The role of adrenoceptor-mediated signals in the modulation of lymphocyte function

Disrupted autonomic pathways in spinal cord injury: Implications for the immune regulation

Spinal Cord Injury (SCI) disrupts critical autonomic pathways responsible for the regulation of the immune function. Consequently, individuals with SCI often exhibit a spectrum of immune dysfunctions ranging from the development of damaging pro-inflammatory responses to severe immunosuppression. Thus, it is imperative to gain a more comprehensive understanding of the extent and mechanisms through which SCI-induced autonomic dysfunction influences the immune response. In this review, we provide an overview of the anatomical organization and physiology of the autonomic nervous system (ANS), elucidating how SCI impacts its function, with a particular focus on lymphoid organs and immune activity. We highlight recent advances in understanding how intraspinal plasticity that follows SCI may contribute to aberrant autonomic activity in lymphoid organs. Additionally, we discuss how sympathetic mediators released by these neuron terminals affect immune cell function. Finally, we discuss emerging innovative technologies and potential clinical interventions targeting the ANS as a strategy to restore the normal regulation of the immune response in individuals with SCI.

T-lymphocyte tyrosine hydroxylase regulates TH17 T-lymphocytes during repeated social defeat stress

Posttraumatic stress disorder (PTSD) is a debilitating psychiatric disorder which results in deleterious changes to psychological and physical health. Patients with PTSD are especially susceptible to life-threatening co-morbid inflammation-driven pathologies, such as autoimmunity, while also demonstrating increased T-helper 17 (TH17) lymphocyte-driven inflammation. While the exact mechanism of this increased inflammation is unknown, overactivity of the sympathetic nervous system is a hallmark of PTSD. Neurotransmitters of the sympathetic nervous system (i.e., catecholamines) can alter T-lymphocyte function, which we have previously demonstrated to be partially mitochondrial redox-mediated. Furthermore, we have previously elucidated that T-lymphocytes generate their own catecholamines, and strong associations exist between tyrosine hydroxylase (TH; the rate-limiting enzyme in the synthesis of catecholamines) and pro-inflammatory interleukin 17A (IL-17A) expression within purified T-lymphocytes in a rodent model of psychological trauma. Therefore, we hypothesized that T-lymphocyte-generated catecholamines drive TH17 T-lymphocyte polarization through a mitochondrial superoxide-dependent mechanism during psychological trauma. To test this, T-lymphocyte-specific TH knockout mice (THT-KO) were subjected to psychological trauma utilizing repeated social defeat stress (RSDS). RSDS characteristically increased tumor necrosis factor-α (TNFα), IL-6, IL-17A, and IL-22, however, IL-17A and IL-22 (TH17 produced cytokines) were selectively attenuated in circulation and in T-lymphocytes of THT-KO animals. When activated ex vivo, secretion of IL-17A and IL-22 by THT-KO T-lymphocytes was also found to be reduced, but could be partially rescued with supplementation of norepinephrine specifically. Interestingly, THT-KO T-lymphocytes were still able to polarize to TH17 under exogenous polarizing conditions. Last, contrary to our hypothesis, we found RSDS-exposed THT-KO T-lymphocytes still displayed elevated mitochondrial superoxide, suggesting increased mitochondrial superoxide is upstream of T-lymphocyte TH induction, activity, and TH17 regulation. Overall, these data demonstrate TH in T-lymphocytes plays a critical role in RSDS-induced TH17 T-lymphocytes and offer a previously undescribed regulator of inflammation in RSDS.

Immunological Tolerance in Liver Transplant Recipients: Putative Involvement of Neuroendocrine-Immune Interactions

The transplantation world changed significantly following the introduction of immunosuppressants, with millions of people saved. Several physicians have noted that liver recipients that do not take their medication for different reasons became tolerant regarding kidney, heart, and lung transplantations at higher frequencies. Most studies have attempted to explain this phenomenon through unique immunological mechanisms and the fact that the hepatic environment is continuously exposed to high levels of pathogen-associated molecular patterns (PAMPs) or non-pathogenic microorganism-associated molecular patterns (MAMPs) from commensal flora. These components are highly inflammatory in the periphery but tolerated in the liver as part of the normal components that arrive via the hepatic portal vein. These immunological mechanisms are discussed herein based on current evidence, although we hypothesize the participation of neuroendocrine-immune pathways, which have played a relevant role in autoimmune diseases. Cells found in the liver present receptors for several cytokines, hormones, peptides, and neurotransmitters that would allow for system crosstalk. Furthermore, the liver is innervated by the autonomic system and may, thus, be influenced by the parasympathetic and sympathetic systems. This review therefore seeks to discuss classical immunological hepatic tolerance mechanisms and hypothesizes the possible participation of the neuroendocrine-immune system based on the current literature.

Peripheral neuroimmune interactions: selected review and some clinical implications

Purpose

To provide a brief and focused review on peripheral neuroimmune interactions and their implications for some clinical disorders.

Methods

Narrative review of the literature including of English-language articles published between 1985 and 2021 using PubMed and MEDLINE.

Results

Many studies on experimental models and in vitro indicate that there are close interactions between the neural and immune systems. Processes from sensory afferents and autonomic efferents co-localize with immune cells and interact at discrete anatomical sites forming neuroimmune units. These neuroimmune interactions are bidirectional and mediated by a wide range of soluble factors including neuropeptides, classical neurotransmitters, cytokines, and other molecules that mediate complex cross-talk among nerves and immune cells. Small-diameter sensory afferents express a wide range of receptors that respond directly to tissue damage or pathogen signals and to chemokines, cytokines, or other molecules released from immune cells. Reciprocally, immune cells respond to neurotransmitters released from nociceptive and autonomic fibers. Neuroimmune interactions operate both at peripheral tissues and at the level of the central nervous system. Both centrally and peripherally, glial cells have a major active role in this bidirectional communication.

Conclusions

Peripheral neuroimmune interactions are complex and importantly contribute to the pathophysiology of several disorders, including skin, respiratory, and intestinal inflammatory disorders typically associated with pain and altered barrier function. These interactions may be relevant for persistence of symptoms in disorders associated with intense immune activation.

Dexmedetomidine attenuates pancreatic injury and inflammatory response in mice with pancreatitis by possible reduction of NLRP3 activation and up-regulation of NET expression

OBJECTIVE

Previous studies have shown that acute inflammation is associated with increased sympathetic activity, which in turn increases the inflammatory response and leads to organ damage. The present study aimed to investigate whether dexmedetomidine administration during acute pancreatitis (AP) lessens pancreatic pathological and functional injury and the inflammatory response, and to explore the underlying mechanisms.

METHODS

Mild pancreatitis was induced in mice with caerulein, and severe pancreatitis was induced with caerulein plus lipopolysaccharide (LPS). After pancreatitis induction, dexmedetomidine at 10 or 20 μg/kg was injected via the tail vein. Pancreatic pathological and functional injury was assessed by histology and serum levels of amylase and lipase, respectively. The inflammatory response was evaluated by determining serum levels of inflammatory factors. The expression of myeloperoxidase (MPO) was examined by immunohistochemistry. The expression of norepinephrine transporter (NET), NLRP3, pro-IL-1β, and interleukin (IL)-1β in pancreatic tissue was detected by Western blot and real-time PCR.

RESULTS

Dexmedetomidine at 20 μg/kg significantly attenuated pancreatic pathological injury, reduced serum levels of amylase, lipase, IL-1β, IL-6, and tumor necrosis factor (TNF)-α, and decreased the expression of MPO in pancreatic tissue in both mouse models of pancreatitis. In addition, dexmedetomidine at 20 μg/kg significantly down-regulated the expression of NLRP3, pro-IL-1β, and IL-1β in pancreatic tissue, but up-regulated the expression of NET in both mouse models.

CONCLUSION

Dexmedetomidine attenuates pancreatic injury and inflammatory response in mice with pancreatitis possibly by reducing NLRP3 activation and up-regulating NET expression.

The mucosal immune system: master regulator of bidirectional gut-brain communications

Communication between the brain and gut is not one-way, but a bidirectional highway whereby reciprocal signals between the two organ systems are exchanged to coordinate function. The messengers of this complex dialogue include neural, metabolic, endocrine and immune mediators responsive to diverse environmental cues, including nutrients and components of the intestinal microbiota (microbiota-gut-brain axis). We are now starting to understand how perturbation of these systems affects transition between health and disease. The pathological repercussions of disordered gut-brain dialogue are probably especially pertinent in functional gastrointestinal diseases, including IBS and functional dyspepsia. New insights into these pathways might lead to novel treatment strategies in these common gastrointestinal diseases. In this Review, we consider the role of the immune system as the gatekeeper and master regulator of brain-gut and gut-brain communications. Although adaptive immunity (T cells in particular) participates in this process, there is an emerging role for cells of the innate immune compartment (including innate lymphoid cells and cells of the mononuclear phagocyte system). We will also consider how these key immune cells interact with the specific components of the enteric and central nervous systems, and rapidly respond to environmental variables, including the microbiota, to alter gut homeostasis.

Mitochondrial Superoxide Signaling Contributes to Norepinephrine-Mediated T-Lymphocyte Cytokine Profiles

Norepinephrine (NE) produces multifaceted regulatory patterns in T-lymphocytes. Recently, we have shown that NE utilizes redox signaling as evidenced by increased superoxide (O2●-) causally linked to the observed changes in these cells; however, the source of this reactive oxygen species (ROS) remains elusive. Herein, we hypothesized that the source of increased O2●- in NE-stimulated T-lymphocytes is due to disruption of mitochondrial bioenergetics. To address this hypothesis, we utilized purified mouse splenic CD4+ and CD8+ T-lymphocytes stimulated with NE and assessed O2●- levels, mitochondrial metabolism, cellular proliferation, and cytokine profiles. We demonstrate that the increase in O2●- levels in response to NE is time-dependent and occurs at later points of T-lymphocyte activation. Moreover, the source of O2●- was indeed the mitochondria as evidenced by enhanced MitoSOX Red oxidation as well as abrogation of this signal by the addition of the mitochondrial-targeted O2●--scavenging antioxidant MitoTempol. NE-stimulated T-lymphocytes also demonstrated decreased mitochondrial respiratory capacity, which suggests disruption of mitochondrial metabolism and the potential source of increased mitochondrial O2●-. The effects of NE in regards to redox signaling appear to be adrenergic receptor-dependent as specific receptor antagonists could reverse the increase in O2●-; however, differential receptors regulating these processes were observed in CD4+ versus CD8+ T-lymphocytes. Finally, mitochondrial O2●- was shown to be mechanistic to the NE-mediated T-lymphocyte phenotype as supplementation of MitoTempol could reverse specific changes in cytokine expression observed with NE treatment. Overall, these studies indicate that mitochondrial metabolism and O2●--mediated redox signaling play a regulatory role in the T-lymphocyte response to NE.

Redox-regulated suppression of splenic T-lymphocyte activation in a model of sympathoexcitation

Sympathoexcitation, increased circulating norepinephrine, and elevated levels of reactive oxygen species are driving forces underlying numerous cardiovascular diseases, including hypertension. However, the effects of elevated norepinephrine and subsequent reactive oxygen species production in splenic T-lymphocytes during hypertension are not currently understood. We hypothesized that increased systemic levels of norepinephrine inhibits the activation of splenic T-lymphocytes via redox signaling. To address this hypothesis, we examined the status of T-lymphocyte activation in spleens of a mouse model of sympathoexcitation-driven hypertension (ie, norepinephrine infusion). Splenic T-lymphocytes from norepinephrine-infused mice demonstrated decreased proliferation accompanied by a reduction in interferon gamma and tumor necrosis factor-α production as compared with T-lymphocytes from saline-infused mice. Additionally, norepinephrine directly inhibited splenic T-lymphocyte proliferation and cytokine production ex vivo in a dose-dependent manner. Furthermore, norepinephrine caused an increase in G1 arrest in norepinephrine-treated T-lymphocytes, and this was accompanied by a decrease in pro-growth cyclin D3, E1, and E2 mRNA expression. Interestingly, norepinephrine caused an increase in cellular superoxide, which was shown to be partially causal to the inhibitory effects of norepinephrine, as antioxidant supplementation (ie, Tempol) to norepinephrine-infused mice moderately restored T-lymphocyte growth and proinflammatory cytokine production. Our findings indicate that suppression of splenic T-lymphocyte activation occurs in a norepinephrine-driven model of hypertension due to, at least in part, an increase in superoxide. We speculate that further understanding of how norepinephrine mediates its inhibitory effects on splenic T-lymphocytes may elucidate novel pathways for therapeutic mimicry to suppress T-lymphocyte-mediated inflammation in an array of diseases.

Autonomic nervous system and immune system interactions

The present review assesses the current state of literature defining integrative autonomic-immune physiological processing, focusing on studies that have employed electrophysiological, pharmacological, molecular biological, and central nervous system experimental approaches. Central autonomic neural networks are informed of peripheral immune status via numerous communicating pathways, including neural and non-neural. Cytokines and other immune factors affect the level of activity and responsivity of discharges in sympathetic and parasympathetic nerves innervating diverse targets. Multiple levels of the neuraxis contribute to cytokine-induced changes in efferent parasympathetic and sympathetic nerve outflows, leading to modulation of peripheral immune responses. The functionality of local sympathoimmune interactions depends on the microenvironment created by diverse signaling mechanisms involving integration between sympathetic nervous system neurotransmitters and neuromodulators; specific adrenergic receptors; and the presence or absence of immune cells, cytokines, and bacteria. Functional mechanisms contributing to the cholinergic anti-inflammatory pathway likely involve novel cholinergic-adrenergic interactions at peripheral sites, including autonomic ganglion and lymphoid targets. Immune cells express adrenergic and nicotinic receptors. Neurotransmitters released by sympathetic and parasympathetic nerve endings bind to their respective receptors located on the surface of immune cells and initiate immune-modulatory responses. Both sympathetic and parasympathetic arms of the autonomic nervous system are instrumental in orchestrating neuroimmune processes, although additional studies are required to understand dynamic and complex adrenergic-cholinergic interactions. Further understanding of regulatory mechanisms linking the sympathetic nervous, parasympathetic nervous, and immune systems is critical for understanding relationships between chronic disease development and immune-associated changes in autonomic nervous system function.

Psychosocial stress and inflammation in cancer

Stress-induced immune dysregulation results in significant health consequences for immune related disorders including viral infections, chronic autoimmune disease, and tumor growth and metastasis. In this mini-review we discuss the sympathetic, neuroendocrine and immunologic mechanisms by which psychosocial stress can impact cancer biology. Both human and animal studies have shown the sympathetic and neuroendocrine responses to psychosocial stress significantly impacts cancer, in part, through regulation of inflammatory mediators. Psychosocial stressors stimulate neuroendocrine, sympathetic, and immune responses that result in the activation of the hypothalamic-pituitary-adrenal (HPA)-axis, sympathetic nervous system (SNS), and the subsequent regulation of inflammatory responses by immune cells. Social disruption (SDR) stress, a murine model of psychosocial stress and repeated social defeat, provides a novel and powerful tool to probe the mechanisms leading to stress-induced alterations in inflammation, tumor growth, progression, and metastasis. In this review, we will focus on SDR as an important model of psychosocial stress in understanding neural-immune mechanisms in cancer.

Association of in vivo β-adrenergic receptor sensitivity with inflammatory markers in healthy subjects

OBJECTIVE

Several stress-related states and conditions that are considered to involve sympathetic overactivation are accompanied by increased circulating levels of inflammatory immune markers. Prolonged sympathetic overactivity involves increased stimulation of the β-adrenergic receptor (β-AR). Although prior research suggests that one mechanism by which sympathetic stimulation may facilitate inflammation is via β-AR activation, little work has focused on the relationship between circulating inflammatory immune markers and β-AR function within the human body (in vivo). We examined whether decreased β-AR sensitivity, an indicator of prolonged β-adrenergic overactivation and a physiological component of chronic stress, is related to elevated levels of inflammatory immune markers.

METHODS

Ninety-three healthy participants aged 19 to 51 years underwent the chronotropic 25 dose isoproterenol test to determine in vivo β-AR function. Circulating levels of C-reactive protein, interleukin 6, and soluble tumor necrosis factor receptor 1 were determined.

RESULTS

β-AR sensitivity was lower in people with higher C-reactive protein concentrations (r = 0.326, p = .003). That relationship remained significant after controlling for sociodemographic and health variables such as age, sex, ethnicity, body mass index, mean arterial blood pressure, heart rate, leisure-time exercise, and smoking status. No significant relationship was found between chronotropic 25 dose and interleukin 6 or soluble tumor necrosis factor receptor 1.

CONCLUSIONS

This study demonstrates a link between in vivo β-adrenergic receptor function and selected circulating inflammatory markers (CRP) in humans. Future studies in specific disease states may be promising.

Do stress responses promote leukemia progression? An animal study suggesting a role for epinephrine and prostaglandin-E2 through reduced NK activity

In leukemia patients, stress and anxiety were suggested to predict poorer prognosis. Oncological patients experience ample physiological and psychological stress, potentially leading to increased secretion of stress factors, including epinephrine, corticosteroids, and prostaglandins. Here we tested whether environmental stress and these stress factors impact survival of leukemia-challenged rats, and studied mediating mechanisms. F344 rats were administered with a miniscule dose of 60 CRNK-16 leukemia cells, and were subjected to intermittent forced swim stress or to administration of physiologically relevant doses of epinephrine, prostaglandin-E₂ or corticosterone. Stress and each stress factor, and/or their combinations, doubled mortality rates when acutely applied simultaneously with, or two or six days after tumor challenge. Acute administration of the β-adrenergic blocker nadolol diminished the effects of environmental stress, without affecting baseline survival rates. Prolonged β-adrenergic blockade or COX inhibition (using etodolac) also increased baseline survival rates, possibly by blocking tumor-related or normal levels of catecholamines and prostaglandins. Searching for mediating mechanisms, we found that each of the stress factors transiently suppressed NK activity against CRNK-16 and YAC-1 lines on a per NK basis. In contrast, the direct effects of stress factors on CRNK-16 proliferation, vitality, and VEGF secretion could not explain or even contradicted the in vivo survival findings. Overall, it seems that environmental stress, epinephrine, and prostaglandins promote leukemia progression in rats, potentially through suppressing cell mediated immunity. Thus, patients with hematological malignancies, which often exhibit diminished NK activity, may benefit from extended β-blockade and COX inhibition.

Restraint stress impairs early wound healing in mice via alpha-adrenergic but not beta-adrenergic receptors

Stress negatively influences wound healing in a clinically relevant manner. In an animal model, repeated restraint stress (RST) impairs wound healing in mice, partially through stress-induced glucocorticoid (GC) release. However, the role of stress-induced catecholamines (i.e., (nor)epinephrine) in healing has not been elucidated. In the present study, two 3.5mm round dermal wounds were placed on the backs of mice. Animals were restrained overnight for 3 days prior to and 5 days post-wounding. Prior to RST, mice were injected with either phentolamine or nadolol: non-specific alpha- and beta-adrenergic receptor antagonists, respectively. Pictures were taken daily to measure the rates of wound closure and contraction. Blockade of alpha-adrenergic, but not beta-adrenergic receptors, attenuated impairments in wound closure and contraction, and normalized edema, in RST mice. Thus, although stress impairment in wound healing clearly involves GCs, catecholamines play an important role via alpha-adrenergic receptor stimulation.

The Blood–Brain Barrier in Psychoneuroimmunology

The very term "psychoneuroimmunology" connotes separate compartments that interact. The BBB is the physical and physiologic dividing line between the immune system and the CNS and is the locale for interaction. Interactions between the immune system and the CNS are mediated at the BBB through a variety of mechanisms. The BBB restricts unregulated mixing of the immune substances in the blood with those in the CNS, directly transports neuroimmune active substances between the blood and the CNS, and secretes neuroimmune substances. All these normal functions of the BBB can be altered in an adaptive or pathologic manner by neuroimmune events. As such, the BBB is an important conduit in the communication of the immune and the central nervous systems.

The immunomodulatory effects of clonidine, an α-2-adrenergic agonist, in laying hens

The ability of the sympathetic nervous system to regulate chicken immune function was examined. Clonidine, an alpha-2 adrenergic receptor agonist, was administrated at 2.5, 5.0, or 10.0 mg/L in the drinking water of White Leghorn hens at 48 wk of age. The hens were randomly housed in conventional cages in pairs. Concentrations of plasma IgG (also named IgY) were detected using chicken IgG ELISA, and the percentage of subpopulations of circulating lymphocytes were analyzed using flow cytometry. Compared with controls, treated hens had higher circulating IgG levels and a greater percentage of circulating B cells (Bu-1+ cells, P < 0.01) after 1 wk of treatment. Additionally, the percentages of CD8+ cells were consistently higher (P = 0.07) in the treated hens compared with controls, whereas the percentages of CD4+ cells and the ratio of CD4+ cell to CD8+ cell were not affected by the treatment (P > 0.05). These effects of clonidine on the IgG concentrations and the proportions of B-cells and CD8+ cells were dose-related. The highest increase was found in the hens treated with 10.0 mg/L of clonidine. These results suggest that the sympathetic nervous system is directly involved in regulating the chicken immune system via regulation of alpha-2-adrenergic receptor activations.

Susceptibility of lupus-prone NZM mouse strains to lead exacerbation of systemic lupus erythematosus symptoms

It has been repeatedly shown that the heavy metal mercury can induce or exacerbate lupus like autoimmunity in susceptible strains of rats and mice. A hallmark of such autoimmune induction is the accompaniment of an immune shift, in which there is usually an initial skewing toward a Th2-like immune environment. Another heavy metal, lead (Pb), has also been found to induce a Th2 shift in mice. However, exposure of normal mouse strains to Pb does not appear to induce autoimmunity. In order to investigate whether mice genetically predisposed to murine systemic lupus erythematosus (SLE) are susceptible to a Pb-induced exacerbation of lupus, males and females of four New Zealand mixed (NZM) mouse strains, along with BALB/c and C57Bl/6 controls, were administered three 100-microliter intraperitoneal injections of either 1.31 mM lead or sodium acetate per week for 3 wk. The four NZM strains chosen, NZM391, NZM2328, NZM88, and NZM2758, have differential genetic penetrance for SLE with variances in certain manifestations of the disease, but all of these strains naturally develop glomerulonephritis and produce high titers of anti-nuclear autoantibodies. The mice were prebled for baseline values and were bled directly after the injection period (d 1) and monthly thereafter for 5 mo. Sera were assessed for anti-double-stranded DNA titers, urea nitrogen levels, and creatine kinase activity, as well as four total immunoglobulin (Ig) G2a and IgG1 levels. Mortality and morbidity of the mice were also recorded. All NZM strains showed an acute, non-gender-based, susceptibility to Pb at d 1, but the control strains were unaffected. Over time, it became apparent that the strains diverged: The NZM391 strain showed gender-independent susceptibility to Pb enhancement of lupus manifestations and mortality; the NZM2328 strain exhibited gender-independent Pb susceptibility to manifestations, although only females had increased mortality; the NZM2758 strain exhibited non-gender-based elevations in urea nitrogen and creatine kinase activity levels; and the NZM88 strain displayed male susceptibility to anti-DNA and life span. Surprisingly, Pb increased the longevity of NZM88 and NZM2758 females. These results indicate that Pb indeed can exacerbate SLE in lupus-prone mice; however, even among lupus-prone strains, genetic differences determine the degree of exacerbation. Using the known phenotype and genetic differences, one can identify and characterize possible traits and loci associated with Pb susceptibility.

Altered lymphocyte catecholamine reactivity in mice subjected to chronic mild stress

There is considerable evidence that the sympathetic nervous system influences the immune response via activation and modulation of beta(2)-adrenergic receptors (beta(2)R). Furthermore, it has been suggested that stress has effects on the sympathetic nervous system. In the present study, we analyzed the influence of catecholamines on the reactivity of lymphocytes from mice exposed to a chronic mild stress (CMS) model of depression (CMS-animals). The effects of the CMS treatment on catecholamine and corticosterone levels and on beta(2)R lymphoid expression were also assessed. For this purpose, animals were subjected to CMS for 8 weeks. Results showed that catecholamines (epinephrine and norepinephrine) exert an inhibitory effect on mitogen-induced normal T-cell proliferation and a stimulatory effect on normal B-cell proliferation in response to selective B lymphocyte mitogens. Specific beta- and beta(2)-antagonists abolished these effects. Lymphocytes from mice subjected to CMS had an increased response to catecholamine-mediated inhibition or enhancement of proliferation in T and B cells, respectively. Moreover, a significant increase in beta(2)R density was observed in animals under CMS compared to normal animals. This was accompanied by an increment in cyclic AMP production after beta-adrenergic stimulation. On the other hand, neither catecholamine levels, determined in both urine and spleen samples, nor serum corticosterone levels showed significant variation between normal and CMS-animals. These findings demonstrate that chronic stress is associated with an increased sympathetic influence on the immune response and may suggest a mechanism through which chronic stress alters immunity.

Phenylethanolamine N-methyl transferase expression in mouse thymus and spleen

Catecholamines usually are found in neurons and chromaffin cells of mammals. In this study, surprisingly high levels of the epinephrine synthesizing enzyme phenylethanolamine N-methyl transferase (PNMT) were detected in the thymus of young mice. Levels of PNMT activity in the thymus were comparable to levels in the brainstem and were suppressed by the PNMT inhibitor LY134046. PNMT mRNA was localized with in situ hybridization throughout the thymus, but levels were approximately twofold higher in the cortex than in the medulla. PNMT activity was barely detectable in the spleen, and only a few cells expressing PNMT mRNA were located in the marginal zone of the white pulp. These findings suggest that cells in the thymus of young mice have the ability to synthesize epinephrine.

Stress increases gene expression of phenylethanolamine N-methyltransferase in spleen of rats via pituitary-adrenocortical mechanism

Gene expression of phenylethanolamine N-methyltransferase (PNMT), the enzyme catalyzing conversion of norepinephrine to epinephrine, has been detected in rat spleen using the reverse transcription polymerase chain reaction. PNMT identity was subsequently verified by Southern blots. Localization of the spleen cells responsible for the PNMT gene expression was investigated by the in situ hybridization and PNMT mRNA was found to be present in the white pulp. The hypothesis that stress may produce an increase in PNMT gene expression in rat spleen was tested and a robust rise in the relative abundance of PNMT mRNA levels was observed after a single or repeated immobilization (about 80%). Adrenalectomy or hypophysectomy completely prevented the immobilization-induced increase in spleen PNMT mRNA levels, suggesting that stress-induced PNMT gene expression in the spleen is regulated predominantly via pituitary-adrenocortical axis. In control animals, however, spleen PNMT was not significantly affected by the ectomies and therefore basal PNMT gene expression might be regulated by different mechanism(s).Thus, PNMT gene expression in the rat spleen is exaggerated by stress stimuli, suggesting its role in physiological regulations.

Immunopathogenesis of rheumatic diseases in the context of neuroendocrine interactions

Growing evidence supports the hypothesis that alterations of the stress response and interactions between the neuroendocrine and immune systems contribute to the pathogenesis of rheumatic diseases such as rheumatoid arthritis (RA). In particular, the hypothalamus-pituitary-adrenal (HPA) axis and the autonomic nervous system (ANS) are of special interest. Polymorphisms of the corticotropin-releasing hormone (CRH)-regulating region have been described recently. These polymorphisms are differentially distributed in RA patients and healthy subjects of various ethnic origin, thus supporting the hypothesis that they represent a new genetic marker for RA susceptibility. The decreased expression of beta(2)-adrenergic receptors (beta(2)-R) on lymphatic cells in rheumatic diseases like RA, together with an impaired influence of catecholamines on immune function in these patients, further underlines the concept of a dysfunction of the ANS in rheumatic diseases. Results from work in this field will provide more insight into the pathogenesis of RA and help to establish novel therapies for this chronic rheumatic disease.

Impaired catecholaminergic signalling of B lymphocytes in patients with chronic rheumatic diseases

OBJECTIVE

To investigate further the influence of the autonomic nervous system on chronic rheumatic diseases.

METHODS

The density and affinity of beta2 adrenergic receptors (beta2R) on CD19+ lymphocytes in patients with rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), and systemic sclerosis (SSc), as well as intracellular cAMP levels in patients with RA and SLE, were determined. Human peripheral blood mononuclear cells were separated from venous blood of patients and healthy controls by Ficoll-Hypaque density centrifugation. CD19+ lymphocytes were purified by magnetic cell sorting, and beta2R were determined by a radioligand binding assay with [125I]iodocyanopindolol. Intracellular cAMP levels and beta2R agonist induced cell death were measured by a radioimmunoassay and flow cytometry using annexin-V binding, respectively. Systemic disease activity of the patients was evaluated using multifactorial scoring systems.

RESULTS

The density of beta2R on peripheral CD19+ lymphocytes was significantly decreased in patients with RA, SLE, and SSc compared with healthy controls. In patients with RA and SSc beta2R density was negatively correlated with systemic disease activity. Furthermore, although basal intracellular cAMP levels were raised in patients with RA and SLE, the increase of cAMP upon stimulation of beta2R was significantly reduced in these patients compared with control subjects. Preliminary data suggest that beta2R agonist induced cell death is diminished in patients with RA exhibiting decreased beta2R densities.

CONCLUSIONS

The results of this study show a reduction of beta2R densities on B lymphocytes mirrored by an impaired intracellular cAMP generation in patients with chronic rheumatic diseases, indicating a decreased influence of the autonomic nervous system on B cells in these conditions.

Cytokine production by naive and primary effector CD4+ T cells exposed to norepinephrine

We recently showed that clones of Th1 cells, but not Th2 cells, expressed a functional beta-2-adrenergic receptor (beta2AR) and that either norepinephrine or the beta2AR agonist terbutaline stimulated this receptor to modulate the level of Th1 cytokines produced. In the present study, we show that norepinephrine and terbutaline stimulate the beta2AR to decrease the level of IL-2 produced by freshly isolated murine splenic naive CD4+ T cells from either Balb/C or DO11.10 transgenic mice and activated polyclonally with anti-CD3 and anti-CD28 mAbs. In contrast, the level of cytokines produced by primary effector Th1 and Th2 cells were unaffected when norepinephrine, terbutaline, or cAMP analogs were added at the time of restimulation. These results suggest that a diversity exists among CD4+ T-cell subsets with respect to the level of adrenergic receptor expression, responsiveness to cAMP, stage of cell differentiation, or a combination of the above.

Interactions of autonomic nervous, neuroendocrine, and immune systems in rheumatoid arthritis

In general, it is assumed that the two pathways (i.e., HPA axis and sympathetic nervous system) probably act cooperatively to maintain homeostasis. The previously mentioned studies clearly point to a disturbance in the interaction between the ANS, the HPA axis, and the immune system in chronic rheumatic diseases (Fig. 2). Even early on in the course of RA, these changes can be observed. Along with the results obtained in animal models, an important role of neuroendocrine interactions in the pathogenesis of RA is proposed. Further studies are required to establish the exact contribution of the ANS in the initiation and perpetuation of RA. To date, it is quite obvious that neuropeptides play a part in the orchestration of the various molecules (e.g., cytokines) exerting modulatory effects on immune cells. One can speculate that therapeutic implications are likely to result from investigations on the ANS-immune interactions. Based on early observations that blocking catecholamine actions ameliorate symptoms of RA, it is quite promising to follow this avenue in investigating ANS-immune interactions of various time points of the disease. Conversely, further studies are required to determine the contribution of the HPA axis to the onset of RA. Results from ongoing studies are eagerly awaited so as to establish new therapeutic options. In the future,it may be possible to interfere with the inflammatory process in RA by an exactly timed neuroendocrine intervention right at or even before the onset of disease. Therapy with steroids in RA might be better planned based on the genetically determined reactivity of an individual's HPA axis. In this respect, a recent report by Masi et al is of special interest. Based on the current literature on the disturbances in the neuroendocrine, immune, and microvascular systems found in early RA, the authors hypothesize that an imbalance in the interactive homeostasis of these systems develops during a long preclinical phase and eventually leads to the outbreak of the disease in genetically predisposed individuals. This interesting hypothesis includes the perspective that individuals prone to develop RA may be identified in a preclinical phase and treated prophylactically. In any event, results from all these studies are promising in two ways: to gain more insight in the pathogenic process of RA and to establish novel therapies to help the patients bear their burden of a chronic rheumatic disease.

Stimulation of the B cell receptor, CD86 (B7-2), and the beta 2-adrenergic receptor intrinsically modulates the level of IgG1 and IgE produced per B cell

Our findings using B cells from either wild-type, CD86-deficient, or beta 2-adrenergic receptor (beta2AR)-deficient mice suggest three mechanisms by which the level of IgG1 and IgE production can be increased on a per cell basis. Trinitrophenyl-specific B cells enriched from unimmunized mouse spleens were pre-exposed to Ag and/or the beta 2AR ligand terbutaline for 24 h before being activated by either a beta 2AR-negative Th2 cell clone or CD40 ligand/Sf9 cells and IL-4 in the presence or absence of an anti-CD86 Ab. Data suggest that the first mechanism involves a B cell receptor (BCR)-dependent up-regulation of CD86 expression that, when CD86 is stimulated, increases the amount of IgG1 and IgE produced in comparison to unstimulated cells. The second mechanism involves a BCR- and beta 2AR-dependent up-regulation of CD86 to a level higher than that induced by stimulation of either receptor alone that, when CD86 is stimulated, further increases the amount of IgG1 and IgE produced. The third mechanism is BCR-independent and involves a beta 2AR-dependent increase in the ability of a B cell to respond to IL-4. Flow cytometric and limiting dilution analyses suggest that the increase in IgG1 and IgE occurs independently from the isotype switching event. These findings suggest that the BCR, the beta 2AR, and CD86 are involved in regulating IL-4-dependent IgG1 and IgE production.

Gestational nicotine exposure alone or in combination with ethanol down-modulates offspring immune function

Prenatal nicotine exposure has been shown to disrupt the development of a number of peripheral organs. In the current study, we examined the effects of gestational nicotine exposure, alone or in combination with ethanol exposure, on offspring immune function. Timed pregnant rats were treated with either nicotine (6 mg/kg/day) from gestation day 4-20 using subcutaneously implanted osmotic mini-pumps or ethanol administered in the drinking water (15% w/v) from gestation day 10-20. The combined exposure group received both treatments. The ability of offspring T and B cells to proliferate in response to nonspecific stimulation by Concanavalin A or lipopolysaccharide, respectively, was determined on postnatal days 9, 15, 22, 29, 64, and 86. Offspring splenocyte beta(2)-adrenoceptor binding was also measured. Nicotine or nicotine+ethanol suppressed splenocyte responsiveness to Concanavalin A or lipopolysaccharide which was similar in timing and magnitude to that seen with ethanol alone. Splenocytes from these groups remained subresponsive to stimulation well into adulthood. The combined drug treatment caused an overall reduction in spleen beta-adrenergic receptor binding whereas the individual drug treatments did not alter the development of spleen beta-adrenergic receptors.Our results indicate that prenatal nicotine exposure can cause long-term suppression of the proliferative response of offspring immune cells. Moreover, the effects of nicotine+ethanol may cause more severe deficits in adulthood.

Reduced catecholamine response of lymphocytes from patients with rheumatoid arthritis

Catecholamines modulate lymphocyte function via stimulation of beta2-adrenergic receptors (beta2R). Previous investigations revealed a decreased density of beta2R on peripheral blood mononuclear cells (PBMC) in patients with chronic rheumatic diseases. Aim of the present study was to determine the impact of this decrease on catecholamine response of PBMC from patients with rheumatoid arthritis (RA) in vitro. PBMC from 17 patients with RA and 12 healthy blood donors (HD) were investigated. Beta2R were determined by a radioligand binding assay. The effects of epinephrine (E) and norepinephrine (NE) on PBMC proliferation were studied using cells activated with pokeweed mitogen (PWM) and monoclonal anti-CD3-antibodies (OKT3), respectively. In parallel, alpha1- or beta-receptor antagonist were added to the culture to determine the specificity of the catecholaminergic effects. The results showed that depending on the stimulus and the catecholamine concentration employed E and NE exert inhibitory (OKT3) or stimulatory signals (PWM) on lymphocyte proliferation. Inhibitory effects could be abolished by adding beta-antagonist, while stimulatory signals were diminished after addition of alpha1- of beta-antagonist. Patients with RA showed a significantly reduced density of beta2R compared to HD paralleled by a significantly reduced influence of catecholamines on lymphocyte function. The study demonstrates the intricate relationship between PBMC reactivity and catecholamine effects that are mediated via alpha1- and beta-adrenergic receptors. In this respect the reduced catecholamine response of PBMC from RA patients may contribute to the pathogenic process of RA.

Exogenous and endogenous catecholamines inhibit the production of macrophage inflammatory protein (MIP) 1 alpha via a beta adrenoceptor mediated mechanism

Noradrenaline (NA) and adrenaline (Ad) are modulators of cytokine production. Here we investigated the role of these neurotransmitters in the regulation of macrophage inflammatory protein (MIP)-1alpha expression. Pretreatment of RAW 264.7 macrophages with NA or Ad decreased, in a concentration-dependent manner (1 nM-100 microM), MIP-1alpha release induced by bacterial lipopolysaccharide (LPS 10 ng ml(-1) LPS). The effect of NA was reversed by the selective beta-adrenoceptor antagonist propranolol (10 microM), but not by the alpha-adrenoceptor antagonist phentolamine (10 microM). In the concentration range of 10 nM-10 microM, isoproterenol, a beta-adrenoceptor agonist, but not phenylephrine (a selective alpha1-adrenoceptor agonist) or UK-14304 (a selective alpha2-adrenoceptor agonist) mimicked the inhibitory effects of catecholamines on MIP-1alpha production. Increases in intracellular cyclic adenosine monophosphate, elicited either by the selective type IV phosphodiesterase inhibitor rolipram (0.1 - 10 microM), or by prostaglandin E2, (10 nM-10 microM) decreased MIP-1alpha release, suggesting that increased cyclic AMP may contribute to the suppression of MIP-1alpha release by beta-adrenoceptor stimulation. Northern blot analysis demonstrated that NA (100 nM-10 microM), Ad, isoproterenol, as well as rolipram (100 nM-10 microM) decreased LPS-induced MIP-1alpha mRNA accumulation. NA and Ad (1-100 microM) also decreased MIP-1alpha production in thioglycollate-elicited murine peritoneal macrophages. Pretreatment of mice with either isoproterenol (10 mg kg(-1), i.p.) or rolipram (25 mg kg(-1), i.p.) decreased LPS-induced plasma levels of MIP-1alpha, while propranolol (10 mg kg(-1), i.p.) augmented the production of this chemokine, confirming the role of a beta-adrenoceptor mediated endogenous catecholamine action in the regulation of MIP-1alpha production in vivo. Thus, based on our data we conclude that catecholamines are important endogenous regulators of MIP-1alpha expression in inflammation.

Role of the Hypothalamic Pituitary Adrenal Axis and IL-6 in Stress-Induced Reactivation of Latent Herpes Simplex Virus Type 1

Hyperthermic stress induces reactivation of herpes simplex virus type 1 (HSV-1) in latently infected mice and also stimulates corticosterone release from the adrenals via activation of the hypothalamic pituitary adrenal axis. In the present study, we tested the hypothesis that stress-induced elevation of corticosterone potentiates HSV-1 reactivation in latently infected mice. Because of the putative role of IL-6 in facilitating HSV-1 reactivation in mice, the effect of hyperthermic stress and cyanoketone treatment on IL-6 expression in the trigeminal ganglion was also measured. Preadministration of cyanoketone, a glucocorticoid synthesis inhibitor, blocked the stress-induced elevation of corticosterone in a dose-dependent manner. Furthermore, inhibition of corticosterone synthesis was correlated with reduced levels of HSV-1 reactivation in latently infected mice. Hyperthermic stress elicited a transient rise in IL-6 mRNA levels in the trigeminal ganglion, but not other cytokine transcripts investigated. In addition, there was a significant reduction in MAC-3+, CD8+, and DX5+ (NK cell marker) cells in the trigeminal ganglion of latent HSV-1-infected mice 24 h after stress. Cyanoketone blocked the stress-induced rise in IL-6 mRNA and protein expression in the trigeminal ganglion latently infected with HSV-1. Collectively, the results indicate that the activation of the hypothalamic pituitary adrenal axis plays an important role in stimulating IL-6 expression and HSV-1 reactivation in the trigeminal ganglion following hyperthermic stress of mice.

Phosphodiesterase profile of human B lymphocytes from normal and atopic donors and the effects of PDE inhibition on B cell proliferation

1. CD19+ B lymphocytes were purified from the peripheral blood of normal and atopic subjects to analyse and compare the phosphodiesterase (PDE) activity profile, PDE mRNA expression and the importance of PDE activity for the regulation of B cell function. 2. The majority of cyclic AMP hydrolyzing activity of human B cells was cytosolic PDE4, followed by cytosolic PDE7-like activity; marginal PDE3 activity was found only in the particulate B cell fraction. PDE1, PDE2 and PDE5 activities were not detected. 3. By cDNA-PCR analysis mRNA of the PDE4 subtypes A, B (splice variant PDE4B2) and D were detected. In addition, a weak signal for PDE3A was found. 4. No differences in PDE activities or mRNA expression of PDE subtypes were found in B cells from either normal or atopic subjects. 5. Stimulation of B lymphocytes with the polyclonal stimulus lipopolysaccharide (LPS) induced a proliferative response in a time- and concentration-dependent manner, which was increased in the presence of interleukin-4 (IL-4). PDE4 inhibitors (rolipram, piclamilast) led to an increase in the cellular cyclic AMP concentration and to an augmentation of proliferation, whereas a PDE3 inhibitor (motapizone) was ineffective, which is in accordance with the PDE profile found. The proliferation enhancing effect of the PDE4 inhibitors was partly mimicked by the cyclic AMP analogues dibutyryl (db) cyclic AMP and 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole-3',5'-cyclic monophosphorothioate, Sp-isomer (dcl-cBIMPS), respectively. However, at concentrations exceeding 100 microM db-cyclic AMP suppressed B lymphocyte proliferation, probably as a result of cytotoxicity. Prostaglandin E2 (PGE2, 1 microM) and forskolin (10 microM) did not affect B cell proliferation, even when given in combination with rolipram. 6. Inhibition of protein kinase A (PKA) by differentially acting selective inhibitors (KT 5720, Rp-8-Br-cyclic AMPS) decreased the proliferative response of control cells and reversed the proliferation enhancing effects of rolipram. 7. Importantly, PDE4 activity in LPS/IL-4-activated B lymphocytes decreased by about 50% compared to unstimulated control values. 8. We conclude that an increase in cyclic AMP, mediated by down-regulation of PDE4 activity, is involved in the stimulation of B cell proliferation in response to LPS/IL-4. B cell proliferation in response to a mitogenic stimulus can be further enhanced by pharmacological elevation of cyclic AMP.

Phenylethanolamine N-methyltransferase mRNA in rat spleen and thymus

Phenylethanolamine N-methyltransferase (PNMT), the final enzyme in the biosynthesis of epinephrine, has been detected in rat and human spleen with radioenzymatic assays, but the presence of PNMT has not been examined in other lymphoid tissues. Using the reverse transcription polymerase chain reaction (RT-PCR) and Southern blot analysis, we tested for PNMT mRNA in rat spleen and thymus. A single PCR fragment from spleen, thymus, adrenal and brainstem gave a strong hybridization signal with a PNMT cDNA probe, whereas a PCR fragment from liver was only faintly visible on Southern blots. These findings indicate that the PNMT gene is expressed in spleen and thymus and raise the possibility that lymphoid organs synthesize epinephrine as an intrinsic regulator.

Persistent T lymphocyte rhythms despite suppressed circadian clock outputs in rats

Circadian rhythms in circulating leukocyte and lymphocyte counts persisted with halved amplitudes in constant light (LL) of 300 lx intensity for 8 wk, whereas circadian rhythms in body temperature, locomotor activity, and plasma catecholamines were completely suppressed. Subsequent exposure to constant darkness (DD) normalized all circadian rhythms within 2 wk. Rhythms in circulating T lymphocyte subsets were studied in LL or DD using double labeling with monoclonal antibodies and flow cytometry. Circadian rhythms were suppressed for leukocytes and lymphocytes but were maintained for both T helper cells (Th) and T cytotoxic cells (Ts) lymphocytes after 11 wk in LL. A group 24-h rhythm was only validated for total lymphocytes after 16 wk in LL. However, individual total, Th, and Ts lymphocytes maintained their usual respective phase relationships in each rat. The alteration of immune cell circulatory rhythms likely stemmed from a progressive loss of circadian synchronization among rats kept in LL. Conversely, after 11 or 16 wk in DD, leukocytes and lymphocyte subsets circadian rhythms were maintained. Thus catecholamines do not drive circulatory T cell rhythms. The loss of coupling between T lymphocyte rhythms and three major outputs of the circadian system further supports the hypothesis of an independent immunologic oscillator.

Neuroimmunomodulation via limbic structures--the neuroanatomy of psychoimmunology

During the last 20 years, mutual communications between the immune, the endocrine and the nervous systems have been defined on the basis of physiological, cellular, and molecular data. Nevertheless, a major problem in the new discipline "Psychoneuroimmunology" is that controversial data and differences in the interpretation of the results make it difficult to obtain a comprehensive overview of the implications of immunoneuroendocrine interactions in the maintenance of physiological homeostasis, as well as in the initiation and the course of pathological conditions within these systems. In this article, we will first discuss the afferent pathways by which immune cells may affect CNS functions and, conversely, how neural tissues can influence the peripheral immune response. We will then review recent data, which emphasize the (patho)physiological roles of hippocampal-amygdala structures and the nucleus accumbens in neuroimmunomodulation. Neuronal activity within the hippocampal formation, the amygdaloid body, and the ventral parts of the basal ganglia has been examined most thoroughly in studies on neuroendocrine, autonomic and cognitive functions, or at the level of emotional and psychomotor behaviors. The interplay of these limbic structures with components of the immune system and vice versa, however, is still less defined. We will attempt to review and discuss this area of research taking into account recent evidences for neuroendocrine immunoregulation via limbic neuronal systems, as well as the influence of cytokines on synaptic transmission, neuronal growth and survival in these brain regions. Finally, the role of limbic structures in stress responses and conditioning of immune reactivity will be commented. Based on these data, we propose new directions of future research.