Relationship between gut bacteria, blood cell development helps immune system fight infection

March 12, 2014
Credit: California Institute of Technology

The human relationship with microbial life is complicated. At almost any supermarket, you can pick up both antibacterial soap and probiotic yogurt during the same shopping trip. Although there are types of bacteria that can make us sick, Caltech professor of biology and biological engineering Sarkis Mazmanian and his team are most interested in the thousands of other bacteria—many already living inside our bodies—that actually keep us healthy. His past work in mice has shown that restoring populations of beneficial bacteria can help alleviate the symptoms of inflammatory bowel disease, multiple sclerosis, and even autism. Now, he and his team have found that these good bugs might also prepare the immune cells in our blood to fight infections from harmful bacteria.

In the recent study, published on March 12 in the journal Cell Host & Microbe, the researchers found that beneficial were necessary for the development of innate —specialized types of white blood cells that serve as the body's first line of defense against invading pathogens.

In addition to circulating in the blood, reserve stores of immune cells are also kept in the spleen and in the bone marrow. When the researchers looked at the immune cell populations in these areas in so-called germ-free , born without gut bacteria, and in healthy mice with a normal population of microbes in the gut, they found that germ-free mice had fewer immune cells—specifically macrophages, monocytes, and neutrophils—than healthy mice.

Germ-free mice also had fewer granulocyte and monocyte progenitor cells, stemlike cells that can eventually differentiate into a few types of mature immune cells. And the innate immune cells that were in the spleen were defective—never fully reaching the proportions found in healthy mice with a diverse population of gut microbes.

"It's interesting to see that these microbes are having an immune effect beyond where they live in the gut," says Arya Khosravi, a graduate student in Mazmanian's lab, and first author on the recent study. "They're affecting places like your blood, spleen, and bone marrow—places where there shouldn't be any bacteria."

Khosravi and his colleagues next wanted to see if the reduction in immune cells in the blood would make the germ-free mice less able to fight off an infection by the harmful bacterium Listeria monocytogenes—a well-studied human pathogen often used to study immune responses in mice. While the healthy mice were able to bounce back after being injected with Listeria, the infection was fatal to germ-free mice. 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 gave injections of Listeria to healthy mice after those mice were dosed with broad-spectrum antibiotics that killed off both harmful and . Interestingly, these mice also had trouble fighting the Listeria infection. "We didn't look at clinical data in this study, but we hypothesize that this might also happen in the clinic," says Mazmanian. "For example, when patients are put on antibiotics for something like hip surgery, are you damaging their gut microbe population and making them more susceptible to an infection that had nothing to do with their hip surgery?"

More importantly, the research also suggests that a healthy population of gut microbes can actually provide a preventative alternative to antibiotics, Khosravi says. "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."

These results appear in a paper titled "Gut Microbiota Promote Hematopoiesis to Control Bacterial Infection."

Explore further: Gut microbes affect MicroRNA response to bacterial infection

More information: Paper: www.sciencedirect.com/science/ … ii/S193131281400064X

Related Stories

Gut microbes affect MicroRNA response to bacterial infection

December 10, 2013
When it comes to fighting off pathogens like Listeria, your best allies may be the billions of microorganisms that line your gut, according to new research published in mBio, the online open-access journal of the American ...

NIH team describes protective role of skin microbiota

July 26, 2012
A research team at the National Institutes of Health has found that bacteria that normally live in the skin may help protect the body from infection. As the largest organ of the body, the skin represents a major site of interaction ...

How our immune system backfires and allows bacteria like Salmonella to grow

February 6, 2014
Our immune system wages an internal battle every day to protect us against a broad range of infections. However, researchers have found that our immune response can sometimes make us vulnerable to the very bacteria it is ...

B cells school gut microbes

November 27, 2013
Your immune system's B cells can respond to an amazing number of pathogens—viruses, bacteria, etc.—without ever having encountered them. That's because, as they develop, your B cells reshuffle their antibody-producing ...

Gut microbes spur development of bowel cancer

March 3, 2014
It is not only genetics that predispose to bowel cancer; microbes living in the gut help drive the development of intestinal tumors, according to new research in mice published in the March issue of The Journal of Experimental ...

Researchers find source of new lineage of immune cells

February 12, 2014
The elusive progenitor cells that give rise to innate lymphoid cells—a recently discovered group of infection-fighting white blood cells—have been identified in fetal liver and adult bone marrow of mice, researchers from ...

Recommended for you

Study explores whole-body immunity

November 21, 2017
Over the next few months, millions of people will receive vaccinations in the hope of staving off the flu—and the fever, pain, and congestion that come with it.

Drug could cut transplant rejection

November 21, 2017
A diabetes drug currently undergoing development could be repurposed to help end transplant rejection, without the side-effects of current immunosuppressive drugs, according to new research by Queen Mary University of London ...

Atopic eczema—one size does not fit all

November 21, 2017
Researchers from the UK and Netherlands have identified five distinct subgroups of eczema, a finding that helps explain how the condition can affect people at different stages of their lives.

Breast milk found to protect against food allergy

November 20, 2017
Eating allergenic foods during pregnancy can protect your child from food allergies, especially if you breastfeed, suggests new research from Boston Children's Hospital. The study, published online today in the Journal of ...

Zika-related nerve damage caused by immune response to the virus

November 20, 2017
The immune system's response to the Zika virus, rather than the virus itself, may be responsible for nerve-related complications of infection, according to a Yale study. This insight could lead to new ways of treating patients ...

How a poorly explored immune cell may impact cancer immunity and immunotherapy

November 17, 2017
The immune cells that are trained to fight off the body's invaders can become defective. It's what allows cancer to develop. So most research has targeted these co-called effector T-cells.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.