The immune system protects the body against invading foreign substances, producing antibodies and white blood cells that recognize and destroy the aliens. Sometimes the system goes awry, and the antibodies and lymphocytes turn against the body's own cells and tissues, a phenomenon called autoimmunity. This abnormal immune response results in a variety of disorders termed autoimmune diseases.

Early researchers of the immune system discovered that immune reactions were not always beneficial. Charles Richet and Paul Portier (1866-1962) in 1902 discovered anaphylaxis, an extreme reaction to an injected toxin that, instead of conferring immunity, caused death. Maurice Arthus also found hypersensitive reaction to antigens in 1903. Clemens von Pirquet (1874-1929) described another negative immune response, serum sickness, in 1906 and coined the term allergy for these cases of altered reactivity.

These early hints at the existence of autoimmunity were not followed up, as immunology entered a long phase of chemical...