Virus travels from gut to brain, altering immune system and contributing to Alzheimer’s-linked cell changes
A virus that can cause infection in the gut and from there travel
to the brain, could be important in the development of Alzheimer's disease,
according to a study.
Existing antiviral drugs may then be looked at for treating or
preventing this form of Alzheimer's disease, researchers, including those at
the Arizona State University, US, said.
Most humans are thought to have been exposed to cytomegalovirus
(HCMV), one of the nine viruses known to cause herpes (painful blisters on the
skin), during the first few decades of their lives. The virus is usually
transmitted through bodily fluids and spreads only when it is active.
Published in Alzheimer's and Dementia: The Journal of the Alzheimer's
Association, the study found that in some people, the herpes-causing virus may
remain active in the gut, from where it can travel to the brain via the vagus
nerve, which connects the gut and the brain.
Once in the brain, the virus can alter the immune system and
contribute to changes in cells associated with Alzheimer's disease, the
researchers explained.
The researchers noted that the herpes-causing virus is recognized
by immune cells in the brain, called microglia, which activate a specific gene
called 'CD83.'
The virus could then contribute to biological changes in the
brain, which are known to be involved in the development of Alzheimer's disease
— a neurodegenerative disorder that progressively deteriorates brain function,
such as memory and cognitive abilities, as one ages.
"We think we've identified a biologically unique subtype of
Alzheimer's that may affect 25-45% of people with the disease," said Ben
Readhead, first author and research associate professor at Arizona State
University.
"This subtype includes the hallmark amyloid plaques and tau
tangles — microscopic brain abnormalities used for diagnosis — and features a
distinct biological profile involving the virus, antibodies, and immune cells
in the brain," Readhead added.
For the study, the researchers analyzed spinal fluid from
Alzheimer's patients and found antibodies produced specifically in response to
the herpes-causing virus. They also found evidence of infection in the
intestines and brain tissue of these individuals caused by the same virus.
Furthermore, the team observed the herpes virus within the vagus
nerve of the patients, suggesting this could be the pathway through which it
travels to the brain.
In another group of Alzheimer's patients, the researchers were
able to replicate the association between the gut infection and CD83(+)
microglia.
A previous study by the researchers conducted a post-mortem
analysis of the brains of Alzheimer's patients and found that these patients
were more likely to harbor CD83(+) microglia specifically.
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