Systemic lupus erythematosus is an autoimmune disease that can affect any system and organ in the body. For the 1.4 million people in the United States who have lupus, an overactive immune system senses that different parts of the body do not belong, and it attacks these parts. The immune system may strike the cells that line the joints or tendons, for example, causing pain and swelling. An incredibly complex disease, lupus must be properly treated for the optimal health and well-being of the person who has it.
The Lupus Encyclopedia: A Comprehensive Guide for Patients and Families (A Johns Hopkins Press Health Book)