Autoimmune diseases are characterized by the body's immune responses being directed against its own tissues, causing prolonged inflammation and subsequent tissue destruction. Autoimmune disorders can either cause immune-responsive cells to attack the linings of the joints (resulting in rheumatoid arthritis) or trigger immune cells to attack the insulin-producing islet cells of the pancreas (leading to insulin-dependent diabetes mellitus).
A healthy immune system recognizes, identifies, remembers, attacks, and destroys bacteria, viruses, fungi, parasites, cancer cells, or any health-damaging agents not normally present in the body. A defective immune system, on the other hand, wreaks havoc throughout the host by directing antibodies against its own tissues.
Any disease in which cytotoxic cells are directed against self-antigens in the body's tissues is considered autoimmune in nature. Such diseases include, but are not limited to, celiac disease, Crohn's disease, pancreatitis, systemic lupus erythematosus, Sjogren's syndrome, Hashimoto's thyroiditis, and other endocrinopathies. Allergies and multiple sclerosis are also the result of disordered immune functioning.