Rheumatoid arthritis, also called RA, is an inflammation in the lining of the joints and other internal body organs. RA belongs to a group of diseases called autoimmune disorders, in which the body makes antibodies against its own tissues. It is a fairly common form of arthritis.

What is going on in the body?

In RA, for reasons unknown, the body's immune system malfunctions and begins making antibodies against its own tissues. Antibodies are proteins that help the body to fight infection. These antibodies are made by the immune system in response to a trigger called an antigen. This trigger is often a substance that the body sees as "foreign." These foreign substances can include things like bacteria and viruses. This immune reaction causes an inflammation of the synovial membrane lining the joints.

This chronic inflammation produces enzymes that can invade and damage cartilage and bone within the joint. Sometimes this form of arthritis is mild, but 70% of people who have it develop chronic problems, and 15% have severe crippling disease. Young children can have a form called juvenile RA.

What are the causes and risks of the disease?

The causes of RA are not yet fully understood. Experts suspect that some type of virus can trigger RA in people who have certain genes that give one a tendency to develop the disease.

RA affects 2.1 million people in the U.S. and can develop at any age. Most often, it starts in middle age, but it is also common in people in their 20s and 30s. More than 70% of the people who have RA are women.

There is currently research into a number of factors that may trigger RA, including: