RA is a disease in which the immune system attacks healthy cells by the body. Autoimmune diseases occur when the natural defense system can't distinguish between the body’s own (and healthy) cells and foreign or diseased cells. In such a case, the body mistakenly attacks and kills normal cells. The result in rheumatoid arthritis is inflammation (swelling) of the tissues.
Rheumatoid Arthritis primarily affects joints. Most commonly, the knees, wrists and hands on both sides of the body are involved. It shows up as warm, swollen, and painful joints. In these joints the lining becomes inflamed, along with thickening of the joint capsule and change to the underlying bone and cartilage. This causes chronic pain, and misshapenness. Rheumatoid Arthritis can also affect other organs such as lungs, heart, and eyes.