Diseases in which the immune system attacks the body's own healthy tissues, forming antibodies in an assault on mistakenly identified "foreign invaders. "

Autoimmune disorders occur when the body's immune system loses its ability to recognize the differences between self and nonself tissues. The body then builds antibodies to attack its own tissues and organs, which culminates in a number of different disorders. Some of these become chronic illnesses and may lead to death.

Two of the earliest illnesses identified as autoimmune disorders were systematic lupus erythematosus (SLE) and rheumatoid arthritis. Today more than 40 conditions are classified as known or probable autoimmune disorders. It is estimated that autoimmune diseases affect between 5-7% of the population. Most begin during or soon after puberty, or when a person reaches his or her forties and fifties. They occur twice as frequently in women as in men.

Rheumatoid arthritis occurs in...