Illustration of arthropathy of the joints and skin rash, the two most common symptoms of systemic lupus erythematosus (SLE). Lupus is a chronic autoimmune disease where the immune system, for unknown reasons, becomes hyperactive and attacks normal tissue. Systemic lupus attacks multiple systems in the body which may include: the skin, joints, lungs, blood, blood vessels, heart, kidneys, liver, brain and the nervous system. The background of this image depicts the antinuclear antibody (ANA) test performed on SLE patient blood serum. This test can determine if autoantibodies to cell nuclei that are indicative of lupus are present in the blood. The linear bright green staining seen around the nuclei through immunofluorescent microscopy is typical of SLE.