Stress-induced immune dysfunction: implications for health

Folk wisdom has long suggested that stressful events take a toll on health. The field of psychoneuroimmunology (PNI) is now providing key mechanistic evidence about the ways in which stressors--and the negative emotions that they generate--can be translated into physiological changes. PNI researchers have used animal and human models to learn how the immune system communicates bidirectionally with the central nervous and endocrine systems and how these interactions impact on health.

Chronic stress and age-related increases in the proinflammatory cytokine IL-6

Overproduction of IL-6, a proinflammatory cytokine, is associated with a spectrum of age-related conditions including cardiovascular disease, osteoporosis, arthritis, type 2 diabetes, certain cancers, periodontal disease, frailty, and functional decline. To describe the pattern of change in IL-6 over 6 years among older adults undergoing a chronic stressor, this longitudinal community study assessed the relationship between chronic stress and IL-6 production in 119 men and women who were caregiving for a spouse with dementia and 106 noncaregivers, with a mean age at study entry of 70.58 (SD = 8.03) for the full sample. On entry into this portion of the longitudinal study, 28 of the caregivers' spouses had already died, and an additional 50 of the 119 spouses died during the 6 years of this study. Levels of IL-6 and health behaviors associated with IL-6 were measured across 6 years. Caregivers' average rate of increase in IL-6 was about four times as large as that of noncaregivers. Moreover, the mean annual changes in IL-6 among former caregivers did not differ from that of current caregivers even several years after the death of the impaired spouse. There were no systematic group differences in chronic health problems, medications, or health-relevant behaviors that might have accounted for caregivers' steeper IL-6 slope. These data provide evidence of a key mechanism through which chronic stressors may accelerate risk of a host of age-related diseases by prematurely aging the immune response.

Slowing of wound healing by psychological stress

There is evidence that psychological stress adversely affects the immune system. We have investigated the effects of such stress, caused by caring for a relative with Alzheimer's disease, on wound healing. We studied 13 women caring for demented relatives (mean age 62.3 [SE 2.3] years) and 13 controls matched for age (60.4 [2.8] years) and family income. All subjects underwent a 3.5 mm punch biopsy wound. Healing was assessed by photography of the wound and the response to hydrogen peroxide (healing was defined as no foaming). Wound healing took significantly longer in caregivers than in controls (48.7 [2.9] vs 39.3 [3.0] days, p < 0.05). Peripheral-blood leucocytes from caregivers produced significantly less interleukin-1 beta mRNA in response to lipopolysaccharide stimulation than did controls' cells. Stress-related defects in wound repair could have important clinical implications, for instance for recovery from surgery.

Emotions, morbidity, and mortality: new perspectives from psychoneuroimmunology

Negative emotions can intensify a variety of health threats. We provide a broad framework relating negative emotions to a range of diseases whose onset and course may be influenced by the immune system; inflammation has been linked to a spectrum of conditions associated with aging, including cardiovascular disease, osteoporosis, arthritis, type 2 diabetes, certain cancers, Alzheimer's disease, frailty and functional decline, and periodontal disease. Production of proinflammatory cytokines that influence these and other conditions can be directly stimulated by negative emotions and stressful experiences. Additionally, negative emotions also contribute to prolonged infection and delayed wound healing, processes that fuel sustained proinflammatory cytokine production. Accordingly, we argue that distress-related immune dysregulation may be one core mechanism behind a large and diverse set of health risks associated with negative emotions. Resources such as close personal relationships that diminish negative emotions enhance health in part through their positive impact on immune and endocrine regulation.

Spousal caregivers of dementia victims: longitudinal changes in immunity and health

Providing long-term care for a demented relative profoundly affects caregivers' lives. We assessed changes in depression, immune function, and health in 69 spousal caregivers who had already been caregiving for an average of five years and 69 sociodemographically matched control subjects. Between the initial sample ("intake") and the follow-up data collected an average of 13 months later, caregivers showed decrements relative to controls on three measures of cellular immunity. Caregivers also reported significantly more days of infectious illness, primarily upper respiratory tract infections. Caregivers had a much greater incidence of depressive disorders than controls, with 25% of caregivers meeting syndromal criteria at intake and 32% at follow-up, compared with no cases among controls at intake and 6% at follow-up. Caregivers who reported lower levels of social support at intake and who were most distressed by dementia-related behaviors showed the greatest and most uniformly negative changes in immune function at follow-up.

Psychosocial modifiers of immunocompetence in medical students

This study addressed the effects of a naturally occurring stressor on components of the immune response. Blood was drawn twice from 75 first-year medical students, with a baseline sample taken one month before their final examinations and a stress sample drawn on the first day of final examinations. Median splits on scores from the Holmes--Rahe Social Readjustment Rating Scale and the UCLA Loneliness Scale produced a 2 X 2 X 2 repeated measures ANOVA when combined with the trials variable. Natural killer (NK) cell activity declined significantly from the first to the second sample. High scorers on stressful life events and loneliness had significantly lower levels of NK activity. Total plasma IgA increased significantly from the first to second sample, while plasma IgG and IgM, C-reactive protein, and salivary IgA did not change significantly.

Chronic stress alters the immune response to influenza virus vaccine in older adults

To determine whether a chronic stressor (caregiving for a spouse with a progressive dementia) is associated with an impaired immune response to influenza virus vaccination, we compared 32 caregivers' vaccine responses with those of 32 sex-, age-, and socioeconomically matched control subjects. Caregivers showed a poorer antibody response following vaccination relative to control subjects as assessed by two independent methods, ELISA and hemagglutination inhibition. Caregivers also had lower levels of in vitro virus-specific-induced interleukin 2 levels and interleukin 1beta; interleukin 6 did not differ between groups. These data demonstrate that down-regulation of the immune response to influenza virus vaccination is associated with a chronic stressor in the elderly. These results could have implications for vulnerability to infection among older adults.

Marital quality, marital disruption, and immune function

Marital disruption is associated with significant increases in a variety of psychologic and physical disorders. In order to examine psychologic and physiologic mediators, self-report data and blood samples were obtained from 38 married women and 38 separated/divorced women. Among married subjects, poorer marital quality was associated with greater depression and a poorer response on three qualitative measures of immune function. Women who had been separated 1 year or less had significantly poorer qualitative and quantitative immune function than their sociodemographically matched married counterparts. Among the separated/divorced cohort, shorter separation periods and greater attachment to the (ex)husband were associated with poorer immune function and greater depression. These data are consistent with epidemiologic evidence linking marital disruption with increased morbidity and mortality.

Hostile marital interactions, proinflammatory cytokine production, and wound healing

CONTEXT

A growing epidemiological literature has suggested that marital discord is a risk factor for morbidity and mortality. In addition, depression and stress are associated with enhanced production of proinflammatory cytokines that influence a spectrum of conditions associated with aging.

OBJECTIVE

To assess how hostile marital behaviors modulate wound healing, as well as local and systemic proinflammatory cytokine production.

DESIGN AND SETTING

Couples were admitted twice to a hospital research unit for 24 hours in a crossover trial. Wound healing was assessed daily following research unit discharge.

PARTICIPANTS

Volunteer sample of 42 healthy married couples, aged 22 to 77 years (mean [SD], 37.04 [13.05]), married a mean (SD) of 12.55 (11.01) years.

INTERVENTIONS

During the first research unit admission, couples had a structured social support interaction, and during the second admission, they discussed a marital disagreement.

MAIN OUTCOME MEASURES

Couples' interpersonal behavior, wound healing, and local and systemic changes in proinflammatory cytokine production were assessed during each research unit admission.

RESULTS

Couples' blister wounds healed more slowly and local cytokine production (IL-6, tumor necrosis factor alpha, and IL-1beta) was lower at wound sites following marital conflicts than after social support interactions. Couples who demonstrated consistently higher levels of hostile behaviors across both their interactions healed at 60% of the rate of low-hostile couples. High-hostile couples also produced relatively larger increases in plasma IL-6 and tumor necrosis factor alpha values the morning after a conflict than after a social support interaction compared with low-hostile couples.

CONCLUSIONS

These data provide further mechanistic evidence of the sensitivity of wound healing to everyday stressors. Moreover, more frequent and amplified increases in proinflammatory cytokine levels could accelerate a range of age-related diseases. Thus, these data also provide a window on the pathways through which hostile or abrasive relationships affect physiological functioning and health.

Depression and immune function: central pathways to morbidity and mortality

OBJECTIVE

The increased morbidity and mortality associated with depression is substantial. In this paper, we review evidence suggesting that depression contributes to disease and death through immune dysregulation.

METHOD

This review focuses on recent human studies addressing the impact of depression on immune function, and the health consequences of those changes.

RESULTS

There is growing evidence that depression can directly stimulate the production of proinflammatory cytokines that influence a spectrum of conditions associated with aging, including cardiovascular disease, osteoporosis, arthritis, type 2 diabetes, certain cancers, periodontal disease, frailty, and functional decline. Additionally, depression can down-regulate the cellular immune response; as a consequence, processes such as prolonged infection and delayed wound healing that fuel sustained proinflammatory cytokine production may be promoted by depression.

CONCLUSIONS

These direct and indirect processes pose the greatest health risks for older adults who already show age-related increases in proinflammatory cytokine production. Thus, aging interacts with depression to enhance risks for morbidity and mortality.

Stress hormones and immune function

Over the past 20 years we have demonstrated both in animal models and in human studies that stress increases neuroendocrine hormones, particularly glucocorticoids and catecholamines but to some extent also prolactin, growth hormone and nerve growth factor. We have also shown that stress, through the action of these stress hormones, has detrimental effects on immune function, including reduced NK cell activity, lymphocyte populations, lymphocyte proliferation, antibody production and reactivation of latent viral infections. Such effects on the immune system have severe consequences on health which include, but are not limited to, delayed wound healing, impaired responses to vaccination and development and progression of cancer. These data provide scientific evidence of the effects of stress on immune function and implications for health.

Chronic stress and immunity in family caregivers of Alzheimer's disease victims

Although acute stress has been associated with transient immunosuppression, little is known about the immunologic consequences of chronic stress in humans. In order to investigate possible health-related consequences of a long-term stressor, we obtained blood samples for immunologic and nutritional analyses and psychologic data from 34 family caregivers of Alzheimer's disease (AD) victims and 34 sociodemographically matched comparison subjects. Family caregivers for AD victims were more distressed than comparison subjects without similar responsibilities. Greater impairment in the AD victim was associated with greater distress and loneliness in caregivers. Caregivers had significantly lower percentages of total T lymphocytes and helper T lymphocytes than did comparison subjects, as well as significantly lower helper-suppressor cell ratios; caregivers also had significantly higher antibody titers to Epstein-Barr virus than did comparison subjects, presumably reflecting poorer cellular immune system control of the latent virus in caregivers. The percentages of natural killer cells and suppressor T lymphocytes did not differ significantly. These data suggest that chronically stressed AD family caregivers do not show immunologic or psychologic adaptation to the level of their well-matched age peers.

Psychological influences on surgical recovery. Perspectives from psychoneuroimmunology

Greater fear or distress prior to surgery is associated with a slower and more complicated postoperative recovery. Although anxiety presumably interferes with recuperation through both behavioral and physiological mechanisms, the pathways have been unclear. Recent work in psychoneuroimmunology (PNI) has demonstrated that stress delays wound healing. In addition, a second line of research has illustrated the adverse effects of pain on endocrine and immune function. A biobehavioral model is described that is based on these and other data; it suggests a number of routes through which psychological and behavioral responses can influence surgery and post-surgical outcomes. Clinical and research implications are highlighted.

Psychoneuroimmunology: psychological influences on immune function and health

This review focuses on human psychoneuroimmunology studies published in the past decade. Issues discussed include the routes through which psychological factors influence immune function, how a stressor's duration may influence the changes observed, individual difference variables, the ability of interventions to modulate immune function, and the health consequences of psychosocially mediated immune dysregulation. The importance of negative affect and supportive personal relationships are highlighted. Recent data suggest that immune dysregulation may be one core mechanism for a spectrum of conditions associated with aging, including cardiovascular disease, osteoporosis, arthritis, Type 2 diabetes, certain cancers, and frailty and functional decline; production of proinflammatory cytokines that influence these and other conditions can be stimulated directly by negative emotions and indirectly by prolonged infection.

Accelerated telomere erosion is associated with a declining immune function of caregivers of Alzheimer's disease patients

Caregivers of Alzheimer's disease patients endure chronic stress associated with a decline of immune function. To assess the psychological and immunological changes of caregivers, we compared depressive symptoms, PBMC composition, in vitro activation-induced proliferation and cytokine production, and telomere length and telomerase activity of 82 individuals (41 caregivers and 41 age- and gender-matched controls). We found depressive symptoms were significantly higher in caregivers than in controls (p < 0.001). Correspondingly, caregivers had significantly lower T cell proliferation but higher production of immune-regulatory cytokines (TNF-alpha and IL-10) than controls in response to stimulation in vitro. We examined the impact of these changes on cellular replicative lifespan and found that caregivers had significantly shorter telomere lengths in PBMC than controls (6.2 and 6.4 kb, respectively, p < 0.05) with similar shortening in isolated T cells and monocytes and that this telomere attrition in caregivers was not due to an increase of shorter telomere possessing T cell subsets in PBMC. Finally, we showed that basal telomerase activity in PBMC and T cells was significantly higher in caregivers than in controls (p < 0.0001), pointing to an unsuccessful attempt of cells to compensate the excessive loss of telomeres in caregivers. These findings demonstrate that chronic stress is associated with altered T cell function and accelerated immune cell aging as suggested by excessive telomere loss.

Norepinephrine up-regulates the expression of vascular endothelial growth factor, matrix metalloproteinase (MMP)-2, and MMP-9 in nasopharyngeal carcinoma tumor cells

Recent studies using ovarian cancer cells have shown that the catecholamine hormones norepinephrine (norepi) and epinephrine (epi) may influence cancer progression by modulating the expression of matrix metalloproteinases (MMP) and vascular endothelial growth factor (VEGF). The purpose of this study is to determine if the stress hormone norepi can influence the expression of MMP-2, MMP-9, and VEGF in nasopharyngeal carcinoma (NPC) tumors by using three NPC tumor cell lines. The NPC cell lines HONE-1, HNE-1, and CNE-1 were treated with norepi. The effects of norepi on MMP-2, MMP-9, and VEGF synthesis were measured by ELISA; functional MMP activity was measured by the invasive potential of the cells using a membrane invasion culture system whereas functional activity of VEGF was analyzed using a human umbilical vein endothelial cell tube formation assay. Norepi treatment increased MMP-2, MMP-9, and VEGF levels in culture supernatants of HONE-1 cells, which could be inhibited by the beta-blocker propranolol. Norepi induced the invasiveness of all NPC cell lines in a dose-dependent manner, which was blocked by CMT-3, an MMP inhibitor, and propranolol. Norepi stimulated the release of functional angiogenic VEGF by HONE-1 cells as well. Finally, HONE-1 cells were shown to express beta-adrenergic receptors as did seven of seven NPC biopsies examined. The data suggest that catecholamine hormones produced by the sympathetic-adrenal medullary axis may affect NPC tumor progression, in part, through modulation of key angiogenic cytokines.

A biobehavioral model of cancer stress and disease course

Approximately 1 million Americans are diagnosed with cancer each year and must cope with the disease and treatments. Many studies have documented the deteriorations in quality of life that occur. These data suggest that the adjustment process is burdensome and lengthy. There is ample evidence showing that adults experiencing other long-term stressors experience not only high rates of adjustment difficulties (e.g., syndromal depression) but important biologic effects, such as persistent downregulation of elements of the immune system, and adverse health outcomes, such as higher rates of respiratory tract infections. Thus, deteriorations in quality of life with cancer are underscored if they have implications for biological processes, such as the immune system, relating to disease progression and spread. Considering these and other data, a biobehavioral model of adjustment to the stresses of cancer is offered, and mechanisms by which psychological and behavioral responses may influence biological processes and, perhaps, health outcomes are proposed. Finally, strategies for testing the model via experiments testing psychological interventions are offered.

Stress, loneliness, and changes in herpesvirus latency

This study used a prospective design to examine the influence of examination stress and loneliness on herpesvirus latency as measured by changes in antibody levels to three herpesviruses, Epstein-Barr virus (EBV), Herpes simplex type I (HSV-1), and cytomegalovirus (CMV). Three blood samples were obtained from 49 first-year medical students, with the first sample drawn 1 month before final examinations, the second on the first day of final examinations, and the third during the first week after their return from summer vacation. A median split on the UCLA Loneliness Scale divided subjects into high- and low-scoring loneliness groups. There were significant changes in the antibody titers to all three herpesviruses across the sample points, with the lowest levels found in the third (low stress) sample. High-loneliness subjects had significantly higher EBV antibody titers than low-loneliness subjects. These data suggest that stress-related immunosuppression can significantly modulate herpesvirus latency.

Stress and immune responses after surgical treatment for regional breast cancer

BACKGROUND

Adults who undergo chronic stress, such as the diagnosis and surgical treatment of breast cancer, often experience adjustment difficulties and important biologic effects. This stress can affect the immune system, possibly reducing the ability of individuals with cancer to resist disease progression and metastatic spread. We examined whether stress influences cellular immune responses in patients following breast cancer diagnosis and surgery.

METHODS

We studied 116 patients recently treated surgically for invasive breast cancer. Before beginning their adjuvant therapy, all subjects completed a validated questionnaire assessing the stress of being cancer patients. A 60-mL blood sample taken from each patient was subjected to a panel of natural killer (NK) cell and T-lymphocyte assays. We then developed multiple regression models to test the contribution of psychologic stress in predicting immune function. All regression equations controlled for variables that might exert short- or long-term effects on these responses, and we also ruled out other potentially confounding variables.

RESULTS

We found, reproducibly between and within assays, the following: 1) Stress level significantly predicted lower NK cell lysis, 2) stress level significantly predicted diminished response of NK cells to recombinant interferon gamma, and 3) stress level significantly predicted decreased proliferative response of peripheral blood lymphocytes to plant lectins and to a monoclonal antibody directed against the T-cell receptor.

CONCLUSIONS

The data show that the physiologic effects of stress inhibit cellular immune responses that are relevant to cancer prognosis, including NK cell toxicity and T-cell responses. Additional, longitudinal studies are needed to determine the duration of these effects, their health consequences, and their biologic and/or behavioral mechanisms.

Stressful early life experiences and immune dysregulation across the lifespan

There is considerable evidence that stressful early life events influence a variety of physical health problems later in life. Childhood adversity has been linked to elevated rates of morbidity and mortality from a number of chronic diseases. Immune dysregulation may be one potential pathway that explains this link. In this mini-review, we summarize human studies demonstrating that severe early life stressors have lasting immune consequences. We propose a model outlining potential biobehavioral pathways that explain how early life stressors leave people vulnerable to these maladaptive outcomes. Finally, we suggest ideas for future work to test different aspects of this model.

Psychological, behavioral, and immune changes after a psychological intervention: a clinical trial

PURPOSE

This randomized clinical trial tests the hypothesis that a psychological intervention can reduce emotional distress, improve health behaviors and dose-intensity, and enhance immune responses.

PATIENTS AND METHODS

We studied 227 women who were surgically treated for regional breast cancer. Before adjuvant therapy, women completed interviews and questionnaires assessing emotional distress, social adjustment, and health behaviors. A 60-mL blood sample was drawn for immune assays. Patients were randomly assigned to either the intervention group or assessment only group. The intervention was conducted in small patient groups, with one session per week for 4 months. The sessions included strategies to reduce stress, improve mood, alter health behaviors, and maintain adherence to cancer treatment and care. Reassessment occurred after completion of the intervention.

RESULTS

As predicted, patients receiving the intervention showed significant lowering of anxiety, improvements in perceived social support, improved dietary habits, and reduction in smoking (all P <.05). Analyses of adjuvant chemotherapy dose-intensity revealed significantly more variability (ie, more dispersion in the dose-intensity values) for the assessment arm (P <.05). Immune responses for the intervention patients paralleled their psychological and behavioral improvements. T-cell proliferation in response to phytohemagglutinin and concanavalin A remained stable or increased for the Intervention patients, whereas both responses declined for Assessment patients; this effect was replicated across three concentrations for each assay (all P <.01).

CONCLUSION

These data show a convergence of significant psychological, health behavior, and biologic effects after a psychological intervention for cancer patients.

Metabolic flux ratio analysis of genetic and environmental modulations of Escherichia coli central carbon metabolism

The response of Escherichia coli central carbon metabolism to genetic and environmental manipulation has been studied by use of a recently developed methodology for metabolic flux ratio (METAFoR) analysis; this methodology can also directly reveal active metabolic pathways. Generation of fluxome data arrays by use of the METAFoR approach is based on two-dimensional (13)C-(1)H correlation nuclear magnetic resonance spectroscopy with fractionally labeled biomass and, in contrast to metabolic flux analysis, does not require measurements of extracellular substrate and metabolite concentrations. METAFoR analyses of E. coli strains that moderately overexpress phosphofructokinase, pyruvate kinase, pyruvate decarboxylase, or alcohol dehydrogenase revealed that only a few flux ratios change in concert with the overexpression of these enzymes. Disruption of both pyruvate kinase isoenzymes resulted in altered flux ratios for reactions connecting the phosphoenolpyruvate (PEP) and pyruvate pools but did not significantly alter central metabolism. These data indicate remarkable robustness and rigidity in central carbon metabolism in the presence of genetic variation. More significant physiological changes and flux ratio differences were seen in response to altered environmental conditions. For example, in ammonia-limited chemostat cultures, compared to glucose-limited chemostat cultures, a reduced fraction of PEP molecules was derived through at least one transketolase reaction, and there was a higher relative contribution of anaplerotic PEP carboxylation than of the tricarboxylic acid (TCA) cycle for oxaloacetate synthesis. These two parameters also showed significant variation between aerobic and anaerobic batch cultures. Finally, two reactions catalyzed by PEP carboxykinase and malic enzyme were identified by METAFoR analysis; these had previously been considered absent in E. coli cells grown in glucose-containing media. Backward flux from the TCA cycle to glycolysis, as indicated by significant activity of PEP carboxykinase, was found only in glucose-limited chemostat culture, demonstrating that control of this futile cycle activity is relaxed under severe glucose limitation.