Gut microbes have been shown to play a role in everything from circadian rhythms and metabolism to weight gain and immunity, but researchers have uncovered one specific area where you probably wouldn’t expect gut microbes to make a difference: eye disease. Researchers at the National Eye Institute (NEI) found that bacteria in the gut may play an active role in the development of an inflammatory eye disease known as autoimmune uveitis.
Autoimmune uveitis is responsible for about 10 percent of severe visual disability in the United States. It occurs when immune cells, called T cells, become activated and penetrate the protective blood-ocular barrier to attack proteins in the eye. T cells are preprogrammed to recognize proteins on bacteria, viruses and cells, but researchers were unsure what was programming the T cells to target eye proteins.
Senior study author Rachel Caspi, Ph.D., of the National Institutes of Health, considered the possibility that activation could take place in the eye itself, but because T cells must be activated before they can enter the eyes, this theory seemed unlikely. Caspi and her colleagues eliminated several other theories before zeroing in on gut microbes. “If indeed they can become activated in the intestinal tissue, this would explain how they are able to afterward enter the eye,” she explained.
Caspi and her team performed a study on mice to test their theory. They found that activated T cells were elevated in the mice’s intestines but not in the lymph nodes, indicating that T cells may be activated in the gut before any signs of disease are present. The researchers then administered antibiotics to the mice in order to wipe out their gut microbes. They noted the autoimmune uveitis was delayed and less severe in the mice with no gut bacteria, compared to mice with normal gut microbes. They also found that mice raised in an environment with no exposure to germs or bacteria displayed similar results. However, once the mice were moved to a typical environment and developed normal gut bacteria, autoimmune uveitis was much more severe.
The next step in this research will focus on identifying the bacteria responsible for activating T cells in autoimmune uveitis. Caspi predicts that future treatments may be able to eliminate or prevent these bacteria from attacking eye proteins. “If found … we may be able in the future to use this knowledge to selectively eliminate the response that leads to the development of this disease” (Source: Healthline).