In uveitis, bacteria in gut may instruct immune cells to attack the eye

NIH | OCTOBER 3, 2015

The inflammatory eye disorder autoimmune uveitis occurs when a person’s immune system goes awry, attacking proteins in the eye. What spurs this response is a mystery, but now a study on mice suggests that bacteria in the gut may provide a kind of training ground for immune cells to attack the eye.

The activated T cells then migrate through the bloodstream to the eye, where they cause the inflammatory response associated with autoimmune uveitis. Image credit: National Eye Institute

In the case of autoimmune uveitis, immune cells (T cells) are thought to penetrate through the blood-ocular barrier. But first, they must become activated, which occurs when they come in contact with the protein that they are pre-programmed to recognize. This is how T cells fight an infection and some types of cancer – by targeting proteins on bacteria, viruses and cells.

The researchers gave the mice an antibiotic cocktail designed to wipe out a broad spectrum of bacteria in the gut and by rearing them in a germ-free environment. They found that mice without gut bacteria developed autoimmune uveitis much later, and with less severity, compared to control mice with normal gut flora.

Bacteria in the gut produce a molecule that, to T cells, looks similar to a protein in the retina. This gives the T cells marching orders to look for that retinal protein and attack it.

Given the huge variety of bacteria in our intestines, if they can mimic a retinal protein, it is conceivable that they could also mimic other self-proteins in the body. That normally harmless bacteria in the gut could be involved in promoting other autoimmune diseases as well.

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