Harmful enzyme may be key in rheumatoid arthritis

LONDON (Reuters) - Joint damage suffered by people with rheumatoid arthritis may be caused by antibodies produced within the joint itself, British researchers said Tuesday in a study that may help development of new drugs.

The study of joint biopsies from people with the condition which was then transplanted into mice found that tiny structures in the joint lining can lead to production of a destructive enzyme called activation-induced cytidine deaminase (AID).

This gives researchers a target to design new drugs for rheumatoid arthritis, a painful condition affecting an estimated 20 million people worldwide, Constantino Pitzalis of Barts and the London School of Medicine and colleagues wrote.

New treatments are critical because immune-suppressing drugs for the condition can produce serious side effects including stomach bleeding, ulcers, heart attacks and stroke while also raising the risk of death from infections and cancer.

"We therefore propose that AID may be targeted for the development of novel therapeutic agents," the researchers wrote in the Public Library of Science Journal PLoS Medicine.

Rheumatoid arthritis is an autoimmune disease caused when the body confuses healthy tissues for foreign substances and attacks itself.

Some drugs to treat the condition seek to reduce inflammation directly while others tone down the immune system's response, which can leave some patients vulnerable to infections and cancer.

The British team collected tissue from the lining of the joints of 55 people with rheumatoid arthritis and transplanted it under the skin of mice without immune systems.

Four weeks later, the researchers found that the transplanted tissue was still making the potentially destructive antibody, suggesting such production within joints can occur independently of the body's lymph nodes.