Multiple Sclerosis

MULTIPLE SCLEROSIS

The ultimate cause of Multiple Sclerosis is unknown. It is hypothesised that a viral infection or other environmental factor in childhood might prime the immune system for an abnormal reaction later in life. On a molecular level, there might be a structural similarity between an unidentified infectious agent and components of the central nervous system, causing confusion in the immune system later in life (a process called "molecular mimicry"). However, so far there is no known "MS virus". Certainly MS is not an infectious disease and not contagious. The importance of genetic factors has been discussed above.

It is widely accepted that a special subset of white blood cells, called T cells, play a key role in the development of MS. Under normal circumstances, these lymphocytes can distinguish between self and non-self. In a person with MS, however, these cells recognize healthy parts of the central nervous system as foreign, and attack them as they would a virus. In MS, the part of the nervous system primarily attacked is myelin. Myelin is a fatty substance that covers the axons of nerve cells, and which is important for proper nerve conduction. Normally, there is a tight barrier between blood and brain, called the blood-brain barrier (BBB), built up of endothelial cells lining the blood vessel walls.

In MS, the BBB breaks down; autoreactive T cells cross the BBB and trigger an inflammatory process, also mediated by other immune cells and soluble factors, such as cytokines and antibodies. Due to this abnormal behavior of the immune system, MS is considered to be an autoimmune disorder. The inflammatory process finally leads to a destruction of myelin called demyelination. Repair processes, called remyelination, also play an important role. This is one of the reasons why, especially in early phases of the disease, symptoms tend to decrease or disappear temporarily after days to months. Nevertheless, axonal damage and irreversible loss of neurons occur early during the course of the disease. However, due to its plasticity the brain can often compensate for some portion of the damage. MS symptoms develop as a result of multiple lesions in the brain and spinal cord, and can vary greatly between different individuals, depending on where the lesions occur.

Above info taken from Wikipedia.com