Rheumatoid arthritis is a progressive, chronic disease that damages the joints. It is an auto-immune disease which means that your body's tissue is mistakenly attacked by your own immune system. By design the immune system is there to destroy invading agents, including infections. The damage to the joints is caused by inflammation of the tissue lining the joints. Rheumatoid arthritis is systemic in that it can affect other organs in the body as well.