Overview of immune-mediated disease and multiple sclerosis
An immune-mediated disease is a condition that results from an abnormal immune system response. In these diseases, the immune system mistakenly targets the body. This creates an inflammatory response that causes damage.
In the case of multiple sclerosis, the immune system mistakenly attacks the central nervous system. The resulting inflammatory response damages certain structures and cells, including:
- Myelin (the fatty sheath that surrounds and protects nerve fibers)
- Oligodendrocytes, the special cells that produce myelin in the central nervous system
- Nerve fibers underlying myelin
This damage produces the symptoms of MS.
“Immune-mediated disease” vs. “autoimmune disease”
Scientists believe that MS is triggered by a combination of one or more environmental factors acting in a genetically susceptible individual. These environmental factors include an unknown foreign substance, (an antigen), such as a virus or toxin. In autoimmune diseases, researchers have identified the specific antigen that is responsible. No specific antigens have been identified in MS. Still, most experts believe MS is an autoimmune disease although no specific antigens have been identified.
Other autoimmune diseases
Doctors have identified more than 80 types of autoimmune diseases. Some examples include:
- Crohn's disease
- Hashimoto's thyroiditis
- Rheumatoid arthritis
- Systemic lupus erythematosus
- Insulin-dependent (type 1) diabetes mellitus
T cells and B cells in MS
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 central nervous system through blood vessels. Once there, 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 in MS can cause damage in the central nervous system through the production of antibodies and by stimulating other proteins.
Therapies for MS directed against the immune-mediated response
The disease-modifying therapies (DMT) for MS
work by various mechanisms, with different therapies having different mechanisms of action. These mechanisms include:
- Interfering with the activation of T cells
- Reducing 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 MS in its tracks, restore what has been lost and end MS forever