The normal immune system is a complex system that protects our bodies from infections. Our skin, lungs and gut have cells that help to protect us. There are also many other cells of the immune system that are called to action if we become infected with a bacteria, virus or parasite.
Two important types of immune system cells are types of white blood cells, or lymphocytes. These are called to action by signals in the immune system that let them know a foreign invader is present. B cells, (so-called because they develop in bone marrow) recognize certain types of foreign cells and produce antibodies. The “T cells” (so-called because they develop in a small organ called the thymus gland) are responsible for a variety of other immune responses.
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.
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 become activated in the lymph system and in MS, enter the CNS through blood vessels. Once in the CNS, T cells release chemicals that cause inflammation and damage. This results in damage to myelin, nerve fibers and the cells that make myelin. T cells are also important to help activate B cells and call on other immune system cells to participate in the immune attack.
- T regulatory cells, a type of T cell, dampen or turn off inflammation. In MS, T regulatory cells do not function correctly and do not effectively turn off inflammation.
- Cytotoxic or “killer” T cells directly attack and destroy cells bearing certain characteristics
- B cells become activated with the help of T cells. B cells produce antibodies and stimulate other proteins and in MS, these cause damage in the CNS.
Therapies for MS directed against the immune mediated response
The disease modifying therapies for MS work by various mechanisms, with different therapies having different mechanisms of action. These mechanisms include:
- Interfering with the activation of T cells
- Turning down the inflammation and immune activity
- Blocking the movement of immune system cells
- Depleting the numbers of immune system cells
- Limiting entry of immune cells into the CNS
While much has been learned about the immune response in MS and the mechanisms that cause inflammation and damage, continued research is underway to better understand the MS disease process including disability progression, and develop treatments that can stop progression, reverse disability and ultimate cure MS.