Possible Cause for Arthritis Found

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Aug. 21, 2002 -- A slimy carbohydrate abundant in the joints may be the key

to rheumatoid arthritis. Its exact role in causing disease is still unclear,

but researchers already are looking for new treatments.

These common carbs are called glycosaminoglycans or GAGs. GAGs are a major

part of joint cartilage, joint fluid, connective tissues, and even skin. A

report at this week's annual meeting of the American Chemical Society

suggests that GAGs somehow prime the immune system to attack the joints.

" We don't know the cause of arthritis -- but in the end, this might turn out

to be the missing link, " Ying Wang, PhD, tells WebMD. Wang is assistant

professor of medicine at Harvard Medical School.

A major feature of rheumatoid arthritis is inflamed joints. For some reason,

the body's immune system attacks joint tissues. In animal experiments, Wang's

team showed that the immune cells that penetrate arthritic joints home in on

GAG-containing cells. They could give arthritis to healthy lab rats by

injecting them with different kinds of GAGs.

Moreover, the researchers found that joint tissues from people with

rheumatoid arthritis are full of immune cells that attack GAGs.

What's happening? GAGs can be found in the outer coat of some common bacteria

and viruses. In response to these germs, the immune system might, under

certain circumstances, teach the body to attack its own GAG-containing

tissues, such as joints. Wang also suggests that bacteria in the joints might

release GAGs into the blood and prime the immune system to cause arthritis.

With an eye to new arthritis treatments, Wang's lab already is looking for

ways to block the GAG-targeted immune cells.

All this sounds very exciting -- but it's not the first time scientists have

discovered substances that seemed to prime the immune system. Upon further

study, none of these substances turned out to be the missing link between the

immune system and arthritis.

S. Firestein, MD, is chief of rheumatology, allergy, and immunology at

the University of California, San Diego. He hopes the Wang team is on to

something -- but experience tells him to wait for more proof.

" These findings are potentially very exciting, " Firestein tells WebMD. " But

there are many things that can cause arthritis in animal models. Some of

these have been associated with human rheumatoid arthritis. Whether [Wang's

GAGs] turn out actually to be involved in human disease remains to be seen. "