- Systemic Lupus Erythematosus (SLE or lupus) is an autoimmune disease, which means the body's immune system mistakenly attacks healthy tissue resulting in inflammation and tissue damage. SLE can involve almost any organ and its symptoms can range in severity from mild to life-threatening; symptoms also vary from person to person. Current treatments for lupus are not effective for some people. Medications used to treat lupus can have serious side effects.