National informational resource. Lupus is an autoimmune disease that can affect various parts of the body, including the skin, joints, heart, lungs, blood, kidneys and brain. Normally the body's immune system makes proteins called antibodies, to protect the body against viruses, bacteria, and other foreign materials. These foreign materials are called antigens.
In an autoimmune disorder like lupus, the immune system cannot tell the difference between foreign substances and its own cells and tissues. The immune system then makes antibodies directed against itself. These antibodies -- called "auto-antibodies" (auto means 'self') -- cause inflammation, pain and damage in various parts of the body.