Cow protein may help eye inflammation.

Uveitis, an eye inflammation, is responsible for about 10 percent of all cases of severe vision impairment and blindness in the United States. It can arise from injury or infection, but it sometimes attacks mysteriously via an autoimmune reaction--the body turning against itself. To suppress the immune system in such cases, patients need to take powerful steroids for long periods, a treatment that can cause harmful side effects, including kidney damage, glaucoma, cataracts, and brittle bones.

Scientists at the National Eye Institute in Bethesda, Md., report in the May American Journal of Ophthalmology that retinal S antigen, a purified protein derived from cow eyes, may enable physicians to wean some patients off steroids without their uveitis flaring up.

Of 45 people whose autoimmune-based uveitis was being held in check with steroids and other medication, 10 received pure retinal S antigen orally, 10 got a mixture of other cow retinal constituents, 10 took a combination of the S antigen and the bovine mixture, and 15 received a placebo. Over 11 weeks, doctors tried to taper off the patients' steroid dosage while keeping inflammation at bay. The 10 patients receiving pure retinal S antigen fared markedly better than those in the other groups. Some were able to stop taking steroids. Surprisingly, the 10 patients who received the mixture without the S antigen. flied badly, even worse than the placebo group, says Robert Nussenblatt, leader of the research team.

How S antigen works is unclear, Nussenblatt says. It may produce substances that "turn off" the immune response in the eye, he says, or it may paralyze T cells, the immune system's roving soldiers.

Uveitis can lead to glaucoma or irreversible destruction of the retina. Although the study population was small, the researchers consider the findings promising and are preparing for a larger clinical trial. S antigen may also prove useful in preventing rejection of corneal grafts, they suggest.