beta-Adrenoreceptors display different efficiency on lymphocyte subpopulations

Ageing and the Autonomic Nervous System

The vertebrate nervous system is divided into central (CNS) and peripheral (PNS) components. In turn, the PNS is divided into the autonomic (ANS) and enteric (ENS) nervous systems. Ageing implicates time-related changes to anatomy and physiology in reducing organismal fitness. In the case of the CNS, there exists substantial experimental evidence of the effects of age on individual neuronal and glial function. Although many such changes have yet to be experimentally observed in the PNS, there is considerable evidence of the role of ageing in the decline of ANS function over time. As such, this chapter will argue that the ANS constitutes a paradigm for the physiological consequences of ageing, as well as for their clinical implications.

Propranolol Suppresses the T-Helper Cell Depletion-Related Immune Dysfunction in Cirrhotic Mice

Bacterial translocation (BT) and splenomegaly contribute to cirrhosis-associated immune dysfunction (CAID) including T cell depletion, infection, and chronic inflammation. β-blockers have been reported to decrease BT and improve splenomegaly. This study explores the modulation of β1 and β2 adrenergic receptors (ADRB1/ADRB2) by propranolol treatment on the peripheral and splenic immune dysfunction of cirrhotic mice. In vivo experiments were performed in bile duct ligation (BDL)- and thioacetamide (TAA)-cirrhotic mice receiving two weeks of propranolol treatment. Acute effects of propranolol were evaluated in T-helper (Th) cells isolated from spleen of cirrhotic mice. Over-expression of β1 and β2 adrenergic receptors (ADRB1/ADRB2) in spleen and T lymphocytes was associated with high peripheral/splenic lipopolysaccharide binding protein levels. Moreover, a decrease in Th cells percentage, increase in Treg subset, and cytokines were accompanied by increased apoptosis, proliferation, and reduced white pulp hyperplasia in cirrhotic mice, which were counteracted by propranolol treatment. The Th-cell depletion, systemic inflammation, BT, and infection were improved by chronic propranolol treatment. Acute propranolol treatment inhibited apoptosis, Treg-conditioned differentiation, and promoted Th2-conditioned differentiation through ADRB-cyclic adenosine monophosphate (cAMP) signals in cirrhotic mice. In conclusion, suppression of ADRB1 and ADRB2 expressions in spleen and splenic T lymphocytes by acute and chronic propranolol treatment ameliorate systemic and splenic immune dysfunction in cirrhosis.

Propranolol for the treatment of vascular sarcomas

Vascular sarcomas are abnormal proliferations of endothelial cells. They range from benign hemangioma to aggressive angiosarcoma, and are characterized by dysregulated angiogenic signaling. Propranolol is a β-adrenergic receptor inhibitor that has demonstrated clinical efficacy in benign infantile hemangioma, and is now being used experimentally for more aggressive vascular sarcomas and other cancers. In this review, we discuss the use of propranolol in targeting these receptors in vascular tumors and other cancers.

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.

EFFECTS OF BETA-ADRENOCEPTOR BLOCKADE ON THE PHENOTYPIC CHARACTERISTICS OF THYMOCYTES AND PERIPHERAL BLOOD LYMPHOCYTES

The study revealed that beta-adrenoceptor blockade with propranolol (0.40 mg/100 g/day, s.c.) in adult male DA rats: (i) increased the thymocyte proliferation and apoptosis, (ii) caused disturbances in kinetics of T cell differentiation leading to distinguishable changes in relative proportion of thymocytes at distinct maturational steps and to an expansion of the most mature single positive (CD4+, CD8+) thymocyte pool, (iii) affected the relative proportion of neither CD4+ nor CD8+ peripheral blood lymphocytes (PBL), and (iv) augmented the relative number of CD8+CD25+ cells. Thus, the results suggest the role of beta-adrenoceptors in fine-tuning of T cell maturation, and, possibly, distribution and activation of distinct PBL subsets.

Sympathetic modulation of immunity: relevance to disease

Optimal host defense against pathogens requires cross-talk between the nervous and immune systems. This paper reviews sympathetic-immune interaction, one major communication pathway, and its importance for health and disease. Sympathetic innervation of primary and secondary immune organs is described, as well as evidence for neurotransmission with cells of the immune system as targets. Most research thus far has focused on neural-immune modulation in secondary lymphoid organs, has revealed complex sympathetic modulation resulting in both potentiation and inhibition of immune functions. SNS-immune interaction may enhance immune readiness during disease- or injury-induced 'fight' responses. Research also indicate that dysregulation of the SNS can significantly affect the progression of immune-mediated diseases. However, a better understanding of neural-immune interactions is needed to develop strategies for treatment of immune-mediated diseases that are designed to return homeostasis and restore normal functioning neural-immune networks.

Characterization of thymocyte phenotypic alterations induced by long-lasting beta-adrenoceptor blockade in vivo and its effects on thymocyte proliferation and apoptosis

Adult male Wistar rats were subjected to propranolol (P, 0.40 mg/100 g/day) or saline (S) administration (controls) over 14 days. The expression of major differentiation molecules on thymocytes and Thy-1 (CD90) molecules, which are shown to adjust thymocyte sensitivity to TCRalphabeta signaling, was studied. In addition, the sensitivity of thymocytes to induction of apoptosis and concanavalin A (Con A) signaling was estimated. The thymocytes from P-treated (PT) rats exhibited an increased sensitivity to induction of apoptosis, as well as to Con A stimulation. Furthermore, P treatment produced changes in the distribution of thymocyte subsets suggesting that more cells passed positive selection and further differentiated into mature CD4+ or CD8+ single positive (SP) TCRalphabeta(high) cells. These changes may, at least partly, be related to the markedly increased density of Thy-1 surface expression on TCRalphabeta(low) thymocytes from these rats. The increased frequency of cells expressing the CD4+25+ phenotype, which has been shown to be characteristic for regulatory cells in the thymus, may also indicate alterations in thymocyte selection following P treatment. Inasmuch as positive and negative selections play an important role in continuously reshaping the T-cell repertoire and maintaining tolerance, the hereby presented study suggests that pharmacological manipulations with beta-AR signaling, or chemically evoked alterations in catecholamine release, may interfere with the regulation of thymocyte selection, and consequently with the immune response.

Altered beta-adrenoceptor function associated to protein kinase C activation in hyperproliferative T lymphocytes

beta-Adrenoceptor (betaAR) expression and function as well as its modulation via intracellular transduction signals, were analyzed on the T cell lymphoma BW5147. Independently to the kinetic of proliferation and relative to the number of receptors displayed in normal T lymphocytes, BW5147 cells displayed a decreased number of betaAR, uncoupled to adenylate cyclase, but coupled to protein kinase C stimulation. This last effect was impaired by a beta-antagonist and by blockers of the enzymatic pathways involved in T lymphocyte proliferation, inducing a recovery of betaAR sites. Down-regulation of betaAR would implicate the loss of a negative neuroimmune control mechanism for lymphocyte proliferation. The coupling of the remaining sites to a positive signal for cellular activation, would contribute to establish an hyperproliferative state.

Mechanisms of conditioned immunomodulation

This article presents some recent work from our laboratory indicating that multiple physiological systems play a role in conditioned immunomodulation. The first study shows that naltrexone, but not N-methylnaltrexone, blocks the suppressive effects of an aversive conditioned stimulus on Con-A-induced proliferation and natural killer cell activity of splenic lymphocytes. This finding indicates that central opioid activity is involved in the conditioned effects. The second study shows that the beta-adrenergic antagonists atenolol and ICI-118,551 block of the suppressive effects of an aversive conditioned stimulus on Con-A-induced proliferation, but have no effect on natural killer cell activity. This result indicates the involvement of the adrenergic system in a subset of the conditioned effects. Collectively, these experiments provide evidence that both the opioid system and the sympathetic nervous system are involved in conditioned immunomodulatory changes elicited by an aversive conditioned stimulus.

Selective coupling of beta 2-adrenergic receptor to hematopoietic-specific G proteins

The coupling of the beta 2-adrenergic receptor (AR) to the alpha subunits of the Gq class of G proteins was investigated in a cotransfection system. COS-7 cells cotransfected with the beta 2-AR cDNA and the G alpha 15 or G alpha 16 cDNA showed marked norepinephrine-induced increases in accumulation of inositol phosphates in a concentration-dependent manner. However, cells cotransfected with the cDNA encoding G alpha q, G alpha 11, or G alpha 14 instead of G alpha 16 gave no ligand-dependent activation of phospholipase C (PLC). The facts that the beta-AR agonist isoprenaline can also induce activation of PLC in cells coexpressing beta 2-AR and G alpha 16 and that the beta 2-AR-specific antagonist propranolol can block norepinephrine-induced activation of PLC in these cotransfected cells further indicate that it is the beta 2-AR that mediates the activation of phospholipase C in these cotransfected cells. To test the possibility of involvement of G beta gamma, a G beta gamma antagonist, G gamma 3 mutant with substitution of a Ser residue for the C-terminal Cys residue, was used because this protein, when expressed in COS-7 cells, can inhibit only G beta gamma-mediated but not G alpha-mediated activation of PLC. The result that the G gamma 3 mutant could not inhibit beta 2-adrenergic receptor-mediated activation of PLC in cells cotransfected with the G alpha 16 cDNA suggests that G beta gamma is unlikely to be a major mediator of beta 2-adrenergic receptor-induced activation of PLC. Thus, we conclude that the beta 2-adrenergic receptor can specifically couple to G alpha 15 and G alpha 16, but not to G alpha q, G alpha 11, or G alpha 14 to activate PLC.

Beta-adrenergic receptor-mediated calcium mobilization in the human Jurkat T cell line

The regulation of Ca2+ mobilization by beta-adrenergic receptor in the human Jurkat T cell line was investigated. Jurkat cells had a single class of beta-adrenergic receptor binding sites. Isoproterenol (ISP) caused the increase in cytosolic free Ca2+ concentration ([Ca2+]i) in a dose-dependent manner. In the absence of extracellular Ca2+, the pretreatment with OKT3, an anti-CD3 antibody, did not affect a transient increase in [Ca2+]i induced by the subsequent addition of ISP, and vice versa. On the other hand, the pretreatment with thapsigargin abolished the response of [Ca2+]i to the subsequent additions of ISP and OKT3. In permeabilized Jurkat cells, the addition of cAMP released Ca2+ from the intracellular Ca2+ pool. Neither nimodipine nor H8, a protein kinase A inhibitor, affected the increase in [Ca2+]i induced by ISP. The results suggest that cAMP accumulated by the activation of beta-adrenergic receptor may directly release Ca2+ from the inositol trisphosphate-insensitive intracellular Ca2+ pool in Jurkat T cells.

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

Adrenoceptors are heterotrimeric glycoproteins that bind specific endogenous ligands, such as the sympathetic neurotransmitter norepinephrine and the neurohormone epinephrine. Ligand binding to an adrenoceptor expressed on the cell surface initiates a cascade of biochemical and molecular responses inside the cell that lead to a change in cellular activity. Initially, the stimulation of an adrenoceptor directly activates G proteins that stimulate enzymes to induce the production of second messengers. The cascade continues as the second messengers activate serine/threonine protein kinases, resulting in either an inhibition or enhancement of cellular activity. The resulting changes in cellular activity are mediated by changes in gene expression that are induced by the phosphorylation of specific transcription factors. Adrenoceptor subtypes are expressed by both T and B lymphocytes. The aim of this review is to summarize and discuss the results from the many studies that have examined the role of adrenoceptor-mediated intracellular signals in the modulation of lymphocyte function. Another aim of this review is to discuss how these studies have advanced our understanding of the mechanisms by which the sympathetic nervous system transmits information to both T and B lymphocytes to maintain immune homeostasis.

Prostanoids synthesis in lymphocyte subpopulations by adrenergic and cholinergic receptor stimulation

The release of eicosanoids (PGE2 and TXB2) as a consequence of specific neurotransmitter receptor agonist stimulation is described herein. The differential expression of beta adrenergic and muscarinic cholinergic receptors on sets and subsets of lymphocytes was first identified. Saturation assays with a specific radioligand for beta adrenergic receptors (3H-DHA) showed that B-, T-, T-helper (Th) and T-suppressor/cytotoxic (Ts/c) lymphocyte enriched populations all displayed beta adrenergic receptors. In contrast, when a specific radioligand for muscarinic cholinergic receptors (3H-QNB) was used, B-lymphocytes showed a lack of high-affinity muscarinic cholinergic receptors, while T-lymphocytes expressed them. Ts/c murine lymphocytes had more muscarinic cholinergic receptors than did Th cells. Specific receptor stimulation by the agonist caused a release of different eicosanoids depending on the cell type. Isoproterenol, triggered the release of TXB2 by B and Th-cells, but had no effect on Ts/c-cells. On the other hand, the muscarinic cholinergic agonist, carbachol only induced the release of PGE2 by Ts/c-cells. These results suggest differences in the expression and function of neurotransmitter receptors in sets and subsets of murine lymphocytes regarding the release of eicosanoids.

Evidence for the involvement of β-adrenergic receptors in conditioned immunomodulation

This study investigates the role of beta-adrenergic receptors in the immunomodulatory effects of a conditioned aversive stimulus (CS). A CS is an environmental event that is not inherently aversive, but acquires aversive properties through pairings with a stimulus such as electric shock. This study evaluated the effects of administration of the beta 1-receptor selective antagonist atenolol, and the beta 2-receptor antagonist ICI 118,551 on conditioned immune alterations. Administration of either antagonist prior to presentation of the CS resulted in a dose-dependent attenuation of the CS-induced suppression of splenic T-cell proliferative response to concanavalin A, phytohemagglutinin, and the combination of ionomycin/phorbol-myristate-acetate. Furthermore, both antagonists dose-dependently attenuated the CS-induced suppression of gamma-interferon production by concanavalin-A (ConA)-stimulated splenocytes. In contrast, neither antagonist significantly attenuated the CS-induced suppression of the B-cell mitogenic response to LPS, interleukin-2 production, natural killer cell activity, or mitogenic responsiveness of blood lymphocytes. Thus it is likely that multiple mechanisms are involved in CS-induced immune alterations and these results clearly implicate beta 1 and beta 2-adrenergic receptors in a subset of immunomodulatory effects.

Beta-adrenoceptor distribution in murine lymphoid cell lines

beta-Adrenergic receptors (R) on several tumor lymphoid cell lines were characterized both directly by beta radioligand binding of 125iodo-cyanopindolol (125I-CYP) to intact cells and membranes, and functionally by assessing hormone-dependent changes in cyclic 3',5' adenosine monophosphate (cAMP) levels on intact cells and measuring adenylate cyclase (a.c.) activity on membranes. Only two lymphoid cell types, BW 5147 (a T cell derived lymphoma cell line) and TIB 221 (a B cell derived line) displayed significant amounts of beta-adrenergic R by 125I-CYP specific binding. Despite this, no stimulation of the a.c. activity was found in the presence of beta-adrenergic agonists in these cells in comparison with native lymphocytes or cells of the well-known S49 cell line used as a positive control. beta-Adrenoceptor specific uncoupling was confirmed by aluminum tetrafluoride (AlFl4) direct activation of the a.c. system in the beta R-bearing cell membranes and by an increase in cAMP production induced by PGE1, another hormone that activates the a.c. Structural characterization of beta-adrenoceptors by photoaffinity-labeling demonstrates that uncoupling was not due to a structural alteration of the beta-adrenergic R expressed in these lymphoma cell lines, as these R gave similar results as native or S49 cells. It can be concluded that functional beta-adrenoceptors are absent in these lymphoma cells. The possible implication of alternative transmission pathways and original neuroendocrine control in tumor lymphoid cells is discussed.

Changes in beta-adrenergic receptor distribution on immunocytes during differentiation: an analysis of T cells and macrophages

The ability of cells of the immune system, immunocytes, to receive signals from the nervous as well as the endocrine system is dependent on the cells' expression of receptors for neurotransmitters and neurohormones. The number of receptors, especially beta adrenergic receptors (BARs), varies with the functional subset of immunocytes. However, little is known about how receptor number may vary during the life span (stem cell to mature activated immunocyte) of a given cell type. In this study, we have addressed this question by examining the affinities (Kd's) and the changes in receptor number (Bmax) on (1) clones of T cells and macrophages, (2) fresh thymocytes and splenocytes before and after activation with Concanavalin A (Con A) and phorbol myristate acetate (PMA)/Ca2+ ionophore (A23187), and (3) the cloned human monocyte U937 and the murine thymic lymphoma cell BW5147, in the presence and absence of PMA and A23187 ionophore. Drug treatments of fresh and cloned immunocytes alter the number but not the affinity of beta-receptors. Con A increases the number of beta-adrenergic receptors per cell, whereas PMA/ionophore decreases it. Similar decreases in BAR number are induced by PMA on cell lines BW5147 and U937. These data indicate that changes in receptor number can be regulated with different states of cell maturation and function. Thus, the immunological status of a given cell can influence the expression of BARs, thereby modulating its ability to respond to signals from the nervous and endocrine systems.

Active alpha 2 and beta adrenoceptors in lymphocytes from patients with chronic lymphocytic leukemia

A single population of alpha 2 adrenoceptors was characterized in intact B lymphocytes from patients with chronic lymphocytic leukemia (B-CLL) by binding and saturation studies with 3H labelled yohimbine and by competition studies with alpha adrenergic antagonists. While the affinity of B-CLL alpha 2 adrenoceptors was low (KD: 9.81 nM-20.98 nM), each cell expressed a large number of receptors. No binding of the alpha 1 adrenoceptor antagonist prazosin was observed and the binding properties of beta adrenergic receptors (assayed with 3H-labelled dihydroalprenolol), were similar to those described for normal lymphocytes. Reaction of B-CLL with the beta adrenergic agonist isoproterenol raised the levels of cAMP in 11/13 patients tested, and in 8 of these, incubation with the alpha 2 adrenergic agonist clonidine prevented the effect and reduced the basal cAMP levels. The presence of active alpha 2 adrenoceptors on B-CLL lymphocytes may be involved in the regulation of metabolic pathways that affect cell functions and favor neoplastic growth.

Influence of adrenergic agonists and antagonists on lymphokine secretion in vitro

Spleen cells of mice and lymph node lymphocytes of rats were cultured with epinephrine, norepinephrine and alpha- and beta-adrenergic drugs to determine effects on lymphokine secretion. After an incubation of 4.5 h it was found that the naturally occurring catecholamines and adrenergic drugs (isoprenaline, orciprenaline, terbutaline, norfenephrine, phenylephrine, clonidine, dobutamine) could induce the secretion of charge-changing lymphokines and lymphokines that stimulate the migration of lymphocytes. The beta-blocker propranolol inhibited the lymphokine secretion evoked by epinephrine and by beta-adrenergic agonists, whereas the alpha-blocker phentolamine antagonized the effects elicited by alpha-adrenergic drugs. Phenylethylamine also induced a significant secretion of lymphokines. Two non-phenylethylamines had no effect. The stimulatory capacity of adrenergic agonists, the inhibitory activity of the appropriate antagonists and the comparison with two non-phenylethylamines support the hypothesis on specific influence of catecholamines on the lymphocyte function.

Beta-adrenergic receptors on human suppressor, helper, and cytolytic lymphocytes

Using the radioligand beta-adrenergic blocker [125I]cyanopindolol (ICYP), we have characterized the beta-adrenergic receptors on Leu 3+ (T helper [TH]), Leu 2+, 9.3- (T suppressor [Ts]) and Leu 2+, 9.3+ (T cytolytic [Tc]) subsets of human lymphocytes. Peripheral blood T cells were isolated by rosetting, and then subsets were purified by their affinities to monoclonal antibodies against their Leu 3 and 9.3 markers. ICYP binding to the subsets was saturable with time and with concentration; the binding was stereoselective and reversible by beta-adrenergic antagonists. A biological response produced by beta agonists increased intracellular concentrations of cAMP and corresponded to the number of binding sites. Each subset of cells had a number of binding sites, which was characteristic for the given subset. The data indicate that the density of distribution of beta-adrenergic receptors was not homogeneous on the precursors of phenotypically and functionally distinct T cells (Ts approximately 2900, Tc approximately 1800 and TH approximately 750 binding sites). The displacement studies using beta-adrenergic agonists were performed on the cytolytic and suppressor T cell subsets, suggesting that the receptors were mainly of the beta-2 type. The immunobiological significance of such selective distribution of numbers and subtypes of beta-adrenergic receptors on distinct T cell subsets is under investigation.