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Battle of the bugs: Beneficial bacteria vital to immune response against infection

By Lynda Searby , 17-Mar-2014
Last updated the 17-Mar-2014 at 14:44 GMT

Battle of the bugs: Beneficial bacteria vital to immune response against infection

Our microbiome may play a central role in immune responses to infections, according to new research revealing how beneficial bacteria are necessary for the development of innate immune cells.

Beneficial bacteria in our gut are needed to fight off infections from harmful bacteria, as well as providing a preventative alternative to antibiotics by limiting the body’s susceptibility to infection, according to the report from US researchers.

The in vivo study, conducted by researchers from the California Institute of Technology, found that beneficial gut bacteria are necessary for the development of innate immune cells – white blood cells that serve as the body’s first line of defence against invading pathogens.

“Today there are more and more antibiotic resistant superbugs out there and we’re running out of ways to treat them. Limiting our susceptibility to infection could be a good protective strategy,” said Arya Khosravi, first author of the study published in this month’s Cell Host & Microbe.

Study details

The researchers compared immune cell populations in ‘germ-free’ mice, born without gut bacteria, and healthy mice with a normal population of microbes in the gut. They found that the germ-free mice had fewer immune cells than the healthy mice.

“Herein, we reveal that gut bacteria regulate hematopoiesis [the formation of blood cellular components] within primary immune sites, providing a unifying explanation for previous observations of the widespread effects by the microbiota on the immune system,” said the researchers.

Next, the scientists wanted to see if the reduction in immune cells in the blood would make germ-free mice less able to fight off infection by the harmful bacterium Listeria monocytogenes.

While the healthy mice were able to survive the Listeria infection, the infection was fatal to germ-free mice. Conversely, when gut microbes that would normally be present were introduced into germ-free mice, the immune cell population increased and the mice were able to survive the Listeria infection.

The researchers also dosed healthy mice with broad spectrum antibiotics that killed off both harmful and beneficial bacteria before injecting them with Listeria. These mice had trouble fighting the Listeria infection too.

An alternative to antibiotics?

The researchers speculated that this might also happen in humans: “Evidence that depletion of the microbiota leads to transient immune suppression suggests factors that disrupt commensal microbes, including clinical antibiotic use, may, paradoxically, be a risk factor for susceptibility to opportunistic pathogens,” wrote the researchers.

For example, the researchers hypothesise that putting patients on antibiotics for something like hip surgery could damage their gut microbe population and make them more susceptible to an infection that had nothing to do with their surgery.

Therefore, the findings could pave the way for developing alternative medical approaches for preventing infections.

“The concepts proposed herein, if validated in humans, may herald future medical approaches that combine antibiotics with immunomodulatory microbial molecules as revolutionary combination treatments to address the re-emerging crisis of infectious diseases,” the researchers concluded.

Source: Cell Host & Microbe
Volume 15, Issue 3 Pages 374 - 381, doi: 10.1016/j.chom.2014.02.006
“Gut Microbiota Promote Hematopoiesis to Control Bacterial Infection”
Authors: Arya Khosravi, Alberto Yáñez, et al

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