedside.

Effect of restraint stress duration on humoral immune response in albino rats: modulation by chlordiazepoxide

We evaluated the effect of restraint stress (1 hr/day) for 6, 10, 14 and 21 days on antibody response against sheep RBC (SRBC) and modulation by chlordiazepoxide (CDP) pretreatment (10 mg/kg/day) in albino rats. Anti-SRBC titer was significantly decreased with increase in number of days of restraint stress exposure. CDP pretreatment significantly reversed the effects of 6, 10 and 14 (but not of 21) days of restraint stress. CDP treatment for 21 days per se suppressed immune response, but no additive effect was observed. CDP was not effective in chronic stress (i.e., 21 days of stress). Hence, the rationale behind benzodiazepines therapy in chronic stress needs to be evaluated.

Enhancing versus Suppressive Effects of Stress on Immune Function: Implications for Immunoprotection versus Immunopathology

It is widely believed that stress suppresses immune function and increases susceptibility to infections and cancer. Paradoxically, stress is also known to exacerbate allergic, autoimmune, and inflammatory diseases. These observations suggest that stress may have bidirectional effects on immune function, being immunosuppressive in some instances and immunoenhancing in others. It has recently been shown that in contrast to chronic stress that suppresses or dysregulates immune function, acute stress can be immunoenhancing. Acute stress enhances dendritic cell, neutrophil, macrophage, and lymphocyte trafficking, maturation, and function and has been shown to augment innate and adaptive immune responses. Acute stress experienced prior to novel antigen exposure enhances innate immunity and memory T-cell formation and results in a significant and long-lasting immunoenhancement. Acute stress experienced during antigen reexposure enhances secondary/adaptive immune responses. Therefore, depending on the conditions of immune activation and the immunizing antigen, acute stress may enhance the acquisition and expression of immunoprotection or immunopathology. In contrast, chronic stress dysregulates innate and adaptive immune responses by changing the type 1-type 2 cytokine balance and suppresses immunity by decreasing leukocyte numbers, trafficking, and function. Chronic stress also increases susceptibility to skin cancer by suppressing type 1 cytokines and protective T cells while increasing suppressor T-cell function. We have suggested that the adaptive purpose of a physiologic stress response may be to promote survival, with stress hormones and neurotransmitters serving as beacons that prepare the immune system for potential challenges (eg, wounding or infection) perceived by the brain (eg, detection of an attacker). However, this system may exacerbate immunopathology if the enhanced immune response is directed against innocuous or self-antigens or dysregulated following prolonged activation, as seen during chronic stress. In view of the ubiquitous nature of stress and its significant effects on immunoprotection and immunopathology, it is important to further elucidate the mechanisms mediating stress-immune interactions and to meaningfully translate findings from bench to bedside.

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.

Stress-induced suppression of in vivo splenic cytokine production in the rat by neural and hormonal mechanisms

The mechanisms mediating the effects of stress on immune function have yet to be fully described. In vitro studies have demonstrated a role for both the sympathetic nervous system (SNS) and the hypothalamic pituitary adrenal axis (HPAA) in regulating immune responses following exposure to various stressors. The purpose of the present set of experiments was to determine the in vivo contribution of the HPAA and SNS in regulating the effects of stress on lipopolysaccharide (LPS) induced splenic cytokine production. For this, rats with combinations of sham surgeries, splenic nerve cuts (SNC), and adrenalectomies (ADX) were exposed to 15 min of 1.6 mA intermittent footshock immediately following the intravenous (i.v.) injection of 0.1 microg of LPS. Although footshock was immunosuppressive to most indices of cytokine production, neither SNC nor ADX alone blocked the effects of stress on splenic immune function. However the combination of these two manipulations significantly abrogated the immunosuppressive effects of stress on cytokine production. Adrenal demedullation of animals with a SNC demonstrated that the SNS, not the HPAA, was primarily responsible for the immunosuppressive effects of stress.

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

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

Stressor-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.

Toxoplasma gondii: cold stress-induced modulation of antibody responses

Physical or psychological stressors have been shown to have significant consequences in the immune function and the outcome of disease in human and animal models. Recent work has demonstrated that products released during stress, such as glucocorticoids and catecholamines, can profoundly influence the in vitro growth of pathogens by modulating immune responses. The present study examined the effects of a physical stressor (cold stress) on antigens of Toxoplasma gondii that elicits an antibody-mediated immune response during the acute and chronic phases of infection. Sera obtained from different groups of mice subjected to cold stress during the acute and chronic phases of T. gondii infection were used to measure the levels of antibodies and to localize by Western blot the dominant antigens eliciting IgG and IgM antibody responses. Serum antibodies collected from stressed and infected mice recognized antigens different from those recognized by infected mice without stress. During the acute phase, a stronger IgM antibody response against antigens of 30, 42, 54, and 60 kDa was detected in stressed animals at 3 weeks postinfection. In addition, a 5-kDa antigen was specifically detected in mice subjected to stress during the acute and chronic phases of infection. Levels of specific IgG were increased in infected and in infected and stressed animals that underwent stress in the chronic phase. IgM production did not increase following cold stress in the chronic phase. These results suggest that the strong antibody response in stressed animals is associated with longer parasite persistence in circulation. Stress modulated not only the host immune response but also the ability of parasite antigens to elicit specific antibody responses by the host.

Differential immune reactivity to stress in BALB/cByJ and C57BL/6J mice: in vivo dependence on macrophages

Inbred BALB/cByJ and C57BL/6J mice not only differ in their neuroendocrine and behavioral reactivity to stress, but also their ability to mount appropriate immune responses to various pathogens. Because evidence suggests that stress may bias humoral or cell-mediated immune responses in these mouse strains, we assessed the effects of acute (1 h) physical restraint on the humoral immune response to keyhole limpet hemocyanin (KLH). Restraint exposure in close proximity to immunization with KLH enhanced the number of primary antigen-specific IgM and IgG producing splenic B cells in BALB/cByJ mice, but not in C57BL/6J mice. These effects might be determined at the level of macrophage antigen presenting cells, because BALB/cByJ mice immunized with KLH as a particulate antigen (i.e., encapsulated in liposomes) displayed the same stressor enhanced antibody response as they did to free, unencapsulated KLH. In addition, these mice showed enhanced production of the IgG1 subtype of IgG, but not the IgG2a subtype. Conversely, stressed C57BL/6J mice revealed an enhanced IgG2a response, although this was observed only under conditions of immunization with liposome-encapsulated KLH. In a final experiment involving only the BALB/cByJ strain, the depletion of macrophages in the spleen by administration of liposomes containing dichloromethylene biphosphonate (DMDP) 2 days before immunizing the mice with free KLH and restraint exposure, blocked the restraint-induced enhancement of humoral immune responses. These data suggest a possible intermediary role for macrophages in stressor-induced immunomodulation in vivo, which may be a potential point of divergence that explains the differential immune reactivity to KLH of BALB/cByJ and C57BL/6J mice exposed to an acute stressor.

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.

Plaque-forming cell responses and antibody titers following injection of sheep red blood cells in nonstressed, acute, and/or chronically stressed handled and nonhandled animals

Given the bidirectional nature of the communication between the immune and hypothalamic-pituitary-adrenal (HPA) systems, we examined whether animals that exhibit differences in HPA responses to stress would also exhibit differences in their plaque-forming cell (PFC) responses to sheep red blood cells (SRBC). Neonatally handled (H) animals exhibit lower HPA responses to a number of acute stressors in adulthood compared to nonhandled (NH) animals. Furthermore, these differences also emerge as a function of chronic, intermittent cold stress. We hypothesized that H and NH animals may exhibit differences in the PFC response to SRBC under conditions of acute and/or chronic stress (H CHR and NH CHR). Exposure to acute (4 hr) cold decreased PFC responses in both H and NH animals compared to nonstressed H and NH animals. The decrease in PFC response produced by chronic, intermittent cold stress was similar in H and NH animals and was not different from that found in acutely stressed animals. In H CHR animals reexposed to cold stress, the PFC response was not different from acutely stressed or chronically stressed H and NH animals. In contrast, the PFC response in NH CHR animals reexposed to cold stress was lower than all other groups studied. Thus, neonatal handling prevented prior chronic stress-induced suppression of the PFC response to a subsequent stress. These data suggest that there may be subpopulations of individuals in whom prior chronic stress does not exacerbate the immune suppression produced by acute stress. However, those chronically stressed individuals in whom immune suppression does occur may be more vulnerable to infection and disease.