The surface of the eye is one of the most inhospitable environments for microbes in the mammalian body, because tears are loaded with anti-microbials. However, some microbes can live on this sparsely populated tissue and may play a key role in preventing eye infection. NIH researchers reporting in the journal Immunity on July 11 found that Corynebacterium mastitidis dwells on the eyes of laboratory mice, and that mice with Corynebacterium could fend off invading pathogenic microbes better than mice without it.
“People have been finding bacterial DNA on the human eye but no one has presented experimental proof that these bacteria actually live there,” says senior co-author Rachel Caspi, an immunologist at the National Eye Institute, National Institutes of Health (NIH). “For all we know, these bacteria may have ‘crash landed’ on the eye and were killed by the anti-microbials in tears or patrolling immune cells. Finding a bug that persists there long term was a bit of a surprise. We were looking for it but not necessarily expecting it.”
The NIH investigation began with a strain of lab mice that develop nasty bacterial conjunctivitis — also known as “pink eye” where the thin mucous membranes that line the inside of the eyelid and cover the whites of the eyes, or “conjunctiva,” become inflamed. These mice lack an immune molecule called IL-17, which summons immune cells to areas of infection. The researchers hypothesized that in common strains of mice, a commensal microbe on the surface of the eye might be setting off an IL-17 response to protect from harmful infection.
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