Definition of Autoimmune disorders:

An autoimmune disorder is a condition that occurs when the immune system mistakenly attacks and destroys healthy body tissue. There are more than 80 different types of autoimmune disorders.

See also: Immune response

Causes, incidence, and risk factors:

Normally the immune system's white blood cells help protect the body from harmful substances, called antigens. Examples of antigens include bacteria, viruses, toxins, cancer cells, and blood or tissues from another person or species. The immune system produces antibodies that destroy these harmful substances.

In patients with an autoimmune disorder, the immune system can't tell the difference between healthy body tissue and antigens. The result is an immune response that destroys normal body tissues. This response is a hypersensitivity reaction similar to the response in allergic conditions.

In allergies, the immune system reacts to an outside substance that it normally would ignore. With autoimmune disorders, the immune system reacts to normal body tissues that it would normally ignore.

What causes the immune system to no longer tell the difference between healthy body tissues and antigens is unknown. One theory is that some microorganisms (such as bacteria or viruses) or drugs may trigger some of these changes, especially in people who have genes that make them more likely to get autoimmune disorders.

An autoimmune disorder may result in:

• The destruction of one or more types of body tissue
• Abnormal growth of an organ
• Changes in organ function

An autoimmune disorder may affect one or more organ or tissue types. Organs and tissues commonly affected by autoimmune disorders include:

• Blood vessels
• Connective tissues
• Endocrine glands such as the thyroid or pancreas
• Joints
• Muscles
• Red blood cells
• Skin

A person may have more than one autoimmune disorder at the same time. Examples of autoimmune (or autoimmune-related) disorders include:

• Addison's disease
• Celiac disease - sprue (gluten-sensitive enteropathy)
• Dermatomyositis
• Graves disease
• Hashimoto's thyroiditis
• Multiple sclerosis
• Myasthenia gravis
• Pernicious anemia
• Reactive arthritis
• Rheumatoid arthritis
• Sjogren syndrome
• Systemic lupus erythematosus
• Type I diabetes