An autoimmune disorder occurs when the body's immune system attacks and destroys healthy body tissue by mistake. There are more than 80 types of autoimmune disorders.

Causes

The blood cells in the body's immune system help protect against harmful substances. Examples include bacteria, viruses, toxins, cancer cells, and blood and tissue from outside the body. These substances contain antigens. The immune system produces antibodies against these antigens that enable it to destroy these harmful substances.

When you have an autoimmune disorder, your immune system does not distinguish between healthy tissue and potentially harmful antigens. As a result, the body sets off a reaction that destroys normal tissues.

The exact cause of autoimmune disorders is unknown. One theory is that some microorganisms (such as bacteria or viruses) or drugs may trigger changes that confuse the immune system. This may happen more often in people who have genes that make them more prone to autoimmune disorders.

An autoimmune disorder may result in:

• The destruction of body tissue
• Abnormal growth of an organ
• Changes in organ function

An autoimmune disorder may affect one or more organ or tissue types. Areas often 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. Common autoimmune disorders include:

Addison disease

Celiac disease - sprue (gluten-sensitive enteropathy)

Dermatomyositis

Graves disease

• Hashimoto thyroiditis
• Multiple sclerosis
• Myasthenia gravis
• Pernicious anemia
• Reactive arthritis
• Rheumatoid arthritis
• Sjögren syndrome
• Systemic lupus erythematosus
• Type I diabetes