Lupus is a disease of the immune system. Normally, the immune system protects the body by making antibodies to fight off viruses, bacteria, and other foreign substances. When the immune system is not working normally, it can make antibodies directed against itself. These antibodies are called autoantibodies ("auto" meaning self). They lead to pain, inflammation, and other symptoms of lupus. Diseases like lupus that produce these antibodies are called autoimmune diseases.
Because it has so many different and varying symptoms, lupus is difficult to define. The important point to remember is that lupus does not have to define the individual. Lupus can be effectively treated and most people who have the disease can lead active lives.