Critical roles of acetylcholine and the muscarinic and nicotinic acetylcholine receptors in the regulation of immune function

doi:10.1016/j.lfs.2012.05.006

Life Sciences

Volume 91, Issues 21–22, 27 November 2012, Pages 1027-1032

https://doi.org/10.1016/j.lfs.2012.05.006 Get rights and content

Abstract

Lymphocytes express both muscarinic and nicotinic acetylcholine (ACh) receptors (mAChRs and nAChRs, respectively), and stimulation of mAChRs and nAChRs produces various biochemical and functional changes. Although it has been postulated that parasympathetic cholinergic nerves directly innervate immune cells, no evidence has supported this hypothesis. We measured ACh in the blood of various animal species and determined its localization in T cells using a sensitive and specific radioimmunoassay. Furthermore, we showed that T cells express choline acetyltransferase (ChAT), an ACh synthesizing enzyme. Immunological T cell activation enhances ACh synthesis through the up-regulation of ChAT expression, suggesting lymphocytic cholinergic activity is related to immunological activity. Most immune cells such as T cells, B cells, and monocytes express all five subtypes of mAChRs (M₁–M₅), and various subunits of the nAChR, such as α3, α5, α7, α9, and α10. Studies on serum antibody production in M₁ and M₅ combined mAChR gene knockout (KO) mice immunized with ovalbumin (OVA) revealed that M₁/M₅ mAChRs up-regulate TNF-α, IFN-γ and IL-6 production in spleen cells, leading to an elevation of serum anti-OVA specific IgG₁. In contrast, studies of nAChR α7 subunit gene KO mice immunized with OVA show that α7 nAChRs down-regulate these proinflammatory cytokines, thereby leading to a reduction of anti-OVA specific IgG₁. Taken together, these findings demonstrate that both mAChRs and nAChRs modulate production of cytokines, such as TNF-α, resulting in a modification of antibody production. These findings support the notion that a non-neuronal cholinergic system is involved in the regulation of immune cell function.

Graphical abstract

Regulation of proinflammatory cytokine production through mAChRs and nAChRs by ACh derived from CD4⁺ T cells during antigen presentation.

Introduction

Expression of both muscarinic and nicotinic acetylcholine (ACh) receptors (mAChRs and nAChRs, respectively) has been demonstrated in various immune cells, such as lymphocytes and thymocytes using radio-labeled ligands (reviewed by Kawashima and Fujii, 2000, Kawashima and Fujii, 2003, Kawashima and Fujii, 2004, Fujii et al., 2008). Furthermore, in vitro stimulation of mAChRs and nAChRs with their respective agonists causes various functional and biochemical changes in immune cells. Therefore, it has long been postulated that ACh released from parasympathetic cholinergic nerve terminals acts on mAChRs and nAChRs expressed on immune cells. However, because acetylcholinesterase (AChE) and butyrylcholinesterase rapidly hydrolyze ACh into choline and acetate in the blood and no evidence has yet been found for direct innervations of cholinergic nerves to immune cells, it is unlikely that a sufficient amount of ACh released from cholinergic nerve terminals reaches the mAChRs and nAChRs expressed on immune cells. More than 80 years ago, Kapfhammer and Bischoff found the presence of ACh in ox blood (reviewed by Kawashima and Fujii, 2000). Although attempts have been made since that study, no studies have been able to convincingly demonstrate the presence of ACh in the blood of various animal species. A lack of availability of sensitive and reliable procedures for the determination of ACh, as well as the enzymatic and physicochemical instability of ACh, has hindered these efforts. However, since 1993, Kawashima et al. have convincingly demonstrated the presence of ACh in the blood (Table 1) and its localization in mononuclear leukocytes (MNLs) in a number of mammalian species, including humans, using a sensitive and specific radioimmunoassay (reviewed by Kawashima and Fujii, 2000). Accumulated evidence over the past 20 years has clarified the origin of blood ACh, subtype expression of mAChRs and nAChRs on immune cells, and their roles in the regulation of immune function. This evidence supports the presence of a non-neuronal cholinergic system in immune cells and its involvement in the regulation of immune function. This review primarily focuses on the detection of ACh, and choline acetyltransferase (ChAT) in immune cells, the expression of various subtypes of AChR in immune cells, and the roles played by AChRs in the regulation of immune function.

Section snippets

Origin of ACh

In 1989, Kawashima et al. demonstrated the presence of a constant amount of ACh in blood cells and its release into the plasma after nicotine stimulation in conscious rabbits (reviewed by Kawashima and Fujii, 2000). After fractionation of human blood into plasma, mononuclear leukocytes (MNLs), polymorphonuclear leukocytes (PMNLs), and red blood cells, about 60% of the total blood ACh content was detected in the MNL fraction, which consists mainly of lymphocytes and a small number of monocytes (

mAChRs

The M₁, M₃ and M₅ mAChR subtypes are coupled to G_q/11. Upon stimulation, these subtypes mediate activation of phospholipase C (PLC), leading to increases in [Ca^2 +]_i. The M₂ and M₄ mAChR subtypes are coupled to G_i/o, and upon stimulation, these subtypes mediate the inhibition of adenylyl cyclase, leading to a decrease in cAMP synthesis. Most human MNLs, human leukemic cell lines and animal immune cells, express all five subtypes of mAChRs (M₁–M₅) (reviewed by Kawashima and Fujii, 2004). However,

mAChRs

Zimring et al. (2005) reported that CD8⁺ T cells of M₁ mAChR gene-knockout (KO) mice show a defect in early differentiation into cytolytic T lymphocytes when stimulated in vitro, while M₁ mAChR does not appear to be required for early activation. Later, these authors observed no further defect in the expansion of CD8⁺ T cells in either M₁ or M₅ mAChR-KO mice infected with either lymphocytic choriomeningitis virus or vesicular stomatitis virus, suggesting that M₁ and M₅ mAChRs are not involved

AChE

Szelenyi et al. (1982) detected AChE activity in T cells and found its augmentation by PHA. Furthermore, Ando et al. (1999) detected expression of mRNAs encoding three different types of AChE in human MNLs and in human leukemic T cell and B cell lines. Tayebati et al. (2002) confirmed AChE protein expression in both T and B cells using immunohistochemical and immunocytochemical techniques. In our study with M₁/M₅ KO mice (Fujii et al., 2007a), we found a slight but significant suppression of

Conclusions and important findings

As shown above, at least in humans, ACh is synthesized primarily in CD4⁺ T cells by ChAT (see a review by Fujii et al., 2003b). However, carnitine acetyltransferase (CarAT), a mitochondrial enzyme, can also synthesize ACh from choline and acetyl coenzyme A. CarAT activity is also detectable in various human leukemic T cell lines as well as other cell lines, such as B cell lines. However, CarAT activity did not correlate with the ACh content in these cell lines. Furthermore, T cell activation by

Conflict of interest statement

There is no conflict of interest.

Acknowledgments

This manuscript was supported in part by a Grant-in-Aid for Scientific Research (20590094) from the Ministry of Education, Science, Sports and Culture (C) of Japan, funding from SSR Foundation, and a generous donation from Dr. Eun Bang Lee, Emeritus Professor, College of Pharmacy, Seoul National University, Korea.

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MinireviewCritical roles of acetylcholine and the muscarinic and nicotinic acetylcholine receptors in the regulation of immune function

Abstract

Graphical abstract

Introduction

Section snippets

Origin of ACh

mAChRs

mAChRs

AChE

Conclusions and important findings

Conflict of interest statement

Acknowledgments

Jpn J Pharmacol

J Neuroimmunol

J Neuroimmunol

J Neuroimmunol

J Neuroimmunol

J Pharmacol Sci

J Neuroimmunol

Pharmacol Ther

Life Sci

J Neuroimmunol

Life Sci

J Neuroimmunol

Life Sci

J Neuroimmunol

Walter Ernest Dixon Memorial Lecture. pharmacology and nerve-endings

Proc R Soc Med

The presence of histamine and acetylcholine in the spleen of the ox and the horse

J Physiol

Minireview
Critical roles of acetylcholine and the muscarinic and nicotinic acetylcholine receptors in the regulation of immune function