By Martin Enserink, Science Now
New Orleans -- 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.
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Mouse corneas infected with bacteria. In the picture on the right,
the SP-D is homing in on the bacteria (i.e., they colocalize).
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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 (see illustration). In petri dish tests, both the human and mouse version of SP-D could reduce P. aeruginosa's 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.
[Much of the work described in this article was carried out by Minjian Ni, a graduate student in the UC Berkeley Vision Science Program. Her research, which is focused on surfactant protein D and its roles at the ocular surface, could lead to new strategies for treating a variety of diseases of the eye and other sites.]
The text of this article originally appeared in Science News, May 26, 2004. You can link to that article
at Medicinal Tears
or search at the Science Now home page. The illustrations above were provided by Prof. Fleiszig and did not appear in the orignial article.
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