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Autoimmune diseases can affect the body in different ways. They occur when the immune cells in your body mistake your body's cells as invaders and attack them. In many people, the first symptoms are fatigue, muscle aches, and low fever. Some of the body systems that these diseases affect include blood and blood vessels, digestive tract, eyes, and glands.

What Are Autoimmune Diseases?

When your body is attacked, your immune system defends you by identifying and killing the germs that might hurt you. However, when the immune system doesn't work right, this process may cause harm, because your immune cells can mistake your body's own cells as invaders and attack them. This can occur in almost any part of the body and can sometimes affect many parts of the body at once. This is called autoimmunity (meaning self-immunity).
 
Autoimmune diseases, also known as autoimmune disorders, can affect the body in different ways. For instance, the autoimmune reaction is directed against the brain in multiple sclerosis and the gut in Crohn's disease. In other diseases, such as systemic lupus erythematosus (SLE or lupus), affected tissues and organs may vary among individuals with the same disease.
 
Many autoimmune diseases are rare. However, as a group, they afflict millions of Americans. Women who are in their childbearing years are affected more often than men.
 

Understanding the Immune System and Autoimmunity

The immune system is a network of cells, tissues, and organs that work together to defend the body against attacks by microbes (germs), which are tiny infection-causing organisms, such as bacteria, viruses, parasites, and fungi. The human body provides an ideal environment for many microbes, which is why they try to break in. It is the immune system's job to keep them out or to seek and destroy them.
 
The immune system is amazingly complex. It can recognize and remember millions of different "enemies," and it can produce secretions and cells to match up with and wipe out each one of them. The secret to its success is an elaborate and dynamic communications network. Millions and millions of cells, organized into sets and subsets, gather like clouds of bees swarming around a hive and pass information back and forth. Once immune cells receive the alarm, they undergo tactical changes and begin to produce powerful chemicals. These substances allow the cells to regulate their own growth and behavior, enlist their fellows, and direct new recruits to trouble spots.
 
Sometimes, the immune system's recognition apparatus breaks down, and the body begins to manufacture cells and antibodies directed against its own cells and organs. This "friendly fire" can affect almost any part of the body, and it can affect many parts of the body at once. This is called autoimmunity.
 
Written by/reviewed by:
Last reviewed by: Arthur Schoenstadt, MD
Last updated/reviewed:
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