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Gut Bacteria May Be to Blame for Some Blindness

October 14, 2015

You might not know it, but your body is host to one million little soldiers in every milliliter of blood. These tiny defenders look like most other cells, but their purpose is very different. They lie in wait for their marching orders to find and attack invading germs or dangerous body cells to keep you safe and healthy. These teeny fighters are T cells, and their job is to protect you.

In the case of autoimmune uveitis, these T cells are overzealous and are given faulty commands. Once activated, they’re almost like heat-seeking missiles trained to find and eradicate the Bad Thing. In this case, they invade the eye and go after helpful proteins that enable vision. They damage its middle layer in a quest for protection; the eye has no way to defend itself. This disease is the leading cause of blindness in the United States and accounts for about ten percent of all severe visual disabilities in this country—meaning that 400,000 Americans have over-reactive T cells.

Autoimmune uveitis is strange because the eye has immune privilege. In other words, it’s physically separated from the rest of the body by a barrier of tissue and blood. It should be protected by this barrier like a fortress safe behind a moat and drawbridge; the T cells are only able to cross if activated by a protein from the eye itself.

Still, in the case of this disease, it’s obvious that T cells are attacking the eye, so something must be activating them and giving the “secret password” to cross the boundary. Researchers have started to wonder if a naturally-occurring bacteria in the gut could be acting as a training ground to activate these cells before they’re truly needed, effectively turning on the missiles.

A new study done by immunologist Rachel Caspi of the National Eye Institute in Bethesda, Maryland sought to learn if this was the case. She genetically engineered some common mice so their T cells responded to the eye proteins. These rodents developed autoimmune uveitis by the time they were barely weaned off their mothers’ milk. However, giving the animals rounds of antibiotics that killed most of their gut bacteria delayed the sickness’ onset and reduced its eventual severity. Finally, Caspi rounded out her experiment by adding so-called “gut goop” from the sick mice’s intestines to cultures of T cells to see if the gut flora truly did activate the cells.

Spoiler alert: it did. The findings suggest that certain bacteria within the intestines make proteins that closely mimic those in the eye, flipping the switch for the T cells. The now-active cells then begin their epic quest up the intestines towards the eye, where they systematically destroy the (benign) proteins.

While Caspi’s findings are exciting, they’re not completely earth-shattering. This theory has existed for quite some time.

“The idea has been there in the back of our minds,” ocular immunologist Andrew Taylor, of the Boston University of Medicine, said. “This is the first time it’s been shown that the gut flora seems to be part of the process.”

There’s no suggestion that taking a probiotic or an antibiotic will solve the problem of autoimmune uveitis, but it is a good start in treating and preventing the disease that’s been robbing people of their vision.

If you’ve been having difficulty with your vision, schedule an appointment at OCLI today. We’re happy to accommodate your schedule and find a timeslot that works for you.



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