A disease produced when the body's normal tolerance of the antigens on its own cells (autoantigens [AAg] or self-antigens) is disrupted. Current theories are that the loss of self-tolerance is the result of damage to AAgs by microorganisms, a strong similarity in appearance between the AAg and a foreign antigen, or a foreign antigen linking with an AAg. Autoantibodies (AAbs) produced either by B lymphocytes or self-reacting T lymphocytes attack normal cells whose surface contains an autoantigen destroying the tissue. Both inherited risk factors and environmental factors are considered significant in the development of autoimmune disease. Researchers have found links between AAb production and the inheritance of certain histocompatibility antigens, indicating that genetic susceptibility is probably a component in autoimmune diseases. Other unknown factors within the immune system may prevent it from stopping the abnormal inflammatory process once it has begun.

Many diseases are based on AAb-AAg reactions. Systemic lupus erythematosus and rheumatoid arthritis are autoimmune diseases in which multiple tissues are affected. Some autoimmune disorders manifest themselves primarily in only one or two tissues even though they, too, are systemic. The damage to cardiac valves in rheumatic fever occurs because AAgs on the valves are similar in structure to antigens on Group A beta-hemolytic streptococci. Insulin-dependent diabetes mellitus is caused by AAb destruction of the islets of Langerhans, and multiple sclerosis is caused by AAb destruction of the myelin sheath covering nerves. Hemolytic anemia, some forms of glomerulonephritis, myasthenia gravis, chronic thyroiditis, Reiter syndrome, and Graves disease are also autoimmune diseases.

SEE: antigen; autoantibody; autoantigen; autoimmunity; histocompatability locus antigen; inflammation; molecular mimicry.