Neural regulation of innate immunity: a coordinated nonspecific host response to pathogens

Exploring the full spectrum of macrophage activation

Macrophages display remarkable plasticity and can change their physiology in response to environmental cues. These changes can give rise to different populations of cells with distinct functions. In this Review we suggest a new grouping of macrophage populations based on three different homeostatic activities - host defence, wound healing and immune regulation. We propose that similarly to primary colours, these three basic macrophage populations can blend into various other 'shades' of activation. We characterize each population and provide examples of macrophages from specific disease states that have the characteristics of one or more of these populations.

Variations in circulating cytokine levels during 52 week course of treatment with SSRI for major depressive disorder

Major depressive disorder (MDD) is a psychiatric condition characterized by hypercortisolism and variations in circulatory cytokines. Previously it has been reported that administration of selective serotonin reuptake inhibitors (SSRI) in MDD patients modify cortisol and cytokine levels but these studies only evaluated changes over a short time period. This work reports the long-term effects of administration of SSRI on the cortisol levels and pro-/anti-inflammatory cytokine profile in a group of MDD patients treated for 52 weeks. A total of 31 patients diagnosed with MDD received anti depressant treatment with SSRI. HDRS and BDI were administered over a year, and levels of interleukin IL-1beta, IL-10, IL-2, IFN-gamma, IL-4, IL-13, and 24-h urine cortisol were determined at weeks (W) 0, 5, 20, 36 and 52 of treatment. Before treatment we found high levels of cortisol, IL-4, IL-13 (Th2) and IL-10 in MDD patients when compared with healthy volunteers. At W20 psychiatric scales indicated a remission of the depressive episode concomitantly with increments in IL-2 and IL-1beta but without changes in cortisol. Towards the end of the treatment (W52) we observed a significant reduction (p<0.01) in cortisol levels, with an increment in IL-1beta and IFN-gamma and a decrease in Th2 cytokines. Our results suggest that depressed patients only reach a partial reestablishment of HPA axis function after the long-term administration of SSRI.

Low cortisol, high DHEA, and high levels of stimulated TNF-alpha, and IL-6 in women with PTSD

Posttraumatic stress disorder (PTSD) has been associated with hypothalamic-pituitary-adrenal (HPA) axis and immune function alterations; however, few studies have simultaneously investigated these systems in participants with PTSD. In this study, HPA axis and immune function in 26 women with PTSD with and without major depressive disorder was compared to 24 traumatized controls and to 21 nontraumatized controls. Posttraumatic stress disorder was associated with low cortisol and higher levels of DHEA and greater production of tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) compared to traumatized and healthy controls. Women with PTSD and depression exhibited greater production of IL-6 and higher levels of dehydroepiandrosterone (DHEA) than those with PTSD, but without depression. These findings suggest dysregulated HPA axis and immune function in women with PTSD, and that comorbid depression may contribute to these abnormalities.

Anti-inflammatory neuropeptides: a new class of endogenous immunoregulatory agents

Resolution of inflammation and induction of immune tolerance are essential to stabilize immune homeostasis and to limit the occurrence of exacerbated inflammatory and autoimmune conditions. Multiple mechanisms act together to ensure the re-establishment of immune homeostasis and maintenance of tolerance. The identification of endogenous factors that regulate these processes is crucial for the development of new therapies for inflammatory/autoimmune conditions. Neuropeptides produced during an ongoing inflammatory response emerged as endogenous anti-inflammatory agents that participate in processes leading to the resolution of inflammation and maintenance of tolerance. Anti-inflammatory neuropeptides and hormones such as vasoactive intestinal peptide, urocortin, adrenomedullin, melanocyte stimulating hormone, ghrelin, and cortistatin have beneficial effects in a variety of experimental inflammatory and autoimmune models. Their therapeutic effect has been attributed to their capacity to downregulate innate immunity, to inhibit antigen-specific T(H)1-driven responses, and to generate regulatory T cells. Finally, some of these neuropeptides have been identified as mediators of innate defense acting as natural antimicrobial peptides. Here we present the research findings in the neuropeptide immunoregulatory field, and examine possible therapies based on anti-inflammatory neuropeptides and hormones as a new pharmacologic platform.

Innate immunity in Caenorhabditis elegans is regulated by neurons expressing NPR-1/GPCR

A large body of evidence indicates that metazoan innate immunity is regulated by the nervous system, but the mechanisms involved in the process and the biological importance of such control remain unclear. We show that a neural circuit involving npr-1, which encodes a G protein-coupled receptor (GPCR) related to mammalian neuropeptide Y receptors, functions to suppress innate immune responses. The immune inhibitory function requires a guanosine 3',5'-monophosphate-gated ion channel encoded by tax-2 and tax-4 as well as the soluble guanylate cyclase GCY-35. Furthermore, we show that npr-1- and gcy-35-expressing sensory neurons actively suppress immune responses of nonneuronal tissues. A full-genome microarray analysis on animals with altered neural function due to mutation in npr-1 shows an enrichment in genes that are markers of innate immune responses, including those regulated by a conserved PMK-1/p38 mitogen-activated protein kinase signaling pathway. These results present evidence that neurons directly control innate immunity in C. elegans, suggesting that GPCRs may participate in neural circuits that receive inputs from either pathogens or infected sites and integrate them to coordinate appropriate immune responses.

A telemetric study of physiologic changes in mice with induced autoimmune encephalomyelitis

Dysfunction of the autonomic nervous system may be an important component of disease progression in multiple sclerosis (MS), a paralytic inflammatory autoimmune disease of the central nervous system. Using the experimental autoimmune encephalomyelitis mouse model of MS, the authors carried out a pilot study to investigate whether telemetric monitoring might be a feasible approach for detecting disturbances in the autonomic control of heart rate and blood pressure after disease induction. Telemetric monitoring devices that were implanted in mice provided useful information regarding the physiologic changes that accompanied disease induction and progression. Changes were observed in heart rate, blood pressure, heart rate variability and diurnal rhythm immediately before and after disease onset. The device implantation procedure did not seem to alter the course of disease. Further investigation may establish these methods as a system for studying the relationships between MS progression and autonomic regulation of physiological status.

Neuroendocrine signals modulate the innate immunity of Caenorhabditis elegans through insulin signaling

Communication between the immune and nervous systems, each of which is able to react rapidly to environmental stimuli, may confer a survival advantage. However, precisely how the nervous system influences the immune response and whether neural modulation of immune function is biologically important are not well understood. Here we report that neuronal exocytosis of neuropeptides from dense core vesicles suppressed the survival of Caenorhabditis elegans and their clearance of infection with the human bacterial pathogen Pseudomonas aeruginosa. This immunomodulatory function was mediated by INS-7, an insulin-like neuropeptide whose induction was associated with Pseudomonas virulence. INS-7 secreted from the nervous system functioned in a non-cell autonomous way to activate the insulin pathway and alter basal and inducible expression of immunity-related genes in intestinal cells.

Harmful molecular mechanisms in sepsis

Sepsis and sepsis-associated multi-organ failure are major challenges for scientists and clinicians and are a tremendous burden for health-care systems. Despite extensive basic research and clinical studies, the pathophysiology of sepsis is still poorly understood. We are now beginning to understand that sepsis is a heterogeneous, dynamic syndrome caused by imbalances in the 'inflammatory network'. In this Review, we highlight recent insights into the molecular interactions that occur during sepsis and attempt to unravel the nature of the dysregulated immune response during sepsis.

Endogenous anti-inflammatory neuropeptides and pro-resolving lipid mediators: a new therapeutic approach for immune disorders

Identification of the factors that regulate the immune tolerance and control the appearance of exacerbated inflammatory conditions is crucial for the development of new therapies of inflammatory and autoimmune diseases. Although much is known about the molecular basis of initiating signals and pro-inflammatory chemical mediators in inflammation, it has only recently become apparent that endogenous stop signals are critical at early checkpoints within the temporal events of inflammation. Some neuropeptides and lipid mediators that are produced during the ongoing inflammatory response have emerged as endogenous anti-inflammatory agents that participate in the regulation of the processes that ensure self-tolerance and/or inflammation resolution. Here we examine the latest research findings, which indicate that neuropeptides participate in maintaining immune tolerance in two distinct ways: by regulating the balance between pro-inflammatory and anti-inflammatory factors, and by inducing the emergence of regulatory T cells with suppressive activity against autoreactive T-cell effectors. On the other hand, we also focus on lipid mediators biosynthesized from omega-3 and omega-6 polyunsaturated fatty-acids in inflammatory exudates that promote the resolution phase of acute inflammation by regulating leucocyte influx to and efflux from local inflamed sites. Both anti-inflammatory neuropeptides and pro-resolving lipid mediators have shown therapeutic potential for a variety of inflammatory and autoimmune disorders and could be used as biotemplates for the development of novel pharmacologic agents.

Hematopoietic response of rats exposed to the impact of an acute psychophysiological stressor on responsiveness to an in vivo challenge with Listeria monocytogenes: modulation by Chlorella vulgaris prophylactic treatment

In this study, we investigated the hematopoietic response of rats pretreated with CV and exposed to the impact of acute escapable, inescapable or psychogenical stress on responsiveness to an in vivo challenge with Listeria monocytogenes. No consistent changes were observed after exposure to escapable footshock. Conversely, the impact of uncontrollable stress (inescapable and psychogenical) was manifested by an early onset and increased severity and duration of myelossuppression produced by the infection. Small size CFU-GM colonies and increased numbers of clusters were observed, concurrently to a greater expansion in the more mature population of bone marrow granulocytes. No differences were observed between the responses of both uncontrollable stress regimens. CV prevented the myelossuppression caused by stress/infection due to increased numbers of CFU-GM in the bone marrow. Colonies of cells tightly packed, with a very condensed nucleus; in association with a greater expansion in the more immature population of bone marrow granulocytes were observed. Investigation of the production of colony-stimulating factors revealed increased colony-stimulating activity (CSA) in the serum of normal and infected/stressed rats treated with the algae. CV treatment restored/enhanced the changes produced by stress/infection in total and differential bone marrow and peripheral cells counts. Further studies demonstrated that INF-gamma is significantly reduced, whereas IL-10 is significantly increased after exposure to uncontrollable stress. Treatment with CV significantly increased INF-gamma levels and diminished the levels of IL-10. Uncontrollable stress reduced the protection afforded by CV to a lethal dose of L. monocytogenes, with survival rates being reduced from (50%) in infected rats to 20% in infected/stressed rats. All together, our results suggest Chlorella treatment as an effective tool for the prophylaxis of post-stress myelossupression, including the detrimental effect of stress on the course and outcome of infections.

Spleen vagal denervation inhibits the production of antibodies to circulating antigens

Background

Recently the vagal output of the central nervous system has been shown to suppress the innate immune defense to pathogens. Here we investigated by anatomical and physiological techniques the communication of the brain with the spleen and provided evidence that the brain has the capacity to stimulate the production of antigen specific antibodies by its parasympathetic autonomic output.

Methodology/Principal Findings

This conclusion was reached by successively demonstrating that: 1. The spleen receives not only sympathetic input but also parasympathetic input. 2. Intravenous trinitrophenyl-ovalbumin (TNP-OVA) does not activate the brain and does not induce an immune response. 3. Intravenous TNP-OVA with an inducer of inflammation; lipopolysaccharide (LPS), activates the brain and induces TNP-specific IgM. 4. LPS activated neurons are in the same areas of the brain as those that provide parasympathetic autonomic information to the spleen, suggesting a feed back circuit between brain and immune system. Consequently we investigated the interaction of the brain with the spleen and observed that specific parasympathetic denervation but not sympathetic denervation of the spleen eliminates the LPS-induced antibody response to TNP-OVA.

Conclusions/Significance

These findings not only show that the brain can stimulate antibody production by its autonomic output, it also suggests that the power of LPS as adjuvant to stimulate antibody production may also depend on its capacity to activate the brain. The role of the autonomic nervous system in the stimulation of the adaptive immune response may explain why mood and sleep have an influence on antibody production.

New insights into the placebo and nocebo responses

In modern medicine, the placebo response or placebo effect has often been regarded as a nuisance in basic research and particularly in clinical research. The latest scientific evidence has demonstrated, however, that the placebo effect and the nocebo effect, the negative effects of placebo, stem from highly active processes in the brain that are mediated by psychological mechanisms such as expectation and conditioning. These processes have been described in some detail for many diseases and treatments, and we now know that they can represent both strength and vulnerability in the course of a disease as well as in the response to a therapy. However, recent research and current knowledge raise several issues that we shall address in this review. We will discuss current neurobiological models like expectation-induced activation of the brain reward circuitry, Pavlovian conditioning, and anxiety mechanisms of the nocebo response. We will further explore the nature of the placebo responses in clinical trials and address major questions for future research such as the relationship between expectations and conditioning in placebo effects, the existence of a consistent brain network for all placebo effects, the role of gender in placebo effects, and the impact of getting drug-like effects without drugs.

A functional genomic fingerprint of chronic stress in humans: blunted glucocorticoid and increased NF-kappaB signaling

BACKGROUND

Chronic stressors are known to increase vulnerability to medical illness, but the mechanisms underlying this phenomenon are poorly understood.

METHODS

To identify transcriptional control pathways that are modified by chronic stress, we conducted genomewide expression microarrays on familial caregivers of brain-cancer patients (n = 11) and matched control subjects (n = 10). Analyses were conducted on peripheral blood monocytes, which are cells that have the ability to initiate and maintain many inflammatory responses. Salivary cortisol was collected over the course of 3 days as volunteers went about normal activities.

RESULTS

Caregivers' patterns of cortisol secretion were similar to those of matched control subjects. However, their monocytes showed diminished expression of transcripts bearing response elements for glucocorticoids, and heightened expression of transcripts with response elements for NF-kappaB, a key pro-inflammatory transcription factor. Caregivers also showed relative elevations in the inflammatory markers C-reactive protein and interleukin-1 receptor antagonist.

CONCLUSIONS

These findings suggest that even in the absence of excess adrenocortical output, stress brings about functional resistance to glucocorticoids in monocytes, which enables activation of pro-inflammatory transcription control pathways. This persistent activation of inflammatory mechanisms may contribute to stress-related morbidity and mortality.

Cell-specific regulation of PTX3 by glucocorticoid hormones in hematopoietic and nonhematopoietic cells

PTX3 (prototypic long pentraxin 3) is a fluid phase pattern recognition receptor, which plays nonredundant roles in the resistance against diverse pathogens, in the assembly of a hyaluronic acid-rich extracellular matrix, and in female fertility. Inflammatory signals induce production of PTX3 in diverse cell types, including myeloid dendritic cells (DC), fibroblasts, and endothelial cells (EC). The present study was designed to explore the effect of glucocorticoid hormones (GC) on PTX3 production in different cellular contexts. In myeloid DC, GC inhibited the PTX3 production. In contrast, in fibroblasts and EC, GC alone induced and, under inflammatory conditions, enhanced and extended PTX3 production. In vivo administration of GC augmented the blood levels of PTX3 in mice and humans. Moreover, patients with Cushing syndrome had increased levels of circulating PTX3, whereas PTX3 levels were decreased in subjects affected by iatrogenic hypocortisolism. In nonhematopoietic cells, GC receptor (GR) functioned as a ligand-dependent transcription factor (dimerization-dependent) to induce PTX3 gene expression. In contrast, in hematopoietic cells, GR repressed PTX3 gene transcription by interfering (dimerization-independent) with the action of other signaling pathways, probably NFkappaB and AP-1. Thus, divergent effects of GC were found to be due to different GR mechanisms. The results presented here indicate that GC have divergent effects on PTX3 production in hematopoietic (DC and macrophages) and nonhematopoietic (fibroblasts and EC) cells. The divergent effects of GC on PTX3 production probably reflect the different functions of this multifunctional molecule in innate immunity and in the construction of the extracellular matrix.

Effect of single or combined climatic and hygienic stress in four layer lines: 2. Endocrine and oxidative stress responses

Effects of long-term climatic stress (heat exposure), short-term hygienic stress [lipopolysaccharide (LPS)], or combined exposure to these stressors on endocrine and oxidative stress parameters of 4 layer lines (B1, WA, WB, and WF) were investigated. The lines were earlier characterized for natural humoral immune competence and survival rate. Eighty hens per line were randomly divided over 2 identical climate chambers and exposed to constant high temperature (32 degrees C) or a control temperature (21 degrees C) for 23 d. Half of the hens housed in each chamber were i.v. injected with LPS at d 1 after the start of the heat stress period. The effect of heat, LPS, or combined exposure on plasma levels of corticosterone, 3,5,3'-triiodothyronine (T(3)), glucose, uric acid (UA), and TBA reacting substances (TBARS) were investigated. Except for UA, there were no interactions between heat stress and LPS administration. Heat stress enhanced levels of corticosterone, glucose, and TBARS, whereas levels of T(3) and UA were decreased. The T(3) levels, however, were enhanced by LPS administration, whereas levels of UA were decreased. Administration of LPS had no effect on levels of corticosterone and TBARS. Because both stressors caused a reduction in feed intake, it is assumed that changes in most of the plasma levels of the endocrine and oxidative stress parameters are related with the reduction in feed intake. Neither natural humoral immune competence nor survival rate, for which the lines have been characterized, was indicative for the endocrine and oxidative stress responses to different stressors. The present data suggest that hens were able to cope with single or combined heat stress and LPS administration and that heat stress and LPS administration acted like 2 independent stressors. Furthermore, the 4 layer lines differed in response patterns and response levels; line WB was physiologically most sensitive to environmental changes.

Posttraumatic stress and immune dissonance

Stress or neuroendocrine response usually occurs soon after trauma, which is central to the maintenance of post-traumatic homeostasis. Immune inflammatory response has been recognized to be a key element both in the pathogenesis of post-traumatic complications and in tissue repair. Despite the existence of multiple and intricate interconnected neuroendocrine pathways, the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic nervous system have been considered to be the most important in trauma. Although the short-term and appropriate activation of these stress responses is vital to the host's adaptation, prolonged duration and exaggerative magnitude of their activity leads to deleterious effects on immune function in trauma, causing immune dissonance. The overall appropriate and controlled activation and termination of the neuroendocrine responses that mediate the necessary physiological functions involved in maintaining and restoring homeostasis in the event of trauma are of critical importance. This review will describe the effects of some important neuroendocrine responses on immune system. Present evidences indicate that the neuroendocrine and immune systems form a cohesive and integrated early host response to trauma, and identify areas for further research to fully elucidate the regulatory role of neuroendocrine system in trauma.

Heart rate variability explored in the frequency domain: a tool to investigate the link between heart and behavior

The neural regulation of circulatory function is mainly effected through the interplay of the sympathetic and vagal outflows. This interaction can be explored by assessing cardiovascular rhythmicity with appropriate spectral methodologies. Spectral analysis of cardiovascular signal variability, and in particular of RR period (heart rate variability, HRV), is a widely used procedure to investigate autonomic cardiovascular control and/or target function impairment. The oscillatory pattern which characterizes the spectral profile of heart rate and arterial pressure short-term variability consists of two major components, at low (LF, 0.04-0.15Hz) and high (HF, synchronous with respiratory rate) frequency, respectively, related to vasomotor and respiratory activity. With this procedure the state of sympathovagal balance modulating sinus node pacemaker activity can be quantified in a variety of physiological and pathophysiological conditions. Changes in sympathovagal balance can be often detected in basal conditions, however a reduced responsiveness to an excitatory stimulus is the most common feature that characterizes numerous pathophysiological states. Moreover the attenuation of an oscillatory pattern or its impaired responsiveness to a given stimulus can also reflect an altered target function and thus can furnish interesting prognostic markers. The dynamic assessment of these autonomic changes may provide crucial diagnostic, therapeutic and prognostic information, not only in relation to cardiovascular, but also non-cardiovascular disease. As linear methodologies fail to provide significant information in conditions of extremely reduced variability (e.g. strenuous exercise, heart failure) and in presence of rapid and transients changes or coactivation of the two branches of autonomic nervous system, the development of new non-linear approaches seems to provide a new perspective in investigating neural control of cardiovascular system.

The role of glucocorticoids and progestins in inflammatory, autoimmune, and infectious disease

A bidirectional communication exists between the CNS and the immune system. The autonomic nervous system, through neurotransmitters and neuropeptides, works in parallel with the hypothalamic-pituitary-adrenal axis through the actions of glucocorticoids to modulate inflammatory events. The immune system, through the action of cytokines and other factors, in turn, activates the CNS to orchestrate negative-feedback mechanisms that keep the immune response in check. Disruption of these interactions has been associated with a number of syndromes including inflammatory, autoimmune, and cardiovascular diseases, metabolic and psychiatric disorders, and the development of shock. The hypothalamic-pituitary-gonadal axis also plays an important part in regulating immunity through the secretion of sex hormones. Although numerous studies have established a role for immunomodulation by estrogen and testosterone, the role of progesterone is less well understood. Progesterone is crucial for reproductive organ development and maintenance of pregnancy, and more recent studies have clearly shown its role as an important immune regulator. The main focus of this review will be about the role of steroid hormones, specifically glucocorticoids and progesterone, in inflammatory responses and infectious diseases and how dysregulation of their actions may contribute to development of autoimmune and inflammatory disease.

Obesity-induced insulin resistance and hyperglycemia: etiologic factors and molecular mechanisms

Obesity is a major cause of type 2 diabetes, clinically evidenced as hyperglycemia. The altered glucose homeostasis is caused by faulty signal transduction via the insulin signaling proteins, which results in decreased glucose uptake by the muscle, altered lipogenesis, and increased glucose output by the liver. The etiology of this derangement in insulin signaling is related to a chronic inflammatory state, leading to the induction of inducible nitric oxide synthase and release of high levels of nitric oxide and reactive nitrogen species, which together cause posttranslational modifications in the signaling proteins. There are substantial differences in the molecular mechanisms of insulin resistance in muscle versus liver. Hormones and cytokines from adipocytes can enhance or inhibit both glycemic sensing and insulin signaling. The role of the central nervous system in glucose homeostasis also has been established. Multipronged therapies aimed at rectifying obesity-induced anomalies in both central nervous system and peripheral tissues may prove to be beneficial.

The complement anaphylatoxin C5a induces apoptosis in adrenomedullary cells during experimental sepsis

Sepsis remains a poorly understood, enigmatic disease. One of the cascades crucially involved in its pathogenesis is the complement system. Especially the anaphylatoxin C5a has been shown to have numerous harmful effects during sepsis. We have investigated the impact of high levels of C5a on the adrenal medulla following cecal ligation and puncture (CLP)-induced sepsis in rats as well as the role of C5a on catecholamine production from pheochromocytoma-derived PC12 cells. There was significant apoptosis of adrenal medulla cells in rats 24 hrs after CLP, as assessed by the TUNEL technique. These effects could be reversed by dual-blockade of the C5a receptors, C5aR and C5L2. When rats were subjected to CLP, levels of C5a and norepinephrine were found to be antipodal as a function of time. PC12 cell production of norepinephrine and dopamine was significantly blunted following exposure to recombinant rat C5a in a time-dependent and dose-dependent manner. This impaired production could be related to C5a-induced initiation of apoptosis as defined by binding of Annexin V and Propidium Iodine to PC12 cells. Collectively, we describe a C5a-dependent induction of apoptotic events in cells of adrenal medulla in vivo and pheochromocytoma PC12 cells in vitro. These data suggest that experimental sepsis induces apoptosis of adrenomedullary cells, which are responsible for the bulk of endogenous catecholamines. Septic shock may be linked to these events. Since blockade of both C5a receptors virtually abolished adrenomedullary apoptosis in vivo, C5aR and C5L2 become promising targets with implications on future complement-blocking strategies in the clinical setting of sepsis.

Catecholamines-crafty weapons in the inflammatory arsenal of immune/inflammatory cells or opening pandora's box?

It is well established that catecholamines (CAs), which regulate immune and inflammatory responses, derive from the adrenal medulla and from presynaptic neurons. Recent studies reveal that T cells also can synthesize and release catecholamines which then can regulate T cell function. We have shown recently that macrophages and neutrophils, when stimulated, can generate and release catecholamines de novo which, then, in an autocrine/paracrine manner, regulate mediator release from these phagocytes via engagement of adrenergic receptors. Moreover, regulation of catecholamine-generating enzymes as well as degrading enzymes clearly alter the inflammatory response of phagocytes, such as the release of proinflammatory mediators. Accordingly, it appears that phagocytic cells and lymphocytes may represent a major, newly recognized source of catecholamines that regulate inflammatory responses.

Stress-induced differences in primary and secondary resistance against bacterial sepsis corresponds with diverse corticotropin releasing hormone receptor expression by pulmonary CD11c+ MHC II+ and CD11c- MHC II+ APCs

Stress responses have been associated with altered immunity and depending upon the type of stressor, can have diverse effects on disease outcomes. As the first line of defense against potential pathogens, alterations in cellular immune responses along the respiratory tract can have a significant impact on the manifestation of local and systemic disease. Utilizing a murine model of respiratory pneumonia, the current study investigated the effects of restraint stress on the induction of primary and secondary immunity along the respiratory tract, influencing host susceptibility. Female CD-1 mice were subjected to three hours of restraint stress over a period of four days followed by primary and secondary Streptococcus pneumoniae infection via intranasal route. Stress exposure led to increased retention of bacterial carriage in the lungs, enhanced polymorphonuclear cells and a preferential decrease in pulmonary CD11c(+) MHC II(+) cells resulting in delayed lethality during primary infection but significant impairment of acquired immune protection after secondary infection. We also provide evidence to support a role for lung-associated corticotropin releasing hormone regulation through peripheral CRH and diverse CRH receptor expression by MHC II(+) antigen presenting cells (APCs). We conclude that repeated restraint stress has distinct influences on immune cell populations that appear to be important in the generation of innate and adaptive immune responses along the respiratory tract with the potential to influence local and systemic protection against disease pathogenesis.

Vagotomy enhances experimental metastases of 4THMpc breast cancer cells and alters substance P level

We have previously demonstrated that inactivation of capsaicin-sensitive sensory neurons enhances lung and heart metastases of breast carcinoma. Because a significant part of sensory innervation of lung tissue is supplied by the vagus nerve, we here examined the effects of unilateral mid-cervical vagotomy in the metastases of 4THMpc breast carcinoma and tissue Substance P (SP) levels. Balb-c mice were injected orthotopically with 4THMpc cells 1 week after vagotomy. Animals were sacrificed 27-30 days after injection of 4THMpc cells and the extent of metastases was determined. Unilateral vagotomy, right or left significantly increased the lung, liver and kidney metastases without altering the growth rate of the primary tumor. Heart metastases were increased only following left vagotomy. The changes in SP levels were somewhat surprising such that vagotomy actually increased while sham-operation decreased SP levels in lung. The effect of sham-operation was reversed by unilateral vagotomy demonstrating that vagal activity decreases total SP levels in the lung. Increased SP levels might be due to decreased degradation of the peptide. Presence of the tumor markedly increased SP level in the lung, which was more prominent in vagotomized animals. These results provide evidence that vagal activity may protect against metastatic disease.

Alterations in diurnal salivary cortisol rhythm in a population-based sample of cases with chronic fatigue syndrome

OBJECTIVE

To examine diurnal salivary cortisol rhythms and plasma IL-6 concentrations in persons with chronic fatigue syndrome (CFS), persons not fulfilling a diagnosis of CFS (we term them cases with insufficient symptoms or fatigue, ISF) and nonfatigued controls (NF). Previous studies of CFS patients have implicated the hypothalamic-pituitary-adrenal axis and the immune system in the pathophysiology of CFS, although results have been equivocal.

METHODS

Twenty-eight people with CFS, 35 persons with ISF, and 39 NF identified from the general population of Wichita, Kansas, were admitted to a research ward for 2 days. Saliva was collected immediately on awakening (6:30 AM), at 08:00 AM, 12 noon, 4:00 PM, 8:00 PM and at bedtime (10:00 PM) and plasma was obtained at 7:30 AM. Salivary cortisol concentrations were assessed using radioimmunoassay, and plasma IL-6 was measured using sandwich enzyme-linked immunosorbent assay.

RESULTS

People with CFS demonstrated lower salivary cortisol concentrations in the morning and higher salivary cortisol concentrations in the evening compared with both ISF and NF groups indicating a flattening of the diurnal cortisol profile. Mean plasma IL-6 concentrations were highest in CFS compared with the other groups, although these differences were no longer significant after controlling for BMI. Attenuated decline of salivary cortisol concentrations across the day and IL-6 concentration were associated with fatigue symptoms in CFS.

CONCLUSIONS

These results suggest an altered diurnal cortisol rhythm and IL-6 concentrations in CFS cases identified from a population-based sample.

Elevated inflammation levels in depressed adults with a history of childhood maltreatment

CONTEXT

The association between depression and inflammation is inconsistent across research samples.

OBJECTIVE

To test whether a history of childhood maltreatment could identify a subgroup of depressed individuals with elevated inflammation levels, thus helping to explain previous inconsistencies.

DESIGN

Prospective longitudinal cohort study.

SETTING

New Zealand.

PARTICIPANTS

A representative birth cohort of 1000 individuals was followed up to age 32 years as part of the Dunedin Multidisciplinary Health and Development Study. Study members were assessed for history of childhood maltreatment and current depression.

MAIN OUTCOME MEASURES

Inflammation was assessed using a clinically relevant categorical measure of high-sensitivity C-reactive protein (>3 mg/L) and a dimensional inflammation factor indexing the shared variance of continuous measures of high-sensitivity C-reactive protein, fibrinogen, and white blood cells.

RESULTS

Although depression was associated with high levels of high-sensitivity C-reactive protein (relative risk,1.45; 95% confidence interval,1.06-1.99), this association was significantly attenuated and no longer significant when the effect of childhood maltreatment was taken into account. Individuals with current depression and a history of childhood maltreatment were more likely to have high levels of high-sensitivity C-reactive protein compared with control subjects (n = 27; relative risk, 2.07; 95% confidence interval, 1.23-3.47). In contrast, individuals with current depression only had a nonsignificant elevation in risk (n = 109; relative risk, 1.40; 95% confidence interval, 0.97-2.01). Results were generalizable to the inflammation factor. The elevated inflammation levels in individuals who were both depressed and maltreated were not explained by correlated risk factors such as depression recurrence, low socioeconomic status in childhood or adulthood, poor health, or smoking.

CONCLUSIONS

A history of childhood maltreatment contributes to the co-occurrence of depression and inflammation. Information about experiences of childhood maltreatment may help to identify depressed individuals with elevated inflammation levels and, thus, at greater risk of cardiovascular disease.

Neuroendocrine factors alter host defense by modulating immune function

An increasing body of evidence demonstrates that there is bidirectional communication between the neuroendocrine and immune systems. Interaction between these systems results in a variety of outcomes, including the well documented "sickness behavior" elicited by cytokines of the immune system that can enter the brain and activate second messengers that modify neuronal activity. Crosstalk between the neuroendocrine and immune systems can also result in production of factors by the nervous and endocrine systems that alter immune cell function and subsequent modulation of immune responses against infectious agents and other pathogens. Continued exposure to molecules produced by the neuroendocrine system has also been known to increase susceptibility and/or severity of disease. Furthermore, neuroendocrine factors are thought to play a major role in gender-specific differences in development of certain disorders, including autoimmune/inflammatory diseases that have a two to tenfold higher incidence in females compared to males. Neuroendocrine factors can affect immune cells at the level of gene transcription but have also been shown to modify immune cell activity by interacting with intracellular molecules, resulting in modified ability of these cells to mount a potent immune response. In this review, we will consider various effects of the neuroendocrine system and its proteins on specific populations of immune cells and associated responses in host immunity against pathogens. We will further discuss how this modification of immune cell activity by the neuroendocrine system can contribute to susceptibility/severity of disease development.

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.

Natural glucocorticoids induce expansion of all developmental stages of murine bone marrow granulocytes without inhibiting function

Natural glucocorticoids (Gc) produced during stress have profound effects on the immune system. It is well known that Gc induce apoptosis in precursor T and B cells, markedly altering lymphopoiesis. However, it has been noted that marrow myeloid cells expanded both in proportion and absolute numbers in the mouse after Gc exposure. Mice were implanted with a corticosterone (CS) tablet that increased serum Gc and caused atrophied thymuses, both classic signs of activation of the stress axis. Blood neutrophil counts were elevated (4.8x), whereas lymphocyte counts declined. Flow cytometric analysis of the marrow revealed that the phenotypic distribution of the various major classes of cells was shifted by Gc exposure. As expected, marrow lymphocyte numbers declined >40% after 3 days of exposure to Gc. Conversely, in the myeloid compartment, both monocytes and granulocytes increased in number by >40%. Further, all granulocyte developmental stages showed large increases in both total number and percentage of cells. To investigate the functional capacity of mature granulocytes from Gc-treated mice, an improved granulocyte isolation method was developed. Gc exposure had little effect on the ability of granulocytes to produce superoxide or undergo chemotaxis or phagocytose bacteria. These results indicate that Gc treatment shifts bone marrow composition and provides evidence that granulocytes and their progenitors are selectively preserved under stressful conditions without losing function.

Effect of restraint stress on the population of intestinal intraepithelial lymphocytes in mice

The impact of restraint stress on the intestinal immune system, particularly on intestinal intraepithelial lymphocytes (i-IEL), has not been described in detail. Thus, the purpose of this study was to assess the effects of restraint stress, including those produced by increases in glucocorticoids and catecholamines, on the population of i-IEL. Mice were exposed to 1 or 4h restraint stress for 4 day, and the number of IEL in the mucosa of the proximal small intestine was determined by immunohistochemistry. The effects of restraint were also analyzed in mice submitted to different procedures: adrenalectomy, chemical sympathectomy, and treatment with a glucocorticoid antagonist (RU486), dexamethasone, and epinephrine. The main findings were that: (1) chronic restraint-stress reduced the i-IEl population in the small intestine; (2) adrenalectomy, treatment with RU-486 and chemical sympathectomy decreased the number of gammadelta, CD4+ and CD8+ T cells in non-stressed groups; (3) dexamethasone reduced the number of gammadelta and CD8+ T cells, and (4) epinephrine reduced the number of gammadelta, CD4+ and CD8+ T cells. These results demonstrated that restraint stress decreased the number of i-IEL in the proximal small intestine of mice, mainly by the combined action of higher concentrations of catecholamines and glucocorticoids, and that lower concentrations of glucocorticoids and catecholamines in unstressed mice preserved the population of i-IEL.

Neuroendocrine-immune interactions in rheumatoid arthritis: mechanisms of glucocorticoid resistance

Rheumatoid arthritis (RA) is characterized by chronic inflammation of the synovial membrane, leading to joint destruction. Many autoimmune diseases and disease states of chronic inflammation are accompanied by alterations in the complex interactions between the endocrine, nervous and immune systems. Glucocorticoids, an end product of the hypothalamic-pituitary-adrenal axis, are a mainstay treatment for many autoimmune diseases, including RA, because of their potent anti-inflammatory action. However, about 30% of patients with RA fail to respond to steroid therapy. There are various mechanisms that may contribute to the development of glucocorticoid resistance in inflammatory disorders, which will be the subject of this review. In addition, glucocorticoid resistance may be a contributing factor in the development of inflammatory/autoimmune diseases themselves. Therefore, further elucidation of these mechanisms will reveal new targets for therapeutic intervention in the treatment of RA.

Sympathetic nervous modulation of the skin innate and adaptive immune response to peptidoglycan but not lipopolysaccharide: involvement of beta-adrenoceptors and relevance in inflammatory diseases

Disorders of the skin immune activity are implicated in the pathogenesis of acquired inflammatory skin disorders. Inflammatory diseases including psoriasis, atopic dermatitis, lichen planus and vitiligo have also been associated with local alterations of adrenergic mechanisms and emotional stress. Here we show that the beta-adrenergic receptors antagonist propranolol along with peptidoglycan, but not LPS, combined with intradermal injection of a soluble protein, shifted the recall memory response to the Th1 type. The specific beta2-AR antagonist ICI 118,551 did not reproduce this effect suggesting that inhibition of both beta1- and beta2-AR caused the Th1 polarization. The underlying mechanism included enhanced local expression of IFN-gamma, IL-12 and IL-23 as well as of IFN-beta and CXCR3 ligands during the innate phase of the response which resulted in an increase of antigen-positive plasmacytoid dendritic cells (pDCs) in the draining lymph node. In particular, modulation of inflammatory cytokines, and IFN-beta inducible genes expression appeared to involve also the beta1-AR. Plasmacytoid dendritic cells and IL-23 were recently reported to play a central role in the pathogenesis of Th1-sustained inflammatory skin diseases such as psoriasis. Thus, primary beta-adrenoceptors signaling defects or altered sympathetic nervous activity together with selected pattern recognition receptors activation might serve as initiation and/or persistence factors for numerous Th1-sustained inflammatory skin diseases.

Acute Stress Promotes Aggressive-Like Behavior in Rats Made Allergic to Tree Pollen

It has been reported that allergies are associated with depression and possibly suicide in women. Aggression is an important behavioral component that predisposes depressed individuals to suicidal acts. In the present study we examined the relationship between allergies and aggression to determine a potential contribution of allergies in factors of risk for suicidal behavior. Because stress plays a critical role in the manifestation of clinical symptoms of allergies and also in suicidal behavior, we also studied the role of acute stress. Female inbred Brown Norway rats known for their susceptibility to respiratory allergies were sensitized and challenged with a mixture of tree pollen and evaluated in the resident-intruder test for detection of aggressive behaviors. They were also subjected to acute stress by sessions of inescapable forced swimming and re-evaluated in the resident intruder test. Animals made allergic to tree pollen and subjected to acute stress displayed increased aggressive-like behavior as compared with control-saline treated animals or to their own aggressive scores previous to the stress session. These results suggest that allergies and stress increases aggressive-like behavior, indicating that these conditions may be important factors promoting altered emotional reactivity with the potential to influence suicidal behavior.

Toll-like receptor signaling is critical for Wallerian degeneration and functional recovery after peripheral nerve injury

Toll-like receptors (TLRs) bind specific components conserved among microorganisms as well as endogenous ligands produced by necrotic cells, injured axons, and the extracellular matrix. Here, we investigated whether TLRs are involved in regulating the immune response, Wallerian degeneration (WD), and nerve regeneration after sciatic nerve lesion. Early expression of interleukin-1beta and monocyte chemoattractant protein-1 was compromised in the sciatic nerve distal stump of mice deficient in TLR signaling. In addition, significantly fewer macrophages were recruited and/or activated in the sciatic nerve distal stump of TLR2-, TLR4-, and MyD88-deficient mice compared with wild-type littermates, whereas WD, axonal regeneration, and recovery of locomotor function were impaired. In contrast, animals that received a single microinjection of TLR2 and TLR4 ligands at the site of sciatic nerve lesion had faster clearance of the degenerating myelin and recovered earlier than saline-injected control rats. Finally, rats that had altered innate immune response through dexamethasone treatment exhibited three times more myelin debris in their sciatic nerve distal stump and a significant delay in recovery of locomotor function. Our results provide strong evidence that TLR signaling plays a critical role in orchestrating the innate immune response leading to efficient and rapid clearance of inhibitory myelin debris and nerve regeneration.

Phagocyte-derived catecholamines enhance acute inflammatory injury

It is becoming increasingly clear that the autonomic nervous system and the immune system demonstrate cross-talk during inflammation by means of sympathetic and parasympathetic pathways. We investigated whether phagocytes are capable of de novo production of catecholamines, suggesting an autocrine/paracrine self-regulatory mechanism by catecholamines during inflammation, as has been described for lymphocytes. Here we show that exposure of phagocytes to lipopolysaccharide led to a release of catecholamines and an induction of catecholamine-generating and degrading enzymes, indicating the presence of the complete intracellular machinery for the generation, release and inactivation of catecholamines. To assess the importance of these findings in vivo, we chose two models of acute lung injury. Blockade of alpha2-adrenoreceptors or catecholamine-generating enzymes greatly suppressed lung inflammation, whereas the opposite was the case either for an alpha2-adrenoreceptor agonist or for inhibition of catecholamine-degrading enzymes. We were able to exclude T cells or sympathetic nerve endings as sources of the injury-modulating catecholamines. Our studies identify phagocytes as a new source of catecholamines, which enhance the inflammatory response.

Antimicrobial peptides: natural effectors of the innate immune system

Antimicrobial peptides (AMPs) are an evolutionarily conserved component of the innate immune system that defend against invading bacteria, viruses, and fungi through membrane or metabolic disruption. The efficiency of host defense via AMPs derives from the ability of these peptides to quickly identify and eradicate foreign pathogens through precise biochemical mechanisms. Recent advances in this field have expanded the repertoire of activities for AMPs to include immunostimulatory and immunomodulatory capacity as a catalyst for secondary host defense mechanisms. Further scrutiny of the biochemical and regulatory mechanisms of AMPs will lead to novel alternative approaches to the treatment of human pathogenic disorders.

Tuning immune tolerance with vasoactive intestinal peptide: a new therapeutic approach for immune disorders

The induction of immune tolerance is essential for the maintenance of immune homeostasis and to limit the occurrence of exacerbated inflammatory and autoimmune conditions. Multiple mechanisms act together to ensure self-tolerance, including central clonal deletion, cytokine deviation and induction of regulatory T cells. Identifying the factors that regulate these processes is crucial for the development of new therapies of autoimmune diseases and transplantation. The vasoactive intestinal peptide (VIP) is a well-characterized endogenous anti-inflammatory neuropeptide with therapeutic potential for a variety of immune disorders. Here, we examine the latest research findings, which indicate that VIP participates in maintaining immune tolerance in two distinct ways: by regulating the balance between pro-inflammatory and anti-inflammatory factors, and by inducing the emergence of regulatory T cells with suppressive activity against autoreactive T-cell effectors.

The emergence of neurotransmitters as immune modulators

Initially, the idea that neurotransmitters could serve as immunomodulators emerged with the discovery that their release and diffusion from nervous tissue could lead to signaling through lymphocyte cell-surface receptors and the modulation of immune function. It is now evident that neurotransmitters can also be released from leukocytes and act as autocrine or paracrine modulators. Here, we review the data indicating that leukocytes synthesize and release 'neurotransmitters' and we also discuss the diverse effects that these compounds exert in a variety of immune cells. The role of neurotransmitters in immune-related diseases is also reviewed succinctly. Current and future developments in understanding the cross-talk between the immune and nervous systems will probably identify new avenues for treating immune-mediated diseases using agonists or antagonists of neurotransmitter receptors.