'Friendly viruses' as beneficial to gut health as 'friendly bacteria'

Date: Dec-02-2014 Researchers believe they have found the first strong indication that the gut

is a natural home to viruses that are as helpful as "friendly bacteria" in

maintaining health and keeping infection at bay.

A team of microbiologists reveals strong evidence that

the gut has a virome of "friendly viruses" that plays a similar role to the

microbiome of "friendly bacteria" in maintaining health.

The human body carries thousands of species of bacteria - collectively known as

the "microbiome" - that we now know are essential to health. The highest diversity

and concentration of these is found in the gastrointestinal tract or the gut.

Now, in the journal Nature, microbiologists at NYU Langone Medical

Center, New York, NY, describe how they discovered evidence in mice of what they call

the "virome" - and how it plays a role in gut health similar to that of the

microbiome.

Over the course of two years, the team undertook several experiments in mice. They

found infection with the common murine norovirus (MNV) helped the mice heal

inflammation-damaged gut tissue and restore their gut's immune system after its

microbiome had been destroyed by antibiotics.

Furthermore, the researchers also discovered that MNV strengthened the ability of

the mice's immune system to defend against tissue damage.

Previous studies have suggested there is a 'virome'

Previous studies have found genetic traces in the gut to suggest there might be

such a thing as a virome. But none has gone so far as to show that a virome might be

a natural thing, and whether it might harm, help or have no particular effect on the

host.

Senior study investigator and assistant professor Ken Cadwell says their study

provides "compelling" evidence about how viruses and bacteria naturally work together

in the mouse gut.

Scientists have long been puzzled by how people get infected all the time with viruses and

bacteria without falling ill.

"Now we have scientific evidence that not every viral infection is bad, but may

actually be beneficial to health, just as we know that many bacterial infections are

good for maintaining health," Prof. Cadwell explains.

The finding "lays the groundwork for further research on precisely how the virome

supports the immune system, which likely applies to humans, as well," he adds.

For their study, the team used mice genetically engineered to be susceptible to

inflammatory bowel disease (IBD) - a collective term for diseases

like ulcerative colitis and Crohn's disease that involve inflammation of the gut.

While the exact cause of IBD is unknown, scientists are coming to the view that it

results from altered interactions between the gut's microbiome and its immune system

- causing the immune system to attack healthy tissue.

In previous work, the team had also found inducing chronic infection with MNV in

the mice led to the same inflammatory damage as chronic exposure to bacteria -

suggesting both types of infection have a similar effect on the immune system.

In the new study, they raised IBD mice in sterile conditions and lacking a normal

microbiome - which meant their intestines and immune systems did not develop

properly - and fed them MNV.

The IBD mice's underdeveloped immune systems lacked white blood cells known as T-cells and B-cells, and their underdeveloped guts had shrunken and thinner villi with

less tissue than normal between them. Villi are long, thin, fleshy fingers that project from the gut wall and give it the

large surface area it needs to absorb a maximum amount of nutrients from digested

food.

Virus helped restore immune system and gut wall

After feeding MNV to the IBD mice, the researchers kept them in the sterile

conditions and did not expose them any other germs. After two weeks, the mice showed

much improved - nearly restored to normal - immune systems and almost complete

restoration of the gut wall.

Further tests showed that it was MNV driving the restoration. The researchers

found evidence of increased immune system signaling by antiviral type 1 interferon

proteins.

The team repeated a similar experiment with normal mice: they fed them MNV after

wiping out their microbiome with antibiotics. They found the mice's blood T-cell

count doubled, and samples of gut wall and blood showed presence of B-cell

antibodies.

The team now plans to repeat these tests with other types of gut viruses and to

find out whether their ability to harm or benefit the gut varies from person to

person.

Prof. Cadwell urges people not to infect themselves with viruses on the basis of

these results - they could do themselves serious harm.

The National Institutes of Health and several other granting bodies funded the

study.

Recently in another article, Medical News Today reported how
metabolic syndrome may be prevented by healthy gut bacteria. Researchers writing

in the journal Gastroenterology explained how an altered microbiome promotes

the inflammation that leads to metabolic syndrome.

Written by Catharine Paddock PhD

Not to be reproduced without permission.

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Courtesy: Medical News Today Note: Any medical information available in this news section is not intended as a substitute for informed medical advice and you should not take any action before consulting with a health care professional.