Bacteria in the gut might activate cells to trigger inflammation associated with a condition that accounts for more than 10% of severe visual disability in the U.S., according to a recent study conducted by researchers at the National Eye Institute, part of the National Institutes of Health.
Autoimmune uveitis, an inflammatory eye disorder, occurs when a person’s immune system goes awry, attacking proteins in the eye. A study on mice suggests bacteria in the gut may provide a training ground for immune cells to attack the eye, according to an NIH news release.
The study was published in the Aug. 18 issue of the journal Immunity.
The NEI researchers studied mice genetically engineered to develop autoimmune uveitis. Before the mice showed signs of the disease, the team discovered the cells that attacked the eye in the mice’s intestines.
To test whether the activation of these cells preceded the first signs of the disease, the researchers gave the mice an antibiotic cocktail to wipe out a broad spectrum of bacteria in the gut, according to the release. Researchers found mice without gut bacteria developed autoimmune uveitis much later, and with less severity, compared with control mice with normal gut flora.
There was a similar delay in uveitis and decline in its severity when the uveitis-prone mice were raised in an environment free of bacteria and other germs. But when the same mice were later moved into normal housing, where they acquired normal gut bacteria, the uveitis increased in severity, according to the study.
Corticosteroids provide a blanket approach to autoimmune uveitis by quelling inflammation, but their long-term use can lead to adverse side effects, according to the release. “Understanding what spurs autoimmune uveitis is fundamental to the development of safer long-term therapies and possibly even strategies for preventing it,” Reiko Horai, PhD, a staff scientist at NEI and a lead author of the study, said in the release.
Recent evidence has shown an association between the microbiota in the gut — bacteria, fungi and viruses — and the development of autoimmune disorders, according to the release.
Findings from this study “have implications about the origins of autoimmune diseases not only in the eye, but also elsewhere in the body,” Rachel R. Caspi, PhD, a senior investigator at NEI, said in the release. Her lab led the study.
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