Medicinal Tears

Researchers have identified a compound in tears that appears to protect the cornea from infection with a notorious microbe. The results, presented here on 26 May at the annual meeting of the American Society for Microbiology, could help prevent eye infections in contact lens wearers or lead to new treatments.


Healthful teardrops A component of tears fights bacterial infections in the eye.
CREDIT: CORBIS
A notorious microbe called Pseudomonas aeruginosa is the leading cause of eye infections in people wearing contacts; in severe cases, infection can lead to permanent vision loss. Previously, Suzanne Fleiszig, a microbiologist at the University of California, Berkeley's School of Optometry, had discovered that human tear fluid can prevent the microbe from damaging or invading cornea cells. For the current study, she collected more tears from volunteers ("onions work pretty well," she says) to find out what component of the chemical soup that makes up tears is responsible.

Among the potential candidates Fleiszig and her colleagues tested was a group of molecules known as collectins, some of which play a role in protecting the lungs against infection. Sure enough, they discovered that one of these, called surfactant protein D (SP-D) is abundant in human tears. They also found that the protein coats the corneas of mice. In petri dish tests, both the human and mouse version of SP-D could reduce P. aeruginosa抯 ability to infect cornea cells; but when SP-D was removed from human tear fluid, the tears no longer offered any protection. Fleiszig now plans to find out if people wearing contact lenses have less SP-D on their corneas or if the lenses somehow impair the protein's activity.

"It's great," Harvard microbiologist Gerald Pier said after studying Fleiszig's poster at the meeting. The risk of cornea infections is low for individual lens wearers, Pier says--but because so many people wear contacts, it's still a big problem. "Finding out why people are resistant when they're not wearing contact lenses is pretty important," he says. And SP-D, or something resembling it, might be used to prevent or treat cornea infections, he says.