Lupus is an autoimmune disease in which the body's own immune system attacks healthy cells and tissues by mistake, causing damage to joints, skin, blood vessels, and organs. There are many kinds of lupus. The most common type, systemic lupus erythematosus (SLE), affects many parts of the body and is most prevalent among young women. It causes a characteristic skin rash with butterfly distribution over the face. LE also causes lung, kidney, and blood disease, largely due to abnormal immunity directed against substances in cell nuclei. Treatment is with steroids and immunosuppressives.