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VanElzakker IACFSME2014 .pdf


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Chronic fatigue syndrome from vagus nerve infection:
A psychoneuroimmunological hypothesis
Michael B. VanElzakker
Tufts University Psychology; Massachusetts General Hospital Psychiatric Neuroscience, Martinos Center for Biomedical Imaging

Controversies in chronic fatigue syndrome (CFS)

“Given that cytokines are autocrine and paracrine communication
factors, their circulating levels have little functional value and represent
mostly spillover from the site of cytokine production and action.”

– Dantzer et al. (2013). The Neuroimmune Basis of Fatigue


There is a general consensus among CFS researchers that the
symptoms seem to reflect an ongoing immune response, perhaps
due to viral infection. However, many unresolved questions remain.

The vagus nerve is a
sensitive cytokine detector

Why have so many different pathogens been associated with CFS?
Why is there no one single predictable cause?

The vagus nerve innervates trunk
organs that are especially poised
to contact pathogens. When local
innate immune cells detect any
pathogen, they produce proinflammatory cytokines, which are
detected by chemoreceptors in
afferent vagus nerve terminals.
The brain receives this signal and
initiates normally-adaptive
sickness behavior and responses.

Why are cytokine studies so inconsistent?
Why isn’t there consistent evidence of active virus in CFS?
Why are women so much more likely to suffer from CFS?
I have proposed a hypothesis that accounts for these questions.
The Vagus Nerve Infection Hypothesis (VNIH) of CFS is as follows:

While the sensory vagus nerve normally signals the body
to rest when it senses a peripheral infection, that fatigue
signal is pathologically exaggerated when an infection is
located on the vagus nerve itself.

The innate immune system and sickness behavior
The more evolutionarily ancient division of the immune system
launches the same general response when any pathogen is
detected. Part of this acute phase response is sickness
behavior, a brain-based and normally-adaptive involuntary
function serving to divert the body’s resources toward fighting
infection. It includes:
ü Fatigue

ü  Cognitive impairments

ü Low-grade fever

ü  Loss of appetite

ü Musculoskeletal pain

ü  Depression/ malaise

ü Hyperalgesia

ü  Zinc depletion

ü Sleep architecture changes
These are all proinflammatory cytokine-mediated aspects
of the innate immune system response to any infection.
They are also all symptoms of CFS.

Proinflammatory cytokines signal infection
Proinflammatory cytokines are produced locally when
pathogens are detected by innate immune cells such as
monocytes, or the glial cells that embed nerve and brain cells.
Cytokines such as IL-1β, TNFα, and IL-6 are hydrophilic
proteins that do not easily diffuse across the blood-brain
barrier to have direct effect upon the brain.
So how does the brain know that the body is
sick if cytokines don’t access the brain through
the bloodstream? Answer: the vagus nerve.

interleukin (IL) 1-β

Pathogen-activated glial cells exaggerate vagus signaling
Normal
vagus
function


monocyte

IL-1β
TNFα
IL-6

Fatigue, fever,
pain, brain fog,
sleep problems

…the cell releases The vagus nerve …initiating
When any
proinflammatory
detects those
normal sickness
pathogen concytokines…
responses.
tacts any innate cytokines locally.
immune cell…
Vagus nerve ganglia and
Neurotropic pathogens such as
paraganglia are embedded HHV-6, enteroviruses, Borrelia
Peripheral vagus nerve
in glia.
burgdorferi (Lyme) & cytomegaloganglionic cell body
Satellite
virus are especially likely to
glial cells
Schwann glial cells
contact (para)ganglionic glial cells.
Vagus axon
The Vagus
Nerve
Infection

Hypothesis


microglia

When any
pathogen infects
a nerve cell, the
surrounding glia
become activated.

IL-1β
TNFα
IL-6
glutamate
NGF, ROS,
prostaglandins, NO, ATP

Like other innate cells, activated glia produce cytokines, but also produce neuroexcitatory substances.
The vagus nerve is not only directly bombarded with
cytokines, but the signal is supercharged. Normal
sickness responses becomes pathologically strong.

Glial activation adapted from Bilbo & Schwartz (2009); sagittal brain adapted from VanElzakker et al. (2013)

Neuropathic pain & shingles as mechanistic models
The neuropathic pain literature demonstrates that pathogeninduced glial activation can cause pathological nerve signaling.
A normal pain signal is enhanced by activated glia, and
becomes hyperalgesia or allodynia. The Vagus Nerve Infection
Hypothesis (VNIH) posits that normal sickness behavior
signaling is enhanced by activated glia to become CFS.
In-situ hybridization showing TNFα
The shingles literature
mRNA expression in the satellite
glial cells of a trigeminal ganglion
demonstrates that
glia

infected with latent herpesvirus.
herpesviruses in sensory
Larger cells are sensory neurons.
neuron


ganglia continue to
Adapted from Hukkanen et al. (2002)
cause an ongoing cytokine response, even months into latency.

Implications:Symptoms
Symptoms
Implications:
•  • During
exertion,
skeletal
muscles
produce
cytokines/myokines
During
exertion,
skeletal
muscles
produce
the cytokine/
such
as IL-6,
which
could
explain
post-exertional
malaise.
myokine
IL-6,
which
could
explain
post-exertional
malaise.
Deconditioned
muscles
produce
more
IL-6.
Deconditioned
muscles
produce
more
IL-6.
•  • Variance
in in
location
of infection
along the
vagus nerve
and
Variance
the severity
and location
of infection
along
thein the
rest
of the
bodyand
could
explain
variance
in symptom
presentation.
vagus
nerve
in the
rest of
the body
could explain
Neurotropic
arepresentation.
known for anterograde
movement
variance inviruses
symptom
Neurotropic
viruses are
through
tissue.
knownnerve
for anterograde
movement through nerve tissue.
•  The vagus nerve is a structurally and functionally sexually
• dimorphic
The vagus
nerve
is a structurally
and
functionally
sexually
organ,
which
could explain
why
CFS is much
more
dimorphic
organ, which
common
in women
than incould
men.explain why CFS is much more
common in women than in men.

Implications: Treatment options
•  According to the VNIH of CFS, possible treatment strategies
include glial inhibitors, specific antivirals, vagus nerve
stimulation (VNS), and local vagotomy.
•  (Para)ganglia are immunoprivileged – meaning protected
from antibodies and drugs, similar to the blood-brain barrier.
•  Individualized medicine will likely be critical.
References
Bilbo & Schwarz (2009). Early-life programming of later-life brain and behavior: A critical role for
the immune system. Frontiers in Behavioral Neuroscience. PMID 19738918
Dantzer et al. (2013). The neuroimmune basis of fatigue. Trends In Neuroscience. PMID
24239063
HHV-6 image adapted from www.hhv-6foundation.org
Hukkanen et al. (2002). Cytokines in experimental herpes simplex virus infection. International
Reviews of Immunology. PMID 12486819
Vagus nerve figure: www.cea1.com/anatomy-sistems/anatomy-of-the-vagus-nerve
VanElzakker (2013). Chronic fatigue syndrome from vagus nerve infection: A psychoneuroimmunological hypothesis. Medical Hypotheses. PMID 23790471
VanElzakker et al. (2013). From Pavlov to PTSD: The extinction of conditioned fear in rodents,
humans, and in anxiety disorders. Neurobiology of Learning & Memory. PMID 24321650
Wikipedia.org images of IL-1β, glia, enterovirus, and cytomegalovirus adapted under fair use.


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