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7/29/2019 Boris Mravec Role of the Vagus Nerve at the Neural Immune Interface
http://slidepdf.com/reader/full/boris-mravec-role-of-the-vagus-nerve-at-the-neural-immune-interface 1/7
Role of the Vagus Nerve at the Neural-Immune Interface
Written by K Ondicova & B Mravec
Friday, 20 August 2010 00:00
Evidence shows that the central nervous system monitors and modulates the activity of both
circulating and tissue immune cells via the neuroendocrine system and autonomic nerves.
Furthermore, findings over the last decade have demonstrated that the vagus nerve represents
an important bi-directional link between the brain and immune system.
Afferent vagal pathways transmit information to the brain related to peripheral inflammation so
as to participate in the activation of adaptive reactions, including fever and sickness behavior.
On the other side, efferent vagal pathways inhibit the synthesis and release of pro-inflammatory
cytokines by peripheral immune cells. Because activation of afferent vagal pathways by immune
stimuli leads to suppression of immune reactions, the term inflammatory reflex was introduced.
The inflammatory reflex adjusts the intensity and duration of inflammatory reactions according
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7/29/2019 Boris Mravec Role of the Vagus Nerve at the Neural Immune Interface
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Role of the Vagus Nerve at the Neural-Immune Interface
Written by K Ondicova & B Mravec
Friday, 20 August 2010 00:00
to actual needs, thus protecting an organism from tissue damage induced by excessive
inflammation. Both experimental and clinical studies suggest that inappropriate activation of the
inflammatory reflex participates in the development of diseases characterized by excessive
production of cytokines.', '
Introduction
Regulation of immune system activity by the central nervous system plays an important role in
both physiological and pathological conditions. This is shown by several studies demonstrating
that the vagus nerve represents one of the key brain structures participating in monitoring
immune system activity. The vagus nerve is involved in the transmission of information from
inflamed peripheral tissues to the brain, and participates in both homeostatic and behavioral
adaptation reactions, including the induction of fever and sickness behavior. Vagal afferent
pathways are activated by immune stimuli either directly or indirectly via vagal paraganglia cells.These paraganglia cells possess receptors for immune signaling molecules (e.g. IL-1) and
transmit signals from immune cells to the afferent vagal pathways. The importance of afferent
vagal pathways in the transmission of immune-related signals is demonstrated by the inhibitory
effect of subdiaphragmatic vagotomy on the development of fever responses induced by
intraperitoneal injection of low doses of IL-1beta [1,2].
Although the role of afferent vagal pathways in the transmission of immune signals to the brain
has been demonstrated over time, the role of efferent vagal pathways in the modulation ofimmune cells activity has only recently been shown. This occurred during the search for a new
compound for the treatment of excessive inflammatory reactions (e.g. sepsis) with the synthesis
of CNI-1493 (tetravalent guanyl-hydrazone). This compound was shown to inhibit the release of
pro-inflammatory cytokines from macrophages, significantly prolonging the survival of animals in
experimental models of sepsis induced by endotoxin [3]. Moreover, it was found that application
of CNI-1493 increased the activity of efferent vagal pathways and that its anti-inflammatory
effects were blocked by vagotomy [4]. Later studies demonstrated that CNI-1493 inhibits both
the synthesis and release of pro-inflammatory cytokines from immune cells through activation of
efferent vagal pathways at the level of central nervous system. Later, this inhibitory effect of the
vagus nerve on immune cells activity was found to be mediated by acetylcholine, and the termcholinergic anti-inflammatory pathway was introduced [5,6].
Inflammatory reflex and cholinergic anti-inflammatory pathway
The synthesis and release of cytokines represents one of the most basic activities during
immune reactions. However, inappropriate cytokine synthesis may stimulate excessive
inflammatory reactions causing damage to peripheral tissues and organs. It is therefore not
surprising that organisms have several mechanisms regulating the intensity of inflammation,
including the inflammatory reflex of the vagus nerve.
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Role of the Vagus Nerve at the Neural-Immune Interface
Written by K Ondicova & B Mravec
Friday, 20 August 2010 00:00
The pathways of the vagus nerve that participate in the monitoring and modulation of immune
reactions in the periphery of an organism make up the sensory arm of the inflammatory reflex.
This “arm” consists of afferent vagal pathways transmitting signals to the brain generated ininflammation-affected tissues. The motor arm of this reflex consists of the efferent vagal
pathways that constitute the cholinergic anti-inflammatory pathway (Fig. 1).
As a result of activating the motor arm, acetylcholine released from vagal nerve endings
potently inhibits the production of cytokines by macrophages, thus protecting peripheral tissuesfrom inflammatory injury [7]. As a result of these observations, it was concluded that the
inflammatory reflex represents a crucial neural mechanism controlling the synthesis and release
of cytokines [5,6].
Either pharmacological or electrical stimulation of efferent vagal pathways significantly inhibits
the release of TNF-alpha in animals given a lethal dose of endotoxin. Furthermore, studies have
shown that stimulation of the efferent pathways of the vagus nerve has beneficial effects such
as inhibiting the development of pathological consequences in animal models ofischemia-reperfusion injury, myocardial ischemia, hemorrhagic shock, shock induced by
occlusion of splanchnic artery, ileus, experimental arthritis, pancreatitis, and burn-induced organ
dysfunction [8-12].
The inhibition of cytokine biosynthesis by the cholinergic anti-inflammatory pathway is caused
by cholinergic neurotransmission acting on alpha7 subtype acetylcholine receptors
(alpha7nAChR) located on macrophages and other cytokine synthesizing cells [13,14]. As
evidence of this, both direct electrical stimulation of the vagus nerve and the application of
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Role of the Vagus Nerve at the Neural-Immune Interface
Written by K Ondicova & B Mravec
Friday, 20 August 2010 00:00
alpha7nAChR agonists inhibit synthesis of TNF-alpha, IL-1beta, IL-6, IL-8, and HMGB1. This
binding of acetylcholine and acetylcholine analogues to the alpha7nAChR of immune cells also
induces a reduction in the nuclear translocation of NF-kappaB, a pro-inflammatory gene
regulatory protein. Furthermore, as other immune cells, including lymphocytes and microglia
express alpha7nAChR, this suggests that the cholinergic anti-inflammatory pathway may havewide effects across various immune cells [14]. This assumption is supported by the finding of
increased proliferation and cytokine secretion by CD4+ T cells in mice that have undergone
subdiaphragmatic vagotomy. Furthermore, administration of nicotine restored the reactivity of
immune cells in these animals, while administration of nicotine receptor antagonists induced an
effect similar to subdiaphragmatic vagotomy. These findings suggest that efferent vagal
pathways modulate a tonic inhibition of macrophage and T cell activity. Regardless of the
whatever else is learned about this system, it can be agreed that the involvement of the vagus
nerve in regulation of immune function is highly complex [15].
The role of the spleen
The spleen plays a key role in the regulation of immune function by the vagus nerve. During
their passage through the spleen, circulating immune cells are exposed to vagus nerve endings
[16]. Moreover, as the spleen is a prominent source of circulating TNF-alpha during
endotoxemia and stimulation of the vagus nerve inhibits endotoxin-induced increases in plasma
TNF-alpha, it is possible that lymphoid compartments of the spleen represent a target for vagal
anti-inflammatory action [17]. However, the role of direct vagal fibers innervating the spleen in
the regulation of inflammation remains questionable. In fact, anatomical and physiological
studies indicate that the vagus nerve modulates the activity of immune cells within the spleenindirectly via activation of sympathetic postganglionic neurons localized in the coeliac ganglia. It
is therefore possible that the vagus nerve modulates immune system activity in the spleen
indirectly through regulation of norepinephrine release from sympathetic nerve endings [18].
The importance of cholinergic anti-inflammatory pathway in human
medicine
The majority of data related to anti-inflammatory effects of the vagus nerve have been obtained
in animal studies. However, several clinical studies on the role of cholinergic anti-inflammatory
pathway in humans were published recently. In one study administration of nicotine before
activation of the immune system by lipopolysaccharide attenuated increases in body
temperature and increased plasma IL-10 and corticosterone levels [19].
Anti-inflammatory effect of the vagus nerve may explain several clinical findings. For example,
increased plasma levels of C reactive protein, IL-6, and TNF-alpha were found in patients with
insulin resistance, diabetes mellitus type 2, hypertension, hyperlipidemia, metabolic syndrome,
and Alzheimer’s disease; all conditions characterized by low-grade inflammation. Interestingly,
increased plasma and tissue activity of butyrylcholinesterase and acetylcholinesterase were
found in these patients. Since increased activation of these enzymes leads to decreased
transmission of cholinergic signals and acetylcholine represents a key molecule in the
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7/29/2019 Boris Mravec Role of the Vagus Nerve at the Neural Immune Interface
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Role of the Vagus Nerve at the Neural-Immune Interface
Written by K Ondicova & B Mravec
Friday, 20 August 2010 00:00
cholinergic anti-inflammatory pathway, increased degradation of acetylcholine may participate in
exaggerated inflammatory reactions [20]. Moreover, the beneficial effects of nicotine treatment
in patients with ulcerative colitis suggests that inappropriate activity of cholinergic
anti-inflammatory pathway may participate in its development as well [18].
Several methods can be used to stimulate the cholinergic anti-inflammatory pathway. For
example, it is possible to activate the afferent and/or efferent arm of inflammatory reflex by
stimulating the cholinergic anti-inflammatory pathway at the central level by administration of
muscarine receptor agonists, ACTH, ghrelin, or centrally acting acetylcholinesterase inhibitors
[5,21,22]. Ingestion of polyunsaturated fatty acids also increases vagal anti-inflammatory activity
[23] and therefore may represent a potent and simple therapeutic method for the treatment of
inflammatory diseases. Moreover, decreased pro-inflammatory immune cell responses were
found in patients with epilepsy treated by electrical stimulation of the vagus nerve [24].
Based on published data it is suggested that activation of cholinergic anti-inflammatory pathway
may represent a useful therapeutic approach. However, exaggerated activation of the
cholinergic anti-inflammatory pathway may excessively suppress immune function, thereby
inducing unfavorable consequences [25]. Therefore, it is necessary to consider two
consequences of activating the cholinergic-anti-inflammatory pathway: 1) inhibition of
inflammation that has beneficial effects during septic or hemorrhagic shock,
ischemia-reperfusion injury, and other situations related to excessive stimulation of immunefunctions; 2) inhibition of immune functions may negatively influence defense mechanisms
against invading pathogens, such as during the early stages of bacterial pancreatitis.
Furthermore, the consequences of activating the cholinergic anti-inflammatory pathway may
depend on not only the pathological situation, but the stage of disease as well. This is seen
during the early stages of inflammatory reaction where induced activation of the cholinergic
anti-inflammatory pathway will produce negative effects; while in later stages it may be
beneficial, protecting organisms from injury induced by excessive inflammatory reaction.
Conclusions
Animal studies have unambiguously shown that the vagus nerve plays an important role in the
regulation of immune reactions in various animal models of inflammatory diseases. While
several studies in humans also indicate the importance of the vagus nerve in the regulation of
immune function, it is necessary to take into consideration the fact that these studies used
mainly ex vivo approaches, using heart rate variability as a marker of cholinergic
anti-inflammatory pathway activity. Therefore, further experimental and clinical studies will be
necessary to elucidate the role of the vagus nerve in the modulation of inflammatory reactions in
humans.
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Role of the Vagus Nerve at the Neural-Immune Interface
Written by K Ondicova & B Mravec
Friday, 20 August 2010 00:00
Acknowledgments
This work was supported by the Slovak Research and Development Agency under the contract
No. APVV-0045-06, VEGA grants (1/0258/10, 1/0260/10, 2/0010/09) and European Regional
Development Fund Research and Development Grant No. NFP26240120024.
Nonstandard Abbreviations: alpha7nAChR, alpha7 subtype acetylcholine receptors;
HMGB1, high-mobility group box 1; IL, interleukin; LPS, lipopolysaccharide; TNF-alpha, tumor
necrosis factor alpha
Author(s) Affiliation
K Ondicova - Institute of Pathophysiology, Faculty of Medicine, Comenius University, 811 08Bratislava
B Mravec - Institute of Experimental Endocrinology, Slovak Academy of Sciences, 833 06
Bratislava, Slovak Republic
References
1. Watkins LR, Maier SF, Goehler LE: Cytokine-to-brain communication: a review & analysis
of alternative mechanisms. Life Sci, 1995; 57: 1011-26
2. Hansen MK, O''Connor KA, Goehler LE, Watkins LR, Maier SF: The contribution of the
vagus nerve in interleukin-1beta-induced fever is dependent on dose. Am J Physiol Regul IntegrComp Physiol, 2001; 280: R929-34
3. Bianchi M, Ulrich P, Bloom O et al: An inhibitor of macrophage arginine transport and
nitric oxide production (CNI-1493) prevents acute inflammation and endotoxin lethality. Mol
Med, 1995; 1: 254-66
4. Borovikova LV, Ivanova S, Nardi D et al: Role of vagus nerve signaling in
CNI-1493-mediated suppression of acute inflammation. Auton Neurosci, 2000; 85: 141-7
5. Andersson J: The inflammatory reflex--introduction. J Intern Med, 2005; 257: 122-5
6. Tracey KJ: The inflammatory reflex. Nature, 2002; 420: 853-9
7. Johnston GR, Webster NR: Cytokines and the immunomodulatory function of the vagus
nerve. Br J Anaesth, 2009; 102: 453-628. Sadis C, Teske G, Stokman G et al: Nicotine protects kidney from renal
ischemia/reperfusion injury through the cholinergic anti-inflammatory pathway. PLoS ONE,
2007; 2: e469
9. Niederbichler AD, Papst S, Claassen L et al: Burn-Induced Organ Dysfunction: Vagus
Nerve Stimulation Improves Cardiac Function. Eplasty, 2010; 10: e45
10. Altavilla D, Guarini S, Bitto A et al: Activation of the cholinergic anti-inflammatory
pathway reduces NF-kappab activation, blunts TNF-alpha production, and protects againts
splanchic artery occlusion shock. Shock, 2006; 25: 500-6
11. Giebelen IA, van Westerloo DJ, LaRosa GJ, de Vos AF, van der Poll T: Local stimulation
of alpha7 cholinergic receptors inhibits LPS-induced TNF-alpha release in the mouse lung.Shock, 2007; 28: 700-3
6 / 7
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Role of the Vagus Nerve at the Neural-Immune Interface
Written by K Ondicova & B Mravec
Friday, 20 August 2010 00:00
12. Tracey KJ: Physiology and immunology of the cholinergic antiinflammatory pathway. J
Clin Invest, 2007; 117: 289-96
13. Gallowitsch-Puerta M, Tracey KJ: Immunologic role of the cholinergic anti-inflammatory
pathway and the nicotinic acetylcholine alpha 7 receptor. Ann N Y Acad Sci, 2005; 1062:
209-1914. Gallowitsch-Puerta M, Pavlov VA: Neuro-immune interactions via the cholinergic
anti-inflammatory pathway. Life Sci, 2007; 80: 2325-9
15. Karimi K, Bienenstock J, Wang L, Forsythe P: The vagus nerve modulates CD4(+) T cell
activity. Brain Behav Immun, 2009:
16. Tracey KJ: Understanding immunity requires more than immunology. Nat Immunol,
2010; 11: 561-4
17. Huston JM, Ochani M, Rosas-Ballina M et al: Splenectomy inactivates the cholinergic
antiinflammatory pathway during lethal endotoxemia and polymicrobial sepsis. J Exp Med,
2006; 203: 1623-8
18. Rosas-Ballina M, Tracey KJ: Cholinergic control of inflammation. J Intern Med, 2009;265: 663-79
19. Wittebole X, Hahm S, Coyle SM, Kumar A, Calvano SE, Lowry SF: Nicotine exposure
alters in vivo human responses to endotoxin. Clin Exp Immunol, 2007; 147: 28-34
20. Das UN: Acetylcholinesterase and butyrylcholinesterase as possible markers of
low-grade systemic inflammation. Med Sci Monit, 2007; 13: RA214-21
21. Wu R, Dong W, Ji Y et al: Orexigenic hormone ghrelin attenuates local and remote
organ injury after intestinal ischemia-reperfusion. PLoS ONE, 2008; 3: e2026
22. Pavlov VA, Parrish WR, Rosas-Ballina M et al: Brain acetylcholinesterase activity
controls systemic cytokine levels through the cholinergic anti-inflammatory pathway. Brain
Behav Immun, 2009; 23: 41-523. Luyer MD, Greve JW, Hadfoune M, Jacobs JA, Dejong CH, Buurman WA: Nutritional
stimulation of cholecystokinin receptors inhibits inflammation via the vagus nerve. J Exp Med,
2005; 202: 1023-9
24. De Herdt V, Bogaert S, Bracke KR et al: Effects of vagus nerve stimulation on pro- and
anti-inflammatory cytokine induction in patients with refractory epilepsy. J Neuroimmunol, 2009;
214: 104-8
25. Kox M, Hoedemaekers AW, Pickkers P, van der Hoeven JG, Pompe JC: A possible role
for the cholinergic anti-inflammatory pathway in increased mortality observed in critically ill
patients receiving nicotine replacement therapy. Crit Care Med, 2007; 35: 2468-9; author reply 9
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