Chicken cartilage soothes aching joints.

An experimental therapy appears to offer significant relief to people suffering from the pain and swelling of rheumatoid arthritis.

Rheumatoid arthritis results when the immune systems mistakenly attacks the body's own tissues -- in this case, the inner lining of the joints. Although nobody knows for certain what causes the disease, some researchers think a virus combined with an inherited vulnerability triggers the autoimmune attack. As the disease progresses, it destroys the rubbery cartilage that cushions the ends of the bones.

Previous research suggested an unusual strategy against this disorder, one that relied on collagen, a fibrous protein found in cartilage. David E. Trentham and his colleagues at the Harvard Medical School in Boston knew that a collagen treatment blocked the development of an arthritic condition in rats. And the team's pilot study of 10 people suggested that this therapy could ameliorate and even eradicate clinical symptoms of the disease in humans.

So Trentham's team embarked on a clinical trial of collagen therapy in 59 people with severe rheumatoid arthritis. All volunteers were takne off the drugs they had been using to control their joint pain for the duration of the study. Each morning, 28 recruits drank a glass of orange juice containing collagen derived from purified chicken cartilage. The remaining 31 volunteers, who served as controls, drank orange juice containing a placebo. Neither the volunteers nor the researchers knew who received the active treatment and who get the placebo.

After three months, the team noticed a decrease in the number of swollen and tender joints reported by most people getting the collagen. Indeed, four of the 28 experienced a complete remission of their disease. "That was an unprecedented and surprising outcome of the study," Trentham says, adding that he doesn't know how long such a remission will last.

The researchers found no such improvement in the placebo group. Their report appears in the Sept. 24 SCIENCE.

Trentham admits his team doesn't know how the collagen therapy works. Perhaps it triggers the release of cytokines, powerful chemical substances that may dampen the revved-up autoimmunie response to the body's cartilage and joints, he speculates. Much more work remains before they can determine the precise mechanism by which this treatment exerts its protective effects, he adds.