The nature of autoimmune disease.

The primary function of the immune system is protection and defense against infection. However, the maintenance of normal immune function is a very intricate process, and the failure of these processes to establish and maintain tolerance to self results in autoimmunity. The damage that results from autoimmune disease can be extensive and can be directed at any tissue in the body. One of the major issues in autoimmunity is whether this is a natural or an unnatural phenomenon. Although there have been numerous and exciting theories proposed to explain the autoimmune response, the basic underlying risk factors remain unclear. Both genetic and environmental factors have been incriminated, but the highly variable expression of autoimmune disease and the multiple genetic and environmental determinants make conclusions difficult. Primary biliary cirrhosis is considered a model autoimmune disease because it reflects a highly directed and highly specific response to an identified target, the biliary epithelium. In this review we attempt to place these issues in perspective both from the generic perspective of autoimmunity and from the specific perspective of primary biliary cirrhosis.