Lupus is a chronic, autoimmune disease which causes inflammation of various parts of the body, especially the skin, joints, blood and kidneys. The body's immune system normally makes proteins called antibodies to protect the body against viruses, bacteria and other foreign materials. These foreign materials are called antigens. In an autoimmune disorder such as lupus, the immune system loses its ability to tell the difference between foreign substances (antigens) and its own cells and tissues. The immune system then makes antibodies directed against "self." These antibodies, called "auto-antibodies," react with the "self" antigens to form immune complexes. The immune complexes build up in the tissues and can cause inflammation, injury to tissues, and pain. For most people, lupus is a mild disease affecting only a few organs. For others, it may cause serious and even life- threatening problems.