Effects of human antithymocyte globulin on acetylcholine synthesis, its release and choline acetyltransferase transcription in a human leukemic T-cell line

Differential Actions of Muscarinic Receptor Subtypes in Gastric, Pancreatic, and Colon Cancer

Cancers arising from gastrointestinal epithelial cells are common, aggressive, and difficult to treat. Progress in this area resulted from recognizing that the biological behavior of these cancers is highly dependent on bioactive molecules released by neurocrine, paracrine, and autocrine mechanisms within the tumor microenvironment. For many decades after its discovery as a neurotransmitter, acetylcholine was thought to be synthesized and released uniquely from neurons and considered the sole physiological ligand for muscarinic receptor subtypes, which were believed to have similar or redundant actions. In the intervening years, we learned this former dogma is not tenable. (1) Acetylcholine is not produced and released only by neurons. The cellular machinery required to synthesize and release acetylcholine is present in immune, cancer, and other cells, as well as in lower organisms (e.g., bacteria) that inhabit the gut. (2) Acetylcholine is not the sole physiological activator of muscarinic receptors. For example, selected bile acids can modulate muscarinic receptor function. (3) Muscarinic receptor subtypes anticipated to have overlapping functions based on similar G protein coupling and downstream signaling may have unexpectedly diverse actions. Here, we review the relevant research findings supporting these conclusions and discuss how the complexity of muscarinic receptor biology impacts health and disease, focusing on their role in the initiation and progression of gastric, pancreatic, and colon cancers.

Regulation of Immune Functions by Non-Neuronal Acetylcholine (ACh) via Muscarinic and Nicotinic ACh Receptors

Acetylcholine (ACh) is the classical neurotransmitter in the cholinergic nervous system. However, ACh is now known to regulate various immune cell functions. In fact, T cells, B cells, and macrophages all express components of the cholinergic system, including ACh, muscarinic, and nicotinic ACh receptors (mAChRs and nAChRs), choline acetyltransferase, acetylcholinesterase, and choline transporters. In this review, we will discuss the actions of ACh in the immune system. We will first briefly describe the mechanisms by which ACh is stored in and released from immune cells. We will then address Ca²⁺ signaling pathways activated via mAChRs and nAChRs on T cells and B cells, highlighting the importance of ACh for the function of T cells, B cells, and macrophages, as well as its impact on innate and acquired (cellular and humoral) immunity. Lastly, we will discuss the effects of two peptide ligands, secreted lymphocyte antigen-6/urokinase-type plasminogen activator receptor-related peptide-1 (SLURP-1) and hippocampal cholinergic neurostimulating peptide (HCNP), on cholinergic activity in T cells. Overall, we stress the fact that ACh does not function only as a neurotransmitter; it impacts immunity by exerting diverse effects on immune cells via mAChRs and nAChRs.

Cholinergic System and Its Therapeutic Importance in Inflammation and Autoimmunity

Neurological and immunological signals constitute an extensive regulatory network in our body that maintains physiology and homeostasis. The cholinergic system plays a significant role in neuroimmune communication, transmitting information regarding the peripheral immune status to the central nervous system (CNS) and vice versa. The cholinergic system includes the neurotransmitter\ molecule, acetylcholine (ACh), cholinergic receptors (AChRs), choline acetyltransferase (ChAT) enzyme, and acetylcholinesterase (AChE) enzyme. These molecules are involved in regulating immune response and playing a crucial role in maintaining homeostasis. Most innate and adaptive immune cells respond to neuronal inputs by releasing or expressing these molecules on their surfaces. Dysregulation of this neuroimmune communication may lead to several inflammatory and autoimmune diseases. Several agonists, antagonists, and inhibitors have been developed to target the cholinergic system to control inflammation in different tissues. This review discusses how various molecules of the neuronal and non-neuronal cholinergic system (NNCS) interact with the immune cells. What are the agonists and antagonists that alter the cholinergic system, and how are these molecules modulate inflammation and immunity. Understanding the various functions of pharmacological molecules could help in designing better strategies to control inflammation and autoimmunity.

Cholinergic modulation of the immune system - A novel therapeutic target for myocardial inflammation

The immune system and the nervous system depend on each other for their fine tuning and working, thus cooperating to maintain physiological homeostasis and prevent infections. The cholinergic system regulates the mobilization, differentiation, secretion, and antigen presentation of adaptive and innate immune cells mainly through α7 nicotinic acetylcholine receptors (α7nAChRs). The neuro-immune interactions are established and maintained by the following mechanisms: colocalization of immune and neuronal cells at defined anatomical sites, expression of the non-neuronal cholinergic system by immune cells, and the acetylcholine receptor-mediated activation of intracellular signaling pathways. Based on these immunological mechanisms, the protective effects of cholinergic system in animal models of diseases were summarized in this paper, such as myocardial infarction/ischemia-reperfusion, viral myocarditis, and endotoxin-induced myocardial damage. In addition to maintaining hemodynamic stability and improving the energy metabolism of the heart, both non-neuronal acetylcholine and neuronal acetylcholine in the heart can alleviate myocardial inflammation and remodeling to exert a significant cardioprotective effect. The new findings on the role of cholinergic agonists and vagus nerve stimulation in immune regulation are updated, so as to develop improved approaches to treat inflammatory heart disease.

Expression and Function of the Cholinergic System in Immune Cells

T and B cells express most cholinergic system components—e.g., acetylcholine (ACh), choline acetyltransferase (ChAT), acetylcholinesterase, and both muscarinic and nicotinic ACh receptors (mAChRs and nAChRs, respectively). Using ChAT^BAC-eGFP transgenic mice, ChAT expression has been confirmed in T and B cells, dendritic cells, and macrophages. Moreover, T cell activation via T-cell receptor/CD3-mediated pathways upregulates ChAT mRNA expression and ACh synthesis, suggesting that this lymphocytic cholinergic system contributes to the regulation of immune function. Immune cells express all five mAChRs (M₁–M₅). Combined M₁/M₅ mAChR-deficient (M₁/M_5-KO) mice produce less antigen-specific antibody than wild-type (WT) mice. Furthermore, spleen cells in M₁/M₅-KO mice produce less tumor necrosis factor (TNF)-α and interleukin (IL)-6, suggesting M₁/M₅ mAChRs are involved in regulating pro-inflammatory cytokine and antibody production. Immune cells also frequently express the α2, α5, α6, α7, α9, and α10 nAChR subunits. α7 nAChR-deficient (α7-KO) mice produce more antigen-specific antibody than WT mice, and spleen cells from α7-KO mice produce more TNF-α and IL-6 than WT cells. This suggests that α7 nAChRs are involved in regulating cytokine production and thus modulate antibody production. Evidence also indicates that nicotine modulates immune responses by altering cytokine production and that α7 nAChR signaling contributes to immunomodulation through modification of T cell differentiation. Together, these findings suggest the involvement of both mAChRs and nAChRs in the regulation of immune function. The observation that vagus nerve stimulation protects mice from lethal endotoxin shock led to the notion of a cholinergic anti-inflammatory reflex pathway, and the spleen is an essential component of this anti-inflammatory reflex. Because the spleen lacks direct vagus innervation, it has been postulated that ACh synthesized by a subset of CD4⁺ T cells relays vagal nerve signals to α7 nAChRs on splenic macrophages, which downregulates TNF-α synthesis and release, thereby modulating inflammatory responses. However, because the spleen is innervated solely by the noradrenergic splenic nerve, confirmation of an anti-inflammatory reflex pathway involving the spleen requires several more hypotheses to be addressed. We will review and discuss these issues in the context of the cholinergic system in immune cells.

Hepatic cholinesterase of laying hens naturally infected by Salmonella Gallinarum (fowl typhoid)

Salmonella is a facultative intracellular pathogen that may cause foodborne gastroenteritis in humans and animals consisting of over 2000 serovars. The serovar Salmonella Gallinarum is an important worldwide pathogen of poultry. However, little is known on the mechanisms of pathogenesis of Salmonella in chickens. The aim of this study was to evaluate cholinesterase and myeloperoxidase activities in hepatic tissue of laying hens naturally infected by S. Gallinarum. Twenty positive liver samples for S. Gallinarum were collected, in addition to seven liver samples from healthy uninfected laying hens (control group). The right liver lobe was homogenized for analysis of acetylcholinesterase (AChE), butyrylcholinesterase (BChE) and myeloperoxidase (MPO), and the left lobe was divided into two fragments, one for histopathology and the other for Salmonella isolation. The results showed changes in AChE and BchE activity in the liver of infected laying hens compared to the control group (P < 0.05), i.e. reduced AChE and increased BChE activities in liver samples. Infected animals showed increased MPO activity compared to healthy animals (P < 0.05). Furthermore, the histopathological findings showed fibrinoid necrosis associated to the infiltration of lymphocytes, plasma cells, macrophages,heterophils in the liver of infected hens. These findings suggest that the inflammatory process was attenuated providing a pro-inflammatory action of both enzyme analyzed in order to reduce the free ACh, a molecule which has an anti-inflammatory action. Therefore, our results lead to the hypothesis that cholinesterase plays an important role on the modulation of immune response against S. Gallinarum with an inflammatory effect, contributing to the response against this bacterium. This study should contribute to a better understanding on the pathogenic mechanisms involved in laying hens infected by S. Gallinarum.

Reconciling neuronally and nonneuronally derived acetylcholine in the regulation of immune function

Immune cells, including lymphocytes, express muscarinic and nicotinic acetylcholine (ACh) receptors (mAChRs and nAChRs, respectively), and agonist stimulation of these AChRs causes functional and biochemical changes in the cells. The origin of the ACh that acts on immune cell AChRs has remained unclear until recently, however. In 1995, we identified choline acetyltransferase mRNA and protein in human T cells, and found that immunological T cell activation potentiated lymphocytic cholinergic transmission by increasing ACh synthesis and AChR expression. We also found that M(1) /M(5) mAChR signaling upregulates IgG(1) and proinflammatory cytokine production, whereas α7 nAChR signaling has the opposite effect. These findings suggest that ACh synthesized by T cells acts as an autocrine and/or paracrine factor via AChRs on immune cells to modulate immune function. In addition, a recently discovered endogenous allosteric α7 nAChR ligand, SLURP-1, also appears to be involved in modulating normal T cell function.

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.

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.

Expression and function of genes encoding cholinergic components in murine immune cells

It is now evident that acetylcholine (ACh) synthesized by choline acetyltransferase (ChAT) and released from T cells during antigen presentation binds to muscarinic and nicotinic ACh receptors (mAChRs and nAChRs, respectively) on T and B cells or dendritic cells, leading to modulation of their function. In the present study, we used reverse transcription-polymerase chain reaction (RT-PCR) to investigate whether mononuclear leukocytes (MNLs), bone marrow-derived dendritic cells (DCs) and macrophages from C57BL/6J mice express components of the cholinergic system. Expression of ChAT mRNA was detected in MNLs activated with ConA and DCs stimulated with LPS, but not in resting MNLs and DCs or in resting and stimulated macrophages. MNLs, DCs and macrophages all expressed mRNAs encoding the five mAChR subtypes (M(1)-M(5)) and the nAChR alpha2, alpha5, alpha6, alpha7, alpha10 and beta2 subunits. Expression of VIP mRNA was detected in MNLs and macrophages, but not in DCs. MNLs, DCs and macrophages all expressed VIP receptor-1 (VPAC1) and -2 (VPAC2) mRNAs, as well as mRNAs encoding secreted mammalian Ly-6/urokinase-type plasminogen activator receptor-related protein (SLURP)-1 and SLURP-2, two endogenous nAChR ligands. These results suggest that the lymphocytic cholinergic system is activated by ACh via mAChR- and nAChR-mediated pathways during antigen presentation between T cells and DCs or macrophages, leading to modulation of immune cell function. Moreover, VIP released from both postganglionic cholinergic neurons and immune cells may play a role in the cholinergic anti-inflammatory reflex, acting via VPAC1 and VPAC2 on immune cells.

Roles played by lymphocyte function-associated antigen-1 in the regulation of lymphocytic cholinergic activity

Lymphocytes possess the essential components of a cholinergic system, including acetylcholine (ACh); choline acetyltransferase (ChAT), its synthesizing enzyme; and both muscarinic and nicotinic ACh receptors (mAChRs and nAChRs, respectively). Stimulation of lymphocytes with phytohemagglutinin, which activates T cells via the T cell receptor/CD3 complex, enhances the synthesis and release of ACh and up-regulates expression of ChAT and M(5) mAChR mRNAs. In addition, activation of protein kinase C and increases in intracellular cAMP also enhance cholinergic activity in T cells, and lymphocyte function associated antigen-1 (LFA-1; CD11a/CD18) is an important mediator of leukocyte migration and T cell activation. Anti-CD11a monoclonal antibody (mAb) as well as antithymocyte globulin containing antibodies against CD2, CD7 and CD11a all increase ChAT activity, ACh synthesis and release, and expression of ChAT and M(5) mAChR mRNAs in T cells. The cholesterol-lowering drug simvastatin inhibits LFA-1 signaling by binding to an allosteric site on CD11a (LFA-1 alpha chain), which leads to immunomodulation. We found that simvastatin abolishes anti-CD11a mAb-induced increases in lymphocytic cholinergic activity in a manner independent of its cholesterol-lowering activity. Collectively then, these results indicate that LFA-1 contributes to the regulation of lymphocytic cholinergic activity via CD11a-mediated pathways and suggest that simvastatin exerts its immunosuppressive effects in part via modification of lymphocytic cholinergic activity.

Simvastatin regulates non-neuronal cholinergic activity in T lymphocytes via CD11a-mediated pathways

Lymphocyte function associated antigen-1 (LFA-1; CD11a/CD18) is an important mediator of leukocyte migration and T cell activation. We previously showed that antithymocyte globulin stimulates an independent, non-neuronal cholinergic system in T cells via LFA-1-mediated pathways, as evidenced by increases in acetylcholine (ACh) synthesis and choline acetyltransferase (ChAT) mRNA expression. The cholesterol-lowering drug simvastatin inhibits LFA-1 signaling by binding to an allosteric site on CD11a (LFA-1 alpha chain), which leads to immunomodulation. In the present study, we investigated whether simvastatin modulates lymphocytic cholinergic activity in T cells. We found that anti-CD11a monoclonal antibody (mAb) increased ChAT activity, ACh synthesis and release, and expression of ChAT and M5 muscarinic ACh receptor mRNA in MOLT-3 cells, a human leukemic T cell line. Simvastatin abolished these anti-CD11a mAb-induced increases in lymphocytic cholinergic activity in a manner independent of its cholesterol-lowering activity. These results indicate that LFA-1 contributes to the regulation of lymphocytic cholinergic activity via CD11a-mediated pathways, and suggest that simvastatin exerts its immunosuppressive effects in part via modification of lymphocytic cholinergic activity.

The endogenous, immunologically active peptide apelin inhibits lymphocytic cholinergic activity during immunological responses

We investigated the effects of apelin, an immunologically active peptide ligand for orphan receptor APJ, on acetylcholine (ACh) synthesis in MOLT-3 human leukemic T cells. We initially confirmed expression of APJ mRNA in several human T- and B-cell lines by reverse transcription-polymerase chain reaction (RT-PCR). We also found that in phytohemagglutinin (PHA)-stimulated MOLT-3 cells, an active apelin fragment, apelin-13, down-regulates expression of choline acetyltransferase (ChAT) mRNA and significantly reduces ChAT activity and cellular ACh content and release. It thus appears that apelin inhibits lymphocytic cholinergic activity via APJ during immunological responses.

[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.

Up-regulation of lymphocytic cholinergic activity by ONO-4819, a selective prostaglandin EP4 receptor agonist, in MOLT-3 human leukemic T cells

We used a selective EP4 receptor agonist, ONO-4819, and a human leukemic T cell line MOLT-3 cells, which express all four prostaglandin E2 (PGE2) receptors (EP1-EP4), to investigate whether the EP4 PGE2 receptor subtype is involved in regulating lymphocytic cholinergic activity. Phytohemagglutinin (PHA), a T cell activator, significantly enhanced the expression of EP4 receptor mRNA during the first 3-6 h of exposure, after which, expression gradually declined. Furthermore, PHA stimulation slightly but significantly up-regulated the expression of EP2 mRNA after 12 h and of EP3 mRNA after 6 h. By contrast, expression level of EP1 receptor mRNA was not affected by PHA. ONO-4819 (1 microM), which was added to cultures after 3 h of PHA stimulation, significantly increased cellular ACh content and release, and up-regulated ChAT mRNA expression and activity but inhibited MOLT-3 cell proliferation. These findings suggest that the activation of T lymphocytes up-regulates EP4 receptor mRNA expression and, to a lesser extent, EP2 and EP3 receptors and that PGE2 enhances nonneuronal lymphocytic cholinergic transmission in activated T cells, at least in part, via EP4 receptor-mediated pathways.

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.

Enzymatic activities of ChAT, GAD65 and PKC in pancreatic carcinoma tissues

AIM

To study on the expression characteristics of ChAT, GAD65 and PKC enzymatic activities and their clinicopathological significance in the tissues of chronic pancreatitis and pancreatic carcinoma.

METHODS

The enzymatic activities of ChAT, GAD65 and PKC were detected by immunohistochemical method of avidin-biotin complex on formalin-fixed and routine paraffin-embedded sections of specimens of chronic pancreatitis (n =10) and pancreatic carcinoma (n =47).

RESULTS

The positive rate and the score of ChAT, GAD65 and PKC were significantly lower in 10 cases of chronic pancreatitis than that of pancreatic carcinoma (ChAT, 0% vs 48.9% , 0.2±0.4 vs 2.2±1.4; GAD65, 10.0% vs 55.3%, 0.6±0.9 vs 2.2±1.2; PKC, 10.0% vs 57.4%, 0.6±0.9 vs 2.1±1.6). The score of ChAT was significantly higher in well-differentiated adenocarcinoma than that of poorly-differentiated adenocarcinoma (P<0.05). The positive rate and the score of GAD65 or PKC were significantly lower (GAD65, P<0.05; PKC, P<0.01) in cases of well-differentiated adenocarcinoma than in cases of poorly-differentiated. No difference was found for the enzyme expressions and the clinicopathological characteristics among different sex, age, with or without metastasis of pancreatic carcinoma. A highly positive correlation was found between the scores of GAD65 and PKC in pancreatic carcinoma.

CONCLUSION

The expression of enzymatic activities of ChAT, GAD65 or PKC might be related to the carcinogenesis, progression and biological behaviors of pancreatic carcinoma. They might be important biological markers of pancreatic carcinoma.

Upregulation of mRNA encoding the M5 muscarinic acetylcholine receptor in human T- and B-lymphocytes during immunological responses

Lymphocytes possess an independent, non-neuronal cholinergic system. Moreover, both T- and B-lymphocytes express multiple muscarinic acetylcholine receptors (mAChR). To obtain a better understanding of the regulatory mechanisms governing mAChR gene expression in the lymphocytic cholinergic system, we examined the effects of lymphocyte activation on expression of mAChR mRNA. Stimulation of T- and B-lymphocytes, respectively, with T-cell activator phytohemagglutinin and B-cell activator Staphylococcus aureus Cowan I upregulated M5 mAChR mRNA expression in the CEM human leukemic T-cell line and in the Daudi B-cell line, which served as models of lymphocytes. In striking contrast, M3 and M4 mAChR mRNA expression was not affected in either cell line. Nonetheless, stimulating lymphocytes with phorbol 12-myristate 13-acetate, a protein kinase C activator, plus ionomycin, a calcium ionophore, upregulated expression of both M3 and M5 mAChR mRNA. This represents the first demonstration that immunological stimulation leads to M5 mAChR gene expression in lymphocytes.

The lymphocytic cholinergic system and its biological function

Lymphocytes are now known to possess the essential components for a 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). Stimulating lymphocytes with phytohemagglutinin, a T-cell activator; Staphylococcus aureus Cowan I, a B-cell activator; or cell surface molecules enhances the synthesis and release of ACh and up-regulates expression of ChAT and M(5) mAChR mRNAs. Activation of mAChRs and nAChRs on lymphocytes elicits increases in the intracellular Ca(2+) concentration and stimulates c-fos gene expression and nitric oxide synthesis. On the other hand, long-term exposure to nicotine down-regulates expression of nAChR mRNA. Abnormalities in the lymphocytic cholinergic system have been detected in spontaneously hypertensive rats and MRL-lpr mice, two animal models of immune disorders. Taken together, these data present a compelling picture in which immune function is, at least in part, under the control of an independent non-neuronal lymphocytic cholinergic system.

Detection of the high-affinity choline transporter in the MOLT-3 human leukemic T-cell line

We previously showed that lymphocytes possess the necessary components to constitute an independent, non-neuronal cholinergic system; these include acetylcholine (ACh) itself, choline acetyltransferase (the ACh-synthesizing enzyme), and both muscarinic and nicotinic ACh receptors (AChRs). In addition, we showed that stimulation of AChRs with their respective agonists elicits a variety of biochemical and functional effects, suggesting that lymphocytic cholinergic system is involved in the regulation of immune function. In nerve terminals, choline taken up via the high-affinity choline transporter (CHT1) is exclusively utilized for ACh synthesis. In the present study, therefore, we investigated the expression of CHT1 in T-lymphocytes. Reverse transcription-polymerase chain reaction analysis revealed that MOLT-3 cells, a human leukemic T-cell line used as a T-lymphocyte model, expressed CHT1 mRNA, but that the CEM and Jurkat T-cell lines did not. Consistent with that finding, specific binding of [3H]hemicholinium-3 (HC-3), an inhibitor of CHT1, and HC-3-sensitive [3H]choline uptake were also detected in MOLT-3 cells. These results suggest that CHT1 plays a role in mediating choline uptake in T-lymphocytes and provides further evidence for the presence of an independent lymphocytic cholinergic system.