Immunochemical and immunocytochemical characterization of cholinergic markers in human peripheral blood lymphocytes

Basic and clinical aspects of non-neuronal acetylcholine: expression of an independent, non-neuronal cholinergic system in lymphocytes and its clinical significance in immunotherapy

Lymphocytes possess all the components required to constitute an independent, non-neuronal cholinergic system. These include acetylcholine (ACh); choline acetyltransferase (ChAT), its synthesizing enzyme; and both muscarinic and nicotinic ACh receptors (mAChRs and nAChRs, respectively). ACh modifies T and B cell function via both mAChR- and nAChR-mediated pathways. Stimulation of lymphocytes with the T cell activator phytohemagglutinin, protein kinase C activator phorbol ester, or cell surface molecules enhances the synthesis and release of ACh and up-regulates ChAT and/or M(5) mAChR gene expression. Furthermore, animal models of immune disorders exhibit abnormal lymphocytic cholinergic activity. The cholesterol-lowering drug simvastatin attenuates the lymphocytic cholinergic activity of T cells by inhibiting LFA-1 signaling in a manner independent of its cholesterol-lowering activity. This suggests that simvastatin exerts its immunosuppressive effects in part by modifying lymphocytic cholinergic activity. Nicotine, an active ingredient of tobacco, ameliorates ulcerative colitis but exacerbates Crohn's disease. Expression of mRNAs encoding the nAChR alpha7 and alpha5 subunits are significantly diminished in peripheral mononuclear leukocytes from smokers, as compared with those from nonsmokers. In addition, long-term exposure of lymphocytes to nicotine reduces intracellular Ca(2+) signaling via alpha7 nAChR-mediated pathways. In fact, studies of humoral antibody production in M(1)/M(5) mAChR-deficient and alpha7 nAChR-deficient animals revealed the role of lymphocytic cholinergic activity in the regulation of immune function. These results provide clues to understanding the mechanisms underlying immune system regulation and could serve as the basis for the development of new immunomodulatory drugs.

Presence of a marked nonneuronal cholinergic system in human colon: study of normal colon and colon in ulcerative colitis

BACKGROUND

The body has not only a neuronal but also a nonneuronal cholinergic system. Both systems are likely to be very important, particularly in inflammatory conditions. The patterns and importance of the nonneuronal cholinergic system in patients with ulcerative colitis (UC) are largely unknown.

METHODS

The colons of UC and non-UC patients were examined for expression patterns of choline acetyltransferase (ChAT), vesicular acetylcholine transporter (VAChT), and the muscarinic receptor of the M(2) subtype.

RESULTS

ChAT and VAChT immunoreactions and mRNA reactions for ChAT were detected in epithelial and endocrine cells, in cells in the lamina propria, and in blood vessel walls. Furthermore, a marked M(2) immunoreaction was noted for epithelium, blood vessel walls, and smooth musculature. ChAT and VAChT immunoreactions were significantly higher in endocrine and epithelial cells, respectively, in non-UC mucosa than in UC mucosa. On the other hand, there was a tendency toward higher M(2) levels in epithelium of UC patients.

CONCLUSIONS

There is a pronounced nonneuronal cholinergic system in the colon, which has previously been ignored when discussing cholinergic influences in UC. Furthermore, it is evident that certain changes in the nonneuronal cholinergic system occur in response to inflammation/derangement in UC. Cholinergic effects in the colon can be considered to be related not only to nerve-related effects but also to effects of acetylcholine from nonneuronal local cells. Thus, the recently discussed phenomenon of a "cholinergic antiinflammatory pathway" in the intestine may have a pronounced nonneuronal component.

Variation in the expression of inflammatory markers and neuroreceptors in human conjunctival epithelial cells

The purpose of this research was to investigate the role of neurogenic involvement in the etiopatho-genesis of ocular surface inflammation, with the final goal of identifying new potential anti-inflammatory agents. We describe the presence of two "classic" markers of inflammation (HLA-DR and ICAM-1) and some neuroreceptors in cultured human conjunctival epithelial cells under basal and pro-inflammatory conditions. Two markers of inflammation (HLA-DR, ICAM-1) and several neuroreceptor subtypes (M1-, M2-, and M3-muscarinic; alpha1A-, alpha1B-, alpha1D-, alpha2A-, alpha2B-, alpha2C-, beta1-, beta2-, and beta3-adrenergic) were analyzed in a normal human conjunctival epithelial cell line (IOBA-NHC). These markers were studied in basal conditions and under the influence of two pro-inflammatory cytokines: tumor necrosis factor alpha (TNF-alpha) and/or interferon gamma (IFN-gamma). Immunofluorescence (confocal microscopy), western blotting, or flow cytometry techniques were used. In basal conditions, epithelial cells expressed all inflammatory markers except HLA-DR. The addition of IFN-gamma enhanced expression of HLA-DR, ICAM-1, and M2-muscarinic receptor. TNF-alpha up-regulated the expression of ICAM-1. When epithelial cells were incubated in the presence of both cytokines together, the cell surface expression of HLA-DR, ICAM-1, alpha1B-, and alpha2B-adrenergic receptors was increased. Cultured human conjunctival epithelial cells have been shown to be susceptible to up-regulation of the expression of inflammatory markers and cell membrane expression of some neuroreceptors under pro-inflammatory conditions. Consequently, pharmacologic neuro-modulation could have a role in the comprehensive management of ocular surface inflammation.

Diminished antigen-specific IgG1 and interleukin-6 production and acetylcholinesterase expression in combined M1 and M5 muscarinic acetylcholine receptor knockout mice

Immunological activation of T cells enhances synthesis of acetylcholine (ACh) and transcription of choline acetyltransferase (ChAT), M5 muscarinic ACh receptor (mAChR) and acetylcholinesterase (AChE). Stimulation of mAChRs on T and B cells causes oscillating Ca(2+)-signaling and up-regulation of c-fos expression; moreover, M1 mAChRs play a crucial role in the differentiation of CD8(+) T cells into cytolytic T lymphocytes. Collectively, these findings suggest that immune cell function is regulated by its own cholinergic system. Bearing that in mind, we tested whether immune function can be regulated via mAChR-mediated pathways by immunizing combined M1 and M5 mAChR knockout (M1/M5 KO) and wild-type (WT) C57BL/6JJcl mice with ovalbumin (OVA) and measuring serum IgG1 and IgM 1 wk later. We found that serum levels of total and anti-OVA-specific IgG1 were significantly lower in M1/M5 KO than WT mice, though there was no difference in serum levels of total and anti-OVA-specific IgM between the two genotypes. Secretion of interleukin (IL)-6 from activated spleen cells was significantly reduced in M1/M5 KO mice, whereas there was no significant change in gamma interferon secretion. Expression of AChE mRNA was significantly reduced in activated spleen cells from M1/M5 KO mice. These results suggest that M1 and/or M5 mAChRs are involved in regulating cytokine (e.g., IL-6) production, leading to modulation of antibody class switching from IgM to IgG1, but are not involved in the initial generation of the antibody response. They also support the notion that a non-neuronal cholinergic system is involved in regulating immune cell function.

Targeting the cholinergic system as a therapeutic strategy for the treatment of pain

Acetylcholine mediates its effects through both the nicotinic acetylcholine receptors (ligand-gated ion channels) and the G protein-coupled muscarinic receptors. It plays pivotal roles in a diverse array of physiological processes and its activity is controlled through enzymatic degradation by acetylcholinesterase. The effects of receptor agonists and enzyme inhibitors, collectively termed cholinomimetics, in antinociception/analgesia are well established. These compounds successfully inhibit pain signaling in both humans and animals and are efficacious in a number of different preclinical and clinical pain models, suggesting a broad therapeutic potential. In this review we examine and discuss the evidence for the therapeutic exploitation of the cholinergic system as an approach to treat pain.

Analysis of CD8+ T cell-mediated anti-viral responses in mice with targeted deletions of the M1 or M5 muscarinic cholinergic receptors

A number of studies have demonstrated that non-neuronal acetylcholine can play a role in the regulation of T cell function. Recently, we reported that CD8(+) T cells, from mice with a targeted deletion of the M(1) muscarinic receptor, had a defect in differentiating into cytolytic T lymphocytes when stimulated in vitro. In the current report, we analyze the in vivo function of CD8(+) T cells from mice with targeted deletions of either M(1) or M(5) muscarinic receptors. M(1) or M(5) knockout mice were infected with either lymphocytic choriomeningitis virus or vesicular stomatitis virus. Expansion of anti-viral CD8(+) T cells was monitored by staining with tetramer reagents specific for the immunodominant peptides of the viruses. No defect in expansion of CD8(+) T cells was observed in either M(1) or M(5) knockout mice. The extent to which one can draw a generalized conclusion that M(1) and M(5) are not involved in anti-viral immunity depends upon issues of antigen strength, genetic background, induction of redundant receptors, and the potential for qualitative defects in the expanded CD8(+) T cells.

Atropine pretreatment enhances airway hyperreactivity in antigen-challenged guinea pigs through an eosinophil-dependent mechanism

Airway hyperreactivity in antigen-challenged animals is mediated by eosinophil major basic protein (MBP) that blocks inhibitory M(2) muscarinic receptors on parasympathetic nerves, increasing acetylcholine release onto M(3) muscarinic receptors on airway smooth muscle. Acutely, anticholinergics block hyperreactivity in antigen-challenged animals and reverse asthma exacerbations in the human, but are less effective in chronic asthma. We tested whether atropine, given before antigen challenge, affected hyperreactivity, M(2) receptor function, eosinophil accumulation, and activation. Sensitized guinea pigs received atropine (1 mg/kg ip) 1 h before challenge and 6 h later. Twenty-four hours after challenge, animals were anesthetized, vagotomized, paralyzed, and ventilated. Airway reactivity to electrical stimulation of the vagi and to intravenous acetylcholine was not altered by atropine pretreatment in nonsensitized animals, indicating that atropine was no longer blocking postjunctional muscarinic receptors. Antigen challenge induced airway hyperreactivity to vagal stimulation that was significantly potentiated by atropine pretreatment. Bronchoconstriction induced by acetylcholine was not changed by antigen challenge or by atropine pretreatment. M(2) receptor function was lost in challenged animals but protected by atropine pretreatment. Eosinophils in bronchoalveolar lavage and within airway tissues were significantly increased by challenge but significantly reduced by atropine pretreatment. However, extracellular MBP in challenged airways was significantly increased by atropine pretreatment, which may account for reduced eosinophils. Depleting eosinophils with antibody to IL-5 before challenge prevented hyperreactivity and significantly reduced MBP in airways of atropine-pretreated animals. Thus atropine pretreatment potentiated airway hyperreactivity by increasing eosinophil activation and degranulation. These data suggest that anticholinergics enhance eosinophil interactions with airway nerves.

Distribution of choline acetyltransferase immunoreactivity in the alimentary tract of the barnacle Balanus amphitrite (Cirripedia, Crustacea)

To date only peptidergic innervation has been described in the alimentary tract of barnacles. In the present work the presence and distribution of choline acetyltransferase (ChAT), the acetylcholine (ACh) synthesizing enzyme, was investigated by immunohistochemistry in the alimentary tract of the adult barnacle Balanus amphitrite. Numerous ChAT-immunoreactive (IR) cells and a net of ChAT-IR cytoplasmic processes were localized inside the epithelium of the posterior midgut, close to the basement membrane; no IR nerve endings were detected in the midgut longitudinal and circular muscle bundles. Epithelial neurons or endocrine cells in the gut epithelium have been described in some invertebrate species belonging to different taxa and their peptidergic features are reported in the literature. Our results point out the presence of neuroepithelial cells also in the gut epithelium of barnacles; moreover, for the first time, a cholinergic feature is suggested for this cell type. These data seem to indicate the involvement of ACh in the gut functions of barnacle and suggest that the barnacle alimentary tract is more complex than previously thought and requires further study.

Acetylcholine and molecular components of its synthesis and release machinery in the urothelium

OBJECTIVES

Previous studies provided indirect evidence for urothelial synthesis and release of acetylcholine (ACh). We aimed to determine directly the ACh content in the urothelium and to characterize the molecular components of its synthesis and release machinery.

METHODS

The study was performed on mouse bladder and abraded urothelium, and human mucosal bladder biopsies. ACh content was measured by high-performance liquid chromatography-electrochemical. Reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry served to investigate expression of ACh-synthesizing enzymes-choline acetyltransferase (ChAT) and carnitine acetyltransferase (CarAT)-vesicular ACh transporter (VAChT), and polyspecific organic cation transporters (OCTs; isoforms 1-3). Transfected cells served to investigate whether the anticholinergic drug trospium chloride interferes with ACh-transporting OCTs.

RESULTS

ACh is present in the urothelium in a nanomolar range per gram of wet weight. RT-PCR data support the presence of CarAT but not ChAT. VAChT, used by neurons to shuffle ACh into synaptic vesicles, is detected in subepithelial cholinergic nerve fibres, but not by RT-PCR or immunohistochemistry in the urothelium. OCT1 and OCT3 are expressed by the urothelium. The quarternary ammonium base trospium chloride inhibits cation transport by OCTs with a potency rank order of OCT2 (IC(50)=0.67+/-0.42micromol/l)>OCT1 (IC(50)=6.2+/-2.1micromol/l)>OCT3 (IC(50)=871+/-177micromol/l).

CONCLUSIONS

This study demonstrates a urothelial non-neuronal cholinergic system that differs widely from that of neurons with respect to molecular components of the ACh synthesis and release machinery. Consequently, these two systems might be differentially targeted by pharmacologic approaches.

Adrenergic and Cholinergic Control in the Biology of Epidermis: Physiological and Clinical Significance

The presence of an autocrine adrenergic and cholinergic intra/intercellular signal transduction network in the human epidermis contributes significantly to homeostatic and compensatory responses regulating vital functions in keratinocytes and melanocytes. The ligands produced control autocrine and paracrine loops to initiate responses through cognate receptors expressed within the same or adjacent cells. The epidermal adrenergic signal controls calcium homeostasis, cell growth, differentiation, motility, and pigmentation via the beta2 and alpha1 adrenoceptors. The cholinergic system is highly complex comprising both nicotinic and muscarinic receptors with multiple subtypes and this system plays an important role in keratinocyte cell cycle progression, differentiation, directional migration, adhesion, and apoptotic secretion. Moreover, lymphocytes also express adrenergic and cholinergic receptors. Both types of signal transduction receptors are coupled to classical intracellular second messenger pathways, including cAMP-, cGMP-, and calcium-mediated downstream responses. To date, it has been recognized that several dermatoses such as psoriasis, atopic dermatitis, Mal de Meleda, vitiligo, palmoplantar pustulosis, and pemphigus may be mediated, in part, by the non-neuronal adrenergic/cholinergic systems. A detailed understanding of the physiology and pathophysiology of the adrenergic/cholinergic network in the skin could offer the development of specific drugs for novel treatment modalities.

The vesicular acetylcholine transporter is present in melanocytes and keratinocytes in the human epidermis

The human epidermis holds the full machinery for cholinergic signal transduction. However, the presence of the vesicular transporter (vesicular acetylcholine (ACh) transporter (VAChT)) for both choline and ACh has never been shown in this compartment. The results of this study confirm the presence of VAChT in cutaneous nerves and in both epidermal melanocytes and keratinocytes as well as in their nuclei using immunofluorescence labelling in situ and in vitro, Western blot analysis of cellular and nuclear extracts and reverse transcription-PCR. These results underline that ACh/choline transport in the non-neuronal epidermis is no different from the neuronal pathway. However, the function of VAChT in the nucleus remains to be shown.

Relationship between platelet monoamine oxidase-B (MAO-B) activity and mercury exposure in fish consumers from the Lake St. Pierre region of Que., Canada

Mercury (Hg) is a widespread neurotoxic compound that bio-accumulates in fish and marine mammals. Monoamine oxidase (MAO; EC 1.4.3.4) regulates biogenic amine concentration in the brain and peripheral tissue and has been shown to be a molecular target of Hg compounds in animal models. Blood platelet monoamine oxidase-B (MAO-B) activity may reflect MAO function in the central nervous tissue. Therefore, the objective of this study was to evaluate the relationship between platelet MAO-B and Hg exposure in fish-eating adults (n=127) living along the St. Lawrence River (Lake St. Pierre, Que., Canada). Hg concentrations were determined in blood and hair samples. A significant negative association was observed between platelet MAO-B activity and blood-Hg (r=-0.193, p=0.029) but not with hair-Hg levels (r=-0.125, p=0.169). Multiple linear regression analysis demonstrated that blood-Hg (beta=-4.6, p=0.011) and heavy smoking (beta=-8.5, p=0.001) were associated with reduced platelet MAO activity in the total population. In addition, this reduction in MAO-B activity appeared to be associated with blood-Hg concentrations above 3.4 microg/L (75th percentile). Possible gender related differences were also observed and are discussed. Our results suggest that MAO-B activity in blood platelets may be a useful tool to assess biochemical effects of Hg exposure in human populations. These changes in platelet MAO-B may reflect enzymatic changes in nervous tissue and should be further investigated as a surrogate marker of neurotoxicity.

Central muscarinic cholinergic regulation of the systemic inflammatory response during endotoxemia

TNF has a critical mediator role in inflammation and is an important therapeutic target. We recently discovered that TNF production is regulated by neural signals through the vagus nerve. Activation of this "cholinergic antiinflammatory pathway" inhibits the production of TNF and other cytokines and protects animals from the inflammatory damage caused by endotoxemia and severe sepsis. Here, we describe a role for central muscarinic acetylcholine receptors in the activation of the cholinergic antiinflammatory pathway. Central muscarinic cholinergic activation by muscarine, the M1 receptor agonist McN-A-343, and the M2 receptor antagonist methoctramine inhibited serum TNF levels significantly during endotoxemia. Centrally administered methoctramine stimulated vagus-nerve activity measured by changes in instantaneous heart-rate variability. Blockade of peripheral muscarinic receptors did not abolish antiinflammatory signaling through the vagus nerve, indicating that peripheral muscarinic receptors on immune cells are not required for the cytokine-regulating activities of the cholinergic antiinflammatory pathway. The role of central muscarinic receptors in activating the cholinergic antiinflammatory pathway is of interest for the use of centrally acting muscarinic cholinergic enhancers as antiinflammatory agents.

Muscarinic acetylcholine receptor subtypes in the rat seminal vesicle

The aim of the present study was to identify the muscarinic acetylcholine receptor (mAChR) mRNA subtypes in the rat seminal vesicle. Furthermore, the mAChR subtypes involved in the contraction of the seminal vesicle were also explored. Reverse transcriptase-polymerase chain reaction (PCR) was performed and five PCR products corresponding to M1-M5 mAChR mRNA subtypes were detected in this tissue. Functional pharmacological studies indicated that the rank order of mAChR antagonists in blocking the contractile effects of carbachol was p-fluoro-hexahydro-sila-difenidol (pF-HHSiD) >> tropicamide > methoctramine = pirenzepine. This antagonist profile indicates that M3 mAChR subtype is predominantly involved in the seminal vesicle contraction. Furthermore, immunohistochemical studies confirmed the presence of the M3 mAChR subtype in the smooth muscle layers. M2 mAChR subtype was also immunolocalized in smooth muscle cells and may be involved in the contraction of this tissue. The presence of M2 and M3 mAChR subtypes in the epithelial cells suggests that these receptors could be involved in the protein secretion. Taken together, the cholinergic neurotransmitter may be a factor controlling contractility and protein secretion in this tissue.

Biochemical characterization of human umbilical vein endothelial cell membrane bound acetylcholinesterase

Acetylcholinesterase is an enzyme whose best-known function is to hydrolyze the neurotransmitter acetylcholine. Acetylcholinesterase is expressed in several noncholinergic tissues. Accordingly, we report for the first time the identification of acetylcholinesterase in human umbilical cord vein endothelial cells. Here we further performed an electrophoretic and biochemical characterization of this enzyme, using protein extracts obtained by solubilization of human endothelial cell membranes with Triton X-100. These extracts were analyzed under polyacrylamide gel electrophoresis in the presence of Triton X-100 and under nondenaturing conditions, followed by specific staining for cholinesterase or acetylcholinesterase activity. The gels revealed one enzymatically active acetylcholinesterase band in the extracts that disappeared when staining was performed in the presence of eserine (an acetylcholinesterase inhibitor). Performing western blotting with the C-terminal anti-acetylcholinesterase IgG, we identified a single protein band of approximately 70 kDa, the molecular mass characteristic of the human monomeric form of acetylcholinesterase. The western blotting with the N-terminal anti-acetylcholinesterase IgG antibody revealed a double band around 66-70 kDa. Using the Ellman's method to measure the cholinesterase activity in human umbilical vein endothelial cells, regarding its substrate specificity, we confirmed the existence of an acetylcholinesterase enzyme. Our studies revealed a predominance of acetylcholinesterase over other cholinesterases in human endothelial cells. In conclusion, we have demonstrated the existence of a membrane-bound acetylcholinesterase in human endothelial cells. In future studies, we will investigate the role of this protein in the endothelial vascular system.

Anti-inflammatory properties of cholinergic up-regulation: A new role for acetylcholinesterase inhibitors

We investigated the anti-inflammatory effects of acetylcholinesterase inhibitors (AChEI) at the cellular and molecular levels. AChEI suppressed lymphocyte proliferation and pro-inflammatory cytokine production, as well as extracellular esterase activity. Anti-inflammatory activity was mediated by the alpha7 nicotinic acetylcholine receptor (neuronal); the muscarinic receptor had the opposite effect. Treatment of the central nervous system (CNS) inflammatory disease, experimental autoimmune encephalomyelitis (EAE), with EN101, an anti-sense oligodeoxynucleotide, targeted to AChE mRNA, reduced the clinical severity of the disease and CNS inflammation intensity. The results of our experiments suggest that AChEI increase the concentration of extracellular acetylcholine (ACh), rendering it available for interaction with a nicotinic receptor expressed on lymphocytes. Our findings point to a novel role for AChEI which may be relevant in CNS inflammatory diseases such as EAE and multiple sclerosis. They also emphasize the importance of cholinergic balance in neurological disorders, such as Alzheimer's disease and myasthenia gravis, in which these drugs are used.

Muscarinic cholinergic receptor subtypes in cerebral cortex of Fisher 344 rats: a light microscope autoradiography study of age-related changes

The density and localization of muscarinic cholinergic M1-M5 receptor subtypes was investigated in frontal and occipital cortex of male Fisher 344 rats aged 6 months (young-adult), 15 months (mature) and 22 months (senescent) by combined kinetic and equilibrium binding and light microscope autoradiography. In 6-month-old rats, the rank order density of muscarinic cholinergic receptor subtypes was M1>M2>M4>M3>M5 both in frontal and occipital cortex. A not homogeneous distribution of different receptor subtypes throughout cerebrocortical layers of frontal or occipital cortex was found. In frontal cortex silver grains corresponding to the M1 and M2 receptor subtypes were decreased in 15- and 22-month-old groups. The M3 receptor density was remarkably and moderately decreased in layers II/III and V, respectively, of rats aged 15 and 22 months. A reduced M4 receptor density was observed in layer I and to a lesser extent in layer V of mature and senescent rats, whereas no age-related changes of M5 receptor were found. In occipital cortex a diminution of M1 receptor was observed in layers II/III and V of mature and senescent rats. The M2 receptor expression decreased in layer I of 15- and 22-month-old senescent rats, whereas M3-M5 receptors were unchanged with exception of a slight decrease of the M4 receptor in layer IV and of M5 receptor in layers II/III. These findings indicate a different sensitivity to aging of muscarinic receptor subtypes located in various cerebrocortical layers. This may account for the difficulty in obtaining relevant results in manipulating cholinoceptors to counter age-related impairment of cholinergic system.

The role of the conjunctival epithelium in ocular allergy

PURPOSE OF REVIEW

The epithelium of target organs is playing an increasing role in allergy. Several studies have shown that epithelial cells participate actively in inflammatory processes. This review will focus on recent advances in the role of conjunctival epithelium in allergy as a potential target for therapeutic interventions.

RECENT FINDINGS

Several studies have already shown the involvement of ocular surface epithelial cells in allergic inflammatory diseases, because they are able to produce and secrete cytokines and chemokines upon stimulation. They also express adhesion molecules as well as receptors for several substances implicated in inflammation. Some studies have also shown that conjunctival epithelial cells express co-stimulatory molecules when they interact with activated T cells, adding more evidence to the important role that epithelial cells play in the pathogenesis of ocular inflammatory diseases. Recent reports have also demonstrated that during inflammatory conditions, conjunctival epithelial cells show an altered expression of their neuroreceptors, suggesting that a modulation of neural regulation may be of therapeutic value.

SUMMARY

The ocular surface epithelium is not just a simple physical barrier to the entrance of foreign bodies. It participates in the allergic inflammatory process by being influenced by inflammatory molecules, and by secreting inflammatory cytokines and chemokines. Moreover, the epithelium not only actively participates in the inflammation process but can also initiate it. This relevant spectrum of actions makes epithelium an attractive target for therapeutic interventions.

Expression and localization of muscarinic acetylcholine receptor subtypes in rat efferent ductules and epididymis

The expression of muscarinic acetylcholine receptor (mAChR) subtypes (M(1)-M(5)) was studied in the rat efferent ductules and epididymis at the mRNA and protein levels. The relative abundance of each mAChR transcript subtype differed depending on the tissue and the epididymal region analyzed. The M(1) mAChR mRNA level was more abundant in the efferent ductules than in the caput and cauda of the epididymis. The M(2) mAChR mRNA level was similar between the efferent ductules and caput of the epididymis and higher in the cauda region. The M(3) mAChR mRNA level was low in the efferent ductules and caput of the epididymis, but high levels were detected in the cauda region. mRNAs for M(4) and M(5) mAChRs were not detected in these tissues. Our studies indicated a variable degree of immunostaining for each mAChR subtype in a cell-type and tissue-specific pattern. M(1) mAChR was detected over the efferent ductule epithelium. M(2) and M(3) mAChRs were observed in the apical region of the ciliated cells. Apical and narrow cells of the initial segment showed distinct staining by M(1) antibody, whereas a supranuclear reaction was noted in the principal cells of the caput of the epididymis. In addition, staining for M(1) and M(2) mAChRs was visible in the apical membrane of some epithelial cells of the cauda region. M(3) mAChR was detected in the peritubular smooth muscle of the efferent ductules and epididymis. Functional studies suggested the involvement of this subtype in epididymal tubule contraction. Thus, the cell-specific expression of the various mAChR subtypes in the efferent ductules and epididymis suggests that these receptors play a role in the modulation of luminal fluid composition and smooth muscle contraction.

Blood cells cholinesterase activity in early stage Alzheimer's disease and vascular dementia

Blood acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) activities have been studied as markers for Alzheimer's disease (AD), but their usefulness as a disease marker is controversial. To determine cholinesterase (ChE) activity during AD progression and whether ChE changes associate to other dementias, ChE activity was measured in lymphocytes, erythrocytes and platelets. Subjects underwent extensive medical and neuropsychological examination. Both early-AD and AD patients had lower AChE activity in lymphocytes compared to control subjects (p < 0.0001). In contrast, erythrocyte AChE activity was higher in patients with vascular dementia (p = 0.004). Low ChE activity in lymphocytes was the best discriminator for AD. Because it was already low at very early stages of AD, ChE could be helpful as an early biomarker of differential diagnosis for the follow-up of patients during their early stages of cognitive impairment before a clinical dementia is established.

Lymphocyte muscarinic receptors and platelet monoamine oxidase-B as biomarkers of CNS function: effects of age and gender in healthy humans

Lymphocyte cholinergic muscarinic receptors (MRs) and platelet monoamine oxidase-B (MAO-B) activity are considered surrogate markers of the same parameters in the central nervous system. Lymphocyte MR binding and platelet MAO-B activity were measured in a consistent number of healthy human adults and analysed according to gender and age. The mean value±S.D. of MR binding neither differed between males (12.2±10.0fmol/10(6)cells, range: 0.5-37.9, n=86) and females (10.7±9.7fmol/10(6)cells, range: 0.5-39.7, n=69) nor among age groups. MAO-B activity was significantly higher in women (geometric mean: 11.3nmol/mgprotein/h, with 65% of values from 7.3 to 17.6; n=43), than in men (7.7nmol/mgprotein/h, with 65% of values from 4.5 to 13; n=95). Males aged 56-66 years displayed a higher, though not statistically significant, basal enzyme activity than younger subjects. Altogether these data indicate gender-related differences in MAO activity, but not in MR binding, and inter-individual differences in the basal values of both peripheral blood markers in healthy subjects.

Sjogren's syndrome

Sjögren's syndrome (SS) is a chronic autoimmune disease affecting the exocrine glands, primarily the salivary and lacrimal glands. It has been suggested that exogenous agents may trigger SS in genetically predisposed individuals. However, at present, the etiology of SS is far from being understood, and no direct evidence for any of these triggers has been presented. The salivary and lacrimal glands from patients with SS harbor unique and highly selected T- and B-cell populations. Disturbance in glandular cell apoptosis may be one possible explanation for the sicca symptoms in SS. However, discrepancies between glandular destruction and salivary flow give rise to processes causing glandular dysfunction preceding or triggering glandular cell destruction. Recent reports suggested autoantibodies inhibiting neuronal innervation of acinar cells and defective water transport to be implicated in salivary secretion deficiency observed in SS. Several types of autoantibodies have been suggested to contribute to the pathogenesis of SS. However, how the tolerance to these structures is broken down is unknown at present. Studies on B-cell activating factor indicated that diminished apoptosis and disturbed B-cell maturation could be responsible for the occurrence of autoreactive B-cells and B-cell hyperreactivity. B-cell activation may also provide a basis for lymphoma development observed in up to 5% of the patients with SS.

Increased lymphocyte dopamine beta-hydroxylase immunoreactivity in Alzheimer's disease: compensatory response to cholinergic deficit?

There is growing interest in the characterization of peripheral blood lymphocytes (PBL) as a biological tool with which to investigate changes in the neurotransmitter-receptor system in neurodegenerative disorders. Here we show a slight decrease in acetylcholinesterase (AChE) and a significant increase in dopamine beta-hydroxylase (DBH) immunoreactivity in the PBL of patients with probable Alzheimer's disease (AD). Therapy with AChE inhibitors completely reversed the increase in DBH immunoreactivity. We hypothesize that the increase in DBH immunoreactivity may represent a compensatory response to cholinergic impairment. Our findings suggest that neurochemical interactions between the noradrenergic and cholinergic systems may be measured at a peripheral level in AD.

The immune system as the sixth sense

One of the truly remarkable discoveries in modern biology is the finding that the nervous system and immune system use a common chemical language for intra- and inter-system communication. This review will discuss some of the pivotal results that deciphered this chemical language. Specifically the nervous and immune systems produce a common set of peptide and nonpeptide neurotransmitters and cytokines that act on a common repertoire of receptors in the two systems. The paper will also review more recent studies that have delineated hardwired and humoral pathways for such bidirectional communication. This is discussed in the context of the idea that the sharing of ligands and receptors allows the immune system to serve as the sixth sense that notifies the nervous system of the presence of entities, such as viruses and bacteria, that are imperceptible to the classic senses. Lastly, this review will suggest ways to apply the newfound knowledge of the sixth sense to understand a placebo effect and to treat human disease.

The role of anticholinergics in chronic obstructive pulmonary disease

Anticholinergics are the bronchodilators of choice in the management of chronic obstructive pulmonary disease (COPD). They work by blocking muscarinic receptors in airway smooth muscle. Cholinergic tone appears to be the only reversible component of COPD. With the discovery of different muscarinic receptor subtypes, the development of more selective anticholinergics is possible. A major advance in this therapeutic area has been the discovery of tiotropium bromide, which has kinetic selectivity for M3 receptors as well as a duration of action of >24 hours. Once-daily administration of tiotropium is well tolerated and has shown significant advantages over ipratropium bromide, given 4 times daily, in the control of COPD.

An in vitro investigation of the effects of the nerve agent pretreatment pyridostigmine bromide on human peripheral blood T-cell function

The current pretreatment against nerve agent poisoning deployed by the UK and US armed forces is the acetylcholinesterase (EC 3.1.1.7) inhibitor pyridostigmine bromide (PB). At higher doses, PB is also used to treat the autoimmune disease myasthenia gravis. In both cases, the therapeutic effect is mediated by inhibition of acetylcholinesterase (AChE) at cholinergic synapses. However, the location of AChE is not restricted to these sites. AChE, acetylcholine (ACh) receptors and choline acetyltransferase have been reported to be expressed by T cells, suggesting that cholinergic signalling may exert some modulatory influence on T-cell function and consequently on the immune system. The aim of this study was to investigate the role of the T-cell cholinergic system in the immunological activation process and to examine whether inhibitors of AChE such as PB affect immune function. To investigate this, human peripheral blood mononuclear cells (PBMC) were stimulated using either mitogen, cross-linking of the T-cell receptor and co-receptors with antibodies (anti-CD3/CD28) or by antigen presentation in the presence of various AChE inhibitors and ACh receptor agonists or antagonist. Several indices were used to assess T-cell activation, including the secretion of IL-2, cell proliferation and expression of CD69. Treatment with PB had no significant effect on the immunological assays selected. Physostigmine (PHY), a carbamate compound similar to PB, consistently showed inhibition of T-cell activation, but only at concentrations in excess of those required to inhibit AChE. No evidence was found to support previously published findings showing muscarinic enhancement of cell proliferation or IL-2 secretion.

Chromosomal aberrations in human lymphocytes exposed to the anticholinesterase pesticide isofenphos with mechanisms of leukemogenesis

Human lymphocytes were exposed to the leukemogenic pesticide isofenphos (IFP) to investigate its effects on chromosomal DNA and cholinergic homeostasis using cholinesterase activity as a marker. Isolated peripheral lymphocytes were administered concentrations of IFP ranging from 0.1 ng/ml to 10 microg/ml. The absence (Group 1) and presence (Group 2) of DNA repair inhibitors 4 mM hydroxyurea (HU), 40 microM cytosine arabinoside (ARA-C) and an NADPH regenerating system (NRS) (Group 3) were analyzed at 1, 6 and 24 h by single cell gel electrophoresis using the comet assay. Significant damage to DNA directly from IFP at 1 h by remarkably low concentrations was observed in Group 1, escalating in Group 2 with DNA repair inhibition, while Group 3 disruptions were highest due to the presence of the NRS P-450 microsomal fraction conducive to producing reactive IFP-oxon and N-desalkyl metabolites. The extent of DNA aberrations increased further in parallel within the groups at 6 and 24 h. Male and female chemical sensitivities were similar on average (P < 0.01). Cholinesterase activity measured in a satellite group was inhibited with 0.1 microg/ml IFP by 69, 62, and 48% at 1, 6, and 24 h, respectively, indicating gradual induction of compensatory synthesis. Restoration of cholinergic homeostasis may be exceptionally impaired at higher IFP concentrations from acetyl-CoA depletion [Leuk. Res. 25 (2001) 883]. In summary, these studies reveal that exposure to the organophosphate pesticide isofenphos induces human DNA mutation beyond endogenous repair capacity and disrupts cholinergic nuclear signaling affectively constructing the mutator phenotype of leukemogenesis.

Effect of Treatment with the Cholinesterase Inhibitor Rivastigmine on Vesicular Acetylcholine Transporter and Choline Acetyltransferase in Rat Brain

A decline of cholinergic neurotransmission probably contributes to cognitive dysfunction occurring in Alzheimer's disease (AD) and vascular dementia (VaD). Acetylcholinesterase (AChE)/cholinesterase (ChE) inhibitors are the only drugs authorized for symptomatic treatment of AD and are also under investigation for VaD. The present study has investigated the influence of two doses of the AChE inhibitor rivastigmine (0.625 mg/Kg/day and 2.5 mg/Kg/day) on vesicular acetylcholine transporter (VAChT) and on choline acetyltransferase (ChAT) expression in frontal cortex, hippocampus, striatum and cerebellum of normotensive and spontaneously hypertensive rats (SHR). Cholinergic markers were assessed by immunochemical (Western blotting) and immunohistochemical techniques. In frontal cortex and striatum of normotensive rats, treatment with the lower dose (0.625 mg/Kg/day) of rivastigmine had no effect on VAChT immunoreactivity and increased slightly ChAT protein immunoreactivity. The higher dose (2.5 mg/Kg/day) of the compound increased significantly VAChT and ChAT protein immunoreactivity. In hippocampus rivastigmine induced a concentration-dependent increase of VAChT protein expression and no significant changes of ChAT protein expression. A similar pattern of VAChT and ChAT protein expression was observed in control SHR, whereas treatment of SHR with rivastigmine induced a more pronounced increase of VAChT protein immunoreactivity in frontal cortex, hippocampus and striatum compared to normotensive rats. Our data showing an increase of VAChT after treatment with rivastgmine further support the notion of an enhancement of cholinergic neurotransmission by AChE/ChE inhibitors. The observation of a greater expression of this cholinergic marker in SHR suggest that AChE inhibition may provide beneficial effects on cholinergic neurotransmission in an animal model of VaD.

Autonomic innervation of immune organs and neuroimmune modulation

1. Increasing evidence indicates the occurrence of functional interconnections between immune and nervous systems, although data available on the mechanisms of this bi-directional cross-talking are frequently incomplete and not always focussed on their relevance for neuroimmune modulation. 2. Primary (bone marrow and thymus) and secondary (spleen and lymph nodes) lymphoid organs are supplied with an autonomic (mainly sympathetic) efferent innervation and with an afferent sensory innervation. Anatomical studies have revealed origin, pattern of distribution and targets of nerve fibre populations supplying lymphoid organs. 3. Classic (catecholamines and acetylcholine) and peptide transmitters of neural and non-neural origin are released in the lymphoid microenvironment and contribute to neuroimmune modulation. Neuropeptide Y, substance P, calcitonin gene-related peptide, and vasoactive intestinal peptide represent the neuropeptides most involved in neuroimmune modulation. 4. Immune cells and immune organs express specific receptors for (neuro)transmitters. These receptors have been shown to respond in vivo and/or in vitro to the neural substances and their manipulation can alter immune responses. Changes in immune function can also influence the distribution of nerves and the expression of neural receptors in lymphoid organs. 5. Data on different populations of nerve fibres supplying immune organs and their role in providing a link between nervous and immune systems are reviewed. Anatomical connections between nervous and immune systems represent the structural support of the complex network of immune responses. A detailed knowledge of interactions between nervous and immune systems may represent an important basis for the development of strategies for treating pathologies in which altered neuroimmune cross-talking may be involved.

[An independent, non-neuronal cholinergic system in lymphocytes and its roles in regulation of immune function]

Acetylcholine (ACh) is classically thought of as a neurotransmitter in mammalian species. However, lymphocytes express most of the cholinergic components found in the nervous system, including ACh, choline acetyltransferase (ChAT), high-affinity choline transporter, and acetylcholinesterase as well as both muscarinic and nicotinic ACh receptors (mAChRs and nAChRs, respectively). Activation of T cells via the T cell receptor/CD3 complex, contact of T cells with antigen presenting cells, or activation of the adenylyl cyclase pathway in T cells modulates cholinergic activity, as evidenced by up-regulation of ChAT and M(5) mAChR mRNA expression. Stimulation of mAChRs on T and B cells with ACh or another mAChR agonists elicits intracellular Ca(2+) signaling, up-regulation of c-fos expression, increased nitric oxide synthesis and interleukin-2-induced signal transduction via M(3) and M(5) mAChR-mediated pathways. Acute stimulation of nAChRs with ACh or nicotine causes rapid and transient Ca(2+) signaling in T and B cells, probably via alpha7 nAChRs subunit-mediated pathways. Chronic nicotine stimulation, by contrast, down-regulates nAChR expression and suppresses T cell activity. Abnormalities in lymphocytic cholinergic system have been seen in animal models of immune deficiency and immune acceleration. Collectively, these data provided a compelling picture in which immune function is, at least partly, under the control of an independent, non-neuronal cholinergic system in lymphocytes.

The lymphocytic cholinergic system and its contribution to the regulation of immune activity

Lymphocytes express most of the cholinergic components found in the nervous system, including acetylcholine (ACh), choline acetyltransferase (ChAT), high affinity choline transporter, muscarinic and nicotinic ACh receptors (mAChRs and nAChRs, respectively), and acetylcholinesterase. Stimulation of T and B cells with ACh or another mAChR agonist elicits intracellular Ca2+ signaling, up-regulation of c-fos expression, increased nitric oxide synthesis and IL-2-induced signal transduction, probably via M3 and M5 mAChR-mediated pathways. Acute stimulation of nAChRs with ACh or nicotine causes rapid and transient Ca2+ signaling in T and B cells, probably via alpha7 nAChR subunit-mediated pathways. Chronic nicotine stimulation, by contrast, down-regulates nAChR expression and suppresses T cell activity. Activation of T cells with phytohemagglutinin or antibodies against cell surface molecules enhances lymphocytic cholinergic transmission by activating expression of ChAT and M5 mAChR, which is suggestive of local cholinergic regulation of immune system activity. This idea is supported by the facts that lymphocytic cholinergic activity reflects well the changes in immune system function seen in animal models of immune deficiency and immune acceleration. Collectively, these data provide a compelling picture in which lymphocytes constitute a cholinergic system that is independent of cholinergic nerves, and which is involved in the regulation of immune function.