Multiple sclerosis is considered to be an immune-mediated disease in which the body's immune system attacks the central nervous system (CNS). Most MS experts believe it to be an autoimmune disease, although no specific antigens (proteins that stimulate the immune system) have been identified in MS. Some diseases thought to have an autoimmune basis are:
- Crohn's disease
- rheumatoid arthritis
- systemic lupus erythematosus, and
- insulin-dependent (Type 1) diabetes mellitus.
In the case of MS, the immune system attacks and damages certain structures and cells within the CNS, including:
- myelin (the fatty sheath that surrounds and protects nerve fibers),
- oligodendrocytes (myelin producing cells), and
- nerve fibers underlying myelin.
T cells, which are one type of white blood cell in the immune system, somehow become sensitized to proteins in the CNS. When T cells become activated, they enter the CNS through blood vessels and produce damaging inflammation. Once in the CNS, these T cells not only injure myelin, but also secrete chemicals that damage nerve fibers (axons) and recruit more damaging immune cells to the site of inflammation. It is not known what causes T cells in persons with MS to become activated but it is thought that both genetic and environmental factors are important.
Many different cells are involved in the abnormal immune response seen in MS. Two important types of immune cells are T cells and B cells.
- T cells are a type of white blood cell that becom activated in the lymph system and in MS, attack cells and tissues in the CNS. This results in damage to myelin, nerve fibers and the cells that make myelin.
- T regulatory cells, a type of T cell, dampen or turn off inflammation. In MS, T regulatory cells to not function correctly and do not effectively turn off inflammation.
- B cells become activated in the blood with the help of T cells. B cells produce antibodies and in MS these cause damage in the CNS.
Research directed at the role of the immune system in MS
Scientists have identified many of the cells that contribute to the abnormal immune response in MS. The National MS Society funds significant research looking for the cause as well as better therapies for MS.