Multiple sclerosis is thought to be an autoimmune disease.
The healthy immune system knows which tissue is part of the person's body and which are 'foreign' - eg a virus or bacterial infection - and need attacking. In some conditions, for reasons that aren't known, this protective mechanism fails to work. The immune system turns on the body's own tissue and attacks it as if it were a foreign invader. These conditions are called autoimmune diseases.
Autoimmune conditions include rheumatoid arthritis, where the lining of the joints become inflamed, and Crohn's disease, which affects the walls of the intestines. In MS the autoimmune response leads to attacks on myelin, which covers the nerves within the central nervous system.
Last updated: 13 August 2014
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