Systemic Lupus Erythematosus (SLE or lupus) is a chronic autoimmune disease that can be fatal, though with recent medical advances, fatalities are becoming increasingly rare. As with other autoimmune diseases, the immune system attacks the body’s cells and tissue, resulting in inflammation and tissue damage. SLE can affect any part of the body, but most often harms the heart, joints, skin, lungs, blood vessels, liver, kidneys and nervous system. The course of the disease is unpredictable, with periods of illness (called flares) alternating with remission. In SLE, the body's immune system produces antibodies against itself, particularly against proteins in the cell nucleus. SLE is triggered by environmental factors which are unknown (but probably include viruses), in people with certain combinations of genes in their immune system. SLE is a chronic inflammatory disease believed to be a type III hypersensitivity response with potential type II involvement.