Microbes in our body -- helping us in everything from maintaining the immune system to digesting our food -- have also been discovered to protect our brains from harmful pathogens, researchers say.
They do that by helping close the so-called blood-brain barrier, the molecular "fence" protecting the brain from pathogens and other molecules that might harm it, they found.
In a previous study, it was discovered that microbes within the human gut could activate genes responsible for coding for so-called gap junction proteins, vital in building the gut wall that keeps gut pathogens from moving into the bloodstream and possibly causing disease.
In this new research, scientists at the Karolinska Institute in Sweden decided to focus on the blood-brain barrier, where gap junction proteins are also found.
In laboratory studies on mice, some were raised in sterile conditions that left them with no discernible microbes in their bodies while others had normal microbiota, researchers injected antibodies -- too large to normally breach the blood-brain barrier -- into embryos that were developing in both germ-free and normal female mice.
The barrier normally closes completely around 17 days into embryo development, and while the antibodies moved into the brains of all embryos younger than 17 days -- as expected -- they continued to be able to enter the brains of embryos of germ-free mothers considerable beyond day 17, the researchers reported in the journal Science Translational Medicine.
Karolinska scientists Sven Pettersson, an intestinal biologist, and Viorica Braniste, a postdoctoral researcher, found that embryos in the microbe-free mothers had fewer gap junction proteins and those detected in their brains were found to be less active than normal.
The findings may have relevance to human health, the researchers suggest; a woman's diet or exposure to antibiotics during pregnancy, which might affect the microbiota in her body, may influence the development of this barrier.
A "leaky" blood-brain barrier is also a factor in some diseases, such as multiple sclerosis, possibly leading to declining brain function, they said.
The findings of the Swedish researchers suggest a "striking effect" for microbes in the body and "a role for the [microbes] in regulating brain development and function," says Elaine Hsiao, a neurobiologist with the California Institute of Technology in Pasadena, Calif., who was not involved in the study.
She did caution that the study was not perfect because of the use of germ-free mice, something not found in nature.
"Germ-free mice are useful tools for studying the microbiota, but the germ-free condition is artificial and involves widespread disruptions" in body functions, possibly involving impairment of the immune system and a loss of gut integrity, Hsiao says.
